Publications
Open Access
1. Self-Assembling of Multilayered Polymorphs with Ion Beams
Authors:
Azarov, A; Radu, C; Galeckas, A; Mercioniu, IF; Cernescu, A; Venkatachalapathy, V; Monakhov, E; Djurabekova, F; Ghica, C; Zhao, J; Kuznetsov, A
Published: JAN 13 2025, NANO LETTERS, 25, DOI: 10.1021/acs.nanolett.4c05727
Polymorphism determines significant variations in materials' properties by lattice symmetry variation. If they are stacked together into multilayers, polymorphs may work as an alternative approach to the sequential deposition of layers with different chemical compositions. However, selective polymorph crystallization during conventional thin film synthesis is not trivial; changes of temperature or pressure when switching from one polymorph to another during synthesis may cause degradation of the structural quality. The present work reports on the single-step ion-beam-assisted fabrication of multilayered polymorph structures while applying the disorder-induced ordering approach. The dynamic annealing of disorder may be tuned, during ion irradiation, toward self-assembling of several polymorph interfaces. Gallium oxide multilayers with two polymorph interface repetitions are obtained. The single-crystal structure of the polymorphs is maintained between interfaces, exhibiting repeatable crystallographic relationships and optical properties. These data pave the way for enhancing materials' functionalities using not previously conceived capabilities of ion beam technology.
2. Bilayered metallic cathodes consisting of pure Mg and Zn:Al thin films optimized by Laser-induced Thermionic Vacuum Arc (LTVA) technology
Authors:
Mandes, A; Vladoiu, R; Dinca, V; Tichy, M; Kudrna, P; Matei, E; Polosan, S
Published: AUG 2025, APPLIED SURFACE SCIENCE ADVANCES, 28, 100787, DOI: 10.1016/j.apsadv.2025.100787
Bilayer metallic electrodes of magnesium and zinc-aluminum alloys Mg/Zn:Al were prepared using combined laser-thermionic vacuum arc methods. Plasma diagnosis suggests laser-plasma interaction by increasing the discharge voltage when the laser is on, which is converted by thermal annealing of plasma ions. A magnesium thin film with a lower work function, covered with a Zn:Al (4:1) layer was successfully used for efficient charge injection into electroluminescent diodes. The zinc-aluminum combination preserved the electrical conductivity of the thin magnesium film and protected it against oxidation. The capacitance-voltage measurements confirmed the integrity of the magnesium layer, whereas the work function was not affected. The zinc-aluminum alloy obtained through a thermionic vacuum arc exhibits good conductivity compared to pure zinc layers and better stability against degradation.
3. Comparative study of the Cu-TiO2 nanostructures obtained by sol-gel and microwave assisted sol-gel methods
Authors:
Predoana, L; Pandele-Cusu, J; Atkinson, I; Petrescu, S; Mocioiu, OC; Culiba, DC; Karajz, DA; Odhiambo, VO; Lemago, HH; Gomes, APB; Varady, ZI; Bohus, M; Costescu, RM; Szilágyi, IM; Pokol, G; Zaharescu, M
Published: JUN 2025, JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 114, DOI: 10.1007/s10971-025-06757-x
In this study, pristine TiO2 and Copper (Cu)-doped TiO2 nanopowders were synthesized using two sol-gel methods: conventional sol-gel (SG) and microwave-assisted sol-gel (MW). The aim was to investigate the effect of the synthesis route and Cu doping on the structural, optical, and photocatalytic properties of TiO2. X-ray diffraction (XRD) analysis confirmed the formation of anatase TiO2 in all samples, with a minor presence of rutile observed in the samples obtained by the MW method. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray analysis (EDX) showed that the nanopowders obtained by the MW method exhibited a greater tendency for particle aggregation compared to those obtained through the SG method. The presence of Cu2+/Cu+ species in the samples was confirmed by X-ray photoelectron spectroscopy (XPS). UV-Vis reflectance measurements revealed a shift in the absorption edge of the 5% Cu-doped samples toward the visible light range, significantly reducing the band gap. Evaluation of photocatalytic activity demonstrated that doping TiO2 with 5% Cu enhanced the degradation of Congo Red dye under visible light. [GRAPHICS] .
4. Beneficial role of silicotungstic acid presence on the WO3-modified boron-doped diamond substrate on the electrocatalytic activity for methanol anodic oxidation of supported platinum
Authors:
Spataru, N; Preda, L; Matei, E; Satulu, V; Mihai, MA; Radu, MM; Donath, C; Moga, OG
Published: APR 17 2025, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 120, DOI: 10.1016/j.ijhydene.2025.03.327
The present paper evidences the beneficial effect that the combination of Pt with WO3 and silicotungstic acid (STA) brings to the methanol oxidation electroactivity. To avoid substrate interferences boron doped diamond (BDD) was used as the electrocatalysts support. SEM measurements have shown that the use of a STA/WO3/BDD substrate allows the electrodeposition of smaller Pt clusters, exhibiting better dispersion, higher homogeneity in terms of size and enhanced electrochemically active surface area. Cyclic voltammetry, polarization and EIS experiments demonstrated than STA addition on the WO3/BDD support induces to the deposited Pt higher activity and improved resistance to fouling during methanol anodic oxidation. Based on the XPS results such behavior was tentatively ascribed to the higher surface concentration of Pt(OH)2 species and adsorbed water that STA presence enables, which may assist in the oxidative desorption of reaction intermediates.
5. MXenes as Heterogeneous Thermal Catalysts: Regioselective Anti-Markovnikov Hydroamination of Terminal Alkynes with 102 h-1 Turnover Frequencies
Authors:
Grau, RR; Garcia-Aznar, P; Sastre, G; Goberna-Ferrón, S; Pavel, O; Tirsoaga, A; Cojocaru, B; Popescu, DG; Parvulescu, VI; Primo, A; García, H
Published: JAN 21 2025, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 147, DOI: 10.1021/jacs.4c13481
Due to their conductive properties and optoelectronic tunability, MXenes have revolutionized the area of electrocatalysis and active materials in supercapacitors. In comparison, there are only a few reports on MXenes as thermal catalysts for general organic reactions. Herein, the unprecedented catalytic activity of Ti3C2 MXene for the hydroamination of alkynes is reported, overcoming the limitations of poor activity, lack of selectivity, and stability, which are generally encountered in the solid catalysts known so far. In the case of Ti3C2, hydroamination exhibits almost complete selectivity for the anti-Markovnikov regioisomer, for both aliphatic amines and less-reactive aromatic amines. Ti3C2 also efficiently catalyzes intramolecular hydroamination, leading to the formation of indol heterocycles. The catalytic hydroamination of C-C multiple bonds is a reaction with complete atom efficiency that may form C-N bonds from convenient reagents. The maximum number of hydroamination sites on the Ti3C2 nanosheets is quantified by thermoprogrammed NH3 desorption. The measured TOF values are on the order of 102 h-1, with the highest TOF value being 350 h-1 for 1-hexyne hydroamination by n -butylamine. Therefore, Ti3C2 is among the few heterogeneous hydroamination catalysts studied, with its activity per site being comparable to the best hydroamination catalysts reported so far. Density functional theory calculations on the models indicate the cooperation of neighboring Ti atoms in the mechanism. Considering the compositional and structural versatility of MXenes, the present findings open the door for further application of MXenes in other general organic reactions.
Open Access
6. Annealing temperature, a key factor in shaping Ag-decorated TiO2 aerogels as efficient visible-light photocatalysts
Authors:
Rostas, AM; Suciu, RC; Rosu, MC; Turza, A; Cosma, DV; Tripon, S; Fort, CI; Danciu, V; Baia, M; Bocirnea, A; Indrea, E
Published: JUN 1 2025, MATERIALS CHEMISTRY AND PHYSICS, 337, 130557, DOI: 10.1016/j.matchemphys.2025.130557
Ag-decorated TiO2 aerogels were synthesized using an acid-catalyzed sol-gel method, followed by drying under supercritical CO2 and annealing within the temperature range of 350-500 degrees C, with 50 degrees C increments. This study explores the preparation-structure-performance relationships of Ag-TiO2 aerogels influenced by the annealing process, focusing on their morphological, (micro)structural, optical, and textural properties and surface defects concerning photocatalytic activity. X-ray diffraction (XRD) and Raman spectroscopy confirmed that all aerogels exhibited a single anatase phase of TiO2, while electron microscopy (SEM/TEM) and XPS analysis demonstrated the presence of components. Increasing the annealing temperature resulted in particle size and pore structure changes, reducing the aerogel's overall surface area and porosity, as observed by SEM and nitrogen (N2) sorption analysis. Additionally, according to the Williamson-Hall (W-H) analysis based on the X-ray peak profile, the lattice microstrain value decreased while the crystallite size increased with rising annealing temperature. Optical investigation showed a strong UV light absorption characteristic of TiO2 and a visible light absorption band attributed to the plasmonic effect of silver nanoparticles. Moreover, a gradual photoluminescence (PL) quenching trend was observed with decreasing annealing temperature, indicating a reduction in the recombination rate of photo-induced electrons and holes in Ag-TiO2, alongside the formation of oxygen vacancies and structural defects, consistent with electron paramagnetic resonance (EPR) measurements. The Ag-decorated TiO2 aerogels demonstrated enhanced visible-light photocatalytic activity for methylene blue (MB) degradation, with the Ag-TiO2 aerogel annealed at 500 degrees C exhibiting the highest photocatalytic performance. This improvement can be attributed to the synergistic effects of chemical composition, plasmonic enhancement, morphological properties, and light absorption characteristics.
7. Electrochemical assay for the quantification of anticancer drugs and their inhibition mechanism
Authors:
Leote, RJB; Sanz, CG; Diculescu, VC; Barsan, MM
Published: SEP 2025, METHODS, 241, DOI: 10.1016/j.ymeth.2025.05.002
Overexpression of pyruvate kinase (PyK) is linked to many kinds of malignant tumors, representing therefore one of the most promising therapeutic targets for cancer treatment. Inhibition of PyK slows down tumor growth or causes tumor cell death, minimizing cancer cell proliferation, and understanding inhibitor mechanism of action can significantly improve cancer therapy. The present work describes the use of an amperometric bienzymatic biosensor, based on PyK and pyruvate oxidase (PyOx), in enzyme inhibition studies of four kinase inhibitors, CPG77675, Nilotinib, Ruxolitinib, Cerdulatinib. Their inhibition mechanism is studied and discussed in detail, with a thorough evaluation of their enzyme-inhibitor complex binding constants (Ki) and the inhibitor concentration required for 50% inhibition (IC50), employing standard inhibition procedure graphical methods. The biosensor is successfully applied for the quantification of the inhibitors by fixed potential amperometry, with excellent detection limit values in the pM range. It is the first detection method reported for the anticancer drugs CPG77675 and Cerdulatinib. The electrochemical assay based on the biosensor brings several advantages over the available assay kits for high-throughput screening (HTS) of kinase inhibitors, namely: low cost, easy operability and robustness demonstrated by biosensor high reproducibility and both operational and storage stability, offering an opportunity to discover new inhibitors and optimize their therapeutic index.
Open Access
8. Electrochemical bienzymatic biosensor for pyruvate kinase activity evaluation and inhibitor screening
Authors:
Leote, RJB; Barsan, MM; Sanz, CG; Diculescu, VC
Published: AUG 15 2025, TALANTA, 291, 127886, DOI: 10.1016/j.talanta.2025.127886
This study describes the development of a pyruvate kinase (PyK)-biosensor for the evaluation of PyK activity, as a diagnostic tool for early cancer screening and detection of kinase inhibitors used in cancer treatment, with the evaluation of the inhibition mechanism. The biosensor was constructed by co-immobilizing the enzymes PyK and pyruvate oxidase (PyOx) on Au film electrodes by crosslinking with glutaraldehyde (GA) and evaluated electrochemically by cyclic voltammetry (CV) and fixed potential amperometry (CA). First, the experimental conditions were optimized in terms of applied potential, enzyme ratio PyK:PyOx and enzyme substrate concentration: phosphoenolpyruvate (PEP) and adenosine diphosphate (ADP). The biosensor sensitivity towards PEP detection was 2.11 +/- 0.08 mu A mM- 1 cm- 2, with very high reproducibility and repeatability, which made it suitable for inhibition studies of PyK inhibitor. The inhibition mechanism of shikonin was determined in relation to both PEP and ADP, with the calculation of IC50 values and binding constants (Ki). Detection of shikonin was possible at very low concentrations in the linear range of 0.1-4.0 pM. The electrochemical results were validated by UV-Vis spectrophotometry. The developed biosensor is a valuable tool for drug screening by enabling enzyme catalytic function examination with applicability to identify inhibitors, estimate their affinity, inhibition mechanism linked to their molecular mechanisms of action and evaluate selectivity, of great interest in both pharmaceutical and medical domains.
Open Access
9. Effects of ligand coordination on Ag8SnS6 as a photoabsorber for thin film solar cells
Authors:
Dallas, P; Tzitzios, VK; Givalou, L; Tsipas, P; Basina, G; Sakellis, E; Boukos, N; Stergiopoulos, T
Published: APR 17 2025, JOURNAL OF MATERIALS CHEMISTRY C, 13, DOI: 10.1039/d5tc00397k
Ag8SnS6 (ATS) nanoparticles, with a band gap of 1.35 eV, which is located exactly at the Schockley-Queisser optimal value for a single-junction solar cell, were utilized as a photoabsorber component in solid state photovoltaic devices. The as-made particles were capped with long aliphatic chains of oleic acid and oleylamine. After surface functionalization of the shorter and extremely basic formamidinium cations, an increase of the absorption coefficient throughout the visible spectrum range was observed. The ligand exchange led also to a slight increase of the band gap, by a value of 0.05 eV. XRD, XPS, UPS, diffuse reflectance, TEM and EDX characterization studies revealed the structure of the nanoparticles and finally proof-of-concept thin film solar cells were fabricated. A maximum photoconversion efficiency of 0.22% was achieved for the as-made particles.
Open Access
10. Phosphorothioated oligonucleotides on gold-coated electrospun polymeric fibers for electrochemical genosensors
Authors:
Aldea, A; Onea, M; Matei, E; Apostol, N; Botta, D; Enculescu, I; Diculescu, VC
Published: JUN 1 2025, ELECTROCHIMICA ACTA, 524, 146006, DOI: 10.1016/j.electacta.2025.146006
This study investigates the development of electrochemical genosensors using gold-coated electrospun polymeric fibers electrodes, Au/PMMA/PET and immobilized phosphorothioated oligonucleotides. Scanning electron microscopy (SEM) with energy-dispersive X-rays spectroscopy (EDS) revealed a uniform distribution of oligonucleotides on the fibers, contrary to planar gold electrodes Au/Ti/SiO2/Si, where network-like films were observed. X-ray photoelectron spectroscopy (XPS) confirmed the successful immobilization of the phosphorothioated oligonucleotides via strong covalent gold-sulfur bonds, while surface plasmon resonance (SPR) indicated superior binding affinity, with significantly lower equilibrium dissociation constants, when compared to unmodified probes. The detection of BCR/ABL fusion gene of chronic myeloid leukemia using differential pulse voltammetry and methylene blue as electroactive indicator, showed that the Au/PMMA/PET electrodes achieved a sensitivity of 379 +/- 12 mu A cm(-)(2) pM(-)(1) and a limit of detection of similar to 5.00 +/- 0.01 fM, outperforming the Au/Ti/SiO2/Si planar electrodes. Reduced non-specific adsorption was observed on the Au/PMMA/PET electrodes and attributed to the inherent charges introduced during the electrospinning process, which created localized electrostatic fields that repelled weakly adsorbing molecules. These findings demonstrate the potential of Au/PMMA/PET electrodes as a robust platform for further development of high-performance clinical diagnostic devices.
11. Bioengineered Y2O3 nanorods and their potential blue-emitting phosphors
Authors:
Diallo, A; Ndiaye, S; Tite, T; Yahsi, U; Diculescu, VC; Seck, A; Dioum, A; Ngom, BD; Ahmad, I; Galca, AC; Azizi, S
Published: MAR 22 2025, BULLETIN OF MATERIALS SCIENCE, 48, 50, DOI: 10.1007/s12034-025-03406-5
This article describes a new synthesis of nanoscaled Y2O3 that is bioinspired. It has been confirmed that Callistemon viminalis flower extract works well as a chelator when used to bioengineer high-shape anisotropy nanorods of single-phase Y2O3 . X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy and photoluminescence spectroscopy were used to analyse the structural, morphological, surface and optical features. The photoluminescent spectra of the bio-engineered nanorods show blue emissions. As the annealing temperature was increased from 300 to 500 degrees C, the blue colour purity values of the synthesized Y2O3 nanorods were 58.1, 80.7 and 77.0% at 300, 400 and 500 degrees C respectively. The chromaticity coordinates (0.2020, 0.1931), (0.1660, 0.1082) and (0.1714, 0.1226) from the photoluminescence spectra of the biosynthesized Y2O3 nanorods were used to determine these values. The CIE y-component coordinate values of the bioengineered blue-emitting nanophosphors suggest their potential for applications in display technology and white light-emitting diodes.
12. Spin configuration of an array of quantum rings controlled by cavity photons
Authors:
Gudmundsson, V; Mughnetsyan, V; Goan, HS; Chai, JD; Abdullah, NR; Tang, CS; Moldoveanu, V; Manolescu, A
Published: MAR 11 2025, PHYSICAL REVIEW B, 111, 115304, DOI: 10.1103/PhysRevB.111.115304
We model a change of the spin configuration in a two-dimensional square array, or a lateral superlattice, of quantum rings in an external perpendicular homogeneous magnetic field. The electron system is placed in a circular cylindrical far-infrared photon cavity with a single circularly symmetric photon mode. Our numerical results reveal that the spin ordering of the two-dimensional electron gas in each quantum ring can be influenced or controlled by the electron-photon coupling strength and the energy of the photons. The Coulomb interaction between the electrons is described by a spin-density functional approach, but the para- and diamagnetic electron-photon interactions are modeled via a configuration interaction formalism in a truncated many-body Fock-space, which is updated in each iteration step of the density functional approach. In the absence of external electromagnetic pulses this reordering of the spin configuration is replicated in the orbital magnetization of the rings. The change in the spin configuration can be suppressed by a strong electron-photon interaction. In addition, fluctuations in the spin configuration are found in dynamical calculations, where the system is excited by a time-dependent coupling scheme to a cylindrical cavity mode for emphasizing the diamagnetic electron-photon interaction not leading to simple electrical dipole oscillations. The diamagnetic interaction is enhanced by the rotational electric field of the particular cavity mode.
13. Advances in 2D Group IV Monochalcogenides: Synthesis, Properties, and Applications
Authors:
Buruiana, AT; Mihai, C; Kuncser, V; Velea, A
Published: MAR 28 2025, MATERIALS, 18, 1530, DOI: 10.3390/ma18071530
The field of newly developed two-dimensional (2D) materials with low symmetry and structural in-plane anisotropic properties has grown rapidly in recent years. The phosphorene analog of group IV monochalcogenides is a prominent subset of this group that has attracted a lot of attention because of its unique in-plane anisotropic electronic and optical properties, crystalline symmetries, abundance in the earth's crust, and environmental friendliness. This article presents a review of the latest research advancements concerning 2D group IV monochalcogenides. It begins with an exploration of the crystal structures of these materials, alongside their optical and electronic properties. The review continues by discussing the various techniques employed for the synthesis of layered group IV monochalcogenides, including both bottom-up methods such as vapor-phase deposition and top-down techniques like mechanical and/or liquid-phase exfoliation. In the final part, the article emphasizes the application of 2D group IV monochalcogenides, particularly in the fields of photocatalysis, photodetectors, nonlinear optics, sensors, batteries, and photovoltaic cells.
Open Access
14. Comprehensive Methodology for Evaluating the Drug Loading of Iron Oxide Nanoparticles Using Combined Magnetometry and Mössbauer Spectroscopy
Authors:
Iacob, N; Palade, P; Comanescu, C; Crisan, O; Toderascu, LI; Socol, G; Schinteie, G; Kuncser, V
Published: FEB 2025, MOLECULES, 30, 676, DOI: 10.3390/molecules30030676
A methodology for the quantitative estimation of the drug loading of iron oxide-based magnetic nanoparticles by corroborating magnetometry and M & ouml;ssbauer spectroscopy investigations is reported. The proposed methodology is exemplified in the case of two series of nanoparticles, namely Fe3O4 nanoparticles covered with citric acid molecules and further functionalized with doxorubicin, and Fe3O4 nanoparticles covered with L-Cysteine molecules and further functionalized with doxorubicin. The general idea of the proposed methodology is to probe the real magnetic structure of the magnetic core via low-temperature M & ouml;ssbauer spectroscopy for the correct estimation of the spontaneous magnetization of the magnetic core. It subsequently uses the ratio between the spontaneous magnetization of the covered nanoparticles and that of the magnetic core for the reliable and nondestructive evaluation of the nanoparticle loading by organic molecules. Although the methodology is exemplified in the case of magnetite-based nanoparticles, it can be successfully considered for a large class of medicine-loaded Fe-containing magnetic nanoparticles where 57Fe M & ouml;ssbauer spectroscopy can be applied.
Open Access
15. Nb2C Mxene as a bifunctional acid-base and oxidation/hydrogenation catalyst
Authors:
Pavel, O; Tirsoaga, A; Cojocaru, B; Popescu, D; Ramírez-Grau, R; González-Durán, P; García-Aznar, P; Tian, L; Sastre, G; Primo, A; Parvulescu, V; Garcia, H
Published: JUL 3 2025, EES CATALYSIS, 3, DOI: 10.1039/d5ey00004a
Nb2C MXene, obtained from Nb2AlC by Al3+ etching and exfoliation, was characterized using XRD, HRTEM and AFM, with the data confirming the crystallinity of the sample and the 2D morphology of the sheets with an average layer thickness of 1.5 nm. Surface analysis using XPS revealed the presence of structural defects, and NH3- and CO2-TPD profiles confirmed the low density of acid and basic sites in the range of tens of mu mol gcatalyst-1 of weak and moderate strengths. The combination of acid and basic sites in close proximity on the solid surface was responsible for the remarkable catalytic activity of Nb2C MXene in promoting aldolic condensation with high turnover frequencies of up to 855 h-1, which was comparable to the values of benchmark catalysts, such as MgO or HZSM-5. Nb2C MXene also catalyzed the aerobic oxidative aniline coupling to azo- and azoxy-benzene and hydrogenation of azoxybenzene to azobenzene.
Open Access
16. Ru/Beta Zeolite Catalysts for Levulinic Acid Hydrogenation: The Importance of Catalyst Synthesis Methodology
Authors:
Petcuta, OA; Guzo, NC; Bordeiasu, M; Nicolaev, A; Parvulescu, VI; Coman, SM
Published: JAN 2025, CATALYSTS, 15, 80, DOI: 10.3390/catal15010080
Ruthenium-based catalysts were prepared through a deposition-precipitation approach, taking beta zeolites with Si/Al ratios of 12.5, 18.5, and 150, respectively, as supports, and 1-3 wt% loadings of metal. Their activation was performed in the presence of either H2 or NaBH4. The dispersion of the Ru species and the acid-base properties were influenced by both the preparation method and the activation protocol. The catalysts reduced under H2 flow presented well-dispersed Ru(0) and RuOx nanoparticles, while the reduction with NaBH4 led to larger RuOx crystallites and highly dispersed Ru(0). These characteristics exerted an important role in the hydrogenation of levulinic acid (LA) to gamma-valerolactone (GVL). The H2 dissociation occurred via a heterolytic mechanism involving Lewis acid-base pairs associated with RuOx and the framework oxygen (Si-O-Al) located near the zeolite pore edge. The Ru(0) nanoparticles activated the -C=O bond of the LA substrate, while the presence of the carrier zeolite Br & oslash;nsted acid sites promoted the ring-closure esterification of the 4-hydroxyvaleric acid (4-HVA) intermediate to GVL. An optimal combination of these features was achieved for the catalyst with 3 wt% Ru and a Si/Al ratio of 150, which selectively converted LA (XLA = 96.5%) to GVL (SGVL = 97.8%) at 130 degrees C and 10 bars of H2.
Open Access
17. 2025 roadmap on 3D nanomagnetism
Authors:
Gubbiotti, G; Barman, A; Ladak, S; Bran, C; Grundler, D; Huth, M; Plank, H; Schmidt, G; van Dijken, S; Streubel, R; Dobrovoloskiy, O; Scagnoli, V; Heyderman, L; Donnelly, C; Hellwig, O; Fallarino, L; Jungfleisch, MB; Farhan, A; Maccaferri, N; Vavassori, P; Fischer, P; Tomasello, R; Finocchio, G; Clérac, R; Sessoli, R; Makarov, D; Sheka, DD; Krawczyk, M; Gallardo, R; Landeros, P; d'Aquino, M; Hertel, R; Pirro, P; Ciubotaru, F; Becherer, M; Gartside, J; Ono, T; Bortolotti, P; Fernández-Pacheco, A
Published: APR 7 2025, JOURNAL OF PHYSICS-CONDENSED MATTER, 37, 143502, DOI: 10.1088/1361-648X/ad9655
The transition from planar to three-dimensional (3D) magnetic nanostructures represents a significant advancement in both fundamental research and practical applications, offering vast potential for next-generation technologies like ultrahigh-density storage, memory, logic, and neuromorphic computing. Despite being a relatively new field, the emergence of 3D nanomagnetism presents numerous opportunities for innovation, prompting the creation of a comprehensive roadmap by leading international researchers. This roadmap aims to facilitate collaboration and interdisciplinary dialogue to address challenges in materials science, physics, engineering, and computing. The roadmap comprises eighteen sections, roughly divided into three blocks. The first block explores the fundamentals of 3D nanomagnetism, focusing on recent trends in fabrication techniques and imaging methods crucial for understanding complex spin textures, curved surfaces, and small-scale interactions. Techniques such as two-photon lithography and focused electron beam-induced deposition enable the creation of intricate 3D architectures, while advanced imaging methods like electron holography and synchrotron x-ray tomography provide nanoscale spatial resolution for studying magnetization dynamics in three dimensions. Various 3D magnetic systems, including coupled multilayer systems, artificial spin-ice, magneto-plasmonic systems, topological spin textures, and molecular magnets are discussed. The second block introduces analytical and numerical methods for investigating 3D nanomagnetic structures and curvilinear systems, highlighting geometrically curved architectures, interconnected nanowire systems, and other complex geometries. Finite element methods are emphasized for capturing complex geometries, along with direct frequency domain solutions for addressing magnonic problems. The final block focuses on 3D magnonic crystals and networks, exploring their fundamental properties and potential applications in magnonic circuits, memory, and spintronics. Computational approaches using 3D nanomagnetic systems and complex topological textures in 3D spintronics are highlighted for their potential to enable faster and more energy-efficient computing.
18. Relaxation of the Irreversible Magnetization in Proton-Irradiated MgB2
Authors:
Sandu, V; Craciun, L; Ivan, I; Ionescu, AMB; Chidthong, R; Mihai, F; Aldica, GV
Published: FEB 2025, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 38, 30, DOI: 10.1007/s10948-024-06877-5
The paper presents the features of the magnetization decay of proton-irradiated MgB2 bulk samples. Irradiation was performed with protons of energies between 8.6 and 15.07 MeV at different fluences. The creep activation energy is sensitive to the ratio between proton range and sample thickness. Experimental data show that the creep exponents are different from the theoretical predictions. When the proton range is shorter than the sample thickness (protons of 8.6 MeV), the thermomagnetic instabilities are strongly emphasized and affect the creep behavior.
19. Induced Effects of Nano-Patterned Substrates on the Electrical and Photo-Electrical Properties of PTB7-Th:ICBA (1:1, wt.%) Bulk-Heterojunction Solar Cells
Authors:
Suteu, T; Antohe, VA; Antohe, S; Stavarache, I; Balasin, MC; Socol, G; Socol, M; Rasoga, O; Iftimie, S
Published: MAY 1 2025, SURFACES, 8, 30, DOI: 10.3390/surfaces8020030
In this study, we detailed the fabrication and characterization of photovoltaic structures based on PTB7:ICBA (1:1, wt.%) bulk-heterojunction on optical glass substrates by spin-coating. Some samples were deposited on a flat substrate, and others were placed on a patterned substrate obtained by nano-imprinting lithography; the induced effects were analyzed. We demonstrated that using a patterned substrate enhanced the maximum output power, primarily because the short-circuit current density increased. This can be considered a direct consequence of reduced optical reflection and improved optical absorption. The topological parameters evaluated by atomic force microscopy, namely, the root mean square, Skewness, and Kurtosis, had small values of around 2 nm and 1 nm, respectively. This proves that the mixture of a conductive polymer and a fullerene derivative creates a thin film network with a high flatness degree. The samples discussed in this paper were fabricated and characterized in air; we can admit that the results are encouraging, but further optimization is needed.
Open Access
20. Strain engineering of epitaxial perovskite-type LaFeO3/ BiFeO3 heterostructures for photoelectrochemical water splitting
Authors:
Andrei, F; Ion, V; Birjega, R; Ghitiu, I; Zamfir, M; Moldovan, A; Teodorescu, VS; Dinescu, M; Marcu, IC; Scarisoreanu, ND
Published: APR 1 2025, SURFACES AND INTERFACES, 62, 106234, DOI: 10.1016/j.surfin.2025.106234
Following the approach of inducing structural constrains for the creation of polar nanodomains/nanoregions in the perovskite thin films, the photoelectrochemical properties of complex heterostructures based on LaFeO3 and BiFeO3 materials have been studied in correlation with the imposed structural strain and polarization orientation anisotropy conditions. The LFO/BFO thin film heterostructures have been tested using photoelectrochemical (PEC) technique. The recorded photocurrent values for the heterostructure with the LFO layer on top- LFO/BFO/STON- in the potentiodinamic regime are considerably higher (similar to 1.64 mA/cm(2) at 2 V vs RHE) than those obtained for BFO/LFO/STON heterostructure where the BFO layer is acting as the surface layer (similar to 0.32 mA/cm(2) at 2 V vs RHE). Moreover, the LFO/BFO/STON heterostructure exhibits both photocathodic and photoanodic behavior. The atomic resolution STEM data demonstrate the polarization orientation anisotropy in LFO/BFO/STON heterostructure, due to the cooperative effects of competing surface chemistry and polarization of the LFO/BFO interface over the magnitude and orientation of the Fe3+ cations displacement within the La3+ cages. For the BFO/LFO/STON heterostructure however, robust single-oriented domains with large Fe3+ cations displacement characteristics for long-range ferroelectric order, has been revealed also. Taking into account the possibility to control the PEC features such as charge distribution/transport characteristics for both photocathodic/photoanodic reactions, as well as the control of the polarization direction without a pre-poling process, this work is of relevance for applications where the use of a top electrode is not possible.
21. Ti-zeolite Y based nanocomposites modified with Au and CeO2 with photocatalytic activity in visible light
Authors:
Petcu, G; Anghel, EM; Atkinson, I; Papa, F; Apostol, NG; Baran, A; Petrescu, S; Trica, B; Tenchev, K; Todorova, S; Parvulescu, V
Published: NOV 1 2025, CATALYSIS TODAY, 459, 115403, DOI: 10.1016/j.cattod.2025.115403
Two series of photocatalysts (TYAu, TYCeAu) were obtained. Ti was incorporated by direct synthesis with zeolite Y, while Ce and Au were immobilized by double incipient wetness impregnation method. The experimental weight percents (XRF analysis) were for titanium (0.7 %, 1.9 %, 3.5 %), Ce (1 %), and Au (0.3 %, 0.1 %). The typical crystalline structure of zeolite Y was preserved in all samples except those with 3.5 % Ti, where XRD revealed reduced pattern intensity. SEM and TEM analyses showed morphological changes at higher Ti contents. CO2-TPD confirmed a decrease in basicity with increasing Ti, consistent with the diminished zeolite contribution. XPS analysis indicated the presence of varying Au0/Au+ and Ce3+/Ce4+ ratios on the surface, depending on the Ti content. The intra- and extraframework TiO2 as amorphous or anatase phases were Raman confirmed in ceriumcontaining samples. For materials with high Ti content, the dominant effect was from the Ce and Ti species, accentuated by gold. The surface plasmon resonance effect of Au nanoparticles and decreasing in band gap energy after Ce immobilization was evidenced by UV-Vis spectroscopy. The photocatalytic properties of the synthesized materials were evaluated in CO2 reduction with water and H2 production via water splitting under visible light (525 nm). Higher Ti content enhanced CO2 conversion and reduced CH4 selectivity, favoring the production of CH3OH and CH2O. A greater amount of hydrogen was produced by the samples with the lowest Ti concentration while the reaction was favored by the presence of cerium in the rich titanium samples.
Open Access
22. Experimental and theoretical perspective on band gap modulation in Sr modified BaTiO3 capacitors 2+
Authors:
Zidi, Y; Khaldi, O; Patru, RE; Leonat, LN; Enculescu, M; Toma, V; Stepanova, A; Ben Younes, R; Galca, AC
Published: MAY 2025, CERAMICS INTERNATIONAL, 51, DOI: 10.1016/j.ceramint.2025.01.591
The present study investigates the influence of strontium (Sr) content on the intrinsic properties of barium strontium titanate (Ba1-xSrxTiO3, BST) which was successfully prepared by the conventional solid-state reaction with different concentrations of strontium (x = 0, 0.3, 0.5, 0.6, 0.7, 1). The resulting samples were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy and diffuse reflectance spectroscopy, the dielectric properties being also investigated. Structural and vibrational analyses reveal a structural phase transition from tetragonal to cubic at x = 0.4, with a linear decline of the tetragonality ratio as well as a shrinkage in the unit cell volume that occur with increasing Sr content. The morphological study shows that the grain size decreases as the Sr content increases in the tetragonal phase. Yet, upon the phase transition from tetragonal to cubic, the grain size initially increases, followed by a subsequent decrease with further Sr addition. It has been found that the band gap shows a decrease as Sr content increases. The temperature dependence of the dielectric parameters reveals that the Curie temperature as well as the dielectric constant and the loss tangent are strongly affected by the addition of Sr. The activation energy derived from the dielectric response, was found to be in the range 0.685-1.065eV, suggesting the dominance of doubly ionized oxygen vacancy for conduction and relaxation mechanism. Ab initio calculations were done employing the Linear Combination of Atomic Orbitals (LCAO) method. The bandgap energy (Eg) and the structural parameters were calculated using various types of exchange-correlation functionals (PWGGA, PBE, B3LYP and PBE0). A good agreement with the experimental results is achieved using the PBE0 functional. This study contributes to a better understanding of the structure-property relationship in BaSrTiO3 and provides valuable insights for optimizing its performance in various technological applications.
23. Gas-Assisted Spray Fabrication of Reticulated TiO2 Scaffolds for Perovskite Solar Applications
Authors:
Handor, S; Tomulescu, AG; Stancu, V; Razouk, A; Galca, AC; Leonat, LN
Published: JUN 5 2025, MICROMACHINES, 16, 685, DOI: 10.3390/mi16060685
This study presents a systematic approach to engineering the electron transport layer (ETL) in perovskite solar cells using a spray deposition technique to fabricate sequentially compact and mesoporous titanium dioxide (c-TiO2, m-TiO2) films. The spray coating method leads to the development of a distinct reticulated morphology characterized by well-defined wavy-like surface features and significantly increased roughness-at least twice that of spin-coated mesoporous films. The increased interfacial area between the mesoporous TiO2 and the perovskite layer facilitates more efficient charge transfer, contributing to higher device performance. By optimizing the deposition parameters, particularly the number of spray cycles for the m-TiO2 layer, we achieve a significant enhancement in device performance, with improvements in power conversion efficiency (PCE), reduced series resistance, and minimized hysteresis. Our results demonstrate that an optimal film thickness promotes better perovskite anchoring, while excessive deposition impedes light transmission and increases sheet resistance. These findings advance the practical fabrication of high-performance perovskite solar cells using simple solution-processing techniques and highlights the potential of scalable spray deposition methods for industrial-scale fabrication.
Open Access
24. Influence of in-situ hydrogenation on photoelectrical properties of amorphous and nanocrystalline GeSn deposited by magnetron sputtering
Authors:
Dascalescu, I; Palade, C; Lungu, GA; Lepadatu, AM; Teodorescu, VS; Braic, M; Ciurea, ML; Stoica, T; Slav, A
Published: JAN 5 2025, JOURNAL OF ALLOYS AND COMPOUNDS, 1010, 177065, DOI: 10.1016/j.jallcom.2024.177065
This study investigates the fabrication of short-wavelength infrared (SWIR) photosensitive amorphous and nanocrystalline Ge1-xSnx:H thin films by magnetron sputtering from separate Ge and Sn targets using different Ar: H mixing ratios as working gas. Amorphous Ge1-xSnx:H films have been obtained on both c-Si and fused quartz substrates at ambient temperature, while dynamic nanocrystallization occurs in-situ when the substrate temperature during deposition is raised to 200 degrees C. Fourier-transform infrared spectroscopy has shown the hydrogen incorporation by detecting an absorption line at 1873 cm(-1), close to the value corresponding to Ge-H bonding, only in the room temperature amorphous films. Based on that, we infer that the hydrogen concentration is very low in the films deposited at high temperature. The higher concentration of hydrogen in the amorphous samples is associated with an increase of the absorption gap to 0.5 eV compared to 0.3 eV in the 200 degrees C samples. In-situ (during deposition) and ex-situ (by subsequent rapid thermal annealing) nanocrystallization have been analyzed by high-resolution transmission electron microscopy, X-ray diffraction and micro-Raman spectroscopy. SWIR spectral photosensitivity up to 2.4 mu m was found to be more than two orders of magnitude improved in hydrogenated amorphous films with high hydrogen content, compared to the nanocrystalline ones that are weakly hydrogenated. These findings demonstrate the potential of hydrogenation to enhance the photoelectric properties of GeSn sputtering films for optoelectronic SWIR infrared applications.
25. Ce-doped ZnO photoanode with enhanced photoelectrochemical performance
Authors:
Sima, M; Preda, N; Negrila, C; Matei, E; Sima, A; Stancu, V
Published: MAR 31 2025, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 114, DOI: 10.1016/j.ijhydene.2025.03.048
Photoanodes based Ce-doped ZnO nanorods arrays were prepared by hydrothermal method in order to improve photoelectrochemical efficiency of ZnO photoanodes in water splitting process. Scanning electron microscopy investigation showed ZnO based nanorods with length of around 500 nm and different thicknesses and growth directions. Some morphological changes were noted following the thermal treatment. Energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy measurements proved the presence of cerium species both in bulk and on the surface of ZnO nanorods. A current density of 2.44 mA/cm(2) at 1.23 V against the reversible hydrogen electrode (0.265 V vs. Ag/AgCl) was obtained for Ce-doped ZnO sample, which is >162% increase over that of ZnO sample. The increased photocurrent value obtained for this sample was correlated with the passivation of surface defects evidenced by photoluminescence study and the increased concentration of Ce3+ on the surface. Also, the electrochemical impedance spectroscopy measurements suggested that Ce doping improves the charge transfer in bulk.
26. Growth of pyramidal nanostructures in CeO2-x thin films: Characterization and morphology modeling
Authors:
Craciun, C; Bercea, A; Radu, C; Stîngescu, ML; Bonciu, A; Satulu, V; Filipescu, M
Published: OCT 1 2025, APPLIED SURFACE SCIENCE, 705, 163499, DOI: 10.1016/j.apsusc.2025.163499
Cerium dioxide (CeO2) thin films with pyramidal nanostructures exhibiting a fractal aspect are suitable for various applications that require a large surface area. An accurate model of these films is valuable not only for optimizing the properties for specific applications but also for predicting and understanding the growth mechanism. In this paper, we present the foundation of a simulation for the growth of CeO2-x nanostructured thin films. We propose a 3-dimensional model of the surface nanostructures and link the morphology with crystallographic orientations and growth modes. To validate our model, we fabricated CeO2_ x thin films with different thicknesses using pulsed laser deposition (PLD) and characterized their morphological and structural properties. The evolution of our films shows the representative features of the Stranski-Krastanov model. The morphology changes from compact and smooth to dendritic with pyramidal nanostructures. The texture of our film also changes with thickness, and the preferential orientations are (111) and (220). Additionally, we characterize the CeO2_ x thin films from the chemical and optical points of view. The stoichiometry of CeO2 is not fully achieved, our thin films present the Ce3+ oxidation state at the surface. The formation of C-type Ce2O3 with fluorite structure can be associated with a small refractive index and small band gap.
27. Evaluation of magnetic inhomogeneities in non-stoichiometric Mg0.5Ca0.5Fe2O4 nanoferrite
Authors:
Tiwari, S; Comanescu, C; Iacob, N; Kuncser, V; Salvi, VK; Kumar, S
Published: FEB 15 2024, CERAMICS INTERNATIONAL, 50, DOI: 10.1016/j.ceramint.2023.11.285
Present work reports a systematic study on the evaluation of magnetic inhomogeneities in non-stoichiometric Mg0 & sdot;5Ca0 & sdot;5Fe2O4 nanoferrite (MCNF) by conducting exhaustive dc -magnetization, ac -susceptibility and Fe-57 Mossbauer spectroscopic measurements and exchange bias investigations using training protocol down to 6 K. Rietveld fitting to PXRD established the formation of anticipated spinel fcc phase of MCNF (non-stoichiometric) along with a minute impurity phase of calcite. Scherrer method and HRTEM micrographs illustrated broad size distribution of MCNF nanoparticles with an average nanocrystallite size of -15 nm. Combined 57Fe Mo center dot ssbauer spectroscopic and dc -magnetization analysis establishes coexistence of ferrimagnetic (67 %) & superparamagnetic (33 %) states at 300 K with notable M-s = 22 emu/g, M-r = 4 emu/g & H-c = 130 Oe and blocking of most of the nanoparticles of MCNF below 300 K. The coercivity followed the size -modified Kneller law for ferrimagnetic nanoparticles and the saturation magnetization abides the Bloch law. Moreover the frequencydependent ac -susceptibility investigations revealed two magnetic transitions: (i) A transition at - 330 K in the low frequency data attributed to the relaxation of blocked particles of bigger sizes under the superparamagnetic (SPM) regime and (ii) an irregularity at low temperatures is assigned to surface spin glass freezing. Surface spin glass freezing was further affirmed by the ageing experiments and dynamic scaling law. Furthermore, even the best fit to the dynamic scaling couldn't assert the existence of conventional spin glass phase due to slower spin -flip time of surface spins. A soft ferrimagnetic core of MCNF is enveloped with disordered surface spins, which manifest spin glass state. Concurrently, the findings of exchange bias at 30 K and training effect at 6 K affirmed that MCNF nanoparticles are presenting themselves as FM core- SG shell system. Our experimental findings suggested magnetic inhomogeneities comprised of superparamagnetism, ferrimagnetism and disordered surface spin glass state in the non-stoichiometric MCNF.
Open Access
28. The Effect of Loading W&V:TiO2 Nanoparticles with Noble Metals for CH4 Detection
Authors:
Scarisoreanu, M; Constantinoiu, I; Goncearenco, E; Morjan, IP; Teodorescu, VS; Viespe, C
Published: AUG 2024, CHEMOSENSORS, 12, 160, DOI: 10.3390/chemosensors12080160
TiO2 nanoparticles (NPs) doped with W (W:TiO2), double-doped with W and V (W&V:TiO2), and loaded with noble metals (W:TiO2 @Pt/Pd/Ag and W&V:TiO2@Pt/Pd/Ag) were synthesized by laser pyrolysis followed by chemical impregnation and reduction. Due to its exceptional properties, TiO2 is considered a key material being used in a wide range of applications. To improve its detection activity, the increase in the specific surface of the material, and the presence of defects in its structure play a decisive role. Doped and double-doped TiO2 nanoparticles with dimensions in the range of 25-30 nm presented a mixture of phases corresponding to titania, with the anatase phase accounting for the majority (95%). By loading these nanoparticles with small particles of noble metals, a significant increase in the specific surface area by three or even five times the original values was achieved. Sensitive thin films for surface acoustic wave (SAW) sensors were made with the NPs, embedded in polyethyleneimine (PEI) polymer and deposited by spin-coating. Each sensor was tested at CH4 concentrations between 0.4 and 2%, at room temperature, and the best results were obtained by the sensor with NPs doped with V and decorated with Pd, with a limit of detection (LOD) of 17 ppm, due to the strong catalytic effect of Pd.
29. Enhancing Short-Wave Infrared Photosensitivity of SiGe Nanocrystals-Based Films through Embedding Matrix-Induced Passivation, Stress, and Nanocrystallization
Authors:
Lepadatu, AM; Stavarache, I; Palade, C; Slav, A; Dascalescu, I; Cojocaru, O; Maraloiu, VA; Teodorescu, VS; Stoica, T; Ciurea, ML
Published: MAR 4 2024, JOURNAL OF PHYSICAL CHEMISTRY C, 128, DOI: 10.1021/acs.jpcc.3c06996
The development of new materials for short-wavelength infrared (SWIR) optical sensors is of high importance for the fast development of different applications, as, for example, Internet of Things, road safety, and pollution monitoring. Group IV SiGe provides more sustainable As-, Cd-, and Pb-free nanomaterials that are cheaper and ecologic and offer easy integration with CMOS technology. This Review is on Ge and SiGe quantum dots/nanocrystals (QDs/NCs) embedded in dielectrics for VIS-SWIR photodetection, in which we highlight and discuss photocurrent mechanisms, correlation of photodetection parameters and characteristics with crystalline structure, morphology and energy bandgap, and applications as photodetectors, optical sensors, phototransistors, and solar cells. The embedding matrix induces NC surface passivation, stress field, and nanocrystallization effects and brings specific advantages depending on the matrix material. SiGe NCs in oxides for VIS-SWIR sensing represents a niche domain, showing high photosensitivity (photocurrent) in SWIR up to 1.8 mu m at room temperature and 2 mu m at 100 K, deeper in SWIR than Ge. By alloying Ge with a small content of Si, NC thermal stability is much improved as the detrimental Ge fast diffusion in oxides is hindered and SWIR photosensing is enhanced due to light absorption in Ge-rich SiGe NCs.
Open Access
30. Magnetic Properties of A Cavity-Embedded Square Lattice of Quantum Dots or Antidots
Authors:
Mughnetsyan, V; Gudmundsson, V; Abdullah, NR; Tang, CS; Moldoveanu, V; Manolescu, A
Published: APR 2024, ANNALEN DER PHYSIK, 536, DOI: 10.1002/andp.202300274
Quantum electrodynamical density functional theory is applied to obtain the electronic density, spin polarization, as well as orbital and spin magnetizations of square periodic arrays of quantum dots or antidots subjected to the influence of a far-infrared cavity photon field. A gradient-based exchange-correlation functional adapted to a 2D electron gas in a transverse homogeneous magnetic field is used in the theoretical framework and calculations. The obtained results predict a non-trivial effect of the cavity field on the electron distribution in the unit cell of the superlattice, as well as on the orbital and spin magnetizations. The number of electrons per unit cell of the superlattice is shown to play a crucial role in the modification of the magnetization via the electron-photon coupling. The calculations show that cavity photons strengthen the diamagnetic effect in the quantum dot structure, while they weaken the paramagnetic effect in the antidot structure. As the number of electrons per unit cell of the lattice increases, the electron-photon interaction reduces the exchange forces that will otherwise promote strong spin splitting for both the dot and the antidot arrays. Electronic density, spin polarization, as well as orbital and spin magnetizations of square periodic arrays of quantum dots or antidots subjected to the influence of a far-infrared cavity photon field are obtained using quantum electrodynamical density functional theory adapted to a 2D electron gas in a transverse homogeneous magnetic field. image
31. Magnetocaloric properties of La0.9K0.1MnO3 and La0.8K0.1Pb0.1MnO3 bulk perovskite manganites
Authors:
Bouzid, SA; Elhamouchi, N; Sajieddine, M; Aitmellal, O; Kuncser, V; Galca, AC; Iacob, N; Enculescu, M; Essoumhi, A
Published: NOV 2024, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 35, 2138, DOI: 10.1007/s10854-024-13873-x
In the present work, we report the synthesis and investigations of La0.9K0.1MnO3 and La0.8K0.1Pb0.1MnO3 bulk samples which could be potential magnetocaloric materials for magnetic refrigeration close to room temperature. A flash combustion reaction and sintering at 1200 degrees C for 10 h are used to prepare the bulk materials. Both compounds crystallized into a rhombohedral structure with R3<overline>\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{3 }$$\end{document}c space group confirmed by X-ray powder diffraction results. Scanning electron microscopy analysis, combined with XRD peak profiles is performed to estimate the particle/crystallite size of the samples. Moreover, the Curie temperature, TC, is found to be higher in lead-rich sample due to the enhancement of the grain size and the Mn3+-O-Mn4+ double exchange (DE) interaction. Therefore, the bulk sample La0.8K0.1Pb0.1MnO3 shows a room temperature phase transition of 289 K as well as a higher saturation magnetization. The La0.8K0.1Pb0.1MnO3 bulk compound exhibits a high and sharp peak in magnetic entropy change up to 5.5 Jkg-1 K-1 under 5 T at the magnetic transition temperature TC. To compare the magnetocaloric performances of the studied compounds, relative cooling power (RCP) was employed. The obtained experimental results revealed that the increase in particle size influences severely the magnetocaloric properties.
32. The influence of the functionalization of polystyrene and graphene oxide composites on the flammability characteristics: modeling with artificial intelligence tools
Authors:
Anghel, I; Lisa, C; Curteanu, S; Preda, DM; Sofran, IE; Baia, M; Stroe, M; Paraschiv, M; Baibarac, M; Danciu, V; Cotet, LC; Baia, L
Published: APR 2024, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 149, DOI: 10.1007/s10973-023-12869-9
This paper tackles the influence of the functionalization of polystyrene and graphene oxide (GO) composites on the flammability characteristics. A microscale combustion calorimeter (MCC) was used to experimentally determine the heat release capacity (HRC), the specific heat release rate (HRR) and the total heat released (THR). Neural models were designed that correlate the THR with a number of parameters related to the composition and type of flame retardant used, the heating rate, the amount of residue, the HRC, the peak heat release rate (PHRR), the temperature at the peak pyrolysis rate (TPHRR) and the time elapsed until the occurrence of the peak heat release rate (Time). The best results in the training, validation and testing stages were achieved with the neural model with 9 neurons in the input layer, 40 neurons in the hidden layer and one neuron in the output layer. This model was incorporated into an optimization procedure, based on a genetic algorithm, to establish the values of the input parameters used in the training of the neural networks, in order to generate a minimum THR value, which is the output parameter. Since the synthesis of polystyrene particles with different GO concentrations is costly, this research helps to reduce the number of experimental tests and allows to determine the best GO concentration by means of neural models and genetic algorithms.
33. GRAPHENE FOR ELECTRONIC DEVICES - SYNTHESIS AND CHARACTERIZATION
Authors:
Apostol, M; Enache, A; Diculescu, V; Tite, T; Onea, M; Enculescu, I; Matei, E; Andronescu, E
Published: 2024, UNIVERSITY POLITEHNICA OF BUCHAREST SCIENTIFIC BULLETIN SERIES B-CHEMISTRY AND MATERIALS SCIENCE, 86, DOI:
In this paper, graphene was obtained on a copper substrate using the CVD method, and then it was transferred to various substrates such as glass and SiO2/Si patterned with metallic interdigitated electrodes. The graphene thus obtained was characterized using Raman spectroscopy, scanning electron microscopy (SEM), current-voltage measurements, and electrochemical methods, in order to be used for sensing applications.
Open Access
34. Phase transitions in ferroelectric ZrO2 thin films
Authors:
Pereira, RMP; Istrate, MC; Figueiras, FG; Lenzi, V; Silva, BM; Benamara, M; Romanyuk, KN; Ghica, C; Almeida, BG; Marques, L; Pereira, M; Silva, JPB
Published: MAR 15 2024, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 172, 108102, DOI: 10.1016/j.mssp.2023.108102
In this work, the formation of the orthorhombic phase of ZrO2 together with the minor monoclinic phase were elucidated by X-ray diffraction and transmission electron microscopy. Moreover, oxidized W can be responsible for the formation of oxygen vacancies in the ZrO2 through oxygen scavenging. The ferroelectric properties of the W/ZrO2/W film capacitors were investigated through piezoresponse force microscopy (PFM) and polarizationvoltage measurements. A second-order phase transition from the polar orthorhombic phase to the non-polar tetragonal phase was observed. Density functional theory calculations confirm our experimental results and propose that oxygen vacancies are responsible for the Curie-Weiss temperature of 130 degrees C, significantly lower than the theoretical value for the bulk.
35. Dielectric characterization of polymer dispersed liquid crystal film with chitosan biopolymer
Authors:
Manaila-Maximean, D; Ilis, M; Ganea, PC; Micutz, M; Boscornea, C; Circu, V
Published: JAN 1 2024, JOURNAL OF MOLECULAR LIQUIDS, 393, 123552, DOI: 10.1016/j.molliq.2023.123552
Polymer Dispersed Liquid Crystals (PDLC) systems were obtained using chitosan as a biopolymer matrix and the nematic liquid crystal (LC) mixture E7 in various concentrations (30, 40 and 50% E7 in chitosan). Several techniques were used to analyze the obtained films: polarizing optical microscopy (POM), IR spectroscopy (FTIR), differential scanning calorimetry (DSC) and dielectric spectroscopy (DS). FTIR spectroscopy revealed minor changes for all PDLC films, suggesting weak interactions between LC and chitosan matrix. For each sample a clear segregation of the nematic droplets could be observed by POM. DSC measurements show that the phase transitions have shifted to lower temperature values for PDLC samples with approximately 2.7 degrees C compare to pure E7. The values of alpha (fraction of LC in the droplets) for compositions of 30, 40 and 50 wt% E7 in Chitosan were 0.48, 0.55 and 0.61 respectively, that are lower than for E7/PMMA system. The qualitative and quantitative analysis of the permittivity spectra obtained by DS reveals the fact that there are no significant changes in the molecular dynamics attributed to pure LC E7 compared to the PDLC composites, leading to the conclusion of the existence of a weak interaction between the two components, fact confirmed by the findings from the FTIR results.
Open Access
36. Magnetic behaviors of exchange-biased Fe(FM)-FeO(AFM)-ZnO nanocomposites of different iron concentrations prepared under non-identical conditions with annealing in a reducing atmosphere
Authors:
Mihalache, V
Published: MAR 2024, RESULTS IN PHYSICS, 58, 107469, DOI: 10.1016/j.rinp.2024.107469
Preparation under non-identical conditions involving the reduction of sol-gel-derived precursors of various Zn:Fe atomic ratios (0.97:0.03, 0.8:0.2 and 0.4:0.6) in a hydrogen-containing atmosphere was used to obtain composites of nanosized ferromagnetic (FM) alpha-Fe and antiferromagnetic (AFM) FeO in different concentrations and of the desired magnetic responses. ZnO nanoparticles, developed in all preparation stages, served primarily as a matrix for the separation of Fe (and FeO) nanoparticles, preventing their agglomeration and coarsening. The average crystallite/particle size is about 5-32 nm, 10-75 nm and 21-31 nm for FeO, Fe and ZnO, respectively. Magnetisation investigations of FeO-Fe-ZnO nanocomposites revealed a coexistence of ferromagnetic and superparamagnetic behaviours ascribed to the Fe nanoparticles in different magnetic states. All samples exhibit the exchange bias effect, EB. Values up to 375 Oe for coercivity at 300 K, 600 Oe for coercivity, 223 for coercivity enhancement and 243 Oe for EB field at 5 K were measured. The magnitude of EB depends on the processing conditions - the EB field and coercivity enhancement are larger for samples processed under conditions of a higher degree of non-equilibrium. The presence of FeO appears crucial for the occurrence of EB, irrespective of its quantity. The EB is ascribed primarily to the exchange coupling between the AFM and FM spins at the FeO/Fe interfaces of nanostructures after field-cooling from above the TN of FeO and below the Curie temperature of Fe. An approach based on magnetically disordered AFM/FM interfaces featuring like spin-glass systems was adopted to explain the EB effects. An aspect of practical relevance is the suppression of room temperature coercivity in apparent correlation with the training of the EB; an attempt has been made to understand the origin of this suppression.
37. Single-Molecule Magnet Behavior and Spin Structure of an FeIII 7 Cartwheel Cluster Revealed by Sub-Kelvin Magnetometry and Mossbauer Spectroscopy: The Final Pieces of the Puzzle
Authors:
Bartolomé, J; Bartolomé, E; Luis, F; Burzurí, E; Camón, A; Filoti, G; Ako, AM; Braun, J; Mereacre, V; Anson, CE; Powell, AK
Published: DEC 9 2024, INORGANIC CHEMISTRY, 63, DOI: 10.1021/acs.inorgchem.4c04191
The spin frustration and other magnetic properties of the "cartwheel" heptanuclear cluster [FeIII 7O3(O2C t Bu)9(Me-dea)3(H2O)3] (Me-deaH2 = N-methyldiethanolamine) have been previously investigated; we present here a Mossbauer spectroscopic study and sub-Kelvin magnetization and ac susceptibility measurements which enable a complete magnetic picture of this frustrated cluster. 57Fe Mossbauer spectra above 150 K showed three doublets in a 1:3:3 ratio, which could be assigned by their respective quadrupole splittings to the central Fe(1) and the peripheral Fe(2) and Fe(3). The field dependence of the corresponding magnetic sextets at 3 K showed that the spins on the central Fe(1) and the three peripheral Fe(2) sites with O5N coordination are oriented mutually coparallel, while these are antiparallel to the spins on the peripheral Fe(3) sites with O6 coordination, resulting in an overall S = 5/2 ground state. This provides experimental confirmation of the previously proposed spin ground state structure. Upon cooling to sub-Kelvin temperatures, a crossover to spin blocking with T B approximate to 0.21 K could be observed. This single-molecule magnet behavior had been expected but had not been observable with a conventional SQUID. The anisotropy barrier, of 3-fold symmetry, can be described in terms of the parameter D/k B = -0.47 K and a fourth-order perturbation; the latter enables thermally activated quantum tunneling through the excited sublevel m z = +/- 3/2, with an activation barrier of U/k B = 1.9 K.
Open Access
38. Improving the control of the electroforming process in oxide-based memristive devices by X-ray nanopatterning
Authors:
Mino, L; Bonino, V; Alessio, A; Picollo, F; Kuncser, A; Mercioniu, I; Vlaicu, AM; Badica, P; Brescia, R; Fretto, M; Goss, K; Dittmann, R; Truccato, M
Published: JUL 25 2024, JOURNAL OF MATERIALS CHEMISTRY C, 12, DOI: 10.1039/d4tc01815j
We explored the possibility to guide the forming process in a Ta/TiO2/Pt memristive device using an X-ray nanopatterning procedure, which enables the manipulation of the oxygen content at the nanoscale. The irradiation of selected areas of the sample by a 65 x 58 nm2 synchrotron X-ray nanobeam locally generated oxygen vacancies which resulted in the formation of a conductive filament in the desired position in the material. The subsequent application of an electric field between the electrodes was exploited to achieve reversible bipolar resistive switching. A multitechnique characterization was then performed, highlighting a local increase in the height of the crystal and the formation of a dislocation network, associated with the presence of Wadsley defects. Our results show that X-ray nanopatterning could open new avenues for a more deterministic implementation of electroforming in oxide-based memristive devices. We tuned the oxygen content in a Ta/TiO2/Pt memristive device at the nanoscale by a synchrotron X-ray nanobeam. We obtained a conductive filament of oxygen vacancies in the desired position in the material to achieve a controlled resistive switching.
Open Access
39. Insulin loaded iron magnetic nanoparticle-graphene oxide composites: synthesis, characterization and application for in vivo delivery of insulin
Authors:
Turcheniuk, K; Khanal, M; Motorina, A; Subramanian, P; Barras, A; Zaitsev, V; Kuncser, V; Leca, A; Martoriati, A; Cailliau, K; Bodart, JF; Boukherroub, R; Szunerits, S
Published: DEC 3 2024, RSC ADVANCES, 14, DOI: 10.1039/d4ra90136c
Open Access
40. Microstructure and coupling mechanisms in MnBi-FeSiB nanocomposites obtained by spark plasma sintering
Authors:
Alexandru-Dinu, A; Locovei, C; Bartha, C; Grigoroscuta, MA; Burdusel, M; Kuncser, A; Palade, P; Schinteie, G; Iacob, N; Lu, W; Batalu, D; Badica, P; Kuncser, V
Published: JUL 24 2024, SCIENTIFIC REPORTS, 14, 17029, DOI: 10.1038/s41598-024-67353-7
Fabrication and extensive characterization of hard-soft nanocomposites composed of hard magnetic low-temperature phase LTP-MnBi and amorphous Fe70Si10B20 soft magnetic phase for bulk magnets are reported. Samples with compositions Mn55Bi45 + x center dot(Fe70Si10B20) (x = 0, 3, 5, 10, 20 wt.%) were prepared by spark plasma sintering of powder mixtures. Characterization has been performed by X-ray diffraction, scanning and transmission electron microscopy, magnetometry and Fe-57 Mossbauer spectroscopy. It was shown that samples contain crystallized and nanometric LTP-MnBi phases with various elemental compositions depending on the degree of Bi clustering. Complex correlations between starting compositions, processes during fabrication, and functional magnetic characteristics were observed. Unexpected special situations of the relation between microstructure and magnetic coupling mechanisms are discovered. Exchange spring effects of different strengths occur, being very sensitive to morpho-structural and compositional features, which in turn are controlled by processing conditions. An in-depth analysis of related microscopic characteristics is provided. Results of this work suggest that fabrication by powder metallurgy routes, such as spark plasma sintering of hard and soft magnetic powder mixtures, of MnBi-based composites with exchange spring phenomena have a high potential in designing and optimization of suitable materials with tunable magnetic properties towards rare-earth-free permanent magnet applications.
41. Biocompatible and antimicrobial chitosan/PVP/PEO/PAA/AgNP composite hydrogels synthesized by e-beam cross-linking
Authors:
Demeter, M; Calina, I; Scarisoreanu, A; Mitran, V; Popa, M; Cîmpean, A; Chifiriuc, MC; Micutz, M; Matei, E; Mitu, B
Published: MAR 2024, RADIATION PHYSICS AND CHEMISTRY, 216, 111391, DOI: 10.1016/j.radphyschem.2023.111391
Novel biocompatible composite hydrogels with good elastic and antimicrobial properties have been fabricated by e-beam cross-linking using chitosan and water-soluble polymers mixed with commercial silver nanoparticles (AgNP). Hydrogels having different formulations were characterized by rheological, swelling, FTIR, SEM, and biodegradation measurements. The network structure, biocompatibility, and antimicrobial properties were evaluated as well. The composite hydrogels showed higher stability and absorb large amounts of fluids specific to an infected wound without losing structural integrity. The rheological, SEM, and network structure results demonstrate that at above 0.1 mg/mL AgNP, hydrogels with high cross-linking density are obtained. The in vitro response of fibroblasts proved the high biocompatibility of the hydrogel's composites. The antimicrobial activity is directly influenced by the amount of AgNP and cross-linking degree of the hydrogel. Significant antimicrobial activity was recorded against Gram-negative bacteria, while for the Gram-positive ones, the growth inhibition seems to require a decrease of the cross-linking degree.
Open Access
42. Hydrothermal carbonization and pyrolysis in wetland engineering: Carbon sequestration, phosphorus recovery, and structural characterization of willow-based chars with X-ray μ-computed tomography
Authors:
Acosta, AC; Arias, CA; Biller, P; Wittig, NK; Baragau, IA; Alhnidi, MJ; Ravenni, G; Sárossy, Z; Benedini, L; Abramiuc, LE; Popescu, DG; Negassa, W; Marulanda, VF; Müller-Stöver, DS; Brix, H
Published: JUL 15 2024, CHEMICAL ENGINEERING JOURNAL, 492, 151916, DOI: 10.1016/j.cej.2024.151916
Willows from engineered wetland systems (EWS) offer a sustainable approach to wastewater treatment and biomass production. Our study assesses their potential for nutrient recovery and carbon sequestration using slow pyrolysis (600 degrees C) and hydrothermal carbonization (250 degrees C). Here, we propose EWS-pyrochars as a ready-to integrate opportunity for soil amendment, as they exhibit a predominant CO2 2 release and the absence of harmful compounds in pyrolysis-chromatograms, indicating higher stability than hydrochars. Using sequential Pextractions, we observed a high bioavailability in the willow-woodchips and a significant P-retention in EWSchars-up to 92 % in pyrochars and near-complete retention in hydrochars, along with a higher labile-P fraction of 21 % in hydrochars than 5 % in pyrochars. Utilizing X-ray-based techniques, Raman spectroscopy, scanning electron microscopy, and gas physisorption, we characterized the EWS-chars' structures. We revealed innovative 3D-visualizations, which transcend previous literature by providing insights into the chars' internal porosity and quantifying, for the first time, their carbonaceous structural thickness via a meshing algorithm and the mean Feret diameter. EWS-pyrochars exhibit remarkable aromaticity with a higher concentration of overall sp2 2 Catoms at 63 % vs. 43 % in hydrochars. Moreover, unlike hydrochars, which depict occluded porosity, EWSpyrochars exhibited 92 % water storage-like pores. Although hydrochars indicated lower carbonization and thermal stability than pyrochars, their higher carbon retention (55 vs. 41 % in pyrochar) suggest superior annual benefits-on a 10 ha EWS scale-of 80-tons of carbon sequestration and 334 kg of phosphorus recovery versus 60-tons of carbon and 298 kg of phosphorus with pyrochars. Our findings suggest innovative materials for resource recovery, advancing the engineered wetland systems field, shifting their traditional use, and opening the opportunity for future integration into biorefineries.
Open Access
43. Magneto-optical properties of a quantum dot array interacting with a far-infrared photon mode of a cylindrical cavity
Authors:
Gudmundsson, V; Mughnetsyan, V; Goan, HS; Chai, JD; Abdullah, NR; Tang, CS; Moldoveanu, V; Manolescu, A
Published: JUN 26 2024, PHYSICAL REVIEW B, 109, 235306, DOI: 10.1103/PhysRevB.109.235306
We model the equilibrium properties of a two-dimensional electron gas in a square lateral superlattice of quantum dots in a GaAs heterostructure subject to an external homogeneous perpendicular magnetic field and a far-infrared circular cylindrical photon cavity with one quantized mode, the TE011 mode. In a truncated linear basis constructed by a tensor product of the single-electron states of the noninteracting system and the eigenstates of the photon number operator, a local spin density approximation of density functional theory is used to compute the electron-photon states of the two-dimensional electron gas in the cavity. The common spatial symmetry of the vector fields for the external magnetic field and the cavity photon field in the long wavelength approximation enhances higher order magnetic single- and multiphoton processes for both the para- and the diamagnetic electron-photon interactions. The electron-photon coupling introduces explicit photon replicas into the band structure and all subbands gain a photon content, constant for each subband, that can deviate from an integer value as the coupling is increased or the photon energy is varied. The subbands show a complex Rabi anticrossing behavior when the photon energy and the coupling bring subbands into resonances. The complicated energy subband structure leads to photon density variations in reciprocal space when resonances occur in the spectrum. The electron-photon coupling polarizes the charge density and tends to reduce the Coulomb exchange effects as the coupling strength increases.
Open Access
44. Bimetallic Mesoporous MCM-41 Nanoparticles with Ta/(Ti, V, Co, Nb) with Catalytic and Photocatalytic Properties
Authors:
Parvulescu, V; Petcu, G; Apostol, NG; Atkinson, I; Petrescu, S; Baran, A; Culita, DC; Ene, R; Trica, B; Anghel, EM
Published: DEC 2024, NANOMATERIALS, 14, 2025, DOI: 10.3390/nano14242025
Bimetallic (Ta/Ti, V, Co, Nb) mesoporous MCM-41 nanoparticles were obtained by direct synthesis and hydrothermal treatment. The obtained mesoporous materials were characterized by XRD, XRF, N2 adsorption/desorption, SEM, TEM, XPS, Raman, UV-Vis, and PL spectroscopy. A more significant effect was observed on the mesoporous structure, typically for MCM-41, and on optic properties if the second metal (Ti, Co) did not belong to the same Vb group with Ta as V and Nb. The XPS showed for the TaTi-MCM-41 sample that framework titanium is the major component. The new nanoparticles obtained were used as catalysts for oxidation with hydrogen peroxide of olefinic compounds (1,4 cyclohexadiene, cyclohexene, styrene) and photodegradation of organic pollutants (phenol, methyl orange) from water. The results showed improvementsin activity and selectivity in oxidation reactions by the addition of the second metal to the Ta-MCM-41 catalyst. The slow addition of H2O2 was also beneficial for the selectivity of epoxide products and the stability of the catalysts. The band gap energy values decreased in the presence of the second metal, and the band edge diagram evidenced positive potential for all the conduction bands of the bimetallic samples. The highestlevels of photocatalytic degradation were obtained for the samples with TaTi and TaV.
45. Tuning of paramagnetic and diamagnetic cavity photon excitations in a square array of quantum dots in a magnetic field
Authors:
Gudmundsson, V; Mughnetsyan, V; Goan, HS; Chai, JD; Abdullah, NR; Tang, CS; Moldoveanu, V; Manolescu, A
Published: NOV 12 2024, PHYSICAL REVIEW B, 110, 205301, DOI: 10.1103/PhysRevB.110.205301
We employ a "real-time" excitation scheme to calculate the excitation spectra of a two-dimensional electron system in a square array of quantum dots placed in a circular cylindrical far-infrared photon cavity subjected to a perpendicular homogeneous external magnetic field. The Coulomb interaction of the electrons is handled via spin density functional theory and the para- and the diamagnetic parts of the electron-photon coupling are updated according to a configuration interaction method in each iteration of the density functional calculation. The results show that an excitation scheme built on using the symmetry of the lateral square superlattice of the dots and the cylindrical cavity produces both para- and diamagnetic resonance peaks with oscillator strengths that can be steered by the excitation pulse parameters. The excitation method breaks the conditions for the generalized Kohn theorem and allows for insight into the subband structure of the electron system and can be used both inside and outside the linear response regime.
Open Access
46. Unlocking superior NO2 sensitivity and selectivity: the role of sulfur abstraction in indium sulfide (InS) nanosheet-based sensors
Authors:
D'Olimpio, G; Boukhvalov, DW; Galstyan, V; Occhiuzzi, J; Vorochta, M; Amati, M; Milosz, Z; Gregoratti, L; Istrate, MC; Kuo, CN; Lue, CS; Ghica, C; Comini, E; Politano, A
Published: APR 30 2024, JOURNAL OF MATERIALS CHEMISTRY A, 12, DOI: 10.1039/d4ta01287a
To advance gas sensor technologies, it is essential to identify materials that exhibit both high selectivity and sensitivity. Here, we unravel the gas-sensing capabilities of indium sulfide (InS) nanosheets, particularly in relation to nitrogen dioxide (NO2) detection. Utilizing a synergistic approach that combines in situ and operando experimental methodologies with density functional theory calculations, we demonstrate that these nanosheets offer outstanding sensitivity toward NO2, characterized by a remarkably low detection threshold of 180 ppb at an operational temperature of 350 degrees C. This remarkable sensitivity is ascribed to the electronic charge redistribution around the Fermi level, facilitated by an oxygen-deficient In2O3-x surface layer that forms naturally when the InS surface is exposed to ambient conditions. A pivotal aspect of our investigation was the exploration of the influence of sulfur abstraction on these surface modifications. We demonstrate that sulfur abstraction plays a critical role in the formation and operational efficacy of the In2O3-x layer, thereby acting as a key element in the sensor mechanism. This unique surface chemistry not only amplifies the sensitivity to NO2 but also confers unparalleled selectivity over other gases and volatile organic compounds. Notably, this level of performance exceeds that of other 2D semiconductors and metal oxides, thus establishing InS nanosheets as an ideal platform for high-performance gas sensors suitable for demanding environments. Moreover, unlike many state-of-the-art sensor materials, InS-based sensors can withstand a wider variety of environmental conditions due to their superior water adsorption resistance.
Open Access
47. MAPLE deposition of hybrid PLGA-Fe3O4-Cypress-PEDOT: PSS coatings
Authors:
Stefan, N; Visan, AI; Grumezescu, V; Kuncser, V; Kuncser, A; Iacob, N; Schinteie, G; Socol, M; Florica, C; Zgura, I; Popescu, RC; Holban, AM; Socol, G
Published: JUN 2024, GIANT, 18, 100250, DOI: 10.1016/j.giant.2024.100250
We report on the Matrix Assisted Pulsed Laser Evaporation, laser technology for depositing biocompatible, antimicrobial, hydrophilic, and biodegradable complex hybrid polymeric system loaded with essential cypress-oil and magnetite nanoparticles as resorbable implants, capable of targeting possible hyperthermia applications, an anticancer moderate field heating therapy. Magnetite nanoparticles based on iron oxide (Fe3O4) coated with Cypress essential oil (denoted: Fe3O4- Cypress) and embedded in PLGA (poly(lactic-co-glycolic acid) (denoted: PLGA-Fe3O4- Cypress-) and PLGA - poly(3,4ethylene dioxythiophene) doped with poly(styrene sulfonate) anions) (PEDOT: PSS) mixture (denoted: PLGA-Fe3O4- Cypress- PEDOT: PSS) were used as MAPLE targets. The controlled drug delivery of the active Cypress oil, an antimicrobial therapeutic agent from Fe3O4- Cypress nanoparticles could be possible by applying an external radio frequency (RF) magnetic field. The Fe3O4-Cypress-based powders as well as the final hybrid coatings have been characterized in terms of stoichiometry, morphology, magnetic, antimicrobial properties, biocompatibility, and response to external physical stimuli. FTIR analyses confirmed the quasi-stoichiometric laser transfer of organic compounds while the XRD evidenced the semicrystalline structure of deposited thin films. SEM and AFM images evidence that conductive polymer addition led to the films' relief flattening and a decrease in the coatings' thickness and roughness by changing the polymeric packaging. The samples containing conductive polymer exhibited 3 times higher current and corrosion rate values. All coatings are hydrophilic and revealed enhanced cellular viability when cultured with osteoblast-like MG-63 cells. The composite structures exhibited significant antimicrobial activity against Gram-positive (Staphylococcus aureus), and Gram -negative (Escherichia coli ) bacteria, as well as to the opportunistic yeast Candida albicans.
48. Palladium-Coated Submicron Electrospun Polymeric Fibers with Immobilized Uricase for Uric Acid Determination in Body Fluids
Authors:
Leote, RJB; Crisan, DN; Matei, E; Enculescu, I; Diculescu, VC
Published: FEB 12 2024, ACS APPLIED POLYMER MATERIALS, 6, DOI: 10.1021/acsapm.3c02811
This work describes the development of a flexible uric acid (UA) biosensor based on palladium-coated submicrometer electrospun poly(methylmethacrylate) (PMMA) fibers metalized with gold and attached to polyethylene terephthalate substrate (Pd/Au/PMMA/PET). The morphological characterization conducted by scanning electron microscopy revealed nanoscale Pd dendritic structures. Electrochemical investigations in the absence and in the presence of redox probes demonstrated that these Pd nanostructures are responsible for a six-fold increase in the electroactive area and enhanced electron transfer kinetics when compared to the gold-coated electrospun fibers. The UA biosensor obtained by immobilizing the uricase enzyme (UrOx) onto the Pd/Au/PMMA/PET electrode surface, allowed UA detection with a sensitivity of 431 mu A cm(-2) mM(-1) and a limit of detection of 12 mu M. Investigation of the redox reactions of hydrogen peroxide (a product of the enzymatic oxidation of UA by UrOx) at the Pd/Au/PMMA/PET electrode demonstrated that the working principle of the biosensor is based on the reduction of PdO produced at the electrode surface during the spontaneous reduction of hydrogen peroxide on Pd. This allows a biosensor operating potential of -0.05 V (vs Ag/AgCl) with high selectivity. The UrOx/Pd/Au/PMMA/PET biosensor was applied for UA detection in body fluids (sweat, urine, and blood serum) with recovery values between 98 and 105%, which were validated by high-performance liquid chromatography analysis. The stability of the device was evaluated over a period of 3 months, retaining 78% of the initial sensitivity, and reproducibility with RSD = 4.9% was achieved. The analytical performance of the biosensor under harsh mechanical deformations and at physiological temperatures demonstrated the potential applications of the device to wearable sensing platforms.
Open Access
49. Thermodynamic and Kinetic Simulations Used for the Study of the Influence of Precipitates on Thermophysical Properties in NiTiCu Alloys Obtained by Spark Plasma Sintering
Authors:
Cirstea, CD; Povoden-Karadeniz, E; Cirstea, V; Tolea, F; Kozeschnik, E
Published: MAR 2024, NANOMATERIALS, 14, 461, DOI: 10.3390/nano14050461
The thermodynamic and kinetic simulations based on the re-assessment of the thermodynamic and kinetic database of the Ni-Ti-Cu system were employed to predict the phenomena of mechanical alloying, spark plasma sintering and thermal properties of the intriguing Ni-Ti-Cu system. Thermodynamic calculations are presented for the stable and unstable phases of NiTiCu materials and support a correlation with the evolving microstructure during the technological process. Also, the thermal conductivity, the thermal diffusivity and the specific heat of spark plasma sintered and aged Cu-alloyed NiTi-based shape memory alloys (NiTiCu) with two compositions, Ni45Ti50Cu5 and Ni40Ti50Cu10, are evaluated and the influence of mechanical alloying and precipitates on thermal properties is discussed. Measurements of these thermal properties were carried out from 25 degrees C up to 175 degrees C using the laser flash method, as well as differential scanning calorimetry. The thermal hysteresis of the 20 mm diameter samples was between 8.8 and 24.5 degrees C. The observed T0 temperatures from DSC experimental transformation features are in reasonable accordance with the thermodynamic predictions. The determined k values are between 20.04 and 26.87 W/m K and in agreement with the literature results. Moreover, this paper can provide some suggestions for the preparation of NiTiCu shape memory alloys and their applications.
Open Access
50. Fractal Behavior of Nanostructured Pt/TiO2 Catalysts: Synthesis, Characterization and Evaluation of Photocatalytic Hydrogen Generation
Authors:
Vasile, A; Dobrescu, G; Bratan, V; Teodorescu, M; Munteanu, C; Atkinson, I; Negrila, C; Papa, F; Balint, I
Published: SEP 2024, CATALYSTS, 14, 619, DOI: 10.3390/catal14090619
The fractal characterization of supported nanoparticles is a useful tool for obtaining structural and morphological information that strongly impacts catalytic properties. We have synthesized and characterized Pt supported on TiO2 nanostructures. Triblock copolymers with thermosensitive properties were used as templating agents during the synthesis process. In addition to the several techniques used for the characterization of the materials, we carried out fractal analysis. The prepared materials showed a reduction in the band gap of TiO2 from 3.44 to 3.01 eV. The extended absorption in the 500-700 nm regions is mostly attributed to the presence of supported Pt nanoparticles. The ability of the nanostructured Pt/TiO2 catalysts to generate H-2 in an aqueous solution was evaluated. The test reaction was carried out in the presence of methanol, as a hole scavenger, under simulated solar light. Pt/TiO2-3TB shows the highest rate of H-2 (4.17 mmol h(-1) g(cat)(-1)) when compared to Pt/TiO2-0TB (3.65 mmol h(-1) g(cat)(-1)) and Pt/TiO2-6TB (2.29 mmol h(-1) g(cat)(-1)) during simulated solar light irradiation. Pt/TiO2-3TB exhibits a more structured organization (fractal dimensions of 1.65-1.74 nm at short scales, 1.27-1.30 nm at long scales) and a distinct fractal behavior. The generation of hydrogen via photocatalysis can be linked to the fractal characteristics.
Open Access
51. Bioactive Hybrids Containing Artificial Cell Membranes and Phyto-Gold-Silver Chloride Bio-Nanoparticles
Authors:
Barbinta-Patrascu, ME; Nichita, C; Enculescu, M; Maraloiu, VA; Bacalum, M; Ungureanu, C; Negrila, CC; Zgura, I
Published: NOV 2024, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 25, 11929, DOI: 10.3390/ijms252211929
This research targets the need for eco-friendly strategies in the synthesis of bioactive materials, addressing the importance of valorization of vegetal waste. This study focuses on developing biohybrids containing biomimetic lipid vesicles and phytosynthesized gold-silver chloride nanoparticles (AuAgCl NPs) derived from Achillea millefolium L. extract. By leveraging the natural antioxidant and antimicrobial properties of the plant, the research proposes a sustainable approach to creating materials with potential biomedical applications. The biomimetic membranes were loaded with chlorophyll a, a natural spectral marker. Three types of bioactive materials (biohybrids) were developed by varying the lipid vesicle/AuAgCl NP ratio. Optical (UV-Vis, fluorescence emission, FTIR), structural (XRD), elemental (EDX, XPS), and morphological (TEM) studies were performed to characterize the bio-developed materials. The hydrophobic/hydrophilic characteristics of the samples were investigated by measuring the water contact angle, and their size was estimated by DLS and TEM. Zeta potential measurements were used to evaluate the physical stability of phyto-developed particles. Antioxidant properties of phyto-particles were investigated through the chemiluminescence technique. The obtained biomaterials exhibited high antioxidant activity and antiproliferative activity against HT-29 and B-16 cancer cells. Therapeutic index values were calculated for each biohybrid. Additionally, the bio-prepared hybrids revealed biocidal action against Staphylococcus aureus and Enterococcus faecalis. The phyto-developed biomaterials are promising in biomedical applications, particularly as adjuvants in cancer therapy.
52. Downscaling grain size toward the nanometre range - A key-factor for tuning the crystalline structure, phase transitions, dielectric and ferroelectric behaviour in Ba 0.8 Sr 0.2 TiO 3 ceramics
Authors:
Patru, RE; Stanciu, CA; Surdu, VA; Soare, EM; Trusca, RD; Vasile, BS; Nicoara, AI; Trupina, L; Pasuk, I; Botea, M; Horchidan, N; Mitoseriu, L; Pintilie, L; Pintilie, I; Ianculescu, AC
Published: JUN 2024, PROGRESS IN SOLID STATE CHEMISTRY, 74, 100457, DOI: 10.1016/j.progsolidstchem.2024.100457
The present study aims to describe the role of the grain size on the properties of submicron- and nano-structured Ba0.8Sr0.2TiO3 (BST) ceramics. Dense (1 - 2% porosity) ceramics with average grain sizes in the range of (77 234) nm were consolidated under different spark plasma sintering conditions starting from nanopowders with a mean particle size of 70 nm, synthesized via the acetate variant of the sol-gel method. The structural analysis based on XRD data revealed a mixture of cubic and tetragonal modifications at room temperature for the precursor powders and for all the investigated ceramics. The structural heterogeneity of the individual ceramic grains with coexistence of cubic and tetragonal polymorphs was confirmed by HR-TEM investigations. Accordingly, a "brick-wall" model with cubic grain boundary regions and tetragonal grain cores is proposed. By increasing the grain size, from 77 to 234 nm, a decrease of the phase transitions diffuseness accompanied by an increase of the permittivity maxima (from 650 to 4500) and dielectric losses (from 5 to 7.5%, at 100 Hz), was detected by broadband dielectric spectroscopy. No variation of the Curie temperature in the investigated Ba0.8Sr0.2TiO3 ceramics was detected, unlike typically reported for BaTiO3 ceramics with similar grain sizes. The Curie-Weiss temperature and the Curie constant decrease when grain size is diminished, indicating an overall reduction of the ferroelectric active volume, as a scaling effect. The ferroelectric switching was demonstrated for all the selected fine-grained BST ceramics, either at nanoscale or macroscopically, with an increased ferroelectric character for the coarser submicron-structured ceramics, with respect to the nanocrystalline one. The observed properties of the fine-grained Ba0.8Sr0.2TiO3 ceramics are explained in the frame of multiphase coexistence and ferroelectricity "dilution" due to the increasing role of non-ferroelectric grain boundaries when reducing grain size and complete the knowledge on the scale-dependent properties of dense fine-grained BaTiO3-based ceramics.
Open Access
53. Customized flexible platform - starting point for the development of wearable sensor for the direct electrochemical detection of kynurenic acid in biological samples
Authors:
Irimes, MB; Tertis, M; Bogdan, D; Diculescu, V; Matei, E; Cristea, C; Oprean, R
Published: DEC 1 2024, TALANTA, 280, 126684, DOI: 10.1016/j.talanta.2024.126684
Kynurenic acid (KA) is an active metabolite of tryptophan with notable biological effects, such as antioxidant, neuroprotective, and anti-inflammatory properties. It often undergoes changes of the concentration in biological fluids in chronic diseases. Thus, detecting KA is of great importance for diagnosing inflammatory and neurodegenerative conditions, monitoring disease progression, and assessing responses to pharmacological treatment. This study aimed to design a tailored, flexible platform for sensitive and direct electrochemical detection of KA in biological fluids. Carbon-based electrodes were custom-printed in the lab using specialized inks and flexible substrates. The working electrodes were further functionalized with graphene oxide and subsequently electrochemically reduced to increase the sensitivity toward the analyte. An optimized differential pulse voltammetry protocol was developed for KA detection. The elaborated platform was firstly characterized and then evaluated regarding the analytical performances. It showed a good limit of detection (3 nM and demonstrated the capability to detect KA across a broad concentration range (0.01-500 mu M). Finally, the elaborated flexible platform, was succesfully applied for KA determination in serum and saliva samples, in comparison with an optimized HPLC-UV method. The developed platform is the first example of in-lab printed flexible platform reported in literature so far for KA detection. It is also the first study reported in the literature of detection of KA in raw saliva collected from 10 subjects. The sensitivity towards the target analyte, coupled with the adaptability and portability, showcases the potential of this platform for thus illustrating great potential for further development of wearable sensors and biomedical applications.
Open Access
54. Nb2O5 Microcolumns for Ethanol Sensing
Authors:
Kumarage, GWC; Panamaldeniya, SA; Maraloiu, VA; Dassanayake, BS; Gunawardhana, N; Comini, E
Published: MAR 2024, SENSORS, 24, 1851, DOI: 10.3390/s24061851
Pseudohexagonal Nb2O5 microcolumns spanning a size range of 50 to 610 nm were synthesized utilizing a cost-effective hydrothermal process (maintained at 180 degrees C for 30 min), followed by a subsequent calcination step at 500 degrees C for 3 h. Raman spectroscopy analysis unveiled three distinct reflection peaks at 220.04 cm(-1), 602.01 cm(-1), and 735.3 cm(-1), indicative of the pseudohexagonal crystal lattice of Nb2O5. The HRTEM characterization confirmed the inter-lattice distance of 1.8 & Aring; for the 110 plain and 3.17 & Aring; for the 100 plain. The conductometry sensors were fabricated by drop-casting a dispersion of Nb2O5 microcolumns, in ethanol, on Pt electrodes. The fabricated sensors exhibited excellent selectivity in detecting C2H5OH (Delta G/G = 2.51 for 10 ppm C2H5OH) when compared to a variety of tested gases, including CO, CO2, NO2, H-2, H2S, and C3H6O. The optimal operating temperature for this selective detection was determined to be 500 degrees C in a dry air environment. Moreover, the sensors demonstrated exceptional repeatability over the course of three testing cycles and displayed strong humidity resistance, even when exposed to 90% relative humidity. This excellent humidity resistance gas sensing property can be attributed to their nanoporous nature and elevated operating temperature.
Open Access
55. Composite Photocatalysts with Fe, Co, and Ni Oxides on Supports with Tetracoordinated Ti Embedded into Aluminosilicate Gel during Zeolite Y Synthesis
Authors:
Petcu, G; Anghel, EM; Atkinson, I; Culita, DC; Apostol, NG; Kuncser, A; Papa, F; Baran, A; Blin, JL; Parvulescu, V
Published: FEB 2024, GELS, 10, 129, DOI: 10.3390/gels10020129
Ti-aluminosilicate gels were used as supports for the immobilization of Fe, Co, and Ni oxides (5%) by impregnation and synthesis of efficient photocatalysts for the degradation of beta-lactam antibiotics from water. Titanium oxide (1 and 2%) was incorporated into the zeolite network by modifying the gel during the zeolitization process. The formation of the zeolite Y structure and its microporous structure were evidenced by X-ray diffraction and N-2 physisorption. The structure, composition, reduction, and optical properties were studied by X-ray diffraction, H-2-TPR, XPS, Raman, photoluminescence, and UV-Vis spectroscopy. The obtained results indicated a zeolite Y structure for all photocatalysts with tetracoordinated Ti4+ sites. The second transitional metals supported by the post-synthesis method were obtained in various forms, such as oxides and/or in the metallic state. A red shift of the absorption edge was observed in the UV-Vis spectra of photocatalysts upon the addition of Fe, Co, or Ni species. The photocatalytic performances were evaluated for the degradation of cefuroxime in water under visible light irradiation. The best results were obtained for iron-immobilized photocatalysts. Scavenger experiments explained the photocatalytic results and their mechanisms. A different contribution of the active species to the photocatalytic reactions was evidenced.
Open Access
56. Physicochemical Characterization of Ca- and Cu-Decorated TiO2 Microparticles and Investigation of Their Antimicrobial Properties
Authors:
Neacsu, A; Chihaia, V; Bucuresteanu, R; Ficai, A; Trusca, RD; Surdu, VA; Nicolaev, A; Cojocaru, B; Ionita, M; Calinescu, I; Parvulescu, V; Ditu, LM
Published: SEP 2024, MATERIALS, 17, 4483, DOI: 10.3390/ma17184483
Ca- and Cu-decorated TiO2 microparticles are titanium dioxide nanoparticles that have been decorated with calcium and copper ions. TiO2, CaO, and CuO are low-cost, non-toxic, and non-hazardous materials. The aim of the present study was the physicochemical characterization of Ca- and Cu-decorated TiO2 microparticles and the evaluation of their antimicrobial activity. Thus, Ca2+ and Cu2+ species were incorporated onto TiO2 surfaces by a two-step wet method. The obtained TiO2-CaO-CuO composites were characterized by several experimental techniques. The electronic structure and charge properties of the composites were investigated by density functional theory calculations. Furthermore, the composites were successfully tested for inhibitory effects on Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans standard strains. The zeta potential data indicate that the physiological condition of investigated microbial strains was strongly affected in presence of a dispersion of 10 mu g/L of composites in a saline phosphate buffer also, the recorded SEM images show a damaged microbial cell surface in the presence of composites.
Open Access
57. Expression of concern: Iron oxide magnetic nanoparticles with versatile surface functions based on dopamine anchors
Authors:
Mazur, M; Barras, A; Kuncser, V; Galatanu, A; Zaitzev, V; Turcheniuk, KV; Woisel, P; Lyskawa, J; Laure, W; Siriwardena, A; Boukherroub, R; Szunerits, S
Published: DEC 19 2024, NANOSCALE, 17, DOI: 10.1039/d4nr90209b
Expression of concern for 'Iron oxide magnetic nanoparticles with versatile surface functions based on dopamine anchors' by Mykola Mazur et al., Nanoscale, 2013, 5, 2692-2702, https://doi.org/10.1039/C3NR33506B.
Open Access
58. Electron transfer and energy exchange between a covalent organic framework and CuFeS2 nanoparticles
Authors:
Bika, P; Tzitzios, VK; Sakellis, E; Orfanoudakis, S; Boukos, N; Alhassan, SM; Tsipas, P; Psycharis, V; Stergiopoulos, T; Dallas, P
Published: JUL 18 2024, JOURNAL OF MATERIALS CHEMISTRY C, 12, DOI: 10.1039/d4tc01989j
CuFeS2 is a prominent chalcogenide that possesses similar optical properties and a significantly lower cost, compared to gold. Additionally, covalent organic frameworks are a class of materials at the forefront of current research, mainly used as photoactive components and porous absorbers. Hence, in this work, hydrophilic CuFeS2 particles are coupled with multi-functional covalent organic frameworks through ionic bonding to produce a hybrid material with unique and optimized properties. To render the CuFeS2 particles negatively charged and dispersible in water, we coated them with sodium dodecyl sulfonate, shifting the surface plasmon resonance of the nanoparticles from 472 to 492 nm. When they are electrostatically assembled with the positively charged COFs, an S-scheme is formed and the fluorescence of the hybrid materials is highly quenched, with the electron transfer happening from the networks to the nanoparticles and a simultaneous energy exchange which is dependent on the emission wavelength. Through detailed fluorescence spectroscopy, time-resolved measurements and Stern-Volmer analysis, we identified an efficient emission quenching that differs from the bulk to the exfoliated hybrid system, while detailed electron microscopy studies demonstrated the strong interaction between the two components. The quenching mechanisms and the on or off surface resonance dependent lifetime could be applied to photocatalytic and photovoltaic applications.
Open Access
59. Enhancing SiGeSn nanocrystals SWIR photosensing by high passivation in nanocrystalline HfO2 matrix
Authors:
Dascalescu, I; Palade, C; Slav, A; Stavarache, I; Cojocaru, O; Teodorescu, VS; Maraloiu, VA; Lepadatu, AM; Ciurea, ML; Stoica, T
Published: FEB 12 2024, SCIENTIFIC REPORTS, 14, 3532, DOI: 10.1038/s41598-024-53845-z
SiGeSn nanocrystals (NCs) in oxides are of considerable interest for photo-effect applications due to the fine-tuning of the optical bandgap by quantum confinement in NCs. We present a detailed study regarding the silicon germanium tin (SiGeSn) NCs embedded in a nanocrystalline hafnium oxide (HfO2) matrix fabricated by using magnetron co-sputtering deposition at room temperature and rapid thermal annealing (RTA). The NCs were formed at temperatures in the range of 500-800 degrees C. RTA was performed to obtain SiGeSn NCs with surfaces passivated by the embedding HfO2 matrix. The formation of NCs and beta-Sn segregation were discussed in relation to the deposition and processing conditions by employing HRTEM, XRD and Raman spectroscopy studies. The spectral photosensitivity exhibited up to 2000 nm in short-wavelength infrared (SWIR) depending on the Sn composition was obtained. Comparing to similar results on GeSn NCs in SiO2 matrix, the addition of Si offers a better thermal stability of SiGeSn NCs, while the use of HfO2 matrix results in better passivation of NCs increasing the SWIR photosensitivity at room temperature. These results suggest that SiGeSn NCs embedded in an HfO2 matrix are a promising material for SWIR optoelectronic devices.
Open Access
60. Deposition of W Nanoparticles by Magnetron Sputtering Gas Aggregation Using Different Amounts of H2/Ar and Air Leaks
Authors:
Acsente, T; Matei, E; Marascu, V; Bonciu, A; Satulu, V; Dinescu, G
Published: AUG 2024, COATINGS, 14, 964, DOI: 10.3390/coatings14080964
This work presents the synthesis of tungsten nanoparticles (W NPs) using a cluster source based on magnetron sputtering combined with gas aggregation (MSGA), operated with up to 81% H-2 in the hydrogen/argon mixture used as a working gas. The results show that, with up to 41% H-2 in discharge, the synthesis rate increases by more than 60 times, rapidly decreasing for over 50% H-2 in discharge. The W dust is still produced for H-2-dominated discharges (81%), and its deposition rate is small but not negligible (0.02 mg/h). The obtained W NPs are isolated, with the diameter decreasing from 50 nm to 15 nm when the amount of H-2 in discharge is smaller than 41%. Over this value, the particles tend to agglomerate, forming structures similar to film-like deposits. Also, the diameter of the dust spots deposited on substrates depends on the H-2 content of the discharge. This allows the efficient coating of substrates up to 26 mm wide by translating them in front of the MSGA cluster source exit aperture. Additionally, for 41% H-2 in discharge, the influence of synthetic air leaks (0%-8.2%) in discharge was investigated. The deposition rate decreases rapidly (ceasing for around 6% air in discharge), and the obtained nanoparticles tend to agglomerate on the substrate (at 3.3% air content, the dust deposit has the aspect of a near-continuous film). Chemical composition investigations show a pronounced tendency for oxidation, nitridation, and oxynitride formation in the presence of air leaks.
61. Formation of skyrmion phase in the Fe-Co-Si system by mechanochemical activation
Authors:
Sorescu, M; Tolea, F; Sofronie, M; Kuncser, V; Craig, AJ; Aitken, JA
Published: SEP 1 2024, PHYSICA B-CONDENSED MATTER, 688, 416153, DOI: 10.1016/j.physb.2024.416153
Fe, Co and Si powders were exposed to mechanochemical activation by high-energy ball milling for 0, 2, 4, 8 and 12 h. The samples were subsequently characterized by Mo<spacing diaeresis>ssbauer spectroscopy, X-ray powder diffraction (XRPD), magnetic measurements and optical diffuse reflectance spectroscopy. The room temperature Mo<spacing diaeresis>ssbauer measurements were consistent with the occurrence of FeCo2Si and Fe0.5Co0.5Si crystalline phases. The low temperature Mo<spacing diaeresis>ssbauer spectra confirmed the absence of superparamagnetism up to 44 K in the milled system. XRPD patterns supported the phase sequence derived from Mo<spacing diaeresis>ssbauer spectroscopy. The coercive field was found to increase with the ball milling time (BMT). Zero-field-cooling-field-cooling (ZFC-FC) measurements performed at 200 Oe in the temperature range 5-300 K evidenced the transition to the skyrmion phase of the Fe0.5Co0.5Si material below the critical temperature of 44 K. The optical absorption in the UV-Vis-NIR region of the spectrum was found to increase with BMT.
62. Annealing Effects on the Charging-Discharging Mechanism in Trilayer Al2O3/Ge/Al2O3 Memory Structures
Authors:
Stavarache, I; Palade, C; Maraloiu, VA; Teodorescu, VS; Stoica, T; Ciurea, ML
Published: JAN 17 2024, ACS APPLIED ELECTRONIC MATERIALS, 6, DOI: 10.1021/acsaelm.3c01454
For the development of memory devices for the continuous advancement of IT engineering, a good understanding of the charging-discharging mechanisms in nanocrystalline floating gate memories is crucial to overcoming the current limitations. The charging-discharging mechanism in Al2O3/Ge/Al2O3 trilayer memory structures obtained by magnetron sputtering deposition is investigated as a function of the postdeposition annealing temperature, up to 900 degrees C. The change by annealing of C-V hysteresis curves from a clockwise type at low temperatures to counterclockwise one in a sample annealed within the intermediary temperature range of 550 to 650 degrees C, and then, a return to a clockwise type for annealing within the higher temperature range of 800-900 degrees C was observed. Up to 700 degrees C, memory performances are constantly improved reaching for 600 degrees C annealed samples, a memory window of 5.6 V for voltage sweep in the range -1 to +15 V, and good retention characteristics for 650 degrees C annealed structures, in which the charge loss is only similar to 2% after 10(8) s. When the annealing temperature was increased above 700 degrees C, a rapid decrease in the memory performance takes place. The annealing-induced changes are explained based on the Ge fast diffusion and nanocrystallization process, in correlation with morphological and structural high-resolution transmission electron microscopy results.
63. Probing geometry-induced magnetic defects in cylindrical modulated nanowires with optically detected spin resonance in nitrogen-vacancy center in diamond
Authors:
Celano, U; Rickhaus, P; Bran, C; Marqués-Marchán, J; Borrás, VJ; Korytov, M; Asenjo, A; Vazquez, M
Published: SEP 19 2024, NANOSCALE, 16, DOI: 10.1039/d4nr01064g
Cylindrical magnetic nanowires (NWs) have gained significant interest as building-blocks of spintronics devices and magnetic sensors thanks to their geometry-tunable magnetic properties and anisotropy. While the synthesis and compositional control of NWs have seen major improvements in recent years, considerable challenges remain for the characterization of local magnetic features at the nanoscale. Here, we demonstrate non-perturbative field distribution mapping and minimally invasive magnetic imaging with scanning nitrogen-vacancy magnetometry. This enables a sensitivity down to 3 mu T Hz-1/2 used to localize ultra-scaled magnetic defects with lateral dimensions below 50 nm. The imaging reveals the presence of magnetic inhomogeneities in correspondence of periodical geometrical modulations/anti-notches in axial magnetized nanowires that are largely undetectable with standard metrology. The features induce local fluctuations of the NWs' magnetization orientation that are sensed by SNVM and compared with magnetic force microscopy. Finally, the strong magnetic field confinement in the nanowires is leveraged to study the interaction between the stray magnetic field and the fluorescence generated by two nitrogen-vacancies contained in the probe sensor, thus clarifying the contrast formation mechanisms. We report on magnetic imaging capability with non-perturbative field distribution mapping and minimally invasive magnetic sensing using scanning nitrogen-vacancy magnetometry in axial magnetized nanowires.
64. In vitro and in vivo investigations of citric acid functionalized magnetic iron oxide nanoparticles for intra-tumoral melanoma treatment
Authors:
Sima, L; Toderascu, LI; Tudor, M; Florian, P; Icriverzi, M; Ionita, F; Maraloiu, V; Iacob, N; Kuncser, V; Antohe, I; Stanciu, G; Trif, M; Roseanu, A; Coman, C; Socol, G
65. Bioactive Carbon@CeO2 Composites as Efficient Antioxidants with Antiamyloid and Radioprotective Potentials
Authors:
Shlapa, Y; Siposova, K; Sarnatskaya, V; Drajnova, M; Silvestre-Albero, J; Lykhova, O; Maraloiu, VA; Solopan, SO; Molcan, M; Musatov, A; Belous, A
Published: SEP 25 2024, ACS APPLIED BIO MATERIALS, 7, DOI: 10.1021/acsabm.4c00912
Blending carbon particles (CPs) and nanoscale bioactive cerium dioxide is a promising approach for designing composites for biomedical applications, combining the sorption and antioxidant potentials of each individual component. To address this issue, it is crucial to assess the correlation between the components' ratio, physicochemical parameters, and biofunctionality of the composites. Thus, the current research was aimed at fabricating C@CeO2 composites with different molar ratios and the examination of how the parameters of the composites affect their bioactivity. XRD, X-ray photoelectron spectroscopy, and electron microscopy data verified the formation of C@CeO2 composites. CeO2 nanoparticles (NPs) of 4-6 nm are highly dispersed on the surfaces of amorphous CPs. The presence of CeO2 NPs on the carbon surface decreased its adsorption potential in a dose-dependent manner. Besides, the coexistence of carbon and CeO2 in a single composite promotes some redox interactions between O-functionalities and Ce3+/Ce4+ species, resulting in changes in the chemical state of the surface of the composites. These observations suggest the strong connection between these parameters and the biofunctionality of the composites. The presence of CeO2 NPs on the surface of carbon led to a significant increase in the stability of the prepared composites in their aqueous suspensions. The enhancement of bioactivity of the newly prepared C@CeO2 compared to bare carbon and CeO2 was validated by testing their pseudomimetic (catalase/peroxidase-like and superoxide dismutase-like), antiamyloid, and radioprotective activities.
Open Access
66. Optimizing SiGe-SiO2 Visible-Short-Wave Infrared Photoresponse by Modulating Interplay Between Strain and Defects Through Annealing
Authors:
Sultan, MT; Stavarache, I; Manolescu, A; Arnalds, UB; Teodorescu, VS; Svavarsson, HG; Ingvarsson, S; Ciurea, ML
Published: AUG 2024, ADVANCED PHOTONICS RESEARCH, 5, DOI: 10.1002/adpr.202300316
SiGe-SiO2-based structures present high interest for their high photosensitivity from visible to short-wavelength infrared. Herein, two postdeposition annealing procedures, that is, rapid thermal annealing (RTA) and rapid-like furnace annealing (FA), are compared. Both RTA and FA are performed at 600 degrees C for 1 min for SiGe nanocrystals (NCs) formation in SiO2 matrix in Si/SiO2/SiGe/SiO2 structures deposited by magnetron sputtering. The FA imitates RTA resulting in enhanced spectral response. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy are carried out showing Ge-rich SiGe NCs with 11.3 +/- 1.2 nm size for RTA and 9.4 +/- 0.8 nm for FA. Photocurrent spectra for both structures show several peaks that are annealing dependent. The photocurrent intensity for FA samples is approximate to 7 times higher than RTA samples while cutoff wavelengths are slightly different, that is, 1365 nm for FA and 1375 nm for RTA. The FA structures show (at -1.5 V) over 4 A W-1 responsivity at 730 nm, 6.4 x 10(7) Jones detectivity at 735 nm, and 2.2 x 10(7) Jones at about 1210 nm. FA structures contain small SiGe NCs with incorporated residual strain, while RTA ones are formed of columnar SiGe NCs separated by SiGeOx amorphous regions and show increased tensile strain in the SiGe.
Open Access
67. Highly Efficient Ru-Based Catalysts for Lactic Acid Conversion to Alanine
Authors:
Podolean, I; Dogaru, M; Guzo, NC; Petcuta, OA; Jacobsen, EE; Nicolaev, A; Cojocaru, B; Tudorache, M; Parvulescu, VI; Coman, SM
Published: FEB 2024, NANOMATERIALS, 14, 277, DOI: 10.3390/nano14030277
The primary objective of this research was to develop efficient solid catalysts that can directly convert the lactic acid (LA) obtained from lignocellulosic biomass into alanine (AL) through a reductive amination process. To achieve this, various catalysts based on ruthenium were synthesized using different carriers such as multi-walled carbon nanotubes (MWCNTs), beta-zeolite, and magnetic nanoparticles (MNPs). Among these catalysts, Ru/MNP demonstrated a remarkable yield of 74.0% for alanine at a temperature of 200 degrees C. This yield was found to be superior not only to the Ru/CNT (55.7%) and Ru/BEA (6.6%) catalysts but also to most of the previously reported catalysts. The characterization of the catalysts and their catalytic results revealed that metallic ruthenium nanoparticles, which were highly dispersed on the external surface of the magnetic carrier, significantly enhanced the catalyst's ability for dehydrogenation. Additionally, the -NH2 basic sites on the catalyst further facilitated the formation of alanine by promoting the adsorption of acidic reactants. Furthermore, the catalyst could be easily separated using an external magnetic field and exhibited the potential for multiple reuses without any significant loss in its catalytic performance. These practical advantages further enhance its appeal for applications in the reductive amination of lactic acid to alanine.
68. Structural and magneto-optical investigations of citrate sol-gel derived barium hexaferrite nanocrystalline powder
Authors:
Secu, M; Secu, CE; Matei, E; Negrilla, C; Turchenko, V; Radu, C; Polosan, S
Published: MAY 5 2024, JOURNAL OF ALLOYS AND COMPOUNDS, 983, 173897, DOI: 10.1016/j.jallcom.2024.173897
Magneto-optical measurements enable the identification of Fe2+ and Fe3+ in the R and S blocks of BaFe12O19 Mhexaferrite powder obtained by sol -gel processing, followed by thermal annealing at 900 C for 3 hours. The ferromagnetic phase is evidenced by the spin-majority configuration (Fe3+) due to their unpaired electrons between d -d orbitals, while the Fe2+ in the low spin possesses diamagnetic behavior strongly dependent on the surrounded crystal field. Additionally, the irradiation with gamma rays changes the ratio between Fe2+/Fe3+, mainly on the surface of BaFe12O19 nanocrystals. These changes were confirmed by X-ray Photoelectron Spectroscopy measurements, in which the concentration of Fe2+ increased from 69% to 82%, while the one of Fe3+ decreased from 31% to 18%. he thermoluminescent measurements reveal the same changes of Fe3+ in Fe2+ by electron capturing during irradiation, which is released as a red emission after recombination processes. The changes are explained by the increasing of some Fe-O bonds along the c-axis, mainly due to breaking a part of these bonds. The X-ray analysis confirms the changing of the parameters for the BaFe12O19 hexagonal structure.
Open Access
69. Ferroelectricity Induced by Oxygen Vacancies in Rhombohedral ZrO2 Thin Films
Authors:
Lenzi, V; Silva, JPB; Smid, B; Matolin, V; Istrate, CM; Ghica, C; MacManus-Driscoll, JL; Marques, L
Published: JAN 2024, ENERGY & ENVIRONMENTAL MATERIALS, 7, DOI: 10.1002/eem2.12500
Rhombohedral phase HfxZr1-xO2 (HZO, x from 0 to 1) films are promising for achieving robust ferroelectric polarization without the need for an initial wake-up pre-cycling, as is normally the case for the more commonly studied orthorhombic phase. However, a large spontaneous polarization observed in rhombohedral films is not fully understood, and there are also large discrepancies between experimental and theoretical predictions. In this work, in rhombohedral ZrO2 thin films, we show that oxygen vacancies are not only a key factor for stabilizing the phase, but they are also a source of ferroelectric polarization in the films. This is shown experimentally through the investigation of the structural properties, chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature (400 degrees C) in an oxygen environment to reduce the V-O concentration compared. The experimental work is supported by density functional theory (DFT) calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO2 films. The DFT calculations also show that V-O contribute to the ferroelectric polarization. Our findings reveal the importance of V-O for stabilizing rhombohedral ZrO2 thin films with superior ferroelectric properties.
Open Access
70. Versatile techniques based on the Thermionic Vacuum Arc (TVA) and laser-induced TVA methods for Mg/Mg:X thin films deposition-A review
Authors:
Vladoiu, R; Mandes, A; Dinca, V; Tichy, M; Kudrna, P; Ciobotaru, CC; Polosan, S
Published: AUG 2024, JOURNAL OF MAGNESIUM AND ALLOYS, 12, DOI: 10.1016/j.jma.2024.08.012
Magnesium and magnesium thin alloy films were deposited using a thermionic vacuum arc (TVA), which has multiple applications in the field of metallic electrodes for diodes and batteries or active corrosion protection. An improved laser-induced TVA (LTVA) method favors the crystallization processes of the deposited magnesium-based films because the interaction between laser and plasma discharge changes the thermal energy during photonic processes due to the local temperature variation. Plasma diagnosis based on current discharge measurements suggests an inelastic collision between the laser beam and the atoms from the plasma discharge. The morphology and surface properties of the obtained thin films differ between these two methods. While the amorphous character is dominant for TVA thin films, enabling a smooth surface, the LTVA method produces rough surfaces with prominent crystallinity, less hydrophobic character and lower surface energy. The smooth surfaces obtained by the TVA methods produce metallic electrodes with good electrical contact, ensuring better diodes and battery charge transport. Both methods allow uniform magnesium alloys to be obtained, but the laser used in the LTVA on the discharge plasma controls the added metal or element ratio. (c) 2024 Chongqing University. Publishing services provided by Elsevier B.V.
71. Integrated architectures of electrodes and flexible porous substrates for point-of-care testing
Authors:
Botta, D; Enculescu, I; Balan, C; Diculescu, VC
Published: DEC 2023, CURRENT OPINION IN ELECTROCHEMISTRY, 42, 101418, DOI: 10.1016/j.coelec.2023.101418
Flexible porous materials have gained a high interest due to their impact on the development of electrochemical point-ofcare devices for monitoring the state of health of individuals. Among the porous materials, paper and textiles are most commonly used due to their innate capillary action on fluids. In this article, attention is paid to the retention of analytes in paper and textile porous substrates, and possible procedures to overcome this effect are discussed. The patterning of hydrophilic and hydrophobic regions for sample flow manipulation, and the folding properties of the flexible substrates for 3D architectures capable of transfer of analytes, are considered in relation to current electrode materials and detection methodologies.
Open Access
72. Revolutionizing n-type Co3O4 Nanowire for Hydrogen Gas Sensing
Authors:
Kumarage, GWC; Zappa, D; Mihalcea, CG; Maraloiu, VA; Stefan, M; Comini, E
Published: OCT 2023, ADVANCED ENERGY AND SUSTAINABILITY RESEARCH, 4, DOI: 10.1002/aesr.202300067
This study presents conductometric sensors based on Co3O4 nanowires for hydrogen detection at ppb levels. The nanowires are synthesized through thermal oxidation of a 50 nm cobalt layer, exhibiting diameters between 6-50 nm and lengths of 1-5 & mu;m, primarily growing along the (311) direction of spinal Co3O4. Raman investigation reveals five characteristic peaks at 195, 482, 521, 620, and 692 cm(-1), corresponding to symmetric phonon modes of crystalline Co3O4. Electron paramagnetic resonance measurements confirm the presence of a ferromagnetic phase, attributed to incomplete cobalt oxidation, which disappears after 8 h of thermal aging at 400 & DEG;C. Conductometry measurements are performed in the temperature range of 300-500 & DEG;C. At temperatures above 300 & DEG;C, sensors exhibit abnormal n-type semiconducting behavior due to lattice oxygen's involvement in the hydrogen sensing mechanism. Operating at 450 & DEG;C in dry air, the sensor shows a higher 232% response to 100 ppm H-2 compared to ethanol, acetone, methane, carbon monoxide, and nitrogen dioxide. Remarkably, the sensor maintains a consistent conductance baseline even under high humidity (90%) for 25 d, with three-cycle repeatability. This distinctive gas-sensing capability is attributed to the catalytic activity and elevated operating temperature.
73. Hybrid nanostructures based on vertically graphenes decorated with tungsten oxide nanoparticles for enhanced capacitive performance
Authors:
Coman, LG; Marcu, M; Acsente, T; Vizireanu, S; Satulu, V; Dinescu, G; Matei, E; Spataru, T; Spataru, N; Preda, L
Published: NOV 2023, DIAMOND AND RELATED MATERIALS, 139, 110316, DOI: 10.1016/j.diamond.2023.110316
Herewith, we investigated the capacitive properties of hybrid nanometric architectures consisting of tungsten oxide nanoparticles deposited on graphite (WOx/G) and graphite coated with highly-porous carbon nanowall layers (WOx/CNW/G). The deposition of the nanostructured oxide was performed by a plasma-assisted sublimation, vapor transport and condensation technique. The samples containing the CNW interlayer show superior areal capacitances making this architecture and its fabrication route promising approaches for supercapacitor applications. Thus, areal capacitances of WOx/CNW/G and WOx/G, estimated from galvanostatic chargedischarge tests (GCD) at an applied density current of 1 mA cm-2, are 1247.2 mF cm-2 and 527.3 mF cm-2, respectively. From SEM and XPS investigations, it was observed that CNW promotes the formation of a high amount of small tungsten oxide particles, homogeneously distributed on electrode surface, and facilitates the formation of highly conductive tungsten nitride species, resulting in electrodes with remarkable charge-storage capacity.
74. Design of Magnetic Fe3O4/CeO2 "Core/Shell"-Like Nanocomposites with Pronounced Antiamyloidogenic and Antioxidant Bioactivity
Authors:
Shlapa, Y; Siposova, K; Veltruska, K; Maraloiu, VA; Garcarova, I; Rajnak, M; Musatov, A; Belous, A
Published: OCT 12 2023, ACS APPLIED MATERIALS & INTERFACES, 15, DOI: 10.1021/acsami.3c10845
Core/shell nanocomposites based on magnetic magnetite (Fe3O4) and redox-active cerium dioxide (CeO2) nanoparticles (NPs) are promising in the field of biomedical interests because they can combine the ability of magnetic NPs to heat up in an alternating magnetic field (AMF) with the pronounced antioxidant activity of CeO2 NPs. Thus, this report is devoted to Fe3O4/CeO2 nanocomposites (NCPs) synthesized by precipitation of the computed amount of "CeO2-shell" on the surface of prefabricated Fe3O4 NPs. The X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy data validated the formation of Fe3O4/CeO2 "core/shell"-like NCPs, in which ultrafine CeO2 NPs with an average size of approximately 3-3.5 nm neatly surround Fe3O4 NPs. The presence of a CeO2 "shell" significantly increased the stability of Fe3O4/CeO2 NCPs in aqueous suspensions: Fe3O4/CeO2 NCPs with "shell thicknesses" of 5 and 7 nm formed highly stable magnetic fluids with zeta-potential values of >+30 mV. The magnetization values of Fe3O4/CeO2 NCPs decreased with a growing CeO2 "shell" around the magnetic NPs; however, the resulting composites retained the ability to heat efficiently in an AMF. The presence of a CeO2 "shell" generates a possibility to precisely regulate tuning of the maximum heating temperature of magnetic NCPs in the 42-50 degrees C range and stabilize it after a certain time of exposure to an AMF by changing the thickness of the "CeO2-shell". A great improvement was observed in both antioxidant and antiamyloidogenic activities. It was found that inhibition of insulin amyloid formation, expressed in IC50 concentration, using NCPs with a "shell thickness" of 7 nm was approximately 10 times lower compared to that of pure CeO2. For these NCPs, more than 2 times higher superoxide dismutase-like activity was observed. The coupling of both Fe3O4 and CeO2 results in higher bioactivity than either of them individually, probably due to a synergistic catalytic mechanism.
Open Access
75. Chiral and Catalytic Effects of Site-Specific Molecular Adsorption
Authors:
Borca, B; Michnowicz, T; Aguilar-Galindo, F; Petuya, R; Pristl, M; Schendel, V; Pentegov, I; Kraft, U; Klauk, H; Wahl, P; Arnau, A; Schlickum, U
Published: 2023 FEB 17 2023, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, DOI: 10.1021/acs.jpclett.2c03575
The changes of properties and preferential interactions based on subtle energetic differences are important characteristics of organic molecules, particularly for their functionalities in biological systems. Only slightly energetically favored interactions are important for the molecular adsorption and bonding to surfaces, which define their properties for further technological applications. Here, prochiral tetracenothiophene molecules are adsorbed on the Cu(111) surface. The chiral adsorption configurations are determined by Scanning Tunneling Microscopy studies and confirmed by first-principles calculations. Remarkably, the selection of the adsorption sites by chemically different moieties of the molecules is dictated by the arrangement of the atoms in the first and second surface layers. Furthermore, we have investigated the thermal effects on the direct desulfurization reaction that occurs under the catalytic activity of the Cu substrate. This reaction leads to a product that is covalently bound to the surface in chiral configurations.
Open Access
76. Partial replacement of Pb2+ in MAPbI2.6Cl0.4 perovskite films and their photovoltaic performance
Authors:
Derbali, S; Nouneh, K; Leonat, LN; Stancu, V; Tomulescu, AG; Galca, AC; Touhami, ME; Pintilie, I; Florea, M
Published: APR 2023, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 34, 903, DOI: 10.1007/s10854-023-10318-9
Replacing lead atoms in halide perovskite materials is of significant importance for the development of environmentally friendly perovskite solar cells. In this paper, we investigated the effect of doping the MAPbI(2.6)Cl(0.4) hybrid perovskite (MA-methyl ammonium) with non-toxic elements, such as alkaline earth metal ions (Mg2+) and transition metal ions (Zn2+). The structural, morphological, and optical properties of the prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-Vis. spectroscopy. Finally, the doped films were used as photoactive layers in solar devices in order to evaluate their photovoltaic performance. Zn proved to be more appropriate to replace partially Pb and films with higher quality were obtained. As a result, the MAPb1(-x)Zn(x)I(2.6)Cl(0.4) based solar cells have demonstrated a slight improvement of the photovoltaic performances, resulting in a uniform and narrower PCEs (power conversion efficiency) range, compared to pristine MAPbI(2.6)Cl(0.4) based devices.
Open Access
77. Columnar Liquid Crystals of Copper(I) Complexes with Ionic Conductivity and Solid State Emission
Authors:
Circu, V; Ganea, CP; Secu, M; Manaila-Maximean, D; Marinescu, GC; Popescu, RG; Pasuk, I
Published: MAY 19 2023, MOLECULES, 28, 4196, DOI: 10.3390/molecules28104196
Two neutral copper(I) halide complexes ([Cu(BTU)(2)X], X = Cl, Br) were prepared by the reduction of the corresponding copper(II) halides (chloride or bromide) with a benzoylthiourea (BTU, N-(3,4-diheptyloxybenzoyl)-N '-(4-heptadecafluorooctylphenyl)thiourea) ligand in ethanol. The two copper(I) complexes show a very interesting combination of 2D supramolecular structures, liquid crystalline, emission, and 1D ionic conduction properties. Their chemical structure was ascribed based on ESI-MS, elemental analysis, IR, and NMR spectroscopies (H-1 and C-13), while the mesomorphic behavior was analyzed through a combination of differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and powder X-ray diffraction (XRD). These new copper(I) complexes have mesomorphic properties and exhibit a hexagonal columnar mesophase over a large temperature range, more than 100 K, as evidenced by DSC studies and POM observations. The thermogravimetric analysis (TG) indicated a very good thermal stability of these samples up to the isotropization temperatures and over the whole temperature range of the liquid crystalline phase existence. Both complexes displayed a solid-state emission with quantum yields up to 8% at ambient temperature. The electrical properties of the new metallomesogens were investigated by variable temperature dielectric spectroscopy over the entire temperature range of the liquid crystalline phase. It was found that the liquid crystal phases favoured anhydrous proton conduction provided by the hydrogen-bonding networks formed by the NH horizontal ellipsis X moieties (X = halide or oxygen) of the benzoylthiourea ligand in the copper(I) complexes. A proton conductivity of 2.97 x 10(-7) S.cm(-1) was achieved at 430 K for the chloro-complex and 1.37 x 10(-6) S.cm(-1) at 440K for the related bromo-complex.
Open Access
78. Controlling the excitation spectrum of a quantum dot array with a photon cavity
Authors:
Gudmundsson, V; Mughnetsyan, V; Abdullah, NR; Tang, CS; Moldoveanu, V; Manolescu, A
Published: SEP 13 2023, PHYSICAL REVIEW B, 108, 115306, DOI: 10.1103/PhysRevB.108.115306
We use a recently proposed quantum electrodynamical density theory functional in a real-time excitation calculation for a two-dimensional electron gas in a square array of quantum dots in an external constant perpendicular magnetic field to model the influence of cavity photons on the excitation spectra of the system. The excitation is generated by a short electrical pulse. The quantum dot array is defined in an AlGaAs-GaAs heterostructure, which is in turn embedded in a parallel plate far-infrared photon microcavity. The required exchange and correlation energy functionals describing the electron-electron and electron-photon interactions have therefore been adapted for a two-dimensional electron gas in a homogeneous external magnetic field. We predict that the energies of the excitation modes activated by the pulse are generally redshifted to lower values in the presence of a cavity. The redshift can be understood in terms of the polarization of the electron charge by the cavity photons and depends on the magnetic flux, the number of electrons in a unit cell of the lattice, and the electron-photon interaction strength. We find an interesting interplay of the exchange forces in a spin-polarized two-dimensional electron gas and the square-lattice structure leading to a small but clear blueshift of the excitation mode spectra when one electron resides in each dot.
Open Access
79. In situ Electrochemical Evaluation of the Interaction of dsDNA with the Proteasome Inhibitor Anticancer Drug Bortezomib
Authors:
Bunea, MC; Enache, TA; Diculescu, VC
Published: APR 2023, MOLECULES, 28, 3277, DOI: 10.3390/molecules28073277
Bortezomib is an inhibitor of proteasomes and an anti-cancer drug. Although bortezomib is considered a safe drug, as confirmed by cytotoxicity assays, recent reports highlighted the possibility of interaction between bortezomib and cellular components, with detrimental long-term effects. The evaluation of the interaction between bortezomib and dsDNA was investigated in bulk solution and using a dsDNA electrochemical biosensor. The binding of bortezomib to dsDNA involved its electroactive centers and led to small morphological modifications in the dsDNA double helix, which were electrochemically identified through changes in the guanine and adenine residue oxidation peaks and confirmed by electrophoretic and spectrophotometric measurements. The redox product of bortezomib amino group oxidation was electrochemically generated in situ on the surface of the dsDNA electrochemical biosensor. The redox product of bortezomib was shown to interact primarily with guanine residues, preventing their oxidation and leading to the formation of bortezomib-guanine adducts, which was confirmed by control experiments with polyhomonucleotides electrochemical biosensors and mass spectrometry. An interaction mechanism between dsDNA and bortezomib is proposed, and the formation of the bortezomib redox product-guanine adduct explained.
Open Access
80. Antiferromagnet-mediated interlayer exchange: Hybridization versus proximity effect
Authors:
Polishchuk, DM; Tykhonenko-Polishchuk, YO; Lytvynenko, YM; Rostas, AM; Kuncser, V; Kravets, AF; Tovstolytkin, AI; Gomonay, OV; Korenivski, V
Published: JUN 28 2023, PHYSICAL REVIEW B, 107, 224432, DOI: 10.1103/PhysRevB.107.224432
We investigate the interlayer coupling between two thin ferromagnetic (F) films mediated by an antiferromagnetic (AF) spacer in F*/AF/F trilayers and show how it transitions between different regimes on changing the AF thickness. Employing layer-selective Kerr magnetometry and ferromagnetic-resonance techniques in a complementary manner enables us to distinguish between three functionally distinct regimes of such ferromagnetic interlayer coupling. The F layers are found to be individually and independently exchange-biased for thick FeMn spacers-the first regime of no interlayer F-F* coupling. F-F* coupling appears on decreasing the FeMn thickness below 9 nm. In this second regime found in structures with 6.0-9.0-nm-thick FeMn spacers, the interlayer coupling exists only in a finite temperature interval just below the effective Neel temperature of the spacer, which is due to magnon-mediated exchange through the thermally softened antiferromagnetic spacer, vanishing at lower temperatures. The third regime, with FeMn thinner than 4 nm, is characterized by a much stronger interlayer coupling in the entire temperature interval, which is attributed to a magnetic-proximity induced ferromagnetic exchange. These experimental results, spanning the key geometrical parameters and thermal regimes of the F*/AF/F nanostructure, complemented by a comprehensive theoretical analysis, should broaden the understanding of the interlayer exchange in magnetic multilayers and potentially be useful for applications in spin thermionics.
81. Structural and flame retardancy properties of GO-DOPO-HAK composite
Authors:
Mihis, AG; Cotet, LC; Cadar, C; Pop, LC; Todea, M; Rusu, MM; Vulpoi, A; Székely, I; Salagean, CA; Magyari, K; Muresan-Pop, M; Cadar, O; Baia, M; Sofran, IE; Lisa, G; Anghel, I; Baibarac, M; Danciu, V; Baia, L
Published: APR 2023, JOURNAL OF MATERIALS SCIENCE, 58, DOI: 10.1007/s10853-023-08456-w
In the view of the advantages of using P, N, Si and graphene oxide (GO) for the development of flame retardants materials, a multi-structure synergistic composite was synthesized by grafting a novel nitrogen-containing polyhedral oligomeric silsesquioxane (HAK) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) on the surface of GO nanosheet. In the first step, 2-hydroxyethyl acrylate was selectively reacted, and then, HAK was synthetized by the condensation of the aza-Michael addition product with 3-(methacryloyloxy)propyltrimethoxysilane. Finally, the GO obtained by an innovative variant of Marcano-Tour improved exfoliation method was functionalized, first with DOPO, and then with HAK. The structural, morphological and surface properties of GO and GO-DOPO-HAK were investigated by means of XRD, TEM-EDX, FT-IR, Raman, zeta potential and XPS techniques, and it was evidenced the functionalization of GO with DOPO, and then with HAK. The performed microscale combustion calorimetry (MCC) and TG measurements indicated a great potential of the GO-DOPO-HAK as flame retardant material as the obtained residual weight for this sample was found to be the highest one compared to the other investigated samples. MCC analyses further revealed a major decrease in heat release capacity (HRC) and a significant increase in char yield, results that confirm the great potential of GO-DOPO-HAK as flame retardancy material. [GRAPHICS] .
Open Access
82. Nanoscale Y3AlFe4O12 garnets: Looking into subtle features of crystalline structure and properties formation
Authors:
Solopan, S; Tovstolytkin, A; Zamorskyi, V; Shlapa, Y; Maraloiu, VA; Fedorchuk, O; Belous, A
Published: DEC 15 2023, JOURNAL OF ALLOYS AND COMPOUNDS, 968, 172248, DOI: 10.1016/j.jallcom.2023.172248
Nanoscale Al-doped yttrium-iron garnets attract enhanced scientific and practical interest in the development of microwave devices due to their remarkable physical-chemical properties, which depend essentially on the method and conditions of synthesis. This work highlights the advantages of a specific two-stage synthesis of Y3AlFe4O12 garnet ferrite nanoparticles by the precipitation in aqueous solutions and deals with the detailed examinations of the precipitates obtained during this process. The results of the complex studies using high resolution transmission microscopy, dynamic light scattering and magnetic measurements have allowed assessing the features of the formation of crystalline structure. It is demonstrated that the sequence of the precipitation of components during the synthesis strongly affects the physical-chemical properties of the formed precipitate (filtration coefficient value, surface charge, micelle's structure) as well as the physical properties of nanoparticles obtained after their heat treatment at 800 degrees C (saturation magnetization, coercive force). Simultaneous precipitation of Fe(OH)3 and Al(OH)3 metal hydroxides, which form one of three crystallographic sub lattices of the garnet structure, at the first stage of the synthesis of ferrite-garnets is revealed to provide higher values of filtration coefficient of the formed precipitate and better technological and physical-chemical parameters of the fabricated garnet nanoparticles that makes this method highly advantageous for industrial application.
83. DATA ANALYSIS FOR GRAVITATIONAL WAVES USING NEURAL NETWORKS ON QUANTUM COMPUTERS
Authors:
Isfan, MC; Caramete, LI; Caramete, A; Basceanu, VA; Popescu, T
In this study, we evaluate the feasibility of using quantum neural networks for classifying gravitational waveforms, using both simulators and quantum computers. The analysis is quite interdisciplinary in its nature, combining knowledge involving astrophysics, quantum information as well as quantum and classical machine learning. We showed that the quantum classifiers and hybrid classical-quantum layers give highly accurate results when tested on a simple dataset and ran on a simulator; also, adding a quantum layer to poorly performing classical neural network can highly improve its accuracy. When running on a real quantum computer, error minimizing algorithms need to be implemented in order to obtain a satisfying accuracy.
84. Liquid phase oxidation of alkenes and glycerol with molecular oxygen over mixed-ligand copper(II) complexes grafted on GO as catalysts
Authors:
Rizescu, C; El Fergani, M; Eftemie, DI; Cojocaru, B; Popescu, D; Andruh, M; Parvulescu, VI
Published: AUG 5 2023, APPLIED CATALYSIS A-GENERAL, 663, 119302, DOI: 10.1016/j.apcata.2023.119302
[Cu(acac)(phen)(H2O)](ClO4) and [Cu(acac)(bipy)(H2O)](ClO4) catalysts were prepared by the immobilization of mixed-ligand complexes on graphene oxide derivatized with monochloroacetic acid. These catalysts were characterized through an ensemble of techniques including XRD, FTIR, Raman, and XPS while the catalytic behavior has been investigated in the oxidation of cyclohexene, 1-octene and glycerol in the presence of molecular oxygen. Cyclohexanone was the dominant product in the oxidation of cyclohexene resulting in selectivities higher than 50% for a conversion of 14.5%. The turnover frequencies were pretty high, namely, 4.5 h(-1) for [Cu(acac)(phen)(H2O)](ClO4) and 2.3 h(-1) for Cu(acac)(bipy)(H2O)](ClO4). The oxidation of 1-octene also occurred with a pretty high selectivity in 2-octanol as the main product. The role of copper in the oxidative dehydrogenation of glyceric acid towards tartronic acid was as well confirmed. Noteworthy, these catalysts were stable and their recycling occurred with no change in the conversion or selectivity.
Open Access
85. Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications
Authors:
Kuncser, V
Published: JAN 2023, NANOMATERIALS, 13, 206, DOI: 10.3390/nano13010206
Multifunctional magnetic nanocomposites are among those heterogeneous nanosized systems where at least one phase component is magnetic and can act as an intermediate of either the actuation or the response of the overall system. The main advantage of heterogeneous nanosystems is the possibility of combining and inter-influencing the electronic properties of constituent interfaced nanophases. Consequently, unique physico-chemical properties of the hybrid materials of interest in various applications can be obtained. This Special Issue of Nanomaterials highlights the most advanced processing and characterization tools of some multifunctional magnetic nanocomposites and heterogeneous systems of interest in various applications, from biomedicine to sensoristics and energy-saving materials.
86. Electrochemical Protein-based Bioanalytical Devices for Drug Analysis
Authors:
Sanz, CG; Diculescu, VC
Published: 2023, CURRENT TOPICS IN MEDICINAL CHEMISTRY, 23, DOI: 10.2174/1568026623666230411152640
Proteins are vital components of living cells and the loss of their native functions has been associated with a wide variety of medical conditions. From this point of view, investigation of the protein microenvironment is crucial to support the development of therapeutic approaches capable of ensuring cellular functions. Therefore, analytical assays for the detection, quantification, and characterization of proteins, drugs, and protein-drug complexes play an essential role in fundamental research and clinical applications. Electrochemistry arises as an alternative methodology for fast assessment of proteins and drugs and is attractive due to the adaptability to miniaturization and scalability of electroanalytical devices, which then can be further employed as strategies towards personalized medical care. Thus, this review summarizes electrochemical investigations in the past 10 years on protein-based analytical devices and biosensors. A general overview of electrochemical assays that integrate proteins with nanostructured materials and conductive polymers is presented. Applications of electrochemical assays and biosensors were divided into four categories. First, those designed for drug screening strategies that focus on targeting specific intracellular, extracellular, or membrane protein subdomains to modulate their functions, aggregation/misfolding of proteins, and protein degradation pathways. Then, drug metabolism assays that involve mimicking natural metabolic pathways to identify potential safety and efficacy issues related to a drug or its metabolites. The third was dedicated to electrochemical drug delivery systems with anchored drugs in the form of bioconjugates, while the fourth was dedicated to electroanalytical methodologies for quantitative drug assays, where the electroactivity of the target species is often used to correlate the electrochemical signal to their concentration.
87. Temperature dependent magnetic properties of NixCo1-xFe2O4: Single- and multidomain particles
Authors:
Msomi, JZ; Nhlapo, TA; Stanciu, A; Greculeasa, S; Kuncser, V; Moyo, T
Published: FEB 1 2023, PHYSICA B-CONDENSED MATTER, 650, 414595, DOI: 10.1016/j.physb.2022.414595
In the present work, nanocrystalline NixCo1-xFe2O4 oxides with average crystallite size between 11 nm and 111 nm have been analyzed by Mossbauer spectroscopy, hysteresis loops, field cooled (FC) and zero field cooled (ZFC) magnetization measurements. A core-shell model has been proposed. Accordingly, the Mossbauer spectra evidence a ferrimagnetic core and a disordered shell (spin-glass), the latter increasing with Ni concentration. Hysteresis curves reveal the ferromagnetic nature of the investigated compounds and transformation from single- to multi-domain behaviour at a critical particle size dependent on Ni2+ ion concentration. The magnetic properties of finest powders (average crystallite size similar to 11 nm) are the most sensitive to the Ni2+ ions content. A general increase in the coercive field, H-C, with reducing temperature according to the modified Kneller's formula H-c(T) = H-c(0)[1-(T/T-B)(beta) where beta = 0.45 occurs. A high saturation magnetization of about 90 emu/g and an increase in H-C from about 0.3 kOe at 300 K to 7 kOe at 10 K have been observed for the sample Ni0.1Co0.9Fe2O4 (x = 0.1). Increasing magnetization and coercive field with reducing temperature are also explained within the core shell model. FC and ZFC data show strong dependence of the magnetic properties on crystallite size and concentration of Ni2+ ions.
Open Access
88. Hydroxyapatite Thin Films of Marine Origin as Sustainable Candidates for Dental Implants
Authors:
Dorcioman, G; Grumezescu, V; Stan, GE; Chifiriuc, MC; Gradisteanu, GP; Miculescu, F; Matei, E; Popescu-Pelin, G; Zgura, I; Craciun, V; Oktar, FN; Duta, L
Published: APR 2023, PHARMACEUTICS, 15, 1294, DOI: 10.3390/pharmaceutics15041294
Novel biomaterials with promising bone regeneration potential, derived from rich, renewable, and cheap sources, are reported. Thus, thin films were synthesized from marine-derived (i.e., from fish bones and seashells) hydroxyapatite (MdHA) by pulsed laser deposition (PLD) technique. Besides the physical-chemical and mechanical investigations, the deposited thin films were also evaluated in vitro using dedicated cytocompatibility and antimicrobial assays. The morphological examination of MdHA films revealed the fabrication of rough surfaces, which were shown to favor good cell adhesion, and furthermore could foster the in-situ anchorage of implants. The strong hydrophilic behavior of the thin films was evidenced by contact angle (CA) measurements, with values in the range of 15-18 degrees. The inferred bonding strength adherence values were superior (i.e., similar to 49 MPa) to the threshold established by ISO regulation for high-load implant coatings. After immersion in biological fluids, the growth of an apatite-based layer was noted, which indicated the good mineralization capacity of the MdHA films. All PLD films exhibited low cytotoxicity on osteoblast, fibroblast, and epithelial cells. Moreover, a persistent protective effect against bacterial and fungal colonization (i.e., 1- to 3-log reduction of E. coli, E. faecalis, and C. albicans growth) was demonstrated after 48 h of incubation, with respect to the Ti control. The good cytocompatibility and effective antimicrobial activity, along with the reduced fabrication costs from sustainable sources (available in large quantities), should, therefore, recommend the MdHA materials proposed herein as innovative and viable solutions for the development of novel coatings for metallic dental implants.
Open Access
89. Partial Replacement of Dimethylformamide with Less Toxic Solvents in the Fabrication Process of Mixed-Halide Perovskite Films
Authors:
Stancu, V; Tomulescu, AG; Leonat, LN; Balescu, LM; Galca, AC; Toma, V; Besleaga, C; Derbali, S; Pintilie, I
Published: FEB 2023, COATINGS, 13, 378, DOI: 10.3390/coatings13020378
The technology of perovskite solar cells (PSC) is getting close to breaching the consumer market. Yet, one of the current challenges is to reduce the toxicity during their fabrication by reducing the use of the toxic solvents involved in the perovskite fabrication process. A good solubilization of lead halides used in hybrid perovskite preparation is required, and it is only possible with polar solvents. A mixture of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is the most popular solvent combination for a perovskite precursor solution. DMF is necessary to ensure a good dissolution of lead iodide, but it is also the most toxic solvent. In this paper, we study the replacement of the dimethylformamide with presumably less toxic alternatives, such as N-methyl-2-Pyrrolidone (NMP) and ethyl acetate (EA), for the preparation of the K(0.1)FA(0.7)MA(0.2)PbI(2.8)Cl(0.2) (KFAMA) hybrid perovskite. The perovskite thin films were investigated by various characterization techniques: X-ray diffraction, atomic force microscopy, scanning electron microscopy, and UV-vis spectroscopy, while the photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. The present study shows that by keeping the same deposition parameters as when only DMF solvent is used, the partial solvent substitution with NMP and EA gives promising results for reducing the toxicity of the fabrication process of KFAMA-based PSCs. Thus, with no specific optimization of the deposition process, and for the maximum possible partial substitution of DMF with NMP and EA solvents, the loss in the power conversion efficiency (PCE) value is only 35% and 18%, respectively, associated with the more structural defects promoted by NMP and EA.
Open Access
90. Experimental Band Structure of Pb(Zr,Ti)O3: Mechanism of Ferroelectric Stabilization
Authors:
Popescu, DG; Husanu, MA; Constantinou, PC; Filip, LD; Trupina, L; Bucur, CI; Pasuk, I; Chirila, C; Hrib, LM; Stancu, V; Pintilie, L; Schmitt, T; Teodorescu, CM; Strocov, VN
Published: FEB 2023, ADVANCED SCIENCE, 10, DOI: 10.1002/advs.202205476
Pb(Zr,Ti)O-3 (PZT) is the most common ferroelectric (FE) material widely used in solid-state technology. Despite intense studies of PZT over decades, its intrinsic band structure, electron energy depending on 3D momentum k, is still unknown. Here, Pb(Zr0.2Ti0.8)O-3 using soft-X-ray angle-resolved photoelectron spectroscopy (ARPES) is explored. The enhanced photoelectron escape depth in this photon energy range allows sharp intrinsic definition of the out-of-plane momentum k and thereby of the full 3D band structure. Furthermore, the problem of sample charging due to the inherently insulating nature of PZT is solved by using thin-film PZT samples, where a thickness-induced self-doping results in their heavy doping. For the first time, the soft-X-ray ARPES experiments deliver the intrinsic 3D band structure of PZT as well as the FE-polarization dependent electrostatic potential profile across the PZT film deposited on SrTiO3 and LaxSrMn1-xO3 substrates. The negative charges near the surface, required to stabilize the FE state pointing away from the sample (P+), are identified as oxygen vacancies creating localized in-gap states below the Fermi energy. For the opposite polarization state (P-), the positive charges near the surface are identified as cation vacancies resulting from non-ideal stoichiometry of the PZT film as deduced from quantitative XPS measurements.
Open Access
91. Microscopic mechanism of ferroelectric properties in barium hexaferrites
Authors:
Turchenko, V; Bondyakov, AS; Trukhanov, S; Fina, I; Korovushkin, VV; Balasoiu, M; Polosan, S; Bozzo, B; Lupu, N; Trukhanov, A
Published: JAN 10 2023, JOURNAL OF ALLOYS AND COMPOUNDS, 931, 167433, DOI: 10.1016/j.jallcom.2022.167433
The microscopic mechanism of the occurrence of ferroelectric properties in M-type barium hexaferrites is investigated by experimental and first-principle computation methods. The analysis of magnetic, X-ray, and Mossbauer measurements of BaFe12O19 samples ascertains the correlation between the thermal factor in the process of annealing samples and their functional properties. The occurrence of the remnant polarization in barium hexaferrites at room temperature contradicts the description of their crystal structure in the fra-mework of centrosymmetric space group P63/mmc (No. 194), in which one of the symmetry operations is inversion center. Therefore, the crystal structure of BaFe12O19 was analyzed in the frameworks of SG P63/mmc (No. 194) and non-centrosymmetric SG P63mc (No. 186). The computed value of polarization for a non-centrosymmetric unit cell is similar to 3.5 mu C/cm2. The analysis of polarization was carried out on a path connecting the polar P63mc and non-polar P63/mmc structures and considered in terms of the total energy barrier. Our result allows ascertaining a direct relationship between the remnant polarization of the unit cell and the broken spatial-inversion symmetry in the crystal structure of M-type barium hexaferrite.(c) 2022 Elsevier B.V. All rights reserved.
Open Access
92. Ferroelectricity and negative piezoelectric coefficient in orthorhombic phase pure ZrO2 thin films
Authors:
Sliva, JPB; Istrate, MC; Hellenbrand, M; Jan, AT; Becker, MT; Symonowicz, J; Figueiras, FG; Lenzi, V; Hill, MO; Ghica, C; Romanyuk, KN; Gomes, MJM; Di Martino, G; Marques, L; MacManus-Driscoll, JL
Published: FEB 2023, APPLIED MATERIALS TODAY, 30, 101708, DOI: 10.1016/j.apmt.2022.101708
A new approach for epitaxial stabilisation of ferroelectric orthorhombic (o-) ZrO2 films with negative piezoelectric coefficient in - 8nm thick films grown by ion-beam sputtering is demonstrated. Films on (011)-Nb: SrTiO3 gave the oriented o-phase, as confirmed by transmission electron microscopy and electron backscatter diffraction mapping, grazing incidence x-ray diffraction and Raman spectroscopy. Scanning probe microscopy techniques and macroscopic polarization-electric field hysteresis loops show ferroelectric behavior, with saturation polarization of -14.3 mu C/cm2, remnant polarization of -9.3 mu C/cm2 and coercive field -1.2 MV/cm. In contrast to the o-films grown on (011)-Nb:SrTiO3, films grown on (001)-Nb:SrTiO3 showed mixed monoclinic (m) and o-phases causing an inferior remnant polarization of -4.8 mu C/cm2, over 50% lower than the one observed for the film grown on (011)-Nb:SrTiO3. Density functional theory (DFT) calculations of the SrTiO3/ZrO2 interfaces support the experimental findings of a stable polar o-phase for growth on (011) Nb:SrTiO3, and they also explain the negative piezoelectric coefficient.
Open Access
93. Mesoporous Composite Bioactive Compound Delivery System for Wound-Healing Processes
Authors:
Purcareanu, B; Ene, MD; Morosan, A; Mihaiescu, DE; Florea, MA; Ghica, A; Nita, RA; Drumea, V; Grigoroscuta, MA; Kuncser, A; Badica, P; Olariu, L
Published: SEP 2023, PHARMACEUTICS, 15, 2258, DOI: 10.3390/pharmaceutics15092258
Currently, the treatment of wounds is still a challenge for healthcare professionals due to high complication incidences and social impacts, and the development of biocompatible and efficient medicines remains a goal. In this regard, mesoporous materials loaded with bioactive compounds from natural extracts have a high potential for wound treatment due to their nontoxicity, high loading capacity and slow drug release. MCM-41-type mesoporous material was synthesized by using sodium trisilicate as a silica source at room temperature and normal pressure. The synthesized mesoporous silica was characterized by using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), N2 absorption-desorption (BET), Dynamic Light Scattering (DLS) and Fourier transform infrared spectroscopy (FT-IR), revealing a high surface area (BET, 1244 m2/g); pore diameter of approx. 2 nm; and a homogenous, ordered and hexagonal geometry (TEM images). Qualitative monitoring of the desorption degree of the Salvia officinalis (SO) extract, rich in ursolic acid and oleanolic acid, and Calendula officinalis (CO) extract, rich in polyphenols and flavones, was performed via the continuous recording of the UV-VIS spectra at predetermined intervals. The active ingredients in the new composite MCM-41/sage and marigold (MCM-41/SO & CO) were quantified by using HPLC-DAD and LC-MS-MS techniques. The evaluation of the biological composites' activity on the wound site was performed on two cell lines, HS27 and HaCaT, naturally involved in tissue-regeneration processes. The experimental results revealed the ability to stimulate collagen biosynthesis, the enzymatic activity of the main metalloproteinases (MMP-2 and MMP-9) involved in tissue remodeling processes and the migration rate in the wound site, thus providing insights into the re-epithelializing properties of mesoporous composites.
Open Access
94. Influence of on-off pulsed current pattern on processes during spark plasma sintering of MgB2 superconductor
Authors:
Aldica, G; Sandu, V; Popa, S; Pasuk, I; Enculescu, M; Ionescu, AM; Badica, P
Published: DEC 2023, OPEN CERAMICS, 16, 100441, DOI: 10.1016/j.oceram.2023.100441
High density samples (92-94.5 %) of MgB2 were prepared by Spark Plasma Sintering (SPS). The on-off pulsed current patterns of SPS processing were 8-4, 12-2, 24-2, 99-1. Patterns with more on pulses favor formation of a higher amount of the secondary MgB4 phase through the decomposition of MgB2. They also promote enhancement of larger MgO crystallites without a strong increase in the amount of this phase. Densification rate and pressure in the SPS chamber show a similar behavior, but their amplitude varies and the temperatures defining different stages present some shifts. As-revealed differences induced by pulsed patterns impact superconducting properties in a complex manner. An attempt to assess correlations between the pattern and different superconducting parameters is presented.
Open Access
95. Solution-processed In2Se3 nanosheets for ultrasensitive and highly selective NO2 gas sensors
Authors:
D'Olimpio, G; Galstyan, V; Ghica, C; Vorokhta, M; Istrate, MC; Kuo, CN; Lue, CS; Boukhvalov, DW; Comini, E; Politano, A
Published: JUN 13 2023, JOURNAL OF MATERIALS CHEMISTRY A, 11, DOI: 10.1039/d3ta01390a
In this work, we demonstrate that solution-processed In2Se3 nanosheets exhibit exceptional selectivity and sensitivity to NO2 gas, making them a promising candidate for gas detection systems. Theoretical simulations and surface-science experiments reveal the unique surface properties of In2Se3 nanosheets, which prevent physisorption of oxygen, carbon monoxide, and carbon dioxide, making them remarkably stable towards oxidation and CO-poisoning. Moreover, we show that NO2 molecules adsorb stably on In2Se3 nanosheets, particularly on Se vacancies, even at high temperatures. The coadsorption of water further enhances NO2 sticking on the In2Se3 surface, making it an ideal material for gas sensing applications in humid and harsh environments. The fabricated In2Se3 gas sensors exhibit excellent and reversible sensing response to NO2 gas, with a limit of detection of 5 ppb at 300 degrees C, and a highly selective response to NO2 compared to other gases and volatile organic compounds. Our sensors outperform other two-dimensional (2D) semiconductors, metal oxides, and their heterostructures, thanks to the unique surface properties of In2Se3 nanosheets. Importantly, the number of layers and termination of the surface almost have no impact on the sensing performance of In2Se3, which is advantageous for practical applications. The high sensitivity, selectivity, and stability of In2Se3 nanosheets make them an exciting platform for the fabrication of high-performance gas sensors, particularly in harsh environments, such as industrial settings or outdoor monitoring. Moreover, our solution processing approach enables scalable production of the sensors. Additionally, their unique surface properties make them an attractive candidate for developing complex composite nanostructures with tailored gas sensing characteristics for various applications.
Open Access
96. Influence of Grain Size on Dielectric Behavior in Lead-Free 0.5 Ba(Zr0.2Ti0.8)O3-0.5 (Ba0.7Ca0.3)TiO3 Ceramics
Authors:
Ene, VL; Lupu, VR; Condor, CV; Patru, RE; Hrib, LM; Amarande, L; Nicoara, AI; Pintilie, L; Ianculescu, AC
Published: NOV 2023, NANOMATERIALS, 13, 2934, DOI: 10.3390/nano13222934
Fine-tuning of grain sizes can significantly influence the interaction between different dielectric phenomena, allowing the development of materials with tailored dielectric resistivity. By virtue of various synthesis mechanisms, a pathway to manipulate grain sizes and, consequently, tune the material's dielectric response is revealed. Understanding these intricate relationships between granulation and dielectric properties can pave the way for designing and optimizing materials for specific applications where tailored dielectric responses are sought. The experimental part involved the fabrication of dense BCT-BZT ceramics with different grain sizes by varying the synthesis (conventional solid-state reaction route and sol-gel) and consolidation methods. Both consolidation methods produced well-crystallized specimens, with Ba0.85Ca0.15O3Ti0.9Zr0.1 (BCTZ) perovskite as the major phase. Conventional sintering resulted in microstructured and submicron-structured BCT-BZT ceramics, with average grain sizes of 2.35 mu m for the solid-state sample and 0.91 mu m for the sol-gel synthesized ceramic. However, spark plasma sintering produced a nanocrystalline specimen with an average grain size of 67.5 nm. As the grain size decreases, there is a noticeable decrease in the maximum permittivity, a significant reduction in dielectric losses, and a shifting of the Curie temperature towards lower values.
Open Access
97. The Depairing Current Density of a Fe(Se,Te) Crystal Evaluated in Presence of Demagnetizing Factors
Authors:
Galluzzi, A; Buchkov, K; Tomov, V; Nazarova, E; Leo, A; Grimaldi, G; Crisan, A; Polichetti, M
Published: DEC 2023, CONDENSED MATTER, 8, 91, DOI: 10.3390/condmat8040091
The effect of the demagnetizing factor, regarding the determination of the de-pairing current density Jdep, has been studied in the case of a Fe(Se,Te) crystal, using DC magnetic measurements as a function of a magnetic field (H) at different temperatures (T). First, the lower critical field Hc1(T) values were obtained, and the demagnetization effects acting on them were investigated after calculating the demagnetizing factor. The temperature behaviors of both the original Hc1 values and the ones obtained after considering the demagnetization effects (Hc1demag) were analyzed, and the temperature dependence of the London penetration depth lambda L(T) was obtained in both cases. In particular, the lambda L(T) curves were fitted with a power law dependence, indicating the presence of low-energy quasiparticle excitations. Furthermore, by plotting lambda L-2 as a function of T, we found that our sample behaves as a multigap superconductor, which is similar to other Fe-11 family iron-based compounds. After that, the coherence length xi values were extracted, starting with the Hc2(T) curve. The knowledge of lambda L and xi allowed us to determine the Jdep values and to observe how they are influenced by the demagnetizing factor.
Open Access
98. Burdock-Derived Composites Based on Biogenic Gold, Silver Chloride and Zinc Oxide Particles as Green Multifunctional Platforms for Biomedical Applications and Environmental Protection
Authors:
Zgura, I; Badea, N; Enculescu, M; Maraloiu, VA; Ungureanu, C; Barbinta-Patrascu, ME
Published: FEB 2023, MATERIALS, 16, 1153, DOI: 10.3390/ma16031153
Green nanotechnology is a rapidly growing field linked to using the principles of green chemistry to design novel nanomaterials with great potential in environmental and health protection. In this work, metal and semiconducting particles (AuNPs, AgClNPs, ZnO, AuZnO, AgClZnO, and AuAgClZnO) were phytosynthesized through a "green" bottom-up approach, using burdock (Arctium lappa L.) aqueous extract. The morphological (SEM/TEM), structural (XRD, SAED), compositional (EDS), optical (UV-Vis absorption and FTIR spectroscopy), photocatalytic, and bio-properties of the prepared composites were analyzed. The particle size was determined by SEM/TEM and by DLS measurements. The phytoparticles presented high and moderate physical stability, evaluated by zeta potential measurements. The investigation of photocatalytic activity of these composites, using Rhodamine B solutions' degradation under solar light irradiation in the presence of prepared powders, showed different degradation efficiencies. Bioevaluation of the obtained composites revealed the antioxidant and antibacterial properties. The tricomponent system AuAgClZnO showed the best antioxidant activity for capturing ROS and ABTS center dot(+) radicals, and the best biocidal action against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The "green" developed composites can be considered potential adjuvants in biomedical (antioxidant or biocidal agents) or environmental (as antimicrobial agents and catalysts for degradation of water pollutants) applications.
99. Temperature Dependence of the Conductivity of InSb Measured by Terahertz Time-Domain Spectroscopy
Authors:
Liu, S; Agulto, VC; Iwamoto, T; Kato, K; Mag-Usara, VK; Ota, M; Dolas, S; Newman, N; Nedelcu, L; Tani, M; Yoshimura, M; Nakajima, M
Published: 2023, 2023 48TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER, AND TERAHERTZ WAVES, IRMMW-THZ, DOI: 10.1109/IRMMW-THz57677.2023.10299341
In this study, we characterized the temperature-dependent electrical conductivity properties of undoped and lightly doped bulk InSb samples using terahertz time-domain spectroscopy. We obtained the permittivity spectra at low temperatures and analyzed the carrier density and mobility by fitting the spectra to the Drude model. Based on our analysis, we show the temperature dependence of the optical constants and explain the underlying physical mechanisms for the observed behavior. Our results provide important insights into the electronic properties of InSb.
Open Access
100. Defect structures and (ferro)magnetism in Zn1-xFexO nanoparticles with the iron concentration level in the dilute regime (x = 0.001 - 0.01) prepared from acetate precursors
Authors:
Mihalache, V; Negrila, C; Secu, M; Mercioniu, I; Iacob, N; Kuncser, V
Published: AUG 2023, RESULTS IN PHYSICS, 51, 106644, DOI: 10.1016/j.rinp.2023.106644
Zn1-xFexO nanoparticles with the iron concentrations level in the dilute regime (x = 0.001---0.01) were produced by a sol-gel route from acetate precursors along with an un-doped and 3 at.% Fe-doped reference. The X-ray diffraction of the un-doped and 0.1-1 at.% Fe-doped samples reveal the reflections for only the ZnO wurtzite structure. Fe doping enhances the a-axis lattice constant, the unit cell volume and the microstrain. Iron doping reduces the average crystallite/particle size (confirmed by Scanning Electron Microscopy), improving the surface-to-volume ratio or the concentration of defective surface sites. XPS identifies the iron in both Fe3+ and Fe2+ states. XPS and Fe-57 Mossbauer spectroscopy indicate a broad distribution (distortion) of Fe3+ sites on the surface of ZnO nanoparticles. The blue shift and broadening of the UV emission, and quenching of defect-related photoluminescence in the Fe-doped samples verify the presence of iron in the ZnO lattice and surface intrinsic defects. 0.1-1 at.% Fe-doped ZnO show room temperature ferromagnetism, RTFM, characteristic of dilute magnetic semiconductors, DMS. The magnetization measurements with temperature evidence an antiferromagnetic alignment and an increase of ferromagnetic contribution with Fe doping up to 1 at.%. Zn0.97Fe0.3O reference is a superparamagnetic ZnO/ZnFe2O4 nanocomposite with a blocking temperature of 20 K; HRTEM shows (ultra)fine ZnFe2O4 particles at the surface of ZnO nanoparticles. The analysis of experimental data of 0.1-1 at.% Fe-doped ZnO was done in terms of iron coupling with intrinsic defects, which can generate surface Fe3+ states with geometries similar to the Fe3+ in inverse spinel ZnFe2O4. The superexchange interaction (resembling that in the inverse spinel ZnFe2O4) between the Fe3+ sites with distorted configuration resulting in ferrimagnetism was hypothesised as a possible mechanism of RTFM. Experimental (structural, local chemical, magnetic, optical) and interpretation results can be used to optimize the processing conditions for Fe-doped ZnO to serve as an effective DMS, e.g. for spintronic applications.
101. Synthetic peptide array on gold for the electrochemical assessment of the 20S proteasome activity and effect of inhibitory compounds
Authors:
Barsan, MM; Serban, A; Onea, M; Wysocka, M; Lesner, A; Diculescu, VC
Published: FEB 1 2023, APPLIED SURFACE SCIENCE, 610, 155620, DOI: 10.1016/j.apsusc.2022.155620
A sensor for the enzymatic activity and inhibition of the 20S proteasome was developed by immobilizing the synthetic peptide ABZ-VVSYAMG-(O2Oc)2-OH at Au electrodes. The detection principle is based on the elec-troactivity of ABZ, part of the ABZ-VVSY-OH moiety released from the peptide upon 20S proteasome chymo-trypsin action. The peptide was immobilized on a para-amino thiophenol (PATP) self-assembled monolayer on Au electrode by cross-linking its amino group to the -(O2Oc)2-OH moiety of the peptide (Au/PATP/peptide). The immobilization of the peptide and its interaction with 20S proteasome was investigated by SEM, QCM, SPR, ATR-FTIR and electrochemistry. The activity of 20S proteasome was assessed electrochemically by cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) after the immersion Au/PATP/peptide in 20S proteasome solution. CV study showed a decrease in both capacitive and faradaic currents corresponding to the ABZ-VVSY-OH removal, allowing the quantification of the 20S proteasome activity. The EIS study revealed that the resis-tance corresponding to charge transfer reactions at the peptide/solution interface correlated to the ABZ redox reaction, decreased linearly with increasing the incubation time in 20S proteasome solution. The perfected assay was applied for the investigation of the inhibitory effect of one synthetic, bortezomib, and two naturally occurring, epoxomicin, and lactacystin inhibitors.
Open Access
102. Synthesis and Anti-Melanoma Activity of L-Cysteine-Coated Iron Oxide Nanoparticles Loaded with Doxorubicin
Authors:
Toderascu, LI; Sima, LE; Orobeti, S; Florian, PE; Icriverzi, M; Maraloiu, VA; Comanescu, C; Iacob, N; Kuncser, V; Antohe, I; Popescu-Pelin, G; Stanciu, G; Ionita, P; Mihailescu, CN; Socol, G
Published: FEB 2023, NANOMATERIALS, 13, 621, DOI: 10.3390/nano13040621
In this study, we report on the synthesis of L-Cysteine (L-Cys)-coated magnetic iron oxide nanoparticles (NPs) loaded with doxorubicin (Dox). The Fe3O4-L-Cys-Dox NPs were extensively characterized for their compositional and morpho-structural features using EDS, SAED, XRD, FTIR and TEM. XPS, Mossbauer spectroscopy and SQUID measurements were also performed to determine the electronic and magnetic properties of the Fe3O4-L-Cys-Dox nanoparticles. Moreover, by means of a FO-SPR sensor, we evidenced and confirmed the binding of Dox to L-Cys. Biological tests on mouse (B16F10) and human (A375) metastatic melanoma cells evidenced the internalization of magnetic nanoparticles delivering Dox. Half maximum inhibitory concentration IC50 values of Fe3O4-L-Cys-Dox were determined for both cell lines: 4.26 mu g/mL for A375 and 2.74 mu g/mL for B16F10, as compared to 60.74 and 98.75 mu g/mL, respectively, for unloaded controls. Incubation of cells with Fe3O4-L-Cys-Dox modulated MAPK signaling pathway activity 3 h post-treatment and produced cell cycle arrest and increased apoptosis by 48 h. We show that within the first 2 h of incubation in physiological (pH = 7.4) media, similar to 10-15 mu M Dox/h was released from a 200 mu g/mL Fe3O4-L-Cys-Dox solution, as compared to double upon incubation in citrate solution (pH = 3), which resembles acidic environment conditions. Our results highlight the potential of Fe3O4-L-Cys-Dox NPs as efficient drug delivery vehicles in melanoma therapy.
Open Access
103. Co- and Ni-Doped TiO2 Nanoparticles Supported on Zeolite Y with Photocatalytic Properties
Authors:
Petcu, G; Papa, F; Atkinson, I; Baran, A; Apostol, NG; Petrescu, S; Richaudeau, L; Blin, JL; Parvulescu, V
Published: AUG 2023, NANOMATERIALS, 13, 2200, DOI: 10.3390/nano13152200
Zeolite Y samples with microporous and hierarchical structures containing Ti-Ni and Ti-Co oxides were obtained as active photocatalysts. Different Ti amounts (5, 10% TiO2) were supported, followed by the loading of Ni or Co oxides (5%). X-ray diffraction evidenced the presence of TiO2 as an anatase. N-2 adsorption-desorption results showed type IV isotherms for hierarchical zeolite Y samples, and a combination of type IV and I isotherms for zeolite Y samples. UV-Vis diffuse reflectance spectra showed a shift in the absorption band to visible with increasing Ti loading and especially after Co and Ni addition. A significant effect of the support was evidenced for Ti and its interaction with Co/Ni species. The zeolite Y support stabilized Ti in the 4+ oxidation state while hierarchical zeolite Y support favored the formation of Ti3+ species, Ni-0 and Ni2+ and the oxidation of Co to 3+ oxidation state. Photocatalytic activity, under UV and visible light irradiation, was evaluated by the degradation of amoxicillin, used as a model test. The photocatalytic mechanism was investigated using ethanol, p-benzoquinone and KI as & BULL;OH and & BULL;O-2(-) radicals and hole (h(+)) scavengers. The best results were obtained for the immobilized Ni-Ti species on the hierarchical zeolite Y support.
Open Access
104. Obtaining and characterisation of thermoelectric Mg2Si compound via wet and dry mechanical alloying and spark plasma sintering
Authors:
Cebotari, V; Popa, F; Marinca, TF; Neamtu, BV; Sechel, NA; Galatanu, M; Galatanu, A; Chicinas, I
Published: SEP-OCT 2023, JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 26, DOI: 10.1016/j.jmrt.2023.09.167
Mg2Si thermoelectric compound was obtained by dry and wet (isohexane and benzene) mechanical alloying route. The Mg2Si compound was characterised by X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), laser particle size analysis and thermoelectric measurements. After 14 h of milling, the complete reaction of the elements is achieved by both routes. The powders particle size distribution obtained after 14 h of dry or wet milling (using benzene) reveals a bimodal curve. The wet milling moves the particle size distribution towards smaller particle sizes. The SEM analysis confirms the results of particles size analysis. DSC analyses performed for samples milled up to 14 h present stress relief and recrystallisation thermal events. For the benzene wet-milled sample, the DSC curve shows an additional thermal event at 350'C, associated with benzene removal. Thermoelectric properties were determined on spark plasma sintered compacts. The milling process with benzene leads to a higher value of Seebeck coefficient (z580 mV/K). The electrical conductivity is low at room temperature and increases exponentially with temperature. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Open Access
105. Copper-/Zinc-Doped TiO2 Nanopowders Synthesized by Microwave-Assisted Sol-Gel Method
Authors:
Predoana, L; Petcu, G; Preda, S; Pandele-Cusu, J; Petrescu, SV; Baran, A; Apostol, NG; Costescu, RM; Surdu, VA; Vasile, BS; Ianculescu, AC
Published: APR 2023, GELS, 9, 267, DOI: 10.3390/gels9040267
Using the microwave-assisted sol-gel method, Zn- and Cu-doped TiO2 nanoparticles with an anatase crystalline structure were prepared. Titanium (IV) butoxide was used as a TiO2 precursor, with parental alcohol as a solvent and ammonia water as a catalyst. Based on the TG/DTA results, the powders were thermally treated at 500 degrees C. XRD and XRF revealed the presence of a single-phase anatase and dopants in the thermally treated nanoparticles. The surface of the nanoparticles and the oxidation states of the elements were studied using XPS, which confirmed the presence of Ti, O, Zn, and Cu. The photocatalytic activity of the doped TiO2 nanopowders was tested for the degradation of methyl-orange (MO) dye. The results indicate that Cu doping increases the photoactivity of TiO2 in the visible-light range by narrowing the band-gap energy.
Open Access
106. A New Hybrid Stepper Motor, Compliant Piezoelectric Micro-Tweezer for Extended Stroke
Authors:
Ivan, IA; Noveanu, DC; Gurgu, VI; Despa, V; Noveanu, S
Published: JUN 2023, MICROMACHINES, 14, 1112, DOI: 10.3390/mi14061112
The revolutionary economic potential of micro and nanotechnology is already recognized. Micro and nano-scale technologies that use electrical, magnetic, optical, mechanical, and thermal phenomena separately or in combination are either already in the industrial phase or approaching it. The products of micro and nanotechnology are made of small quantities of material but have high functionality and added value. This paper presents such a product: a system with micro-tweezers for biomedical applications-a micromanipulator with optimized constructive characteristics, including optimal centering, consumption, and minimum size, for handling micro-particles and constructive micro components. The advantage of the proposed structure consists mainly in obtaining a large working area combined with a good working resolution due to the double actuation principle: electromagnetic and piezoelectric.
107. Structural and Electrical Properties of Novel Cr/Fe Mixed Transition-Metal Phosphates
Authors:
Mighri, Z; Souiwa, K; Rostas, AM; Patru, RE; Bocirnea, AE; Iacob, N; Kuncser, V; El Khouja, O; Leonat, LN; Hidouri, M; Nasri, H; Galca, AC
Published: MAY 24 2023, INORGANIC CHEMISTRY, 62, DOI: 10.1021/acs.inorgchem.2c04389
The phosphate KCoCr-(PO4)(2) and iron-substitutedvariants KCoCr1-x Fe x (PO4)(2) (x =0.25, 0.5, and 0.75) were synthesized by a solid-state reaction route,while a high substitution level of Fe was achieved. Their structureswere refined using powder X-ray diffraction and indexed in a monoclinicsystem with a P2(1)/n spacegroup. A 3D framework with six-sided tunnels parallel to the [101]direction was formed in which the K atoms are located. Mo''ssbauerspectroscopy confirms the exclusive presence of octahedral paramagneticFe(3+) ions, with isomer shifts increasing slightly with x substitution. Electron paramagnetic resonance spectroscopyconfirmed the presence of paramagnetic Cr3+ ions. The activationenergy, determined by dielectric measurements, shows that the iron-containingsamples present higher ionic activity. Relative to the electrochemicalactivity of K, these materials could be good candidates for positiveand/or negative electrode materials for energy storage applications. The synthesized phosphate KCoCr-(PO4)(2) and Fe-substituted variants KCoCr1-x Fe x (PO4)(2) (x = 0.25, 0.5, and 0.75) present a 3D frameworkwith six-sided tunnels in which the K atoms are located. The activationenergy, determined by dielectric measurements, shows that the iron-containingsamples present improved ionic activity, making these materials goodcandidates for positive and/or negative electrode materials for energystorage applications.
Open Access
108. Highly Coercive L10-Phase Dots Obtained through Low Temperature Annealing for Nano-Logic Magnetic Structures
Authors:
Crisan, O; Crisan, AD; Schinteie, G; Kuncser, V; Carotenuto, G
Published: DEC 2023, COATINGS, 13, 2068, DOI: 10.3390/coatings13122068
Nano-logic magnetic structures are of great interest for spintronic applications. While the methods used for developing arrays of magnetic L1(0)-phase dots are, in most cases, based on deposition followed by annealing at high temperatures, usually around 700 degrees C, we demonstrate here a technique where a much lower annealing temperature (i.e., 400 degrees C) is needed in order to promote fully the disorder-order phase transformation and achievement of highly coercive L1(0)-phase dots. In order to develop building blocks based on arrays of L1(0)-phase FePt dots for further spintronic applications, an engraving technique using electron beam lithography is employed. This paper describes the fabrication, as well as the morphological and magnetic characterization, of regularly placed FePt dots of various shapes, as pre-requisites for integration into nano-logic devices. As a proof of concept, regular arrays of FePt circular dots were devised and their structural characterization, using X-ray diffraction (XRD) and transmission electron microscopy (TEM), was performed. It has been shown that annealing at only 400 degrees C for 30 min proved the occurrence of the tetragonal L1(0) phase. Moreover, structural characterization showed that the disorder-order phase transformation was complete with only the L1(0) phase detected in high resolution TEM. The magnetic characterization provided more insight into the potential of such arrays of magnetic devices with convenient values of magnetic coercivity, remanent and saturation magnetization. These findings show good potential for developing regular arrays of uniformly shaped magnetic entities with encouraging magnetic performances in view of various applications.
Open Access
109. Synthesis of TiO2-(B) Nanobelts for Acetone Sensing
Authors:
Kumarage, GWC; Panamaldeniya, SA; Maddumage, DC; Moumen, A; Maraloiu, VA; Mihalcea, CG; Negrea, RF; Dassanayake, BS; Gunawardhana, N; Zappa, D; Galstyan, V; Comini, E
Published: OCT 2023, SENSORS, 23, 8322, DOI: 10.3390/s23198322
Titanium dioxide nanobelts were prepared via the alkali-hydrothermal method for application in chemical gas sensing. The formation process of TiO2-(B) nanobelts and their sensing properties were investigated in detail. FE-SEM was used to study the surface of the obtained structures. The TEM and XRD analyses show that the prepared TiO2 nanobelts are in the monoclinic phase. Furthermore, TEM shows the formation of porous-like morphology due to crystal defects in the TiO2-(B) nanobelts. The gas-sensing performance of the structure toward various concentrations of hydrogen, ethanol, acetone, nitrogen dioxide, and methane gases was studied at a temperature range between 100 and 500 C-degrees. The fabricated sensor shows a high response toward acetone at a relatively low working temperature (150 C-degrees), which is important for the development of low-power-consumption functional devices. Moreover, the obtained results indicate that monoclinic TiO2-B is a promising material for applications in chemo-resistive gas detectors.
110. Climbing the anisotropy barrier of single-molecule magnets with spin-vibron interaction
Authors:
Moldoveanu, V; Dragomir, R
Published: JUL 20 2023, PHYSICAL REVIEW B, 108, 024416, DOI: 10.1103/PhysRevB.108.024416
Using the master equation approach, we look for fingerprints of the interaction between the localized spin S of a nanomagnet coupled to spin-polarized leads and its quantized vibrational modes. We find that the stationary and transient currents are sensitive to vibron-assisted transitions of the molecular spin on both sides of the anisotropy barrier. Such transitions are associated with vibron-dressed states and triggered under resonant conditions. Transport calculations are presented for two antiparallel configurations of the spin-polarized electrodes. In the first configuration, and far from a resonance point, a blockade is imposed on both the electronic and molecular spins via their exchange interaction. When sweeping the magnetic field through resonance, the spin-vibron interaction removes this blockade and allows the indirect reading of resonant transitions as the molecular spin climbs the left side of the anisotropy barrier. In the second configuration, the anisotropy barrier is overcome but the vibron-assisted transitions on the right side of the anisotropy barrier "delocalize" the molecular spin and do not allow the complete current-induced magnetic switching -S & RARR; S. In both configurations, the stationary current increases on resonance, due to additional transport channels triggered by the spin-vibron coupling. Therefore, the switching of the spin-vibron coupling could be detected in future transport experiments.
111. Resistive-like Behavior of Ferroelectric p-n Bilayer Structures Based on Epitaxial Pb(Zr0.2Ti0.8)O3 Thin Films
Authors:
Boni, AG; Chirila, C; Trupina, L; Radu, C; Filip, LD; Moldoveanu, V; Pintilie, I; Pintilie, L
Published: 2023 JAN 25 2023, ACS APPLIED ELECTRONIC MATERIALS, DOI: 10.1021/acsaelm.2c01497
The p-n junctions are the building blocks of nowadays electronic devices. The n- or p-type conductivity is obtained in classic semiconductors, like Si, by doping with atoms acting as donors or acceptors, respectively. Doping was used in ferroelectrics to influence the transition temperature, magnitude of some physical properties, but not necessarily conduction type. Therefore, comprehensive studies to obtain true ferroelectric p-n junctions by controlled doping are missing. Recently, it has been shown that Pb(Zr0.2Ti0.8)O-3 films doped with & AP;1% atomic Nb (n-type doping) or Fe (p-type doping) have different orientations of polarization in the as-grown state. Knowing that polarization orientation depends on doping type, the next step is to build ferroelectric p-n homojunctions and to study their properties in relation to ferroelectric polarization. p-n and n-p structures were grown for this purpose by successive deposition of Nb-doped and Fe-doped Pb(Zr,Ti)O-3 layers with different thicknesses. We find that these p-n homojunctions are ferroelectric, but the magnitude of the polarization and coercive field, as well as the dominant polarization orientation in the as-grown state, depend on the conduction type of the first grown layer. The I-V characteristics are quasi-linear, although the interfaces with the electrodes behaves as Schottky contacts. The resistance extracted from the I-V characteristics displays an exponential dependence on temperature, with an activation energy in the range of 0.14-0.17 eV. These results are explained assuming that the total current in the junction is the total of electron and hole injections at the electrode interfaces. It is shown that for relatively low doping concentrations, the current density contains a dominant term with a linear voltage dependence and an exponential temperature dependence, as observed experimentally, and a secondary (correction) term that is dependent on the free carrier density and can induce non-linear voltage dependence when this density is significant.
Open Access
112. 3D Porous Collagen Matrices-A Reservoir for In Vitro Simultaneous Release of Tannic Acid and Chlorhexidine
Authors:
Brazdaru, L; Staicu, T; Kaya, MGA; Chelaru, C; Ghica, C; Cîrcu, V; Leca, M; Ghica, MV; Micutz, M
Published: JAN 2023, PHARMACEUTICS, 15, 76, DOI: 10.3390/pharmaceutics15010076
The treatment of wounds occurring accidentally or as a result of chronic diseases most frequently requires the use of appropriate dressings, mainly to ensure tissue regeneration/healing, at the same time as treating or preventing potential bacterial infections or superinfections. Collagen type I-based scaffolds in tandem with adequate antimicrobials can successfully fulfill these requirements. In this work, starting from the corresponding hydrogels, we prepared a series of freeze-dried atelocollagen type I-based matrices loaded with tannic acid (TA) and chlorhexidine digluconate (CHDG) as active agents with a broad spectrum of antimicrobial activity and also as crosslinkers for the collagen network. The primary aim of this study was to design an original and reliable algorithm to in vitro monitor and kinetically analyze the simultaneous release of TA and CHDG from the porous matrices into an aqueous solution of phosphate-buffered saline (PBS, pH 7.4, 37 degrees C) containing micellar carriers of a cationic surfactant (hexadecyltrimethylammonium bromide, HTAB) as a release environment that roughly mimics human extracellular fluids in living tissues. Around this central idea, a comprehensive investigation of the lyophilized matrices (morpho-structural characterization through FT-IR spectroscopy, scanning electron microscopy, swelling behavior, resistance against the collagenolytic action of collagenase type I) was carried out. The kinetic treatment of the release data displayed a preponderance of non-Fickian-Case II diffusion behavior, which led to a general anomalous transport mechanism for both TA and CHDG, irrespective of their concentrations. This is equivalent to saying that the release regime is not governed only by the gradient concentration of the releasing components inside and outside the matrix (like in ideal Fickian diffusion), but also, to a large extent, by the relaxation phenomena of the collagen network (determined, in turn, by its crosslinking degree induced by TA and CHDG) and the dynamic capacity of the HTAB micelles to solubilize the two antimicrobials. By controlling the degree of physical crosslinking of collagen with a proper content of TA and CHDG loaded in the matrix, a tunable, sustainable release profile can be obtained.
Open Access
113. Magnetoelectric properties of CoFe2O4/BNT-BT0.08 biphasic nanocomposites, with 0-3 connectivity, prepared by sol-gel method
Authors:
Cernea, M; Radu, R; Amorín, H; Vasile, BS; Surdu, VA; Trusca, R; Gavrila, R; Galassi, C
Published: AUG 15 2023, JOURNAL OF ALLOYS AND COMPOUNDS, 952, 170041, DOI: 10.1016/j.jallcom.2023.170041
Motivated by the goal of developing ultralow power, smart and multifunctional nano (micro) electronic devices, research has shown unwavering interest in synthesis methods, architectures and interphase connectivity of composites containing magnetostrictive and piezoelectric phases, known as magnetoelectric (ME) materials. Herein we report on CoFe2O4/0.92Bi0.5Na0.5TiO3-0.08BaTiO3 biphasic ME composites, obtained by sol-gel chemistry, by mixing the precursor sols of the two phases into one precursor sol and further transforming it into gel, with the goal of obtaining homogeneous nanocomposites with magnetoelectric properties. The structural properties, the temperature dependance of dielectric properties, the magnetic and magnetoelectric properties of these biphasic mixtures, with various molar ratios CoFe2O4/ BNT-BT0.08 = 0.5:1, 1:1 and 1.5:1, are investigated. It is observed that the amount of CoFe2O4 and the synthesis in situ of these composites influences their macroscopic properties showing a high difficulty of carrying out an efficient poling resulting in small piezoelectric and magnetoelectric response. It was concluded that the synthesis procedure, the type of architecture and the interphase connectivity are of outmost importance for magnetoelectric properties based on lead-free materials. (c) 2023 Published by Elsevier B.V.
Open Access
114. Defect characterization studies on irradiated boron-doped silicon pad diodes and Low Gain Avalanche Detectors
Authors:
Himmerlich, A; Castello-Mor, N; Rivera, EC; Gurimskaya, Y; Maulerova-Subert, V; Moll, M; Pintilie, I; Fretwurst, E; Liao, C; Schwandt, J
Published: MAR 2023, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 1048, 167977, DOI: 10.1016/j.nima.2022.167977
High-energy physics detectors with internal charge multiplication, like Low Gain Avalanche Detectors (LGADs), that will be used for fast timing in the High Luminosity LHC experiments, have to exhibit a significant radiation tolerance. In this context, the impact of radiation on the highly boron-doped gain layer is of particular interest, since due to the so-called Acceptor Removal Effect (ARE) a radiation-induced deactivation of active boron dopants takes place, that is causing a progressive loss in the gain with increasing irradiation level. In this paper we present defect-spectroscopy measurements (Deep-Level Transient Spectroscopy and Thermally Stimulated Current technique) on neutron, proton and electron irradiated p-type silicon pad diodes of different resistivity as well as LGADs neutron irradiated at fluences up to 1 x 1015 neq/cm2. We show that compared to silicon pad diodes the determination of LGAD defect introduction rates is less straightforward as they are strongly influenced by the impact of the gain layer. The measured gain layer capacitance has a strong frequency and temperature dependence which makes DLTS measurements challenging to perform with results difficult to interpret. With the TSC technique the defects formed in the LGADs are nicely observed and can be compared to the defects formed in the silicon pad diodes. However, the exact assignment of defects to the gain layer or bulk region remains challenging and the charge amplification effect of the LGADs impacts the exact determination of defect concentrations. We also demonstrate that, depending on the TSC measurement conditions, defect induced internal electric fields are built up in the irradiated LGADs which impact the signal current.
Open Access
115. High-Entropy Lead-Free Perovskite Bi0.2K0.2Ba0.2Sr0.2Ca0.2TiO3 Powders and Related Ceramics: Synthesis, Processing, and Electrical Properties
Authors:
Surdu, VA; Marinica, MA; Patru, RE; Oprea, OC; Nicoara, AI; Vasile, BS; Trusca, R; Ianculescu, AC
Published: NOV 2023, NANOMATERIALS, 13, 2974, DOI: 10.3390/nano13222974
A novel high-entropy perovskite powder with the composition Bi0.2K0.2Ba0.2Sr0.2Ca0.2TiO3 was successfully synthesized using a modified Pechini method. The precursor powder underwent characterization through Fourier Transform Infrared Spectroscopy and thermal analysis. The resultant Bi0.2K0.2Ba0.2Sr0.2Ca0.2TiO3 powder, obtained post-calcination at 900 C-degrees, was further examined using a variety of techniques including X-ray diffraction, Raman spectroscopy, X-ray fluorescence, scanning electron microscopy, and transmission electron microscopy. Ceramic samples were fabricated by conventional sintering at various temperatures (900, 950, and 1000 C-degrees). The structure, microstructure, and dielectric properties of these ceramics were subsequently analyzed and discussed. The ceramics exhibited a two-phase composition comprising cubic and tetragonal perovskites. The grain size was observed to increase from 35 to 50 nm, contingent on the sintering temperature. All ceramic samples demonstrated relaxor behavior with a dielectric maximum that became more flattened and shifted towards lower temperatures as the grain size decreased.
Open Access
116. Microstructural and Morphological Characterization of the Cobalt-Nickel Thin Films Deposited by the Laser-Induced Thermionic Vacuum Arc Method
Authors:
Dinca, V; Mandes, A; Vladoiu, R; Prodan, G; Ciupina, V; Polosan, S
Published: JUN 2023, COATINGS, 13, 984, DOI: 10.3390/coatings13060984
Laser Induced-Thermionic Vacuum Arc (LTVA) technology was used for depositing uniform intermetallic CoNi thin films of 100 nm thickness. LTVA is an original deposition method using a combination of the typical Thermionic Vacuum Arc (TVA) system and a laser beam provided by a QUANTEL Q-Smart 850 Nd:YAG compact Q-switched laser with a second harmonic module. The novelty is related to the simultaneous deposition of a bi-component metallic thin film using photonic processes of the laser over the plasma deposition, which improves the roughness but also triggers the composition of the deposited thin film. Structural analysis of the deposited thin films confirms the formation of face-centered cubic (fcc) as the main phase CoNi and hexagonal Co3Ni as the minority phase, observed mainly using high-resolution transmission electron microscopy. The magneto-optical measurements suggest an isotropic distribution of the CoNi alloy thin films for the in-plan angular rotation. From the low coercive field of H-c = 40 Oe and a saturation field at 900 Oe, the CoNi thin films obtained by LTVA are considered semi-hard magnetic materials. Magnetic force microscopy reveals spherical magnetic nanoparticles with mean size of about 40-50 nm. The resistivity was estimated at rho = 34.16 mu Omega cm, which is higher than the values for bulk Co and Ni.
117. Growth and characterization of Cu-Ni-Sn-S films electrodeposited at different applied potentials
Authors:
El Khouja, O; Nouneh, K; Touhami, ME; Matei, E; Stancu, V; Enculescu, M; Galca, AC
Published: MAR 2023, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 34, 760, DOI: 10.1007/s10854-023-10173-8
Cu2NiSnS4 (CNTS) absorber layers are elaborated by electrodeposition at various applied potentials followed by sulfurization treatment at 450 degrees C under sulfur atmosphere. The microstructural investigations revealed the presence of Cu4SnS4 secondary phases which can be reduced using an applied potential of -1.15 V vs. Ag/AgCl. Using the corresponding cathodic potential for Ni2+, the competing detrimental hydrogen evolution regresses the morphology and composition. The film with the highest Ni concentration has a band gap of 1.44 eV as inferred from diffuse reflectance data. The Randles cell model is probed by electrochemical impedance spectroscopy.
Open Access
118. Effect of P2O5 Content on Luminescence of Reduced Graphene-Oxide-Doped ZnO-P2O5 Nano-Structured Films Prepared via the Sol-Gel Method
Authors:
Vasiliu, IC; Filip, AV; Chilibon, I; Elisa, M; Bartha, C; Kuncser, V; Leca, A; Boroica, L; Sava, BA; Trusca, R; Eftimie, M; Nicoara, A
Published: SEP 2023, MATERIALS, 16, 6156, DOI: 10.3390/ma16186156
A convenient and low-cost sol-gel approach for the one-step synthesis of ZnO-P2O5-rGO nanostructures with tuned bandgap and fluorescence was investigated. The obtained hybrid nanostructures exploit the properties of zinc oxide, graphene oxide and phosphorous oxide as promising candidates for a wide range of optoelectronic applications. A predominant amorphous structure, ZnO-P2O5-rGO, containing ZnO nanorods was evidenced by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The estimated size of the ZnO nanorods in nanostructures with P2O5 was noticed to decrease when the P2O5/ZnO ratio was increased. The presence of ZnO, P2O5 and rGO was confirmed by Fourier-transform infrared spectroscopy (FTIR) and Raman investigation. P2O5 was noticed to tune the bandgap and the fluorescence emissions of the nanostructured films, as estimated by UV-Vis-NIR and fluorescence spectroscopy, respectively. The electrical measurements performed at room temperature showed that the main influence on the film's resistivity does not come from the 1% rGO doping but from the P2O5/ZnO ratio. It was found that a 10/90 molar ratio of P2O5/ZnO decreases the resistivity almost seven-fold compared with rGO-doped ZnO films.
119. Surface species of nematic mixture E7 in hard confinement: spectroscopic investigations cannot distinguish among the E7 components interacting with the support surface
Authors:
Frunza, L; Zgura, I; Ganea, CP; Loiko, VA; Manaila-Maximean, D
Published: AUG 9 2023, LIQUID CRYSTALS, 50, DOI: 10.1080/02678292.2023.2182379
Properties of surface species of the nematic mixture E7 in contact with inorganic oxides (especially those containing more or less aluminium ions) are in detail investigated by infrared spectroscopy and thermogravimetry. The absorption infrared peaks were decomposed into Gaussian components, the procedure allowing an easier comparison with the behaviour of related composites. We worked at enough small concentrations of the E7 relatively to support this ratio permitting the (partial) elimination of the species belonging to the bulk. Species put here in evidence are species that are hydrogen bonded to the surface of OH groups, molecules randomly oriented on the surface, some species bonded by involvement of pi electrons of the CN group to the aluminium ions, thus implying a strong interaction to the support. Supramolecular assemblies of E7 molecules are thus followed up.
120. Photo-stable, 1D-nanofilaments TiO2-based lepidocrocite for photocatalytic hydrogen production in water-methanol mixtures
Authors:
Badr, HO; Natu, V; Neatu, S; Neatu, F; Kuncser, A; Rostas, AM; Racey, M; Barsoum, MW; Florea, M
Published: SEP 6 2023, MATTER, 6, DOI: 10.1016/j.matt.2023.05.026
Water and sunlight are the cleanest, most renewable, and abundant resources on Earth. Developing inexpensive, scalable photocatalysts that are highly stable for hydrogen (H-2) production has long been a cherished dream of humanity. Herein, we report on one-dimensional lepidocrocite-based sub-nanofilaments (NFs), approximate to 5 x 7 & Aring;(2) in cross-section, that generate H-2 from 80:20 v/v water/methanol mixtures when illuminated by simulated sunlight. The NFs were stable in the mixtures for times >4,300 h, 300 h of which were under irradiation. Apparent quantum yields as high as 11.7% were obtained. Based on deuterated water results, we conclude that water is the H-2 source. Further, no carbon dioxide (CO2) due to photocatalytic degradation of methanol was detected. Therefore, the NFs have strong green credentials and lucrative economic prospects for large scale up. We expect these NFs will lead to new lines for developing cheap and ultra-stable materials to produce H-2 photochemically for a long time.
Open Access
121. Ferroelectric Orthorhombic ZrO2 Thin Films Achieved Through Nanosecond Laser Annealing
Authors:
Crema, APS; Istrate, MC; Silva, A; Lenzi, V; Domingues, L; Hill, MO; Teodorescu, VS; Ghica, C; Gomes, MJM; Pereira, M; Marques, L; MacManus-Driscoll, JL; Silva, JPB
Published: MAY 2023, ADVANCED SCIENCE, 10, DOI: 10.1002/advs.202207390
A new approach for the stabilization of the ferroelectric orthorhombic ZrO2 films is demonstrated through nanosecond laser annealing (NLA) of as-deposited Si/SiOx/W(14 nm)/ZrO2(8 nm)/W(22 nm), grown by ion beam sputtering at low temperatures. The NLA process optimization is guided by COMSOL multiphysics simulations. The films annealed under the optimized conditions reveal the presence of the orthorhombic phase, as confirmed by X-ray diffraction, electron backscatter diffraction, and transmission electron microscopy. Macroscopic polarization-electric field hysteresis loops show ferroelectric behavior, with saturation polarization of 12.8 mu C cm(-2), remnant polarization of 12.7 mu C cm(-2) and coercive field of 1.2 MV cm(-1). The films exhibit a wake-up effect that is attributed to the migration of point defects, such as oxygen vacancies, and/or a transition from nonferroelectric (monoclinic and tetragonal phase) to the ferroelectric orthorhombic phase. The capacitors demonstrate a stable polarization with an endurance of 6.0 x 10(5) cycles, demonstrating the potential of the NLA process for the fabrication of ferroelectric memory devices with high polarization, low coercive field, and high cycling stability.
Open Access
122. Deciphering the role of water and a zinc-doping process in a polyol-based approach for obtaining Zn/Co/Al-based spinels: toward "green" mesoporous inorganic pigments
Authors:
Alexandru, MG; Ianculescu, AC; Carp, O; Culita, DC; Preda, S; Ene, CD; Vasile, BS; Surdu, VA; Nicoara, AI; Neatu, F; Pintilie, I; Visinescu, D
Published: AUG 1 2023, DALTON TRANSACTIONS, 52, DOI: 10.1039/d3dt00972f
Two new families of zinc/cobalt/aluminum-based pigments, with a unique composition, were obtained through the polyol method. The hydrolysis process of a mixture of Co(CH3COO)(2), Zn(acac)(2) and Al(acac)(3) (acac(-) = acetylacetonate ion) in 1,4-butanediol afforded dark blue gels (wPZn(x)Co(1-x)Al), in the presence of a supplementary amount of water, and light green powders (PZnxCo1-xAl), respectively, for the water-free procedure (x = 0, 0.2, 0.4). The calcination of the precursors yielded dark green (wZn(x)Co(1-x)Al) and blue (ZnxCo1-xAl) products. XRD measurements and Rietveld refinement indicate the co-existence of three spinel phases, in different proportions: ZnxCo1-xAl2O4, Co3O4 and the defect spinel, ?-Al2.67O4. The Raman scattering and XPS spectra are in agreement with the compositions of the samples. The morphology of wZn(x)Co(1-x)Al consists of large and irregular spherical particle aggregates (ca. 5-100 mm). Smaller agglomerates (ca. 1-5 mm) with a unique silkworm cocoon-like hierarchical morphology composed of cobalt aluminate cores covered with flake-like alumina shells are formed for ZnxCo1-xAl. TEM and HR-TEM analyses revealed the formation of crystalline, polyhedral particles of 7-43 nm sizes for wZn(x)Co(1-x)Al, while for ZnxCo1-xAl, a duplex-type morphology, with small (7-13 nm) and larger (30-40 nm) particles, was found. BET assessment showed that both series of oxides are mesoporous materials, with different pore structures, with the water-free samples exhibiting the largest surface areas due, most likely, to the high percent of aluminum oxide. A chemical mechanism is proposed to highlight the role of the water amount and the nature of the starting compounds in the hydrolysis reaction products and, further, in the morpho-structural features and composition of the resulting spinel oxides. The CIE L*a*b* and C* colorimetric parameters indicate that the pigments are bright, with a moderate degree of luminosity, presenting an outstanding high blueness.
Open Access
123. Fabrication of CuO (p)-ZnO (n) Core-Shell Nanowires and Their H2-Sensing Properties
Authors:
Sisman, O; Zappa, D; Maraloiu, VA; Comini, E
Published: JUL 2023, MATERIALS, 16, 4802, DOI: 10.3390/ma16134802
Unlike the conventional one-dimensional (1D) core-shell nanowires (NWs) composed of p-type shells and n-type cores, in this work, an inverse design is proposed by depositing n-type ZnO (shell) layers on the surface of p-type CuO (core) NWs, to have a comprehensive understanding of their conductometric gas-sensing kinetics. The surface morphologies of bare and core-shell NWs were investigated by field emission scanning electron microscope (FE-SEM). The ZnO shell layer was presented by overlay images taken by electron dispersive X-ray spectroscopy (EDX) and high-resolution transmission electron microscopy (HRTEM). The pronounced crystalline plane peaks of ZnO were recorded in the compared glancing incident X-ray diffraction (GI-XRD) spectra of CuO and CuO-ZnO core-shell NWs. The ZnO shell layers broaden the absorption curve of CuO NWs in the UV-vis absorption spectra. As a result of the heterostructure formation, the intrinsic p-type sensing behavior of CuO NWs towards 250 and 500 ppm of hydrogen (H-2) switched to n-type due to the deposition of ZnO shell layers, at 400 & DEG;C in dry airflow.
124. Grain size-driven effect on the functional properties in Ba0.6Sr0.4TiO3 ceramics consolidated by spark plasma sintering
Authors:
Patru, RE; Stanciu, CA; Soare, EM; Surdu, VA; Trusca, RD; Nicoara, AI; Vasile, BS; Boni, G; Amarande, L; Horchidan, N; Curecheriu, LP; Mitoseriu, L; Pintilie, L; Pintilie, I; Ianculescu, AC
Published: JUL 2023, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 43, DOI: 10.1016/j.jeurceramsoc.2023.02.013
Dense fine-grained Ba0.6Sr0.4TiO3 ceramics with submicronic grains sizes (GS) have been prepared using nanopowders synthesized via sol-gel route and consolidated by Spark Plasma Sintering (SPS). By changing SPS parameters, the GS was reduced from 214 nm to 74 nm. Diffuse ferroelectric-paraelectric phase transitions and low values of dielectric permittivity (<1000) at the Curie temperature (T-C similar to 280 K) were revealed by Impedance Spectroscopy in all sintered ceramics. The GS reduction from submicron to nanoscale range reflects in a gradually diminishment of dielectric constant, tunability, polarisation and storage energy properties. Raman spectroscopy investigations pointed out the presence of polar nanoclusters above the T-C. The short-range polar order is affected by the GS decrease, but becomes more thermally stable. The observed properties of Ba0.6Sr0.4TiO3 nanostructured ceramics are interpreted by considering the interplay between the GS reduction, the role of low-permittivity grain boundaries and the diffuse character of the ferroelectric-to-paraelectric transformation.
Open Access
125. Lead-Free Perovskite Thin Films with Tailored Pockels-Kerr Effects for Photonics
Authors:
Ion, V; Teodorescu, V; Birjega, R; Dinescu, M; Mitterbauer, C; Alexandrou, I; Ghitiu, I; Craciun, F; Scarisoreanu, ND
Published: JUL 27 2023, ACS APPLIED MATERIALS & INTERFACES, 15, DOI: 10.1021/acsami.3c06499
Pockels and Kerr effects are linear and nonlinear electro-opticaleffects, respectively, used in many applications. The modulation ofthe refractive index is employed in different photonic circuits. However,the greatest challenge is in photonic elements for quantum computingat room temperature. For this aim, materials with strong Pockels/Kerreffects and & chi;((2))/& chi;((3)) nonlinearsusceptibilities are necessary. Here, we demonstrate composition-modulatedstrong electro-optical response in epitaxial films of (Ba,Ca)(Ti,Zr)O-3 perovskite titanate. These films are grown by pulsed laserdeposition on SrTiO3. Depending on the ratios of Ca/Baand Ti/Zr, films show high Pockels or Kerr optical nonlinearities.We relate the variable electro-optic response to the occurrence ofnanopolar domains with different symmetries in a selected compositionrange. These findings open the route to easily implement nonlinearoptical elements in integrated photonic circuits.
Open Access
126. Up-conversion emission in transition metal and lanthanide co-doped systems: dimer sensitization revisited
Authors:
Avram, D; Colbea, C; Patrascu, AA; Istrate, MC; Teodorescu, V; Tiseanu, C
Published: FEB 7 2023, SCIENTIFIC REPORTS, 13, 2165, DOI: 10.1038/s41598-023-28583-3
Lanthanide (Ln) co-doped transition metal (TM) upconversion (UC) co-doped systems are being intensively investigated for their exciting applications in photonics, bioimaging, and luminescence thermometry. The presence of TM, such as Mo6 + /W6 +, Mn2 +, or Fe3 + determines significant changes in Ln UC emission, such as intensity enhancement, colour modulation, and even the alteration of the photon order. The current mechanism assumes a ground-state absorption/excited-state absorption (ESA/GSA) in TM-Yb dimer followed by direct energy transfer to Er/Tm excited states. We revisit this mechanism by addressing two issues that remain ignored: a dynamical approach to the investigation of the upconversion mechanism and the intrinsic chemical complexity of co-doped TM, Ln systems. To this aim, we employ a pulsed, excitation variable laser across a complete set of UC measurements, such as the emission and excitation spectra and emission decays and analyze multiple grains with transmission electron microscopy (TEM). In the Mo co-doped garnet, the results sustain the co-existence of Mo-free garnet and Mo oxide impurity. In this Mo oxide, the Er upconversion emission properties are fully explained by a relatively efficient sequential Yb to Er upconversion process, with no contribution from Yb-Mo dimer sensitization.
127. The use of a new selective AB3 aptamer for the hematologic tumor cells' detection
Authors:
Rus, I; Tertis, M; Pop, A; Fizesan, I; Bogdan, D; Matei, E; Oprea, D; Diculescu, V; Sandulescu, R; Cristea, C
Published: NOV 1 2023, SENSORS AND ACTUATORS B-CHEMICAL, 394, 134389, DOI: 10.1016/j.snb.2023.134389
Hematologic malignancies represent cancer diseases that affect the bone marrow and blood cells and include various subtypes depending mostly on the morphology of the cells. It is well known that an early diagnosis could be very useful for increasing survival rates in cancer, especially in the aggressive forms which can quickly progress to untreatable forms. The development of an easy, fast, and sensitive analytical tool with indicative applications in diagnosis and follow-up care, that could bring benefits in the discovery of new malignant diseases or relapses is reported. Oncofetal antigen/immature laminin receptor protein (OFA/iLRP) is an immunogenic protein found in fetal cells as well as overexpressed on the surface of some malignant tumors, including some hematologic malignancies. An aptamer, AB3, was selected and reported in the literature, having as a target the immature laminin receptor protein. Using the AB3 aptamer and its affinity to immature laminin receptor protein-positive cells an aptasensor was developed and tested on Jurkat cells. For the immobilization of the aptamer, graphene oxide modified screen printed electrodes were used and subjected to an activation procedure. The aptasensor development and cell caption were evaluated using electrochemical methods as well as microscopic techniques. The limit of detection of the developed aptasensor was 3.3 x 10(3) cells mL(-1), meaning 16 cells in the 5 mu L of suspension tested.
128. Influence of Ferroelectric Filler Size and Clustering on the Electrical Properties of (Ag-BaTiO3)-PVDF Sub-Percolative Hybrid Composites
Authors:
Padurariu, L; Horchidan, N; Ciomaga, CE; Curecheriu, LP; Lukacs, VA; Stirbu, RS; Stoian, G; Botea, M; Florea, M; Maraloiu, VA; Pintilie, L; Rotaru, A; Mitoseriu, L
Published: 2023 JAN 18 2023, ACS APPLIED MATERIALS & INTERFACES, DOI: 10.1021/acsami.2c15641
The paper presents a study concerning the role of ferroelectric filler size and clustering in the dielectric properties of 20%BaTiO3-80%PVDF and of 20% (2%Ag-98%BaTiO3)-PVDF hybrid nanocomposites. By finite element calculations, it was shown that using fillers with epsilon > 103 does not provide a permittivity rise in the composites and the effective dielectric constant tends to saturate to specific values determined by the filler size and agglomeration degree. Irrespective of the ferroelectric filler sizes, the addition of metallic ultrafine nanoparticles (Ag) results in permittivity intensification and the effect is even stronger if the metallic nanoparticles are connected to a higher degree with the ferroelectric particles' surfaces. When using coarse ferroelectric fillers, the probability of clustering is higher, thus favoring the permittivity increase by field concentration in small regions close to the interfaces separating dissimilar materials. The modeling results were validated by an experimental dielectric analysis performed in a series of PVDF-based thick films with the same amount of BaTiO3 fillers or with Ag-BaTiO3 hybrid fillers. Similar trends as predicted by simulations were found experimentally but with slightly higher permittivity values which were assigned to the modifications of the polymer phase composition due to the presence of nanofillers and the local sample inhomogeneity (the presence of clustering, in particular for coarse BaTiO3 grains), which create regions with enhanced local fields.
Open Access
129. Magnetite-Based Nanostructured Coatings Functionalized with Nigella sativa and Dicloxacillin for Improved Wound Dressings
Authors:
Dorcioman, G; Hudita, A; Galateanu, B; Craciun, D; Mercioniu, I; Oprea, OC; Negut, I; Grumezescu, V; Grumezescu, AM; Ditu, LM; Holban, AM
Published: JAN 2023, ANTIBIOTICS-BASEL, 12, 59, DOI: 10.3390/antibiotics12010059
In this study, we report the performance improvement of wound dressings by covering them with magnetite-based nanostructured coatings. The magnetite nanoparticles (Fe3O4 NPs) were functionalized with Nigella sativa (N. sativa) powder/essential oil and dicloxacillin and were synthesized as coatings by matrix assisted pulsed laser evaporation (MAPLE). The expected effects of this combination of materials are: (i) to reduce microbial contamination, and (ii) to promote rapid wound healing. The crystalline nature of core/shell Fe3O4 NPs and coatings was determined by X-ray diffraction (XRD). Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA) have been coupled to investigate the stability and thermal degradation of core/shell nanoparticle components. The coatings' morphology was examined by scanning electron microscopy (SEM). The distribution of chemical elements and functional groups in the resulting coatings was evidenced by Fourier transform infrared (FTIR) spectrometry. In order to simulate the interaction between wound dressings and epithelial tissues and to evaluate the drug release in time, the samples were immersed in simulated body fluid (SBF) and investigated after different durations of time. The antimicrobial effect was evaluated in planktonic (free-floating) and attached (biofilms) bacteria models. The biocompatibility and regenerative properties of the nanostructured coatings were evaluated in vitro, at cellular, biochemical, and the molecular level. The obtained results show that magnetite-based nanostructured coatings functionalized with N. sativa and dicloxacillin are biocompatible and show an enhanced antimicrobial effect against Gram positive and Gram negative opportunistic bacteria.
Open Access
130. Antibacterial Activity of PVA Hydrogels Embedding Oxide Nanostructures Sensitized by Noble Metals and Ruthenium Dye
Authors:
Pelinescu, D; Anastasescu, M; Bratan, V; Maraloiu, VA; Negrila, C; Mitrea, D; Calderon-Moreno, J; Preda, S; Gifu, IC; Stan, A; Ionescu, R; Stoica, I; Anastasescu, C; Zaharescu, M; Balint, I
Published: AUG 2023, GELS, 9, 650, DOI: 10.3390/gels9080650
Nanostructured oxides (SiO2, TiO2) were synthesized using the sol-gel method and mod-ified with noble metal nanoparticles (Pt, Au) and ruthenium dye to enhance light harvesting and promote the photogeneration of reactive oxygen species, namely singlet oxygen (O-1(2)) and hydroxyl radical (center dot OH). The resulting nanostructures were embedded in a transparent polyvinyl alcohol (PVA) hydrogel. Morphological and structural characterization of the bare and modified oxides was performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), UV-Vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). Additionally, electrokinetic potential measurements were conducted. Crystallinity data and elemental analysis of the investigated systems were obtained through X-ray diffraction and X-ray fluorescence analyses, while the chemical state of the elements was determined using XPS. The engineered ma-terials, both as simple powders and embedded in the hydrogel, were evaluated for their ability to generate reactive oxygen species (ROS) under visible and simulated solar light irradiation to establish a correlation with their antibacterial activity against Staphylococcus aureus. The generation of singlet oxygen (O-1(2)) by the samples under visible light exposure can be of significant importance for their potential use in biomedical applications.
Open Access
131. Efficient Sintering of Mo Matrix Composites-A Study of Temperature Dependences and the Use of the Sinter Additive Ni
Authors:
Solodkyi, I; Petrusha, V; Grigoroscuta, MA; Schmelzer, J; Hasemann, G; Betke, U; Badica, P; Krüger, M
Published: OCT 2023, METALS, 13, 1715, DOI: 10.3390/met13101715
Mo matrix composites (MMC) with Mo-9Si-8B inclusions were fabricated by pressure-less sintering (PLS) and spark plasma sintering (SPS) techniques at temperatures between 1200-1500 degrees C using 1 wt.% Ni sinter additive. The positive impact of the addition Ni addition on the sinterability and formation of a continuous Mo matrix of MMC with randomly distributed Mo3Si and Mo5SiB2 inclusions was determined. The Ni addition increased the shrinkage of MMC during PLS by almost a third. The continuous Mo matrix of MMC and a relative density of more than 98% was obtained after SPS at 1400-1500 degrees C. The composite with the maximum relative density of 98% showed a Vickers hardness of 482 +/- 9 (HV20). The potential of using Ni-activated PLS and SPS to produce high-density MMC is shown.
Open Access
132. Carbon Inks-Based Screen-Printed Electrodes for Qualitative Analysis of Amino Acids
Authors:
Enache, TA; Enculescu, M; Bunea, MC; Zubillaga, EA; Tellechea, E; Aresti, M; Lasheras, M; Asensio, AC; Diculescu, VC
Published: JAN 2023, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 24, 1129, DOI: 10.3390/ijms24021129
Due to the great significance of amino acids, a substantial number of research studies has been directed toward the development of effective and reliable platforms for their evaluation, detection, and identification. In order to support these studies, a new electrochemical platform based on PANI/ZnO nanowires' modified carbon inks screen-printed electrodes was developed for qualitative analysis of electroactive amino acids, with emphasis on tyrosine (Tyr) and tryptophan (Trp). A comparative investigation of the carbon ink before and after modification with the PANI/ZnO was performed by scanning electron microscopy and by Raman spectroscopy, confirming the presence of PANI and ZnO nanowires. Electrochemical investigations by cyclic voltammetry and electrochemical impedance spectroscopy have shown a higher charge-transfer rate constant, which is reflected into lower charge-transfer resistance and higher capacitance values for the PANI/ZnO modified ink when compared to the simple carbon screen-printed electrode. In order to demonstrate the electrochemical performances of the PANI/ZnO nanowires' modified carbon inks screen-printed electrodes for amino acids analysis, differential pulse voltammograms were obtained in individual and mixed solutions of electroactive amino acids. It has been shown that the PANI/ZnO nanowires' modified carbon inks screen-printed electrodes allowed for tyrosine and tryptophan a peak separation of more than 100 mV, enabling their screening and identification in mixed solutions, which is essential for the electrochemical analysis of proteins within the proteomics research field.
Open Access
133. Titania nanoparticles for photocatalytic degradation of ethanol under simulated solar light
Authors:
Goncearenco, E; Morjan, IP; Fleaca, CT; Dumitrache, F; Dutu, E; Scarisoreanu, M; Teodorescu, VS; Sandulescu, A; Anastasescu, C; Balint, I
Published: MAY 22 2023, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 14, DOI: 10.3762/bjnano.14.51
TiO2 nanoparticles were synthesized by laser pyrolysis from TiCl4 vapor in air in the presence of ethylene as sensitizer at different working pressures (250-850 mbar) with and without further calcination at 450 degrees C. The obtained powders were analyzed by energydispersive X-ray spectroscopy, X- ray photoelectron spectroscopy, X-ray diffractometry, and transmission electron microscopy. Also, specific surface area and photoluminescence with optical absorbance were evaluated. By varying the synthesis parameters (especially the working pressure), different TiO2 nanopowders were obtained, whose photodegradation properties were tested compared to a commercial Degussa P25 sample. Two series of samples were obtained. Series "a" includes thermally treated TiO2 nanoparticles (to remove impurities) that have different proportions of the anatase phase (41.12-90.74%) mixed with rutile and small crystallite sizes of 11-22 nm. Series "b" series represents nanoparticles with high purity, which did not require thermal treatment after synthesis (ca. 1 atom % of impurities). These nanoparticles show an increased anatase phase content (77.33-87.42%) and crystallite sizes of 23-45 nm. The TEM images showed that in both series small crystallites form spheroidal nanoparticles with dimensions of 40-80 nm, whose number increases with increasing the working pressure. The photocatalytic properties have been investigated regarding the photodegradation of ethanol vapors in Ar with 0.3% O2 using P25 powder as reference under simulated solar light. During the irradiation H-2 gas production has been detected for the samples from series "b", whereas the CO2 evolution was observed for all samples from series "a".
Open Access
134. Iron oxide/hydroxide-nitrogen doped graphene-like visible-light active photocatalytic layers for antibiotics removal from wastewater
Authors:
Ivan, R; Popescu, C; Antohe, VA; Antohe, S; Negrila, C; Logofatu, C; del Pino, AP; György, E
Published: FEB 15 2023, SCIENTIFIC REPORTS, 13, 2740, DOI: 10.1038/s41598-023-29927-9
Hybrid layers consisting of Fe oxide, Fe hydroxide, and nitrogen doped graphene-like platelets have been synthesized by an eco-friendly laser-based method for photocatalytic applications. The complex composite layers show high photodecomposition efficiency towards degradation of antibiotic molecules under visible light irradiation. The photodecomposition efficiency was investigated as a function of relative concentrations of base materials, Fe oxide nanoparticles and graphene oxide platelets used for the preparation of target dispersions submitted to laser irradiation. Although reference pure Fe oxide/Fe hydroxide layers have high absorption in the visible spectral region, their photodecomposition efficiency is negligible under the same irradiation conditions. The high photocatalytic decomposition efficiency of the nanohybrid layer, up to 80% of the initial antibiotic molecules was assigned to synergistic effects between the constituent materials, efficient separation of the electron-hole pairs generated by visible light irradiation on the surface of Fe oxide and Fe hydroxide nanoparticles, in the presence of conducting graphene-like platelets. Nitrogen doped graphene-like platelets contribute also to the generation of electron-hole pairs under visible light irradiation, as demonstrated by the photocatalytic activity of pure, reference nitrogen doped graphene-like layers. The results also showed that adsorption processes do not contribute significantly to the removal of antibiotic molecules from the test solutions. The decrease of the antibiotic concentration under visible light irradiation was assigned primarily to photocatalytic decomposition mechanisms.
Open Access
135. Epoxy Coatings Containing Modified Graphene for Electromagnetic Shielding
Authors:
Bontas, MG; Diacon, A; Calinescu, I; Necolau, MI; Dinescu, A; Toader, G; Ginghina, R; Vizitiu, AM; Velicu, V; Palade, P; Istrate, M; Rusen, E
Published: JUN 2022, POLYMERS, 14, 2508, DOI: 10.3390/polym14122508
This study presents the functionalization and characterization of graphene and electromagnetic interference (EMI) attenuation capacity in epoxy-nanocomposites. The modification of graphene involved both small molecules and polymers for compatibilization with epoxy resin components to provide EMI shielding. The TGA and RAMAN analyses confirmed the synthesis of graphene with a different layer thickness of the graphene sheets. Graphene samples with different layer thicknesses (monolayer, few layers, and multilayer) were selected and further employed for epoxy coating formulation. The obtained nanocomposites were characterized in terms of EMI shielding effectiveness, SEM, micro-CT, magnetic properties, and stress-strain resistance. The EMI shielding effectiveness results indicated that the unmodified graphene and hexamethylene diamine (HMDA) modified graphene displayed the best EMI shielding properties at 11 GHz. However, the epoxy nanocomposites based on HMDA modified graphene displayed better flexibility with an identical EMI shielding effectiveness compared to the unmodified graphene despite the formation of aggregates. The improved flexibility of the epoxy nanocomposites and EMI shielding characteristics of HMDA functionalized graphene offers a practical solution for textile coatings with microwave absorbing (MA) capacity.
136. Luminescent heteroleptic copper(I) complexes with phosphine and N-benzoyl thiourea ligands: Synthesis, structure and emission properties
Authors:
Tudor, CA; Ilis, M; Secu, M; Ferbinteanu, M; Cîrcu, V
Published: JAN 1 2022, POLYHEDRON, 211, 115542, DOI: 10.1016/j.poly.2021.115542
The reactions between [CuX(PPh3)](4) or [CuX(PPh3)(3)], X = Cl or Br, and N-benzoyl-N'-(4-methoxyphenyl)thio-urea (BTU-OMe), N-benzoyl-N'-(4-methylphenyl)thiourea (BTU-Me) in toluene gave new four-coordinated tetrahedral copper(I) complexes of two types: [CuX(BTU)(PPh3)(2)] (1, 2) and [CuX(BTU)(2)(PPh3)] (3,4) [BTU = N-benzoyl-N'-(4-methoxy/methyl phenyl)thiourea derivatives, X = Cl (a) and Br (b)]. These complexes were fully characterized by several analytical and spectroscopic (IR, UV/VIS, H-1, C-13 and P-31 NMR) techniques. The molecular structure of a representative complex, [Cu(BTU-OMe)(PPh3)(2)Cl] (3a), was determined by the single crystal X-ray diffraction method which reveals a distorted tetrahedral geometry where the Cu(I) ion is surrounded by one BTU ligand molecule, two PPh3 groups and one chloride anion. These eight heteroleptic complexes were found to emit in solid state with lifetimes in the 12-99 mu s range and with the highest quantum yield of 4.0% for 3b. The reaction between [CuBr(PPh3)](4) and N-benzoyl-N',N'-(di-n-butyl)thiourea (BTU-Bu-2) ligand gave the simple [CuBr(BTU-Bu-2)(3)] complex (5), when the PPh3 molecules were completely removed by the BTU derivative. The spectroscopic data indicated a distorted tetrahedral geometry produced by three BTU ligand molecules and one bromide anion. Complex 5 has the highest quantum yield (11%) with the lifetime of 29 mu s in solid-state.
Open Access
137. SiGeSn Quantum Dots in HfO2 for Floating Gate Memory Capacitors
Authors:
Palade, C; Slav, A; Cojocaru, O; Teodorescu, VS; Stoica, T; Ciurea, ML; Lepadatu, AM
Published: MAR 2022, COATINGS, 12, 348, DOI: 10.3390/coatings12030348
Group IV quantum dots (QDs) in HfO2 are attractive for non-volatile memories (NVMs) due to complementary metal-oxide semiconductor (CMOS) compatibility. Besides the role of charge storage centers, SiGeSn QDs have the advantage of a low thermal budget for formation, because Sn presence decreases crystallization temperature, while Si ensures higher thermal stability. In this paper, we prepare MOS capacitors based on 3-layer stacks of gate HfO2/floating gate of SiGeSn QDs in HfO2/tunnel HfO2/p-Si obtained by magnetron sputtering deposition followed by rapid thermal annealing (RTA) for nanocrystallization. Crystalline structure, morphology, and composition studies by cross-section transmission electron microscopy and X-ray diffraction correlated with Raman spectroscopy and C-V measurements are carried out for understanding RTA temperature effects on charge storage behavior. 3-layer morphology and Sn content trends with RTA temperature are explained by the strongly temperature-dependent Sn segregation and diffusion processes. We show that the memory properties measured on Al/3-layer stack/p-Si/Al capacitors are controlled by SiGeSn-related trapping states (deep electronic levels) and low-ordering clusters for RTA at 325-450 degrees C, and by crystalline SiGeSn QDs for 520 and 530 degrees C RTA. Specific to the structures annealed at 520 and 530 degrees C is the formation of two kinds of crystalline SiGeSn QDs, i.e., QDs with low Sn content (2 at.%) that are positioned inside the floating gate, and QDs with high Sn content (up to 12.5 at.%) located at the interface of floating gate with adjacent HfO2 layers. The presence of Sn in the SiGe intermediate layer decreases the SiGe crystallization temperature and induces the easier crystallization of the diamond structure in comparison with 3-layer stacks with Ge-HfO2 intermediate layer. High frequency-independent memory windows of 3-4 V and stored electron densities of 1-2 x 10(13) electrons/cm(2) are achieved.
Open Access
138. Effect of the Cadmium Telluride Deposition Method on the Covering Degree of Electrodes Based on Copper Nanowire Arrays
Authors:
Panaitescu, AM; Antohe, I; Locovei, C; Iftimie, S; Antohe, S; Piraux, L; Suchea, MP; Antohe, VA
Published: AUG 2022, APPLIED SCIENCES-BASEL, 12, 7808, DOI: 10.3390/app12157808
In this work, we report the preparation of nanostructured electrodes based on dense arrays of vertically-aligned copper (Cu) nanowires (NWs) to be subsequently covered by cadmium telluride (CdTe) thin films, with great potential to be used within "substrate"-type photovoltaic cells based on A(II)-BVI heterojunctions. In particular, the multi-step preparation protocol presented here involves an electrochemical synthesis procedure within a supported anodic aluminum oxide (AAO) nanoporous template for first generating a homogeneous array of vertically-aligned Cu NWs, which are then further embedded within a compact CdTe thin film. In a second stage, we tested three deposition methods (vacuum thermal evaporation, VTE; radio-frequency magnetron sputtering, RF-MS; and electrochemical deposition, ECD) for use in obtaining CdTe layers potentially able to consistently penetrate the previously prepared Cu NWs array. A comparative analysis was performed to critically evaluate the morphological, optical, and structural properties of the deposited CdTe films. The presented results demonstrate that under optimized processing conditions, the ECD approach could potentially allow the cost-effective fabrication of absorber layer/collecting electrode CdTe/Cu nanostructured interfaces that could improve charge collection mechanisms, which in turn could allow the fabrication of more efficient solar cells based on A(II)-BVI semiconducting compounds.
Open Access
139. Unified approach to cyclotron and plasmon resonances in a periodic two-dimensional GaAs electron gas hosting the Hofstadter butterfly
Authors:
Gudmundsson, V; Mughnetsyan, V; Abdullah, NR; Tang, CS; Moldoveanu, V; Manolescu, A
Published: APR 7 2022, PHYSICAL REVIEW B, 105, 155302, DOI: 10.1103/PhysRevB.105.155302
We present theoretical calculations for the cyclotron resonance and various magnetoplasmon modes of a Coulomb interacting two-dimensional GaAs electron gas (2DEG) modulated as a lateral superlattice of quantum dots subjected to an external perpendicular constant magnetic field. We use a real-time excitation approach based on the Liouville???von Neumann equation for the density operator, that can go beyond linear response delivering information of all longitudinal and transverse collective modes of interest to the same order. We perform an extensive analysis of the coexisting collective modes due to the lateral confinement and the magnetic field for a different number of electrons in each dot. In the limit of vanishing dot modulation of the 2DEG we find signs of the structure of the Hofstadter butterfly in the excitation spectra.
Open Access
140. Band-Gap Engineering of Layered Perovskites by Cu Spacer Insertion as Photocatalysts for Depollution Reaction
Authors:
Raciulete, M; Anastasescu, C; Papa, F; Atkinson, I; Bradu, C; Negrila, C; Eftemie, DI; Culita, DC; Miyazaki, A; Bratan, V; Pandele-Cusu, J; Munteanu, C; Dobrescu, G; Sandulescu, A; Balint, I
Published: DEC 2022, CATALYSTS, 12, 1529, DOI: 10.3390/catal12121529
A multi-step ion-exchange methodology was developed for the fabrication of Cu(LaTa2O7)(2) lamellar architectures capable of wastewater depollution. The (001) diffraction line of RbLaTa2O7 depended on the guest species hosted by the starting material. SEM and TEM images confirmed the well-preserved lamellar structure for all intercalated layered perovskites. The UV-Vis, XPS, and photocurrent spectroscopies proved that Cu intercalation induces a red-shift band gap compared to the perovskite host. Moreover, the UV-Vis spectroscopy elucidated the copper ions environment in the Cu-modified layered perovskites. H-2-TPR results confirmed that Cu species located on the surface are reduced at a lower temperature while those from the interlayer occur at higher temperature ranges. The photocatalytic degradation of phenol under simulated solar irradiation was used as a model reaction to assess the performances of the studied catalysts. Increased photocatalytic activity was observed for Cu-modified layered perovskites compared to RbLaTa2O7 pristine. This behavior resulted from the efficient separation of photogenerated charge carriers and light absorption induced by copper spacer insertion.
141. New superdielectric materials: (1-x) SrFe12O19 - x BNT-BT nanocomposites
Authors:
Greculeasa, SG; Comanescu, C; Iacob, N; Kuncser, A; Smaranda, I; Amarande, L; Cioangher, M; Burdusel, M; Teodorescu, V
Published: OCT 1 2022, PHYSICA B-CONDENSED MATTER, 642, 414139, DOI: 10.1016/j.physb.2022.414139
Novel (1-x) SrFe12O19 - x BNT-BT0.08 (x = 0; 0.5; 0.8; 1) nanocomposites were explored in this study. The samples were produced by sol-gel method and compacted by conventional sintering. The composition, morphology, local structure, dielectric and magnetic properties were investigated by X-ray diffraction, Transmission Electron Microscopy, Impedance Analysis, Mossbauer spectroscopy, and SQUID magnetometry. The desired composition and the presence of the magnetoplumbite SrFe12O19 and perovskite BNT-BT structures were verified by X-ray diffraction. Irregular morphology and large size distributions are evidenced in the electron microscopy micrographs. The reported room temperature dielectric constants in this study are the highest values obtained in multiferroic composites at room temperature: giant dielectric constants (similar to 1.3 x 10(6)) were obtained, relative to 0.13 x 10(4) in BNT-BT. The hyperfine parameters allowed the identification of the Wyckoff positions of the Fe ions corresponding closely to the theoretical case. The hard magnetic character of the SrFe12O19 phase is evidenced from the magnetic measurements. For the first time in multifermic composites, superdielectric characteristics are evidenced at room temperature.
Open Access
142. Nanometric-Thick Metal-Free h-Boron Nitride/Graphene Films as Base Catalyst for the Synthesis of Benzoxazoles
Authors:
Rendon-Patiño, A; Primo, A; Cojocaru, B; Ion, SG; Popescu, DG; Parvulescu, V; García, H
Published: JUN 22 2022, CHEMCATCHEM, 14, e202200356, DOI: 10.1002/cctc.202200356
Catalysts are frequently used as pelletized powdered materials, but rarely as thin films. The present work reports the use of 2D h-boron nitride on few layers defective graphene (h-BN/fl-G) films of about 10 nm thickness as base catalyst for the synthesis of benzoxazoles by coupling a 2-amino-phenol with p-substituted benzaldehydes. The synthesis of benzoxazole derivatives has aroused much interest in the last decades due to their application as potent anticancer agents against MCF-7 and MDA-MB-231 breast cancer cells. The results demonstrate that these nanometer-thick films exhibit three orders of magnitude higher activity than K2CO3 taken as benchmark base catalyst. The activity and selectivity of h-BN/fl-G films depend on the nature of substituents on benzaldehyde, the solvent and reaction temperature.
Open Access
143. C-doped TiO2 nanotubes with pulsed laser deposited Bi2O3 films for photovoltaic application
Authors:
Bjelajac, A; Petrovic, R; Stan, GE; Socol, G; Mihailescu, A; Mihailescu, IN; Veltruska, K; Matolin, V; Siketic, Z; Provatas, G; Jaksic, M; Janackovic, D
Published: FEB 15 2022, CERAMICS INTERNATIONAL, 48, DOI: 10.1016/j.ceramint.2021.10.251
Anodization was used to obtain a nanotubular TiO2 photoanode on F-SnO2 glass. Subsequent annealing in the CH4 atmosphere promoted the C-doping and improved the crystallinity of the TiO2 nanotubes. The pulsed laser deposition was applied to cover the nanotubes with Bi2O3, serving as a hole transport material. X-ray photoelectron spectroscopy analyses of the doped samples reveal a shift in the valence band's maximum position towards lower binding energy as compared to those observed for the undoped samples (annealed in the air). The doping positively affects the absorption by shifting the absorption edge to 567 nm. I-V measurements under illumination show that the C-doping of TiO2 increases the current density following the absorbance results. The highest open circuit voltage was reached for the samples with the 300 degrees C-deposited Bi2O3 layer, pointing to better quality of the p-n junction, hence of the contact between Bi2O3 and TiO2. This in situ annealing provided the formation of close contact between Bi2O3 and TiO2, which enabled a faster charge transport as compared to the contact obtained with no annealing or even with post annealing.
144. Monodispersed nanoplatelets of samarium oxides for biosensing applications in biological fluids
Authors:
Leote, RJB; Matei, E; Apostol, NG; Enculescu, M; Enculescu, I; Diculescu, VC
Published: JAN 10 2022, ELECTROCHIMICA ACTA, 402, 139532, DOI: 10.1016/j.electacta.2021.139532
A nanostructured samarium oxide electrode was constructed by electrodeposition onto the surface of a gold electrode on SiO2/Si wafer. The samarium oxides electrode's surface morphology was investigated by scanning electron microcopy showing a quasi-monodispersed nanoplatelets like structure. X-rays diffraction analysis demonstrated a mixture of monoclinic and hexagonal phases while the X-rays photoelectron spectroscopy indicated the co-existence of both Sm2+ and Sm3+ species in a 1:3 proportion. Cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the charge transfer processes at the surface of the samarium oxide electrode in the absence and in the presence of redox probes. A roughness factor of 2.5 was determined from the samarium oxide electrode while the charge transfer constant was almost double when compared to the planar gold electrode. Then, the samarium oxide electrode was used for the H2O2 detection by fixed potential amperometry at -0.20 V (vs. Ag/AgCl) with a linear region between 0.01 and 1.00 mM, a sensitivity of 153 mu A cm(-2) mM(-1) and a LoD = 2.70 mu M. Glucose oxidase was used as a model enzyme in order to test the capacity of the samarium oxides electrode for biosensing. The enzyme was immobilized by physical adsorption and the optimum conditions for glucose analysis investigated. The biosensor showed a linear range for glucose detection between 0.10 and 1.20 mM with a sensitivity of 8.40 mu A cm(-2) mM(-1) and a LoD = 8.00 mu M. Selectivity was tested toward common interfering species, and the results revealed the lack of biosensor response. The glucose biosensor on samarium oxides was tested for glucose detection in serum samples with a recovery factor of 90%, and the result validated with a commercial glucometer. (C) 2021 Elsevier Ltd. All rights reserved.
Open Access
145. Effects of a far-infrared photon cavity field on the magnetization of a square quantum dot array
Authors:
Gudmundsson, V; Mughnetsyan, V; Abdullah, NR; Tang, CS; Moldoveanu, V; Manolescu, A
Published: SEP 26 2022, PHYSICAL REVIEW B, 106, 115308, DOI: 10.1103/PhysRevB.106.115308
The orbital and spin magnetization of a cavity-embedded quantum dot array defined in a GaAs heterostruc-ture are calculated within quantum-electrodynamical density-functional theory. To this end, a gradient-based exchange-correlation functional recently employed for atomic systems is adapted to the hosting two-dimensional electron gas submitted to an external perpendicular homogeneous magnetic field. Numerical results reveal the polarizing effects of the cavity photon field on the electron charge distribution and nontrivial changes of the orbital magnetization. We discuss its intertwined dependence on the electron number in each dot, and on the electron-photon coupling strength. In particular, the calculated dispersion of the photon-dressed electron states around the Fermi energy as a function of the electron-photon coupling strength indicates the formation of magnetoplasmon-polaritons in the dots.
Open Access
146. Antimicrobial Properties of TiO2 Microparticles Coated with Ca- and Cu-Based Composite Layers
Authors:
Bucuresteanu, R; Ionita, M; Chihaia, V; Ficai, A; Trusca, RD; Ilie, CI; Kuncser, A; Holban, AM; Mihaescu, G; Petcu, G; Nicolaev, A; Costescu, RM; Husch, M; Parvulescu, V; Ditu, LM
Published: JUL 2022, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 23, 6888, DOI: 10.3390/ijms23136888
The ability of TiO2 to generate reactive oxygen species under UV radiation makes it an efficient candidate in antimicrobial studies. In this context, the preparation of TiO2 microparticles coated with Ca- and Cu-based composite layers over which Cu(II), Cu(I), and Cu(0) species were identified is presented here. The obtained materials were characterized by a wide range of analytical methods, such as X-ray diffraction, electron microscopy (TEM, SEM), X-ray photoelectron (XPS), and UV-VIS spectroscopy. The antimicrobial efficiency was evaluated using qualitative and quantitative standard methods and standard clinical microbial strains. A significant aspect of this composite is that the antimicrobial properties were evidenced both in the presence and absence of the light, as result of competition between photo and electrical effects. However, the antibacterial effect was similar in darkness and light for all samples. Because no photocatalytic properties were found in the absence of copper, the results sustain the antibacterial effect of the electric field (generated by the electrostatic potential of the composite layer) both under the dark and in light conditions. In this way, the composite layers supported on the TiO2 microparticles' surface can offer continuous antibacterial protection and do not require the presence of a permanent light source for activation. However, the antimicrobial effect in the dark is more significant and is considered to be the result of the electric field effect generated on the composite layer.
Open Access
147. Memory Properties of Zr-Doped ZrO2 MOS-like Capacitor
Authors:
Palade, C; Slav, A; Stavarache, I; Maraloiu, VA; Negrila, C; Ciurea, ML
Published: SEP 2022, COATINGS, 12, 1369, DOI: 10.3390/coatings12091369
The high-k-based MOS-like capacitors are a promising approach for the domain of non-volatile memory devices, which currently is limited by SiO2 technology and cannot face the rapid downsizing of the electronic device trend. In this paper, we prepare MOS-like trilayer memory structures based on high-k ZrO2 by magnetron sputtering, with a 5% and a 10% concentrations of Zr in the Zr-ZrO2 floating gate layer. For crystallization of the memory structure, rapid thermal annealing at different temperatures between 500 degrees C and 700 degrees C was performed. Additionally, Al electrodes were deposited in a top-down configuration. High-resolution transmission electron microscopy reveals that ZrO2 has a polycrystalline-columnar crystallization and a tetragonal crystalline structure, which was confirmed by X-ray diffraction measurements. It is shown that the tetragonal phase is stabilized during the crystallization by the fast diffusion of oxygen atoms. The capacitance-voltage characteristics show that the widest memory window (Delta V = 2.23 V) was obtained for samples with 10% Zr annealed at 700 degrees C for 4 min. The charge retention characteristics show a capacitance decrease of 36% after 10 years.
148. The effect of noble metal addition on the properties of oxide semiconductors nanoparticles
Authors:
Goncearenco, E; Morjan, IP; Dutu, E; Scarisoreanu, M; Fleaca, C; Gavrila-Florescu, L; Dumitrache, F; Banici, AM; Teodorescu, VS; Anastasescu, C; Sandulescu, A; Balint,
Published: MAR 2022, JOURNAL OF SOLID STATE CHEMISTRY, 307, 122817, DOI: 10.1016/j.jssc.2021.122817
This work presents the preparation of W and V co-doped TiO2 nanoparticles (W:TiO2 and W:V:TiO2) using laser pyrolysis technique subsequently modified with noble metals Pt or Pd using chemical impregnation method. By using well defined TiO2 nanoparticles, the enhancement of catalytic activity is expected mainly due to their higher surface area and density defects relative to bulk material. Structural, morphological and optical properties of the as-obtained nanopowders have been characterized by transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, UV-VIS diffuse reflectance spectroscopy and photoluminescence techniques. The phase composition analysis reveals the preponderance of anatase (95%) in addition to ruffle phase, its particle average size ranging from 25 to 30 nm. The TiO 2 based nanomaterials were supplementary modified by noble metals deposition (Pt particles with dimensions of 3-4 nm and spherical Pd crystallites with a diameter between 3 and 9 nm) and their photocatalytic activity was tested in oxidative photo degradation of CH3OH, under simulated solar light. The metal modified samples displayed higher specific surface areas (3-6 times) and improved photocatalytic properties, the W:V:TiO2@Pt material showing better conversion efficiency of CH3OH to CH2O than the reference Degussa P25 sample (1.54 versus 0.90%).
Open Access
149. Relationship between the Formation of Magnetic Clusters and Hexagonal Phase of Gold Matrix in AuxFe1-x Nanophase Thin Films
Authors:
Locovei, C; Radu, C; Kuncser, A; Iacob, N; Schinteie, G; Stanciu, A; Iftimie, S; Kuncser, V
Published: APR 2022, NANOMATERIALS, 12, 1176, DOI: 10.3390/nano12071176
AuxFe1-x nanophase thin films of different compositions and thicknesses were prepared by co-deposition magnetron sputtering. Complex morpho-structural and magnetic investigations of the films were performed by X-ray Diffraction, cross-section Transmission Electron Microscopy, Selected Area Electron Diffraction, Magneto Optical Kerr Effect, Superconducting Quantum Interference Device magnetometry and Conversion Electron Mossbauer Spectroscopy. It was proven that depending on the preparation conditions, different configurations of defect alpha-Fe magnetic clusters, i.e., randomly distributed or auto-assembled in lamellar or filiform configurations, can be formed in the Au matrix. A close relationship between the Fe clustering process and the type of the crystalline structure of the Au matrix was underlined, with the stabilization of a hexagonal phase at a composition close to 70 at. % of Au and at optimal thickness. Due to different types of inter-cluster magnetic interactions and spin anisotropies, different types of magnetic order from 2D Ising type to 3D Heisenberg type, as well as superparamagnetic behavior of non-interacting Fe clusters of similar average size, were evidenced.
150. BaTiO3 nanocubes-Gelatin composites for piezoelectric harvesting: Modeling and experimental study
Authors:
Ciomaga, CE; Horchidan, N; Padurariu, L; Stirbu, RS; Tiron, V; Tufescu, FM; Topala, I; Condurache, O; Botea, M; Pintilie, I; Pintilie, L; Rotaru, A; Caruntu, G; Mitoseriu, L
Published: SEP 15 2022, CERAMICS INTERNATIONAL, 48, DOI: 10.1016/j.ceramint.2022.05.264
Flexible composites containing BaTiO3 nanoparticles into Gelatin bio-polymer matrix were designed and investigated. Following the idea that the electric field concentration in corners/edges at the interfaces between dissimilar materials give rise to enhanced effective permittivity in composites, cuboid-like BaTiO3 nanoparticles have been employed as nanofillers into Gelatin matrix by using an inexpensive solution-based processing method. As predicted by finite element method simulations developed for cubic-like inclusions into a homogeneous polymer matrix, the experimental permittivity of xBT-(1-x)Gelatin composites increases when increasing the high-permittivity filler addition. For the composition x = 40 wt% (corresponding to 12 vol% BaTiO3 addition), permittivity reaches epsilon r -15.7 with respect to epsilon r -9.8 of pure Gelatine (measured at 105 Hz), while the average piezoelectric coefficient d33 as determined by piezoelectric force microscopy shows a remarkable increase up to 21 pm/V in composites with x = 40 wt%, in comparison to -7 pm/V in pure Gelatin. By using the experimentally determined material constants, the simulated piezoelectric voltage output vs. time has shown a similar increase (about a doubling of its amplitude) of the harvesting signal in the composite with x = 40 wt% BT, with respect to one of the polymer matrix, thus demonstrating the beneficial role of embedding BT nanoparticles into the biopolymer for increasing the mechanical harvesting response.
151. Doped microporous graphitic carbons as metal-free catalysts for the selective hydrogenation of alkynes to alkenes
Authors:
Primo, A; Rendón-Patiño, A; Bucur, C; Jurca, A; Cojocaru, B; Parvulescu, VI; Garcia, H
Published: JAN 2022, JOURNAL OF CATALYSIS, 405, DOI: 10.1016/j.jcat.2021.11.034
Microporous graphitic carbons obtained by pyrolysis of a-cyclodextrin have been conveniently doped with N and P elements by performing the thermal graphitization adding urea or phosphoric acid as source of these elements. Electron microscopy shows that doping does not influence the structure and dimensions of the micropores, while XPS reveals the distribution of these dopant elements in two main families corresponding to pyridinic and pryrrolic N atoms and to triphenylphosphine and triphenylphosphine oxide for P doping. Thermo-programmed desorption of H2, CO2 and NH3 indicates that the presence of dopant element is responsible for chemisorption of these gases and introduces basic and acid sites. These desorption measurements agree with the catalytic performance of the series of carbons for the chemo and stereo selective hydrogenation of internal aliphatic and aromatic alkynes to cis configured alkenes. N/P doped microporous carbons were found to be stable under the reaction conditions, according to the constant TOF values and XRD and XPS characterization of the materials after their use as catalysts. In addition microporosity appears to play a positive effect by comparing the activity of microporous carbons with the performance of analogous N/P-doped graphenes. (c) 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Open Access
152. Comparative characterization study of LYSO:Ce crystals for timing applications
Authors:
Addesa, FM; Barria, P; Bianco, R; Campana, M; Cavallari, F; Cemmi, A; Cipriani, M; Dafinei, I; D'Orsi, B; del Re, D; Diemoz, M; D'Imperio, G; Di Marco, E; Di Sarcina, I; Enculescu, M; Longo, E; Lucchini, MT; Marchegiani, F; Meridiani, P; Nisi, S; Organtini, G; Pandolfi, F; Paramatti, R; Pettinacci, V; Quaranta, C; Rahatlou, S; Rovelli, C; Santanastasio, F; Soffi, L; Tramontano, R; Tully, CG
Published: AUG 2022, JOURNAL OF INSTRUMENTATION, 17, P08028, DOI: 10.1088/1748-0221/17/08/P08028
Cerium-doped Lutetium-Yttrium Oxyorthosilicate (LYSO:Ce) is one of the most widely used Cerium-doped Lutetium based scintillation crystals. Initially developed for medical detectors it rapidly became attractive for High Energy Particle Physics (HEP) applications, especially in the frame of high luminosity particle colliders. In this paper, a comprehensive and systematic study of LYSO:Ce ([Lu((1-x))Y-x](2)SiO5 : Ce) crystals is presented. It involves for the first time a large number of crystal samples (180) of the same size from a dozen of producers. The study consists of a comparative characterization of LYSO:Ce crystal products available on the market by mechanical, optical and scintillation measurements and aims specifically, to investigate key parameters of timing applications for HEP.
Open Access
153. Mud and burnt Roman bricks from Romula
Authors:
Badica, P; Alexandru-Dinu, A; Grigoroscuta, MA; Burdusel, M; Aldica, GV; Sandu, V; Bartha, C; Polosan, S; Galatanu, A; Kuncser, V; Enculescu, M; Locovei, C; Porosnicu, I; Tiseanu, I; Ferbinteanu, M; Savulescu, I; Negru, M; Batalu, ND
Published: SEP 23 2022, SCIENTIFIC REPORTS, 12, 15864, DOI: 10.1038/s41598-022-19427-7
Sesquipedalian mud and burnt bricks (second to third century AD) were excavated from the Roman city of Romula located in the Lower Danube Region (Olt county, Romania). Along with local soils, bricks are investigated by petrographic analysis, X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), electron microscopy (SEM/EDX), X-ray microtomography (XRT), thermal analysis (DTA-TG), M.ssbauer spectroscopy, magnetometry, colorimetry, and mechanical properties assessment. The results correlate well with each other, being useful for conservation/restoration purposes and as reference data for other ceramic materials. Remarkably, our analysis and comparison with literature data indicate possible control and wise optimization by the ancient brickmakers through the recipe, design (size, shape, and micro/ macrostructure), and technology of the desired physical-chemical-mechanical properties. We discuss the Roman bricks as materials that can adapt to external factors, similar, to some extent, to modern "smart" or "intelligent" materials. These features can explain their outstanding durability to changes of weather/climate and mechanical load.
Open Access
154. Evidence of Counterion Size Effect on the Stability of Columnar Phase of Ionic Liquid Crystals Based on Pyridinium Salts Derived from N-3,4,5-Tri(alkyloxy)-benzyl-4-pyridones
Authors:
Dumitru, I; Chiriac, FL; Ilis, M; Pasuk, I; Manaila-Maximean, D; Micutz, M; Staicu, T; Cîrcu, V
Published: MAY 2022, CRYSTALS, 12, 715, DOI: 10.3390/cryst12050715
The synthesis and characterization of novel ionic liquid crystals based on pyridinium salts with Br- and PF6- counterions are described in this work. These pyridinium salts were derived from 4-hydroxypyridine, both by N- and O-alkylation. The 3,4,5-tri(alkyloxy)-benzyl mesogenic unit was attached to the nitrogen atom of the pyridinium ring. Alkyl chains with a different number of carbon atoms (6, 8, 10, 12 and 14) were employed in order to show the effect on the stability of mesophase. The POM (polarizing optical microscopy) and XRD (powder X-ray diffraction) studies indicated that bromide salts with shorter chains C-6, C-8 and C-10 do not show mesomorphic properties, while longer chain analogues with C-12 and C-14 exhibit two enantiotropic columnar phases. Surprisingly, the pyridinium salts with the larger size PF6- counterion do not exhibit liquid crystal properties.
Open Access
155. Multifunctional Zn-Doped ITO Sol-Gel Films Deposited on Different Substrates: Application as CO2-Sensing Material
Authors:
Gartner, M; Anastasescu, M; Calderon-Moreno, JM; Nicolescu, M; Stroescu, H; Hornoiu, C; Preda, S; Predoana, L; Mitrea, D; Covei, M; Maraloiu, VA; Teodorescu, VS; Moldovan, C; Petrik, P; Zaharescu, M
Published: SEP 2022, NANOMATERIALS, 12, 3244, DOI: 10.3390/nano12183244
Undoped and Zn-doped ITO (ITO:Zn) multifunctional thin films were successfully synthesized using the sol-gel and dipping method on three different types of substrates (glass, SiO2/glass, and Si). The effect of Zn doping on the optoelectronic, microstructural, and gas-sensing properties of the films was investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), spectroscopic ellipsometry (SE), Raman spectroscopy, Hall effect measurements (HE), and gas testing. The results showed that the optical constants, the transmission, and the carrier numbers were correlated with the substrate type and with the microstructure and the thickness of the films. The Raman study showed the formation of ITO films and the incorporation of Zn in the doped film (ITO:Zn), which was confirmed by EDX analysis. The potential use of the multifunctional sol-gel ITO and ITO:Zn thin films was proven for TCO applications or gas-sensing experiments toward CO2. The Nyquist plots and equivalent circuit for fitting the experimental data were provided. The best electrical response of the sensor in CO2 atmosphere was found at 150 degrees C, with activation energy of around 0.31 eV.
156. Metallized electrospun polymeric fibers for electrochemical sensors and actuators
Authors:
Leote, RJB; Beregoi, M; Enculescu, I; Diculescu, VC
Published: AUG 2022, CURRENT OPINION IN ELECTROCHEMISTRY, 34, 101024, DOI: 10.1016/j.coelec.2022.101024
Electrospun polymeric fibers present an emerging alternative for the development of flexible electronics, enabling applications in wearable sensors and biosensors for continuous monitoring, and actuators for tissue engineering. The possibility to prepare sub-micrometric polymeric scaffolds, their processing for increasing the conductivity, their modification with different materials, conductive polymers and biomolecules in order to obtain functional flexible electrodes, allows the development of innovative devices for healthcare, and biomedical applications. In this review, the impact of metallized electrospun polymeric fibers in electrochemical (bio)sensors and actuators is discussed. A relation between their structure and functionality is provided, alongside with an overview of the different methods to obtain functional conductive fibers.
157. Effect of chlorine and bromine on the perovskite crystal growth in mesoscopic heterojunction photovoltaic device
Authors:
Mehdi, H; Leonat, LN; Stancu, V; Saidi, H; Enculescu, M; Tomulescu, AG; Toma, V; Pintilie, I; Bouazizi, A; Galca, AC
Published: JUN 1 2022, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 143, 106558, DOI: 10.1016/j.mssp.2022.106558
Organic-inorganic hybrid perovskite solar cells are within the emerging photovoltaic technologies. The combination of different halogen ions, in certain fill fractions, is one of the methods to improve the perovskite film properties. Herein, fabrication and characterization of perovskite cells in standard mesoscopic architecture using one-step deposition method has been done. The role of the halogen ions (Chlorine or Bromine) on crystal structure growth and photoelectric performance has been investigated. X-ray diffraction, scanning electron microscopy, atomic force microscopy and optical microscopy analysis were performed. The microstructure, composition and morphology of CH3NH3PbI1.8Br1.2 and CH3NH3PbI1.8Cl1.2 films are dissimilar, although identical fabrication method was used. Same holds for optical properties, band gap energies of 1.84 eV and 1.63 eV, respectively, being obtained. Integrated in solar cells, the maximum power conversion efficiency of the Br based devices is beyond 10%, while for those based on Cl, the efficiency drops around 5%.
Open Access
158. Soft Chemistry Synthesis and Characterization of CoFe1.8RE0.2O4 (RE3+ = Tb3+, Er3+) Ferrite
Authors:
Gingasu, D; Mindru, I; Ianculescu, AC; Diamandescu, L; Surdu, VA; Marinescu, G; Bartha, C; Preda, S; Popa, M; Chifiriuc, MC
Published: FEB 2022, MAGNETOCHEMISTRY, 8, 12, DOI: 10.3390/magnetochemistry8020012
Nanosized CoFe1.8RE0.2O4 (RE3+ = Tb3+, Er3+) ferrites were obtained through wet ferritization method. These ferrites were characterized by X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM/HR-TEM), Fourier transform infrared spectroscopy (FTIR), Mossbauer spectroscopy and magnetic measurements. The XRD results revealed that the average crystallite size is 5.77 nm for CoFe1.8Tb0.2O4 and 6.42 nm for CoFe1.8Er0.2O4. Distribution of metal cations in the spinel structure estimated from X-ray diffraction data showed that the Tb3+ and Er3+ ions occupy the octahedral sites. TEM images indicated the presence of polyhedral particles with average size 5.91 nm for CoFe1.8Tb0.2O4 and 6.80 nm for CoFe1.8Er0.2O4. Room temperature Mossbauer spectra exhibit typical nanoscaled cobalt ferrite spectra in good agreement with XRD and TEM data. The saturation magnetization value (M-s) is 60 emu/g for CoFe1.8Tb0.2O4 and 80 emu/g for CoFe1.8Er0.2O4. CoFe1.8RE0.2O4 nanoparticles showed similar antimicrobial efficacy against the five tested microbial strains, both in planktonic and biofilm state. The results highlight the promising potential of these types of nanoparticles for the development of novel anti-biofilm agents and materials.
159. Enhanced magnetocaloric properties of La0.8K0.2-xPbxMnO3 nanoparticles by optimizing Pb doping concentrations
Authors:
Bouzid, SA; Essoumhi, A; Rostas, AM; Kuncser, AC; Negrila, CC; Iacob, N; Galatanu, A; Popescu, B; Sajieddine, M; Galca, AC; Kuncser, V
Published: JUN 15 2022, CERAMICS INTERNATIONAL, 48, DOI: 10.1016/j.ceramint.2022.02.239
Polycrystalline La(0.8)K(0.2-x)Pb(x)MnO3 (x = 0.05, 0.10, 0.15, 0.20) ceramics were successfully prepared by flash combustion route and their structural, morphological, magnetic and magnetocaloric properties were investi-gated. Structural analyses using X-ray diffraction reveal that all samples are crystallized in the rhombohedral structure and belong to R <(3) over bar > c space group. The increase of Pb doping does not modify the crystalline structure but changes the grain size and lattice parameters. X-ray photoelectron spectroscopy (XPS) fitting results of Mn 2p peaks confirmed the coexistence of Mn3+ and Mn4+ ions which contribute to the double exchange interactions improving the ferromagnetic order in the samples. The magnetization's temperature and magnetic field de-pendences indicate a second-order ferromagnetic-paramagnetic transition of the ceramics. A significant mag-netic entropy change near room temperature was observed for La0.8K0.1Pb0.1MnO3, showing considerable magnetocaloric properties. Furthermore, electron paramagnetic resonance spectroscopy (EPR) was also used to examine the ferromagnetic-paramagnetic transition.
160. MgB2 with Addition of Cubic BN and Ge2C6H10O7 Obtained by Spark Plasma Sintering Technique
Authors:
Ionescu, AM; Aldica, G; Popa, S; Enculescu, M; Sandu, V; Pasuk, I; Burdusel, M; Grigoroscuta, MA; Miu, L; Badica, P
Published: DEC 2022, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 35, DOI: 10.1007/s10948-022-06350-1
High density (94-98% of the theoretical density) MgB2 samples added with C6H10Ge2O7 and cubic BN with compositions (MgB2)(1-x)(Ge2C6H10O7)(0.0028)(cBN)(x) (x = 0.003, 0.005, 0.007, 0.01) and (MgB2)(1-y)(Ge2C6H10O7)(y)(cBN)(0.005) (y = 0.0014, 0.0028, 0.005, 0.0075) were obtained by spark plasma sintering technique. For optimum doped samples with x = 0.005-0.007 and y = 0.0028-0.005, a weak enhancement of zero-field critical current density J(c0), irreversibility field H-irr, and volume pinning force F-p,F-max was determined. This behavior is very different from similar samples added with a single additive for which H-irr has a large enhancement. Consequently, it suggests the presence of opposite structural and microstructural effects induced by the additives. These effects, on the one hand, are discussed to decrease the sensitivity of MgB2 superconducting properties in the co-added samples comparative to samples added with C6H10Ge2O7, and, on the other hand, they contribute to anomalies that were found when assessing the pinning force-related parameters by the universal scaling law.
161. Dielectric, piezoelectric and magnetic behavior of CoFe2O4/BNT-BT0.08 monolayer thin films composites
Authors:
Cernea, M; Radu, R; Craciun, F; Gavrila, R; Surdu, VA; Trusca, R; Mihalache, V
Published: AUG 2022, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 282, 115770, DOI: 10.1016/j.mseb.2022.115770
We report in this paper on the monolayer composites thin films that have the magnetic spinel CoFe2O4 and the piezoelectric perovskite BNT-BT0.08 as constituent phases. Composite thin films of CoFe2O4 and BNT-BT0.08, with molar ratios of 0.5:1, 1:1 and 1.5:1, have been deposited by spin coating method from a sol precursor, mixture type, of CoFe2O4 and BNT-BT0.08. The monolayer thin films, deposited on Si/SiO2/TiO2/Pt substrate, were characterized using selected methods, such as: X-ray diffraction, scanning electron microscopy, atomic force microscopy/piezoelectric force microscopy, dielectric spectroscopy, and vibrating sample magnetometer. X-ray diffraction demonstrated the two phases: cubic CoFe2O4 and rhombohedral BNT-BT0.08. Furthermore, the Si/ SiO2/TiO2/Pt/BNT-BT0.08/CoFe2O4 monolayers show a simultaneous enhancement of both the magnetization and coercivity with the increase of the magnetic phase, accompanied by a decrease of the dielectric constant. The obtained results reveal that the investigated monolayer structures present superior properties compared to those of bilayer composites.
Open Access
162. Structural, Optical, and Sensing Properties of Nb-Doped ITO Thin Films Deposited by the Sol-Gel Method
Authors:
Nicolescu, M; Mitrea, D; Hornoiu, C; Preda, S; Stroescu, H; Anastasescu, M; Calderon-Moreno, JM; Predoana, L; Teodorescu, VS; Maraloiu, VA; Zaharescu, M; Gartner, M
Published: NOV 2022, GELS, 8, 717, DOI: 10.3390/gels8110717
The aim of the present study was the development of Nb-doped ITO thin films for carbon monoxide (CO) sensing applications. The detection of CO is imperious because of its high toxicity, with long-term exposure having a negative impact on human health. Using a feasible sol-gel method, the doped ITO thin films were prepared at room temperature and deposited onto various substrates (Si, SiO2/glass, and glass). The structural, morphological, and optical characterization was performed by the following techniques: X-ray diffractometry (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV/Vis/NIR spectroscopic ellipsometry (SE). The analysis revealed a crystalline structure and a low surface roughness of the doped ITO-based thin films. XTEM analysis (cross-sectional transmission electron microscopy) showed that the film has crystallites of the order of 5-10 nm and relatively large pores (around 3-5 nm in diameter). A transmittance value of 80% in the visible region and an optical band-gap energy of around 3.7 eV were found for dip-coated ITO/Nb films on SiO2/glass and glass supports. The EDX measurements proved the presence of Nb in the ITO film in a molar ratio of 3.7%, close to the intended one (4%). Gas testing measurements were carried out on the ITO undoped and doped thin films deposited on glass substrate. The presence of Nb in the ITO matrix increases the electrical signal and the sensitivity to CO detection, leading to the highest response for 2000 ppm CO concentration at working temperature of 300 degrees C.
Open Access
163. Impact of band-bending on the k-resolved electronic structure of Si-doped GaN
Authors:
Lev, LL; Maiboroda, IO; Grichuk, ES; Chumakov, NK; Schröter, NBM; Husanu, MA; Schmitt, T; Aeppli, G; Zanaveskin, ML; Valeyev, VG; Strocov, VN
Published: MAR 4 2022, PHYSICAL REVIEW RESEARCH, 4, 013183, DOI: 10.1103/PhysRevResearch.4.013183
Band bending at semiconductor surfaces and interfaces is the key to applications ranging from classical transistors to topological quantum computing. A semiconductor particularly important for optical as well as microwave devices is GaN. What makes the material useful is not only its large bandgap but also that it can be heavily doped to become metallic. Here, we apply soft-x-ray angle-resolved photoelectron spectroscopy (ARPES) to metallic Si-doped GaN to explore the electron density and momentum-resolved band dispersions of the valence and conduction electrons varying through the surface band-bending region. We find an upward band bending, where the measured band occupation reduces toward the surface, as probed with low photon energies <0.5 keV. The band occupation approaches the bulk value, matching Hall effect measurements, as the photon energy increases to >1.4 keV, where the photoelectron mean free path exceeds the spatial extent of the band-bending region. Our quantitative analysis of the experimental data describes the potential variation in the band-bending region via self-consistent Poisson-Schrodinger equations. We put forward an insightful model to simulate the ARPES spectra from this region through summing up the contribution from all atomic layers, weighted by the photoelectron mean free path, under in-phase conditions achieved at particular values of the photoelectron out-of-plane momentum. The model adequately describes the peculiarities of the ARPES spectra caused by the surface band bending, including the photon-energy dependence of the apparent band occupation and Fermi-surface area, and allows accurate determination of the band-bending profile and values of the photoelectron mean free path. Finally, comparison of our data with supercell density functional theory calculations reveals the preferential location of Si atoms as substitutional for Ga, with the doped electrons entering the GaN conduction bands without formation of separate impurity states as would occur for Si interstitials. Our theoretical and experimental results resolve fundamental questions underpinning device performance of the GaN-based and other semiconductor materials in general and demonstrate a general methodology for quantitative studies of electron states in the band-bending region.
Open Access
164. Effect of the supersaturation with nitrogen on the structure refinement and magnetic properties of mechanically alloyed and heated Fe14Cr ferritic alloys
Authors:
Mihalache, V; Pasuk, I; Mercioniu, I
Published: SEP-OCT 2022, JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 20, DOI: 10.1016/j.jmrt.2022.07.190
Nano-nitride reinforcement of Fe-Cr alloys are under intense investigations, e.g., along with oxide-strengthened, nitride-strengthened reduced activation steels with superior high temperature mechanical properties are developed as materials for nuclear energy applications. Fe14Cr alloy powders were produced by mechanical milling for up to 170 h under a nitrogen atmosphere followed by heating under an Ar5%H-2 atmosphere to 600 degrees C-1120 degrees C. The samples were investigated by means of X-ray diffraction, DTA/TG and magnetic measurements. CrN, detected after milling for 58 h, reached 39 wt % (5.3 wt.% total N) at 170 h milling. The ferrite supersaturated with nitrogen shows a strong decrease in grain size and saturation magnetization, an increase in lattice constant, microstrain and coercivity, H-c. Upon heating, the metastable ultrafine alpha-ferrite and CrN in the as-milled samples undergo transformations and recrystallization into ferrite grains free of super-saturation, whose microstructure follows a continuous relaxation. The supersaturation with nitrogen was retained upon heating in the relatively stable ferrite crystalized at the milling stage. This microstructure undergoes a discontinuous relaxation in the 800 degrees C-1120 degrees C region: a pronounced decrease of grain size (down to similar to 25 nm), an increase of lattice constant, microstrain and H-c. These improvements were associated with features of discontinuous precipitation reaction of coherent nitride precipitates (involving a new alpha ''-phase with expanded lattice), in connection with the heating in the austenite phase field. Such microstructure refinement or (nitride) strengthening of Fe14Cr alloys can be achieved on powders milled for much less time as compared to previously reported (oxide dispersion) strengthening of Fe14Cr-W-Ti ferritic steels. (C) 2022 The Authors. Published by Elsevier B.V.
165. Effect of annealing on the structural, optical and electrical properties of (F, Zn) double doped SnO2 nanoparticles obtained by the laser pyrolysis method
Authors:
Morjan, IP; Dutu, E; Fleaca, CT; Dumitrache, F; Morjan, I; Mihailescu, N; Demian, M; Teodorescu, VS; Scarisoreanu, M
Published: MAY 2022, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 142, 106511, DOI: 10.1016/j.mssp.2022.106511
SnO2 nanoparticles have a great potential in photocatalytic and optoelectronic applications by extending their absorbtion and emission from UV to the visible domain. The effect of annealing at 750 degrees C and 1000 degrees C for 3 h in ambient conditions on structural, optical and electrical properties of F&Zn double doped SnO2 nanoparticles synthesized by continuous wave CO2 laser pyrolysis method were investigated for the first time. X-Ray diffraction studies confirmed the expected crystallite size increasing and also the vanishing of divalent tin phases (SnF2, SnO) upon air annealing. Detailed X ray photoelectron spectroscopy (XPS) analysis confirmed that fluorine disappears completely from SnO2 structure at 1000 degrees C. The annealing also induced a reduction in oxygen vacancies as confirmed by Raman spectroscopy and XPS. Transmission FTIR spectroscopy was used for revealing the existence of Sn-O, O-Sn-O, O-H and H-O-H vibrational modes. The optical band gap energies of all annealed samples are in the visible region, decreasing for those that were initially doped with F, and increasing for the only Zn doped sample. Photoluminescence (PL) measurements showed a broad dominant peak in green visible region, around 530 nm. For the sample with the highest content of Zn, PL spectrum shifted to higher wavelengths, respectively to the orange and red regions. The oxygen vacancies concentrations after annealing are correlated with the electrical conductivity of F, F&Zn, and Zn doped SnO2 samples.
Open Access
166. Influence of the Photodegradation of Azathioprine on DNA and Cells
Authors:
Bunea, MC; Diculescu, VC; Enculescu, M; Oprea, D; Enache, TA
Published: NOV 2022, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 23, 14438, DOI: 10.3390/ijms232214438
Azathioprine (AZA) is a pharmacologic immunosuppressive agent administrated in various conditions such as autoimmune disease or to prevent the rejection of organ transplantation. The mechanism of action is based on its biologically active metabolite 6-mercaptopurine (6-MP), which is converted, among others, into thioguanine nucleotides capable of incorporating into replicating DNA, which may act as a strong UV chromophore and trigger DNA oxidation. The interaction between azathioprine and DNA, before and after exposure to solar simulator radiation, was investigated using UV-vis spectrometry and differential pulse voltammetry at a glassy carbon electrode. The results indicated that the interaction of AZA with UV radiation was pH-dependent and occurred with the formation of several metabolites, which induced oxidative damage in DNA, and the formation of DNA-metabolite adducts. Moreover, the viability assays obtained for the L929 cell culture showed that both azathioprine and degraded azathioprine induced a decrease in cell proliferation.
Open Access
167. Controlling polarization direction in epitaxial Pb(Zr0.2Ti0.8)O3 films through Nb (n-type) and Fe (p-type) doping
Authors:
Chirila, CF; Stancu, V; Boni, GA; Pasuk, I; Trupina, L; Filip, LD; Radu, C; Pintilie, I; Pintilie, L
Published: JAN 14 2022, SCIENTIFIC REPORTS, 12, 755, DOI: 10.1038/s41598-022-04802-1
Fe (acceptor) and Nb (donor) doped epitaxial Pb(Zr0.2Ti0.8)O-3 (PZT) films were grown on single crystal SrTiO3 substrates and their electric properties were compared to those of un-doped PZT layers deposited in similar conditions. All the films were grown from targets produced from high purity precursor oxides and the doping was in the limit of 1% atomic in both cases. The remnant polarization, the coercive field and the potential barriers at electrode interfaces are different, with lowest values for Fe doping and highest values for Nb doping, with un-doped PZT in between. The dielectric constant is larger in the doped films, while the effective density of charge carriers is of the same order of magnitude. An interesting result was obtained from piezoelectric force microscopy (PFM) investigations. It was found that the as-grown Nb-doped PZT has polarization orientated upward, while the Fe-doped PZT has polarization oriented mostly downward. This difference is explained by the change in the conduction type, thus in the sign of the carriers involved in the compensation of the depolarization field during the growth. In the Nb-doped film the majority carriers are electrons, which tend to accumulate to the growing surface, leaving positively charged ions at the interface with the bottom SrRuO3 electrode, thus favouring an upward orientation of polarization. For Fe-doped film the dominant carriers are holes, thus the sign of charges is opposite at the growing surface and the bottom electrode interface, favouring downward orientation of polarization. These findings open the way to obtain p-n ferroelectric homojunctions and suggest that PFM can be used to identify the type of conduction in PZT upon the dominant direction of polarization in the as-grown films.
Open Access
168. Catalytic Hydrotreatment of Humins Waste over Bifunctional Pd-Based Zeolite Catalysts
Authors:
El Fergani, M; Candu, N; Podolean, I; Cojocaru, B; Nicolaev, A; Teodorescu, CM; Tudorache, M; Parvulescu, VI; Coman, SM
Published: OCT 2022, CATALYSTS, 12, 1202, DOI: 10.3390/catal12101202
The catalytic hydrotreatment of humins, the solid byproduct produced from the conversion of C6 sugars (glucose, fructose) to 5-hydroxymethylfurfural (HMF), using supported Pd@zeolite (Beta, Y, and USY) catalysts with different amounts of Pd (i.e., 0.5, 1.0 and 1.5 wt%) was investigated under molecular hydrogen pressure. The highest conversion of humins (52.0%) was obtained on 1.5Pd@USY catalyst while the highest amount of humins oil (27.3%) was obtained in the presence of the 1Pd@Beta zeolite sample, at P-H2 = 30 bars and T = 250 degrees C. The major compounds in the humins oil evidenced by GC-MS are alcohols, organic acids, ethers, and alkyl-phenolics. However, although all these classes of compounds are obtained regardless of the nature of the catalyst used, the composition of the mixture differs from one catalyst to another. Furanic compounds were not identified in the reaction products. A possible explanation may be related to their high reactivity under the reaction conditions, in the presence of the Pd-based catalysts these compounds lead to alkyl phenolics, important intermediates in the petrochemical industry.
169. Effect of polysilane addition on spark plasma sintering and superconducting properties of MgB2 bulks
Authors:
Sandu, V; Aldica, G; Grigoroscuta, MA; Burdusel, M; Pasuk, ; Ching, YC; Ionescu, AM; Badica, P
Published: NOV 1 2022, CERAMICS INTERNATIONAL, 48, DOI: 10.1016/j.ceramint.2022.07.127
Polycrystalline MgB2 bulk samples were produced by ex-situ spark plasma sintering (SPS) using the oxygen-free preceramic polymer additive poly(dimethylsilane) as a source for carbon doping and as a sintering aid. Two major effects were identified. One is the significant enhancement of the densification kinetics during sintering for all tested compositions. The second one is the improvement of the high field critical current density for a certain level of the poly(dimethylsilane) addition.
170. Electrochemical characterization of shikonin and in-situ evaluation of interaction with DNA
Authors:
Leote, RJB; Sanz, CG; Diculescu, VC
Published: SEP 15 2022, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 921, 116663, DOI: 10.1016/j.jelechem.2022.116663
Shikonin, a natural compound with pharmaceutical properties, has attracted interest due to its anti-oxidant properties, potential anti-cancer activity and activity over several biological pathways, such as dsDNA transcription/replication of cancer cells and inhibition of pyruvate kinase M2. The electrochemical behavior of shikonin in aqueous media was investigated at glassy carbon electrodes by cyclic and differential pulse voltammetry. The reduction involves the quinone moiety and formation of a semiquinone intermediate. In the absence of dissolved oxygen, the reduction is reversible while in normal atmosphere leads to formation of superoxide cation. The oxidation occurs at the dihydroxy moiety and reversibility was only observed in acid electrolytes. A redox mechanism was proposed. The interaction between shikonin and dsDNA was evaluated in incubated solutions and in situ with the dsDNA-electrochemical biosensor. The mechanism of interaction is time-dependent and follows an initial binding step at the grooves of the double strand leading to conformational modifications recognized through the variation of guanine and adenine oxidation peaks. The in-situ electrochemical production of the semiquinone intermediate leads to a preferential interaction with guanine residues, promoting their oxidation and consequently occurrence 8-oxo-guanine. An interaction mechanism was proposed.
Open Access
171. Increasing Permittivity and Mechanical Harvesting Response of PVDF-Based Flexible Composites by Using Ag Nanoparticles onto BaTiO3 Nanofillers
Authors:
Horchidan, N; Ciomaga, CE; Curecheriu, LP; Stoian, G; Botea, M; Florea, M; Maraloiu, VA; Pintilie, L; Tufescu, FM; Tiron, V; Rotaru, A; Mitoseriu, L
Published: MAR 2022, NANOMATERIALS, 12, 934, DOI: 10.3390/nano12060934
The role of Ag addition on the structural, dielectric, and mechanical harvesting response of 20%(xAg - (1 - x)BaTiO3) - 80%PVDF (x = 0, 2, 5, 7 and 27 vol.%) flexible composites is investigated. The inorganic fillers were realized by precipitating fine (similar to 3 nm) silver nanoparticles onto BaTiO3 nanoparticles (similar to 60 nm average size). The hybrid admixtures with a total filling factor of 20 vol.% were embedded into the PVDF matrix. The presence of filler enhances the amount of beta-PVDF polar phase and the BaTiO3 filler induces an increase of the permittivity from 11 to 18 (1 kHz) in the flexible composites. The addition of increasing amounts of Ag is further beneficial for permittivity increase; with the maximum amount (x = 27 vol.%), permittivity is three times larger than in pure PVDF (epsilon(r) similar to 33 at 1 kHz) with a similar level of tangent losses. This result is due to the local field enhancement in the regions close to the filler-PVDF interfaces which are additionally intensified by the presence of silver nanoparticles. The metallic addition is also beneficial for the mechanical harvesting ability of such composites: the amplitude of the maximum piezoelectric-triboelectric combined output collected in open circuit conditions increases from 0.2 V/cm(2) (PVDF) to 30 V/cm(2) for x = 27 vol.% Ag in a capacitive configuration. The role of ferroelectric and metallic nanoparticles on the increasing mechanical-electric conversion response is also been explained.
Open Access
172. Electric Energy Storage Effect in Hydrated ZrO2-Nanostructured System
Authors:
Doroshkevich, AS; Lyubchyk, AI; Oksengendler, BL; Zelenyak, TY; Appazov, NO; Kirillov, AK; Vasilenko, TA; Tatarinova, AA; Gorban, OO; Bodnarchuk, VI; Nikiforova, NN; Balasoiu, M; Mardare, DM; Mita, C; Luca, D; Mirzayev, MN; Nabiyev, AA; Popov, EP; Stanculescu, A; Konstantinova, TE; Aleksiayenak, YV
Published: JUN 2022, NANOMATERIALS, 12, 1783, DOI: 10.3390/nano12111783
The dimensional effect of electric charge storage with a density of up to 270 mu F/g by the hydrated ZrO2-nanoparticles system was determined. It was found that the place of localization of different charge carriers is the generalized heterophase boundary-nanoparticles surface. The supposed mechanism of the effect was investigated using the theory of dispersed systems, the band theory, and the theory of contact phenomena in semiconductors, which consists of the formation of localized electronic states in the nanoparticle material due to donor-acceptor interaction with the adsorption ionic atmosphere. The effect is relevant for modern nanoelectronics, microsystem technology, and printed electronics because it allows overcoming the basic physical restrictions on the size, temperature, and operation frequency of the device, caused by leakage currents.
173. Water denitration over titania-supported Pt and Cu by combined photocatalytic and catalytic processes: Implications for hydrogen generation properties in a photocatalytic system
Authors:
Vasile, A; Papa, F; Bratan, V; Munteanu, C; Teodorescu, M; Atkinson, I; Anastasescu, M; Kawamoto, D; Negrila, C; Ene, CDD; Spataru, T; Balint, I
Published: APR 2022, JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING, 10, 107129, DOI: 10.1016/j.jece.2022.107129
The present work provides a new approach to the water denitration process and a facile strategy of catalyst preparation for the efficient hydrogen generation. The main focus of the research reported here was nitrate removal from aqueous solutions and simultaneous hydrogen generation under UV-Vis-light irradiation. This is a very important aspect in case of practical applications, eliminating the external source of hydrogen. Aiming to get a deeper understanding on the role of surface structures (size and shape of nanoparticles) towards the reduction mechanism and to establish basic principles for an efficient process, Pt-Cu/TiO2 and Pt-Cu/TiO2 modified with well-defined Pt nanoparticles were employed. The synthesized materials were characterized using various physicochemical techniques and tested comparatively for: (i) nitrate catalytic reduction by hydrogen (dark reaction) and (ii) nitrate photocatalytic reduction by in-situ generated solar hydrogen. In order to enhance overall denitration reaction by combined photocatalytic and catalytic processes, photo-generated charges and in-situ generated H-2 as reducing agent were used. Improvement of catalytic performances of nitrate hydrogenation reaction (~100% NO3 over line conversion) related to intimate contact between Pt and Cu was obtained. The in-situ generated H-2 by water splitting over the studied catalysts reduces efficiently NO3 over line ions. Enhanced photo-catalytic activity toward solar H-2 production by deposited well-defined Pt nanoparticles (~10 nm) was achieved. In order to make possible decontamination of polluted waters using in-situ generated H-2 under light exposure, the future optimization of such photo-catalytic systems looks promising.
Open Access
174. Ageing studies of Multi-Strip Multi-Gap Resistive Plate Counters based on low resistivity glass electrodes in high irradiation dose
Authors:
Bartos, D; Burducea, C; Burducea, I; Caragheorgheopol, G; Constantin, F; Craciun, L; Dorobantu, D; Ghena, M; Iancu, D; Marcu, A; Mateescu, G; Mereuta, P; Moise, V; Negrila, C; Negut, D; Petris, M; Petrovici, M; Radulescu, L; Aprodu, V; Prodan, L; Radu, A; Stoian, G
Published: FEB 1 2022, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 1024, 166122, DOI: 10.1016/j.nima.2021.166122
Detailed tests and analysis of ageing effects of high irradiation dose on Multi-Strip Multi-Gap Resistive Plate Counters (MSMGRPC) based on low resistivity glass electrodes, foreseen to be used for the most forward polar angles covered by the Time-of Flight (ToF) sub-detector of the Compressed Baryonic Matter (CBM) experiment at Facility for Antiprotons and Ion Research (FAIR) - Darmstadt are reported. The tests were performed at a multi-purpose irradiation facility of IFIN-HH based on Co-60 source. MSMGRPC efficiency, cluster size, surface and volume resistivity of the glass electrodes after irradiation are measured and compared with their values before irradiation. The results of a comprehensive analysis of the composition and properties of the deposited layers on the glass electrodes, based on different methods, i.e. Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), foil Elastic Recoil Detection Analysis (ERDA), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Terahertz Time Domain Spectroscopy (THz-TDS), are presented.
Open Access
175. The Rectifying Contact of Hydrated Different Size YSZ Nanoparticles for Advanced Electronics
Authors:
Doroshkevich, AS; Zakharova, AS; Oksengendler, BL; Lyubchyk, AI; Lyubchyk, SI; Lyubchyk, SB; Tatarinova, AA; Kirillov, AK; Vasilenko, TA; Gorban, OO; Bodnarchuk, VI; Nikiforova, NN; Zakharova, EA; Balasoiu, M; Mardare, DM; Mita, C; Stanculescu, A; Mirzayev, MN; Nabiyev, AA; Popov, EP; Khiem, L; Donkov, AA; Teofilovic, V; Jasinska, B; Chicea, D; Konstantinova, TY
Published: DEC 2022, NANOMATERIALS, 12, 4493, DOI: 10.3390/nano12244493
The paper considers the new effects of the nanoscale state of matter, which open up prospects for the development of electronic devices using new physical principles. The contacts of chemically homogeneous nanoparticles of yttrium-stabilized zirconium oxide (ZrO2-x mol% Y2O3, x = 0, 3, 4, 8; YSZ) with different sizes of 7.5 nm and 9 nm; 7.5 nm and 11 nm; and 7.5 nm and 14 nm, respectively, was studied on direct current using nanostructured objects in the form of compacts obtained by high-hydrostatic pressure (HP-compacts of 300MPa). A unique size effect of the nonlinear (rectifying-type contact) dependence of the electrical properties (in the region U < 2.5 V, I <= 2.7 mA) of the contact of different-sized YSZ nanoparticles of the same chemical composition is revealed, which indicates the possibility of creating semiconductor structures of a new type (homogeneous electronics). The electronic structure of the near-surface regions of nanoparticles of studied oxide materials and the possibility of obtaining specifically rectifying properties of the contacts were studied theoretically. Models of surface states of the Tamm-type are constructed considering the Coulomb long-range action. The discovered energy variance and its dependence on the curvature of the surface of nanoparticles made it possible to study the conditions for the formation of a contact potential difference in cases of nanoparticles of the same radius (synergistic effect), different radii (doped and undoped variants), as well as to discover the possibility of describing a group of powder particles within the Anderson model. The determined effect makes it possible to solve the problem of diffusion instability of semiconductor heterojunctions and opens up prospects for creating electronic devices with a fundamentally new level of properties for use in various fields of the economy and breakthrough critical technologies.
Open Access
176. The sustainable materials roadmap
Authors:
Titirici, M; Baird, SG; Sparks, TD; Yang, SM; Brandt-Talbot, A; Hosseinaei, O; Harper, DP; Parker, RM; Vignolini, S; Berglund, LA; Li, YY; Gao, HL; Mao, LB; Yu, SH; Díez, N; Ferrero, GA; Sevilla, M; Szilágyi, PA; Stubbs, CJ; Worch, JC; Huang, YP; Luscombe, CK; Lee, KY; Luo, H; Platts, MJ; Tiwari, D; Kovalevskiy, D; Fermin, DJ; Au, H; Alptekin, H; Crespo-Ribadeneyra, M; Ting, VP; Fellinger, TP; Barrio, J; Westhead, O; Roy, C; Stephens, IEL; Nicolae, SA; Sarma, SC; Oates, RP; Wang, CG; Li, ZB; Loh, XJ; Myers, RJ; Heeren, N; Grégoire, A; Périssé, C; Zhao, XY; Vodovotz, Y; Earley, B; Finnveden, G; Björklund, A; Harper, GDJ; Walton, A; Anderson, PA
Published: JUL 1 2022, JOURNAL OF PHYSICS-MATERIALS, 5, 032001, DOI: 10.1088/2515-7639/ac4ee5
Over the past 150 years, our ability to produce and transform engineered materials has been responsible for our current high standards of living, especially in developed economies. However, we must carefully think of the effects our addiction to creating and using materials at this fast rate will have on the future generations. The way we currently make and use materials detrimentally affects the planet Earth, creating many severe environmental problems. It affects the next generations by putting in danger the future of the economy, energy, and climate. We are at the point where something must drastically change, and it must change now. We must create more sustainable materials alternatives using natural raw materials and inspiration from nature while making sure not to deplete important resources, i.e. in competition with the food chain supply. We must use less materials, eliminate the use of toxic materials and create a circular materials economy where reuse and recycle are priorities. We must develop sustainable methods for materials recycling and encourage design for disassembly. We must look across the whole materials life cycle from raw resources till end of life and apply thorough life cycle assessments (LCAs) based on reliable and relevant data to quantify sustainability. We need to seriously start thinking of where our future materials will come from and how could we track them, given that we are confronted with resource scarcity and geographical constrains. This is particularly important for the development of new and sustainable energy technologies, key to our transition to net zero. Currently 'critical materials' are central components of sustainable energy systems because they are the best performing. A few examples include the permanent magnets based on rare earth metals (Dy, Nd, Pr) used in wind turbines, Li and Co in Li-ion batteries, Pt and Ir in fuel cells and electrolysers, Si in solar cells just to mention a few. These materials are classified as 'critical' by the European Union and Department of Energy. Except in sustainable energy, materials are also key components in packaging, construction, and textile industry along with many other industrial sectors. This roadmap authored by prominent researchers working across disciplines in the very important field of sustainable materials is intended to highlight the outstanding issues that must be addressed and provide an insight into the pathways towards solving them adopted by the sustainable materials community. In compiling this roadmap, we hope to aid the development of the wider sustainable materials research community, providing a guide for academia, industry, government, and funding agencies in this critically important and rapidly developing research space which is key to future sustainability.
Open Access
177. Magnetic Properties of Nanosized Fe and FeCo Systems on Trenched Mo Templates
Authors:
Stanciu, AE; Schinteie, G; Kuncser, AC; Locovei, C; Trupina, L; Iacob, N; Leca, A; Borca, B; Kuncser, V
Published: SEP 2022, COATINGS, 12, 1366, DOI: 10.3390/coatings12091366
The manipulation of magnetic anisotropy represents the fundamental prerequisite for the application of magnetic materials. Here we present the vectorial magnetic properties of nanostructured systems and thin films of Fe and FeCo prepared on linearly trenched Mo templates with thermally controlled periodicity. The magnetic properties of the nanosystems are engineered by tuning the shape, size, thickness, and composition parameters of the thin films. Thus, we control coercivity, magnetization, orientation of the easy axis of magnetization, and the long-range magnetic order of the system in the function of the temperature. We distinguish magnetic components that emerge from the complex morpho-structural features of the undulating Fe or FeCo nanostructured films on trenched Mo templates: (i) assembly of magnetic nanowires and (ii) assembly of magnetic islands/clusters. Uniaxial anisotropy at room temperature was proven, characterized, and explained in the case of all systems. Our work contributes to the understanding of magnetic properties necessary for possible further applications of linear systems and undulated thin films.
Open Access
178. Ferroelectricity modulates polaronic coupling at multiferroic interfaces
Authors:
Husanu, MA; Popescu, DG; Bisti, F; Hrib, LM; Filip, LD; Pasuk, I; Negrea, R; Istrate, MC; Lev, L; Schmitt, T; Pintilie, L; Mishchenko, A; Teodorescu, CM; Strocov, VN
Published: AUG 15 2022, COMMUNICATIONS PHYSICS, 5, 209, DOI: 10.1038/s42005-022-00983-3
A deeper understanding of the coupling at the interface of multiferroics heterostructures is being achieved by the use of synchrotron radiation techniques. Here, the authors use k-resolved soft X-ray photoemission spectroscopy and first principles calculations to investigate the band structure of several multiferroic heterostructures, isolating the distinct signature of the interface. Physics of the multiferroic interfaces is currently understood mostly within a phenomenological framework based on screening of the polarization field and depolarizing charges. Additional effects still unexplored are the band dependence of the interfacial charge modulation and the associated changes of the electron-phonon interaction, coupling the charge and lattice degrees of freedom. Here, multiferroic heterostructures of the colossal-magnetoresistance manganite La1-xSrxMnO3 buried under ferroelectric BaTiO3 and PbZrxTi1-xO3 are investigated using soft-X-ray angle-resolved photoemission. The experimental band dispersions from the buried La1-xSrxMnO3 identify coexisting two-dimensional hole and three-dimensional electron charge carriers. The ferroelectric polarization modulates their charge density, affecting the coupling of the 2D holes and 3D electrons with the lattice which forms large Frohlich polarons inherently reducing mobility of the charge carriers. Our k-resolved results on the orbital occupancy, band filling and electron-lattice interaction in multiferroic oxide heterostructures modulated by the ferroelectric polarization disclose most fundamental physics of these systems needed for further progress of beyond-CMOS ferro-functional electronics.
179. Sonogashira Synthesis of New Porous Aromatic Framework-Entrapped Palladium Nanoparticles as Heterogeneous Catalysts for Suzuki-Miyaura Cross-Coupling
Authors:
Cata, L; Terenti, N; Cociug, C; Hadade, ND; Grosu, I; Bucur, C; Cojocaru, B; Parvulescu, V; Mazur, M; Cejka, J
Published: MAR 2 2022, ACS APPLIED MATERIALS & INTERFACES, 14, DOI: 10.1021/acsami.1c24429
Palladium nanoparticles entrapped in porous aromatic frameworks (PAFs) or covalent organic frameworks may promote heterogeneous catalytic reactions. However, preparing such materials as active nanocatalysts usually requires additional steps for palladium entrapment and reduction. This paper reports as a new approach, a simple procedure leading to the self-entrapment of Pd nanoparticles within the PAF structure. Thus, the selected Sonogashira synthesis affords PAF-entrapped Pd nanoparticles that can catalyze the C-C Suzuki-Miyaura cross-coupling reactions. Following this new concept, PAFs were synthesized via Sonogashira cross-coupling of the tetraiodurated derivative of tetraphenyl aLam an tan e or spiro-9,9'-bifluorene with 1,6-diethynylpyrene, then characterized them using powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, high-resolution scanning transmission electron microscopy, and textural properties (i.e., adsorption-desorption isotherms). The PAF-entrapped Pd nanocatalysts showed high catalytic activity in Suzuki-Miyaura coupling reactions (demonstrated by preserving the turnover frequency values) and stability (demonstrated by palladium leaching and recycling experiments). This new approach presents a new class of PAFs with unique structural, topological, and compositional complexities as entrapped metal nanocatalysts or for other diverse applications.
180. SOME ASPECTS REGARDING PRECIPITATES IN THE NiTi SHAPE MEMORY MATERIALS
Authors:
Cirstea, CD; Tolea, F; Patroi, D; Cirstea, V; Tsakiris, V
NiTi cylindrical materials were obtained by spark plasma sintering at 850??C or 900??C from high purity Ni and Ti powders. These mixtures were previously processed by mechanical alloying for 8 and 15 hours. In order to increase the alloy homogeneity, the NiTi materials were subjected to post aging treatment in protective atmosphere at constant temperature 400??C and cooling in water with ice. All samples were characterized by optical microscopy, differential calorimetry (DSC), X-ray measurements (XRD) and micro/nanoindentation measurements. The results demonstrate that the NiTi materials obtained by this preparation route have good mechanical properties and can serve as a quantitative reference for the microstructure design of shape memory materials for various applications, such as the biomedical ones.
181. Enhanced photoelectrochemical activity of WO3-decorated native titania films by mild laser treatment
Authors:
Spataru, T; Mihai, MA; Preda, L; Marcu, M; Radu, MM; Becherescu, ND; Velea, A; Zaki, MY; Udrea, R; Satulu, V; Spataru, N
Published: SEP 15 2022, APPLIED SURFACE SCIENCE, 596, 153682, DOI: 10.1016/j.apsusc.2022.153682
The effectiveness of the electrochemical WO3-modification as a method for improving the photoactivity of native air-formed TiO2 layers was assessed. The way in which a mild laser treatment influences the photo-electrochemical performances of the thus obtained WO3/TiO2 systems was also investigated. At laser-treated electrodes (L-WO3/TiO2), the melting-solidification process induced by the treatment led to a smaller size of the deposited WO3 particles and to their better dispersion on the surface. The treatment also enhanced the surface oxygen deficiency and ensured better relative absorptivity of the oxygenated species on the surface. These features, together with the intrinsic narrower bandgap of the WO3/TiO2 composites, the higher donor density and the lower flat band potential of L-WO3/TiO2 enabled faster kinetic of the oxygen photoanodic evolution. Importantly, the same process exhibited a cathodic shift of its onset potential. The laser treatment also strongly enhanced the photoelectrocatalytic performances for UV-assisted methanol anodic oxidation.
182. Quantification of cell oxygenation in 2D constructs of metallized electrospun polycaprolactone fibers encapsulating human valvular interstitial cells
Authors:
Sanz, CG; Mihaila, AC; Evanghelidis, A; Diculescu, VC; Butoi, E; Barsan, MM
Published: JAN 15 2022, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 905, 116005, DOI: 10.1016/j.jelechem.2021.116005
The present study brings developments in the area of tissue engineering of heart valves, with the design and application of a new 2D model for human heart valve. This model contains valvular interstitial cells (VIC) encapsulated in gold covered electrospun polycaprolactone (PCL/Au) fibers, the latter serving also as an electrochemical sensor that enables the monitoring of oxygen levels of cellular media. The biocompatibility of PCL and PCL/Au with VIC was evaluated after the encapsulation of VIC in both scaffolds using the lactate dehydrogenase assay. Fluorescence microscopy of the encapsulated cells was used for the investigation of cell morphology, by employing phalloidin labelled F-actin (red) and DAPI nuclear staining (blue). The electrochemical techniques allowed to investigate the effect of cell encapsulation within the PCL/Au 2D constructs and to quantify the dissolved oxygen levels in cell culture media at both PCL/Au and PCL/Au with encapsulated cells (PCL/ Au/cells). Experiments were performed in a hypoxistation, which allowed a fine control on the cellular media oxygenation. Electrochemical impedance spectroscopy (EIS) was used to evaluate the electrochemical behavior of the 2D constructs, PCL/Au and PCL/Au/cells, in cellular media at different O-2 concentration. Results were analyzed and both impedance values at a fixed frequency and values of the equivalent circuit elements were used to construct calibration curves for dissolved O-2 determination. The second electrochemical technique used to monitor the levels of O-2 at PCL/Au and PCL/Au/cells in the cellular media was square wave voltammetry with sensitivities of 1.5 and 2.5 mu A cm(-2) mu M-1, for PCL/Au and PCL/Au/cells, respectively.
Open Access
183. 'Put variety in White': Multi-analytical investigation of the white pigments inlaid on Early Chalcolithic pottery from Southern Romania
Authors:
Opris, V; Velea, A; Secu, M; Rostas, AM; Buruiana, AT; Simion, CA; Mirea, DA; Matei, E; Bartha, C; Dimache, M; Lazar, C
Published: APR 2022, JOURNAL OF ARCHAEOLOGICAL SCIENCE-REPORTS, 42, 103402, DOI: 10.1016/j.jasrep.2022.103402
The current study aims to present and discuss the results obtained by complementary archaeometric methods applied for the first time on white pigments inlaid on excised pottery of the Boian-Vidra tradition (Early Chalcolithic, c. 4900-4600 BCE). The samples came from three settlements located in Southern Romania (Sultana-Ghetarie, Vidra, and Vladiceasca). They were selected considering that the pottery was produced in approximately contemporary sites, located relatively close to each other in the same geographical region, namely the Romanian Plain. The experimental part included the analysis of local samples of carbonate concretions and prehistoric animal bone ash as reference materials. Archaeometric investigations consisted in applying "in-air" PIXE and EDX methods for the chemical composition, XRD and FTIR for mineralogical data, SEM for microstructure observation, and EPR for the characterisation of the paramagnetic centres. Calcite, bone ash, and silica rich sediments were identified as the primary decorating pigments. The mixtures of calcite and bone-ash observed in 13 samples were specific to the sites at Vidra and Vladiceasca. Silica-rich sediments from distant sources were the main whitening materials in two samples from Vladiceasca, while for the samples from Sultana-Ghetarie, calcite was the only whitening mineral. The results show with a high degree of confidence the use of both local (i.e., carbonate neo-formations and bone ash) and exotic (silica-rich sediments) raw materials to obtain the white pigment applied to Boian-Vidra pottery. Thus, the current data show the adaptability of the potters with respect to the surrounding resources and also provide new evidence for a vast trade network of raw materials and/or finished products in the Lower Danube area during the Early Chalcolithic. The deliberate mixing of two whitening materials from different sources could be a technological choice and may highlight complex symbolic behaviours.
184. Catalytic transformation of the marine polysaccharide ulvan into rare sugars, tartaric and succinic acids
Authors:
Podolean, I; Coman, SM; Bucur, C; Teodorescu, C; Kikionis, S; Ioannou, E; Roussis, V; Primo, A; Garcia, H; Parvulescu, V
Published: JAN 1 2022, CATALYSIS TODAY, 383, DOI: 10.1016/j.cattod.2020.06.086
The green macroalga Ulva rigida represents a promising feedstock for biorefinary due to its fast growth and cosmopolitan distribution. The main component of the cell walls of U. rigida is a sulfated glucuronorhamnan polysaccharide known as ulvan. Herein it was found that due to the high (hydrogen)sulfate group content of ulvan, hydrothermal autohydrolysis at 130 degrees C renders a high percentage of rhamnose (78-79 % recovery from the initial content in the raw material), a rare sugar of high added value. In addition, acid catalysis by a triflate-based graphene oxide under oxygen-free conditions at 180 degrees C affords moderate amounts of tartaric acid (24-26 %). The same triflate-based graphene oxide catalyst under oxygen pressure yields remarkably high percentages of succinic acid (65 %). The catalyst preserves its activity for at least five consecutive reuses.
185. Structural and transport properties of Cu2CoSnS4 films prepared by spray pyrolysis
Authors:
El Khouja, O; Assahsahi, I; Nouneh, K; Touhami, ME; Secu, M; Talbi, A; Khaaissa, Y; Matei, E; Stancu, V; Galatanu, A; Galca, AC
Published: NOV 1 2022, CERAMICS INTERNATIONAL, 48, DOI: 10.1016/j.ceramint.2022.07.185
In the present work, stannite Cu2CoSnS4 (CCTS) films were elaborated using spray pyrolysis method on soda-lime glass, at different deposition temperatures (T-d = 250, 300, and 350 degrees C), followed by different chosen sulfurization temperatures (T-s = 450, 500, and 550 degrees C). X-ray diffraction (XRD) revealed the nearly single-phase formation of CCTS films at 300 degrees C deposition temperature. After sulfurization in argon flow, the XRD lines become narrower, the average crystallite size expanding above 70 nm. The Raman spectroscopy analysis confirmed the stannite structure formation, as well as the presence CoS2 secondary phases, which reduces at higher sulfurization temperature (550 degrees C). The energy dispersive spectroscopy results indicated atomic ratios of Cu/Co/Sn/S close to the ideal stoichiometric ratio 2:1:1:4. The room temperature photoluminescence emission is recorded with maximum in the 1.35-1.40 eV range. Thermoelectric properties are measured up to 130 degrees C, the films show poor power factor as a result of small positive Seebeck coefficients 10-45 Of K -1 and low electrical conductivity despite of having relatively high carrier concentration (similar to 10(20) cm(-3)).
186. Effect of disubstitution pattern of the terminal alkyl chains on the mesophase of liquid crystals based on lanthanide(III) complexes: A study of the thermal, emission and dielectric behavior
Authors:
Ilinca, TA; Chiriac, LF; Ilis, M; Manaila-Maximean, D; Ganea, PC; Pasuk, I; Cîrcu, V
Published: AUG 15 2022, JOURNAL OF MOLECULAR LIQUIDS, 360, 119425, DOI: 10.1016/j.molliq.2022.119425
In the present work, new luminescent lanthanide complexes with extended mesomorphic range were prepared by coordination to lanthanide ions (Eu3+, Sm3+ and Tb3+) of the new 4-pyridone based organic ligands (L) with 3,4-(7-n) and 3,5-di(alkyloxy)benzyl (8-n) mesogenic groups and variable length (n = 12 or 14 carbon atoms) onto the benzyl unit. The cumulative results of the elemental analyses as well as the H-1, C-13 NMR and IR spectroscopies support the structure of the organic derivatives and their lanthanide complexes [LnL(3)(NO3)(3)] (9-n/Ln and 10-n/Ln) described in this work. These complexes show characteristic lanthanide solid state emission, both at room and elevated temperatures corresponding to crystalline, glassy or liquid crystal states. The long range SmA phases displayed by all complexes were supported by a combination of characterization methods, including: differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and variable-temperature powder X-ray diffraction (XRD). This work shows that the number, substitution pattern and length of flexible alkoxy chains are important parameters to control the phase-transition characteristics of the lanthanide complexes. Complexes with 3,4-disubstituted pattern (9-n/Ln) show higher clearing temperatures (nearly 60 degrees C for Eu3+, 70 degrees C for Sm3+ and 85 degrees C for Tb3+ complexes) compared to their counterparts with 3,5-disubstituted pattern (10-n/Ln). Moreover, complexes 9-n/Ln crystallize when cooling their LC phase while complexes 10-n/Ln are stable in glassy state at room temperature as a consequence of the different close interdigitated molecular packing evidenced by XRD measurements. Dielectric spectroscopy was employed to detect the changes of order degree specific to each phases (crystalline, LC or isotropic). The variation of dielectric constant and the electrical conductivity versus temperature shows three transition intervals for selected complexes 10-14/Sm and 10-14/Tb, which delimit the main intervals: 45-60 degrees C, 90-110 degrees C; 140-160 degrees C corresponding to the Cr-1-Cr-2, Cr-2 - SmA and SmA-Iso transitions, and agree very well with the DSC results. The change of characteristic time, obtained by Havriliak-Negami fit function, with temperature also provides a very good correlation with the DSC and POM results. (C) 2022 Elsevier B.V. All rights reserved.
Open Access
187. Magnetic Core-Shell Iron Oxides-Based Nanophotocatalysts and Nanoadsorbents for Multifunctional Thin Films
Authors:
Musat, V; Stanica, N; Anghel, EM; Atkinson, I; Culita, DC; Polosan, S; Crintea, L; Ceoromila, AC; Buruiana, CT; Carp, O
Published: MAY 2022, MEMBRANES, 12, 466, DOI: 10.3390/membranes12050466
In recent years, iron oxides-based nanostructured composite materials are of particular interest for the preparation of multifunctional thin films and membranes to be used in sustainable magnetic field adsorption and photocatalysis processes, intelligent coatings, and packing or bio-medical applications. In this paper, superparamagnetic iron oxide (core)-silica (shell) nanoparticles suitable for thin films and membrane functionalization were obtained by co-precipitation and ultrasonic-assisted sol-gel methods. The comparative/combined effect of the magnetic core co-precipitation temperature (80 and 95 degrees C) and ZnO-doping of the silica shell on the photocatalytic and nano-sorption properties of the resulted composite nanoparticles were investigated by ultraviolet-visible (UV-VIS) spectroscopy monitoring the discoloration of methylene blue (MB) solution under ultraviolet (UV) irradiation and darkness, respectively. The morphology, structure, textural, and magnetic parameters of the investigated powders were evidenced by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) measurements, and saturation magnetization (vibrating sample magnetometry, VSM). The intraparticle diffusion model controlled the MB adsorption. The pseudo- and second-order kinetics described the MB photodegradation. When using SiO2-shell functionalized nanoparticles, the adsorption and photodegradation constant rates are three-four times higher than for using starting core iron oxide nanoparticles. The obtained magnetic nanoparticles (MNPs) were tested for films deposition.
188. Influence of erbium doping on the structural, magnetic and optical properties of hematite (?-Fe2O 3) nanorods
Authors:
Popov, N; Ristic, M; Kuncser, V; Zadro, K; Velinov, N; Badica, P; Alexandru-Dinu, A; Iacob, N; Krehula, LK; Music, S; Krehula, S
Published: OCT 2022, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 169, 110857, DOI: 10.1016/j.jpcs.2022.110857
Pure and Er-doped hematite (alpha-Fe2O3) nanorods were prepared by a two-step method involving hydrothermal synthesis and calcination of pure and Er-doped goethite (alpha-FeOOH) nanorods. Substitution of Fe3+ by Er3+ in the crystal structure of hematite caused morpho-structural changes such as expansion of the unit cell and gradual shortening and rounding of hematite nanorods towards formation of nanoellipsoids. These changes induced modification of magnetic and optical properties suggesting the possibility of a systematic control of physical properties via rare earth substitution. A decrease in the hyperfine magnetic field, coercive field and Morin transition temperature, as well as an increase of the magnetic susceptibility and a narrowing of the optical band gap were observed by substitution. Intimate mechanisms related to the formation of more and more defect-like hematite phases with decreased temperatures for the transition to the low temperature antiferromagnetic phase at increased doping level were evidenced via temperature dependent Mo center dot ssbauer spectroscopy.
189. Bulk and surface characteristics of co-electrodeposited Cu2FeSnS4 thin films sulfurized at different annealing temperatures
Authors:
El Khouja, O; Negrila, CC; Nouneh, K; Secu, M; Touhami, ME; Matei, E; Stancu, V; Enculescu, M; Kuncser, V; Galca, AC
Published: JUN 15 2022, JOURNAL OF ALLOYS AND COMPOUNDS, 906, 164379, DOI: 10.1016/j.jallcom.2022.164379
In this study, stannite, Cu2FeSnS4 (CFTS), absorber films were obtained by electrodeposition on Molybdenum-coated soda-lime substrates, followed by sulfurization treatment at certain temperatures in the 400-550 degrees C range. The purposes of this work were to control the manufacturing of CFTS films with good stoichiometry, high crystallinity and to study the annealing temperature impact on CFTS films properties. The X-ray diffraction and the Raman spectroscopy measurement distinguished the CFTS phase formation, with a presence of SnS2 secondary phase. The energy dispersive spectroscopy results reveal compositional differences between samples as well as the in-depth gradients. The photoluminescence emission band around 1.35-1.40 eV is slightly below the direct bandgap inferred from the conventional spectroscopy (diffuse reflectance). X-ray photoelectron spectroscopy results indicate clearly a high amount of Sn on the surface. The Conversion Electron Mossbauer unveiled the presence of Fe in the chalcogenide unit cell. The electrochemical characteristics of the synthesized films are also given. (c) 2022 Elsevier B.V. All rights reserved.
Open Access
190. Chitosan-Hyaluronan Nanoparticles for Vinblastine Sulfate Delivery: Characterization and Internalization Studies on K-562 Cells
Authors:
Cannavà, C; De Gaetano, F; Stancanelli, R; Venuti, V; Paladini, G; Caridi, F; Ghica, C; Crupi, V; Majolino, D; Ferlazzo, G; Tommasini, S; Ventura, CA
Published: MAY 2022, PHARMACEUTICS, 14, 942, DOI: 10.3390/pharmaceutics14050942
In the present study, we developed chitosan/hyaluronan nanoparticles (CS/HY NPs) for tumor targeting with vinblastine sulfate (VBL), that can be directed to the CD44 transmembrane receptor, over-expressed in cancer cells. NPs were prepared by coating with HY-preformed chitosan/tripolyphosphate (CS/TPP) NPs, or by polyelectrolyte complexation of CS with HY. NPs with a mean hydrodynamic radius (R-H) of 110 nm, 12% polydispersity index and negative zeta potential values were obtained by a direct complexation process. Transmission Electron Microscopy (TEM) images showed spherical NPs with a non-homogeneous matrix, probably due to a random localization of CS and HY interacting chains. The intermolecular interactions occurring between CS and HY upon NPs formation were experimentally evidenced by micro-Raman (mu-Raman) spectroscopy, through the analysis of the spectral changes of characteristic vibrational bands of HY during NP formation, in order to reveal the involvement of specific chemical groups in the process. Optimized NP formulation efficiently encapsulated VBL, producing a drug sustained release for 20 h. In vitro studies demonstrated a fast internalization of labeled CS/HY NPs (within 6 h) on K-562 human myeloid leukemia cells. Pre-saturation of CD44 by free HY produced a slowing-down of NP uptake over 24 h, demonstrating the need of CD44 for the internalization of HY-based NPs.
Open Access
191. Microstructural Investigations of VO2 Thermochromic Thin Films Grown by Pulsed Laser Deposition for Smart Windows Applications
Authors:
Rai, A; Iacob, N; Leca, A; Locovei, C; Kuncser, V; Mihailescu, CN; Delimitis, A
Published: DEC 2022, INORGANICS, 10, 220, DOI: 10.3390/inorganics10120220
The structural properties of VO2 thin films, grown on either LSAT or Si substrates by pulsed laser deposition (PLD), are elucidated by means of transmission electron microscopy (TEM) methods. The TEM observations confirmed the successful growth of VO2 by PLD in variable thicknesses, by optimizing the O-2 partial pressure and growth temperature. The films adopt a columnar polycrystalline morphology with narrow columns, up to the film thickness height. Four VO2 polymorphs have been detected by electron diffraction and high-resolution TEM (HRTEM) analysis, with M1 being by far the most abundant phase. Post-experimental strain measurements in HRTEM images have revealed that the actual residual strain is minimized due to the columnar morphology of the VO2 grains, as well as intrinsic oxide layers in the VO2/Si epitaxy. The TEM outcomes confirmed the complementary electrical and magnetic measurements in the films, where a transition from a monoclinic M1 to a rutile VO2 R phase has been identified, influenced by the initial percentage of phases in thick VO2 films.
Open Access
192. Graphene/Ferroelectric (Ge-Doped HfO2) Adaptable Transistors Acting as Reconfigurable Logic Gates
Authors:
Dragoman, M; Dinescu, A; Dragoman, D; Palade, C; Teodorescu, VS; Ciurea, ML
Published: JAN 2022, NANOMATERIALS, 12, 279, DOI: 10.3390/nano12020279
We present an array of 225 field-effect transistors (FETs), where each of them has a graphene monolayer channel grown on a 3-layer deposited stack of 22 nm control HfO2/5 nm Ge-HfO2 intermediate layer/8 nm tunnel HfO2/p-Si substrate. The intermediate layer is ferroelectric and acts as a floating gate. All transistors have two top gates, while the p-Si substrate is acting as a back gate. We show that these FETs are acting memtransistors, working as two-input reconfigurable logic gates with memory, the type of the logic gate depending only on the values of the applied gate voltages and the choice of a threshold current.
Open Access
193. The Synergistic Effect of the Laser Beam on the Thermionic Vacuum Arc Method for Titanium-Doped Chromium Thin Film Deposition
Authors:
Vladoiu, R; Mandes, A; Dinca, V; Ciupina, V; Matei, E; Polosan, S
Published: APR 2022, COATINGS, 12, 470, DOI: 10.3390/coatings12040470
Laser-Induced Thermionic Vacuum Arc (LTVA) provides a better way to produce uniform metallic thin films than the classical Thermionic Vacuum Arc (TVA) method. In Ti-doped chromium thin films produced using LTVA, the amorphous chromium is superimposed with small bcc chromium nanoparticles. These amorphous/crystalline structures with small crystallites induce lower roughness and electrical resistivity, reducing electron-phonon scattering and increasing charge transport across LTVA thin films. A significant shift in resistivity for the LTVA samples is observed due to electron scattering on the phonon-crystalline structures in the TVA samples which exhibit larger crystallites. Meanwhile, the wettability measurements reveal a higher contact angle, resulting in a lower surface free energy and consecutively lower dissociation energy for the LTVA-produced thin films than the TVA samples.
Open Access
194. Synthesis of Cobalt-Nickel Aluminate Spinels Using the Laser-Induced Thermionic Vacuum Arc Method and Thermal Annealing Processes
Authors:
Vladoiu, R; Mandes, A; Dinca, V; Matei, E; Polosan, S
Published: NOV 2022, NANOMATERIALS, 12, 3895, DOI: 10.3390/nano12213895
To obtain highly homogeneous cobalt-nickel aluminate spinels with small crystallite sizes, CoNiAl alloy thin films were primarily deposited using Laser-induced Thermionic Vacuum Arc (LTVA) as a versatile method for performing processing of multiple materials, such as alloy/composite thin films, at a nanometric scale. Following thermal annealing in air, the CoNiAl metallic thin films were transformed into ceramic oxidic (Co,Ni)Al2O4 with controlled composition and crystallinity suitable for thermal stability and chemical resistance devices. Structural analysis revealed the formation of (Co,Ni)Al2O4 from the amorphous CoNiAl alloys. The mean crystallite size of the spinels was around 15 nm. Thermal annealing induces a densification process, increasing the film thickness together with the migration process of the aluminum toward the surface of the samples. The sheet resistance changed drastically from 200-240 omega/sq to more than 10(6) omega/sq, revealing a step-by-step conversion of the metallic character of the thin film to a dielectric oxidic structure. These cermet materials can be used as inert anodes for the solid oxide fuel cells (SOFCs), which require not only high stability with respect to oxidizing gases such as oxygen, but also good electrical conductivity. These combination metal-ceramics are known as bi-layer anodes. By controlling the crystallite size and the interplay between the oxide/metal composite, a balance between stability and electrical conductivity can be achieved.
Open Access
195. Structural evolution of carbon dots during low temperature pyrolysis
Authors:
Luo, H; Lari, L; Kim, H; Hérou, S; Tanase, LC; Lazarov, VK; Titirici, MM
Published: JAN 20 2022, NANOSCALE, 14, DOI: 10.1039/d1nr07015k
Carbon dots (CDs) are an emerging class of photoluminescent material. Their unique optical properties arise from the discrete energy levels in their electronic states, which directly relate to their crystalline and chemical structure. It is expected that when CDs go through structural changes via chemical reduction or thermal annealing, their energy levels will be altered, inducing unique optoelectronic properties such as solid-state photoluminescence (PL). However, the detailed structural evolution and how the optoelectronic characteristics of CDs are affected remain unclear. Therefore, it is of fundamental interest to understand how the structure of CDs prepared by hydrothermal carbonisation (HTC) rearranges from a highly functionalised disordered structure into a more ordered graphitic structure. In this paper, detailed structural characterisation and in situ TEM were conducted to reveal the structural evolution of CDs during the carbonisation process, which have demonstrated a growth in aromatic domains and reduction in oxidation sites. These structural features are correlated with their near-infrared (NIR) solid-state PL properties, which may find a lot of practical applications such as temperature sensing, solid-state display lighting and anti-counterfeit security inks.
Open Access
196. Synthesis and characterization of some C-Ti based multilayer and composite nanostructures
Authors:
Ciupina, V; Lungu, CP; Vladoiu, R; Prodan, GC; Porosnicu, C; Vasile, E; Prodan, M; Nicolescu, V; Dinca, V; Cupsa, O; Velea, A; Manu, R
Published: MAR-APR 2022, JOURNAL OF OVONIC RESEARCH, 18, DOI: 10.15251/JOR.2022.182.177
Carbon-Titanium multilayer and composite thin films were obtained by Thermionic Vacuum Arc (TVA) method. The nanostructured films consisted by a carbon base layer and seven alternatively Titanium and Carbon layers were deposed on Silicon substrate. As well, to give C-Ti multilayer films with different percentages in Ti and C of layers, a thick Carbon base layer was deposed on Si substrate, and then seven Ti-C layers. In order to achieve the successively layers with C, and Ti different percentages, were adjusted the discharge parameters of C and Ti plasma sources to obtain the desired composition of layers. By changing of substrate temperature, and on the other hand the bias potential up to ???700V, different batches of samples were obtained. Characterization of structural properties of films was achieved by Grazing Incidence X-ray Diffraction (GIXRD) and Electron Microscopy technique (TEM). The measurements show that increase of the substrate temperature reveal the changes in TixCy lattice parameters. The tribological measurements were performed using a ball-on-disk system with normal forces of 0.5, 1, 2, 3N respectively and a Bruker Hystrion TI 980 TriboIndenter. Was found that the coefficient of friction depends on the synthesis temperature, bias voltage and also by the C content, Ti content and amount of TiC nanocrystallites. To characterize the electrical conductive properties, the electrical surface resistance versus temperature have been measured, and then the electrical conductivity is calculated. Using the Wiedeman-Frantz law was obtained the thermal conductivity.
Open Access
197. Unidirectional Magnetic Anisotropy in Molybdenum Dioxide-Hematite Mixed-Oxide Nanostructures
Authors:
Tolea, F; Sorescu, M; Diamandescu, L; Iacob, N; Tolea, M; Kuncser, V
Published: MAR 2022, NANOMATERIALS, 12, 938, DOI: 10.3390/nano12060938
MoO2-Fe2O3 nanoparticle systems were successfully synthesized by mechanochemical activation of MoO2 and alpha-Fe2O3 equimolar mixtures throughout 0-12 h of ball-milling. The role of the long-range ferromagnetism of MoO2 on a fraction of more defect hematite nanoparticles supporting a defect antiferromagnetic phase down to the lowest temperatures was investigated in this work. The structure and the size evolution of the nanoparticles were investigated by X-ray diffraction, whereas the magnetic properties were investigated by SQUID magnetometry. The local electronic structure and the specific phase evolution in the analyzed system versus the milling time were investigated by temperature-dependent Mossbauer spectroscopy. The substantially shifted magnetic hysteresis loops were interpreted in terms of the unidirectional anisotropy induced by pinning the long-range ferromagnetic order of the local net magnetic moments in the defect antiferromagnetic phase, as mediated by the diluted magnetic oxide phase of MoO2, to those less defect hematite nanoparticles supporting Morin transition. The specific evolutions of the exchange bias and of the coercive field versus temperature in the samples were interpreted in the frame of the specific phase evolution pointed out by Mossbauer spectroscopy. Depending on the milling time, a different fraction of defect hematite nanoparticles is formed. Less nanoparticles supporting the Morin transition are formed for samples exposed to a longer milling time, with a direct influence on the induced unidirectional anisotropy and related effects.
Open Access
198. Facile synthesis of low toxicity iron oxide/TiO2 nanocomposites with hyperthermic and photo-oxidation properties
Authors:
Popescu, T; Matei, CO; Culita, DC; Maraloiu, VA; Rostas, AM; Diamandescu, L; Iacob, N; Savopol, T; Ilas, MC; Feder, M; Lupu, AR; Iacoban, AC; Vlaicu, ID; Moisescu, MG
Published: APR 27 2022, SCIENTIFIC REPORTS, 12, 6887, DOI: 10.1038/s41598-022-11003-3
The present study aimed to assess the feasibility of developing low-cost multipurpose iron oxide/TiO2 nanocomposites (NCs) for use in combined antitumor therapies and water treatment applications. Larger size (approximate to 100 nm) iron oxide nanoparticles (IONPs) formed magnetic core-TiO2 shell structures at high Fe/Ti ratios and solid dispersions of IONPs embedded in TiO2 matrices when the Fe/Ti ratio was low. When the size of the iron phase was comparable to the size of the crystallized TiO2 nanoparticles (approximate to 10 nm), the obtained nanocomposites consisted of randomly mixed aggregates of TiO2 and IONPs. The best inductive heating and ROS photogeneration properties were shown by the NCs synthesized at 400 degrees C which contained the minimum amount of alpha-Fe2O3 and sufficiently crystallized anatase TiO2. Their cytocompatibility was assessed on cultured human and murine fibroblast cells and analyzed in relation to the adsorption of bovine serum albumin from the culture medium onto their surface. The tested nanocomposites showed excellent cytocompatibility to human fibroblast cells. The results also indicated that the environment (i.e. phosphate buffer or culture medium) used to disperse the nanomaterials prior to performing the viability tests can have a significant impact on their cytotoxicity.
Open Access
199. TiO2 Nanotubes Film/FTO Glass Interface: Thermal Treatment Effects
Authors:
Vujancevic, J; Bjelajac, A; Veltruska, K; Matolin, V; Siketic, Z; Provatas, G; Jaksic, M; Stan, GE; Socol, G; Mihailescu, IN; Pavlovic, VB; Janackovic, D
Published: 2022, SCIENCE OF SINTERING, 54, DOI: 10.2298/SOS2202235V
Pure Ti films deposited by radio-frequency magnetron sputtering on FTO glass were anodized to fabricate TiO2 nanotubes (NTs) arrays. The TiO2 NTs/FTO samples were sintered at 450, 550 and 630 degrees C, in ambient air. The thermal treatment did not influence the crystal phase composition, preserving in all cases the anatase single phase. As expected, the crystalline anatase quality improved with the annealing temperature. Nevertheless, slight differences in nanotubular morphology, such as the appearance of grains inside the walls, were observed in the case of the sample sintered at 630 degrees C. Chemical analysis by X-ray Photoelectron Spectroscopy of annealed samples revealed the presence of Sn inside TiO2 NTs, due to diffusion of Sn from the substrate to TiO2. For the substrate was used FTO glass whose top layer consists of SnO2 doped with F. Rutherford Backscattering Spectrometry and Time-of-Flight Elastic Recoil Detection Analysis were carried out to study the elemental depth profile of the films. It was found that the temperature of sintering controls the Sn diffusion inside TiO2 film. Sn atoms diffuse towards the TiO2 NTs surface for the samples annealed at 450 and 550 degrees C. The diffusion is however hindered in the case of the heat treatment at 630 degrees C. Besides, the Ti diffusion into the SnO2 underlayer was observed, together with the formation of TiO2/SnO2 interfaces. One then expected but not a great difference in absorption between samples, since all contained anatase phase, as confirmed by Diffuse Reflectance Spectroscopy. A higher amount of Sn was however detected for the sample annealed at 550 degrees C, which accounts for a slight red absorption shift. The importance of controlling the annealing parameters of the anodized TiO2/FTO structures was highlighted through the formation of TiO2-SnO2 interfaces and the Sn insertion from FTO, which can play an essential role in increasing the photoperformances of TiO2 NTs/FTO based structures of photovoltaic cells.
Open Access
200. Thin Film Fabrication by Pulsed Laser Deposition from TiO2 Targets in O2, N2, He, or Ar for Dye-Sensitized Solar Cells
Authors:
Albu, DF; Lungu, J; Popescu-Pelin, G; Mihailescu, CN; Socol, G; Georgescu, A; Socol, M; Banica, A; Ciupina, V; Mihailescu, IN
Published: MAR 2022, COATINGS, 12, 293, DOI: 10.3390/coatings12030293
Active semiconductor layers of TiO2 were synthesized via pulsed laser deposition in He, N-2, O-2, or Ar to manufacture DSSC structures. As-prepared nanostructured TiO2 coatings grown on FTO were photosensitized by the natural absorption of the N719 (Ruthenium 535-bis TBA) dye to fabricate photovoltaic structures. TiO2 photoanode nanostructures with increased adsorption areas of the photosensitizer (a combination with voluminous media) were grown under different deposition conditions. Systematic SEM, AFM, and XRD investigations were carried out to study the morphological and structural characteristics of the TiO2 nanostructures. It was shown that the gas nature acts as a key parameter of the architecture and the overall performance of the deposited films. The best electro-optical performance was reached for photovoltaic structures based on TiO2 coatings grown in He, as was demonstrated by the short-circuit current (Isc) of 5.40 mA, which corresponds to the higher recorded roughness (of 44 +/- 2.9 nm RMS). The higher roughness is thus reflected in a more efficient and deeper penetration of the dye inside the nanostructured TiO2 coatings. The photovoltaic conversion efficiency (eta) was 1.18 and 2.32% for the DSSCs when the TiO2 coatings were deposited in O-2 and He, respectively. The results point to a direct correlation between the electro-optical performance of the prepared PV cells, the morphology of the TiO2 deposited layers, and the crystallinity features, respectively.
Open Access
201. Dimensionality of mobile electrons at x-ray-irradiated LaAlO3/SrTiO3 interfaces
Authors:
Strocov, VN; Lechermann, F; Chikina, A; Alarab, F; Lev, LL; Rogalev, VA; Schmitt, T; Husanu, MA
Published: MAR 1 2022, ELECTRONIC STRUCTURE, 4, 015003, DOI: 10.1088/2516-1075/ac4e74
Electronic structure of LaAlO3/SrTiO3 (LAO/STO) samples, grown at low oxygen pressure and post-annealed ex situ, was investigated by soft-x-ray ARPES focussing on the Fermi momentum (k (F)) of the mobile electron system (MES). X-ray irradiation of these samples at temperatures below 100 K creates oxygen vacancies (V(O)s) injecting Ti t (2g)-electrons into the MES. At this temperature the oxygen out-diffusion is suppressed, and the V(O)s should appear mostly in the top STO layer. The x-ray generated MES demonstrates, however, a pronounced three-dimensional (3D) behavior as evidenced by variations of its experimental k (F) over different Brillouin zones. Identical to bare STO, this behavior indicates an unexpectedly large extension of the x-ray generated MES into the STO depth. The intrinsic MES in the standard LAO/STO samples annealed in situ, in contrast, demonstrates purely two-dimensional (2D) behaviour. The relevance of our ARPES data analysis is supported by model calculations to compare the intensity vs gradient methods of the k (F) determination as a function of the energy resolution ratio to the bandwidth. Based on self-interaction-corrected DFT calculations of the MES induced by V(O)s at the interface and in STO bulk, we discuss possible scenarios of the puzzling 3D-ity. It may involve either a dense ladder of quantum-well states formed in a long-range interfacial potential or, more likely, x-ray-induced bulk metallicity in STO accessed in the ARPES experiment through a short-range interfacial barrier. The mechanism of this metallicity may involve remnant V(O)s and photoconductivity-induced metallic states in the STO bulk, and even more exotic mechanisms such as x-ray induced formation of Frenkel pairs.
Open Access
202. Ferrofluids and bio-ferrofluids: looking back and stepping forward
Authors:
Socoliuc, V; Avdeev, M; Kuncser, ; Turcu, R; Tombácz, E; Vékás, L
Published: MAR 31 2022, NANOSCALE, 14, DOI: 10.1039/d1nr05841j
Ferrofluids investigated along for about five decades are ultrastable colloidal suspensions of magnetic nanoparticles, which manifest simultaneously fluid and magnetic properties. Their magnetically controllable and tunable feature proved to be from the beginning an extremely fertile ground for a wide range of engineering applications. More recently, biocompatible ferrofluids attracted huge interest and produced a considerable increase of the applicative potential in nanomedicine, biotechnology and environmental protection. This paper offers a brief overview of the most relevant early results and a comprehensive description of recent achievements in ferrofluid synthesis, advanced characterization, as well as the governing equations of ferrohydrodynamics, the most important interfacial phenomena and the flow properties. Finally, it provides an overview of recent advances in tunable and adaptive multifunctional materials derived from ferrofluids and a detailed presentation of the recent progress of applications in the field of sensors and actuators, ferrofluid-driven assembly and manipulation, droplet technology, including droplet generation and control, mechanical actuation, liquid computing and robotics.
Open Access
203. Magnetocaloric and Giant Magnetoresistance Effects in La-Ba-Mn-Ti-O Epitaxial Thin Films: Influence of Phase Transition and Magnetic Anisotropy
Authors:
Oumezzine, M; Chirila, CF; Pasuk, I; Galca, AC; Leca, A; Borca, B; Kuncser, V
Published: NOV 2022, MATERIALS, 15, 8003, DOI: 10.3390/ma15228003
Magnetic perovskite films have promising properties for use in energy-efficient spintronic devices and magnetic refrigeration. Here, an epitaxial ferromagnetic La0.67Ba0.33Mn0.95Ti0.05O3 (LBMTO-5) thin film was grown on SrTiO3(001) single crystal substrate by pulsed laser deposition. High-resolution X-ray diffraction proved the high crystallinity of the film with tetragonal symmetry. The magnetic, magnetocaloric and magnetoresistance properties at different directions of the applied magnetic field with respect to the ab plane of the film were investigated. An in-plane uni-axial magnetic anisotropy was evidenced. The LBMTO-5 epilayer exhibits a second-order ferromagnetic-paramagnetic phase transition around 234 K together with a metal-semiconductor transition close to this Curie temperature (T-C). The magnetic entropy variation under 5 T induction of a magnetic field applied parallel to the film surface reaches a maximum of 17.27 mJ/cm(3) K. The relative cooling power is 1400 mJ/cm(3) K (53% of the reference value reported for bulk Gd) for the same applied magnetic field. Giant magnetoresistance of about 82% under 5 T is obtained at a temperature close to T-C. Defined as the difference between specific resistivity obtained under 5 T with the current flowing along the magnetic easy axis and the magnetic field oriented transversally to the current, parallel and perpendicular to the sample plane, respectively, the in-plane magneto-resistance anisotropy in 5 T is about 9% near the T-C.
Open Access
204. Hybrid Nanostructures Obtained by Transport and Condensation of Tungsten Oxide Vapours onto CNW Templates
Authors:
Carpen, LG; Acsente, T; Satulu, V; Matei, E; Vizireanu, S; Bita, BI; Dinescu, G
Published: APR 2021, NANOMATERIALS, 11, 835, DOI: 10.3390/nano11040835
We present hybrid nanomaterial architectures, consisting of carbon nanowalls (CNW) templates decorated with tungsten oxide nanoparticles, synthesized using a mechanism based on tungsten oxide sublimation, vapor transport, followed by vapor condensation, in the absence or presence of plasma. The key steps in the decoration mechanism are the sublimation of tungsten oxides, when are exposed in vacuum at high temperature (800 degrees C), and their redeposition on colder surfaces (400-600 degrees C). The morphology and chemical composition of the hybrid architectures, as obtained from Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy, are discussed with respect to substrate nature and the physical conditions of synthesis. We pointed out that the decoration process is strongly dependent on the temperature of the CNW templates and plasma presence. Thus, the decoration process performed with plasma was effective for a wider range of template temperatures, in contrast with the decoration process performed without plasma. The results are useful for applications using the sensing and photochemical properties of tungsten oxides, and have also relevance for fusion technology, tungsten walls erosion and material redeposition being widely observed in fusion machines.
205. A nanoscale continuous transition from the monoclinic to ferroelectric orthorhombic phase inside HfO2 nanocrystals stabilized by HfO2 capping and self-controlled Ge doping
Authors:
Palade, C; Lepadatu, AM; Slav, A; Cojocaru, O; Iuga, A; Maraloiu, VA; Moldovan, A; Dinescu, M; Teodorescu, VS; Stoica, T; Ciurea, ML
Published: SEP 28 2021, JOURNAL OF MATERIALS CHEMISTRY C, 9, DOI: 10.1039/d1tc02921e
Orthorhombic HfO2 exhibits nanoscale ferroelectricity that opens the perspective of ultra-scalable CMOS integration of ferroelectric memories. However, many aspects of the metastable orthorhombic crystallization mechanisms still need to be elucidated and new fabrication methods are of high interest. In this paper, the atomically resolved crystal structure of HfO2 is a 3-layer structure with a Ge-rich HfO2 intermediate layer capped by a top (cap) HfO2 layer and cladded by a bottom HfO2 layer. There is a continuity of crystal growth from the top and bottom HfO2 layers into the intermediate layer. A spatial transition from a monoclinic phase to an orthorhombic phase was revealed within a region of a few atomic layers at the interface between capped and intermediate HfO2 layers. This result suggests the mechanism of orthorhombic and monoclinic phase formation by a martensitic-like transformation of the initially grown tetragonal phase. The sample fabrication method we used involved magnetron sputtering deposition of the 3-layer structures, i.e. a stack of top HfO2/Ge-rich HfO2 intermediate/bottom HfO2 layers, followed by rapid thermal annealing. It results in self-optimized orthorhombic crystallization of HfO2 by Ge nanoparticle segregation in the intermediate layer. The ferroelectric effects are revealed by polarization-voltage hysteresis loops and piezoresponse force microscopy measurements. The atomistic computations performed by using the density functional theory support the experimental results by showing that the Ge doping of HfO2 leads to orthorhombic phase stabilization and increased Berry phase polarization.
Open Access
206. Antimicrobial Activity of MgB2 Powders Produced via Reactive Liquid Infiltration Method
Authors:
Padhi, SK; Baglieri, N; Bonino, V; Agostino, A; Operti, L; Batalu, ND; Chifiriuc, MC; Popa, M; Burdusel, M; Grigoroscuta, MA; Aldica, GV; Radu, D; Badica, P; Truccato, M
Published: AUG 2021, MOLECULES, 26, 4966, DOI: 10.3390/molecules26164966
We report for the first time on the antimicrobial activity of MgB2 powders produced via the Reactive Liquid Infiltration (RLI) process. Samples with MgB2 wt.% ranging from 2% to 99% were obtained and characterized, observing different levels of grain aggregation and of impurity phases. Their antimicrobial activity was tested against Staphylococcus aureus ATCC BAA 1026, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, and Candida albicans ATCC 10231. A general correlation is observed between the antibacterial activity and the MgB2 wt.%, but the sample microstructure also appears to be very important. RLI-MgB2 powders show better performances compared to commercial powders against microbial strains in the planktonic form, and their activity against biofilms is also very similar.
207. Novel Christmas Branched Like NiO/NiWO4/WO3 (p-p-n) Nanowire Heterostructures for Chemical Sensing
Authors:
Kaur, N; Zappa, D; Maraloiu, VA; Comini, E
Published: SEP 2021, ADVANCED FUNCTIONAL MATERIALS, 31, 2104416, DOI: 10.1002/adfm.202104416
Establishing a platform comprising different nanostructured oxides is an emerging idea to develop highly sensitive and selective sensing devices. Herein, novel 3D-heterostructures (p-p-n) consisting of 1D nanowires of NiO and WO3 along with their intermediate reactive product, i.e., NiWO4 seed, are produced by a two-steps vapor phase growth method. In-depth morphological and structural investigations describing the growth mechanism of these heterostructures are presented. Finally, the p-p-n heterostructures are integrated into conductometric sensing devices and their performances are investigated toward different gases. It is observed that by modulating the charge-carrier transport with temperature, the heterostructure sensors exhibit selective behavior toward different gas analytes. Indeed, at 300 degrees C, the heterostructure sensors show relatively selective behavior toward NO2, while at 400 degrees C, high selectivity toward VOCs is observed. The improvement in sensing performances is mainly based on charge carrier transport through the two interfaces (one at WO3/NiWO4 (n-p) and the other at NiWO4/NiO (p-p)) and the modulation of charge carriers in the electron depletion layer of WO3 and hole accumulation layer of NiO and NiWO4. The remarkable performance of these complex heterostructures with low ppb-level detection limits makes them excellent candidates for chemical/ gas sensing applications in e-noses.
208. High-Performance Functionalized Magnetic Nanoparticles with Tailored Sizes and Shapes for Localized Hyperthermia Applications
Authors:
Craciunescu, I; Palade, P; Iacob, N; Ispas, GM; Stanciu, AE; Kuncser, V; Turcu, RP
Published: MAY 27 2021, JOURNAL OF PHYSICAL CHEMISTRY C, 125, DOI: 10.1021/acs.jpcc.1c01053
Magnetite (Fe3O4) and ferrite (MFe2O4, M = Mn, Zn) hydrophobic magnetic nanoparticles with various shapes and sizes were synthesized by high-temperature reaction of organic precursor solutions. Spherical, cubic, hexagonal, and octahedral shapes and sizes ranging from 10 to 100 nm were obtained. It has been proven that the reported high capability of tailoring the shape and the size of the surface-coated nanoparticles allows controlling a variety of properties that are relevant to many potential applications. Structurally well-formed hydrophobic magnetic nanoparticles with high saturation magnetization values are reported. The hydrophobic oleic acid shell was successfully transformed by a simple and environmentally friendly oxidative scission method into azelaic acid. The morphostructural characteristics, size distributions, chemical composition, and magnetic properties of the resulting hydrophilic nanoparticles were investigated by electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Mossbauer spectroscopy, superconducting quantum interference device, and vibrating sample magnetometry. Magnetic hyperthermia measurements have been performed in a specially designed sample holder placed in an inductor with copper windings assuring alternating magnetic fields of safely biological amplitude-frequency products. The optimal shape with a specific size range for nanoparticles dispersed in various carriers providing the best heating efficiency is reported.
209. Properties of Ni0.5Zn0.5Fe2O4 nanoparticles with the spinel structure synthesized via cryo-chemical method
Authors:
Timashkov, I; Shlapa, Y; Maraloiu, VA; Rajnak, M; Timko, M; Belous, A
Published: SEP 2021, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 127, 650, DOI: 10.1007/s00339-021-04795-0
Ni0.5Zn0.5Fe2O4 nanoparticles (NPs) with the spinel structure were synthesized by the cryo-chemical method with further heat treatment in the temperature range of 200-800 degrees C. Crystalline NPs began to form in one-stage and the degree of crystallinity grew with the increase of the heating temperature. Particles sizes, their size distributions and magnetization also tended to growth directly with the increasing the heating temperature of NPs. Magnetic fluids based on the obtained Ni0.5Zn0.5Fe2O4 NPs demonstrated effective and self-controlled heating up to the certain temperatures under the effect of an alternating magnetic field in contrast to known in literature Fe3O4 NPs with the spinel structure, which heated up uncontrolled to the extremely high phase transition temperature.
210. Morpho-structural properties of ZnSe, TiO2-ZnSe materials and enzymatic activity of their bioinorganic hybrids with lysozyme
Authors:
Anastasescu, C; Gifu, IC; Negrila, C; Socoteanu, R; Atkinson, I; Calderon-Moreno, JM; Munteanu, C; Plavan, G; Strungaru, SA; Cheatham, B; Malaroiu, AV; Teodorescu, VS; Anastasescu, M; Zaharescu, M; Balint, I; Lazarescu, V
Published: OCT 2021, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 272, 115350, DOI: 10.1016/j.mseb.2021.115350
Structural and functional changes induced by TiO2 addition to spherical zinc selenide together with lysozyme adsorption lead to valuable bioinorganic catalysts with enhanced activity. Spherical zinc selenide and its composite with TiO2 were obtained by hydrothermal method and subsequently modified by lysozyme adsorption. Morphological, structural and functional characteristics of zinc selenide based materials (ZnSe, TiO2-ZnSe) and their hybrids with lysozyme (Lys/ZnSe, Lys/TiO2-ZnSe) were investigated. TiO2 addition to ZnSe results in significant changes of surface composition, electrochemical behavior and lysozyme retention capacity. The lysozyme modified ZnSe and TiO2-ZnSe surfaces doubles the biocatalysts efficiency for 4-Methylumbelliferyl p-D-N,N',N ''-triacetylchitotrioside hydrolysis reaction compared to free lysozyme.
Open Access
211. Advancements on Basic Working Principles of Photo-Driven Oxidative Degradation of Organic Substrates over Pristine and Noble Metal-Modified TiO2. Model Case of Phenol Photo Oxidation
Authors:
Sandulescu, A; Anastasescu, C; Papa, F; Raciulete, M; Vasile, A; Spataru, T; Scarisoreanu, M; Fleaca, C; Mihailescu, CN; Teodorescu, VS; Spataru, N; Zaharescu, M; Balint, I
Published: APR 2021, CATALYSTS, 11, 487, DOI: 10.3390/catal11040487
The specific roles played by both support and noble metals in light absorption, charge separation, and the formation of center dot OH and O-2(-) (ROS) are analyzed for light-triggered oxidation of phenol (Ph) over pristine and over noble metal (Ag, Au, Pt) -loaded TiO2. Experiments show that the supported noble metals act as a light visible absorber, assist the separation of photo-charges and reduction of O-2 to O-2(-). The O-2(-) oxidizes mildly Ph to oxygenated products (hydroquinone, benzoquinone, and 1,2-dihydroxibenzene). In a parallel process, center dot OH radicals, yielded by TiO2, mineralize Ph to CO2 by fast reaction sequences. Radical quenching and photo electrochemical measurements (surface photovoltage) confirm independently that the production of center dot OH and O-2(-) scale with oxidative conversion of Ph. The selectivity to CO2 and mild oxidation products is the result of the interplay between catalyst activity for center dot OH and for O-2(-) production.
212. Hard/soft effects of multivalence co-dopants in correlation with their location in PZT ceramics
Authors:
Amarande, L; Cioangher, MC; Toma, V; Miclea, CF; Stefan, M; Pasuk, I; Iuga, AR; Negrila, C; Matei, E; Palici, AM; Joita, AC
Published: DEC 1 2021, CERAMICS INTERNATIONAL, 47, DOI: 10.1016/j.ceramint.2021.08.243
Piezoelectric hard/soft effects of multivalence co-dopants (Sb and Mn) in correlation with their location in the lattice, were investigated in PZT ceramics, prepared by conventional ceramic technology, with the following compositions: Pb0.98Sr0.02 ((Ti0.49Zr0.51)(1-0.015-x)Mn0.015Sbx)O-3 with x = 0, 0.005, 0.01, 0.02, 0.03, where antimony was initially assumed to substitute for Ti/Zr ions. The antimony valence state was found to be +3 in all samples by X-ray Photoelectron Spectroscopy investigations. The Electron Paramagnetic Resonance spectra evidenced a steep enhancement of the Mn2+ concentration upon increasing antimony doping level, explained by a charge compensation mechanism, between the Sb3+ ions substituting Pb2+ at the A-sites and the Mn2+ ions, localized at the B-sites. The incorporation of Sb3+ at the A-site of the PZT lattice is also supported by the variation of the lattice parameters, determined by X-ray Diffraction, with the increasing Sb concentration. The investigation of the dielectric, electromechanical and ferroelectric properties evidenced a hard piezoelectric behavior, mainly attributed to the presence of large sized Mn2+ ions, localized at B-sites. Our results prove that the piezoelectric hard/soft response is decisively influenced by the interplay between multiple valence states and locations of the co-dopants, on one hand, and the charge compensation mechanisms, on the other hand. This provides indirect information about the location of some co-dopants which can substitute for both cationic sites in the PZT based ceramics.
213. Potassium-containing triple-cation mixed-halide perovskite materials: Toward efficient and stable solar cells
Authors:
Derbali, S; Nouneh, K; Florea, M; Leonat, LN; Stancu, V; Tomulescu, AG; Galca, AC; Secu, M; Pintilie, L; Touhami, ME
Published: MAR 25 2021, JOURNAL OF ALLOYS AND COMPOUNDS, 858, 158335, DOI: 10.1016/j.jallcom.2020.158335
In this paper, potassium based triple cation mixed-halide perovskite films were explored in order to enhance the stability and photovoltaic performance of perovskite based solar cells. It was found that adding potassium (K+) to a double cation mixed halide perovskite (FA(0.80)MA(0.20)PbI(2.8)Cl(0.2)), structural, morphological and optoelectronic properties of perovskites are improved. The perovskite films were prepared by one-step spin coating method with and without K+ and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL). The results indicate that potassium incorporation reduces significantly the yellow non-perovskite delta-phase formation and improves the perovskite film quality, thus contributing to the reduction of hysteresis, improves the stability and increases the PCE up to 12.51%. Furthermore, the doped devices exhibit reduced hysteresis and provide remarkable shelf stability by retaining more than 70% of the initial efficiency with low humidity over 850 h. (C) 2020 Elsevier B.V. All rights reserved.
Open Access
214. MgB2 powders and bioevaluation of their interaction with planktonic microbes, biofilms, and tumor cells
Authors:
Badica, P; Batalu, ND; Chifiriuc, MC; Burdusel, M; Grigoroscuta, MA; Aldica, G; Pasuk, I; Kuncser, A; Enculescu, M; Popa, M; Marutescu, LG; Gheorghe, I; Thamer, O; Bleotu, C; Pircalabioru, GG; Operti, L; Bonino, V; Agostino, A; Truccato, M
Published: MAY-JUN 2021, JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 12, DOI: 10.1016/j.jmrt.2021.04.003
Commercial nanopowders of MgB2 were characterized from the viewpoint of granulometric distribution, structure, microstructure, and pH behavior in water. The powders are very different: a higher amount of the MgB2 phase with a lower tendency for agglomeration determines a higher rate of pH-increase. A higher rate of pH-increase usually produces a stronger antimicrobial activity against Staphylococcus aureus, Enterococcus faecium, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, and Candida parapsilosis reference strains. The variation of the pH-increase rate suggests the possibility of temporo-spatial control of MgB2 bioactivity, although the contribution of other factors should not be neglected. Remarkably, the efficiency of the MgB2 powders is higher against biofilms than on microbes in the planktonic state. Further, our experiments confirm the antimicrobial efficiency of MgB2 in the in vitro tests against 29 methicillin resistant clinical S. aureus isolates and 33 vancomycin resistant E. faecium/faecalis strains, but in this case the biofilms are more resistant than planktonic cells. The MgB2 treatment of infected mice led to a significant decrease of E. coli colonization in liver, spleen and peritoneal liquid and it also caused changes in the intestinal microbiota. The activity of powders on HeLa and HT-29 tumor cell lines was assessed by inverted microscopy, flow cytometry, and evaluation of the cellular cycle. MgB2 inhibits tumor cell growth influencing DNA synthesis (S-phase). The obtained results indicate that the tested powders could provide promising solutions for the development of large-spectrum multifunctional antimicrobial and anti-biofilm agents, and/or for anti-cancer therapies. (C) 2021 The Authors. Published by Elsevier B.V.
215. Operation of a magnetron sputtering gas aggregation cluster source in a plasma jet regime for synthesis of core-shell nanoparticles
Authors:
Acsente, T; Istrate, MC; Satulu, V; Bita, B; Dinescu, G
Published: JAN 14 2021, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 54, 02LT01, DOI: 10.1088/1361-6463/abbb05
Operation of a magnetron sputtering gas aggregation cluster source in a plasma jet regime is presented. In specific experimental conditions, the plasma extends from the inside of the cluster source in the deposition chamber as a plasma jet, transporting also the nanoparticles (NPs) produced in the cluster source. The chemistry of the NP surface is modified in-flight by injecting a chemical precursor in the plasma jet, resulting in core-shell NPs. Also, the plasma jet presents a low gas temperature, safely interacting with materials sensitive to thermal degradation (like polymers). These findings prove the potential of the presented plasma jet for applications in nanotechnology.
216. Optical, microstructural and vibrational properties of sol-gel ITO films
Authors:
Nicolescu, M; Anastasescu, M; Calderon-Moreno, JM; Maraloiu, AV; Teodorescu, VS; Preda, S; Predoana, L; Zaharescu, M; Gartner, M
Published: APR 2021, OPTICAL MATERIALS, 114, 110999, DOI: 10.1016/j.optmat.2021.110999
The aim of this paper is to prepare multi-layered ITO thin films by a low cost and environmental-friendly method for different applications (optoelectronics, sensors, etc.). ITO films with 15 layers were obtained by successive depositions using the sol-gel & dip-coating method on three different substrates: glass, SiO2/glass and SiO2/Si. Comparative structural, morphological and optical characterization were performed by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), Cross Section Transmission Electron Microscopy (XTEM) coupled with Selected Area Electron Diffraction (SAED), Infrared Spectroscopic Ellipsometry (IRSE) and Raman spectroscopy analyses. The optical constants (refractive index n and extinction coefficient k) were determined in a large spectral range (300-27500 cm-1) by spectroscopic ellipsometry (SE). The thicknesses determined by SE were confirmed by HRTEM (High Resolution TEM) measurements which also presents in detail the textural properties of the ITO films at nanometric level. A comparison between IRSE and Raman analysis in the infrared active region was presented.
Open Access
217. Nanocrystallized Ge-Rich SiGe-HfO2 Highly Photosensitive in Short-Wave Infrared
Authors:
Palade, C; Lepadatu, AM; Slav, A; Teodorescu, VS; Stoica, T; Ciurea, ML; Ursutiu, D; Samoila, C
Published: NOV 2021, MATERIALS, 14, 7040, DOI: 10.3390/ma14227040
Group IV nanocrystals (NCs), in particular from the Si-Ge system, are of high interest for Si photonics applications. Ge-rich SiGe NCs embedded in nanocrystallized HfO2 were obtained by magnetron sputtering deposition followed by rapid thermal annealing at 600 & DEG;C for nanostructuring. The complex characterization of morphology and crystalline structure by X-ray diffraction, mu-Raman spectroscopy, and cross-section transmission electron microscopy evidenced the formation of Ge-rich SiGe NCs (3-7 nm diameter) in a matrix of nanocrystallized HfO2. For avoiding the fast diffusion of Ge, the layer containing SiGe NCs was cladded by very thin top and bottom pure HfO2 layers. Nanocrystallized HfO2 with tetragonal/orthorhombic structure was revealed beside the monoclinic phase in both buffer HfO2 and SiGe NCs-HfO2 layers. In the top part, the film is mainly crystallized in the monoclinic phase. High efficiency of the photocurrent was obtained in a broad spectral range of curves of 600-2000 nm at low temperatures. The high-quality SiGe NC/HfO2 matrix interface together with the strain induced in SiGe NCs by nanocrystallization of both HfO2 matrix and SiGe nanoparticles explain the unexpectedly extended photoelectric sensitivity in short-wave infrared up to about 2000 nm that is more than the sensitivity limit for Ge, in spite of the increase of bandgap by well-known quantum confinement effect in SiGe NCs.
218. Tuning the magnetic properties of amorphous Fe-Gd thin films by variation of thickness and composition
Authors:
Locovei, C; Iacob, N; Schinteie, G; Stanciu, AE; Leca, A; Kuncser, V
Published: DEC 2021, HYPERFINE INTERACTIONS, 242, 44, DOI: 10.1007/s10751-021-01763-1
Fe-Gd amorphous thin films of different compositions and thicknesses were analyzed with respect to their magnetic and magneto-optical behavior. By preparing samples with the same Fe/Gd elemental ratio at different thicknesses, and of various Fe/Gd ratios at constant thickness, respectively, we were able to show the influences of these two parameters on the interconnected behavior of the two magnetic sub-lattices, one of Fe and the other of Gd, which are antiferromagnetically coupled. Magneto-Optical Kerr Effect (MOKE) measurements revealed reversed hysteresis loops for sample compositions crossing the magnetic compensation point. Temperature dependent magnetization curves highlighted the variation of the overall net contribution of the two magnetic sub-lattices by changing either the Fe/Gd elemental ratio or the film thickness. Fe-57 Conversion Electron Mossbauer (CEM) spectra give additional support to the specific magnetic behavior evidenced by temperature and field dependent Superconducting Quantum Interference Device (SQUID) magnetometry.
219. Zn-Fe-oxide nanostructures of different iron concentrations for multifunctional applications: properties and precursor influence
Authors:
Mihalache, V; Negrila, C; Mercioniu, I; Iacob, N; Kuncser, V
Published: AUG 14 2021, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 23, DOI: 10.1039/d1cp01002f
Zn-Fe-O nanoparticle systems (Z3F, Z20F and Z60F) were produced by changing the Zn:Fe ratio (0.97 : 0.03, 0.8 : 0.2 and 0.4 : 0.6 in at%, respectively) in Zn(ii)-Fe(iii)-carboxylate precursors. According to X-ray diffraction, Z60F is nearly single-phase ZnFe2O4 (5.9 nm crystallite size), Z20F is a ZnO/ZnFe2O4 nanocomposite consisting of 48.8% ZnFe2O4 (4.7 nm crystallite size), and Z3F is apparently pure ZnO (9.5 nm). We found evidence for a ZnFe2O4 spinel of high inversion degree (80-100%) and with superparamagnetic (SPM) behaviour at room temperature in all three samples by a remarkable correlation between HRTEM, FTIR, XPS, Mossbauer and magnetization analyses. Iron modifies the decomposition process of the precursor and enhances its viscosity, which appears to favour the separation of Zn- and Fe-rich phases. As a consequence, two-phase systems of individual nanocrystals/nanoparticles (ZnO and ZnFe2O4) are formed. The large anisotropy constant, 10(6)-10(7) erg cm(-3), of the ZnFe2O4 nanoparticles and the concentration dependence of their magnetic energy barrier are explained in terms of interparticle interactions interlinked with finite size effects and high inversion degree; these factors also control the other parameters of importance for applications, including the blocking temperature (13-111 K), saturation magnetization (1.08-17.7 emu g(-1) at 300 K, 4.6-44.8 emu g(-1) at 5 K) and coercivity (85.4-491 Oe at 5 K). Magnetic dynamic results, particularly modelled by the Neel-Brown and Vogel-Fulcher laws, yield fitting parameters which validate the presence of concentration-dependent dipole-like interactions between ZnFe2O4 nanoparticles. A fraction of iron was found in the Fe2+ state, presumably substituting for Zn2+ in zinc oxide; however, the samples behave like ZnFe2O4 SPM nanoclusters/nanoparticles dispersed in a nonmagnetic ZnO particle assembly, rather than Zn(Fe)O dilute magnetic semiconductors. The relevance of the properties of the investigated material for specific applications is highlighted throughout the manuscript.
Open Access
220. Homogeneous versus Inhomogeneous Polarization Switching in PZT Thin Films: Impact of the Structural Quality and Correlation to the Negative Capacitance Effect
Authors:
Pintilie, L; Boni, GA; Chirila, CF; Stancu, V; Trupina, L; Istrate, CM; Radu, C; Pintilie, I
Published: AUG 2021, NANOMATERIALS, 11, 2124, DOI: 10.3390/nano11082124
Polarization switching in ferroelectric films is exploited in many applications, such as non-volatile memories and negative capacitance field affect transistors. This can be inhomogeneous or homogeneous, depending on if ferroelectric domains are forming or not during the switching process. The relation between the polarization switching, the structural quality of the films and the negative capacitance was not studied in depth. Here, Pb(Zr0.2Ti0.8)O-3 (PZT) layers were deposited by pulse laser deposition (PLD) and sol-gel (SG) on single crystal SrTiO3 (STO) and Si substrates, respectively. The structural quality was analyzed by X-ray diffraction and transmission electron microscopy, while the electric properties were investigated by performing hysteresis, dynamic dielectric measurements, and piezo-electric force microscopy analysis. It was found that the PZT layers grown by PLD on SRO/STO substrates are epitaxial while the layers deposited by SG on Pt/Si are polycrystalline. The polarization value decreases as the structure changes from epitaxial to polycrystalline, as well as the magnitude of the leakage current and of the differential negative capacitance, while the switching changes from homogeneous to inhomogeneous. The results are explained by the compensation rate of the depolarization field during the switching process, which is much faster in epitaxial films than in polycrystalline ones.
Open Access
221. Semiconductor/relaxor 0-3 type composites: A novel strategy for energy storage capacitors
Authors:
Jayakrishnan, AR; Silva, JPB; Kamakshi, K; Annapureddy, V; Mercioniu, IF; Sekhar, KC
Published: MAR 2021, JOURNAL OF SCIENCE-ADVANCED MATERIALS AND DEVICES, 6, DOI: 10.1016/j.jsamd.2020.09.012
We report a novel strategy to enhance the dielectric breakdown strength and the energy storage performance of lead-free relaxor ferroelectric ceramics through the fabrication of semiconductor/relaxor 0-3 type composites based on 0.6Ba(Zr0.2Ti0.8)O-3-0.4(Ba0.7Ca0.3)TiO3 [BZCT] and ZnO. X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) measurements confirm the formation of semiconductor/relaxor 0-3 type composites, in which ZnO particles are randomly distributed at the grain boundaries of BZCT. Further, the XRD analysis suggests a structural phase change from a tetragonal to a pseudocubic phase as the ZnO content increases from 0 to 5 wt. % in BZCT/ZnO composites. The pseudocubic phase favors the relaxor behavior of the composites as is evident from dielectric studies. The polarization-electric field (P-E) loops reveal the ferroelectric nature of the BZCT/ZnO composites. The energy storage properties of BZCT/ZnO composite ceramics as a function of different wt. % of ZnO are found to be optimum at 1 wt. % with a recoverable energy density of 2.61 J/cm(3) and an efficiency of 74.2%, at an electric field of 282 kV/cm. Besides, an enhancement of 166% in the electric breakdown and 220% in the recoverable energy density was achieved compared to the BZCT ceramics due to the improved density and the large value of Delta P = P-m - P-r (25.55 mu C/cm(2)). Therefore, this work evidences that the formation of the semiconductor/relaxor 0-3 type composites can be an effective way to significantly improve the energy storage performance of lead-free relaxor ferroelectric ceramics. (C) 2020 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
222. Effects of Ge-related storage centers formation in Al2O3 enhancing the performance of floating gate memories
Authors:
Stavarache, I; Cojocaru, O; Maraloiu, VA; Teodorescu, VS; Stoica, T; Ciurea, ML
Published: MAR 15 2021, APPLIED SURFACE SCIENCE, 542, 148702, DOI: 10.1016/j.apsusc.2020.148702
In this paper, we report studies on Al2O3/Ge/Al2O3 trilayer memory structures deposited by magnetron sputtering at room temperature on p-Si substrates coated with 3 nm SiO2. The changes of the structure, morphology and memory properties induced by rapid thermal annealing (RTA) in a broad temperature range 550-900 degrees C have been carefully investigated. High resolution transmission electron microscopy (HRTEM) revealed the existence of distinct RTA effects for different temperature ranges, in correlation with memory properties measured on Al/Al2O3/Ge/Al2O3/SiO2/p-Si/Al devices. Thus, at temperatures smaller than 650 degrees C, Ge diffuses into adjacent Al2O3, the layers remaining amorphous. The memory window increases from as-deposited samples to those annealed at 600 degrees C reaching the maximum of 5.4 V. After RTA at 700 degrees C, Ge nanocrystals (NCs) in intermediate Ge layer and Ge-rich amorphous nanoparticles in Al2O3 tunnel oxide are formed. Increasing RTA temperature to 800 and 900 degrees C, Ge NCs are no longer formed due to Ge strong diffusion. Instead, Ge-rich mixed GeAl oxide NCs of unknown crystalline structure are evidenced by HRTEM. The memory window continuously decreases with annealing temperature in the range 650-900 degrees C. The ON (OFF) charge loss of only 11% (9.8%) was found by extrapolation to 10 years.
223. Alternative lignopolymer-based composites useful as enhanced functionalized support for enzymes immobilization
Authors:
Lite, C; Ion, S; Tudorache, M; Zgura, I; Galca, AC; Enache, M; Maria, GM; Parvulescu, VI
Published: NOV 1 2021, CATALYSIS TODAY, 379, DOI: 10.1016/j.cattod.2020.05.060
Amino-derivatized lignocomposite (ADL-composite) has been designed as an artificial lignin polymer (P1) of monolignol (coniferyl alcohol, CA) enhanced by aniline insertion (P2). The derivatized lignopolymeric (P2) layer covered the surface of a methacrylate particles (SC2/SC6) functionalized previously with amino phenolic crosslinker (p-phenylenediamine (p-Ph-2-NH2) or p-amino-2-hydroxybenzoic acid (p-NH2-SalA)). One-pot biocatalytic approach allowed to combine the preparation of the polymeric materials and also its attachment on the particles surface. Thus, the monolignol (CA) will be oxi-copolymerized together with aniline on the amino prefunctionalized support surface. The oxidation process was performed using H2O2 reagent and catalyzed by peroxidase enzyme (horseradish peroxidase, HRP). The biocatalytic process was evaluated in term of aromatic monomers (CA and aniline) conversion. The chemical structure and properties of the resulted ADL-composites were investigated using specific techniques (e.g. FTIR, TPD, TGA, static contact angle, elemental analysis, and gel permeation chromatography). Attachment of P1/P2 polymer on the particles improved the hydrophobicity and also the basicity of the composite surface. Lipase enzyme was immobilized on the ADL-composites for testing the applicability of ADL-composites for biocatalyst preparation. SEM analysis allowed to notice the modification of ADL-composites surface after enzyme immobilization. Immobilized lipase exhibited better activity compared with free lipase demonstrating the efficiency of ADL-composite as support for enzyme immobilization.
224. Magnesium-silver cathodes for efficient charge injection into Organic Light Emitting Diodes deposited by LTVA method
Authors:
Vladoiu, R; Mandes, A; Dinca, V; Kudrna, P; Tichy, M; Polosan, S
Published: JUL 15 2021, JOURNAL OF ALLOYS AND COMPOUNDS, 869, 159364, DOI: 10.1016/j.jallcom.2021.159364
The Laser-induced Thermionic Vacuum Arc method was applied to optimize magnesium-silver (Mg:Ag) alloys, which can be potentially used as stable metallic cathodes for optoelectronic devices. Besides lowering the cathode work function given by the magnesium that improves the electron injection, Mg:Ag alloys induce a higher electrical conductivity, estimated here to be 3.42 x 10(7) S m(-1) for AgMg3, compared with 2.64 x 10(7) S m(-1), estimated here for Mg thin films. Mg:Ag alloys avoid the critical issue of Mg oxidation for better charge injection in optoelectronic active layers. By improving the Thermionic Vacuum Arc technique with the laser beam, this method enables the control of the silver concentration in these alloys due to photonic processes. The uniformity of metallic thin films, compactness, and high purity are the primary advantages of the Laser-induced Thermionic Vacuum Arc method. (C) 2021 Elsevier B.V. All rights reserved.
Open Access
225. Beyond Nitrogen in the Oxygen Reduction Reaction on Nitrogen-Doped Carbons: A NEXAFS Investigation
Authors:
Tanasa, E; Maxim, FI; Erniyazov, T; Iacob, MT; Skála, T; Tanase, LC; Ianasi, C; Moisescu, C; Miron, C; Ardelean, I; Antohe, VA; Fagadar-Cosma, E; Stamatin, SN
Published: MAY 2021, NANOMATERIALS, 11, 1198, DOI: 10.3390/nano11051198
Polymer electrolyte membrane fuel cells require cheap and active electrocatalysts to drive the oxygen reduction reaction. Nitrogen-doped carbons have been extensively studied regarding their oxygen reduction reaction. The work at hand looks beyond the nitrogen chemistry and brings to light the role of oxygen. Nitrogen-doped nanocarbons were obtained by a radio-frequency plasma route at 0, 100, 250, and 350 W. The lateral size of the graphitic domain, determined from Raman spectroscopy, showed that the nitrogen plasma treatment decreased the crystallite size. Synchrotron radiation photoelectron spectroscopy showed a similar nitrogen chemistry, albeit the nitrogen concentration increased with the plasma power. Lateral crystallite size and several nitrogen moieties were plotted against the onset potential determined from oxygen reduction reaction curves. There was no correlation between the electrochemical activity and the sample structure, as determine from Raman and synchrotron radiation photoelectron spectroscopy. Near-edge X-ray absorption fine structure (NEXAFS) was performed to unravel the carbon and nitrogen local structure. A difference analysis of the NEXAFS spectra showed that the oxygen surrounding the pyridinic nitrogen was critical in achieving high onset potentials. The work shows that there were more factors at play, other than carbon organization and nitrogen chemistry.
226. Design of highly transparent conductive optical coatings optimized for oblique angle light incidence
Authors:
Nedelcu, N; Chiroiu, V; Munteanu, L; Girip, I; Rugina, C; Lorinczi, A; Matei, E; Sobetkii, A
Published: AUG 2021, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 127, 575, DOI: 10.1007/s00339-021-04726-z
In this paper, three deposition techniques are combined to create a window material with high average transmission at oblique angles of incidence. Spectrophotometry and ellipsometry measurements, respectively, yield the optical constants n and k. In contrast with other analyses on the subject, a high average transmission, higher than 91% in the 450-900 nm spectral range, is obtained at incident angles of 20-25 degrees. The refractive index and extinction coefficient are determined by the Swanepoel method. The iterative optimization performed using the OpenFilters software leads to an antireflection (AR) multilayer with low reflection and high transmission. The surface quality of the films was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), which revealed compact, continuous, and smooth films.
Open Access
227. All-Oxide p-n Junction Thermoelectric Generator Based on SnOx and ZnO Thin Films
Authors:
Vieira, EMF; Silva, JPB; Veltruská, K; Istrate, CM; Lenzi, V; Trifiletti, V; Lorenzi, B; Matolín, V; Ghica, C; Marques, L; Fenwick, O; Goncalves, LM
Published: JUL 28 2021, ACS APPLIED MATERIALS & INTERFACES, 13, DOI: 10.1021/acsami.1c09748
Achieving thermoelectric devices with high performance based on low-cost and nontoxic materials is extremely challenging. Moreover, as we move toward an Internet-of-Things society, a miniaturized local power source such as a thermoelectric generator (TEG) is desired to power increasing numbers of wireless sensors. Therefore, in this work, an all-oxide p-n junction TEG composed of low-cost, abundant, and nontoxic materials, such as n-type ZnO and p-type SnOx thin films, deposited on borosilicate glass substrate is proposed. A type II heterojunction between SnOx and ZnO films was predicted by density functional theory (DFT) calculations and confirmed experimentally by X-ray photoelectron spectroscopy (XPS). Moreover, scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDS) show a sharp interface between the SnOx and ZnO layers, confirming the high quality of the p-n junction even after annealing at 523 K. ZnO and SnOx thin films exhibit Seebeck coefficients (alpha) of similar to 121 and similar to 258 mu V/K, respectively, at 298 K, resulting in power factors (PF) of 180 mu W/m K-2 (for ZnO) and 37 mu W/m K-2 (for SnOx). Moreover, the thermal conductivities of ZnO and SnOx films are 8.7 and 1.24 W/m K, respectively, at 298 K, with no significant changes until 575 K. The four pairs all-oxide TEG generated a maximum power output (P-out) of 1.8 nW (approximate to 126 mu W/cm(2)) at a temperature difference of 160 K. The output voltage (V-out) and output current (I-ou(t)) at the maximum power output of the TEG are 124 mV and 0.0146 mu A, respectively. This work paves the way for achieving a high-performance TEG device based on oxide thin films.
Open Access
228. Accidental Impurities in Epitaxial Pb(Zr0.2Ti0.8)O3 Thin Films Grown by Pulsed Laser Deposition and Their Impact on the Macroscopic Electric Properties
Authors:
Boni, GA; Chirila, CF; Stancu, V; Amarande, L; Pasuk, I; Trupina, L; Istrate, CM; Radu, C; Tomulescu, A; Neatu, S; Pintilie, I; Pintilie, L
Published: MAY 2021, NANOMATERIALS, 11, 1177, DOI: 10.3390/nano11051177
Structural and electrical properties of epitaxial Pb(Zr0.2Ti0.8)O-3 films grown by pulsed laser deposition from targets with different purities are investigated in this study. One target was produced in-house by using high purity precursor oxides (at least 99.99%), and the other target was a commercial product (99.9% purity). It was found that the out-of-plane lattice constant is about 0.15% larger and the a domains amount is lower for the film grown from the commercial target. The polarization value is slightly lower, the dielectric constant is larger, and the height of the potential barrier at the electrode interfaces is larger for the film deposited from the pure target. The differences are attributed to the accidental impurities, with a larger amount in the commercial target as revealed by composition analysis using inductive coupling plasma-mass spectrometry. The heterovalent impurities can act as donors or acceptors, modifying the electronic characteristics. Thus, mastering impurities is a prerequisite for obtaining reliable and reproducible properties and advancing towards all ferroelectric devices.
Open Access
229. Immobilized Antibodies on Mercaptophenylboronic Acid Monolayers for Dual-Strategy Detection of 20S Proteasome
Authors:
Barsan, MM; Sanz, CG; Onea, M; Diculescu, VC
Published: APR 2021, SENSORS, 21, 2702, DOI: 10.3390/s21082702
A dual strategy for the electrochemical detection for 20S proteasome (20S) is proposed, based on the oriented immobilization of a capture monoclonal antibody (Ab beta) on a self-assembled monolayer of 4-mercaptophenylboronic acid (4-MPBA) on gold electrodes, which led to the Au/4-MPBA/Ab beta immunosensor. The methodology comprises the correlation of 20S concentration with (i) its proteolytic activity toward the Z-LLE-AMC substrate, using the Au/4-MPBA/Ab beta/20S, and (ii) the enzymatic activity of an alkaline phosphatase (AlkP) from the AlkP-labeled secondary antibody (Ab(core)-AlkP), which involves the conversion of aminophenylphosphate to the electroactive aminophenol using Au/4-MPBA/Ab beta/20S/Ab(core)-AlkP. The step-by-step construction of the immunosensor and the interactions at its surface were evaluated by surface plasmon resonance and gravimetric analysis with quartz crystal microbalance, showing a high affinity between both antibodies and 20S. Morphological analysis by scanning electron microscopy demonstrated a pattern of parallel lines upon immobilization of Ab beta on 4-MPBA and morphological changes to a well-organized granular structure upon binding of 20S. A voltametric and impedimetric characterization was performed after each step in the immunosensor construction. The two detection strategies were evaluated. It was shown that the immunosensor responds linearly with 20S concentration in the range between 5 and 100 mu g mL(-1), which corresponds to proteasome levels in serum in the case of diverse pathological situations, and LoD values of 1.4 and 0.2 mu g mL(-1) were calculated for the detection strategies. The immunosensor was applied to the detection of 20S in serum samples with recovery values ranging from 101 to 103%.
Open Access
230. In Vitro Evaluation of MgB2 Powders as Novel Tools to Fight Fungal Biodeterioration of Heritage Buildings and Objects
Authors:
Gheorghe, I; Avram, I; Corbu, VM; Marutescu, L; Popa, M; Balotescu, I; Blajan, I; Mateescu, V; Zaharia, D; Dumbrava, AS; Zetu, OE; Pecete, I; Cristea, VC; Batalu, D; Grigoroscuta, MA; Burdusel, M; Aldica, GV; Badica, P; Datcu, AD; Ianovici, N; Bleotu, C; Lazar, V; Ditu, LM; Chifiriuc, MC
Published: JAN 13 2021, FRONTIERS IN MATERIALS, 7, 601059, DOI: 10.3389/fmats.2020.601059
The 17th-19th century wooden and stone churches are an iconic symbol for the Romanian national heritage, raising urgent needs for the development of efficient and ecofriendly restoration and preservation solutions. Nanotechnology has a great but largely unexplored potential in this field, providing new tools and methods to achieve higher consolidation and protection efficiency, mainly due to the ability of nanoparticles to inhibit the growth and metabolic activity of different biodeteriorating agents, including fungi. The purpose of the present study was to report for the first time on the efficiency of MgB2 materials, mainly prized for their practical superconducting properties, against a large collection of filamentous fungal strains recently isolated from biodeteriorated wooden and stone heritage objects. Four types of MgB2 powders, with a crystallite size of 42-113 nm, were tested by qualitative (on 149 strains) and quantitative (on 87 strains) assays. The cytotoxicity was evaluated by the microscopic analysis of SiHa cells morphology and Hep2 cell cycle analysis and the ecotoxicity by the Allium test. The tested filamentous fungal strains belonged to 11 different genera, and those isolated from mural paintings and wooden objects exhibited the best capacity to colonize the inert substratum. All MgB2 powders exhibited similar and relatively low minimal inhibitory concentrations (MIC) values against the Aspergillus and Penicillium isolates, which were predominated among isolates. From the tested powders, PVZ and CERAC proved to be more efficient against the strains isolated from stone and wood materials, while LTS was active against the fungal strains colonizing the mural paintings and museum objects. The cytotoxicity results indicated that the tested powders are toxic for the human cells at concentrations higher than 50 mu g/ml, but, however, the very short lifetime of these NPs prevents their accumulation in the natural environment and, thus, the occurrence of toxic effects. The tested powders proved to be ecofriendly at the active antifungal concentrations, as suggested by the phytotoxicity test results. Taken together, our results suggest the potential of the MgB2 materials for the development of environmentally safe antifungal substances, which can be used in the control of the material cultural heritage biodeterioration process.
Open Access
231. Structural, functional properties and enhanced thermal stability of bulk graded (Ba,Sr)TiO3 structures obtained by spark plasma sintering
Authors:
Botea, M; Pintilie, I; Surdu, VA; Stanciu, CA; Trusca, RD; Vasile, BS; Patru, R; Ianculescu, AC; Pintilie, L
Published: MAY-JUN 2021, JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 12, DOI: 10.1016/j.jmrt.2021.04.011
Graded structures with different architectures were obtained by spark plasma sintering from (Ba1-xSrx)TiO3 (BST, x = 0.10; 0.20; 0.30) powders. The presence of the composition gradient was confirmed by structural and compositional investigations using X-ray diffraction and electron microscopy combined with energy dispersive X-ray spectroscopy. The concentration gradient was either asymmetric (3 layers, starting with x = 0.10 and ending with x = 0.30) or symmetric (5 or 6 layers, starting and ending with x = 0.10, and with a single or double x = 0.30 layer in the middle, respectively). Electrical measurements reveal a decrease of the dielectric constant with increasing the number of the layers. It was found that the symmetric graded structure with 6 layers has the best thermal stability of both, the dielectric constant (variation of only 8% between zero and 100 degrees C) and the py-roelectric coefficient (6% variation between zero and 80 degrees C). In addition, an enhancement of the pyroelectric signal for frequencies above 100 Hz is obtained in symmetric structures, an effect that is attributed to the additive contributions of the signals originated from the layers with different Sr content. (C) 2021 The Author(s). Published by Elsevier B.V.
Open Access
232. Engineering hydrogenation active sites on graphene oxide and N-doped graphene by plasma treatment
Authors:
Magureanu, M; Mandache, NB; Rizescu, C; Bucur, C; Cojocaru, B; Man, IC; Primo, A; Parvulescu, V; Garcia, H
Published: JUN 15 2021, APPLIED CATALYSIS B-ENVIRONMENT AND ENERGY, 287, 119962, DOI: 10.1016/j.apcatb.2021.119962
Graphene oxide (GO) and N-doped graphene [(N)G] graphenes were submitted to H-2 glow discharge under different discharge regimes, in both the negative glow and positive column plasma regions. The resulted catalysts were fully characterized using several techniques such as Raman, DRIFT and XPS spectroscopy, powder X-ray diffraction, H-2 pulse chemisorption and H-2-, CO2- and NH3-TPD experiments. Density functional theory calculations were performed taking a slab model of graphene sheet with an optimized C-C bond length (1.426 angstrom) and a 16 angstrom vacuum layer between sheets. An overview of these characterizations showed that the O/C atomic ratio of GO is influenced by the plasma regime, indicating the occurrence of O removal, as also predicted by DFT calculations. In the case of (N)G, the plasma treatment also removes pyridinic N with an increase of the C/N ratio. The efficiency of the plasma modification has been checked through catalytic tests in hydroisomerization of 1-octene and hydrogenation of alpha-methyl-styrene. Contrarily to classical thermal activation requiring high temperatures, the generation of the defects by treating with plasma occurs at voltages in the range of 2 5 kV. In consequence, the hydrogenation and isomerization of alkenes resulted with high yields and good selectivities. Graphene prepared from sodium alginate from brown algae was considered as reference in these investigations.
Open Access
233. Micrometer Sized Hexagonal Chromium Selenide Flakes for Cryogenic Temperature Sensors
Authors:
Buruiana, AT; Sava, F; Iacob, N; Matei, E; Bocirnea, AE; Onea, M; Galca, AC; Mihai, C; Velea, A; Kuncser, V
Published: DEC 2021, SENSORS, 21, 8084, DOI: 10.3390/s21238084
Nanoscale thermometers with high sensitivity are needed in domains which study quantum and classical effects at cryogenic temperatures. Here, we present a micrometer sized and nanometer thick chromium selenide cryogenic temperature sensor capable of measuring a large domain of cryogenic temperatures down to tenths of K. Hexagonal Cr-Se flakes were obtained by a simple physical vapor transport method and investigated using scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray photoelectron spectroscopy measurements. The flakes were transferred onto Au contacts using a dry transfer method and resistivity measurements were performed in a temperature range from 7 K to 300 K. The collected data have been fitted by exponential functions. The excellent fit quality allowed for the further extrapolation of resistivity values down to tenths of K. It has been shown that the logarithmic sensitivity of the sensor computed over a large domain of cryogenic temperature is higher than the sensitivity of thermometers commonly used in industry and research. This study opens the way to produce Cr-Se sensors for classical and quantum cryogenic measurements.
Open Access
234. Preliminary Study on Light-Activated Antimicrobial Agents as Photocatalytic Method for Protection of Surfaces with Increased Risk of Infections
Authors:
Bucuresteanu, R; Ditu, LM; Ionita, M; Calinescu, I; Raditoiu, V; Cojocaru, B; Cinteza, LO; Curutiu, C; Holban, AM; Enachescu, M; Enache, LB; Mustatea, G; Chihaia, V; Nicolaev, A; Borcan, EL; Mihaescu, G
Published: SEP 2021, MATERIALS, 14, 5307, DOI: 10.3390/ma14185307
Preventing and controlling the spread of multidrug-resistant (MDR) bacteria implicated in healthcare-associated infections is the greatest challenge of the health systems. In recent decades, research has shown the need for passive antibacterial protection of surfaces in order to reduce the microbial load and microbial biofilm development, frequently associated with transmission of infections. The aim of the present study is to analyze the efficiency of photocatalytic antimicrobial protection methods of surfaces using the new photocatalytic paint activated by light in the visible spectrum. The new composition is characterized by a wide range of analytical methods, such as UV-VIS spectroscopy, electron microscopy (SEM), X-ray powder diffraction (PXRD) or X-ray photoelectron spectroscopy (XPS). The photocatalytic activity in the UV-A was compared with the one in the visible light spectrum using an internal method developed on the basis of DIN 52980: 2008-10 standard and ISO 10678-2010 standard. Migration of metal ions in the composition was tested based on SR EN1186-3: 2003 standard. The new photocatalytic antimicrobial method uses a type of photocatalytic paint that is active in the visible spectral range and generates reactive oxygen species with inhibitory effect against all tested microbial strains.
Open Access
235. Low Blue Dose Photodynamic Therapy with Porphyrin-Iron Oxide Nanoparticles Complexes: In Vitro Study on Human Melanoma Cells
Authors:
Nistorescu, S; Udrea, AM; Badea, MA; Lungu, I; Boni, M; Tozar, T; Dumitrache, F; Maraloiu, VA; Popescu, RG; Fleaca, C; Andronescu, E; Dinischiotu, A; Staicu, A; Balas, M
Published: DEC 2021, PHARMACEUTICS, 13, 2130, DOI: 10.3390/pharmaceutics13122130
The purpose of this study was to investigate the effectiveness in photodynamic therapy of iron oxide nanoparticles (gamma-Fe2O3 NPs), synthesized by laser pyrolysis technique, functionalized with 5,10,15,20-(Tetra-4-sulfonatophenyl) porphyrin tetraammonium (TPPS) on human cutaneous melanoma cells, after only 1 min blue light exposure. The efficiency of porphyrin loading on the iron oxide nanocarriers was estimated by using absorption and FTIR spectroscopy. The singlet oxygen yield was determined via transient characteristics of singlet oxygen phosphorescence at 1270 nm both for porphyrin functionalized nanoparticles and rose bengal used as standard. The irradiation was performed with a LED (405 nm, 1 mW/cm(2)) for 1 min after melanoma cells were treated with TPPS functionalized iron oxide nanoparticles (gamma-Fe2O3 NPs_TPPS) and incubated for 24 h. Biological tests revealed a high anticancer effect of gamma-Fe2O3 NPs_TPPS complexes indi-cated by the inhibition of tumor cell proliferation, reduction of cell adhesion, and induction of cell death through ROS generated by TPPS under light exposure. The biological assays were combined with the pharmacokinetic prediction of the porphyrin.
Open Access
236. On the pinning force in high density MgB2 samples
Authors:
Sandu, V; Ionescu, AM; Aldica, G; Grigoroscuta, MA; Burdusel, M; Badica, P
Published: MAR 15 2021, SCIENTIFIC REPORTS, 11, 5951, DOI: 10.1038/s41598-021-85209-2
An analysis of the field dependence of the pinning force in different, high density sintered samples of MgB2 is presented. The samples were chosen to be representative for pure MgB2, MgB2 with additives, and partially oriented massive samples. In some cases, the curves of pinning force versus magnetic field of the selected samples present peculiar profiles and application of the typical scaling procedures fails. Based on the percolation model, we show that most features of the field dependence of the critical force that generate dissipation comply with the Dew-Hughes scaling law predictions within the grain boundary pinning mechanism if a connecting factor related to the superconducting connection of the grains is used. The field dependence of the connecting function, which is dependent on the superconducting anisotropy, is the main factor that controls the boundary between dissipative and non-dissipative current transport in high magnetic field. Experimental data indicate that the connecting function is also dependent on the particular properties (e.g., the presence of slightly non-stoichiometric phases, defects, homogeneity, and others) of each sample and it has the form of a single or double peaked function in all investigated samples.
Open Access
237. Influence of Thickness on the Magnetic and Magnetotransport Properties of Epitaxial La0.7Sr0.3MnO3 Films Deposited on STO (001)
Authors:
Greculeasa, SG; Stanciu, AE; Leca, A; Kuncser, A; Hrib, L; Chirila, C; Pasuk, I; Kuncser, V
Published: DEC 2021, NANOMATERIALS, 11, 3389, DOI: 10.3390/nano11123389
Epitaxial La0.7Sr0.3MnO3 films with different thicknesses (9-90 nm) were deposited on SrTiO3 (0 0 1) substrates by pulsed laser deposition. The films have been investigated with respect to morpho-structural, magnetic, and magneto-transport properties, which have been proven to be thickness dependent. Magnetic contributions with different switching mechanisms were evidenced, depending on the perovskite film thickness. The Curie temperature increases with the film thickness. In addition, colossal magnetoresistance effects of up to 29% above room temperature were evidenced and discussed in respect to the magnetic behavior and film thickness.
Open Access
238. Mesoporous TiO2 from Metal-Organic Frameworks for Photoluminescence-Based Optical Sensing of Oxygen
Authors:
Alfè, M; Gargiulo, V; Amati, M; Maraloiu, VA; Maddalena, P; Lettieri, S
Published: JUL 2021, CATALYSTS, 11, 795, DOI: 10.3390/catal11070795
Metal-organic frameworks (MOFs) are a class of porous coordination networks extraordinarily varied in physicochemical characteristics such as porosity, morphologies, and compositions. These peculiarities make MOFs widely exploited in a large array of applications, such as catalysis, chemicals and gas sensing, drug delivery, energy storage, and energy conversion. MOFs can also serve as nanostructured precursors of metal oxides with peculiar characteristics and controlled shapes. In this work, starting from MIL125-(Ti), a 1,4-benzenedicarboxylate (BDC)-based MOF with Ti as metallic center, mesoporous TiO2 powders containing both anatase and rutile crystalline phases were produced. A challenging utilization of these porous MOF-derived Ti-based oxides is the optically-based quantitative detection of molecular oxygen (O-2) in gaseous and/or aqueous media. In this study, the photoluminescence (PL) intensity changes during O-2 exposure of two MOF-derived mixed-phase TiO2 powders were probed by exploiting the opposite response of rutile and anatase in VIS-PL and NIR-PL wavelength intervals. This result highlights promising future possibilities for the realization of MOF-derived doubly-parametric TiO2-based optical sensors.
239. Spectroscopic Ellipsometry of InSb in the Terahertz Region
Authors:
Agulto, VC; Iwamoto, T; Toya, K; Mag-usara, VK; Dolas, S; Newman, N; Nedelcu, L; Tani, M; Nakajima, M
Published: 2021, 2021 46TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER AND TERAHERTZ WAVES (IRMMW-THZ), DOI: 10.1109/IRMMW-THz50926.2021.9567607
Herein we show the terahertz (THz) time-domain ellipsometry investigation of the InSb semiconductor. At room temperature, the carriers of InSb are thermally excited to the conduction band due to its narrow bandgap. We, nevertheless, show that THz ellipsometry can detect subtle differences between carrier densities of undoped and lightly doped InSb bulk semiconductors. The advantage of THz ellipsometry over other THz time-domain spectroscopy techniques is that it does not require reference measurements through an aperture or standard mirrors.
Open Access
240. Synthesis of titanium nitride via hybrid nanocomposites based on mesoporous TiO2/acrylonitrile
Authors:
Locovei, C; Chiriac, AL; Miron, A; Iftimie, S; Antohe, VA; Sârbu, A; Dumitru, A
Published: MAR 3 2021, SCIENTIFIC REPORTS, 11, 5055, DOI: 10.1038/s41598-021-84484-3
In the present study, the synthesis of titanium nitride (TiN) by carbothermal reduction nitridation (CRN) reaction using nanocomposites made of mesoporous TiO2/acrylonitrile with different content of inorganic phase were explored. The choice of hybrid nanocomposite as precursor for the synthesis of TiN was made due to the possibility of having an intimate interface between the organic and inorganic phases in the mixture that can favours CRN reaction. Subsequently, the hybrid composites have been subjected to four-step thermal treatments at 290 degrees C, 550 degrees C, 1000 degrees C and 1400 degrees C under nitrogen atmosphere. The XRD results after thermal treatment at 1000 degrees C under nitrogen flow show the coexistence of two crystalline phases of TiO2, i.e. anatase and rutile, as well as TiN phase, together with the detection of amorphous carbon that proved the initiation of CRN reaction. Furthermore, the observations based on XRD patterns of samples thermally treated at 1400 degrees C in nitrogen atmosphere were in agreement with SEM analysis, that shows the formation of TiN by CRN reaction via hybrid nanocomposites mesoporous TiO2/acrylonitrile.
Open Access
241. Band-Order Anomaly at the γ-Al2O3/SrTiO3 Interface Drives the Electron-Mobility Boost
Authors:
Chikina, A; Christensen, D; Borisov, V; Husanu, MA; Chen, YZ; Wang, XQ; Schmitt, T; Radovic, M; Nagaosa, N; Mishchenko, AS; Valentí, R; Pryds, N; Strocov, VN
Published: MAR 23 2021, ACS NANO, 15, DOI: 10.1021/acsnano.0c07609
The rich functionalities of transition-metal oxides and their interfaces bear an enormous technological potential. Its realization in practical devices requires, however, a significant improvement of yet relatively low electron mobility in oxide materials. Recently, a mobility boost of about 2 orders of magnitude has been demonstrated at the spinel-perovskite gamma-Al2O3/SrTiO3 interface compared to the paradigm perovskite-perovskite LaAlO3/SrTiO3 interface. We explore the fundamental physics behind this phenomenon from direct measurements of the momentum-resolved electronic structure of this interface using resonant soft-X-ray angle-resolved photoemission. We find an anomaly in orbital ordering of the mobile electrons in gamma-Al2O3/SrTiO3 which depopulates electron states in the top SrTiO3 layer. This rearrangement of the mobile electron system pushes the electron density away from the interface, which reduces its overlap with the interfacial defects and weakens the electron-phonon interaction, both effects contributing to the mobility boost. A crystal-field analysis shows that the band order alters owing to the symmetry breaking between the spinel gamma-Al2O3 and perovskite SrTiO3. Band-order engineering, exploiting the fundamental symmetry properties, emerges as another route to boost the performance of oxide devices.
242. Niobia-based magnetic nanocomposites: Design and application in direct glucose dehydration to HMF
Authors:
Tirsoaga, A; Kuncser, V; Parvulescu, VI; Coman, SM
Published: APR 15 2021, CATALYSIS TODAY, 366, DOI: 10.1016/j.cattod.2020.09.033
Niobia-based magnetic nanocomposites were prepared by covering magnetite nanoparticle cores (Fe3O4, MNP) with either Nb2O5 or Nb2O5-SiO2 shells using a two-step procedure. In the first step magnetite nanoparticles were prepared by the coprecipitation method. The second step involved their coverage with either Nb2O5 shells, through a precipitation method, or with Nb2O5-SiO2 shells, through a sol-gel protocol followed by precipitation in the presence of the CTAB surfactant. The obtained materials were exhaustively characterised by X-ray diffraction, Mossbauer spectroscopy, magnetic measurements, ICP-OES, DRIFT and Raman spectroscopy, and CO2 - and NH3-TPD measurements, and investigated for glucose dehydration to HMF. The catalytic performances were directly correlated to the nature of the supported niobia phases, which, in turn, has been dictated by the niobia content and the preparation route. The high selectivity to HMF was correlated with to the large pseudohexagonal niobium oxide (TT-Nb2O5) phase while the catalytic activity was directly correlated to the small nanoparticles size. A proper combination of these features led to an optimum catalytic system for the selective production of HMF through glucose dehydration. A third important feature making the developed catalyst promising is its magnetic property, ensured by the magnetite nanoparticles core. This allowed its easy separation from the reaction products.
243. Structural features, magnetic and ferroelectric properties of SrFe10.8In1.2O19 compound
Authors:
Turchenko, V; Kostishin, VG; Trukhanov, S; Damay, F; Balasoiu, M; Bozzo, B; Fina, I; Burkhovetsky, VV; Polosan, S; Zdorovets, MV; Kozlovskiy, AL; Astapovich, KA; Trukhanov, A
Published: JUN 2021, MATERIALS RESEARCH BULLETIN, 138, 111236, DOI: 10.1016/j.materresbull.2021.111236
The effect of temperature on the features of the crystal and magnetic structures, as well as the magnetic properties of the solid solution of SrFe10.8In1.2O19 hexaferrite was investigated. The appearance of ferroelectric properties was detected at room temperature, which contradicts the generally accepted opinion on the description of the crystal structure of hexaferrites within the framework of the centrosymmetric P6(3)/mmc (No. 194) space group. The reasons of spontaneous polarization in solid solutions of hexaferrites remain controversial. No deviation from the collinear magnetic structure was found in the investigated temperature range from 1.5 to 350 K, while the thermal expansion of the unit cell was practically absent in the range from 1.5 to 50 K. The crystal structure of hexaferrites was considered in the framework of both centrosymmetric P6(3)/mmc and non-centrosymmetric P6(3)mc space groups, which allowed us to associate the emerging spontaneous polarization with unequal distortions of neighboring oxygen polyhedra.
244. The origin of the dual ferroic properties in quasi-centrosymmetrical SrFe12-xInxO19 hexaferrites
Authors:
Trukhanov, AV; Turchenko, VA; Kostishin, VG; Damay, F; Porcher, F; Lupu, N; Bozzo, B; Fina, I; Polosan, S; Silibin, MV; Salem, MM; Tishkevich, DI; Trukhanov, SV
Published: DEC 15 2021, JOURNAL OF ALLOYS AND COMPOUNDS, 886, 161249, DOI: 10.1016/j.jallcom.2021.161249
The local crystal/magnetic structures of the SrFe12-xInxO19 solid solutions (x = 0.1; 0.3; 0.6 and 1.2) were investigated using neutron powder diffraction. The measurements of the electric polarization for all investigated samples were carried out as a function of the external electric field. The presence of the ferroelectric and ferromagnetic ordering (dual ferroic ordering) in the SrFe12-xInxO19 hexaferrites at 300 K was found. This appearance contradicts to the conventional opinion describing their crystal structure (centrosymmetric space group P6(3)/mmc (No. 194)). The reason for the existence of a spontaneous polarization (nonzero dipole moment) in the SrFe12-xInxO19 hexaferrites continues controversial. The crystal structure of the hexaferrites was considered both the centrosymmetric P6(3)/mmc and non-centrosymmetric P6(3)mc space groups. This fact made it possible to find a connection between the emerging dipole moment and not equal distortions of the neighbor oxygen polyhedral. The nature description of the nonzero dipole moment formation in a quasi-centrosymmetrical system of the In-substituted SrFe12-xInxO19 hexaferrites was presented based on the neutron diffraction data. (C) 2021 Elsevier B.V. All rights reserved.
245. Preparation of isocyanate-free composite coating with controlled molecular architecture: A new convergent approach to functional macromolecules
Authors:
Haniffa, MAM; Chee, CY; Illias, HA; Halil, A; Munawer, K; Sandu, V; Chuah, CH
Published: FEB 2021, PROGRESS IN ORGANIC COATINGS, 151, 106039, DOI: 10.1016/j.porgcoat.2020.106039
Isocyanate-free composite coating can improve radiative cooling, energy storage and harvesting applications. This study reports the development and use of a isocyanate-free green surface coating(GSC) matrix derived from (2,2,6,6-tetramethylpiperidin-1-yl)oxy radical (TEMPO)-oxidized cellulose-(3-Aminopropyl)trimethoxysilane (APTMS)-ZnO nanoparticles-green polymer matrix that possesses upto similar to 220 degrees C thermal stability. The GSC exhibited excellent UV block and IR active capacity while achieving good coating hardness. The NMR, TGA-DTG and Pencil hardness studies revealed that this attribute by GSC was due to the formation of uniform crosslinking and reinforcement network. Using electrochemical impedance spectroscopy, the GSC had a low resistance. A high charge transfer resistance of similar to 15.826 k Omega was measured using electrochemical impedance spectroscopy for the GSC, high enough to attenuate photon radiation, making GSC material stable for application. Also, UV-weathering study was performed to investigate coating stability of the GSC. This is the first time application of TEMPO-cellulose based reinforcement of the green polymer matrix for the development of GSC through convergent approach to functional macromolecules. The study opens an opportunity of utilizing green material in energy applications, especially in windows shielding by a sufficient attenuation of photon radiations.
246. Spin-vibron coupling effects in single-molecule magnets grafted to a nanoelectromechanical system
Authors:
Moldoveanu, V; Dragomir, R
Published: AUG 23 2021, PHYSICAL REVIEW B, 104, 075441, DOI: 10.1103/PhysRevB.104.075441
We present a theoretical analysis of the interplay between the spin-vibron and electron-vibron interactions in a hybrid system made of a single-molecule magnet and a suspended conductor. The latter is coupled to particle reservoirs and supports quantized vibrational modes which, once activated, interact with the localized magnetic moment S of the nanomagnet. The dynamics of the molecular spin, the average vibron number, and the transient currents are calculated from the reduced density operator of the hybrid system. We focus on the effect of the vibron-assisted transitions from the lowest energy spin doublet S-z = +/- S to higher energy excited states. The numerical simulations performed for the simplest case S = 2 prove that the vibron-assisted spin transitions and dynamics can be described in terms of a three-level Lambda model borrowed from quantum optics. In particular we predict the existence of Rabi oscillations of the transient currents as fingerprints of the spin-vibron coupling. The role of symmetric or asymmetric bias configurations in setting different mixtures of molecular spin states in the steady-state regime is also emphasized.
247. New photoactive mesoporous Ce-modified TiO2 for simultaneous wastewater treatment and electric power generation
Authors:
Mureseanu, M; Chivu, V; Osiac, M; Ciobanu, M; Bucur, C; Parvulescu, V; Cioatera, N
Published: APR 15 2021, CATALYSIS TODAY, 366, DOI: 10.1016/j.cattod.2020.09.035
In the present paper is presented an efficient strategy for synthesis of mesoporous TiO2 modified with different Ce concentrations through a sol-gel process in the presence of triblock Pluronic P123 as structure directing agent, integrated with evaporation-induced self- assembly (EISA) approach. The nanocomposite consisted mostly of small crystallite of anatase. The presence of a new crystal phase corresponding to cerium titanate was evidenced in Ce-modified powder samples. All materials were characterized by SEM and TEM microscopies, UV-vis, XPS and N-2 adsorption-desorption isotherms in order to examine the textural and structural characteristics and the chemical nature of their surface. Furthermore, the photoelectrochemical characterization evidenced the effect of the TiO2 mesoporous structure, the amount of cerium and the oxidation state of Ti and Ce in the new photocatalysts on the enhanced photovoltaic performance. The photocatalytic activity of the as-synthesized materials was evaluated for phenol photodegradation in aqueous media and the reactive species involved in photocatalytic process were established by using some radical scavengers in the photodegradation experiments. Based on the obtained results, these new Ce-modified mesoporous TiO2 photocatalysts could be considered for degradation of organic compounds from wastewaters by advanced oxidation processes or for photoanodes construction for efficient photoelectrochemical fuel cell (PFC) systems.
Open Access
248. Structural, functional properties and enhanced thermal stability of bulk graded (Ba,Sr) TiO3 structures obtained by spark plasma sintering (vol 12, pg 2085, 2021)
Authors:
Botea, M; Pintilie, I; Surdu, VA; Stanciu, CA; Trusca, RD; Vasile, BS; Patru, R; Udrea, M; Ianculescu, AC; Pintilie, L
Published: JUL-AUG 2021, JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 13, DOI: 10.1016/j.jmrt.2021.06.001
Open Access
249. Thickness-Dependent Photoelectrochemical Water Splitting Properties of Self-Assembled Nanostructured LaFeO3 Perovskite Thin Films
Authors:
Andrei, F; Ion, V; Bîrjega, R; Dinescu, M; Enea, N; Pantelica, D; Mihai, MD; Maraloiu, VA; Teodorescu, VS; Marcu, IC; Scarisoreanu, ND
Published: JUN 2021, NANOMATERIALS, 11, 1371, DOI: 10.3390/nano11061371
Tuning the intrinsic structural and stoichiometric properties by different means is used for increasing the green energy production efficiency of complex oxide materials. Here, we report on the formation of self-assembled nanodomains and their effects on the photoelectrochemical (PEC) properties of LaFeO3 (LFO) epitaxial thin films as a function of layer's thickness. The variation with the film's thickness of the structural parameters such as in-plane and out-of-plane crystalline coherence length and the coexistence of different epitaxial orientation-SrTiO3// LFO, SrTiO3// LFO and [110] LFO//[10] STO, as well as the appearance of self-assembled nanodomains for film's thicknesses higher than 14 nm, is presented. LFO thin films exhibit different epitaxial orientations depending on their thickness, and the appearance of self-assembled nanopyramids-like domains after a thickness threshold value has proven to have a detrimental effect on the PEC functional properties. Using Nb:SrTiO3 as conductive substrate and 0.5 M NaOH aqueous solution for PEC measurements, the dependence of the photocurrent density and the onset potential vs. RHE on the structural and stoichiometric features exhibited by the LFO photoelectrodes are unveiled by the X-ray diffraction, high-resolution transmission electron microscopy, ellipsometry, and Rutherford backscattering spectroscopy results. The potentiodynamic PEC analysis has revealed the highest photocurrent density J(photocurrent) values (up to 1.2 mA/cm(2)) with excellent stability over time, for the thinnest LFO/Nb:SrTiO3 sample, both cathodic and anodic behavior being noticed. Noticeably, the LFO thin film shows unbiased hydrogen evolution from water, as determined by gas chromatography in aqueous 0.5 M NaOH solution under constant illumination.
250. An antibody-based amperometric biosensor for 20S proteasome activity and inhibitor screening†
Authors:
Barsan, MM; Diculescu, VC
Published: MAY 21 2021, ANALYST, 146, DOI: 10.1039/d0an02426k
The 20S proteasome enzyme complex is involved in the proteolytic degradation of misfolded and oxidatively damaged proteins and is a focus of medical research for the development of compounds with pharmaceutical properties, which are active in cancer cells and/or neurodegenerative diseases. The present study aims to develop a biosensor for investigating the 20S proteasome activity and inhibition by means of electrochemical methods. The 20S proteasome is best immobilized at the electrode surface through bio-affinity interactions with antibodies that target different subunits on the 20S proteasome, enabling the investigation of the effect of an enzyme's orientation on biosensor response. The enzymatic activity is analyzed by fixed potential amperometry with the highest sensitivity of 24 mu A cm(-2) mM(-1) and a LOD of 0.4 mu M. The detection principle involves the oxidation of an electroactive probe that is released from the enzyme's substrates upon proteolysis. The most sensitive biosensor is then used to study the multicatalytic activity of the 20S proteasome, i.e. the caspase-, trypsin- and chymotrypsin-like activity, by analyzing the biosensor's sensitivity towards different substrates. The behavior of the immobilized 20S proteasome is investigated as a function of substrate concentration. The kinetic parameters are derived and compared with those obtained when the enzyme was free in solution, with K-0.5 values being one to two orders of magnitude lower in the present case. Two 20S inhibitors, epoxomicin and bortezomib, are investigated by analyzing their influence on the 20S biosensor response. The proposed analytical method for proteasome activity and inhibitor screening has the main advantage of being cost-effective compared to the ones typically employed.
251. Mossbauer spectroscopy investigation of Fe oxide nanoparticles synthesized by a novel hydrothermal process over a wide pH range (3-13)
Authors:
Comanescu, C; Palade, P; Kuncser, V
Published: DEC 2021, HYPERFINE INTERACTIONS, 242, 42, DOI: 10.1007/s10751-021-01775-x
Fe oxide magnetic nanoparticles (MNPs) in general and cobalt ferrite nanoparticles in particular have immense potential for applications in catalysis, medicine, information and energy storage, etc. MNPs feature interesting physical and chemical properties, different to those of corresponding bulk materials. The magnetic anisotropy constant of almost spherical CoFe2O4 MNPs is much higher than that of magnetite (Fe3O4) MNPs of similar geometrical parameters due to the magnetocrystalline contribution. CoFe2O4 shows significant magnetization at saturation, high coercive field and Curie temperature, and good chemical and magnetic stability, being therefore preferable to the most usual Fe3O4 MNPs. A surfactant-assisted synthetic route was employed to synthesize Fe oxide and in particular cobalt ferrite MNPs over a wide pH range (3-13), endeavor which allowed analysis of transient and parasitic phase identified in acidic reaction conditions.
252. New superconductor/ferromagnet heterostructure formed by YBa2Cu3O7-x and CaRuO3
Authors:
Ivan, I; Pasuk, I; Crisan, A; Sandu, V; Onea, M; Leca, A; Cosar, C; Burdusel, M
Published: NOV 2021, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 34, 115009, DOI: 10.1088/1361-6668/ac2622
Almost all proposed configurations and practical achievements based on superconductor/ferromagnet (S/F) heterostrucutres focus on s-wave superconductors. However, several attempts targeted also high temperature superconductors, most of them using manganite ferromagnets LaXMnO3 (X: Ca or Sr) and Y1Ba2Cu3O7-x (YBCO). Here we propose a new ferromagnetic material that can be used with YBCO for the fabrication of S/F hybrid structures. We show that a ferromagnetic order can be induced in a thin layer (similar to 130 nm thickness) of CaRuO3 grown by pulsed laser deposition on epitaxial YBCO film. Detailed magnetic and structural investigations show that the observations of the weak ferromagnetism are consistent with the magnetic order induced by in-plane tensile strain of about 1.7% and the easy-magnetization axis forms an angle of similar to 180o with the layer plane. The value of the Curie temperature T (Curie) estimated using the Curie-Weiss law was 340 K. An unusual temperature dependence of the magnetic moment around the superconducting transition was observed in both field-cooled and zero-field-cooled configurations which is attributed to the paramagnetic Meissner effect.
253. Gold coated electrospun polymeric fibres as new electrode platform for glucose oxidase immobilization
Authors:
Aldea, A; Leote, RJB; Matei, E; Evanghelidis, A; Enculescu, I; Diculescu, VC
Published: JUN 2021, MICROCHEMICAL JOURNAL, 165, 106108, DOI: 10.1016/j.microc.2021.106108
Fibres of poly(methyl methacrylate) were obtained by electrospinning, subjected to coating with a gold layer and then attached on a thin polyethylene terephthalate substrate in order to obtain flexible electrodes for biosensing applications. The morphology of these electrodes, investigated by scanning electron microscopy showed multilayers of random oriented fibres of approx. 400 nm diameter. The electrochemical characterization of these flexible electrodes was performed by cyclic voltammetry and electrochemical impedance spectroscopy in acid and neutral media, in the absence and in the presence of redox probes, proving their superior performance (e.g. 5fold current density value) when compared to planar gold electrodes obtained on silicon wafers. The electrodes obtained from conductive electrospun polymeric fibres nets were tested by cyclic voltammetry and amperometry for the detection of hydrogen peroxide with a sensitivity of 0.84 mA cm-2 mM-1 and a detection limit of 20.40 ?M. The immobilization of the model enzyme glucose oxidase at the surface of the gold-coated electrospun polymeric fibres electrode was investigated and the obtained biosensor was applied for glucose determination in aqueous solutions by fixed potential amperometry with a sensitivity of 3.10 ?A cm-2 mM-1, a detection limit of 0.33 mM, and reduced interferences. Also, the practical applicability of the biosensor was tested for the detection of glucose in artificial sweat and serum samples.
254. Comparison between lead free BaTio3/PDMS and doped- PZT/PDMS composite on ferroelectric characteristics
Authors:
Amarande, L; Stancu, V; Botea, M; Toma, V; Ciobanu, R; Pintilie, L
Published: JUL-SEP 2021, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 16, DOI:
Composites of BaTiO3 (BT) and doped-PZT (d-PZT) micro-particles randomly dispersed in a PDMS matrix were prepared by a molding process. The morpho-structural characterization, performed by SEM and XRD, showed ceramic micro-grains of cubic BT and orthorhombic d-PZT, randomly dispersed in the PDMS matrix. Polarization (P) as a function of the applied field (E) was measured for composite samples, as well as for polymer samples. Hysteresis loops typical for a dielectric material were obtained, but also atypical ones, especially for higher fraction of polymer in composite, lower fields and shorter measuring periods, as a result of the dielectric relaxation in polymer and the presence of interfacial polarization charges at the contact between polymer and ferroelectric. All these composites show very low polarizations (less than 0.2 mu C/cm(2) and 0.05 mu C/cm(2) the maximum and remnant polarization, respectively), caused by the very low dielectric constant of the polymer (less than 10), which drastically reduces, up to 100 times, the electric field effectively applied to the ferroelectric. Weak pyroelectric response was recorded on BT/PDMS, but a typical behavior of a pyroelectric detector was observed. A figure of merit of the material which exceeds 10(-4) m(2) /C was estimated.
255. Pyrolysis and combustion of polystyrene composites based on graphene oxide functionalized with 3-(methacryloyloxy)-propyltrimethoxysilane
Authors:
Anghel, I; Lisa, G; Sofran, IE; Mitroi-Symeonidis, FC; Rusu, MM; Baia, M; Baia, L; Magyari, K; Danciu, V; Cotet, LC; Stroe, M; Baibarac, M
Published: 2021, JOURNAL OF POLYMER ENGINEERING, 41, DOI: 10.1515/polyeng-2021-0071
In this study, polystyrene composites (PS-GO(f)) with variable concentration (0.5; 1; 2; 3; 4; and 5 wt%) of GO(f) were obtained through the in-situ polymerisation of the styrene in the presence of benzoyl peroxide and graphene oxide(GO) functionalized with 3-(methacryloyloxy)-propyltrimethoxysilane(gamma-MPTS). For determining the morphological and structural particularities of polymeric composites transmission electron microscopy (TEM) measurements were performed. The influence of functionalized GO on thermal and combustion properties of polystyrene (PS)-based composite materials was determined through several methods: Thermogravimetry (TGA); derived thermogravimetry (DTG); microscale combustion calorimetry analysis (MCC); and chemical kinetic studies through TGA and MCC determinations at similar heating rates.
Open Access
256. Influences of Dispersions' Shapes and Processing in Magnetic Field on Thermal Conductibility of PDMS-Fe3O4 Composites
Authors:
Stancu, V; Galatanu, A; Enculescu, M; Onea, M; Popescu, B; Palade, P; Aradoaie, M; Ciobanu, R; Pintilie, L
Published: JUL 2021, MATERIALS, 14, 3696, DOI: 10.3390/ma14133696
Composites of magnetite (Fe3O4) nanoparticles dispersed in a polydimethylsiloxane (PDMS) matrix were prepared by a molding process. Two types of samples were obtained by free polymerization with randomly dispersed particles and by polymerization in an applied magnetic field. The magnetite nanoparticles were obtained from magnetic micrograins of acicular goethite (alpha-FeOOH) and spherical hematite (alpha-Fe2O3), as demonstrated by XRD measurements. The evaluation of morphological and compositional properties of the PDMS:Fe3O4 composites, performed by SEM and EDX, showed that the magnetic particles were uniformly distributed in the polymer matrix. Addition of magnetic dispersions promotes an increase of thermal conductivity compared with pristine PDMS, while further orienting the powders in a magnetic field during the polymerization process induces a decrease of the thermal conductivity compared with the un-oriented samples. The shape of the magnetic dispersions is an important factor, acicular dispersions providing a higher value for thermal conductivity compared with classic commercial powders with almost spherical shapes.
257. Antioxidant activity of thirty-six peppers varieties and vasorelaxant of selected varieties
Authors:
Machado, FB; de Mace, IYL; Campos, HM; Moreno, EKG; Silva, MFB; de Oliveira, JR; Ramalho, RRF; Nascimento, AD; Vaz, BG; da Cunha, LC; Ghedini, PC; Diculescu, VC; Gil, ED
Published: JUN 2021, FOOD BIOSCIENCE, 41, 100989, DOI: 10.1016/j.fbio.2021.100989
Peppers are consumed all over the world, have several benefits to human health, such as antioxidant properties that can prevent diseases related to free radicals such as cardiovascular, inflammatory diseases, cancer, among others. This work aimed to evaluate the antioxidant capacity (AOC) of 36 varieties of peppers through ABTS and DPPH radical scavenging, electroanalytical assays, and to verify the vasorelaxant properties of selected samples. The greater the amount of capsaicin found in the extracts, the higher the AOC the greater the vasorelaxation. Naga had the highest scoring for antioxidant capacity, pout showed the lowest antioxidant capacity, vase pyramid intermediate level, whereas the capsaicin content followed the same trend. Extracts from all pepper varieties studied presented vasorelaxant properties in independent and dependent endothelial pathways.
258. In-situ magnetron sputtering co-deposition of Ge nanoparticles in Si3N4 films for near infrared detection
Authors:
Stavarache, I; Palade, C; Prepelita, P; Teodorescu, VS; Ciurea, ML
Published: 2021, 2021 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), DOI: 10.1109/CAS52836.2021.9604124
Deposition of Ge nanoparticles in Si3N4 films by heating Si and quartz substrates at 500 degrees C were obtained using co-sputtering Ge, and Si3N4. Their structure and photo-electrical behaviour were investigated by transmission electron microscopy, current - voltage and spectral photo-current investigations, respectively. The spectral photoresponse were correlated with microscopy results. Depending on the measuring temperature, the current under illumination increases with about five orders of magnitude compared with the dark one. The photo-current spectra measured in photovoltaic regime and at -1 V show a single cut-off wavelength in near infrared domain at about 1362 nm.
Open Access
259. The Influence of the Structural and Morphological Properties of WO3 Thin Films Obtained by PLD on the Photoelectrochemical Water-Splitting Reaction Efficiency
Authors:
Andrei, F; Andrei, A; Birjega, R; Sirjita, EN; Radu, AI; Dinescu, M; Ion, V; Maraloiu, VA; Teodorescu, VS; Scarisoreanu, ND
Published: JAN 2021, NANOMATERIALS, 11, 110, DOI: 10.3390/nano11010110
Due to its physical and chemical properties, the n-type tungsten oxide (WO3) semiconductor is a suitable photoanode for water decomposition reaction. The responses of the photoelectrochemical PEC water-splitting properties as an effect of structural and optical changes of WO3 thin films, as well as the nature of electrolyte solutions, were studied in this work. The WO3 thins films have been obtained by pulsed laser deposition (PLD) on silicon (Si(001)) covered with platinum substrates using three different laser wavelengths. As the XRD (X-ray diffraction) and XTEM (cross-section transmission electron microscopy) analysis shows, the formation of highly crystalline monocline WO3 phase is formed for the film deposited at 1064 nm wavelength and poor crystalline phases with a large ordering anisotropy, characteristic of 2D structures for the films deposited at 355 nm and 193 nm wavelengths, respectively. The photogenerated current densities J(ph) depend on the laser wavelength, in both alkaline and acidic electrolyte. The maximum values of the photocurrent density have been obtained for the sample prepared with laser emitting at 355 nm. This behavior can be correlated with the coherent crystallized atomic ordering that appear for long distances (10-15 nm) in the (001) plane of the monoclinic WO3 phase structure films obtained at 355 nm laser wavelength. All the samples show poor current density in dark conditions and they are very stable in both acidic and alkaline solutions. The highest photocurrent density value is obtained in acidic solution for the WO3 thin film prepared by 355 nm laser (29 mA/cm(2) at 1.6 V vs. RHE (1.35 V vs. Ag/AgCl)).
Open Access
260. Experimental tuning of AuAg nanoalloy plasmon resonances assisted by machine learning method
Authors:
Koziol, R; Lapinski, M; Syty, P; Sadowski, W; Sienkiewicz, JE; Nurek, B; Maraloiu, VA; Koscielska, B
Published: NOV 30 2021, APPLIED SURFACE SCIENCE, 567, 150802, DOI: 10.1016/j.apsusc.2021.150802
Plasmonic nanostructures based on AuAg nanoalloys were fabricated by thermal annealing of metallic films in an argon atmosphere. The nanoalloys were chosen because they can extend the wavelength range in which plasmon resonance occurs and thus allow the design of plasmonic platforms with the desired parameters. The influence of initial fabrication parameters and experimental conditions on the formation of nanostructures was investigated. For the surface morphology studies, chemical composition analysis and nanograin structure, Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), Energy Dispersive X-Ray Spectroscopy (EDS) and High-Resolution Transmission Electron Microscopy (HR TEM) measurements were performed. The position of the resonance band was successfully tuned in the 100 nm range. The EDS together with the XPS analysis confirmed the formation of an alloy with the aspect ratio of individual metals in a single nanoisland similar to the ratio of the thicknesses of the initially sputtered layers. The experimental research was complemented by the neural network model, which enables the calculation of the absorbance peak depending on the thickness of Au and Ag layers and the annealing time. The proposed model of machine learning makes it possible to fine-tune the desired position of the plasmon resonance.
Open Access
261. Redox Mechanism of Azathioprine and Its Interaction with DNA
Authors:
Bunea, MC; Diculescu, VC; Enculescu, M; Iovu, H; Enache, TA
Published: JUL 2021, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 22, 6805, DOI: 10.3390/ijms22136805
The electrochemical behavior and the interaction of the immunosuppressive drug azathioprine (AZA) with deoxyribonucleic acid (DNA) were investigated using voltammetric techniques, mass spectrometry (MS), and scanning electron microscopy (SEM). The redox mechanism of AZA on glassy carbon (GC) was investigated using cyclic and differential pulse (DP) voltammetry. It was proven that the electroactive center of AZA is the nitro group and its reduction mechanism is a diffusion-controlled process, which occurs in consecutive steps with formation of electroactive products and involves the transfer of electrons and protons. A redox mechanism was proposed and the interaction of AZA with DNA was also investigated. Morphological characterization of the DNA film on the electrode surface before and after interaction with AZA was performed using scanning electron microscopy. An electrochemical DNA biosensor was employed to study the interactions between AZA and DNA with different concentrations, incubation times, and applied potential values. It was shown that the reduction of AZA molecules bound to the DNA layer induces structural changes of the DNA double strands and oxidative damage, which were recognized through the occurrence of the 8-oxo-deoxyguanosine oxidation peak. Mass spectrometry investigation of the DNA film before and after interaction with AZA also demonstrated the formation of AZA adducts with purine bases.
262. Magneto-optical properties of borophosphate glasses co-doped with Tb3+ and Dy3+ions
Authors:
Dinca, MC; Sava, BA; Galca, AC; Kuncser, V; Iacob, N; Stan, GE; Boroica, L; Filip, AV; Elisa, M
Published: SEP 15 2021, JOURNAL OF NON-CRYSTALLINE SOLIDS, 568, 120967, DOI: 10.1016/j.jnoncrysol.2021.120967
Glasses from lithium-aluminum-zinc-boron-phosphorous oxide system co-doped with terbium (Tb3+) and dysprosium (Dy3+) oxides were studied for magneto-optical applications in lasers. The Fourier Transform Infrared and Raman Spectroscopy complementary analysis suggested the depolymerization of the borophosphate glass network by adding and increasing the rare-earth (RE) oxide content. Main UV-vis absorption maxima of Tb and Dy ions were identified at 348 and 1266 nm. Spectroscopic ellipsometry indicated a maximum refractive index of 1.56, at 400 nm, for the highest RE content. The Verdet constant amplified by increasing the RE content, reaching for the 9 mol% RE co-doped sample a value of -0.075 min/Oe/cm at 630 nm. The Faraday rotation angle was additionally confirmed by using a Faraday Cell Device, being also related to the specific paramagnetic behavior evidenced by Superconducting Quantum Interference Device magnetometry. The magneto-optical properties recommend such vitreous co-doped materials for magneto-optical devices.
263. Structural, electrical properties and photoluminescence analyses of the terbium doped barium titanate
Authors:
Cernea, M; Secu, M; Radu, R; Ganea, P; Surdu, VA; Trusca, R; Vasile, ET; Secu, EC
Published: OCT 15 2021, JOURNAL OF ALLOYS AND COMPOUNDS, 878, 160380, DOI: 10.1016/j.jallcom.2021.160380
Multifunctional materials integrating optical and electric properties into a composite or into a doped single-phase material have attracted much attention from scientists for future optoelectronic devices. In this work, polycrystalline Ba1-xTbxTiO3, x = 0.00, 0.01 and 0.05 materials were synthesized by hydrothermal route and their photoluminescence and dielectric properties were studied. The as-prepared powders showed a microstructure consisting of grains with the shape of cube; and average particle size ranging from 75 nm to 150 nm. The investigated temperature dependence of dielectric permittivity of Ba1-xTbxTiO3 ceramics revealed a decrease of the Curie temperature (Tc) with increasing terbium content, and a more pronounced degree of diffuseness of phase transition. The resistivity at room temperature was discussed in terms of positive temperature coefficient of resistance (PTRC) effect. UV-vis reflectance spectra of Ba1-xTbxTiO3 samples showed a decrease of the band gap energy with the increase of Tb amount, due to the band-gap narrowing effect. The photoluminescence spectra recorded for Tb doped BaTiO3 materials, at 80 K, evidenced the typical f-f luminescence lines of the Tb3+ accompanied the broad luminescence band at about 425 nm due to self-trapped exciton recombination. These results demonstrated that the terbium enhances the dielectric properties and photoluminescence simultaneously, being suitable for electronic applications. (C) 2021 Elsevier B.V. All rights reserved.
Open Access
264. THERMAL BEHAVIOR OF Cu-DOPED TiO2 GELS SYNTHESIZED BY THE SOL-GEL METHOD
Authors:
Pandele-Cusu, J; Atkinson, I; Rusu, A; Apostol, N; Teodorescu, V; Predoana, L; Szilágyi, IM; Pokol, G; Zaharescu, M
Published: MAR 2021, REVUE ROUMAINE DE CHIMIE, 66, DOI: 10.33224/rrch.2021.66.3.01
The thermal behavior of Cu-doped TiO2 gels obtained by the sol-gel method was investigated by thermogravimetric and differential thermal analysis (TG/DTG/DTA) and differential scanning calorimetry (DSC) measurements. The comparative investigation of the structure and morphology of the as-prepared gels and of the nanopowders obtained by annealing them was realized by transmission electron microscopy (TEM), Fourier transmission infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Significant differences were noticed depending on the amount of dopant (0.5 or 2.0 mol % CuO). A higher dopant concentration resulted in a more complex decomposition of the sample. This behavior was associated with the formation of various molecular species in the sol-gel solutions before gelation, determined by the different amount of the dopant used.
265. Insight on Ni(II) and Cu(II) complexes of biguanide derivatives developed as effective antimicrobial and antitumour agents
Authors:
Badea, M; Grecu, MN; Chifiriuc, MC; Bleotu, C; Popa, M; Iorgulescu, EE; Avram, S; Uivarosi, V; Munteanu, AC; Ghica, D; Olar, R
Published: APR 2021, APPLIED ORGANOMETALLIC CHEMISTRY, 35, e6155, DOI: 10.1002/aoc.6155
Six compounds of the types [M(dmbg)(2)]center dot nH(2)O ((1) M: Ni, n = 0; (4) M: Cu, n = 1; Hdmbg: N,N '-dimethylbiguanide) and, respectively, [ML]center dot nH(2)O (where (2) M: Ni, L: L-1, n = 0; (3) M: Ni, L: L-2, n = 0; (5) M: Cu, L: L-1, n = 0 and (6) M: Cu, L: L-2, n = 3, H2L1: ligand resulted from the condensation of (1) with ammonia and formaldehyde and H2L2: ligand resulted from the condensation of (4) with hydrazine and formaldehyde) were characterized as mononuclear species through information provided by NMR, electronic paramagnetic resonance (EPR) and UV-Vis spectroscopy as well as cyclic voltammetry. All data are consistent with macrocyclic formation by condensation. The complexes adopt a distorted square planar geometry resulting from the chelating behaviour of the corresponding ligands. The EPR spectra recorded after the addition of Cu(II) complexes into the corresponding Ni(II) complexes show a well resolved hyperfine structure with the superhyperfine pattern corresponding to four nitrogen atom donors. The cathodically shift of E-pc2 for both series can be correlated with the increased stability of the M(I) species through macrocyclic ligands. Geometry optimization studies for complexes (2), (3), (5) and (6) have further confirmed the experimental data. The pharmacokinetic computational results indicate that the complexes exhibit medium to low intestinal absorption and slow blood-brain barrier permeability but low toxicity. Their predictive pharmacodynamic profiles show that the compounds present the ability to inhibit protease activity. By corroborating the results of the in silico analysis with the experimental ones, the most promising complexes for antimicrobial applications are (1) and (2) and, respectively, (4) and (6) for the development of novel antitumour strategies.
266. STUDIES ABOUT STRUCTURAL AND THERMAL INVESTIGATIONS ON Ti50Ni30Cu20 ALLOYS OBTAINED BY DIFFERENT TECHNOLOGICAL PROCESSES
Authors:
Cirstea, CD; Lucaci, M; Valeanu, M; Sofronie, M; Bujoreanu, LG; Lungu, MV; Tsakiris, V; Cucos, A; Talpeanu, D; Enescu, E
The paper presents the research results in the field of TiNiCu shape memory alloys processed by powder metallurgy techniques. The powders mixtures used to synthesize Ti50Ni30Cu20 alloys were obtained by blended constitutive elemental powders or by mechanical alloying of powder mixtures for 10 and 20 hours, respectively. Finally, a subsequent annealing process was carried out, followed by a rapid cooling in ice water. All experiments were performed under 99.9% argon atmosphere. At room temperature, the obtained materials contained monoclinic and orthorhombic martensite type. The structural and thermal investigation of these materials were discussed in view of the potential development of actuators.
Open Access
267. Antibacterial composite coatings of MgB2 powders embedded in PVP matrix
Authors:
Badica, P; Batalu, ND; Burdusel, M; Grigoroscuta, MA; Aldica, G; Enculescu, M; Pircalabioru, GG; Popa, M; Marutescu, LG; Dumitriu, BG; Olariu, L; Bicu, A; Purcareanu, B; Operti, L; Bonino, V; Agostino, A; Truccato, M; Chifiriuc, MC
Published: MAY 5 2021, SCIENTIFIC REPORTS, 11, 9591, DOI: 10.1038/s41598-021-88885-2
Three commercial powders of MgB2 were tested in vitro by MTS and LDH cytotoxicity tests on the HS27 dermal cell line. Depending on powders, the toxicity concentrations were established in the range of 8.3-33.2 mu g/ml. The powder with the lowest toxicity limit was embedded into polyvinylpyrrolidone (PVP), a biocompatible and biodegradable polymer, for two different concentrations. The self-replenishing MgB2-PVP composite materials were coated on substrate materials (plastic foil of the reservoir and silicon tubes) composing a commercial urinary catheter. The influence of the PVP-reference and MgB2-PVP novel coatings on the bacterial growth of Staphylococcus aureus ATCC 25923, Enterococcus faecium DMS 13590, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, in planktonic and biofilm state was assessed in vitro at 6, 24, and 48 h of incubation time. The MgB2-PVP coatings are efficient both against planktonic microbes and microbial biofilms. Results open promising applications for the use of MgB2 in the design of anti-infective strategies for different biomedical devices and systems.
268. Multilevel Memristive GeTe Devices
Authors:
Velea, A; Dumitru, V; Sava, F; Galca, AC; Mihai, C
Published: MAR 2021, PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, 15, 2000475, DOI: 10.1002/pssr.202000475
Phase-change memories have reached an advanced degree of maturity, although, to be able to meet the increasing storage demand, multilevel capability is needed. A GeTe memristor is obtained in an amorphous state and it is subjected to a specific thermal treatment which initiates the transition toward the crystalline state. It is found that this crystalline state initialization process is highly beneficial for subsequently obtaining a large number of intermediate resistive states between the high and low resistive states. Multiple resistance levels are achieved by operating the devices in both DC sweeps and rectangular pulse modes in the low-voltage subthreshold regime. The conduction is modeled using a space charge limited conduction model, showing three distinct conduction regions in the high resistive state which merge toward a single conduction region as the low resistive state is approached. The obtained memristors can be used as multilevel nonvolatile memories or as synapses in neuromorphic computing.
Open Access
269. Sintered and 3D-Printed Bulks of MgB2-Based Materials with Antimicrobial Properties
Authors:
Badica, P; Batalu, ND; Chifiriuc, MC; Burdusel, M; Grigoroscuta, MA; Aldica, GV; Pasuk, I; Kuncser, A; Popa, M; Agostino, A; Operti, L; Padhi, SK; Bonino, V; Truccato, M
Published: OCT 2021, MOLECULES, 26, 6045, DOI: 10.3390/molecules26196045
Pristine high-density bulk disks of MgB2 with added hexagonal BN (10 wt.%) were prepared using spark plasma sintering. The BN-added samples are machinable by chipping them into desired geometries. Complex shapes of different sizes can also be obtained by the 3D printing of polylactic acid filaments embedded with MgB2 powder particles (10 wt.%). Our present work aims to assess antimicrobial activity quantified as viable cells (CFU/mL) vs. time of sintered and 3D-printed materials. In vitro antimicrobial tests were performed against the bacterial strains Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 25923, Enterococcus faecium DSM 13590, and Enterococcus faecalis ATCC 29212; and the yeast strain Candida parapsilosis ATCC 22019. The antimicrobial effects were found to depend on the tested samples and microbes, with E. faecium being the most resistant and E. coli the most susceptible.
Open Access
270. Self-induction and magnetic effects in electron transport through a photon cavity
Authors:
Gudmundsson, V; Abdullah, NR; Tang, CS; Manolescu, A; Moldoveanu, V
Published: MAR 2021, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 127, 114544, DOI: 10.1016/j.physe.2020.114544
We explore higher order dynamical effects in the transport through a two-dimensional nanoscale electron system embedded in a three-dimensional far-infrared photon cavity. The nanoscale system is considered to be a short quantum wire with a single circular quantum dot defined in a GaAs heterostructure. The whole system, the external leads and the central system are placed in a constant perpendicular magnetic field. The Coulomb interaction of the electrons, the paraand diamagnetic electron-photon interactions are all treated by a numerically exact diagonalization using step-wise truncations of the appropriate many-body Fock spaces. We focus on the difference in transport properties between a description within an electric dipole approximation and a description including all higher order terms in a single photon mode model. We find small effects mostly caused by an electrical quadrupole and a magnetic dipole terms that depend strongly on the polarization of the cavity field with respect to the transport direction and the photon energy. When the polarization is aligned along the transport direction we find indications of a weak self-induction that we analyze and compare to the classical counterpart, and the self-energy contribution of high-order interaction terms to the states the electrons cascade through on their way through the system. Like expected the electron-photon interaction is well described in the dipole approximation when it is augmented by the lowest order diamagnetic part for a nanoscale system in a cavity in an external magnetic field.
271. Influence of Ce addition and Pt loading upon the catalytic properties of modified mesoporous PtTi-SBA-15 in total oxidation reactions
Authors:
Ciobanu, M; Petcu, G; Anghel, EM; Papa, F; Apostol, NG; Culita, DC; Atkinson, I; Todorova, S; Shopska, M; Naydenov, A; Velinova, R; Parvulescu, V
Published: JUN 5 2021, APPLIED CATALYSIS A-GENERAL, 619, 118123, DOI: 10.1016/j.apcata.2021.118123
A series of PtCeTi-SBA-15 catalysts, with different concentrations of Pt (0.25 %, 0.5 %, 1.0 %), were synthesized. New Ti-SBA-15 material was obtained by direct synthesis and used as support in successive immobilization of Pt and Ce precursors, changing their order of addition. The characterization of the catalysts has been achieved taking an ensemble of techniques which showed preservation of the support porous structure, high dispersion of the amorphous metal oxides and Pt?, the formation of metal crystals for samples with 1wt% Pt and variation of Pt? content on surface in condition of ceria addition. The best conversion (100 %) was obtained in oxidation of hydrocarbons (CH4, C3H8 and C6H14) for the samples with 1% Pt and a significant diminish of activity was obtained for catalyst in which Ce was added on PtTi-SBA-15 sample. Differently of these, CO oxidation was totally irrespective of the catalyst composition.
Open Access
272. Temperature and thickness dependent magnetostatic properties of [Fe/Py]/FeMn/Py multilayers
Authors:
Polishchuk, DM; Nakonechna, OI; Lytvynenko, YM; Kuncser, V; Savina, YO; Pashchenko, VO; Kravets, AF; Tovstolytkin, AI; Korenivski, V
Published: JUN 2021, LOW TEMPERATURE PHYSICS, 47, DOI: 10.1063/10.0004971
The magnetic properties of thin-film multilayers [Fe/Py]/FeMn/Py are investigated as a function of temperature and thickness of the antiferromagnetic FeMn spacer using SQUID magnetometry. The observed behavior differs substantially for the structures with 6 nm and 15 nm FeMn spacers. While the 15 nm FeMn structure exhibits exchange pinning of both ferromagnetic layers in the entire measurement temperature interval from 5 to 300 K, the 6 nm FeMn structure becomes exchange de-pinned in the vicinity of room temperature. The depinned state is characterized by a single hysteresis loop centered at zero field and having enhanced magnetic coercivity. The observed properties are explained in terms of finite-size effects and possible ferromagnetic interlayer coupling through the thin antiferromagnetic spacer.
273. Enhancing stability of hybrid perovskite solar cells by imidazolium incorporation
Authors:
Tomulescu, AG; Leonat, LN; Neatu, F; Stancu, V; Toma, V; Derbali, S; Neatu, S; Rostas, AM; Besleaga, C; Patru, R; Pintilie, I; Florea, M
Published: AUG 1 2021, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 227, 111096, DOI: 10.1016/j.solmat.2021.111096
Hybrid perovskites based solar cells have demonstrated high conversion efficiency but poor long-term stability. This study reports on the results obtained after doping the CH3NH3PbI2.6Cl0.4 mixed halide perovskite with imidazolium (C3N2H5+, denoted IM) on the "A site" position of a perovskite, to improve photovoltaic performances and stability of hybrid perovskite solar cells. The perovskite films were investigated exhaustively by different characterization techniques: X-ray diffraction, Atomic Force Microscopy, Scanning Electron Microscopy, UV-Vis, X-ray Photoelectron Electron Paramagnetic Resonance spectroscopies, Impedance Spectroscopy and Incident Photon-to-Electron Conversion Efficiency. The photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. The amount of IM inserted in the perovskite play a key role on the film properties. The calculated new tolerance factors according to the "globularity factor" are experimentally proved and thus at doping concentrations greater than 20% for CH3NH3PbI2.6Cl0.4 perovskite the 3D structure is no longer obtained. However, below this value, the IM substituted perovskite film possesses an improved film quality and crystallinity as compared to the pristine film. Substituting MA+ with IM+ provides a favorable way to reduce recombination processes and shows great potential to achieve high stability, and an improved charge generation, resulting in increased PCE values. We find that the optimal percentage of imidazolium incorporation to achieve better stability of solar cells is 6%.
Open Access
274. Thermal and Emission Properties of a Series of Lanthanides Complexes with N-Biphenyl-Alkylated-4-Pyridone Ligands: Crystal Structure of a Terbium Complex with N-Benzyl-4-Pyridone
Authors:
Chiriac, FL; Ilis, M; Madalan, A; Manaila-Maximean, D; Secu, M; Cîrcu, V
Published: APR 2021, MOLECULES, 26, 2017, DOI: 10.3390/molecules26072017
This work focuses on the investigation of the liquid crystalline behavior and luminescence properties of the lanthanide complexes of Eu(III), Sm(III) and Tb(III) with N-biphenyl-alkylated-4-pyridone ligands. The organic ligands having a biphenyl group attached via a long flexible spacer with either 9 or 10 carbon atoms were synthesized by the reaction between 4-hydroxypyridine and the corresponding bromide compounds. The chemical structures of the organic and lanthanide complexes were assigned based on elemental analysis, single-crystal X-ray diffraction, H-1, C-13 NMR and IR spectroscopies, and thermogravimetric analysis (TGA). The X-ray diffraction analysis of a parent compound shows that the lanthanide ions are surrounded by three monodentate pyridone ligands and three bidentate nitrate ions, giving a 9-coordinate environment. The mesogenic behavior and the type of liquid crystalline phases exhibited by the new complexes were analyzed by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM), and powder X-ray diffraction (XRD) studies. Only the lanthanide complexes with longer spacer (10) display a monotropic SmA phase, typically on a short thermal range (less than 10 degrees C). The complexes with shorter flexible chains (9) show no liquid crystalline properties with melting temperatures lower than their analogs with longer spacers. The emission spectra recorded in solid state at room temperatures show typical emission bands for each lanthanide ion employed (Eu(III), Tb(III) and Sm(III)).
275. Partially-oriented MgB2 superconducting bulks with addition of B4C and cubic BN obtained by slip casting under high magnetic field and spark plasma sintering
Authors:
Grigoroscuta, MA; Aldica, G; Pasuk, I; Burdusel, M; Sandu, V; Kuncser, A; Suzuki, TS; Vasylkiv, O; Badica, P
Published: FEB 2021, MATERIALS RESEARCH BULLETIN, 134, 111103, DOI: 10.1016/j.materresbull.2020.111103
Partially-oriented MgB2 bulk discs (13 and 9 %) with the starting compositions of (MgB2)(0.99)(B4C)(0.01) and (MgB2)(0.99)(c-BN)om were fabricated by slip casting under an H-0 = 12 T magnetic field (perpendicular to the disc surface) and subsequent spark plasma sintering. The maximum critical current density and irreversibility field are for H//H-0 (H=applied field). These values are higher or similar to the randomly-oriented samples with the same composition. The maximum volume pinning force (F-p) is lower in the partially-oriented ones than in the randomly-oriented samples. The pinning-force-related parameters depend on the additive and orientation. Assessment of the major pinning mechanism within the scaling and percolation models considering these parameters shows significant limitations. A method to scale F-p is proposed; for the randomly and partially-oriented samples (that show an extra peak in F-p), the single and double Gaussian functions fit well. The results suggest an anisotropic influence of carbon substituting for boron in the MgB2.
Open Access
276. TiO2 nanoparticles coated with bio-inspired ligands for the safer-by-design development of photocatalytic paints
Authors:
Laisney, J; Rosset, A; Bartolomei, V; Predoi, D; Truffier-Boutry, D; Artous, S; Bergé, V; Brochard, G; Michaud-Soret, I
Published: JAN 1 2021, ENVIRONMENTAL SCIENCE-NANO, 8, DOI: 10.1039/d0en00947d
Addition of titanium dioxide nanoparticles (TiO2 NPs) in photocatalytic paints represents a promising alternative aiming to mineralize gaseous pollutants, such as volatile organic compounds (VOCs). However, the risks of release of nanoparticles to human health and the environmental impact have to be taken carefully into account for their development. To take into account these risks, we develop a new method of TiO2 NP synthesis. Here, we report the electrostatic stabilization in aqueous medium with pyrophosphate buffers of different pH ranges followed by coating with bio-inspired molecules (lysine, deferoxamine, dopamine) and polymers (polyacrylic acid, polyethylene glycol, polydopamine) of 4-5 nm spherical photocatalytic TiO2 NPs for the development of safer-by-design photocatalytic paint. Characterization of the so-formed TiO2 nanocomposites by dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS) showed the good grafting of the ligands on the TiO2 surface and an enhanced stability in water compared to the pristine TiO2 NPs. The photocatalytic activity of the TiO2 nanocomposites was investigated by following the degradation of methylene blue (MB) under irradiation. The results showed a modulation of the photocatalytic activity (decrease or increase of the MB degradation rate) as a function of the nature/binding strength of the bio-inspired coating on the oxide surface. Finally, the most promising nanocomposites were incorporated in paints on which preliminary chalking assays were performed after storage for one year in the dark or in interior daylight.
Open Access
277. Thermal Gating of Magnon Exchange in Magnetic Multilayers with Antiferromagnetic Spacers
Authors:
Polishchuk, DM; Tykhonenko-Polishchuk, YO; Lytvynenko, YM; Rostas, AM; Gomonay, OV; Korenivski, V
Published: JUN 4 2021, PHYSICAL REVIEW LETTERS, 126, 227203, DOI: 10.1103/PhysRevLett.126.227203
We observe a strong thermally controlled magnon-mediated interlayer coupling of two ferromagnetic layers via an antiferromagnetic spacer in spin-valve type trilayers. The effect manifests itself as a coherent switching as well as collective resonant precession of the two ferromagnets, which can be controlled by varying temperature and the spacer thickness. We explain the observed behavior as due to a strong hybridization of the ferro- and antiferromagnetic magnon modes in the trilayer at temperatures just below the Neel temperature of the antiferromagnetic spacer.
Open Access
278. Biocompatible Silver Nanoparticles: Study of the Chemical and Molecular Structure, and the Ability to Interact with Cadmium and Arsenic in Water and Biological Properties
Authors:
Bertelà, F; Marsotto, M; Meneghini, C; Burratti, L; Maraloiu, VA; Iucci, G; Venditti, I; Prosposito, P; D'Ezio, V; Persichini, T; Battocchio, C
Published: OCT 2021, NANOMATERIALS, 11, 2540, DOI: 10.3390/nano11102540
In the field of research for designing and preparing innovative nanostructured systems, these systems are able to reveal the presence of heavy metals in water samples, and can efficiently and selectively interact with them, allowing for future applications in the field of water remediation. We investigated the electronic and molecular structure, as well as the morphology, of silver nanoparticles stabilized by mixed biocompatible ligands (the amino acid L-cysteine and the organic molecule citrate) in the presence of cadmium and arsenic ions. The molecular, electronic, and local structure at the ligands/silver nanoparticles interface was probed by the complementary synchrotron radiation-induced techniques (SR-XPS, NEXAFS and XAS). The optical absorption (in the UV-Vis range) of the nanosystem was investigated in the presence of Cd(II) and As(III) and the observed behavior suggested a selective interaction with cadmium. In addition, the toxicological profile of the innovative nanosystem was assessed in vitro using a human epithelial cell line HEK293T. We analyzed the viability of the cells treated with silver nanoparticles, as well as the activation of antioxidant response.
Open Access
279. Quantum turnstile regime of nanoelectromechanical systems
Authors:
Dragomir, R; Moldoveanu, V; Stanciu, S; Tanatar, B
Published: APR 7 2020, PHYSICAL REVIEW B, 101, 165409, DOI: 10.1103/PhysRevB.101.165409
The effects of a turnstile operation on the current-induced vibron dynamics in nanoelectromechanical systems (NEMS) are analyzed in the framework of the generalized master equation. In our simulations each turnstile cycle allows the pumping of up to two interacting electrons across a biased mesoscopic subsystem which is electrostatically coupled to the vibrational mode of a nanoresonator. The time-dependent mean vibron number is very sensitive to the turnstile driving, rapidly increasing/decreasing along the charging/discharging sequences. This sequence of heating and cooling cycles experienced by the nanoresonator is due to specific vibron-assisted sequential tunneling processes along a turnstile period. At the end of each charging/discharging cycle the nanoresonator is described by a linear combination of vibron-dressed states s(v). associated to an electronic configuration nu. If the turnstile operation leads to complete electronic depletion the nanoresonator returns to its equilibrium position, i.e., its displacement vanishes. It turns out that a suitable bias applied on the NEMS leads to a slow but complete cooling at the end of the turnstile cycle. Our calculations show that the quantum turnstile regime switches the dynamics of the NEMS between vibron-dressed subspaces with different electronic occupation numbers. We predict that the turnstile control of the electron-vibron interaction induces measurable changes on the input and output transient currents.
280. GeSn/SiO2 Multilayers by Magnetron Sputtering Deposition for Short-Wave Infrared Photonics
Authors:
Slav, A; Dascalescu, I; Lepadatu, AM; Palade, C; Zoita, NC; Stroescu, H; Iftimie, S; Lazanu, S; Gartner, M; Buca, D; Teodorescu, VS; Ciurea, ML; Braic, M; Stoica, T
Published: DEC 16 2020, ACS APPLIED MATERIALS & INTERFACES, 12, DOI: 10.1021/acsami.0c15887
The development of short-wave infrared (SWIR) photonics based on GeSn alloys is of high technological interest for many application fields, such as the Internet of things or pollution monitoring. The manufacture of crystalline GeSn is a major challenge, mainly because of the low miscibility of Ge and Sn. The use of embedded GeSn nanocrystals (NCs) by magnetron sputtering is a cost-effective and efficient method to relax the growth conditions. We report on the use of GeSn/SiO2 multilayer deposition as a way to control the NC size and their insulation. The in situ prenucleation of NCs during deposition was followed by ex situ rapid thermal annealing. The nanocrystallization of 20X(11nm_Ge0.865S0.135/1.5nm_SiO2) multilayers leads to formation of GeSn NCs with similar to 16% Sn concentration and similar to 9 nm size. Formation of GeSn domes that are vertically correlated contributes to the nanocrystallization process. The absorption limit of similar to 0.4 eV in SWIR found by ellipsometry is in agreement with the spectral photosensitivity. The ITO/20x(GeSn NC/SiO2)/p-Si/Al diodes show a maximum value of the SWIR photosensitivity at a reverse voltage of 0.5 V, with extended sensitivity to wavelengths longer than 2200 nm. The multilayer diodes have higher photocurrent efficiency compared to diodes based on a thick monolayer of GeSn NCs.
281. SWIR photoresponse of SiGe/TiO2 multilayers with Ge-rich SiGe nanocrystals
Authors:
Lepadatu, AM; Palade, C; Slav, A; Dascalescu, I; Cojocaru, O; Iftimie, S; Teodorescu, VS; Stoica, T; Ciurea, ML
Published: 2020, CAS 2020 PROCEEDINGS: 2020 INTERNATIONAL SEMICONDUCTOR CONFERENCE, DOI:
The 1600 nm-extended SWIR photoresponse of SiGe/TiO2 multilayers with Ge-rich SiGe nanocrystals (NCs) is demonstrated. The SiGe NCs based multilayers are obtained by magnetron sputtering deposition of TiO2/ 6x(Ge/SiGe/Ge/TiO2) layers on heated p-Si substrate followed by rapid thermal annealing (RTA). Grazing incidence X-ray diffraction and Raman spectroscopy evidence the formation of cubic Ge-rich SiGe NCs and anatase TiO2. ITO/Ge-rich SiGe NCs based multilayer /p-Si heterostructure diodes, fabricated by depositing top ITO and bottom Al contacts, show n-p behavior. Photocurrent-voltage characteristics measured at 100 K under integral light illumination of reverse biased diode present a photocurrent higher with up to 2 orders of magnitude than the dark current. Spectral photocurrent increases with bias voltage increase and presents a bandgap-related cutoff wavelength of similar to 1600 nm due to the high Ge content of SiGe NCs.
Open Access
282. Charge transfer reaction mechanisms of epoxyketone and boronated peptides at glassy carbon and boron doped diamond electrodes
Authors:
de Jesus, CSH; Enache, TA; Diculescu, VC
Published: DEC 1 2020, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 878, 114733, DOI: 10.1016/j.jelechem.2020.114733
The ubiquitin-proteasome system regulates the level of proteins within cells through controlled proteolysis. In some diseases, the system function is dysregulated turning the ubiquitin-proteasome complex into a target for drug development. The redox behavior of proteasome inhibitors, epoxyketone and boronated peptides carfilzomib, oprozomib and delanzomib was investigated by voltammetric methods using glassy carbon and boron doped diamond electrodes. It was showed that the oxidation of epoxyketone peptides carfilzomib and oprozomib occurred in one step at glassy carbon electrode surface while at boron doped diamond two consecutive charge transfer reactions due to different adsorption orientation at the electrode surface were observed. The moieties of these peptides, involved in the oxidation process, were morpholine for carfilzomib and thiazole for oprozomib. For the boronated peptide delanzomib, two irreversible and independent redox processes, oxidation at +0.80 V and reduction at -1.40 V were identified in neutral media at both electrodes. The oxidation reaction occurred at the amino group close to the pyridine moiety of delanzomib with the transfer of one electron and one proton whereas the reduction process takes place at pyridine ring in a two-electrons two-protons mechanism. Redox mechanisms were proposed and the implications on the proteasome inhibition discussed.
Open Access
283. Nonisocyanate Poly(Hydroxyl Urethane)-Based Green Polymer Hybrid Coating Systems: Tailoring of Biomacromolecular Compound Architecture Using APTMS-ZnO/TEMPO-Oxidized Cellulose Nanoparticles
Authors:
Haniffa, MAM; Illias, HA; Chee, CY; Ibrahim, S; Sandu, V; Chuah, CH
Published: MAY 12 2020, ACS OMEGA, 5, DOI: 10.1021/acsomega.9b04388
Hybrid bionanocomposite coating systems (HBCSs) are green polymer materials consisting of an interface between a coating matrix and nanoparticles. The coating matrix was prepared by using a nonisocyanate poly(hydroxyl urethane) (NIPHU) prepolymer crosslinked via 1,3-diaminopropane and epoxidized Jatropha curcas oil. TEMPO-oxidized cellulose nanoparticles (TARC) were prepared from microcrystalline cellulose, and (3-aminopropyl)trimethoxysilane (APTMS)-coated ZnO nanoparticles (APTMS-ZnO) and their suspensions were synthesized separately. The suspensions at different weight ratios were incorporated into the coating matrix to prepare a series of HBCSs. FT-IR, H-1-NMR, C-13-NMR, XRD, SEM, and TEM were used to confirm the chemical structures, morphology, and elements of the coating matrix, nanomaterials, and HBCSs. The thermomechanical properties of the HBCSs were investigated by TGA-DTG and pencil hardness analyses. The UV and IR absorption spectra of the HBCSs were obtained using UV-vis spectroscopy and FTIR spectroscopy, respectively. The HBCSs exhibited good thermal stability at about 200 degrees C. The degradation temperature at 5% mass loss of all samples was over around 280 degrees C. The HBCSs exhibited excellent UV block and IR active properties with a stoichiometric ratio of the NIPHU prepolymer and EJCO of 1:1 (wt/wt) containing 5 wt % TARC and 15 wt % APTMS-ZnO nanoparticles. It was observed that the sample with 5 wt % TARC and 15 wt % APTMS-ZnO (HBCS-2) exhibited a uniform crosslinking and reinforcement network with a T-onset of 282 degrees C. This sample has successfully achieved good coating hardness and excellent UV and IR absorption.
284. Polarized emission and dielectric studies of novel lanthanidomesogens based on 4-pyridone ligands
Authors:
Ilinca, T; Manaila-Maximean, D; Ganea, PC; Pasuk, I; Cîrcu, V
Published: 2020, ADVANCED TOPICS IN OPTOELECTRONICS, MICROELECTRONICS AND NANOTECHNOLOGIES X, 11718, 117182U, DOI: 10.1117/12.2572109
Novel lanthanidomesogens based on lanthanide nitrates carrying three 4-pyridone ligands having two alkoxy chains at the periphery were synthesized and their structure was assigned based on IR spectroscopy and elemental analysis. Their thermal stability was evaluated by TG analysis confirming that the decomposition starts at very high temperatures around 300 degrees C. The liquid crystalline properties were investigated by using a combination of techniques: polarized optical microscopy (POM) and differential scanning calorimetry (DSC) and, for selected compounds, by variable-temperature powder X-ray diffraction. The new liquid crystal display a hexagonal columnar phase (Col(h)) between 63 degrees C and 242 degrees C, depending on the length of the alkyl chain Dielectric spectroscopy on a wide frequency range was used to evaluate the dipolar relaxation processes. The emission properties of a mixture of E7 doped with a selected europium complex filled in a planar cell were investigated on changing the applied voltage, ranging from 0V up to 15V.
Open Access
285. Lead-Free BNT-BT0.08/CoFe2O4 Core-Shell Nanostructures with Potential Multifunctional Applications
Authors:
Cernea, M; Radu, R; Amorín, H; Greculeasa, SG; Vasile, BS; Surdu, VA; Ganea, P; Trusca, R; Hattab, M; Galassi, C
Published: APR 2020, NANOMATERIALS, 10, 672, DOI: 10.3390/nano10040672
Herein we report on novel multiferroic core shell nanostructures of cobalt ferrite (CoFe2O4) bismuth, sodium titanate doped with barium titanate (BNT-BT0.08), prepared by a two step wet chemical procedure, using the sol gel technique. The fraction of CoFe2O4 was varied from 1:0.5 to 1:1.5 = BNT-BT0.08/CoFe2O4 (molar ratio). X-ray diffraction confirmed the presence of both the spinel CoFe2O4 and the perovskite Bi0.5Na0.5TiO3 phases. Scanning electron microscopy analysis indicated that the diameter of the core shell nanoparticles was between 15 and 40 nm. Transmission electron microscopy data showed two phase composite nanostructures consisting of a BNT-BT0.08 core surrounded by a CoFe2O4 shell with an average thickness of 4-7 nm. Cole-Cole plots reveal the presence of grains and grain boundary effects in the BNT-BT0.08/CoFe2O4 composite. Moreover, the values of the dc conductivity were found to increase with the amount of CoFe2O4 semiconductive phase. Both X-ray photoelectron spectroscopy (XPS) and Mossbauer measurements have shown no change in the valence of the Fe3+, Co2+, Bi3+ and Ti4+ cations. This study provides a detailed insight into the magnetoelectric coupling of the multiferroic BNT-BT0.08/CoFe2O4 core shell composite potentially suitable for magnetoelectric applications.
286. Effect of titanium oxide nanoparticles on the dielectric properties and ionic conductivity of a new smectic bis-imidazolium salt with dodecyl sulfate anion and cyanobiphenyl mesogenic groups
Authors:
Ganea, CP; Cîrcu, V; Manaila-Maximean, D
Published: NOV 1 2020, JOURNAL OF MOLECULAR LIQUIDS, 317, 113939, DOI: 10.1016/j.molliq.2020.113939
A new bis-imidazolium salt with two cyanobiphenyl groups and dodecyl sulfate counterion (BIC) was prepared by the metathesis reaction of the bromide salt with sodium dodecyl sulfate. The ILC shows at room-temperature a stable smectic A phase, confirmed by differential scanning calorimetry, polarized optical microscopy, and powder X-ray diffraction investigations. The ILC was doped with TiO2 nanoparticles, having a high specific area, in concentrations of 0.1%, 0.2%, 1% and 2%. Broadband Dielectric Spectroscopy spectra have been registered in the (10-1-107) Hz frequency range, and (250-330) K temperature domain. The study shows that at constant frequency, the conductivity increases with the temperature and dopant concentration. The characteristic times of the observed relaxation processes showed a temperature variation according to the Vogel-Fulcher-Tammann law. Higher values of characteristic times were calculated at the increase of the thickness of the sample. On the other hand, the increase of the concentration of TiO2 nanoparticles leads to a decrease of the characteristic relaxation times. In order to detectwhether the obtained high permittivity increase is due to the Maxwell-Wagner or Electrode Polarization (EP) type phenomena, studies were made on samples of the same concentration, but different thicknesses, and EP was assigned as the main cause of this dielectric constant variation. (C) 2020 Elsevier B.V. All rights reserved.
287. Highly Efficient Ultralow Pd Loading Supported on MAX Phases for Chemoselective Hydrogenation
Authors:
Trandafir, MM; Neatu, F; Chirica, IM; Neatu, S; Kuncser, AC; Cucolea, EI; Natu, V; Barsoum, MW; Florea, M
Published: MAY 15 2020, ACS CATALYSIS, 10, DOI: 10.1021/acscatal.0c00082
Palladium is one of the most efficient metals for the hydrogenation of organic compounds. However, when molecules, such as nitroaromatics, with several reducible functionalities, are hydrogenated, Pd, like any other very active metal, such as nickel or platinum, often behaves unselectively. One strategy to render Pd more selective is to choose the proper support. Herein, we show that MAX phase powders of Ti3SiC2, Ti2AlC, or Ti3AlC2 can chemoselectively hydrogenate 4-nitrostyrene to 4-aminostyrene, with 100% selectivity, at around 3-4% conversion. To boost the latter, we loaded Ti3SiC2 with 0.0005 wt % Pd and increased the conversion to 100% while maintaining the 4-AS selectivity at >90%. By optimizing the Pd loading, we were also able to increase the turnover frequency 100-fold relative to previous literature results. The identification of this highly efficient and chemoselective system has broad implications for the design of cost-effective, earth-abundant, nontoxic, metal catalysts, with ultralow noble metal loadings.
Open Access
288. Magnetic Fe@Y Composites as Efficient Recoverable Catalysts for the Valorization of the Recalcitrant Marine Sulfated Polysaccharide Ulvan
Authors:
Prech, J; Ioannou, E; Roussis, V; Kuncser, V; Podolean, I; Coman, SM; Valtchev, V; Parvulescu, VI
Published: JAN 13 2020, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, 8, DOI: 10.1021/acssuschemeng.9b05406
Magnetic Fe@Y composites (carbon-coated magnetic iron nanoparticles incorporated in zeolite Y) with 5-8 wt % Fe were synthesized and characterized. Overall acidity of the samples ranged between 2.0 and 2.47 mmol/g and is mostly attributed to Lewis acid sites. The obtained materials were proven to catalyze the hydrolysis of the marine sulfated polysaccharide ulvan with high conversion rates. The distribution of the reaction products depended on the reaction conditions and the concentration of ulvan. The catalytic property catalytic performance correlations clearly showed that the acid zeolite Y is the active phase for the hydrolysis of ulvan, while the iron nanoparticles enable the catalyst separation in a magnetic field. Under oxygen pressure, the selectivity was completely changed to favor succinic acid production. All Fe@Y composites were recycled 10 times with no change in their catalytic performance after recovery via a simple magnetic separation and washing with water.
289. Adsorption, wicking behavior and photodegradation tests of Rhodamine B solution upon wool substrates
Authors:
Frunza, L; Cotorobai, VF; Enculescu, M; Zgura, I; Ganea, CP; Birzu, M; Manaila-Maximean, D
Published: 2020, ADVANCED TOPICS IN OPTOELECTRONICS, MICROELECTRONICS AND NANOTECHNOLOGIES X, 11718, 117182W, DOI: 10.1117/12.2572130
Behavior of some wool fabrics as such or functionalized with semiconductor nanoparticles against the photodegradation of Rhodamine B was investigated. The wool samples were commercially purchased, they were chosen to differ by the chemical nature of the yarns, by the size of the 2D texture elements and by the applied pretreatment. The samples were routinely characterized both in the original form and in the form coated with the oxide particles as well to consider the structure, the surface morphology and their changes due to dye deposition. Several techniques were routinely applied: optical microscopy, XRD, SEM, TGA, UV-Vis spectroscopy and FTIR-ATR. Data have shown that TiO2 layer has either an amorphous structure or is highly dispersed. Drops of Rhodamine B solution were deposited by sessile drop method. We have obtained optical images of the wet/colored spot during the radial wicking, collected with a usual camera. Image comparison was made by direct visualisation. The optical images of the spot on fabrics were taken immediately after the dye was applied, after the fabric was dried and afterwards, after the system illumination by UV-vis light as function of the time. The obtained final spots speak about the dye photodegradation in the studied cases.
290. Structural Changes in Palladium Nanofilms during Thermal Oxidation
Authors:
Samoylov, AM; Ivkov, SA; Pelipenko, D; Sharov, MK; Tsyganova, VO; Agapov, BL; Tutov, EA; Badica, P
Published: OCT 2020, INORGANIC MATERIALS, 56, DOI: 10.1134/S0020168520100131
Nanocrystalline PdO films have been characterized by X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. The results demonstrate that thermal oxidation in an O-2 atmosphere causes similar to 35-nm-thick nanocrystalline Pd films on SiO2/Si(100) substrates to undergo a sequence of phase transformations resulting in PdO formation, followed by PdO decomposition into metallic Pd atT > 1120 K. In the range 670-970 K, theaandctetragonal cell parameters of the nanocrystalline PdO films increase monotonically with increasing temperature. The present and previously reported data have been used to construct a model for the unit cell in the crystal structure of palladium(II) oxide. Based on the quasi-chemical approach, we propose a model that accounts for the observed increase in the tetragonal cell parameters and thep-type conductivity of the nanocrystalline PdO films in terms of the formation of excess interstitial oxygen atoms.
291. Polarization-dependent magnetism of the Ni/BaTiO3 interface
Authors:
Bocirnea, AE; Popescu, DG; Chirila, C; Costescu, RM; Kuncser, V; Stancu, V; Trupina, L; Pasuk, I; Vlaicu, AM; Husanu, MA
Published: MAR 4 2020, PHYSICAL REVIEW MATERIALS, 4, 034402, DOI: 10.1103/PhysRevMaterials.4.034402
We explore the cross coupling between the ferroelectric and ferromagnetic phases in Ni/BaTiO3(001) heterostructures and demonstrate the modulation of the magnetism and incidence of exchange bias in the ultrathin metallic Ni overlayer, depending on the ferroelectric state of the bottom layer. We establish that 5-nm-thick monocrystalline Ni film deposited on BaTiO3 with ferroelectric polarization pointing towards the surface (P+) favors the organization of Ni into uniform ferromagnetic domains. Ni grown on BaTiO3 with opposite ferroelectric polarization is featured by emerging exchange-bias coupling between the ferromagnetic Ni top layers and the antiferromagnetic reacted interface, as theoretically explained by first-principles calculations. We explicitly obtain the morphology of the magnetic domains of the crystalline Ni layer in atomic and magnetic force microscopy measurements (AFM/MFM). The resemblance of AFM and MFM images indicate that, although with radically different morphologies, in both cases all spins orient in the Ni plane. Consequently, the distinct signature of the ferroelectric-ferromagnetic coupling extracted from the magneto-optical Kerr effect measurements encodes all the information of sample magnetism. The peculiar magnetic coupling depending on the ferroelectric state indicates new ways of engineering the functionality of metal/ferroelectric interfaces.
292. PVDF-ferrite composites with dual magneto-piezoelectric response for flexible electronics applications: synthesis and functional properties
Authors:
Gheorghiu, F; Stanculescu, R; Curecheriu, L; Brunengo, E; Stagnaro, P; Tiron, V; Postolache, P; Buscaglia, MT; Mitoseriu, L
Published: MAR 2020, JOURNAL OF MATERIALS SCIENCE, 55, DOI: 10.1007/s10853-019-04279-w
In the present work, a magnetodielectric flexible thick film composite with a quaternary Ba12Fe28Ti15O84 ferrite filler (<= 9 vol%) embedded into PVDF polymer matrix was investigated. The role of filler volume on the macroscopic dielectric, magnetic and ferroelectric properties as well as on the nanoscale magnetic and piezoelectric response was analyzed. The formation of small amounts of polar phases besides the majority alpha-phase of PVDF was shown by XRD and FTIR combined analysis. The electrical properties are dominated by the polymer response, while magnetic order is derived as sum property from the ferrite ones, having a predominant soft magnetic character with small coercivity of H-c similar to 60 Oe and high saturation magnetization of M-s = 2.6 emu/g for the highest concentration of 9 vol%. Permittivity and losses slightly increase with ferrite filler addition, and the composite maintains a dielectric character for all the compositions. Local PFM and MFM investigations have shown a combined ferro/piezoelectric character and magnetic order, with magnetoelectric coupling demonstrated by the reorientation of filler particles and modifications of local piezoresponse when applying a static magnetic field.
293. Estimation of the pyroelectric coefficient for ceramic Pb(Zr,Ti)O3 samples: Comparison of the results obtained by two easy to implement methods
Authors:
Pintilie, L; Iuga, A; Stancu, V; Botea, M
Published: MAY 2020, INFRARED PHYSICS & TECHNOLOGY, 106, 103269, DOI: 10.1016/j.infrared.2020.103269
The pyroelectric coefficient of some Pb(Zr,Ti)O-3 type ceramics was estimated using two methods: a direct method, based on the temperature dependence of the charge/current generated by pyroelectric effect; an indirect method based on the frequency dependence of the pyroelectric signal generated by a pyroelectric element under modulated irradiation with infrared light. The purpose was to compare the results and to assess if the indirect method is enough accurate for rapid estimation of the pyroelectric coefficient of a material envisaged for infrared detection. The direct method is more accurate and requires accurate control of temperature and heating rate, while the indirect method is less accurate, with an error up to 20%, and requires the knowledge of quantities such as dielectric constant, electric conductance, and incident power. However, the indirect method can be more easily implemented and can provide a rapid assessment on the pyroelectric quality of a material with potential use in infrared detectors.
294. THICKNESS INFLUENCE ON THE PYROELECTRIC SIGNAL OF DOPPED PZT CERAMIC PELLETS
Authors:
Stancu, V; Botea, M; Amarande, L; Pintilie, L
Published: JUL-SEP 2020, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 15, DOI:
Pb0.98Bi0.02Zr0.5Fe0.1Nb0.09Ti0.31O3 (PBiZFNT) powder obtained by a solid state reaction technique was uniaxial pressed and sintered at 1200 degrees C in order to fabricate dense thin disk ceramics with different thickness (200 mu up to 600 mu m). The pyroelectric response was influenced by the thickness of the ceramics. The thin ceramic disks of 250 mu m thickness show better pyroelectric signal (approximate to 35 mV) which recommend them for potential use in laser energy meters.
Open Access
295. Unidirectional Magnetic Anisotropy in Dense Vertically-Standing Arrays of Passivated Nickel Nanotubes
Authors:
Locovei, C; Filipoiu, N; Kuncser, A; Stanciu, AE; Antohe, S; Florica, CF; Costas, A; Enculescu, I; Piraux, L; Kuncser, V; Antohe, VA
Published: DEC 2020, NANOMATERIALS, 10, 2444, DOI: 10.3390/nano10122444
We report the facile and low-cost preparation as well as detailed characterization of dense arrays of passivated ferromagnetic nickel (Ni) nanotubes (NTs) vertically-supported onto solid Au-coated Si substrates. The proposed fabrication method relies on electrochemical synthesis within the nanopores of a supported anodic aluminum oxide (AAO) template and allows for fine tuning of the NTs ferromagnetic walls just by changing the cathodic reduction potential during the nanostructures' electrochemical growth. Subsequently, the experimental platform allowed further passivation of the Ni NTs with the formation of ultra-thin antiferromagnetic layers of nickel oxide (NiO). Using adequately adapted magnetic measurements, we afterwards demonstrated that the thickness of the NT walls and of the thin antiferromagneticNiO layer, strongly influences the magnetic behavior of the dense array of exchange-coupled Ni/NiO NTs. The specific magnetic properties of these hybrid ferromagnetic/antiferromagnetic nanosystems were then correlated with the morpho-structural and geometrical parameters of the NTs, as well as ultimately strengthened by additionally-implemented micromagnetic simulations. The effect of the unidirectional anisotropy strongly amplified by the cylindrical geometry of the ferromagnetic/antiferromagnetic interfaces has been investigated with the magnetic field applied both parallel and perpendicular to the NTs axis.
Open Access
296. Mesoporous Cobalt Ferrite Nanosystems Obtained by Surfactant-Assisted Hydrothermal Method: Tuning Morpho-structural and Magnetic Properties via pH-Variation
Authors:
Palade, P; Comanescu, C; Kuncser, A; Berger, D; Matei, C; Iacob, N; Kuncser, V
Published: MAR 2020, NANOMATERIALS, 10, 476, DOI: 10.3390/nano10030476
A facile and cheap surfactant-assisted hydrothermal method was used to prepare mesoporous cobalt ferrite nanosystems with BET surface area up to 151 m(2)/g. These mesostructures with high BET surface areas and pore sizes are made from assemblies of nanoparticles (NPs) with average sizes between 7.8 and 9.6 nm depending on the initial pH conditions. The pH proved to be the key factor for controlling not only NP size, but also the phase purity and the porosity properties of the mesostructures. At pH values lower than 7, a parasite hematite phase begins to form. The sample obtained at pH = 7.3 has magnetization at saturation M-s = 38 emu/g at 300 K (54.3 emu/g at 10 K) and BET surface area S-BET = 151 m(2)/g, whereas the one obtained at pH = 8.3 has M-s = 68 emu/g at 300 K (83.6 emu/g at 10 K) and S-BET = 101 m(2)/g. The magnetic coercive field values at 10 K are high at up to 12,780 Oe, with a maximum coercive field reached for the sample obtained at pH = 8.3. Decreased magnetic performances are obtained at pH values higher than 9. The iron occupancies of the tetrahedral and octahedral sites belonging to the cobalt ferrite spinel structure were extracted through decomposition of the Mossbauer patterns in spectral components. The magnetic anisotropy constants of the investigated NPs were estimated from the temperature dependence of the hyperfine magnetic field. Taking into consideration the high values of BET surface area and the magnetic anisotropy constants as well as the significant magnetizations for saturation at ambient temperature, and the fact that all parameters can be adjusted through the initial pH conditions, these materials are very promising as recyclable anti-polluting agents, magnetically separable catalysts, and targeted drug delivery vehicles.
297. Transport, AC susceptibility, DC magnetization, and magnetic relaxation studies of YBa2Cu3O7 films with synergetic pinning centers grown by PLD
Authors:
Crisan, A; Ivan, I; Miu, L; Becherscu, N; Dang, VS
Published: JUL 20 2020, MODERN PHYSICS LETTERS B, 34, 2040060, DOI: 10.1142/S0217984920400606
We have grown, by Pulsed Laser Deposition (PLD), a large number of YBa2Cu3O7 films with artificial pinning centers, with various impurities, various architectures and thickness, and various techniques of nano-scale pinning engineering: substrate decoration, BaZrO3 (BZO) nano-inclusions, and (quasi) multilayer architecture. Here we will present the results regarding vortex matter, dynamics, and pinning, in some of our best samples. Magnetic relaxation studies with magnetic field perpendicular to the film show that in both cases the splayed defects and/or nanoscale inclusions help reduce the dissipation in certain field-temperature range, by inhibiting the detrimental double vortex-kink formation. The response of the vortex system to AC excitation is rather complex but extremely useful for the characterization of the vortex dynamics. We have measured AC susceptibility in various DC fields, with various AC fields and frequencies and found that the effective vortex activation energy U-eff has a logarithmic dependence on the AC-field-induced current density J. Synergetic pinning centers assured a low anisotropy of the critical current for various field orientations, a property desired in coil/solenoid applications.
Open Access
298. Sn-doped TiO2 nanotubular thin film for photocatalytic degradation of methyl orange dye
Authors:
Bjelajac, A; Petrovic, R; Vujancevic, J; Veltruska, K; Matolin, V; Siketic, Z; Provatas, G; Jaksic, M; Stan, GE; Socol, G; Mihailescu, IN; Janackovic, D
Published: DEC 2020, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 147, 109609, DOI: 10.1016/j.jpcs.2020.109609
We fabricated Sn-doped TiO2 nanotubular film via annealing of anodized TiO2 nanotubes grown on F-SnO2 (FTO) glass. Annealing was carried out at 500 degrees C in ambient air. Anatase crystal structure was achieved with no change in nanotubular morphology in respect to as-anodized amorphous TiO(2 )nanotubes. The X-ray photoelectron spectroscopy analysis revealed Sn on the surface of TiO2 film, following the thermal treatment, probably caused by the diffusion from FTO glass. Depth profile examination of the film chemical composition was conducted by elastic recoil detection analysis, which showed that in addition to the diffusion of Sn from FTO, diffusion of Ti to FTO concurrently occurred. Thus, a higher concentration of Sn was found at the bottom of the tubes, while a lower concentration was present on the tubes' surface top. This explains the improved optical response revealed by a diffuse reflectance spectroscopy. The absorption enhancement demonstrated that Sn-doped TiO2 film was efficient in the degradation of methyl orange dye under visible light.
Open Access
299. Strategy for Modifying Layered Perovskites toward Efficient Solar Light-Driven Photocatalysts for Removal of Chlorinated Pollutants
Authors:
Raciulete, M; Papa, F; Negrila, C; Bratan, V; Munteanu, C; Pandele-Cusu, J; Culita, DC; Atkinson, I; Balint, I
Published: JUN 2020, CATALYSTS, 10, 637, DOI: 10.3390/catal10060637
We have explored an efficient strategy to enhance the overall photocatalytic performances of layered perovskites by increasing the density of hydroxyl group by protonation. The experimental procedure consisted of the slow replacement of interlayer Rb(+)cation of RbLaTa(2)O(7)Dion-Jacobson (DJ) perovskite by H(+)via acid treatment. Two layered perovskites synthesized by mild (1200 degrees C for 18 h) and harsh (950 and 1200 degrees C, for 36 h) annealing treatment routes were used as starting materials. The successful intercalation of proton into D-J interlayer galleries was confirmed by FTIR spectroscopy, thermal analyses, ion chromatography and XPS results. In addition, the ion-exchange route was effective to enlarge the specific surface area, thus enhancing the supply of photocharges able to participate in redox processes involved in the degradation of organic pollutants. HLaTa_01 protonated layered perovskite is reported as a efficient photocatalyst for photomineralization of trichloroethylene (TCE) to Cl(-)and CO(2)under simulated solar light. The enhanced activity is attributed to combined beneficial roles played by the increased specific surface area and high density of hydroxyl groups, leading to an efficiency of TCE mineralization of 68% moles after 5 h of irradiation.
300. Synthesis and characterization of a titanium phosphate-tellurite glass for Faraday rotators
Authors:
Elisa, M; Boroica, L; Sava, BA; Iordache, SM; Iordache, AM; Vasiliu, IC; Stefan, RC; Galca, AC; Kuncser, V; Eftimie, M
Published: JUL 2020, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 103, DOI: 10.1111/jace.17071
This work is focused on investigation of thermal, structural, optical, magnetic, and magneto-optical properties of novel titanium phosphate-tellurite glass applied as Faraday rotators. The glass belonging to the system 35Li(2)O-10Al(2)O(3)-5TiO(2)-45P(2)O(5)-5TeO(2) was prepared by a nonconventional wet route of raw materials processing, followed by melting-quenching-annealing steps. Some important physical properties of the investigated glass have been measured and calculated, providing knowledge related to glass compactness, electronic structure, glass forming capability, etc. XRD analysis evidenced an amorphous network structure of the investigated glass. The optical absorption in the Vis domain is mainly due to Ti3+ ions and Te-2 clusters formed during the glass melting process. A relatively low optical absorption is noticed over 600 nm that activates a significant Faraday magneto-optical effect. Photoluminescence bands in the blue, red, and infrared domains are observed, caused by Te-2 clusters formed during the glass melting process. The magnetization in dependency on applied magnetic field reveals a complex behavior of the glass, depending on temperature. Thus, it is found a ferromagnetic behavior up to 2000 Oe, a paramagnetic component up to 40 000 Oe, followed by a diamagnetic one over 40 000 Oe. Faraday rotation angle and Verdet constant values in the visible domain are correlated with the reduced TeO2 content of the glass.
301. Perovskite ferroelectric thin film as an efficient interface to enhance the photovoltaic characteristics of Si/SnOxheterojunctions
Authors:
Silva, JPB; Vieira, EMF; Silva, JMB; Gwozdz, K; Figueiras, FG; Veltruská, K; Matolín, V; Istrate, MC; Ghica, C; Sekhar, KC; Kholkin, AL; Goncalves, LM; Chahboun, A; Pereira, M
Published: JUN 14 2020, JOURNAL OF MATERIALS CHEMISTRY A, 8, DOI: 10.1039/d0ta02198a
The photovoltaic (PV) response of SnOx/Si heterojunctions (HJs) through the change of the SnO and SnO(2)ratio in the samples that allows us to obtain p- or n-type SnO(x)films is investigated in this work. The values of short-circuit photocurrent density (J(sc)), open-circuit voltage (V-OC), fill factor (FF) and power conversion efficiency (PCE) are found to be 12.6 mA cm(-2), 0.23 V, 27% and 8.3%, for the p-SnOx/n-Si HJ and 10.3 mA cm(-2), 0.20 V, 20% and 4.5% for the n-SnOx/p-Si HJ. The enhanced PV effect observed in the p-SnOx/n-Si HJs can be attributed to a small band offset between SnO(x)and Si, which lowers the diffusion length that can contribute to higher recombination rate and smaller series resistance. Furthermore, the values ofJ(sc),V-OC, FF and PCE were enhanced up to 30.9 mA cm(-2), -2.0 V, 19% and 10.9%, respectively, through the insertion of a 0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3(BCZT) ferroelectric layer between n-Si and p-SnOx. The built-in field developed at the Si/BCZT/SiOx/SnO(x)interfaces together with the depolarizing field, provides a favorable electric potential for the separation and further transport of photo generated electron-hole (e-h) pairs. This work provides a viable approach by combining ferroelectrics with p-SnOx/n-Si HJs for building efficient ferroelectric-based solar cells.
302. Wafer-scale graphene-ferroelectric HfO2/Ge-HfO2/HfO2 transistors acting as three-terminal memristors
Authors:
Dragoman, M; Dinescu, A; Dragoman, D; Palade, C; Moldovan, A; Dinescu, M; Teodorescu, VS; Ciurea, ML
Published: DEC 4 2020, NANOTECHNOLOGY, 31, 495207, DOI: 10.1088/1361-6528/abb2bf
In this paper we report a set of experiments at the wafer level regarding field-effect transistors with a graphene monolayer channel transferred on the ferroelectric HfO2/Ge-HfO2/HfO(2)three-layer structure. This kind of transistor has a switching ratio of 10(3)between on and off states due to the bandgap in graphene induced by the ferroelectric structure. Both top and back gates effectively control the carriers' charge flow in graphene. The transistor acts as a three-terminal memristor, termed a memtransistor, with applications in neuromorphic computation.
303. (Ba,Sr)TiO3 solid solutions sintered from sol-gel derived powders: An insight into the composition and temperature dependent dielectric behavior
Authors:
Patru, RE; Ganea, CP; Stanciu, CA; Surdu, VA; Trusca, R; Ianculescu, AC; Pintilie, I; Pintilie, L
Published: MAR 2020, CERAMICS INTERNATIONAL, 46, DOI: 10.1016/j.ceramint.2019.10.136
Single-phase Ba1-xSrxTiO3 (BST) perovskite ceramics with 0.3 <= x <= 0.4 were prepared from powders synthesized via sol-gel route. The compositions have the ferroelectric-paraelectric phase transition close to room temperature. At 20 degrees C the BST ceramics are ferroelectric for 0.3 <= x <= 0.35 and paraelectric for x = 0.375 and x = 0.40. The study follows the relation between the structural changes produced when increasing the Sr content and the dielectric properties at low intensity electric fields. It is found that the grain size and tetragonality decreases as the Sr content increases. Analyses of complex permittivity and impedance spectroscopy reveal the temperature and frequency dependencies of the dielectric properties. The phase transitions seem to be of first order for all compositions, with a thermal hysteresis that decreases with increasing the Sr content, fact attributed to the corresponding increase of the grain boundaries weight allowing a more efficient stress relaxation in the structure during the change of the symmetry from cubic to tetragonal. The diffusiveness degree during the phase transition is increasing with Sr content, suggesting some relaxor-type contribution attributed to smaller grain size. The ac conductivity follows the universal Jonscher law, with an ac component having the power parameter s independent of Sr content, and a dc component that it is thermally activated with an activation energy of about 0.7-0.77 eV attributed to oxygen vacancies acting as donor-like defects. The fit of impedance spectra at different temperatures and frequencies is obtained by using an equivalent circuit accounting the grains, grain boundaries, electrode interfaces and the local contributions produced by reorientation of defect dipoles or defect clusters. All the component circuits have significant variations around phase transitions. These are discussed in relation to structural changes occurring during transition and considering the changes in the distribution of various charges when polarization vanishes.
304. Spectroscopic investigations on PVDF-Fe2O3 nanocomposites
Authors:
Chipara, D; Kuncser, V; Lozano, K; Alcoutlabi, M; Ibrahim, E; Chipara, M
Published: AUG 10 2020, JOURNAL OF APPLIED POLYMER SCIENCE, 137, 48907, DOI: 10.1002/app.48907
Polyvinylidene fluoride-iron oxide (PVDF-Fe2O3) nanocomposites have been obtained my melt mixing of PVDF with Fe2O3 nanoparticles. The interactions between the polymeric matrix and the nanofiller have been investigated by wide angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, using both red and green excitations (lasers). WAXS, FTIR, and Raman spectra confirm that all samples contain alpha PVDF as the major crystalline form of the polymeric matrix. Experimental data revealed small changes in the positions of X-ray lines as well as modifications of the width of X-ray lines upon loading by Fe2O3 nanoparticles. FTIR and Raman spectra are dominated by the lines of the polymeric matrix. Within the experimental errors, the positions of Raman lines are not affected by the wavelength of the incoming electromagnetic radiation, although they are sensitive to the strain of the polymeric matrix induced by addition of the nanofiller. The loading of the polymeric matrix with nanoparticles stretches the macromolecular chains, affecting their vibrational spectra (FTIR and Raman). A complex dependence of the positions of some Raman and FTIR lines on the loading with Fe2O3 is reported. The manuscript provides a detailed analysis of the effects of nanofiller on the position of WAXS, FTIR, and Raman lines. (c) 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48907.
Open Access
305. Magnetic and ferroelectric properties, crystal and magnetic structures of SrFe11.9In0.1O19
Authors:
Turchenko, VA; Trukhanov, A; Trukhanov, S; Damay, F; Porcher, F; Balasoiu, M; Lupu, N; Chiriac, H; Bozzo, B; Fina, I; Waliszewski, J; Kostishyn, VG; Recko, K; Polosan, S
Published: APR 2020, PHYSICA SCRIPTA, 95, 044006, DOI: 10.1088/1402-4896/ab60fb
The structural investigations of SrFe11.9In0.1O19 compound synthesized by solid-state method have been carried by neutron diffraction method in a wide temperature range. The appearace of spontaneous polarization that coexists with ferrimagnetic ordering has been found out at room temperature in strontium hexaferrite partially substituted with In ions. In order to explaine the presence of ferroelectric properties in SrFe11.9In0.1O19 compound, its crystal structure has been refined within the framework of both centrosymmetric P6(3)/mmc (No. 194) and non-centrosymmetric P6(3)mc (No. 186) space groups. The analysis of refinement results allows to understand microscopic mechanism of appearance ferroelectric properties in strontium hexaferrites.
306. Unexpected magneto-functionalities of amorphous Fe-Gd thin films crossing the magnetization compensation point
Authors:
Stanciu, AE; Schinteie, G; Kuncser, A; Iacob, N; Trupina, L; Ionita, I; Crisan, O; Kuncser, V
Published: MAR 15 2020, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 498, 166173, DOI: 10.1016/j.jmmm.2019.166173
A complex investigation of the morpho-structural, magnetic, magneto-optical and magneto-transport properties of amorphous Fe-Gd thin films crossing the magnetization compensation point is reported and the unexpected observed magneto-functionalities are discussed. A tendency of magnetic domain formation with increasing the Fe content over the compensation concentration is observed. The switch from a reversed Magneto-optical Kerr Effect loop to a direct loop when increasing the Fe content over the compensation point is explained via the specific contribution to the rotation of the polarization vector from each magnetic sublattice, belonging to Fe and Gd, respectively. Local atomic configurations and magnetic interactions ascertained the amorphous character and revealed an out-ofplane orientation of the magnetic moment of Fe above the compensation point. The thermomagnetic curves prove a concentration dependent behavior, explained by weakly coupled magnetization relaxation processes of the two magnetic sub-lattices. On the other hand, the magnetic hysteresis loops gave evidence of two exchange coupled magnetic phases with different coercive fields. According to structural and Fe-57 Mossbauer Spectroscopy results, the two phases correspond to definite nanosized volumes of two different average concentrations (one of them closer to the compensation point) which are randomly distributed in the film. The unexpected single step-like behavior of the magneto-resistivity curves was explained by dissimilar switching of the spins in these two magnetic phases distributed in nano-sized volumes.
Open Access
307. Crystal and magnetic structures, magnetic and ferroelectric properties of strontium ferrite partially substituted with in ions
Authors:
Turchenko, V; Kostishyn, VG; Trukhanov, S; Damay, F; Porcher, F; Balasoiu, M; Lupu, N; Bozzo, B; Fina, I; Trukhanov, A; Waliszewski, J; Recko, K; Polosan, S
Published: APR 25 2020, JOURNAL OF ALLOYS AND COMPOUNDS, 821, 153412, DOI: 10.1016/j.jallcom.2019.153412
The influence of temperature factor to crystal structure as well as magnetic and electric properties of strontium hexaferrite partially substituted with diamagnetic indium ions has been investigated. Ferroelectric properties have been found out in SrFe11.9In0.1O19 compound that contradicts to conventional opinion, which describe its crystal structure within the framework of centrosymmetric space group P6(3)/mmc (No. 194). For determination features of the crystal structure, which are responsible for ferroelectric properties of strontium hexaferrite, have been carried out neutron diffraction measurements with high resolution in temperature range from 1.5 to 740 K. The analysis of hexaferrite structure has been executed within the framework both centrosymmetric and non-centrosymmetric space group. Values of coefficients of magneto crystalline anisotropy at 5 and 300 K and influence of ambient temperature to linear size of magnetic regions have been determined from magnetic measurements. (C) 2019 Elsevier B.V. All rights reserved.
308. Temperature dependence and defect related structure, photoluminescence, (ferro)magnetism and ammonia sensitivity of un-doped nanocrystalline ZnO
Authors:
Mihalache, V; Secu, M; Negrila, C; Bercu, V; Mercioniu, I; Leca, A
Published: DEC 2020, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 262, 114748, DOI: 10.1016/j.mseb.2020.114748
ZnO nanostructures with intrinsic and extended defects were prepared by rapid decomposition of zinc-propio-nate and annealing at 400 degrees C-970 degrees C. The correlation between the structure/morphology, type of native defects (photoluminescence (PL), EPR) and ferromagnetism was investigated, together with ammonia adsorption capacity. All the samples show room temperature ferromagnetism (RTFM). Crystallite size increases while the unit cell volume, c-axis constant, microstrain and saturation magnetization relax with increasing temperature; morphology varies from aggregated nanoparticles to frameworks of well-welded crystals. 400 degrees C-800 degrees C annealed samples show a broad visible and/or a prominent violet-blue PL emission and, two narrow g = 2.0065 and g = 1.9632 EPR signals. 800 degrees C-970 degrees C annealed samples exhibit very intense green-yellow photoluminescence. The intrinsic defects in conjunction with a deformed lattice and/or pinned by grain-boundaries appear responsible for RTFM and Curie temperature exceeding 700 degrees C. Tuning the morphology, PL intensity and ferromagnetic signal by choice of annealing temperature can find applications in (gas) sensing, photonic/optoelectronic and spintronic devices.
Open Access
309. Electron-polaron dichotomy of charge carriers in perovskite oxides
Authors:
Husanu, MA; Vistoli, L; Verdi, C; Sander, A; Garcia, V; Rault, J; Bisti, F; Lev, LL; Schmitt, T; Giustino, F; Mishchenko, AS; Bibes, M; Strocov, VN
Published: APR 2 2020, COMMUNICATIONS PHYSICS, 3, 62, DOI: 10.1038/s42005-020-0330-6
The underlying mechanisms of the metal-insulator transition in correlated oxides are a rich source of interesting physics and a topic of long-standing investigation. Here, the authors use angle-resolved photoelectron spectroscopy to investigate changes in charge carrier properties and electron-phonon interactions as a function of Ce-doping across the metal-insulator transition in CaMnO3. Many transition metal oxides (TMOs) are Mott insulators due to strong Coulomb repulsion between electrons, and exhibit metal-insulator transitions (MITs) whose mechanisms are not always fully understood. Unlike most TMOs, minute doping in CaMnO3 induces a metallic state without any structural transformations. This material is thus an ideal platform to explore band formation through the MIT. Here, we use angle-resolved photoemission spectroscopy to visualize how electrons delocalize and couple to phonons in CaMnO3. We show the development of a Fermi surface where mobile electrons coexist with heavier carriers, strongly coupled polarons. The latter originate from a boost of the electron-phonon interaction (EPI). This finding brings to light the role that the EPI can play in MITs even caused by purely electronic mechanisms. Our discovery of the EPI-induced dichotomy of the charge carriers explains the transport response of Ce-doped CaMnO3 and suggests strategies to engineer quantum matter from TMOs.
310. Investigation of the effect of sodium azide on the coordination mode of flexible ONO-donor hydrazone ligand in preparing manganese coordination compounds
Authors:
Bikas, R; Darvishvand, M; Kuncser, V; Schinteie, G; Siczek, M; Lis, T
Published: NOV 1 2020, POLYHEDRON, 190, 114751, DOI: 10.1016/j.poly.2020.114751
Mononuclear Mn(II) coordination compound, [Mn(H2L)Cl-2] (1), was synthesized by the reaction of H2L and MnCl2 center dot 4H(2)O in methanol where H2L is tridentate ONO-donor hydrazone ligand [H2L = (E)-N'-(2-hydroxy-5-iodobenzylidene)isonicotinohydrazide]. The reaction of H2L with MnCl2 center dot 4H(2)O in the presence of excess amount of NaN3 in methanol gave an azido bridged dinuclear Mn(III) coordination compound, [Mn-2(L)(mu-N-3)(2)(CH3OH)(2)] (2), whereas in the presence of low amount of NaN3, a phenolate bridged dinuclear Mn(II) coordination compound, [Mn-2(HL)(2)(CH3OH)(2)Cl-2]center dot CH3OH (3), was obtained. These compounds were characterized by elemental analysis, spectroscopic methods, single crystal X-ray analysis and magnetic measurements. The structural studies indicated that the ligand is coordinated as ONO-donor ligand in 1-3 and behave as a neutral, dianionic and monoanionic ligand in compounds 1, 2 and 3, respectively. There is a good agreement between spectroscopic properties and structures of the compounds. Several synthetic attempts indicated that the azide anion has considerable effect on the formation of phenolate bridged dinuclear Mn(II) coordination compound which attributed to its general basic properties. Magnetic measurements indicate the formation of dinuclear molecules with ferromagnetic intramolecular couplings in the case of 2 and 3 as well as with much weaker and distributed antiferromagnetic interactions among the dinuclear units of these compounds. (C) 2020 Elsevier Ltd. All rights reserved.
Open Access
311. Controlling Single Molecule Conductance by a Locally Induced Chemical Reaction on Individual Thiophene Units
Authors:
Michnowicz, T; Borca, B; Pétuya, R; Schendel, V; Pristl, M; Pentegov, I; Kraft, U; Klauk, H; Wahl, P; Mutombo, P; Jelínek, P; Arnau, A; Schlickum, U; Kern, K
Published: APR 6 2020, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 59, DOI: 10.1002/anie.201915200
Among the prerequisites for the progress of single-molecule-based electronic devices are a better understanding of the electronic properties at the individual molecular level and the development of methods to tune the charge transport through molecular junctions. Scanning tunneling microscopy (STM) is an ideal tool not only for the characterization, but also for the manipulation of single atoms and molecules on surfaces. The conductance through a single molecule can be measured by contacting the molecule with atomic precision and forming a molecular bridge between the metallic STM tip electrode and the metallic surface electrode. The parameters affecting the conductance are mainly related to their electronic structure and to the coupling to the metallic electrodes. Here, the experimental and theoretical analyses are focused on single tetracenothiophene molecules and demonstrate that an in situ-induced direct desulfurization reaction of the thiophene moiety strongly improves the molecular anchoring by forming covalent bonds between molecular carbon and copper surface atoms. This bond formation leads to an increase of the conductance by about 50 % compared to the initial state.
Open Access
312. Electrospun conductive gold covered polycaprolactone fibers as electrochemical sensors for O2 monitoring in cell culture media
Authors:
Serban, A; Evanghelidis, A; Onea, M; Diculescu, V; Enculescu, I; Barsan, MM
Published: FEB 2020, ELECTROCHEMISTRY COMMUNICATIONS, 111, 106662, DOI: 10.1016/j.elecom.2020.106662
This work reports the use of electrospun conductive gold covered polycaprolactone fibers for the quantification of dissolved O-2. The morphologies of the electrospun fibers obtained at a static and a dynamic drum collector were investigated by scanning electron microscopy. The reduction process of O-2 at negative potentials is analyzed by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) in sodium phosphate buffer (NaPB) pH 7.0 and in cellular media pH 7.4. The electrochemical sensing performance of Au/PCL towards O-2 quantification in NaPB and cellular media is compared by using three electrochemical techniques: cyclic and linear sweep voltammetry and EIS. Measurements are done in a two electrode configuration, using a silver wire as reference, to show the applicability of the method for O-2 quantification in cellular culture media.
313. Simple Ethanol Refluxing Method for Production of Blue-Colored Titanium Dioxide with Oxygen Vacancies and Visible Light-Driven Photocatalytic Properties
Authors:
Lettieri, S; Gargiulo, V; Alfe, M; Amati, M; Zeller, P; Maraloiu, VA; Borbone, F; Pavone, M; Muñoz-García, AB; Maddalena, P
Published: FEB 13 2020, JOURNAL OF PHYSICAL CHEMISTRY C, 124, DOI: 10.1021/acs.jpcc.9b08993
We show that a simple ethanol (EtOH) refluxing treatment at mild temperature (120 degrees C) allows producing blue-colored and reduced titanium dioxide (TiO2-x) exhibiting improved visible-light (VIS) photocatalytic properties. The treatment causes an increase in the density of Ti(III) species and the appearance of two optical absorption features: a broad absorption band-responsible for the blue coloration- extending from the green region (similar to 2.3 eV) up to the near-infrared and a subgap absorption tail close to the band gap energy. The experimental results combined with a computation of the density of states via hybrid Hartree-Fock density functional support the hypothesis that the EtOH reflux treatment leads to formation of surface and subsurface oxygen (O) vacancies. We also show that the excitation-resolved photoluminescence technique allows a high-contrast detection of a subgap optical excitation band peaked at about 430 nm (similar to 2.9 eV), associated with anatase photoluminescence, whose intensity increases after the EtOH reflux treatment. This result gives a very direct support to the debated hypothesis identifying O vacancy states as the energy levels involved in the radiative transition of anatase TiO2. Improved photocatalytic degradation by the processed TiO2 under VIS illumination is demonstrated, and the possible mechanism involved in the formation of surface O vacancies is discussed. The method outlines a very simple, low-cost, and fast procedure to target the formation of O vacancies in the TiO2 surface region.
314. Magneto-functionalities of La 1-x A x MnO 3 (A = K; Ba) synthesized by flash combustion method
Authors:
Bouzid, SA; Galca, AC; Sajieddine, M; Kuncser, V; Rostas, AM; Iacob, N; Enculescu, M; Amarande, L; Pasuk, I; Essoumhi, A
Published: OCT 25 2020, JOURNAL OF ALLOYS AND COMPOUNDS, 839, 155546, DOI: 10.1016/j.jallcom.2020.155546
Open Access
315. A New Zinc Phosphate-Tellurite Glass for Magneto-Optical Applications
Authors:
Elisa, M; Stefan, RC; Vasiliu, IC; Iordache, SM; Iordache, AM; Sava, BA; Boroica, L; Dinca, MC; Filip, AV; Galca, AC; Bartha, C; Iacob, N; Rusu, MI; Eftimie, M; Kuncser, V
Published: SEP 2020, NANOMATERIALS, 10, 1875, DOI: 10.3390/nano10091875
This work investigates the structural, magnetic and magneto-optical properties of a new zinc phosphate-tellurite glass belonging to the 45ZnO-10Al(2)O(3)-40P(2)O(5)-5TeO(2)system. The glass was prepared by a wet method of processing the starting reagents followed by suitable melting-stirring-quenching-annealing steps. Specific parameters such as density, average molecular mass, molar volume, oxygen packaging density, refractive index, molar refractivity, electronic polarizability, reflection loss, optical transmission, band gap and optical basicity have been reported together with thermal, magnetic and magneto-optical characteristics. Absorption bands appear in the blue and red visible region, while over 600 nm the glass becomes more transparent. FTIR and Raman spectra evidenced phosphate-tellurite vibration modes proving the P(2)O(5)and TeO(2)network forming role. Magnetic measurements reveal the diamagnetic character of the Te-doped glass with an additional weak ferromagnetic signal, specific to diluted ferromagnetic oxides. Positive Faraday rotation angle with monotonous decreasing value at increasing wavelength was evidenced from magneto-optical measurements. The final product is a composite material comprising of a non-crystalline vitreous phase and Te-based nanoclusters accompanied by oxygen vacancies. The metallic-like Te colloids are responsible for the dark reddish color of the glass whereas the accompanying oxygen vacancies might be responsible for the weak ferromagnetic signal persisting up to room temperature.
316. Undoped SnO2 as a Support for Ni Species to Boost Oxygen Generation through Alkaline Water Electrolysis
Authors:
Neatu, S; Neatu, F; Diculescu, VC; Trandafir, MM; Petrea, N; Somacescu, S; Krumeich, F; Wennmacher, JTC; Knorpp, AJ; van Bokhoven, JA; Florea, M
Published: APR 22 2020, ACS APPLIED MATERIALS & INTERFACES, 12, DOI: 10.1021/acsami.9b19541
In this study, the synergistic behavior of Ni species and bimodal mesoporous undoped SnO2 is investigated in oxygen evolution reactions (OERs) under alkaline conditions without any other modification of the compositional phases or using noble metals. An efficient and environmentally friendly hydrothermal method to prepare bimodal mesoporous undoped SnO2 with a very high surface area (>130 m(2) g(-1)) and a general deposition-precipitation method for the synthesis of well-dispersed Ni species on undoped SnO2 are reported. The powders were characterized by adsorption-desorption isotherms, TG-DTA, XRD, SEM, TEM, Raman, TPRH2, and XPS. The best NiSn composite generates, under certain experimental conditions, a very high TOF value of 1.14 s(-1) and a mass activity higher than 370 A g(-1), which are remarkable results considering the low amount of Ni deposited on the electrode (3.78 ng). Moreover, in 1 M NaOH electrolyte, this material produces more than 24 mA cm(-2) at an overpotential value of approximately +0.33 V, with only 5 wt % Ni species. This performance stems from the dual role of undoped SnO2, on the one hand, as a support for active and well-dispersed Ni species and on the other hand as an active player through the oxygen vacancies generated upon Ni deposition.
317. Optimization of magnetic fluid hyperthermia with respect to nanoparticle shape-related parameters: case of magnetite ellipsoidal nanoparticles
Authors:
Iacob, N; Kuncser, A; Comanescu, C; Palade, P; Kuncser, V
Published: MAY 22 2020, JOURNAL OF NANOPARTICLE RESEARCH, 22, 138, DOI: 10.1007/s11051-020-04842-6
Issues related to the optimization of heat transfer mechanisms dominated by superparamagnetic relaxation are considered in the case of AC (alternating current) magnetic field hyperthermia procedures. The key role in the conversion of electromagnetic energy to the thermal one via the superparamagnetic relaxation mechanism is played by the magnetic anisotropy of nanoparticles, easily to be controlled via the shape anisotropy component. The optimization process has been discussed in the case of magnetite (Fe3O4) ellipsoidal nanoparticles with dominant shape anisotropy dispersed in different media. Nanoparticles of different sizes and aspect ratios have been considered in correlation with those specific parameters of the actuating AC magnetic field which respect an established biological safely criterion. It has been proven that the dissipated power can be maximized for a given set of biological compatible RF (radiofrequency) field parameters (frequency and field amplitude at the sample space) only for specific pairs of particle sizes and aspect ratios. For instance, it has been shown that ellipsoidal magnetite nanoparticles with 10 nm equatorial size and aspect ratio of 2 are optimal for a maximum transferred power under radiofrequency excitations of 250 kHz and field amplitude of 20 kA/m, if high viscosity dispersion media are used. The methodology for deriving the optimal shape (geometrical) parameters of a specific type of nanoparticles in conditions of using available radiofrequency excitations, or vice versa, for deriving the optimal radiofrequency working parameters in the case of ferrofluids with specific nanoparticles (type and geometry) is described and discussed in detail.
318. Electron paramagnetic resonance and microstructural insights into the thermal behavior of simonkolleite nanoplatelets
Authors:
Rostas, AM; Kuncser, AC; Ghica, D; Palici, A; Maraloiu, VA; Vlaicu, ID
Published: MAY 7 2020, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 22, DOI: 10.1039/d0cp00641f
The aim of this paper is the study of the thermal behavior of the simonkolleite Zn-5(OH)(8)Cl-2 center dot H2O (ZHC) by electron paramagnetic resonance (EPR) spectroscopy, in particular. It is well known that during heating ZHC undergoes a complex transformation which involves several overlapping stages. However, with reference to the data reported on this subject, it can be concluded that there is still an ongoing debate regarding the intermediate stages of this process. The data presented in this study support a simple decomposition process of the ZHC prepared using the precipitation method. The EPR data correlated to the data obtained by other experimental techniques, such as XRD, TEM, SEM and EDX, indicate that during the thermal treatment the ZHC suffers a partial decomposition to ZnO with no intermediate products. After annealing at 500 degrees C for 1 h, a recombination process of ZHC is observed. Moreover, the kinetics associated to these decomposition steps were determined and the evolution of the paramagnetic centers was also followed and studied. This study offers new information related to the thermal behavior of ZHC, especially regarding the EPR data which is reported for the first time on this subject and material.
Open Access
319. Secondary Crystalline Phases Influence on Optical Properties in Off-Stoichiometric Cu2S-ZnS-SnS2 Thin Films
Authors:
Sava, F; Diagne, O; Galca, AC; Simandan, ID; Matei, E; Burdusel, M; Becherescu, N; Becherescu, V; Mihai, C; Velea, A
Published: OCT 2020, MATERIALS, 13, 4624, DOI: 10.3390/ma13204624
Cu2ZnSnS4 (CZTS) is an economically and environmentally friendly alternative to other toxic and expensive materials used for photovoltaics, however, the variation in the composition during synthesis is often followed by the occurrence of the secondary binary and ternary crystalline phases. These phases produce changes in the optical absorption edge important in cell efficiency. We explore here the secondary phases that emerge in a combinatorial Cu2S-ZnS-SnS2 thin films library. Thin films with a composition gradient were prepared by simultaneous magnetron sputtering from three binary chalcogenide targets (Cu2S, SnS2 and ZnS). Then, the samples were crystallized by sulfurization annealing at 450 degrees C under argon flow. Their composition was measured by energy dispersive X-ray spectroscopy (EDX), whereas the structural and optical properties were investigated by grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy and optical transmission measurements. As already known, we found that annealing in a sulfur environment is beneficial, increasing the crystallinity of the samples. Raman spectroscopy revealed the presence of CZTS in all the samples from the library. Secondary crystalline phases such as SnS2, ZnS and Cu-S are also formed in the samples depending on their proximity to the binary chalcogenide targets. The formation of ZnS or Cu-S strongly correlates with the Zn/Sn and Cu/Zn ratio of the total sample composition. The presence of these phases produces a variation in the bandgap between 1.41 eV and 1.68 eV. This study reveals that as we go further away from CZTS in the composition space, in the quasi-ternary Cu2S-ZnS-SnS2 diagram, secondary crystalline phases arise and increase in number, whereas the bandgap takes values outside the optimum range for photovoltaic applications.
320. Structural and functional properties of BaTiO3 porous ceramics produced by using pollen as sacrificial template
Authors:
Lukacs, VA; Stanculescu, R; Curecheriu, L; Ciomaga, CE; Horchidan, N; Cioclea, C; Mitoseriu, L
Published: JAN 2020, CERAMICS INTERNATIONAL, 46, DOI: 10.1016/j.ceramint.2019.08.292
The present paper reports the dependence of structural and functional properties on the porosity level with values down to 50% in BaTiO3 ceramics. Micro-porosity (pore size below 15 pm) with (0-3) connectivity has been produced by using dried pollen particles as sacrificial template. The properties of such porous ceramics are mostly affected by porosity, but also by possible small doping with foreign ions resulted from the template and by small variations of Ba/Ti stoichiometry at the ceramic-pore interfaces, as observed by a shift of the Curie temperature towards lower values when porosity level increases. The dielectric relaxation evidenced a few processes characterised by different activation energies which seem to be not affected by porosity, i.e. they might be assigned to the ceramic part and not to the ceramic-pore interfaces. When increasing porosity, a regular tilting of P(E) loops and increasing of coercivity and reducing polarization were observed, as result of reduction of active ferroelectric component and to the field inhomogeneity in such ceramics.
Open Access
321. Surface states mediated charge transfer in redox behavior of hemin at GaAs(100) electrodes
Authors:
Enache, M; Negrila, C; Lazarescu, V
Published: MAR 29 2020, RSC ADVANCES, 10, DOI: 10.1039/d0ra01508c
EIS and XPS investigations on the interaction of hemin with p- and n-doped GaAs(100) electrodes in PBS solution revealed significant differences concerning both the adsorbed species and the mechanism of the redox process caused by dopant nature. XPS data show that hemin is adsorbed on p-GaAs(100) by its carboxyl groups and adopts a vertical position favorable to a polymeric film formation whereas on n-GaAs(100), the adsorbed hemin is monomeric and has a rather planar configuration involving mainly the OH groups of the organic molecule. Hemin gives rise to a reversible redox process at the p-GaAs(100) electrode whereas at n-GaAs(100), there is only one reduction wave of a considerably lower current density appearing at a more negative potential. The effects of the applied potential on the phase angle measured at p-GaAs(100) point out major changes not only in the insulating properties of the adsorbed layer, as found at n-GaAs(100), but also in the electronic properties of the semiconductor triggered by the hemin redox process. Analysis of the experimental data points to a mechanism of charge transfer through surface states, the observed differences being related to the location of the surface states with respect to the formal potential of the hemin redox couple.
322. Magnetic properties and thermal stability of polyvinylidene fluoride-Fe2O3 nanocomposites
Authors:
Kuncser, V; Chipara, D; Martirosyan, KS; Schinteie, GA; Ibrahim, E; Chipara, M
Published: JAN 28 2020, JOURNAL OF MATERIALS RESEARCH, 35, DOI: 10.1557/jmr.2019.375
Nanocomposites of polyvinylidene fluoride loaded with various amounts of gamma-Fe2O nanoparticles, with an average size ranging between 20 and 40 nm, have been obtained by melt mixing and investigated using various experimental techniques [Superconducting Quantum Interference Device, Mossbauer, and Thermogravimetric Analysis]. Magnetic and Mossbauer measurements confirmed the presence of maghemite and a trace of a paramagnetic iron compound. Magnetic data are consistent with a blocking temperature close to room temperature (RT), showing a decrease in the coercive field as the temperature is increased. A weak exchange bias was noticed in all nanocomposites investigated at all temperatures and tentatively ascribed to surface spin disorder. The temperature dependence of the coercive field obeys the Kneller law. The nanocomposites exhibit superparamagnetic behavior near RT. Most magnetic measurements have been performed below the blocking temperature, revealing thus a complex behavior. The dependence of the mass loss derivative versus temperature, as obtained by thermogravimetric analysis, exhibits a single peak due to the thermal degradation of the polymeric matrix. A weak increase in the thermal stability of the polymeric matrix upon loading with maghemite is reported.
Open Access
323. Tuning structural and magnetic properties of Fe oxide nanoparticles by specific hydrogenation treatments
Authors:
Greculeasa, SG; Palade, P; Schinteie, G; Leca, A; Dumitrache, F; Lungu, I; Prodan, G; Kuncser, A; Kuncser, V
Published: OCT 14 2020, SCIENTIFIC REPORTS, 10, 17174, DOI: 10.1038/s41598-020-74188-5
Structural and magnetic properties of Fe oxide nanoparticles prepared by laser pyrolysis and annealed in high pressure hydrogen atmosphere were investigated. The annealing treatments were performed at 200 degrees C (sample A200C) and 300 degrees C (sample A300C). The as prepared sample, A, consists of nanoparticles with similar to 4 nm mean particle size and contains C (similar to 11 at.%), Fe and O. The Fe/O ratio is between gamma-Fe2O3 and Fe3O4 stoichiometric ratios. A change in the oxidation state, crystallinity and particle size is evidenced for the nanoparticles in sample A200C. The Fe oxide nanoparticles are completely reduced in sample A300C to alpha-Fe single phase. The blocking temperature increases from 106 K in A to 110 K in A200C and above room temperature in A300C, where strong inter-particle interactions are evidenced. Magnetic parameters, of interest for applications, have been considerably varied by the specific hydrogenation treatments, in direct connection to the induced specific changes of particle size, crystallinity and phase composition. For the A and A200C samples, a field cooling dependent unidirectional anisotropy was observed especially at low temperatures, supporting the presence of nanoparticles with core-shell-like structures. Surprisingly high M-S values, almost 50% higher than for bulk metallic Fe, were evidenced in sample A300C.
324. EFFECTS OF ANNEALING ON THE PHYSICAL PROPERTIES OF ITO THIN FILMS GROWN BY RADIO FREQUENCY MAGNETRON SPUTTERING
Authors:
Radu, A; Locovei, C; Antohe, VA; Socol, M; Coman, D; Manica, M; Dumitru, A; Dan, L; Radu, C; Raduta, AM; Ion, L; Iftimie, S; Antohe, S
Published: JUL-SEP 2020, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 15, DOI:
Indium-doped tin oxide (ITO) thin films were fabricated by radio frequency magnetron sputtering and were subjected to in-situ and ex-situ annealing, at 200 degrees C, 300 degrees C and 400 degrees C, respectively. The in-situ thermal treatment consisted to intentionally heating the samples' substrates, while the ex-situ annealing was performed using an oven, under ambient atmosphere. For the ITO samples subjected to ex-situ annealing, the density of oxygen vacancies increased leading to the decrease of the electrical resistivity. No significant changes were noticed in terms of transmission spectroscopy after the thermal treatment; while by evaluating the Skewness parameter was determined that the annealing improves the planarity of samples' surface.
Open Access
325. The Influence of Synthesis Parameters on Structural and Magnetic Properties of Iron Oxide Nanomaterials
Authors:
Cursaru, LM; Piticescu, RM; Dragut, DV; Tudor, IA; Kuncser, V; Iacob, N; Stoiciu, F
Published: JAN 2020, NANOMATERIALS, 10, 85, DOI: 10.3390/nano10010085
Magnetic iron oxides have been used in biomedical applications, such as contrast agents for magnetic resonance imaging, carriers for controlled drug delivery and immunoassays, or magnetic hyperthermia for the past 40 years. Our aim is to investigate the effect of pressure and temperature on the structural, thermal, and magnetic properties of iron oxides prepared by hydrothermal synthesis at temperatures of 100-200 degrees C and pressures of 20-1000 bar. It has been found that pressure influences the type of iron oxide crystalline phase. Thus, the results obtained by Mossbauer characterization are in excellent agreement with X-ray diffraction and optical microscopy characterization, showing that, for lower pressure values (<100 bar), hematite is formed, while, at pressures >100 bar, the major crystalline phase is goethite. In addition, thermal analysis results are consistent with particle size analysis by X-ray diffraction, confirming the crystallization of the synthesized iron oxides. One order of magnitude higher magnetization has been obtained for sample synthesized at 1000 bar. The same sample provides after annealing treatment, the highest amount of good quality magnetite leading to a magnetization at saturation of 30 emu/g and a coercive field of 1000 Oe at 10 K and 450 Oe at 300 K, convenient for various applications.
326. Ionophore- Nafion™ modified gold-coated electrospun polymeric fibers electrodes for determination of electrolytes
Authors:
Aldea, A; Matei, E; Leote, RJB; Rau, I; Enculescu, I; Diculescu, VC
Published: DEC 10 2020, ELECTROCHIMICA ACTA, 363, 137239, DOI: 10.1016/j.electacta.2020.137239
The present work describes the electrochemical properties of ionophores immobilized at the surface of electrodes obtained from electrospun polymeric fibers, in order to develop sensors for the analysis of electrolytes. Poly(methyl methacrylate) submicrometer fibers were prepared by electrospinning, coated with a gold layer by magnetron sputtering and then transferred on polyethylene terephthalate (PET) in order to obtained flexible electrodes. The ionophores were immobilized at the surface of these electrodes by drop-casting a ionophore-Nafion mixed solution. The sensor surface was investigated by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy in order to understand the morphology and distribution of a model Ca2+ ionophore over the electrode surface. Also, Fourier-transformed infrared spectroscopy was performed and demonstrated that the model Ca2+ ionophore can be immobilized in the nafion matrix maintaining its conformation, while cyclic voltammetry and electrochemical impedance spectroscopy demonstrated that the Ca2+ ionophore allows the diffusion of target ions through this this type of membrane. In order to prove the concept of ionophore-based sensors for the analysis of some electrolytes, Ca2+, NH4+, Cl- and H+ ionophore immobilized in a nafion matrix at the surface of these flexible electrodes were tested and the determination of the target ions performed by potentiometry in different media including artificial sweat. Finally, sensitivities, limits of detection, selectivity coefficients were determined. (C) 2020 Elsevier Ltd. All rights reserved.
Open Access
327. Optical Properties of Composites Based on Graphene Oxide and Polystyrene
Authors:
Stroe, M; Cristea, M; Matei, E; Galatanu, A; Cotet, LC; Pop, LC; Baia, M; Danciu, V; Anghel, I; Baia, L; Baibarac, MA
Published: MAY 2020, MOLECULES, 25, 2419, DOI: 10.3390/molecules25102419
In this work, new optical properties of composites based on polystyrene (PS) microspheres and graphene oxide (GO) are reported. The radical polymerization of styrene in the presence of benzoyl peroxide, pentane and GO induces the appearance of new ester groups in the PS macromolecular chains remarked through an increase in the absorbance of the infrared (IR) band at 1743 cm(-1). The decrease in the GO concentration in the PS/GO composites mass from 5 wt.% to 0.5 wt.% induces a diminution in the intensities of the D and G Raman bands of GO simultaneous with a down-shift of the D band from 1351 to 1322 cm(-1). These variations correlated with the covalent functionalization of the GO layers with PS. For the first time, the photoluminescent (PL) properties of PS/GO composites are reported. The PS microspheres are characterized by a PL band at 397 nm. Through increasing the GO sheets' concentration in the PS/GO composite mass from 0.5 wt.% to 5 wt.%, a PS PL quenching process is reported. In addition, in the presence of ultraviolet A (UVA) light, a photo-degradation process of the PS/GO composite having the GO concentration equal to 5 wt.% is demonstrated by the PL studies.
328. Obtaining SiGe nanocrystallites between crystalline TiO2 layers by HiPIMS without annealing
Authors:
Sultan, MT; Gudmundsson, JT; Manolescu, A; Teodorescu, VS; Ciurea, ML; Svavarsson, HG
Published: MAY 1 2020, APPLIED SURFACE SCIENCE, 511, 145552, DOI: 10.1016/j.apsusc.2020.145552
Formation of SiGe nanocrystals in an oxide matrix via deposition and subsequent annealing is a widely applied approach as it gives good control over optical properties by varying the Ge atomic fraction, the size, shape and crystallinity of the nanocrystals. A common drawback of annealing is a strain relaxation in the structure creating dislocations, point defects, dangling bonds, Ge clustering and altered interface morphology. All these phenomena are well-known to degrade the optoelectronic and electrical properties of the structure. As a proof of concept, in this study we have utilized a modern technique of high impulse power magnetron sputtering (HiPIMS) to obtain a crystalline TiO2/SiGe/TiO2 structure without any pre-/post-annealing. It is furthermore demonstrated how a control of the nano-crystallite size is obtained by altering the HiPIMS discharge power alone. Grazing incidence X-ray diffraction analysis was carried out for the structural characterization, while photocurrent measurements were utilized to access the role of TiO2 structural morphology over interface integrity in determining spectral feature and sensitivity. An increase of 1 - 2 orders magnitude in spectral intensity was achieved for as-grown structures fabricated via HiPIMS in comparison to annealed structure, sputtered with conventional direct current magnetron sputtering.
329. Influence of doping the inorganic cation with Eu or Sb on the properties of perovskite films
Authors:
Stancu, V; Leonat, LN; Tomulescu, AG; Derbali, S; Pintilie, L; Besleaga, C; Galca, AC; Neatu, F; Neatu, T; Florea, M; Pintilie, I
Published: JUL 2020, PHYSICA SCRIPTA, 95, 075707, DOI: 10.1088/1402-4896/ab90be
This study reports on the results obtained after doping the [CH3NH3](0.94)[C3N2H5](0.06)PbI2.6Cl0.4 mixt halide perovskite with europium or antimony (Eu3+/Sb3+) at the 'B site'. This way two new complex compounds were obtained, [CH3NH3](0.94)[C3N2H5](0.06)Pb1-yByI2.6Cl0.4 (B = Eu or Sb and y = 0-0.05) as perovskite precursor solutions and deposited as thin films. The properties of the perovskite films were investigated by various characterization techniques: x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), UV-vis spectroscopy while the photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. We find that doping the mixt halide perovskite with very small quantities of Sb improves the quality of the perovskite films and further improves the stability of perovskite solar cells.
330. Magnetic properties of BaNi x Fe 12-x O 19 (x=0.0-1.0) hexaferrites, synthesized by citrate -gel auto -combustion and sintered by conventional and spark plasma methods
Authors:
Cernea, M; Greculeasa, SG; Radu, R; Aldica, G; Ganea, P; Surdu, VA; Tanasa, ET; Cioangher, M; Iacob, N; Costescu, RM
Published: AUG 5 2020, JOURNAL OF ALLOYS AND COMPOUNDS, 831, DOI:
331. Hierarchical composites of B4C-TiB2 eutectic particles reinforced with Ti
Authors:
Solodkyi, I; Bogomol, I; Bolbut, V; Loboda, P; Kuncser, A; Vasylkiv, O; Badica, P
Published: DEC 15 2020, CERAMICS INTERNATIONAL, 46, DOI: 10.1016/j.ceramint.2020.07.312
Eutectic particles of B4C-TiB2 were reinforced with Ti by spark plasma sintering (SPS) or infiltration. The SPSed samples with 20, 30 and 40 wt. % Ti consisted of ceramic phases, and had a bicontinuous macrostructure formed by the Ti-rich region and the eutectic particles region, while the infiltrated sample was a complex composite comprised of a 3D Ti-rich continuous network, composite in nature, that contained Ti-metal and in which are embedded isolated ceramic (eutectic) particles. The SPSed samples are brittle with the maximum bending strength of 300 MPa for the 30 wt. % Ti, higher than for a reference sample produced by SPS from directionally solidified eutectic particles. A higher amount of added Ti results in a higher displacement in the bending test suggesting a higher fracture toughness. Simultaneous strengthening and toughening of the composite was realized. The infiltrated sample was ductile, while its bending strength (220 MPa) was comparable to the values measured for the brittle as-introduced reference sample and the sample with 20 wt. % Ti, both produced by SPS. In the SPSed and infiltrated samples at the interface between the Ti-rich region and B4C-TiB2 eutectic particles, a local 'pull-out' intergranular fracturing mechanism mainly involving Ti-B 1D-grains was observed. This local micromechanism together with a 'pull out' macromechanism of the eutectic grains from the Ti-rich component are considered important for the bridging/anchoring behavior responsible for the strengthening and toughening processes in our novel hierarchical composites.
332. Effect of proton fluence on the superconducting properties of MgB2. irradiated with protons of high energy
Authors:
Sandu, V; Ionescu, AM; Ivan, I; Craciun, L; Aldica, G
Published: NOV 15 2020, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 578, 1353734, DOI: 10.1016/j.physc.2020.1353734
Effects of proton irradiation on the superconducting properties of sintered MgB2 samples were investigated as a function of proton fluence at fixed energy. All experimental data suggest that critical current densities, irreversibility field and creep activation energy are enhanced because of the complex disorder, which mainly affects the grain boundaries, brought on the crystalline structure by the energetic protons.
333. Exploring the effect of aliovalent substitution of Pb2+ by Eu3+ on structural, morphological and optical properties of CH3NH3PbI3 perovskite films
Authors:
Derbali, S; Nouneh, K; Florea, M; Neatu, F; Neatu, S; Leonat, LN; Secu, M; Tomulescu, AG; Stancu, V; Pintilie, L; Touhami, ME; Galca, AC
Published: APR 2020, PHYSICA SCRIPTA, 95, 044003, DOI: 10.1088/1402-4896/ab5baa
In this work, the effect of aliovalent substitution of Pb2+ by Eu3+ on structural, morphological and optical properties of CH3NH3PbI3 (MAPbI(3)) was studied, aiming to improve the properties of perovskite films used in solar cells application. The surface morphology, the microstructure and the optical properties of the obtained films containing different Europium (Eu) concentrations were characterized by atomic force microscopy, x-ray photoelectron spectroscopy, x-ray diffraction, UV-vis spectroscopy and photoluminescence spectroscopy.
Open Access
334. SiGe nanocrystals in SiO2 with high photosensitivity from visible to short-wave infrared
Authors:
Stavarache, I; Logofatu, C; Sultan, MT; Manolescu, A; Svavarsson, HG; Teodorescu, VS; Ciurea, ML
Published: FEB 24 2020, SCIENTIFIC REPORTS, 10, 3252, DOI: 10.1038/s41598-020-60000-x
Films of SiGe nanocrystals (NCs) in oxide have the advantage of tuning the energy band gap by adjusting SiGe NC s composition and size. In this study, SiGe-SiO2 amorphous films were deposited by magnetron sputtering on Si substrate followed by rapid thermal annealing at 700, 800 and 1000 degrees C. We investigated films with Si:Ge:SiO2 compositions of 25:25:50 vol.% and 5:45:50 vol.%. TEM investigations reveal the major changes in films morphology (SiGe NCs with different sizes and densities) produced by Si:Ge ratio and annealing temperature. XPS also show that the film depth profile of SiGe content is dependent on the annealing temperature. These changes strongly influence electrical and photoconduction properties. Depending on annealing temperature and Si:Ge ratio, photocurrents can be 10(3) times higher than dark currents. The photocurrent cutoff wavelength obtained on samples with 25:25 vol% SiGe ratio decreases with annealing temperature increase from 1260 nm in SWIR for 700 degrees C annealed films to 1210 nm for those at 1000 degrees C. By increasing Ge content in SiGe (5:45 vol%) the cutoff wavelength significantly shifts to 1345 nm (800 degrees C annealing). By performing measurements at 100 K, the cutoff wavelength extends in SWIR to 1630 nm having high photoresponsivity of 9.35 AW(-1).
335. HfO2-Al2O3 Dielectric Layer for a Performing Metal-Ferroelectric-Insulator-Semiconductor Structure with a Ferroelectric 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 Thin Film
Authors:
Silva, JPB; Sekhar, KC; Veltruská, K; Matolín, V; Negrea, RF; Ghica, C; Oliveira, MJS; Moreira, JA; Pereira, M; Gomes, MJM
Published: SEP 22 2020, ACS APPLIED ELECTRONIC MATERIALS, 2, DOI: 10.1021/acsaelm.0c00480
In this work, the ferroelectric and fatigue characteristics of Au/0.5Ba(Zr0.2Ti0.8)O-3-0.5(Ba0.7Ca0.3)TiO3(BCZT)/Si metal-ferroelectric-semiconductor (MFS) structures are investigated. Moreover, the effect of introducing a thin dielectric HfO2-Al2O3 (HAO) layer with different thicknesses between the BCZT layer and the Si substrate on the ferroelectric characteristics in the metal-ferroelectric-insulator-semiconductor (MFIS) configuration is evaluated. It is evidenced that the insertion of the HAO layer with a thickness of 8 nm improves the memory window of the capacitance-voltage (C-V) curves by 106% compared to the value obtained in the MFS structure and reduces the leakage currents. Furthermore, the Au/BCZT/HAO (8 nm)/Si structure shows a remarkable remnant polarization (P-r) of 7.8 mu C/cm(2), with a coercive voltage of 1.9 V. The obtained value for P-r corresponds to a six times enhancement when compared to the value obtained in the Au/BCZT/Si structure. In addition, the fatigue studies reveal that the P-r obtained in the Au/BCZT/HAO/Si structure slightly decreases (3%) with continuous cycling, up to 10(9) cycles. The present work evidences that Au/BCZT/HAO/Si structures are promising for nonvolatile memory applications.
Open Access
336. MORPHOLOGICAL AND STRUCTURAL INVESTIGATION OF THE POLY(VINYL CHLORIDE)/GRAPHENE OXIDE COMPOSITES
Authors:
Stingescu, L; Cadar, C; Cotet, LC; Baia, L; Saszet, K; Magyari, K; Mihis, AG; Fort, CI; Stroe, M; Matei, E; Nila, A; Anghel, I; Baia, M; Baibarac, M; Danciu, V
Published: 2020, STUDIA UNIVERSITATIS BABES-BOLYAI CHEMIA, 65, DOI: 10.24193/subbchem.2020.3.19
The morphological and structural properties of the poly(vinyl chloride)/graphene oxide (PVC/GO) composites are reported. By the mixture of the two constituents, the PVC/GO composite membranes with a concentration of the GO sheets varying from 0 wt.% to 0.5, 1, 2, 3, 4 and 5 wt.% were prepared. Using scanning electron microscopy (SEM) and the analysis of the atomic force microscopy (AFM) images we observed that as increasing the GO concentration in the PVC mass from 0 wt.% to 5 wt.%, the average surface roughness decreases from 235 mu m to 227 mu m. Using Raman scattering, we report that as increasing the GO concentration in the PVC mass, the ratio between the relative intensities of the Raman lines situated in the spectral ranges 600-650 and 2850-3000 cm(-1) (I600-650/I2850-3000) increases as a consequence of the change of GO carbon atoms hybridization from sp(2) to sp(3). An increase in the number of C-C bonds, simultaneous with the appearance of O-C=O bonds and the decrease of the chlorine concentration, when the GO concentration increases in the PVC weight is reported by X-ray photoelectron spectroscopy (XPS). The down-shift of the main diffraction signal from 24 degrees to 26 degrees when the GO concentration increases in the PVC/GO composite mass from 0 wt.% to 5 wt.%, confirms the incorporation of GO in the polymeric matrix and the modification of the original PVC sample structure. Using transmission electron microscopy (TEM), no agglomerations of the GO structures within the PVC/GO matrix contrast limit were observed.
337. Influence of SiGe Nanocrystallization on Short-Wave Infrared Sensitivity of SiGe-TiO2 Films and Multilayers
Authors:
Lepadatu, AM; Palade, C; Slav, A; Cojocaru, O; Maraloiu, VA; Iftimie, S; Comanescu, F; Dinescu, A; Teodorescu, VS; Stoica, T; Ciurea, ML
Published: NOV 12 2020, JOURNAL OF PHYSICAL CHEMISTRY C, 124, DOI: 10.1021/acs.jpcc.0c06290
Continuous development of Si photonics requires ecological and cost-effective materials. In this work, SiGe nanocrystals (NCs) embedded in TiO2 are investigated as a photosensitive material for visible (VIS) to short-wave infrared (SWIR) broad-range detection. The TiO2 matrix has the advantage of a lower band gap than SiO2, facilitating transport of photogenerated carriers in NCs. The advantage of SiGe NCs over Ge NCs is emphasized by elucidating the mechanisms involved in rapid thermal annealing (RTA)-induced nanocrystallization. An efficiently increased NC stabilization is achieved by avoiding the detrimental fast Ge diffusion. For this, the structure, morphology, and composition were carefully characterized by high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy. Two types of structures were investigated, a film of SiGe-TiO2 alloy and a multilayer of a stack of six SiGe/TiO2 pairs. The layers have been deposited on Si wafers using magnetron sputtering of Si, Ge, and TiO2 followed by RTA in an inert atmosphere. The stabilization of SiGe NCs is achieved by the formation during RTA of protective SiO2 thin layers through Si oxidation at the SiGe NC surface, acting as a barrier for Ge diffusion. Thus, embedded Ge-rich SiGe NCs are obtained, resulting in the SWIR extension of the spectral photocurrent up to 1700 nm for films and 1600 nm for multilayers. This study has shown that in multilayers, the local anisotropy of crystallization is compensated by the stress field developed in the SiGe lattice, highly visible in the bottom part. Also, SiGe crystallizes faster than TiO2 in the rutile phase, and therefore, TiO2 remains mainly amorphous.
Open Access
338. ZnO nanostructures grown on ITO coated glass substrate by hybrid microwave-assisted hydrothermal method
Authors:
Filip, A; Musat, V; Tigau, N; Polosan, S; Pimentel, A; Ferreira, S; Gomes, D; Calmeiro, T; Martins, R; Fortunato, E
Published: APR 2020, OPTIK, 208, 164372, DOI: 10.1016/j.ijleo.2020.164372
Over the last decades, zinc oxide nanostructures (NSs) have been studied due to outstanding chemical and physical properties, able to serve a plethora of applications. The growth of NSs on different substrates coated with ITO film allow their direct implementation in various micro-/nano-devices. The microwave-assisted hydrothermal method is a new hybrid approach used for synthesis of oxide NSs due to unique advantages in energy efficiency/high reaction rate and possibility of obtaining different morphologies with size and shape-controlled, which are relevant for some applications. In this paper, we present a simple one step synthesis of ZnO 1D and 2D NSs with homogeneous distribution and orientation perpendicular to substrates covered with ITO film, using a microwave-assisted hydrothermal method. The effect of seed layer treatment on the structure, morphology and optical properties of the obtained NSs have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), UV/VIS/NIR and photoluminescence spectroscopy. The obtained ZnO NSs with 1D and 2D morphologies show high visible transmittance between 80-90 % and band gap energy values between 3.27 and 3.22 eV. The I-V curves and photoluminescence spectra indicate good ohmic contacts on both sides (ITO and Au-top electrodes) and highlight the effect of the thermal treatment of seed layer on the photoluminescence emission and electrical conductivity of the obtained NSs.
Open Access
339. Combining Fluorinated Polymers with Ag Nanoparticles as a Route to Enhance Optical Properties of Composite Materials
Authors:
Satulu, V; Mitu, B; Ion, V; Marascu, V; Matei, E; Stancu, C; Dinescu, G
Published: AUG 2020, POLYMERS, 12, 1640, DOI: 10.3390/polym12081640
Polymer-based nanocomposites have recently received considerable attention due to their unique properties, which makes them feasible for applications in optics, sensors, energy, life sciences, etc. The present work focuses on the synthesis of nanocomposites consisting of a polytetrafluorethylene-like matrix in which metallic nano-silver are embedded, by using multiple magnetron plasmas. By successively exposing the substrate to separate RF magnetrons using as combination of target materials polytetrafluorethylene (PTFE) and silver, individual control of each deposition process is insured, allowing obtaining of structures in which silver nanoparticles are entrapped in-between two PTFE layers with given thicknesses. The topographical and morphological characteristics investigated by means of Scanning Electron Microscopy and Atomic Force Microscopy techniques evidenced the very presence of Ag nanoparticles with typical dimension 7 nm. The chemical composition at various depositing steps was evaluated through X-ray Photoelectron Spectroscopy. We show that the presence of the top PTFE layer prevents silver oxidation, while its thickness allows the tailoring of optical properties, as evidenced by spectroellipsometry. The appearance of chemical bonds between silver atoms and PTFE atoms at interfaces is observed, pointing out that despite of pure physical deposition processes, a chemical interaction between the polymeric matrix and metal is promoted by plasma.
340. Polymer Dispersed Liquid Crystals doped with nanoparticles: electric and electro-optical properties
Authors:
Manaila-Maximean, D; Ganea, P; Loiko, VA; Konkolovich, AV; Cîrcu, V; Danila, O; Barar, A
Published: 2020, ADVANCED TOPICS IN OPTOELECTRONICS, MICROELECTRONICS AND NANOTECHNOLOGIES X, 11718, 117182R, DOI: 10.1117/12.2572104
Polymer Dispersed Liquid Crystal (PDLC) films are composite materials consisting of LC droplets embedded in polymers. In order to decrease the switching voltage of these devices, we prepared PDLC films doped with single wall carbon nanotubes (SWCNTs). The mesomorphic properties of the films were investigated by polarizing optical microscopy (POM). The electrical characteristics have been investigated using a Broadband Dielectric Spectrometer in a frequency domain (0.01-10(7)) Hz and a temperature range (280-350) K. Some key aspects of an optical model for the analysis of the coherent transmittance of PDLC - NP films are presented.
341. Electrochemical Immunosensing Platform for the Determination of the 20S Proteasome Using an Aminophenylboronic/Poly-indole-6-carboxylic Acid-Modified Electrode
Authors:
Martínez-Rojas, F; Diculescu, VC; Armijo, F
Published: AUG 17 2020, ACS APPLIED BIO MATERIALS, 3, DOI: 10.1021/acsabm.0c00478
The first electrochemical immunosensor for the determination of the 20S proteasome (P20S) was developed, entailing the immobilization of an antibody on an aminophenylboronic/poly-indole-6-carboxylic acid-modified electrode. The proposed electrochemical bioplatform is a simple and feasible analytical tool applicable for the determination of P20S in human plasma, considering its high clinical and biological relevance. Cyclic voltammetry, electrochemical impedance spectroscopy, and square wave voltammetry (SWV) were used to determine the optimal step-by-step process to obtain the electrochemical immunosensor. The interaction of P20S with the recognition layer of the immobilized antibody on the nanostructured surface took place by incubating the electrode in a P20S solution at 20 degrees C for 2 h. Using SWV as an electro-analytical technique, this immunosensor can quantify P20S. The current was linear with the P20S concentration within two dynamic concentration ranges from 20.0 to 80.0 and 80.0 to 200.0 ng.mL(-1) (r(2) = 0.992 and 0.98, respectively) with a limit of detection and quantification of 6 and 18 ng.mL(-1), respectively. Moreover, the immunosensor showed considerable repeatability and reproducibility, when the determination was done in human serum, which confirms that it is a promising alternative for direct detection of P20S in biological fluids with minimal interference.
342. UAV identification system based on memristor physical unclonable functions
Authors:
Ionescu, O; Besleaga, C; Dumitru, V; Pricop, E
Published: 2020, PROCEEDINGS OF THE 2020 12TH INTERNATIONAL CONFERENCE ON ELECTRONICS, COMPUTERS AND ARTIFICIAL INTELLIGENCE (ECAI-2020), DOI: 10.1109/ecai50035.2020.9223154
The latest decades presented a large development of various size and types of Unmanned Aerial Vehicles (UAVs). Nowadays, there are over 200 million UAVs used in various applications and there it is a large effort to adopt national and international regulation for using them. There it is a real need for the development of a reliable system for UAVs identity verification that can be implemented and used at global level. To this moment the software-based methods such as MAC address, IDs memorized on devices are prone to a large number of cyber-security vulnerabilities and attacks. This paper presents an innovative hardware-based identification solution which could be adapted to UAVs in a non-intrusive manner. The proposed solution is based on physical unclonable functions (PUF), which are implemented by using memristors. The proposed solution is very low cost and high performance. By using memristors, it is possible to generate a very large number of unclonable IDs, using only a few electrical components. This solution could be incorporated in any UAVs systems without major modifications and not affecting their flight parameters.
343. High magnetic shielding properties of an MgB2 cup obtained by machining a spark-plasma-sintered bulk cylinder
Authors:
Gozzelino, L; Gerbaldo, R; Ghigo, G; Torsello, D; Bonino, V; Truccato, M; Grigoroscuta, MA; Burdusel, M; Aldica, GV; Sandu, V; Pasuk, I; Badica, P
Published: APR 2020, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 33, 044018, DOI: 10.1088/1361-6668/ab7846
Superconductors are key materials for shielding quasi-static magnetic fields. In this work, we investigated the shielding properties of an MgB2 cup-shaped shield with small aspect-ratio of height/outer radius. Shape and aspect-ratio were chosen in order to address practical requirements of both high shielding factors (SFs) and space-saving solutions. To obtain large critical current densities (J(c)), which are crucial for achieving high magnetic-mitigation performance, a high-purity starting MgB2 powder was selected. Then, processing of the starting MgB2 powder into high density bulks was performed by spark plasma sintering. The as-obtained material is fully machinable and was shaped into a cup-shield. Assessment of the material by scaling of the pinning force showed a non-trivial pinning behaviour. The MgB2 powder selection was decisive in enlarging the range of external fields where efficient shielding occurs. The shield's properties were measured in both axial- and transverse-field configurations using Hall probes. Despite a height/outer radius aspect ratio of 2.2, shielding factors higher than 10(4) at T = 20 K up to a threshold field of 1.8 T were measured in axial-field geometry at a distance of 1 mm from the closed extremity of the cup, while SFs > 10(2) occurred in the inner half of the cup. As expected, this threshold field decreased with increased temperature, but SFs still exceeding the above mentioned values were found up to 0.35 T at 35 K. The shield's shape limits the SF values achievable in transverse-field configuration. Nevertheless, the in-field J(c) of the sample supported SFs over 40 at T = 20 K up to a field of 0.8 T, 1 mm away from the cup closure.
344. Epitaxial GeSn Obtained by High Power Impulse Magnetron Sputtering and the Heterojunction with Embedded GeSn Nanocrystals for Shortwave Infrared Detection
Authors:
Dascalescu, I; Zoita, NC; Slav, A; Matei, E; Iftimie, S; Comanescu, F; Lepadatu, AM; Palade, C; Lazanu, S; Buca, D; Teodorescu, VS; Ciurea, ML; Braic, M; Stoica, T
Published: JUL 29 2020, ACS APPLIED MATERIALS & INTERFACES, 12, DOI: 10.1021/acsami.0c06212
GeSn alloys have the potential of extending the Si photonics functionality in shortwave infrared (SWIR) light emission and detection. Epitaxial GeSn layers were deposited on a relaxed Ge buffer on Si(100) wafer by using high power impulse magnetron sputtering (HiPI-MS). Detailed X-ray reciprocal space mapping and HRTEM investigations indicate higher crystalline quality of GeSn epitaxial layers deposited by Ge HiPI-MS compared to commonly used radio frequency magnetron sputtering (RF-MS). To obtain a rectifying heterostructure for SWIR light detection, a layer of GeSn nanocrystals (NCs) embedded in oxide was deposited on the epitaxial GeSn one. Embedded GeSn NCs are obtained by cosputtering deposition of (Ge1-xSnx)(1-y)(SiO2)(y) layers and subsequent rapid thermal annealing at a low temperature of 400 degrees C. Intrinsic GeSn structural defects give p-type behavior, while the presence of oxygen leads to the n-character of the embedded GeSn NCs. Such an embedded NCs/epitaxial GeSn p-n heterostructure shows superior photoelectrical response up to 3 orders of magnitude increase in the 1.2-2.5 mu m range, as compared to performances of diode based only on embedded NCs.
Open Access
345. Analog IGZO Memristor With Extended Capabilities
Authors:
Dumitru, V; Besleaga, C; Ionescu, ON
Published: 2020, IEEE JOURNAL OF THE ELECTRON DEVICES SOCIETY, 8, DOI: 10.1109/JEDS.2020.3006000
In this paper an IGZO memristor with multiple states and analog tuning extended capability is reported. The device has a planar structure and is fabricated by magnetron sputtering on glass substrate. The device resistance could be gradually increased and decreased within the range of one order of magnitude. Larger resistance changes are also possible but they are mostly irreversible. The obtained memristor looks promising to be used as electronic synapse in hardware implemented artificial neural networks or for applications in analog computing and cryptography.
346. Synthesis and characterization of magnetic oxide nanoparticles and corresponding thin films for wastewaters treatment
Authors:
Crintea, L; Musat, V; Polosan, S; Cantaragiu, A; Basliu, V; Dediu, A; Dinica, R
Published: JUL 2020, OVIDIUS UNIVERSITY ANNALS OF CHEMISTRY, 31, DOI: 10.2478/auoc-2020-0021
Industrial wastewater can be properly treated using nanotechnologies and nanomaterials. This paper presents the synthesis and characterization of three series of magnetic nanoparticles (MNPs) and corresponding thin films, used for the degradation of organic compounds and removal of heavy metals from industrial wastewater. The samples were obtained by co-precipitation from a ferric (Fe3+) and ferrous (Fe2+) ions solution in a molar ratio of 2:1, at temperatures between 80-95 degrees C. The characterization of the samples was performed by scanning electron microscopy (SEM), and X-ray diffraction (XRD) methods. The magnetic nanoparticles were deposited on glass substrates by the centrifugal coating technique and the optical and magneto-optical activity was investigated by UV- Vis spectroscopy and magnetic circular dichroism technique (MCD). The effect of the investigated samples on the decomposition under UV irradiation of organic dyes was monitored by UV-Vis spectroscopy. Our preliminary results have shown that the magnetite and maghemite MNPs can be effective in UV degradation of methylene blue (MB) dye.
347. Characterization of C-Ti multilayer thin films obtained by TVA technology
Authors:
Ciupina, V; Lungu, CP; Vladoiu, R; Prodan, GC; Porosnicu, C; Vasile, E; Prodan, M; Nicolescu, V; Dinca, V; Manu, R; Cupsa, O; Velea, A
Published: 2020, NANOENGINEERING: FABRICATION, PROPERTIES, OPTICS, THIN FILMS, AND DEVICES XVII, 11467, 114671R, DOI: 10.1117/12.2567927
Carbon-Titanium multilayer thin films were obtained by Thermionic Vacuum Arc (TVA) method. The nanostructured films consisting by 100nm Carbon base layer and seven 40nm alternatively Titanium and Carbon layers were deposed on Silicon substrate. As well, to give C-Ti multilayer films with different percentages in Ti and C of layers, a 100nm thick Carbon base layer was deposed on Si substrate, and then seven Ti-C layers, each of these having thickness of 40nm. In order to achieve the successively layers with C, and Ti different percentages, were adjusted the discharge parameters of C and Ti plasma sources to obtain the desired composition of layers. Also, were obtained composite films having a variable C: Ti atomic ratio 9:1 at interface to 1:9 at the surface. By changing of substrate temperature from room temperature to 100 degrees C, 200 degrees C, 300 degrees C, 400 degrees C respectively, and on the other hand the bias potential up to -700V, different batches of samples were obtained. Characterization of structural properties of films was achieved by Electron Microscopy technique (TEM, STEM) and GIXRD techniques. The measurements show that increase of the substrate temperature reveal changes in TixCy lattice parameters. Thus, according to GIXRD analysis it was found out that the Ti:C atomic ratio changes with increase of synthesis temperature. Also, in the case of composite films an increase of amount and sizes of TiC nanocrystals with the increase of energy of Ti ions determined by increase of bias voltage was observed. The tribological measurements were performed using a ball-on-disk system with normal forces of 0.5, 1, 2, 3N respectively. Was found that the coefficient of friction depends on the synthesis temperature and on the bias voltage. It is also noted that the friction coefficient depends on the pure C content, Ti content and amount of TiC nanocrystallites. These results are due to atomic diffusion at Ti/C interfaces and also are associated with amount of TiC nanocrystallites. To characterize the electrical conductive properties, the electrical surface resistance versus temperature have been measured, and then the electrical conductivity is calculated. Using the Wiedemann-Frantz law was obtained the thermal conductivity.
348. Dielectric investigations on carbon nanotubes doped polymer dispersed liquid crystal films
Authors:
Ganea, CP; Manaila-Maximean, D; Cîrcu, V
Published: OCT 8 2020, EUROPEAN PHYSICAL JOURNAL PLUS, 135, 797, DOI: 10.1140/epjp/s13360-020-00795-w
We obtained carbon nanotubes (CNTs) doped polymer dispersed liquid crystal (PDLC) films using the nematic E7 and polymethyl methacrylate, a composite that combines the benefic characteristic of the liquid crystals (LC) and carbon nanoparticles. The clearing temperatures recorded by differential scanning calorimetry for the PDLC blends were found to be lower than the value recorded for pure E7 LC mixture with no significant impact of the CNTs' concentration. Broadband dielectric spectroscopy (DS) measurements were performed in the (10(-1) / 107) Hz frequency range, in the temperature domain (280-350) K. From the DS study, a two order magnitude variation of the conductivity over the entire temperature range was observed. The presence of CNTs results in an increase of electrical conductivity, with increasing concentration. Because the loss tangent spectra have complex shapes, they were fitted using the generalized Havriliak-Negami functions, and the characteristic relaxation times were extracted. The dependency of the characteristic relaxation time on temperature was modeled using the Vogel-Fulcher-Tammann function, and it showed a temperature variation according to the Arrhenius law. The increase of the CNT concentration increases the activation energy of the molecular electric dipoles of the LC. The interface LC-polymer interactions influence the nematic to isotropic phase transition of the LC.
349. Mechano-chemical versus co-precipitation for the preparation of Y-modified LDHs for cyclohexene oxidation and Claisen-Schmidt condensations
Authors:
Pavel, OD; Stamate, AE; Zavoianu, R; Bucur, IC; Bîrjega, R; Angelescu, E; Parvulescu, VI
Published: SEP 5 2020, APPLIED CATALYSIS A-GENERAL, 605, 117797, DOI: 10.1016/j.apcata.2020.117797
Y-modified LDHs with atomic Mg2+/(Al3+ + Y3+) of 3 and Al3+/Y3+ ratios of 0.5, 1 and 1.5 were prepared following two preparation methods, i.e. the co-precipitation and mechano-chemical one. The substitution of Al by Y in the brucite-type layer was less effective for the samples prepared by co-precipitation compared to those prepared via mechano-chemical route. In spite the fact yttrium has a larger ionic radius (0.9 angstrom) the structural characterizations of these solids confirmed that the layered structure incorporates part of it in the octahedral positions. Further, the reconstruction of the layered structure after an exposure to water for 1 h was more effective for the solid prepared by co-precipitation. The yttrium modified LDHs showed better catalytic activities for cyclohexene oxidation to the corresponding epoxide than the un-modified LDH sample. Then, mixed oxides derived from yttrium-LDH showed very high conversions and selectivities for the synthesis of chalcone.
350. Multilayer protective coatings obtained by pulsed laser deposition
Authors:
Ion, V; Scarisoreanu, ND; Bonciu, A; Moldovan, A; Ghenescu, V; Ghenescu, M; Banciu, MG; Andrei, A; Dinescu, M
Published: JUN 15 2019, APPLIED SURFACE SCIENCE, 479, 1131, DOI: 10.1016/j.apsusc.2019.02.186
Devices developed for the aeronautic or space industries must be able to operate in harsh environments. In order to protect devices such as microstrip antennae, various coatings have to be used. Herein, we present the results of obtaining YSZ/Al2O3 heterostructures by Pulsed Laser Deposition (PLD) for the protection of planar monopole antennas without changing their performances after the deposition process. The theoretical SRIM-TRIM simulation code results on the effects of ionized radiations incident on a YSZ/Al2O3 heterostructure, as well as the physical properties of the YSZ/Al2O3 thin films obtained by the PLD technique are also presented. The SRIM studies show that at the same energy range the proton penetration depth is higher than the alpha penetration depth, giving insights about the penetration depth of proton and alpha particles in the studied targets. Our goal is to obtain a multilayer structure able to enhance the endurance of the antenna and microwave circuitry in harsh space environment without reducing the performances under nominal operation conditions.
351. Multiferroic (Nd,Fe)-doped PbTiO3 thin films obtained by pulsed laser deposition
Authors:
Dumitru-Grivei, M; Ion, V; Birjega, R; Moldovan, A; Craciun, F; Cernea, M; Galassi, C; Dinescu, M
Published: FEB 2019, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 125, DOI: 10.1007/s00339-019-2403-5
We report the successful growth of multiferroic (Nd,Fe)-doped PbTiO3 thin films with the composition (Pb0.88Nd0.08)(Ti0.93Fe0.05Mn0.02)O-3 (PNFT) using pulsed laser deposition. The deposited films have been investigated by XRD, SEM, energy-dispersive X-ray spectroscopy (EDS), secondary-ion mass spectroscopy (SIMS), atomic force microscopy, magnetic force microscopy, piezoforce microscopy, spectroscopic ellipsometry (SE) and dielectric spectroscopy measurements. PNFT films deposited on different substrates (MgO, SrTiO3 and Nb:SrTiO3) are (001) oriented, preserving the orientation of the single-crystal substrates. EDS mapping and SIMS across the film thickness probed the uniform distribution of all the elements. The refractive index and extinction coefficient have been obtained with the SE software package and refined with an optical-graded model. Magnetic domains and ferroelectric domains have been evidenced at microscopic scale. Good dielectric properties and low loss, comparable to those of bulk materials, have been obtained.
352. Complex exchange coupling mechanisms in SRO/BFO/Fe heterostructures
Authors:
Greculeasa, SG; Schinteie, G; Hrib, LM; Stancu, V; Pasuk, I; Kuncser, A; Kuncser, V
Published: JAN 30 2019, JOURNAL OF ALLOYS AND COMPOUNDS, 773, 345, DOI: 10.1016/j.jallcom.2018.09.208
Temperature dependent interfacial coupling mechanisms in SRO/BFO/Fe layered structures were investigated. The BFO/Fe heterostructures were prepared by PLD and sputtering, respectively, on the STO(0 0 1) substrate with a 20 nm SRO buffer layer. An annealing treatment in external magnetic field was further applied. Complex characterizations with X-ray diffraction, atomic force microscopy, Transmission Electron Microscopy, Mossbauer spectroscopy, magneto-optic Kerr effect and SQUID magnetometry were performed. Before annealing, the films show good crystallization and epitaxy of the SRO and BFO layers with smooth interfaces. Two coupling mechanisms of the ferromagnetic layers (top Fe and bottom SRO, respectively) to the epitaxial BFO film with mainly antiferromagnetic structure were evidenced in the as deposited samples at low temperatures. Negative exchange bias fields of up to 67(10) Oe and 37(5) Oe at low temperatures were observed for the two ferromagnetic components, respectively, depending on the thickness of the Fe layer. The field annealing treatments induce a specific morphology and magnetic spin structure at both interfaces of the BFO spacer layer, giving rise to a long range magnetostatic coupling between the two ferromagnetic films, in addition to the interfacial couplings. Moreover, the experimentally evidenced Fe clusters penetrating the BFO/Fe interface toward the BFO layer give support for this interaction. As an additional consequence, a considerable enhancement of both uniaxial and unidirectional anisotropies as well as an increased blocking temperature of exchange bias were obtained. The involved exchange coupling mechanisms were discussed in detail. (C) 2018 Elsevier B.V. All rights reserved.
353. Probing single-unit-cell resolved electronic structure modulations in oxide superlattices with standing-wave photoemission
Authors:
Yang, W; Chandrasena, RU; Gu, M; dos Reis, RMS; Moon, EJ; Arab, A; Husanu, MA; Nemsak, S; Gullikson, EM; Ciston, J; Strocov, VN; Rondinelli, JM; May, SJ; Gray, AX
Published: SEP 9 2019, PHYSICAL REVIEW B, 100, DOI: 10.1103/PhysRevB.100.125119
Control of structural coupling at complex-oxide interfaces is a powerful platform for creating ultrathin layers with electronic and magnetic properties unattainable in the bulk. However, with the capability to design and control the electronic structure of such buried layers and interfaces at a unit-cell level, a new challenge emerges to be able to probe these engineered emergent phenomena with depth-dependent atomic resolution as well as element- and orbital selectivity. Here, we utilize a combination of core-level and valence-band soft x-ray standing-wave photoemission spectroscopy, in conjunction with scanning transmission electron microscopy, to probe the depth-dependent and single-unit-cell resolved electronic structure of an isovalent manganite superlattice [Eu0.7Sr0.3MnO3/La0.7Sr0.3MnO3] x 15 wherein the electronic-structural properties are intentionally modulated with depth via engineered oxygen octahedra rotations/tilts and A-site displacements. Our unit-cell resolved measurements reveal significant transformations in the local chemical and electronic valence-band states, which are consistent with the layer-resolved first-principles theoretical calculations, thus opening the door for future depth-resolved studies of a wide variety of heteroengineered material systems.
354. Phase Control in Hafnia: New Synthesis Approach and Convergence of Average and Local Structure Properties
Authors:
Cojocaru, B; Avram, D; Negrea, R; Ghica, C; Kessler, VG; Seisenbaeva, GA; Parvulescu, VI; Tiseanu, C
Published: MAY 2019, ACS OMEGA, 4, 8891, DOI: 10.1021/acsomega.9b00580
Technologically relevant tetragonal/cubic phases of HfO2 can be stabilized at room temperature by doping with trivalent rare earths using various approaches denoted generically as bulk coprecipitation. Using in situ/ex situ X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy, and in situ/ex situ site-selective, time-gated luminescence spectroscopy, we show that wet impregnation of hafnia nanoparticles with 10% Eu oxide followed by mild calcination in air at 500 degrees C produces an efficient stabilization of the cubic phase, comparable to that obtained by bulk precipitation. The physical reasons behind the apparently conflictual data concerning the actual crystallographic phase and the local symmetry around the Eu stabilizer and how these can be mediated by luminescence analysis are also discussed. Apparently, the cubic crystal structure symmetry determined by XRD results in a pseudocubic/tetragonal local structure around Eu determined by luminescence. Considering the recent findings on wet impregnated CeO2 and ZrO2, it is concluded that CeO2, ZrO2, and HfO2 represent a unique case of a family of oxides that is extremely tolerant to heavy doping by wet impregnation. In this way, the same batch of preformed nanoparticles can be doped with different lanthanide concentrations or with various lanthanides at a fixed concentration, allowing a systematic and reliable investigation of the effect of doping, lanthanide type, and lanthanide concentration on the various functionalities of these technologically relevant oxides.
355. Electrochemical Sensor for Carbonyl Groups in Oxidized Proteins
Authors:
Enache, TA; Matei, E; Diculescu, VC
Published: FEB 5 2019, ANALYTICAL CHEMISTRY, 91, 1927, DOI: 10.1021/acs.analchem.8b03969
The interaction of proteins with free radicals leads, among other types of damages, to the production of stable carbonyl groups, which can be used as a quantification of oxidative stress at proteins level. The aim of this study was the development of an electrochemical sensor for the detection of carbonyl groups in proteins oxidized by reactive oxygen species. Its working principle is based on the redox properties of dinitrophenylhydrazine (DNPH). BSA was used as a model protein and its oxidation achieved through Fenton reactions. Using differential pulse voltammetry at glassy carbon electrode, the electrochemical behavior of DNPH and of the native and oxidized BSA was investigated in solution. It has been shown that the hydrazine moiety of the DNPH is the electroactive center and is responsible for carbonyl complexation. Special attention was paid to the immobilization of the DNPH in order to retain its redox properties, and this was achieved on a mixed 4-styrenesulfonic acid-nafion matrix. The sensor's surface characterization and the detection of carbonyl groups in oxidized protein were performed by voltammetry, Fourier-transformed infrared spectroscopy and scanning electron microscopy while the voltammetric results were confirmed by surface plasmon resonance measurements. It has been shown that upon interaction with carbonyl groups of the oxidized protein, the oxidation peak of the hydrazine moiety of DNPH decreases as a function of incubation time and protein concentration. The sensor sensitivity was 0.015 nmol carbonyl per mg of oxidized protein and detection limits of 50 mu g oxidized BSA and 0.75 pmol carbonyls.
356. k-resolved electronic structure of buried heterostructure and impurity systems by soft-X-ray ARPES
Authors:
Strocov, VN; Lev, LL; Kobayashi, M; Cancellieri, C; Husanu, MA; Chikina, A; Schroter, NBM; Wang, X; Krieger, JA; Salman, Z
Published: OCT 2019, JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, 236, 8, DOI: 10.1016/j.elspec.2019.06.009
Angle-resolved photoelectron spectroscopy (ARPES) is the main experimental tool to explore electronic structure of solids resolved in the electron momentum k. Soft-X-ray ARPES (SX-ARPES), operating in a photon energy range around 1 keV, benefits from enhanced probing depth compared to the conventional VUV-range ARPES, and elemental/chemical state specificity achieved with resonant photoemission. These advantages make SX-ARPES ideally suited for buried heterostructure and impurity systems, which are at the heart of current and future electronics. These applications are illustrated here with a few pioneering results, including buried quantum-well states in semiconductor and oxide heterostructures, their bosonic coupling critically affecting electron transport, magnetic impurities in diluted magnetic semiconductors and topological materials, etc. High photon flux and detection efficiency are crucial for pushing the SX-ARPES experiment to these most photon-hungry cases.
357. The Quality of Fe14Cr ODS Powder Alloys During Milling and Upon Heating and Its Impact on the Mechanical Properties of Consolidated Steels
Authors:
Mihalache, V; Walter, M; Mercioniu, I; Ordas, N
Published: JUL 2019, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 50A, 3294, DOI: 10.1007/s11661-019-05264-3
Oxide dispersion-strengthened ferritic steels (ODSFSs) are promising structural materials for applications in fusion and fission power reactors, but further improvement in their (high-temperature) mechanical properties and ferrite phase stability is required. This work demonstrates that an approach to produce Fe14Cr ODSFSs with a stable ferrite phase and improved strength could involve grain size strengthening by long-term milling with a tiny amount of nitrogen. Fe-14Cr-3W-0.4Ti-0.25Y(2)O(3) powders were ball-milled up to 170 hours under an argon atmosphere. In addition to X-ray diffraction, the change in product quality during milling and upon heating was thoroughly investigated by more sensitive magnetic and thermal analysis by measuring the saturation magnetization sigma(s), coercivity H-c, Curie temperature T-c, and temperature of ferrite-austenite (alpha ->gamma) transition T-alpha ->gamma. A pronounced modification of magnetic and microstructure parameters was observed when milling over 70 hours and upon heating above 800 degrees C and was found to be generated by long-term milling with a tiny amount of nitrogen. Upon heating, the nitrogen, incorporated during milling, developed a transition region, with the decomposition of nitrides precipitated at the earlier stage of heating followed by austenite decomposition, nitrogen degassing, and microstructure refinement to a grain size of a few tenths of a nm (e.g., 28 nm by heating at 910 degrees C of 100-hour milled powder). The resulting ferrite phase with refined grains is highly stable to (further) heating. The powders milled for 70 and 100 hours containing 0.175 and 0.500 wt pct nitrogen, respectively, were consolidated at 1100 degrees C with subsequent annealing at 1050 degrees C and subjected to Vickers hardness and 3-point bending tests. The steel produced from the powder milled for 70 hours shows lower hardness, higher density (close to the theoretical value of 7.8 g/cm(3)), and fracture strain. The ductility of this ODS alloy (0.075 fracture strain) is comparable with Eurofer97 (0.075 fracture strain), whereas its strength (2070 MPa ultimate stress) is significantly higher than that of Eurofer97 (1222 MPa ultimate stress). This improvement was attributed to grain size strengthening-the refined grains (promoted by milling with nitrogen) could be effectively pinned by Y-Ti-O dispersoids.
358. Direct Immobilization of Biomolecules through Magnetic Forces on Ni Electrodes via Ni Nanoparticles: Applications in Electrochemical Biosensors
Authors:
Barsan, MM; Enache, TA; Preda, N; Stan, G; Apostol, NG; Matei, E; Kuncser, A; Diculescu, VC
Published: JUN 5 2019, ACS APPLIED MATERIALS & INTERFACES, 11, 19877, DOI: 10.1021/acsami.9b04990
The present work describes a new simple procedure for the direct immobilization of biomolecules on Ni electrodes using magnetic Ni nanoparticles (NiNPs) as biomolecule carriers. Ni electrodes were fabricated by electroplating, and NiNPs were chemically synthesized. The chemical composition, crystallinity, and granular size of Ni electrodes, NiNP, and NiNP-modified Ni electrodes (NiNP/Ni) were determined by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS). The electrochemical characterization of Ni electrodes by cyclic voltammetry and electrochemical impedance spectroscopy confirmed the existence of nickel oxides, hydroxides, and oxohydroxide films at the surface of Ni. Magnetic characterization and micromagnetic simulations were performed in order to prove that the magnetic force is responsible for the immobilization process. Further, Ni electrodes were employed as amperometric sensors for the detection of hydrogen peroxide because it is an important performance indicator for a material to be applied in biosensing. The working principle for magnetic immobilization of the enzyme-functionalized NiNP, without the use of external magnetic sources, was demonstrated for glucose oxidase (GOx) as a model enzyme. XPS results enabled to identify the presence of GOx attached to the NiNP (GOx-NiNP) on Ni electrodes. Finally, glucose detection and quantification were evaluated with the newly developed GOx-NiNP/Ni biosensor by amperometry at different potentials, and control experiments at different electrode materials in the presence and absence of NiNP demonstrated their importance in the biosensor architecture.
359. Bi1-xEuxFeO3 Powders: Synthesis, Characterization, Magnetic and Photoluminescence Properties
Authors:
Surdu, VA; Trusca, RD; Vasile, BS; Oprea, OC; Tanasa, E; Diamandescu, L; Andronescu, E; Ianculescu, AC
Published: OCT 2019, NANOMATERIALS, 9, DOI: 10.3390/nano9101465
Europium substituted bismuth ferrite powders were synthesized by the sol-gel technique. The precursor xerogel was characterized by thermal analysis. Bi1-xEuxFeO3 (x = 0-0.20) powders obtained after thermal treatment of the xerogel at 600 degrees C for 30 min were investigated by X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectroscopy, and Mossbauer spectroscopy. Magnetic behavior at room temperature was tested using vibrating sample magnetometry. The comparative results showed that europium has a beneficial effect on the stabilization of the perovskite structure and induced a weak ferromagnetism. The particle size decreases after the introduction of Eu3+ from 167 nm for x = 0 to 51 nm for x = 0.20. Photoluminescence spectroscopy showed the enhancement of the characteristic emission peaks intensity with the increase of Eu3+ concentration.
360. Efficacy of annealing and fabrication parameters on photo-response of SiGe in TiO2 matrix
Authors:
Sultan, MT; Gudmundsson, JT; Manolescu, A; Teodorescu, VS; Ciurea, ML; Svavarsson, HG
Published: SEP 6 2019, NANOTECHNOLOGY, 30, DOI: 10.1088/1361-6528/ab260e
SiGe nanoparticles dispersed in a dielectric matrix exhibit properties different from those of bulk and have shown great potential in devices for application in advanced optoelectronics. Annealing is a common fabrication step used to increase crystallinity and to form nanoparticles in such a system. A frequent downside of such annealing treatment is the formation of insulating SiO2 layer at the matrix/SiGe interface, degrading the optical properties of the structure. An annealing process that could bypass this downside would therefore be of great interest. In this work, a short-time furnace annealing of a SiGe/TiO2 system is applied to obtain SiGe nanoparticles without formation of the undesired SiO2 layer between the dielectric matrix (TiO2) and SiGe. The structures were prepared by depositing alternate layers of TiO2 and SiGe films, using direct-current magnetron sputtering technique. A wide range spectral response with a response-threshold up to similar to 1300 nm was obtained, accompanied with an increase in photo-response of more than two-orders of magnitude. Scanning electron microscopy, transmission electron microscopy, energy-dispersive x-ray spectroscopy and grazing incidence x-ray diffraction were used to analyze the morphological changes in respective structures. Photoconductive properties were studied by measuring photocurrent spectra using applied dc-voltages at various temperatures.
361. Charge separation and ROS generation on tubular sodium titanates exposed to simulated solar light
Authors:
Preda, S; Anastasescu, C; Balint, I; Umek, P; Sluban, M; Negrila, CC; Angelescu, DG; Bratan, V; Rusu, A; Zaharescu, M
Published: MAR 15 2019, APPLIED SURFACE SCIENCE, 470, 1063, DOI: 10.1016/j.apsusc.2018.11.194
The research focuses on a few key points concerning the light-driven processes taking place on TiO2 anatase and sodium titanates with tubular morphology, such as the relationship between the morphology and activity for H-2 and CO2 production, density of surface hydroxyl groups, ROS (center dot OH and center dot O-2(-)) production and photocatalytic activity, and charge separation at the interface of semiconducting domains and enhancement of activity. One key point discussed is whether the materials with peculiar morphologies (i.e. tubular) are superior to the conventional ones. The experimental evidences show that the main advantage of the tubular morphology of sodium titanate is given by its significantly higher surface area compared to parental anatase. FTIR and XPS progressive analyses evidence that the density of surface hydroxyl groups decreases with the development of the tubular morphology. The radical trapping experiments show that the variation of surface hydroxyl density is, generally, followed by activities for center dot OH and center dot O-2(-) generation, as well as by the photocatalytic production of H-2 and CO2 from water/methanol mixture. Consequently, the ROS, formed by action of photogenerated electrons and holes on adsorbed O-2 and hydroxyl groups, respectively, play an important role in determining the photocatalytic activity of titania-based materials. The other major aspect revealed by this research is that the charge separation at the interfaces formed between anatase and sodium titanate crystalline phases has remarkable effect on the activity formation rates of H-2 and CO2.
362. Antibacterial efficiency of alkali-free bio-glasses incorporating ZnO and/or SrO as therapeutic agents
Authors:
Popa, AC; Fernandes, HR; Necsulescu, M; Luculescu, C; Cioangher, M; Dumitru, V; Stuart, BW; Grant, DM; Ferreira, JMF; Stan, GE
Published: MAR 2019, CERAMICS INTERNATIONAL, 45, 4380, DOI: 10.1016/j.ceramint.2018.11.112
A series of seven alkali-free silica-based bioactive glasses (SBG) with ZnO and/or SrO additives (in concentrations of 0-12 mol%) were synthesized by melt-quenching, aiming to delineate a candidate formulation possessing (i) a coefficient of thermal expansion (CTE) similar to the one of titanium (Ti) and its medical grade super alloys (crucial for the future development of mechanically adherent implant-type SBG coatings) and (ii) antibacterial efficiency, while (iii) conserving a good cytocompatibility. The SBGs powders were multi-parametrically evaluated by X-ray diffraction, Fourier transform infrared and micro-Raman spectroscopy, dilatometry, inductively coupled plasma mass spectrometry, antibacterial (against Staphylococcus aureus and Escherichia coli strains) suspension inhibition and agar diffusion tests, and human mesenchymal stem cells cytocompatibility assays. The results showed that the coupled incorporation of zinc and strontium ions into the parent glass composition has a combinatorial and additive benefit. In particular, the "Z6S4" formulation (mol%: SiO2-38.49, CaO-32.07, P2O5-5.61, MgO-13.24, CaF2-0.59, ZnO-6.0, SrO-4.0) conferred strong antimicrobial activity against both types of strains, minimal cytotoxicity combined with good stem cells viability and proliferation, and a CTE (similar to 8.7 x 10(-6) x degrees C-1) matching well those of the Ti-based implant materials.
363. CO2 methanation catalyzed by oriented MoS2 nanoplatelets supported on few layers graphene
Authors:
Primo, A; He, JB; Jurca, B; Cojocaru, B; Bucur, C; Parvulescu, VI; Garcia, H
Published: MAY 15 2019, APPLIED CATALYSIS B-ENVIRONMENTAL, 245, 359, DOI: 10.1016/j.apcatb.2018.12.034
Powders of molybdenum disulfide platelets strongly grafted on graphene have been prepared by pyrolysis of ammonium alginate containing adsorbed various proportions of (NH4)(2)MoS4. After pyrolysis, formation of MoS2 supported on graphene was determined by XRD and electron microscopy and spectroscopic techniques. MoS2/G exhibits catalytic activity for the methanation of CO2, the performance being optimal at intermediate loadings. The catalytic activity of sharply contrasts with that of bulk MoS2 that promotes the reverse water gas shift, affording CO as the main product. Characterization of the spent MoS2/G catalyst shows the partial conversion of external MoS2 into MoO3. Comparison of the catalytic activity of MoS2/G with that of MoO3/G shows that the latter is less efficient, but more selective for CO2 methanation.
364. N-Doped Defective Graphene from Biomass as Catalyst for CO2 Hydrogenation to Methane
Authors:
Jurca, B; Bucur, C; Primo, A; Concepcion, P; Parvulescu, VI; Garcia, H
Published: FEB 6 2019, CHEMCATCHEM, 11, 990, DOI: 10.1002/cctc.201801984
N-doped, defective graphene obtained by pyrolysis of chitosan at 900 degrees C under Ar exhibits catalytic activity for the Sabatier hydrogenation of CO2 to CH4 at temperatures about 500 degrees C with estimated turnover frequencies and activation energy values of 73.17s(-1) and 24.3 kcal x mol(-1), respectively. It has been found that this enhanced catalytic activity compared to other related doped defective graphenes derives from the presence of pyridinic N atoms that adsorbs CO2 forming carbamate-type adsorbates.
365. Electrochemical assay for 20S proteasome activity and inhibition with anticancer drugs
Authors:
de Jesus, CSH; Chiorcea-Paquim, AM; Barsan, MM; Diculescu, VC
Published: JUL 1 2019, TALANTA, 199, 39, DOI: 10.1016/j.talanta.2019.02.052
The majority of eukaryotic regulated protein turnover is performed by the proteasome, a multi-catalytic enzyme. Due to the fact that proteasome enzyme abnormal functioning was observed in different malignant cells, the proteasome is becoming a target for medical treatment. In order to evaluate the mechanisms of action of pharmaceutical compounds on proteasome enzyme inhibition, detecting and characterizing its activity is essential. An electrochemical assay that allows the monitoring of the chymotrypsin-like activity and inhibition of the 20S proteasome enzyme, based on the electrochemical detection of an electroactive compound released upon proteolysis of an adequate chymotrypsin-substrate is described. By employing differential pulse voltammetric measurement, the activity of the 20S proteasome enzyme was investigated for different incubation times of 20S with oligopeptide substrate as well as for different concentrations of substrate. Enzyme kinetic parameters were determined by voltammetry and the electrochemical assay compared with fluorescence spectroscopy. Electrochemical quartz crystal microbalance and atomic force microscopy were also used to investigate substrate interaction with the 20S proteasome and their adsorption at the electrode surface. Finally, the new electrochemical assay allowed to investigate the mechanisms of two different proteasome inhibitor drugs, bortezomib and oprozomib, underlying the applicability of the assay for understanding proteasome inhibitor action.
366. Next frontiers in cleaner synthesis: 3D printed graphene-supported CeZrLa mixed -oxide nanocatalyst for CO2 utilisation and direct propylene carbonate production
Authors:
Middelkoop, V; Slater, T; Florea, M; Neatu, F; Danaci, S; Onyenkeadi, V; Boonen, K; Saha, B; Baragau, LA; Kellici, S
Published: MAR 20 2019, JOURNAL OF CLEANER PRODUCTION, 214, 614, DOI: 10.1016/j.jclepro.2018.12.274
A rapidly-growing 3D printing technology is innovatively employed for the manufacture of a new class of heterogenous catalysts for the conversion of CO2 into industrially relevant chemicals such as cyclic carbonates. For the first time, directly printed graphene-based 3D structured nanocatalysts have been developed combining the exceptional properties of graphene and active CeZrLa mixed-oxide nano particles. It constitutes a significant advance on previous attempts at 3D printing graphene inks in that it does not merely explore the printability itself, but enhances the efficiency of industrially relevant reactions, such as CO2 utilisation for direct propylene carbonate (PC) production in the absence of organic solvents. In comparison to the starting powder, 3D printed GO-supported CeZeLa catalysts showed improved activity with higher conversion and no noticeable change in selectivity. This can be attributed to the spatially uniform distribution of nanoparticles over the 2D and 3D surfaces, and the larger surface area and pore volume of the printed structures. 3D printed GO-supported CeZeLa catalysts compared to unsupported 3D printed samples exhibited higher selectivity and yield owing to the great number of new weak acid sites appearing in the supported sample, as observed by NH3-TPD analysis. In addition, the catalyst's facile separation from the product has the capacity to massively reduce materials and operating costs resulting in increased sustainability. It convincingly shows the potential of these printing technologies in revolutionising the way catalysts and catalytic reactors are designed in the general quest for clean technologies and greener chemistry. 2019 Elsevier Ltd. All rights reserved.
367. Laser Processed Antimicrobial Nanocomposite Based on Polyaniline Grafted Lignin Loaded with Gentamicin-Functionalized Magnetite
Authors:
Visan, AI; Popescu-Pelin, G; Gherasim, O; Grumezescu, V; Socol, M; Zgura, I; Florica, C; Popescu, RC; Savu, D; Holban, AM; Cristescu, R; Matei, CE; Socol, G
Published: FEB 2019, POLYMERS, 11, DOI: 10.3390/polym11020283
Composite thin coatings of conductive polymer (polyaniline grafted lignin, PANI-LIG) embedded with aminoglycoside Gentamicin sulfate (GS) or magnetite nanoparticles loaded with GS (Fe3O4@GS) were deposited by the matrix-assisted pulsed laser evaporation (MAPLE) technique. The aim was to obtain such nanostructured coatings for titanium-based biomedical surfaces, which would induce multi-functional properties to implantable devices, such as the controlled release of the therapeutically active substance under the action of a magnetic and/or electric field. Thus, the unaltered laser transfer of the initial biomaterials was reported, and the deposited thin coatings exhibited an appropriate nanostructured surface, suitable for bone-related applications. The laser processing of PANI-LIG materials had a meaningful impact on the composites' wettability, since the contact angle values corresponding to the composite laser processed materials decreased in comparison with pristine conductive polymer coatings, indicating more hydrophilic surfaces. The corrosion resistant structures exhibited significant antimicrobial activity against Escherichia coli, Staphylococcus aureus, and Candida albicans strains. In vitro cytotoxicity studies demonstrated that the PANI-LIG-modified titanium substrates can allow growth of bone-like cells. These results encourage further assessment of this type of biomaterial for their application in controlled drug release at implantation sites by external activation.
368. GeSn Nanocrystals in GeSnSiO2 by Magnetron Sputtering for Short-Wave Infrared Detection
Authors:
Slav, A; Palade, C; Logofatu, C; Dascalescu, I; Lepadatu, AM; Stavarache, I; Comanescu, F; Iftimie, S; Antohe, S; Lazanu, S; Teodorescu, VS; Buca, D; Ciurea, ML; Braic, M; Stoica, T
Published: JUN 2019, ACS APPLIED NANO MATERIALS, 2, +, DOI: 10.1021/acsanm.9b00571
Detection in short-wave infrared (SWIR) has become a very stringent technology requirement for developing fields like hyperspectral imaging or climate changes. In a market dominated by III-V materials, GeSn, a Si compatible semiconductor, has the advantage of cost efficiency and inerrability by using the mature Si technology. Despite the recent progress in material growth, the easy fabrication of crystalline GeSn still remains a major challenge, and different methods are under investigation. We present the formation of GeSn nanocrystals (NCs) embedded in oxide matrix and their SWIR characterization. The simple and cost-effective fabrication method is based on thermal treatment of amorphous (Ge1-xSnx)(y)(SiO2)(1-y) layers deposited by magnetron sputtering. The nanocrystallization for Ge1-xSnx with 9-22 at. % Sn composition in SiO2 matrix with 9% to 15% mole percent was studied under low thermal budget annealing in the 350-450 degrees C temperature range. While the Sn at.% content is the main parameter influencing the band-structure of the NCs, the SWIR sensitivity can be optimized by SiO2 content and H-2 gas component in the deposition atmosphere. Their role is not only changing the crystallization parameters but also to reduce the carrier recombination by passivation of NCs defects. The experiments indicate a limited composition dependent temperature range for GeSn NCs formation before beta-Sn phase segregation occurs. NCs with an average size of 6 nm are uniformly distributed in the film, except the surface region where larger GeSn NCs are formed. Spectral photovoltaic current measured on SiO2 embedded GeSn NCs deposited on p-Si substrate shows extended SWIR sensitivity up to 2.4 mu m for 15 at. % Sn in GeSn NCs. The large extension of the SWIR detection is a result of many factors related to the growth parameters and also to the in situ or ex situ annealing procedures that influence the uniformity and size distribution of NCs.
369. Effect of the process control agent in the ball-milled powders and SPS-consolidation temperature on the grain refinement, density and Vickers hardness of Fe14Cr ODS ferritic alloys
Authors:
Mihalache, V; Mercioniu, I; Velea, A; Palade, P
Published: APR 1 2019, POWDER TECHNOLOGY, 347, 113, DOI: 10.1016/j.powtec.2019.02.006
Fe-14Cr-0.4Ti-0.25Y(2)O(3) ferritic steels were produced by varying the amount of residual process control agent, PCA (ethanol), in the ball-milled powders and changing the spark-plasma-sintering, SPS, temperature. Near the-oretical density (99.3%), high Vickers hardness (501-920 HV, measured by applying a load of 100 g for 5 s) and fine grain size (26-36 nm), very stable against heating, can be achieved on ODS ferritic steels, consolidated from powders with a low amount of PCA and processing temperature in the range of 1000 degrees C-1100 degrees C. Additional grain refinement occurs near alpha -> gamma transition which is generated by the reaction of the traces of PCA with the ferritic matrix upon heating. High local temperatures and the evolved thermally activated processes, at the contact points between particles/at the particle surfaces during SPS-consolidation, were demonstrated to be the main factors responsible for improved densities and hardness. The role of PCA in the sintering, thermal and microstructure particularities and its impact on the quality of the final steel was thoroughly analysed throughout the work. (C) 2019 Elsevier B.V. All rights reserved.
370. Effect of dilute doping and non-equilibrium synthesis on the structural, luminescent and magnetic properties of nanocrystalline Zn1-xNixO (x=0.0025-0.03)
Authors:
Mihalache, V; Negrila, C; Bercu, V; Secu, M; Vasile, E; Stan, GE
Published: JUL 2019, MATERIALS RESEARCH BULLETIN, 115, 48, DOI: 10.1016/j.materresbull.2019.03.001
We report on the influence of dilute doping combined with the processing conditions on the morphological, structural, chemical states, photoluminescence and magnetic properties of Zn1-xNixO nanopowders. Ni doping changes the ZnO powder morphology from randomly-aggregated nanocrystals to densely-packed nanocrystals arranged in columnar particles, modifies the high-energy-component of O1 s spectrum and increases the modified Auger parameter in XPS, enhances the blue photoluminescence (PL) emission, suppresses the green PL emission and the intensity of the g = 1.997 EPR signal. Ni-ZnO nanostructures show room-temperature ferro-magnetism (implying they can serve as dilute magnetic semiconductors). The saturation magnetization, crystallite size and microstrain increase with the doping level; the c-axis constant and unit cell volume decrease, however, being unexpectedly higher with respect to a (reference) ZnO powder with a relaxed lattice. We demonstrate that the investigated properties were controlled by both (dilute) doping level and donor native defects produced by non-equilibrium (oxygen-deficiency and high rate of) ZnO formation.
371. Fabrication and characterization of Ru-doped LiCuFe2O4 nanoparticles and their capacitive and resistive humidity sensor applications
Authors:
Manikandan, V; Tudorache, F; Petrila, J; Mane, RS; Kuncser, V; Vasile, B; Morgan, D; Vigneselvan, S; Mirzaei, A
Published: MAR 15 2019, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 474, 569, DOI: 10.1016/j.jmmm.2018.11.072
Polycrystalline ruthenium-doped lithium-copper-ferrite (Ru - LiCuFe2O4)nanoparticles (NPs) are synthesized using a simple and cost-effective chemical co-precipitation method and annealed at different temperatures for increasing the crystallinity. The transmission and scanning electron microscopy images have confirmed the presence of soft agglomerations and cuboids for the samples annealed at 1100 degrees C. X-ray photoelectron results along with Raman spectra have collectively demonstrated the presence of Ru in the structure of Ru - LiCuFe2O4 NPs. The dielectric properties of as-synthesized Ru - LiCuFe2O4 NPs are investigated using LCR meter where the smaller NPs demonstrates a higher dielectric constant. Also, the results of magnetic measurements of annealed Ru - LiCuFe2O4 NPs have corroborated a soft magnetic nature due to the pinning sites that endow lower coercivity, remanence and saturation magnetization than that of the pristine one. The variation of permittivity and electrical resistivity with respect to frequency under humidity conditions suggested that this material has a potential to use as capacitive and resistive humidity sensor. The results of this study open the doors for utilization of metal-doped magnetic ferrites for humidity sensing applications.
372. Passive magnetic shielding by machinable MgB2 bulks: measurements and numerical simulations
Authors:
Gozzelino, L; Gerbaldo, R; Ghigo, G; Laviano, F; Torsello, D; Bonino, V; Truccato, M; Batalu, D; Grigoroscuta, MA; Burdusel, M; Aldica, GV; Badica, P
Published: MAR 2019, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 32, DOI: 10.1088/1361-6668/aaf99e
We report on a combined experimental and modelling approach towards the design and fabrication of efficient bulk shields for low-frequency magnetic fields. To this aim, MgB2 is a promising material when its growing technique allows the fabrication of suitably shaped products and a realistic numerical modelling can be exploited to guide the shield design. Here, we report the shielding properties of an MgB2 tube grown by a novel technique that produces fully machinable bulks, which can match specific shape requirements. Despite a height/radius aspect ratio of only 1.75, shielding factors higher than 175 and 55 were measured at temperature T = 20 K and in axially-applied magnetic fields mu H-0(appl) = 0.1 and 1.0 T, respectively, by means of cryogenic Hall probes placed on the tube's axis. The magnetic behaviour of the superconductor was then modelled as follows: first we used a two-step procedure to reconstruct the macroscopic critical current density dependence on magnetic field, J(c)(B), at different temperatures from the local magnetic induction cycles measured by the Hall probes. Next, using these J(c)(B) characteristics, by means of finite-element calculations we reproduced the experimental cycles remarkably well at all the investigated temperatures and positions along the tube's axis. Finally, this validated model was exploited to study the influence both of the tube's wall thickness and of a cap addition on the shield performance. In the latter case, assuming the working temperature of 25 K, shielding factors of 10(5) and 10(4) are predicted in axial applied fields it mu H-0(appl) = 0.1 and 1.0 T, respectively.
373. Spirobifluorene-based Porous Organic Polymers as Efficient Porous Supports for Pd and Pt for Selective Hydrogenation
Authors:
Trandafir, MM; Pop, L; Hadade, ND; Hristea, I; Teodorescu, CM; Krumeich, F; van Bokhoven, JA; Grosu, I; Parvulescu, VI
Published: JAN 9 2019, CHEMCATCHEM, 11, 549, DOI: 10.1002/cctc.201801247
Spirobifluorene-based porous organic polymers (POP) were synthesized following two different protocols; the acetylenic coupling reaction conditions and the Sonogashira cross-coupling reaction. These were utilized as support for the hydrogenation of a series of species containing unsaturated C=C and C=O bonds (4-nitrostyrene, 4-bromobenzophenone, acetophenone, 7-nitro-1-tetralone and 1,2-naphtoquinone confirmed their efficiency). POP1 prepared via a copper-catalysis protocol was completely inactive, while POP2-4 containing residual Pd exhibited different activities in accordance to the accessibility of the substrates to the metal. Further deposition of 0.5wt% Pd led to active and stable catalysts. They were easily separated by filtration, and after re-dispersion, afforded the same performances for ten successive cycles. This study also evidenced the specific role of the support in these reactions by comparing the behavior of Pd/POP with that of a Pd/C catalyst with the same loading of palladium. The deposition of Pt on these supports led to sub-nanometric particles and, in accordance, to a different catalytic behavior reflected merely by differences in the selectivity.
374. Core-shell nanowire arrays based on ZnO and CuxO for water stable photocatalysts
Authors:
Florica, C; Costas, A; Preda, N; Beregoi, M; Kuncser, A; Apostol, N; Popa, C; Socol, G; Diculescu, V; Enculescu, I
Published: NOV 21 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-53873-0
Staggered gap radial heterojunctions based on ZnO-CuxO core-shell nanowires are used as water stable photocatalysts to harvest solar energy for pollutants removal. ZnO nanowires with a wurtzite crystalline structure and a band gap of approximately 3.3 eV are obtained by thermal oxidation in air. These are covered with an amorphous CuxO layer having a band gap of 1.74 eV and subsequently form core-shell heterojunctions. The electrical characterization of the ZnO pristine and ZnO-CuxO core-shell nanowires emphasizes the charge transfer phenomena at the junction and at the interface between the nanowires and water based solutions. The methylene blue degradation mechanism is discussed taking into consideration the dissolution of ZnO in water based solutions for ZnO nanowires and ZnO-CuxO core-shell nanowires with different shell thicknesses. An optimum thickness of the CuxO layer is used to obtain water stable photocatalysts, where the ZnO-CuxO radial heterojunction enhances the separation and transport of the photogenerated charge carriers when irradiating with UV-light, leading to swift pollutant degradation.
375. Deposition temperature influence on the wear behaviour of carbon-based coatings deposited on hardened steel
Authors:
Feldiorean, D; Cristea, D; Tierean, M; Croitoru, C; Gabor, C; Jakab-Farkas, L; Cunha, L; Barradas, NP; Alves, E; Craciun, V; Marin, A; Moura, C; Leme, J; Socol, M; Craciun, D; Cosnita, M; Munteanu, D
Published: MAY 1 2019, APPLIED SURFACE SCIENCE, 475, 773, DOI: 10.1016/j.apsusc.2019.01.028
This paper presents an evaluation regarding the influence of substrate material characteristics and deposition parameters on the tribological behaviour of carbon-based coatings. Chromium nitride ceramic interlayers and carbon-based thin films were deposited by magnetron sputtering on hardened AISI 5115 (16MnCr5) case hardening steel. The physical vapour deposition (PVD) deposition was performed at three different temperatures: 180 degrees C, 200 degrees C and 250 degrees C. The chemical composition of the samples was assessed by Rutherford Backscattering Spectroscopy (RBS), the structure by X-ray Diffraction (XRD), and the surface morphology by Atomic Force Microscopy (AFM). The surface chemistry was analysed by X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy. The coatings are homogeneous, amorphous, with a smooth surface. The mechanical behaviour has been assessed on a pin-on disk rotational tribometer (wear characteristics), on a micro scratch tester (adhesion to the substrate), by ball-cratering (film thickness) and by nanoindentation (hardness and the modulus of elasticity). A strong correlation has been observed between the substrate characteristics and, more importantly, the deposition temperature, and the mechanical properties of the assembly. The fracture toughness is positively influenced by the presence of the ceramic chromium nitride interlayer. The modulus of elasticity and friction coefficient (both in dry and lubricated conditions) are decreased for higher deposition temperatures, however the higher deposition temperature negatively affects the mechanical characteristics of the steel substrate.
376. Efficient glucose dehydration to HMF onto Nb-BEA catalysts
Authors:
Candu, N; El Fergani, M; Verziu, M; Cojocaru, B; Jurca, B; Apostol, N; Teodorescu, C; Parvulescu, VI; Coman, SM
Published: MAR 15 2019, CATALYSIS TODAY, 325, 116, DOI: 10.1016/j.cattod.2018.08.004
The one-pot production of HMF from glucose was investigated in pure hot water and biphasic water/methyli-sobutylketone (MIBK) solvent using mesoporous Nb(0.02 and 0.05 mol%)-Beta zeolites obtained by a post synthesis methodology. The mesoporous Nb-Beta zeolites present residual framework Al-acid sites, extra-framework isolated Nb(V) and Nb2O5 pore-encapsulated clusters in which Nb(V) O-H exhibit moderate strength Bronsted acidity. After optimization, the dehydration of glucose onto the Nb-modified Beta-zeolites occurred with a selectivity of 84.3% in HMF for a glucose conversion of 97.4%. This result has been obtained in a biphasic water/ MIBK solvent and in the presence of NaCl, at 180 degrees C, after 12 h.
377. A Dyson Equation for Non-Equilibrium Green's Functions in the Partition-Free Setting
Authors:
Cornean, HD; Moldoveanu, V; Pillet, CA
Published: JUL 2019, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 256, DOI: 10.1002/pssb.201800447
Here a small interacting sample, coupled to several non-interacting leads is considered. Initially, the system is at thermal equilibrium. At some instant t(0) the system is set into the so-called partition-free transport scenario by turning on a bias on the leads. Using the theory of Volterra operators we rigorously formulate a Dyson equation for the retarded Green's function and we establish a closed formula for the associated proper interaction self-energy.
378. Comparison between dielectric and pyroelectric properties of PZFNT and BST type ceramics
Authors:
Stancu, V; Amarande, L; Botea, M; Iuga, A; Leonat, LN; Tomulescu, AG; Cioangher, M; Balescu, LM; Pintilie, L
Published: 2019, PROCESSING AND APPLICATION OF CERAMICS, 13, 276, DOI: 10.2298/PAC1903269S
Ba0.75Sr0.25TiO3 (BST) and PbZr0.68Fe0.14Nb0.14Ti0.04O3 (PZFNT) ceramic pellets were obtained by ceramic technology and their structural, ferroelectric and pyroelectric properties were investigated. The relative density of BST and PZFNT is about 93% and 90%, respectively, with an average grain size of 102 mu m and 6.45 mu m. Both materials have similar room temperature dielectric constants (similar to 2000), but PZFNT shows higher remnant polarization (similar to 15 mu C/cm(2)) and better pyroelectric properties (similar to 1.69 . 10(-4) C/m(2)K), which recommend it for pyroelectric detectors, infrared radiation- and laser pulse energy-meters.
379. Rapid thermal annealing for high-quality ITO thin films deposited by radio-frequency magnetron sputtering
Authors:
Prepelita, P; Stavarache, I; Craciun, D; Garoi, F; Negrila, C; Sbarcea, BG; Craciun, V
Published: JUL 25 2019, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 10, 1522, DOI: 10.3762/bjnano.10.149
In this work, rapid thermal annealing (RTA) was applied to indium tin oxide (ITO) films in ambient atmosphere, resulting in significant improvements of the quality of the ITO films that are commonly used as conductive transparent electrodes for photovoltaic structures. Starting from a single sintered target (purity 99.95%), ITO thin films of predefined thickness (230 nm, 300 nm and 370 nm) were deposited at room temperature by radio-frequency magnetron sputtering (rfMS). After deposition, the films were subjected to a RTA process at 575 degrees C (heating rate 20 degrees C/s), maintained at this temperature for 10 minutes, then cooled down to room temperature at a rate of 20 degrees C/s. The film structure was modified by changing the deposition thickness or the RTA process. X-ray diffraction investigations revealed a cubic nanocrystalline structure for the as-deposited ITO films. After RTA, polycrystalline compounds with a textured (222) plane were observed. X-ray photon spectroscopy was used to confirm the beneficial effect of the RTA treatment on the ITO chemical composition. Using a Tauc plot, values of the optical band gap ranging from 3.17 to 3.67 eV were estimated. These values depend on the heat treatment and the thickness of the sample. Highly conductive indium tin oxide thin films (rho = 7.4 x 10(-5) Omega cm) were obtained after RTA treatment in an open atmosphere. Such films could be used to manufacture transparent contact electrodes for solar cells.
380. Formation of a Bistable Interstitial Complex in Irradiated p-Type Silicon
Authors:
Makarenko, LF; Lastovski, SB; Yakushevich, HS; Gaubas, E; Pavlov, J; Kozlovski, VV; Moll, M; Pintilie, I
Published: SEP 2019, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 216, DOI: 10.1002/pssa.201900354
The influence of the injection of minority charge carriers on the formation of a divalent bistable defect (DBH) having two energy levels of E-v + 0.44 eV and E-v + 0.53 eV in its metastable configuration is investigated. Using forward current injection, the formation temperature of this defect in p-type silicon can be lowered by about 50 degrees C. The production of such bistable defect is enhanced in materials with a high ratio of boron to carbon concentrations. This allows one to conclude that the boron atom is one of the constituents of the defect under study. There is also a correlation between the behavior of the bistable hole traps and a metastable electron trap observed earlier. It is concluded that these traps are related to metastable and stable configurations of the DBH defect, which has inverse occupancy level ordering in its stable configuration.
381. Voltammetric and mass spectrometry investigation of methionine oxidation
Authors:
Diculescu, VC; Enache, TA
Published: FEB 1 2019, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 834, 129, DOI: 10.1016/j.jelechem.2018.12.058
The electro-oxidation mechanism of free methionine and bound within different peptide sequences was investigated by voltammetry, at glassy carbon electrode, and mass spectrometry. It is proposed that the electro-oxidation of free methionine occurs in two steps, each involving the transfer of one electron and turns pH-independent from mild acid to mild alkaline electrolytes. The first oxidation reaction leads to the formation of a cation radical stabilized either through the amino group resulting in the dehydromethionine intermediate, or by interaction with a neutral methionine molecule leading to production of a dimer cationic radical. The dehydromethionine hydrolysis gave methionine sulfoxide as final oxidation product, whereas a future oxidation of methionine dimer cation radical, i.e. the second electro-oxidation step, results in a methionine dimer dication. Moreover, at high acid media, the protonated amino group influence the electro-oxidation process to take place via proton transfer mechanism. The presence of methionine sulfoxide and of the dimer cationic radical as oxidation products of methionine was confirmed by mass spectroscopy.
382. PHOTO-ELECTRICAL PROPERTIES OF THIN FILMS WITH GE NANOPARTICLES EMBEDDED IN TIO2 MATRIX
We present photo-electrical properties of thin films formed of Ge nanoparticles in TiO2 correlated with structure and morphology. The films co-deposited on Si using magnetron sputtering were annealed in conventional oven at 550 degrees C. We performed structure investigations by X-ray diffraction, transmission electron microscopy and measured current-voltage characteristics in dark and under illumination at different temperatures. We show that the films are formed of cubic Ge nanoparticles in nanostructured anatase TiO2 matrix. Also, (TiGe)O-2 with rutile structure was observed. The films have high photosensitivity under white light as the ratio between photo- and dark currents (-1 V) is of similar to 10(2).
383. High performance NIR photosensitive films of Ge nanoparticles in Si3N4
Authors:
Stavarache, I; Prepelita, P; Lalau, I; Cojocaru, O; Teodorescu, VS; Ciurea, ML
Published: 2019, 2019 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS 2019), 42ND EDITION, 228, DOI:
Films of amorphous Ge nanoparticles in Si3N4 on heated Si and quartz substrates at 300 degrees C were obtained by co-sputtering Ge, and Si3N4. The films structure and photo-electrical behaviour were studied through transmission electron microscopy and, current voltage and spectral photo-current investigations, respectively. The spectral photo-current were correlated with results obtained from transmission electron microscopy. Under illumination the current present a high increase with about one order of magnitude compared with the dark one. The photo-current spectra show a widening in near infrared to 0.97eV. Internal quantum efficiency values for -1V and 0V were determined.
384. Electronic Structure of a Graphene-like Artificial Crystal of NdNiO3
Authors:
Arab, A; Liu, XR; Koksal, O; Yang, WB; Chandrasena, RU; Middey, S; Kareev, M; Kumar, S; Husanu, MA; Yang, ZZ; Gu, L; Strocov, VN; Lee, TL; Minar, J; Pentcheva, R; Chakhalian, J; Gray, AX
Published: NOV 2019, NANO LETTERS, 19, 8317, DOI: 10.1021/acs.nanolett.9b03962
Artificial complex-oxide heterostructures containing ultrathin buried layers grown along the pseudocubic [111] direction have been predicted to host a plethora of exotic quantum states arising from the graphene-like lattice geometry and the interplay between strong electronic correlations and band topology. To date, however, electronic-structural investigations of such atomic layers remain an immense challenge due to the shortcomings of conventional surface-sensitive probes with typical information depths of a few angstroms. Here, we use a combination of bulk-sensitive soft X-ray angle-resolved photoelectron spectroscopy (SX-ARPES), hard X-ray photoelectron spectroscopy (HAXPES), and state-of-the-art first-principles calculations to demonstrate a direct and robust method for extracting momentum-resolved and angle-integrated valence-band electronic structure of an ultrathin buckled graphene-like layer of NdNiO3 confined between two 4-unit cell-thick layers of insulating LaAlO3. The momentum-resolved dispersion of the buried Ni d states near the Fermi level obtained via SX-ARPES is in excellent agreement with the first-principles calculations and establishes the realization of an antiferro-orbital order in this artificial lattice. The HAXPES measurements reveal the presence of a valence-band bandgap of 265 meV. Our findings open a promising avenue for designing and investigating quantum states of matter with exotic order and topology in a few buried layers.
385. Generalized Master Equation Approach to Time-Dependent Many-Body Transport
Authors:
Moldoveanu, V; Manolescu, A; Gudmundsson, V
Published: AUG 2019, ENTROPY, 21, DOI: 10.3390/e21080731
We recall theoretical studies on transient transport through interacting mesoscopic systems. It is shown that a generalized master equation (GME) written and solved in terms of many-body states provides the suitable formal framework to capture both the effects of the Coulomb interaction and electron-photon coupling due to a surrounding single-mode cavity. We outline the derivation of this equation within the Nakajima-Zwanzig formalism and point out technical problems related to its numerical implementation for more realistic systems which can neither be described by non-interacting two-level models nor by a steady-state Markov-Lindblad equation. We first solve the GME for a lattice model and discuss the dynamics of many-body states in a two-dimensional nanowire, the dynamical onset of the current-current correlations in electrostatically coupled parallel quantum dots and transient thermoelectric properties. Secondly, we rely on a continuous model to get the Rabi oscillations of the photocurrent through a double-dot etched in a nanowire and embedded in a quantum cavity. A many-body Markovian version of the GME for cavity-coupled systems is also presented.
386. Palladium/palladium oxide coated electrospun fibers for wearable sweat pH-sensors
Authors:
Diculescu, VC; Beregoi, M; Evanghelidis, A; Negrea, RF; Apostol, NG; Enculescu, I
Published: JUN 20 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-45399-2
The work describes the development of a flexible, hydrogel embedded pH-sensor that can be integrated in inexpensive wearable and non-invasive devices at epidermal level for electrochemical quantification of H+ ions in sweat. Such a device can be useful for swift, real time diagnosis and for monitoring specific conditions. The sensors' working electrodes are flexible poly(methyl methacrylate) electrospun fibers coated with a thin gold layer and electrochemically functionalized with nanostructured palladium/palladium oxide. The response to H+ ions is investigated by cyclic voltammetry and electrochemical impedance spectroscopy while open circuit potential measurements show a sensitivity of aprox. -59 mV per pH unit. The modification of the sensing interface upon basic and acid treatment is characterized by scanning and transmission electron microscopy and the chemical composition by X-ray photoelectron spectroscopy. In order to demonstrate the functionality of the pH-sensor at epidermal level, as a wearable device, the palladium/palladium oxide working electrode and silver/silver chloride reference electrode are embedded within a pad of polyacrylamide hydrogel and measurements in artificial sweat over a broad pH range were performed. Sensitivity up to -28 mV/pH unit, response time below 30 s, temperature dependence of approx. 1 mV/degrees C as well as the minimum volume to which the sensor responses of 250 nanoliters were obtained for this device. The proposed configuration represents a viable alternative making use of low-cost and fast fabrication processes and materials.
387. Cavity-Photon-Induced High-Order Transitions between Ground States of Quantum Dots
Authors:
Gudmundsson, V; Abdullah, NR; Tang, CS; Manolescu, A; Moldoveanu, V
Published: NOV 2019, ANNALEN DER PHYSIK, 531, DOI: 10.1002/andp.201900306
It is shown that quantum electromagnetic transitions to high orders are essential to describe the time-dependent path of a nanoscale electron system in a Coulomb blockade regime when coupled to external leads and placed in a 3D rectangular photon cavity. The electronic system consists of two quantum dots embedded asymmetrically in a short quantum wire. The two lowest in energy spin degenerate electron states are mostly localized in each dot with only a tiny probability in the other dot. In the presence of the leads, a slow high-order transition between the ground states of the two quantum dots is identified. The Fourier power spectrum for photon-photon correlations in the steady state shows a Fano type of resonance for the frequency of the slow transition. Full account is taken of the geometry of the multilevel electronic system, and the electron-electron Coulomb interactions together with the para- and diamagnetic electron-photon interactions are treated with step-wise exact numerical diagonalization and truncation of appropriate many-body Fock spaces. The matrix elements for all interactions are computed analytically or numerically exactly.
388. Physical properties of indium zinc oxide and aluminium zinc oxide thin films deposited by radio-frequency magnetron sputtering
Authors:
Vasile, N; Iftimie, S; Acsente, T; Locovei, C; Calugar, AI; Radu, A; Ion, L; Antohe, VA; Manica, D; Toma, O; Dinescu, G; Antohe, S
Published: DEC 2019, MATERIALS RESEARCH EXPRESS, 6, DOI: 10.1088/2053-1591/ab688d
Indium-doped zinc oxide (IZO) and aluminium-doped zinc oxide (AZO) thin films were grown by radio-frequency (RF) magnetron sputtering onto optical glass substrates and their structural, morphological, and optical properties were discussed in terms of varying the sputtering power as 40 W, 60 W, 80 W, and 100 W. No heating substrate or any post-thermal treatment was performed. The structural features were analyzed by grazing incidence X-ray diffraction and revealed the amorphous phase for IZO samples, while the AZO thin films inherited the Wurtzite structure of zinc oxide. The morphological properties were investigated by atomic force microscopy (AFM), in tapping mode and scanning electronmicroscopy (SEM). The AFM images showed relatively uniform and smooth surfaces for all prepared structures. The optical transmission spectra proved the excellent theoretical values of transparency for metallic oxides in the visible region of the electromagnetic spectrum, i.e. similar to 60% for IZO and similar to 70% for AZO. The obtained results showed that even without any thermal treatment the structural, morphological, and optical properties of IZO and AZO thin films prepared by RF magnetron sputtering are similar with those for samples subjected to medium or high temperatures.
389. Annealing of preexisting defects in silicon single crystals by ion irradiation
Authors:
Mihai, MD; Ionescu, P; Pantelica, D; Petrascu, H; Craciun, D; Craciun, V; Vasiliu, F; Vasile, BS; Mercioniu, I
Published: JUL 1 2019, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 450, 89, DOI: 10.1016/j.nimb.2018.09.005
The annealing of crystalline defects in Si single crystals created by ion implantation at room temperature was investigated. Silicon single crystals were firstly implanted at room temperature with 1.345 MeV Au1+ ions at fluences from 1 x 10(13) to 1 x 10(14) at/cm(2) to induce damage. A second implantation at room temperature was afterwards performed with 10 MeV Co3+ ions at a fluence of 3 x 10(14) at/cm(2). All samples were analyzed afterwards by Rutherford backscattering in random and channeling geometry to assess the crystalline damage present in the surface region. The results showed a significant reduction of the degree of damage or a reduction of the size of damaged region. The morphology and local atomic structure, studied using high -resolution electron microscopy, selected area electron diffraction and high resolution X-ray diffraction confirmed the reduction of damage degree and volume caused by Au implantation after Co implantation.
390. Energy-enhanced deposition of copper thin films by bipolar high power impulse magnetron sputtering
Authors:
Velicu, IL; Ianos, GT; Porosnicu, C; Mihaila, I; Burducea, I; Velea, A; Cristea, D; Munteanu, D; Tiron, V
Published: FEB 15 2019, SURFACE & COATINGS TECHNOLOGY, 359, 107, DOI: 10.1016/j.surfcoat.2018.12.079
Bipolar Pulse High Power Impulse Magnetron Sputtering (BP-HiPIMS) was investigated and used in this work to control the ion bombardment process of growing thin films and to improve their structure and properties. Energy-resolving mass spectroscopy was used to investigate the effect of reverse target voltage on the ion energies and fluxes during BP-HiPIMS of a high-purity copper target, in argon gas. It was found that the reverse target voltage provides a wide range of ion energies and fluxes incident to the growing film, which, in turn, produce a wide variety of effects during the deposition process, improving the adhesion strength and influencing both surface and bulk properties. Fast ICCD imaging was used to investigate both HiPIMS and BP-HiPIMS plasma dynamics. The temporal and spatial distributions of plasma potential measurements were performed in order to explain the mechanisms for accelerating the ions. The topological, structural and mechanical properties of the deposited coatings were investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), thermal desorption spectroscopy (TDS), scanning electron microscopy (SEM), nanoindentation and scratch tests. The obtained results indicate an energy-enhanced deposition process during BP-HiPIMS, the deposited films being characterized by smooth surfaces, dense microstructure, small inert gas inclusions, high elastic strain to failure, scratch resistance and good adhesion to the substrate. These improvements in the films' structure and properties may be attributed to the intense and energetic ion bombardment taking place during the deposition process. During BP-HiPIMS operation, there is no net increase in the deposition rate as compared to the monopolar regime due to the re-sputtering process.
391. New electrochemical sensor based on CoQ(10) and cyclodextrin complexes for the detection of oxidative stress initiators
Authors:
Barsan, MM; Diculescu, VC
Published: APR 10 2019, ELECTROCHIMICA ACTA, 302, 448, DOI: 10.1016/j.electacta.2019.02.060
The development of coenzyme Q(10) (CoQ(10)) based electrochemical sensor for the detection of oxidative stress initiators is described for the first time. The sensor relies on CoQ(10) redox properties. CoQ(10) was immobilized at the surface of glassy carbon electrodes (GCE) in combination with cyclodextrins (CD), alpha-CD or beta-CD, that ensure the formation of a well dispersed CoQ(10) film. Nanostructured thin films of CoQ(10) alone and in complexes with alpha-CD or beta-CD at the electrode surface were characterized by scanning electron microscopy (SEM) and Fourier-transformed infrared spectroscopy (FTIR), enabling to identify the morphology of the films and the interactions between the CoQ(10) and CD. Nafion (R) was used to ensure sensor stability. The optimization of the CoQ(10) sensor configuration was made by assessing CoQ(10) redox properties through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), correlated with the results obtained from SEM and FTIR characterization. Next, the sensor in the optimized configuration, GCE/alpha-CD + CoQ(10)/Nafion (R), was applied for the detection of oxidant molecules, hydrogen peroxide and the superoxide radical, through the evaluation of the CoQ(10) redox properties monitored by fixed potential chronoamperometry and square wave voltammetry (SWV). (C) 2019 Elsevier Ltd. All rights reserved.
392. Antireflective coatings with high damage threshold prepared by laser ablation
Authors:
Filipescu, M; Palla-Papavlu, A; Bercea, A; Rusen, L; Cernaianu, MO; Ion, V; Calugar, A; Nistor, LC; Dinescu, M
Published: DEC 2019, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 125, DOI: 10.1007/s00339-019-3110-y
Latest developments in the field of high power ultra-short pulse lasers have led to intensive studies dedicated to the fabrication possibility of new antireflective coatings which exhibit high damage threshold. Therefore, this study is focused on the deposition and characterization of metal oxide heterostructures followed by laser-induced damage threshold tests which evidence their application in high power laser optics. Al2O3, SiO2, and HfO2 layers are combined to obtain different heterostructures, i.e. HfO2/Al2O3/HfO2/Al2O3/HfO2 and HfO2/SiO2/HfO2/SiO2/HfO2. The metal oxide heterostructures are deposited in a controllable oxygen atmosphere, either at room temperature or high temperatures (600 degrees C) by pulsed laser deposition (PLD). The morphological, structural and optical properties of the as-deposited heterostructures are first investigated. Atomic force microscopy and spectroscopic ellipsometry investigations reveal a lower roughness of the heterostructures based on HfO2/Al2O3 layers grown at 600 degrees C as compared to those grown at room temperature. Furthermore, following the laser-induced damage threshold (LIDT) tests carried out with a Ti-Sapphire laser, higher LIDT values are obtained for the HfO2/Al2O3-based heterostructures than for the HfO2/SiO2-based heterostructures. The ability to control the morphological and structural properties of the antireflective coatings by modifying the deposition parameters of the metal oxide heterostructures demonstrates that PLD is a suitable technique for the manufacturing of antireflective coatings for high power ultra-short laser systems.
393. Formation peculiarities and optical properties of highly-doped (Y(0.86)La(0.09)Vb(0.05))(2)O-3 transparent ceramics
Authors:
Kryzhanovska, OS; Baumer, VN; Parkhomenko, SV; Doroshenko, AG; Yavetskiy, RP; Balabanov, AE; Tolmachev, AV; Skorik, SN; Li, J; Kuncser, A
Published: SEP 2019, CERAMICS INTERNATIONAL, 45, 16007, DOI: 10.1016/j.ceramint.2019.05.111
Formation peculiarities of highly-doped (Y(0.86)La(0.09)Vb(0.05))(2)O-3 transparent ceramics have been studied by X-ray diffraction and electron microscopy methods. The phase composition evolution of 1.81Y(2)O(3).0.18La(2)O(3)0.01Yb(2)O(3) powder mixtures annealed at the temperatures of 1100, 1200, 1300, and 1400 degrees C has been studied by XRD. It has been shown that Yb2O3 phase dissolves in Y2O3 matrix in the calcination temperature range of 1300-1400 degrees C. Complete dissolution of La2O3 in Y2O3 matrix occurs at temperatures above 1400 degrees C. La3+ ions enter in Y2O3 and Yb2O3 crystal structures simultaneously in the 1200-1300 degrees C range, which leads to a remarkable increase in the volume of the corresponding crystal lattices. The possible reasons for suppressing the crystalline growth of Y2O3 and Yb2O3 cubic phases have been discussed. Finally, (Y(0.86)La(0.09)Vb(0.05))(2)O-3 transparent ceramics have been obtained by solid-state vacuum sintering at 1650-1750 degrees C. Ceramics synthesized at a temperature of 1750 degrees C have been characterized by an in-line optical transmittance of 60% and a homogeneous distribution of constituent components within the volume and along the grain boundaries.
394. Naturally-Derived Biphasic Calcium Phosphates through Increased Phosphorus-Based Reagent Amounts for Biomedical Applications
Authors:
Mocanu, AC; Stan, GE; Maidaniuc, A; Miculescu, M; Antoniac, IV; Ciocoiu, RC; Voicu, SI; Mitran, V; Cimpean, A; Miculescu, F
Published: FEB 1 2019, MATERIALS, 12, DOI: 10.3390/ma12030381
Calcium carbonate from marble and seashells is an eco-friendly, sustainable, and largely available bioresource for producing natural bone-like calcium phosphates (CaPs). Based on three main objectives, this research targeted the: (i) adaptation of an indirect synthesis route by modulating the amount of phosphorus used in the chemical reaction, (ii) comprehensive structural, morphological, and surface characterization, and (iii) biocompatibility assessment of the synthesized powdered samples. The morphological characterization was performed on digitally processed scanning electron microscopy (SEM) images. The complementary 3D image augmentation of SEM results also allowed the quantification of roughness parameters. The results revealed that both morphology and roughness were modulated through the induced variation of the synthesis parameters. Structural investigation of the samples was performed by Fourier transform infrared spectroscopy and X-ray diffraction. Depending on the phosphorus amount from the chemical reaction, the structural studies revealed the formation of biphasic CaPs based on hydroxyapatite/brushite or brushite/monetite. The in vitro assessment of the powdered samples demonstrated their capacity to support MC3T3-E1 pre-osteoblast viability and proliferation at comparable levels to the negative cytotoxicity control and the reference material (commercial hydroxyapatite). Therefore, these samples hold great promise for biomedical applications.
395. Fabrication and characterization of Si1-xGex nanocrystals in as-grown and annealed structures: a comparative study
Authors:
Sultan, MT; Maraloiu, AV; Stavarache, I; Gudmundsson, JT; Manolescu, A; Teodorescu, VS; Ciurea, ML; Svavarsson, HG
Published: SEP 17 2019, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 10, 1882, DOI: 10.3762/bjnano.10.182
Multilayer structures comprising of SiO2/SiGe/SiO2 and containing SiGe nanoparticles were obtained by depositing SiO2 layers using reactive direct current magnetron sputtering (dcMS), whereas, Si and Ge were co-sputtered using dcMS and high-power impulse magnetron sputtering (HiPIMS). The as-grown structures subsequently underwent rapid thermal annealing (550-900 degrees C for 1 min) in N-2 ambient atmosphere. The structures were investigated using X-ray diffraction, high-resolution transmission electron microscopy together with spectral photocurrent measurements, to explore structural changes and corresponding properties. It is observed that the employment of HiPIMS facilitates the formation of SiGe nanoparticles (2.1 +/- 0.8 nm) in the as-grown structure, and that presence of such nanoparticles acts as a seed for heterogeneous nucleation, which upon annealing results in the periodically arranged columnar self-assembly of SiGe core-shell nanocrystals. An increase in photocurrent intensity by more than an order of magnitude was achieved by annealing. Furthermore, a detailed discussion is provided on strain development within the structures, the consequential interface characteristics and its effect on the photocurrent spectra.
396. STRUCTURAL, DIELECTRIC AND PYROELECTRIC PROPERTIES OF Nb AND Fe DOPED PZT CERAMICS
Authors:
Stancu, V; Amarande, L; Botea, M; Cioangher, M; Tomulescu, A; Iuga, A; Pintilie, L
Published: JAN-MAR 2019, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 14, 230, DOI:
Lead zirconate titanate doped with iron and niobium (PZFNT) was prepared by conventional processing technique, solid state synthesis method. The influence of dopants on the microstructure, ferroelectric and pyroelectric properties was investigated. XRD data reveals a perovskite structure near to the lead zirconate phase. The relative density of PZFNT is approximate 90%, with average grains size of 6.45 mu m.
397. Enhancement in magnetic and dielectric properties of the ruthenium-doped copper ferrite(Ru - CuFe2O4) nanoparticles
Authors:
Manikandan, V; Kuncser, V; Vasile, B; Kavita, S; Vigneselvan, S; Mane, RS
Published: APR 15 2019, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 476, 23, DOI: 10.1016/j.jmmm.2018.12.050
Ruthenium-doped copper ferrite(Ru - CuFe2O4) nanoparticles (NPs) have been synthesized using a simple and cost-effective wet chemical co-precipitation deposition method. The crystallographic scanning electron microscopy images confirm cubic crystal structure and agglomerated-type surface appearance. The crystallite sizes are 6-24 nm in the range. Dielectric measurement analysis estimates the dielectric constant and loss of Ru - CuFe2O4 NPs. In this connection, dielectric constant and loss are reduced virtue of air annealing for various temperatures. Also, the dielectric loss confirms the relaxation peak. From magnetic measurement results, the coercivity decreases whereas saturation and remanence magnetization are increased. These features have approved the soft magnetic nature in the Ru - CuFe2O4 NPs.
398. Nitrogen-doped graphene as metal free basic catalyst for coupling reactions
Authors:
Candu, N; Man, I; Simion, A; Cojocaru, B; Coman, SM; Bucur, C; Primo, A; Garcia, H; Parvulescu, VI
Published: AUG 2019, JOURNAL OF CATALYSIS, 376, 247, DOI: 10.1016/j.jcat.2019.07.011
N-doped defective graphene [(N)G] obtained by pyrolysis at 900 degrees C of chitosan contains about 3.7% of residual N atoms, distributed as pyridinic, pyrrolic and graphitic N atoms. It has been found that (N)G acts as basic catalyst promoting two classical C-C bond forming nucleophilic additions in organic chemistry, such as the Michael and the Henry additions. Computational calculations at DFT level of models corresponding to the various N atoms leads to the conclusion that N atoms are more stable at the periphery of the graphene sheets and that H adsorption on these sites is a suitable descriptor to correlate with the catalytic activity of the various sites. According to these calculations the most active sites are pyridinic N atoms at zig-zag edges of the sheets. In addition, N as dopant changes the reactivity of the neigh. bour C atoms. Water was found a suitable solvent to achieve high conversions in both reactions. In this solvent the initial distribution of N atoms is affected due to the easy protonation of the N-py to N-pyH sites. As an effect, C edge sites adjacent at N-PyH with an appropriate reactivity towards the alpha-C-H bond breaking are formed. The present results show the general activity of N-doped graphene as base catalysts and illustrate the potential of carbocatalysis to promote reactions of general interest in organic synthesis. (C) 2019 Elsevier Inc. All rights reserved.
399. On the development of a robust cyber security system for Internet of Things devices
Authors:
Ionescu, O; Dumitru, V; Pricop, E; Buiu, O; Cobianu, C; Raneti, M; Pircalabu, S; Marica, C
Published: 2019, PROCEEDINGS OF THE 11TH INTERNATIONAL CONFERENCE ON ELECTRONICS, COMPUTERS AND ARTIFICIAL INTELLIGENCE (ECAI-2019), DOI:
Cyber security threats have escalated dramatically in the past few years, this being the main reason why the development of Internet of Things (IoT) devices was hindered and the full potential of their utility was not reached. A major step forward could be taken only by providing reliable and cheap protection against unauthorized interference from malicious users and other threats so that people can feel safe keeping their devices connected to the cloud. This paper is focused on the development of a robust cyber security solution for IoT. The device developed and presented in this paper has the capability of solving cyber security problem by using a simple and low-cost solution, that comes with the advantage of being less intrusive and easily adaptable to any Ethernet connected IoT device. The developed device has two embodiments, the first one being a simple hardware control of the communication line using a parallel channel, and the second one extending the features of the first by using the physical unclonable functions (PUF) generated by a controlled memristor for securing the data sent over the communication channel.
400. Coexisting spin and Rabi oscillations at intermediate time regimes in electron transport through a photon cavity
Authors:
Gudmundsson, V; Gestsson, H; Abdullah, NR; Tang, CS; Manolescu, A; Moldoveanu, V
Published: MAR 1 2019, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 10, 616, DOI: 10.3762/bjnano.10.61
In this work, we theoretically model the time-dependent transport through an asymmetric double quantum dot etched in a two-dimensional wire embedded in a far-infrared (FIR) photon cavity. For the transient and the intermediate time regimes, the current and the average photon number are calculated by solving a Markovian master equation in the dressed-states picture, with the Coulomb interaction also taken into account. We predict that in the presence of a transverse magnetic field the interdot Rabi oscillations appearing in the intermediate and transient regime coexist with slower non-equilibrium fluctuations in the occupation of states for opposite spin orientation. The interdot Rabi oscillation induces charge oscillations across the system and a phase difference between the transient source and drain currents. We point out a difference between the steady-state correlation functions in the Coulomb blocking and the photon-assisted transport regimes.
401. Electronic phase separation at LaAlO3/SrTiO3 interfaces tunable by oxygen deficiency
Authors:
Strocov, VN; Chikina, A; Caputo, M; Husanu, MA; Bisti, F; Bracher, D; Schmitt, T; Granozio, FM; Vaz, CAF; Lechermann, F
Published: OCT 7 2019, PHYSICAL REVIEW MATERIALS, 3, DOI: 10.1103/PhysRevMaterials.3.106001
Electronic phase separation is crucial for the fascinating macroscopic properties of the LaAlO3/SrTiO3 (LAO/STO) paradigm oxide interface, including the coexistence of superconductivity and ferromagnetism. We investigate this phenomenon using angle-resolved photoelectron spectroscopy (ARPES) in the soft-x-ray energy range, where the enhanced probing depth combined with resonant photoexcitation allow us access to fundamental electronic structure characteristics - momentum-resolved spectral function, dispersions and ordering of energy bands, Fermi surface - of buried interfaces. Our experiment uses x-ray irradiation of the LAO/STO interface to tune its oxygen deficiency, building up a dichotomic system where mobile weakly correlated Ti t(2g) electrons coexist with localized strongly correlated Ti e(g) ones. The ARPES spectra dynamics under x-ray irradiation shows a gradual intensity increase under constant Luttinger count of the Fermi surface. This fact identifies electronic phase separation (EPS) where the mobile electrons accumulate in conducting puddles with fixed electronic structure embedded in an insulating host phase, and allows us to estimate the lateral fraction of these puddles. We discuss the physics of EPS invoking a theoretical picture of oxygen-vacancy clustering, promoted by the magnetism of the localized Ti e(g) electrons, and repelling of the mobile t(2g) electrons from these clusters. Our results on the irradiation-tuned EPS elucidate the intrinsic one taking place at the stoichiometric LAO/STO interfaces.
402. Ferroelectric Field Effect Transistors Based on PZT and IGZO
Authors:
Besleaga, C; Radu, R; Balescu, LM; Stancu, V; Costas, A; Dumitru, V; Stan, G; Pintilie, L
Published: 2019, IEEE JOURNAL OF THE ELECTRON DEVICES SOCIETY, 7, 275, DOI: 10.1109/JEDS.2019.2895367
Ferroelectric field effect transistors (FeFETs) based on lead zirconate titanate (PZT) ferroelectric material and amorphous-indium-gallium-zinc oxide (a-IGZO) were developed and characterized. The PZT material was processed by a sol-gel method and then used as ferroelectric gate. The a-IGZO thin films, having the role of channel semiconductor, were deposited by radio-frequency magnetron sputtering, at a temperature of similar to 50 degrees C. Characteristics of a typical field effect transistor with SiO2 gate insulator, grown on highly doped silicon, and of the PZT-based FeFET were compared. It was proven that the FeFETs had promising performances in terms of I-on/I-off ratio (i.e., 10(6)) and IDS retention behavior.
403. Structural Change in Ni-Fe-Ga Magnetic Shape Memory Alloys after Severe Plastic Deformation
Authors:
Gurau, G; Gurau, C; Tolea, F; Sampath, V
Published: JUN 2 2019, MATERIALS, 12, DOI: 10.3390/ma12121939
Severe plastic deformation (SPD) is widely considered to be the most efficient process in obtaining ultrafine-grained bulk materials. The aim of this study is to examine the effects of the SPD process on Ni-Fe-Ga ferromagnetic shape memory alloys (FSMA). High-speed high-pressure torsion (HSHPT) was applied in the as-cast state. The exerted key parameters of deformation are described. Microstructural changes, including morphology that were the result of processing, were investigated by optical and scanning electron microscopy. Energy-dispersive X-ray spectroscopy was used to study the two-phase microstructure of the alloys. The influence of deformation on microstructural features, such as martensitic plates, intragranular gamma phase precipitates, and grain boundaries' dependence of the extent of deformation is disclosed by transmission electron microscopy. Moreover, the work brings to light the influence of deformation on the characteristics of martensitic transformation (MT). Vickers hardness measurements were carried out on disks obtained by SPD so as to correlate the hardness with the microstructure. The method represents a feasible alternative to obtain ultrafine-grained bulk Ni-Fe-Ga alloys.
404. STRUCTURAL EVOLUTION OF THE NiTi/NiFeGa SMART HYBRID MATERIAL DURING SEVERE PLASTIC DEFORMATION
Authors:
Gurau, C; Gurau, G; Tolea, F; Sampath, V
Published: JUL-SEP 2019, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 14, 546, DOI:
High speed high pressure torsion (HSHPT) a patented new approach is proposed to fabricate nanocomposites. The goal of this work is to investigate the NiTi/NiFeGa bilayer hybrid material with nano- and submicrocrystalline structure under the influence of HSHPT. Apart from the grain refinement, the effectiveness of the joint are revealed scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mechanical properties of the composite layers in bulk and after severe plastic deformation are investigated. Bi-layered composite disks consisting of NiTi shape memory alloy and NiFeGa - Heusler type alloy, exhibit thermoelastic structural martensitic transformation. Submicrocrystalline structure is formed in the both layers of the hybrid material. It is also ascertained significant hardening of each layer of the hybrid as a result of HSHPT. The results highlight market differences between the bulk and the hybrid and the role of severe plastic deformation on martensitic transformation.
405. Effects of high temperature and ultraviolet radiation on polymer composites
Authors:
Ching, YC; Gunathilake, TMSU; Ching, KY; Chuah, CH; Sandu, V; Singh, R; Liou, NS
Published: 2019, DURABILITY AND LIFE PREDICTION IN BIOCOMPOSITES, FIBRE-REINFORCED COMPOSITES AND HYBRID COMPOSITES, 426, DOI: 10.1016/B978-0-08-102290-0.00018-0
406. Addition of carbon fibers into B4C infiltrated with molten silicon
Authors:
Solodkyi, I; Bezdorozhev, O; Vterkovskiy, M; Bogomol, I; Bolbut, V; Kruger, M; Badica, P; Loboda, P
Published: JAN 2019, CERAMICS INTERNATIONAL, 45, 174, DOI: 10.1016/j.ceramint.2018.09.148
Boron carbide added with 0-20 wt% carbon fibers was subject to Si infiltration. Samples mainly consist of B13C2, beta-SiC and unreacted Si. Some amount of SiB6 and alpha-SiC was also detected, while formation of B-12(B,C,Si)(3) phase was suppressed due to short infiltration time. The carbon fibers react with Si and result in formation of a composite core-shell fiber with SiC-shell and C-core. Theoretical estimations suggest that these composite fibers have a strong influence on the enhancement of the bending strength. Although apparently in good agreement with experimental data showing an increase of bending strength up to 510 +/- 27 MPa in the sample with 10 wt% carbon fiber, the implications of phase changes with the carbon fiber amount has to be carefully considered. At higher amounts of carbon fibers, bending strength decreases.
407. Tailoring the Dopant Distribution in ZnO:Mn Nanocrystals
Authors:
Ghica, D; Vlaicu, ID; Stefan, M; Maraloiu, VA; Joita, AC; Ghica, C
Published: MAY 3 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-43388-z
The synthesis of semiconductor nanocrystals with controlled doping is highly challenging, as often a significant part of the doping ions are found segregated at nanocrystals surface, even forming secondary phases, rather than incorporated in the core. We have investigated the dopant distribution dynamics under slight changes in the preparation procedure of nanocrystalline ZnO doped with manganese in low concentration by electron paramagnetic resonance spectroscopy, paying attention to the formation of transient secondary phases and their transformation into doped ZnO. The acidification of the starting solution in the co-precipitation synthesis from nitrate precursors lead to the decrease of the Mn2+ ions concentration in the core of the ZnO nanocrystals and their accumulation in minority phases, until similar to 79% of the Mn2+ ions were localized in a thin disordered shell of zinc hydroxynitrate (ZHN). A lower synthesis temperature resulted in polycrystalline Mn-doped ZHN. Under isochronal annealing up to 250 degrees C the bulk ZHN and the minority phases from the ZnO samples decomposed into ZnO. The Mn2+ ions distribution in the annealed nanocrystals was significantly altered, varying from a uniform volume distribution to a preferential localization in the outer layers of the nanocrystals. Our results provide a synthesis strategy for tailoring the dopant distribution in ZnO nanocrystals for applications ranging from surface based to ones involving core properties.
408. Thermal, structural, magnetic and magneto-optical properties of dysprosium-doped phosphate glass
Authors:
Elisa, M; Stefan, R; Vasiliu, IC; Rusu, MI; Sava, BA; Boroica, L; Sofronie, M; Kuncser, V; Galca, AC; Beldiceanu, A; Volceanov, A; Eftimie, M
Published: OCT 1 2019, JOURNAL OF NON-CRYSTALLINE SOLIDS, 521, DOI: 10.1016/j.jnoncrysol.2019.119545
The work is dedicated to the investigation of optical, structural, magnetic and magneto-optical properties of an aluminophosphate glass doped with Dy3+ ions, for specific applications as Faraday rotators in the visible spectral domain. The vitreous material belongs to the 16Li(2)O-8Al(2)O(3)-6BaO center dot 60P(2)O(5)-10Dy(2)O(3) system. Optical homogeneity measured by a polariscopic method, as well as by polarimetry and interferometry revealed an optical quality glass. Time dependent electrical conductance measurements have shown a high chemical strength of the glass. Optical absorption of the doped glass in the visible domain evidenced the specific absorption lines of dysprosium ions, whereas structural investigations made by FTIR and Raman spectroscopy put in evidence the vitreous network forming role of phosphorous pentoxide. Magnetic and magneto-optical measurements demonstrated paramagnetic features of the doped glass, as well as a Verdet constant of about -0.05 min/Oe/cm at 600 nm wavelength.
409. Tryptophan/Dextran70 Based-Fluorescent Silver Nanoparticles: Synthesis and Physicochemical Properties
Authors:
Voicescu, M; Ionescu, S; Calderon-Moreno, JM; Teodorescu, VS; Anastasescu, M; Culita, DC
Published: JUL 2019, JOURNAL OF FLUORESCENCE, 29, 992, DOI: 10.1007/s10895-019-02411-2
Nano-size and shape of fluorescent silver nanostructures are important for a wide range of bio-applications, especially as drug delivery systems, imaging and sensing. The aim of the work is to develop a fluorescent silver nano-structured system, synthesized by chemical reduction of aqueous AgNO3 solution by Tryptophan using Dextran 70 as stabilizing agent (SNPs(FL)). The formed fluorescent nano-system was analyzed by UV-Vis absorption, DLS, SEM, TEM, AFM, steady-state and time resolved fluorescence spectroscopy. TEM analysis showed multi-twined nanoparticle, with the size within 15-40 nm. SNPs(FL) shows the fluorescence emission at 346 nm, the fluorescence quantum yield, phi = 0.034 and the integrated fluorescence lifetime, = 1.82 ns. Riboflavin fluorescence behaviour in the RF/SNPs(FL) system, has been also studied. The results have relevance in using SNPs(FL) as a potential marker/emissive system to solve various biological barriers in humans, like drug release and protein structure.
410. Ge nanoparticles in SiO2 for near infrared photodetectors with high performance
Authors:
Stavarache, I; Teodorescu, VS; Prepelita, P; Logofatu, C; Ciurea, ML
Published: JUL 16 2019, SCIENTIFIC REPORTS, 9, DOI: 10.1038/s41598-019-46711-w
In this work we prepared films of amorphous germanium nanoparticles embedded in SiO2 deposited by magnetron sputtering on Si and quartz heated substrates at 300, 400 and 500 degrees C. Structure, morphology, optical, electrical and photoconduction properties of all films were investigated. The Ge concentration in the depth of the films is strongly dependent on the deposition temperature. In the films deposited at 300 degrees C, the Ge content is constant in the depth, while films deposited at 500 degrees C show a significant decrease of Ge content from interface of the film with substrate towards the film free surface. From the absorption curves we obtained the Ge band gap of 1.39 eV for 300 degrees C deposited films and 1.44 eV for the films deposited at 500 degrees C. The photocurrents are higher with more than one order of magnitude than the dark ones. The photocurrent spectra present different cutoff wavelengths depending on the deposition temperature, i.e. 1325 nm for 300 degrees C and 1267 nm for 500 degrees C. These films present good responsivities of 2.42 AW(-1) (52 mu W incident power) at 300 degrees C and 0.69 AW(-1) (57 mW) at 500 degrees C and high internal quantum efficiency of similar to 445% for 300 degrees C and similar to 118% for 500 degrees C.
411. The hysteresis-free behavior of perovskite solar cells from the perspective of the measurement conditions
Authors:
Nemnes, GA; Besleaga, C; Tomulescu, AG; Leonat, LN; Stancu, V; Florea, M; Manolescu, A; Pintilie, I
Published: MAY 14 2019, JOURNAL OF MATERIALS CHEMISTRY C, 7, 5274, DOI: 10.1039/c8tc05999c
We investigate how far the hysteresis-free behavior of perovskite solar cells can be reproduced using particular pre-conditioning and measurement conditions. As there are currently more and more reports of perovskite solar cells without J-V hysteresis it is crucial to distinguish between genuine performance improvements and measurement artifacts. We focus on two of the parameters that influence the dynamic J-V scans, namely the bias scan rate and the bias poling voltage, and point out measurement conditions for achieving a hysteresis-free behavior. In this context we discuss the suitability of defining a hysteresis index (HI) for the characterization of dynamic J-V scans. Using HI, aging effects are also investigated, establishing a potential connection between the sample degradation and the variation of the maximal hysteresis on one hand, and the relaxation time scale of the slow process on the other hand. Pre-poling induced recombination effects are identified. In addition, our analysis based on sample pre-biasing reveals potential indications regarding two types of slow processes, with two different relaxation time scales, which provides further insight regarding ionic migration.
412. Physical properties of Cu and Dy co-doped ZnO thin films prepared by radio frequency magnetron sputtering for hybrid organic/inorganic electronic devices
Authors:
Locovei, C; Coman, D; Radu, A; Ion, L; Antohe, VA; Vasile, N; Dumitru, A; Iftimie, S; Antohe, S
Published: SEP 1 2019, THIN SOLID FILMS, 685, 384, DOI: 10.1016/j.tsf.2019.06.027
Copper (Cu) and dysprosium (Dy) co-doped zinc oxide (ZnO) thin films were fabricated by radio frequency magnetron sputtering (RF-magnetron sputtering) using a homemade target having the atomic percentage of Cu and Dy of 1%, onto optical glass substrates and quartz substrates. The structural, morphological, optical, and electrical properties of fabricated ZnO:(Cu, Dy) structures were analyzed and discussed. It was found that all samples have hexagonal Wurtzite structure. Optical transmission measurements indicate values larger than 75% in the 400-2500 nm ranges. The current-voltage characteristics of hybrid heterojunctions based on ZnO:(Cu, Dy) and poly(3-hexylthiophene-2.5-diyl) (P3HT) or copper (II) phthalocyanine (CuPc) thin films were acquired in the dark, in ambient atmosphere, and they exhibit the typical diode behavior, almost free of electrical hysteresis.
413. Particularities of trichloroethylene photocatalytic degradation over crystalline RbLaTa2O7 nanowire bundles grown by solid-state synthesis route
Authors:
Raciulete, M; Papa, F; Kawamoto, D; Munteanu, C; Culita, DC; Negrila, C; Atkinson, I; Bratan, V; Pandele-Cusu, J; Balint, I
Published: FEB 2019, JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING, 7, DOI: 10.1016/j.jece.2018.11.034
This is the first report on synthesis and photocatalytic activity for trichloroethylene (TCE) degradation under simulated solar light over RbLaTa2O7 layered perovskites with predominant nanowire or platelet morphologies. SEM images witnessed that the one step thermal treatment at 1200 degrees C lead to formation of RbLaTa2O7 nanowires with diameter of 80-320 nm and several microns in length associated in bundles and sharp-edged, merged platelets (minor phase). The two-step annealing at 950 degrees C and 1200 degrees C resulted in decrease of wires bundle population and increase in that of platelets merged in facetted particles. The RbLaTa2O7 nanowires are made of by well-aligned atomic rows with preferred orientation toward the c-axis, relatively free of defect. High density of hydroxyl groups on the sample calcined in mild conditions (RbLaTa_01) favors the photo mineralization of TCE. In contrast, the activity of RbLaTa_02 annealed in harsh conditions (950 and 1200 degrees C), poor in surface hydroxyl groups, remained modest. The weak surface basicity directed the reaction mainly to generation of intermediate chlorinated compounds. Pd and Au were supported on RbLaTa2O7 perovskites as an alternative strategy to boost the removal of chlorinated pollutants by combining photocatalytic (mineralization) and catalytic (hydrodechlorination, HDC) processes. The mineralization of TCE to Cl- was drastically hindered in presence of methanol due to quenching of -OH radicals by alcohol. The results suggested that the density of RbLaTa2O7 surface hydroxyl groups is essential for photo mineralization of TCE whereas the surface carbonate is beneficial for the formation of intermediate chlorinated product.
414. Synthesis and thermal, emission and dielectric properties of liquid crystalline Eu(III), Sm(III) and Tb(III) complexes based on mesogenic 4-pyridone ligands functionalized with cyanobiphenyl groups
Authors:
Chiriac, LF; Ganea, PC; Manaila-Maximean, D; Pasuk, I; Circu, V
Published: SEP 15 2019, JOURNAL OF MOLECULAR LIQUIDS, 290, DOI: 10.1016/j.molliq.2019.111184
New thermotropic lanthanidomesogens based on Eu(III), Sm(III) and Tb(III) with N-alkylated 4-pyridones mesogenic ligands, having two cyanobiphenyl groups attached via long alkoxy spacers, with 6, 9 and 10 carbons atoms in 3,5-positions of a benzyl unit, have been designed and investigated. The liquid crystal behavior was assessed by differential scanning calorimetry, the mesophases being assigned by polarized light microscopy based on their characteristic textures and confirmed by variable temperature X-ray powder diffraction analysis. The three N-alkylated 4-pyridones nematic ligands reacted with lanthanide nitrates to yield new lanthanidomesogens with a stable and reproducible smectic A phase up to 125 degrees C. The emission spectra of the complexes have shown the characteristic emission of the lanthanide trivalent ions, over the entire temperature range of SmA phase up to isotropic state. The dielectric spectroscopy measurements performed in the temperature range of existence of the liquid crystal phase, both in the low frequency (LF) domain 0.01-10 MHz and in the high frequency (HF) range, 1 MHz-3 GHz, revealed three dipolar relaxation processes. The characteristic times have been obtained by fitting the spectra of the dielectric loss with a two component Havriliak-Negami function. The activation constant/energy was determined from the Vogel-Fiilcher-Tammann law. (C) 2019 Elsevier B.V. All rights reserved.
415. Do topology and ferromagnetism cooperate at the EuS/Bi2Se3 interface?
Authors:
Krieger, JA; Ou, Y; Caputo, M; Chikina, A; Dobeli, M; Husanu, MA; Keren, I; Prokscha, T; Suter, A; Chang, CZ; Moodera, JS; Strocov, VN; Salman, Z
Published: FEB 19 2019, PHYSICAL REVIEW B, 99, DOI: 10.1103/PhysRevB.99.064423
We probe the local magnetic properties of interfaces between the insulating ferromagnet EuS and the topological insulator Bi2Se3 using low energy muon spin rotation (LE-mu SR). We compare these to the interface between EuS and the topologically trivial metal, titanium. Below the magnetic transition of EuS, we detect strong local magnetic fields which extend several nm into the adjacent layer and cause a complete depolarization of the muons. However, in both Bi(2)Se(3 )and titanium we measure similar local magnetic fields, implying that their origin is mostly independent of the topological properties of the interface electronic states. In addition, we use resonant soft x-ray angle resolved photoemission spectroscopy (SX-ARPES) to probe the electronic band structure at the interface between EuS and Bi2Se3. By tuning the photon energy to the Eu antiresonance at the Eu M-5 pre-edge we are able to detect the Bi2Se3 conduction band, through a protective Al2O3 capping layer and the EuS layer. Moreover, we observe a signature of an interface-induced modification of the buried Bi2Se3 wave functions and/or the presence of interface states.
416. Superconducting MgB2 textured bulk obtained by ex situ spark plasma sintering from green compacts processed by slip casting under a 12T magnetic field
Authors:
Grigoroscuta, MA; Sandu, V; Kuncser, A; Pasuk, I; Aldica, G; Suzuki, TS; Vasylkiv, O; Badica, P
Published: DEC 2019, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 32, DOI: 10.1088/1361-6668/ab4620
MgB2 green bodies were prepared by magnetic field slip casting in ethyl alcohol with added polyethyleneimine dispersing agent under a high magnetic field, mu H-0(0) = 12 T. Samples were further processed by spark plasma sintering (SPS) and characterized for superconducting properties. Slip casting provides texturing of MgB2 (the degree of c-axis orientation is approximately 3.5%), which is further increased significantly (to about 21%) in the SPSed sample. The critical current density (J(c)) displays anisotropy relative to the orientation of the measuring magnetic field. Specific features of J(c)(H, T) and of the pinning force extracted from magnetic measurements with the field parallel and perpendicular to H-0 are discussed.
417. Multiferroic (Nd,Fe)-doped PbTiO3 ceramics with coexistent ferroelectricity and magnetism at room temperature
Authors:
Craciun, F; Cordero, F; Cernea, M; Fruth, V; Atkinson, I; Stanica, N; Vasile, BS; Trusca, R; Iuga, A; Galizia, P; Galassi, C
Published: MAY 2019, CERAMICS INTERNATIONAL, 45, 9396, DOI: 10.1016/j.ceramint.2018.08.147
We report the structural, dielectric, elastic, ferroelectric and ferromagnetic properties of multiferroic (Nd, Fe)doped PbTiO3 perovskite ceramics with composition (Pb-0.88 Nd-0.08 )(Ti-0.94 Fe-0 .04 Mn-0.02)O-3, prepared by different solid state reaction methods: the first one based on a single-stage calcination (Method I) and the second based on a double-stage calcination (Method II). Structural, dielectric and anelastic measurements evidenced a double phase transition for samples prepared by Method I, which has been attributed to phase separation. This phase separation has been confirmed also by TEM and HRTEM investigations. Samples prepared by Method II showed a single phase transition from paraelectric to ferroelectric phase. We found coexistent ferroelectric and ferromagnetic properties, also at room-temperature, but only for ceramics prepared by Method II. The crucial role of calcination process for avoiding phase separation and obtaining homogeneous structures with ferroelectric and ferromagnetic order is underlined.
418. Composite BNT-BT0.08/CoFe2O4 with core-shell nanostructure for piezoelectric and ferromagnetic applications
Authors:
Cernea, M; Vasile, BS; Ciuchi, IV; Surdu, VA; Bartha, C; Iuga, A; Galizia, P; Galassi, C
Published: JAN 2019, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 240, 15, DOI: 10.1016/j.mseb.2019.01.001
In this work, we report on the synthesis and characterization of BNT-BT0.08/CoFe2O4 biphasic composite with core-shell structure. This artificial core (BNT-BT0.08/shell (CoFe2O4) heterostructure was prepared by sol-gel method and the resulting composite was characterized in term of microstructure, dielectric, piezoelectric and magnetic properties. BNT-BT0.08/CoFe2O4 sintered ceramic shows high permittivity (epsilon' >= 30) and high dielectric losses (tan delta >= 10) in the low frequency range (nu <= 10(4) Hz), remnant polarization (Pr) of similar to 7.7 mu C/cm(2) and, remanent magnetization (Mr) of 24 emu/g at 5 K and of 14 emu/g, at room temperature. The present study reveals that the ferroelectric, piezoelectric and magnetic properties of this new architectured composite depend on the amount of each component and, can be tailored by adjusting their synthesis conditions. BNT-BT0.08/CoFe2O4 core-shell material investigated in this work provides a novel way to exploit new applications for the multifunctional composite, such as piezoelectric sensor, magnetoelectronic sensors and data storage devices.
419. Sub-lattice polarization states in anti-ferroelectrics and their relaxation process
Authors:
Vopson, MM; Tan, X; Namvar, E; Belusky, M; Thompson, SP; Kuncser, V; Plazaola, F; Unzueta, I; Tang, CC
Published: MAY 2019, CURRENT APPLIED PHYSICS, 19, 656, DOI: 10.1016/j.cap.2019.03.009
We report studies of quasi-remanent polarization states in Pb0.99Nb0.02[(Zr0.57Sn0.43)(0.94)Ti-0.06](0.98)O-3 (PNZST) anti-ferroelectric ceramics and investigation of their relaxation effects using unique in-situ electrically activated time-resolved Synchrotron X-ray powder diffraction (SXPD) and Sn-119 Mossbauer Spectroscopy (MS). The SXPD patterns are consistent with a phase transition from quasi-tetragonal perovskite in 0 V relaxed anti-ferroelectric state to rhombohedral distortion in ferroelectric state under saturating applied voltages of +/- 2 kV. The observed quasi-remanent polarization relaxation processes are due to the fact that tetragonal to rhombohedral distortion does not occur at the applied voltage required to access the quasiremanent polarization states, and the tetragonal symmetry restored after the removal of the applied electric field is preserved. Since these quasi-remanent polarization states were seen as possibly suitable for memory applications, the implications of this study are that anti-ferroelectrics are more feasible for multi-state dynamic random access memories (DRAM), while their application to non-volatile memories requires development of more sophisticated "read-out" protocols, possibly involving dc electrical biasing.
420. On the relaxation time of interacting superparamagnetic nanoparticles and implications for magnetic fluid hyperthermia
Authors:
Kuncser, A; Iacob, N; Kuncser, VE
Published: JUN 24 2019, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 10, 1289, DOI: 10.3762/bjnano.10.127
A critical discussion on the presently available models for the relaxation time of magnetic nanoparticles approaching the superparamagnetic regime in the presence of interparticle dipolar interactions is considered. The direct implications of such interactions for magnetic fluid hyperthermia therapy through susceptibility loss mechanisms give rise to an indirect method for their study via specific absorption rate measurements performed on ferrofluids of different volume fractions. The theoretical support for the specific evolution of the relaxation time constant and the anisotropy energy barrier versus the interparticle interactions in a perturbation approach of the simple Neel expression for the relaxation time is provided via static and time-dependent micromagnetic simulations.
421. Nanostructured palladium doped nickel electrodes for immobilization of oxidases through nickel nanoparticles
Authors:
Barsan, MM; Matei, E; Enculescu, M; Costescu, R; Preda, N; Enache, TA; Enculescu, I; Diculescu, VC
Published: AUG 20 2019, ELECTROCHIMICA ACTA, 315, 113, DOI: 10.1016/j.electacta.2019.04.143
The present investigation deals with the development, characterization and application of nano-structured Pd doped Ni electrodes (Pd@Ni), which uses the electrochemical properties of Pd in synergy with the magnetic properties of Ni for biosensors development. The Pd@Ni electrodes have been characterized by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. It has been shown that palladium presented spherical assemblies ranging 150-200 nm medium diameter size that covers large areas of the electrode surface while metallic nickel, which confers magnetic properties, showed a uniform granular structure with sizes between 20 and 50 nm. Cyclic voltammetry and electrochemical impedance spectroscopy were performed to understand the electrochemical process at the Pd@Ni electrodes in neutral media. The Pd@Ni electrodes were applied for the electrochemical detection of H2O2. Finally, Ni nanoparticles (NiNP) functionalized with the model enzyme glucose oxidase (GOx-NiNP) have been attached to the Pd@Ni electrode solely through magnetic interactions, and the obtained GOx-NiNP/Pd@Ni biosensor applied for glucose determination in aqueous solutions by fixed potential amperometry at -0.05 V (vs Ag/AgCl) with reduced interferences. (C) 2019 Elsevier Ltd. All rights reserved.
422. Backaction effects in cavity-coupled quantum conductors
Authors:
Moldoveanu, V; Dinu, IV; Manolescu, A; Gudmundsson, V
Published: SEP 12 2019, PHYSICAL REVIEW B, 100, DOI: 10.1103/PhysRevB.100.125416
We study the electronic transport through a pair of distant nanosystems (S-a and S-b) embedded in a single-mode cavity. Each system is connected to source and drain particle reservoirs and the electron-photon coupling is described by the Tavis-Cummings model. The generalized master equation approach provides the reduced density operator of the double system in the dressed-states basis. It is shown that the photon-mediated coupling between the two subsystems leaves a signature on their transient and steady-state currents. In particular, a suitable bias applied on subsystem S-b induces a photon-assisted current in the other subsystem S-a which is otherwise in the Coulomb blockade. We also predict that a transient current passing through one subsystem triggers a charge transfer between the optically active levels of the second subsystem even if the latter is not connected to the leads. As a result of backaction, the transient current through the open system develops Rabi oscillations (ROs) whose period depends on the initial state of the closed system.
423. Orthorhombic HfO2 with embedded Ge nanoparticles in nonvolatile memories used for the detection of ionizing radiation
Authors:
Palade, C; Slav, A; Lepadatu, AM; Stavarache, I; Dascalescu, I; Maraloiu, AV; Negrila, C; Logofatu, C; Stoica, T; Teodorescu, VS; Ciurea, ML; Lazanu, S
Published: NOV 1 2019, NANOTECHNOLOGY, 30, DOI: 10.1088/1361-6528/ab352b
Trilayer memory capacitors of control HfO2/floating gate of Ge nanoparticles in HfO2/tunnel HfO2/Si substrate deposited by magnetron sputtering and subsequently annealed are investigated for the first time for applications in radiation dosimetry. In the floating gate (FG), amorphous Ge nanoparticles (NPs) are arranged in two rows inside the HfO2 matrix. The HfO2 matrix is formed of orthorhombic/tetragonal nanocrystals (NCs). The adjacent thin films to the FG are also formed of orthorhombic/tetragonal HfO2 NCs. This phase is formed during annealing, in samples with thick control HfO2, in the presence of Ge, being induced by the stress. In the rest of the control oxide, HfO2 NCs are monoclinic. Orthorhombic HfO2 has ferroelectric properties and therefore enhances the memory window produced by charge storage in Ge NPs to above 6 V. The high sensitivity of 0.8 mV Gy(-1) to a particle irradiation from a Am-241 source was measured by monitoring the flatband potential during radiation exposure after electrical writing of the memory.
424. Negative ion-induced deuterium retention in mixed W-Al layers co-deposited in dual-HiPIMS
Authors:
Dinca, P; Tiron, V; Velicu, IL; Porosnicu, C; Butoi, B; Velea, A; Grigore, E; Costin, C; Lungu, CP
Published: APR 15 2019, SURFACE & COATINGS TECHNOLOGY, 363, 281, DOI: 10.1016/j.surfcoat.2019.02.019
Co-sputtering of tungsten-aluminum fusion relevant materials in a dual-High Power Impulse Magnetron Sputtering discharge, operated in different Ar-D-2 gas mixtures, was investigated in gas phase by means of energy-resolving mass spectrometry. Experimental results indicate that the total ion flux and its composition are strongly dependent on sputtering gas composition and the average power applied to the targets. During single HiPIMS operation with W target, the D- ions are the most abundant species. The measured D- ion flux shows an increase with the rising of D-2 content in Ar-D-2 gas mixture and a linear increase with the power applied to the W target. In contrast, during dual-HiPIMS operation, a decrease of D- ion flux was observed when the input power applied to the Al target was increased. The origin of different deuterium ion species and retention mechanisms are discussed. The surface morphology, microstructure and chemical composition of the W-Al coatings obtained in Ar-D-2, were investigated by means of, Atomic Force Microscopy, X-ray diffraction and Glow Discharge Optical Emission Spectroscopy. GDOES depth profiles show the presence of a large amount of deuterium (up to 21 at.%) in the mixed W-Al layers and indicate that the D retention in the mixed W-Al layers is mainly related to the W in-depth concentration and less dependent on the Al one. The intense and energetic bombardment of the growing film with D- ions seems to be responsible for the large amount of D retained in the W-Al layers.
425. 3D hybrid structures based on biomimetic membranes and Caryophyllus aromaticus - "green" synthesized nano-silver with improved bioperformances
Authors:
Barbinta-Patrascu, ME; Badea, N; Bacalum, M; Ungureanu, C; Suica-Bunghez, IR; Lordache, SM; Pirvu, C; Zgura, I; Maraloiu, VA
Published: AUG 2019, MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS, 101, 137, DOI: 10.1016/j.msec.2019.03.069
The paper describes an innovative bio-design of some hybrid nanoarchitectures containing bioartificial membranes and silver nanoparticles phytogenerated by using a natural extract Caryophyllus aromaticus (cloves) that contains many bioactive compounds. Two kinds of liposomes with and without chlorophyll a (Chla) obtained through thin film hydration method were used to achieve bio-green-generated hybrids by a simple, cost effective bottom-up approach. The characteristic peaks of CE-nAg monitored by UV-Vis absorption have firstly demonstrated the biohybrids formation. The slightly blue shift and fluorescence quenching observed by fluorescence emission spectra highlighted the formation of hybrid systems by biointeraction between lipid vesicles and silver nanoparticles. The incorporation of silver nanoparticles in lipid vesicles resulted in significant changes of FT-IR spectra of liposomes, indicating a reorganization of biomimetic membranes. All the microscopic methods (SEM, AFM and TEM) confirmed the biosynthesis of "green" AgNPs together with associated biohybrids, their spherical and quasi-spherical shapes with nano-scaled size. By TEM assay it was shown that CE-nAg are surrounded by petal like cloud structures that consist of biopolymers like proteins or polysaccharides and other phytochemicals arising from clove extract. EDS spectra confirmed the formation of phyto-nanoAg and also the presence of silver in the biohybrids. In addition, Selected Area Electron Diffraction showed characteristic polycrystalline ring patterns for a cubic structure of the clove-generated AgNPs. The hybrid materials showed efficient physical stability, ie. xi value of - 28.0 mV (for biohybrids without Chla, BH) and of - 31.7 mV (for biohybrids labelled with Chla, Chla-BH), assured by strong electrostatic repulsive forces between particles. The "green" nano-silver particles (CE-nAg) showed remarkable antioxidant activity (AA = 90.2%). The biohybrids loaded with clove-AgNPs proved to be more effective, scavenging about 98.8% of free radicals (in case of ChlaBH), and of 92.6% (in case of BH). The antibacterial effectiveness showed that green AgNPs combine in a synergistic manner the antibacterial properties of clove extract with those of silver, resulting in an enhancement of inhibition diameter, by 20%. Chla-BH proved to be more potent against Escherichia coli, than BH, exhibiting an inhibition diameter of 42 mm. Regarding the in vitro cytotoxicity against tumour cells, the CE-nAg concentration significantly influenced the cell viability, ie. IC50 was 3.6% (v/v) for HT-29 cells. Chla-BH was more effective against HT-29 cancer cells at the concentrations ranging from 0 to 18% (v/v), when the normal cells were not affected. Clove-generated AgNPs exhibited haemolytic activity against hRBCs, while the biohybrids were haemocompatible. The action mechanism on the two cell lines (mouse fibroblast L929 cells and human colorectal adenocarcinoma HT-29 cells) investigated by fluorescence microscopy demonstrated that CE-nAg killed almost all the cells (94%) through necrosis at a concentration of 33.4% (v/v). The treatment of HT-29 cells with BH resulted in: 71.5% viable cells, 19.5% apoptotic and only 9% necrotic cells, while in the case of Chla-BH treatment, only 77.5% cells were viable, 16% cells were apoptotic and 6.5% were necrotic. In this way, the developed silver-based nanoparticles can represent viable promoters to develop new biohybrids with improved features, e.g. antioxidant and antibacterial effectiveness, haemolytic activity and greater specificity towards tumour cells.
426. Enhanced photoconductivity of SiGe nanocrystals in SiO2 driven by mild annealing
Authors:
Sultan, MT; Manolescu, A; Gudmundsson, JT; Torfason, K; Nemnes, GA; Stavarache, I; Logofatu, C; Teodorescu, VS; Ciurea, ML; Svavarsson, HG
Published: MAR 1 2019, APPLIED SURFACE SCIENCE, 469, 878, DOI: 10.1016/j.apsusc.2018.11.061
Photosensitive films based on finely dispersed semiconductor nanocrystals (NCs) in dielectric films have great potential for sensor applications. Here we report on preparation and characterization of photosensitive Si1-xGex NCs sandwiched between SiO2 matrix. A radio-frequency magnetron sputtering was applied to obtain a multilayer-structures (MLs) by depositing SiO2/SiGe/SiO2 films on Si (0 0 1) substrate. The Si1-xGex NCs were formed by a post-deposition annealing at 100-700 degrees C for 1-5 min. The effect of annealing temperature and time on MLs morphology and NCs size and density was studied using grazing incidence X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and measurements of spectral distribution of photocurrent. It is demonstrated how the photoconductive properties of the MLs can be enhanced and tailored by controlling the NCs formation conditions and the presence of stress field in MLs and defects acting as traps and recombination centers. All these features can be adjusted/controlled by altering the annealing conditions (temperature and time). The MLs photosensitivity was increased of more than an order of magnitude by the annealing process. A mechanism, where a competition between crystallization process (NCs formation and evolution i.e. size and shapes) and stress field appearance determines the peak position in the photocurrent spectra, was identified.
427. Synthesis and characterization of biocompatible polymer-ceramic film structures as favorable interface in guided bone regeneration
Authors:
Dascalu, CA; Maidaniuc, A; Pandele, AM; Voicu, SI; Machedon-Pisu, T; Stan, GE; Cimpean, A; Mitran, V; Antoniac, IV; Miculescu, F
Published: NOV 15 2019, APPLIED SURFACE SCIENCE, 494, 352, DOI: 10.1016/j.apsusc.2019.07.098
The bone regeneration field targeted lately the development of new products based on precursors of natural origin. This study aimed to obtain the optimal design of polymer-ceramic composites for guided bone regeneration application from cellulose acetate (CA) and hydroxyapatite (HA) by varying three relevant parameters: the amount of HA powder added to the CA matrix (in the 20-40 wt% range), the HA particles size (max. 20 mu m vs. max. 40 mu m) and the homogenization time required for HA powder dispersion in the CA matrix (1 min vs. 4 min). For polymer-ceramic film structures preparation, the phase inversion by immersion in water method was used. This involved the deposition of composite solution (i.e. CA with 20-40 wt% HA) on a glass support, followed by sizing it at a thickness of 0.2 mm. The obtained film structures were investigated in terms of morphocompositional and structural properties. The surface features evaluation was achieved by surface wettability, roughness, water permeation, protein retention and in vitro evaluation of MC3T3-E1 morphology and viability. Further, ceramic particle distribution throughout samples volume was provided by computed tomography methods. These investigations targeted the validation of the prepared composite film structures as viable solutions for guided bone regeneration.
428. Interaction and Size Effects in Open Nano-Electromechanical Systems
Authors:
Tanatar, B; Moldoveanu, V; Dragomir, R; Stanciu, S
Published: JUN 2019, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 256, DOI: 10.1002/pssb.201800443
The time-dependent transport of a 2D quantum wire (QW) connected to source/drain leads and electrostatically coupled to a singly-clamped InAs cantilever is investigated. The latter is placed above the nanowire and acts as a nanoresonator (NR) in the quantum regime. The vibron dynamics and the transport properties of this nano-electromechanical system (NEMS) are described within a generalized master equation approach which is exact with respect to the electron-vibron coupling. A detailed description of the electron-vibron coupling by taking into account its dependence on the wavefunctions of the quantum nanowire is introduced. It is shown that the tunneling processes in the QW trigger periodic oscillations of the average vibron number even in the absence of a bias. The time-dependent filling of the vibronic states changes as the nanoresonator is swept along the quantum wire.
429. Structure and magnetic behavior of unpredictable EE-azide bridged tetranuclear Mn(II) complex with ONO-donor hydrazone ligand and its transformation to dinuclear Mn(III) complex
Authors:
Bikas, R; Kuncser, V; Sanchiz, J; Schinteie, G; Siczek, M; Hosseini-Monfared, H; Lis, T
Published: JUN 1 2018, POLYHEDRON, 147, 151, DOI: 10.1016/j.poly.2018.03.019
The reaction of manganese(II) chloride tetrahydrate with sodium azide and ONO-donor hydrazone ligand, (H2L = (E)-3-hydroxy-N'-((2)-4-hydroxy-4-phenylbut-3-en-2-ylidene)-2-naphthohydrazide), in methanol gives rise to the formation of red crystals which are stable out of the solvent. The red crystals slowly transform to brown crystals in the methanolic solution. In the last case, the rate of the transformation from red to brown crystals mainly depends on the presence of molecular oxygen and reaction temperature. Both compounds are characterized by elemental analysis, spectroscopic methods and single crystal X-ray diffraction studies. The X-ray analysis indicates that the red crystals consist of a tetranuclear Mn(II) complex molecules, [Mn-4(H0.5L)(4) (mu(1.3)-N-3)(2)(CH3OH)(4)] (1), while the brown crystals consist of dinucelar Mn(III), [Mn2L2(mu(1.1)-OCH3)(1.5)(mu(1.1)-N-3)(0.5)] (2) molecules. In complex 1 with molecules of D2 (222) point symmetry, four Mn(II) ions are connected together by four ONO-donor hydrazone ligands and two end-to-end (EE) bridging azide anions. In complex 2 two Mn(III) ions are connected together by azide or methoxy bridging groups. Magnetic susceptibility measurements on complex 1 reveal the occurrence of antiferromagnetic couplings through azide ligands and enolate oxygen atom of the ligand in which the magnetic coupling constants have been determined. (C) 2018 Elsevier Ltd. All rights reserved.
430. Vortex dynamics driven by AC magnetic field in YBCO thin films with complex pinning structures
Authors:
Ivan, I; Ionescu, AM; Sandu, V; Crisan, A; Miu, L
Published: OCT 2018, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 31, DOI: 10.1088/1361-6668/aadbfd
We investigated the AC magnetic response of a YBa2Cu3O7 film with embedded BaZrO3 nanorods and Y2O3 nanoparticles at a static magnetic field H-dc lower than the matching field H-Phi. We proposed a practical formula for the determination of the induced current J during AC susceptibility measurements, which allows us to directly obtain the pinning potential U-c from the characteristics of electric field E versus J. We show that the dynamic critical current J(d) induced at the depinning frequency f(d) can be experimentally obtained by measuring m'(T) and m ''(T) at different frequencies and amplitudes. It was found that the value of f(d) obtained by extrapolation of J to J(d) in the PHz domain is much higher than the frequency reported for ordinary YBa2Cu3O7 thin films as determined by microwave impedance measurements. AC susceptibility, vortex dynamics, pinning energy, depinning frequency, dynamic critical current, microwave impedance measurements
431. k-space imaging of anisotropic 2D electron gas in GaN/GaAlN high-electron-mobility transistor heterostructures
Authors:
Lev, LL; Maiboroda, IO; Husanu, MA; Grichuk, ES; Chumakov, NK; Ezubchenko, IS; Chernykh, IA; Wang, X; Tobler, B; Schmitt, T; Zanaveskin, ML; Valeyev, VG; Strocov, VN
Published: JUL 11 2018, NATURE COMMUNICATIONS, 9, DOI: 10.1038/s41467-018-04354-x
Nanostructures based on buried interfaces and heterostructures are at the heart of modern semiconductor electronics as well as future devices utilizing spintronics, multiferroics, topological effects, and other novel operational principles. Knowledge of electronic structure of these systems resolved in electron momentum k delivers unprecedented insights into their physics. Here we explore 2D electron gas formed in GaN/AlGaN high-electron-mobility transistor heterostructures with an ultrathin barrier layer, key elements in current high-frequency and high-power electronics. Its electronic structure is accessed with angle-resolved photoelectron spectroscopy whose probing depth is pushed to a few nanometers using soft-X-ray synchrotron radiation. The experiment yields direct k-space images of the electronic structure fundamentals of this system-the Fermi surface, band dispersions and occupancy, and the Fourier composition of wavefunctions encoded in the k-dependent photoemission intensity. We discover significant planar anisotropy of the electron Fermi surface and effective mass connected with relaxation of the interfacial atomic positions, which translates into nonlinear (high-field) transport properties of the GaN/AlGaN heterostructures as an anisotropy of the saturation drift velocity of the 2D electrons.
432. One-Pot Enzymatic Production of Lignin-Composites
Authors:
Ion, S; Opris, C; Cojocaru, B; Tudorache, M; Zgura, I; Galca, AC; Bodescu, AM; Enache, M; Maria, GM; Parvulescu, VI
Published: APR 20 2018, FRONTIERS IN CHEMISTRY, 6, DOI: 10.3389/fchem.2018.00124
A novel and efficient one-pot system for green production of artificial lignin bio-composites has been developed. Monolignols such as sinapyl (SA) and coniferyl (CA) alcohols were linked together with caffeic acid (CafAc) affording a polymeric network similar with natural lignin. The interaction of the dissolved SA/CA with CafAc already bound on a solid support (S-C2/S-C6 CafAc) allowed the attachment of the polymeric product direct on the support surface (S-C2/S-C6-CafAc-L-1 and S-C2/S-C6-CafAc-L-2, from CA and SA, respectively). Accordingly, this procedure offers the advantage of a simultaneous polymer production and deposition. Chemically, oxi-copolymerization of phenolic derivatives (SA/CA and CAfAc) was performed with H2O2 as oxidation reagent using peroxidase enzyme (2-1B mutant of versatile peroxidase from Pleurotus eryngii) as catalyst. The system performance reached a maximum of conversion for SA and CA of 71.1 and 49.8%, respectively. The conversion is affected by the system polarity as resulted from the addition of a co-solvent (e.g., MeOH, EtOH, or THF). The chemical structure, morphology, and properties of the bio-composites surface were investigated using different techniques, e.g., FTIR, TPD-NH3, TGA, contact angle, and SEM. Thus, it was demonstrated that the SA monolignol favored bio-composites with a dense polymeric surface, high acidity, and low hydrophobicity, while CA allowed the production of thinner polymeric layers with high hydrophobicity.
433. Zinc incorporation in marine bivalve shells grown in mine-polluted seabed sediments: a case study in the Malfidano mining area (SW Sardinia, Italy)
Authors:
Medas, D; Carlomagno, I; Meneghini, C; Aquilanti, G; Araki, T; Bedolla, DE; Buosi, C; Casu, MA; Gianoncelli, A; Kuncser, AC; Maraloiu, VA; De Giudici, G
Published: DEC 2018, ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH, 25, 36660, DOI: 10.1007/s11356-018-3504-y
Zinc incorporation into marine bivalve shells belonging to different genera (Donax, Glycymeris, Lentidium, and Chamelea) grown in mine-polluted seabed sediments (Zn up to 1% w/w) was investigated using x-ray diffraction (XRD), chemical analysis, soft x-ray microscopy combined with low-energy x-ray fluorescence (XRF) mapping, x-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). These bivalves grew their shells, producing aragonite as the main biomineral and they were able to incorporate up to 2.0-80mg/kg of Zn, 5.4-60mg/kg of Fe and 0.5-4.5mg/kg of Mn. X-ray absorption near edge structure (XANES) analysis revealed that for all the investigated genera, Zn occurred as independent Zn mineral phases, i.e., it was not incorporated or adsorbed into the aragonitic lattice. Overall, our results indicated that Zn coordination environment depends on the amount of incorporated Zn. Zn phosphate was the most abundant species in Donax and Lentidium genera, whereas, Chamelea shells, characterized by the highest Zn concentrations, showed the prevalence of Zn-cysteine species (up to 56% of total speciation). Other Zn coordination species found in the investigated samples were Zn hydrate carbonate (hydrozincite) and Zn phosphate. On the basis of the coordination environments, it was deduced that bivalves have developed different biogeochemical mechanisms to regulate Zn content and its chemical speciation and that cysteine plays an important role as an active part of detoxification mechanism. This work represents a step forward for understanding bivalve biomineralization and its significance for environmental monitoring and paleoreconstruction.
434. Large positive linear magnetoresistance in the two-dimensional t(2g) electron gas at the EuO/SrTiO3 interface
Authors:
Kormondy, KJ; Gao, LY; Li, X; Lu, SR; Posadas, AB; Shen, SD; Tsoi, M; McCartney, MR; Smith, DJ; Zhou, JS; Lev, LL; Husanu, MA; Strocov, VN; Demkov, AA
Published: MAY 16 2018, SCIENTIFIC REPORTS, 8, DOI: 10.1038/s41598-018-26017-z
The development of novel nano-oxide spintronic devices would benefit greatly from interfacing with emergent phenomena at oxide interfaces. In this paper, we integrate highly spin-split ferromagnetic semiconductor EuO onto perovskite SrTiO3 (001). A careful deposition of Eu metal by molecular beam epitaxy results in EuO growth via oxygen out-diffusion from SrTiO3. This in turn leaves behind a highly conductive interfacial layer through generation of oxygen vacancies. Below the Curie temperature of 70 K of EuO, this spin-polarized two- dimensional t(2g) electron gas at the EuO/SrTiO3 interface displays very large positive linear magnetoresistance (MR). Soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) reveals the t(2g) nature of the carriers. First principles calculations strongly suggest that Zeeman splitting, caused by proximity magnetism and oxygen vacancies in SrTiO3, is responsible for the MR. This system offers an as-yet-unexplored route to pursue proximity-induced effects in the oxide two- dimensional t(2g) electron gas.
435. New bio-active, antimicrobial and adherent coatings of nanostructured carbon double-reinforced with silver and silicon by Matrix-Assisted Pulsed Laser Evaporation for medical applications
Authors:
Duta, L; Ristoscu, C; Stan, GE; Husanu, MA; Besleaga, C; Chifiriuc, MC; Lazar, V; Bleotu, C; Miculescu, F; Mihailescu, N; Axente, E; Badiceanu, M; Bociaga, D; Mihailescu, IN
Published: MAY 31 2018, APPLIED SURFACE SCIENCE, 441, 883, DOI: 10.1016/j.apsusc.2018.02.047
We report on Matrix-Assisted Pulsed Laser Evaporation (MAPLE) deposition of Carbon thin films, simple or reinforced with intended concentrations of Ag and Si. A KrF* (lambda = 248 nm, tau(FWHM) < 25 ns, v = 10 Hz) excimer laser was used for irradiation. The effect of a post-deposition thermal treatment in vacuum was studied. Besides detailed morphological, compositional, structural and pull-out adherence characterizations, the potential of the carbonaceous films for medical applications was investigated in vitro by anti-biofilm and cytocompatibility assays. The microscopic images evidenced no delaminations. Micro-Raman spectroscopy revealed a graphitization tendency depending on preparation conditions, thermal treatment and reinforcing agents' presence. Adherence values improved considerably after thermal treatment. In vitro biological evaluation showed that the films containing similar to 1.85 at.% Ag were non-cytotoxic for MG63 cells, while eliciting a limited antimicrobial activity. The increase of Ag content to 3.6 at.% results in a significant enhancement of antimicrobial activity, whilst maintaining the cytotoxic action and adherence characteristics at acceptable levels. We propose a new class of metamaterials based on C reinforced with Ag and Si obtained by MAPLE for medical applications, i.e. the prevention and treatment of various infections associated with biofilms developed on implants and other medical equipments. (C) 2018 Elsevier B.V. All rights reserved.
436. Theoretical investigation of the structural, optical and magnetic properties of Mn doped and (Mn, Cr) co-doped CdS in its cubic structure
Authors:
Aimouch, DE; Meskine, S; Birsan, A; Kuncser, V; Zaoui, A; Boukortt, A
Published: JUL 1 2018, MATERIALS CHEMISTRY AND PHYSICS, 213, 258, DOI: 10.1016/j.matchemphys.2018.03.089
The electronic, magnetic and optical properties of doped CdS:Mn and co-doped CdS:Mn, Cr cubic structures were studied via Density Functional Theory and subsequently compared with the properties of undoped CdS. The doped compound presents semiconducting character similar to the undoped CdS, while the co-doped compound exhibits half metallic properties with a high spin polarization at the Fermi energy. The magnetic moments as well as the trend of magnetic exchange parameters of CdS:Mn and CdS:Mn,Cr, have been analyzed, in addition to the dielectric functions, by starting from calculated density of states for spin polarized configurations. The calculated absorption coefficients lead to direct information on the spectral energy distribution in the range of optoelectronic applications. The optical band gaps of doped and co-doped compounds are higher as compared to the undoped CdS, making the first compounds more interesting for possible technological applications for high density magneto-optical recording. (C) 2018 Elsevier B.V. All rights reserved.
437. Voltammetric and atomic force microscopy characterization of chymotrypsin, trypsin and caspase activities of proteasome
Authors:
de Jesus, CSH; Paquim, AMC; Diculescu, VC
Published: MAY 15 2018, CATALYSIS TODAY, 306, 293, DOI: 10.1016/j.cattod.2017.01.012
Proteasome is a multicatalytic enzyme complex responsible for proteolysis of damaged proteins and an important target for drug discovery in the pharmaceutical industry. Development of fast and economic strategies for detection of proteasome activity and inhibition is a topic of intensive research. The activity of the 20S proteasome was investigated by voltammetry and atomic force microscopy. The hydrolysis of peptide bonds was studied in incubated solutions of proteasome with oligopeptide sequences specific to each chymotrypsin, trypsin and caspase activity of proteasome, before and after inhibition with epoxomicin. The time-dependence of the proteolysis and the effect of substrate and inhibitor concentrations on the rate of enzymatic reaction were investigated. Different interaction mechanisms were characterized and enzyme kinetic parameters determined. The adsorption patterns of reaction mixture components were characterized by atomic force microscopy in order to understand the processes when saturation of enzyme catalytic centres occurs for high substrate concentrations. (C) 2017 Elsevier B.V. All rights reserved.
438. Spherical cobalt/cobalt oxide - Carbon composite anodes for enhanced lithium-ion storage
Authors:
Patrinoiu, G; Etacheri, V; Somacescu, S; Teodorescu, VS; Birjega, R; Culita, DC; Hong, CN; Calderon-Moreno, JM; Pol, VG; Carp, O
Published: FEB 20 2018, ELECTROCHIMICA ACTA, 264, 202, DOI: 10.1016/j.electacta.2018.01.098
Herein we report a simple and scalable route to synthesize porous cobalt/cobalt oxide - carbon sphere composites as anode material for rechargeable lithium-ion batteries. It involves the impregnation of starch-derived hydrochar spheres with a cobalt salt, followed by a heat treatment (700 degrees C) under inert atmosphere. The obtained high surface area (similar to 670 m(2) g(-1)), submicron spheres (similar to 300 nm diameter) with high-degree of microporosity (81%) consist of an amorphous carbon matrix with embedded Co/CoO nanoparticles (similar to 6 nm sized), having a total cobalt content of 6.2 wt%. The hybrid sphere anodes demonstrated superior specific capacity, rate performance and cycling stability. Discharge capacities of 520 and 310 mA h g(-1) are observed at charge-discharge rates of 0.1 and 1C respectively. No significant capacity fading is identified on prolonged cycling at various current densities. The electrode also demonstrated excellent structural stability during extended charge-discharge processes. (c) 2018 Elsevier Ltd. All rights reserved.
439. Effect of green body annealing on laser performance of YAG:Nd3+ ceramics
Authors:
Yavetskiy, RP; Parkhomenko, SV; Vorona, IO; Tolmachev, AV; Kosyanov, DY; Kuryavyi, VG; Mayorov, VY; Gheorghe, L; Croitoru, G; Enculescu, M
Published: MAR 2018, CERAMICS INTERNATIONAL, 44, 4490, DOI: 10.1016/j.ceramint.2017.11.192
Annealing temperature of green bodies has been shown to influence greatly the optical properties and laser characteristics of Y3Al5O12:Nd3+ (1 at%) ceramics. Increase the annealing temperature above some critical one (800 degrees C) results in appearance of submicron pores due to Y4Al2O9 phase formation accompanied by specific volume expansion. The energy changes associated with the chemical reaction can lead to the development of microstructures that possess lower sinterability. As a result, Y3Al5O12:Nd3+ ceramics prepared from unannealed green bodies and those annealed at 600 and 800 degrees C possess higher optical transmittance and enhanced slope efficiency (63-67%) compared with that obtained using green bodies annealed at 1000 degrees C (41%). Further investigations are necessary in order to explain this behavior.
440. Combined use of Mossbauer spectroscopy, XPS, HRTEM, dielectric and anelastic spectroscopy for estimating incipient phase separation in lead titanate-based multiferroics
Authors:
Craciun, F; Cordero, F; Vasile, BS; Fruth, V; Zaharescu, M; Atkinson, I; Trusca, R; Diamandescu, L; Tanase, LC; Galizia, P; Cernea, M; Galassi, C
Published: JUN 7 2018, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 20, 14663, DOI: 10.1039/c8cp01456f
The formation of separate phases in crystalline materials is promoted by doping with elements with different valences and ionic radii. Control of the formation of separate phases in multiferroics is extremely important for their magnetic, ferroelectric and elastic properties, which are relevant for multifunctional applications. The ordering of dopants and incipient phase separation were studied in lead titanate-based multiferroics with the formula (Pb0.88Nd0.08)(Ti0.98-xFexMn0.02)O-3 (x = 0.00, 0.03, 0.04, 0.05) by means of a combination of Mossbauer spectroscopy, XPS, HRTEM, dielectric and anelastic spectroscopy. We found that Fe ions are substituted as Fe3+ at Ti sites and preferentially exhibit pentahedral coordination, whereas Ti ions have coexisting valences of Ti4+/Ti3+. Fe3+ ions are preferentially ordered in clusters, and there exists a transition temperature T-C1, below which phase separation occurs between a tetragonal phase T1 free of magnetic clusters and a cubic phase, and a lower transition temperature T-C2, below which the cubic phase rich in magnetic clusters is transformed into a tetragonal phase T2. The phase separation persists at the nanoscale level down to room temperature and is visible in HRTEM images as a mixing of nanodomains with different tetragonality ratios. This phase separation was observed over the whole studied concentration range of x(Fe) values. It occurs progressively with the value of x(Fe), and the transition temperature T-C2 decreases with the concentration from about 620 K (x(Fe) = 0.03) to about 600 K (x(Fe) = 0.05), while T-C1 remains nearly constant.
441. Flexible Delivery Patch Systems based on Thermoresponsive Hydrogels and Submicronic Fiber Heaters
Authors:
Evanghelidis, A; Beregoi, M; Diculescu, VC; Galatanu, A; Ganea, P; Enculescu, I
Published: DEC 3 2018, SCIENTIFIC REPORTS, 8, DOI: 10.1038/s41598-018-35914-2
This paper proposes a novel, flexible, low cost administration patch which could be used as a non-invasive, controlled transdermal drug delivery system. The fabricated device consists in a flexible microfiber architecture heater covered with a thermoresponsive hydrogel, namely poly(N-isopropylacrylamide), as a matrix for the incorporation of active molecules. The manufacturing process consists of two main steps. First, the electrospun poly(methyl methacrylate) fiber networks are sputter coated with a thin gold layer and attached to flexible poly(ethylene terephthalate) substrates to obtain the heating platforms. Second, the heaters are encapsulated in poly(ethylene terephthalate) foils and covered with poly(N-isopropylacrylamide) hydrogel sheets. In order to illustrate the functionality of the fabricated patch, the hydrogel layer is loaded with methylene blue aqueous solution and is afterwards heated via Joule effect, by applying a voltage on the metalized fibers. The methylene blue releasing profiles of the heated patch are compared with those of the unheated one and the influence of parameters such as hydrogel composition and morphology, as well as the applied voltage values for microheating are investigated. The results indicate that the fabricated patch can be used as a drug administration instrument, while its performance can be tuned depending on the targeted application.
442. Dielectric properties of a bisimidazolium salt with dodecyl sulfate anion doped with carbon nanotubes
Authors:
Manaila Maximean, D; Circu, V; Ganea, CP
Published: JAN 16 2018, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 9, 174, DOI: 10.3762/bjnano.9.19
A new bisimidazolium salt with dodecyl sulfate as counterion has been designed and prepared. This salt shows a SmA phase that is stable at room temperature. The new ionic liquid crystal (ILC) was characterized by H-1 NMR, C-13 NMR and IR spectroscopy. Its liquid crystalline properties were analyzed by polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) studies. The dielectric spectra of the ILC doped with different concentrations of carbon nanotubes (CNT) were recorded over a wide frequency and temperature range of 10(-1) to 10(7) Hz and 293-338 K, respectively. The values of the activation energy were found in the range of 0.46-0.61 eV; the characteristic time was obtained by fitting the spectra of the dielectric loss with the Havriliak-Negami functions. As a result of doping the ILC with CNT, the electric conductivity increases significantly. Ionic conductivity is dominant and it was indirectly observed through the electrode polarization (EP) effect. The very high dielectric permittivity values and the decrease of the electric conductivity at low frequencies confirm the presence of EP.
443. Piezoelectric ferromagnetic BNT-BT0.08/CoFe2O4 coaxial core-shell composite nanotubes for nanoelectronic devices
Authors:
Cernea, M; Vasile, BS; Surdu, VA; Trusca, R; Sima, M; Craciun, F; Galassi, C
Published: JUL 5 2018, JOURNAL OF ALLOYS AND COMPOUNDS, 752, 388, DOI: 10.1016/j.jallcom.2018.04.146
In this paper we report on a novel 1-D piezoelectric/ferroelectric nanostructure. Composites of piezoelectric (0.92Na(0.5)Bi(0.5)TiO(3)-0.08BaTiO(3) abbreviated as BNT-BT0.08) and ferromagnetic (CoFe2O4) nanotubes were assembled and studied in order to envisage new multifunctional applications. Using a polycarbonate membrane template and sols precursors of BNT-BT(0.08 )and CoFe2O4, heterostructured BNT-BT0.08/CoFe2O4 core-shell composite nanotubes were created. Selective methods such as SEM, TEM, AFM, PFM and MFM were used for the characterization of the as-prepared hybrid piezoelectric/ferromagnetic coaxial nanotubes structure. This composite shows two crystalline phases: rhombohedral BNT-BT0.08 and cubicCoFe(2)O(4). The piezoelectric and ferromagnetic properties have been characterized. Piezo force microscopy (PFM) images evidenced ferroelectric domains with opposite polarity due to lead free piezoelectric BNT-BT0.08 outer tube. Magnetic force microscopy (MFM) images evidenced magnetic domains attributed to the CoFe2O4 inner tube. Magnetic hysteresis curves demonstrate a weak ferromagnetic behavior, accompanied by a linear variation of the magnetization at higher magnetic fields, especially at room temperature. From dielectric measurements, high tunability values reaching about 70% at 0.5 kHz and E = 80 kV/cm have been obtained. An effective dielectric constant epsilon(r) = 32 has been measured. The results obtained from this work provide a base for the design of tubular multi-layered materials with novel functionalities and applications in various multifunctional electronic devices such as actuators, transducers, and energy storage microsystems. (C) 2018 Elsevier B.V. All rights reserved.
444. Structural and optical properties of optimized amorphous GeTe films for memory applications
Authors:
Galca, AC; Sava, F; Simandan, ID; Bucur, C; Dumitru, V; Porosnicu, C; Mihai, C; Velea, A
Published: NOV 1 2018, JOURNAL OF NON-CRYSTALLINE SOLIDS, 499, 7, DOI: 10.1016/j.jnoncrysol.2018.07.007
Chalcogenide amorphous materials, such as GeTe, are known to exhibit deposition dependent optical and structural properties. The formation of a single and homogeneous amorphous GeTe (a-GeTe) phase is questionable since the deposited films can be mixtures of monoelemental nanoclusters. In this work, we employed two deposition techniques, pulsed laser deposition from a polycrystalline GeTe target and co-sputtering from two distinct Ge and Te targets, respectively, to obtain a-GeTe films. To improve the homogeneity of the amorphous phase obtained by magnetron sputtering, the substrate temperature was varied from room temperature up to 180 degrees C. The samples were investigated by X-ray diffraction, X-ray reflectometry, X-ray photoelectron spectroscopy and spectroscopic ellipsometry. It was found that the film mass density, optical bandgap, refractive index and absolute reflectivity become progressively larger with increasing substrate temperature, due to the minimization of voids fraction and the number of dangling bonds in the amorphous structure. Moreover, X-ray photoelectron spectroscopy results prove the formation of Ge-Te bonds and therefore of the GeTe alloy at the optimal substrate temperature of 180 degrees C. This study reveals the importance of optimizing the deposition conditions for obtaining a specific amorphous phase, which enables the atomic rearrangements responsible for fast phase-change needed in memory applications.
445. Many-body effects in transport through a quantum-dot cavity system
Authors:
Dinu, IV; Moldoveanu, V; Gartner, P
Published: MAY 25 2018, PHYSICAL REVIEW B, 97, DOI: 10.1103/PhysRevB.97.195442
We theoretically describe electric transport through an optically active quantum dot embedded in a single-mode cavity, and coupled to source-drain particle reservoirs. The populations of various many-body configurations (e.g., excitons, trions, biexciton) and the photon-number occupancies are calculated from a master equation which is derived in the basis of dressed states. These take into account both the Coulomb and the light-matter interaction. The former is essential in the description of the transport, while for the latter we identify situations in which it can be neglected in the expression of tunneling rates. The fermionic nature of the particle reservoirs plays an important role in the argument. The master equation is numerically solved for the s-shell many-body configurations of disk-shaped quantum dots. If the cavity is tuned to the biexciton-exciton transition, the most efficient optical processes take place in a three-level A system. The alternative exciton-ground-state route is inhibited as nonresonant due to the biexciton binding energy. The steady-state current is analyzed as a function of the photon frequency and the coupling to the leads. An unexpected feature appears in its dependence on the cavity loss rate, which turns out to be nonmonotonic.
446. Surface States- and Field-Effects at GaAs(100) Electrodes in Sodium Dodecyl Sulfate Acid Solution
Authors:
Enache, M; Negrila, C; Anastasescu, M; Dobrescu, G; Lazarescu, MF; Lazarescu, V
Published: 2018, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 165, H3017, DOI: 10.1149/2.0031804jes
Sodium dodecyl sulfate (SDS) effects at the electrified p- and n-GaAs(100)/H2SO4 interfaces were investigated by EIS, XPS and AFM. XPS data revealed that under the open circuit conditions, SDS adsorption on GaAs(100) results in a protective overlayer which prevents the further oxidation in air of both types of semiconductor surfaces. The dopant nature is, however, decisive for the way of bonding the surfactant molecule to the surface. At the p-doped substrate, SDS adsorbs mainly at As sites by its hydrocarbon tail and by the anion head to the Ga sites at the n-doped one. Although the surfactant behaves as a dipole under the applied potential control, the dopant type plays a key role in the SDS interaction with GaAs(100) electrodes too. EIS data evidenced that SDS interaction with n-GaAs(100) electrode brings a pronounced decrease of the capacitive contribution of the surface states and a shift of the flatband potential to less negative values, unlike the p-doped one, where no significant change in its electronic properties was observed. These results were rationalized in terms of surface states- and field-effects operating at the electrified interfaces under discussion. (C) The Author(s) 2017. Published by ECS.
447. Synthesis and characterization of CoFe2O4/BNT-BT0.08 core shell nanotubes by a template based sol-gel method
Authors:
Cernea, M; Vasile, BS; Surdu, VA; Trusca, R; Craciun, F; Galassi, C
Published: JUN 15 2018, CERAMICS INTERNATIONAL, 44, 10819, DOI: 10.1016/j.ceramint.2018.03.123
In this work we report on a new 1-1 composite coaxial nanostructure containing nanotubes of CoFe2O4 and BET-BT0.08 prepared by a template-based fabrication technique using the sol-gel chemistry. In this regard, CoFe2O4/BNT-BT0.08 core-shell nanotubes were prepared using a polycarbonate membrane template and sols precursors of CoFe2O4 and BNT-BT0.08. The deposition of nanotubes was performed by pore wetting of the porous membranes via capillary action and subsequent pyrolysis. The studies with scanning electron microscopy and transmission electron microscopy (TEM) revealed that the composite material is characterized by the 1-D tubular structure. Analysis by X-ray diffraction, high-resolution TEM imaging and selected-area electron diffraction pattern demonstrated that the synthetic composite nanotube CoFe2O4/BNT-BT0.08 has crystalline structure with cubic CoFe2O4 and rhombohedral BNT-BT0.08 phases. CoFe2O4/BNT-BT0.08 coaxial nanotubes show dielectric properties, piezoelectric and ferromagnetic behavior.
448. Magneto-optical properties of Ce3+ and Tb3+-doped silico-phosphate sol-gel thin films
Authors:
Stefan, CR; Elisa, M; Vasiliu, IC; Sava, BA; Boroica, L; Sofronie, M; Tolea, F; Enculescu, M; Kuncser, V; Beldiceanu, A; Volceanov, A; Eftimie, M
Published: AUG 1 2018, APPLIED SURFACE SCIENCE, 448, 480, DOI: 10.1016/j.apsusc.2018.04.067
Ce3+ and Tb3+-doped silico-phosphate films were obtained by using the sol-gel method, followed by the spin-coating deposition on silicon substrate. The homogeneity of the films was investigated by the conoscopy method. It was observed that the analysed films are isotropic but relatively inhomogeneous due to the specificity of the deposition technique. The morphology of the sol-gel films was investigated by Scanning Electron Microscopy and Atomic Force Microscopy. The elemental composition was determined by Energy Dispersive X-ray analysis. The magneto-optical investigations evidenced the capability of Ce and Tb-doped films of less than 2 mu m thickness to produce measurable Kerr rotations of 1 mdeg/T and 0.28 mdeg/T, respectively. (C) 2018 Elsevier B.V. All rights reserved.
449. From Glucose Direct to Succinic Acid: an Optimized Recyclable Bi-functional Ru@MNP-MWCNT Catalyst
Authors:
Podolean, I; Cojocaru, B; Garcia, H; Teodorescu, C; Parvulescu, VI; Coman, SM
Published: NOV 2018, TOPICS IN CATALYSIS, 61, 1876, DOI: 10.1007/s11244-018-1012-4
Ru@MNP-MWCNT catalysts were obtained via functionalization of nanostructured carbon-based carriers (ie, MWCNT) with base molecules (ie, 2-aminophenol and ethylenediamine) followed by the complexation with RuCl3. These structures demonstrated a highly efficient behavior for the selective wet oxidation of levulinic acid and glucose to succinic acid. However, to ensure an easy recovery and high recyclability the MWCNTs nanotubes were modified by incorporation of super-paramagnetic Fe3O4 nanoparticles into porous structure. Besides the catalytic performances the resulted composites showed a good mechanical resistance.
450. Enhanced photocurrent in GeSi NCs/TiO2 multilayers
Authors:
Palade, C; Slav, A; Cojocaru, O; Teodorescu, VS; Lazanu, S; Stoica, T; Sultan, MT; Svavarsson, HG; Ciurea, ML
Published: 2018, CAS 2018 PROCEEDINGS: 2018 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 76, DOI:
GeSi NCs / TiO2 multilayers with enhanced photocurrent properties were prepared and studied. Multilayers of TiO2 /(GeSi/TiO2)x2 /Si-p were deposited by magnetron sputtering and annealed by RTA at 700 degrees C for GeSi NCs formation. A post-annealing hydrogenation in plasma was performed on multilayers for healing of defects acting as traps and/or recombination centers and consequently producing the photocurrent enhancement. We studied the electrical and photoconductive properties of multilayers annealed by RTA and post-annealing hydrogenated. The current - temperature dependence reveals the conduction mechanisms in GeSi NCs / TiO2 multilayers RTA annealed, i.e. thermal activation of carriers to extended states (0.31 eV activation energy), the electron tunneling mechanism to nearest neighbors (T-1/2 behavior) and Mott variable range hopping (T-1/4 dependence). The photocurrent spectra made on multilayers structures hydrogenated for 10, 20 and 30 min evidence the photocurrent increasing up to 50%, showing that the hydrogenation is a suitable treatment for enhancing photocurrent. All photocurrent spectra present a dominant maximum (920 nm) and two shoulders (similar to 770 and similar to 1060 nm).
451. Magnetism and magnetoresistance of single Ni-Cu alloy nanowires
Authors:
Costas, A; Florica, C; Matei, E; Toimil-Molares, ME; Stavarache, I; Kuncser, A; Kuncser, V; Enculescu, I
Published: AUG 30 2018, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 9, 2355, DOI: 10.3762/bjnano.9.219
Arrays of magnetic Ni-Cu alloy nanowires with different compositions were prepared by a template-replication technique using electrochemical deposition into polycarbonate nanoporous membranes. Photolithography was employed for obtaining interdigitated metallic electrode systems of Ti/Au onto SiO2/Si substrates and subsequent electron beam lithography was used for contacting single nanowires in order to investigate their galvano-magnetic properties. The results of the magnetoresistance measurements made on single Ni-Cu alloy nanowires of different compositions have been reported and discussed in detail. A direct methodology for transforming the magnetoresistance data into the corresponding magnetic hysteresis loops was proposed, opening new possibilities for an easy magnetic investigation of single magnetic nanowires in the peculiar cases of Stoner-Wohlfarth-like magnetization reversal mechanisms. The magnetic parameters of single Ni-Cu nanowires of different Ni content have been estimated and discussed by the interpretation of the as derived magnetic hysteresis loops via micromagnetic modeling. It has been theoretically proven that the proposed methodology can be applied over a large range of nanowire diameters if the measurement geometry is suitably chosen.
452. H2S sensing mechanism of SnO2-CuWO4 operated under pulsed temperature modulation
Authors:
Simion, CE; Somacescu, S; Teodorescu, VS; Osiceanu, P; Stanoiu, A
Published: APR 15 2018, SENSORS AND ACTUATORS B-CHEMICAL, 259, 268, DOI: 10.1016/j.snb.2017.12.027
This paper reports the sensing mechanism of SnO2-CuWO4 mixed oxides towards H2S detection revealed through Pulsed Temperature Mode (PTM). After thick film deposition onto commercial substrates, the final annealing temperature enhances the material reliability through the changes occurred during the experimental conditions. PTM approach represents a tradeoff in terms of sensing mechanism versus sensing performance, in order to get insights about the fundamental aspects. The measurements have been done under dynamic gas flow conditions, in the presence of 50% relative humidity (RH). The gas sensors based on SnO2-CuWO4 exhibit sensor signals higher than 100 to 10 ppm H2S, low cross-sensitivity to common gaseous interfering agents (CO, CH4, NH3, SO2), average selective sensitivity of 8.64 towards the main interfering NO2 gas, moderate response (4 min)/recovery (5 min) transients and power consumption. In order to emphasize the role of moisture towards H2S detection mechanism, the photoacoustic spectroscopic insights were correlated with Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy results. Such approach has shown promising aspects towards further operational sensitive devices. (c) 2017 Elsevier B.V. All rights reserved.
453. Modeling issues regarding thermal conductivity of graphene-based nanocomposites
Authors:
Sandu, T; Gologanu, M; Voicu, R; Boldeiu, G; Moagar-Poladian, V
Published: 2018, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 21, 92, DOI:
Modeling thermal conductivity of graphene-based nanocomposites is analyzed from an effective medium approximation point of view, where interfacial thermal resistance and arbitrary shape of the fillers are considered. Two approximations, Maxwell-Garnett and coherent potential approximation, are used to show that the usual oblate spheroidal shape approximation of graphene nanodots is not satisfactory to model thermal conductivity in graphene-based composites.
454. Synthesis and characterization of novel ferrite-piezoelectric multiferroic core-shell-type structure
Authors:
Cernea, M; Vasile, BS; Ciuchi, IV; Surdu, VA; Bartha, C; Iuga, A; Galizia, P; Galassi, C
Published: JUL 2018, JOURNAL OF MATERIALS SCIENCE, 53, 9661, DOI: 10.1007/s10853-018-2264-x
Hybrid ferromagnetic/piezoelectric core-shell nanoparticles and ceramics have potential for a wide range of applications due to their tunability, electronic and magnetic properties. In this study, we designed a core-shell-type nanostructure of composition CoFe2O4/BNT-BT0.08, where BNT-BT0.08 is the abbreviation of bismuth, sodium titanate (Bi0.5Na0.5TiO3, BNT) doped with 8 mol% barium titanate (BaTiO3, BT). This multiferroic composite was prepared by covering CoFe2O4 nanoparticles with a shell of BNT-BT0.08 using the sol-gel technique. Scanning and transmission electron microscopy confirmed formation of a core-shell structure. The results of microstructure, dielectric, piezoelectric and magnetic investigations demonstrated that this heterostructure shows simultaneously electrical and magnetic behavior, at room temperature. XRD pattern of core-shell composite CoFe2O4/BNT-BT0.08 powder reveals only cubic CoFe2O4 and rhombohedral Bi0.5Na0.5TiO3 phases. CoFe2O4/BNT-BT0.08 core-shell nanostructure sample shows high values of permittivity (epsilon >= 600) together with high dielectric losses (tan delta >= 1) in the low-frequency range (nu <= 10(4) Hz). PFM and polarization hysteresis indicated a ferroelectric domains structure and remnant polarization of similar to 2.6 A mu C/cm(2) for the ceramics pellets samples of CoFe2O4/BNT-BT0.08. The present study reveals the possibility of coating nanoparticles onto nanometer-sized core particles, using controlled sol-gel process, in order to prepare multifunctional core-shell composites for piezoelectric and magnetoelectronic sensors.
455. Doped ceria prepared by precipitation route for steam reforming of methane
Authors:
Florea, M; Matei-Rutkovska, F; Postole, G; Urda, A; Neatu, F; Parvulescu, VI; Gelin, P
Published: MAY 15 2018, , DOI: 10.1016/j.cattod.2016.12.006
456. Influence of the modulated two-step synthesis of biogenic hydroxyapatite on biomimetic products' surface
Authors:
Miculescu, F; Mocanu, AC; Stan, GE; Miculescu, M; Maidaniuc, A; Cimpean, A; Mitran, V; Voicu, SI; Machedon-Pisu, T; Ciocan, LT
Published: APR 30 2018, APPLIED SURFACE SCIENCE, 438, 157, DOI: 10.1016/j.apsusc.2017.07.144
Processing calcium-rich natural resources, such as marble and mussel seashells, into biomimetic products could constitute an environmentally-friendly and economically sustainable alternative given their geographical widespread. Hitherto, their value for biomedicine was demonstrated only for seashells, with the technological exploitation approaches still facing challenges with respect to the identification of generic synthesis parameters capable to allow the reproducible and designed synthesis of calcium phosphate at an industrial-ready level. In this study was targeted the optimization of Rathje synthesis method for the fabrication of biogenic calcium phosphates, by conveniently adjusting the chemical composition of employed reagents. It was shown that post-synthesis heat-treatment of compacted powders is the key step for inducing structural transformations suitable to attain biomimetic products for reconstructive orthopedic applications. The sintered materials have been multi-parametricallyevaluated from morpho-compositional, structural, wettability, mechanical and cytocompatibility points of view and the results have been cross-examined and discussed. Convenient and efficient preparation routes to produce biogenic hydroxyapatite have been identified. The functional performances of the as-prepared biogenic ceramics endorse their use as a solid and inexpensive alternative source material for the fabrication of various bone regenerative products and implant coatings. (C) 2017 Elsevier B.V. All rights reserved.
457. Full Tetragonal Phase Stabilization in ZrO2 Nanoparticles Using Wet Impregnation: Interplay of Host Structure, Dopant Concentration and Sensitivity of Characterization Technique
Authors:
Colbea, C; Avram, D; Cojocaru, B; Negrea, R; Ghica, C; Kessler, VG; Seisenbaeva, GA; Parvulescu, V; Tiseanu, C
Published: DEC 2018, NANOMATERIALS, 8, DOI: 10.3390/nano8120988
Here, we show that wet impregnation of ZrO2 nanoparticles with 10% and 20% Eu oxide followed by thermal anneal in air above 500 degrees C produces full stabilization of the tetragonal phase of ZrO2 without evidencing any phase separation. The bare ZrO2 nanoparticles were obtained using three synthetic methods: oil in water microemulsion, rapid hydrothermal, and citrate complexation methods. The homogeneity of the solid solutions was assessed using X-ray diffraction, Raman spectroscopy, high resolution transmission electron microscopy, and advanced luminescence spectroscopy. Our findings show that wet impregnation, which is a recognized method for obtaining surface doped oxides, can be successfully used for obtaining doped oxides in the bulk with good homogeneity at the atomic scale. The limits of characterization technique in detecting minor phases and the roles of dopant concentration and host structure in formation of phase stabilized solid solutions are also analyzed and discussed.
458. Investigation of the interactions of PVDF shell films with Ni core submicron wires and AAO matrix
Authors:
Sima, M; Baibarac, M; Vasile, E; Sima, M; Schinteie, GA; Kuncser, V
Published: SEP 15 2018, PHYSICA B-CONDENSED MATTER, 545, 509, DOI: 10.1016/j.physb.2018.07.015
Arrays of Ni submicron wires surrounded by poly (vinylidene fluoride) (PVDF) submicron tubes were prepared via solution-processed polymer and Ni electrodeposition into anodic aluminum oxide template. The PVDF solution was filtered in vacuum through the template and the resulting dried structure was used for the electrodeposition of Ni wires. The obtained core-shell submicron wire structure consists of a metallic magnetic nanowire core of about 50 mu m in length and about 300 nm diameter surrounded by a polymer tube shell with thickness less than 10 nm. The specific ferroelectric beta-phase of the polymer was obtained whereas the magnetic behavior of the Ni-cores was proven to be specific to an array of ferromagnetic Ni cylindrical wires (about 0.62 mu(B)/Ni atom) with magnetization reversal mechanisms dominated by dipolar interactions and domain wall displacements. No significant differences of the magnetization reversal mechanism were observed in case of Ni submicron wires surrounded by PVDF tubes and similar Ni wires without PVDF shell, suggesting that magneto-coupling effects in such systems might be observed only by measuring the perturbation of the electric state of the polymer shell under a magnetic excitation of the Ni cores.
459. On the hydrophilicity of Ni-doped TiO2 thin films. A study by X-ray absorption spectroscopy
Authors:
Macovei, D; Tiron, V; Adomnitei, C; Luca, D; Dobromir, M; Antohe, S; Mardare, D
Published: JUL 1 2018, THIN SOLID FILMS, 657, 49, DOI: 10.1016/j.tsf.2018.04.045
Undoped and Ni-doped TiO2 thin films, with Ni concentration in the range 3-9 at.%, were obtained by reactive magnetron co-sputtering. A combined analysis by X-ray photoelectron spectroscopy and extended X-ray absorption-edge fine structure shows that Ni2+ substitutes for Ti4+ in the TiO2 lattice and promotes, at higher Ni amounts, a structural transition of the host from anatase to rutile. Several difficulties of the extended X-ray absorption-edge fine structure analysis, in the case of Ni-doped TiO2, are also discussed. X-ray diffraction data revealed that a large amount of the films material is in amorphous state. The films are very smooth, with root mean square roughness values (below 1.5 nm) decreasing with the increase of the Ni content. The hydrophilic properties of TiO2, modified by Ni doping, are also investigated.
460. Dense Ge nanocrystals embedded in TiO2 with exponentially increased photoconduction by field effect
Authors:
Lepadatu, AM; Slav, A; Palade, C; Dascalescu, I; Enculescu, M; Iftimie, S; Lazanu, S; Teodorescul, VS; Ciurea, ML; Stoica, T
Published: MAR 20 2018, SCIENTIFIC REPORTS, 8, DOI: 10.1038/s41598-018-23316-3
Si and Ge nanocrystals in oxides are of a large interest for photo-effect applications due to the fine-tuning of the optical bandgap by quantum confinement in nanocrystals. In this work, dense Ge nanocrystals suitable for enhanced photoconduction were fabricated from 60% Ge in TiO2 amorphous layers by low temperature rapid thermal annealing at 550 degrees C. An exponential increase of the photocurrent with the applied voltage was observed in coplanar structure of Ge nanocrystals composite films deposited on oxidized Si wafers. The behaviour was explained by field effect control of the Fermi level at the Ge nanocrystals-TiO2 layer/substrate interfaces. The blue-shift of the absorption gap from bulk Ge value to 1.14 eV was evidenced in both photocurrent spectra and optical reflection-transmission experiments, in good agreement with quantum confinement induced bandgap broadening in Ge nanocrystal with sizes of about 5 nm as found from HRTEM and XRD investigations. A nonmonotonic spectral dependence of the refractive index is associated to the Ge nanocrystals formation. The nanocrystal morphology is also in good agreement with the Coulomb gap hopping mechanism of T-1/2 -type explaining the temperature dependence of the dark conduction.
461. CoFe2-xCrxO4 ferrites: synthesis, characterization and their catalytic activity
Authors:
Mindru, I; Gingasu, D; Diamandescu, L; Patron, L; Marinescu, G; Culita, DC; Calderon-Moreno, JM; Preda, S; Oprea, O; Parvulescu, V
Published: DEC 2018, CHEMICAL PAPERS, 72, 3213, DOI: 10.1007/s11696-018-0553-0
Chromium substituted cobalt ferrites CoFe2-xCrxO4 (x=0; 1; 1.5) were synthesized through a soft chemistry methodthe gluconate precursor route. The gluconate precursors were characterized by infrared spectroscopy (IR), ultraviolet-visible spectroscopy and thermal analysis. The spinel oxide powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mossbauer spectroscopy and Brunauer-Emmett-Teller N-2 adsorption-desorption analyses. XRD indicated the formation of the spinel-type phase with good crystallinity. The mean crystalline domains size decreased from 23.8 to 17.8nm with the increase in the chromium content. SEM revealed faceted particles for which the particle sizes varied significantly with the chromium content. The chromium substituted cobalt ferrites were found to have high catalytic performance.
462. Ambiguous Role of Growth-Induced Defects on the Semiconductor-to-Metal Characteristics in Epitaxial VO2/TiO2 Thin Films
Authors:
Mihailescu, CN; Symeou, E; Svoukis, E; Negrea, RF; Ghica, C; Teodorescu, V; Tanase, LC; Negrila, C; Giapintzakis, J
Published: APR 25 2018, ACS APPLIED MATERIALS & INTERFACES, 10, 14144, DOI: 10.1021/acsami.8b01436
Controlling the semiconductor-to-metal transition temperature in epitaxial VO2 thin films remains an unresolved question both at the fundamental as well as the application level. Within the scope of this work, the effects of growth temperature on the structure, chemical composition, interface coherency and electrical characteristics of rutile VO2 epitaxial thin films grown on TiO2 substrates are investigated. It is hereby deduced that the transition temperature is lower than the bulk value of 340 K. However, it is found to approach this value as a function of increased growth temperature even though it is accompanied by a contraction along the V4+-V4+ bond direction, the crystallographic c-axis lattice parameter. Additionally, it is demonstrated that films grown at low substrate temperatures exhibit a relaxed state and a strongly reduced transition temperature. It is suggested that, besides thermal and epitaxial strain, growth-induced defects may strongly affect the electronic phase transition. The results of this work reveal the difficulty in extracting the intrinsic material response to strain, when the exact contribution of all strain sources cannot be effectively determined. The findings also bear implications on the limitations in obtaining the recently predicted novel semi-Dirac point phase in VO2/TiO2 multilayer structures.
463. Synthesis and characterization of dextran-coated iron oxide nanoparticles
Authors:
Predescu, AM; Matei, E; Berbecaru, AC; Pantilimon, C; Dragan, C; Vidu, R; Predescu, C; Kuncser, V
Published: MAR 2018, ROYAL SOCIETY OPEN SCIENCE, 5, DOI: 10.1098/rsos.171525
Synthesis and characterization of iron oxide nanoparticles coated with a large molar weight dextran for environmental applications are reported. The first experiments involved the synthesis of iron oxide nanoparticles which were coated with dextran at different concentrations. The synthesis was performed by a co-precipitation technique, while the coating of iron oxide nanoparticles was carried out in solution. The obtained nanoparticles were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectrometry, Fourier transform infrared spectroscopy and superconducting quantum interference device magnetometry. The results demonstrated a successful coating of iron oxide nanoparticles with large molar weight dextran, of which agglomeration tendency depended on the amount of dextran in the coating solution. SEM and TEM observations have shown that the iron oxide nanoparticles are of about 7 nm in size.
464. Engineering active sites on reduced graphene oxide by hydrogen plasma irradiation: mimicking bifunctional metal/supported catalysts in hydrogenation reactions
Authors:
Primo, A; Franconetti, A; Magureanu, M; Mandache, NB; Bucur, C; Rizescu, C; Cojocaru, B; Parvulescu, VI; Garcia, H
Published: JUN 7 2018, GREEN CHEMISTRY, 20, 2623, DOI: 10.1039/c7gc03397d
H2 plasma has been used to generate carbon vacancies on reduced graphene oxide to increase its catalytic activity as a hydrogenation catalyst. A relationship between the power of the plasma treatment and the exposure time with the activity of the material was observed for CvC double bond hydrogenation. The activity data in the case of 1-octene, showing skeletal isomerization besides hydrogenation, indicate that H2 plasma treatment can introduce hydrogenating and acid sites rendering a bifunctional catalyst that is reminiscent of the activity of noble metals supported on acid supports.
465. CHARACTERIZATION OF SURFACE AND INTERFACE OF Fe-C STEEL UNDER ELECTROLYTIC GALVANIZATION
Authors:
Bibicu, I; Bulea, C; Diamandescu, L; Rus, V; Popescu, T; Mercioniu, I
Published: JUL-SEP 2018, PROCEEDINGS OF THE ROMANIAN ACADEMY SERIES A-MATHEMATICS PHYSICS TECHNICAL SCIENCES INFORMATION SCIENCE, 19, 430, DOI:
Low carbon Fe-C steel surface has been studied before and after electrolytic galvanization. The corrosion products formed under atmospheric conditions on the Fe-C steel were identified and characterised by X-ray diffraction (XRD), transmission Mossbauer spectroscopy, conversion electron Mossbauer spectroscopy (CEMS), and conversion X-ray Mossbauer spectroscopy (CXMS). In decreasing order of abundance the found corrosion phases were magnetite, hematite, and goethite. After the surface preparation, an electrolytic galvanization process was applied. A magnetic anisotropy was evidenced after preparation, in the superficial layer of around 250 nm thickness. Scanning electron microscopy (SEM) analyses evidenced the formation of a uniform thin Zn film of 8 mu m at the surface of steel. No other Fe-Zn phases were identified at the steel-Zn interface.
466. Rolling dopant and strain in Y-doped BiFeO3 epitaxial thin films for photoelectrochemical water splitting
Authors:
Haydous, F; Scarisoreanu, ND; Birjega, R; Ion, V; Lippert, T; Dumitrescu, N; Moldovan, A; Andrei, A; Teodorescu, VS; Ghica, C; Negrea, R; Dinescu, M
Published: OCT 25 2018, SCIENTIFIC REPORTS, 8, DOI: 10.1038/s41598-018-34010-9
We report significant photoelectrochemical activity of Y-doped BiFeO3 (Y-BFO) epitaxial thin films deposited on Nb: SrTiO3 substrates. The Y-BFO photoanodes exhibit a strong dependence of the photocurrent values on the thickness of the films, and implicitly on the induced epitaxial strain. The peculiar crystalline structure of the Y-BFO thin films and the structural changes after the PEC experiments have been revealed by high resolution X-ray diffraction and transmission electron microscopy investigations. The crystalline coherence breaking due to the small ionic radius Y-addition was analyzed using Willliamson-Hall approach on the 2 theta-omega scans of the symmetric (00l) reflections and confirmed by high resolution TEM (HR-TEM) analysis. In the thinnest sample the lateral coherence length (L-parallel to) is preserved on larger nanoregions/ nanodomains. For higher thickness values L-parallel to is decreasing while domains tilt angles (alpha(tilt)) is increasing. The photocurrent value obtained for the thinnest sample was as high as J(ph) = 0.72 mA/cm(2), at 1.4 V(vs. RHE). The potentiostatic scans of the Y-BFO photoanodes show the stability of photoresponse, irrespective of the film's thickness. There is no clear cathodic photocurrent observation for the Y-BFO thin films confirming the n-type semiconductor behavior of the Y-BFO photoelectrodes.
467. ESR Study of Irradiated Polysaccharides ESR investigation of gamma irradiated pectin
Authors:
Slave, RM; Grecu, MN; Grecu, VV
Published: 2018, 4TH INTERNATIONAL SCIENTIFIC CONFERENCE SEA-CONF 2018, 172, DOI: 10.1088/1755-1315/172/1/012003
Polysaccharides irradiation is usually used for their decontamination of fungi, pathogenic bacteria, toxigenic molds, parasitic organisms. ESR studies are performed just to evidence their irradiation. Therefore the accent is put on radical stability in time and ESR signal intensity dependence on irradiation dose. Less attention is given to radical nature and their dependence on plant nature. In this report a study of gamma irradiated pectin is given. Dose dependence of double integrated ESR signal is analyzed in terms of a recombination reaction during the radiation period. Radical stability dependence on water content is put in evidence.
468. Enhanced photocurrent in GeSi NCs / TiO2 multilayers
Authors:
Palade, C; Slav, A; Cojocaru, O; Teodorescu, VS; Lazanu, S; Stoica, T; Sultan, MT; Svavarsson, HG; Ciurea, ML
GeSi NCs / TiO2 multilayers with enhanced photocurrent properties were prepared and studied. Multilayers of TiO2 /(GeSi/TiO2)x2 /Si-p were deposited by magnetron sputtering and annealed by RTA at 700 degrees C for GeSi NCs formation. A post-annealing hydrogenation in plasma was performed on multilayers for healing of defects acting as traps and/or recombination centers and consequently producing the photocurrent enhancement. We studied the electrical and photoconductive properties of multilayers annealed by RTA and post-annealing hydrogenated. The current - temperature dependence reveals the conduction mechanisms in GeSi NCs / TiO2 multilayers RTA annealed, i.e. thermal activation of carriers to extended states (0.31 eV activation energy), the electron tunneling mechanism to nearest neighbors (T-1/2 behavior) and Mott variable range hopping (T-1/4 dependence). The photocurrent spectra made on multilayers structures hydrogenated for 10, 20 and 30 min evidence the photocurrent increasing up to 50%, showing that the hydrogenation is a suitable treatment for enhancing photocurrent. All photocurrent spectra present a dominant maximum (920 nm) and two shoulders (similar to 770 and similar to 1060 nm).
469. Osteoblast Cell Response to Naturally Derived Calcium Phosphate-Based Materials
Authors:
Mitran, V; Ion, R; Miculescu, F; Necula, MG; Mocanu, AC; Stan, GE; Antoniac, IV; Cimpean, A
Published: JUL 2018, MATERIALS, 11, DOI: 10.3390/ma11071097
The demand of calcium phosphate bioceramics for biomedical applications is constantly increasing. Efficient and cost-effective production can be achieved using naturally derived materials. In this work, calcium phosphate powders, obtained from dolomitic marble and Mytilus galloprovincialis seashells by a previously reported and improved Rathje method were used to fabricate microporous pellets through cold isostatic pressing followed by sintering at 1200 degrees C. The interaction of the developed materials with MC3T3-E1 pre-osteoblasts was explored in terms of cell adhesion, morphology, viability, proliferation, and differentiation to evaluate their potential for bone regeneration. Results showed appropriate cell adhesion and high viability without distinguishable differences in the morphological features. Likewise, the pre-osteoblast proliferation overtime on both naturally derived calcium phosphate materials showed a statistically significant increase comparable to that of commercial hydroxyapatite, used as reference material. Furthermore, evaluation of the intracellular alkaline phosphatase activity and collagen synthesis and deposition, used as markers of the osteogenic ability of these bioceramics, revealed that all samples promoted pre-osteoblast differentiation. However, a seashell-derived ceramic demonstrated a higher efficacy in inducing cell differentiation, almost equivalent to that of the commercial hydroxyapatite. Therefore, data obtained demonstrate that this naturally sourced calcium-phosphate material holds promise for applications in bone tissue regeneration.
470. Irreversibility in Rolled Tantalum
Authors:
Sandu, V; Cimpoiasu, E
Published: JUL 2018, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 31, 2054, DOI: 10.1007/s10948-017-4433-6
We investigated the magnetic and thermodynamic properties of rolled tantalum in superconducting state. The magnetization shows a crossover from type I to type II superconductivity as the magnetic field increases beyond the thermodynamic critical field. In both regimes, the sample shows a substantial irreversibility of the magnetization which we attribute to the pinning of the entities that characterize the intermediate and mixed states. Magnetic relaxation data taken in the intermediate state shows an important contribution of the quantum tunnelling below 3.7 K.
471. Networked mesoporous SnO2 nanostructures templated by Brij (R) 35 with enhanced H2S selective performance
Authors:
Stanoiu, A; Simion, CE; Sackmann, A; Baibarac, M; Florea, OG; Osiceanu, P; Teodorescu, VS; Somacescu, S
Published: NOV 1 2018, MICROPOROUS AND MESOPOROUS MATERIALS, 270, 101, DOI: 10.1016/j.micromeso.2018.05.008
Sensors based networked mesoporous SnO2 nanostructures templated by non-ionic surfactant - Brij (R) 35 were prepared via hydrothermal chemistry route. Specific patterns of the structure, morphology, surface chemistry and sensing properties were obtained by pH and autogenous pressure tuning. Consequently, the as-obtained SnO2 powders were subjected to extensive BET, Raman, TEM, HRTEM and XPS complementary investigations. The sensitive films were obtained by screen printing deposition of the powders onto commercial Al2O3 substrates. The gas sensing properties were assessed towards different hazardous gas species: CO, CH4, NH3, NO2, SO2 and H2S over a wide range of operating temperatures. Our particular SnO2 HP sensor synthesized at high autogenous pressure showed the highest selective-sensitivity to H2S (< 5 ppm) under 50% relative humidity (RH). The enhancement in the H2S sensitivity at low operating temperature under infield conditions was found to be closely connected to the morphological aspects and surface chemistry, peculiarities that can be assessed as consequences of the chemical tuning.
472. Highly Efficient, Easily Recoverable, and Recyclable Re-SiO2-Fe3O4 Catalyst for the Fragmentation of Lignin
Authors:
Tudorache, M; Opris, C; Cojocaru, B; Apostol, NG; Tirsoaga, A; Coman, SM; Parvulescu, VI; Duraki, B; Krumeich, F; van Bokhoven, JA
Published: AUG 2018, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, 6, 9618, DOI: 10.1021/acssuschemeng.7b04294
A series of Fe3O4@SiO2@Re catalysts were prepared by deposition of rhenium by means of the precipitation-deposition and impregnation procedures. Characterization of the catalysts confirmed that the deposition of silica protected the magnetite nanoparticles, resulting in a stable SiO(2)pFe(3)O(4) composite, which was not affected by the treatments during the further deposition of rhenium. Rhenium was silent in XRD over the range of concentrations, at which it was deposited. Furthermore, XPS detected rhenium, only in the impregnation series; this may confirm that dispersion was high. As expected, rhenium was not reduced to the metallic state and generated weakly acidic Bronsted-type centers as detected by NH3-TPD. H-2-TPD and chemisorption experiments demonstrate the capacity of these catalysts to chemisorb hydrogen. In line with these properties, rhenium catalyzed both C-C hydrogenolysis and C-O hydrolysis in successive steps. The performance of these catalysts was checked for a series of lignins of different origin and by means of different separation procedures. A very important finding is that these catalysts were highly stable and easy to recover.
473. Material parameters from frequency dispersion simulation of floating gate memory with Ge nanocrystals in HfO2
Authors:
Palade, C; Lepadatu, AM; Slav, A; Lazanu, S; Teodorescu, VS; Stoica, T; Ciurea, ML
Published: JAN 15 2018, APPLIED SURFACE SCIENCE, 428, 702, DOI: 10.1016/j.apsusc.2017.09.038
Trilayer memory capacitors with Ge nanocrystals (NCs) floating gate in HfO2 were obtained by magnetron sputtering deposition on p-type Si substrate followed by rapid thermal annealing at relatively low temperature of 600 degrees C. The frequency dispersion of capacitance and resistance was measured in accumulation regime of Al/HfO2 gate oxide/Ge NCs in HfO2 floating gate/HfO2 tunnel oxide/SiOx/p-Si/Al memory capacitors. For simulation of the frequency dispersion a complex circuit model was used considering an equivalent parallel RC circuit for each layer of the trilayer structure. A series resistance due to metallic contacts and Si substrate was necessary to be included in the model. A very good fit to the experimental data was obtained and the parameters of each layer in the memory capacitor, i.e. capacitances and resistances were determined and in turn the intrinsic material parameters, i.e. dielectric constants and resistivities of layers were evaluated. The results are very important for the study and optimization of the hysteresis behaviour of floating gate memories based on NCs embedded in oxide. (C) 2017 Published by Elsevier B.V.
474. AlN/Si based SAW resonators for very high sensitivity temperature sensors
Authors:
Nicoloiu, A; Muller, A; Zdru, I; Vasilache, D; Stan, GE; Nastase, C; Dumitru, V; Dinescu, A
Published: 2018, 2018 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS), DOI:
In the current work we present AlN/Si based Surface Acoustic Wave (SAW) devices exploited as high sensitivity temperature sensors. The experimental results show that the resonance frequency varies between 3.2 and 5.5 GHz, depending on the finger/Interdigit spacing width and metal thickness. The temperature measurements were performed between -250 degrees C and +150 degrees C in a cryostat. The sensitivities were investigated between 24-150 degrees C and the values were compared to the results obtained for similar GaN/Si based SAW structures.
475. GeSi nanocrystals in SiO2 matrix with extended photoresponse in near infrared
Authors:
Stavarache, I; Nedelcu, L; Teodorescu, VS; Maraloiu, VA; Dascalescu, I; Ciurea, ML
Published: 2018, CAS 2018 PROCEEDINGS: 2018 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 256, DOI:
The films of SiGe nanocrystals in SiO2 on Si substrate were obtained by co-sputtering Si, Ge, and SiO2 followed by rapid thermal annealing. The films structure and morphology together with electrical and photoelectrical properties were studied by x-ray diffraction, transmission electron microscopy, current - voltage and spectral photocurrent measurements. The photocurrent spectra at 300, 200 and 100 K were correlated with results obtained from X-ray diffractograms and transmission electron microscopy. The photocurrent spectra show an extension in near infrared due to the enriching SiGe nanocrystals in Ge.
476. Production and Structural Characterization of Some Magnesium Matrix Composites Reinforced with Amorphous/Nanocrystalline NiTi Particulates
Authors:
Ciurdas, M; Necsulescu, DA; Pantilimon, CM; Ion, V; Galatanu, M; Ruiu, G; Dumitrescu, RE
Two mixtures of elemental nickel and titanium powders in atomic proportions of 50% Ni + 50% Ti and 32% Ni + 68% Ti, respectively, were ground for 40 hours in a high energy planetary mill. In the case of the first mixture, the mechanical alloying was totally produced, while for the second, the alloying was partial. In both mixtures, qualitative X-ray diffraction phase analysis revealed the presence of metastable phases, such as Ni HC and NiTi- R-phase. Also, the equiatomic mixture is characterized by a partially amorphous structure. 10% of each type of mixture submitted to milling was used as reinforcing element in the form of particulates for two magnesium matrix composites. They were obtained by sintering in the plasma at 590 degrees C. In the case of the reinforced with the second mixture composite, the production of new phases other than the matrix and those present in the mixture of nickel and titanium powders after milling were recorded. The electron microscopy images of the two composites have resistant, free of micropores or microcracks matrix / particulates interfaces. The Mg-10% (32 at% Ni + 68 at% Ti) composite is characterized by Vickers hardness higher than that of the composite reinforced with the equiatomic mixture.
477. The Cu- and Zn-complex-catalyzed methanolysis of the chemical warfare nerve agents soman, sarin, and VX
Authors:
Petrea, N; Petre, R; Pretorian, A; Toader, C; Somoghi, V; Neatu, F; Florea, M; Neatu, S
Published: MAR-APR 2018, COMPTES RENDUS CHIMIE, 21, 345, DOI: 10.1016/j.crci.2017.08.006
The catalytic methanolysis of the chemical warfare nerve agents soman, sarin, and VX was investigated by using Cu or Zn complexes. Although VX withstood decontamination, the decomposition yield being around 96%, the soman and sarin deposited on different surfaces were almost fully destroyed under ambient conditions. The catalytic tests performed on a wide range of contaminated surfaces confirm the activity of the investigated catalytic systems, these complexes being suitable, from an economical point of view, for use in the formulation of a possible decomposition kit with military or civilian applicability. (C) 2017 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
478. OPTICAL COATINGS FOR ELI EXPERIMENTS PREPARED BY LASER ABLATION
Authors:
Bercea, A; Filipescu, M; Moldovan, A; Brajnicov, S; Colceag, D; Ion, V; Nistor, LC; Zorila, A; Dinescu, M
Dielectric materials (HfO2, A1(2)O(3), SiO2 and Ta2O5) processed as thin films have been studied extensively for applications in microelectronics, biology, medicine, etc. In the last decade, antireflection coatings based on these types of materials have received considerable attention for applications in the field of high power laser optics. In this paper we report on multi-layers from materials with low and high refractive indices deposited on quartz substrates by laser ablation. Damage tests performed with a Ti-Sapphire laser (775 nm wavelength, 220 fs pulse duration) evidenced higher threshold values for hafnia based heterostructures than for the others heterostructures.
479. Exploiting surface plasmon resonance in Au/ZnO photocatalysts for the selective oxidation of phenols
Authors:
Lin, F; Cojocaru, B; Colaciello, LW; Cadigan, C; Tian, CX; Grecu, M; Xin, HL; Vyas, S; Parvulescu, V; Richards, R
Published: MAR 18 2018, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 255, DOI:
480. A Mathematical Account of the NEGF Formalism
Authors:
Cornean, HD; Moldoveanu, V; Pillet, CA
Published: FEB 2018, ANNALES HENRI POINCARE, 19, 442, DOI: 10.1007/s00023-017-0638-2
The main goal of this paper is to put on solid mathematical grounds the so-called non-equilibrium Green's function transport formalism for open systems. In particular, we derive the Jauho-Meir-Wingreen formula for the time-dependent current through an interacting sample coupled to non-interacting leads. Our proof is non-perturbative and uses neither complex-time Keldysh contours nor Langreth rules of 'analytic continuation.' We also discuss other technical identities (Langreth, Keldysh) involving various many-body Green's functions. Finally, we study the Dyson equation for the advanced/retarded interacting Green's function and we rigorously construct its (irreducible) self-energy, using the theory of Volterra operators.
481. Local configurations and atomic intermixing in as-quenched and annealed Fe1-xCrx and Fe1-xMox ribbons
Authors:
Stanciu, AE; Greculeasa, SG; Bartha, C; Schinteie, G; Palade, P; Kuncser, A; Leca, A; Filoti, G; Birsan, A; Crisan, O; Kuncser, V
Published: 2018, PHILOSOPHICAL MAGAZINE, 98, 1067, DOI: 10.1080/14786435.2018.1425556
Local atomic configuration, phase composition and atomic intermixing in Fe-rich Fe1-xCrx and Fe1-xMox ribbons (x = 0.05, 0.10, 0.15), of potential interest for high-temperature applications and nuclear devices, are investigated in this study in relation to specific processing and annealing routes. The Fe-based thin ribbons have been prepared by induction melting, followed by melt spinning and further annealed in He at temperatures up to 1250 degrees C. The complex structural, compositional and atomic configuration characterisation has been performed by means of X-ray diffraction (XRD), transmission Mossbauer spectroscopy and differential scanning calorimetry (TG-DSC). The XRD analysis indicates the formation of the desired solid solutions with body-centred cubic (bcc) structure in the as-quenched state. The Mossbauer spectroscopy results have been analysed in terms of the two-shell model. The distribution of Cr/Mo atoms in the first two coordination spheres is not homogeneous, especially after annealing, as supported by the short-range order parameters. In addition, high-temperature annealing treatments give rise to oxidation of Fe (to haematite, maghemite and magnetite) at the surface of the ribbons. Fe1-xCrx alloys are structurally more stable than the Mo counterpart under annealing at 700 degrees C. Annealing at 1250 degrees C in He enhances drastically the Cr clustering around Fe nuclei.
482. Heavy doping of ceria by wet impregnation: a viable alternative to bulk doping approaches
Authors:
Florea, M; Avram, D; Maraloiu, VA; Cojocaru, B; Tiseanu, C
Published: OCT 7 2018, NANOSCALE, 10, 18054, DOI: 10.1039/c8nr03695k
To avoid the deleterious effects of dopant segregation, synthesis methods that facilitate a homogenous dopant distribution in the ceria lattice were employed. Though doping ceria by wet impregnation was also credited to induce a homogeneous solid solution even in the heavy regime (concentration >= 20%, A. Corma, P. Atienzar, H. Garcia and J. Chane-Ching, Nat. Mater., 2004, 3, 394-397), no follow up investigation has been reported. Herein, we investigated ceria nanoparticles (1% Tm-CeO2 and 1% Eu-CeO2) wetimpregnated with trivalent rare-earth (Yb, 20%), bivalent (Ca, 20%) and isovalent (Zr, 30%) metals, followed by annealing in air. Homogeneity of the solid solutions of Yb-impregnated ceria was confirmed by a two-feature characterization toolbox that included X-ray diffraction, Raman spectroscopy, transmission electron microscopy, as well as up-conversion emission as a probe tool. Since the up-conversion emission of Tm was not detectable in the absence of Yb while its efficiency depends on the average distance between Yb and Tm ions, the Yb incorporation and its migration from the surface to the lattice bulk sites in wet-impregnated ceria can be "visualized" and compared with that of the Yb bulk-doped counterpart. The use of Eu luminescence as a local probe confirmed the homogeneity of solid solutions of Ca and Zr-impregnated ceria and also sustained the opposite roles of Ca and Zr as the repeller and the scavenger of oxygen vacancies, respectively. All these results suggested that heavy doping of ceria by wet impregnation with metals with +2, +3 and +4 valencies represent a facile alternative to conventional doping approaches. Therefore, the effects of the amount and the type of metal dopant on the structural properties of CeO2 could be investigated in a more systematic and probably a more reproducible manner, which would significantly increase the potential of ceria in catalysis and other applications.
483. Polymer Dispersed Liquid Crystals films doped with carbon nanotubes - preparation methods
Authors:
Manaila-Maximean, D; Circu, V; Ganea, P; Barar, A; Danila, O; Staicu, T; Loiko, VA; Konkolovich, AV; Miskevich, AA
Published: 2018, ADVANCED TOPICS IN OPTOELECTRONICS, MICROELECTRONICS, AND NANOTECHNOLOGIES IX, 10977, DOI: 10.1117/12.2326186
Polymer Dispersed Liquid Crystals (PDLC) are composite materials consisting of small liquid crystal (LC) droplets surrounded by a polymer matrix. Due to their relatively easy preparation and processing, the PDLC devices found many applications such as displays, architectural windows, energy control devices, projection displays, spatial light modulators, polarizers. Carbon nanotubes (CNT) have excellent mobility and are suitable as doping nanoparticles in order to improve the electrically-controlled orientation of LC. This paper presents the methods of preparation of PDLC doped with CNT. Experimental results are presented for the films obtained by solvent induced polymerization method, using polymethyl methacrylate and a nematic LC, E7. The obtained films are characterized by polarized optical microscopy, differential scanning calorimetry and electro-optical transmission.
484. Bismuth and lead oxides codoped boron phosphate glasses for Faraday rotators
Authors:
Sava, BA; Boroica, L; Elisa, M; Shikimaka, O; Grabco, D; Popa, M; Barbos, Z; Iordanescu, R; Niculescu, AM; Kuncser, V; Galca, AC; Eftimie, M; Monteiro, RCC
Published: APR 15 2018, CERAMICS INTERNATIONAL, 44, 6025, DOI: 10.1016/j.ceramint.2017.12.205
New magneto-optical vitreous materials were obtained by melting-quenching technique comprising wet route raw materials preparation. The glass has the following composition in oxide mol. % 10 Li2O, 9 Al2O3, 5 ZnO, (35; 20; 50) B2O3,,(35; 50; 20) P2O5, 3 Bi2O3, 3 PbO, phosphorus and boron oxide being the vitreous network formers. It was also prepared a similar reference glass composition but without Bi2O3 and PbO. Optical and structural characterization by ultraviolet-visible (UV-Vis), Fourier Transform Infrared (FTIR) and Raman Spectroscopy of the bulk glasses showed a transmission over 90%, metaphosphate structure of glass together with Q(2) boron oxide units and P-O-B bonds. The mechanical parameters, hardness (H), Youngs modulus (E) and fracture toughness (KO of boron phosphate glasses, evaluated by micro- and nanoindentation techniques, demonstrated mostly higher values in comparison with those for alumino-phosphate glasses due to mixed borophosphate network. Thermal behavior was investigated by Differential Scanning Calorimetry (DSC) putting in evidence the vitreous transition temperature which decreases with about 45 degrees C when Bi and Pb oxides were added and two crystallization effects. The diamagnetic character of a highly transparent Bi and Pb oxide co doped boron phosphate glass was confirmed by ellipsometry, and the glass presented high magneto-optical properties at the top of the commercial bulk products.
485. H2S selective sensitivity of Cu doped BaSrTiO3 under operando conditions and the associated sensing mechanism
Authors:
Stanoiu, A; Piticescu, RM; Simion, CE; Rusti-Ciobota, CF; Florea, OG; Teodorescu, VS; Osiceanu, P; Sobetkii, A; Badilita, V
Published: JUL 1 2018, SENSORS AND ACTUATORS B-CHEMICAL, 264, 336, DOI: 10.1016/j.snb.2018.03.013
Nanostructured Cu mol. 5% doped perovskite material Ba0.75Sr0.25TiO3 was synthesized under hydrothermal conditions and further on deposited via RF sputtering technique onto commercial Al2O3 substrates provided with Au interdigital electrodes and Pt heater. The obtained thin films have been analyzed by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM, TEM), X-ray photoelectron spectroscopy (XPS), Differential Scanning Calorimetry-Thermogravimetry (DSC-TG) and electrical investigations. The H2S (5-90 ppm) gas-surface interaction at moderate operating temperature (T-op = 250 degrees C) associated with the interplay between the pre-adsorbed oxygen species and surface dipolar hydroxyl groups, has been highlighted by simultaneous work function and electrical resistance measurements. By correlation with the XPS spectra, the dominant role of surface hydroxylation was revealed and the subsequent gas sensing mechanism under operando conditions has been addressed. (C) 2018 Elsevier B.V. All rights reserved.
486. Defect states and room temperature ferromagnetism in cerium oxide nanopowders prepared by decomposition of Ce-propionate
Authors:
Mihalache, V; Secu, M; Grivel, JC
Published: APR 15 2018, MATERIALS CHEMISTRY AND PHYSICS, 209, 133, DOI: 10.1016/j.matchemphys.2018.01.053
Four batches of cerium oxide powders (with nanocrystallite size of 6.9 nm-572 nm) were prepared from four precursor nanopowders by thermal decomposition of Ce-propionate and annealing in air between 250 degrees C-1200 degrees C for 10 min-240 min. Ceria formation reactions, structure, vibrational, luminescence and magnetic properties were investigated by differential scanning calorimetry, x-ray diffraction, electron microscopy, infrared spectroscopy, photoluminescence and SQUID. All the samples exhibit room temperature ferromagnetism, RTFM, (with coercivity, H-c, of 8 Oe - 121 Oe and saturation magnetization, M-s, of up to 6.7*10(-3) emu/g) and a broad defect-related photoluminescence, PL, emission in the visible range. The samples derived from the same precursor show M-s proportional to the peak area of defect-related PL emission whereas this is not valid for the samples derived from the different precursors. An improvement of ferromagnetism and intensity of defect-related PL emission was observed when annealing the products in which nanocrystalline cerium oxide coexists with Ce - oxicarbonate traces, Ce2O2CO3. The experimental results were explained based on the following considerations: room temperature ferromagnetism was induced by the defective ceria with high concentration of oxygen vacancies generated by decomposition of Ce-propionate; oxygen vacancies of the starting precursor nanopowders could be redistributed (at the surfaces/grain boundaries, GBs) upon heating under conditions that promote an inert local environment; the decomposition of Ce2O2CO3 residues can provide an excess of oxygen vacancies at the nanoparticles surfaces or GBs, which can induce or enhance ferromagnetism; surfaces/GBs rather than bulk defects appear responsible for RTFM - this can explain the (often reported in literature) inconsistency between oxygen vacancies concentration and M-s. (C) 2018 Elsevier B.V. All rights reserved.
487. Probing the dielectric, piezoelectric and magnetic behavior of CoFe2O4/BNT-BT0.08 composite thin film fabricated by sol-gel and spin-coating methods
Authors:
Cernea, M; Vasile, BS; Surdu, VA; Trusca, R; Bartha, C; Craciun, F; Galassi, C
Published: DEC 14 2018, SCIENTIFIC REPORTS, 8, DOI: 10.1038/s41598-018-36232-3
We investigated in this paper a novel bilayer composite obtained by sol-gel and spin coating of the ferroelectric 0.92Na(0.5)Bi(0.5)TiO(3)-0.08BaTiO(3) (abbreviated as BNT-BT0.08) and ferromagnetic CoFe2O4 phases, for miniature low-frequency magnetic sensors and piezoelectric sensors. This heterostructure, deposited on Si-Pt substrate (Si-Pt/CoFe2O4/BNT-BT0.08), was characterized using selected method such as: X-ray diffraction, dielectric spectroscopy, piezoelectric force microscopy, SQUID magnetometry, atomic force microscopy/magnetic force microscopy, and advanced methods of transmission electron microscopy. CoFe2O4/BNT-BT0.08 ferromagnetic-piezoelectric thin films show good magnetization, dielectric constant and piezoelectric response. The results of analyses and measurements reveal that this heterostructure can have applications in high-performance magnetoelectric devices at room temperature.
488. Impact of thickness variation on structural, dielectric and piezoelectric properties of (Ba, Ca) (Ti, Zr)O-3 epitaxial thin films
Authors:
Ion, V; Craciun, F; Scarisoreanu, ND; Moldovan, A; Andrei, A; Birjega, R; Ghica, C; Di Pietrantonio, F; Cannata, D; Benetti, M; Dinescu, M
Published: FEB 1 2018, SCIENTIFIC REPORTS, 8, DOI: 10.1038/s41598-018-20149-y
It is shown that the dielectric and piezoelectric properties of Ba(Ti0.8Zr0.2)O-3-x(Ba0.7Ca0.3)TiO3 (x = 0.45) (BCTZ 45) epitaxial thin films have a nontrivial dependence on film thickness. BCTZ 45 epitaxial films with different thicknesses (up to 400 nm) have been deposited on SrTiO3 by pulsed laser deposition and investigated by different combined techniques: conventional and off-axis X-ray diffraction, high resolution transmission electron microscopy and dielectric and piezoforce microscopy. The changes occurring in epitaxial films when their thickness increases have been attributed to a partial relaxation of misfit strain, driving the induced tetragonal symmetry in very thin films to the original rhombohedral symmetry of the bulk material in the thickest film, which influences directly and indirectly the dielectric and piezoelectric properties.
489. Orbital Ordering of the Mobile and Localized Electrons at Oxygen-Deficient LaAlO3/SrTiO3 If Interfaces
Authors:
Chikina, A; Lechermann, F; Husanu, MA; Caputo, M; Cancellieri, C; Wang, XQ; Schmitt, T; Radovic, M; Strocov, VN
Published: AUG 2018, ACS NANO, 12, 7935, DOI: 10.1021/acsnano.8b02335
Interfacing different transition-metal oxides opens a route to functionalizing their rich interplay of electron, spin, orbital, and lattice degrees of freedom for electronic and spintronic devices. Electronic and magnetic properties of SrTiO3-based interfaces hosting a mobile two-dimensional electron system (2DES) are strongly influenced by oxygen vacancies, which form an electronic dichotomy, where strongly correlated localized electrons in the in-gap states (IGSs) coexist with noncorrelated delocalized 2DES. Here, we use resonant soft-X-ray photoelectron spectroscopy to prove the e(g) character of the IGSs, as opposed to the t(2g) character of the 2DES in the paradigmatic LaAlO3/SrTiO3 interface. We furthermore separate the d(xy) and d(xz)/d(xz) orbital contributions based on deeper consideration of the resonant photoexcitation process in terms of orbital and momentum selectivity. Supported by a self-consistent combination of density functional theory and dynamical mean field theory calculations, this experiment identifies local orbital reconstruction that goes beyond the conventional e(g)-vs-t(2g) band ordering. A hallmark of oxygen-deficient LaAlO3/SrTiO3 is a significant hybridization of the e(g) and t(2g) orbitals. Our findings provide routes for tuning the electronic and magnetic properties of oxide interfaces through "defect engineering" with oxygen vacancies.
490. Electric and magnetic properties of ferromagnetic/piezoelectric bilayered composite
Authors:
Cernea, M; Vasile, BS; Surdu, VA; Trusca, R; Bartha, C; Craciun, F; Galassi, C
Published: OCT 2018, JOURNAL OF MATERIALS SCIENCE, 53, 14171, DOI: 10.1007/s10853-018-2673-x
One of the most promising ways for the realization of multi-functional materials is the integration of oxides with different properties in artificial heterostructures. In this paper, a novel piezoelectric-ferromagnetic heterostructure consisting of 0.92Na(0.5)Bi(0.5)TiO(3)-0.08BaTiO(3) (abbreviated as BNT-BT0.08) and CoFe2O4 layers is fabricated on Si-Pt substrate, by sol-gel method coupled with spin-coating technique. The composite thin film shows only perovskite Bi0.5Na0.5TiO3-like rhombohedral phase and CoFe2O4 cubic phase. The thickness of CoFe2O4 and BNT-BT0.08 layers is similar to 280 and similar to 400 nm, respectively. BNT-BT0.08/CoFe2O4 heterostructure thin film shows a saturation magnetization of 0.11 emu/g at 5 K and 0.07 emu/g at 295 K, dielectric constant of 235 at 1 kHz and tunability of 70% at 1 kHz and an electric field E = 110 kV/cm. The results reveal that the investigated hybrid piezoelectric/ferromagnetic structure shows piezoelectric behavior, good ferroelectric and ferromagnetic properties. This bilayer composite can be used in miniature low-frequency magnetic sensor and piezoelectric sensor for biomedical domain.
491. Lincomycin-embedded PANI-based coatings for biomedical applications
Authors:
Popescu-Pelin, G; Fufa, O; Popescu, RC; Savu, D; Socol, M; Zgura, I; Holban, AM; Vasile, BS; Grumezescu, V; Socol, G
Published: OCT 15 2018, APPLIED SURFACE SCIENCE, 455, 666, DOI: 10.1016/j.apsusc.2018.06.016
We report on the successful laser transfer of biocompatible composite coatings based on polyaniline (PANI) embedded with magnetite (PANI-Fe3O4) and Lincomycin hydrochloride (PANI-Lincomycin) or Lincomycin-functionalized magnetite (PANI-Fe3O4@Lincomycin) by matrix assisted pulsed laser evaporation (MAPLE) technique. The physico-chemical investigations revealed relevant data regarding the stoichiometric deposition, morphology and topography of the as-deposited coatings. Regarding the MAPLE coatings, the FTIR studies evidenced the vibrational bands characteristic to pristine PANI material, while the SEM investigations unveiled a preferential particulate morphology (with aggregates shape and size depending on the deposited material). Additionally, the AFM measurements indicated variations of RMS value, following the Lincomycin and magnetite incorporation. The wettability measurements displayed a hydrophilic behavior of the synthesized coatings, while the electrochemical studies emphasized an enhanced resistance against corrosion in simulated body fluid when compared with bare Ti. Cellular viability, immunofluorescence and SEM results proved that the MAPLE coatings were suitable materials for beneficial adhesion, spreading and proliferation of osteoblast-like cells (MG-63). Moreover, an increased efficiency was evidenced against Staphylococcus aureus biofilm development. The multifunctional properties of the laser processed composite coatings - confirmed by cumulative biocompatible, antimicrobial and anticorrosive behaviors - recommend them as promising solutions for biomedical applications.
492. Wide-Range Columnar and Lamellar Photoluminescent Liquid-Crystalline Lanthanide Complexes with Mesogenic 4-Pyridone Derivatives
Authors:
Chiriac, LF; Pasuk, I; Secu, M; Micutz, M; Circu, V
Published: SEP 12 2018, CHEMISTRY-A EUROPEAN JOURNAL, 24, 13522, DOI: 10.1002/chem.201801781
A series of liquid crystals with various lanthanide ions (Eu-III, Sm-III, and Tb-III) was designed and prepared starting from the corresponding lanthanide nitrates and N-alkylated 4-pyridone derivatives bearing mesogenic 3,4,5-tris(alkyloxy)-benzyl moieties (alkyl=hexyl, octyl, decyl, dodecyl, tetradecyl, or hexadecyl). These new lanthanidomesogens were investigated for their mesogenic properties by a combination of differential scanning calorimetry, polarizing optical microscopy, and temperature-dependent powder X-ray diffraction (XRD). Their thermal stability was assessed by thermogravimetric analysis. All of these complexes show enantiotropic liquid-crystalline behavior with lamellar (SmA) phases in the case of shorter-chain complexes (C-6 and C-8) or hexagonal columnar phases (Col(h)) for complexes with longer alkyl chains (C-12, C-14, and C-16), which were assigned on the basis of their characteristic textures and XRD studies. For complexes with an intermediate number of carbon atoms in the side chains (C-10), both a lamellar phase at lower temperatures and a Col(h) phase at higher temperatures were evidenced. In the solid state, all these complexes show characteristic emissions assigned to the corresponding lanthanide ion. In addition, the luminescence decay curves showed single-exponential decays with characteristic times in the millisecond range (0.75-0.90 ms for Eu-III, 0.045-0.060 ms for Sm-III, and 0.75-1.05 ms for Tb-III).
493. Strain induced magnetism and superexchange interaction in Cr substituted nanocrystalline cobalt ferrite
Authors:
Kumar, L; Kumar, P; Kuncser, V; Greculeasa, S; Sahoo, B; Kar, M
Published: JUN 1 2018, MATERIALS CHEMISTRY AND PHYSICS, 211, 64, DOI: 10.1016/j.matchemphys.2018.02.008
Distribution of magnetic relaxation time using Mossbauer spectroscopy has been observed for CoFe2-xCrxO4 (0.1 <= x <= 0.4) annealed at lower temperature (<= 400 degrees C). The estimated cation distribution over A and B sites observed by Mossbauer spectroscopy is consistent with that obtained by the Rietveld analysis of the X-ray diffraction patterns. Saturation magnetization and magnetocrystalline anisotropy constant increase up to 20% of Cr (x = 0.2) substitution and, decrease with further increase of x. However, the coercive field as well as the Neel temperature decreases with increase in Cr3+ concentration, i.e., a crossover from the hard magnetic to soft magnetic nature by Cr substitution at the Fe site of CoFe2O4 has been observed. This behavior is attributed to the competition between strain induced magnetism and superexchange interaction between cations. (C) 2018 Elsevier B.V. All rights reserved.
494. Synthesis and Characterization of Jellified Composites from Bovine Bone-Derived Hydroxyapatite and Starch as Precursors for Robocasting
Authors:
Miculescu, F; Maidaniuc, A; Miculescu, M; Batalu, ND; Ciocoiu, RC; Voicu, SI; Stan, GE; Thakur, VK
Published: JAN 2018, ACS OMEGA, 3, 1349, DOI: 10.1021/acsomega.7b01855
Hydroxyapatite-starch composites solidify rapidly via jellification, making them suitable candidates for robocasting. However, many aspects related to hydroxyapatite powder characteristics, hydroxyapatite-starch interaction, and composites composition and properties need to be aligned with robocasting requirements to achieve a notable improvement in the functionality of printed scaffolds intended for bone regeneration. This article presents a preliminary evaluation of hydroxyapatite-starch microcomposites. Thermal analysis of the starting powders was performed for predicting composites' behavior during heat-induced densification. Also, morphology, mechanical properties, and hydroxyapatite-starch interaction were evaluated for the jellified composites and the porous bodies obtained after conventional sintering, for different starch additions, and for ceramic particle size distributions. The results indicate that starch could be used for hydroxyapatite consolidation in limited quantities, whereas the composites shall be processed under controlled temperature. Due to a different mechanical behavior induced by particle size and geometry, a wide particle size distribution of hydroxyapatite powder is recommended for further robocasting ink development.
495. Thermal analysis, microstructure and impurity phases evolution in Fe14Cr ferritic steel powders ball-milled in air and under an argon atmosphere
Authors:
Mihalache, V; Mercioniu, I; Aldica, G; Pasuk, I
Published: OCT 2018, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 134, 474, DOI: 10.1007/s10973-018-7274-z
Refined structure of the ferritic phase induced by mechanical milling (under reducing atmosphere) and its thermal stability are required in various applications of nanostructured ferritic alloys. The impurification with nitrogen and oxygen uptaken from the air is very probable during ball-milling, especially at the long-time high-energy milling conditions. As a rule, these interstitial impurities in as-milled powders are in quantities under the sensibility limit of conventional measurement techniques, such as XRD and SEM/ EDS. To evidence the tendency for microstructure modification by impurities introduced during milling, the Fe-14Cr-3W-0.4Ti-0.25Y(2)O(3) (Fe14Cr) ferritic steel powders (re)loaded in air and milled up to 170 h with interruption of the milling process, and heated up to 1373 K were investigated by thermal analysis in correlation with X-ray diffraction and scanning electron microscopy. XRD failed to detect the impurities in powders milled up to 38 h in air although a consistent mass loss related to the degassing of N-2 was registered in thermogravimetric, TG, curves. (Fe,Cr)(4)N, fcc-c, (Fe, Cr)(2)O-3 impurity phases in powders milled over 38 h in air and (Fe,Cr)(2)O-4 formed upon heating were readily detected by XRD. The analysis of these results allowed to better understand the impurification process and to generalise it for any as-milled Fe-Cr-based alloy powder processed in any milling conditions irrespective of the milling atmosphere, duration and thus, of amounts of contaminants. The quality of three powders milled for 170 h in three different conditions was compared: in air, under an argon atmosphere with interruptions of the milling process and under an argon atmosphere without interruption of the milling process. The contamination of powder milled for 170 h under an argon atmosphere without interruption of the milling process is insignificant (corresponding to less than 0.5 mass% mass loss in TG) as compared to powders obtained in the other two milling conditions. New approaches for minimising the contamination from air are suggested.
496. Flux Channeling in YBa2Cu3O7 Superlattices
Authors:
Mollatt, HJS; Dang, VS; Qureishy, T; Mikheenko, P; Crisan, A
Published: 2018, PROCEEDINGS OF THE 2018 IEEE 8TH INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATION & PROPERTIES (NAP-2018), DOI:
We report unusual effect of channeled magnetic flux motion in YBa2Cu3O7-delta/PrBa2Cu3O7-delta superlattices grown by pulsed laser deposition. Magneto-optical imaging reveals that flux moves along a set of parallel and perpendicular lines, while optical microscopy does not show any features on the surface that may be linked to this effect. In contrast, scanning electron microscopy registers sub-micron fractures in the superlattices corresponding to these flux lines, but the magnetic flux channels are much wider than the width of these fractures. To further clarify the origin of flux channels, electrical transport measurements on the superlattices have been performed. Their current-voltage characteristics reveal the presence of distinctive branches related to the flux motion along the selective channels, following which magnetic flux crosses sample in a shortest and least resistive way. The application of very large current overheated the superlattice along these channels, evaporating superconducting material and exposing, wider than in the superconductor, fractures in the substrate. It is concluded that motion of flux in the channels is controlled not only by the presence of nano-fractures in YBa2Cu3O7-delta/PrBa2Cu3O7_delta, but also by stress developed in the superconducting material due to the fracturing of the substrate.
497. Titanium implants' surface functionalization by pulsed laser deposition of TiN, ZrC and ZrN hard films
Authors:
Floroian, L; Craciun, D; Socol, G; Dorcioman, G; Socol, M; Badea, M; Craciun, V
Published: SEP 30 2017, APPLIED SURFACE SCIENCE, 417, 182, DOI: 10.1016/j.apsusc.2017.03.068
Thin films of TiN, ZrC, and ZrN were deposited at room temperature on highly polished Ti and Si samples using the pulsed laser deposition technique. Grazing incidence X-ray diffraction investigations showed that films were nanocrystalline, with grain sizes from 5 to 12 nm and under compression. Simulations of X-ray reflectivity curves acquired from the samples indicated that the deposited layers were dense and smooth. Electrochemical tests performed in simulated body fluid showed that the deposited coatings significantly improved the corrosion resistance of Ti samples. The comparative study found out that the best sample was ZrN/Ti, its corrosion current after 32 days immersion in simulated body fluids being half of that measured for the bare Ti sample and in the same time almost unchanged from the initial value. (C) 2017 Elsevier B.V. All rights reserved.
498. High hexitols selectivity in cellulose hydrolytic hydrogenation over platinum (Pt) vs. ruthenium (Ru) catalysts supported on micro/mesoporous carbon
Authors:
Lazaridis, PA; Karakoulia, SA; Teodorescu, C; Apostol, N; Macovei, D; Panteli, A; Delimitis, A; Coman, SM; Parvulescu, VI; Triantafyllidis, KS
Published: OCT 5 2017, APPLIED CATALYSIS B-ENVIRONMENTAL, 214, 14, DOI: 10.1016/j.apcatb.2017.05.031
The "one-pot" hydrolyltic hydrogenation of cellulose towards C2-C6 sugar alcohols has been recognized as one of the most promising biomass valorization routes for the production of high added-value chemicals. In this work, we studied the performance of Ru and Pt catalysts supported on micro/mesoporous activated carbon, in the hydrolytic hydrogenation of microcrystalline and ball-milled cellulose, in neat water, at 180 C and at relatively low hydrogen pressure of 2 MPa. The impact of metal loading (1-5 wt.%), metal reduction method (H2 at 350 C or NaBH4) and acidification (sulfonation) of the AC support on cellulose conversion and selectivity to the various products were systematically addressed. It was shown that Pt is significantly more selective towards hexitols (sorbitol and mannitol) compared to Ru, in glucose rich reaction media, such as those offered by the easily hydrolyzed ball-milled cellulose. For example, the 5wt%PtIAC-SO3H catalyst afforded hexitols yield of 69.5 wt.% (at 96.1% conversion) compared to 10.9 wt.% (at 95.2% wt.% conversion) obtained by the corresponding Ru catalyst, the latter being also selective towards glycerol and propane-1,2-diol (propylene glycol). A relatively moderate metal loading, such as in 3 wt.%Ru/AC-SO3H, was more favorable for hexitols production (44.5 wt.% yield, at 94.8 wt.% conversion) with Ru catalysts. These results were also verified by glucose hydrogenation experiments that were conducted at the same experimental conditions. Both Pt and Ru exhibited relatively high glucose hydrogenation activity towards hexitols, versus retro-aldol reactions that lead directly to smaller C2-C4 compounds, while the difference in the final product yields between the two metals was attributed to the higher hexitols hydrogenolysis (C C cleavage) reactivity of Ru. HRTEM data showed the formation of metallic crystalline Pt and Ru nanoparticles (<= 4 nm, depending on loading) as well as of amorphous oxygen-rich M(O)(x)(delta+) phases, which were also confirmed by the XPS data. The presence of these phases which may be a source of acidity, as well as the bacisity of the parent AC used in this study, were mainly responsible for inducing isomerization, retro-aldol and dehydration reactions leading eventually to increased glycerol and propylene glycol selectivity, as was observed for both low-metal catalysts, i.e. 1 wt.% Pt or Ru/AC. (C) 2017 Elsevier B.V. All rights reserved.
499. Biocomposite coatings based on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/calcium phosphates obtained by MAPLE for bone tissue engineering
Authors:
Rasoga, O; Sima, L; Chiritoiu, M; Popescu-Pelin, G; Fufa, O; Grumezescu, V; Socol, M; Stanculescu, A; Zgura, I; Socol, G
Published: SEP 30 2017, APPLIED SURFACE SCIENCE, 417, 212, DOI: 10.1016/j.apsusc.2017.01.205
The aim of our research was to synthesize and investigate the physico-chemical and biological features of composite coatings based on poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) and commercial calcium phosphates (CaPs), hydroxyapatite and beta-tricalcium phosphate, obtained by means of matrix assisted pulsed laser evaporation (MAPLE) technique. In this respect, laser fluence and dropcast studies were performed for pristine polymer and PHBV-CaPs composites. The microstructure of the synthesized coatings was investigated by scanning electron microscopy, while for the chemical structure and functional integrity we performed Fourier transform infrared spectroscopy comparative analysis. By using the X-ray diffraction measurements we experimentally evaluated the crystalline nature of the obtained composite materials, while relevant data regarding the hydrophilic/hydrophobic behavior of the synthesized coatings were obtained by performing static CA measurements. The biocompatibility of PHBV/CaPs coatings was evaluated by performing cellular adhesion and differentiation in vitro assays on mesenchymal stem cells. (C) 2017 Elsevier B.V. All rights reserved.
500. Magnetic and magneto-optical properties of Bi and Pb-containing aluminophosphate glass
Authors:
Elisa, M; Iordanescu, R; Vasiliu, C; Sava, BA; Boroica, L; Valeanu, M; Kuncser, V; Galca, AC; Volceanov, A; Eftimie, M; Melinescu, A; Beldiceanu, A
Published: JUN 1 2017, JOURNAL OF NON-CRYSTALLINE SOLIDS, 465, 58, DOI: 10.1016/j.jnoncrysol.2016.11.010
Bi3+, Pb2+ and Bi3+-Pb2+-containing aluminophosphate glasses were obtained by unconventional wet method, the molar formula of the glasses being: i) 58LiPO(3), 29Al(PO3)(3), 10Ba(PO3)(2), 3Bi(2)O(3); ii) 58LiPO(3), 29Al(PO3)(3), 10Ba(PO3)(2), 3PbO and iii) 6LiPO(3), 3Al(PO3)(3), 1Ba(PO3)(2), 10Bi(PO3)(3), 80Pb(PO3)(2). The glass samples were investigated to determine the density, the thermal expansion coefficients and the chemical stability. The magnetic measurements for Bi and Pb-single doped glasses revealed a diamagnetic behavior and those of Bi-Pb-containing glass disclosed a diamagnetic behavior superposed a small paramagnetic contribution, observed in low magnetic fields that can be attributed to the impurities presented in the matrix. The Verdet constant for the analyzed glasses appeared to have positive values proving a diamagnetic behavior of the investigated material. (C) 2016 Published by Elsevier B.V.
501. Synergetic pinning centres in BaZrO3-doped YBa2Cu3O7-x films induced by SrTiO3 nanolayers
Authors:
Crisan, A; Dang, VS; Mikheenko, P; Ionescu, AM; Ivan, I; Miu, L
Published: APR 2017, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 30, DOI: 10.1088/1361-6668/aa5edf
We report on the enhancement of critical current density (J(c)) and the unusual behaviour of its dependence on field orientation in YBa2Cu3O7-x (YBCO) nanostructured films by a combination of substrate decoration with Ag nano-dots, of the incorporation of BaZrO3 (BZO) nano-particles and nano-rods, and of multilayer architecture (a thin SrTiO3 layer separating two 1.5 mu m-thick YBCO layers). SrTiO3 insulating layers were 15, 30 or 45 nm thick. The highest improvement of J(c) in applied magnetic fields along the c-axis and smaller than 1 T occurs in the bi-layer with 30 nm-thick STO, but the influence of STO thickness is small. Our thick nanostructured films show significant improvement of J(c) in the magnetic field along the ab-plane direction. The presence of BZO nano-rods, ab-plane defects and nano particles of BZO and Y2O3 was observed in transmission electron microscopy (TEM) images of the film. The peculiarities of artificial pinning centres revealed in the TEM images of the nanostructured films are used to explain an unusual split of the peak in the J(c) dependence on the magnetic field along the ab-plane of YBCO. Effective pinning potentials in high magnetic fields have rather high values for such thick films.
502. Influence of preparation conditions on structure and photosensing properties of GeSi/TiO2 multilayers
Authors:
Slav, A; Palade, C; Stavarache, I; Teodorescu, VS; Ciurea, ML; Muller, R; Dinescu, A; Sultan, MT; Manolescu, A; Gudmundsson, JT; Svavarsson, HG
Published: 2017, 2017 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 40TH EDITION, 66, DOI:
The photosensing properties related to the structure of GeSi/TiO2 multilayers prepared under different conditions are studied. TiO2 cap/(GeSi/TiO2)(2) multilayers (ML) were deposited by magnetron sputtering (MS) and annealed by rapid thermal annealing. Trilayers of TiO2 cap/GeSi/TiO2 (TL) were also deposited using reactive high power impulse MS (HiPIMS) for TiO2 layers and dc MS for the GeSi layer. For TL samples a two-step annealing was employed, one before and the second after depositing TiO2 cap. Structure and morphology characterization (X-ray diffraction, scanning and transmission electron microscopy) was carried out and photocurrent measurements (voltage dependences, spectral curves) were performed. The annealed ML samples are formed of GeSi NCs with 5 - 10 nm sizes, while in the annealed TL samples, the GeSi NCs are larger (20 - 30 nm). These morphologies determine the multilayers photosensing properties in VIS-NIR of ML structures and in UV in TL ones, respectively.
503. Laser deposition of poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) - lysozyme microspheres based coatings with anti-microbial properties
Authors:
Grumezescu, V; Holban, AM; Sima, LE; Chiritoiu, MB; Chiritoiu, GN; Grumezescu, AM; Ivan, L; Safciuc, F; Antohe, F; Florica, C; Luculescu, CR; Chifiriuc, MC; Socol, G
Published: APR 15 2017, INTERNATIONAL JOURNAL OF PHARMACEUTICS, 521, 195, DOI: 10.1016/j.ijpharm.2017.01.069
The purpose of this study was to obtain, characterize and evaluate the cytotoxicity and antimicrobial activity of coatings based on poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) -Lysozyme (P(3HB3HV)/ Lys) and P(3HB-3HV) -Polyethylene glycol -Lysozyme (P(3HB-3HV)/PEG/Lys) spheres prepared by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique, in order to obtain functional and improved Ti-based implants. Morphological investigation of the coatings by Infrared Microscopy (IRM) and SEM revealed that the average diameter of P(3HB-3HV)/Lys spheres is around 2 mm and unlike the drop cast samples, IRM recorded on MAPLE films revealed a good distribution of monitored functional groups on the entire scanned surface. The biological evaluation of MAPLE structured surfaces revealed an improved biocompatibility with respect to osteoblasts and endothelial cells as compared with Ti substrates and an enhanced anti-biofilm effect against Gram positive (Staphylococcus aureus) and Gram negative (Pseudomonas aeruginosa) tested strains. Thus, we propose that the fabricated P(3HB-3HV)/PEG/Lys and P(3HB-3HV)/Lys microspheres may be efficiently used as a matrix for controlled local drug delivery, with practical applications in developing improved medical surfaces for the reduction of implant-associated infections. (C) 2017 Elsevier B. V. All rights reserved.
504. Nano-engineered pinning centres in YBCO superconducting films
Authors:
Crisan, A; Dang, VS; Mikheenko, P
Published: FEB 15 2017, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 533, 132, DOI: 10.1016/j.physc.2016.06.011
For practical applications of superconducting materials in applied magnetic fields, artificial pinning centres in addition to natural ones are required to oppose the Lorentz force. These pinning centres are actually various types of defects in the superconductor matrix. The pinning centres can be categorised on their dimension (volume, surface or point) and on their character (normal cores or AK cores). Different samples have been produced by Pulsed Laser Deposition, with various thicknesses, temperatures and nanostructured additions to the superconducting matrix. They have been characterized by SQUID Magnetic Properties Measurement System and Physical Properties Measurement System, as well as by Transmission Electron Microscopy (TEM). Correlations between pinning architecture, TEM images, and critical currents at various fields and field orientations will be shown for a large number of YBa2Cu3Ox films with various types and architectures of artificial pinning centres. (C) 2016 Elsevier B.V. All rights reserved.
505. Development and Biocompatibility Evaluation of Photocatalytic TiO2/Reduced Graphene Oxide-Based Nanoparticles Designed for Self-Cleaning Purposes
Authors:
Nica, IC; Stan, MS; Popa, M; Chifiriuc, MC; Pircalabioru, GG; Lazar, V; Dumitrescu, I; Diamandescu, L; Feder, M; Baibarac, M; Cernea, M; Maraloiu, VA; Popescu, T; Dinischiotu, A
Published: SEP 2017, NANOMATERIALS, 7, DOI: 10.3390/nano7090279
Graphene is widely used in nanotechnologies to amplify the photocatalytic activity of TiO2, but the development of TiO2/graphene composites imposes the assessment of their risk to human and environmental health. Therefore, reduced graphene oxide was decorated with two types of TiO2 particles co-doped with 1% iron and nitrogen, one of them being obtained by a simultaneous precipitation of Ti3+ and Fe3+ ions to achieve their uniform distribution, and the other one after a sequential precipitation of these two cations for a higher concentration of iron on the surface. Physico-chemical characterization, photocatalytic efficiency evaluation, antimicrobial analysis and biocompatibility assessment were performed for these TiO2-based composites. The best photocatalytic efficiency was found for the sample with iron atoms localized at the sample surface. A very good anti-inhibitory activity was obtained for both samples against biofilms of Gram-positive and Gram-negative strains. Exposure of human skin and lung fibroblasts to photocatalysts did not significantly affect cell viability, but analysis of oxidative stress showed increased levels of carbonyl groups and advanced oxidation protein products for both cell lines after 48 h of incubation. Our findings are of major importance by providing useful knowledge for future photocatalytic self-cleaning and biomedical applications of graphene-based materials.
506. Single layer of Ge quantum dots in HfO2 for floating gate memory capacitors
Authors:
Lepadatu, AM; Palade, C; Slav, A; Maraloiu, AV; Lazanu, S; Stoica, T; Logofatu, C; Teodorescu, VS; Ciurea, ML
Published: APR 28 2017, NANOTECHNOLOGY, 28, DOI: 10.1088/1361-6528/aa66b7
High performance trilayer memory capacitors with a floating gate of a single layer of Ge quantum dots (QDs) in HfO2 were fabricated using magnetron sputtering followed by rapid thermal annealing (RTA). The layer sequence of the capacitors is gate HfO2/floating gate of single layer of Ge QDs in HfO2/tunnel HfO2/p-Si wafers. Both Ge and HfO2 are nanostructured by RTA at moderate temperatures of 600-700 degrees C. By nanostructuring at 600 degrees C, the formation of a single layer of well separated Ge QDs with diameters of 2-3 nm at a density of 4-5 x 1015 m(-2) is achieved in the floating gate (intermediate layer). The Ge QDs inside the intermediate layer are arranged in a single layer and are separated from each other by HfO2 nanocrystals (NCs) about 8 nm in diameter with a tetragonal/orthorhombic structure. The Ge QDs in the single layer are located at the crossing of the HfO2 NCs boundaries. In the intermediate layer, besides Ge QDs, a part of the Ge atoms is segregated by RTA at the HfO2 NCs boundaries, while another part of the Ge atoms is present inside the HfO2 lattice stabilizing the tetragonal/orthorhombic structure. The fabricated capacitors show a memory window of 3.8. +/-. 0.5 V and a capacitance-time characteristic with 14% capacitance decay in the first 3000-4000 s followed by a very slow capacitance decrease extrapolated to 50% after 10 years. This high performance is mainly due to the floating gate of a single layer of well separated Ge QDs in HfO2, distanced from the Si substrate by the tunnel oxide layer with a precise thickness.
507. Electrochemically shape-controlled transformation of magnetron sputtered platinum films into platinum nanostructures enclosed by high-index facets
Authors:
Khalakhan, I; Lavkova, J; Matolinova, I; Vorokhta, M; Potin, V; Kus, P; Vaclavu, M; Maraloiu, VA; Kuncser, AC; Matolin, V
Published: JAN 15 2017, SURFACE & COATINGS TECHNOLOGY, 309, 11, DOI: 10.1016/j.surfcoat.2016.11.017
A new method based on transformation of magnetron sputtered platinum thin films into platinum nanostructures enclosed by high-index facets, using electrochemical potential cycling in a twin working electrode system is reported. The controllable formation of various Pt nanostructures, described in this paper, indicates that this method can be used to control a selective growth of high purity Pt nanostructures with specific shapes (facets or edges). The method opens up new possibilities for electrochemical preparation of nanostructured Pt catalysts at high yield. (C) 2016 Elsevier B.V. All rights reserved.
508. Optimized silicon reinforcement of carbon coatings by pulsed laser technique for superior functional biomedical surfaces fabrication
Authors:
Mihailescu, IN; Bociaga, D; Popescu-Pelin, G; Stan, GE; Duta, L; Socol, G; Chifiriuc, MC; Bleotu, C; Lazar, V; Husanu, MA; Zgura, I; Miculescu, F; Negut, I; Hapenciuc, C
Published: JUN 1 2017, BIOFABRICATION, 9, DOI: 10.1088/1758-5090/aa7076
We report on the fabrication of silicon-reinforced carbon (C: Si) structures by combinatorial pulsed laser deposition to search for the best design for a new generation of multi-functional coated implants. The synthesized films were characterized from the morphological, structural, compositional, mechanical and microbiological points of view. Scanning electron microscopy revealed the presence, on top of the deposited layers, of spheroid particulates with sizes in the micron range. No microcracks or delaminations were observed. Energy dispersive x-ray spectroscopy and grazing incidence x-ray diffraction pointed to the existence of aC to Si compositional gradient from one end of the film to the other. Raman investigation revealed a relatively high sp(3) hybridization of up to 80% at 40-48 mm a part from the edge with higher Ccontent. Si addition was demonstrated to significantly increase C: Si film bonding to the substrate, with values above the ISO threshold for coatings to be used in high-loading biomedical applications. Surface energy studies pointed to an increase in the hydrophilic character of the deposited structures along with Si content up to 52 m Nm(-1'). In certain cases, the Si-reinforced Ccoatings elicited an antimicrobial biofilm action. The presence of Si was proven to be benign to HEp-2 cells of human origin, without interfering with their cellular cycle. On this basis, reliable C: Si structures with good adherence to the substrate and high efficiency against microbial biofilms can be developed for implant coatings and other advanced medical devices.
509. Magnetite-based glass-ceramics prepared by controlled crystallization of borosilicate glasses: Effect of nucleating agents on magnetic properties and relaxation
Authors:
Sandu, V; Cimpoiasu, E; Greculeasa, S; Kuncser, A; Nicolescu, MS; Kuncser, V
Published: FEB 15 2017, CERAMICS INTERNATIONAL, 43, 3413, DOI: 10.1016/j.ceramint.2016.11.188
The specific magnetic structure and magnetic relaxation phenomena in magnetite nanoentities grown in a glassy matrix by controlled crystallization of Fe-containing borosilicate and boroaluminosilicate glasses in the presence of two types of nucleating agents, Cr2O3 and P2O5, were investigated. The structure, morphology and magnetic properties are strongly influenced by the nucleating agents. Cr2O3 generates magnetite-based glass ceramics with magnetite configurations showing an upward relaxation of magnetization at low and high temperatures but downward at intermediate temperatures. The magnetite grown with P2O5 displays only downward relaxation but with different signs of the temperature derivative of the relaxation rate S in different temperature ranges. The observed effects are discussed with respect to the following factors: i) the existence of a multimodal size distribution of the magnetite (nano)particles as revealed by high resolution electron microscopy; ii) the degree of occupation of different sublattices of the magnetite structure with Fe3+ and Fe2+ ions; and the interplay between the relaxation mechanisms in different temperature ranges.
510. Effect of in-plane ordering on dielectric properties of highly {111}-oriented bismuth-zinc-niobate thin films
Authors:
Le Febvrier, A; Deputier, S; Demange, V; Bouquet, V; Galca, AC; Iuga, A; Pintilie, L; Guilloux-Viry, M
Published: OCT 2017, JOURNAL OF MATERIALS SCIENCE, 52, 11313, DOI: 10.1007/s10853-017-1297-x
Bi1.5-xZn0.92-yNb1.5O6.92-delta (BZN) thin films were grown by pulsed laser deposition on two different Pt-covered substrates, namely textured {111} Pt/TiO2/SiO2/(100) Si substrate (Pt/Si) and epitaxial {111} Pt/R-plane sapphire substrate (Pt/sapphire). In both cases, the BZN films present {111} and {100} out-of-plane orientations, in relative ratios of 65: 35 on Pt/Si and 80: 20 on Pt/sapphire, respectively. The film grown on Pt/Si is textured, while the film deposited on Pt/sapphire presents epitaxial-like relationships with the substrate, for both out-of-plane orientations. Dielectric measurements were taken on both types of thin films, using Pt/BZN/Pt planar capacitor structures. The BZN/Pt/sapphire film presents higher dielectric constant (245 at 100 kHz) and higher tunability (12% at 600 kV/cm) than the BZN/Pt/Si film (200; 6%), while the dielectric losses values are nearly same (similar to 0.05).
511. Combined Electrochemical Impedance Spectroscopy, X-ray Photoelectron Spectroscopy, and Atomic Force Microscopy study of the distinct behavior of L-cysteine-thiolate formed at p- and n-GaAs(100) electrodes in Sodium Dodecyl Sulfate solution
Authors:
Lazarescu, V; Enache, M; Anastasescu, M; Dobrescu, G; Negrila, C; Lazarescu, MF
Published: JAN 20 2017, ELECTROCHIMICA ACTA, 225, 558, DOI: 10.1016/j.electacta.2016.12.156
Electrochemical impedance spectroscopy (EIS), X-ray spectroscopy (XPS), and atomic force microscopy (AFM) have been used to investigate the effects of the sodium dodecyl sulfate (SDS) interaction with the L-cysteine-thiolate covered p- and n-GaAs(100) electrodes in H2SO4 solution. The potential-induced reversible proton transfer found to occur within the L-cysteine-thiolate layer in the simple acid solution during the cathodic as well as the anodic potential scans at the p-doped semiconductor electrode and only in the anodic scan at the n-doped one is suppressed in both cases. XPS data revealed that the anionic surfactant has a complex interaction with the L-cysteine-thiolate covered GaAs(100) electrodes, which implicates both electrostatic and chemical forces. The SO42 head group interacts electrostatically with the NH3+ group of the cysteine-thiolate but it is also chemically involved in a chemisorption bond with the available Ga atoms. The amount of Ga-bound SDS species is much more pronounced at the L-cysteine-thiolate/p-GaAs(100) than at the L-cysteine thiolate/n-doped GaAs(100) electrodes meaning that cysteine-thiolate is mainly formed at As sites in the first case and at Ga sites in the latter one. This outcome strengthens the previous conclusions concerning the role of the dopant in determining the bonding way of the L-cysteine on GaAs(100) surfaces. (C) 2016 Elsevier Ltd. All rights reserved.
512. Significant change of local atomic configurations at surface of reduced activation Eurofer steels induced by hydrogenation treatments
Authors:
Greculeasa, SG; Palade, P; Schinteie, G; Kuncser, A; Stanciu, A; Lungu, GA; Porosnicu, C; Lungu, CP; Kuncser, V
Published: APR 30 2017, APPLIED SURFACE SCIENCE, 402, DOI: 10.1016/j.apsusc.2017.01.056
Reduced-activation steels such as Eurofer alloys are candidates for supporting plasma facing components into kamak-like nuclear fusion reactors. In order to investigate the impact of hydrogen/deuterium insertion in their crystalline lattice, annealing treatments in hydrogen atmosphere have been applied on Eurofer slabs. The resulting samples have been analyzed with respect to local structure and atomic configuration both before and after successive annealing treatments, by X-ray diffractometry (XRD), scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and conversion electron Mossbauer spectroscopy (CEMS). The corroborated data point out for a bcc type structure of the non-hydrogenated alloy, with an average alloy composition approaching Fe0.9Cr0.1 along a depth of about 100 nm. EDS elemental maps do not indicate surface inhomogeneities in concentration whereas the Mossbauer spectra prove significant deviations from a homogeneous alloying. The hydrogenation increases the expulsion of the Cr atoms toward the surface layer and decreases their oxidation, with considerable influence on the surface properties of the steel. The hydrogenation treatment is therefore proposed as a potential alternative for a convenient engineering of the surface of different Fe-Cr based alloys.(C) 2017 Elsevier B.V. All rights reserved.
513. Double band inversion in alpha-Sn: Appearance of topological surface states and the role of orbital composition
Authors:
Rogalev, VA; Rauch, T; Scholz, MR; Reis, F; Dudy, L; Fleszar, A; Husanu, MA; Strocov, VN; Henk, J; Mertig, I; Schafer, J; Claessen, R
Published: APR 27 2017, PHYSICAL REVIEW B, 95, DOI: 10.1103/PhysRevB.95.161117
The electronic structure of alpha-Sn (001) thin films strained compressively in-plane was studied both experimentally and theoretically. A new topological surface state (TSS) located entirely within the gapless projected bulk bands is revealed by ab initio-based tight-binding calculations as well as directly accessed by soft x-ray angle-resolved photoemission. The topological character of this state, which is a surface resonance, is confirmed by unravelling the band inversion and by calculating the topological invariants. In agreement with experiment, electronic structure calculations show the maximum density of states in the subsurface region, while the already established TSS near the Fermi level is strongly localized at the surface. Such varied behavior is explained by the differences in orbital composition between the specific TSS and its associated bulk states, i.e., their hybridization, respectively.
514. Dimensionality-Driven Metal-Insulator Transition in Spin-Orbit-Coupled SrIrO3
Authors:
Schutz, P; Di Sante, D; Dudy, L; Gabel, J; Stubinger, M; Kamp, M; Huang, Y; Capone, M; Husanu, MA; Strocov, VN; Sangiovanni, G; Sing, M; Claessen, R
Published: DEC 22 2017, PHYSICAL REVIEW LETTERS, 119, DOI: 10.1103/PhysRevLett.119.256404
Upon reduction of the film thickness we observe a metal-insulator transition in epitaxially stabilized, spin-orbit-coupled SrIrO3 ultrathin films. By comparison of the experimental electronic dispersions with density functional theory at various levels of complexity we identify the leading microscopic mechanisms, i.e., a dimensionality-induced readjustment of octahedral rotations, magnetism, and electronic correlations. The astonishing resemblance of the band structure in the two-dimensional limit to that of bulk Sr2IrO4 opens new avenues to unconventional superconductivity by "clean" electron doping through electric field gating.
515. Sol-gel preparation and structural investigations of silico-phosphate glasses doped with Fe ions
Authors:
Sava, BAC; Elisa, M; Boroica, L; Kuncser, V; Valeanu, M; Vasiliu, IC; Feraru, I; Iordanescu, R
Published: JAN 2017, JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 81, 302, DOI: 10.1007/s10971-016-4192-z
Different aspects related to the sol-gel preparation and structural investigation of silico-phosphate glasses (SiO2-P2O5 system) doped with Fe ions are reported. During the preparation process, tetraethoxysilane was used as a precursor for SiO2 and phosphoric acid (H3PO4-HP) for P2O5. Ferric chloride was used as precursor for Fe ions, water as reagent for hydrolysis reaction and ethylic alcohol as solvent. The pH of the sols was modified by adding hydrochloric acid and ammonia. It was observed that a slight increase of the solution temperature (up to 40 degrees C) allows a drastic decrease of the gelation time (from days to hours). The structure of the obtained powders dried in air at room temperature and at 100 degrees C for 10 h and subsequently thermally treated at different temperatures was investigated by Fourier transformed infrared (FTIR) and Raman spectroscopy. Vibration modes specific to Si-O-Et, Si-OH, PO-P, P-O-Si, hydrogen bonds and H2O, as well as combined modes have been observed. The local structure and electron configurations of the doping Fe ions have been investigated by Fe-57 Mossbauer spectroscopy.
516. In-gap corner states in core-shell polygonal quantum rings
Authors:
Sitek, A; Tolea, M; Nita, M; Serra, L; Gudmundsson, V; Manolescu, A
Published: JAN 10 2017, SCIENTIFIC REPORTS, 7, DOI: 10.1038/srep40197
We study Coulomb interacting electrons confined in polygonal quantum rings. We focus on the interplay of localization at the polygon corners and Coulomb repulsion. Remarkably, the Coulomb repulsion allows the formation of in-gap states, i.e., corner-localized states of electron pairs or clusters shifted to energies that were forbidden for non-interacting electrons, but below the energies of corner-side-localized states. We specify conditions allowing optical excitation to those states.
517. Synthesis and liquid crystalline properties of novel fluorinated N-benzoyl thiourea compounds. Effect of perfluoroalkyl chains on the thermal behavior and smectic phases stability
Authors:
Ilis, M; Micutz, M; Pasuk, I; Staicu, T; Circu, V
Published: DEC 2017, JOURNAL OF FLUORINE CHEMISTRY, 204, 89, DOI: 10.1016/j.jfluchem.2017.10.008
A series of novel N-benzoyl-N'-aryl thiourea derivatives (BTU) bearing different number of alkoxy groups in terminal positions of benzoyl unit and a perfluorooctyl group on the other side have been designed and prepared. Their liquid crystalline properties were investigated by a combination of three techniques: polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and variable-temperature powder X-ray diffraction (XRD). Their thermal stability was studied by thermogravimetric analysis (TG). It was found that only the compounds which have only one alkoxy chain attached to benzoyl unit, 1a and 1b, show calamitic mesomorphic behavior, with smectic A and C phases being displayed. The type and stability of these mesophases are greatly influenced by the alkyl chain length as well as by the presence of perfluorooctyl group. The clearing and the mesophase ranges are significantly increased with the incorporation of perfluoroalkyl chains when compared to non-fluorinated analogues, with almost 40 degrees C. The attachment of additional alkoxy groups on the benzoyl moiety led to a significant decrease of the clearing points and suppression of the mesogenic character.
518. Photo-sensitive Ge nanocrystal based films controlled by substrate deposition temperature
Authors:
Stavarache, I; Maraloiu, VA; Negrila, C; Prepelita, P; Gruia, I; Iordache, G
Published: OCT 2017, SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 32, DOI: 10.1088/1361-6641/aa8154
Lowering the temperature of crystallization by deposition of thin films on a heated substrate represents the easiest way to find new means to develop and improve new working devices based on nanocrystals embedded in thin films. The improvements are strongly related with the increasing of operation speed, substantially decreasing the energy consumption and reducing unit fabrication costs of the respective semiconductor devices. This approach avoids major problems, such as those related to diffusion or difficulties in controlling nanocrystallites size, which appear during thermal treatments at high temperatures after deposition. This article reports on a significant progress given by structuring Ge nanocrystals (Ge-NCs) embedded in silicon dioxide (SiO2) thin films by heating the substrate at 400 degrees C during co-deposition of Ge and SiO2 by magnetron sputtering. As a proof-of-concept, a Si/Ge-NCs:SiO2 photo-sensitive structure was fabricated thereof and characterized. The structure shows superior performance on broad operation bandwidth from visible to near-infrared, as strong rectification properties in dark, significant current rise in the inversion mode when illuminated, high responsivity, high photo-detectivity of 10(14) Jones, quick response and significant conversion efficiency with peak value reaching 850% at -1 V and about 1000 nm. This simple preparation approach brings an important contribution to the effort of structuring Ge nanocrystallites in SiO2 thin films at a lower temperature for the purpose of using these materials for devices in optoelectronics, solar cells and electronics on flexible substrates.
519. Unpinning of heavy hole spin in magnetic quantum dots
Authors:
Dinu, IV; Moldoveanu, V; Dragomir, R; Tanatar, B
Published: MAY 2017, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 254, DOI: 10.1002/pssb.201600800
Using the k<bold>p theory and configuration interaction method</bold>, we analyze the effect of heavy hole-light hole (HH-LH) mixing in CdTe quantum dots (QDs) with a single manganese (Mn) ion. We find that the hole-Mn exchange switches the coupling between two excitons whose Luttinger spinors have both HH and LH components. If the magnetic dopant is off-centered and the QD is subjected to a single pulse the system periodically bounces between bright and dark mostly HH excitons with opposite HH spins. A pump-and-probe setup allows to estimate the efficiency of this HH spin unpinning from the biexciton response. The biexciton absorption spectrum is also discussed.
520. Exact and approximate analytical solutions of Weiss equation of ferromagnetism and their experimental relevance
Authors:
Barsan, V; Kuncser, V
Published: 2017, PHILOSOPHICAL MAGAZINE LETTERS, 97, 371, DOI: 10.1080/09500839.2017.1366081
The recent progress in the theory of generalised Lambert functions makes possible to solve exactly the Weiss equation of ferromagnetism. However, this solution is quite inconvenient for practical purposes. Precise approximate analytical solutions are obtained, giving the temperature dependence of the spontaneous magnetization, and also the dependence of the magnetization on both temperature and external magnetic field. The experimental relevance of these results, mainly for the determination of the Curie temperature, is discussed.
521. A general perspective on the magnetization reversal in cylindrical soft magnetic nanowires with dominant shape anisotropy
Authors:
Kuncser, A; Antohe, S; Kuncser, V
Published: FEB 1 2017, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 423, 38, DOI: 10.1016/j.jmmm.2016.09.066
Peculiarities of the magnetization reversal process in cylindrical Ni-Cu soft magnetic nanowires with dominant shape anisotropy are analyzed via both static and time dependent micromagnetic simulations. A reversible process involving acoherent-like spin rotation is always observed for magnetic fields applied perpendicularly to the easy axis whereas nucleation of domain walls is introduced for fields applied along the easy axis. Simple criteria for making distinction between a Stoner-Wohlfarth type rotation and a nucleation mechanism in systems with uniaxial magnetic anisotropy are discussed. Superposed reversal mechanisms can be in action for magnetic fields applied at arbitrary angles with respect to the easy axis within the condition of an enough strong axial component required by the nucleation. The dynamics of the domain wall, involving two different stages (nucleation and propagation), is discussed with respect to initial computing conditions and orientations of the magnetic field. A nucleation time of about 3 ns and corkscrew domain walls propagating with a constant velocity of about 150 m/s are obtained in case of Ni-Cu alloy (Ni rich side) NWs with diameters of 40 nm and high aspect ratio.
522. Electronic band structure of the buried SiO2/SiC interface investigated by soft x-ray ARPES
Authors:
Woerle, J; Bisti, F; Husanu, MA; Strocov, VN; Schneider, CW; Sigg, H; Gobrecht, J; Grossner, U; Camarda, M
Published: MAR 27 2017, APPLIED PHYSICS LETTERS, 110, DOI: 10.1063/1.4979102
The electronic structure of the SiO2/SiC (0001) interface, buried below SiO2 layers with a thickness from 2 to 4 nm, was explored using soft X-ray angle-resolved photoemission spectroscopy with photon energies between 350 and 1000 eV. The measurements have detected the characteristic k-dispersive energy bands of bulk Silicon Carbide (SiC) below the SiO2 layer without any sign of additional dispersive states, up to an estimated instrumental sensitivity of approximate to 5 x 10(9) cm 2 eV. This experimental result supports the physical picture that the large density of interface traps observed in macroscopic measurements results from dangling bonds randomized by the SiO2 rather than from Shockley-Tamm surface derived states extending into the bulk SiC. Published by AIP Publishing.
523. Normal and Inverted Hysteresis in Perovskite Solar Cells
Authors:
Nemnes, GA; Besleaga, C; Stancu, V; Dogaru, DE; Leonat, LN; Pintilie, L; Torfason, K; Ilkov, M; Manolescu, A; Pintilie, I
Published: JUN 1 2017, JOURNAL OF PHYSICAL CHEMISTRY C, 121, 11214, DOI: 10.1021/acs.jpcc.7b04248
Hysteretic effects are investigated in perovskite solar cells in the standard FTO/TiO2/CH3NH3PbI3-xClx/spiro-OMeTAD/Au configuration. We report normal (NH) and inverted hysteresis (IH) in the J-V characteristics occurring for the same device structure, and the behavior strictly depends on the prepoling bias. NH typically appears at prepoling biases larger than the open circuit bias, while pronounced IH occurs for negative bias prepoling. The transition from NH to IH is marked by an intermediate mixed hysteresis behavior characterized by a crossing point in the J-V characteristics. The measured J-V characteristics are explained quantitatively by the dynamic electrical model. Furthermore, the influence of the bias scan rate on the NH/IH hysteresis is discussed based on the time evolution of the accumulated ionic and electronic polarization charge at the interfaces. Introducing a three-step measurement protocol, which includes stabilization, prepoling, and measurement, we put forward the difficulties and possible solutions for a correct photoconversion efficiency evaluation.
524. Electric-Field-Driven Direct Desulfurization
Authors:
Borca, B; Michnowicz, T; Petuya, R; Pristl, M; Schendel, V; Pentegov, I; Kraft, U; Klauk, H; Wahl, P; Gutzler, R; Arnau, A; Schlickum, U; Kern, K
Published: MAY 2017, ACS NANO, 11, 4709, DOI: 10.1021/acsnano.7b00612
The ability to elucidate the elementary steps of a chemical reaction at the atomic scale is important for the detailed understanding of the processes involved, which is key to uncover avenues for improved reaction paths. Here, we track the chemical pathway of an irreversible direct desulfurization reaction of tetracenothiophene adsorbed on the Cu(111) closed-packed surface at the submolecular level. Using the precise control of the tip position in a scanning tunneling microscope and the electric field applied across the tunnel junction, the two carbon-sulfur bonds of a thiophene unit are successively cleaved. Comparison of spatially mapped molecular states close to the Fermi level of the metallic substrate acquired at each reaction step with density functional theory calculations reveals the two elementary steps of this reaction mechanism. The first reaction step is activated by an electric field larger than 2 V nm(-1), practically in absence of tunneling electrons, opening the thiophene ring and leading to a transient intermediate. Subsequently, at the same threshold electric field and with simultaneous injection of electrons into the molecule, the exergonic detachment of the sulfur atom is triggered. Thus, a stable molecule with a bifurcated end is obtained, which is covalently bound to the metallic surface. The sulfur atom is expelled from the vicinity of the molecule.
525. Tuning magneto-transport properties of Fe-Au granular thin films by cluster organization
Authors:
Stanciu, AE; Kuncser, A; Schinteie, G; Palade, P; Leca, A; Greculeasa, SG; Catrina, A; Kuncser, V
Published: JUL 12 2017, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 50, DOI: 10.1088/1361-6463/aa7405
A comparative study of morpho-structural, magnetic and magneto-transport properties of two Fe-Au granular films with different concentrations of Fe nanoclusters of almost similar size is reported. Different organizations of the Fe clusters, i.e. in lamellar-like or random-like configuration, were obtained by varying the amount of Fe in the Fe-Au films. The specific magnetic behaviour was investigated with respect to local structure and morpho-structural aspects by combining magneto-optic Kerr effect and superconducting quantum interference device magnetometry, Fe-57 conversion electron Mossbauer spectroscopy and a wide range of electron microscopy techniques. A strong in-plane magnetic texture with uniaxial anisotropy was observed in the case of the lamellar-like organization of the clusters (specific to the Fe-Au film with higher Fe concentration) whereas a superparamagnetic behaviour was evidenced in the case of random distribution of the clusters (specific to the Fe-Au film with lower Fe concentration), despite the similar average size of the clusters in the two samples. Specific magnetoresistance effects were investigated with respect to both the involved magnetic configurations and magnetic interactions of the Fe clusters.
526. Chalcogenide thin films deposited by rfMS technique using a single quaternary target
Authors:
Prepelita, P; Stavarache, I; Negrila, C; Garoi, F; Craciun, V
Published: DEC 1 2017, APPLIED SURFACE SCIENCE, 424, 427, DOI: 10.1016/j.apsusc.2016.11.071
Thin films of chalcogenide, Cu(In, Ga) Se-2 have been obtained using a single quaternary target by radio frequency magnetron sputtering method, with thickness in the range 750 nm to 1200 nm. X-ray photoelectron spectroscopy investigations showed, that the composition of Cu(In, Ga) Se-2 thin films was very similar to that of the used target CuIn0.75Ga0.25Se2. Identification of the chemical composition of Cu(In, Ga) Se-2 thin films by XPS performed in high vacuum, emphasized that the samples exhibit surface features suitable to be integrated into the structure of solar cells. Atomic Force Microscopy and Scanning Electron Microscopy investigations showed that surface morphology was influenced by the increase in thickness of the Cu(In, Ga) Se-2 layer. From X-Ray Diffraction investigations it was found that all films were polycrystalline, having a tetragonal lattice with a preferential orientation along the (112) direction. The optical reflectance as a function of wavelength was measured for the studied samples. The increase in thickness of the Cu(In, Ga) Se-2 absorber determined a decrease of its optical bandgap value from 1.53 eV to 1.44 eV. The results presented in this paper showed an excellent alternative of obtaining Cu(In, Ga) Se-2 compound thin films from a single target. (C) 2016 Elsevier B.V. All rights reserved.
527. Laser processing of Yb3+/Er3+ co-doped LiYF4 thin films with up-conversion properties
Authors:
Secu, CE; Secu, M; Stokker-Cheregi, F; Ion, V; Brajnicov, S; Dinescu, M
Published: MAR 1 2017, THIN SOLID FILMS, 625, 10, DOI: 10.1016/j.tsf.2017.01.057
We present a comparative study between the properties of Yb3+/Er3+ co-doped LiYF4 thin films obtained by pulsed laser deposition (PLD) and matrix-assisted pulsed evaporation (MAPLE) growth techniques, respectively. We performed structural, morphological, and optical analyses in order to draw a conclusion about the potential of MAPLE as a growth technique used for the obtaining of RE-doped fluoride thin films having up-conversion properties. For both techniques the surface morphology is typical for laser processed thin films of RE-doped fluorides, with roughness values of the order of few hundreds of nanometers and a higher density of defects in the sample obtained by MAPLE. Up-conversion properties do not exhibit major differences between the thin film samples and the pressed target. Under 980 nm laser light pumping, both Yb3+/Er3+ co-doped LiYF4 thin film samples, obtained by PLD and MAPLE, show green ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and red (F-4(9/2) -> I-4(15/2)) up-conversion luminescence explained by a two-photon processes. Therefore MAPLE is a viable growth technique for the fundamental study of RE-doped fluoride thin films and their respective functional properties. (C) 2017 Elsevier B.V. All rights reserved.
528. Structural, morphological, ferromagnetic and photoluminescence properties of Fe-doped ZnO, prepared by hydrothermal route
Authors:
Cernea, M; Mihalache, V; Secu, EC; Trusca, R; Bercu, V; Diamandescu, L
Published: APR 2017, SUPERLATTICES AND MICROSTRUCTURES, 104, 373, DOI: 10.1016/j.spmi.2017.02.048
Fe doped ZnO particles of flower-like shape, hexagonal prisms and hybrid structures flower-prisms have been synthesized by hydrothermal technique, and their luminescence and magnetic properties have been investigated as a function of the morphology changes due to iron dopant (0-0.03 at.% Fe3+). The X-ray diffractograms of Zn1-xFexO powders indicated a hexagonal wurtzite polycrystalline structure. SEM images reveal the change of Zn1-xFexO grains shape from flower-like to hexagonal prisms as the Fe concentration (x) increases from 0 to 3 at.% Fe. Undoped ZnO shown weak room temperatures ferromagnetism, with high coercivity (H-c = 107 Oe) and saturation magnetization M-s of 1.5-10(-3) emu/g. ZnO doped with 1 and 3 at.% Fe presented a significant increase of the magnetization in comparison with the undoped ZnO. For ZnO doped with 3 at.% Fe, Ms = 32.5-10(-3) emu/g and M-rem = 0.78-10(-3) emu/g. Compared with other reports on magnetic properties of undoped and Fe doped ZnO, these results indicated higher coercivity and smaller magnetizations. The drop in the intensity of characteristic green-yellow photoluminescence band of ZnO at about 550-600 nm was attributed to the decrease of the number of oxygen vacancies and interstitial oxygen. By increasing the Fe concentration, the electron paramagnetic resonance (EPR) signal of undoped ZnO decreases due to the decrease of defects concentration. (C) 2017 Elsevier Ltd. All rights reserved.
529. Spectroscopic perspective on the interplay between electronic and magnetic properties of magnetically doped topological insulators
Authors:
Krieger, JA; Chang, CZ; Husanu, MA; Sostina, D; Ernst, A; Otrokov, MM; Prokscha, T; Schmitt, T; Suter, A; Vergniory, MG; Chulkov, EV; Moodera, JS; Strocov, VN; Salman, Z
Published: NOV 2 2017, PHYSICAL REVIEW B, 96, DOI: 10.1103/PhysRevB.96.184402
We combine low energy muon spin rotation (LE-mu SR) and soft-x-ray angle-resolved photoemission spectroscopy (SX-ARPES) to study the magnetic and electronic properties of magnetically doped topological insulators, (Bi, Sb)(2)Te-3. We find that one achieves a full magnetic volume fraction in samples of (V/Cr)(x)(Bi, Sb)(2-x)Te-3 at doping levels x greater than or similar to 0.16. The observed magnetic transition is not sharp in temperature indicating a gradual magnetic ordering. We find that the evolution of magnetic ordering is consistent with formation of ferromagnetic islands which increase in number and/or volume with decreasing temperature. Resonant ARPES at the V L-3 edge reveals a nondispersing impurity band close to the Fermi level as well as V weight integrated into the host band structure. Calculations within the coherent potential approximation of the V contribution to the spectral function confirm that this impurity band is caused by V in substitutional sites. The implications of our results on the observation of the quantum anomalous Hall effect at mK temperatures are discussed.
530. Tunable dielectric properties in polyacrylonitrile/multiwall carbon nanotube composites
Authors:
Palade, S; Pantazi, A; Vulpe, S; Berbecaru, C; Tucureanu, V; Oprea, O; Negrea, RF; Dragoman, D
Published: AUG 2017, POLYMER COMPOSITES, 38, 1748, DOI: 10.1002/pc.23744
Composites containing polyacrylonitrile (PAN) and different mass contents of multiwall carbon nanotubes (MWCNTs) were prepared and structurally investigated. X-ray Diffraction of pristine PAN reveals the presence of crystalline and amorphous phases which change their ratio under thermal annealing and addition of MWCNT. For as prepared samples, thermal analysis reveals two glass transition temperatures, which support the hypothesis that unoriented PAN is a two-phase material. Infrared spectrum of as prepared PAN suggests that the polymer is not stabilized. Dielectric investigations of PAN/MWCNT composites show that permittivity has a strong increase as the MWCNT mass content increases, while the dielectric losses are comparable in all samples. These results suggest that PAN/MWCNT composites could find important applications in electronics. POLYM. COMPOS., 38:1741-1748, 2017. (c) 2015 Society of Plastics Engineers
531. Discovery of Lorentz-violating type II Weyl fermions in LaAlGe
Authors:
Xu, SY; Alidoust, N; Chang, GQ; Lu, H; Singh, B; Belopolski, I; Sanchez, DS; Zhang, X; Bian, G; Zheng, H; Husanu, MA; Bian, Y; Huang, SM; Hsu, CH; Chang, TR; Jeng, HT; Bansil, A; Neupert, T; Strocov, VN; Lin, H; Jia, SA; Hasan, MZ
Published: JUN 2017, SCIENCE ADVANCES, 3, DOI: 10.1126/sciadv.1603266
In quantum field theory, Weyl fermions are relativistic particles that travel at the speed of light and strictly obey the celebrated Lorentz symmetry. Their low-energy condensed matter analogs are Weyl semimetals, which are conductors whose electronic excitations mimic the Weyl fermion equation of motion. Although the traditional (type I) emergent Weyl fermions observed in TaAs still approximately respect Lorentz symmetry, recently, the so-called type II Weyl semimetal has been proposed, where the emergent Weyl quasiparticles break the Lorentz symmetry so strongly that they cannot be smoothly connected to Lorentz symmetric Weyl particles. Despite some evidence of nontrivial surface states, the direct observation of the type II bulk Weyl fermions remains elusive. We present the direct observation of the type II Weyl fermions in crystalline solid lanthanum aluminum germanide (LaAlGe) based on our photoemission data alone, without reliance on band structure calculations. Moreover, our systematic data agree with the theoretical calculations, providing further support on our experimental results.
532. Synthesis, physicochemical characterization and cytotoxic properties of riboflavin loaded Myrj52-silver nanoparticles
Authors:
Voicescu, M; Ionescu, S; Craciunescu, O; Tatia, R; Moldovan, L; Teodorescu, VS; Nistor, CL
Published: JUL 7 2017, NEW JOURNAL OF CHEMISTRY, 41, 5541, DOI: 10.1039/c7nj00571g
The synthesis and physicochemical characterization of riboflavin (RF) loaded Myrj52-silver nanoparticles (SNPs) were performed and their cytotoxic properties were evaluated. Transmission electron microscopy analysis showed the formation of colloidal spherical SNPs with an average size of similar to 12 nm. The structure, stability, dynamics and conformation of human serum albumin (HSA) binding RF on SNPs have been studied. The influence of RF on the secondary structure of HSA in the presence of SNPs showed a predominant alpha-helix structure (61.7%). No changes induced by RF binding to HSA were observed. The cytotoxicity of RF and RF-HSA loaded Myrj52-SNPs was evaluated in vitro using the Neutral Red assay and cell morphology observations in a culture of L929 fibroblast cells. The results have relevance with regard to the RF loaded Myrj52-SNP formulation for pharmaceuticals.
533. Progress in Hydroxyapatite-Starch Based Sustainable Biomaterials for Biomedical Bone Substitution Applications
Authors:
Miculescu, F; Maidaniuc, A; Voicu, SI; Thakur, VK; Stan, GE; Ciocan, LT
Published: OCT 2017, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, 5, 8512, DOI: 10.1021/acssuschemeng.7b02314
Hydroxyapatite is a calcium phosphate intensively proposed as a bone substitution material because of its resemblance to the constituents of minerals present in natural bone. Since hydroxyapatite's properties are mainly adequate for nonload bearing applications, different solutions are being tested for improving these properties and upgrading them near the target values of natural bone. On the other hand, starch (a natural and biodegradable polymer) and its blends with other polymers have been proposed as constituents in hydroxyapatite mixtures due to the adhesive, gelling, and swelling abilities of starch particles, useful in preparing well dispersed suspensions and consolidated ceramic bodies. This article presents the perspectives of incorporating starch and starch blends in hydroxyapatite materials. Based on the role of starch within the materials, the review covers its use as (i) a polymeric matrix in hydroxyapatite composites used as adhesives, bone cements, bone waxes, drug-delivery devices or scaffolds and (ii) a sacrificial binder for fabrication of porous hydroxyapatite scaffolds. The suitability of these materials for bone reconstruction has becomes a reachable aim considering the recent advancements in ceramic fabrication and the current possibilities of controlling the processing parameters.
534. Intermediate selectivity in the oxidation of phenols using plasmonic Au/ZnO photocatalysts
Authors:
Lin, F; Cojocaru, BE; Williams, LS; Cadigan, CA; Tian, CX; Grecu, MN; Xin, HL; Vyas, S; Parvulescu, VI; Richards, RM
Published: JUL 21 2017, NANOSCALE, 9, 9364, DOI: 10.1039/c7nr03868b
Tunable reaction selectivity on a single catalyst is a continual goal in chemical syntheses. Herein, we report an unexpected light-directed intermediate selectivity using well-known plasmonic photocatalysts. We observed distinct intermediate selectivity behaviors between using UV and visible light irradiations. Chemical computations and quenching experiments suggest that the radicals generated by the plasmonic excitation govern the light-directed selectivity. The broader impact of this work ranges from selective yield of desirable intermediates for subsequent syntheses without tedious separation procedures, to arousing interest in examining new opportunities for plasmonic photocatalysts.
535. WETTABILITY BY WATER CONTACT ANGLE UPON THE SURFACE OF WOOL FABRICS COVERED WITH OXIDE NANOPARTICLES
Authors:
Birzu, M; Frunza, L; Zgura, I; Cotorobai, VF; Ganea, CP; Preda, N; Enculescu, M
Published: JUL-SEP 2017, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 12, 931, DOI:
Wetting properties of wool textiles were studied either for the raw samples or for those functionalized via covering them at low temperature with nanoparticles of titanium dioxide or zinc oxide. Oxygen plasma pretreatment was performed before deposition. Characterization used optical examination, scanning electron microscopy, infrared spectroscopy, thermogravimetry, X-ray diffraction. Wetting properties were tested under static conditions by estimating the water contact angle. The sessile drop method was applied. The deposited matter represents 3 to 8 wt%, covering rather uniformly the fiber surface. Treated samples show mostly lower values of contact angle than the pristine ones. Cassie-Baxter model is discussed in relation to the equilibrium contact angle of the support.
536. Properties of perovskite ferroelectrics deposited on F doped SnO2 electrodes and the prospect of their integration into perovskite solar cells
Authors:
Pintilie, I; Stancu, V; Tomulescu, A; Radu, R; Stan, CB; Trinca, L; Pintilie, L
Published: DEC 5 2017, MATERIALS & DESIGN, 135, 121, DOI: 10.1016/j.matdes.2017.09.013
The integration of ferroelectrics in perovskite solar cells is proposed as possible way to enhance charge collection efficiency. First results on solar cellmanufactured with PbTiO3 (PTO) instead of TiO2 have shown negligible values for the power conversion efficiency (PCE). This is explained by the high serial resistance of sol-gel deposited PTO on F:SnO2 electrodes (FTO). Although PTO layer has remnant polarization of 22 mu C/cm(2), the high potential barrier (0.25 +/- 0.05 eV) at the FTO/PTO interface and lowcarriermobility (10(-8) cm(2) V-1 s(-1)) compared to TiO2 leads to high serial resistance. Better results were obtained with thinner PTO layers grown by pulsed laser deposition, with PCE values up to 0.6%. Further enhancement was obtained by replacing PTO with BaTiO3 (BTO), with PCE value reaching about 0.8% after poling the cell with +3 V. The most important finding was that the magnitude of the short circuit current increases with the amplitude of the poling voltage while the value of the open-circuit voltage remains about the same, around 0.9 V. This is explained through more efficient collection of the charges generated under illumination in the absorber layer due to the polarization that is present in the ferroelectric film. (C) 2017 Elsevier Ltd. All rights reserved.
537. Bis-imidazolium salts with alkyl sulfates as counterions: synthesis and liquid crystalline properties
Authors:
Ilinca, TA; Pasuk, I; Circu, V
Published: OCT 7 2017, NEW JOURNAL OF CHEMISTRY, 41, 11124, DOI: 10.1039/c7nj02561k
A series of flexibly linked bis-imidazolium salts with alkyl sulfate anions having different chain lengths (10, 12, 14) was designed and prepared starting from 1,1'-(alpha,omega-alkanediyl)-bisimidazole and alkyl bromides (14 or 16 carbon atoms) followed by metathesis with the corresponding sodium salts. These compounds were investigated because of their liquid crystalline properties using a combination of differential scanning calorimetry (DSC), polarized optical microscopy (POM) and temperature dependent powder X-ray diffraction (XRD). All nine bis-imidazolium compounds with alkyl sulfate anions show liquid crystalline properties which were influenced by flexible spacer length, alkyl tail length and, finally, the length of alkyl chains attached to sulfate groups. Broader mesophase ranges were found for compounds with a shorter spacer (six carbon atoms), about 70 degrees C. For compounds with a spacer of ten carbon atoms, higher mesophase ranges and clearing temperatures were found for longer alkyl tails (sixteen carbon atoms). Increasing the length of alkyl chains attached to sulfate anions resulted in higher clearing temperatures for compounds with the longer spacer. The variation in the carbon atom number of the alkyl sulfate anion for bis-imidazolium compounds with the shorter spacer has almost no impact on their SmA phase stability.
538. Magnetic properties of glass-ceramics obtained by crystallization of iron-rich borosilicate glasses
Authors:
Sandu, V; Cimpoiasu, E; Kuncser, A; Nicolescu, MS
Published: SEP 2017, JOURNAL OF ADVANCED CERAMICS, 6, 261, DOI: 10.1007/s40145-017-0236-2
The specific dynamic magnetic response and magnetic relaxation phenomena in magnetite-based glass-ceramics by controlled crystallization of Fe-rich borosilicate glasses with 25 wt% Fe2O3, in the presence of two types of nucleating agents, Cr2O3 and P2O5, were investigated. The magnetic response is complex and shows contributions arising from two subsystems: a system with collective characteristics, superspin-glass like, and another one with single particle characteristics (superparamagnetic) with dipolar interaction. The nucleating agents have strong influence on the characteristic temperatures and anisotropy energy.
539. Insight on thermal behaviour of new complexes of Ni(II), Cu(II) and Zn(II) with a bismacrocyclic ligand developed as biologically active species
Authors:
Badea, M; Bucur, C; Chifiriuc, MC; Bleotu, C; Grecu, MN; Lazar, V; Marinescu, D; Olar, R
Published: JAN 2017, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 127, 497, DOI: 10.1007/s10973-016-5502-y
A multi-component reaction involving metal ion, amines and formaldehyde has been used for a series of decaaza bismacrocyclic complexes M2L(CH3COO)(4)center dot nH(2)O [(1) M: Ni, n = 2.5; (2) M:Cu, n = 1; (3) M:Zn, n = 10; L:1,3-bis(N,N-1,3,6,9,12-pentaazacyclotridecane)-benzene] preparation. Elemental analyses, ESI-MS, IR, UV-Vis-NIR, NMR and EPR spectra, magnetic susceptibility at room temperature, molar conductivities, as well as thermogravimetric analysis, provided data concerning complexes features. The macrocyclic ligand behaves as bischelate, resulting in either a square planar or an octahedral stereochemistry. The in vitro screening of the antimicrobial activity was performed against both reference and clinical isolates multi-drug-resistant strains. The overall antimicrobial potency of complexes was enhanced in comparison with the free ligand, against both planktonic and biofilm-embedded pathogenic strains. Complexes exhibit no cytotoxicity on the HCT 8 tumour cells. Thermogravimetric curves (TG, DTG and DTA) evidenced in air processes as water elimination, acetate into carbonate transformation as well as oxidative degradation of the bismacrocyclic ligand. The powder X-ray diffraction data indicate MO (M: Ni, Cu, Zn) as final product.
540. Easy batch-scale production of cobalt ferrite nanopowders by two-step milling: Structural and magnetic characterization
Authors:
Galizia, P; Cernea, M; Mihalache, V; Diamandescu, L; Maizza, G; Galassi, C
Published: SEP 15 2017, MATERIALS & DESIGN, 130, 335, DOI: 10.1016/j.matdes.2017.05.062
Cobalt ferrite (CF) powder was synthesized by solid state reaction method at two different calcination temperatures (1120 K and 1320 K) then milled in two steps, gradually reducing the milling media size. The first milling step results in CF nanoparticles with crystallite size of 33 nm showing fairly high coercivity (3.7 kOe), > 5 times higher than the non-milled material (0.7 kOe). The high coercivity was correlated to the crystallite size close to the single-domain limit, and to the strain increase up to 2.1%. This value of strain is the highest ever reported in literature for the CF and brings to the highest figure of merit for permanent magnets, (BH)(max)= 2.16 MGOe. After the second milling step the powder displays particle size of 9 nm, release of strain (epsilon = 1.2%), coercivity reduction that approaches 250 Oe and decrease of the deblocking temperature from 421 K to 317 K. The large tunability obtained by multi-step milling allows to use CF in different applications. In particular, the milled CF powder characterized by high microstrain is a good candidate for the realization of rare-earth-free permanent magnets (at least on the basis of the (BH)(max) product). For the first time, a correlation between the spin-canting angle and the degree of inversion, the crystallite size and the microstrain is presented and discussed. [GRAPHICS] .
541. Applications of DNA-Electrochemical Biosensors in Cancer Research
Authors:
Chiorcea-Paquim, AM; Oliveira, SCB; Diculescu, VC; Oliveira-Brett, AM
Published: 2017, PAST, PRESENT AND FUTURE CHALLENGES OF BIOSENSORS AND BIOANALYTICAL TOOLS IN ANALYTICAL CHEMISTRY: A TRIBUTE TO PROFESSOR MARCO MASCINI, 77, 336, DOI: 10.1016/bs.coac.2017.06.003
542. N-Doped graphene as a metal-free catalyst for glucose oxidation to succinic acid
Authors:
Rizescu, C; Podolean, I; Albero, J; Parvulescu, VI; Coman, SM; Bucur, C; Puche, M; Garcia, H
Published: APR 21 2017, GREEN CHEMISTRY, 19, 2005, DOI: 10.1039/c7gc00473g
N-Containing graphenes obtained either by simultaneous amination and reduction of graphene oxide or by pyrolysis of chitosan under an inert atmosphere have been found to act as catalysts for the selective wet oxidation of glucose to succinic acid. Selectivity values over 60% at complete glucose conversion have been achieved by performing the reaction at 160 degrees C and 18 atm O-2 pressure for 20 h. This activity has been attributed to graphenic-type N atoms on graphene. The active N-containing graphene catalysts were used four times without observing a decrease in conversion and selectivity of the process. A mechanism having tartaric and fumaric acids as key intermediates is proposed.
543. Review on peculiar issues of field emission in vacuum nanoelectronic devices
Authors:
Filip, V; Filip, LD; Wong, H
Published: DEC 2017, SOLID-STATE ELECTRONICS, 138, 15, DOI: 10.1016/j.sse.2017.09.010
Some of the modern aspects of field emission based electron sources have been collated in a short and comprehensive review. The usually overlooked peculiar aspects in this research field have been particularly emphasized in order to increase the interest in further fundamental studies and technological applications. The vast material was roughly split in two main branches which occasionally overlap: the electron emission devices based on chemically homogeneous nanostructured surfaces and the more complex nanocomposite emitting surfaces.
544. Characterization of PLD grown WO3 thin films for gas sensing
Authors:
Boyadjiev, SI; Georgieva, V; Stefan, N; Stan, GE; Mihailescu, N; Visan, A; Mihailescu, IN; Besleaga, C; Szilagyi, IM
Published: SEP 30 2017, APPLIED SURFACE SCIENCE, 417, 223, DOI: 10.1016/j.apsusc.2017.03.212
Tungsten trioxide (WO3) thin films were grown by pulsed laser deposition (PLD) with the aim to be applied in gas sensors. The films were studied by atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and profilometry. To study the gas sensing behavior of these WO3 films, they were deposited on quartz resonators and the quartz crystal microbalance (QCM) method was applied to analyze their gas sensitivity. Synthesis of tetragonal-WO3 films starting from a target with predominantly monoclinic WO3 phase was observed. The films deposited at 300 degrees C presented a surface topology favorable for the sorption properties, consisting of a film matrix with protruding craters/cavities. QCM prototype sensors with such films were tested for NO2 sensing. The PLD grown WO3 thin films show good sensitivity and fast reaction at room temperature, even in as-deposited state. With the presented technology, the manufacturing of QCM gas sensors is simple, fast and cost-effective, and it is also suitable for energy-effective portable equipment for on-line monitoring of environmental changes. (C) 2017 Elsevier B.V. All rights reserved.
545. Defect-related light absorption, photoluminiscence and photocatalytic activity of SiO2 with tubular morphology
Authors:
Anastasescu, C; Zaharescu, M; Angelescu, D; Munteanu, C; Bratan, V; Spataru, T; Negrila, C; Spataru, N; Balint, I
Published: JAN 2017, SOLAR ENERGY MATERIALS AND SOLAR CELLS, 159, 335, DOI: 10.1016/j.solmat.2016.09.032
The research describes the synthesis, optical, photocatalytic, electrochemical and photoelectrocatalytical properties of highly defected, low surface area, tubular SiO2. High surface density of light-absorbing defects is obtained by conducting the synthesis at low temperature (0 degrees C) and by optimizing the ratios between reactants. The calcined tubular SiO2 is characterized by intense and broad absorption band centered at approximate to 320 nm, spanning from deep UV to green. The formation of Si3+ surface defects by calcination is accompanied by a substantial intensification of light absorbing characteristics. The annealing leads also to appearance of intense photoluminescence bands centered at around 433 and 533 nm for excitation wavelengths 320-380 nm. The photocatalytic generation of H-2 and CO2 from water-methanol mixture under solar (AM 1.5) and visible (lambda > 390 nm) irradiation is performed to probe the capability of light-absorbing defects of SiO2 to work as active sites and to gather indirect information on nature of active sites. The electrochemical and photoelectrochemical activity of tubular SiO2 are highlighted by employing [Ru(bpy)(3)]Cl-2 complex as electron transfer witness. According to our results, highly defected nanotubular SiO2 exhibit uncommon optical, light harvesting, electronic and electrochemical properties with great potential for practical applications in numerous fields. (C) 2016 Elsevier B.V. All rights reserved.
546. Relationship between ferromagnetism and, structure and morphology in un-doped ZnO and Fe-doped ZnO powders prepared by hydrothermal route
Authors:
Mihalache, V; Cernea, M; Pasuk, I
Published: AUG 2017, CURRENT APPLIED PHYSICS, 17, 1135, DOI: 10.1016/j.cap.2017.03.020
The magnetic properties, in the 5 K-350 K temperature range, were investigated in relationship with the structure and morphology of Zn1-xFexO (x = 0, 0.01, 0.03) powders prepared by hydrothermal route. The magnetization measurements reveal that all powders are ferromagnetic at room temperature, with Curie temperature TT, higher than 350 K. The coercivity Hc takes values between 58 Oe and 107 Oe at 300 K and, between 217 Oe and 613 Oe at 5 K. The weak magnetization of the un-doped ZnO powder is temperature independent and was associated with the high surface to volume ratio of the powder particles (or the number of surface defects). The saturation magnetization M-s, was substantially enhanced (up to a factor of about 20 at 300 K and of about 200 at 5 K) at all temperatures as Fe concentration increased, in spite of reduction of the surface to volume ratio of the powder particles. The Hc vs. Tand FC/ZFC curves for the un-doped ZnO show typical ferromagnetic behavior, whereas for the Fe doped powders exhibit Ruderman-Kittel-Kasuya-Yosida (RKKY) - like and spin-glass-like behavior. The observed magnetic phenomena in Fe doped ZnO can be explained on the basis of "donor defects concentration magnetic cations concentration" phase diagram for dilute magnetic semiconductors. (C) 2017 Elsevier B.V. All rights reserved.
547. Mechanical, Corrosion and Biological Properties of Room-Temperature Sputtered Aluminum Nitride Films with Dissimilar Nanostructure
Authors:
Besleaga, C; Dumitru, V; Trinca, LM; Popa, AC; Negrila, CC; Kolodziejczyk, L; Luculescu, CR; Ionescu, GC; Ripeanu, RG; Vladescu, A; Stan, GE
Published: NOV 2017, NANOMATERIALS, 7, DOI: 10.3390/nano7110394
Aluminum Nitride (AlN) has been long time being regarded as highly interesting material for developing sensing applications (including biosensors and implantable sensors). AlN, due to its appealing electronic properties, is envisaged lately to serve as a multi-functional biosensing platform. Although generally exploited for its intrinsic piezoelectricity, its surface morphology and mechanical performance (elastic modulus, hardness, wear, scratch and tensile resistance to delamination, adherence to the substrate), corrosion resistance and cytocompatibility are also essential features for high performance sustainable biosensor devices. However, information about AlN suitability for such applications is rather scarce or at best scattered and incomplete. Here, we aim to deliver a comprehensive evaluation of the morpho-structural, compositional, mechanical, electrochemical and biological properties of reactive radio-frequency magnetron sputtered AlN nanostructured thin films with various degrees of c-axis texturing, deposited at a low temperature (similar to 50 degrees C) on Si (100) substrates. The inter-conditionality elicited between the base pressure level attained in the reactor chamber and crystalline quality of AlN films is highlighted. The potential suitability of nanostructured AlN (in form of thin films) for the realization of various type of sensors (with emphasis on bio-sensors) is thoroughly probed, thus unveiling its advantages and limitations, as well as suggesting paths to safely exploit the remarkable prospects of this type of materials.
548. Interaction of New-Developed TiO2-Based Photocatalytic Nanoparticles with Pathogenic Microorganisms and Human Dermal and Pulmonary Fibroblasts
Authors:
Nica, IC; Stan, MS; Popa, M; Chifiriuc, MC; Lazar, V; Pircalabioru, GG; Dumitrescu, I; Ignat, M; Feder, M; Tanase, LC; Mercioniu, I; Diamandescu, L; Dinischiotu, A
Published: FEB 2017, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 18, DOI: 10.3390/ijms18020249
TiO2-based photocatalysts were obtained during previous years in order to limit pollution and to ease human daily living conditions due to their special properties. However, obtaining biocompatible photocatalysts is still a key problem, and the mechanism of their toxicity recently received increased attention. Two types of TiO2 nanoparticles co-doped with 1% of iron and nitrogen (TiO2-1% Fe-N) atoms were synthesized in hydrothermal conditions at pH of 8.5 (HT1) and 5.5 (HT2), and their antimicrobial activity and cytotoxic effects exerted on human pulmonary and dermal fibroblasts were assessed. These particles exhibited significant microbicidal and anti-biofilm activity, suggesting their potential application for microbial decontamination of different environments. In addition, our results demonstrated the biocompatibility of TiO2-1% Fe-N nanoparticles at low doses on lung and dermal cells, which may initiate oxidative stress through dose accumulation. Although no significant changes were observed between the two tested photocatalysts, the biological response was cell type specific and time- and dose-dependent; the lung cells proved to be more sensitive to nanoparticle exposure. Taken together, these experimental data provide useful information for future photocatalytic applications in the industrial, food, pharmaceutical, and medical fields.
549. C-N cross-coupling on supported copper catalysts: The effect of the support, oxidation state, base and solvent (vol 341, pg 205, 2016)
Authors:
Tirsoaga, A; Cojocaru, B; Teodorescu, C; Vasiliu, F; Grecu, MN; Ghica, D; Parvulescu, VI; Garcia, H
Published: JAN 2017, JOURNAL OF CATALYSIS, 345, 329, DOI: 10.1016/j.jcat.2016.11.016
550. Effect of Cr2O3 on the magnetic properties of magnetite-based glass-ceramics obtained by controlled crystallization of Fe-containing aluminoborosilicate glass
Authors:
Sandu, V; Greculeasa, S; Kuncser, A; Nicolescu, MS; Kuncser, V
Published: AUG 2017, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 37, 3099, DOI: 10.1016/j.jeurceramsoc.2017.03.055
The phase structure and magnetic properties of magnetite-based glass-ceramics obtained by crystallization of Fe-containing boroaluminosilicate glass melts are presented. The use of Cr2O3 as nucleating agent generated magnetite configurations showing a complex temperature dependence of the relaxation of the remanent magnetization. Specifically, the expected decrease in time of the remanent magnetization occurs only in a limited temperature range, whereas it increases at low and high temperatures (upward relaxation). We tentatively attribute these effects to the complex spin structure of the tiny magnetite nanoparticles, their complex size distribution and the interplay between the relaxation mechanisms in different temperature ranges. (C) 2017 Elsevier Ltd. All rights reserved.
551. Sensors based on mesoporous SnO2-CuWO4 with high selective sensitivity to H2S at low operating temperature
Authors:
Stanoiu, A; Simion, CE; Calderon-Moreno, JM; Osiceanu, P; Florea, M; Teodorescu, VS; Somacescu, S
Published: JUN 5 2017, JOURNAL OF HAZARDOUS MATERIALS, 331, 160, DOI: 10.1016/j.jhazmat.2017.02.038
Development of new sensitive materials by different synthesis routes in order to emphasize the sensing properties for hazardous H2S detection is one of a nowadays challenge in the field of gas sensors. In this study we obtained mesoporous SnO2-CuWO4 with selective sensitivity to H2S by an inexpensive synthesis route with low environmental pollution level, using tripropylamine (TPA) as template and polyvinylpyrrolidone (PVP) as dispersant/stabilizer. In order to bring insights about the intrinsic properties, the powders were characterized by means of a variety of complementary techniques such as: X-Ray Diffraction, XRD; Transmission Electron Microscopy, TEM; High Resolution TEM, HRTEM; Raman Spectroscopy, RS; Porosity Analysis by N-2 adsorption/desorption, BET; Scanning Electron Microscopy, SEM and X-ray Photoelectron Spectroscopy, XPS. The sensors were fabricated by powders deposition via screen printing technique onto planar commercial Al2O3 substrates. The sensor signals towards H2S exposure at low operating temperature (100 degrees C) reaches values from 10(5) (for SnWCu600) to 10(6) (for SnWCu800) over the full range of concentrations (5-30 ppm). The recovery processes were induced by a short temperature trigger of 500 degrees C. The selective sensitivity was underlined with respect to the H2S, relative to other potential pollutants and relative humidity (10-70% RH). (C) 2017 Elsevier B.V. All rights reserved.
552. Lignin Fragmentation onto Multifunctional Fe3O4@Nb2O5@Co@Re Catalysts: The Role of the Composition and Deposition Route of Rhenium
Authors:
Opris, C; Cojocaru, B; Gheorghe, N; Tudorache, M; Coman, SM; Parvulescu, VI; Duraki, B; Krumeich, F; van Bokhoven, JA
Published: MAY 2017, ACS CATALYSIS, 7, 3267, DOI: 10.1021/acscatal.6b02915
Multifunctional Fe3O4@Nb2O5@Co@Re catalysts with metal loadings in the range of 2-7 wt % were prepared via a multistep process. Magnetic nanoparticles prepared by coprecipitation were covered with a niobia shell precipitated from an ammonium niobate oxalate complex in the presence of hexadecyltrimethylammonium bromide. The deposition of cobalt was performed using a deposition/precipitation procedure. Finally, rhenium has been deposited following three different routes: (i) impregnation, (ii) deposition and precipitation of rhenium chloride (ImC and PP, respectively), and (iii) impregnation with ammonium perrhenate (ImA). The characterization of these catalysts was achieved by X-ray diffraction, Raman, H-2 and NH3 temperature-programmed desorption, X-ray photoelectron spectroscopy, and transmission electron microscopy showing the influence of the preparation procedure, reduction, and Re/Co cooperation on the degree of dispersion and reduction. ImC and ImA routes led to more reduced catalysts, and the decrease in cobalt content corresponded to more reduced rhenium. An inverse relation between the acidity and the degree of reduction has been found. The screening of these catalysts in the fragmentation of the lignin confirmed the role of the structural characteristics and solvent. ImC catalysts exhibited better catalytic activity, especially for low metal loadings [2%Co@3%Re, 85% yield of LF, 15.5% yield of LR in tetrahydrofuran (THF), and 14.5% yield of insoluble LR in THF]. Although the extent was smaller, the PP catalysts allowed a more advanced fragmentation of the lignin to fragments with molecular weights between 200 and 400 Da. The catalysts were totally recovered by application of a magnetic field and recycled six times without any loss of activity or selectivity.
553. Photosensitive GeSi/TiO2 multilayers in VIS-NIR
Authors:
Palade, C; Dascalescu, I; Slav, A; Lepadatu, AM; Lazanu, S; Stoica, T; Teodorescu, VS; Ciurea, ML; Comanescu, F; Muller, R; Dinescu, A; Enuica, A
Published: 2017, 2017 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 40TH EDITION, 70, DOI:
The electrical and photosensing properties correlated with structure and morphology of TiO2/(GeSi/TiO2)(2) multilayers are investigated. The multilayers are prepared by magnetron sputtering followed by rapid thermal annealing. Studies of Raman spectroscopy, transmission electron microscopy and X-ray diffraction are carried out. Measurements of dark current versus voltage and temperature are done. The photosensing properties are studied by measuring photocurrent spectra at different temperatures. We obtain multilayers with 10 - 15 nm Ge0.6Si0.4 nanocrystals (NCs) by annealing at 800 degrees C. We evidence the tunneling mechanism between neighbor NCs (T-1/2 law) in the dark current-temperature dependence. The photocurrent spectrum has a maximum with position shifting from 940 to 980 nm when the measurement temperature increases from 150 to 300 K, being due to the GeSi NCs.
554. Studies of vanadium and vanadium oxide based nanocomposite structures
Authors:
Prilepov, V; Gashin, P; Popescu, M; Zalamai, V; Spoiala, D; Ketrush, P; Nasedchina, N
Published: MAY-JUN 2017, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 19, 405, DOI:
The results of the surface morphology studies as well as optical and electrical properties of nano -dimensional vanadium oxide composite structures deposited on various substrates- silica, glass substrates covered by conducting layer of SnO2, pure pyroceramics plates and the same covered by Al(2)O3, SiO2, Ta2O5 layers are presented. According to Raman spectroscopy results the thin film structure obtained on quartz corresponds to the a, -V2O5 orthorhombic phase. In contrast with this the Raman spectra of V2O5 films obtained on pyroceramics substrates, passivated by Al2O3, Ta2O5, SiO2 oxides, do not appear clearly marked narrow lines which indicate their amorphous character. The investigation of the optical properties of the fabricated layers in the spectral range of 200-1000 nm had revealed the presence of both allowed direct and indirect electron transitions. In the frequency range of 10(3)-10(7) Hz the real Z' and imaginary Z '' part of the total impedance of pyroceramics/Al2O3/Al/V2O5/AI structure were studied. The applied direct bias leads to a considerable Z', as well as Z '' decrease. The analysis of the obtained dependencies is carried out by using the method of equivalent circuits.
555. TEMPERATURE INFLUENCE ON THE CAPACITANCE-VOLTAGE HYSTERESIS OF TRANSPARENT a-IGZO/PZT/FTO MFS-HETEROSTRUCTURE
Authors:
Trinca, LM; Besleaga, C; Stancu, V; Radu, R; Iuga, A; Boni, AG; Galca, AC; Pintilie, L
Capacitance-voltage (C-V) hysteresis of metal-ferroelectric-semiconductor (MFS) structure based on a-In2GaZnO5.5 and Pb0.2Zr0.8TiO3 layers are recorded in the 350-470 K range. The structure is grown on FTO/glass to obtain a transparent MFS. The memory functionality of the heterostructure is proved through C-V and P-V characteristics. The memory window is dependent on the temperature, the largest value of 2.5 V being obtained at 470 K, where the contribution of the ferroelectric-semiconductor interface defect states is minimized. The direction of C-V hysteresis is clockwise at 350 K, and it turns counterclockwise at higher temperatures where the ferroelectric polarization has the main contribution.
556. Cyclometalated palladium(II) metallomesogens with Schiff bases and N-benzoyl thiourea derivatives as co-ligands
Authors:
Ilis, M; Batalu, D; Pasuk, I; Circu, V
Published: MAY 2017, JOURNAL OF MOLECULAR LIQUIDS, 233, 51, DOI: 10.1016/j.molliq.2017.02.114
Two series of cyclometalated palladium(II) complexes based on Schiff bases and N-benzoylthiourea (BTU) ligands having four alkoxy groups at their periphery, with different number of carbon atoms, have been designed and prepared. The liquid crystalline behavior of these palladium(II) complexes was investigated by a combination of polarized optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis (TGA). The palladium(II) complexes are thermally stable on a broad temperature range up to 230 degrees C showing, depending on the alkoxy chain length, either monotropic or, for longest alkyl chain, enantiotropic smectic A and C phases. The luminescent properties of palladium(II) complexes were reported. These complexes show a yellow-orange solid-state emission at room temperature with two emission maxima at lambda(max) around 580 and 650 nm, respectively, with a shoulder around 710 nm, when the samples are irradiated in the 330-380 nm range. (C) 2017 Elsevier B.V. All rights reserved.
557. Structure, transition temperature, and magnetoresistance of titanium-doped lanthanum barium manganite epilayers onto STO 001 substrates
Authors:
Galca, AC; Oumezzine, M; Leca, A; Chirila, CF; Kuncser, V; Kuncser, A; Ghica, C; Pasuk, I; Oumezzine, M
Published: OCT 30 2017, APPLIED PHYSICS LETTERS, 111, DOI: 10.1063/1.4998011
We have developed a thin film structure with a maximum magnetoresistance effect (MRE) at room temperature, which is one of the operating requirements for many applications. It is shown that La0.67Ba0.33Ti0.02Mn0.98O3 epilayers obtained by pulsed laser deposition onto (001) SrTiO3 single crystal substrates exhibit the highest MRE, Delta R/R(H) approximate to 150% or Delta R/R(0) approximate to 60% under 5 T, at 300 K, a temperature near to the corresponding Curie temperature (T-C). Both doping with a tiny amount of titanium and induced stress due to lattice mismatch between the thin film and the substrate contribute to a decrease in T-C as compared to the pristine compound and therefore to the decrease in the temperature where the highest MRE is recorded. Published by AIP Publishing.
558. POWDER-IN-TUBE TAPES OF MgB2 IN Fe-SHEATH PROCESSED BY EX-SITU SPARK PLASMA SINTERING
Authors:
Burdusel, M; Ionescu, AM; Grigoroscuta, M; Batalu, D; Enculescu, M; Popa, S; Mihalache, V; Aldica, G; Badica, P
Published: 2017, UNIVERSITY POLITEHNICA OF BUCHAREST SCIENTIFIC BULLETIN SERIES B-CHEMISTRY AND MATERIALS SCIENCE, 79, 172, DOI:
Commercial MgB2 powder was loaded into a Fe-tube, by plastic deformation a tape of similar to 0.5 mm in thickness and 6.9 mm in width was obtained. Short pieces were processed by Spark Plasma Sintering (SPS) at 950, 1050 and 1150 degrees C for 3 min. The optimum sintering temperature is 1050 degrees C. From magnetic/electrical measurements, the onset critical temperature and the irreversibility field at 5 K were 38.7 / 38.9 K and 6.2 / 13.5 T, respectively. The pinning-force-related parameters indicate that the dominant flux pinning mechanism is of point pinning type. Contribution of grain boundary pinning is stronger at lower temperatures.
559. Production of Se-82 enriched Zinc Selenide (ZnSe) crystals for the study of neutrinoless double beta decay
Authors:
Dafinei, I; Nagorny, S; Pirro, S; Cardani, L; Clemenza, M; Ferroni, F; Laubenstein, M; Nisi, S; Pattavina, L; Schaeffner, K; Di Vacri, ML; Boyarintsev, A; Breslavskii, I; Galkin, S; Lalayants, A; Rybalka, I; Zvereva, V; Enculescu, M
Published: OCT 1 2017, JOURNAL OF CRYSTAL GROWTH, 475, 170, DOI: 10.1016/j.jcrysgro.2017.06.013
High purity Zinc Selenide (ZnSe) crystals are produced starting from elemental Zn and Se to be used for the search of the neutrinoless double beta decay (0vDBD) of Se-82. In order to increase the number of emitting nuclides, enriched Se-82 is used. Dedicated production lines for the synthesis and conditioning of the (ZnSe)-Se-82 powder in order to make it suitable for crystal growth were assembled compliant with radiopurity constraints specific to rare event physics experiments. Besides routine check of impurities concentration, high sensitivity measurements are made for radio-isotope concentrations in raw materials, reactants, consumables, ancillaries and intermediary products used for ZnSe crystals production. Indications are given on the crystals perfection and how it is achieved. Since very expensive isotopically enriched material (Se-82) is used, a special attention is given for acquiring the maximum yield in the mass balance of all production stages. Production and certification protocols are presented and resulting ready-to-use (ZnSe)-Se-82 crystals are described. (C) 2017 Elsevier B. V. All rights reserved.
560. A comparative study of the structural, mechanical and tribological characteristics of TiSiC-Cr coatings prepared in CH4 and C2H2 reactive atmosphere by cathodic vacuum arc
Authors:
Braic, M; Vladescu, A; Balaceanu, M; Luculescu, C; Padmanabhan, SC; Constantin, L; Morris, MA; Braic, V; Grigorescu, CEA; Ionescu, P; Dracea, MD; Logofatu, C
Published: APR 1 2017, APPLIED SURFACE SCIENCE, 400, 328, DOI: 10.1016/j.apsusc.2016.12.160
TiSiC-Cr coatings, with Cr and Si as additional elements, were deposited on Si, C 45 and 316 L steel substrates via cathodic arc evaporation. Two series of coatings with thicknesses in the range of 3.6-3.9 mu m were produced, using either CH4 or C2H2 as carbon containing gas. For each series, different coatings were prepared by varying the carbon rich gas flow rate between 90 and 130 sccm, while maintaining constant cathode currents (110 and 100A at TiSi and Cr cathodes, respectively), substrate bias (-200 V) and substrate temperature (similar to 320 degrees C). The coatings were analyzed for their mechanical characteristics (hardness, adhesion) and tribological performance (friction, wear), along with their elemental and phase composition, chemical bonds, crystalline structure and cross-sectional morphology. The coatings were found to be formed with nano-scale composite structures consisting of carbide crystallites (grain size of 3.1-8.2 nm) and amorphous hydrogenated carbon. The experimental results showed significant differences between the two coating series, where the films formed from C2H2 exhibited markedly superior characteristics in terms of microstructure, morphology, hardness, friction behaviour and wear resistance. For the coatings prepared using CH4, the measured values of crystallite size, hardness, friction coefficient and wear rate were in the ranges of 7.2-8.2 nm, 26-30 GPa, 0.3-0.4 and 2.1-4.8 x 10(-6) mm(3) N-1 m(-1), respectively, while for the coatings grown in C2H2, the values of these characteristics were found to be in the ranges of 3.1-3.7 nm, 41-45 GPa, 0.1-0.2 and 1.4-3.0 x 10(-6) mm(3) N-1 m(-1), respectively. Among the investigated coatings, the one produced using C2H2 at the highest flow rate (130 sccm) exhibited the highest hardness (45.1 GPa), the lowest friction coefficient (0.10) and the best wear resistance (wear rate of 1.4 x 10(-6) mm(3) N-1 m(-1)). (C) 2016 Elsevier B.V. All rights reserved.
561. Polypyrrole Actuator Based on Electrospun Microribbons
Authors:
Beregoi, M; Evanghelidis, A; Diculescu, VC; Iovu, H; Enculescu, I
Published: NOV 1 2017, ACS APPLIED MATERIALS & INTERFACES, 9, 38075, DOI: 10.1021/acsami.7b13196
The development of soft actuators by using inexpensive raw materials and straightforward fabrication techniques, aiming at creating and developing muscle like micromanipulators, represents an important challenge nowadays. Providing such devices with biomimetic qualities, for example, sensing different external stimuli, adds even more complexity to the task. We developed electroactive polymer coated microribbons that undergo conformational changes in response to external physical and chemical parameters. These were prepared following three simple steps. During the first step nylon-6/6 microribbons were fabricated by electrospinning. In a second step the microribbons were one side coated with a metallic layer. Finally, a conducting layer of polypyrrole was added by means of electrochemical deposition. Strips of polypyrrole-coated aligned microribbon meshes were tested as actuators responding to current, pH, and temperature. The electrochemical activity of the microstructured actuators was investigated by recording cyclic voltammograms. Chronopontentiograms for specific current, pH, and temperature values were obtained in electrolytes with different compositions. It was shown that, upon variation of the external stimulus, the actuator undergoes conformational changes due to the reduction processes of the polypyrrole layer. The ability of the actuator to hold and release thin wires, and to collect polystyrene microspheres from the bottom of the electrochemical cell, was also investigated.
562. Physical Mechanisms of Exchange Coupling Effects in Nanoparticulate Diluted Magnetic Oxides Obtained by Laser Pyrolysis
Authors:
Kuncser, VE; Schinteie, GA; Kuncser, AC; Leca, A; Scarisoreanu, M; Morjan, I; Filoti, G
Published: APR 27 2017, JOURNAL OF PHYSICAL CHEMISTRY C, 121, 9069, DOI: 10.1021/acs.jpcc.7b01500
TiO2 nanoparticles, undoped and doped with Fe, have been prepared by laser pyrolysis and further investigated with respect to morphological, structural and magnetic aspects by transmission electron microscopy, diffractometry, Mossbauer spectroscopy, and magnetometry. The obtained nanoparticles, consisting of mainly anatase phase, agglomerate in clusters of tenths of units and present a large size distribution in the range from 5 to 40 nm. The anatase to rutile weight ratio (about 9) and the morphology of particles is similar in all analyzed samples (doped by up to 12 0,0 at. % Fe). Only Fe3+ ions in high spin-configuration were observed mainly at the, surface of TiO2 nanoparticles, either distributed or forming fine clusters of Fe oxide.;:Both a paramagnetic phase and a superparamagnetic one with blocking temperature lower than 50 K are superposed over a long-range ferromagnetic phase specific to diluted magnetic oxide systems. The influence of doping Fe ions on the magnetic behavior of each phase is discussed in detail. Evidences for interface exchange couplings (with unidirectional anisotropy in specific conditions) between the long-range ferromagnetic phase and the fine clusters (antiferromagnetic in nature), which become frozen below temperature of 50, K, are provided. The specificity of the processing route and the physical mechanisms responsible observed relevant magnetic features, which can be tailored for suitable applications, are discussed.
563. Oriented Au nanoplatelets on graphene promote Suzuki-Miyaura coupling with higher efficiency and different reactivity pattern than supported palladium
Authors:
Candu, N; Dhakshinamoorthy, A; Apostol, N; Teodorescu, C; Corma, A; Garcia, H; Parvulescu, VI
Published: AUG 2017, JOURNAL OF CATALYSIS, 352, 66, DOI: 10.1016/j.jcat.2017.04.034
Facet 111 oriented Au nanoplatelets (20-40 nm wide, 3-4 nm height) grafted on graphene ((Au) over bar /fl-G) are about three orders of magnitude more efficient than Pd nanoparticles supported on graphene to promote Suzuki-Miyaura coupling. In contrast to Pd catalysis, it is shown here that the product yields in Suzuki-Miyaura coupling catalyzed by Au nanoparticles follow the order chlorobenzene > bromobenzene > iodobenzene. Kinetic studies show that this reactivity order is the result of the poisoning effect of halides for Au that is much higher for I- than Br- and much higher than for Cl-, due to adsorption. This strong iodide adsorption leading to Au catalyst deactivation was predicted by DFT calculations of Au clusters. (Au) over bar /fl-G are about one order of magnitude more efficient than small Au nanoparticles (4-6 nm) obtained by the polyol method supported on graphene. Our results can have impact in organic synthesis, showing the advantage of (Au) over bar /fl-G as catalyst for Suzuki-Miyaura couplings. (C) 2017 Elsevier Inc. All rights reserved.
564. Local Ordering at the Interface of the TiO2-WO3 Bi-Layers
Authors:
Macovei, D; Dascaleanu, V; Teodorescu, CM; Luca, D
Published: 2016, NANOSTRUCTURES AND THIN FILMS FOR MULTIFUNCTIONAL APPLICATIONS: TECHNOLOGY, PROPERTIES AND DEVICES, 331, DOI: 10.1007/978-3-319-30198-3_10
Reducing the recombination rate of photo-generated electron-hole pairs in the surface of pristine TiO2 materials can be done, among others, via local spatial charge separation in the photocatalytically active surface region. A local electric field acting for this purpose can be ensured, for instance, in hetero-junction regions formed at the interface between a TiO2 film and a WO3 ultra-thin layer. The option for the WO3-TiO2 semiconductor pair is related to the suitable fit of their band structures. To model the interface, a more in-depth knowledge of local atomic environment is required. Here, we discuss the local atomic ordering and the related effects in the interface region of TiO2/WO3 and WO3/TiO2 structures grown on Si (100) substrates. Materials characterization was done by using XRD, XPS and XAS techniques. We demonstrate that tungsten atoms enter as W6+ or W4+ cations into the rutile-type TiO2 lattice, by substituting the Ti4+ cations. While W6+-Ti4+ substitution leaves the surrounding rutile matrix unchanged, the W4+-Ti4+ substitution induces a local rutile-to-anatase transition. The current results are relevant in designing new applications structures with enhanced photocatalytic performances.
565. Methanol oxidation at carbon paste electrodes modified with (Pt-Ru)/carbon aerogels nanocomposites
Authors:
Fort, CI; Cotet, LC; Vasiliu, F; Marginean, P; Danciu, V; Popescu, IC
Published: APR 1 2016, MATERIALS CHEMISTRY AND PHYSICS, 172, 188, DOI: 10.1016/j.matchemphys.2016.01.061
Mesoporous carbon aerogels (CAs) impregnated with (Pt-Ru) nanoparticles were prepared, incorporated into carbon paste electrodes (CPEs) and investigated as electrocatalysts for CH3OH electro-oxidation. The sol gel method, followed by supercritical drying with liquid CO2 and thermal pyrolysis in an inert atmosphere, was used to obtain high mesoporous CAs. (Pt-Ru)/CAs nanocomposites with various (Pt-Ru) loading were prepared by using Ru(AcAc)(3) and H2PtCl6 as metal precursors and the impregnation method. The morpho-structural peculiarities of the so prepared (Pt-Ru)/CAs electrocatalysts were examined by using elemental analysis, N2 adsorption -desorption isotherms, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX) and selected area electron diffraction (SAED). Cyclic voltammetry measurements, carried out at (Pt-Ru)/CA-CPEs incorporating nanocomposites with various Pt-Ru loading and different specific surface areas, showed that CA with the highest specific surface area (843 m(2)/g) and impregnated with 6% (w/w) (Pt Ru) nanoparticles exhibit the best CH3OH electro-oxidation efficiency. The Michaelis Menten formalism was used to describe the dependence of the oxidation peak current on the CH3OH concentration, allowing the estimation of the modified electrodes sensitivities. Thus, for (Pt-Ru, 10%)/CA(535)-CPE was observed the highest sensitivity (12.5 +/- 0.8 mA/M) and, at the same time, the highest maximum current density ever reported (153.1 mA/cm(2) for 2 M CH3OH and an applied potential of 600 mV vs. SHE). (C) 2016 Elsevier B.V. All rights reserved.
566. Aggregates of Mn2+ Ions in Mesoporous Self-Assembled Cubic ZnS:Mn Quantum Dots: Composition, Localization, Structure, and Magnetic Properties
Authors:
Nistor, SV; Stefan, M; Nistor, LC; Kuncser, V; Ghica, D; Vlaicu, ID
Published: JUL 7 2016, JOURNAL OF PHYSICAL CHEMISTRY C, 120, 14466, DOI: 10.1021/acs.jpcc.6b04866
The source of collective magnetism in II-VI semiconductor quantum dots (QDs) doped with Mn2+ ions at high nominal impurity levels is still under debate. In the particular case of mesoporous, self-assembled cubic ZnS:Mn QDs, quantitative electron paramagnetic resonance (EPR) studies have shown that the Mn2+ ions incorporated in the core and on the surface of the QDs cannot be responsible for the observed collective magnetism because they remain in a diluted paramagnetic state up to the 50 000 ppm nominal concentration. Here we investigate the composition, localization, structure, and magnetic properties of the aggregates of Mn2+ ions incorporated in the mesoporous cZnS:Mn as a possible source of the observed collective magnetism. Samples of mesoporous cubic ZnS:Mn prepared by coprecipitation at several nominal impurity levels from 200 to 50 000 ppm are investigated by EPR, magnetometry, and analytical high resolution (scanning) transmission electron microscopy. The low temperature magnetic properties of the Mn2+ aggregates change from paramagnetic-like, for samples with nominal impurity levels up to 2000 ppm, to ones specific to larger clusters with distributed antiferromagnetic coupling at higher concentrations, behaving superparamagnetically above a certain temperature. There is also strong evidence that the Mn2+ aggregates responsible for the observed low temperature collective magnetism are incorporated as an amorphous phase of mainly Mn-Zn-O composition, localized in the interstices and pores of the mesoporous structure of the cubic ZnS:Mn QDs.
567. Ultra-High Tunability of Ba(2/3)Sr(1/3) TiO3-Based Capacitors Under Low Electric Fields
Authors:
Ghalem, A; Rammal, M; Huitema, L; Crunteanu, A; Madrangeas, V; Dutheil, P; Dumas-Bouchiat, F; Marchet, P; Champeaux, C; Trupina, L; Nedelcu, L; Banciu, MG
Published: JUL 2016, IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, 26, 506, DOI: 10.1109/LMWC.2016.2576455
We report the high-frequency electrical characterization of Ba2/3Sr1/3 TiO3 (BST) thin films exhibiting a very high dielectric tunability with low losses at 2.45 GHz under very low applied electrical fields. BST layers were integrated in out-of-plane Metal-Insulator-Metal (MIM) devices with optimized Ir/MgO(100) bottom electrodes. The high frequency properties of BST films with thicknesses of 200 nm, 450 nm and 1450 nm were thoroughly investigated in the 100 MHz-10 GHz domain and exhibit extremely high capacitance tuning abilities of 82%, 81% and 70% respectively, under applied voltages as low as 10 V. MIM devices responses show the onset of acoustic resonances associated with the BST electrostrictive behavior under an electric field. By combining high tunability with low resistive losses under low applied voltages, these devices are opening promising avenues for their integration in high-performance tunable devices in the microwave domain and particularly at 2.45 GHz, corresponding to the widely used ISM (industrial, scientific and medical) frequency band.
568. Laser-induced forward transfer of carbon nanowalls for soft electrodes fabrication
Authors:
Constantinescu, C; Vizireanu, S; Ion, V; Aldica, G; Stoica, SD; Lazea-Stoyanova, A; Alloncle, AP; Delaporte, P; Dinescu, G
Published: JUN 30 2016, APPLIED SURFACE SCIENCE, 374, 55, DOI: 10.1016/j.apsusc.2015.09.089
Carbon nanowalls (CNW) are two-dimensional interconnected graphitic nanostructures that have a few mu m in length and height, reaching typical thicknesses of a few tens of nm. We present results on such layers synthesized in a low pressure argon plasma jet, injected with acetylene and hydrogen, on transparent substrates (quartz) heated at 600 degrees C, without catalyst. Thermogravimetric analysis reveals that the CNW are stable up to 420 degrees C in air, and Raman spectroscopy investigations highlight their graphene-like structure. Finally, using a pulsed Nd:YAG laser device (355 nm, 50 ps), we show that 2D-arrays of CNW (pixels and lines) can be printed by laser-induced forward transfer (LIFT), preserving their architecture and structure. Electrical measurements on 1 mu m thick CNW demonstrate typical values in the range of 357.5-358.4 Omega for the samples grown on Au/Cr electrodes, and in the range of 450.1-474.7 Omega for the LIFT printed lines (under positive, negative, and neutral polarization; 1 kHz-5 MHz frequency range; 500 mV and 1 V, respectively). Their morphology is highlighted by means of optical and electronic microscopy. Such structures have potential applications as soft conductive lines, in sensor development and/or embedding purposes. (C) 2015 Elsevier B.V. All rights reserved.
569. Submicrometer Hollow Bioglass Cones Deposited by Radio Frequency Magnetron Sputtering: Formation Mechanism, Properties, and Prospective Biomedical Applications
Authors:
Popa, AC; Stan, GE; Besleaga, C; Ion, L; Maraloiu, VA; Tulyaganov, DU; Ferreira, JMF
Published: FEB 24 2016, ACS APPLIED MATERIALS & INTERFACES, 8, 4367, DOI: 10.1021/acsami.6b00606
This work reports on the unprecedented magnetron sputtering deposition of submicrometric hollow cones of bioactive glass at low temperature in the absence of any template or catalyst. The influence of sputtering conditions on the formation and development of bioglass cones was studied. It was shown that larger populations of well-developed cones could be achieved by increasing the argon sputtering pressure. A mechanism describing the growth of bioglass hollow cones is presented, offering the links for process control and reproducibility of the cone features. The composition, structure, and morphology of the as-synthesized hollow cones were investigated by energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), grazing incidence geometry X-ray diffraction (GIXRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM)-selected area electron diffraction (SAED). The in vitro biological performance, assessed by degradation tests (ISO 10993-14) and cytocompatibility assays (ISO 10993-5) in endothelial cell cultures, was excellent. This allied with resorbability and the unique morphological features make the submicrometer hollow cones interesting candidate material devices for focal transitory permeabilization of the blood brain barrier in the treatment of carcinoma and neurodegenerative disorders.
570. Lignin fragmentation over magnetically recyclable composite Co@Nb2O5@Fe3O4 catalysts
Authors:
Opris, C; Cojocaru, B; Gheorghe, N; Tudorache, M; Coman, SM; Parvulescu, VI; Duraki, B; Krumeich, F; van Bokhoven, JA
Published: JUL 2016, JOURNAL OF CATALYSIS, 339, 227, DOI: 10.1016/j.jcat.2016.04.002
Recoverable catalysts for lignin fragmentation were prepared as Xwt%Co@Nb2O5@Fe3O4 composites having magnetite as an inner core. A shell of niobia covering the magnetic nanoparticles (leading to intermediate Nb2O5@Fe3O4 composite) was deposed from a solution of ammonium niobate (V) oxalate complex by precipitation with NH3. Finally, the deposition of cobalt following the deposition-precipitation method generated the Xwt%Co3O4@Nb2O5@Fe3O4 composites that were reduced with hydrogen to Xwt %Co@Nb2O5@Fe3O4. Catalysts with loading of cobalt in the range X = 1-20 were prepared using this procedure. The different steps of the preparation were followed using various techniques such as surface area measurements, XRD, Raman and NH3-DRIFT spectroscopy, XPS, Mossbauer and TEM. On this basis it was concluded that the synthesized composites exhibit both Lewis and Bronsted acid sites associated with the niobia shell and contain finely dispersed cobalt nanoparticles. The fragmentation of lignin occurred on the constituent parts of this composite, i.e. Fe3O4, Nb2O5, Nb2O5@Fe3O4 but with lower performances. The addition of cobalt (Co@Nb2O5@Fe3O4 catalysts) led to a complete fragmentation of lignin where the dominant fragments were those containing C20-C28 molecules. This catalytic behavior is explained on the capability of niobia to catalyze the acidic hydrolysis of the beta-O-4' bounds and of Co to break the C-C bonds via hydrogenolysis. The optimization of the catalyst composition indicated a loading of 4 wt% as optimal. Working at 180 degrees C and 10 atm H-2 this catalyst allowed a conversion of 53% leading to a mixture containing over 96% in C20-C28 and C29-C37 fragments. The investigated catalysts were completely recyclable as it was showed in six successive cycles. No leaching of the elements included in the composition was determined by ICP-OES. (C) 2016 Elsevier Inc. All rights reserved.
571. Photocatalytic, Antimicrobial and Biocompatibility Features of Cotton Knit Coated with Fe-N-Doped Titanium Dioxide Nanoparticles
Authors:
Stan, MS; Nica, IC; Dinischiotu, A; Varzaru, E; Iordache, OG; Dumitrescu, I; Popa, M; Chifiriuc, MC; Pircalabioru, GG; Lazar, V; Bezirtzoglou, E; Feder, M; Diamandescu, L
Published: SEP 2016, MATERIALS, 9, DOI: 10.3390/ma9090789
Our research was focused on the evaluation of the photocatalytic and antimicrobial properties, as well as biocompatibility of cotton fabrics coated with fresh and reused dispersions of nanoscaled TiO2-1% Fe-N particles prepared by the hydrothermal method and post-annealed at 400 degrees C. The powders were characterized by X-ray diffraction (XRD), Mossbauer spectroscopy and X-ray photoelectron spectroscopy. The textiles coated with doped TiO2 were characterized by scanning electron microscopy and energy dispersive X-ray analyses, and their photocatalytic effect by trichromatic coordinates of the materials stained with methylene blue and coffee and exposed to UV, visible and solar light. The resulting doped TiO2 consists of a mixture of prevailing anatase phase and a small amount (similar to 15%-20%) of brookite, containing Fe3+ and nitrogen. By reusing dispersions of TiO2-1% Fe-N, high amounts of photocatalysts were deposited on the fabrics, and the photocatalytic activity was improved, especially under visible light. The treated fabrics exhibited specific antimicrobial features, which were dependent on their composition, microbial strain and incubation time. The in vitro biocompatibility evaluation on CCD-1070Sk dermal fibroblasts confirmed the absence of cytotoxicity after short-term exposure. These results highlight the potential of TiO2-1% Fe-N nanoparticles for further use in the development of innovative self-cleaning and antimicrobial photocatalytic cotton textiles. However, further studies are required in order to assess the long-term skin exposure effects and the possible particle release due to wearing.
572. CoFe2O4 magnetic ceramic derived from gel and densified by spark plasma sintering
Authors:
Cernea, M; Galizia, P; Ciuchi, I; Aldica, G; Mihalache, V; Diamandescu, L; Galassi, C
Published: JAN 25 2016, JOURNAL OF ALLOYS AND COMPOUNDS, 656, 862, DOI: 10.1016/j.jallcom.2015.09.271
Cobalt ferrite (CoFe2O4) has been successfully synthesized by sol-gel technique. Pellets were prepared by spark plasma sintering technique (SPS) from CoFe2O4 sol-gel derived powder. The rapid sintering of CoFe2O4 pellet by SPS at 950 degrees C, leads to a dense ceramic (97%(rho theoretic)) with average crystallite size of 71 nm. As revealed by X-ray diffraction and Mossbauer measurements, the obtained powder and SPS pellets are spinel ferrite with a cubic symmetry. Complex dielectric investigation performed on CoFe2O4 ceramic reveals multiple relaxation mechanisms while the magnetic measurements indicated a saturation magnetization value of similar to 83 A m(2)/kg at room temperature, which make them useful for applications in microwave domain. (C) 2015 Elsevier B.V. All rights reserved.
573. Characterization of TiNi shape memory alloys obtained by spark plasma sintering process
Authors:
Cirstea, CD; Tolea, F; Leonat, L; Lungu, M; Cucos, A; Cirstea, V; Tsakiris, V
Published: SEP-OCT 2016, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 18, 862, DOI:
This paper presents the research results on the thermal behavior of the 48.5% at Ti-Ni alloys, obtained by spark plasma sintering in vacuum under a pressure of 50 MPa, at temperatures of 850 degrees C and 900 degrees C and holding time of 5 minutes, and subsequently aged in argon for up to 30 minutes at 450 degrees C. Differential scanning calorimetry, dynamic mechanical and dilatometry analysis were used to characterize the transformation properties of the TiNi samples. All the results of differential scanning calorimetry and dynamic mechanical analysis confirmed the hypothesis that the stress-free thermally induced martensitic transformation exists in the investigated TiNi alloys. Annealing at lower temperatures (450 degrees C) in Ni-rich TiNi alloys led to precipitation process which facilitates the formation of the R-phase due to internal stress contributed by precipitates.
574. An adamantane-based COF: stability, adsorption capability, and behaviour as a catalyst and support for Pd and Au for the hydrogenation of nitrostyrene (vol 6, pg 8344, 2016)
Authors:
Trandafir, MM; Pop, L; Hadade, ND; Florea, M; Neatu, F; Teodorescu, CM; Duraki, B; van Bokhoven, JA; Grosu, I; Parvulescu, VI; Garcia, H
Published: 2016, CATALYSIS SCIENCE & TECHNOLOGY, 6, 8573, DOI: 10.1039/c6cy90113a
575. Ferritin surplus in mouse spleen 14 months after intravenous injection of iron oxide nanoparticles at clinical dose
Authors:
Tamion, A; Hillenkamp, M; Hillion, A; Maraloiu, VA; Vlaicu, ID; Stefan, M; Ghica, D; Rositi, H; Chauveau, F; Blanchin, MG; Wiart, M; Dupuis, V
Published: AUG 2016, NANO RESEARCH, 9, 2410, DOI: 10.1007/s12274-016-1126-6
In this study, we followed the biodegradation of ultra-small superparamagnetic iron oxide nanoparticles injected intravenously at clinical doses in mice. An advanced fitting procedure for magnetic susceptibility curves and low-temperature hysteresis loops was used to fully characterize the magnetic size distribution as well as the magnetic anisotropy energy of the injected P904 nanoparticles (Guerbet Laboratory). Additional magnetometry measurements and transmission electronic microscopy observations were systematically performed to examine dehydrated samples from the spleen and liver of healthy C57B16 mice after nanoparticle injection, with sacrifice of the mice for up to 14 months. At 3 months after injection, the magnetic properties of the spleen and liver were dramatically different. While the liver showed no magnetic signals other than those also present in the reference species, the spleen showed an increased magnetic signal attributed to ferritin. This surplus of ferritin remained constant up to 14 months after injection.
576. Be/W and W/Be bilayers deposited on Si substrates with hydrogenated Fe-Cr and Fe-Cr-Al interlayers for plasma facing components
Authors:
Greculeasa, SG; Palade, P; Schinteie, G; Lungu, GA; Porosnicu, C; Jepu, I; Lungu, CP; Kuncser, V
Published: DEC 2016, JOURNAL OF NUCLEAR MATERIALS, 481, DOI: 10.1016/j.jnucmat.2016.09.010
Be/W and W/Be bilayers, of interest in regard to the specific behavior of plasma facing components (PFCs) were deposited on Si substrates by thermionic vacuum arc, with Fe, Fe-Cr and Fe-Cr-Al interlayers. The interlayers, with compositions approaching the one of the reduced activation steels used in supporting PFCs, were subsequently annealed in hydrogen atmosphere. The multilayers were characterized with respect to morphologic, structural, diffusional and atomic intermixing aspects via XRD, XRR, X-ray photoemission spectroscopy and Mossbauer spectroscopy. All as-prepared samples present partially amorphous structures. A main alpha-Fe phase is observed, as well as (superparamagnetic) secondary Fe oxides, metallic Fe with Si, Cr, W and Be neighbors, Be-rich Fe-Be and Fe-Si phases. High amounts of tungsten and tungsten oxides were also evidenced in the Fe layer. The strong atomic intermixing of W and Be layers was indirectly supported by the unusual densities of Wand Be layers and Fe-57 Mossbauer spectroscopy results. (C) 2016 Elsevier B.V. All rights reserved.
577. Hydrogenation of Condensed Aromatic Compounds over Mesoporous Bifunctional Catalysts Following a Diels-Alder Adduct Pathway
Authors:
Huyen, PT; Krivec, M; Kocevar, M; Bucur, IC; Rizescu, C; Parvulescu, VI
Published: MAR 18 2016, CHEMCATCHEM, 8, 1156, DOI: 10.1002/cctc.201501295
Pt(0.5wt%)-Al-SBA-15 and Pt(0.5wt%)-Al-MCM-41 bifunctional catalysts were prepared by wet impregnation and investigated in the hydrogenation of anthracene and the hydrogenolysis/hydrogenation of a series of synthesized Diels-Alder adducts with anthracene and anthracene derivatives. The mesoporous texture of the investigated catalysts allowed the hydrogenation of these substrates to a large extent. In direct correlation with the size of the Pt particles, Pt-Al-SBA-15 exhibited a higher activity. Both catalysts exhibited a strong Lewis acidity associated with the presence of the Al extra-framework species. The acidity of these catalysts afforded the esterification of the reaction byproduct, that is, succinic anhydride, with methanol or ethanol, and the hydrocracking/decyclization of one hydrogenated ring to lead to 1,2,3,4-tetrahydronaphthalene derivatives. A good correlation with the calculated values of the reaction Gibbs free energy has been evidenced.
578. Combined ab initio and XPS Investigations of the Electronic Interactions of L-Cysteine Adsorbed on GaAs(100)
Authors:
Juarez, MF; Toader, AM; Negrila, C; Santos, E; Lazarescu, V
Published: AUG 16 2016, CHEMISTRYSELECT, 1, 3634, DOI: 10.1002/slct.201600589
The adsorption of L-cysteine from ethanol solutions on GaAs(1 0 0) surfaces has been studied by XPS and density-functional theory (DFT). XPS data reveal that the formation of the adsorbate involves preferentially the As-sites for p-GaAs(1 0 0) and the Ga-sites for n-GaAs(1 0 0). The adsorbed species show different orientations of the functional groups to the surface for the different substrates. DFT calculations performed for both Ga-dimers and As-dimers terminated surfaces show that the adsorption is energetically favourable on both substrates. However, the adsorption energy is more negative on top of Ga-atoms. Here an important contribution for the stabilization of the adsorbate is the interaction of the functional groups with the surface. The parallel orientation found for the Ga-bound species by DFT calculations is in good agreement with the shift in the binding energy of the NH2/NH3+ species observed by XPS analysis.
579. Investigations of Ar ion irradiation effects on nanocrystalline SiC thin films
Authors:
Craciun, V; Craciun, D; Socol, G; Behdad, S; Boesl, B; Himcinschi, C; Makino, H; Socol, M; Simeone, D
Published: JUN 30 2016, APPLIED SURFACE SCIENCE, 374, 345, DOI: 10.1016/j.apsusc.2015.12.130
The effects of 800 keV Ar ion irradiation on thin nanocrystalline SiC films grown on (100) Si substrates using the pulsed laser deposition (PLD) technique were investigated. On such PLD grown films, which were very dense, flat and smooth, X-ray reflectivity, glancing incidence X-ray diffraction and nanoindentation investigations were easily performed to evaluate changes induced by irradiation on the density, surface roughness, crystalline structure, and mechanical properties. Results indicated that the SiC films retained their crystalline nature, the cubic phase partially transforming into the hexagonal phase, which had a slightly higher lattice parameter then the as-deposited films. Simulations of X-ray reflectivity curves indicated a 3% decrease of the films density after irradiation. Nanoindentation results showed a significant decrease of the hardness and Young's modulus values with respect to those measured on as-deposited films. Raman and X-ray photoelectron spectroscopy investigations found an increase of the C-C bonds and a corresponding decrease of the Si-C bonds in the irradiated area, which could explain the degradation of mechanical properties. (C) 2015 Elsevier B.V. All rights reserved.
580. Investigation of atmospheric corrosion by photon energy dependent luminescence and Raman spectroscopy in aged and freshly fractured g-,c-As2S3 with photosensitive realgar inclusions
Authors:
Mitsa, V; Holomb, R; Marton, A; Veres, M; Toth, S; Himics, L; Lorinczi, A; Popescu, M
Published: DEC 1 2016, JOURNAL OF NON-CRYSTALLINE SOLIDS, 453, 27, DOI: 10.1016/j.jnoncrysol.2016.09.022
We have studied the light emission properties of aged glassy (g-) and crystalline (c-) As2S3 and freshly fractured glassy As2S3 with photosensitive realgar inclusions in the 1.5-4.5 eV spectral range and applying different excitation photon energies. Additionally, Raman scattering measurements were performed on g-As40S60 to investigate structural changes caused by corrosion of the glass in air. Major features in the luminescence spectra were observed at 1.65,1.87, 2.04, 226, 2.80 and 325 eV photon energies. The 1.65 eV band in photoluminescence spectra of g-As2S3 was identified to be related to the As side by comparison of the photoluminescence spectrum with literature data for As4S4 realgar crystal. A newly observed band at 1.87 eV was assigned to the As side in pararealgar occurring due to the light induced transformation from realgar to pararealgar phase. An oxidation process was found to take place during the aging and photo-aging accompanied with formation of As oxides, indicated by the emission bands at 2.04 and 226 eV. A rapid photo-oxidation process was observed in freshly fractured surfaces at room temperature which was connected with the light stimulated realgar-pararealgar transformation. (C) 2016 Elsevier B.V. All rights reserved.
581. An adamantane-based COF: stability, adsorption capability, and behaviour as a catalyst and support for Pd and Au for the hydrogenation of nitrostyrene
Authors:
Trandafir, MM; Pop, L; Hadade, ND; Florea, M; Neatu, F; Teodorescu, CM; Duraki, B; van Bokhoven, JA; Grosu, I; Parvulescu, VI; Garcia, H
Published: 2016, Catalysis Science & Technology, 6, 8354, DOI: 10.1039/c6cy01631f
A bimodal (micro/mesoporous) COF was synthesized by coupling tetrakis-1,3,5,7-(4'-iodophenyl) adamantane with 4,4'-diethynylbiphenyl following a Sonogashira protocol. The COF preparation strategy led, however, to the incomplete recovery of the palladium catalyst and ICP-OES analysis indicated that around 0.1 wt% palladium remained inside the pores. Noteworthily, the remnant palladium catalyst is still accessible and can be valorised in additional catalytic reactions like the hydrogenation of nitrostyrene. Further deposition of 0.5 wt% active metals (like palladium or gold) enhanced the catalytic activity and tuned the catalyst selectivity with respect to analogous metal catalysts prepared using active carbon as a support. The resulting COF-supported metal NPs are stable and recyclable catalysts. Under normal conditions, this COF is also able to adsorb large amounts of weak electrophilic gases like carbon dioxide.
582. Novel multiferroic (Pb-1 (-) Nd-3x/2(x))(Ti-0.98 (-) yFeyMn0.02)O-3 ceramics with coexisting ferroelectricity and ferromagnetism at ambient temperature
Authors:
Craciun, F; Cernea, M; Fruth, V; Zaharescu, M; Atkinson, I; Stanica, N; Tanase, LC; Diamandescu, L; Iuga, A; Galassi, C
Published: NOV 15 2016, MATERIALS & DESIGN, 110, 704, DOI: 10.1016/j.matdes.2016.08.046
We report the evolution of structural, dielectric, ferroelectric and ferromagnetic properties in novel (Pb1 - 3x/2Ndx) (Ti0.98 - yFeyMn0.02)O-3 perovskite ceramics (x = 0.08, 0 < y < 0.05). We found room-temperature ferroelectric polarization and ferromagnetism for higher amount of iron ions(y >= 0.04). The paraelectric-ferroelectric phase transition occurred between 650 and 670 K for 0 <= y <= 0.05. Ferromagnetic hysteresis was measured at different temperatures on samples with y >= 0.04. Detailed structural analysis evidenced the variation of unit cell parameters with y increasing, confirming the substitution of the iron element in the lattice. Fe-57 Mtissbauer spectroscopy evidenced that iron ions occupy Ti positions in the perovskite lattice, with the oxidation state Fe3+ and two coordination types. X-ray photoelectron spectroscopy confirmed the presence of iron only as Fe3+ and, moreover, evidenced the presence of a substantial amount of Ti3+ ions in the structure. The presence of both Fe3+ (spin 5/2) in different coordinations as well as Ti3+ (spin 1/2) magnetic ions in B-site positions drives the occurrence of magnetic properties from low temperature to above room temperature, through superexchange Fe3+-O-Fe3+, Fe3+-O-Ti3+ and Ti3+-O-Ti3+ interactions. The finding of coexistent ferroelectric and ferromagnetic properties in these compounds ground the route to facile synthesis of multiferroics by simply doping a classical perovskite ferroelectric material like PbTiO3 with an adequate amount of transition magnetic ions. (C) 2016 Elsevier Ltd. All rights reserved.
583. Joining Chemical Pressure and Epitaxial Strain to Yield Y-doped BiFeO3 Thin Films with High Dielectric Response
Authors:
Scarisoreanu, ND; Craciun, F; Birjega, R; Ion, V; Teodorescu, VS; Ghica, C; Negrea, R; Dinescu, M
Published: MAY 9 2016, SCIENTIFIC REPORTS, 6, DOI: 10.1038/srep25535
BiFeO3 is one of the most promising multiferroic materials but undergoes two major drawbacks: low dielectric susceptibility and high dielectric loss. Here we report high in-plane dielectric permittivity (epsilon' similar to 2500) and low dielectric loss (tan delta < 0.01) obtained on Bi0.95Y0.05FeO3 films epitaxially grown on SrTiO3 (001) by pulsed laser deposition. High resolution transmission electron microscopy and geometric phase analysis evidenced nanostripe domains with alternating compressive/tensile strain and slight lattice rotations. Nanoscale mixed phase/domain ensembles are commonly found in different complex materials with giant dielectric/electromechanical (ferroelectric/relaxors) or magnetoresistance (manganites) response. Our work brings insight into the joined role of chemical pressure and epitaxial strain on the appearance of nanoscale stripe structure which creates conditions for easy reorientation and high dielectric response, and could be of more general relevance for the field of materials science where engineered materials with huge response to external stimuli are a highly priced target.
584. Enhancing antimicrobial activity of TiO2/Ti by torularhodin bioinspired surface modification
Authors:
Ungureanu, C; Dumitriu, C; Popescu, S; Enculescu, M; Tofan, V; Popescu, M; Pirvu, C
Published: FEB 2016, BIOELECTROCHEMISTRY, 107, 24, DOI: 10.1016/j.bioelechem.2015.09.001
Implant-associated infections are a major cause of morbidity and mortality. This study was performed using titanium,samples coated by anodization with a titanium dioxide (TiO2) shielded nanotube layer. TiO2/Ti surface was modified by simple immersion in torularhodin solution and by using a mussel-inspired method based on polydopamine as bio adhesive for torularhodin immobilization. SEM analysis revealed tubular microstructures of torularhodin and the PDA ability to function as a catchy anchor between torularhodin and TiO2 surface. Corrosion resistance was associated with TiO2 barrier oxide layer and nano-organized oxide layer and the torularhodin surface modification does not bring significant changes in resistance of the oxide layer. Our results demonstrated that the torularhodin modified TiO2/Ti surface could effectively prevent adhesion and proliferation of Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis, and Pseudomonas aeruginosa. The new modified titanium surface showed good biocompatibility and well-behaved haemocompatibility. This biomaterial with enhanced antimicrobial activity holds great potential for future biomedical applications. (C) 2015 Elsevier B.V. All rights reserved.
585. Multiscale investigation of USPIO nanoparticles in atherosclerotic plaques and their catabolism and storage in vivo
Authors:
Maraloiu, VA; Appaix, F; Broisat, A; Le Guellec, D; Teodorescu, VS; Ghezzi, C; van der Sanden, B; Blanchin, MG
Published: JAN 2016, NANOMEDICINE-NANOTECHNOLOGY BIOLOGY AND MEDICINE, 12, 200, DOI: 10.1016/j.nano.2015.08.005
The storage and catabolism of Ultrasmall SuperParamagnetic Iron Oxide (USPIO) nanoparticles were analyzed through a multiscale approach combining Two Photon Laser Scanning Microscopy (TPLSM) and High-Resolution Transmission Electron Microscopy (HRTEM) at different times after intravenous injection in an atherosclerotic ApoE(-/-) mouse model. The atherosclerotic plaque features and the USPIO heterogeneous biodistribution were revealed down from organ's scale to subcellular level. The biotransformation of the nanoparticle iron oxide (maghemite) core into ferritin, the non-toxic form of iron storage, was demonstrated for the first time ex vivo in atherosclerotic plaques as well as in spleen, the iron storage organ. These results rely on an innovative spatial and structural investigation of USPIO's catabolism in cellular phagolysosomes. This study showed that these nanoparticles were stored as non-toxic iron compounds: maghemite oxide or ferritin, which is promising for MRI detection of atherosclerotic plaques in clinics using these USPIOs. From the Clinical Editor: Advance in nanotechnology has brought new contrast agents for clinical imaging. In this article, the authors investigated the use and biotransformation of Ultrasmall Super-paramagnetic Iron Oxide (USPIO) nanoparticles for analysis of atherosclerotic plagues in Two Photon Laser Scanning Microscopy (TPLSM) and High-Resolution Transmission Electron Microscopy (HRTEM). The biophysical data generated from this study could enable the possible use of these nanoparticles for the benefits of clinical patients. (C) 2015 Elsevier Inc. All rights reserved.
586. AMMONIA SENSING WITH 5 MOL% LANTHANUM DOPED BARIUM STRONTIUM TITANATE UNDER HUMID AIR BACKGROUND
Authors:
Simion, CE; Stanoiu, A; Teodorescu, VS; Rusti, CF; Piticescu, RM; Vasile, E; Vasile, E; Tudor, IA
Nanostructured Ba0.7Sr0.3TiO3 (BST) with 5 molar % of Lanthanum (La) have been synthesized using a high pressure hydrothermal chemical route. The structural and morphological investigations were performed. Termogravimetry/differential scanning calorimetry and Raman investigations have been also employed to analyse the as-prepared material. The gas sensing investigations have indicated the ability of La doped BST to detect ammonia, when operated at room temperature in humid background. The obtained results were discussed with respect to the possible gas-sill-face interaction mechanism. In addition, the said material showed low cross-sensitivity to other possible interfering gases: methane, carbon monoxide, nitrogen dioxide, sulphur dioxide and hydrogen sulphide.
587. Physical Properties of Polycrystalline CuGeO3 Prepared by Field-assisted Sintering Technique
Authors:
Ion, I; Sandu, V; Enculescu, M; Aldica, G; Ionescu, AM
Published: MAR 2016, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 29, 780, DOI: 10.1007/s10948-015-3343-8
The Peierls transition of polycrystalline CuGeO3 samples was investigated by thermal and magnetic investigations. We find that spin disorder induced by chain breaking and grain boundaries has similar effects to doping but without suppressing the spin-Peierls transition temperature or the spin-Peierls gap.
588. Characterization of hydrogenated and deuterated silicon carbide films codeposited by magnetron sputtering
Authors:
Pantelica, D; Ionescu, P; Petrascu, H; Dracea, MD; Statescu, M; Matei, E; Rasoga, O; Stancu, C; Marascu, V; Ion, V; Acsente, T; Dinescu, G
Published: MAR 15 2016, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 371, 326, DOI: 10.1016/j.nimb.2015.10.060
In this work we present the deposition of amorphous SiC thin films by radiofrequency dual magnetron sputtering. The dependence of the deposited films properties over the discharges electrical power and the effect of hydrogenous species (H-2 and/or D-2) addition to main discharge gas (Ar) were investigated. Accurate elemental analysis of the samples, including detection of hydrogen and deuterium, was performed by ion beam analysis (IBA) techniques: RBS (Rutherford Backscattering Spectrometry) and ERDA (Elastic Recoil Detection Analysis). SiCx thin films with thicknesses between 1700 and 4500 angstrom and C/Si ratio between 0.2/1 and 1.25/1 were obtained in different deposition conditions. The results prove that thin films of amorphous SiC with well controlled properties can be produced using radiofrequency dual magnetron sputtering. (C) 2015 Elsevier B.V. All rights reserved.
589. BIOLOGICAL STUDIES ON DEXTRIN COATED IRON OXIDE NANOPARTICLES
Authors:
Iconaru, SL; Turculet, C; Le Coustumer, P; Bleotu, C; Chifiriuc, MC; Lazar, V; Surugiu, A; Badea, M; Iordache, FM; Soare, M; Prodan, AM
Published: 2016, ROMANIAN REPORTS IN PHYSICS, 68, 1544, DOI:
In this study, dextrin coated iron oxide nanoparticles were obtained using an adapted chemical co-precipitation method. The size and morphology of the dextrin coated iron oxide nanoparticles (DIO-NPs) were analyzed by transmission electron microscopy (TEM). The scanning electron microscopy (SEM) analysis depicted information on the morphology of DIO-NPs. The elemental analysis was conducted by Energy-dispersive X-ray spectroscopy (EDAX). The iron oxide particles coated with dextrin have a spherical shape at nanometric scale with a narrow size distribution. The cytotoxicity assay was performed by quantification of HeLa cells viability, while the antimicrobial activities of the DIO-NPs were determined against ATCC reference and clinical microbial strains, i.e. Gram-positive bacteria (Staphylococcus aureus ATCC 6538) and yeast (Candida albicans 393). The obtained nanoparticles did not have cytotoxic effect on HeLa cells after a 24 h exposure to DIO-NPs and the morphology of the cells was not affected. A low toxic effect on HeLa cells was noticed after 48 h. The minimal inhibitory concentration of DIO-NPs was 1 mg/mL for both tested microbial strains.
590. Structural, magnetic and magnetocaloric effects in epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 ferromagnetic thin films grown on 001-oriented SrTiO3 substrates
Authors:
Oumezzine, M; Galca, AC; Pasuk, I; Chirila, CF; Leca, A; Kuncser, V; Tanase, LC; Kuncser, A; Ghica, C; Oumezzine, M
Published: 2016, DALTON TRANSACTIONS, 45, 15040, DOI: 10.1039/c6dt01914e
Epitaxial La0.67Ba0.33Ti0.02Mn0.98O3 (denoted as LBTMO hereafter) thin films of approximately 95 nm thickness were deposited by a pulsed laser deposition technique onto SrTiO3 (STO) (001) substrates. High-resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM) investigations revealed that the films are epilayers with a four-fold symmetry around the [001] direction. Cross-sectional TEM and the presence of Pendellosung fringes in the XRD profiles demonstrate smooth interfaces. The STO substrate induces an in-plane compressive strain, which leads to a slight tetragonality of the film structure. The epilayers exhibit paramagnetic-to-ferromagnetic phase transitions at the Curie temperature T-C (286 K), close to room temperature. The magnetization easy axis lies in the film plane along the [100] direction of the (001) substrate. The magnetic entropy change (Delta S-M) associated with the second-order magnetic phase transition was determined via magnetization measurements in the temperature range between 210 and 350 K under different magnetic fields. The relative cooling power (RCP) of this film is about 220 J kg(-1), somewhat lower than that of bulk Gd (410 J kg(-1)) for a 50 kOe field change, making the LBTMO ferromagnetic thin films a promising candidate for micro/nanomagnetic refrigeration around room temperature. The proposed universal curve provides a simple method for extrapolating Delta S-M in a wide range of fields and temperatures, thus confirming the order of the magnetic transition in this system. The magnetic entropy (Delta S-M)(max) around T-C is proportional to (mu H-0/T-C)(2/3) in agreement with the mean-field theory, indicating the existence of long-range ferromagnetic interactions in epitaxial LBTMO thin films.
591. Columnar bis(pyridinium) ionic liquid crystals derived from 4-hydroxypyridine: synthesis, mesomorphism and emission properties
Authors:
Pana, A; Ilis, M; Staicu, T; Pasuk, I; Circu, V
Published: FEB 19 2016, LIQUID CRYSTALS, 43, 392, DOI: 10.1080/02678292.2015.1116630
A series of flexibly linked bis(pyridinium) salts with various counterions (Br-, PF6-, BF4- and OTf-) was designed and prepared starting from corresponding N-alkylated 4-pyridones precursors with mesogenic 3,4,5-tris(alkyloxy)benzyl moieties (alkyl=dodecyl or tetradecyl). These salts were investigated for their liquid crystalline properties by a combination of differential scanning calorimetry, polarising optical microscopy and temperature-dependent powder X-ray diffraction (XRD). Their thermal stability was checked by thermogravimetric analysis. All bis(pyridinium) salts, except the triflate salt with shorter terminal carbon chain, display an enantiotropic liquid crystalline behaviour with a hexagonal columnar (Col(h)) phase assigned on the basis of its characteristic texture and XRD studies. It was found that these luminescent bis(pyridinium) salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. The emission properties of these bis(pyridinium) salts do not depend significantly on the nature of counterion employed.
592. Thermal analysis of repa-germanium (Ge-132)
Authors:
Batalu, D; Paun, A; Ferbinteanu, M; Aldica, G; Vlaicu, AM; Teodorescu, VS; Badica, P
Published: NOV 20 2016, THERMOCHIMICA ACTA, 644, 27, DOI: 10.1016/j.tca.2016.10.005
Thermal behavior of repa-germanium (C6H10Ge2O7, Ge-132) during heating in air or in argon is investigated using DSC-TGA, XRD, SEM,TEM, and FT-IR measurements. Nine domains of thermal transformations were identified from room temperature to 1200 degrees C, in air or argon. The first reversible transformation is below 220 degrees C and it was assigned to an isomerization process, based on DSC, XRD and IR measurements. The next five transformation domains (220-910 degrees C) are decompositions accompanied by weight loss. The main product of thermal decomposition is Ge. The next transformation domain (910-970 degrees C) corresponds to melting of Ge, both in argon and air. In the air, this step is followed by oxidation of Ge (970-1100 degrees C) and, finally, by melting of GeO2. Amorphous phases formed between 220 and 720 degrees C. Observed processes are discussed based on crystal chemistry and bonds dynamics considerations. (C) 2016 Elsevier B.V. All rights reserved.
593. Ultra-Thin Epitaxial Tungsten Carbide Schottky Contacts in 4H-SiC
Authors:
Knoll, L; Teodorescu, V; Minamisawa, RA
Published: OCT 2016, IEEE ELECTRON DEVICE LETTERS, 37, 1320, DOI: 10.1109/LED.2016.2604488
We demonstrate the fabrication and characterization of epitaxial W2C Schottky contacts into 4H-SiC via sputtering deposition of ultra-thin W followed by thermal annealing. The alloying reaction occurs below 600 degrees C, yielding a stable layer up to 1200 degrees C. The epitaxial layer is hexagonal, unexpectedly forming W2C phase even at the lowest annealing temperature, which is predicted to occur at 1500 degrees C in bulk systems. Schottky contacts based on epitaxial W2C films exhibit smoother interface morphology, higher thermal stability, lower turn-ON voltage and about similar to 50% reduction in Schottky-contact resistance compared with thick Ti Schottky contacts.
594. Effect of P2O5 on the Structural and Magnetic Properties of Magnetite-Based Glass-Ceramics
Authors:
Sandu, V; Greculeasa, S; Kuncser, A; Kuncser, V
Published: DEC 2016, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 99, 4021, DOI: 10.1111/jace.14457
The specific morphology and magnetic properties of magnetite-based glass-ceramics obtained by crystallization of Fe-containing borosilicate glassmelts in the presence of P2O5 as nucleating agent are investigated. We found that the distribution of the tiny nanoparticles of magnetite determines the low temperature response to magnetic field. The observed effects are discussed with respect to the following factors: (1) the existence of a multimodal size distribution of the tiny grains as revealed by Mossbauer spectroscopy, magnetometry, and high-resolution electron microscopy; (2) the existence of a disordered layer at the grain surface which is driven by field in a magnetically ordered state; and (3) the interplay between the relaxation mechanisms in different temperature ranges.
595. POLYESTER FABRICS COVERED WITH AMORPHOUS TITANIUM DIOXIDE LAYERS: COMBINING WETTABILITY MEASUREMENTS AND PHOTOINDUCED HYDROPHILICITY TO ASSESS THEIR SURFACE PROPERTIES
Authors:
Zgura, I; Frunza, S; Frunza, L; Enculescu, M; Florica, C; Cotorobai, VF; Ganea, CP
Wettability properties of thin TiO2 amorphous layers obtained by sputtering or sol-gel onto polyester textile materials were investigated. Contact angle (CA) measurements by the sessile drop method were used to evaluate these properties. Comparison was performed with coated samples of related poly(lactic acid) material. The samples coated by sol gel have CAs a few degrees higher than those coated by sputtering. Wetting properties were conversely changed under alternate darkness/illumination conditions. Photoinduced hydrophilicity was observed even for these amorphous coating particles, being higher for sputtered samples than for sol gel ones.
596. Oxidation of 5-hydroxymethyl furfural to 2,5-diformylfuran in aqueous media over heterogeneous manganese based catalysts
Authors:
Neatu, F; Petrea, N; Petre, R; Somoghi, V; Florea, M; Parvulescu, VI
Published: DEC 1 2016, , DOI: 10.1016/j.cattod.2016.03.031
597. Wicking behavior of fabrics described by simultaneous acquiring the images of the wet region and monitoring the liquid weight
Authors:
Cotorobai, VF; Zgura, I; Birzu, M; Frunza, S; Frunza, L
Published: MAY 20 2016, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 497, 153, DOI: 10.1016/j.colsurfa.2016.02.040
An experimental study on the radial spreading of the liquid from a virtually infinite reservoir onto a horizontal fabric sample was performed using a simple setup which is presented in two variants: One variant (the simplest) collects the images of the wet spot during the radial outward wicking and the other variant collects the images simultaneously with the monitoring of the weight decrease of the liquid reservoir. We notice that recording with a webcam gives advantages in the subsequent data processing. Afterward, the resulting image series were processed with routines developed in LabVIEW to determine the area of the wet spot. The programs are better adapted to the inhomogeneous and anisotropic structure specific to textiles than the existent edge-finding algorithms. The time dependence of the wet area provides information about the wicking kinetics and further, by modeling the data, to the possible mechanism. The experiments were performed using solutions of red (rhodamin 6B) or blue (brilliant blue E133) dyes in linen and polyester samples differing besides the chemical structure in the roughness of their surfaces as well. The data allow an easy comparison between the textile behavior. Determination of the mass loss of the test liquid might be useful especially for the colored fabrics. The infinite reservoir case is compared with that of the finite reservoir. (C) 2016 Elsevier B.V. All rights reserved.
598. Synthesis of Terephthalic Acid by p-Cymene Oxidation using Oxygen: Toward a More Sustainable Production of Bio-Polyethylene Terephthalate
Authors:
Neatu, F; Culica, G; Florea, M; Parvulescu, VI; Cavani, F
Published: NOV 9 2016, , DOI: 10.1002/cssc.201600718
599. Microwave dielectric properties of BNT-BT0.08 thin films prepared by sol-gel technique
Authors:
Huitema, L; Cernea, M; Crunteanu, A; Trupina, L; Nedelcu, L; Banciu, MG; Ghalem, A; Rammal, M; Madrangeas, V; Passerieux, D; Dutheil, P; Dumas-Bouchiat, F; Marchet, P; Champeaux, C
Published: APR 14 2016, JOURNAL OF APPLIED PHYSICS, 119, DOI: 10.1063/1.4945822
We report for the first time the microwave characterization of 0.92(Bi0.5Na0.5)TiO(3-)0.08BaTiO(3) (BNT-BT0.08) ferroelectric thin films fabricated by the sol-gel method and integrated in both planar and out-of-plane tunable capacitors for agile high-frequency applications and particularly on the WiFi frequency band from 2.4 GHz to 2.49 GHz. The permittivity and loss tangent of the realized BNT-BT0.08 layers have been first measured by a resonant cavity method working at 12.5 GHz. Then, we integrated the ferroelectric material in planar inter-digitated capacitors (IDC) and in out-of-plane metal-insulator-metal (MIM) devices and investigated their specific properties (dielectric tunability and losses) on the whole 100 MHz-15 GHz frequency domain. The 3D finite-elements electromagnetic simulations of the IDC capacitances are fitting very well with their measured responses and confirm the dielectric properties determined with the cavity method. While IDCs are not exhibiting an optimal tunability, the MIM capacitor devices with optimized Ir/MgO(100) bottom electrodes demonstrate a high dielectric tunability, of 30% at 2.45 GHz under applied voltages as low as 10 V, and it is reaching 50% under 20V voltage bias at the same frequency. These high-frequency properties of the MIM devices integrating the BNT-BT0.08 films, combining a high tunability under low applied voltages indicate a wide integration potential for tunable devices in the microwave domain and particularly at 2.45 GHz, corresponding to the widely used industrial, scientific, and medical frequency band. (C) 2016 AIP Publishing LLC.
600. Defect induced tunable near infrared emission of Er-CeO2 by heterovalent co-dopants
Authors:
Florea, M; Avram, D; Cojocaru, B; Tiseanu, I; Parvulescu, V; Tiseanu, C
Published: JUL 21 2016, , DOI: 10.1039/c6cp02754g
601. Graphene from Alginate Pyrolysis as a Metal-Free Catalyst for Hydrogenation of Nitro Compounds
Authors:
Trandafir, MM; Florea, M; Neatu, F; Primo, A; Parvulescu, VI; Garcia, H
Published: JUL 7 2016, , DOI: 10.1002/cssc.201600197
602. Gamma irradiation effects on the properties of indium zinc oxide thin films
Authors:
Craciun, D; Socol, G; Le Caer, S; Trinca, LM; Galca, AC; Pantelica, D; Ionescu, P; Craciun, V
Published: SEP 1 2016, THIN SOLID FILMS, 614, 6, DOI: 10.1016/j.tsf.2016.04.041
Thin films of amorphous and polycrystalline indium zinc oxide (IZO) having various In/(In + Zn) nominal compositions from 0.3 to 0.9 were grown by the pulsed laser deposition technique at room temperature or at 400 degrees C on oxidized Si and quartz substrates. After deposition, the films were gamma irradiated at doses of 10, 20 and 30 kGy under Ar atmosphere. Grazing incidence X-ray diffraction investigations could not find measurable changes of the structure after irradiation. Simulations of the X-ray reflectivity (XRR) and diffuse scattering curves acquired from the films showed a small density decrease after irradiation, accompanied by an increase of the thickness and surface roughness. Spectroscopic ellipsometry investigations confirmed the increase of the IZO films' thickness after irradiation, being in agreement with the XRR results. Small changes in the refractive index, most probably caused by changes in the film density were also observed. Four point probe measurements showed very small resistivity increases after irradiation, with the films containing higher In concentration presenting negligible changes. (C) 2016 Elsevier B.V. All rights reserved.
603. Cross-coupling of p-xylene to 2,2 ',5,5 '-tetramethyl 1,1 '-biphenyl on supported vanadia catalysts
Authors:
Mitran, G; Pavel, OD; Florea, M; Parvulescu, VI
Published: MAR 25 2016, , DOI: 10.1016/j.apcata.2016.01.010
604. Synthesis of ceria nanopowders by microwave-assisted hydrothermal method for dry reforming of methane
Authors:
Matei-Rutkovska, F; Postole, G; Rotaru, CG; Florea, M; Parvulescu, VI; Gelin, P
Published: JAN 30 2016, , DOI: 10.1016/j.ijhydene.2015.12.097
605. Light-hole exciton mixing and dynamics in Mn-doped quantum dots
Authors:
Moldoveanu, V; Dinu, IV; Dragomir, R; Tanatar, B
Published: APR 18 2016, PHYSICAL REVIEW B, 93, DOI: 10.1103/PhysRevB.93.165421
We investigate theoretically the spectral and dynamical effects of the short-range exchange interaction between a single manganese (Mn) atom hosted by cylindrical CdTe quantum dots and its light-hole excitons or biexcitons. Our approach is based on the Kohn-Luttinger k . p theory and configuration interaction method, the dynamics of the system in the presence of intraband relaxation being derived from the von Neumann-Lindblad equation. The complex structure of the light-hole exciton absorption spectrum reveals the exchange-induced exciton mixing and depends strongly on the Mn position. In particular, if the Mn atom is closer to the edges of the cylinder, the bright and dark light-hole excitons are mixed by the hole-Mn exchange alone. Consequently, their populations exhibit exchange-induced Rabi oscillations which can be viewed as optical signatures of light-hole spin reversal. Similar results are obtained for mixed biexcitons, in this case the exchange-induced Rabi oscillations being damped by the intraband hole relaxation processes. The effect of light-hole heavy-hole mixing is also discussed.
606. Dense, Regular GaAs Nanowire Arrays by Catalyst-Free Vapor Phase Epitaxy for Light Harvesting
Authors:
Jin, JH; Stoica, T; Trellenkamp, S; Chen, Y; Anttu, N; Migunov, V; Kawabata, RMS; Buenconsejo, PJS; Lam, YM; Haas, F; Hardtdegen, H; Grutzmacher, D; Kardynal, BE
Published: AUG 31 2016, ACS APPLIED MATERIALS & INTERFACES, 8, 22492, DOI: 10.1021/acsami.6b05581
Density dependent growth and optical properties of periodic arrays of GaAs nanowires (NWs) by fast selective area growth MOVPE are investigated. As the period of the arrays is decreased from 500 nm down to 100 nm, a volume growth enhancement by a factor of up to four compared with the growth of a planar layer is observed. This increase is explained as resulting from increased collection of precursors on the side walls of the nanowires due to the gas flow redistribution in the space between the NWs. Normal spectral reflectance of the arrays is strongly reduced compared with a flat substrate surface in all fabricated arrays. Electromagnetic modeling reveals that this reduction is caused by antireflective action of the nanowire arrays and nanowire-diameter dependent light absorption. Irrespective of the periodicity and diameter, Raman scattering and grazing angle X-ray diffraction show signal from zinc blende and wurtzite phases, the latter-originating from stacking faults, as observed by high resolution transmission electron microscopy. Raman spectra contain intense surface phonons peaks, whose intensity depends strongly on the nanowire diameters as a result of potential structural changes and as well as variations of optical field distribution in the nanowires.
607. Role of the dithiolate backbone on the passivation of p-GaAs(111)B surface
Authors:
Preda, L; Anastasescu, M; Dobrescu, G; Negrila, C; Lazarescu, V
Published: JUN 15 2016, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 771, 63, DOI: 10.1016/j.jelechem.2016.03.046
Effects of the self-assembled layers of biphenyl 4,4'-dithiol (BPDT) and 1,8-octanedithiol (ODT) on the chemical and electronic properties of p-doped GaAs (111)-As terminated substrate, (p-GaAs(111)B), were investigated in order to evidence whether the hydrocarbon moiety plays a role in tailoring the semiconductor surface properties. The electrochemical properties of the BPDT and ODT coated p-GaAs(111)B substrates were studied by Electrochemical Impedance Spectroscopy (EIS). The structural and chemical changes caused by the dithiolate layers formed on p-GaAs(111)B substrates were monitored by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) investigations, respectively. The XPS data showed that BPDT and ODT bind to pGaAs(111)B via the thiol group. The ODT layer provides better protection against the further oxidation in air of p-GaAs(111)B substrate compared to the BPDT layer. The EIS investigations are in good agreement with XPS results, pointing to better insulating properties of the ODT layer compared to the BPDT layer in the electron transfer at the electrode/solution interface. The results evidenced that backbone plays an important role in tailoring the properties of p-GaAs(111)B substrate. (C) 2016 Elsevier B.V. All rights reserved.
608. How morphology determines the charge storage properties of Ge nanocrystals in HfO2
Authors:
Slav, A; Palade, C; Lepadatu, AM; Ciurea, ML; Teodorescu, VS; Lazanu, S; Maraloiu, AV; Logofatu, C; Braic, M; Kiss, A
Published: MAR 1 2016, SCRIPTA MATERIALIA, 113, 138, DOI: 10.1016/j.scriptamat.2015.10.028
The strong correlation between morphology and charge storage properties of HfO2/Ge/HfO2/Si trilayer structures was evidenced. The morphology of structures deposited by magnetron sputtering and electron beam evaporation was tailored by rapid thermal annealing and investigated by transmission electron microscopy, Raman and X-ray photoelectron spectroscopies. The best hysteresis loops (capacitance-voltage characteristics) were obtained for trilayers with high density Ge nanocrystals located in the position of as-deposited Ge layer. The decrease of Ge nanocrystals density narrows the memory window, by spreading Ge atoms into HfO2 matrix (sputtered trilayers), or by Ge atoms expulsion toward HfO2 nanocrystals surface (evaporated trilayers). (C) 2015 Elsevier Ltd. All rights reserved.
609. Low level NO2 detection under humid background and associated sensing mechanism for mesoporous SnO2
Authors:
Stanoiu, A; Somacescu, S; Calderon-Moreno, JM; Teodorescu, VS; Florea, OG; Sackmann, A; Simion, CE
Published: AUG 2016, SENSORS AND ACTUATORS B-CHEMICAL, 231, 174, DOI: 10.1016/j.snb.2016.02.137
Mesoporous SnO2 prepared by a hydrothermal synthesis route assisted by the ionic surfactant Cetyltrimethylammonium bromide, has rutile-type tetragonal symmetry, small homogeneous nanocrystallite size of similar to 4 nm and good thermal stability. Porosity analysis revealed high surface area similar to 127 m(2)/g and a narrow pore size distribution, with an average pore diameter similar to 4 nm. The mesoporous structure is likewise advantageous towards enhancing the surface reactivity and subsequent gas sensing performances. The role played by the surface hydroxylation on the NO2 sensing mechanism was discussed with respect to the associated photoelectron spectral components. Under humid air, associated with the in-field conditions, the highest sensitivity was attained at 150 degrees C, were the sensor signal towards NO2 is 4 times higher than the one recorded in dry air. This feature has been experimentally demonstrated by simultaneous electrical resistance and work function changes measurements conducted in the range of 400-5000 ppb NO2. (C) 2016 Elsevier B.V. All rights reserved.
610. Structural and electrical properties of Nb doped TiO2 films prepared by the sol-gel layer-by-layer technique
Authors:
Duta, M; Simeonov, S; Teodorescu, V; Predoana, L; Preda, S; Nicolescu, M; Marin, A; Spasov, D; Gartner, M; Zaharescu, M; Szekeres, A
Published: FEB 2016, MATERIALS RESEARCH BULLETIN, 74, 20, DOI: 10.1016/j.materresbull.2015.10.009
Thin films of 5 and 10-layered sol gel TiO2 were doped with 1.2 at.% Nb and their structural, optical and electrical properties were investigated. The films crystallized only in anatase phase, as evidenced by X-ray diffraction and selected area electron diffraction analyses. High resolution transmission electron microscopy revealed nanosized crystallites with amorphous boundaries. Current-voltage measurements on metal-TiO2 Si structures showed the formation of ri+ n heterojunction at the TiO2-Si interface with a rectification ratio of 10(4). The effective donor density varies between 10(16) and 10(17) cm(-3), depending on film thickness. The sheet energy densities under forward and reverse bias are in the order of 10(12) and 10(10) cm(-2) respectively. These values and the high specific resistivity (10(4) Omega cm) support the existence of compensating acceptor levels in these films. It was established that the conduction mechanism is based on space charge limited current via deep levels with different energy positions in the band gap. (C) 2015 Elsevier Ltd. All rights reserved.
611. Pyramidal growth of ceria nanostructures by pulsed laser deposition
Authors:
Barca, ES; Filipescu, M; Luculescu, C; Birjega, R; Ion, V; Dumitru, M; Nistor, LC; Stanciu, G; Abrudeanu, M; Munteanu, C; Dinescu, M
Published: FEB 15 2016, APPLIED SURFACE SCIENCE, 363, 251, DOI: 10.1016/j.apsusc.2015.12.064
We report in this paper on the deposition and characterization of CeO2 nanostructured thin films with hierarchical morphology. Micro -sized ceria powder (CeO2, 99.9% purity) was pressed to obtain a ceramic target. An ArF laser working at 193 nm irradiated the target in controlled oxygen gas flow at constant pressure (0.1 mbar). Silicon wafers used as substrates for thin films were heated at different temperatures, up to 773 K. The influence of substrate temperature on the structure and surface morphology of ceria thin films was studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy and scanning electron microscopy (SEM). The refractive indices and information about roughness and thickness were revealed by spectroellipsometry. Crystalline cubic ceria thin films exhibiting a hierarchical structure that combines columnar and dendritic growth were obtained at temperatures above 473 K. For the samples obtained at 773 K, columns ending in pyramidal formations with sharp edges and sizes of hundreds of nanometers were observed, indicating a high crystallinity of the layer. XRD analysis reveals a consistent increase of the X-ray coherence length/crystallite size along the [111] direction with increasing temperature. Using a semi -empirical formula, Raman crystallites sizes were calculated and it was found that size increases with the temperature increasing. The spectroellipsometry investigations evidenced the increasing of refractive index with the substrate temperature increase. High surface roughness and pyramidal structures were noticed from the atomic force microscopy images for layers deposited at substrate temperature above 473 K. (C) 2015 Elsevier B.V. All rights reserved.
612. First principle investigations of the structural, electronic and magnetic properties of predicted new zirconium based full-Heusler compounds, Zr(2)MnZ (Z=Al, Ga and In)
Authors:
Birsan, A; Kuncser, V
Published: MAY 15 2016, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 406, 288, DOI: 10.1016/j.jmmm.2016.01.032
The crystal structure, electronic and magnetic properties of predicted new full-Heusler compounds Zr(2)MnZ (Z=Al, Ga, In) were studied within the density functional theory (DFT) framework. These materials exhibit unique properties that connect the spin gapless semiconducting character with the completely compensated ferrimagnetism. Magnetically ordered Zr(2)MnZ (Z=Al, Ga, In) compounds crystallize in inverse Heusler structure are stable against decomposition and have zero magnetic moment per formula unit, in agreement with Slater-Pauling rule. The Zr2MnAl compound presents semiconducting properties with an energy band gap of 0.41 eV in the majority spin channel and a zero band gap in the minority spin channel. By substituting completely the Al in Zr2MnAl via Ga and In elements, semiconducting pseudo band gaps are formed in the majority spin channels due to different neighborhoods around the manganese atoms, which decreases the energy of Mn triple degenerated anti-bonding states. (C) 2016 Elsevier B.V. All rights reserved.
613. Effects of magnetic dipolar interactions on the specific time constant in superparamagnetic nanoparticle systems
Authors:
Iacob, N; Schinteie, G; Bartha, C; Palade, P; Vekas, L; Kuncser, V
Published: JUL 27 2016, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 49, DOI: 10.1088/0022-3727/49/29/295001
A quantitative treatment of the effects of magnetic mutual interactions on the specific absorption rate of a superparamagnetic system of iron oxide nanoparticles coated with oleic acid is reported. The nanoparticle concentration of the considered ferrofluid samples varied from a very low (0.005) to a medium (0.16) value of the volume fraction, whereas the amplitude of the exciting AC magnetic field ranged from 14-35 kA m(-1). It was proved that a direct effect of the interparticle interactions resides in the regime of the modified superparamagnetism, dealing, besides the usual increase in the anisotropy energy barrier per nanoparticle, with the decrease in the specific time constant tau(0) of the relaxation law, usually considered as a material constant. Consequently, the increase in the specific absorption rate versus the volume fraction is significantly diminished in the presence of the interparticle interactions compared to the case of non-interacting superparamagnetic nanoparticles, with direct influence on the magnetic hyperthermia efficiency.
614. Superconductivity in MgB2 irradiated with energetic protons
Authors:
Sandu, V; Craciun, L; Ionescu, AM; Aldica, G; Miu, L; Kuncser, A
Published: SEP 15 2016, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 528, 34, DOI: 10.1016/j.physc.2016.07.006
A series of MgB2 samples were irradiated with protons of 11.3 and 13.2 MeV. Magnetization data shows an insignificant reduction of the critical temperatures but a continuous decrease of the Meissner fraction with increasing fluence or energy. All samples show a consistent improvement of the critical current density compared to the virgin sample and an increase of the pinning energy at high fields as resulted from relaxation data. (C) 2016 Elsevier B.V. All rights reserved.
615. The relationship between magnetism and magneto-optical effects in rare earth doped aluminophosphate glasses
Authors:
Valeanu, M; Sofronie, M; Galca, AC; Tolea, F; Elisa, M; Sava, B; Boroica, L; Kuncser, V
Published: FEB 25 2016, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 49, DOI: 10.1088/0022-3727/49/7/075001
Aluminophosphate glasses from the Li2O-BaO-Al2O3-P2O5 system with the addition of nonmagnetic and paramagnetic rare earth ions, were prepared using a wet nonconventional method to process the raw materials, followed by a melting-quenching procedure. The glasses obtained were characterized with respect to their magnetic and magneto-optical properties using superconducting quantum interference device magnetometry and spectroscopic ellipsometry. The assumption of a linear dependence of the Verdet constant on the magnetic susceptibility, with a proportionality constant dependent on the type of vitreous matrix and doping ion, is critically discussed. The diamagnetic and paramagnetic contributions to the Faraday rotation were separately analyzed and specific designs for optimal active and passive elements are proposed.
616. Tellurium addition as a solution to improve compactness of ex-situ processed MgB2-SiC superconducting tapes
Authors:
Sandu, V; Aldica, G; Popa, S; Enculescu, M; Badica, P
Published: JUN 2016, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 29, DOI: 10.1088/0953-2048/29/6/065012
Ex-situ spark plasma sintering (SPS) was used to obtain dense MgB2-based tapes in a Fe sheath with the starting composition (MgB2)(0.975) + (SiC)(0.025) + Te-0.01. Prior to the SPS procedure of tape formation, the samples were submitted to a series of cold working processes typical for the powder-in-tube technique. The tapes were compared with optimal doped bulk samples (having the same starting composition) and a pristine MgB2 tape. The morphology of the composite samples, the phase structure of both the core and the inner face of the metallic sheath shows the formation of a plethora of traces as a result of interaction between MgB2, additives, and the Fe sheath. Important critical parameters, like critical current density and the irreversibility field, show that there is a field and temperature range where the SiC and Te-added tapes display better critical parameters comparative to either pristine MgB2 tapes in the Fe sheath or SiC and Te doped MgB2 bulk samples.
617. Nanostructured germanium deposited on heated substrates with enhanced photoelectric properties
Authors:
Stavarache, I; Maraloiu, VA; Prepelita, P; Iordache, G
Published: OCT 21 2016, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 7, 1500, DOI: 10.3762/bjnano.7.142
Obtaining high-quality materials, based on nanocrystals, at low temperatures is one of the current challenges for opening new paths in improving and developing functional devices in nanoscale electronics and optoelectronics. Here we report a detailed investigation of the optimization of parameters for the in situ synthesis of thin films with high Ge content (50 %) into SiO2. Crystalline Ge nanoparticles were directly formed during co-deposition of SiO2 and Ge on substrates at 300, 400 and 500 degrees C. Using this approach, effects related to Ge-Ge spacing are emphasized through a significant improvement of the spatial distribution of the Ge nanoparticles and by avoiding multi-step fabrication processes or Ge loss. The influence of the preparation conditions on structural, electrical and optical properties of the fabricated nanostructures was studied by X-ray diffraction, transmission electron microscopy, electrical measurements in dark or under illumination and response time investigations. Finally, we demonstrate the feasibility of the procedure by the means of an Al/n-Si/Ge:SiO2/ITO photodetector test structure. The structures, investigated at room temperature, show superior performance, high photoresponse gain, high responsivity (about 7 AW(-1)), fast response time (0.5 mu s at 4 kHz) and great optoelectronic conversion efficiency of 900% in a wide operation bandwidth, from 450 to 1300 nm. The obtained photoresponse gain and the spectral width are attributed mainly to the high Ge content packed into a SiO2 matrix showing the direct connection between synthesis and optical properties of the tested nanostructures. Our deposition approach put in evidence the great potential of Ge nanoparticles embedded in a SiO2 matrix for hybrid integration, as they may be employed in structures and devices individually or with other materials, hence the possibility of fabricating various heterojunctions on Si, glass or flexible substrates for future development of Si-based integrated optoelectronics.
618. Innovative Self-Cleaning and Biocompatible Polyester Textiles Nano-Decorated with Fe-N-Doped Titanium Dioxide
Authors:
Nica, IC; Stan, MS; Dinischiotu, A; Popa, M; Chifiriuc, MC; Lazar, V; Pircalabioru, GG; Bezirtzoglou, E; Iordache, OG; Varzaru, E; Dumitrescu, I; Feder, M; Vasiliu, F; Mercioniu, I; Diamandescu, L
Published: NOV 2016, NANOMATERIALS, 6, DOI: 10.3390/nano6110214
The development of innovative technologies to modify natural textiles holds an important impact for medical applications, including the prevention of contamination with microorganisms, particularly in the hospital environment. In our study, Fe and N co-doped TiO2 nanoparticles have been obtained via the hydrothermal route, at moderate temperature, followed by short thermal annealing at 400 degrees C. These particles were used to impregnate polyester (PES) materials which have been evaluated for their morphology, photocatalytic performance, antimicrobial activity against bacterial reference strains, and in vitro biocompatibility on human skin fibroblasts. Microscopic examination and quantitative assays have been used to evaluate the cellular morphology and viability, cell membrane integrity, and inflammatory response. All treated PES materials specifically inhibited the growth of Gram-negative bacilli strains after 15 min of contact, being particularly active against Pseudomonas aeruginosa. PES fabrics treated with photocatalysts did not affect cell membrane integrity nor induce inflammatory processes, proving good biocompatibility. These results demonstrate that the treatment of PES materials with TiO2-1% Fe-N particles could provide novel biocompatible fabrics with short term protection against microbial colonization, demonstrating their potential for the development of innovative textiles that could be used in biomedical applications for preventing patients' accidental contamination with microorganisms from the hospital environment.
619. High atomic diffusivity during pulsed laser irradiation of TiON quasi-amorphous films
Authors:
Teodorescu, VS; Maraloiu, AV; Negrea, RF; Ghica, D; Scarisoreanu, ND; Dinescu, M; Gartner, M; Blanchin, MG
Published: JUN 30 2016, APPLIED SURFACE SCIENCE, 374, 251, DOI: 10.1016/j.apsusc.2015.11.188
Quasi-amorphous titanium oxynitride (TiON) films were obtained by annealing sol-gel anatase TiO2 films in NH3 atmosphere at 600 degrees C. These films were irradiated with 50 laser pulses using the fourth harmonic (266 nm) radiation of the Nd-YAG laser, with an average fluence of 20 mJ/cm(2). HRTEM observations of the pulsed laser irradiated films evidenced the rutile TiO2 nanocrystallites formation. The rutile structure was not present either in the TiON films before the laser irradiation, or in the initial sol-gel anatase TiO2 films. During the laser irradiation, the film structure remains in the solid state phase, as it results from the temperature estimation and microscopic observations. For the rutile nanocrystals formation, the atomic diffusion length of the oxygen and titanium atoms should be in the nanometric range during the laser pulse action, which implies a diffusivity close to the values observed in the liquid phase. We consider that the rutile phase formation is a proof of the fast atomic diffusion in the solid amorphous matrix, during the laser irradiation. (C) 2015 Published by Elsevier B.V.
620. The combined action of methanolysis and heterogeneous photocatalysis in the decomposition of chemical warfare agents
Authors:
Petrea, N; Petre, R; Epure, G; Somoghi, V; Tanase, LC; Teodorescu, CM; Neatu, S
Published: 2016, CHEMICAL COMMUNICATIONS, 52, 12959, DOI: 10.1039/c6cc07551g
We report the applicability of a hybrid system comprising a La3+-based catalyst and an Au/TiO2 photocatalyst in the decomposition of chemical weapons. This system is able to perform complete degradation of soman, sarin and VX in less than 1 minute under low basic conditions and visible light irradiation.
621. CdS quantum dots sensitized TiO2 nanotubes by matrix assisted pulsed laser evaporation method
Authors:
Bjelajac, A; Petrovic, R; Socol, G; Mihailescu, IN; Enculescu, M; Grurriezescu, V; Pavlovic, V; Janackovic, D
Published: MAY 15 2016, CERAMICS INTERNATIONAL, 42, 9017, DOI: 10.1016/j.ceramint.2016.02.159
Within this study a matrix assisted pulsed laser evaporation technique was employed for deposition of CdS quantum dots onto TiO2 nanotubes. The number of laser pulses and laser fluence were varied to control the amount of CdS deposit. TiO2 nanotubes were obtained via anodization technique of sputtered Ti film on FTO glass. For CdS synthesis, dimethyl sulfoxide (DMSO) was used as a matrix of the target which absorbs radiation of KrF* laser (lambda=248 nm), then evaporates enabling the deposition of CdS quantum dots dispersed into DMSO. This study showed that the size of the CdS nanoparticles synthetized in DMSO can be controlled with microwave treatment that causes the release of S2- ions from DMSO for creation of CdS nuclei and/or their further growth. The optimization of CdS synthesis is achieved by varying the duration of the microwave treatment and the microwave power. The obtained TiO2 photo anodes with different amounts of CdS were assembled with PbS cathodes and the polysulfide electrolyte was injected between. The influence of amount of CdS deposit and the microwave treatment of CdS on photovoltaic performance of the fabricated solar cells were analyzed under AM1.5. The results showed that microwave treatment produced a Cd(S)-DMSO complex onto CdS nanoparticles which led to a higher current density of the solar cells obtained using microwave treated CdS target. Also, the increase of CdS content by increasing the number of laser pulses provided the enhance of I-V characteristics of the solar cells. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
622. Possible Enhancement of Spin Fluctuations by Ag addition to SmFeAsO1-x F (x)
Authors:
Sandu, V; Suo, HL; Aldica, G; Ionescu, AM; Suo, C; Liu, ZY
Published: FEB 2016, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 29, 308, DOI: 10.1007/s10948-015-3279-z
We investigate the effect of silver addition to polycrystalline SmFeAsO1-x F (x) (Sm-1111) superconductor. Transport and magnetic measurement data reveal the enhancement of the magnetic fluctuation with increasing silver content.
623. Flexible heterostructures based on metal phthalocyanines thin films obtained by MAPLE
Authors:
Socol, M; Preda, N; Rasoga, O; Breazu, C; Stavarache, I; Stanculescu, F; Socol, G; Gherendi, F; Grumezescu, V; Popescu-Pelin, G; Girtan, M; Stefan, N
Published: JUN 30 2016, APPLIED SURFACE SCIENCE, 374, 410, DOI: 10.1016/j.apsusc.2015.10.166
Heterostructures based on zinc phthalocyanine (ZnPc), magnesium phthalocyanine (MgPc) and 5,10,15,20-tetra(4-pyrydil)21H,23H-porphine (TPyP) were deposited on ITO flexible substrates by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. Organic heterostructures containing (TPyP/ZnPc(MgPc)) stacked or (ZnPc(MgPc):TPyP) mixed layers were characterized by X-ray diffraction-XRD, photoluminescence-PL, UV-vis and FTIR spectroscopy. No chemical decomposition of the initial materials was observed. The investigated structures present a large spectral absorption in the visible range making them suitable for organic photovoltaics applications (OPV). Scanning electron microscopy-SEM and atomic force microscopy-AFM revealed morphologies typical for the films prepared by MAPLE. The current-voltage characteristics of the investigated structures, measured in dark and under light, present an improvement in the current value (similar to 3 order of magnitude larger) for the structure based on the mixed layer (Al/MgPc:TPyP/ITO) in comparison with the stacked layer (Al/MgPc//TPyP/ITO). A photogeneration process was evidenced in the case of structures Al/ZnPc:TPyP/ITO with mixed layers. (C) 2015 Elsevier B.V. All rights reserved.
624. Non-volatile memory structures with Ge NCs-HfO2 intermediate layer
Authors:
Palade, C; Slav, A; Lepadatu, AM; Maraloiu, AV; Lazanu, S; Logofatu, C; Teodorescu, VS; Ciurea, ML
Published: 2016, 2016 39TH INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 166, DOI:
The structure and charge storage properties of a trilayer structure with Ge nanocrystals embedded in HfO2 oxide were studied. The trilayer structure HfO2/Ge-HfO2/HfO2/p-Si was prepared by magnetron sputtering and subsequent rapid thermal annealing at 600 degrees C. The TEM investigations reveal the formation of Ge NCs embedded in crystalline HfO2 at the position of the Ge-HfO2 layer. The capacitors were made by Al evaporation on both front and backside of the trilayer structure. The C-V characteristics show a counterclockwise hysteresis with large memory window of 0.85 V which is given only by the contribution of the Ge NCs embedded in HfO2. The I-V characteristics show an asymmetric behavior, the currents are three times higher for the negative voltage than the positive one.
625. Iodine Migration and Degradation of Perovskite Solar Cells Enhanced by Metallic Electrodes
Authors:
Besleaga, C; Abramiuc, LE; Stancu, V; Tomulescu, AG; Sima, M; Trinca, L; Plugaru, N; Pintilie, L; Nemnes, GA; Iliescu, M; Svavarsson, HG; Manolescu, A; Pintilie, I
Published: DEC 15 2016, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 7, 5175, DOI: 10.1021/acs.jpclett.6b02375
We monitored the evolution in time of pinhole-free structures based on FTO/TiO2/CH3NH3PbI2.6Cl0.4 layers, with and without spiro-OMeTAD and counter electrodes (Ag, Mo/Ag, and Au), aged at 24 degrees C in a dark nitrogen atmosphere. In the absence of electrodes, no degradation occurs. While devices with Au show only a 10% drop in power conversion efficiency, remaining stable after a further overheating at 70 degrees C, >90% is lost when using Ag, with the process being slower for Mo/Ag. We demonstrate that iodine is dislocated by the electric field between the electrodes, and this is an intrinsic cause for electromigration of I- from the perovskite until it reaches the anode. The iodine exhaustion in the perovskite layer is produced when using Ag electrodes, and AgI is formed. We hypothesize that in the presence of Au the iodine migration is limited due to the buildup of I- negative space charge accumulated at the perovskite-OMeTAD interface.
626. Thermal analysis of ball-milled Fe-14Cr-3W-0.4Ti-0.25Y(2)O(3) ferritic steel powder Evidence for contamination from the air
Authors:
Mihalache, V
Published: JUN 2016, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 124, 1192, DOI: 10.1007/s10973-016-5304-2
The contamination from the air (the identification of the impurity phases and their thermal evolution) of Fe-14Cr-3W-0.4Ti-0.25Y(2)O(3) oxide dispersion-strengthened ferritic steel powders ball-milled for different times was evidenced by thermal analysis in correlation with X-ray diffraction and scanning electron microscopy. The powders loaded under an argon atmosphere and milled up to 170 h with and without interruption of the milling process were compared. A steady state of Fe-Cr alloying was reached within the first 12 h. The reflections corresponding to a new phase with an fcc-CrN structure were found in XRD patterns of powders milled for a long time with interruption. The differential thermal analysis of powders milled over 12 h with interruption shows an exothermic peak at 625.5-653 degrees C, ascribed to the coarsening of the fcc-CrN, and an endothermic reaction above 1000 degrees C accompanied by a mass loss in thermogravimetric analysis. (Cr,Fe)(2)O-3 and retained austenite were also found upon the heating of as-milled (with interruption) powders to different temperatures. The endothermic feature was associated with the decomposition of CrN accompanied by the degassing of N-2. The observed phenomenon was explained to be the manifestation of contamination with nitrogen and oxygen from the air during the milling; the rate of contamination with nitrogen was estimated to be 0.011 mass% h(-1). The contamination level depends on the degree of alloying at the moment of the interruption of milling process. The contamination of the powders milled without interruption of milling process was insignificant. The experimental conditions described in this work can be further developed for the removal of impurities (e.g. nitrogen, nitrides, oxides) from alloyed ferritic steel powders.
627. Nematic ionic liquid crystals based on pyridinium salts derived from 4-hydroxypyridine
Authors:
Pana, A; Pasuk, I; Micutz, M; Circu, V
Published: 2016, CRYSTENGCOMM, 18, 5069, DOI: 10.1039/c6ce00618c
A series of pyridinium salts with various counterions (Br-, NO3-, BF4-, PF6-, OTf- and SCN-) and different spacer chain lengths, which display a nematic phase, have been designed and prepared. They are derived from 4-hydroxypyridine and possess two mesogenic cyanobiphenyl groups attached to the pyridinium unit via a flexible long alkyl spacer (6, 9, 10). These salts exhibit solely a nematic phase with the thermal range influenced by the counterion employed and spacer length.
628. BST thin film capacitors integrated within a frequency tunable antenna
Authors:
Rammal, M; Huitema, L; Crunteanu, A; Passerieux, D; Cros, D; Monediere, T; Madrangeas, V; Dutheil, P; Champeaux, C; Dumas-Bouchiat, F; Marchet, P; Nedelcu, L; Trupina, L; Banciu, G; Cernea, M
Published: 2016, 2016 IEEE INTERNATIONAL WORKSHOP ON ANTENNA TECHNOLOGY (IWAT), 47, DOI:
Ferroelectric (FE) thin film varactors can be a convenient technology for tuning miniature antennas. In this paper we present the design of a compact, agile, wire patch antenna integrating barium strontium titanate (Ba(1-x)SrxTiO3, BST) thin film interdigitated capacitors (IDC). The IDCs values were measured at different temperatures and bias voltages ranging from 0 to 120 V showing a capacitance variation of more than 40% between 11-13 GHz and up to 28% in the 2-3 GHz frequency interval. Their integration within a compact antenna design allows tuning its operating frequency on the whole WiFi band, with efficiencies higher than 70%.
629. MAGNETIC AND MOSSBAUER SPECTROSCOPY STUDY OF Fe-Cr-Al THIN FILMS SPUTTERED ON Si SUBSTRATES
Authors:
Greculeasa, SG; Schiniteie, G; Palade, P; Filoti, G; Ghita, IS; Kuncser, V
Fe and Fe-Cr-Al thin films, both as sputtered on Si substrates as well as after subsequent annealing treatments in hydrogen atmosphere, have been investigated by means of X-ray reflectometry, magneto-optic Kerr effect and Mossbauer spectroscopy with respect to structural and related magnetic characteristics. The as deposited films are showing chemically disordered bcc structures, assigned to Fe-Si and Fe-Cr-Al-Si phases, respectively, with soft magnetism and magnetic texture, both influenced by the presence of Si, Cr and Al atoms. The softness of the films as well as the magnetic texture are strongly modified via hydrogenation treatments. In addition, such treatments induce the expulsion of Si, Cr and Al atoms from the as deposited phases, providing almost pure Fe films of much well crystallized bcc structure.
630. Fast atomic diffusion in amorphous films induced by laser pulse annealing
Authors:
Teodorescu, VS; Ghica, C; Maraloiu, AV; Kuncser, A; Lepadatu, AM; Stavarache, I; Ciurea, ML; Scarisoreanu, ND; Andrei, A; Dinescu, M
Published: 2016, 2016 39TH INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 158, DOI:
Fast atomic diffusion was evidenced in the surface layer of amorphous thin films of oxides and semiconductors irradiated with low fluence UV pulse laser. This process takes place in a surface layer with a thickness related to the laser radiation absorption depth in the target material and was revealed by the cross section transmission electron microscopy studies. These high values of diffusivity can be explained by supposing the glass transition transformation in the amorphous structure, triggered by the action of the laser pulse field. This effect can have application for controlling structural modifications at nanoscale of the thin films surface and also for inducing structural modification of interfaces between the film and substrate.
631. Partially disordered antiferromagnetism and multiferroic behavior in a frustrated Ising system CoCl2-2SC(NH2)(2)
Authors:
Mun, E; Weickert, F; Kim, J; Scott, BL; Miclea, CF; Movshovich, R; Wilcox, J; Manson, J; Zapf, VS
Published: MAR 7 2016, PHYSICAL REVIEW B, 93, DOI: 10.1103/PhysRevB.93.104407
We investigate partially disordered antiferromagnetism in CoCl2-2SC(NH2)(2), in which ab-plane hexagonal layers are staggered along the c axis rather than stacked. A robust 1/3 state forms in applied magnetic fields in which the spins are locked, varying as a function of neither temperature nor field. By contrast, in zero field and applied fields at higher temperatures, partial antiferromagnetic order occurs, in which free spins are available to create a Curie-like magnetic susceptibility. We report measurements of the crystallographic structure and the specific heat, magnetization, and electric polarization down to T = 50 mK and up to mu H-0 = 60 T. The Co2+ S = 3/2 spins are Ising-like and form distorted hexagonal layers. The Ising energy scale is well separated from the magnetic exchange, and both energy scales are accessible to the measurements, allowing us to cleanly parametrize them. In transverse fields, a quantum Ising phase transition can be observed at 2 T. Finally, we find that magnetic exchange striction induces changes in the electric polarization up to 3 mu C/m(2), and single-ion magnetic anisotropy effects induce a much larger electric polarization change of 300 mu C/m(2).
632. Spark plasma sintered MgB2 co-added with c-BN and C-60
Authors:
Ionescu, AM; Aldica, G; Popa, S; Enculescu, M; Sandu, V; Pasuk, I; Kuncser, A; Miu, L; Badica, P
Published: FEB 15 2016, MATERIALS CHEMISTRY AND PHYSICS, 170, 209, DOI: 10.1016/j.matchemphys.2015.12.040
High density (above 92%) superconducting bulks of MgB2 co-added with cubic BN (c-BN) and fullerenes (C-60) were obtained by the ex-situ spark plasma sintering (SPS). Compositions were (MgB2)((1-x))(C)(x)(c-BN)(0.01), x = 0.0125, 0.025, 0.05, 0.075. The co-added sample (MgB2)(0.975)(C)(0.025)(c-BN)(0.01) shows a marginally higher critical current density J(c) at intermediate magnetic fields and below 15 K than for optimum samples added with c-BN or C-60. For this sample, pinning is in the point pinning limit and the delta T-c mechanism is dominant. At high magnetic fields co-added samples are inferior to samples added with one additive, but are superior to pristine sample. Co-addition of c-BN and C-60 is not effective for vortex pinning when compared with individual addition. The result is discussed based on phase formation aspects, microstructural details and residual strain. It was found that in the presence of C-60, c-BN consumption with formation of MgNB9 is intensified with implications on different elements that influence pinning. (C) 2015 Elsevier B.V. All rights reserved.
633. Characterization of a n+3C/n-4H SiC heterojunction diode
Authors:
Minamisawa, RA; Mihaila, A; Farkas, I; Teodorescu, VS; Afanas'ev, VV; Hsu, CW; Janzen, E; Rahimo, M
Published: APR 4 2016, APPLIED PHYSICS LETTERS, 108, DOI: 10.1063/1.4945332
We report on the fabrication of n+3C/n-4H SiC heterojunction diodes (HJDs) potentially promising the ultimate thermal stability of the junction. The diodes were systematically analyzed by TEM, X-ray diffraction, AFM, and secondary ion mass spectroscopy, indicating the formation of epitaxial 3C-SiC crystal on top of 4H-SiC substrate with continuous interface, low surface roughness, and up to similar to 7 x 10(17) cm(-3) dopant impurity concentration. The conduction band off-set is about 1 V as extracted from CV measurements, while the valence bands of both SiC polytypes are aligned. The HJDs feature opening voltage of 1.65 V, consistent with the barrier height of about 1.5 eV extracted from CV measurement. We finally compare the electrical results of the n+3C/n-4H SiC heterojunction diodes with those featuring Si and Ge doped anodes in order to evaluate current challenges involved in the fabrication of such devices. (C) 2016 AIP Publishing LLC.
634. Tuning Hydroxyapatite Particles' Characteristics for Solid Freeform Fabrication of Bone Scaffolds
Authors:
Miculescu, F; Maidaniuc, A; Stan, GE; Miculescu, M; Voicu, SI; Cimpean, A; Mitran, V; Batalu, D
Restoration of damaged bone tissue involves two traditional approaches: tissue grafting and alloplastic replacement. Recently, their limitations led to the development of tissue engineering, which uses degradable porous supports named "scaffolds". These porous structures (used both for tissue engineering and classic bone substitution applications) with customizable designs may be constructed by solid freeform fabrication (SFF) techniques. SFF uses various synthetic materials and may be adapted for creating ceramic-based scaffolds, which became popular due to increased demands for bone substitution materials. Among these materials, naturally derived ceramics are suitable candidates for bone replacement due to their resemblance with the mineral bone. Innovative optimization routes for preparing naturally derived ceramics with modulated properties implies the management of key parameters involved in heat treatment of animal hard tissues: temperature, heating environment, and cooling conditions. Both powders and bulk pieces are evaluated with complementary techniques that focus on compositional, morphological, and structural features. Finally, qualitative and quantitative biological assay in relevant cell culture of the compacted powders may assist extensive testing programs for further evaluation of different ceramic scaffolds. All these results contribute to effective assessment of ceramics tuning strategies and to subsequent modulation of their enhanced properties and long-term functionality.
635. HfO2 with embedded Ge nanocrystals with memory effects
Authors:
Palade, C; Slav, A; Lepadatu, AM; Maraloiu, AV; Teodorescu, VS; Ciurea, ML
Published: 2015, 2015 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 48, DOI:
The charge storage properties of Ge nanocrystals-based MOS-like capacitors with tunnel and gate HfO2 are studied. HfO2/Ge/HfO2/Si trilayer structures were prepared by magnetron sputtering (in Ar) and subsequent rapid thermal annealing (650 degrees C). HfO2/Si structures were also prepared, some under similar conditions, while others were deposited in Ar:O-2. TEM investigations and C-V measurements were performed. TEM on annealed trilayers evidences the formation of ordered and precisely positioned array of Ge nanocrystals embedded in crystalline HfO2. The annealed Al/HfO2/Ge/HfO2/p-Si/Al capacitors present counterclockwise C-V hysteresis (0.8 V memory window) mainly given by Ge nanocrystals, with negligible contribution from crystallized-HfO2 traps.
636. Surface-enhanced Raman scattering activity of niobium surface after irradiation with femtosecond laser pulses
Authors:
Ivanov, VG; Vlakhov, ES; Stan, GE; Zamfirescu, M; Albu, C; Mihailescu, N; Negut, I; Luculescu, C; Socol, M; Ristoscu, C; Mihailescu, IN
Published: NOV 28 2015, JOURNAL OF APPLIED PHYSICS, 118, DOI: 10.1063/1.4936363
The chemical modification of the niobium (Nb) surface after irradiation with femtosecond laser pulses was investigated by scanning electron microscopy coupled with energy dispersive spectroscopy, atomic force microscopy, grazing incidence X-ray diffraction, and micro-Raman spectroscopy. The physical-chemical analyses indicated that the laser treatment results in oxidation of the Nb surface, as well as in the formation of Nb hydrides. Remarkably, after the samples' washing in ethanol, a strong Surface-Enhanced Raman Scattering (SERS) signal originating from the toluene residual traces was evidenced. Further, it was observed that the laser irradiated Nb surface is able to provide a SERS enhancement of similar to 1.3 x 10(3) times for rhodamine 6G solutions. Thus, for the first time it was shown that Nb/Nb oxide surfaces could exhibit SERS functionality, and so one can expect applications in biological/biochemical screening or for sensing of dangerous environmental substances. (C) 2015 AIP Publishing LLC.
637. Atomic scale elemental mapping of light elements in multilayered perovskite coatings
Authors:
Negrea, RF; Teodorescu, VS; Ghica, C
Published: NOV 15 2015, APPLIED SURFACE SCIENCE, 355, 255, DOI: 10.1016/j.apsusc.2015.07.106
Spherical aberration corrected transmission electron microscopes offer unprecedented capabilities in materials structural characterization down to atomic resolution. Electron energy loss spectroscopy (EELS) - spectrum imaging (SI) and annular bright field (ABF) imaging allow to simultaneously identify both the position and nature of the atomic species in a crystalline material. These techniques, along with conventional high-resolution transmission electron microscopy are particularly useful in heterostructures interfaces like epitaxial multilayers characterization, for identifying possible atomic interdiffusion at sub-nanometric scale. This paper presents the structural and compositional microanalysis down to atomic resolution of an epitaxial BaTiO3/SrRuO3/SrTiO3 ferroelectric heterostructure using complex complementary analytical electron microscopy techniques. The atomic arrangement of both heavy and light atomic species across the interfaces in the BaTiO3/SrRuO3/SrTiO3 heterostructures is revealed. (C) 2015 Elsevier B.V. All rights reserved.
638. Nanostructuring of GeTiO amorphous films by pulsed laser irradiation
Authors:
Teodorescu, VS; Ghica, C; Maraloiu, AV; Vlaicu, M; Kuncser, A; Ciurea, ML; Stavarache, I; Lepadatu, AM; Scarisoreanu, ND; Andrei, A; Ion, V; Dinescu, M
Published: APR 7 2015, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 6, 900, DOI: 10.3762/bjnano.6.92
Laser pulse processing of surfaces and thin films is a useful tool for amorphous thin films crystallization, surface nanostructuring, phase transformation and modification of physical properties of thin films. Here we show the effects of nanostructuring produced at the surface and under the surface of amorphous GeTiO films through laser pulses using fluences of 10-30 mJ/cm(2). The GeTiO films were obtained by RF magnetron sputtering with 50:50 initial atomic ratio of Ge:TiO2. Laser irradiation was performed by using the fourth harmonic (266 nm) of a Nd:YAG laser. The laser-induced nanostructuring results in two effects, the first one is the appearance of a wave-like topography at the film surface, with a periodicity of 200 nm and the second one is the structure modification of a layer under the film surface, at a depth that is related to the absorption length of the laser radiation. The periodicity of the wave-like relief is smaller than the laser wavelength. In the modified layer, the Ge atoms are segregated in spherical amorphous nanoparticles as a result of the fast diffusion of Ge atoms in the amorphous GeTiO matrix. The temperature estimation of the film surface during the laser pulses shows a maximum of about 500 degrees C, which is much lower than the melting temperature of the GeTiO matrix. GeO gas is formed at laser fluences higher than 20 mJ/cm(2) and produces nanovoids in the laser-modified layer at the film surface. A glass transition at low temperatures could happen in the amorphous GeTiO film, which explains the formation of the wave-like topography. The very high Ge diffusivity during the laser pulse action, which is characteristic for liquids, cannot be reached in a viscous matrix. Our experiments show that the diffusivity of atomic and molecular species such as Ge and GeO is very much enhanced in the presence of the laser pulse field. Consequently, the fast diffusion drives the formation of amorphous Ge nanoparticles through the segregation of Ge atoms in the GeTiO matrix. The nanostructuring effects induced by the laser irradiation can be used in functionalizing the surface of the films.
639. MAPLE fabrication of thin films based on kanamycin functionalized magnetite nanoparticles with anti-pathogenic properties
Authors:
Grumezescu, V; Andronescu, E; Holban, AM; Mogoanta, L; Mogosanu, GD; Grumezescu, AM; Stanculescu, A; Socol, G; Iordache, F; Maniu, H; Chifiriuc, MC
Published: MAY 1 2015, APPLIED SURFACE SCIENCE, 336, 195, DOI: 10.1016/j.apsusc.2014.10.177
In this study we aimed to evaluate the biocompatibility and antimicrobial activity of kanamycin functionalized 5 nm-magnetite (Fe3O(4)@ KAN) nanoparticles thin films deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. A laser deposition regime was established in order to stoichiometrically transfer Fe3O4@ KAN thin films on silicone and glass substrates. Morphological and physico-chemical properties of powders and coatings were characterized by XRD, TEM, SEM, AFM and IR microscopy(IRM). Our nanostructured thin films have proved efficiency in the prevention of microbial adhesion and mature biofilms development as a result of antibiotic release in its active form. Furthermore, kanamycin functionalized nanostructures exhibit a good biocompatibility, both in vivo and in vitro, demonstrating their potential for implants application. This is the first study reporting the assessment of the in vivo biocompatibility of a magnetite-antimicrobial thin films produced by MAPLE technique. (C) 2014 Elsevier B.V. All rights reserved.
640. On the role of Fe ions on magnetic properties of doped TiO2 nanoparticles
Authors:
Tolea, F; Grecu, MN; Kuncser, V; Constantinescu, SG; Ghica, D
Published: APR 6 2015, APPLIED PHYSICS LETTERS, 106, DOI: 10.1063/1.4917037
The role of iron doping on magnetic properties of hydrothermal anatase TiO2:Fe-57 (0-1 at. %) nanoparticles is investigated by combining superconducting quantum interference device magnetometry with Mossbauer and electron paramagnetic resonance techniques. The results on both as-prepared and thermally treated samples in reduced air atmosphere reveal complexity of magnetic interactions, in connection to certain iron ion electron configurations and defects (oxygen vacancies, F-center, and Ti3+ ions). The distribution of iron ions is predominantly at nanoparticle surface layers. Formation of weak ferromagnetic domains up to 380 K is mainly related to defects, supporting the bound magnetic polaron model. (C) 2015 AIP Publishing LLC.
641. Crystallographic holes: new insights for a beneficial structural feature for photocatalytic applications
Authors:
Vajda, K; Kasa, Z; Dombi, A; Nemeth, Z; Kovacs, G; Danciu, V; Radu, T; Ghica, C; Baia, L; Hernadi, K; Pap, Z
Published: 2015, NANOSCALE, 7, 5786, DOI: 10.1039/c4nr07157c
One of the most fundamental aspects of the heterogeneous catalysis field is the manipulation of the catalysts' activity. In photocatalysis this is carried out by maximizing the right crystal plane of a semiconductor oxide. Until now, most of the papers have achieved this by a combination of different oxides, with noble metals and sometimes with carbon nanomaterials. In this work MWCNTs (multiwalled carbon nanotubes) were applied as "crystallization promoters" in a very simple, safe, one-step hydrothermal method. By this method TiO2 nano/micro crystals with exposed {001} facets were obtained in the first step. The next episode in the crystal manipulation "saga" was the modification of the (001) crystallographic plane's structure by creating ordered/own faceted "crystallographic holes". These elements are capable of further enhancing the obtained activity of titania microcrystals to a higher extent, as shown by the UV driven photocatalytic phenol degradation experiments. The appearance of the holes was "provoked" by simple calcination and their presence and influence were demonstrated by XPS and HRTEM.
642. Heterogeneous Gold Catalyst: Synthesis, Characterization, and Application in 1,4-Addition of Boronic Acids to Enones
Authors:
Moragues, A; Neatu, F; Parvulescu, VI; Marcos, MD; Amoros, P; Michelet, V
Published: SEP 2015, ACS CATALYSIS, 5, 5067, DOI: 10.1021/acscatal.5b01207
The new 1 wt % Au/TiO2-UVM-7 catalyst was prepared and fully characterized. This heterogeneous catalyst proved to be active, selective and recyclable for the unprecedented gold-catalyzed 1,4-addition of various functionalized arylboronic acids to 2-cyclohexen-1-one and other selected enones using toluene as a solvent. The gold-based catalyst was recycled two times and played an active role in this reaction, and the nature of the solvent determined a remarkable change in the products' selectivities.
643. Growth and Characterization of Arc Evaporated TiSiC-Ni Coatings
Authors:
Balaceanu, M; Parau, AC; Braic, M; Vladescu, A; Luculescu, CR; Logofatu, C; Braic, V
Published: JUN 2015, TRIBOLOGY LETTERS, 58, DOI: 10.1007/s11249-015-0521-6
TiSiC-Ni coatings, with Ni as alloying element, were prepared on Si, C 45, and 316 L steel substrates by cathodic arc technique in a reactive atmosphere of CH4. The coatings, with three different Ni contents (3.2, 6.8 and 16.2 at.%), were investigated in terms of microchemical and microstructural properties, mechanical characteristics and tribological performance using energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, hardness and adhesion measurements, and ball-on disc tribological testing. The coatings were found to consist of a mixture of different phases: face-centred cubic crystalline carbide, metallic Ni, and amorphous Si and C, with relative amounts depending on Ni concentration. All of the coatings exhibited dense and featureless morphologies. Ni addition to TiSiC coatings led to residual stress reduction (from -0.50 to -0.59 GPa) and improved adhesion strength (in the range 44-46 N). The TiSiC-Ni coatings with Ni contents below 7 at.% exhibited the best tribological properties under dry conditions (friction coefficients of similar to 0.32; wear rates from 3.16 to 3.66 x 10(-6) mm(3) N-1 m(-1)).
644. PULSED LASER DEPOSITION METHOD FOR FABRICATION OF CdS/TiO2 AND PbS PHOTOELECTRODES FOR SOLAR ENERGY APPLICATION
Authors:
Bjelajac, A; Djokic, V; Petrovic, R; Stan, GE; Socol, G; Popescu-Pelin, G; Mihailescu, IN; Janackovic, D
Published: OCT-DEC 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 1418, DOI:
Titanium films sputtered on FTO glass were used for obtaining highly oriented titania nanotubes via anodization technique. Then, pulsed laser deposition of CdS was carried out for sensitizing of similar to 60 nm wide titania nanotubes by applying 50, 100, 150 or 200 subsequent laser pulses. Scanning electron microscopy was used to indicate which samples had the open nanotubular structure of titania preserved after the deposition of CdS. Energy dispersive spectroscopy showed that a higher number of applied laser pulses results in the increase of Cd and S quantity within samples. Pulsed laser deposition technique was also employed for the fabrication of PbS counter electrode. I-V characteristics of the photovoltaic cells consisting the obtained electrodes were measured and compared under one-sun illumination. The photovoltaic cell with photoanode sensitized with CdS by applying 150 laser pulses showed the highest current density and voltage among the investigated cell.
645. Pattern formation on silicon by laser-initiated liquid-assisted colloidal lithography
Authors:
Ulmeanu, M; Petkov, P; Ursescu, D; Maraloiu, VA; Jipa, F; Brousseau, E; Ashfold, MNR
Published: NOV 13 2015, NANOTECHNOLOGY, 26, DOI: 10.1088/0957-4484/26/45/455303
We report sub-diffraction limited patterning of Si substrate surfaces by laser-initiated liquid-assisted colloidal lithography. The technique involves exposing a two-dimensional lattice of transparent colloidal particles spin coated on the substrate of interest (here Si) immersed in a liquid (e.g. methanol, acetone, carbon tetrachloride, toluene) to a single picosecond pulse of ultraviolet laser radiation. Surface patterns formed using colloidal particles with different radii in the range 195 nm <= R <= 1.5 mu m and liquids with differing indices of refraction (n(liquid)) are demonstrated, the detailed topographies of which are sensitively dependent upon whether the index of refraction of the colloidal particle (n(colloid)) is greater or smaller than n(liquid) (i.e. upon whether the incident light converges or diverges upon interaction with the particle). The spatial intensity modulation formed by diffraction of the single laser pulse by the colloidal particles is imprinted into the Si substrate.
646. B4C in ex-situ spark plasma sintered MgB2
Authors:
Burdusel, M; Aldica, G; Popa, S; Enculescu, M; Mihalache, V; Kuncser, A; Pasuk, I; Badica, P
Published: OCT 2015, CURRENT APPLIED PHYSICS, 15, 1270, DOI: 10.1016/j.cap.2015.07.017
Powder mixtures of MgB2 and B4C with composition ((MgB2) + (B4C) x, x = 0.005, 0.01, 0.03) were consolidated by Spark Plasma Sintering at 1150 degrees C for 3 min. The average particle size of B4C raw powder was relatively high of 4 mm. Despite this, it is shown that processing processes are fast and, as in the case of the in-situ routes, for our ex-situ method carbon substitutes for the boron in the crystal lattice of MgB2. Specifics of microstructure are discussed based on electron microscopy observations. Carbon substitution and microstructure contribute to enhancement of the critical current density J(c) at high magnetic fields and of the irreversibility field H-irr. Samples are shown to be in the point pinning limit with some tendency toward the grain boundary pinning depending on B4C doping amount and temperature. An optimum composition is found for x = 0.01: for this sample, at 20 K, a J(c) of 100 A/cm(2) is obtained at 5.35 T. This value is higher than for the pristine MgB2 sample and for an optimum ex-situ nano-SiC-doped sample obtained for the same SPS processing conditions. (C) 2015 Elsevier B.V. All rights reserved.
647. Dielectric Properties of LDH-Type Layered Materials Containing Zn or Mg Ions : On the Non Monotonous Temperature Dependence of Relaxation Times
Authors:
Frunza, L; Frunza, S; Ganea, CP; Zgura, I; Neatu, F; Parvulescu, VI
Published: 2015, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 18, 328, DOI:
The electrical behavior of layered double hydroxides containing Al or Ga as the trivalent ions and Mg or Zn as bivalent ions was evaluated using broadband dielectric spectroscopy in a wide temperature range. Besides conduction effects a relaxation peak is observable at high frequencies which is assigned to the reorientational fluctuations of water molecules adsorbed on the oxide surface or in the interlayer voids. The Maxwell-Wagner-Sillars peak, superimposed to the conductivity phenomenon is observable at low frequencies. A non-monotonous temperature dependence of the relaxation rates of the relaxation process has been found. A quantitative description of this dependence was possible based on a model assuming two competing processes: rotational fluctuation of water molecules and formation of additional defects. Reasonable values for the characteristic parameters were obtained. Thus the water behavior in the studied layered oxides is similar to that observed for water in other porous materials. However, the activation energy of the rotational fluctuation, the pre exponential factor and the number of defects are higher whereas the value of the energy of defect formation is lower in the layered oxide materials than for water confined to nanoporous molecular sieves, porous glasses or in bulk ice.
648. Effects of annealing in Be/W and Be/C bilayers deposited on Si(001) substrates with Fe buffer layers
Authors:
Schinteie, G; Greculeasa, SG; Palade, P; Lungu, GA; Porosnicu, C; Jepu, I; Lungu, CP; Filoti, G; Kuncser, V
Published: FEB 2015, JOURNAL OF NUCLEAR MATERIALS, 457, DOI: 10.1016/j.jnucmat.2014.11.029
Atomic intermixing processes in relation to structural aspects and phase formation in Be based thin films subjected to different annealing treatments simulating the case of re-deposited layered structures on plasma facing components in nuclear fusion devices are reported. Accordingly, bilayers of Be/W and Be/C have been deposited on Si(001) substrates with Fe buffer layers. The Fe films have been prepared by radiofrequency sputtering and further processed by annealing in hydrogen atmosphere at 300 degrees C, for 90 min, at a pressure of 10 bars of H-2. After the Be/W and Be/C bilayer deposition by means of thermionic vacuum arc method, annealing in vacuum at 600 degrees C, for 10 min has been applied to the complex structures. The influence of annealing on the phase composition and atomic intermixing processes in the complex structures has been studied by means of X-ray photoelectron spectroscopy (XPS) and conversion electron Mossbauer spectroscopy (CEMS). The layered structures present an oxidation gradient with oxide phases in the uppermost layers and non-oxidized phases in the lower layers, as observed from the XPS data. The CEMS results revealed that the as-deposited structures contain a main metallic Fe phase and secondary superparamagnetic Fe oxide phases at the Fe/Be interface, while annealed samples present a large contribution of Fe-Be and Fe-C mixtures. The annealing treatment induces considerable atomic interdiffusion, strongly dependent on the nature of the upper layer. In the case of Be/W system, the annealing provides a much rougher Be/W interface, while in case of the Be/C structure, the annealing treatment only homogenize the structure over the whole depth. (C) 2014 Elsevier B.V. All rights reserved.
649. NIR to Vis - NIR up - conversion and X-ray excited emission of Er doped high Z BiOCl
Authors:
Avram, D; Cojocaru, B; Florea, M; Teodorescu, V; Tiseanu, I; Tiseanu, C
Published: MAY 1 2015, OPTICAL MATERIALS EXPRESS, 5, 962, DOI: 10.1364/OME.5.000951
Herein, we investigate the emission properties of Er - BiOCl in the range of similar to 500 to 1700 nm under down - (488 and 973 nm) and NIR (telecom - wavelength at similar to 1500 nm) up - conversion excitation as well high energy X-ray excitation. The dependencies of red (similar to 670 nm) and NIR (similar to 800 nm) to green emission (similar to 543 nm) ratio with Er concentration, excitation mode and delay after laser pulse as well as the up - conversion excitation spectra and decays are analyzed in terms of competitive ground state absorption/excited state absorption and energy transfer up - conversion mechanisms. The CIE chromaticity diagram show single excitation (similar to 1500 nm), delay induced emission color change from yellowish green (delay of 0.001 ms) to reddish orange (delay of 1 ms). The X-ray induced emission of Er - BiOCl presents an atypical red to green emission ratio that exceeds that measured under optical down - conversion excitation by a factor of 13. The potential of Er - BiOCl for optical/X-ray imaging applications is discussed. (C)2015 Optical Society of America
650. On the photocatalytic reduction of MU tetrazolium salt on the surface of TiO2 nanoparticles: Formazan production kinetics and mechanism
Authors:
Popescu, T; Lupu, AR; Raditoiu, V; Purcar, V; Teodorescu, VS
Published: NOV 1 2015, JOURNAL OF COLLOID AND INTERFACE SCIENCE, 457, 120, DOI: 10.1016/j.jcis.2015.07.005
Hypothesis: The MU [3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide] cell cytotoxicity indicator is photocatalytically reduced on the surface of TiO2 nanoparticles in phosphate-buffered-saline (PBS) environment. We hypothesize that specific phosphate adsorption may be used to modulate the efficiency of the TiO2 MU reaction through colloidal and semiconductor-liquid interface processes. Experiments: The TiO2 MU reaction kinetics was studied in PBS, with respect to photocatalyst and MIT concentrations and irradiation wavelength. The effects of PBS and electron scavengers (Fe3+ ions) on reaction efficiency and the role of colloidal surface charge in the photocatalytic process were investigated. The structural and spectroscopic characteristics of relevant TiO2-formazan systems were studied by X-ray diffraction, transmission electron microscopy and IR-spectroscopy. Findings: The reaction was pseudo-first order with respect to photocatalyst and showed a negative and fractional partial order with respect to MU. Formazan production rates were directly proportional to radiation wavelength and TiO2 concentration and inversely proportional to the MIT initial concentration. The addition of Fe3+ ions, as well as the absence of PBS, induced strong reaction inhibition. Reaction efficiency and catalyst Zeta potential were enhanced by Na2HPO4 (PBS component) and showed a maximum around the phosphate concentration 0.005 M. Findings: Structural/spectroscopic characterization confirmed the formation of amorphous MU-formazan on the surface of TiO2 and the TiO2-phosphate binding. (C) 2015 Elsevier Inc. All rights reserved.
651. Synthesis of Copper Particles by Non-thermal Atmospheric Pressure Plasma Jet
Authors:
Lazea-Stoyanova, A; Vlad, A; Vlaicu, AM; Teodorescu, VS; Dinescu, G
Published: AUG 2015, PLASMA PROCESSES AND POLYMERS, 12, 709, DOI: 10.1002/ppap.201400197
The present study reveals the synthesis of metallic particles at atmospheric pressure using a radiofrequency low-temperature argon plasma jet. Copper bulk material of the powered electrode acted as solid precursor in the process and the metallic particles were obtained directly in gaseous environment. The particles were collected onto Si (100)-oriented substrates downstream of the atmospheric plasma jet and were ex situ characterized via optical microscopy, scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. We obtained copper particles, reddish brown in color, either of nano-or micro-metric sizes. Additionally, the plasma species and gas temperature were determined by OES. In conclusion, it was demonstrated that conversion of bulk metals into particles is possible at atmospheric pressure using a radiofrequency plasma jet and the development of several applications is recommended.
652. Field - dipole interactions in L-cysteine-thiolate self assembled at p- and n-GaAs(100) electrodes
Authors:
Lazarescu, V; Toader, AM; Enache, M; Preda, L; Anastasescu, M; Dobrescu, G; Negrila, C; Lazarescu, MF
Published: SEP 10 2015, ELECTROCHIMICA ACTA, 176, 124, DOI: 10.1016/j.electacta.2015.06.121
L-cysteine-thiolate monolayers spontaneously self-assembled on p- and n-GaAs(100) electrodes have been investigated by electrochemical impedance spectroscopy in H2SO4 solutions. On p-doped samples a potential-induced reversible proton transfer occurs within the L-cysteine-thiolate layer during both forward and backward potential scans; in contrast, on n-doped samples it is observed only in the reverse scan. The XPS data and the fractal analysis of the AFM images point to the field - dipole interactions operating distinctively in the L-cysteine-thiolate layer formed at p-and n-doped semiconducting substrates as the origin of the observed difference. The interaction of this small but highly polar molecule with the electrostatic field driven by the diffuse distribution of the excess charge in the semiconductor subsurface region both in equilibrium and under polarization conditions turned out to play a key role in determining the optimal orientation of the two polar groups. The latter one seems to be a prerequisite for the potential-induced internal proton transfer. (C) 2015 Elsevier Ltd. All rights reserved.
653. Effect of optical coating in the thin-film system of chalcogenide glassy semiconductor-dielectric when recording the holographic optical information
Authors:
Chirita, A; Prilepov, V; Popescu, M; Andries, I; Caraman, M; Jidcov, IU
Published: JUL-AUG 2015, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17, 929, DOI:
In this paper we show that the possibility of obtaining the high values of efficiency of relief-phase holographic gratings formed in the photo-thermoplastic recording process holds not only due to the non-sinusoidal profile form, but also due to the effect of optical coating that appears in the two-layer system of photo-semiconductor deformed thermoplastic. Analyzed are the conditions, under which takes place the antireflection optical coating, reducing unwanted reflections from surfaces and thereby enhancing efficiency. It is shown that by careful choice of the thicknesses and refractive indices of the layers materials the efficiency of holographic gratings can be improved by 2-5 %.
654. Simulation of the capacitance-voltage characteristic in the case of epitaxial ferroelectric films with Schottky contacts
Authors:
Filip, LD; Pintilie, L; Stancu, V; Pintilie, I
Published: OCT 1 2015, THIN SOLID FILMS, 592, 206, DOI: 10.1016/j.tsf.2015.08.046
The current-voltage (C-V) characteristic of epitaxial ferroelectric films is simulated assuming the presence of Schottky-type contacts at the two electrode interfaces. The model assumes that the overall capacitance of the metal-ferroelectric-metal (MFM) structure is composed of two parts: (i) one associated with the Schottky contacts, in which the ferroelectric polarization is saturated, the dielectric constant is independent on the voltage and only the linear response to the applied electric field is taken into account; (ii) one related to the ferroelectric volume, where the dielectric constant is voltage dependent through the hysteresis response of the ferroelectric polarization. Themost important result of the model is that it can simulate the experimentally observed thickness dependence of the dielectric constant without considering a so-called "dead layer" at the electrode interface. The model renders C-V characteristics in good qualitative agreement with the experimental ones in the case of an MFM structure based on epitaxial PZT films. The quantitative fit suggests that the behaviour of the ferroelectric polarization during the C-V measurement may be very different from its behaviour during the hysteresis measurement. This is explained by the fact that the two measurements have very different principles. It is also found that the dielectric constant of the ferroelectric volume has a different voltage dependence compared to the one derived from the hysteresis loop or from the experimental C-V characteristic. This is also related to the different measurement principles and to the fact that the measured capacitance of the MFM structure includes, besides the ferroelectric volume, the voltage dependent capacitance of the Schottky contacts. (C) 2015 Elsevier B.V. All rights reserved.
655. Structural and biological evaluation of lignin addition to simple and silver-doped hydroxyapatite thin films synthesized by matrix-assisted pulsed laser evaporation
Authors:
Jankovic, A; Erakovic, S; Ristoscu, C; Mihailescu, N; Duta, L; Visan, A; Stan, GE; Popa, AC; Husanu, MA; Luculescu, CR; Srdic, VV; Janackovic, D; Miskovic-Stankovic, V; Bleotu, C; Chifiriuc, MC; Mihailescu, IN
Published: JAN 2015, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 26, DOI: 10.1007/s10856-014-5333-y
We report on thin film deposition by matrix-assisted pulsed laser evaporation of simple hydroxyapatite (HA) or silver (Ag) doped HA combined with the natural biopolymer organosolv lignin (Lig) (Ag:HA-Lig). Solid cryogenic target of aqueous dispersions of Ag:HA-Lig composite and its counterpart without silver (HA-Lig) were prepared for evaporation using a KrF* excimer laser source. The expulsed material was assembled onto TiO2/Ti substrata or silicon wafers and subjected to physical-chemical investigations. Smooth, uniform films adherent to substratum were observed. The chemical analyses confirmed the presence of the HA components, but also evidenced traces of Ag and Lig. Deposited HA was Ca deficient, which is indicative of a film with increased solubility. Recorded X-ray Diffraction patterns were characteristic for amorphous films. Lig presence in thin films was undoubtedly proved by both X-ray Photoelectron and Fourier Transform Infra-Red Spectroscopy analyses. The microbiological evaluation showed that the newly assembled surfaces exhibited an inhibitory activity both on the initial steps of biofilm forming, and on mature bacterial and fungal biofilm development. The intensity of the antibiofilm activity was positively influenced by the presence of the Lig and/or Ag, in the case of Staphylococcus aureus, Pseudomonas aeruginosa and Candida famata biofilms. The obtained surfaces exhibited a low cytotoxicity toward human mesenchymal stem cells, being therefore promising candidates for fabricating implantable biomaterials with increased biocompatibility and resistance to microbial colonization and further biofilm development.
656. Effect of counterion on the mesomorphic behavior and optical properties of columnar pyridinium ionic liquid crystals derived from 4-hydroxypyridine
Authors:
Pana, A; Badea, FL; Ilis, M; Staicu, T; Micutz, M; Pasuk, I; Circu, V
Published: MAR 5 2015, JOURNAL OF MOLECULAR STRUCTURE, 1083, 251, DOI: 10.1016/j.molstruc.2014.11.059
A series of 3,4,5-tridodecyloxybenzyl pyridinium salts derived from 4-hydroxypyridine has been designed and prepared. The liquid crystalline properties of these compounds were investigated by polarized optical microscopy, differential scanning calorimetry and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis. The N-3,4,5-tridodecyloxybenzyl-4-pyridone intermediate shows a monotropic columnar hexagonal mesophase ranging from 56 degrees C down to room temperature while the corresponding bromide dodecyl O-alkylated pyridinium salt shows one enantiotropic columnar mesophase and one additional monotropic columnar phase at lower temperatures. Replacing bromide ion (Br-) with other counterions (NO3-, BF4- and PF6-) resulted in mesophase suppression. These luminescent pyridinium salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. Photoluminescent properties of the pyridinium salts do not depend significantly on the nature of counterion employed. (C) 2014 Elsevier B.V. All rights reserved.
657. IN-SITU IODINE DOPED POLYTHIOPHENE-LIKE THIN FILMS OBTAINED BY POST-DISCHARGE RF PLASMA
Authors:
Satulu, V; Ion, V; Aldica, G; Mitu, B; Dinescu, G
Published: 2015, ROMANIAN JOURNAL OF PHYSICS, 60, 1560, DOI:
This work reports on the synthesis of polythiophene-like thin films by using a post-discharge RF plasma configuration in which thiophene vapors are introduced in the substrate proximity. The deposition process is assisted by a controlled iodine flow for in-situ doping leading to a material with improved conductivity. The influence of iodine mass flow rate on the deposition rate, optical parameters, composition, chemical structure and electrical properties of the material obtained in various discharge conditions is reported.
658. Ferromagnetic behaviour of bismuth germanate oxides glass-ceramic materials
Authors:
Polosan, S; Negrea, R; Ciobotaru, IC; Schinteie, G; Kuncser, V
Published: FEB 25 2015, JOURNAL OF ALLOYS AND COMPOUNDS, 623, 196, DOI: 10.1016/j.jallcom.2014.10.104
The content of defects in Bi4Ge3O12 (BGO) glass-ceramic materials together with their ordering during crystallization induces ferromagnetic behaviours in these materials. The observed ferromagnetism has to be associated strictly with the GeO4 related defects in the atypical amorphous phase. The photoluminescence of BGO glass-ceramic materials can give useful information about the nature of defects, especially the oxygen vacancies from the GeO4 tetrahedra and Bi4Ge3O12 cubic structures. The concentration of these defects depends on annealing between 600 degrees C and 700 degrees C where orthorhombic and cubic phases coexist. The magnetization at saturation is higher in the samples dominated by the amorphous phase and the strength of the exchange interaction is higher in the samples dominated by the cubic phase, obtained over 700 degrees C, when the GeO4 tetrahedra are rearranged during crystallization together with their oxygen vacancies. (C) 2014 Elsevier B.V. All rights reserved.
659. Arylation of alkynes over hydrotalcite docked Rh-m-TPPTC complex
Authors:
Neatu, F; Ciobanu, M; Stoflea, LE; Frunza, L; Parvulescu, VI; Michelet, V
Published: JUN 1 2015, CATALYSIS TODAY, 247, 162, DOI: 10.1016/j.cattod.2014.07.004
Rh-m-TPPTC complex was successful immobilized onto a hydrotalcite Zn-Al to convert selectively in aqueous media both the symmetric and nonsymmetric alkynes into functionalized alkenes, with boronic acids. The complex preserved its activity after the ionic exchange, leading to excellent results (similar to 87%) for the symmetric alkynes and also for the non-symmetrical alkynes (up to 99%). (C) 2014 Elsevier B.V. All rights reserved.
660. Analysis of bimodal thermally-induced denaturation of type I collagen extracted from calfskin
Authors:
Staicu, T; Circu, V; Ionita, G; Ghica, C; Popa, VT; Micutz, M
Published: 2015, RSC ADVANCES, 5, 38406, DOI: 10.1039/c5ra02708j
The most widely occurring collagen in the extracellular matrix of the mammalian tissues - type I collagen has attracted huge interest from both theoretical and practical points of view. The results presented herein are mainly confined to a study of the thermal stability of type I collagen (CI) extracted from calfskin in acidic solutions (10(-2) M HCl). A two-step process associated with the heat-induced denaturation of CI was revealed by using ultra sensitive differential scanning calorimetry. The minor endothermic transition (peak temperatures of about 30.5-30.8 degrees C) has been assigned to the defibrillation of small supramolecular CI assemblies (occurring in solution) while the major endothermic transition (about 34.8-35.0 degrees C) has been ascribed to denaturation of CI, consisting of a complete unfolding of the native triple-helical conformation of the collagen molecule. The calorimetric data were supported by information obtained from capillary viscometry performed on the same solutions. The native state of CI (molecular integrity and triple-helical conformation) for all the systems studied in this paper was confirmed by transmission electron microscopy, ultraviolet circular dichroism and capillary viscometry. At the same time, based on the sodium dodecyl sulphate-polyacrylamide gel electrophoresis and an appropriate image processing of the corresponding electropherogram, a certain degree of intramolecular crosslinking of CI was detected, mainly between alpha 1 and alpha 2 chains of the collagen triple-helix. Such a feature seems to be caused by both the nature of the extraction procedure and the storage conditions.
661. Room temperature ammonia sensing with barium strontium titanate under humid air background
Authors:
Simion, CE; Sackmann, A; Teodorescu, VS; Rusti, CF; Stanoiu, A
Published: DEC 1 2015, SENSORS AND ACTUATORS B-CHEMICAL, 220, 1246, DOI: 10.1016/j.snb.2015.07.045
Within the field of chemical gas sensing, ammonia detection represents one of the nowadays challenges, due to its adverse effects for human health. Real operating investigations are imposed by the high solubility potential of NH3 at room temperature. Thick films of Ba0.75Sr0.25TiO3 material have been investigated by means of electrical resistance and capacitance changes and correlated with the photoacoustic outputs. The experimental findings have been discussed in terms of Grotthuss mechanism, with respect to the ionic/electronic conduction within BST, toward ammonia detection enhanced by the presence of water vapors when operated at room temperature. So an appropriate NH3 sensing mechanism was proposed. (C) 2015 Elsevier B.V. All rights reserved.
662. Hydrothermal synthesis of nanostructured hybrids based on iron oxide and branched PEI polymers. Influence of high pressure on structure and morphology
Authors:
Popescu, LM; Piticescu, RM; Petriceanu, M; Ottaviani, MF; Cangiotti, M; Vasile, E; Dirtu, MM; Wolff, M; Garcia, Y; Schinteie, G; Kuncser, V
Published: JUL 1 2015, MATERIALS CHEMISTRY AND PHYSICS, 161, 95, DOI: 10.1016/j.matchemphys.2015.05.018
Homogeneous hybrids in which iron oxide nanoparticles are entrapped within polymer structure are of interest for their potential applications in biomedical field, such as diagnostic, therapeutic and theranostic purposes. For this reason, hybrid nanomaterials based on branched polyethyleneimine (PEI) and iron oxide with different ratios were synthesized in a single step by hydrothermal procedure at high pressure and low temperature. Iron oxide is formed in the presence of branched PEI and the interaction between them takes place in the reaction medium. The influence of synthesis parameters on the hybrid formation, as well as chemical and structural properties was studied by means of FTIR, DSC-TG, HRTEM, electron paramagnetic resonance (EPR), magnetic measurements (SQUID) and Fe-57 Mossbauer analyses. It has been shown that synthesis parameters influence thermal stability and morphology of the hybrids. FeO(OH) crystallites of 2-5 nm are formed. Iron oxyhydroxide nanoparticles strongly entrapped in PEI structure are obtained. The low and distributed values of the specific spontaneous magnetisation in samples prepared under the same pressure conditions support the presence of very fine FeO(OH) nanoparticles, which formation and magnetic properties are depending on the mass ratio between iron oxide and PEI. (C) 2015 Elsevier B.V. All rights reserved.
663. GMR ON CuNiCo THIN LAYERS DEPOSITED USING TVA METHOD
Authors:
Prioteasa, I; Porosnicu, C; Lungu, CP; Jepu, I; Schinteie, G; Ciupina, V; Prodan, G; Vasile, E; Dinca, P
Published: APR-JUN 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 436, DOI:
Thermionic vacuum arc was successfully used to prepare high quality nanostructure thin films with different fields of applicability. One advantage of this deposition technique was the ability to have a controlled range of thicknesses starting from few nanometers to hundreds of nanometers. The purity of the thin films was insured by a high vacuum pressure and a lack of any kind of buffer gas inside the coating chamber. The aim of this work was to obtain significant magnetic response and to compare the MR to the structures obtained for two different granular combinatorial structures. The samples were investigated using scaning and transmision electron mycroscopy while SEM and The magnetic properties were first studied by measuring the electrical resistance behavior for a magnetic field of 0.3 T, at different values of the sample temperature and using a non-destructive optical method called Magneto-Optical Kerr Effect (MOKE). The magnetoresistive effect obtained for the studied samples varied from 0.6% to 19% in respect sample structure and temperature for a constant magnetic field.
664. Encapsulation of iron atoms between framgments of graphene planes
Authors:
Siklitskaya, AV; Ivanov-Omskii, VI; Chekulaev, MS; Yastrebov, SG; Smith, R; Slav, A; Morosanu, C; Kozyrev, SV
Published: OCT 2015, NANOSYSTEMS-PHYSICS CHEMISTRY MATHEMATICS, 6, DOI: 10.17586/2220-8054-2015-6-5-680-688
In this paper, we apply results of analysis of the Raman spectrum from an amorphous carbon film modified with iron (a - C : Fe) which leads to construction of clusters containing fragments of graphene and a layer of iron atoms. Such clusters may be candidates for the role of microwave radiation absorbers. For the Raman experiments we performed deposition of a thin film of a -C : Fe. Details of the film deposition process, together with the corresponding Raman experiments are presented in this paper. Comparison with a literature model was performed for the intensity ratio of the maxima for specific Raman bands, using the letter D to represent " disorder" and the letter G to represent "graphite". Comparison gives evidence for the existence of nanosize fragments of graphene embedded in an amorphous matrix of the a - C : Fe film. The diameter of the fragments is predicted to attain a value of about 1.2 nm. Moreover, in a comparison with experimental data for defective graphite, the position of the maximum of the D band for a- C : Fe appeared to be red shifted. This could support the proposition that damping of Raman-active oscillations occurs by an electron gas in fragments of graphene after introduction of iron, e. g. after intercalation. On the basis of these estimates, we modeled a symmetrical polycyclic aromatic hydrocarbon having a similar size and converted it into fragment of a graphene plane by removal of hydrogen atoms occupying the edge states. To preserve symmetry, we placed atoms of iron on top of the fragment, situating them exactly above the centers of hexagons at a certain distance and placed another fragment of graphene on the top of the iron atoms, symmetrically. For a distance of 2.52 angstrom between the centers of the hexagon and the iron atom, distortions of carbon-carbon valence bonds and angles were found to be minimal, as shown through optimization of the system's geometry using the Avogadro molecular editor. This result supports an hypothesis of graphene fragments during the growth of an amorphous carbon film modified by simultaneous addition of a dopant metal such as iron. This example may illustrate the stability of a two-dimensional electron gas confined between the fragments.
665. Structural, magnetic and catalytic properties of cobalt chromite obtained through precursor method
Authors:
Gingasu, D; Mindru, I; Culita, DC; Patron, L; Calderon-Moreno, JM; Osiceanu, P; Preda, S; Oprea, O; Parvulescu, V; Teodorescu, V; Walsh, JPS
Published: FEB 2015, MATERIALS RESEARCH BULLETIN, 62, 64, DOI: 10.1016/j.materresbull.2014.11.009
Cobalt chromite (CoCr2O4) was synthesized through the precursor method. The precursors: (NH4)(3)[CoCr2(C4O6H4)(4)(OH)(3)]center dot 4H(2)O, (NH4)(3)[CoCr2(C6O7H10)(4)(C6O7H9)]center dot 5H(2)O were characterized by elemental chemical analysis, infrared (IR) and ultraviolet-visible (UV-vis) spectroscopy, and thermal analysis. The final oxides were characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM/TEM), UV-vis, IR, Raman spectroscopy (RS), magnetic measurements, N-2 adsorption-desorption analyses and X-ray photoelectron spectroscopy (XPS). XRD confirmed the cubic CoCr2O4 phase only and determined average crystallite sizes between 14 and 21 nm. Electron microscopy revealed morphology corresponding to the complete crystallization into cubic CoCr2O4. All the samples presented ferrimagnetic ordering below the Currie temperature (T-c), and a phase transition at T-s similar to 26 K attributed to the onset of long-range spiral magnetic order. The CoCr2O4 nanoparticles generated through the gluconate route following calcination at 700 degrees C for 1 h were found to have the best catalytic activity in the total oxidation of methane. (C) 2014 Elsevier Ltd. All rights reserved.
666. Layered materials of LDH-type containing Zn ions: dielectric measurements show rotational fluctuations of water molecules
Authors:
Frunza, L; Ganea, P; Zgura, I; Frunza, S; Neatu, F; Parvulescu, VI
Published: 2015, 2015 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 70, DOI:
Layered double hydroxide (LDH) materials containing Zn ions were studied by broadband dielectric spectroscopy to follow up rotational molecular dynamics of confined water. One main relaxation process was observed in the experimental window; it was assigned to fluctuations of water molecules forming a strongly adsorbed thin layer upon the oxide surface. The temperature dependence of the relaxation rates has an unusual shape characterized by the presence of a maximum. Despite the characteristic parameters, this non-monotonous dependence is shown to be a rather general feature for water confined to LDHs.
667. INVESTIGATIONS OF PULSED LASER DEPOSITED TiN THIN FILMS FOR TITANIUM IMPLANTS
Authors:
Popescu-Pelin, G; Craciun, D; Socol, G; Cristea, D; Floroian, L; Badea, M; Socol, M; Craciun, V
Published: 2015, ROMANIAN REPORTS IN PHYSICS, 67, 1502, DOI:
TiN thin films were deposited at room temperature on polished Ti samples by PLD. GIXRD investigations showed that films were crystalline, with grain sizes around 25 run. Simulations of XRR curves indicated that the layers were dense and only slightly rougher than Ti substrates. Nanoindentation results showed that TiN films possessed a hardness of 26.8 GPa, much harder than Ti substrate, while scratch and wear tests found that films were adherent and exhibited a low friction coefficient of 0.16. Electrochemical tests performed in SBF indicated that the coated Ti samples exhibited significantly better behavior against corrosion than bare Ti samples.
668. Low Power Resistive Oxygen Sensor Based on Sonochemical SrTi0.6Fe0.4O2.8 (STFO40)
Authors:
Stratulat, A; Serban, BC; de Luca, A; Avramescu, V; Cobianu, C; Brezeanu, M; Buiu, O; Diamandescu, L; Feder, M; Ali, SZ; Udrea, F
Published: JUL 2015, SENSORS, 15, 17506, DOI: 10.3390/s150717495
The current paper reports on a sonochemical synthesis method for manufacturing nanostructured (typical grain size of 50 nm) SrTi0.6Fe0.4O2.8 (Sono-STFO40) powder. This powder is characterized using X ray-diffraction (XRD), Mossbauer spectroscopy and Scanning Electron Microscopy (SEM), and results are compared with commercially available SrTi0.4Fe0.6O2.8 (STFO60) powder. In order to manufacture resistive oxygen sensors, both Sono-STFO40 and STFO60 are deposited, by dip-pen nanolithography (DPN) method, on an SOI (Silicon-on-Insulator) micro-hotplate, employing a tungsten heater embedded within a dielectric membrane. Oxygen detection tests are performed in both dry (RH = 0%) and humid (RH = 60%) nitrogen atmosphere, varying oxygen concentrations between 1% and 16% (v/v), at a constant heater temperature of 650 degrees C. The oxygen sensor, based on the Sono-STFO40 sensing layer, shows good sensitivity, low power consumption (80 mW), and short response time (25 s). These performance are comparable to those exhibited by state-of-the-art O-2 sensors based on STFO60, thus proving Sono-STFO40 to be a material suitable for oxygen detection in harsh environments.
669. Chemically assembled light harvesting CuOx-TiO2 p-n heterostructures
Authors:
Anastasescu, C; Spataru, N; Culita, D; Atkinson, I; Spataru, T; Bratan, V; Munteanu, C; Anastasescu, M; Negrila, C; Balint, I
Published: DEC 1 2015, CHEMICAL ENGINEERING JOURNAL, 281, 311, DOI: 10.1016/j.cej.2015.06.098
CuOx nanorods grown by calcination on a Cu plate and TiO2 successive layers were assembled by chemical means to obtain a broad band light captor. The synthesis of composite with complex architecture aimed at maximization of light absorption and at improvement of electron-holes separation of via the multiple n-p heterojunctions created at TiO2-CuOx boundaries, formed mostly by filling the pore network composite material with CuOx. Au nanoparticles were embedded into TiO2 matrix to enhance the light harvesting ability in visible domain via surface plasmon resonance (SPR) phenomenon and to help the photo-generated charge separation through the formation of Schottky barriers. Dual p-n semiconducting character of the composite was clearly evidenced by photoelectrochemical measurements. The composite material exhibited photoresponse even at wavelengths higher than 420 nm (in visible domain), both in cathodic and anodic regions. The enhanced light adsorption characteristics, the advancement in synthesis procedure of CuOx-Au_TiO2 composite material provide rationale for further development of novel light captor composites for photoenergy conversion. Other applications such electronics and gas sensors are envisaged. (C) 2015 Elsevier B.V. All rights reserved.
670. Reconstruction of superparamagnetic particle grain size distribution from Romanian loess using frequency dependent magnetic susceptibility and temperature dependent Mossbauer spectroscopy
Authors:
Necula, C; Panaiotu, C; Schinteie, G; Palade, P; Kuncser, V
Published: AUG 2015, GLOBAL AND PLANETARY CHANGE, 131, 103, DOI: 10.1016/j.gloplacha.2015.05.009
Previous studies have shown that the magnetic parameters of the Romanian loess/paleosol sequences have recorded Quaternary glacial/interglacial cycles over the last 600 kyr. Previous rock magnetic investigations pointed out that the magnetic enhancement in Romanian loess sequences is mainly due to pedogenic magnetite close to superparamagnetic/stable single domain boundary. We report the first reconstruction of grain size distribution (GSD) of the superparamagnetic (SP) particles for two Romanian loess deposits, Costinesti and Mircea Voda, located in the Dobrogea Plateau between the Danube River and the Black Sea. The GSDs were obtained using both the wide-band frequency spectrum of magnetic susceptibility (FSMS) method and low temperature Mossbauer spectroscopy. The FSMS method shows that the SP particles are present both in loess and paleosols. The GSDs in loess are shifted to slightly higher diameters with respect to paleosols. The concentration of SP particles has an opposite trend. The largest value is reached in the forest paleosol and the lowest in the loess samples. Both loess and paleosols indicated almost the same dominant grain size (about 17 nm in paleosols and 18 nm in loess samples). However the GSD shapes in loess are different than those found in paleosols. in the paleosols, the shape of GSDs seems to be independent of climate and degree of pedogenesis. These factors control only the concentration of SP particles present in each paleosol. Temperature dependent Mossbauer spectroscopy also supports the presence of SP particles both in loess and paleosol with a mean diameter around 13-14 nm. Dispersion of the diameters in the case of Mossbauer spectroscopy varies from sample to sample being probably affected by random surface defects. (C) 2015 Elsevier B.V. All rights reserved.
671. High Permittivity (1-x)Ba(Zr0.2Ti0.8)O-3 - x(Ba0.7Ca0.3)TiO3 (x=0.45) Epitaxial Thin Films with Nanoscale Phase Fluctuations
Authors:
Scarisoreanu, ND; Craciun, F; Moldovan, A; Ion, V; Birjega, R; Ghica, C; Negrea, RF; Dinescu, M
Published: NOV 4 2015, ACS APPLIED MATERIALS & INTERFACES, 7, 23992, DOI: 10.1021/acsami.5b06745
Epitaxial (1 - x)Ba(Ti0.8Zr0.2)TiO3 - x(Ba0.7Ca0.3)TiO3, x = 0.45 (BCZT 45), thin films have been deposited on (001) SrTiO3 (STO) and (001/100) SrLaAlO4 (SLAO) substrates by pulsed laser deposition. X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) confirmed the epitaxial growth of the films. A high structural quality has been evidenced for the BCZT/STO films. Geometric phase analysis (GPA) associated with the HRTEM enabled us to obtain microstrain analysis and the in-plane and out-of-plane lattice parameter variation on different areas. Tetragonality ratio fluctuations at nanoscale level which are relevant for the existence of nanodomains have been evidenced on the BCZT/STO films. The in-plane dielectric constant has been measured on interdigital electrodes deposited by lift-off technique on the top of the films. High values of dielectric permittivity (>3000) combined with low dielectric loss (<0.01) are obtained for BCZT 45 film deposited on STO substrate, showing nearly constant values between 1 kHz and 10 MHz. The high dielectric permittivity of BCZT thin films was attributed to their high structural quality and to the loss of rotation stability of the polarization associated with the presence of nanodomains. This results into a divergence of fluctuations of polarization direction and a peak of dielectric susceptibility. The enhanced switching of such nanodomain configuration was probed by piezoforce microscopy, by writing and reading domains during topography scanning.
672. Physicochemical Characterization and In Vitro Cytotoxic Effect of 3-Hydroxyflavone in a Silver Nanoparticles Complex
Authors:
Voicescu, M; Craciunescu, O; Moldovan, L; Anastasescu, M; Angelescu, DG; Teodorescu, VS
Published: SEP 2015, JOURNAL OF FLUORESCENCE, 25, 1223, DOI: 10.1007/s10895-015-1608-z
The aim of this work was to characterize the physico-chemical properties of 3-hydroxyflavone (3-HF) in a silver nanoparticles complex (SNPs) using UV-vis and Fluorescence spectroscopy, Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) analysis. One also evaluated its effect on the cell viability and morphology of L929 mouse fibroblast cells in vitro. The contribution of the carrier protein, Bovine Serum Albumin (BSA) to 3-HF properties has also been investigated. 3-HF in BSA/SNPs systems presented no cytotoxic effect in L929 mouse fibroblast cells at any of the tested concentrations. The results are discussed with relevance to the oxidative stress process.
673. Approach for an improved experimental evaluation of the specific absorption rate in magnetic fluid hyperthermia
Authors:
Iacob, N; Schinteie, G; Palade, P; Kuncser, V
Published: APR 18 2015, JOURNAL OF NANOPARTICLE RESEARCH, 17, DOI: 10.1007/s11051-015-2997-2
A new methodology for the accurate determination of the specific absorption rate of ferrofluids with magnetite nanoparticles of average size of about 10 nm subjected to alternative current magnetic fields is proposed. A simple numerical compensation of the heating rates by the cooling rates obtained at similar temperatures is employed. Comparisons of the as-obtained adiabatic heating curves with theoretical evaluations are discussed.
674. Mesostructured vanadia-alumina catalysts for the synthesis of vitamin K-3
Authors:
Florea, M; Marin, RS; Palasanu, FM; Neatu, F; Parvulescu, VI
Published: OCT 1 2015, , DOI: 10.1016/j.cattod.2014.12.026
675. Deoxygenation of oleic acid: Influence of the synthesis route of Pd/mesoporous carbon nanocatalysts onto their activity and selectivity
Authors:
Dragu, A; Kinayyigit, S; Garcia-Suarez, EJ; Florea, M; Stepan, E; Velea, S; Tanase, L; Colliere, V; Philippot, K; Granger, P; Parvulescu, VI
Published: SEP 5 2015, , DOI: 10.1016/j.apcata.2015.01.008
676. Toward a Unified Description of Luminescence-Local Structure Correlation in Ln Doped CeO2 Nanoparticles: Roles of Ln Ionic Radius, Ln Concentration, and Oxygen Vacancies
Authors:
Avram, D; Sanchez-Dominguez, M; Cojocaru, B; Florea, M; Parvulescu, V; Tiseanu, C
Published: JUL 16 2015, , DOI: 10.1021/acs.jpcc.5b02240
677. Dry reforming of methane on ceria prepared by modified precipitation route
Authors:
Rotaru, CG; Postole, G; Florea, M; Matei-Rutkovska, F; Parvulescu, VI; Gelin, P
Published: MAR 25 2015, , DOI: 10.1016/j.apcata.2015.01.024
678. Non-equilibrium transport and spin dynamics in single-molecule magnets
Authors:
Moldoveanu, V; Dinu, IV; Tanatar, B
Published: NOV 2015, SUPERLATTICES AND MICROSTRUCTURES, 87, 76, DOI: 10.1016/j.spmi.2015.06.027
The time-dependent transport through single-molecule magnets (5MM) coupled to magnetic or non-magnetic electrodes is studied in the framework of the generalized Master equation (GME) method. We calculate the transient currents which develop when the molecule is smoothly coupled to the source and drain electrodes. The signature of the electrically induced magnetic switching on these transient currents is investigated. Our simulations show that the magnetic switching of the molecular spin can be read indirectly from the transient currents if one lead is magnetic and it is much faster if the leads have opposite spin polarizations. We identify effects of the transverse anisotropy on the dynamics of molecular states. (C) 2015 Elsevier Ltd. All rights reserved.
679. Advanced ceramics in the SnO2-ZnO binary system
Authors:
Mihaiu, S; Toader, A; Atkinson, I; Mocioiu, OC; Hornoiu, C; Teodorescu, VS; Zaharescu, M
Published: APR 2015, CERAMICS INTERNATIONAL, 41, 4945, DOI: 10.1016/j.ceramint.2014.12.056
In the present work, we report a systematic study of the phase formation and sintering ability of different oxide compositions in the SnO2-ZnO binary system using solid state reactions. For some selected compositions mechanically activated powders were also investigated. Structural and morphological characterizations of the samples were performed by X-ray diffraction (XRD), FT-IR Spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Only the formation of Zn2SnO4 binary compound was revealed in the experimental conditions. Based on the structural results the subsolidus equilibrium phase diagram was established. The sintering ability of the studied samples was also determined, establishing the compositions domains of obtaining dense or porous ceramics. The investigation by impedance spectroscopy in the 300-600 K temperature range shows that all studied samples exhibit n-type semiconductor behavior with low values of the activation energy (0.18-0.34 eV). (C) 2014 Elsevier Ltd and Teclma Group S.r.l. All rights reserved.
680. SHAPE MEMORY PROPERTIES OF FeNiCoTi RIBBONS EVIDENCED BY MAGNETIC MEASUREMENTS
Authors:
Tolea, F; Sofronie, M; Tolea, M; Kuncser, V; Valeanu, M
Published: APR-JUN 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 575, DOI:
The present work addresses the shape memory and (ferro) magnetic properties of Fe52Ni29-xCo15+xTi4 (with x=0, 3 and 6) alloys. The analysed samples were prepared as ribbons by the melt spinning method and subjected to thermal treatments. X-ray diffraction, DSC, thermomagnetic measurements and Mossbauer spectroscopy were used for a complete structural and magnetic characterization. Both the preparation route and the different Co addition induce specific effects which are discussed in detail. The sample with x=0 sustains an irreversible transformation, while a partial reversible transformation and a relatively increased Curie temperature were observed for sample with x=3. However, further increasing the Co content to x= 6 leads to a loss of the martensitic transformation.
681. Electron Reconfiguration and Enhanced Phonon Activation in the Superconducting State of a FeSe0.3Te0.7 Single Crystal, as Evidenced by Mossbauer Spectroscopy
Authors:
Greculeasa, S; Miu, L; Badica, P; Nie, J; Tolea, M; Kuncser, V
Published: JAN 15 2015, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84, DOI: 10.7566/JPSJ.84.014701
The Mossbauer spectra of a FeSe0.3Te0.7 single crystal grown by the Bridgman method were analysed across the superconducting transition by considering the interplay between the structure and electron configuration of the transition metal. The magnetically determined superconducting critical temperature is T-C similar to 14 K. The Fe-57 Mossbauer spectra collected in the temperature range from 5 to 200K mainly have an asymmetric doublet pattern, which was conveniently fitted by the full Hamiltonian method. No effective magnetic moment ascribed to the superconducting phase was observed down to 5K. The unusual behaviour observed below similar to 17K for the chemical isomer shift and quadrupole splitting may be associated with an electron reconfiguration process intimately related to an unusual lattice distortion accompanying the superconducting transition. The decreasing trend of the total absorption spectral area and second-order Doppler shift during cooling the sample below the critical temperature, point to enhanced phonon activation in the superconducting state.
682. Magnetization reversal via a Stoner-Wohlfarth model with bi-dimensional angular distribution of easy axis
Authors:
Kuncser, A; Kuncser, V
Published: DEC 1 2015, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 395, 40, DOI: 10.1016/j.jmmm.2015.07.035
A numerical extension of the simple Stoner-Wohlfarth model to the case of bi-dimensional angular distributions of easy axis is provided. The results are particularized in case of step-like, Gaussian-like and user defined distributions. In spite of its simplicity, the model can be applied to magnetically textured thin films and multilayers with in-plane magnetic anisotropy, independently on the texture source. Exemplifications are provided for a simple ferromagnetic textured FeCo film as well as for a FeMn/FeCoi CufFeCo spin valve structure. (C) 2015 Elsevier B.V. All rights reserved.
683. Bipolar Conductance Switching of Single Anthradithiophene Molecules
Authors:
Borca, B; Schendel, V; Petuya, R; Pentegov, I; Michnowicz, T; Kraft, U; Klauk, H; Arnau, A; Wahl, P; Schlickum, U; Kern, K
Published: DEC 2015, ACS NANO, 9, 12512, DOI: 10.1021/acsnano.5b06000
Single molecular switches are basic device elements in organic electronics. The pentacene analogue anthradithiophene (ADT) shows a fully reversible binary switching between different adsorption conformations on a metallic surface accompanied by a charge transfer. These transitions are activated locally in single molecules in a low-temperature scanning tunneling microscope. The switching induces changes between bistable orbital structures and energy level alignment at the interface. The most stable geometry, the "off" state, which all molecules adopt upon evaporation, corresponds to a short adsorption distance at which the electronic interactions of the acene rings bend the central part of the molecule toward the surface accompanied by a significant charge transfer from the metallic surface to the ADT molecules. This leads to a shift of the lowest unoccupied molecular orbital down to the Fermi level (E-F). In the "on" state the molecule has a flat geometry at a larger distance from the surface; consequently the interaction is weaker, resulting in a negligible charge transfer with an orbital structure resembling the highest occupied molecular orbital when imaged close to E-F. The potential barrier between these two states can be overcome reversibly by injecting charge carriers locally into individual molecules. Voltage-controlled current traces show a hysteresis characteristic of a bipolar switching behavior. The interpretation is supported by first-principles calculations.
684. Qualitative comparative analysis of MgB2 powder-in-tube wires: superconductivity and X-ray cone-bean microtomography
Authors:
Badica, P; Tiseanu, I; Aldica, G; Craciunescu, T; Sandu, V; Jakob, G; Rindfleisch, M
Published: NOV-DEC 2015, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17, 1649, DOI:
Commercial wires of MgB2 with different architectures and two different heat treatments were characterized with respect to their superconducting properties (T-c, J(c), H-irr, pinning force, macro flux jumps behaviour) through magnetic measurements and were visualized by 3D x-ray micro-tomography (XRT). For a particular architecture, heat treatment conditions of 625 degrees C/3 hrs or 700 degrees C/30 min produced relatively small differences, whereas the architecture of the wires showed a strong influence on superconducting characteristics. XRT checks the integrity of the wires easily detecting in a non-invasive way 3D macro defects and shows their hidden extended shape. XRT also allows a comparative geometry analysis between similar elements (e.g. filaments or filaments-matrix interfaces) from a particular wire or from wires with different architectures. Namely, XRT shows that the geometrical perfection (defined as the degree of departure of the geometry from the designed one) of the inner MgB2 filaments from the wires with 18 elements was lower than for the outermost ones from the same wires and was also lower than for the filaments from the wires with 7 elements. It is proposed that these results of geometrical perfection correlate with better overall superconducting quality of the wires with 7 filaments (except for the stronger presence of macro flux jumps in the wires with 7 filaments).
685. Applicability of the Stoner-Wohlfarth Model for Ni-Fe Graded Thin Films
Authors:
Kuncser, A; Schinteie, G; Ghica, C; Antohe, S; Kuncser, V
Published: MAR 2015, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 28, 969, DOI: 10.1007/s10948-014-2684-z
Fe-Ni graded films have been prepared by co-sputtering permalloy and Fe targets at different time-power sequences. Morpho-structural and magnetic investigations have been performed by transmission electron microscopy, Xray reflectometry, conversion electron Mossbauer spectroscopy and magneto-optic Kerr effect vector magnetometry, proving the thickness dependence of the properties. A magnetization reversal involving the displacement of Bloch-type walls is characteristic for a 115 nm thick Fe-Ni graded film whereas an in-plane coherent rotation of the spins, according to a Stoner-Wohlfarth mechanism was evidence for a 23 nm thick Fe-Ni graded film.
686. INDIRECT AMPLIFICATION OF THE PYROELECTRIC SIGNAL IN Pb(Zr,Ti)O-3 THIN FILMS BY THE PHOTO-GENERATION OF CARRIERS IN THE Si SUBSTRATES
Authors:
Botea, M; Pintilie, L; Pintilie, I; Stancu, V
Published: APR-JUN 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 347, DOI:
An amplification of near three orders of magnitude was observed in Pb(Zr,Ti)O-3 (PZT) thin films deposited on Pt/Si substrates when the Si substrate is included as an impedance in series with the PZT capacitor. The effect is present only at wavelengths below 1100 nm, where the incident light can be absorbed in the Si substrate with generation of free carriers. These carriers in turns modulate the internal electric field inside the ferroelectric layer leading to a much larger variation of the polarization compared to the one generated only by the temperature variation. This fact leads to a considerable enhancement of the pyroelectric signal. The finding can be useful in designing pyroelectric detectors with enhanced characteristics for visible and near infrared region of the electromagnetic spectrum.
687. Quantum turnstile operation of single-molecule magnets
Authors:
Moldoveanu, V; Dinu, IV; Tanatar, B; Moca, CP
Published: AUG 11 2015, NEW JOURNAL OF PHYSICS, 17, DOI: 10.1088/1367-2630/17/8/083020
The time-dependent transport through single-molecule magnets coupled to magnetic or nonmagnetic electrodes is studied in the framework of the generalized master equation method. We investigate the transient regime induced by the periodic switching of the source and drain contacts. If the electrodes have opposite magnetizations the quantum turnstile operation allows the stepwise writing of intermediate excited states. In turn, the transient currents provide a way to read these states. Within our approach we take into account both the uniaxial and transverse anisotropy. The latter may induce additional quantum tunneling processes which affect the efficiency of the proposed read-and-write scheme. An equally weighted mixture of molecular spin states can be prepared if one of the electrodes is ferromagnetic.
688. INTRABAND RELAXATION OF p-SHELL EXCITONS IN DISK-SHAPED QUANTUM DOTS
Authors:
Dragomir, R; Moldoveanu, V; Dinu, IV
We study the generation of p-shell excitons in optically active disk-shaped quantum dots subjected to ultrafast optical pulses. The single-particle spectral properties are obtained from the four-band kp theory, whereas the Coulomb interaction is taken into account within the configuration-interaction approach, particular attention being payed to configuration mixing due to electron-hole correlations. The effect of intraband relaxation processes is included in the non-unitary dynamics derived from the von-Neumann Lindblad equation. We find that the fast hole relaxation processes drive the p-shell excitons to intermediate states which eventually evolve to s-shell excitons via slower electron relaxation.
689. A new class of thermotropic lanthanidomesogens: Eu(III) nitrate complexes with mesogenic 4-pyridone ligands
Authors:
Pana, A; Chiriac, FL; Secu, M; Pasuk, I; Ferbinteanu, M; Micutz, M; Circu, V
Published: 2015, DALTON TRANSACTIONS, 44, 14199, DOI: 10.1039/c5dt01197c
A new class of thermotropic lanthanidomesogens has been designed and prepared. They are based on 4-pyridone ligands that possess mesogenic cyanobiphenyl groups attached to the 4-pyridone unit via a flexible long alkyl spacer and show a very high thermal stability (decomposition temperatures near 300 degrees C). Depending on the alkyl length spacer, these complexes exhibit a SmA phase with transition temperatures influenced by the number of mesogenic groups employed and the spacer length.
690. Exotic Superconductivity in Correlated Electron Systems
Authors:
Mu, G; Sandu, V; Li, W; Shen, B
Published: 2015, ADVANCES IN CONDENSED MATTER PHYSICS, 2015, DOI: 10.1155/2015/180195
691. GeO2-added MgB2 superconductor obtained by Spark Plasma Sintering
Authors:
Batalu, D; Aldica, G; Popa, S; Kuncser, A; Mihalache, V; Badica, P
Published: OCT 2015, SOLID STATE SCIENCES, 48, 30, DOI: 10.1016/j.solidstatesciences.2015.06.013
Dense samples (relative density > 93%) of bulk MgB2 with GeO2 additions were obtained by Spark Plasma Sintering. The critical current density J(c) of the added samples is improved at high magnetic fields when compared to the pristine sample. The optimum composition is for MgB2(GeO2)(0.005). For this sample, a J(c)(20 K) = 10(2) A/cm(2) is obtained at 5.1 T versus 3.9 T for the pristine sample. Ge substitution in the crystal lattice of MgB2 can be considered negligible, and T-c,T-onset and T-c,T-midpoint from magnetization measurements scatter within 0.2 and 0.6 K, respectively. TEM investigations show some specific details at nano scale: the tendency to form secondary phases (25-100 nm) with sphere-like or irregular shapes is observed and discussed. Samples are composites and the residual strain of MgB2 is constant for pristine and GeO2-added samples. Therefore, pinning enhancement leading to improvement of Jc for the GeO2 added samples is purely a 'microstructure' effect due to the presence of secondary phases. The point pinning is determined to be the predominant mechanism. Addition of a higher amount of GeO2 is shifting the pinning mechanism toward a grain boundary pinning. (C) 2015 Elsevier Masson SAS. All rights reserved.
692. NbF5-AIF(3) Catalysts: Design, Synthesis, and Application in Lactic Acid Synthesis from Cellulose
Authors:
Coman, SM; Verziu, M; Tirsoaga, A; Jurca, B; Teodorescu, C; Kuncser, V; Parvulescu, VI; Scholz, G; Kemnitz, E
Published: MAY 2015, ACS CATALYSIS, 5, 3026, DOI: 10.1021/acscatal.5b00282
A series of niobium-modified aluminum hydroxide fluorides (denoted Nb@AIF(3)), prepared via a fluorolytic sol gel synthesis was investigated for the catalytic one-pot conversion of cellulose to lactic acid. The structure of the new acid catalysts is the result of the dispersion of niobium fluoride in an aluminum hydroxide fluoride matrix. The calcination of the catalysts at a relatively low temperature (350 degrees C) stabilized this structure. Catalytic performances in terms of lactic acid yields are directly correlated with the niobium content.
693. Stepped heating procedure for experimental SAR evaluation of ferrofluids
Authors:
Iacob, N; Schinteie, G; Palade, P; Ticos, CM; Kuncser, V
Published: JUN 23 2015, EUROPEAN PHYSICAL JOURNAL E, 38, DOI: 10.1140/epje/i2015-15057-8
The aim of this paper is to present a reliable procedure for the experimental determination of the specific absorption rate (SAR) in case of superparamagnetic Fe oxide nanoparticles dispersed in liquid environments. It is based on the acquisition of consecutive steps of time-temperature dependences along of both heating and cooling processes. Linear fitting of these recorded steps provides the heating and cooling speeds at different temperatures, which finally allow the determination of the heating profile in adiabatic-like conditions over a broad temperature range. The presented methodology represents on one hand, a useful alternative tool for the experimental evaluation of the heating capability of nanoparticulate systems for magnetic hyperthermia applications and on the other hand, gives support for a more accurate modeling of bio-heat transfer phenomena.
694. Rapid determination of Faraday rotation in optical glasses by means of secondary Faraday modulator
Authors:
Sofronie, M; Elisa, M; Sava, BA; Boroica, L; Valeanu, M; Kuncser, V
Published: MAY 2015, REVIEW OF SCIENTIFIC INSTRUMENTS, 86, DOI: 10.1063/1.4920920
A rapid high sensitive method for determining the Faraday rotation of optical glasses is proposed. Starting from an experimental setup based on a Faraday rod coupled to a lock-in amplifier in the detection chain, two methodologies were developed for providing reliable results on samples presenting low and large Faraday rotations. The proposed methodologies were critically discussed and compared, via results obtained in transmission geometry, on a new series of aluminophosphate glasses with or without rare-earth doping ions. An example on how the method can be used for a rapid examination of the optical homogeneity of the sample with respect to magneto-optical effects is also provided. (C) 2015 AIP Publishing LLC.
695. Electro-optical properties of As-Se-S-dielectric structure for optical information recording in real time
Authors:
Chirita, A; Prlepov, V; Popescu, M; Corsac, O; Chetrus, P; Nasedchina, N
Published: JUL-AUG 2015, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 9, 923, DOI:
The results of electro-optical properties studies of chalcogenide glassy semiconductors thin film structures based on Xat.%As2S3:(100-X)at.%As2Se3 system for holographic information recording on to photo-thermoplastic carriers in stationary and pulsed modes.
696. The Role of Ambient Gas and Pressure on the Structuring of Hard Diamond-Like Carbon Films Synthesized by Pulsed Laser Deposition
Authors:
Popescu, AC; Stan, GE; Duta, L; Nita, C; Popescu, C; Surdu, VA; Husanu, MA; Bita, B; Ghisleni, R; Himcinschi, C; Craciun, V
Published: JUN 2015, MATERIALS, 8, 3305, DOI: 10.3390/ma8063284
Hard carbon thin films were synthesized on Si (100) and quartz substrates by the Pulsed Laser Deposition (PLD) technique in vacuum or methane ambient to study their suitability for applications requiring high mechanical resistance. The deposited films' surface morphology was investigated by scanning electron microscopy, crystalline status by X-ray diffraction, packing and density by X-ray reflectivity, chemical bonding by Raman and X-ray photoelectron spectroscopy, adherence by pull-out measurements and mechanical properties by nanoindentation tests. Films synthesized in vacuum were a-C DLC type, while films synthesized in methane were categorized as a-C:H. The majority of PLD films consisted of two layers: one low density layer towards the surface and a higher density layer in contact with the substrate. The deposition gas pressure played a crucial role on films thickness, component layers thickness ratio, structure and mechanical properties. The films were smooth, amorphous and composed of a mixture of sp(3)-sp(2) carbon, with sp(3) content ranging between 50% and 90%. The thickness and density of the two constituent layers of a film directly determined its mechanical properties.
697. Synthesis and optical properties of TiO2-based magnetic nanocomposites
Authors:
Scarisoreanu, M; Morjan, I; Fleaca, CT; Morjan, IP; Niculescu, AM; Dutu, E; Badoi, A; Birjega, R; Luculescu, C; Vasile, E; Danciu, V; Filoti, G
Published: MAY 1 2015, APPLIED SURFACE SCIENCE, 336, 342, DOI: 10.1016/j.apsusc.2014.12.125
Magnetic titania nanoparticles covered/embedded in SiO2 shell/matrix were simultaneously manufactured by the single-step laser pyrolysis. The present study is a continuation of our previous investigations on the TiO2/Fe and TiO2/HMDSO (hexamethyldisiloxane) derived-systems. The aim of this work is to study the synthesis by IR (Infrared) laser pyrolysis of magnetic TiO2 based nanocomposites which implies many concurrent processes induced in the gas phase by the laser radiation. The dependence between characteristic properties and the synthesis parameters was determined by many analytical and complementary methods: XRD (X-ray diffraction) structural analysis, UV-vis (ultraviolet-visible) and EDAX (energy-dispersive X-ray) spectroscopy, TEM and HRTEM (transmission electron microscopy at low and high resolution) analysis and magnetic measurements. The results of analysis indicate the presence of disordered silica, Fe, alpha-Fe2O3 and mixtures of anatase and rutile phases with mean crystallite dimensions (in the 14-34 nm range) with typical character of diluted magnetic oxide systems and a lower bandgap energy (E-g = 1.85 eV) as compared with TiO2 P25 Degussa sample. (C) 2014 Elsevier B.V. All rights reserved.
698. Effect of thermal treatments on the structural and magnetic transitions in melt-spun Ni-Fe-Ga-(Co) ribbons
Authors:
Tolea, F; Sofronie, M; Crisan, AD; Enculescu, M; Kuncser, V; Valeanu, M
Published: NOV 25 2015, JOURNAL OF ALLOYS AND COMPOUNDS, 650, 670, DOI: 10.1016/j.jallcom.2015.07.296
The effect of thermal treatments on the martensitic transformation in three representative Ni-Fe-Ga alloys with or without Co substitutions has been studied by calorimetry, X-ray diffractometry, scanning electron microscopy and magnetometry. The alloys were prepared as ribbons, by the melt spinning technique. The thermal treatments promote a reduction of the martensitic transformation temperature in all investigated samples, with the most pronounced decrease for the alloys with lower Ga content. Three different mechanisms induced by specific thermal treatments and responsible for the characteristic behaviour of the martensitic transformation, with respect to temperature and heat of transition, were observed and discussed in details. (C) 2015 Elsevier B.V. All rights reserved.
699. Theoretical investigations of electronic structure and magnetism in Zr2CoSn full-Heusler compound
Authors:
Birsan, A; Kuncser, V
Published: AUG 15 2015, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 388, 4, DOI: 10.1016/j.jmmm.2015.04.007
The half-metallic properties of a new and promising full-Heusler compound, Zr2CoSn, are investigated by means of ab initio calculations within the Density Functional Theory framework. It was shown that the ferromagnetic ordered Hg2CuTi-type crystal structure is energetically the most favorable for this compound. The total magnetic moment is 3 mu(B)/f.u. and follows a typical Stater-Pauling dependence. The half metallicity disappears if the unit cell volume is contracted by more than 5%. 2015 Elsevier B.V. All rights reserved.
700. MORPHOLOGICAL AND OPTICAL INVESTIGATION OF CuO FIBERS PREPARED VIA ELECTROSPINNING
Authors:
Busuioc, C; Surdu, VA; Andronescu, E
Published: 2015, UNIVERSITY POLITEHNICA OF BUCHAREST SCIENTIFIC BULLETIN SERIES B-CHEMISTRY AND MATERIALS SCIENCE, 77, DOI:
The objective of the paper was the synthesis and characterization of CuO nanofibers. These were obtained by electrospinning a solution of copper (II) acetate monohydrate and polyvinylpyrrolidone in N,N-dimethylformamide, followed by calcination at 400, 450, 500 or 600 degrees C for 2 or 8 h. The compositional, structural, morphological and optical properties of the resulting fibers were investigated by Xray diffraction, scanning electron microscopy and reflectance spectroscopy. The thermally treated samples exhibit CuO unique phase with polycrystalline monoclinic structure. SEM analysis revealed a five times decrease of fiber diameter after calcination, as well as a fiber porosity reduction with calcination temperature increasing. The optical studies led to band gap values of 1.36 +/- 0.01 eV.
701. Magneto-Structural Properties and Magnetic Behavior of Fe-Pd Ribbons
Authors:
Sofronie, MI; Tolea, F; Kuncser, V; Valeanu, MC; Filoti, G
Published: JAN 2015, IEEE TRANSACTIONS ON MAGNETICS, 51, DOI: 10.1109/TMAG.2014.2359226
Ribbons of Fe-Pd ferromagnetic shape memory alloys were prepared by rapid solidification via the melt-spinning technique. The effect of moderate and high temperature heat treatments on the martensitic transformation and the related changes of the magnetic behavior was analyzed by X-ray diffraction, differential scanning calorimetry and temperature, and field-dependent magnetometry. In addition, information about magnetic easy axis and magnetically field-induced strains (MFIS) were achieved from linear thermal expansion measurements performed under cooling at different applied fields. The observed low values of MFIS in the as-prepared ribbons are due, besides to the small size and random orientation of the grains, to the high atomic disorder inside the crystalline grains. The anisotropy field is enhanced by the reduced atomic disorder, as reflected by the increased MFIS values after thermal treatments.
702. Magnetic nanocomposites for an efficient valorization of biomass
Authors:
Kuncser, V; Coman, SM; Kemnitz, E; Parvulescu, VI
Published: MAY 7 2015, JOURNAL OF APPLIED PHYSICS, 117, DOI: 10.1063/1.4918763
The recovery of the catalysts from the reaction mixture and their recycling is important goals of the current applied catalysis. The stringent ecological and economical demands for sustainability made this concern even more important for the solid catalysts used in the area of biomass catalytic transformations where the raw material usually is not soluble in most of the organic solvents. Therefore, the solid catalyst cannot be easily separated from the mixture of untransformed raw material and by-products (e. g., humines). However, these goals can be achieved by using magnetic nanoparticles (MNPs) based catalysts. This study reports on the magnetic response of two types of new magnetic nanocomposite catalytic systems, Ru@MNP and Nb@AlF3, used in the synthesis of sorbitol/glycerol and of lactic acid, respectively, by direct cellulose degradation. The results showed that the recovering possibilities of the Nb@AlF3 catalysts, with a weaker magnetic response associated to the so called diluted magnetic oxide systems, are much diminished as compared to Ru@MNP, where the magnetic response is generated using MNP supported catalysts. (C) 2015 AIP Publishing LLC.
703. EFFECTS OF PROCESS PARAMETERS ON GROWTH OF METAL PARTICLES BY ATMOSPHERIC PRESSURE PLASMA JET
Authors:
Lazea-Stoyanova, A; Enculescu, M; Vizireanu, S; Marascu, V; Dinescu, G
Published: JUL-SEP 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 1247, DOI:
In this paper we report a procedure of growing metallic particles at atmospheric pressure by using a radiofrequency plasma jet, operated in inert gaseous atmosphere (argon). Iron metallic particles are manufactured, with sizes in the range of hundreds of nm up to a few microns, having as metal source the electrodes of the plasma jet discharge. The obtained particles are characterized with respect to their shape, size, morphology and size distribution. An emphasis is put on the relationship between the particle size distribution and process parameters, namely the substrate to nozzle distance and applied radiofrequency power.
704. Studies on thermal, spectral, magnetic and biological properties of new Ni(II), Cu(II) and Zn(II) complexes with a bismacrocyclic ligand bearing an aromatic linker
Authors:
Bucur, C; Badea, M; Chifiriuc, MC; Bleotu, C; Iorgulescu, EE; Badea, IA; Grecu, MN; Lazar, V; Patriciu, OI; Marinescu, D; Olar, R
Published: MAR 2014, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 115, 2189, DOI: 10.1007/s10973-013-3460-1
Novel complexes of M2LCl4 center dot nH(2)O type (M:Ni, n = 4; M:Cu, n = 3 and M:Zn, n = 0; L: ligand resulted from 1,4-phenylenediamine, 3,6-diazaoctane-1,8-diamine and formaldehyde one-pot condensation) were synthesized and characterised by microanalytical, ESI-MS, IR, UV-Vis, H-1 NMR and EPR spectra, magnetic data at room temperature and molar conductivities as well. The electrochemical behaviour of complexes was investigated by cyclic voltammetry. Simultaneous TG/DTA measurements were performed in order to evidence the thermal behaviour of the obtained complexes. Processes such as water elimination, fragmentation and oxidative degradation of the organic ligand as well as chloride elimination occurred during thermal decomposition. The antimicrobial assays demonstrate that the compounds exhibited good antibacterial activity, especially against S. aureus and E. coli strains, the most active being the copper(II) complex, which also exhibited the most prominent anti-biofilm effect, suggesting its potential use for the development of new antimicrobial agents. The biological activity was correlated with log P (ow) values. All complexes disrupt the membrane integrity of HCT 8 tumour cells.
705. Metallic Nanowires and Nanotubes Prepared by Template Replication
Authors:
Matei, E; Enculescu, M; Preda, N; Florica, C; Costas, A; Busuioc, C; Molares, MET; Kuncser, V; Enculescu, I
Published: 2014, SIZE EFFECTS IN NANOSTRUCTURES: BASICS AND APPLICATIONS, 205, 165, DOI: 10.1007/978-3-662-44479-5_6
Low dimensional nanostructures represent a hot scientific field nowadays due mainly to the tremendous potential for applications. Low dimensions open the possibilities for both ultra-miniaturization and increase in functionality. Numerous procedures were developed for fabricating such nanostructures. Template replication represents a highly effective method in fabricating metallic nanowires and nanotubes. The approach is characterized by the excellent control in obtaining nano objects with the desired shape and dimensions. A large variety of templates are available ranging from viruses and proteins to nanoporous membranes fabricated by using swift heavy ion accelerators. In the following chapter the main steps involved in employing the method for fabricating metalic nanowires and nanotubes by replicating ion track nanoporous membranes were described. The steps include here membrane fabrication and replication and involve track etching and electrochemical metal deposition. The influence of the process parameters on the properties of the nanoobjects prepared by this approach was reviewed. It was found that simple experimental parameters can be chosen in such a way that the functionality of the nanowires or nanotubes can be finely tuned.
706. Thermal behaviour and characterisation of new biologically active Cu(II) complexes with benzimidazole as main ligand
Authors:
Badea, M; Vlaicu, ID; Olar, R; Constand, M; Bleotu, C; Chifiriuc, MC; Marutescu, L; Lazar, V; Grecu, MN; Marinescu, D
Published: NOV 2014, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 118, 1133, DOI: 10.1007/s10973-014-3745-z
Four coordination compounds of copper(II) were synthesised and characterised in solid state by elemental analysis, infrared, electronic and EPR spectroscopy, as well as by thermal analysis (TG/DTA). The complexes were formulated on the basis of experimental data as: [Cu(BzIm)(2)(H2O)]center dot H2O (1), [Cu-2(Acr)(4)(HBzIm)(2)] (2), [Cu(Acr)(2)(HBzIm)(2)] (3) and [Cu(Acr)(2)(HBzIm)(2)(H2O)]center dot H2O (4). IR data are in accordance with the unidentate nature of benzimidazole, in complexes (2), (3) and (4), and bridge bidentate nature of benzimidazole, in complex (1), while acrylato acts as uni- or bridge/chelate ligand. The electronic spectra display the characteristic pattern of square planar, square pyramidal, or octahedral stereochemistry, also confirmed by EPR spectra. Thermal decomposition evidenced several well-defined steps as dehydration of complexes (1) and (4), benzimidazole molecule releases for all complexes and acrylate decomposition in carbonate for complexes (3) and (4). In all four cases, the final residue after thermal treatment in air flow is copper(II) oxide, formed during the decomposition steps for complexes (3) and (4), and, respectively, after the oxidation of the metallic copper for complexes (1) and (2). Antimicrobial activities of the complexes have been determined by in vitro assays, against various Gram-negative and Gram-positive bacterial and fungal strains. Copper(II) complexes were also evaluated for their cytotoxicity on eukaryotic cells.
707. Insulin loaded iron magnetic nanoparticle-graphene oxide composites: synthesis, characterization and application for in vivo delivery of insulin
Authors:
Turcheniuk, K; Khanal, M; Motorina, A; Subramanian, P; Barras, A; Zaitsev, V; Kuncser, V; Leca, A; Martoriati, A; Cailliau, K; Bodart, JF; Boukherroub, R; Szunerits, S
Published: 2014, RSC ADVANCES, 4, 875, DOI: 10.1039/c3ra46307a
One of the focal subjects in insulin delivery is the development of insulin formulations that protect the native insulin from degradation under acidic pH in the stomach. In this work we show, for the first time, that a graphene oxide (GO) based matrix can ensure the stability of insulin at low pH. GO and GO modified with 2-nitrodopamine coated magnetic particle (GO-MPdop) matrices loaded with insulin were prepared and the pH triggered release of the insulin was studied. The loading of insulin on the GO nanomaterials proved to be extremely high at pH < 5.4 with a loading capacity of 100 +/- 3% on GO and 88 +/- 3% on GO-MPdop. The insulin-containing GO matrices were stable at acidic pH, while insulin was released when exposed to basic solutions (pH = 9.2). Using Xenopus laevis oocytes as a model we showed that the meiotic resumption rate of GO and GO-MPdop remained unaltered when pre-treated in acidic conditions, while pre-incubated insulin (without GO nanomaterials) has lost almost entirely its maturation effect. These results suggest that GO based nanomatrices are promising systems for the protection of insulin.
708. Structural and magnetic properties of Li2O-Fe2O3 ceramic nanostructures
Authors:
Sorescu, M; Bushunow, V; Diamandescu, L; Tolea, F; Valeanu, M; Xu, TH
Published: MAY 2014, CERAMICS INTERNATIONAL, 40, 5395, DOI: 10.1016/j.ceramint.2013.10.120
xLi(2)O-(1 x)alpha-Fe2O3 (x=0.1, 0.3, 0.5, and 0.7) nanoparticle systems were successfully synthesized by mechanochemical activation of Li2O and alpha-Fe2O3 mixtures for 0-12 h of ball milling time. The study aims at exploring the formation of magnetic oxide semiconductors at the nanoscale, which is of crucial importance for catalysis, sensing and electrochemical applications. X-ray powder diffraction (XRD), Mossbauer spectroscopy and magnetic measurements were used to study the phase evolution of xLi(2)O-(1 x)alpha-Fe2O3 nanoparticle systems under the mechanochemical activation process. Rietveld refinement of the XRD patterns yielded the values of the particle size as function of composition and milling times and indicated the presence of Li-substituted hematite and tetra lithium iron oxide LiFeO2, along with the formation of multiple phases for large x values and long milling times. The Mossbauer studies showed that the spectrum of the mechanochemically activated composites evolved from a sextet for hematite to sextets and a doublet upon duration of the milling process with lithium oxide. Magnetic measurements recorded at 5 K to room temperature (RT) in an applied magnetic field of 50,000 Oe showed that the magnetization of the milled samples is larger at low temperatures than at RT and increases with decreasing particle size. Zero field cooling measurements made possible the determination of the blocking temperatures of the specimens as function of ball milling time and evidenced the occurrence of superparamagnetism in the studied samples. This result correlates well with the observed presence of a quadrupole-split doublet in the Mossbauer spectra. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
709. Effect of Silver Addition to Superconducting SmFeAsO1-x F (x)
Authors:
Sandu, V; Aldica, G; Liu, ZY; Zhang, ZL; Suo, HL
Published: JUL 2014, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 27, 1641, DOI: 10.1007/s10948-014-2503-6
We investigate the effect of silver addition to polycrystalline Sm-1111 superconductor. We show that Ag improves the phase homogeneity of the samples drastically reducing the weight of the low temperature, hence, leading to less fluorinated phases. The intragranular critical current density is enhanced by adding a small amount of Ag in all pinning regimes but a higher content of Ag leads to a decrease of this quantity. A tentative explanation for this dependence is proposed.
710. Strain-induced long range ferroelectric order and linear electro-optic effect in epitaxial relaxor thin films
Authors:
Scarisoreanu, ND; Craciun, F; Birjega, R; Andrei, A; Ion, V; Negrea, RF; Ghica, C; Dinescu, M
Published: AUG 21 2014, JOURNAL OF APPLIED PHYSICS, 116, DOI: 10.1063/1.4893364
Relaxor ferroelectrics have neither long range ferroelectric order nor structural transformation down to the lowest temperatures, and display isotropic optical properties like quadratic electro-optic effect. However, if an anisotropy is forced through an external agent, like electric field or uniaxial strain, a ferroelectric and structural long range order can be induced in these materials. Here, we show that epitaxial strain in relaxor ferroelectric thin films can be employed to induce a linear electro-optic effect, opening the path to new strain-controlled electro-optic materials. Epitaxial thin films with Pb1-3x/2LaxZr0.2Ti0.8O3 (x = 0.22) composition grown by pulsed laser deposition on (001) SrRuO3/SrTiO3 single crystal heterostructures become tetragonal below the susceptibility peak, which occurs at a temperature 140K higher as compared to bulk. These films show piezoelectric properties and almost linear electro-optic behaviour. (C) 2014 AIP Publishing LLC.
711. Influence of film thickness on the morphological and electrical properties of epitaxial TiC films deposited by reactive magnetron sputtering on MgO substrates
Authors:
Zoita, NC; Braic, V; Danila, M; Vlaicu, AM; Logofatu, C; Grigorescu, CEA; Braic, M
Published: MAR 1 2014, JOURNAL OF CRYSTAL GROWTH, 389, 98, DOI: 10.1016/j.jcrysgro.2013.11.076
Epitaxial TiC films were deposited on MgO (001) by DC magnetron sputtering in a reactive atmosphere of Ar and CH4 at 800 degrees C. The films elemental composition and chemical bonding was investigated by Auger electron spectroscopy (AE5), X-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy. The crystallographic structure, investigated by X-ray diffraction, exhibited an increased degree of (001) orientation with the film thickness, with a cube-on-cube epitaxial relationship with the substrate. The films morphology and electrical properties were determined by atomic force microscopy (AFM) and Hall measurements in Van der Pauw geometry. The influences of the film thickness (57-545 nm) on the morphological and electrical properties were investigated. The thinnest film presented the lowest resistivity, 160 [152, cm, showing an atomically flat surface, while higher values were obtained for the thicker films, explained by their different morphology dominated by low aspect ratio nanoislands/ nanocolumns. (C) 2013 Elsevier B.V. All rights reserved
712. Dynamics and relaxation of sp biexcitons in disk-shaped quantum dots
Authors:
Moldoveanu, V; Dinu, IV; Dragomir, R
Published: JUN 12 2014, PHYSICAL REVIEW B, 89, DOI: 10.1103/PhysRevB.89.245415
We study the effects of intraband relaxation processes on optical manipulation protocols for sp biexcitons hosted by CdTe disk-shaped quantum dots. The many-body states are calculated within the configuration interaction method starting from single-particle states given by the k.p theory. The time-dependent occupations of relevant many-body states are extracted from the von Neumann-Lindblad equation for the density operator. We mainly investigate the generation of sp biexcitons with two pulses of different polarizations sigma(+) and sigma(-). The fast hole relaxation processes prevent a high-fidelity controlled operation on sp biexcitons and lead to the occupation of some transient states which can be optically probed. More importantly, the many-body structure of the transient states consists of two holes on the s shell and antiparallel sp triplet states for electrons. Our simulations show that these triplet states are more stable against decoherence as they can only be damaged through slow electron relaxation. The configuration mixing due to correlation effects is also discussed.
713. Improved laser efficiency by direct diode laser pumping of the radiation-resistant Nd:gadolinium-scandium-gallium garnet
Authors:
Lupei, V; Pavel, N; Lupei, A
Published: APR 2014, LASER PHYSICS, 24, DOI: 10.1088/1054-660X/24/4/045801
Spectroscopic investigation of the radiation-resistant Nd:GSGG crystals and ceramics reported in this paper evidences that the absorption line at 883 nm corresponding to the unusual situation of quasi-degenerate absorption transitions I-4(9/2)(2) -> F-4(3/2)(1) and I-4(9/2)(3) -> F-4(3/2)(2) can be used for efficient direct diode laser pumping of this material, with stable absorption over an extended temperature range. It is inferred that the reduction of the quantum defect at this wavelength of pump compared to the traditional 807 nm pumping could improve the laser parameters and reduce drastically the heat generation, leading to a considerable extension of the power scalability. This possibility is demonstrated for the first time in the case of the 1061 nm laser emission in a continuous-wave and in the repetitive active acousto-optic and passive Q-switched laser emission. In all regimes this manifests in the reduction of the laser threshold, increase of slope efficiency and extension of the average power range. Additionally, in the active Q-switching this enables increased pulse energy and reduced pulse duration. The direct pumping could revitalize the utilization of Nd:GSGG for construction of lasers with storage of population inversion or working in an ionizing radiation environment.
714. Engineering Magnetic Properties of Nanostructures via Size Effects and Interphase Interactions
Authors:
Kuncser, V; Palade, P; Kuncser, A; Greculeasa, S; Schinteie, G
Published: 2014, SIZE EFFECTS IN NANOSTRUCTURES: BASICS AND APPLICATIONS, 205, 237, DOI: 10.1007/978-3-662-44479-5_7
Finite size effects and interfacial interactions as well as their influence on the magnetic properties of nanosized systems are discussed by starting from very basic principles of magnetism. Some preparation and subsequent processing tools for a proper engineering of the properties of such magnetic nanosized systems are introduced together with specific characterization tools. A summary of the most important technological applications related to size effects and interfacial interactions, with exemplifications starting from bio-medical applications of magnetic fluids to magnetoresitive multilayers for sensor applications are also provided.
715. Room Temperature Ferromagnetic Mn:Ge(001)
Authors:
Lungu, GA; Stoflea, LE; Tanase, LC; Bucur, IC; Radutoiu, N; Vasiliu, F; Mercioniu, I; Kuncser, V; Teodorescu, CM
Published: JAN 2014, MATERIALS, 7, DOI: 10.3390/ma7010106
We report the synthesis of a room temperature ferromagnetic Mn-Ge system obtained by simple deposition of manganese on Ge(001), heated at relatively high temperature (starting with 250 degrees C). The samples were characterized by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID), and magneto-optical Kerr effect (MOKE). Samples deposited at relatively elevated temperature (350 degrees C) exhibited the formation of similar to 5-8 nm diameter Mn5Ge3 and Mn11Ge8 agglomerates by HRTEM, while XPS identified at least two Mn-containing phases: the agglomerates, together with a Ge-rich MnGe similar to 2.5 phase, or manganese diluted into the Ge(001) crystal. LEED revealed the persistence of long range order after a relatively high amount of Mn (100 nm) deposited on the single crystal substrate. STM probed the existence of dimer rows on the surface, slightly elongated as compared with Ge-Ge dimers on Ge(001). The films exhibited a clear ferromagnetism at room temperature, opening the possibility of forming a magnetic phase behind a nearly ideally terminated Ge surface, which could find applications in integration of magnetic functionalities on semiconductor bases. SQUID probed the co-existence of a superparamagnetic phase, with one phase which may be attributed to a diluted magnetic semiconductor. The hypothesis that the room temperature ferromagnetic phase might be the one with manganese diluted into the Ge crystal is formulated and discussed.
716. Investigation of the bulk pinning force in YBCO superconducting films with nano-engineered pinning centres
Authors:
Crisan, A; Dang, VS; Yearwood, G; Mikheenko, P; Huhtinen, H; Paturi, P
Published: AUG 15 2014, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 503, 93, DOI: 10.1016/j.physc.2014.03.028
For practical applications of superconducting materials in applied magnetic fields, artificial pinning centres in addition to natural ones are required to oppose the Lorentz force. These pinning centres are actually various types of defects in the superconductor matrix. The pinning centres can be categorised on their dimension (volume, surface, or point) and on their character (normal cores or Delta kappa cores). We have used the Dew Hughes approach to determine the types of pinning centres present in various samples, with various thicknesses, temperatures and nanostructured additions to the superconducting matrix. Results show that normal surface pinning centres are present throughout almost all the samples, as dominant pinning mechanism. Such 2D extended pinning centres are mainly due to dislocations, grain boundaries, nanorods. Strong normal point pinning centres were found to be common in BZO doped YBCO samples. Other types of pinning centres, in various (minor) concentrations were also found in some of the samples. (C) 2014 Elsevier B.V. All rights reserved.
717. Enhancement of smectic C mesophase stability by using branched alkyl chains in the auxiliary ligands of luminescent Pt(II) and Pd(II) complexes
Authors:
Ilis, M; Micutz, M; Dumitrascu, F; Pasuk, I; Molard, Y; Roisnel, T; Circu, V
Published: FEB 17 2014, POLYHEDRON, 69, 39, DOI: 10.1016/j.poly.2013.11.015
A novel series of Pd(II) and Pt(II) complexes based on cyclometallated imine ligands and N-benzoylthiourea (BTU) derivatives as auxiliary ligands has been prepared and their liquid crystalline properties as well as photophysical properties have been investigated. The crystal structure of one cyclometallated Pt(II) complex with N-(p-F-phenyl)-N'-benzoylthiourea as a co-ligand has been solved. The liquid crystalline properties have been investigated by a combination of DSC, POM and variable temperature powder X-ray diffraction. These new metallomesogens display either a monotropic SmC phase or both SmA and SmC phases, depending on the number of alkoxy groups attached to the imine ligand, alkyl chain length or the use of branched alkoxy terminal groups. We found that the introduction of branched alkoxy terminal groups lead to lower transition temperatures and stabilization of the SmC phase in both the Pd(II) and Pt(II) complexes. While the Pd(II) complexes display no emission, the Pt(II) complexes show good emission properties in solution, in the solid state and as a PMMA film at room temperature, and their investigation is reported. (C) 2013 Elsevier Ltd. All rights reserved.
718. Biocatalytic designs for the conversion of renewable glycerol into glycerol carbonate as a value-added product
Authors:
Tudorache, M; Ghemes, G; Nae, A; Matei, E; Mercioniu, I; Kemnitz, E; Ritter, B; Coman, S; Parvulescu, VI
Published: DEC 2014, CENTRAL EUROPEAN JOURNAL OF CHEMISTRY, 12, 1270, DOI: 10.2478/s11532-014-0547-x
A comparative study of two different biocatalytic models, e.g. enzyme immobilized on magnetic particles (EIMP) and cross-linking enzyme aggregates onto magnetic particles (CLEMPA) was performed. The first model was designed as enzyme-immobilized on the magnetic particles surface (EIMP). The second model was constructed as a network structure with the enzyme aggregates and magnetic particles placed into the nodes and polyglutaraldehyde cross-linker as the network ledges. The design was called cross-linking enzyme aggregates onto magnetic particles (CLEMPA). The biocatalysts were prepared using lipase enzyme from Aspergillus niger for catalyzing the glycerol (Gly) conversion to glycerol carbonate (GlyC). The biocatalyst characteristics for both designs (EIMP and CLEMPA) were evaluated using scanning electron microscopy (SEM), laser light scattering (LLS) and UV-Vis techniques. The EIMP model was strongly influenced by the composition of the polymeric layer covering the particles surface, while the size of the magnetic particles affected mostly the CLEMPA design. Also, the biocatalytic capacity of the tested models was evaluated as maximum 52% Gly conversion with 90% GlyC selectivity for EIMP, and 73% Gly conversion with 77% GlyC selectivity for CLEMPA. Both biocatalytic models were successfully used to prepare GlyC from "crude" glycerol collected directly from the biodiesel process (e.g. 49% Gly conversion with 91% GlyC selectivity for EIMP and 70% Gly conversion with 80% GlyC selectivity for CLEMPA).
719. Technology of vanadium and its oxides based nanocomposite structures
Authors:
Prilepov, V; Gasin, P; Chirita, A; Midoni, V; Spoiala, D; Keirush, P
Published: JAN-FEB 2014, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 16, 231, DOI:
The peculiarities of vanadium and its oxides based nanocomposite structures fabrication are brought in this paper. The selected fabrication technological conditions allow creating a V2O5 based dielectric matrix in which conducting clusters are uniformly distributed. Some optical and electrical properties of such structures are presented. It was shown that the obtained layers possess high charge sensitivity.
720. COVERING OBLIQUELY DEPOSITED SiOx WITH POLYVINYL CARBAZOLE CHANGES THE ORIENTATION PROPERTIES
Authors:
Frunza, S; Zgura, I; Frunza, L; Rasoga, O; Gheorghe, P; Petris, A; Vlad, VI
Alignment layers of polyvinylcarbazole (PVK) were obtained by withdrawing from different solutions in toluene onto glass plates having SiOx layers obliquely evaporated in vacuum at 82 degrees. The alignment direction of nematic liquid crystal molecules with cyan-end group imposed by bare SiOx layers is changed when these layers are coated with PVK; the same happens with over layers of polyvinylimidazole or of polyvinylcinnamate. The effect is inhibited by doping PVK with fullerene C60 (0.1%), when the liquid crystal orientation specific for bare SiOx obliquely evaporated substrates is obtained. Other nematic (with methoxy-end group) does not show change of the orientation properties by covering the SiOx obliquely deposited layers with the mentioned polymer over layers.
721. Evidence of A-B site cooperation in the EuFeO3 perovskite from Eu-151 and Fe-57 Mossbauer spectroscopy, EXAFS, and toluene catalytic oxidation
Authors:
Florea, M; Alifanti, M; Kuncser, V; Macovei, D; Apostol, N; Granger, P; Parvulescu, VI
Published: JUL 2014, JOURNAL OF CATALYSIS, 316, 140, DOI: 10.1016/j.jcat.2014.04.016
EuFeO3 perovskite was considered as a case study of the cooperative effects of the rare earth and transition metal elements in the total catalytic oxidation of aromatic hydrocarbons. For this purpose, a EuFeO3 perovskite was prepared using the citrate route. Extensive characterization was performed via ex situ and in situ methods. EXAFS revealed that oxygen vacancies are formed in the nearest neighborhood of Fe and next-nearest neighborhood of Eu. Combining Eu-151 and Fe-57 Mossbauer experiments also suggested local oxygen defects in the proximity of the Eu cations during the reaction, as well as cooperative electron delocalization effects between Eu and Fe. XPS has shown the +3 oxidation state of both Eu and Fe cations and the relatively strong ionicity of the Fe-O chemical bonds, as suggested by the weakened 2p(3/2) satellite in the Fe2p spectrum. A systematic change of this satellite with the A cation in AFeO(3) perovskites was also discussed. The thermal treatment of the catalyst at 623 K, in air or toluene, was accompanied by a partial reduction of Fe and a partial oxidation of Eu, respectively. The interaction between the two elements appeared to be influenced mainly by the temperature and only slightly by the sample environment during further treatments. Catalytic oxidation of toluene on this perovskite led only to the production of carbon dioxide and water with no side-product formation from partial oxidation reactions. All the characterization and catalytic results preferably agree with a Volkenstein mechanism. (C) 2014 Elsevier Inc. All rights reserved.
722. The Influence of the Microstructure and Morphology of CeO2 Buffer Layer on the Properties of YBCO Films PLD Grown on Ni Tape
Authors:
Mihalache, V; Stefan, N; Enculescu, I; Mihailescu, IN; Socol, M; Miroi, M
Published: NOV 2014, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 27, 2485, DOI: 10.1007/s10948-014-2679-9
YBa2Cu3O7-delta films were deposited on CeO2-buffered nickel substrates, with different buffer thickness. Full width at half maximum of rocking curve, Delta(omega), of CeO2 and yttrium barium copper oxide (YBCO), as well as the critical temperature, T-c, of YBCO were shown to be strongly dependent on buffer thickness. They behave similarly but not proportional to the buffer thickness increase. This and the fact that Delta(omega) vs. buffer thickness and T-c vs. buffer thickness for YBCO behave similar with RMS roughness vs. thickness of CeO2 indicates that the surface peculiarity of buffers is responsible for YBCO properties. More precisely, the surface of CeO2 films prepared by the chemical solution route based on propionic acid is prone to agglomerate (de-wet) and the degree of agglomeration depends in an intricate way on buffer thickness. We showed that nor RMS roughness neither (00l) texture degree can define alone the surface suitable for c-axis YBCO nucleation. The {111} faceted grains (even in the case of high (00l) texture) and other defects generated by agglomeration supply a low fraction of (00l) flat terminations of buffer that affect the nucleation of c-axis-oriented YBCO phase. Moreover, the thermal instability of the surface morphology of CeO2 buffers (further development of de-wetting process, {111} faceted grains, etc. during superconducting layer deposition) influence the quality of YBCO films.
723. Transition in conduction mechanism in GeSi nanostructures
Authors:
Palade, C; Lepadatu, AM; Stavarache, I; Teodorescu, VS; Ciurea, ML
Published: 2014, 2014 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 58, DOI:
GeSi-based nanostructures show unique properties which make them suitable for integrated circuit technology. The strong interest is to enhance their electronic properties in order to improve the device performance. In order to obtain fundamental knowledge on the electrical transport taking place in GeSi nanostructures we have investigated the effects of different microstructures on the electrical behavior of GeSi nanostructured films, by modifying the annealing conditions. We manufactured GeSi nanostructured films with equiatomic composition and different structures by co-sputtering followed by adequate annealing under different temperatures. For determining the electrical behavior we performed and modeled current-temperature I - T characteristics taking into account the films structures. We found that the electrical behavior changes with the film structure by evidencing a transition in conduction mechanism. In films that are almost crystallized, being formed of small GeSi nanocrystals separated by thin amorphous regions, the I - T dependence at low temperature is due to thermally activated tunneling of carriers between neighboring nanocrystals. In contrast, in the completely crystallized films with big GeSi nanocrystals and crystallized borders between them, the electrical behavior is a typical polycrystalline one. Our findings help to clarify the conduction mechanisms taking place in GeSi nanostructures and to provide a route to electronic devices with high performance based on these materials.
724. Tuned Sensitivity Towards H2S and NH3 with Cu Doped Barium Strontium Titanate Materials
Authors:
Simion, CE; Sackmann, A; Teodorescu, VS; Rusti, CF; Piticescu, RM; Stanoiu, A
Published: 2014, ELECTROCERAMICS XIV CONFERENCE, 1627, 97, DOI: 10.1063/1.4901664
The different amount of Cu-doped Barium Strontium Titanate (BST) thick film materials have been tested for their gas-sensing performances towards NH3 and H2S under dry and 50% relative humidity (RH) background conditions. The optimum NH3 sensitivity was attained with 0.1mol% Cu-doped BST whereas the selective detection of H2S was highlighted using 5mol% Cu-doped BST material. No cross-sensitivity effects to CO, NO2, CH4 and SO2 were observed for all tested materials operated at their optimum temperature (200 degrees C) under humid conditions (50% RH). The presence of humidity clearly enhances the gas sensitivity to NH3 and H2S detection.
725. Annealing induced changes in the structure, optical and electrical properties of GeTiO2 nanostructured films
Authors:
Stavarache, I; Lepadatu, AM; Teodorescu, VS; Galca, AC; Ciurea, ML
Published: AUG 1 2014, APPLIED SURFACE SCIENCE, 309, 174, DOI: 10.1016/j.apsusc.2014.04.212
The GeTiO2 amorphous films were deposited by magnetron sputtering and subsequently annealed at 400, 550, 600 and 700 degrees C for nanostructuring. The structure of annealed films was investigated by X-ray diffraction and transmission electron microscopy. The transmittance spectra of all annealed GeTiO2 films were measured and simulated by using Bruggeman effective medium approximation considering components of TiO2 anatase, crystalline Ge, GeO2 and voids determined from the structure investigations. The electrical behavior of 400, 600 and 700 degrees C annealed films was studied by measuring current-voltage characteristics. We found that by increasing the annealing temperature the films thickness decreases from 330 nm (as-deposited films) to 290 nm (700 degrees C annealed films). The 400 degrees C annealed films are amorphous, while all the others annealed at higher temperatures are crystallized (X-ray diffraction and transmission electron microscopy). In the 550 and 600 degrees C annealed films we found the (TiGe)O-2 rutile structure which is formed by starting from the GeO2 tetragonal structure with high Ti content. Additionally, these films contain TiO2 anatase structure and cubic Ge nanocrystals. At 700 degrees C annealing temperature, a surface layer of GeO2 tetragonal nanocrystals is formed by Ge diffusion and a part of Ge is lost. The experimental transmittance spectra indicate a broadening of the transparency range by increasing the annealing temperature, and the simulated ones also indicate this behavior with the decrease of Ge content, the experimental and simulated spectra being in good agreement. Also, the increase of annealing temperature produces an increase of electrical conductivity. (C) 2014 Elsevier B.V. All rights reserved.
726. GeSiO Based Nanostructures: Electrical Behaviour Related to Morphology and Preparation Method
Authors:
Ciurea, ML; Teodorescu, VS; Stavarache, I; Lepadatu, AM
Published: 2014, SIZE EFFECTS IN NANOSTRUCTURES: BASICS AND APPLICATIONS, 205, 73, DOI: 10.1007/978-3-662-44479-5_3
The structure of GeSiO films resulted from deposition and annealing conditions draws their electrical behaviour. GeSiO films prepared either by magnetron sputtering or sol-gel method and subsequently annealed are formed of Ge nanocrystals and/or amorphous Ge nanoparticles embedded in amorphous SiO2 matrix. Firstly, the size effect which is the main effect in these systems produces specific quantum confinement energy levels in the enlarged forbidden energy band gap in nanocrystals. Secondly, these films are percolative systems, so that the main conduction mechanisms which govern the electrical behaviour are the tunnelling and hopping between neighbouring Ge nanocrystals or amorphous nanoparticles. Accordingly, the charge transport is strongly determined by the structure and morphology of films.
727. Intrinsic energy band alignment of functional oxides
Authors:
Li, SY; Chen, F; Schafranek, R; Bayer, TJM; Rachut, K; Fuchs, A; Siol, S; Weidner, M; Hohmann, M; Pfeifer, V; Morasch, J; Ghinea, C; Arveux, E; Gunzler, R; Gassmann, J; Korber, C; Gassenbauer, Y; Sauberlich, F; Rao, GV; Payan, S; Maglione, M; Chirila, C; Pintilie, L; Jia, LC; Ellmer, K; Naderer, M; Reichmann, K; Bottger, U; Schmelzer, S; Frunza, RC; Ursic, H; Malic, B; Wu, WB; Erhart, P; Klein, A
Published: JUN 2014, PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, 8, 576, DOI: 10.1002/pssr.201409034
The energy band alignment at interfaces between different materials is a key factor, which determines the function of electronic devices. While the energy band alignment of conventional semiconductors is quite well understood, systematic experimental studies on oxides are still missing. This work presents an extensive study on the intrinsic energy band alignment of a wide range of functional oxides using photoelectron spectroscopy with in-situ sample preparation. The studied materials have particular technological importance in diverse fields as solar cells, piezotronics, multiferroics, photoelectrochemistry and oxide electronics. Particular efforts have been made to verify the validity of transitivity, in order to confirm the intrinsic nature of the obtained band alignment and to understand the underlying principles. Valence band offsets up to 1.6 eV are observed. The large variation of valence band maximum energy can be explained by the different orbital contributions to the density of states in the valence band. The framework provided by this work enables the general understanding and prediction of energy band alignment at oxide interfaces, and furthermore the tailoring of energy level matching for charge transfer in functional oxides. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
728. New multicomponent catalysts for the selective aerobic oxidative condensation of benzylamine to N-benzylidenebenzylamine
Authors:
Opris, CM; Pavel, OD; Moragues, A; El Haskouri, J; Beltran, D; Amoros, P; Marcos, MD; Stoflea, LE; Parvulescu, VI
Published: 2014, CATALYSIS SCIENCE & TECHNOLOGY, 4, 4355, DOI: 10.1039/c4cy00795f
Aerobic oxidative condensation of benzylamine to N-benzylidenebenzylamine was carried out on new gold-based catalysts using as support bimodal UVM-7-like mesoporous silica containing Ni and Ce (or Sn) as oxide nanodomains partially embedded inside the mesoporous UVM-7 silica walls. These nanodomains acted as effective and stable inorganic anchors favoring the nucleation, growth and stability of supported gold particles. Following the atrane method ( a "one-pot" strategy able to harmonize the hydrolytic reactivity of different heteroelements through the use of complexes containing triethanolamine-derived ligands (atranes) as precursors) the stability of the oxide nanodomains during oxidation and thermal treatments was ensured. The catalysts were prepared using a two-step synthesis in which gold was incorporated through impregnation of previously synthesized bimodal porous silicas containing different heteroelements trapped by the silica mesostructure. The versatility of the preparative approach allowed the high surface area and accessibility of mesoporous silica and also an easy and homogeneous inclusion of heteroelements in one pot. Aerobic oxidative condensation of benzylamine on these catalysts occurred selectively only with the formation of N-benzylidenebenzylamine. While selectivity was total, the productivities (mol(product) g(cat)(-1) h(-1)) varied in a wide range as a function of catalyst composition (chemical composition and atomic ratios of the constitutive support elements). The catalytic behavior was merely controlled by the size of gold particles, but the support also exerts an influence. The best results were obtained on the mesoporous Au/Ce-60-Ni-10-UVM-7 catalyst having a 0.97( wt.%) gold content ( in the form of nanoparticles of ca. 4 nm) and preserving a relatively high surface area ( 566 m(2) g(-1)) and pore volume ( 0.91 cm(3) g(-1)). The comparison with the individual or bicomponent catalysts led to the conclusion of a cooperative interaction between the catalyst components. However, gold itself exhibits a higher activity than the promoters or co-catalysts (i.e. phases containing Ni and/or Ce).
729. Structural, down- and phase selective up-conversion emission properties of mixed valent Pr doped into oxides with tetravalent cations
Authors:
Tiseanu, C; Parvulescu, V; Avram, D; Cojocaru, B; Apostol, N; Vela-Gonzalez, AV; Sanchez-Dominguez, M
Published: 2014, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 16, 5802, DOI: 10.1039/c3cp54899f
We report on structure-property relationships in Pr-doped CeO2 and ZrO2 using X-ray diffraction (XRD), Raman, UV to Vis Diffuse Reflectance (DR-UV/Vis), X-ray Photoelectron (XPS), and luminescence (PL) spectroscopies. Both 3+ and 4+ valence states of Pr are evidenced, irrespective of the host and calcination temperature, T (T = 500 and 1000 degrees C) with consequences on absorption, surface, vibrational and luminescence properties. Only zirconia represents a suitable host for Pr3+ luminescence. The distinct trivalent Pr centers and their excitation mechanism are identified in relation to the tetragonal and monoclinic phases of ZrO2. A near-infrared to visible up-conversion (UPC) emission of Pr3+ is observed upon excitation at 959 nm which occurs, most probably, via a two-photon excited state process. By using a multi-wavelength, time-gated excitation, the UPC process is established as phase selective, i.e. only Pr3+ located in the monoclinic sites of the mixed phase, monoclinic and tetragonal ZrO2 (T = 1000 degrees C) contribute to the UPC emission. We believe that, besides the local symmetry, a key role in phase selective UPC is played by the presence of Pr3+ low-lying 4f 5d levels. To the best of our knowledge, this is the first report of phase selective up-conversion emission in a lanthanide doped multi-phase host.
730. Combinatorial Fe-Co thin film magnetic structures obtained by thermionic vacuum arc method
Authors:
Jepu, I; Porosnicu, C; Lungu, CP; Mustata, I; Luculescu, C; Kuncser, V; Iacobescu, G; Manin, A; Ciupina, V
Published: FEB 15 2014, SURFACE & COATINGS TECHNOLOGY, 240, 352, DOI: 10.1016/j.surfcoat.2013.12.050
Magnetoresistive Fe-Co based thin film structures were produced using thermionic vacuum arc method. The purpose of this work was to obtain significant magnetic response on different granular combinatorial structures. The Giant Magnetoresistive (GMR) and combination between GMR and Tunneling Magnetoresistive (TMR) properties of the thin film structures were the aim of the work. The proposed method in order to obtain the desired granular structures is based on electron beam emitted by an externally heated cathode, accelerated by a high anodic potential. The work consisted in preparing two sets of samples, first being a combination between Fe-Co as magnetic materials embedded in a Cu matrix, with a total thickness of 200 nm. The second structure was a combination between Fe-Co (50%-50%) alloy, embedded in a matrix of Cu combined with MgO with a thickness of 200 nm. Both sets of samples were obtained by three simultaneous types of discharges. Because of the substrate positioning in respect with the three anode-cathode systems, different material concentrations were obtained, confirmed by Energy Dispersive Spectroscopy (EDS) measurement results. Structural and morphological properties were investigated using Scanning Electron Microscopy; Atomic Force Microscopy and EDS. Electrical properties of the obtained samples were studied using the 4 point measurement method. The magnetic properties were first studied using a non-destructive optical method called MOKE (Magneto-Optical Kerr Effect). Electrical resistance behavior of the granular type structures was studied for different values of the magnetic field, up to 03 T, at different values of the sample temperature. The magnetoresistive effect obtained for the two sets of samples varied from 1.5% to 81% in respect with the substrate positioning and sample temperature for a constant magnetic field. (C) 2014 The Authors. Published by Elsevier B.V. All rights reserved.
731. Electrical properties related to the structure of GeSi nanostructured films
Authors:
Ciurea, ML; Stavarache, I; Lepadatu, AM; Pasuk, I; Teodorescu, VS
Published: JUL 2014, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 251, 1346, DOI: 10.1002/pssb.201350112
GeSi nanostructured films were obtained by cosputtering from two Ge and Si targets and subsequent annealing in furnace in N-2 for 5 h at 700, 800 and 900 degrees C, with the aim to show the correlation between electrical properties and crystalline structure of the films. The as-deposited films are amorphous, have a Ge: Si composition of 55: 45 and 185 nm thickness. The film structure was investigated by XRD and TEM, and the electrical behaviour was studied by measuring current-voltage (I-V) and current-temperature (I-T) characteristics and by discussing them in correlation with the structure. Different electrical behaviours of GeSi films corresponding to different structures have been evidenced. The 700 degrees C annealed GeSi films are formed of nanocrystals (7-15 nm) separated by amorphous regions (1-2 nm). These films present a superlinear I-V characteristic typical of high field-assisted tunnelling through potential barriers (amorphous regions) between nanocrystals. The I-T characteristic at low temperature follows a T-1/2 law showing a thermally activated tunnelling of carriers between neighboring GeSi nanocrystals. The films annealed at 800 and 900 degrees C have a like behavior, they are completely crystallized and present linear I-V and Arrhenius I-T dependences reflecting the polycrystalline behaviour. [GRAPHICS] . (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
732. Doping of MgB (2) Using Molecular Magnets as Precursors
Authors:
Sandu, V; Badica, P; Aldica, G; Ferbinteanu, M; Hayasaka, Y
Published: AUG 2014, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 27, 1843, DOI: 10.1007/s10948-014-2538-8
We present the effect of single molecular magnet ([Fe(bpca) Dy-2(NO (3))(4)] a <...H (2) Oa <...4.5 CH (3) NO (2) and [Mn (2)(naften) (2)(CH 3COO)(CH 3OH)] a <...BPh (4)) thermolysis on the superconducting properties of polycrystalline MgB (2) samples when inserted and sintered by spark plasma sintering technique. As a result of pyrolysis, Fe- and Dy-magnetic compounds grow within the MgB (2) matrix and give a paramagnetic behavior in normal state, whereas the Mn-based compounds display negligible magnetic properties. We find that the magnetic critical current density of the as-obtained superconducting composites, as well as the pinning mechanism, is dependent on the magnetic background, with a noticeable advantage for the sample with magnetic compounds.
733. BaFBr:Eu2+ nanophosphor-SiO2 hybrid entrapped in Anodise Alumina membrane pores array
Authors:
Secu, CE; Matei, E; Secu, M; Damian, V
Published: SEP 2014, RADIATION MEASUREMENTS, 68, 41, DOI: 10.1016/j.radmeas.2014.07.001
Sol-gel template method has been used to prepare BaFBr:Eu2+ nanophosphor-SiO2 hybrid entrapped within the nanopores array (of about 200 nm size) of a comercial anodized alumina (AA) membrane. Structural and morphological measurements using electron microscopy (SEM) and X-ray diffraction (XRD) have shown the presence of the BaFBr:Eu2+ nanophosphor in the silica xerogel entrapped within the nanopores array; photoluminescence and X-ray excited luminescence measurements have shown Eu2+ luminescence at 395 nm accompanied by a broad band due to AA membrane. The method assures a relatively uniform spreading of the BaFBr nanophosphor into the AA membrane pores array without the nanoparticles agglomeration. Preliminary imaging tests have shown a spatial resolution in the micrometer range and even in the submicrometer range can be expected. As BaFBr:Eu2+ is a very efficient Xray phosphor the material might be used as X-ray micro-imaging detector. (C) 2014 Elsevier Ltd. All rights reserved.
734. Indium-tin nanoscaled oxides synthesized under hydrothermal supercritical and postannealing pathway: Phase dynamics and characterization
Authors:
Diamandescu, L; Tarabasanu-Mihaila, D; Feder, M; Enculescu, M; Teodorescu, VS; Constantinescu, S; Popescu, T; Bartha, C; Pap, Z
Published: FEB 14 2014, MATERIALS CHEMISTRY AND PHYSICS, 143, 1549, DOI: 10.1016/j.matchemphys.2013.11.064
With the aim of synthesizing the mixed nanoparticle system xIn(2)O(3)-(1-x)SnO2 over all molar concentration range 0 <= x <= 1, Delta x = 0.1, we performed hydrothermal supercritical experiments on indium-tin hydrogel resulted from InCl3-SnCl4 water solution. Nanophases isostructural with InOOH and SnO2 were obtained by hydrothermal reaction at 400 degrees C, in the molar concentration range of 0.1 <= x <= 0.7; at x = 0.8 and x = 0.9 only one phase, isostructural with InOOH, was observed. Samples calcined at 500 degrees C with x in the range of 0.2 <= x <= 0.7 contain a nanoscaled phase isostructural with rhombohedral In2O3 and a second one isostructural with tetrahedral SnO2. At x = 0.8 and x = 0.9 only one phase isostructural with rhombohedral In2O3 appears: rhombohedral ITO phase. The determined band gap energies could recommend the rhombohedral ITO structure for visible light photocatalytic applications. The phase dynamics together with the concentration range for existence of the solid solutions in the InOOH-SnO2 and In2O3-SnO2 composite semiconducting nanoparticle systems have been evidenced and discussed. (C) 2013 Elsevier B.V. All rights reserved.
735. Tuning structural and magnetic properties of Fe films on Si substrates by hydrogenation processing
Authors:
Sandu, SG; Palade, P; Schinteie, G; Birsan, A; Trupina, L; Kuncser, V
Published: FEB 2014, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 181, 32, DOI: 10.1016/j.mseb.2013.11.004
In order to study specific phenomena at ferromagnetic/semiconducting interfaces, of potentially high interest in spintronics and information technology, structural aspects and magnetic properties of Fe thin films grown on Si(001) substrates by RF sputtering have been investigated using Fe-57 conversion electron Mossbauer spectroscopy (CEMS) and magneto-optic Keer effect (MOKE). Films of different thicknesses have been deposited either directly on crystalline Si substrates or on Cu buffer layers. An inherent Fe oxide layer is observed in all as prepared films, with a relative thickness decreasing drastically with the deposition time. The Cu buffer layer does not diminish either the interfacial diffusion or the oxidation process. An efficient method to prepare sharper oxygen- and silicon-free interfaces for an improved spin injection, via thermal treatment in hydrogen atmosphere, is proposed. Accordingly, the hydrogenation treatments are very efficient in the modification of the ferromagnetic film structure, phase composition, magnetic properties and interfacial mixing. (C) 2013 Elsevier B.V. All rights reserved.
736. Charge storage properties of HfO2/Ge-HfO2/SiO2 trilayer structures
Authors:
Palade, C; Slav, A; Lepadatu, AM; Teodorescu, VS; Ciurea, ML
Published: 2014, 2014 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 62, DOI:
We report on the charge storage properties of trilayer structures consisting in sputtered gate HfO2/co-sputtered Ge-HfO2 layer/rapid thermal tunneling SiO2 oxide. Investigations of transmission electron microscopy and X-ray diffraction evidence the formation of HfO2 with mixed structure of monoclinic and tetragonal in the annealed structures. Capacitance-voltage (C-V) characteristics were measured on Al/HfO2/Ge-HfO2/SiO2/Si/Al metal-oxide-semiconductor capacitors based on as-deposited and annealed structures. Large C-V hysteresis is observed for the as-deposited structures and is controlled by traps present in oxide and interface. The annealing yields a C-V hysteresis with smaller memory window being due to injected charges in Ge nanocrystals.
737. Recent progress in the synthesis of magnetic titania/iron-based, composite nanoparticles manufactured by laser pyrolysis
Authors:
Fleaca, CT; Scarisoreanu, M; Morjan, I; Alexandrescu, R; Dumitrache, F; Luculescu, C; Morjan, IP; Birjega, R; Niculescu, AM; Filoti, G; Kuncser, V; Vasile, E; Danciu, V; Popa, M
Published: MAY 30 2014, APPLIED SURFACE SCIENCE, 302, 204, DOI: 10.1016/j.apsusc.2013.10.138
We report the continuous, single step synthesis of titania/iron-based magnetic nanocomposites in a single step using gas-phase laser pyrolysis technique by separately and simultaneously introducing the precursors (together with C2H4 sensitizer) in the reaction zone: Fe(CO)(5) on the central flow and, using air as carrier, TiCl4 on the annular coflow. The laser power and, for the last experiment, the injection geometry were modified in order to change the Fe/Ti ratio in the resulted nanopowders. Due to the specific geometry, the reaction zone (visible as a flame) have a reductive inner central zone surrounded by and oxidative environment, allowing the formation of the metallic-carbidic iron and/or iron-doped titania and iron oxide nanophases. The raw Fe-containing nanopowders have a ferromagnetic behavior, those synthesized at higher laser power and gas velocities show significant saturation magnetization M-s values (10-12 emu/g), whereas those obtained (with higher yield and carbon content) at lower laser power and gas velocities (using wider central nozzle cross-section) have a very weak magnetization (M-s similar to 0.05 emu/g) in spite of the higher ethylene carried Fe(CO)(5) flow. The powders were annealed in air at 400 degrees C show lower carbon content and, for those highly Fe-doped, the hematite phase formation. Preliminary tests using UV light confirm the photocatalytic action of the annealed nanopowders in salicylic acid degradation process in solution. (C) 2013 Elsevier B.V. All rights reserved.
738. Lanthanide-lanthanide and lanthanide-defect interactions in co-doped ceria revealed by luminescence spectroscopy
Authors:
Avram, D; Gheorghe, C; Rotaru, C; Cojocaru, B; Florea, M; Parvulescu, V; Tiseanu, C
Published: DEC 15 2014, , DOI: 10.1016/j.jallcom.2014.07.059
739. Graphenes in the absence of metals as carbocatalysts for selective acetylene hydrogenation and alkene hydrogenation
Authors:
Primo, A; Neatu, F; Florea, M; Parvulescu, V; Garcia, H
Published: OCT 2014, , DOI: 10.1038/ncomms6291
740. Antifungal activity of Ag:hydroxyapatite thin films synthesized by pulsed laser deposition on Ti and Ti modified by TiO2 nanotubes substrates
Authors:
Erakovic, S; Jankovic, A; Ristoscu, C; Duta, L; Serban, N; Visan, A; Mihailescu, IN; Stan, GE; Socol, M; Iordache, O; Dumitrescu, I; Luculescu, CR; Janackovic, D; Miskovic-Stankovic, V
Published: FEB 28 2014, APPLIED SURFACE SCIENCE, 293, 45, DOI: 10.1016/j.apsusc.2013.12.029
Hydroxyapatite (HA) is a widely used biomaterial for implant thin films, largely recognized for its excellent capability to chemically bond to hard tissue inducing the osteogenesis without immune response from human tissues. Nowadays, intense research efforts are focused on development of antimicrobial HA doped thin films. In particular, HA doped with Ag (Ag:HA) is expected to inhibit the attachment of microbes and contamination of metallic implant surface. We herewith report on nano-sized HA and Ag:HA thin films synthesized by pulsed laser deposition on pure Ti and Ti modified with 100 nm diameter TiO2 nanotubes (fabricated by anodization of Ti plates) substrates. The HA-based thin films were characterized by SEM, AFM, EDS, FUR, and XRD. The cytotoxic activity was tested with HEp2 cells against controls. The antifungal efficiency of the deposited layers was tested against the Candida albicans and Aspergillus niger strains. The Ti substrates modified with TiO2 nanotubes covered with Ag:HA thin films showed the highest antifungal activity. (C) 2013 Elsevier B.V. All rights reserved.
741. On the Steady State Correlation Functions of Open Interacting Systems
Authors:
Cornean, HD; Moldoveanu, V; Pillet, CA
Published: OCT 2014, COMMUNICATIONS IN MATHEMATICAL PHYSICS, 331, 295, DOI: 10.1007/s00220-014-1925-0
We address the existence of steady state Green-Keldysh correlation functions of interacting fermions in mesoscopic systems for both the partitioning and partition-free scenarios. Under some spectral assumptions on the non-interacting model and for sufficiently small interaction strength, we show that the system evolves to a NESS which does not depend on the profile of the time-dependent coupling strength/bias. For the partitioned setting we also show that the steady state is independent of the initial state of the inner sample. Closed formulae for the NESS two-point correlation functions (Green-Keldysh functions), in the form of a convergent expansion, are derived. In the partitioning approach, we show that the 0(th) order term in the interaction strength of the charge current leads to the Landauer-Buttiker formula, while the 1(st) order correction contains the mean-field (Hartree-Fock) results.
743. Structural Characterization of Impurified Zinc Oxide Thin Films
Authors:
Trinca, LM; Galca, AC; Stancu, V; Chirila, C; Pintilie, L
Published: 2014, ELECTROCERAMICS XIV CONFERENCE, 1627, 128, DOI: 10.1063/1.4901669
Europium doped zinc oxide (Eu:ZnO) thin films have been obtained by pulsed laser deposition (PLD). 002 textured thin films were achieved on glass and silicon substrates, while hetero-epilayers and homo-epilayers have been attained on single crystal SrTiO3 and ZnO, respectively. X-ray Diffraction (XRD) was employed to characterize the Eu:ZnO thin films. Extended XRD studies confirmed the different thin film structural properties as function of chosen substrates.
744. SYNTHESIS AND CHARACTERIZATION OF GLASS-CERAMIC SUPERCONDUCTORS IN (Pb, B)-DOPED Bi-Sr-Ca-Cu-O SYSTEM
Authors:
Fruth, V; Tanase, G; Atkinson, I; Pandele Cusu, J; Aldica, G; Zaharescu, M
Published: JUN-JUL 2014, REVUE ROUMAINE DE CHIMIE, 59, 383, DOI:
Glass-ceramic superconductors in the Bi-Sr-Ca-Cu-O system were prepared by melt-quenching method in the presence of some additives (Pb, B). The studied glasses were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (DTA/TGA) and differential scanning calorimetry (DSC). On the crystallized ceramics obtained by the annealing the glasses, transport resistance and XRD measurements were also done. The glass transition temperatures (T-g) was found to range in the 380-430 degrees C domain, followed by a set of exothermal effects that could be assigned to the crystallization of the superconducting phases. The nucleation and growth of the crystals is influenced by both the nature of the oxides used as additives and by their ratio. So, the samples doped with low amount of B (x=0.1 and 0.2) present obvious transitions at about 110 K, highlighting the presence of the 2223 phase in highest amount and well interconnected.
745. Si/SiO2 quantum dots cause cytotoxicity in lung cells through redox homeostasis imbalance
Authors:
Stan, MS; Memet, I; Sima, C; Popescu, T; Teodorescu, VS; Hermenean, A; Dinischiotu, A
Published: SEP 5 2014, CHEMICO-BIOLOGICAL INTERACTIONS, 220, 115, DOI: 10.1016/j.cbi.2014.06.020
Si/SiO2 quantum dots (QDs) are novel particles with unique physicochemical properties that promote them as potential candidates for biomedical applications. Although their interaction with human cells has been poorly investigated, oxidative stress appears to be the main factor involved in the cytotoxicity of these nanoparticles. In this study, we show for the first time the influence of Si/SiO2 QDs on cellular redox homeostasis and glutathione distribution in human lung fibroblasts. The nanoparticles morphology, composition and structure have been investigated using high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis. MRC-5 cells (human lung fibroblasts) were incubated with various concentrations of Si/SiO2 QDs ranging between 25 and 200 mu g/mL for up to 72 h. The results of the MTT and sulforhodamine B assays showed that exposure to QDs led to a time-dependent decrease in cell viability and biomass. The increase in reactive oxygen species (ROS) and malondialdehyde (MDA) levels together with the lower glutathione content suggested that the cellular redox homeostasis was altered. Regarding GSH distribution, the first two days of treatment resulted in a localization of GSH mainly in the cytoplasm, while at longer incubation time the nuclear/cytoplasmic ratio indicated a nuclear localization. These modifications of cell redox state also affected the redox status of proteins, which was demonstrated by the accumulation of oxidized proteins and actin S-glutathionylation. In addition, the externalization of phosphatidylserine provided evidence that apoptosis might be responsible for cell death, but necrosis was also revealed. Our results suggest that Si/SiO2 quantum dots exerted cytotoxicity on MRC-5 cells by disturbing cellular homeostasis which had an effect upon protein redox status. (C) 2014 Elsevier Ireland Ltd. All rights reserved.
746. Quantitative analysis of amorphous indium zinc oxide thin films synthesized by Combinatorial Pulsed Laser Deposition
Authors:
Axente, E; Socol, G; Beldjilali, SA; Mercadier, L; Luculescu, CR; Trinca, LM; Galca, AC; Pantelica, D; Ionescu, P; Becherescu, N; Hermann, J; Craciun, V
Published: OCT 2014, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 117, 236, DOI: 10.1007/s00339-014-8427-y
The use of amorphous and transparent oxides is a key for the development of new thin film transistors and displays. Recently, indium zinc oxide (IZO) was shown to exhibit high transparency in the visible range, low resistivity, and high mobility. Since the properties and the cost of these films depend on the In/(In + Zn) values, the measurement of this ratio is paramount for future developments and applications. We report on accurate analysis of the elemental composition of IZO thin films synthesized using a Combinatorial Pulsed Laser Deposition technique. The monitoring of the thin films elemental composition by Laser-Induced Breakdown Spectroscopy was chosen in view of further in situ and real-time technological developments and process control during IZO fabrication. Our analytical approach is based on plasma modeling, the recorded spectra being then compared to the spectral radiance computed for plasmas in local thermal equilibrium. The cation fractions measured were compared to values obtained by complementary measurements using energy dispersive X-ray spectroscopy and Rutherford backscattering spectrometry. Spectroscopic ellipsometry assisted the scientific discussion. A good agreement between methods was found, independently of the relative fraction of indium and zinc that varied from about 65 to 90 and 35 to 10 at%, respectively, and the measurement uncertainties associated to each analytical method.
747. Electrochemical impedance spectroscopy investigations on the L-cysteine-thiolate self-assembled monolayers formed at p-GaAs(100) electrodes
Authors:
Lazarescu, V; Enache, M; Anastasescu, M; Dobrescu, G; Negrila, C; Lazarescu, MF
Published: JUN 10 2014, ELECTROCHIMICA ACTA, 131, 51, DOI: 10.1016/j.electacta.2013.11.103
Electrochemical impedance spectroscopy investigations carried out in solutions with different pH brought evidence that the monolayers of L-cysteine-thiolate self-assembled on GaAs (hid) electrodes exert a complex molecular control over their electrochemical behavior. The analysis of the impedance spectra coupled with that of the XPS data and the AFM images taken before and after the EIS measurements reveled that both pH and applied potential brings significant changes at the electrified interface. The most important effect of pH is the conformational change of the L-cysteine-thiolate molecule observed at pH 11 that allows the interaction of the carboxyl group with the substrate atoms. A similar conformational change occurs at pH 5.5 but only under the applied potential control, being just a consequence of another major effect of the applied electric field. This is the H+ transfer inside the L-cysteine-thiolate film, an electric field driven process but pH dependent, which results in significant charge diminution both in the organic overlayer and in the semiconductor depletion region. (C) 2013 Elsevier Ltd. All rights reserved.
748. Nanomechanical characterization of bioglass films synthesized by magnetron sputtering
Authors:
Popa, AC; Marques, VMF; Stan, GE; Husanu, MA; Galca, AC; Ghica, C; Tulyaganov, DU; Lemos, AF; Ferreira, JMF
Published: FEB 28 2014, THIN SOLID FILMS, 553, 172, DOI: 10.1016/j.tsf.2013.10.104
Bioactive glasses are osteoproductive-type inorganic materials possessing the highest indices of bioactivity in both bulk and thin film forms. The prerequisites for reliable implant-type coatings are both their biological and mechanical performances. Whilst the bioglass films' structural, chemical and biological properties have been studied extensively, information about their mechanical performance is scarce. Here, transmission electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, nanoindentation and pull-out measurements were employed to assess the morphological, chemical, structural and mechanical properties of the bioglass films deposited onto Ti substrates by radio-frequency magnetron sputtering (RF-MS). The biological safety of the thin bioglass films was evaluated preliminarily in vitro by investigating the adherence, proliferation and cytotoxicity of fibroblast cells cultivated on their surface. Our study emphasize the versatility of RF-MS, showing how bioglass films' features such as composition, structure, bonding strength, hardness, elastic modulus and biological response can be conveniently adapted by tuning the RF-MS working conditions, and therefore demonstrating the unexplored potential of this deposition technique for preparing quality biomimetic glass coatings. (C) 2013 Elsevier B. V. All rights reserved.
749. Luminescent liquid crystalline materials based on palladium(II) imine derivatives containing the 2-phenylpyridine core
Authors:
Micutz, M; Ilis, M; Staicu, T; Dumitrascu, F; Pasuk, I; Molard, Y; Roisnel, T; Circu, V
Published: 2014, DALTON TRANSACTIONS, 43, 1161, DOI: 10.1039/c3dt52137k
In this work we report our studies concerning the synthesis and characterisation of a series of imine derivatives that incorporate the 2-phenylpyridine (2-ppy) core. These derivatives were used in the cyclo-metalating reactions of platinum(II) or palladium(II) in order to prepare several complexes with liquid crystalline properties. Depending on the starting materials used as well as the solvents employed, different metal complexes were obtained, some of them showing both liquid crystalline behaviour and luminescence properties at room temperature. It was found that, even if there are two competing coordination sites, the cyclometalation process takes place always at the 2-ppy core with (for Pt) or without (for Pd) the imine bond cleavage. We successfully showed that it is possible to prepare emissive room temperature liquid crystalline materials based on double cyclopalladated heteroleptic complexes by varying the volume fraction of the long flexible alkyl tails on the ancillary benzoylthiourea (BTU) ligands.
750. Pulsed laser deposition of nanocrystalline SiC films
Authors:
Socol, G; Galca, AC; Craciun, D; Hanna, M; Taylor, CR; Lambers, E; Craciun, V
Published: JUL 1 2014, APPLIED SURFACE SCIENCE, 306, 69, DOI: 10.1016/j.apsusc.2014.01.201
Thin SiC films were grown on (1 0 0) Si substrates at temperatures from 400 to 1000 degrees C under various CH4 pressures by the pulsed laser deposition (PLD) technique using a KrF excimer laser. After deposition, films were in situ annealed at their deposition temperature under 500 mbar of CH4 for 1.0-1.5h. X-ray reflectivity investigations showed that films exhibited mass densities similar to SiC single crystal samples, while symmetrical and grazing incidence X-ray diffraction investigations found that films deposited at 800 degrees C or higher substrate temperatures were nanocrystalline. Modeling of spectroscopic ellipsometry measurements indicated that the refractive index values were similar to those reported for bulk SiC, while X-ray photoelectron spectroscopy investigations found that films contained in bulk a relatively low oxygen concentration of around 1.0 at.%. Nanoindentation results showed that the deposited SiC films were very hard, with hardness values above 40 GPa for films deposited at temperatures higher than 800 degrees C. (C) 2014 Elsevier B.V. All rights reserved.
751. Transport in a hybrid normal metal/topological superconductor Kondo model
Authors:
Chirla, R; Dinu, IV; Moldoveanu, V; Moca, CP
Published: NOV 5 2014, PHYSICAL REVIEW B, 90, DOI: 10.1103/PhysRevB.90.195108
We investigate the equilibrium and nonequilibrium transport through a quantum dot in the Kondo regime, embedded between a normal metal and a topological superconductor supportingMajorana bound states at its end points. We find that the Kondo physics is significantly modified by the presence of theMajorana modes. When the Majorana modes are coupled, aside from the Kondo scale T-K, a new energy scale T* << T-K emerges, that controls the low-energy physics of the system. At lowtemperatures, the ac conductance is suppressed for frequencies below T*, while the noise spectrum acquires a similar to omega(3) dependence. At high temperatures, T >> T-K, the regular logarithmic dependence in the differential conductance is also affected. Under nonequilibrium conditions, and in particular in the {T, B}-> 0 limit, the differential conductance becomes negative. These findings indicate that the changes in transport may serve as clues for detecting the Majorana bound states in such systems. In terms of methods used, we characterize the transport by using a combination of perturbative and renormalization-group approaches.
752. Physical properties of AlxIn1-xN thin film alloys sputtered at low temperature
Authors:
Besleaga, C; Galca, AC; Miclea, CF; Mercioniu, I; Enculescu, M; Stan, GE; Mateescu, AO; Dumitru, V; Costea, S
Published: OCT 21 2014, JOURNAL OF APPLIED PHYSICS, 116, DOI: 10.1063/1.4898565
In this paper, we report on the structural, optical, and electrical properties of a wide compositional range of AlxIn1-xN thin layers deposited on glass and polyethylene terephthalate substrates. AlxIn1-xN layers of controlled composition were obtained by a simple reactive magnetron co-sputtering protocol, using a single aluminium target with indium insets, by varying the Al/In target surface area ratio, and the composition of the deposition atmosphere. The relevant physical properties were investigated and discussed. It is shown that the texture of the thin films is dependent on the cation ratio, while the bowing parameters of lattice constants and band gap values are larger than those of epitaxial layers. (C) 2014 AIP Publishing LLC.
754. UV SENSING EFFECT IN LANGMUIR-BLODGETT COMPLEX FILMS CONTAINING A NOVEL SYNTHESIZED Fe(III) PORPHYRIN
Authors:
Baschir, L; Fagadar-Cosma, E; Creanga, I; Palade, A; Lascu, A; Birdeanu, M; Savastru, D; Savu, V; Antohe, S; Velea, A; Fagadar-Cosma, G; Popescu, M; Simandan, ID
Published: APR-JUN 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 857, DOI:
A novel structure of metalloporphyrin, namely: 5,10,15,20-tetrakis(3,4-dimethoxyphenyl)-porphyrin Fe(III) chloride, was successfully synthesized. UV sensitive structure based on barium stearate functionalized with the novel synthesized porphyrin and carbon nanotubes was obtained. A five monolayers structure was deposited from solution by Langmuir - Blodgett technique onto a ceramic substrate with interdigital platinum electrodes. The complex film shows sensitivity to UV radiation due to the fact that an electron is excited from a Fe d orbital into a porphyrin antibonding pi orbital and is moved onto the ligand that is attached, facilitating the charge separation, while the presence of SWCNT activates the transport of the charge carriers.
755. In vitro toxicity evaluation of Ti4+-stabilized gamma-Bi2O3 sillenites
Authors:
Popescu, T; Lupu, AR; Feder, M; Tarabasanu-Mihaila, D; Teodorescu, VS; Vlaicu, AM; Diamandescu, L
Published: DEC 2014, TOXICOLOGY IN VITRO, 28, 1530, DOI: 10.1016/j.tiv.2014.07.003
We report results regarding the in vitro toxicology of gamma-Bi2O3 represented by its isomorphous phase Bi12TiO20 (gamma-BTO). The gamma-BTO microparticles were synthesized by two methods: coprecipitation from a bismuth nitrate tetrabutyl titanate solution and solid state reaction of Bi2O3 and TiO2 oxides. The structural and morphological characteristics of the obtained materials were determined using X-ray diffraction (XRD), selected area electron diffraction (SAED), transmission (TEM) and scanning (SEM) electron microscopy. The elemental composition was investigated using energy dispersive spectrometry (EDS). The cytotoxicity and oxidative/nitrosative stress (intracellular reactive oxygen species (ROS) and nitric oxide (NO) release) induced by the studied microparticles in HepG2, SH-SY5Y and 3T3-L1 cell cultures were determined using the MIT, DCF-DA (2 ',7 '-dichlorfluorescein-diacetate) and Griess methods respectively. Depending on the cell type and gamma-BTO concentration, results showed only weak cytotoxic effects after 24 h of gamma-BTO exposure and cell proliferation effects for longer treatment times. Only reduced NO release increases (corresponding to high gamma-BTO concentrations) were detected in case of SH-SY5Y and 3T3-L1 cells. The intracellular ROS production (higher for HepG2 cells) appeared inversely proportional to the gamma-BTO concentration. The obtained results indicated a promising in vitro biocompatibility of gamma-BTO and encourage further studies regarding its potential for biomedical applications. (C) 2014 Elsevier Ltd. All rights reserved.
756. Magnetic nanoparticles in MgB2
Authors:
Sandu, V; Chee, CY
Published: MAR 15 2014, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 498, 37, DOI: 10.1016/j.physc.2013.12.008
Additional pinning generated by magnetic nanoparticles which were created or inserted within polycrystalline MgB2 superconductor is analyzed. The composites were built in two ways: (i) ceramization of polysiloxane-co-ferrocene based copolymers and (ii) insertion of coated nanoparticles. The composites present two types of pinning: core pinning based on the variation of the superconducting parameter when a non-superconducting particle is present and a magnetic pinning resulting from the interaction of the screening currents around the particle and the flux line. All samples show a consistent improvement of the critical current density when the magnetic moment of the sample in normal state is finite but small, showing a maximum for a magnetic moment of 0.015 emu/cm(3). A tentative description of the effect of magnetic pinning is presented in the framework of the collective pinning. (C) 2014 Elsevier B.V. All rights reserved.
757. Substrate impact on optical and microstructural properties of TiO2-PEG sol-gel films
Authors:
Anastasescu, M; Teodorescu, VS; Buiu, O; Osiceanu, P; Calderon-Moreno, JM; Predoana, L; Preda, S; Nicolescu, M; Marin, A; Serban, B; Mihaila, M; Stoica, M; Zaharescu, M; Gartner, M
Published: SEP 2014, CERAMICS INTERNATIONAL, 40, 11811, DOI: 10.1016/j.ceramint.2014.04.012
Nanosized TiO2 layers containing polyethylene glycol (PEG) with 20,000 molecular weight were prepared by sol gel method and deposited on three different substrates: microscope standard slides, Fluorine doped Tin Oxide (FTO) glass and Silicon, followed by thermal treatment at 450 degrees C. The effects of the substrate on the microstructural, morphological, chemical and optical properties of the films have been studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), Atomic Force Microscopy (AFM), X-ray Photo-electron Spectroscopy (XPS) and Spectroscopic Ellipsometry (SE). The XRD showed that the film crystallization depends very much on the substrate used, thus the films deposited on glass are amorphous even after 1 h thermal treatment at 450 degrees C, while the films deposited on Silicon and FTO substrates are crystallized in anatase phase, in good agreement with the TEM analysis. The XPS analysis showed that a rather high carbon relative concentration in the TiO2 film (without PEG) exists; this suggests that an unavoidable carbon contamination occurs and is not related on the presence or absence of PEG. The thickness and surface roughness of the films are clearly dependent on the substrate type. The flat surfaces of glass and Si lead to the formation of thinner TiO2 films (around 30 nm thicknesses), while the FTO substrate surface leads to thicker film (thickness similar to 100 nm). The porosity of TiO2 films as found by SEM and TEM analyzes is dependent of substrate type; small pore sizes up to 20 nm are characteristic for the films deposited on glass, while larger pore sizes up to 200 nm are found for the films deposited on FTO substrate. Not least, the film transmissions in the visible region are also substrate dependent and the highest values (80%) were obtained for the films deposited on glass. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
758. Liquid crystals based on silver carbene complexes derived from dimeric bis(imidazolium) bromide salts
Authors:
Pana, A; Ilis, M; Micutz, M; Dumitrascu, F; Pasuk, I; Circu, V
Published: 2014, RSC ADVANCES, 4, 59497, DOI: 10.1039/c4ra11023d
A series of bis(imidazolium) salts with different mesogenic groups (cyanobiphenyl or cholesteryl) and their silver carbene complexes with Br- anion has been designed and prepared. The liquid crystalline behaviour of these ionic liquids and their corresponding silver-carbene complexes was investigated by polarised optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis (TGA). The silver complexes are thermally stable on a broad temperature range with accessible transition temperatures close to ambient temperature. The compounds with cholesteryl groups show higher transition temperatures than the compounds possessing cyanobiphenyl mesogenic groups, but their thermal stability is limited by a slight decomposition before reaching the isotropic state. Interestingly, the bis(imidazolium) salt with two cyanobiphenyl groups at each side shows an enantiotropic nematic phase on a short range, being one of the few examples of ILC displaying nematic phase.
759. Red blood cells interaction with vanadium and its oxides based nanocomposite structures
Authors:
Prilepov, V; Gasin, P; Prilepov, I; Midoni, V; Chirita, A; Spoiala, D; Ketrush, P
Published: JAN-FEB 2014, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 8, 167, DOI:
The results of the investigation of vanadium and its oxides based nanocomposite structures interaction with the water are brought in this paper. It was established, that at the non-contact interaction of the nanocomposite structures with the water, its activation occurs, which is revealed in a change in the sign of the redox potential of the water from the initial positive to the negative one. Besides, the activation effect is interconnected, i.e. the activation both of the water as well as of nanocomposite structures occurs. The observed effect is explained in the frame of the resonance interaction of the oscillating dipoles theory (the conductive clusters uniformly distributed in V2O5 dielectric matrix with the water molecule dipoles. On the basis of the experimental results, one can affirm that the vanadium and its oxides based nanocomposite structures are a biologic activators and can be used in a modern biomedicine.
760. Experimental study on phase formation of SiC doped MgB2: processing of Mg-B-SiC powders by spark plasma sintering
Authors:
Guo, Z; Suo, H; Sandu, V; Aldica, G
Published: OCT 2014, MATERIALS RESEARCH INNOVATIONS, 18, 411, DOI: 10.1179/1433075X13Y.0000000164
In order to study the effect of spark plasma sintering (SPS) technique synthesis SiC-MgB2 on the phase formation, the MgB2 and SiC-MgB2 bulks were fabricated with mixed powders by various SPS synthesis routes. The phase formation processes were investigated with the aid of X-ray diffraction analysis, TEM investigations and sintering theories. The solid-solid reaction between Mg and B powders formed MgB2 at low temperature. As the sintering temperature increases, the reactions of molten Mg with B form MgB2, and simultaneously, the molten Mg promotes the decomposition of SiC and nuclei of Mg2Si may form on the surface of SiC grains; the nascent MgB2 incorporates the carbon into lattice, hereby enhancing the SiC decomposition. The experimental results are in good agreement with the assumed chemical reaction.
761. Volume fraction dependent magnetic behaviour of ferrofluids for rotating seal applications
Authors:
Schinteie, G; Palade, P; Vekas, L; Iacob, N; Bartha, C; Kuncser, V
Published: OCT 2 2013, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 46, DOI: 10.1088/0022-3727/46/39/395501
Ferrofluid samples consisting of magnetite nanoparticles (NPs) coated with oleic acid and dispersed in a non-polar organic solvent have been synthesized by chemical routes. Different volume fractions, phi, of magnetic NPs were considered. The overall structural characterization of NPs has been performed by x-ray diffractometry, with lattice parameters and average coherence lengths evaluated via Rietveld refinements. The magnetic properties of different samples have been analysed by SQUID magnetometry and temperature-dependent Mossbauer spectroscopy and finally explained by adequate magnetic relaxation mechanisms. Zero field cooling-field cooling protocols provided useful information about specific volume fraction dependent magnetic relaxation and de-freezing processes, the lack of the Verwey transition and stronger dipolar interactions at higher volume fractions. Anisotropy energies as obtained by both temperature dependent Mossbauer spectroscopy and magnetometry data are compared and a new procedure for a quantitative characterization of the dipolar interactions is proposed.
762. Novel Fe@C-TiO2 and Fe@C-SiO2 water-dispersible magnetic nanocomposites
Authors:
Fleaca, CT; Dumitrache, F; Morjan, I; Alexandrescu, R; Luculescu, C; Niculescu, A; Vasile, E; Kuncser, V
Published: AUG 1 2013, APPLIED SURFACE SCIENCE, 278, 288, DOI: 10.1016/j.apsusc.2013.01.172
We report the synthesis of novel nanocomposites based on Fe@C nanoparticles obtained from Fe(CO)(5) and C2H4/H-2 by laser pyrolysis technique using a three nozzles injector. The alpha Fe-FexCy@C particles (below 24 nm diameter) were first functionalized with hydrophilic groups using Na carboxymethylcellulose. Oxidic precursors (Si(OC2H5)(4) or Ti(OC2H5)(4)) dissolved in ethanol were mixed with ethanolic suspensions of hydrophilized Fe@C nanoparticles using strong ultrasonication, then with water (at different pH values) and finally the Fe-containing composites were recovered by magnetic separation. The SiO2 and TiO2-coated powders were characterized by XRD, FT-IR and TEM techniques and their magnetic hysteresis curves were recorded at different temperatures. Both composites contain submicron aggregates of Fe@C nanoparticles embedded in/surrounded by a disordered porous oxidic matrix/shell. Near superparamagnetic behavior and room temperature and 26 Am-2/kg (for Fe@C/SiO2) or 57Am(2)/kg (for Fe@C/TiO2) saturation magnetization values were recorded and a blocking temperature around 500K was extrapolated. (C) 2013 Elsevier B.V. All rights reserved.
763. Miniature x-ray tubes: current state and future prospects
Authors:
Filip, V; Filip, LD; Okuyama, F
Published: MAR 2013, JOURNAL OF INSTRUMENTATION, 8, DOI: 10.1088/1748-0221/8/03/T03005
Over the last decade, field emission miniature x-ray tubes emerged as cutting-edge applications of nanotechnology, possessing massive potential for use in various important fields, including that of precision medical therapy. The article essentially presents a review of such new devices reported in the literature. Additional discussions on the necessity of stabilizing the electron beam that generates x-rays are also included, and a simple technique for minimizing the current fluctuations is described. It is also pointed out that further miniaturization of field emission x-ray sources may need new concepts in designing the tube in shapes acting as "self focusing" structures for the electron beams.
764. Influence of the TiO2 precursors on the thermal and structural stability of titanate-based nanotubes
Authors:
Preda, S; Teodorescu, VS; Musuc, AM; Andronescu, C; Zaharescu, M
Published: FEB 2013, JOURNAL OF MATERIALS RESEARCH, 28, 303, DOI: 10.1557/jmr.2012.362
The influence of different TiO2 precursors (laboratory-prepared sol-gel powders, dried and thermally treated at 400 degrees C, and commercial powders such as anatase by Aldrich and P25 Aeroxide by Evonik) on the structure and morphology of the titanate nanotubes obtained by hydrothermal method was investigated by x-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. In all cases, titanate-based nanotubes were obtained, having similar structure and morphology. The effect of the thermal treatment on the structural stability was also studied by differential thermal analysis and thermogravimetry analysis (TG/DTA) and differetial scanning calorimetry (DSC) measurements up to 600 degrees C, to determine the transformation of titanate nanotubes into other phases. Complementarily, by XRD investigation, the phases that develop after the thermal treatment of the titanate nanotubes in 110-400 degrees C temperature range were identified. The TEM micrographs come to confirm the deterioration of morphology and transformation from nanotubes to particles. The thermal stability of the investigated nanotubes led to the conclusion that this property depends not only on the sodium content but also on the type of precursor. The highest thermal stability was noticed for the nanotubes synthesized starting with anatase (Aldrich) commercial powder.
765. Structure and dielectric properties of low fluence excimer laser annealing of sol-gel HfO2 thin films deposited on Si wafer
Authors:
Teodorescu, VS; Maraloiu, AV; Blanchin, MG; Yamada, T; Sandu, CS; Delaporte, P; Zaharescu, M
Published: 2013, 2013 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1-2, 80, DOI:
Sol-gel HfO2 thin films, prepared from etoxid precursor, were deposited onto silicon wafer substrates by dipcoating. Low fluence multipulse excimer laser processing was used for sol-gel film densification. The small duration of the laser pulse heating limits the quantity of oxygen atoms arriving from the surface at the HfO2/Si interface. Laser irradiations were performed using a XeCl (308 nm) excimer laser, with a homogeneous laser beam. The nanostructure evolution of the laser irradiated films, using different laser fluences between 30 and 120 mJ/cm(2) and different number of pulses, was studied by systematic cross section transmission electron microscope (XTEM) observations. Dielectric constant measurements were performed on the sol-gel HfO2 films samples after laser annealing. The optimum laser processing conditions were found to be a laser fluence of 80 mJ/cm(2) and 5000 to 10000 laser pulses. In these conditions, uniform densified HfO2 amorphous films with a dielectric constant of about 25 were obtained.
766. Enhancement of Superconductivity in Quenched alpha-FeSe Flakes
Authors:
Zhao, PH; Yan, W; Han, YL; Shen, SC; Aldica, G; Sandu, V; Badica, P; Nie, JC
Published: DEC 2013, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 26, 3353, DOI: 10.1007/s10948-013-2194-4
Tetragonal alpha-FeSe flakes were fabricated by a simple method. Enhancement of superconductivity was observed in the quenched samples. The properties were characterized by X-ray diffraction, a superconductivity quantum interference device, and physical property measurement system. It is interesting that the superconducting transition temperature of the quenched samples is about 2 K higher than that of unquenched samples, but after reannealed, the enhancement of superconductivity disappeared. The reduction of the c/a ratio might be responsible for the enhancement of superconductivity in the quenched FeSe flakes.
767. Enhancing Oxidative Dehydrogenation Selectivity of Ceria-Based Catalysts with Phosphorus as Additive
Authors:
Trotus, IT; Teodorescu, CM; Parvulescu, VI; Marcu, IC
Published: MAR 2013, CHEMCATCHEM, 5, 765, DOI: 10.1002/cctc.201200699
Surface- and bulk-phosphated ceria catalysts were prepared and studied in propane oxidative dehydrogenation (ODH) at 823 and 873K. The catalysts were characterized by N2 adsorption at 77K, XRD, TEM, and diffuse reflectance IR Fourier transform (DRIFT), Raman, X-ray photoelectron (XPS), and energy dispersive X-ray (EDX) spectroscopies. Both series of catalysts presented an increase in the ODH selectivity with respect to pure ceria mainly at the expense of total oxidation selectivity. Thus, the selectivity to propene was approximately 74% with surface-phosphated catalysts and 62% with bulk-phosphated catalysts. For the surface-phosphated samples, P is confined to the surface and subsurface regions of the ceria particles, whereas P is also dispersed in the bulk of the oxide in the bulk-phosphated samples. Finally, all the characterization techniques led us to the conclusion that Ce4+ cations that interact with P are responsible for the observed increase in the ODH.
768. On the Scaling Law of the Pinning Force in MgB2 Superconducting Composites with Magnetic Nanoinclusions
Authors:
Sandu, V; Chee, CY
Published: JAN 2013, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 26, 131, DOI: 10.1007/s10948-012-1732-9
Dense superconducting composites with magnetic nanoparticles were prepared by spark plasma sintering. In addition to structure and magnetic properties, we focused on the pinning properties as described by the field and temperature dependence of the scaled pinning force analyzed. We found that the pinning force does not obey any scaling law and attributed this effect to the anisotropy of the MgB2 and the almost random distribution of the orientation of the superconducting grains within the polycrystalline sample.
769. Structural changes during toluene complete oxidation on supported EuFeO3 monitored by in situ Eu-151 and Fe-57 Mossbauer spectroscopy
Authors:
Florea, M; Alifanti, M; Kuncser, V; Parvulescu, VI
Published: JUN 1 2013, CATALYSIS TODAY, 208, 59, DOI: 10.1016/j.cattod.2012.09.035
Pure EuFeO3 and ceria were prepared via a sol-gel citrate route and were calcined at 700 degrees C. Separately, a 20 wt% EuFeO3/CeO2 was prepared via incipient wetness impregnation of calcined ceria with citrate precursors and calcined in the same conditions. SBET, XRD, toluene chemisorption, toluene-TPD and in situ Eu-151 and Fe-57 Mossbauer investigations were performed. All characterization data indicate the formation of a well-dispersed EuFeO3 at the surface of CeO2. During the oxidation of toluene Eu-151 and Fe-57 Mossbauer spectroscopy suggested a cooperative effect of the cations. The catalysts were tested in total oxidation of toluene. In terms of intrinsic activity for toluene combustion, supported catalysts were more active than bulk EuFeO3. All structural changes during operation time were reversible. (C) 2012 Elsevier B.V. All rights reserved.
770. Iron oxide magnetic nanoparticles with versatile surface functions based on dopamine anchors
Authors:
Mazur, M; Barras, A; Kuncser, V; Galatanu, A; Zaitzev, V; Turcheniuk, KV; Woisel, P; Lyskawa, J; Laure, W; Siriwardena, A; Boukherroub, R; Szunerits, S
Published: 2013, NANOSCALE, 5, 2702, DOI: 10.1039/c3nr33506b
The synthesis of multifunctional magnetic nanoparticles (MF-MPs) is one of the most active research areas in advanced materials as their multifunctional surfaces allow conjugation of biological and chemical molecules, thus making it possible to achieve target-specific diagnostic in parallel to therapeutics. We report here a simple strategy to integrate in a one-step reaction several reactive sites onto the particles. The preparation of MF-MPs is based on their simultaneous modification with differently functionalized dopamine derivatives using simple solution chemistry. The formed MF-MPs show comparable magnetic properties to those of naked nanoparticles with almost unaltered particle size of around 25 nm. The different termini, amine, azide and maleimide functions, enable further functionalization of MF-MPs by the grafting-on approach. Michael addition, Cu(I) catalyzed << click >> chemistry and amidation reactions are performed on the MF-MPs integrating subsequently 6-(ferrocenyl)-hexanethiol, horseradish peroxidase (HRP) and mannose.
771. Microstructure and electrical properties of zirconia and composite nanostructured ceramics sintered by different methods
Authors:
Vasile, BS; Andronescu, E; Ghitulica, C; Vasile, OR; Curechiu, L; Scurtu, R; Vasile, E; Trusca, R; Pall, L; Aldica, V
Published: APR 2013, CERAMICS INTERNATIONAL, 39, 2543, DOI: 10.1016/j.ceramint.2012.09.013
The aim of this study is the preparation and characterization of dense cubic zirconia ceramics and zirconia nanocomposites (reinforced with 5 wt% alumina). The powders were obtained through sol-gel methods and densified using classical sintering and spark plasma sintering (SPS) methods. The obtained ceramics were characterized through X-ray diffraction, scanning electron microscopy and impedance spectroscopy at room and high temperature. The average grain size of cubic zirconia particles was found to be approximately 8 and 2.5 mu m for the classical sintering and 99 nm for SPS. The alumina particles in composites have an average grain size of 0.7 mu m for classical sintering and 53 nm for SPS ones. The total conductivity for nanocomposites sintered through both methods was also determined. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
772. FERROMAGNETISM AND REACTIVITY OF FE DEPOSITED ON GaAs(001) BY MAGNETRON SPUTTERING
Authors:
Vasilache, V; Lungu, GA; Logofatu, C; Medianu, RV; Teodorescu, CM
Published: JAN-MAR 2013, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 8, DOI:
Iron layers are grown on GaAs(001) single crystal wavers by magnetron sputtering and characterized by magneto-optical Kerr effect (MOKE) and X-ray photoelectron spectroscopy (XPS). It is found that all deposited layers, starting with 2 nm thickness, are ferromagnetic at room temperature with a relatively high coercitive field (500 to 750 Oe). The average Fe magnetic moment is larger for the thinnest Fe film deposited, of about 0.52 Bohr magnetons per Fe atom. The average Fe magnetic moment decreases to 0.26 Bohr magnetons, then to 0.17 Bohr magnetons for 4 and 8 nm, resepctively. XPS evidenced that the outermost Fe layers are oxidized; however, the thinnest Fe film presented the lower oxidation state. We may connect this reaction with Fe-As bonds, resulting in a nonferromagnetic interface compound. Indeed, XPS depth profiling of the 8 nm sample evidenced the formation of a very thin (about 1.4 nm) Fe metal layer immediately at the interface with GaAs. In this layer, Fe may reach an atomic magnetic moment as high as 1 Bohr magneton.
773. Direct Synthesis of Sorbitol and Glycerol from Cellulose over Ionic Ru/Magnetite Nanoparticles in the Absence of External Hydrogen
Authors:
Negoi, A; Trotus, IT; Steiner, OM; Tudorache, M; Kuncser, V; Macovei, D; Parvulescu, VI; Coman, SM
Published: NOV 2013, CHEMSUSCHEM, 6, 2094, DOI: 10.1002/cssc.201300554
774. Influence of mechanical milling on the physical properties of SmCo5/Fe65Co35 type hard/soft magnetic nanocomposite
Authors:
Dorolti, E; Trifu, AV; Isnard, O; Chicinas, I; Tolea, F; Valeanu, M; Pop, V
Published: MAY 25 2013, JOURNAL OF ALLOYS AND COMPOUNDS, 560, 194, DOI: 10.1016/j.jallcom.2013.01.140
The influence of milling type on the structural and magnetic behaviour of mechanically milled SmCo5/Fe65Co35 has been studied. By adjusting the mill speed parameters, (Omega/omega), three types of milling have been performed: shock mode process (SMP), friction mode process (FMP) and a combined shock followed by a friction mode process. It was found that in SMP conditions the remanent magnetization and composite coercivity increase with increasing milling time. The best exchange coupling, with a coercivity of 1.05 T, was obtained for samples milled for 8 h in SMP and annealed for 2 h at 550 degrees C. On the other hand, the low energy of FMP does not succeed in producing a microstructure adapted to favour the interphase exchange interactions between the soft and hard magnetic phases. A combined milling process does not change significantly the microstructure obtained previously after 8 h of SMP. This indicates that the microstructure of the composite is formed primarily during SMP while FMP, less energetic, does not drastically affect the crystallite size and crystallite shape of SMP samples. X-ray diffraction patterns were used to follow the evolution of the structure and microstructure. The diffusion of Fe and Co from Fe65Co35 to SmCo5 phase leads to the formation of Sm-2(Co,Fe)(17)/Fe-Co composite. The magnetic behaviour was checked from hysteresis curves and dM/dH vs. H plots. (C) 2013 Elsevier B.V. All rights reserved.
775. Ru-based magnetic nanoparticles (MNP) for succinic acid synthesis from levulinic acid
Authors:
Podolean, L; Kuncser, V; Gheorghe, N; Macovei, D; Parvulescu, VI; Coman, SM
Published: 2013, GREEN CHEMISTRY, 15, 3082, DOI: 10.1039/c3gc41120f
Ru(III)/functionalized silica-coated magnetic nanoparticles (Ru(III)-MNP) were proven to be a highly active, selective and easily recoverable catalyst for the oxidation of levulinic acid to succinic acid under green conditions.
776. Magnetic configurations of Ni-Cu alloy nanowires obtained by the template method
Authors:
Matei, E; Enculescu, I; Toimil-Molares, ME; Leca, A; Ghica, C; Kuncser, V
Published: AUG 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1863-3
High aspect ratio nanowires of Ni-Cu alloys have been synthesized by potentiostatic electrochemical deposition in etched ion-track membranes. The nickel-to-copper ratio in the nanowires was controlled via the deposition potential and electrochemical bath composition. We present a detailed study of nanowire properties including morphology, composition, and magnetic behavior. We report the magnetic configurations measured as function of the nanowire composition and discuss domain formation, anisotropy aspects, and local easy axis distributions.
777. TECHNOLOGY OF CHALCOGENIDE GLASSY SEMICONDUCTOR LAYERS FABRICATION
Authors:
Prilepov, V; Popescu, M; Chirita, A; Korshak, O; Ketrush, P; Nasedchina, N
The results of the studies of thin layer structures based on chalcogenide glassy semiconductors (CGS) of As-Se-S system fabrication are presented in the given paper. The possibility of of As-Se-S system thin films obtaining with the given electro-physical parameters, was shown.
778. Maghemite and poly-DL-alanine based core-shell multifunctional nanohybrids for environmental protection and biomedicine applications
Authors:
Covaliu, CI; Paraschiv, G; Biris, SS; Jitaru, I; Vasile, E; Diamandescu, L; Velickovic, TC; Krstic, M; Ionita, V; Iovu, H; Matei, E
Published: NOV 15 2013, APPLIED SURFACE SCIENCE, 285, 95, DOI: 10.1016/j.apsusc.2013.08.059
This paper deals with the synthesis of two nanohybrid materials based on maghemite (gamma-Fe2O3) and poly-DL-alanine using a two-step procedure consisting of maghemite nanoparticles synthesis by microemulsion method and nanohybrids obtaining by coating of maghemite nanoparticles with poly-DL-alanine biopolymer in two different molar ratios (H1:5 and H1: 15). The maghemite and their corresponding nanohybrids were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoemission spectroscopy, Mossbauer spectroscopy, Transmission electron microscopy, High resolution transmission electron microscopy with selected area electron diffraction and Atomic absorption spectroscopy. The two nanohybrids under the investigation have the average particle sizes of 22 nm and 23 nm. The Fourier transform infrared spectroscopy spectra and X-ray photoemission spectroscopy data indicate the existence of some interactions between the maghemite nanoparticles and poly-DL-alanine shell. The saturation magnetization values for maghemite and the two nanohybrids determined by a Vibrating Sample Magnetometer correspond to a typical superparamagnetic behavior suitable for applying in biomedical field. Also, with respect of biomedical application the biological activity of maghemite and its corresponding nanohybrids was investigated on healthy human cells (PBMC) and cancerous cells (HeLa). Furthermore, in order to support the multifunctionality of the gamma-Fe2O3 sample and nanohybrids we also investigated their wastewater treatment properties by measuring the removal efficiency of heavy metal Cd (II) ions. (C) 2013 Elsevier B. V. All rights reserved.
779. Phenylboronic-Acid-Modified Nanoparticles: Potential Antiviral Therapeutics
Authors:
Khanal, M; Vausselin, T; Barras, A; Bande, O; Turcheniuk, K; Benazza, M; Zaitsev, V; Teodorescu, CM; Boukherroub, R; Siriwardena, A; Dubuisson, J; Szunerits, S
Published: DEC 11 2013, ACS APPLIED MATERIALS & INTERFACES, 5, 12498, DOI: 10.1021/am403770q
Phenylboronic-acid-modified nanoparticles (NPs) are attracting considerable attention for biological and biomedical applications. We describe here a convenient and general protocol for attaching multiple copies of para-substituted phenylboronic acid moieties onto either iron-oxide-, silica-or diamond-derived NPs. The boronic acid fiinctionalized NPs are all fabricated by first modifying the surface of each particle type with 4-azidobenzoic ester functions. These azide-terminated nanostructures were then reacted with 4-[1-ozo-4-pentyn-1-yl) amino]phenylboronic acid units via a Cu(I) catalyzed Huisgen cycloaddition to furnish, conveniently, the corresponding boronic-acid modified NPs (or "borono-lectins") targeted in this work. The potential of these novel "borono-lectins" as antiviral inhibitors was investigated against the Hepatitis C virus (HCV) exploiting a bioassay that measures the potential of drugs to interfere with the ability of cell-culture-derived JFH1 virus particles to infect healthy hepatocytes. As far as we are aware, this is the first report that describes NP-derived viral entry inhibitors and thus serves as a "proof-of-concept" study. The novel viral entry activity demonstrated, and the fact that the described boronic-acid-functionalized NPs all display much reduced cellular toxicities compared with alternate NPs, sets the stage for their further investigation. The data supports that NP-derived borono-lectins should be pursued as a potential therapeutic strategy for blocking viral entry of HCV.
780. Formation mechanism of CdS nanoparticles with tunable luminescence via a non-ionic microemulsion route
Authors:
Angelescu, DG; Munteanu, G; Anghel, DF; Peretz, S; Maraloiu, AV; Teodorescu, VS
Published: JAN 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-012-1376-5
We investigated the synthesis of CdS nanoparticles via an optimized water-in-oil microemulsion route that used the non-ionic surfactantbased system H2O-n-octane-Brij30/1-octanol. For that purpose, a microemulsion that contained Cd(II) ions (mu e1) and another microemulsion that contained S2- ions (mu e2) were combined. To investigate the ways in which the non-ionic microemulsion characteristics controlled the size and emission properties of colloidal CdS quantum dots, mu e1 and mu e2 with tunable and robust similar structure were prepared. This requirement was fulfilled by matching the water emulsification failure boundary (wefb) of the two microemulsions and carrying out synthesis along this boundary. Dynamic light scattering and fluorescence probe techniques were used to investigate the size and interfacial organization of the microemulsion water droplets, and the CdS nanoparticles were characterized by UV-Vis and static fluorescence spectrometry, TEM and HRTEM. Nanoparticles of diameter 4.5-5.5 nm exhibiting enhanced band edge emission were produced by increasing the water content of the precursor microemulsions. The experimental results were combined with a Monte Carlo simulation approach to demonstrate that growth via coagulation of seed nuclei represented the driving mechanism for the CdS nanoparticle formation in the water-in-oil microemulsion.
781. Prediction of half metallic properties in Ti2CoSi Heusler alloy based on density functional theory
Authors:
Birsan, A; Palade, P; Kuncser, V
Published: APR 2013, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 331, 112, DOI: 10.1016/j.jmmm.2012.11.029
The electronic and magnetic properties of Ti2CoSi Heusler compound are investigated using density functional calculations. The optimized lattice constant is found to be 6.030 angstrom. The compound is a half-metallic ferromagnet with an energy gap in minority spin channel of 0.652 eV at equilibrium lattice constant, which leads to a 100% spin-polarization. The obtained total magnetic moment from spin-polarized calculations is 3.0 mu(B)for values of lattice constants higher than 5.941 angstrom. The half-metallicity is spoiled for a compressed volume of 4%, suggesting a possible application as pressure sensitive material. (C) 2012 Elsevier B.V All rights reserved.
782. Thermal stability of new biologic active copper(II) complexes with 5,6-dimethylbenzimidazole
Authors:
Vlaicu, ID; Constand, M; Olar, R; Marinescu, D; Grecu, MN; Lazar, V; Chifiriuc, MC; Badea, M
Published: SEP 2013, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 113, 1377, DOI: 10.1007/s10973-013-2948-z
Three new coordinative compounds that contain mixed ligands (5,6-dimethylbenzimidazole and acrylato anion) were synthesized and characterized. The features of complexes have been assigned from microanalytical, IR, UV-Vis and EPR spectra as well as thermal analysis. IR data are in accordance with unidentate nature of 5,6-dimethylbenzimidazole while the acrilato ion acts as uni- or bidentate ligand. The electronic spectra display the characteristic pattern of square pyramidal or octahedral stereochemistry, which were confirmed by the EPR spectra. Antibacterial and antifungal activities of the complexes have been determined in vitro, against various Gram-negative and Gram-positive bacteria and fungi. The tested complexes exhibited different spectra of antimicrobial activity and inhibited the microbial ability to colonize the inert surfaces, acting as potential anti-adherence and biofilm-controlling agents. Thermal decomposition evidenced several well-defined steps as dehydration (complex 2), 5,6-dimethylbenzimidazole molecule release (all complexes) and the acrylate decomposition in carbonate (complex 3). The final residue is in all cases copper (II) oxide.
783. Magnetic properties of iron-carbon nanocomposites obtained by laser pyrolysis in specific configurations
Authors:
Schinteie, G; Kuncser, V; Palade, P; Dumitrache, F; Alexandrescu, R; Morjan, I; Filoti, G
Published: JUL 5 2013, JOURNAL OF ALLOYS AND COMPOUNDS, 564, 34, DOI: 10.1016/j.jallcom.2013.02.126
New nanometric systems were produced by using specific parameters of the laser pyrolysis process. Relevant results related to the magnetic behavior of the samples were obtained via SQUID magnetometry and Mossbauer spectroscopy, the data being corroborated with those previously obtained from X-ray diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy. The formed nanocomposites contain iron carbides, iron oxides and metallic iron nanoparticles which relative content and average size depend strongly on experimental specific parameters of the pyrolysis process. The magnetic properties and the local interaction mechanisms were explained by adequate magnetic relaxation and static models. (C) 2013 Elsevier B.V. All rights reserved.
784. Laser induced breakdown spectroscopy surface analysis correlated with the process of nanoparticle production by laser ablation in liquids
Authors:
Apostol, I; Damian, V; Damian, R; Nistor, LC; Pascu, A; Staicu, A; Udrea, C
Published: APR 2013, HYPERFINE INTERACTIONS, 216, 143, DOI: 10.1007/s10751-012-0739-8
Laser induced ablation of solids situated in liquids (LAL) was used in order to produce nanoparticles. Laser induced breakdown spectroscopy (LIBS) surface analysis correlated with the process of nanoparticle production by LAL was applied to explain the composition of the obtained nanoparticles as determined by Electron Dispersive X-ray Spectroscopy (EDS). In the case of aluminum rods placed in distilled water irradiated with pulsed laser radiation (355 nm wavelength, 6 ns pulse length) we have obtained spheric nanoparticles with dimensions lower than 100 nm. Quantitative EDS analyses on the obtained spheres showed the presence of, Al, O, and Si. This indicates that probably the composition of the nanoparticles is an aluminum silicate. LIBS analysis on the aluminum target have shown the presence of a Si line with low intensity indicating a small quantity of silicon in the first ablated layers. The LIBS spectra for a sequence of pulses evidenced also that the intensity of the aluminum lines after a number of pulses decreases. This means that the quantity of ablated material becomes smaller due to the ablation depth decrease.
785. SOL-GEL HYBRID NANOCOMPOSITES WITH OXIDE NANOPARTICLES
Authors:
Predoana, L; Gartner, M; Teodorescu, VS; Nicolescu, M; Anastasescu, M; Zaharescu, M
Published: FEB-MAR 2013, REVUE ROUMAINE DE CHIMIE, 58, 249, DOI:
In the present work the influence of the method of preparation on the characteristics of sol-gel hybrid nanocomposites with oxide nanoparticles was studied. The chosen system consists of a SiO2 matrix based on methyltriethoxysilane (MTEOS) and laboratory made TiO2:CeO2 (4:1) nanopowder. The doping of the matrix was realized either by dispersion of previously prepared binary nanopowder in the matrix solution or by in situ generation of the TiO2-CeO2 nanoparticles during the matrix hydrolysis-condensation processes. Films were deposited on silicon wafer and glass substrates by dip-coating method and were characterized as prepared and annealed at 120 degrees C. The optical and morphological properties were determined by spectroellipsometry (SE), scanning electron microscopy (SEM), atomic force microscopy (AFM), their structural characterization was realized by IR spectroscopy and the thermal behavior was determined by thermogravimetric and differential-thermal analysis (TG/DTA). All characterization methods have shown that by the two preparation routes materials with different characteristics were obtained.
786. Wireless AlN sensor for condition based monitoring of industrial equipment
Authors:
Ionescu, G; Ionescu, O; Popovici, S; Costea, S; Dumitru, V; Brezeanu, M; Stan, GE; Pasuk, I
Published: 2013, 2013 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1-2, 58, DOI:
This paper reports on the experimental realization and characterization of a wireless sensing system for machine-tool condition based monitoring. The system comprises a vibration sensor, an ARDUINO Leonardo development board and an RM 42 Blue tooth module. The sensing principle is based on a vibration sensor which includes a piezoelectric AlN layer deposited by sputtering on a flexible stainless steel foil. The functional testing of the sensor using a test stand for asynchronous engines equipped with frequency convertors is demonstrated.
787. Microstructure-related magnetic properties in Co-implanted ZnO thin films
Authors:
Nistor, LC; Ghica, C; Kuncser, V; Pantelica, D; Grob, JJ; Epurescu, G; Dinescu, M
Published: FEB 13 2013, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 46, DOI: 10.1088/0022-3727/46/6/065003
Highly textured ZnO thin films were implanted with Co ions at fluences of 1 x 10(16) and 1 x 10(17) ions cm(-2). Although their microstructure observed by analytical high-resolution electron microscopy was very different, SQUID magnetometer measurements showed qualitatively similar magnetic properties. In the low-fluence film, only small modifications, such as a slight amorphization, planar defects or very small (<1-1.5 nm) Co clusters, were hardly observable. Implantation at a higher fluence led to important changes in the film structure: heavy amorphization and metallic Co precipitates were identified by electron diffraction, energy dispersive x-ray spectroscopy (EDS), electron energy loss spectroscopy and scanning transmission electron microscopy spectrum imaging. EDS microanalysis additionally revealed the presence of similar to 2 at% Co atoms that were likely dissolved in the ZnO lattice at the atomic level. No Co oxides or other secondary oxide phases were detected. For both implanted samples, the dimensions of Co precipitates were below the superparamagnetic limit at room temperature. Thermo-magnetization curves and magnetic hysteresis loops measured in the temperature range from 5 to 300 K indicated two superimposed magnetic regimes, one predominant above 50 K and the other below 50 K. We analysed the possible mechanisms and quantitative contributions to explain the observed magnetic behaviour at low and room temperature.
788. TRANSMISSION ELECTRON MICROSCOPY STUDY OF Ge NANOPARTICLES FORMED IN GeSiO FILMS BY ANNEALING IN HYDROGEN
Authors:
Teodorescu, VS; Maraloiu, AV; Stavarache, I; Lepadatu, AM; Ciurea, ML
Published: OCT-DEC 2013, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 8, 1780, DOI:
This paper presents a detailed transmission electron microscopy (TEM) study of GeSiO films with Ge nanoparticles. The films with 2.5 mu m thickness were deposited by magnetron sputtering and subsequently annealed in H-2 at 2 atm and 500 degrees C for 2 h for nanostructuring. After H-2 annealing, the majority of the resulted Ge nanoparticles are amorphous, less than 5 nm in size, forming a uniform network in the film volume. Big Ge nanoparticles with sizes between 20 and 50 nm are also formed. Some of them are identified to be crystallized in the (Ge-III/ST12) tetragonal phase. The high resolution TEM observation induces the amorphysation of the Ge tetragonal phase, followed by the crystallization of the amorphous Ge phase in the cubic diamond structure (Ge-I), as an effect of electron irradiation. A secondary annealing performed in N-2 at 800 degrees C and 1 atm for 2 h induces formation of faceted cubic Ge nanoparticles distributed in the SiO2 matrix.
789. Core-shell hybrid nanomaterials based on CoFe2O4 particles coated with PVP or PEG biopolymers for applications in biomedicine
Authors:
Covaliu, CI; Jitaru, I; Paraschiv, G; Vasile, E; Biris, SS; Diamandescu, L; Ionita, V; Iovu, H
Published: MAR 2013, POWDER TECHNOLOGY, 237, 426, DOI: 10.1016/j.powtec.2012.12.037
Monodisperse core-shell hybrid nanoparticles based on cobalt ferrite (CoFe2O4) particles coated with polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG) biopolymers were obtained employing a two-step procedure: the CoFe2O4 of 21 nm mean particle size were first synthesized by coprecipitation method assisted by PVP soft template and then were coated by PVP or PEG biopolymers. The effect of the thermal treatment upon the phase evolution of the obtained precursor from the coprecipitation step was monitored by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. The FTIR spectra also indicated the interaction between the cobalt ferrite particles and the two polymers were used as bio-compatible coatings. Transmission electron microscopy (TEM) and Selected Area Electron Diffraction (SAED) analyses revealed the formation of approximately 22 nm CoFe2O4-PVP and CoFe2O4-PEG hybrid nanoparticles. The magnetic measurements indicated that all synthesized hybrids were appropriate for applying in biomedical field. Testing the bioeffect of the uncoated cobalt ferrite nanoparticles and corresponding hybrids on Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, Salmonella enterica serovar typhimurium bacteria and Candida scotti yeast it was clear that no significant toxic activity was obtained. Moreover, all the prepared nanohybrids and their components possess antioxidant activity. (C) 2012 Elsevier B.V. All rights reserved.
790. Ga and As competition for thiolate formation at p-GaAs(111) surfaces
Authors:
Preda, L; Negrila, C; Lazarescu, MF; Enache, M; Anastasescu, M; Toader, AM; Ionescu, S; Lazarescu, V
Published: AUG 1 2013, ELECTROCHIMICA ACTA, 104, 11, DOI: 10.1016/j.electacta.2013.04.077
Self-assembled layers of 4,4'-thio-bis-benzene-thiolate spontaneously adsorbed on p-doped GaAs(1 1 1)A and GaAs(1 1 1)B electrodes were examined by EIS, XPS, and AFM investigations. XPS data provide evidence that (i) both As and Ga atoms are involved in the thiolate formation no matter which one is prevailing on the semiconducting surface and (ii) only one of the two thiol groups participates in the chemisorption bond. EIS and AFM results point to a more stable thiolate layer formed on the As-terminated surface than that formed on the Ga-terminated surface due to stronger self-assembling effects developed between the adsorbed species. (C) 2013 Elsevier Ltd. All rights reserved.
791. InN Based Water Condensation Sensors on Glass and Flexible Plastic Substrates
Authors:
Dumitru, V; Costea, S; Brezeanu, M; Stan, GE; Besleaga, C; Galca, AC; Ionescu, G; Ionescu, O
Published: DEC 2013, SENSORS, 13, 16949, DOI: 10.3390/s131216940
792. Superhydrophobic properties of cotton fabrics functionalized with ZnO by electroless deposition
Authors:
Preda, N; Enculescu, M; Zgura, I; Socol, M; Matei, E; Vasilache, V; Enculescu, I
Published: FEB 15 2013, MATERIALS CHEMISTRY AND PHYSICS, 138, 261, DOI: 10.1016/j.matchemphys.2012.11.054
Cotton fabrics were coated with arrays of ZnO hexagonal prisms using an electroless (catalytic/auto-catalytic) deposition process. A typical three step method, similar to those used for electroless deposition of metals on insulating substrates, consisting of pre-activation, activation and deposition steps was employed. The low-dimensional ZnO particles were grown from an aqueous solution containing zinc nitrate as source of zinc ions and dimethylamineborane as reducing agent. The as-obtained ZnO-coated cotton fabrics were characterized from the point of view of structure by X-ray diffraction (XRD) and morphology by scanning electron microscopy (SEM). The XRD studies demonstrate that the ZnO particles have a hexagonal wurtzite crystalline structure. The SEM observations prove that the cotton fibers are homogeneously covered by hexagonal prisms which have uniform base size of approximately 500 nm and height of 1 mu m. Optical spectroscopy measurements show that the functionalization with ZnO strongly decreases the transmittance in the UV vis region of the cotton fabrics. An important characteristic is that the ZnO-functionalized cotton fabrics exhibit superhydrophobicity, with water contact angles exceeding 150 degrees. The technique described is highly reproducible, easy scalable and cheap, allowing a wide range of applications. (C) 2012 Elsevier B.V. All rights reserved.
793. Detailed characterization of functionalized magnetite and ascertained effects
Authors:
Culita, DC; Patron, L; Oprea, O; Bartha, C; Palade, P; Teodorescu, V; Filoti, G
Published: SEP 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1916-7
The paper reports on magnetite successfully functionalized with two new molecules. The investigations, involving chemical and physical methods, provided relevant features involving cell parameters and grain sizes, or the intermingling ratio between magnetite and functionalizing molecules, as deduced from magnetic measurements. A large amount of interesting data concerning various surface and local interaction mechanisms was supplied by detailed Mossbauer measurements. The new outputs are explained in terms of material processing and intimate mixing of the involved molecules.
794. High Vortex Depinning Temperatures in YBCO Films with BZO Nanorods
Authors:
Miu, L; Ivan, I; Miu, D; Mele, P; Matsumoto, K; Mikheenko, P; Dang, VS; Crisan, A
Published: APR 2013, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 26, 1173, DOI: 10.1007/s10948-012-2019-x
The Bose glass theory for the vortex matter in superconductors with correlated disorder predicts the depinning of vortices due to the renormalization of the vortex pinning barriers by thermal fluctuations. For YB2Cu3O7 (YBCO) in external magnetic fields H oriented along the columnar pins generated by various techniques theoretical estimates give a depinning temperature T (dp) very close to the critical temperature T (c) (T (dp)similar to 0.95T (c)), whereas the results of standard magnetization relaxation experiments are repeatedly interpreted in terms of a much lower T (dp) (similar to 0.5T (c)). We investigated the temperature T variation of the normalized magnetization relaxation rate S for YBCO thin films containing BaZrO3 (BZO) nanorods preferentially oriented along the c axis, with H along the nanorods. The nonmonotonous S(T) variation below the matching field observed up to close to T (c) does not support a low T (dp). The often considered S(T) maximum occurring at relatively low T (which was connected to a disappointing T (dp)) is related to the occurrence of thermomagnetic instabilities. We show that the accommodation of vortices to the columnar pins in the presence of the T dependent macroscopic currents induced in the sample is signaled by a pronounced S(T) deep located at high T, in agreement with a T (dp) close to T (c). By increasing the film thickness and using the substrate decoration the BZO nanorods splay out, leading to the inhibition of (detrimental) vortex excitations involving double vortex kink or superkink formation, characteristic for high-quality thin films and single crystals with columnar pins along the c axis.
795. Spectroscopic analysis of the riboflavin-serum albumins interaction on silver nanoparticles
Authors:
Voicescu, M; Angelescu, DG; Ionescu, S; Teodorescu, VS
Published: APR 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1555-z
Spectrophotometric behavior of riboflavin (RF) adsorbed on silver nanoparticles as well as its interaction with two serum albumins, BSA and HSA, respectively, has been evidenced. The time evolution of the plasmonic features of the complexes formed by RF/BSA/HSA and Ag(0) nanoparticles having an average diameter of 10.0 +/- 2.0 nm have been investigated by UV-Vis absorption spectroscopy. Using steady-state and time-resolved fluorescence spectroscopy, the structure, stability, and dynamics of the serum albumins have been studied. The efficiency of energy transfer process between RF and serum albumins on silver nanoparticles has been estimated. A reaction mechanism of RF with silver nanoparticles is also proposed and the results are discussed with relevance to the involvement of the silver nanoparticles to the redox process of RF and to the RF-serum albumins interaction into a silver nanoparticles complex.
796. Weighting the influence of TiO2 anatase/brookite ratio in TiO2-Ag porous nanocomposites on visible photocatalytic performances
Authors:
Iancu, V; Baia, M; Diamandescu, L; Pap, Z; Vlaicu, AM; Danciu, V; Baia, L
Published: AUG 15 2013, MATERIALS CHEMISTRY AND PHYSICS, 141, 239, DOI: 10.1016/j.matchemphys.2013.05.005
Nanocomposites based on TiO2 aerogel and Ag nanoparticles have been successfully obtained through different synthesis methods and their specific surface areas have been determined by N-2 sorption (BET method). The photocatalytic potential for salicylic acid degradation has been evaluated. It was found that under visible light irradiation, all synthesized nanocomposites exhibit higher photocatalytic activity than the commercially available Aeroxide P25. By correlating the structural parameters with the photocatalytic performances, it has been found that the Ag nanoparticles and brookite phase presence alongside the anatase play important roles on the visible photocatalysts behavior. For the Ag containing samples with mixed anatase brookite phases, it has been observed that the visible photocatalytic performance decreases with the increase in brookite crystalline phase content. On the other hand, the addition of Ag nanoparticles results, as expected, in a clear enhancement of the visible photocatalytic activity. (C) 2013 Elsevier B.V. All rights reserved.
797. Magnetic properties of BaxSr1-xFe12O19 (x=0.05-0.35) ferrites prepared by different methods
Authors:
Cernea, M; Sandu, SG; Galassi, C; Radu, R; Kuncser, V
Published: JUN 5 2013, JOURNAL OF ALLOYS AND COMPOUNDS, 561, 128, DOI: 10.1016/j.jallcom.2013.01.081
Hexagonal ferrites BaxSr1-xFe12O19 (x = 0.05, 0.15, 0.25, 0.35) were prepared by sol-gel and conventional solid state reaction techniques. Their magnetic properties, investigated by magnetometry and Mossbauer spectroscopy, were discussed in correlation to structural aspects. Whereas the hexaferrites obtained by sol-gel are almost single phase, the ones prepared by the conventional solid state reaction technique present a low amount of BaFe2O4 as secondary phase. All samples show a relative high coercive field and remanent magnetization, as specific features for permanent magnet behavior. The five Fe3+ sites of the specific elemental cell have been revealed and their relative occupancy has been derived from the Mossbauer spectra. The analyzed samples show a sensitivity of the magnetic properties (magnetic moment and anisotropy) with respect to the occupancy of the different Fe sites. (C) 2013 Elsevier B. V. All rights reserved.
798. Postsynthetic Modification of a Metal-Organic Framework (MOF) Structure for Enantioselective Catalytic Epoxidation
Authors:
Candu, N; Tudorache, M; Florea, M; Ilyes, E; Vasiliu, F; Mercioniu, I; Coman, SM; Haiduc, I; Andruh, M; Parvulescu, VI
Published: MAY 2013, CHEMPLUSCHEM, 78, 450, DOI: 10.1002/cplu.201300076
Postsynthetic modification of [Cu2(mand)2(hmt)] (mand=mandelic acid, hmt=hexamethylenetetramine) with a chiral, dimeric chromium(III)salen complex led to a robust structure. Characterization of this new material showed that it perfectly preserved the textural and structural properties of the parent metalorganic framework (MOF). Although epoxidation of trans-methyl cinnamate with hydrogen peroxide led to copper leaching of 23%, experiments performed with N-methylmorpholine-N-oxide indicated no leaching, even after 72h of exposure. The obtained chiral MOF is an effective catalyst for the enantioselective epoxidation of trans-methyl cinnamate and leads to (2R,3S)-phenylglycidate with a high enantiomeric excess at room temperature.
799. Behavior of gold nanoparticles in a titania aerogel matrix: Photocatalytic activity assessment and structure investigations
Authors:
Pap, Z; Radu, A; Hidi, IJ; Melinte, G; Diamandescu, L; Popescu, T; Baia, L; Danciu, V; Baia, M
Published: APR 2013, CHINESE JOURNAL OF CATALYSIS, 34, 740, DOI: 10.1016/S1872-2067(11)60500-7
TiO2-Au aerogels containing different amounts of gold nanoparticles of different sizes (5 and 16 nm) were successfully synthesized using a sol-gel procedure, and were tested for salicylic acid photo-degradation under UV irradiation. The structure and morphology of the obtained materials were investigated using X-ray diffraction, transmission electron microscopy, and N-2 adsorption-desorption measurements. UV-Vis spectroscopy was used to study the optical properties. The effects of the gold nanoparticles on the TiO2 crystallization process were twofold, as follows: (i) the number of crystallized zones was strongly related to the concentration of the gold nanoparticles, and (ii) the smaller gold particles increased the time taken for the crystallization of the samples. It was found that the noble metal-doped samples exhibited higher degradation rates compared with bare titania. It was found that the most active photocatalyst in each studied system was the sample with the highest concentration of gold nanoparticles. Additionally, the highest degradation rate value was obtained with the smallest Au nanoparticles (46.4 x 10(-3) mu mol/(L.s). (C) 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier By. All rights reserved.
800. One-Step Synthesis and Sintering of MgB2 by Spark Plasma Sintering
Authors:
Sandu, V; Aldica, G; Damian, R; Guo, ZC; Suo, HL
Published: FEB 2013, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 26, 369, DOI: 10.1007/s10948-012-1766-z
We have studied the one-step procedure for simultaneous synthesis and sintering of SiC-doped MgB2 by the spark plasma sintering technique. Two types of composition, one in which Mg is strongly deficient, with the atomic ratio , and one in which Mg content is slightly higher than the stoichiometric value, specifically , were investigated. The amount of SiC was 12 wt.% and 9 wt.%, respectively. For comparison we also studied the way the deficit of Mg can be compensated in a second process of sintering. The sample with Mg deficit shows that SiC is left almost unreacted but the results are spectacular: the highest critical temperature, 36.5 K, the highest upper critical field and the highest self-field critical current density 6.7x10(5) A/cm(2) at 10 K. In the sample with overstoichiometric Mg, SiC is decomposed, carbon diffuses within MgB2 but the critical temperature is only of 35.8 K and the zero-field critical current density is one order of magnitude lower. The compensation of the deficit of Mg in the two-step procedure is not efficient. The critical temperature is even lower, 35.8 K, the upper critical field is also lower despite SiC decomposition and C diffusion within MgB2 and the critical current density is slightly above 10(5) A/cm(2). However, at low temperatures and fields of order 7 T the sample with overstoichiometric Mg and the sample prepared by the two-step procedure have higher critical current density.
801. Conduction mechanism versus annealing in SiO2 films with Ge nanoparticles
Authors:
Palade, C; Lepadatu, AM; Stavarache, I; Teodorescu, VS; Ciurea, ML
Published: 2013, 2013 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1-2, 34, DOI:
This paper analyses and discusses the effect of Ge/Si atomic ratio and annealing temperature on the conduction mechanisms governing the electrical behavior of Ge-SiO2 films containing Ge nanoparticles embedded in amorphous SiO2 matrix. For this, the experimental conductance-temperature curves are modeled in correlation with the microstructure findings for two types of films. One type of films has a lower Ge/Si ratio of 0.73 and was obtained by magnetron sputtering followed by annealing in H-2, at 500 degrees C, while the second one has a higher ratio of 1.86 and was obtained also by sputtering, but was annealed in N-2, at 800 degrees C. Both types of films show an electrical behavior with a T-1/4 conductance dependence on temperature, typical for hopping mechanism.
802. Stoichiometry dependence of the optical properties of amorphous-like Inx-wGawZn1-xO1+0.5x-delta thin films
Authors:
Galca, AC; Socol, G; Trinca, LM; Craciun, V
Published: SEP 15 2013, APPLIED SURFACE SCIENCE, 281, 99, DOI: 10.1016/j.apsusc.2013.01.176
The paper investigates the dependence of the optical properties on cation concentration of amorphous-like indium gallium zinc oxide thin films (Inx-wGawZn1-xO1+0.5x-delta) with various (In + Ga)/(In + Ga + Zn) and Ga/(In + Ga) ratios obtained by pulsed laser deposition. X-ray reflectivity and spectroscopic ellipsometry thickness results were in good agreement. The proportionality between density and the refractive index in the transparency range is evidenced. The extracted physical parameters are clearly influenced by the variation of cation concentration. (C) 2013 Elsevier B. V. All rights reserved.
803. Surface free energy of smooth and dehydroxylated fused quartz from contact angle measurements using some particular organics as probe liquids
Authors:
Zgura, I; Moldovan, R; Negrila, CC; Frunza, S; Cotorobai, VF; Frunza, L
Published: JUL-AUG 2013, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 15, 634, DOI:
The dispersion and the polar independent contributions to the surface free energy in the case of fused quartz plates were evaluated by contact angle measurements against a series of liquids like water, glycerol, ethylene glycol, dimethyl sulfoxide and a nematic mixture NP5 of azoxybenzene type compounds. The smooth fused quartz plates were thermally pretreated at 240 degrees C and 1000 degrees C to decrease the number of surface hydroxyl groups; their surface was characterized by X-ray photoelectron spectroscopy. The contact angle data were further processed applying either the approach of Owens-Wendt with geometric mean or the Wu's approach of harmonic mean of nonpolar and polar interactions. The liquids were chosen thus to fulfill Della Volpe and Siboni's criterion namely that these have the condition number of system matrix low enough. The values obtained for the components of surface free energy were discussed in comparison with the results obtained in literature for crystalline quartz or for other silica forms as bulk or films. The study has shown a decrease of the polar component of the surface tension by increase of the pretreatment temperature.
804. Structural, electric and magnetic properties of Pb(Zr0.2Ti0.8)O-3-CoFe2O4 heterostructures
Authors:
Chirila, C; Ibanescu, G; Hrib, L; Negrea, R; Pasuk, I; Kuncser, V; Pintilie, I; Pintilie, L
Published: OCT 31 2013, THIN SOLID FILMS, 545, 7, DOI: 10.1016/j.tsf.2013.06.033
Electric and magnetic properties of symmetric and asymmetric Pb(Zr-0.2 Ti-0.8)O-3-CoFe2O4 (PZT/CFO) heterostructures, grown by pulsed laser deposition on SrTiO3 (100) substrates with a 25 nm SrRuO3 (SRO) buffer layer as bottom electrode, were investigated by using hysteresis and capacitance measurements. X-ray diffraction, and transmission electron microscopy investigations reveal the high quality crystalline structure and the epitaxial relationship between SRO, PZT and CFO. The electric polarization-voltage hysteresis reveals that the remnant polarization and the coercive field are significantly affected by the CFO layer. The frequency dependence of capacitance suggests a Maxwell-Wagner type relaxation at low frequencies and is also affected by the presence of the PZT/CFO interface(s). The magnetic hysteresis measurements infer the possible presence of another spinel phase (Co3O4) in the CFO film, due to the lattice mismatch at the PZT/CFO interfaces, and with direct influence on the magnetic response of the structure. According to the electric and magnetic characterization, better room temperature multiferroic properties would be expected for the symmetric heterostructure. (C) 2013 Published by Elsevier B. V.
805. A new green, ascorbic acid-assisted method for versatile synthesis of Au-graphene hybrids as efficient surface-enhanced Raman scattering platforms
Authors:
Iliut, M; Leordean, C; Canpean, V; Teodorescu, CM; Astilean, S
Published: 2013, JOURNAL OF MATERIALS CHEMISTRY C, 1, 4104, DOI: 10.1039/c3tc30177j
A new green method for the synthesis of reduced graphene oxide-gold nanoparticle (rGO-AuNP) hybrids in aqueous solution that exploits the ability of ascorbic acid (AA) to operate as an effective dual agent for both graphene oxide (GO) and gold ion reduction is reported. Through careful investigation of the production of rGO-AuNP hybrids stabilized with polyvinylpyrrolidone (PVP), several versatile routes were devised with the aim of controlling the size, shape and distribution of AuNPs anchored onto the graphene sheets as well as the GO reduction. Particularly, when rGO is used as a platform for Au ion nucleation, a relative sparse distribution of AuNPs of size ranging from 20 nm to 50 nm is noticed. In contrast, when gold ions are added to the solution prior to any GO reduction, the density of large AuNPs is rather low relative to the uniformly packed small sized AuNPs (3-12 nm). The progress of GO reduction is explained by considering the contribution of the catalytic activity of AuNPs, besides the reducing activity of AA. Finally, a plausible mechanism for the nucleation and distribution of AuNPs onto the graphenic surface is assumed, highlighting the significance of oxygen moieties. The green method developed here is promising for the fabrication of gold-graphene nanocomposites with tunable surface "decoration", suitable for surface-enhanced Raman spectroscopy (SERS).
806. Effect of tritiation on the superconducting properties of MgB2
Authors:
Sandu, V; Aldica, G; Baibarac, M; Enachescu, M; Sandu, E; Chee, CY
Published: APR 2013, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 26, DOI: 10.1088/0953-2048/26/4/045014
We investigated the effect of tritium upload in the dense, polycrystalline MgB2 superconductor for 2 and 216 h. One basic property, the critical temperature T-c, slowly changes in time but is independent of the duration of tritium uptake. Immediately after tritiation, T-c shows a slight increase to 39.1 K but decreases to the critical temperature of the untritiated (pristine) sample, T-c = 38.8 K, after 370 days. The critical current density is strongly dependent on the tritium upload time, mainly at high magnetic fields. The underlying physics is discussed. This behaviour makes the use of MgB2 based conductors advantageous in tritium environments like fusion reactors.
807. Dense Ge nanocrystal layers embedded in oxide obtained by controlling the diffusion-crystallization process
Authors:
Lepadatu, AM; Stoica, T; Stavarache, I; Teodorescu, VS; Buca, D; Ciurea, ML
Published: SEP 15 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1981-y
Amorphous Ge/SiO2 multilayer structures deposited by magnetron sputtering have been annealed at different temperatures between 650 and 800 degrees C for obtaining Ge nanocrystals in oxide matrix. The properties of the annealed structures were investigated by transmission electron microscopy, Raman spectroscopy, and low temperature photoluminescence. The Ge crystallization is partially achieved at 650 degrees C and increases with annealing temperature. Insight of the Ge nanocrystal formation was acquired by comparing two annealing procedures, i.e., in a conventional tube furnace and by a rapid thermal annealing. By rapid thermal annealing in comparison to conventional furnace one, the Ge crystallization process is faster than Ge diffusion, resulting in the formation of more compact layers of Ge nanocrystals with 8-9.5-nm size as Raman spectroscopy reveals. These findings are important to improve the annealing efficiency in the nanocrystals formation for a precise control of their sizes and location in oxide matrix and for the possibility to create systems with interacting nanoparticles for charge or excitonic transfer. The infrared photoluminescence of Ge nanocrystals at low temperatures shows strong emission with two sharp peaks at about 1,000 meV.
808. Increased Diffusion Coefficient of Polymeric Nanocomposite Layer for Gas Sensing Applications
Authors:
Nicolae, I; Viespe, C; Serban, N; Negrila, CC; Teodorescu, VS; Trupina, L
Published: DEC 2013, SENSOR LETTERS, 11, 2332, DOI: 10.1166/sl.2013.3083
A high-performance polymeric nanostructured sensing layer for a surface acoustic wave sensor, deposited using a modified matrix assisted pulsed laser evaporation direct write technique, exhibited improved performance in terms of response time and frequency deviation. In the present work, we assessed the factors and mechanisms that account for the layer's increased sensing capabilities. The increase in the sensing performance was attributed to an increased diffusion constant, due to greater molecular mobility of polymeric chains caused by the nanoparticles embedded in the polymer matrix.
809. Luminescent Eosin Y-SiO2 hybrid nano and microrods prepared by sol-gel template method
Authors:
Secu, M; Secu, CE; Sima, M; Negrea, RF; Bartha, C; Dinescu, M; Damian, V
Published: NOV 2013, JOURNAL OF LUMINESCENCE, 143, 92, DOI: 10.1016/j.jlumin.2013.04.043
Sol-gel chemistry within the pores of a polycarbonate template membrane was used for the preparation of Eosin Y-SiO2 hybrid nano- and microrods, using tetraethylorthosilicate [TEOS, Si(OC2H5)(4)] as the precursor in the presence of trifluoroacetic acid (TFA) catalyst. The ethanolic solution of Eosin-Y was added to the silica sal to trap dye molecules inside the SiO2 gel network during the gelation. Structural and morphological characterization using scanning electron microscopy (SEM) and luminescence microscopy have shown the formation of rods with 200 nm and 1.2 mu m diameter and about 30 mu m length, exhibiting luminescence properties. Spectroscopic characterization has shown that the luminescence is due to Eosin-Y molecule in the xerogel porous network, surrounded by a solvation shell given mainly by the water. (C) 2013 Elsevier B.V. All rights reserved.
810. Effects of TiO2 nanoparticles on the NO2- levels in cell culture media analysed by Griess colorimetric methods
Authors:
Popescu, T; Lupu, AR; Diamandescu, L; Tarabasanu-Mihaila, D; Teodorescu, VS; Raditoiu, V; Purcar, V; Vlaicu, AM
Published: FEB 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1449-0
The Griess assay has been used to determine the possible changes in the measured NO2- concentrations induced by TiO2 nanoparticles in three types of nitrite-containing samples: aqueous NaNO2 solutions with known concentrations, and two types of cell culture media-Roswell Park Memorial Institute medium (RPMI-1640) and Dulbecco's Modified Eagle Medium (DMEM-F12) used either as delivered or enriched in NO2- by NaNO2 addition. We have used three types of titania with average particle sizes between 10 and 30 nm: Degussa P25 and two other samples (undoped and Fe3+-doped anatase TiO2) synthesised by a hydrothermal route in our laboratory. The structural, morphological, optical and physicochemical characteristics of the used materials have been studied by X-ray diffraction, transmission electron microscopy (EDX), Mossbauer spectroscopy, Brunauer-Emmett-Teller nitrogen adsorption, UV-Vis reflectance spectroscopy, dynamic light scattering and diffuse reflectance infrared Fourier transform spectroscopy. The opacity and sedimentation behaviour of the studied TiO2 suspensions have been investigated by photometric attenuance measurements at 540 nm. To account for the photocatalytic properties of titania in a biologically relevant context, multiple Griess tests have been performed under controlled exposure to laboratory natural daylight illumination. The results show significant variations of light attenuance (associated with NO2- concentrations in the Griess test) depending on the opacity, sedimentation behaviour, NO2- adsorption and photocatalytic properties of the tested TiO2 nanomaterials. These findings identify material characteristics recommended to be considered when analysing the results of Griess tests performed in biological studies involving TiO2 nanoparticles.
811. Spectroscopic Investigation of Iron Substitution in EuCoO3: Related Impact on the Catalytic Properties in the High-Temperature N2O Decomposition
Authors:
Wu, Y; Dujardin, C; Granger, P; Tiseanu, C; Sandu, S; Kuncser, V; Parvulescu, VI
Published: JUL 11 2013, JOURNAL OF PHYSICAL CHEMISTRY C, 117, 13999, DOI: 10.1021/jp402211c
812. The Influence of the Au Nanoparticles Dimension on the Photocatalytic Performances of TiO2-Au Porous Composites
Authors:
Melinte, G; Baia, M; Georgescu, D; Baia, L; Iancu, V; Diamandescu, L; Popescu, T; Cotet, LC; Barbu-Tudoran, L; Danciu, V; Simon, S
Published: JAN 2012, ACTA PHYSICA POLONICA A, 121, 210, DOI: 10.12693/APhysPolA.121.208
The influence of Au nanoparticles dimension on the photocatalytic performances of the TiO2 aerogels-Au composites was evaluated. Structural and morphological peculiarities of the TiO2 aerogel, unloaded and loaded with 5 and 22 nm Au nanoparticles, were studied by transmission electron microscopy technique, X-ray diffraction and N-2-sorption measurements. UV-Vis diffuse reflectance measurements were performed to determine the band gap energies. The photocatalytic activity was evaluated by monitoring the salicylic acid photodegradation. It was found that the Au nanoparticles promote the anatase phase crystallization and produce the decrease of the specific surface area and band gap energy values. The porous composite with the smallest Au nanoparticles dimension exhibits the best photocatalytic performances.
813. Half-metallic state and magnetic properties versus the lattice constant in Ti2CoSn Heusler compound: An ab initio study
Authors:
Birsan, A; Palade, P; Kuncser, V
Published: DEC 2012, SOLID STATE COMMUNICATIONS, 152, 2150, DOI: 10.1016/j.ssc.2012.09.013
The half-metallic properties of Ti2CoSn full-Heusler compound is studied within the framework of the density of states theory with the Perdew Burke Ernzerhof generalized gradient approximation (GGA). Structural optimization was performed and the calculated equilibrium lattice constant is 6.340 angstrom. The spin up band of compound has metallic character and spin down band is semiconducting with an indirect gap of 0.598 eV at equilibrium lattice constant. For the lattice parameter, ranging from 6.193 to 6.884 angstrom the compound presents 100% spin polarization and a total magnetic moment of 3 mu(B). (C) 2012 Elsevier Ltd. All rights reserved.
814. Structural, Optical, and Dielectric Properties of Bi1.5-xZn0.92-yNb1.5O6.92-delta Thin Films Grown by PLD on R-plane Sapphire and LaAlO3 Substrates
Authors:
Le Febvrier, A; Galca, AC; Corredores, Y; Deputier, S; Bouquet, V; Demange, V; Castel, X; Sauleau, R; Lefort, R; Zhang, LY; Tanne, G; Pintilie, L; Guilloux-Viry, M
Published: OCT 2012, ACS APPLIED MATERIALS & INTERFACES, 4, 5233, DOI: 10.1021/am301152r
Bi1.5-xZn0.92-yNb1.5O6.92-delta thin films have the potential to be implemented in microwave devices. This work aims to establish the effect of the substrate and of the grain size on the optical and dielectric properties. Bi1.5-xZn0.92-yNb1.5O6.92-delta thin films were grown at 700 degrees C via pulsed-laser deposition on R-plane sapphire and (100)(pc) LaAlO3 substrates at various oxygen pressures (30, 50, and 70 Pa). The structure, morphology, dielectric and optical properties were investigated. Despite bismuth and zinc deficiencies, with respect to the Bi1.5Zn0.92Nb1.5O6.92 stoichiometry, the films show the expected cubic pyrochlore structure with a (100) epitaxial-like growth. Different morphologies and related optical and dielectric properties were achieved, depending on the substrate and the oxygen pressure. In contrast to thin films grown on (100)(pc) LaAlO3, the films deposited on R-plane sapphire are characterized by a graded refractive index along the layer thickness. The refractive index (n) at 630 nm and the relative permittivity (epsilon(t)) measured at 10 GHz increase with the grain size: on sapphire, n varies from 2.29 to 2.39 and epsilon(r) varies from 85 to 135, when the grain size increases from 37 nm to 77 nm. On the basis of this trend, visible ellipsometry can be used to probe the characteristics in the microwave range quickly, nondestructively, and at a low cost.
815. Angular magnetoresistance of stretched carbon nanotube sheets
Authors:
Cimpoiasu, E; Sandu, V; Levin, GA; Simpson, A; Lashmore, D
Published: JUN 15 2012, JOURNAL OF APPLIED PHYSICS, 111, DOI: 10.1063/1.4729538
We studied the anisotropic properties of mechanically stretched bulk carbon nanotube sheets using magnetoresistance (MR) measurements in magnetic fields applied under different orientations with respect to the stretching direction. The stretching direction was either parallel or perpendicular to the direction of the electric current. The magnetic field was rotated either in-the-plane or out-of-the-plane of the sheets. We found that the angular dependence of the MR is a superposition of two terms, one with twofold symmetry and the other one with fourfold symmetry. We also found that the field-dependence of the MR is composed of two terms, one positive and one negative, whose magnitudes are largest when the field is parallel with the stretching direction. If the sheets are treated with nitric acid, the positive term is removed and the MR is smallest when the field is aligned with the magnetic field. We attribute these anisotropic features to magnetoelastic effects induced by the coupling between the magnetic catalyst nanoparticles, the magnetic field, and the network of nanotubes. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729538]
816. On the scaling of pinning force in ceramic MgB2
Authors:
Sandu, V; Ivan, I
Published: 2012, 26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5, 400, DOI: 10.1088/1742-6596/400/2/022102
We present an investigation of the field dependence of the pinning force of dense MgB2-based superconducting composites as obtained by spark plasma sintering with different ingredients which are designated to enhance the pinning force F. Generally, the latter quantity, scaled to the maximum pinning force F-max, obeys a scaling law as a function of the scaled field h when the irreversibility field B-irr is considered as scaling field. The scaled function is described in terms of a generalized scaled function h(p)(1-h)(q). However, in our samples the scaling is absent. In addition, the peak of the scaled function shifts to higher reduced fields h when the temperature increases. Depending on the level of doping and the nature of the nanosized particles used to built the superconducting composites, we found that the scaled force can be depicted either with a combination of generalized scaled functions with different exponents or with a single function but multiplied with an envelope, usually an exponential factor. The former dependence is present in the samples with a high amount of nanoparticles and mirrors two types of pinning of close weights. The presence of the exponential factor in the latter dependence is attributed to the combined effect of the intrinsic anisotropy of MgB2 and the random orientation of the grains relative to the magnetic field.
817. THEORETICAL STUDY OF THE REACTION OF LiBH4 WITH MgH2 IN PRESENCE OF CARBON SUBSTRATE
Authors:
Chihaia, V; Munteanu, C; Scurtu, R; Palade, P
Published: APR-MAY 2012, REVUE ROUMAINE DE CHIMIE, 57, 442, DOI:
In this work we design some atomic scale simulation methods as investigative tools in the study of the formation of compounds for the reversible storage of hydrogen in bulk materials. It was verified that the reaction between the LiBH4 and MgH2 is energetically favored for temperatures above 280 K and that this system can be used in the hydrogen storage and the fuel cell application. To identify the reaction mechanism at the interface of LiBH4, MgH2 and carbon layers we performed some Molecular Dynamics simulations and QM/MM calculations. The results show that the layers of ions formed at the interface with the graphite may assure the right arrangement of the atoms to start the formation of the crystals. Moreover, the presence of the hexagonal layers of graphite may play a role as a pattern template for the layers of boron atoms in the MgB2 lattice.
818. Neutron field parameter measurements on the JET tokamak by means of super-heated fluid detectors
Authors:
Gherendi, M; Zoita, VL; Craciunescu, T; Johnson, MG; Pantea, A; Baltog, I; Edlington, T; Hellesen, C; Kiptily, V; Conroy, S; Murari, A; Popovichev, S
Published: OCT 2012, REVIEW OF SCIENTIFIC INSTRUMENTS, 83, DOI: 10.1063/1.4739410
The neutron field parameters (fluence and energy distribution) at a specific location outside the JET Torus Hall have been measured by means of super-heated fluid detectors (or "bubble detectors") in combination with an independent, time-of-flight, technique. The bubble detector assemblies were placed at the end of a vertical line of sight at about 16 m from the tokamak mid plane. Spatial distributions of the neutron fluence along the radial and toroidal directions have been obtained using two-dimensional arrays of bubble detectors. Using a set of three bubble detector spectrometers the neutron energy distribution was determined over a broad energy range, from about 10 keV to above 10 MeV, with an energy resolution of about 30% at 2.5 MeV. The very broad energy response allowed for the identification of energy features far from the main fusion component (around 2.45 MeV for deuterium discharges). [http://dx.doi.org/10.1063/1.4739410]
819. Morphological, optical and electrical properties of samarium oxide thin films
Authors:
Constantinescu, C; Ion, V; Galca, AC; Dinescu, M
Published: AUG 1 2012, THIN SOLID FILMS, 520, 6397, DOI: 10.1016/j.tsf.2012.06.049
We present here results on samarium oxide thin films, obtained by pulsed laser deposition and by radio frequency assisted pulsed laser deposition. Three different substrate types were used: silicon, platinum covered silicon and titanium covered silicon. The influence of the deposition parameters (oxygen pressure and laser fluence) on the structure and morphology of the thin films was studied. The substrate-thin film interface zone was investigated; the optical and electrical properties (the losses, dielectric constant and leakage currents) were also determined. (C) 2012 Elsevier B.V. All rights reserved.
820. Manganese-based room temperature ferromagnetism in gallium arsenide
Authors:
Vasilache, V; Apostol, NG; Lungu, GA; Macovei, D; Teodorescu, CM
Published: NOV-DEC 2012, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 6, DOI:
Manganese is deposited onto GaAs(001) substrates in high vacuum conditions (10(-7) hPa), with substrates held at 300 degrees C. It is shown that this procedure yields to the diffusion of magnanese into gallium arsenide and the formation of a layer which exhibits room temperature ferromagnetism, with highly diluted Mn (below 1 atomic percent). X-ray absorption fine structure determinations at the Mn and Ga K-edges evidenced that Mn is not placed into substitutional Ga sites in GaAs. Most probably, Mn forms MnO clusters with rocksalt local structure. These clusters are the origin of the detected ferromagnetism.
821. Persistent oscillatory currents in a 1D ring with Rashba and Dresselhaus spin-orbit interactions excited by a terahertz pulse
Authors:
Nita, M; Marinescu, DC; Manolescu, A; Ostahie, B; Gudmundsson, V
Published: SEP 2012, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 46, 20, DOI: 10.1016/j.physe.2012.08.017
Persistent, oscillatory charge and spin currents are shown to be driven by a two-component terahertz laser pulse in a one-dimensional mesoscopic ring with Rashba and Dresselhaus spin-orbit interactions (SOI) linear in the electron momentum. The characteristic interference effects result from the opposite precession directions imposed on the electron spin by the two SOI couplings. The time dependence of the currents is obtained by solving numerically the equation of motion for the density operator, which is later employed in calculating statistical averages of quantum operators on few electron eigenstates. The parameterization of the problem is done in terms of the SOI coupling constants and of the phase difference between the two laser components. Our results indicate that the amplitude of the oscillations is controlled by the relative strength of the two SOI's, while their frequency is determined by the difference between the excitation energies of the electron states. Furthermore, the oscillations of the spin current acquire a beating pattern of higher frequency that we associate with the nutation of the electron spin between the quantization axes of the two SOI couplings. This phenomenon disappears at equal SOI strengths, whereby the opposite precessions occur with the same probability. (c) 2012 Elsevier B.V. All rights reserved.
822. Laser synthesis of magnetic iron-carbon nanocomposites with size dependent properties
Authors:
Morjan, I; Dumitrache, F; Alexandrescu, R; Fleaca, C; Birjega, R; Luculescu, CR; Soare, I; Dutu, E; Filoti, G; Kuncser, V; Prodan, G; Popa, NC; Vekas, L
Published: JAN 2012, ADVANCED POWDER TECHNOLOGY, 23, 96, DOI: 10.1016/j.apt.2010.12.014
Iron-carbon nanocomposites have gained interest due to their new engineering and biomedical applications. Carbon coated iron nanoparticles (Fe@C) were obtained continuously and in a single step using the laser pyrolysis method. The continuous wave CO2 laser beam was used to continuously heat a sensitized (with ethylene) precursor gas mixture, in which iron pentacarbonyl (vapor) and acetylene were the iron and carbon donors, respectively. The effect of varying the residence time in the reaction zone through the variation of the internal nozzle diameter was explored in order to improve the particle size and the phase distributions. At increased nozzle diameter, (i) the particle mean diameter increases (from about 3.5 to 10.5 nm), (ii) higher ordering of the crystallographic network seems to occur, (iii) the dominance of the alpha-Fe and iron carbide phases is revealed. Onion-like graphenic layers often cover the buried iron cores. Magnetic measurements and temperature dependent Mossbauer spectroscopy were used in order to find correlations concerning the magnetic behavior and the Fe phase composition of samples. Preliminary experiments for obtaining stable water-based magnetic nanofluids are discussed. (C) 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
823. Synthesis and association of Ag(0) nanoparticles in aqueous Pluronic F127 triblock copolymer solutions
Authors:
Angelescu, DG; Vasilescu, M; Anastasescu, M; Baratoiu, R; Donescu, D; Teodorescu, VS
Published: JAN 20 2012, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 394, 66, DOI: 10.1016/j.colsurfa.2011.11.025
Triblock copolymers poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-poly(ethylene oxide) (PEO) Pluronic F127 was employed as capping agent for the Ag(0) metallic nanoparticles synthesized by the chemical reduction of silver nitrate, AgNO3, with excess of sodium borohydride, NaBH4. The morphology and the kinetics of Ag(0) nanoparticles were studied by transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS), UV-vis absorption and fluorescence probe technique. Spherical polydisperse particles of 12 +/- 4 nm mean diameter at varying the Pluronic concentration in the range of 0.13-13 wt.% were reported. Apart from the stabilizing role, the triblock copolymer promoted the agglomeration of individual Ag(0) nanoparticles in small assemblies whose plasmon band features differed from those of the individual nanoparticles. The formation of Ag(0) nanoparticles-F127 complex took place after full reduction of the Ag ions and it was controlled by the F127 concentration. The nanoparticle morphology and the fluorescence probe technique suggested that the excess PI uronic drove indirectly the Ag(0) nanoparticles association. Free F127 polymeric micelles encountered above critical micellar concentration (cmc) promoted the partial desorption of the adsorbed triblock copolymer and subsequently weakened the stability of the individual nanoparticles. (C) 2011 Elsevier B.V. All rights reserved.
824. As-grown superconducting MgB2 thin films prepared at extreme deposition conditions
Authors:
Sahoo, B; Keune, W; Kuncser, V; Rohlsberger, R
Published: JAN 2012, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 25, DOI: 10.1088/0953-2048/25/1/015004
Superconducting (SC) MgB2 thin films were prepared in situ in one step by vacuum co-deposition at extremely low growth temperature (T-s similar to 110-150 degrees C) and at very low Mg deposition rate, far off from the MgB2 stability regime of the thermodynamic phase diagram. As-grown films are nanocrystalline and exhibit (002) texture, moderate surface roughness and SC onset up to T-c(on) = 18 K. This is the highest critical temperature ever observed in low-T-s as-grown MgB2 films. Our preparation method at very low T-s is favorable for the fabrication of layered SC hybrid electronic devices, where deposition and post-annealing at high temperature are detrimental to device functioning. Simple post-annealing of our films in ultrahigh vacuum enhances T-c(on) up to 22 K due to the improvement in structural properties.
825. Quantum critical scaling at a Bose-glass/superfluid transition: Theory and experiment for a model quantum magnet
Authors:
Yu, R; Miclea, CF; Weickert, F; Movshovich, R; Paduan, A; Zapf, VS; Roscilde, T
Published: OCT 23 2012, PHYSICAL REVIEW B, 86, DOI: 10.1103/PhysRevB.86.134421
In this paper we investigate the quantum phase transition from magnetic Bose Glass to magnetic Bose-Einstein condensation induced by amagnetic field in NiCl2 center dot 4SC(NH2)(2) (dichloro-tetrakis-thiourea-nickel, or DTN), doped with Br (Br-DTN) or site diluted. Quantum Monte Carlo simulations for the quantum phase transition of the model Hamiltonian for Br-DTN, as well as for site-diluted DTN, are consistent with conventional scaling at the quantum critical point and with a critical exponent z verifying the prediction z = d; moreover the correlation length exponent is found to be nu = 0.75(10), and the order parameter exponent to be beta = 0.95(10). We investigate the low-temperature thermodynamics at the quantum critical field of Br-DTN both numerically and experimentally, and extract the power-law behavior of the magnetization and of the specific heat. Our results for the exponents of the power laws, as well as previous results for the scaling of the critical temperature to magnetic ordering with the applied field, are incompatible with the conventional crossover-scaling Ansatz proposed by Fisher et al. [Phys. Rev. B 40, 546 (1989)]. However they can all be reconciled within a phenomenological Ansatz in the presence of a dangerously irrelevant operator.
826. Interface characterization and atomic intermixing processes in Be/W bilayers deposited on Si(001) substrates with Fe buffer layers
Authors:
Kuncser, V; Palade, P; Schinteie, G; Sandu, SG; Trupina, L; Lungu, GA; Gheorghe, NG; Teodorescu, CM; Porosnicu, C; Jepu, I; Lungu, CP; Filoti, G
Published: JAN 25 2012, JOURNAL OF ALLOYS AND COMPOUNDS, 512, DOI: 10.1016/j.jallcom.2011.09.063
Structural aspects and atomic intermixing processes in Be/W bilayers deposited on Si(0 0 1) substrates with Fe buffer layers enriched in the (57)Fe Mossbauer isotope have been studied via atomic force microscopy, grazing incidence X-ray diffractometry, X-ray reflectometry, X-ray photoelectron spectroscopy and conversion electron Mossbauer spectroscopy. The mentioned investigations allowed a full sequential characterization of the involved interfaces. Various ionic configurations appeared for Fe or W, while an amorphous state was observed in the case of Be. It has been proven that the Be layer has a negative influence on the roughness of the whole structure, which however presents an oxidation gradient from more oxidized elements at the surface towards more reduced elements in deeper layers. A strong diffusion of the W atoms inside the Be layer, induced by the deposition method, as well as of the Fe atoms inside the Be layer, induced by thermal annealing, has been evidenced. (C) 2011 Elsevier B.V. All rights reserved.
827. Noncollinear Fe spin structure in (Sm-Co)/Fe exchange-spring bilayers: Layer-resolved Fe-57 Mossbauer spectroscopy and electronic structure calculations
Authors:
Uzdin, VM; Vega, A; Khrenov, A; Keune, W; Kuncser, VE; Jiang, JS; Bader, SD
Published: JAN 11 2012, PHYSICAL REVIEW B, 85, DOI: 10.1103/PhysRevB.85.024409
Magnetization reversal in nanoscale (Sm-Co)/Fe (hard/soft) bilayer exchange-spring magnets with in-plane uniaxial magnetic anisotropy was investigated by magnetometry, conversion-electron Mossbauer spectroscopy (CEMS) and atomistic Fe spin-structure calculations. Magnetization loops along the easy direction exhibit signatures typical of exchange-spring magnets. In-field CEMS at inclined gamma-ray incidence onto thin (2 nm) Fe-57 probe layers embedded at various depths in the 20-nm-thick natural (soft) Fe layer provides depth-dependent information (via the line-intensity ratio R-23 as a function of the applied field H) about the in-plane rotation of Fe spins. A minimum in the R-23-vs-H dependence at (H-min, R-min) determines the field where Fe magnetic moments roughly adopt an average perpendicular orientation during their reversal from positive to negative easy-axis orientation. A monotonic decrease of H-min with distance from the hard/soft interface is observed. Rotation of Fe spins takes place even in the interface region in applied fields far below the field of irreversible switching, H-irr, of the hard phase. Formation of an Fe-Co alloy is detected in the interface region. For comparison, the noncollinear Fe spin structure during reversal and the resulting R-23 ratio were obtained by electronic-structure calculations based on a quantum-mechanical Hamiltonian for itinerant electrons. The coupling at the hard/soft interface is described by the uniaxial exchange-anisotropy field, h(int), as a parameter. Our calculated R-23 ratios as a function of the (reduced) applied field h exhibit similar features as observed in the experiment, in particular a minimum at (h(min), R-min). R-min is found to increase with h(int), thus providing a measure of the interface coupling. Evidence is provided for the existence of fluctuations of the interface coupling. The calculations also show that the Fe spin spiral formed during reversal is highly inhomogeneous. In general, our simulation of the Fe spin structure is applicable for the interpretation of experimental results on layered exchange-spring magnets.
828. CoNb2O6 Ceramic with Geometric Frustration
Authors:
Sandu, V; Nicolescu, MS; Banciu, MG; Popa, S; Burdusel, M
Published: 2012, AUTOMATION EQUIPMENT AND SYSTEMS, PTS 1-4, 468-471, 545, DOI: 10.4028/www.scientific.net/AMR.468-471.542
We present the preparation, structure and physical properties of CoNb2O6 ceramics using spark plasma sintering technique. Magnetic data reveal the two antiferromagnetic transitions at 2.9 and 2 K. Microwave measurements gives epsilon(r) = 23.5 and a loss tangent of 29x10(-3).
829. ICOSAHEDRAL AlMnLn (Ln = Ce, Gd, Dy, Ho) ALLOYS - AN EXAFS STUDY AND CATALYTIC BEHAVIOR
Authors:
Coman, SM; Macovei, D; Parvulescu, VI
Published: APR-MAY 2012, REVUE ROUMAINE DE CHIMIE, 57, 529, DOI:
Two series of icosahedral Al(100-x-y)Mn(x)Ln(y) alloys, first consisting of AlMnCe with variable Ce (x = 6 and y = 1, 2, 3, 4: Al93Mn6Ce, Al92Mn6Ce2, Al91Mn6Ce3, and Al90Mn6Ce4) or Mn (x = 8, 10; y = 1: Al89Mn10Ce and Al91Mn8Ce) concentration, and the second consisting of constant alloy composition (Al(91)Mn(6)Ln(3)), while varying the Ln nature (Gd, Dy, and Ho) were prepared. The icosahedral structure of the samples was confirmed by X-ray diffraction (XRD). As shown by EXAFS, the sample Al89Mn10Ce, with the lowest Ce/Mn ratio, display an advanced degree of disorder around the Ce atoms in the structure. Catalytic behavior highly depended on the alloys structure, the higher the degree of disorder around the rare-earth element in the structure, the higher catalytic activity. Replacing Ce with Gd, Dy or Ho in AlMnLn alloys does not result in a significant enhancement of the catalytic performances.
830. Bose glass and Mott glass of quasiparticles in a doped quantum magnet
Authors:
Yu, R; Yin, L; Sullivan, NS; Xia, JS; Huan, C; Paduan, A; Oliveira, NF; Haas, S; Steppke, A; Miclea, CF; Weickert, F; Movshovich, R; Mun, ED; Scott, BL; Zapf, VS; Roscilde, T
Published: SEP 20 2012, NATURE, 489, 384, DOI: 10.1038/nature11406
The low-temperature states of bosonic fluids exhibit fundamental quantum effects at the macroscopic scale: the best-known examples are Bose-Einstein condensation and superfluidity, which have been tested experimentally in a variety of different systems. When bosons interact, disorder can destroy condensation, leading to a 'Bose glass'. This phase has been very elusive in experiments owing to the absence of any broken symmetry and to the simultaneous absence of a finite energy gap in the spectrum. Here we report the observation of a Bose glass of field-induced magnetic quasiparticles in a doped quantum magnet (bromine-doped dichloro-tetrakis-thiourea-nickel, DTN). The physics of DTN in a magnetic field is equivalent to that of a lattice gas of bosons in the grand canonical ensemble; bromine doping introduces disorder into the hopping and interaction strength of the bosons, leading to their localization into a Bose glass down to zero field, where it becomes an incompressible Mott glass. The transition from the Bose glass (corresponding to a gapless spin liquid) to the Bose-Einstein condensate (corresponding to a magnetically ordered phase) is marked by a universal exponent that governs the scaling of the critical temperature with the applied field, in excellent agreement with theoretical predictions. Our study represents a quantitative experimental account of the universal features of disordered bosons in the grand canonical ensemble.
831. Sn-Doped Hydroxylated MgF2 Catalysts for the Fast and Selective Saccharification of Cellulose to Glucose
Authors:
Wuttke, S; Negoi, A; Gheorghe, N; Kuncser, V; Kemnitz, E; Parvulescu, V; Coman, SM
Published: SEP 2012, CHEMSUSCHEM, 5, 1711, DOI: 10.1002/cssc.201200303
832. Structure and electrical transport in films of Ge nanoparticles embedded in SiO2 matrix
Authors:
Stavarache, I; Lepadatu, AM; Maraloiu, AV; Teodorescu, VS; Ciurea, ML
Published: JUL 2012, JOURNAL OF NANOPARTICLE RESEARCH, 14, DOI: 10.1007/s11051-012-0930-5
The films containing Ge nanoparticles embedded in SiO2 matrix were prepared by RF magnetron sputtering and subsequently by thermal annealing. Their structure was investigated by conventional transmission electron microscopy and high resolution transmission electron microscopy together with energy-dispersive X-ray spectroscopy. The electrical behavior of films was studied by measuring current-temperature and current-voltage characteristics. The structure investigation reveals two kinds of features: a low density of big Ge nanoparticles with sizes from 20 to 50 nm and a network of small amorphous Ge nanoregions/nanoparticles (5 nm size or less) with high density, both being embedded in amorphous SiO2 matrix. The electrical transport was shown to take place through the network of amorphous Ge nanoregions. At low temperature, the T-1/4 dependence of the current was evidenced, while at high temperature, the T-1 Arrhenius dependence was found. At both low and high temperatures, the conductivity is nearly constant. The behavior at low temperature was explained by the hopping mechanism on localized states located in a band near the Fermi energy, while at high temperature by the charge excitation to the extended states.
833. FABRICATION AND CHARACTERIZATION OF THIN POLYANILINE FILMS OBTAINED BY GLANCING ANGLE DEPOSITION (GLAD) TECHNIQUE
Authors:
Ion, FM; Barna, V; Vulpe, S; Radu, A; Filimon, A; Gentiana, H
Published: OCT-DEC 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 1490, DOI:
In this manuscript we present interesting scientific results following the physical characterization of thin polyaniline polymer films achieved by means of Glancing Angle Deposition (GLAD) method. Aniline monomer was used as precursor in a cold plasma polymerization chamber and the resulting thin films were investigated by various physical techniques (Atomic Force Microscopy - AFM and Scanning Electron Microscopy - SEM), while also considering their conductive electrical properties.
834. Pulsed laser deposition of transparent conductive oxide thin films on flexible substrates
Authors:
Socol, G; Socol, M; Stefan, N; Axente, E; Popescu-Pelin, G; Craciun, D; Duta, L; Mihailescu, CN; Mihailescu, IN; Stanculescu, A; Visan, D; Sava, V; Galca, AC; Luculescu, CR; Craciun, V
Published: NOV 1 2012, APPLIED SURFACE SCIENCE, 260, 46, DOI: 10.1016/j.apsusc.2012.02.148
The influence of target-substrate distance during pulsed laser deposition of indium zinc oxide (IZO), indium tin oxide (ITO) and aluminium-doped zinc oxide (AZO) thin films grown on polyethylene terephthalate (PET) substrates was investigated. It was found that the properties of such flexible transparent conductive oxide (TCO)/PET electrodes critically depend on this parameter. The TCO films that were deposited at distances of 6 and 8 cm exhibited an optical transmittance higher than 90% in the visible range and electrical resistivities around 5 x 10(-4) Omega cm. In addition to these excellent electrical and optical characteristics the films grown at 8 cm distance were homogenous, smooth, adherent, and without cracks or any other extended defects, being suitable for opto-electronic device applications. (C) 2012 Elsevier B. V. All rights reserved.
835. DROP IMAGES WITH REFLECTION SPOTS: IMPROVED PROCESSING FOR DETERMINATION OF WETTING CONTACT ANGLES
Improvements in automatic processing of movie frames taken on commercial Drop Shape Analysis systems are presented, regarding the use of particular edge detection algorithms that account for optical peculiarities of the drop image formed on digital video camera sensors. These improvements can lead to better measurements of contact angles for drop images that present spots of reflected light close to edge and in the case of very low contact angles.
836. Superparamagnetic magnetite-divinylbenzene-maleic anhydride copolymer nanocomposites obtained by dispersion polymerization
Authors:
Donescu, D; Raditoiu, V; Spataru, CI; Somoghi, R; Ghiurea, M; Radovici, C; Fierascu, RC; Schinteie, G; Leca, A; Kuncser, V
Published: OCT 2012, EUROPEAN POLYMER JOURNAL, 48, 1716, DOI: 10.1016/j.eurpolymj.2012.07.012
Magnetite alternating copolymers divinylbenzene-maleic anhydride (DVB-MA) composites were prepared by dispersion polymerization. Because magnetite is used as a complex with oleic acid (Fe(3)O(4)OLA), the final hybrids show good dispersion of inorganic nanofillers in the polymer matrix. The obtained composites were analyzed by infrared absorption spectrometry, diffuse reflectance in visible light, thermogravimetry, X-ray fluorescence, X-ray diffraction, dynamic light scattering, scanning electron microscopy and vibrating sample magnetometry. The obtained results indicate the successful preparation of magnetite nanoparticles with an average size of about 23 nm dispersed in micrometer size copolymer spherical particles, which relative content can be controlled via the processing parameters. A relationship between the relative content of magnetite nanoparticles and the size of the polymer particles, with direct influence on the diffuse reflectance in the visible domain, was observed. A superparamagnetic behavior was evidenced at room temperature with a blocking temperature lower than as expected from the bulk anisotropy constant and the average size of the magnetite nanoparticles. Both the unexpected low blocking temperature and the observed low specific magnetizations were explained by a defected and poor crystalline structure of the magnetite nanoparticles, giving rise to spin disorder and diminished crystalline anisotropy constant. (C) 2012 Elsevier Ltd. All rights reserved.
837. Magnetic glass-ceramics
Authors:
Sandu, V; Nicolescu, MS; Kuncser, V; Damian, R; Sandu, E
Published: JUN 2012, JOURNAL OF ADVANCED CERAMICS, 1, 143, DOI: 10.1007/s40145-012-0010-4
We present the magnetic properties of magnetic glass ceramics obtained by crystallization of Fe containing borosilicate glass. Two types of nucleators have been used: Cr2O3 and P2O5. The role of the nucleators proved to be crucial in the size and morphology of the crystallites developed within glassy matrix as well in the magnetic response. The former stimulates the growth of regular single crystals uniformly dispersed within the matrix whereas the latter leads to the formation of grains made of tiny (30 nm), nanocrystals. The magnetic response depends on the amount of Fe ions left dispersed within glassy matrix as paramagnetic ions. Although P2O5 leads to the best structural magnetite, almost 42% of Fe ions are left dispersed in the matrix without magnetic interaction. In the case of Cr2O3, the paramagnetic Fe is decreased to 12% but structural deficiency in the occupancy of the Fe sites of magnetite is revealed by Mossbauer spectroscopy.
838. TRANSPORT MECHANISMS IN SiO2 FILMS WITH EMBEDDED GERMANIUM NANOPARTICLES
Authors:
Palade, C; Lepadatu, AM; Stavarache, I; Maraloiu, AV; Teodorescu, VS; Ciurea, ML
Published: 2012, 2012 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 2, 94, DOI:
This paper reports on the conduction mechanisms in amorphous SiO2 films with embedded Ge nanoparticles. For this, measurements of current-temperature and current-voltage were employed and correlated with the microstructure results obtained from transmission electron microscopy (TEM). TEM images reveal that our films contain big Ge nanoparticles with low density and small Ge nanoparticles with high density, the last ones being the only responsible for the electrical transport. Two transport mechanisms were found at low and high temperature respectively, namely hopping on localized states in a band near Fermi level and charge excitation to the extended states at mobility edge.
839. Monoesterase Activity of a Purple Acid Phosphatase Mimic with a Cyclam Platform
Authors:
Comba, P; Gahan, LR; Hanson, GR; Mereacre, V; Noble, CJ; Powell, AK; Prisecaru, I; Schenk, G; Zajaczkowski-Fischer, M
Published: FEB 2012, CHEMISTRY-A EUROPEAN JOURNAL, 18, 1710, DOI: 10.1002/chem.201100229
The synthesis and characterization of a novel dinucleating ligand L (L=4,11-dimethyl-1,8-bis{2-[N-(di-2-pyridylmethyl)amino]ethyl}cyclam) and its mu-oxo-bridged diferric complex [(H2L){Fe-2(III)(O)}(Cl)(4)](2+) are reported. This diiron(III) complex is the first example of a truly functional purple acid phosphatase (PAP) mimic as it accelerates the hydrolysis of the activated phosphomonoester 2,4-dinitrophenyl phosphate (DNPP). The spectroscopic and kinetic data indicate that only substrates that are monodentately bound to one of the two ferric ions can be attacked by a suitable nucleophile. This is, most probably, a terminal iron(III)-bound hydroxide. DFT calculations support this assumption and also highlight the importance of secondary interactions, exerted by the protonated cyclam platform, for the positioning and activation of the iron(III)-bound substrate. Similar effects are postulated in the native enzyme but addressed in PAP mimics for the first time.
840. Catalytic hydroprocessing of lignin under thermal and ultrasound conditions
Authors:
Finch, KBH; Richards, RM; Richel, A; Medvedovici, AV; Gheorghe, NG; Verziu, M; Coman, SM; Parvulescu, VI
Published: NOV 30 2012, CATALYSIS TODAY, 196, 10, DOI: 10.1016/j.cattod.2012.02.051
Lignin isolated from Miscanthus x giganteus using acidic (FAL) and basic (AL) conditions was thereafter subjected to catalytic depolymerization under thermal or ultrasonic activation. The characterization of lignin samples was achieved by thermogravimetric analysis and FTIR. Three different classes of catalysts containing nickel as the active species have been prepared in this respect: (i) nano-Ni(0) by reduction of NiCl2 with NaBH4 under ultrasonication, (ii) Fe3O4-(NiMgAlO)(x) and (NiAlO)(x) by calcination of Mg(Ni)-Al hydrotalcite incorporating Fe3O4, followed by reduction with hydrogen, and (iii) NiO(1 1 1) nanosheets by reduction of Ni(NO3)(2) with urea using benzyl alcohol as a structure directing agent. The catalysts were characterized by XRD and XPS techniques. Reduced mixed oxides displayed a moderate activity while a significant increase in conversion (up to 90%) was observed with nano-Ni(0) and NiO(1 1 1) nanosheets catalysts. The conversion and the mass distribution of the reaction products were strongly related to the procedure used for the extraction of lignin. In all the reactions AL samples had a greater extent of depolymerization. The performance from the tested catalysts under ultrasonic conditions was inferior to those tested under conventional heating conditions. The nature of the solvent was also found to be very important to this process, with the ionic liquid, 1-butyl-3-methylimidazolium acetate ([BMIM]OAc) demonstrating the best results in autoclave conditions and methanol under ultrasonic conditions. (C) 2012 Elsevier B. V. All rights reserved.
841. Transparent indium zinc oxide thin films used in photovoltaic cells based on polymer blends
Authors:
Besleaga, C; Ion, L; Ghenescu, V; Socol, G; Radu, A; Arghir, I; Florica, C; Antohe, S
Published: SEP 1 2012, THIN SOLID FILMS, 520, 6806, DOI: 10.1016/j.tsf.2012.07.030
Indium zinc oxide (IZO) thin films were obtained using pulsed laser deposition. The samples were prepared by ablation of targets with In concentrations, In/(In + Zn), of 80 at.%, at low substrate temperatures under reactive atmosphere. IZO films were used as transparent electrodes in polymer-based -poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 1:1 blend - photovoltaic cells. The action spectra measurements revealed that IZO-based photovoltaic structures have performances comparable with those using indium-tin-oxide as transparent electrode. (C) 2012 Elsevier B.V. All rights reserved.
842. Influence of the substrate and nitrogen amount on the microstructural and optical properties of thin r.f.-sputtered ZnO films treated by rapid thermal annealing
Authors:
Nicolescu, M; Anastasescu, M; Preda, S; Stroescu, H; Stoica, M; Teodorescu, VS; Aperathitis, E; Kampylafka, V; Modreanu, M; Zaharescu, M; Gartner, M
Published: NOV 15 2012, APPLIED SURFACE SCIENCE, 261, 823, DOI: 10.1016/j.apsusc.2012.08.104
N-doped ZnO (ZnO: N) thin films, intended to be used as one of the layers in solar cell applications were deposited by r.f. sputtering, using ZnN target (99.9% purity), on silicon and fused silica substrates. In the gas flow composition, Ar was kept constant (50%) and the O-2/N-2 ratio was varied as: 40%/10%, 25%/25% and 10%/40%. After deposition, rapid thermal annealing (RTA) at 400 and 550 degrees C for 1 min in N-2 ambient has been performed. The RTA impact on the optical and microstructural properties of ZnO: N thin films have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX), UV-vis-NIR spectroscopy, UV-vis-NIR spectroscopic ellipsometry (SE) and infrared ellipsometry (IR-SE). The as-deposited (ad) ZnO: N films are polycrystalline with preferentially oriented columnar crystals. After RTA we found ZnO: N films with improved crystallinity and fewer boundary defects. We report optical constants of ZnO: N from UV to IR spectral range as well as the infrared active phononic modes. (C) 2012 Elsevier B. V. All rights reserved.
843. Tuning exchange spring effects in FePt/Fe(Co) magnetic bilayers
Authors:
Reddy, VR; Crisan, O; Gupta, A; Banerjee, A; Kuncser, V
Published: JAN 1 2012, THIN SOLID FILMS, 520, 2189, DOI: 10.1016/j.tsf.2011.10.143
Structural and magnetic properties of exchange spring magnets consisting of hard magnetic (FePt) and soft magnetic (Fe and Co) bilayers. prepared by ion beam sputtering method are studied via X-ray diffraction (XRD), magneto-optic Kerr effect (MOKE) and vibrating sample magnetometry (VSM). Thin tracer layers of Fe-57 were introduced in the soft layer in order to observe the Fe spin structure and interfacial diffusion by Conversion Electron Mossbauer Spectroscopy (CEMS). The observed in-plane exchange spring behavior extends also to the magnetic hard layer, whose switching field can be tuned in an unexpected manner via the top soft magnetic layer. To explain the observed phenomenon it is suggested that the increased switching field, found in the system with a Co/Fe bilayer acting as a single soft magnetic layer, is compatible with a peculiar behavior of the stiffness coefficient of the heterogeneous soft magnetic layer. According to this observation, possibilities to maximize the exchange spring effects via suitably chosen non-homogeneous soft magnetic layers are open. (C) 2011 Elsevier B.V. All rights reserved.
844. A Robust Metal-Organic Framework Constructed from Alkoxo-Bridged Binuclear Nodes and Hexamethylenetetramine Spacers: Crystal Structure and Sorption Studies
Authors:
Ilyes, E; Florea, M; Madalan, AM; Haiduc, I; Parvulescu, VI; Andruh, M
Published: AUG 6 2012, , DOI: 10.1021/ic301139j
845. Excitation of collective modes in a quantum flute
Authors:
Torfason, K; Manolescu, A; Moldoveanu, V; Gudmundsson, V
Published: JUN 14 2012, PHYSICAL REVIEW B, 85, DOI: 10.1103/PhysRevB.85.245114
We use a generalized master equation (GME) formalism to describe the nonequilibrium time-dependent transport of Coulomb interacting electrons through a short quantum wire connected to semi-infinite biased leads. The contact strength between the leads and the wire is modulated by out-of-phase time-dependent potentials that simulate a turnstile device. We explore this setup by keeping the contact with one lead at a fixed location at one end of the wire, whereas the contact with the other lead is placed on various sites along the length of the wire. We study the propagation of sinusoidal and rectangular pulses. We find that the current profiles in both leads depend not only on the shape of the pulses, but also on the position of the second contact. The current reflects standing waves created by the contact potentials, like in a wind musical instrument (for example, a flute), but occurring on the background of the equilibrium charge distribution. The number of electrons in our quantum "flute" device varies between two and three. We find that for rectangular pulses the currents in the leads may flow against the bias for short time intervals, due to the higher harmonics of the charge response. The GME is solved numerically in small time steps without resorting to the traditional Markov and rotating wave approximations. The Coulomb interaction between the electrons in the sample is included via the exact diagonalization method. The system (leads plus sample wire) is described by a lattice model.
846. Ferroelectric and dielectric multilayer heterostructures based on KTa0.65Nb0.35O3 and Bi1.5-xZn0.92-yNb1.5O6.92-1.5x-y grown by pulsed laser deposition and chemical solution deposition for high frequency tunable devices
Authors:
Le Febvrier, A; Deputier, S; Bouquet, V; Demange, V; Ollivier, S; Galca, AC; Dragoi, C; Radu, R; Pintilie, L; Guilloux-Viry, M
Published: MAY 1 2012, THIN SOLID FILMS, 520, 4567, DOI: 10.1016/j.tsf.2011.10.142
Epitaxial growth of Bi1.5-xZn0.92-yNb1.5O6.92-1.5x-y (BZN) thin films was achieved on (100)(pc) LaAlO3 substrate by pulsed laser deposition (PLD) and by chemical solution deposition based on Pechini process. Effect of bismuth and zinc deficiency on the BZN thin films obtained by PLD was discussed, in relation with the starting target composition. Dielectric permittivity and bandgap values were determined from electrical and spectroscopic ellipsometry measurements performed on randomly oriented films grown on Pt/Si substrate. BZN thin films obtained by PLD exhibit, at 100 kHz, a dielectric constant of epsilon(r) = 203 and quite low dielectric losses of tan delta = 5 x 10(-2). Epitaxial ferroelectric - dielectric KTa0.65Nb0.35O3 (KTN) -Bi1.5-xZn0.92-yNb1.5O6.92-1.5x-y (KTN on BZN and BZN on KIN) bilayers were obtained by PLD on (100)(pc) LaAlO3 with the insertion of a suitable buffer layer of KNbO3 in the case of KTN on BZN. Such multilayer heterostructures with an epitaxial growth control of each layer are promising candidates for potential integration in microwave devices. (C) 2011 Elsevier B.V. All rights reserved.
847. The critical current density of SiC-doped MgB2 as determined from the Campbell penetration depth using the tunnel-diode resonator technique
Authors:
Guo, ZC; Suo, HL; Liu, ZY; Sandu, V; Aldica, G; Badica, P
Published: NOV-DEC 2012, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 6, 979, DOI:
The tunnel-diode resonator (TDR) technique for accurate measurements of the magnetic penetration depth is used to measure the London and Campbell penetration depths of polycrystalline SiC doped (10wt.%) MgB2. The Campbell length was used to investigate the field and temperature dependence of the critical current density. The as determined critical current density provides values as high as 6x10(6) A/cm(2) at 4.2K, 1T, which is higher than values estimated by Bean method.
848. Effect of Nucleators and Intermediates on the Magnetic Properties of Nanosized Magnetite Obtained by Glass Crystallization
Authors:
Sandu, V; Nicolescu, MS; Kuncser, V; Popa, S; Pasuk, L; Sandu, E
Published: SEP 2012, JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE, 9, 1545, DOI: 10.1166/jctn.2012.2241
We investigate the role of chromium and phosphorous oxides on the growth and magnetic properties of crystallized Fe-containing borosilicate glasses as well as their evolution under different thermal processing. The glasses have the ratio between SiO2 and Fe2O3 in the range 1.49 to 2.68 and Al2O3/MgO as intermediate/modifier oxides. X-ray diffraction and Mossbauer spectroscopy data revealed the presence of magnetite as the major crystalline phase in all as-prepared samples but additional amounts of hematite and of Fe-rich paramagnetic phases are also visible in some samples. The magnetic response is correlated with the disorder observed in the different sites (tetrahedral and octahedral) of the magnetite.
849. Broadband near-infrared emission of chromium-doped sulfide glass-ceramics containing Ga2S3 nanocrystals
Authors:
Ren, J; Li, B; Yang, G; Xu, WN; Zhang, ZH; Secu, M; Bercu, V; Zeng, HD; Chen, GR
Published: DEC 15 2012, OPTICS LETTERS, 37, 5045, DOI: 10.1364/OL.37.005043
Upon 808 nm excitation, an intense broadband near-infrared emission from Cr4+ has been observed in 80GeS(2)-20Ga(2)S(3) chalcogenide glass-ceramics (GCs) containing Ga2S3 nanocrystals. The emission band peaking at 1250 nm covers the O, E, S bands (1000-1500 nm). The formation of Ga2S3 nanocrystals (similar to 20 nm) increases the emission intensity of Cr4+ by more than three times. The quantum efficiency of the present GCs is as great as 36% at room temperature. (C) 2012 Optical Society of America
850. Analysis of the phase lapse problem in closed interferometers
Authors:
Tolea, M; Moldoveanu, V; Dinu, IV; Tanatar, B
Published: OCT 1 2012, PHYSICS LETTERS A, 376, 3234, DOI: 10.1016/j.physleta.2012.07.007
We investigate the connection between the asymmetry of the Fano resonances in a mesoscopic interferometer with an embedded quantum dot and the pi lapses in the phase of the "bare" dot transmittance. Consecutive Fano resonances with the same (opposite) sign of the Fano parameter imply the presence (absence) of a phase lapse with pi between the corresponding resonances of the dot. Our results suggest that the famous "phase lapse" problem, first reported by Schuster et al. [R. Schuster, E. Buks, M. Heiblum, D. Mahalu, V. Umansky, H. Shtrikman, Nature 385 (1997) 417], can therefore be experimentally addressed in closed interferometers. It is also proposed that the Fano effect can be used to extract the phase distributions of the eigenfunctions for a mesoscopic 20 shape, via the parity of the resonances. In the presence of electron-electron interaction, one can calculate the phases of the T-matrix elements. The numerical results lead to the same conclusions as for the non-interacting case. (C) 2012 Elsevier B.V. All rights reserved.
851. ELECTRICAL BEHAVIOUR RELATED TO STRUCTURE OF NANOSTRUCTURED GeSi FILMS ANNEALED AT 700 degrees C
Authors:
Lepadatu, AM; Stavarache, I; Maraloiu, A; Palade, C; Teodorescu, VS; Ciurea, ML
Published: 2012, 2012 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 2, 112, DOI:
In this paper we continue the previous investigations on nanostructured GexSi1-x films. The films were deposited by magnetron sputtering and annealed in N-2 atmosphere at 700 degrees C. Their structure was investigated and correlated with the electrical behavior. For this, conventional and high-resolution transmission electron microscopy together with selected area electron diffraction was used. Electrical measurements of current-voltage and current-temperature curves were made. The majority of crystallites that forms the films have the composition Ge50Si50 and 15 - 30 nm size. The I - T characteristics have Arrhenius dependence, with two activation energies interpreted as transitions between quantum confinement levels.
852. Generalized Master equation approach to mesoscopic time-dependent transport
Authors:
Torfason, K; Manolescu, A; Molodoveanu, V; Gudmundsson, V
Published: 2012, ADVANCED MANY-BODY AND STATISTICAL METHODS IN MESOSCOPIC SYSTEMS, 338, DOI: 10.1088/1742-6596/338/1/012017
We use a generalized Master equation (GME) formalism to describe the non-equilibrium time-dependent transport through a short quantum wire connected to semi-infinite biased leads. The contact strength between the leads and the wire are modulated by out-of-phase time-dependent functions which simulate a turnstile device. One lead is fixed at one end of the sample whereas the other lead has a variable placement. The system is described by a lattice model. We find that the currents in both leads depend on the placement of the second lead. In the rather small bias regime we obtain transient currents flowing against the bias for short time intervals. The GME is solved numerically in small time steps without resorting to the traditional Markov and rotating wave approximations. The Coulomb interaction between the electrons in the sample is included via the exact diagonalization method.
853. A Simple Fabrication of FeSe Superconductors with High Upper Critical Field
Authors:
Zhao, PH; Yan, W; Yang, JY; Han, YL; Aldica, G; Sandu, V; Badica, P; Nie, JC
Published: AUG 2012, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 25, 1785, DOI: 10.1007/s10948-012-1540-2
A simple and reproducible fabrication process for the synthesis of FeSe superconductors has been developed. The properties were characterized by X-ray diffraction, scanning electron microscope, superconductivity quantum interference device, and physical property measurement system. It showed a zero resistance superconducting critical temperature of similar to 7.9 K and an onset critical temperature of similar to 13.9 K. The upper critical magnetic field at zero temperature was estimated to be 31 T. The growth mechanism of FeSe flakes was also discussed.
854. Mossbauer, TEM/SAED and XRD investigation on waste dumps of the Valea lui Stan gold mines
Authors:
Constantinescu, SG; Udubasa, SS; Udubasa, G; Kuncser, V; Popescu-Pogrion, N; Mercioniu, I; Feder, M
Published: MAR 2012, HYPERFINE INTERACTIONS, 208, 84, DOI: 10.1007/s10751-011-0490-6
The complementary investigation techniques, Mossbauer spectroscopy, transmission electron microscopy with selected area electron diffraction (TEM/SAED), X-ray diffraction (XRD) have been used to investigate the fate of the Valea lui Stan, Romania, gold-ore nanoscale-minerals during the long time of residence in the waste dumps. The preliminary investigations showed such waste dumps to contain significant amount of metals which cannot be identified by conventional methods. An intense research activity started up in order to evaluate the possibilities to recycle Valea lui Stan waste dumps and to recover metals by chemical or phytoextraction procedures. The waste dumps naturally show different mineral constituents with clay minerals as major phases, observed by XRD-technique. Although the waste dumps materials have whitish-yellowish colours, MOSSBAUER technique evidences the presence of the finely dispersed iron bearing minerals. The authors are focusing to inspect and analyze Fe-compounds in the samples collected from Valea lui Stan's waste dumps in order to identify the magnetic phases by Mossbauer technique.
855. Nonadiabatic generation of spin currents in a quantum ring with Rashba and Dresselhaus spin-orbit interactions
Authors:
Nita, M; Marinescu, DC; Ostahie, B; Manolescu, A; Gudmundsson, V
Published: 2012, ADVANCED MANY-BODY AND STATISTICAL METHODS IN MESOSCOPIC SYSTEMS, 338, DOI: 10.1088/1742-6596/338/1/012013
When subjected to a linearly polarized terahertz pulse, a mesoscopic ring endowed with spin-orbit interaction (SOT) of the Rashba-Dresselhaus type exhibits non-uniform azimuthal charge and spin distributions. Both types of SOT couplings are considered linear in the electron momentum. Our results are obtained within a formalism based on the equation of motion satisfied by the density operator which is solved numerically for different values of the angle 0, the angle determining the polarization direction of the laser pulse. Solutions thus obtained are later employed in determining the time-dependent charge and spin currents, whose values are calculated in the stationary limit. Both these currents exhibit an oscillatory behavior complicated in the case of the spin current by a beating pattern. We explain this occurrence on account of the two spin-orbit interactions which force the electron spin to oscillate between the two spin quantization axes corresponding to Rashba and Dresselhaus interactions. The oscillation frequencies are explained using the single particle spectrum.
856. Electronic effects at self-assembled 4,4 '-thio-bis-benzenethiolate protected Au nanoparticles on p-GaAs (100) electrodes
Authors:
Enache, M; Preda, L; Negrila, C; Lazarescu, MF; Mercioniu, I; Santos, E; Anastasescu, M; Dobrescu, G; Lazarescu, V
Published: AUG 30 2012, ELECTROCHIMICA ACTA, 77, 16, DOI: 10.1016/j.electacta.2012.04.161
The effects of the self-assembled 4,4'-thio-bis-benzenethiolate protected gold nanoclusters onto a p-GaAs (1 0 0) electrode were examined by AFM, XPS, SHG and EIS investigations. The AFM and XPS results revealed a well-ordered overlayer exhibiting a bi-modal highly correlated fractal behavior which, however, cannot fully protect the semiconducting surface against the oxidation in air. The EIS data pointed out the influence exerted by the gold-monolayer protected clusters (Au-MPCs) over the charging/discharging processes observed at p-GaAs (1 0 0) electrode. Although the applied potential is varied linearly, the potential drop within the semiconductor space charge region as well as that across the Au-MPCs layer undergoes stepped changes supposed to result in the discrete charging of the Au-MPCs. These effects point to an electronic equilibrium between the Au-MPCs and the semiconducting substrate. Fermi level pinning and enhancement of the SHG response in the potential range where the surface/interface states in the semiconductor band gap become electrically active bring further proof in this respect. (c) 2012 Elsevier Ltd. All rights reserved.
857. Laser processing issues of nanosized intermetallic Fe-Sn and metallic Sn particles
Authors:
Alexandrescu, R; Morjan, I; Dumitrache, F; Birjega, R; Fleaca, C; Morjan, I; Scarisoreanu, M; Luculescu, CR; Dutu, E; Kuncser, V; Filoti, G; Vasile, E; Ciupina, V
Published: SEP 15 2012, APPLIED SURFACE SCIENCE, 258, 9426, DOI: 10.1016/j.apsusc.2012.01.159
Intermetallic Fe-Sn and nanocrystalline metallic Sn nanoparticles have been successfully synthesized from organic precursors using the laser pyrolysis technique with ethylene as sensitizer. Nano-structured Sn (single phase) was prepared by the pyrolysis of Sn(CH3)(4) (TMT) vapors. Controlled Fe/Sn atomic ratios, ranging from 0.69 to 1.64 were obtained for the prepared Fe-Sn nanopowders by the control of Fe(CO)(5) and TMT flows, respectively. XRD studies evidence three main phases: the tetragonal metallic Sn phase and the intermetallic FeSn2 phase and, to a much lesser extent, the cubic ternary carbide Fe3SnC. Complex core-shell structural characteristics were found by HRTEM analysis. More complete information about the Fe phase distributions in the new intermetallic Fe-Sn nanomaterial is provided by temperature dependent Fe-57 Mossbauer spectroscopy. (c) 2012 Elsevier B.V. All rights reserved.
858. Electronic transmittance phase extracted from mesoscopic interferometers
Authors:
Tolea, M; Moldoveanu, V; Dinu, IV; Tanatar, B
Published: OCT 13 2012, NANOSCALE RESEARCH LETTERS, 7, 7, DOI: 10.1186/1556-276X-7-568
The usual experimental set-up for measuring the wave function phase shift of electrons tunneling through a quantum dot (QD) embedded in a ring (i.e., the transmittance phase) is the so-called 'open' interferometer as first proposed by Schuster et al. in 1997, in which the electrons back-scattered at source and the drain contacts are absorbed by additional leads in order to exclude multiple interference. While in this case one can conveniently use a simple two-path interference formula to extract the QD transmittance phase, the open interferometer has also a number of draw-backs, such as a reduced signal and some uncertainty regarding the effects of the extra leads. Here we present a meaningful theoretical study of the QD transmittance phase in 'closed' interferometers (i.e., connected only to source and drain leads). By putting together data from existing literature and giving some new proofs, we show both analytically and by numerical simulations that the existence of phase lapses between consecutive resonances of the 'bare' QD is related to the signs of the corresponding Fano parameters - of the QD + ring system. More precisely, if the Fano parameters have the same sign, the transmittance phase of the QD exhibits a I lapse. Therefore, closed mesoscopic interferometers can be used to address the 'universal phase lapse' problem. Moreover, the data from already existing Fano interference experiments from Kobayashi et al. in 2003 can be used to infer the phase lapses.
859. A facile hydrothermal route for the synthesis of alpha-FeOOH with controlled morphology
Authors:
Raditoiu, V; Diamandescu, L; Corobea, MC; Raditoiu, A; Popescu-Pogrion, N; Nicolae, CA
Published: JUN 1 2012, JOURNAL OF CRYSTAL GROWTH, 348, 46, DOI: 10.1016/j.jcrysgro.2012.03.032
Nanoscaled alpha-FeOOH (goethite) with controlled morphology was synthesized via hydrothermal reaction at 145-155 degrees C from ferrous ions and an oxidant in the presence of a cationic surfactant. The formation of alpha-FeOOH was confirmed by X-ray diffraction (XRD), Mossbauer spectroscopy, FT-IR analysis and visible diffuse reflectance spectroscopy. The morphology of the product was analyzed by transmission electron microscopy (TEM). The particles obtained by the proposed method have a medium size of about 35 nm. The proposed growth mechanism takes into account two possible simultaneous pathways consisting of direct electrostatic interaction between FeOH groups and cetyltrimethylammonium bromide (CTAB) and adsorption of bicarbonate ions on the alpha-FeOOH surface followed by complexation of CTAB through ammonium head groups. (C) 2012 Elsevier B.V. All rights reserved.
860. Use of preceramic polymers for magnesium diboride composites
Authors:
Sandu, V; Cimpoiasu, E; Aldica, G; Popa, S; Sandu, E; St Vasile, B; Hurduc, N; Nor, I
Published: OCT 2012, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 480, 107, DOI: 10.1016/j.physc.2012.03.052
We used preceramic polysiloxane polymers to fabricate superconducting MgB2 composites that are doped with carbon and nanosized inclusions to improve the pinning properties. The polysiloxanes were prepared by atom transfer radical polymerization and the composites were fabricated by the short time spark plasma sintering method. We found that the superconducting critical temperatures were higher than expected from the carbon content found from the X-ray diffraction analysis of the (110) peak of MgB2. To explain this finding we propose that the grains are unevenly doped, with a core-shell distribution. We also found that both, the upper critical fields and the critical current densities are higher in the preceramic-doped samples than in pure MgB2, in agreement with the carbon doping level. When ferrocene-grafted polysiloxane is used, the upper critical field is the largest, while the critical current density is the lowest. We attribute this fact to the fact that the polymer pyrolysis results in iron-based nanostructures which have a pair breaking effect. (C) 2012 Elsevier B. V. All rights reserved.
861. One-Pot Hydroacetylation of Menadione (Vitamin K3) to Menadiol Diacetate (Vitamin K4) by Heterogeneous Catalysis
Authors:
Dobrinescu, C; Iorgulescu, EE; Mihailciuc, C; Macovei, D; Wuttke, S; Kemnitz, E; Parvulescu, VI; Coman, SM
Published: MAY 2012, ADVANCED SYNTHESIS & CATALYSIS, 354, 1306, DOI: 10.1002/adsc.201100718
Vitamin K4 (menadiol diacetate, MDD) can be easily synthesized through cleaner and more efficient catalytic alternatives following the green chemistry principles. Ionic gold-based hydroxylated fluorides are active bi-functional catalysts for the one-pot hydroacetylation of menadione leading to MDD with 77% selectivity. Unprecedent results were obtained in the presence of oxide-fluoride catalysts by using a microwave-assisted hydrogen-transfer (MeerweinPonndorfVerley reaction) coupled with an acetylation approach, yielding very high selectivities for the target product (95%).
862. Heterogeneous amination of bromobenzene over titania-supported gold catalysts
Authors:
Ciobanu, M; Cojocaru, B; Teodorescu, C; Vasiliu, F; Coman, SM; Leitner, W; Parvulescu, VI
Published: DEC 2012, JOURNAL OF CATALYSIS, 296, 54, DOI: 10.1016/j.jcat.2012.09.002
Amination of bromobenzene with aniline was carried out on heterogeneous Au-TiO2 catalysts prepared using the deposition-precipitation method. The deposition of gold in loadings in the range 0.1-0.9 wt.% on titania occurred with the formation of gold particles with controlled size and oxidation state as demonstrated from TEM and XPS measurements. In addition, Raman and DR-UV-Vis investigation of these catalysts showed that the interaction of Au particles with the support stabilized the metallic state of gold. Catalytic results demonstrated that the conversion and selectivity depended on the gold-particle size and dispersion, while the mechanism of reaction was in direct relation with the reaction medium. Working in DMC, the solvent was playing the role of base. The advantage of working in DMC was avoiding the formation of KBr which is very difficult to be separated from the reaction products. HBr resulted as a by-product formed adducts with the coupling product, which was separated as crystals at room temperature by a simple filtration. However, in DMC, the reaction occurred with low selectivities. In dioxane, the presence of potassium ethoxide as base was mandatory. The reaction occurred with very high selectivities for moderate conversions. The conversion was limited by KBr released from the reaction. However, the use of the heterogeneous catalyst has the advantage of scavenger, since KBr becomes chemisorbed on the surface and could be simple removed by percolation and the catalyst can be reused. (C) 2012 Elsevier Inc. All rights reserved.
863. Structure and Magnetic Properties of Nanosized Magnetite Obtained by Glass Recrystallization
Authors:
Sandu, V; Nicolescu, MS; Kuncser, V; Popa, S; Pasuk, I; Ghica, C; Sandu, E
Published: JUN 2012, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 12, 5050, DOI: 10.1166/jnn.2012.4943
We present the preparation, structural and magnetic properties of nanosized magnetite obtained by the crystallization of a series of Fe-containing borosilicate glasses. Several compositions with the ratio Fe2O3/SiO2 spanning from 0.37 to 0.67 were investigated as a function of two nucleators Cr2O3 and P2O5, respectively, and modifiers and intermediates (Al2O3 and MgO). Mossbauer spectroscopy revealed the degree, the type and the location of disorder induced by a specific composition and nucleators. In addition to magnetite, it was also revealed the presence of large amounts of Fe-rich paramagnetic phases. The magnetic response is analysed in relation with the amount of Fe ions which remain dispersed in the glassy matrix as noninteracting (paramagnetic) ions. We discuss the role of the nucleators on the disorder in both tetrahedral and octahedral sites of the magnetite.
864. Effect of Tritium Loading on the Superconducting Properties of Niobium and Tantalum
Authors:
Sandu, V; Popa, S; Nicolescu, MS; Enachescu, M; Sandu, E
Published: AUG 2012, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 25, 1804, DOI: 10.1007/s10948-012-1551-z
Niobium and tantalum sheets were loaded with tritium and their superconducting properties were investigated. Superconductivity is rather robust in both materials though they belong to different types of superconductors. The critical temperature does not change in the case of Nb at low field but decreases slightly in the case of Ta. The tritium-loaded Nb shows a higher remanent magnetization which we attribute to the subsurface accumulation of defects, but the high field irreversible magnetization is smaller than for the bare sample. In the case of Ta, both the remanent magnetization and the irreversible magnetization are slightly reduced after tritiation.
865. Mesoscopic Fano effect in a spin splitter with a side-coupled quantum dot
Authors:
Moldoveanu, V; Tolea, M; Tanatar, B
Published: FEB 20 2012, PHYSICS LETTERS A, 376, 1083, DOI: 10.1016/j.physleta.2012.02.017
We investigate the interplay between the spin interference and the Fano effect in a three-lead mesoscopic ring with a side-coupled quantum dot (QD). A uniform Rashba spin-orbit coupling and a perpendicular magnetic field are tuned such that the ring operates as a spin splitter in the absence of the QD: one lead is used to inject unpolarized electrons and the remaining (output) leads collect almost polarized spin currents. By applying a gate potential to the quantum dot a pair of spin-split levels sweeps the bias window and leads to Fano interference. The steady-state spin and charge currents in the leads are calculated for a finite bias applied across the ring via the non-equilibrium Green's function formalism. When the QD levels participate to transport we find that the spin currents exhibit peaks and dips whereas the charge currents present Fano lineshapes. The location of the side-coupled quantum dot and the spin splitting of its levels also affect the interference and the output currents. The opposite response of output currents to the variation of the gate potential allows one to use this system as a single parameter current switch. We also analyze the dependence of the splitter efficiency on the spin splitting on the QD. (C) 2012 Elsevier B.V. All rights reserved.
866. Magnetic pinning effects of epitaxial LaxSr1-xMnO3 nanostructured thin films on YBa2Cu3O7-delta layers
Authors:
Petrisor, T; Gabor, MS; Tiusan, C; Galluzzi, V; Celentano, G; Popa, S; Boulle, A; Petrisor, T
Published: SEP 1 2012, JOURNAL OF APPLIED PHYSICS, 112, DOI: 10.1063/1.4748049
The present paper presents the effects of a nanostructured, ferromagnetic La1-xSrxMnO3(LSMO) thin film on the pinning characteristics of an epitaxial YBa2Cu3O7(YBCO) thin film deposited on top. Ordered arrays of LSMO grains were obtained upon growing the film on a terraced (001) SrTiO3 substrate. The analyses of magnetic measurements revealed the presence of a complex vortex pinning mechanism within the YBCO film. With respect to a reference single YBCO layer, an additional pinning potential was observed. Its temperature evolution suggests that a magnetic pinning mechanism is responsible for improved pinning characteristics in the high temperature and field region. Based on the morphology of the underlying LSMO buffer, a strong pinning force is expected to arise due to the anti-dot formations, where a high magnetization gradient exists. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4748049]
867. PINNING-FORCE SCALING AND ITS LIMITATION IN INTERMEDIATE AND HIGH TEMPERATURE SUPERCONDUCTORS
Authors:
Sandu, V
Published: JUN 10 2012, MODERN PHYSICS LETTERS B, 26, DOI: 10.1142/S0217984912300074
We present the scaling law of the pinning force F-P in intermediate and high temperature superconductors, the factors which influence its field and temperature dependence, the limitations imposed by the enlarged anisotropy and high operating temperatures, giant creep included. The theoretical developments which incorporate the new features of these classes of superconductors, most of them based on the Anderson-Kim theory, prove to be a useful source of information relative to the nature of the pinning and the characteristic fields. The use of models based on thermal activation integrates into scaling the tail of pinning force and also substantiates the use of the irreversibility field H-irr as scale field. Finally, the data on scaling law in the two class of superconductors are presented and discussed.
868. Fabrication of Superconducting MgB2-Based Nanocomposites with Magnetic Inclusions by Spark Plasma Sintering
Authors:
Sandu, V; Ion, I; Litra-Cristian, P; Sandu, E
Published: 2012, ADVANCED MATERIALS DESIGN AND MECHANICS, 569, +, DOI: 10.4028/www.scientific.net/AMR.569.3
We present the fabrication, structural, and transport properties of MgB2-based ceramic composites with magnetic nanospheres fabricated by spark plasma sintering. The nanospheres are either carbon encapsulated iron or iron oxide. The former nanospheres have been prepared by laser pyrolysis whereas the iron oxide was obtained by the pyrolysis of the polysiloxane-based copolymers embedded into MgB2 matrix during the sintering process. The structural data show the shrinkage of the a-axis lattice constant as a result of the partial carbon substitution for boron. However, the transport data suggest that carbon diffusion is limited to the outer layer of the MgB2 grains in both cases.
869. Optical properties of amorphous-like indium zinc oxide and indium gallium zinc oxide thin films
Authors:
Galca, AC; Socol, G; Craciun, V
Published: MAY 1 2012, THIN SOLID FILMS, 520, 4725, DOI: 10.1016/j.tsf.2011.10.194
The paper presents the optical properties of amorphous-like indium zinc oxide and indium gallium zinc oxide thin films with various In/(In + Zn) ratios obtained by Pulsed Laser Deposition. Thickness results obtained from simulations of X-ray Reflectivity and Spectroscopic Ellipsometry data were very similar. The dependence of density on stoichiometry resembles the corresponding dependence of the refractive index in the transparency range. A free carrier absorption was noted in the visible spectral range, leading to a weak absorbing thin transparent conductive oxide. On the other hand, the refractive index is smaller than those of based oxides (ZnO and In2O3), and counterbalance therefore the weak light absorption. (C) 2011 Elsevier B.V. All rights reserved.
870. Biocatalytic microreactor incorporating HRP anchored on micro-/nano-lithographic patterns for flow oxidation of phenols
Authors:
Tudorache, M; Mahalu, D; Teodorescu, C; Stan, R; Bala, C; Parvulescu, VI
Published: MAY 2011, JOURNAL OF MOLECULAR CATALYSIS B-ENZYMATIC, 69, 139, DOI: 10.1016/j.molcatb.2011.01.007
A highly durable and versatile micro scale biocatalytic reactor has been designed and investigated in the heterogeneous enzyme-catalytic oxidation of phenols. It consisted of optical or electron beam lithographic gold deposited layer with different thickness from nano- to micro-scale on a semiconductor surface. Horseradish peroxidase (H RP) enzyme was immobilized on the gold-surface using two different approaches (i.e., physical adsorption and self-assembled monolayer). Characterization of those HRP-gold surfaces was made using AFM (atomic force microscopy) coupled with ellipsometry measurements, SEM (scanning electron microscopy), STM (scanning tunneling microscopy) and spectrophotometric technique. The catalytic performances of the developed structures were investigated after their incorporation in microreactors using a recycling-flow system dedicated to phenols oxidation. In order to optimize the efficiency of the oxidation process it was checked the effect of the successively addition of the reagent, the influence of the reaction time, the stability and the reuse of the biocatalytic micro-system. Maximum phenol conversion was of 35.1%. In addition to phenol the system has also been investigated in oxidation of other phenolic compounds such as cathecol, hydroquinone, rezorcine, beta-naphtol, o/p-aminophenol and 4-metoxyphenol. (C) 2011 Elsevier B.V. All rights reserved.
871. PRODUCTION AND CHARACTERIZATION OF CdTe WIRE ARRAYS FOR HYBRID INORGANIC/ORGANIC PHOTOVOLTAIC CELLS
Authors:
Florica, C; Arghir, I; Ion, L; Enculescu, I; Antohe, VA; Radu, A; Radu, M; Chisulescu, G; Dina, N; Antohe, S
Published: JAN-MAR 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 27, DOI:
A new approach for obtaining hybrid inorganic/organic photovoltaic structures, based on CdTe nanowires and organic dye films is reported. The wire arrays of CdTe (10(6) wires/cm(2)) were electrochemically grown using a template method. Ion track polycarbonate foils (30 micrometer thick) were used as templates and the growth conditions for obtaining good quality and stoichiometric CdTe nanowires were identified. After dissolving the polycarbonate template, a CdTe thin film (300 nm) has been deposited by thermal vacuum evaporation onto the wire array before the deposition of ZnPc film as organic absorber. Finally a ZnO thin film was deposited by Electron Pulsed Deposition on ZnPc, working as TCO top electrode. The structural, morphological, electrical and optical properties of each component layer are investigated. Typical parameters of the prepared photovoltaic structures are determined. The external quantum efficiency of the Au/wire array CdTe/CdTe(300 nm)/ZnPc/ZnO structures was significantly increased, with respect to that of Au/wire arrays CdTe/ZnPc/ZnO structures.
872. Nonadiabatic generation of a pure spin current in a one-dimensional quantum ring with spin-orbit interaction
Authors:
Nita, M; Marinescu, DC; Manolescu, A; Gudmundsson, V
Published: APR 18 2011, PHYSICAL REVIEW B, 83, DOI: 10.1103/PhysRevB.83.155427
We demonstrate the theoretical possibility of obtaining a pure spin current in a 1D ring with spin-orbit interaction by irradiation with a nonadiabatic, two-component terahertz laser pulse, whose spatial asymmetry is reflected by an internal phase difference phi. The solutions of the equation of motion for the density operator are obtained for a spin-orbit coupling linear in the electron momentum (Rashba) and they are used to calculate the time-dependent charge and spin currents. We find that there are critical values of phi at which the charge current disappears, while the spin current reaches a maximum or a minimum value.
873. High quality amorphous indium zinc oxide thin films synthesized by pulsed laser deposition
Authors:
Socol, G; Craciun, D; Mihailescu, IN; Stefan, N; Besleaga, C; Ion, L; Antohe, S; Kim, KW; Norton, D; Pearton, SJ; Galca, AC; Craciun, V
Published: DEC 1 2011, THIN SOLID FILMS, 520, 1277, DOI: 10.1016/j.tsf.2011.04.196
Indium zinc oxide films were grown from targets with two different In atomic concentration [In/(In+Zn)] of 40% and 80% by the pulsed laser deposition technique on glass substrates from room temperature up to 100 degrees C. X-ray diffraction and reflectometry investigations showed that films were amorphous and dense. Thin films (thickness<100 nm) exhibited higher optical transmittance and resistivities than thick films (thickness>1000 nm), probably caused by a significant decrease of oxygen vacancies due to atmosphere exposure. Films deposited from the In rich target under an oxygen pressure of 1 Pa exhibited optical transmittance higher than 85%, resistivities around 5-7x10(-4) Omega cm and mobilities in the 47-54 cm(2)/V s range. (C) 2011 Elsevier B. V. All rights reserved.
874. Optical properties of phase change memory Ge1Sb2Te4 glasses
Authors:
Iovu, MS; Colomeico, EP; Benea, VG; Popescu, M; Lorinczi, A; Velea, A
Published: NOV-DEC 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 1486, DOI:
Phase change memory materials are promising for the next-generation of non-volatile flash memory that will serve in new mobile computing, entertainment and other handheld electronics. Among them are chalcogenide glasses Ge-Sb-Te (GST) which can exist in two separates structural states - amorphous and cristalline. Switching of the material from one to another state can be done by heating applying an electrical pulse or by exposure to intense laser beam. We report the changes of optical parameters of amorphous Ge1Sb2Te4 films under heat treatment and light exposure.
875. Improved Critical Current Densities in YBa2Cu3O7-delta Multilayer Films Interspaced with Palladium Nano-dots
Authors:
Sarkar, A; Mikheenko, P; Dang, VS; Kechik, MMA; Abell, JS; Crisan, A
Published: JAN 2011, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 24, 177, DOI: 10.1007/s10948-010-0914-6
Power applications of superconducting coated conductors in high magnetic fields require thick films with high critical current density J (c) and strong artificial pinning centers. Here, we report on the artificial pinning centers induced in YBCO quasi-multilayer films interspaced with palladium (Pd) nano-dots. Quasi-multilayered (QM) YBa2Cu3O7-delta (YBCO) films composed of YBCO layers interspaced with quasi-layers of palladium nano-dots were grown by pulsed laser deposition on SrTiO3(100) substrates. DC magnetization and frequency-dependent measurements showed high J (c) comparable with best YBCO films in thin quasi-multilayers and significant improvement of J (c) in thick quasi-multilayers. TEM study shows regions of planar defects, stacking faults, and pore formations suitable for immobilizing vortices. These defects significantly contribute to the pinning of magnetic flux and increase critical current in the films.
876. Structural investigations of Ge nanoparticles embedded in an amorphous SiO2 matrix
Authors:
Stavarache, I; Lepadatu, AM; Gheorghe, NG; Costescu, RM; Stan, GE; Marcov, D; Slav, A; Iordache, G; Stoica, TF; Iancu, V; Teodorescu, VS; Teodorescu, CM; Ciurea, ML
Published: JAN 2011, JOURNAL OF NANOPARTICLE RESEARCH, 13, 232, DOI: 10.1007/s11051-010-0021-4
Transmission electron microscopy and X-ray photoelectron spectroscopy analyses are performed to investigate Ge nanoparticles embedded in an amorphous SiO2 matrix. GeSiO thin films are prepared by two methods, sol-gel and radio frequency magnetron sputtering. After the deposition, the sol-gel films are annealed in either N-2 (at 1 atm and 800 A degrees C) or H-2 (at 2 atm and 500 A degrees C), and the sputtered films in H-2 (at 2 atm and 500 A degrees C), to allow Ge segregation. Amorphous Ge-rich nanoparticles (3-7 nm size) are observed in sol-gel films. Crystalline Ge nanoparticles in the high pressure tetragonal phase (10-50 nm size) are identified in the sputtered films. The size of the nanoparticles increases with Ge concentration in the volume of the film. At the film surface, the Ge concentration is much larger that in the volume for both sol-gel and sputtered films. At the same time, at the film surface, only oxidized Ge is observed.
877. Step-shape angular spin distribution in layered systems by Fe-57 Mossbauer spectroscopy: A general treatment
Authors:
Kuncser, V; Keune, W
Published: AUG 2011, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 323, 2201, DOI: 10.1016/j.jmmm.2011.03.030
In the so-called 'step-shape' angular spin distribution model for layered systems, the non-collinear directions of the atomic magnetic moments are confined to the film plane and form a homogeneous fan spanning inside an (in-plane) angular interval Delta phi centered at an angle phi(0). A general approach for deriving the two parameters phi(0) and Delta phi via Fe-57 Mossbauer spectroscopy measurements is discussed. The analysis extends our previously reported treatment, which assumed that the angular aperture Delta phi develops symmetrically versus a fixed direction phi(0) (e.g., the in-plane easy axis of magnetization) oriented either along or perpendicular to the in-plane projection of the Mossbauer gamma-ray direction. The proposed approach is also applicable for those cases when not only the spin aperture Delta phi is changing but also the aperture center phi(0) is rotating under the influence of different external parameters, such as applied field, temperature, stress, etc. The method is suitable for applications to nanoscale layered heterostructures with in-plane uniaxial or unidirectional magnetic anisotropy. The method is applied to experimental data obtained on a 2-nm thick defected Fe layer with in-plane magnetic texture. (C) 2011 Elsevier B.V. All rights reserved.
878. PREPARATION AND ELECTRICAL CHARACTERIZATION OF SiGe NANOSTRUCTURES
Authors:
Stavarache, I; Lepadatu, AM; Pasuk, I; Teodorescu, VS; Ciurea, ML
Published: 2011, 2011 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS 2011), 34TH EDITION, VOLS 1 AND 2, 52, DOI:
This paper presents the preparation and investigation of structure and electrical properties of nanostructures consisting of Si1-xGex nanocrystals. Nanostructures were prepared by RF magnetron sputtering, followed by thermal annealing. X-ray diffraction, TEM, high resolution TEM and SAED measurements were performed. Current-voltage and current-temperature characteristics were taken. Nanostructures have different electrical behavior. Current-voltage curves are linear, while current-temperature curves are dependent on the annealing temperature. In films annealed at 650 degrees C, electrical transport is controlled by quantum confinement effect and localized states (current-temperature characteristics), while in films annealed at 900 degrees C it is controlled by tunneling of thermally activated carriers between neighboring nanocrystals.
879. Transport properties of superconducting MgB2 composites with carbon-encapsulated Fe nanospheres
Authors:
Sandu, V; Aldica, G; Popa, S; Badica, P; Cimpoiasu, E; Dumitrache, F; Sandu, E
Published: DEC 15 2011, JOURNAL OF APPLIED PHYSICS, 110, DOI: 10.1063/1.3672820
We present the magnetic and transport properties of superconducting composites fabricated by admixing carbon-encapsulated Fe nanospheres and MgB2 powder. The addition of nanoparticles is expected to enhance the critical current density by carbon-doping the MgB2 matrix and by providing artificial pinning sites. Three samples with estimated amounts of 0.35, 0.6, and 1.0 wt. % metallic Fe were prepared using the spark plasma sintering technique. The average size of these nanoparticles is comparable to the superconducting coherence length of MgB2 at approximately 5 nm. We found that the additions do not significantly alter the critical temperature which is very high, close to that of the pure MgB2 samples. We have also observed improved current densities, as high as 1100 kA/cm(2) for the samples with 0.35 wt. % metallic Fe at 5 K and 1 T. A core-shell model for explaining the transport data is presented. The field and temperature dependence of the reduced pinning force is described in terms of pinning on grain boundaries and/or on point defects. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3672820]
880. Surface versus volume effects in luminescent ceria nanocrystals synthesized by an oil-in-water microemulsion method
Authors:
Tiseanu, C; Parvulescu, VI; Boutonnet, M; Cojocaru, B; Primus, PA; Teodorescu, CM; Solans, C; Dominguez, MS
Published: 2011, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13, 17145, DOI: 10.1039/c1cp21135h
Pure and europium (Eu3+) doped cerium dioxide (CeO2) nanocrystals have been synthesized by a novel oil-in-water microemulsion reaction method under soft conditions. In-situ X-ray diffraction and RAMAN spectroscopy, high-resolution transmission electron microscopy, UV/Vis diffuse-reflectance and Fourier transform infrared spectroscopy as well as time-resolved photoluminescence spectroscopy were used to characterize the nanaocrystals. The as-synthesized powders are nanocrystalline and have a narrow size distribution centered on 3 nm and high surface area of similar to 250 m(2) g(-1). Only a small fraction of the europium ions substitutes for the bulk, cubic Ce4+ sites in the europium-doped ceria nanocrystals. Upon calcination up to 1000 degrees C, a remarkable high surface area of similar to 120 m(2) g (-1) is preserved whereas an enrichment of the surface Ce4+ relative to Ce3+ ions and relative strong europium emission with a lifetime of similar to 1.8 ms and FWHM as narrow as 10 cm(-1) are measured. Under excitation into the UV and visible spectral range, the europium doped ceria nanocrystals display a variable emission spanning the orange-red wavelengths. The tunable emission is explained by the heterogeneous distribution of the europium dopants within the ceria nanocrystals coupled with the progressive diffusion of the europium ions from the surface to the inner ceria sites and the selective participation of the ceria host to the emission sensitization. Effects of the bulk-doping and impregnation with europium on the ceria host structure and optical properties are also discussed.
881. Retrospective dosimetry assessment using the 380 degrees C thermoluminescence peak of tooth enamel
Authors:
Secu, CE; Cherestes, M; Secu, M; Cherestes, C; Paraschiva, V; Barca, C
Published: OCT 2011, RADIATION MEASUREMENTS, 46, 1112, DOI: 10.1016/j.radmeas.2011.07.014
The thermoluminescence (TL) response to gamma-ray irradiation of tooth enamel is reported. The tooth enamel was separated from dentine by using mechanical and physico-chemical procedures followed by grinding (grain size 100 urn) and etching. Then was attributed to the recombination of CO(2)(-) radicals incorporated into or attached to the surface of hydroxyapatite crystals. The growth of the 380 degrees C peak with absorbed dose was examined with irradiated tooth enamel samples and reconstructed doses evaluated for tooth enamel samples from four human subjects. (C) 2011 Elsevier Ltd. All rights reserved.
882. The pinning force density in polycrystalline Bi1.8Pb0.4Sr2Ca2-xYxCu3Oy multiphase systems
Authors:
Mihalache, V; Deac, IG; Pop, AV; Miu, L
Published: JUL 2011, CURRENT APPLIED PHYSICS, 11, 1014, DOI: 10.1016/j.cap.2011.01.015
ac susceptibility measurements as a function of temperature T and the ac magnetic field amplitude, Hac, have been performed on five superconducting Bi1.8Pb0.4Sr2Ca2-xYxCu3Ox polycrystalline samples (x = 0, 0.005, 0.04, 0.15 and 0.36, and with the volume fraction of the Bi2Sr2Ca2Cu3Oy (2223) phase, f approximate to 100%, 100%, 64%, 0% and 0%, respectively. By using the Muller model for granular superconductors, we found that the pinning force density obtained from the imaginary peak of chi ''(T) is strongly dependent on the doping level. To describe this dependence we adopted the multilayer model (a stack of superconducting, S, and normal, N, layers) of a superconductor. In the framework of this model, we demonstrated that (a) the yttrium addition influences the degree of coupling between the adjacent S layers (and thereby, the pinning strength) through the modification of the carrier concentration and of the effective thickness of the N layers, and (b) the intergrowth of Bi2Sr2CaCu2O delta (2212) layers within the 2223 grains has an important influence on the thickness of N. (C) 2011 Elsevier B.V. All rights reserved.
883. Numerical analysis of J-V characteristics of a polymer solar cell
Authors:
Mitroi, MR; Iancu, V; Fara, L; Ciurea, ML
Published: MAY 2011, PROGRESS IN PHOTOVOLTAICS, 19, 306, DOI: 10.1002/pip.1026
A numerical method to determine the cell parameters from the analysis of the J-V characteristics of a polymer solar cell is proposed. This method uses the equations given by the diode model, experimental data from the literature, and an adequate fitting procedure with seven fit parameters. Different aspects of the obtained results are discussed. Information concerning cell design optimization is also obtained. The method is of general application in the field of polymer solar cells, as well as to any kind of diode-like cell. Copyright (C) 2010 John Wiley & Sons, Ltd.
884. Nonequilibrium steady states for interacting open systems: Exact results
Authors:
Moldoveanu, V; Cornean, HD; Pillet, CA
Published: AUG 11 2011, PHYSICAL REVIEW B, 84, DOI: 10.1103/PhysRevB.84.075464
Under certain conditions, we prove the existence of a steady-state transport regime for interacting mesoscopic systems coupled to reservoirs (leads). The partitioning and partition-free scenarios are treated on an equal footing. Our time-dependent scattering approach is exact and proves, among other things, the independence of the steady-state quantities from the initial state of the sample. Closed formulas for the steady-state current amenable for perturbative calculations with regard to the interaction strength are also derived. In the partitioning case, we calculate the first-order correction and recover the mean-field (Hartree-Fock) results.
885. Intensity parameters of Tm3+ doped Sc2O3 transparent ceramic laser material
Authors:
Gheorghe, C; Lupei, A; Lupei, V; Ikesue, A; Enculescu, M
Published: JAN 2011, OPTICAL MATERIALS, 33, 505, DOI: 10.1016/j.optmat.2010.10.032
This work is focused on spectral investigations of Tm3+ doped Sc2O3 transparent ceramic as potential material for diode-pumped solid-state laser emitting around 2 mu m. In the context of the Judd-Ofelt J-O) theory a series of spectroscopic parameters such as J-O intensity parameters, oscillator strengths, radiative transitions probabilities, and radiative lifetimes as well as branching ratios are evaluated. The gain cross-sections which lead to an estimation of the probable operating laser wavelength for the F-3(4) -> H-3(6) Tm3+ laser transition were also calculated. (C) 2010 Elsevier B.V. All rights reserved.
886. Turnstile pumping through an open quantum wire
Authors:
Gainar, CM; Moldoveanu, V; Manolescu, A; Gudmundsson, V
Published: JAN 2011, NEW JOURNAL OF PHYSICS, 13, DOI: 10.1088/1367-2630/13/1/013014
We use a non-Markovian generalized master equation (GME) to describe the time-dependent charge transfer through a parabolically confined quantum wire of a finite length coupled to semi-infinite quasi-two-dimensional (2D) leads. The quantum wire and the leads are in a perpendicular external magnetic field. The contacts to the left and right leads depend on time and are kept out of phase to model a quantum turnstile of finite size. The effects of the driving period of the turnstile, the external magnetic field, the character of the contacts and the chemical potential bias on the effectiveness of the charge transfer of the turnstile are examined, in both the absence and the presence of the magnetic field. The interplay between the strength of the coupling and the strength of the magnetic field is also discussed. We observe how the edge states created in the presence of the magnetic field contribute to the pumped charge.
887. Time-dependent magnetotransport in semiconductor nanostructures via the generalized master equation
Authors:
Gudmundsson, V; Tang, CS; Gainar, CM; Moldoveanu, V; Manolescu, A
Published: JAN 2011, COMPUTER PHYSICS COMMUNICATIONS, 182, 48, DOI: 10.1016/j.cpc.2010.08.006
Transport of electrons through two-dimensional semiconductor structures on the nanoscale in the presence of perpendicular magnetic field depends on the interplay of geometry of the system the leads and the magnetic length We use a generalized master equation (GME) formalism to describe the transport through the system without resorting to the Markov approximation Coupling to the leads results in elastic and inelastic processes in the system that are described to a high order by the integro-differential equation of the GME formalism Geometrical details of systems and leads leave their fingerprints on the transport of electrons through them The GME formalism can be used to describe both the initial transient regime immediately after the coupling of the leads to the system and the steady state achieved after a longer time (C) 2010 Elsevier BV All rights reserved
888. Shape Memory NiTi Alloys Obtained by Powder Metallurgy Route
Authors:
Lucaci, M; Valeanu, M; Orban, RL; Tsakiris, V; Cirstea, DC; Leonat, L
Published: 2011, RESEARCHES IN POWDER METALLURGY, 672, +, DOI: 10.4028/www.scientific.net/MSF.672.99
The effect of Fe, respective Cu, additions as substitute for Ni in NiTi shape memory alloys (SMAs) on the delaying of its phase transition and narrowing hysteresis are well known, NiTi-Fe and NiTi-Cu SMAs having applications especially to the actuators that require such properties. These SMAs are currently produced by conventional melting methods, which are energo-intensive and impose very severe processing conditions to avoid contamination. The results of researches presented in this paper prove the possibility of these SMAs obtaining by powder metallurgy via reactive sintering - more advantageous from both technical and economic point of view. A beneficial effect on both sintering and homogeneity of the obtained SMAs proved to have a controlled mechanical alloying applied to powder mixture before compacting and sintering.
889. Silicon detectors for the sLHC
Authors:
Affolder, A; Aleev, A; Allport, PP; Andricek, L; Artuso, M; Balbuena, JP; Barabash, L; Barber, T; Barcz, A; Bassignana, D; Bates, R; Battaglia, M; Beimforde, M; Bemardini, J; Betancourt, C; Bilei, GM; Bisello, D; Blue, A; Bohm, J; Bolla, G; Borgia, A; Borrello, L; Bortoletto, D; Boscardin, M; Bosma, MJ; Bowcock, TJV; Breindl, M; Broz, J; Bruzzi, M; Brzozowski, A; Buhmann, P; Buttar, C; Campabadal, F; Candelori, A; Casse, G; Charron, S; Chren, D; Cihangir, S; Cindro, V; Collins, P; Gil, EC; Costinoaia, CA; Creanza, D; Cristobal, C; Dalla Betta, GF; de Boer, W; De Palma, M; Demina, R; Dierlamm, A; Diez, S; Dobos, D; Doherty, F; Kittelmann, ID; Dolezal, Z; Dolgolenko, A; Dragoi, C; Driewer, A; Dutta, S; Eckstein, D; Eklund, L; Eremin, I; Eremin, V; Erfle, J; Fadeeva, N; Fahrer, M; Fiori, F; Fleta, C; Focardi, E; Forshaw, D; Fretwurst, E; Frey, M; Bates, AG; Gallrapp, C; Garcia, C; Gaubas, E; Genest, MH; Giolo, K; Glaser, M; Goessling, C; Golubev, A; Gorelov, I; Gregoire, G; Gregori, P; Grigoriev, E; Grillo, AA; Grinstein, S; Groza, A; Guskov, J; Hansen, TE; Harkonen, J; Hartjes, FG; Hartmann, F; Hoeferkamp, M; Horisberger, R; Houdayer, A; Hynds, D; Ilyashenko, I; Junkes, A; Kadys, A; Kaminski, P; Karpenko, A; Kaska, K; Kazuchits, N; Kazukauskas, V; Kharchuk, A; Khivrich, V; Kierstead, J; Klanner, R; Klingenberg, R; Kodys, P; Koffeman, E; Kohler, M; Kohout, Z; Korjenevski, S; Korolkov, I; Kozlowski, R; Kozubal, M; Kramberger, G; Kuhn, S; Kuleshov, S; Kuznetsov, A; Kwan, S; La Rosa, A; Lacasta, C; Lange, J; Lassila-Perini, K; Lastovetsky, V; Lazanu, I; Lazanu, S; Lebel, C; Lefeuvre, G; Lemaitre, V; Leroy, C; Li, Z; Lindstrom, G; Litovchenko, A; Litovchenko, P; Lozano, M; Luczynski, Z; Luukka, P; Macchiolo, A; Macraighne, A; Maenpaa, T; Makarenko, LF; Mandic, I; Maneuski, D; Manna, N; Marco, R; Garcia, SII; Marunko, S; Masek, P; Mathieson, K; Matysek, M; Mekki, J; Messineo, A; Metcalfe, J; Mikestikova, M; Mikuz, M; Militaru, O; Minano, M; Miyamoto, J; Moll, M; Monokhov, E; Mori, R; Moser, HG; Muenstermann, D; Sanchez, FJM; Naletko, A; Nisius, R; Oshea, V; Pacifico, N; Pantano, D; Parkes, C; Parzefall, U; Passeri, D; Pawlowski, M; Pellegrini, G; Pernegger, H; Petasecca, M; Piemonte, C; Pignatel, GU; Pintilie, I; Pintilie, L; Piotrzkowski, K; Placekett, R; Pohlsen, T; Polivtsev, L; Popule, J; Pospisil, S; Preiss, J; Radicci, V; Radu, R; Raf, JM; Rando, R; Richter, R; Roeder, R; Roger, R; Rogozhkin, S; Rohe, T; Ronchin, S; Rott, C; Roy, A; Rummler, A; Ruzin, A; Sadrozinski, HFW; Sakalauskas, S; Samadashvili, N; Scaringella, M; Schumm, B; Seidel, S; Seiden, A; Shipsey, I; Sibille, J; Sicho, P; Slavicek, T; Solar, M; Soldevila-Serrano, U; Son, S; Sopko, V; Sopko, B; Spencer, N; Spiegel, L; Srivastava, A; Steinbrueck, G; Stewart, G; Stolze, D; Storasta, J; Surma, B; Svensson, BG; Tan, P; Tomasek, M; Toms, K; Tsiskaridze, S; Tsvetkov, A; Tuboltsev, Y; Tuominen, E; Tuovinen, E; Tuuva, T; Tylchin, M; Uebersee, H; Ullan, M; Vaitkus, JV; van Beuzekom, M; Verbitskaya, E; Alvarez, IV; Visser, J; Vossebeld, J; Vrba, V; Walz, M; Weigell, P; Wiik, L; Wilhelm, I; Wunstorf, R; Zaluzhny, A; Zavrtanik, M; Zelazko, J; Zen, M; Zhukov, V; Zontar, D; Zorzi, N
Published: DEC 1 2011, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 658, 16, DOI: 10.1016/j.nima.2011.04.045
In current particle physics experiments, silicon strip detectors are widely used as part of the inner tracking layers. A foreseeable large-scale application for such detectors consists of the luminosity upgrade of the Large Hadron Collider (LHC), the super-LHC or sLHC, where silicon detectors with extreme radiation hardness are required. The mission statement of the CERN RD50 Collaboration is the development of radiation-hard semiconductor devices for very high luminosity colliders. As a consequence, the aim of the R&D programme presented in this article is to develop silicon particle detectors able to operate at sLHC conditions. Research has progressed in different areas, such as defect characterisation, defect engineering and full detector systems. Recent results from these areas will be presented. This includes in particular an improved understanding of the macroscopic changes of the effective doping concentration based on identification of the individual microscopic defects, results from irradiation with a mix of different particle types as expected for the sLHC, and the observation of charge multiplication effects in heavily irradiated detectors at very high bias voltages. (C) 2011 Elsevier B.V. All rights reserved.
890. The study of the electric and magnetic properties of PbZr0.2Ti0.8O3-BiFeO3 multilayers
Authors:
Stancu, V; Dragoi, C; Kuncser, V; Schinteie, G; Trupina, L; Vasile, E; Pintilie, L
Published: JUL 29 2011, THIN SOLID FILMS, 519, 6277, DOI: 10.1016/j.tsf.2011.03.136
The results of the electric and magnetic measurements performed on PbZr0.2Ti0.8O3-BiFeO3 symmetric structures, deposited on Pt/Si wafers, were compared for different number of layers in order to analyse the effect of interfaces over the macroscopic properties. It was found that the shape and magnitude of the capacitance-voltage characteristic, as well as the shape and parameters of the ferroelectric and magnetic hysteresis, depend on the number of interfaces in the intended multilayer structure. A temperature induced gradual transition from a magnetically disordered spin glass like phase of low temperature to an uncompensated antiferromagnetic phase at room temperature takes place in the BiFeO3 films, under low applied magnetic fields. A partial ferromagnetic like order can be obtained at low temperatures by increasing the field. The observed changes in the electric and magnetic behaviour of the systems were related to an increased degree of disorder for electric dipoles and magnetic moments, due to the increased number of layers and crystallization treatments. (C) 2011 Elsevier B.V. All rights reserved.
891. On the scaling law of some characteristic fields in Y1-xPrxBa2Cu3O7-delta
Authors:
Sandu, V; Almasan, CC
Published: MAR 2011, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 471, 136, DOI: 10.1016/j.physc.2010.12.010
We investigated the anisotropy dependence of the characteristic fields of the second peak magnetization, specifically, the onset field B-on and the peak field B-sp, in Y1-xPrxBa2Cu3O7-delta single crystals. The empirical dependence arising from data analysis suggests a logarithmic dependence of both these fields on the anisotropy factor gamma which disagrees with the universal scaling law gamma(2)(B) = F(t) proposed previously. We attribute the faster decrease of the two fields at high anisotropy to the dramatic changes in the magnetic state of the system which starts to display a noticeable paramagnetic contribution at high Pr-doping, hence high anisotropy. The incipient phase separation could also reduce the elastic properties of the flux line lattice which determines onset of the second peak magnetization. (C) 2010 Elsevier B.V. All rights reserved.
892. On the cotunneling regime of interacting quantum dots
Authors:
Cornean, HD; Moldoveanu, V
Published: JUL 29 2011, JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL, 44, DOI: 10.1088/1751-8113/44/30/305002
Consider a bunch of interacting electrons confined in a quantum dot. The later is suddenly coupled to semi-infinite biased leads at an initial instant t = 0. We identify the dominant contribution to the ergodic current in the off-resonant transport regime, in which the discrete spectrum of the quantum dot is well separated from the absolutely continuous spectrum of the leads. Our approach allows for arbitrary strength of the electron-electron interaction while the current is expanded in even powers of the (weak) lead-dot hopping constant tau. We provide explicit calculations for sequential tunneling and cotunneling contributions to the current. In the interacting case, it turns out that the cotunneling current depends on the initial many-body configuration of the sample, while in the non-interacting case, it does not and coincides with the first term in the expansion of the Landauer formula w.r.t. tau.
893. Metallurgical phases and their magnetism at the interface of nanoscale MgB2/Fe layered structures
Authors:
Sahoo, B; Keune, W; Kuncser, V; Becker, HW; Rohlsberger, R
Published: NOV 30 2011, JOURNAL OF PHYSICS-CONDENSED MATTER, 23, DOI: 10.1088/0953-8984/23/47/475702
We report on the characterization of metallurgical phases and their magnetism at the interfaces of nanoscale MgB2/Fe layered structures. MgB2/Fe-57 multilayers with varying layer thicknesses were prepared by vacuum deposition and investigated, before and after annealing by electrical resistance measurements, x-ray diffraction and Fe-57 conversion-electron Mossbauer spectroscopy (CEMS) down to 5 K. Interfacial Fe-B phases, such as Fe2B, were identified by CEMS. A superparamagnetic-to-ferromagnetic transition is observed with increasing Fe-57 film thickness. Ultrahigh vacuum annealing at 500 degrees C of the multilayers leads to strong diffusion of Fe atoms into the boundary regions of the MgB2 layers. MgB2 in the as-grown multilayers is non-superconducting. Structural disorder and the effect of Fe interdiffusion contribute to the suppression of superconductivity in the MgB2 films of all the as-grown multilayers and the thinner annealed multilayers. However, an annealed MgB2/Fe-57/MgB2 trilayer with thicker (500 angstrom) MgB2 layers is observed to be superconducting with an onset temperature of 25 K. At 5 K, the annealed trilayer can be conceived as being strongly chemically modulated, consisting of two partially Fe-doped superconducting MgB2 layers separated by an interdiffused weakly magnetic Fe-B interlayer, which is characterized by a low hyperfine magnetic field B-hf of similar to 11 T. This chemically modulated layer structure of the trilayer after annealing was verified by Rutherford backscattering.
894. Substrate-target distance dependence of structural and optical properties in case of Pb(Zr,Ti)O-3 films obtained by pulsed laser deposition
Authors:
Galca, AC; Stancu, V; Husanu, MA; Dragoi, C; Gheorghe, NG; Trupina, L; Enculescu, M; Vasile, E
Published: MAR 1 2011, APPLIED SURFACE SCIENCE, 257, 5943, DOI: 10.1016/j.apsusc.2011.01.056
The paper presents the influence of pulsed laser deposition (PLD) parameters on the structural and optical properties of PZT thin films grown on platinum substrate. X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS) are used to determine the thin film properties. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are employed to get additional information. By changing the distance between target and substrate, different crystalline orientations of PZT are obtained. The thin film thickness and its roughness, as well as the refractive index are also influenced by the chosen distance. (C) 2011 Elsevier B.V. All rights reserved.
895. Stress-induced traps in multilayered structures
Authors:
Ciurea, ML; Lazanu, S; Stavarache, I; Lepadatu, AM; Iancu, V; Mitroi, MR; Nigmatullin, RR; Baleanu, CM
Published: JAN 1 2011, JOURNAL OF APPLIED PHYSICS, 109, DOI: 10.1063/1.3525582
The trap parameters of defects in Si/CaF2 multilayered structures were determined from the analysis of optical charging spectroscopy measurements. Two kinds of maxima were observed. Some of them were rather broad, corresponding to "normal" traps, while the others, very sharp, were attributed to stress-induced traps. A procedure of optimal linear smoothing the noisy experimental data has been developed and applied. This procedure is based on finding the minimal value of the relative error with respect to the value of the smoothing window. In order to obtain a better accuracy for the description of the trapping-detrapping process, a Gaussian temperature dependence of the capture cross-sections characterizing the stress-induced traps was introduced. Both the normal and the stress-induced traps have been characterized, including some previously considered as only noise features. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3525582]
896. CuS NANOPARTICLES OBTAINED IN PRESENCE OF ONE SURFACTANT
Authors:
Simonescu, CM; Capatina, C; Teodorescu, VS; Florea, G
In this study, copper sulfide CuS (covellite) was obtained, starting from the Cu(CH3COO)(2)center dot H2O and thiourea ((NH2CSNH2) system, and working in presence or absence of sodium-bis(2-ohylhexyl) sulfosuccinate (Na-AOT). Samples obtained from Cu(CH3COO)(2)center dot H2O:NH2CSNH2:Na-AOT system were deposited as thin films on the glass substrates. CuS samples obtained were characterized by X ray diffraction, IR spectroscopy, TEM transmission electron microscopy and SAED - selected area electron diffraction. The influence of surfactant on the shape and size of CuS (covellite) nanocrystals was established.
897. Shaping distinct magnetic interactions in molecular compounds
Authors:
Filoti, G; Bartolome, J; Palade, P; Prisecaru, I; Valsangiacom, C; Kuncser, V; Mindru, I; Patron, L
Published: APR 2011, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 323, 1053, DOI: 10.1016/j.jmmm.2010.12.002
Oxalates containing various 3d transitional elements and positive NH(4) or negative OH groups were newly synthesized. Each above-mentioned component has directly influenced the structure, the electronic or interaction properties, while some unexpected behaviors were revealed by various magnetic and Mossbauer measurements. The main magnetic parameters, the long-range anti-ferromagnetic couplings observed at very low temperature and, particularly the uncompensated moment are discussed in detail. The induced lower spin states for bivalent ions and especially the anti-parallel arrangement of the spins belonging to trivalent and bivalent iron inside the molecule are also emphasized. (C) 2010 Elsevier B.V. All rights reserved.
898. Combination of Ag Substrate Decoration with Introduction of BaZrO3 Nano-Inclusions for Enhancing Critical Current Density of YBa2Cu3O7 Films
Authors:
Dang, VS; Mikheenko, P; Sarkar, A; Kechik, MMA; Abell, JS; Paturi, P; Huhtinen, H; Crisan, A
Published: JAN 2011, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 24, 509, DOI: 10.1007/s10948-010-0981-8
The combination of two methods: Ag substrate decoration and introduction of BZO nano-inclusions has been used in a pulsed laser deposition (PLD) method to increase the critical density (J (c) ) of YBCO films. The films were deposited on single crystal SrTiO3 (STO) substrates decorated with various architecture of Ag nano-dots. We have studied the diameter and density of Ag nano-dots and their influence on J (c) of BZO-added YBCO films. We found that 15 laser pulses on the Ag target gives an optimum result in increasing J (c) in comparison with BZO-doped YBCO films of the same thickness in self-field and low applied magnetic fields. A higher number of laser pulses on the Ag target led to increasing critical current density in high applied magnetic fields only (above 2 T). We have studied films of the thickness from 0.4 mu m to 3.8 mu m and found that the highest J (c) at all applied fields investigated is achieved for a 1.2 mu m thick film. The transmission electron microscopy clearly shows BZO nano-rods that provide strong c-axis pinning centres in the films.
899. Grain growth, microstructure and surface modification of textured CeO2 thin films on Ni substrate
Authors:
Mihalache, V; Pasuk, I
Published: JUL 2011, ACTA MATERIALIA, 59, 4885, DOI: 10.1016/j.actamat.2011.04.029
CeO2 films were prepared from solutions of different concentrations (0.05-1.0 M) on textured Ni substrates. Homogeneous nucleation and growth of CeO2 nanocrystals <8 nm occurs upon calcination at 350-500 degrees C. At the heating and sintering stage, the homogeneous growth is inhibited in favor of the development of grains with (0 0 1) texture. The grain growth normal to the film surface is well described by a stretched exponential function with a relaxation time of up to 60 min and with Kohlrausch exponent values of less than unity. The increase in grain size is accompanied by the relaxation of the microstrain. During the relaxation time, the grain coarsening is controlled by surface diffusion characterized by an activation energy as low as 0.6 eV. At the relaxation time, the surface morphology is strongly concentration dependent. The surface morphology changes from separated (agglomerated) grains to a continuous grain configuration as the concentration increases from 0.05 M to 0.8 M. After the relaxation time, both the grain size normal to the film surface and the lateral grain size continue to grow, and the grain configuration continues to change. These processes are concentration dependent. In the films with a nominal thickness >170 nm (>0.8 M), the transition to classical curvature-driven grain-growth kinetics is evident (at 1000 degrees C, below the literature value of 1100 degrees C). The decrease in the Kohlrausch exponent for these thick films suggests that the grain coarsening through grain boundary migration is responsible for the stretched regime of grain-size relaxation. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
900. Martensitic transformation of Ti50Ni30Cu20 alloy prepared by powder metallurgy
Authors:
Valeanu, M; Lucaci, M; Crisan, AD; Sofronie, M; Leonat, L; Kuncser, V
Published: MAR 31 2011, JOURNAL OF ALLOYS AND COMPOUNDS, 509, 4498, DOI: 10.1016/j.jallcom.2011.01.154
Phase transformation behavior of Ti50Ni30Cu20 shape memory alloys prepared by powder metallurgy is analyzed with respect to the duration of mechanical alloying. The processed blends were studied by differential scanning calorimetry and room temperature X-ray diffraction. The martensitic transformations evidenced by thermal scans are discussed in correlation with the relative phase content obtained from the refinement of the X-ray diffraction patterns. (c) 2011 Elsevier B.V. All rights reserved.
901. Parametric studies on iron-carbon composite nanoparticles synthesized by laser pyrolysis for increased passivation and high iron content
Authors:
Dumitrache, F; Morjan, I; Fleaca, C; Birjega, R; Vasile, E; Kuncser, V; Alexandrescu, R
Published: APR 1 2011, APPLIED SURFACE SCIENCE, 257, 5269, DOI: 10.1016/j.apsusc.2010.11.069
Iron/iron carbide core and carbon shell nanoparticles with improved magnetic properties were successfully synthesized by laser pyrolysis. As iron and carbon precursors, iron pentacarbonyl and pure or argon-diluted acetylene/ethylene mixtures, respectively, were used. The aim of the present optimization is the improvement of the magnetic properties of the nanomaterials by the increase of the iron percent in powders simultaneously to the maintaining of the protective character of the carbon coverage of nanoparticles. The chemical content and the crystalline structure were monitored by EDX, XRD and TEM techniques. In the first study, the content of acetylene as carbon source was diminished from 75% to 0%. Consequently the percent iron increased from 10 at.% to 28 at.% while oxygen remained relatively constant (around 5 at.%). In the second step, only diluted ethylene was used (maximum 87.5 vol.% Ar). In this case, an increase of iron to 46 at.% is observed. An optimum 50% carbon source dilution was found. Above this value, the carbon content increases and below it, superficial oxidation increases through the diminishing of the carbon shell. The magnetic properties and the Fe phase composition of the Fe-C samples were analyzed by temperature dependent Mossbauer spectroscopy. (C) 2010 Elsevier B.V. All rights reserved.
902. Benzylation of benzene with benzyl alcohol on zeolite catalysts
Authors:
Candu, N; Florea, M; Coman, SM; Parvulescu, VI
Published: FEB 15 2011, , DOI: 10.1016/j.apcata.2010.11.044
903. The integral magneto-refractive effect: A method of probing magneto-resistance
Authors:
Vopsaroiu, M; Cain, MG; Kuncser, V
Published: SEP 1 2011, JOURNAL OF APPLIED PHYSICS, 110, DOI: 10.1063/1.3631778
We show that the optical infrared magneto-refractive effect can be used to probe magneto-resistance effects in absolute terms. A spin valve sample with synthetic anti-ferromagnet has been studied using non-contact infrared reflection spectroscopy measurements. Direct experimental comparison shows excellent agreement between electrical and optical measurements in both shape of the magneto-resistance curves and absolute values. This opens the possibility of developing fast and efficient tests of magneto-resistive samples and sensors using an in situ, non-contact, non-destructive optical approach, without the need to determine a calibration factor between the electrical and optical measurements. [doi:10.1063/1.3631778]
904. Calculation of the quantum efficiency for the absorption on confinement levels in quantum dots
Authors:
Iancu, V; Mitroi, MR; Lepadatu, AM; Stavarache, I; Ciurea, ML
Published: APR 2011, JOURNAL OF NANOPARTICLE RESEARCH, 13, 1612, DOI: 10.1007/s11051-010-9913-6
The quantum efficiency of the absorption on quantum confinement levels is investigated. This is achieved by modeling the electron confinement in a spherical quantum dot (QD). The confinement levels are calculated using both infinite and finite rectangular quantum wells. The spectral internal quantum efficiency is evaluated within both the models, by computing Einstein's coefficients for the transitions between confinement levels. The size of QDs (1-3 nm radius) leads to negligible many body effects. The nature of the QD material and of the matrix embedding is taken into account in the finite rectangular quantum well approximation and introduces only a small correction. The temperature dependence of the efficiency is also taken into account. A numerical application is performed for a silicon QD of 2.5 nm radius, embedded in amorphous silica. It is proved that the absorption threshold shifts toward the far infrared limit and that the spectral internal quantum efficiency reaches 4-5% at the threshold.
905. Stability Characterization of Quinazoline Derivative BG1188 by Optical Methods
Authors:
Militaru, A; Smarandache, A; Mahamoud, A; Damian, V; Ganea, P; Alibert, S; Pages, JM; Pascu, ML
Published: 2011, ADVANCES IN LASEROLOGY - SELECTED PAPERS OF LASER FLORENCE 2010: THE 50TH BIRTHDAY OF LASER MEDICINE WORLD, 1364, 23, DOI: 10.1063/1.3626907
3-[2-(dimethylamino) ethyl]-6-nitroquinazolin-4(3H)-one, labeled BG1188, is a new synthesized compound, out of a series of quinazoline derivatives developed to fight the multidrug resistance of antibiotics acquired by bacteria. A characterization of the BG1188 powder was made using FTIR spectra in order to evidence the functional groups in the medicine's molecule. The ultraviolet-visible (UV-Vis) absorption spectra were used to study the stability of the BG1188 solutions in two solvents and at different temperatures. BG1188 concentration in ultrapure water was varied between 2x10(-3)M (stock solution) and 10(-6)M. The concentration recommended by higher activity on bacteria was 10(-3)M. For the same reason, this was the utilized concentration of BG1188 in dimethyl sulfoxide (DMSO). Time stability was characterized by comparing the time evolution of the UV-Vis absorption spectra of the BG1188 solutions in ultrapure deionized water or in DMSO. The spectra were recorded daily for about 4 months after the preparation for the BG1188 solutions in ultrapure water. Generally, samples are stable within the experimental errors at concentrations higher than 10(-5)M, but the stability time interval may vary from 119 days at 10(-4)M to 34 days at 10-5M. Time evolution of the absorption spectra at 10-3M in ultrapure water shows reproducibility within the measuring errors (+/- 1.045%) for time intervals up to 1032 hours (more than 40 days) after preparation. On the other hand, BG1188 solutions in DMSO may be considered unstable because the absorption spectra modify in terms of peak shapes and intensities, indicating that the samples exhibit modifications immediately after preparation. Regardless the solvent used, some aggregation phenomena took place and wire-like aggregates were observed in all the solutions with the naked eye. These aggregates were analyzed, tentatively, using optical microscopy and FTIR.
906. THE EFFECT OF HYDROGENATION ON THE MAGNETIC PROPERTIES OF LAYERED SPIN VALVE STRUCTURES
Authors:
Kuncser, V; Tolea, F; Schinteie, G; Jepu, I; Palade, P
Published: JAN-MAR 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 206, DOI:
Multilayer spin valve structures of type AF/F/Cu/F and AF/F/MgO/F (AF=antiferromagnetic layer and F=ferromagnetic layer) have been prepared by sputtering in radiofrequence. The samples were investigated at room temperature by magneto-optic Kerr effect and conversion electron Mossbauer spectroscopy, before and after thermal hydrogenation. Additional magnetic peculiarities were observed at low temperatures via SQUID magnetometry. The effect of the thermal hydrogenation on the magnetic properties of the systems was discussed with respect to the changes in the local spin configuration, observed by Mssbauer spectroscopy.
907. TAILORING OF OPTICAL, COMPOSITIONAL AND ELECTRICAL PROPERTIES OF THE InxZn1-xO THIN FILMS OBTAINED BY COMBINATORIAL PULSED LASER DEPOSITION
Authors:
Socol, G; Galca, AC; Luculescu, CR; Stanculescu, A; Socol, M; Stefan, N; Axente, E; Duta, L; Mihailescu, CM; Craciun, V; Craciun, D; Sava, V; Mihailescu, IN
Published: JAN-MAR 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 115, DOI:
Indium Zinc Oxide compositional libraries were fabricated by combinatorial pulsed laser deposition technique on glass substrate at room temperature. Two pairs of targets with In atomic concentrations, In/(In+Zn), of 28 at.% and 56 at.% or 42 at.% and 70 at.% were employed. A high transparency was observed for all the coatings with transmittance values better than 95%. The maximum thicknesses of the samples, inferred by spectroscopic ellipsometry, were within the 174-310 nm range for the simple PLD films, whereas in case of combinatorial PLD coatings were 341 or 467 nm. Energy dispersive X-ray spectroscopy revealed that In content in the combinatorial films was in the 27-52 at. % range. From atomic force microscopy histograms we evidenced a decrease of the RMS roughness down to 1 nm with the increase of the In content. As a result of the compositional library studies two minimum values of the electrical resistivity were identified at 2.3x10(-3) Omega.cm and 8.6 x 10(-4) Omega.cm, which correspond to 28.8-29.5 at.% and 44-49 at% range of Indium content.
908. X-ray absorption fine structure investigations on heat-treated Cr-doped titania thin films
Authors:
Mardare, D; Nica, V; Pohoata, V; Macovei, D; Gheorghe, N; Luca, D; Teodorescu, CM
Published: DEC 1 2011, THIN SOLID FILMS, 520, 1352, DOI: 10.1016/j.tsf.2011.04.124
Chromium-doped titanium oxide thin films were investigated in the as-deposited state and after thermal treatment (723 K for 3 h in air). X-ray diffraction data revealed an improvement in film crystallinity induced by the thermal treatment. Extended X-ray absorption fine structure data revealed similar atomic neighboring around Cr atoms in both as-deposited and annealed samples. A lattice contraction of similar to 2% is observed in the annealed samples. The 67% enhancement of the amplitude of the Cr 1 s X-ray absorption fine structure pre-edge peak after thermal treatment, which is a sign of "dipole-forbidden" 1 s -> 3 d transitions, suggests strong alteration in the number of Cr 3 d vacancies, in spite of similar Cr local environment in the two kinds of investigated samples. We discuss here the Cr+ -> Cr4+ and Cr2+ -> Cr6+ changes induced by thermal treatment, and/or the evolution in local structures without inversion center. Refractive index dispersion spectra in the visible wavelength domain allowed us to compute the values of the dispersion energy, the single-oscillator energy and the coordination number of Ti atoms in both as-deposited and annealed samples. (C) 2011 Elsevier B. V. All rights reserved.
909. OPTICALLY INDUCED BIREFRINGENCE OF A p-AMINOAZOBENZENE-EPDXY RESIN DERIVATIVE
Authors:
Beica, T; Zgura, I; Frunza, L; Ganea, P; Frunza, S; Dumitrache, L; Raditoiu, V; Wagner, L
A derivative of p-aminoazobenzene-epoxy resin was studied. Visually examination between crossed polarizers does not show birefringence but it can be optically induced. Changing the polarization direction of the irradiating light leads to the changing of the privileged direction of the induced birefringence. The birefringence value was evaluated and compared with liquid crystals as anisotropic compounds.
910. (Ti,Cr,Nb)CN coatings deposited on nitrided high-speed steel by cathodic arc method
Authors:
Braic, M; Braic, V; Balaceanu, M; Vladescu, A; Zoita, CN; Lungu, CP; Grigorescu, CEA; Grigore, E; Logoftu, C
Published: JUL 25 2011, SURFACE & COATINGS TECHNOLOGY, 205, S213, DOI: 10.1016/j.surfcoat.2011.03.030
The combined processes of plasma nitriding and cathodic arc deposition of (Ti,Cr,Nb)CN coatings were applied to HSS substrates. The nitrided layers, obtained in a mixture of H-2 (70%) and N-2 (30%) at two different temperatures (480 degrees C and 510 degrees C), were examined for the microhardness depth profiles. Characterization of the duplex coatings was performed by investigating elemental and phase composition, texture, hardness, friction and wear. XRD and XPS analyses revealed the formation of a mixture of a carbonitride fcc solid solution, in a dominant proportion, and metallic chromium. The film hardness was measured to be similar to 34 GPa. The duplex (Ti,Cr,Nb)CN coatings exhibited superior tribological behavior as compared to both nitrided layers and non-duplex coatings. (C) 2011 Elsevier B.V. All rights reserved.
911. SIMULTANEOUSLY THERMIONIC VACUUM ARC DISCHARGES IN OBTAINING FERROMAGNETIC THIN FILMS
Authors:
Jepu, I; Porosnicu, C; Mustata, I; Lungu, CP; Kunkser, V; Osiac, M; Iacobescu, G; Ionescu, V; Tudor, T
High quality granular ferromagnetic thin films on glass and silicon wafer substrates were obtained using the original thermionic vacuum arc (TVA) method developed at National Institute for Laser, Plasma and Radiation Physics. We report obtaining of 77-200 nm thick Cu/Ni/Fe structures. An experimental set-up, with three simultaneously discharges, was made to obtain the desired thin film composition and thickness. The structural and morphological properties of the prepared nanostructured films were analyzed by AFM (Atomic Force Microscopy), XRD (X-ray Diffraction) and SEM (Scanning Electron Microscopy). Magneto-Optical Kerr Effect studies were made in order to infer the changes in polarization of an optical radiation due to the magnetic field influence. In order to obtain concluding electrical measurements results, cooper electrodes were deposited using the same method before and after the actual three material thin structures. In this way significant changes in the electrical resistance behavior were noticed and were correlated with TVA plasma parameters used for film preparation.
912. Synergetic Pinning Centers in YBa2Cu3OX Films Through a Combination of Ag Nano-Dot Substrate Decoration, Ag/YBCO Quasi-Multilayers, and the Use of BaZrO3-Doped Target
Authors:
Mikheenko, P; Dang, VS; Kechik, MMA; Sarkar, A; Paturi, P; Huhtinen, H; Abell, JS; Crisan, A
Published: JUN 2011, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 21, 3188, DOI: 10.1109/TASC.2010.2086041
We report on an original technique for nanoengineered pinning centers that combine three previously reported approaches: substrate decoration, quasi-multilayers and targets with secondary phase nanoinclusions. We have used a 4% BZO-doped YBCO target, and Ag nanodots, all grown by PLD. Such an approach gave interesting results in terms of pinning landscape, as proved by TEM studies. Angle-dependent measurements of critical current I-c showed that, for smaller fields, the absolute maximum in I-c occur for fields perpendicular to the a-b planes, while at larger fields the absolute maximum in I-c occurs for fields parallel to the a-b planes, in both cases with a clear second, local maxima. Measurements also showed a smooth change in the character of pinning with magnetic field, from the out-of-plane to in-plane-dominant pinning. For the out-of-plane magnetic field, the highest Ic-w (critical current per cm width) obtained so far, at 77.3 K, occurred in a 5.8 mu m Ag nanodots / BZO-doped YBCO trilayer: 782 A/cm-w in self-field, 167 A/cm-w in 1 T and 18 A/cm-w in 3 T.
913. Dielectric and Ferroelectric Characterization of Ba0.95Tm0.05TiO3 Ceramics Derived from Sol to Gel
Authors:
Cernea, M; Vasile, BS; Ganea, P; Radu, R; Mihalache, V; Husanu, A
Published: MAR 2011, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 94, 741, DOI: 10.1111/j.1551-2916.2010.04179.x
Barium titanate (BaTiO3) has been doped in situ with 5 mol% thulium by a sol-gel method. The as-prepared gel powder consists of nanosized grains (20-30 nm) and crystallizes on the cubic BaTiO3 lattice, at 700 degrees C. Ba0.95Tm0.05TiO3 ceramics derived from this powder have tetragonal perovskite structure and contain a small amount of Tm2Ti2O7 pyrochlore phase. These ceramics exhibit dielectric constants of 4282-3240 and dielectric loss (tan delta) of 0.1077-0.0161 at Curie temperature T-c=132 degrees C and at 10 Hz-100 kHz, respectively. For a drive voltage of 400 V, the hysteresis loop recorded at the frequency of 100 Hz shows a remnant polarization (P-r) value of 76 mu C/cm2 and a coercive field (E-c) of 124 V and for 1 kHz a remnant polarization (P-r) value of 58 mu C/cm2 and a coercive field (E-c) of 116 V.
914. Magnetic nanoparticles coated with polysaccharide polymers for potential biomedical applications
Authors:
Covaliu, CI; Berger, D; Matei, C; Diamandescu, L; Vasile, E; Cristea, C; Ionita, V; Iovu, H
Published: NOV 2011, JOURNAL OF NANOPARTICLE RESEARCH, 13, 6180, DOI: 10.1007/s11051-011-0452-6
This study reports a two-steps route for obtaining magnetic nanoparticles-polysaccharide hybrid materials consisting of Fe3O4, NiFe2O4 and CuFe2O4 nanoparticles synthesis by coprecipitation method in the presence of a soft template followed by coating of ferrite nanoparticles of 8-10-nm size range with polysaccharide type polymers-sodium alginate or chitosan. Magnetic oxide nanoparticles and the corresponding hybrid materials were characterized by X-ray diffraction (XRD), Mossbauer spectroscopy, atomic absorption spectroscopy (AAS), FTIR spectroscopy, scanning and transmission electron microscopy (SEM and TEM) and specific surface area measurements. The vibrating sample magnetometry confirms the superparamagnetic properties of the synthesized ferrites and hybrids. Using this route, the percent of magnetic nanoparticles retained in chitosan-based hybrid materials is nearly double in comparison with that of sodium alginate-based materials. The biological activity tests on Escherichia coli ATCC 25922, Pseudomonas aeroginosa ATCC 27853, Staphylococcus aureus ATCC 25923 and Candida scotti microorganisms show the non-toxic properties of prepared hybrid materials.
915. Tailoring immobilization of immunoglobulin by excimer laser for biosensor applications
Authors:
Sima, F; Axente, E; Ristoscu, C; Mihailescu, IN; Kononenko, TV; Nagovitsin, IA; Chudinova, G; Konov, VI; Socol, M; Enculescu, I; Sima, LE; Petrescu, SM
Published: FEB 2011, JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 96A, 394, DOI: 10.1002/jbm.a.32991
The sheltered transfer and immobilization of rabbit anti-human antiserum immunoglobulin G (IgG) by matrix-assisted pulsed laser evaporation (MAPLE) are reported. The iced targets submitted to laser irradiation consisted of 0.2-2 mg/mL IgG blended or not with lipid (L-a-phosphatidylcholine dipalmitoyl) dissolved in distilled water-based saline buffer. Thin IgG coatings were obtained at room temperature onto glass, fused silica, or silicon substrates. Ten thousand subsequent laser pulses of 0.33, 0.5, or 0.67 J/cm(2) fluence were applied for the synthesis of each sample. Morphology and composition of the thin films were studied by optical, scanning, and atomic force microscopy and Fourier transformed infrared spectrometry. Optical labeling methods such as spectrofluorimetry and fluorescence microscopy were selected to verify the biosensor transduction principle because of their high sensitivity for detecting low amounts of antigen (IgG). Protein immobilization to the substrate surface was demonstrated for all obtained structures after immersion in the donkey anti-rabbit secondary antibody solution. The IgG transfer and immobilization onto substrates were improved by addition of lipid to MAPLE solutions. (C) 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 96A: 384-394, 2011.
916. Spectroscopic Analysis of the Interstitial Anions in Some Layered Double Hydroxide Materials
Authors:
Frunza, L; Gheorghe, N; Iova, F; Ganea, P; Neatu, F; Parvulescu, VI
Layered double hydroxide materials with Zn2+ and Mg2+ as bivalent cations and Al3+ and Ga3+ as trivalent cations were studied. The anions to balance the positive charge of the network were carbonate and/or nitrate. The samples were prepared in laboratory and routinely characterized. Here the investigations by Fourier transform infrared spectra and thermogravimetric measurements are detailed. On the basis of calibration curves for carbonate and nitrate ions obtained from IR spectra of the corresponding salts, the sample analysis of the interlayer anions was performed quantitatively.
917. Electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride
Authors:
Stavarache, I; Lepadatu, AM; Teodorescu, VS; Ciurea, ML; Iancu, V; Dragoman, M; Konstantinidis, G; Buiculescu, R
Published: 2011, NANOSCALE RESEARCH LETTERS, 6, DOI: 10.1186/1556-276X-6-88
The electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride is studied by measuring the voltage and temperature dependences of the current. The microstructure of the network is investigated by cross-sectional transmission electron microscopy. The multi-walled carbon nanotube network has an uniform spatial extension in the silicon nitride matrix. The current-voltage and resistance-temperature characteristics are both linear, proving the metallic behavior of the network. The I-V curves present oscillations that are further analyzed by computing the conductance-voltage characteristics. The conductance presents minima and maxima that appear at the same voltage for both bias polarities, at both 20 and 298 K, and that are not periodic. These oscillations are interpreted as due to percolation processes. The voltage percolation thresholds are identified with the conductance minima.
918. Unusual Behavior of a Novel Heterogeneous Chiral Dimer Cr(III)-Salen Complex in the Epoxidation/Epoxide Ring-Opening Reaction of trans-Methylcinnamate Ester
Authors:
Protesescu, L; Tudorache, M; Neatu, S; Grecu, MN; Kemnitz, E; Filip, P; Parvulescu, VI; Coman, SM
Published: FEB 3 2011, JOURNAL OF PHYSICAL CHEMISTRY C, 115, 1122, DOI: 10.1021/jp106281z
A dimer chromium(III)-salen complex immobilized on modified silica is an effective catalyst for the epoxidation/epoxide ring-opening reaction of trans-methylcinnamate ester and gave significantly high ee in methyl (2R,3S)-2,3-dihydroxy-3-phenylpropionate. For the first time, it is shown that a donor ligand (e.g., Et3N) can be involved into the enantioselective mechanism of the product configuration. It is suggested that the additive is interacting with the reaction intermediate in a manner that prolongs its lifetime, thus affording a free rotation of the C-C single bond in this species and a selective collapse to the cis-epoxide product. In the presence of water, this epoxide led to methyl (2S,3R)-2,3-dihydroxy-3-phenylpropionate. Alternatively, the donor additives may give rise to a new chromium-based oxidant that effects epoxidation and its consecutive ring opening to diols via an unusual pathway.
919. Bean-Livingston surface barriers for flux penetration in Bi2Sr2CaCu2O8+delta single crystals near the transition temperature
Authors:
Mihalache, V; Dede, M; Oral, A; Miu, L
Published: OCT 2011, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 471, 565, DOI: 10.1016/j.physc.2011.04.015
The first field for magnetic flux penetration H in Bi2Sr2CaCu2O8+delta (Bi-2212) single crystals near the critical temperature T-c was investigated from the local magnetic hysteresis loops registered for different magnetic field H sweeping rates by using a scanning Hall probe microscope (SHPM) with similar to 1 mu m effective spatial resolution. Evidences for a significant role of the surface barrier were obtained: the asymmetric shape of the magnetization loops and an anomalous change in the slope of H-p(T) close to T-c. (C) 2011 Elsevier B.V. All rights reserved.
920. Optical and structural investigations on iron-containing phosphate glasses
Authors:
Elisa, M; Iordanescu, R; Sava, BA; Aldica, G; Kuncser, V; Valsangiacom, C; Schinteie, G; Nastase, F; Nastase, C; Bercu, V; Volceanov, A; Peretz, S
Published: MAR 2011, JOURNAL OF MATERIALS SCIENCE, 46, 1570, DOI: 10.1007/s10853-010-4963-9
The article reports the preparation and complex characterization of iron-containing phosphate glasses considered to be ecological materials, as they contain nontoxic compounds related to environment. The oxide system Li2O-MgO-(CaO)-Al2O3-P2O5-(FeO/Fe2O3) was investigated in respect to its structural changes caused by MgO replacement with CaO and by the iron addition. UV-vis-NIR (ultraviolet-visible-near infrared) spectroscopy as well as thermo-gravimetric (TG) measurements, differential thermo-analysis (DTA), X-ray diffraction (XRD) analysis, electronic paramagnetic resonance (EPR), and Mossbauer (nuclear gamma resonance) spectroscopy have been used to investigate redox states and coordination symmetry of iron, together with vitreous network changes during the heat treatment up to 1000 degrees C. UV-vis-NIR transmission spectroscopy revealed no structural modifications when MgO was substituted by CaO, but noteworthy absorption bands attributed to Fe2+/Fe3+ species. TG analysis made in the 20-1000 degrees C range shows low weight loss accompanied by several thermal effects, as evidenced by DTA. XRD patterns for the glass samples heat treated at about 700 degrees C revealed the presence of different phosphate crystalline phases containing Mg, Al, and Fe ions. EPR spectroscopy revealed the presence of paramagnetic Fe3+ ions and the change of the first coordination symmetry, when the samples are heated below the vitreous transition temperature. Mossbauer spectroscopy has evidenced two paramagnetic species, Fe2+ and Fe3+, both in octahedral coordination symmetry and a clustering process supported by only Fe3+ ions.
921. Efficient dual functionality of highly porous nanocomposites based on TiO2 and noble metal particles
Authors:
Baia, L; Diamandescu, L; Barbu-Tudoran, L; Peter, A; Melinte, G; Danciu, V; Baia, M
Published: FEB 10 2011, JOURNAL OF ALLOYS AND COMPOUNDS, 509, 2678, DOI: 10.1016/j.jallcom.2010.11.154
Porous nanocomposites based on TiO2 aerogels and Au and, respectively, Ag particles were synthesized and their dual functionality to decontaminate water, via photocatalysis, and to detect low concentrations of pollutants from water, via SERS technique, was evaluated using model pollutants. The apparent photodegradation rate constants of a standard pollutant molecule revealed a considerable improvement of the composites photocatalytic performances (even better than one order of magnitude) in comparison with the commercial product Degussa P25. The essential role of the contact between TiO2 and Au nanoparticles was demonstrated and the potential of all synthesized porous composites for photocatalytic experiments with visible light was pointed out. The lowest concentrations of contaminants adsorbed on the noble metal particles detectable by SEAS were found to depend on the composite and pollutant species type and were determined to be between 10(-3) and 5 x 10(-6) M, and 10(-8) and 10(-10) M for off and under resonant excitation, respectively. The morphological (BET, pore size distribution, TEM) and structural (Raman, XRD, diffuse reflectance) particularities of the obtained porous composites were also discussed. (C) 2010 Elsevier B.V. All rights reserved.
922. Nano Techniques for Enhancing Critical Current in Superconducting YBCO Films
Authors:
Mikheenko, P; Dang, VS; Kechik, MMA; Wang, Y; Sarkar, A; Tanner, JL; Abell, JS; Crisan, A
Published: JAN 2011, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 24, 1064, DOI: 10.1007/s10948-010-0861-2
A range of nano techniques is explored in order to increase the critical current in pulsed laser deposited (PLD) superconducting YBa2Cu3O (x) (YBCO) thin films. The structural measurements are linked with magnetic and transport measurements of the films. The effectiveness of PLD techniques is analyzed from the point of view of the dimensionality of nanostructures formed prior to and during the film growth. It is shown that a combination of two-dimensional substrate decoration with nanoparticles before the film deposition and one-dimensional growth of external phase nanorods during the deposition offers a high critical current in magnetic field both along the c-axis and in the ab-plane of YBCO.
923. Recent developments in the formation and structure of tin-iron oxides by laser pyrolysis
Authors:
Alexandrescu, R; Morjan, I; Dumitrache, F; Birjega, R; Fleaca, C; Soare, I; Gavrila, L; Luculescu, C; Prodan, G; Kuncser, V; Filoti, G
Published: APR 1 2011, APPLIED SURFACE SCIENCE, 257, 5464, DOI: 10.1016/j.apsusc.2010.11.114
Complex oxides demonstrate specific electric and magnetic properties which make them suitable for a wide variety of applications, including dilute magnetic semiconductors for spin electronics. A tin-iron oxide Sn(1-x)FexO(2) nanoparticulate material has been successfully synthesized by using the laser pyrolysis of tetramethyl tin-iron pentacarbonyl-air mixtures. Fe doping of SnO2 nanoparticles has been varied systematically in the 3-10 at% range. As determined by EDAX, the Fe/Sn ratio (in at%) in powders varied between 0.14 and 0.64. XRD studies of Sn(1-x)FexO(2) nanoscale powders, revealed only structurally modified SnO2 due to the incorporation of Fe into the lattice mainly by substitutional changes. The substitution of Fe3+ in the Sn4+ positions (Fe3+ has smaller ionic radius as compared to the ionic radius of 0.69 angstrom for Sn4+) with the formation of a mixed oxide Sn1-xFexO(2) is suggested. A lattice contraction consistent with the determined Fe/Sn atomic ratios was observed. The nanoparticle size decreases with the Fe doping (about 7 nm for the highest Fe content). Temperature dependent 57Fe Mossbauer spectroscopy data point to the additional presence of defected Fe3+-based oxide nanoclusters with blocking temperatures below 60 K. A new Fe phase presenting magnetic order at substantially higher temperatures was evidenced and assigned to a new type of magnetism relating to the dispersed Fe ions into the SnO2 matrix. (C) 2010 Elsevier B.V. All rights reserved.
924. Current enhancement and negative differential conductance in parallel quantum dot systems
Authors:
Tanatar, B; Moldoveanu, V
Published: 2011, PHYSICS OF SEMICONDUCTORS: 30TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, 1399, DOI: 10.1063/1.3666366
We present calculations on the transport properties of a double quantum dot (DQD) capacitively coupled to another individually biased dot. The effects of the intradot and interdot Coulomb interaction are included within the random-phase approximation (RPA) implemented in the Keldysh formalism. We show that by increasing the bias on the nearby dot the inelastic Coulomb scattering modifies the current in the double dot. The sign of the current depends on the detuning of the double dot levels and intradot transitions lead to negative differential conductance. The enhancement of the current due to the energy quanta transferred from the strongly biased dot suggests a quantum ratchet or Coulomb drag mechanism.
925. Fabrication and Superconducting Properties of MgB2 Doped With Polysiloxane Based Copolymers
Authors:
Sandu, V; Cimpoiasu, E; Aldica, G; Popa, S; Sandu, E; Hurduc, N; Nor, I
Published: JUN 2011, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 21, 2634, DOI: 10.1109/TASC.2010.2078434
We present the fabrication and the superconducting properties of MgB2 ceramic samples doped with carbon via preceramic polymers: linear and cyclic polysiloxane-co-styrene and linear polysiloxane-co-vinyl-ferrocene. The samples were produced using the spark plasma sintering technique. The use of polysiloxane copolymers was suggested by the appropriate content of carbon, silicon, and oxygen which are necessary to increase the upper critical field and to create pinning centers. The short processing time limits the diffusion length of the chemical elements from the polymer into the superconducting grains. Therefore, in addition to doping with carbon, the rest of the components create pinning centers along the polymeric chain, able to better pin the flux lines. The copolymerization allowed us to obtain both linear and cyclic copolymers as well as to control the content of chemical elements, including the presence of small amounts of iron oxides. The latter are responsible for magnetic pinning.
926. PROPERTIES OF RARE EARTH Ga-La-S GLASSES OBTAINED BY RF INDUCTOR HEATING
Authors:
Popescu, AA; Savastru, D; Miclos, S; Braic, V; Popescu, M; Manea, A; Kiss, A
Published: APR-JUN 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 348, DOI:
A new synthesis method for 70Ga(2)S(3)30La(2)S(3) (GLS) lanthanum based glass, which uses a RF-heating inductor, has been developed. The method gives the possibility to quench the melt without taking the crucible out of the reaction chamber. Glasses with good optical quality were obtained. The samples characterized by X-ray diffraction prove the amorphous state. The re-heating of GaLaS at temperatures of 620 degrees C leads to the appearance of large 30-80 mu m crystals, Ga3La1.66S7 structure being the main crystal form. High quality GLS thin films have been obtained by RF sputtering. The calculated refractive index was 2.48 for the thin films obtained by RF sputtering and 2.55 for bulk samples. Two kinds of the Urbach-density of state distribution are distinguished from optical transmission measurements corresponding to activation energies of 0.12 eV and 0.66 eV.
927. One-pot synthesis of an unusual manganese-lanthanide-ferrocene cluster: A combination of d-, f-metals and an organometallic fragment
Authors:
Mereacre, V; Ako, AM; Filoti, G; Bartolome, J; Anson, CE; Powell, AK
Published: JAN 13 2010, POLYHEDRON, 29, 247, DOI: 10.1016/j.poly.2009.07.046
Reaction of the preformed cluster [Mn6O2(Piv)(10)(4-Me-py)(2.5)(PivH)(1.5)] with Nd(NO3)(3)center dot 6H(2)O, N-butyldiethanolamine (bdeaH(2)) and ferrocene-1,1'-dicarboxylic acid (fcdcH(2)) resulted in the formation of the first 3d-4f complex incorporating organometallic ferrocene [Mn4Nd4(OH)(4)(fcdc)(2)(Piv)(8)(bdea)(4)]center dot H2O; we report the X-ray structure and preliminary magnetic studies of this high-nuclearity cluster. (C) 2009 Elsevier Ltd. All rights reserved.
928. BINARY VANADIUM-CERIUM OXIDE NANOPOWDERS OBTAINED BY SOFT CHEMISTRY
Authors:
Zaharescu, M; Todan, L; Predoana, L; Atkinson, I; Rusu, A; Andronescu, C; Teodorescu, V; Osiceanu, P
Published: NOV-DEC 2010, REVUE ROUMAINE DE CHIMIE, 55, +, DOI:
Vanadium-cerium oxide gels and films obtained by the sot-gel method have been widely studied, due to their catalytic, electrochemical, electronic and ionic properties, a result of their ability to form combinations in more than one valence state. V-Ce oxide powders were synthesized by wet chemical methods, in the presence and absence of polyols. The preparation of an aqueous dispersion of mixed vanadium oxide/CeO2 started from a solution of the corresponding metal oxide and metal salt, V2O5 and Ce(NH4)(NO3)(6), respectively. The powders were characterized by IR-spectroscopy, X-ray photoelectronic spectroscopy, X-ray diffraction, electronic microscopy (TEM, SAED, HRTEM). The influence of the ratio of the components (V/Ce) and of the polyol complexation agent on the structure and morphology of the obtained binary oxide powders was established.
929. Self-assembled artificial pinning centres in thick YBCO superconducting films
Authors:
Mikheenko, P; Abell, JS; Sarkar, A; Dang, VS; Kechik, MMA; Tanner, JL; Paturi, P; Huhtinen, H; Babu, NH; Cardwell, DA; Crisan, A
Published: 2010, 9TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS 09), 234, DOI: 10.1088/1742-6596/234/2/022022
Strong, artificial pinning centres are required in superconducting films of large thickness for power applications in high magnetic fields. One of the methods for the introduction of pinning centres in such films is substrate decoration, i.e., growing nanoscale islands of certain materials on the substrate prior to the deposition of the superconducting film. Two other methods are building up a layered distribution of a second phase and homogeneous incorporation of second phase inclusions from a compositional target. In this paper, we compare the effectiveness of these methods in terms of the type of the self-assembly of nanoparticles. The comparison is made over a large set of YBa2Cu3O7 films of thickness up to 6.6 mu m deposited with Au, Ag, Pd, LaNiO3, PrBa2Cu3O7, YBCO, BaZrO3 and Gd2Ba4CuWOy nanoparticles. It is found that substrate-decoration self-assembly is able to provide higher critical current in low magnetic field than the incorporation of homogeneous second phase in the sample microstructure. By specific modification of substrate decoration we achieved the self-field critical current per centimetre of width of 896 A/cm at 77.3 K and 1620 A/cm at 65 K in a film of thickness of 4.8 mu m.
930. Investigation of microstructural properties of nitrogen doped ZnO thin films formed by magnetron sputtering on silicon substrate
Authors:
Nicolescu, M; Anastasescu, M; Preda, S; Calderon-Moreno, JM; Osiceanu, P; Gartner, M; Teodorescu, VS; Maraloiu, AV; Kampylafka, V; Aperathitis, E; Modreanu, M
Published: MAY 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 1051, DOI:
Zinc oxide (ZnO) is a semiconductor with a wurtzite-type structure, useful for a variety of optical, optoelectronic and piezoelectric applications. We report here on the post deposition treatment (Rapid Thermal Annealing at 400 and 550 degrees C) impact on the microstructural properties of N-doped ZnO (ZnO:N) thin films grown on silicon substrate by r.f. magnetron sputtering of ZnN target. The ZnO:N films have been characterized by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning (SEM) and Transmission (TEM) Electron Microscopy coupled with Energy Dispersive X-ray (EDX) and Selected Area Electron Diffraction (SAED) respectively and Fourier Transform Infrared (FTIR) Spectroscopy. XRD confirms that ZnO:N films are polycrystalline in the as deposited state. SEM, TEM and XRD measurements revealed a polycrystalline film with preferentially oriented columnar crystals. AFM studies reveal a drastic change of ZnO surface morphology upon RTA and the existence of areas with different roughness in the sample thermally treated at 400 degrees C. FTIR, XRD and TEM results shows that disorder associated mainly with grain boundary defects decreases as the annealing temperature increases.
931. Magnetic properties of Fe-Co ferromagnetic layers and Fe-Mn/Fe-Co bilayers obtained by thermo-ionic vacuum arc
Authors:
Kuncser, V; Schinteie, G; Palade, P; Jepu, I; Mustata, I; Lungu, CP; Miculescu, F; Filoti, G
Published: JUN 4 2010, JOURNAL OF ALLOYS AND COMPOUNDS, 499, 29, DOI: 10.1016/j.jallcom.2010.03.129
Simple Fe-Co ferromagnetic films and Fe-Mn antiferromagnetic films of different compositions were grown on epitaxial Si substrates with Ta buffer layers via thermo-ionic vacuum arc method. Fe-Co/Fe-Mn bilayer structures were obtained by following similar growing conditions as for the simple films. The magnetic behavior concerning easy axis distribution, anisotropy energy and coercive field of the Fe-Co films exchange coupled to the antiferromagnetic layers were discussed with respect to the magnetic behavior of the simple, uncoupled, ferromagnetic films. The composition of the antiferromagnetic films has a sensible influence on the magnetic parameters of the exchange coupled ferromagnetic films. The largest coupling and the narrowest easy axis distribution are induced in the bilayer system with equatomic composition of the Fe-Mn antiferromagnetic layer. (C) 2010 Elsevier B.V. All rights reserved.
932. Magnetic Nanocomposites for Permanent Magnets
Authors:
Tolea, F; Sofronie, M; Birsan, A; Schinteie, G; Kuncser, V; Valeanu, M
Published: 2010, TRENDS IN NANOPHYSICS: THEORY, EXPERIMENT AND TECHNOLOGY, 296, DOI: 10.1007/978-3-642-12070-1_12
The influence of different crystallization conditions on the microstructure and magnetic hardening of RE-Fe-B amorphous ribbons with different Fe concentrations and Pr and Nd as rare earth elements was analyzed. The microalloying effects of Zr and Ti substitution on the evolution of crystallization process and the magnetic hardening was also discussed. The final aim of this experimental study was to obtain performing exchange spring magnets with as much as lower content of the expensive RE material.
933. COLUMN STUDY OF CADMIUM ADSORPTION ONTO POLYACRYLONITRILE/HYDROXYAPATITE COMPOSITE BEAD
Authors:
Wang, X; Min, BG; Lyoo, WS; Chihaia, V; Gartner, M; Stoica, TF; Bae, JY; Suh, SH
Published: AUG 2010, REVUE ROUMAINE DE CHIMIE, 55, 447, DOI:
Macroporous polyacrylonitrile/hydroxyapatite (PAN/HAp) composite bead was studied for cadmium removal in a fixed-bed column. The morphology of PAN/HAp composite bead was measured. The adsorption performance of PAN/HAp composite bead in the column was examined by varying bed height and HAp amount in PAN bead. The maximum adsorption capacity and the exhaustion time were determined from the breakthrough curves. Experimental data was described using the Adams-Bohart model. Bed height did not exert large influence on the maximum adsorption capacity and the exhaustion time. The kinetic rate constant and the adsorption capacity of the bed were found to be affected by the total HAp amount.
934. Films and crystalline powder of BiI3 intercalated with ammonia
Authors:
Preda, N; Mihut, L; Baibarac, M; Baltog, I; Pandele, J; Andronescu, C; Fruth, V
Published: JAN 2010, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 30, 479, DOI: 10.1016/j.jeurceramsoc.2009.05.046
Intercalation, i.e. the insertion of guest species in a crystalline layered structure, is an efficient route for generating new materials with novel properties. Thin films and crystalline powder of BiI3 layered semiconductor were intercalated by exposure to ammonia vapors at room temperature. The intercalated compound was studied by thermo-gravimetric analysis, differential scanning calorimetry, X-ray diffraction, UV-vis optical absorption, FTIR spectroscopy and Raman scattering. After exposure of BiI3 to ammonia the formation of a new phase, BiI3(NH3)(3.83), was evidenced by thermal analysis. The intercalation process leads to a blue shift of the BiI3 Optical absorption edge by 0.5 eV. The appearance of new Raman lines at 135 and 353 cm(-1) in the Raman spectrum of intercalated BiI3 is considered as an evidence of the chemical interaction between the ammonia molecules and BiI3 lattice. (C) 2009 Elsevier Ltd. All rights reserved.
935. EFFECTS OF PROTON IRRADIATION ON THE SPECTRAL PERFORMANCE OF PHOTOVOLTAIC CELLS BASED ON CdS/CdTe THIN FILMS
Authors:
Ion, L; Enculescu, I; Iftimie, S; Ghenescu, V; Tazlaoanu, C; Besleaga, C; Mitran, TL; Antohe, VA; Gugiu, MM; Antohe, S
Due to their physical and chemical properties (such as suitable band gaps, large absorption coefficients and good chemical stability) CdTe thin films are interesting for electronic and optoelectronic devices, including particularly photovoltaic cells for space technology. For that specific application, it is of prime importance to study in this type of materials the influence of ionizing radiations on their physical (structural, electrical and optical) properties. In this paper, the photovoltaic cells based on CdS/CdTe thin films, produced by thermal vacuum sublimation, were irradiated with 3 MeV protons at room temperature. The effects of irradiation were studied by investigating the changes in the electrical and optical properties of the cells. It was found that proton irradiation in the above mentioned conditions results mainly in the introduction of defects at the CdS/CdTe interface. A discussion about the possible origin of those defects is given.
936. Pinning potential in thick PrBa2Cu3Ox/YBa2Cu3O7-delta quasi-multilayers
Authors:
Crisan, A; Dang, VS; Mikheenko, P; Tse, YY; Sarkar, A; Bowen, J; Abell, JS
Published: JAN 1 2010, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 470, 60, DOI: 10.1016/j.physc.2009.10.006
Using Pulsed Laser Deposition we have fabricated thick quasi-multilayers composed of incomplete layers of PrBa2Cu3Ox (PrBCO) nano-dots and layers of YBa2Cu3O7-delta (YBCO). The number of such sequences was between 2 and 6, with the thickness of individual YBCO layers between 565 and 885 rim, and total thickness between 1.13 and 5.31 mu m. For the thinner quasi-multilayer, DC magnetization studies showed an increase in the critical current density J(c) at all fields in comparison with a pure YBCO reference sample, while the thicker samples showed an increased J(c) only in high fields. We have also investigated the frequency dependence of J(c) from AC susceptibility studies and found that the pinning potential is well described by a logarithmic dependence on current density. Pinning potentials in PrBCO/YBCO quasi-multilayers also proved to be higher than in the reference sample at high fields. From angle-dependent transport measurements we have found indications of strong pinning centres induced by the (PrBCO) nanodots, both isotropic and c-axis correlated. (C) 2009 Elsevier B.V. All rights reserved.
937. Synthesis and structural characteristics of nitrogen doped TiO2 aerogels
Authors:
Popa, M; Macovei, D; Indrea, E; Mercioniu, I; Popescu, IC; Danciu, V
Published: JUL 2010, MICROPOROUS AND MESOPOROUS MATERIALS, 132, 86, DOI: 10.1016/j.micromeso.2009.12.024
Nitrogen doped TiO2 aerogels were obtained by sol gel process followed by supercritical drying with liquid CO2. Urea and NH3 (25% aqueous solution) were used as nitrogen sources. The as-prepared aerogels were submitted to thermal treatments performed under different experimental conditions (temperature and heating time). Increasing the temperature from 450 degrees C to 550 degrees C a decrease about 32% and 15.4% of the particle size and surface OH groups' concentration, respectively and an increase about 21.4% of the incorporated nitrogen in TiO2 lattice were observed. The immersion of the TiO2 aerogels in NH3 solution induced a decreasing by 48.86% and by 80% of the S-BET and the aerogel porosity, respectively. The photocatalytic activity of the obtained N-doped TiO2 was found to depend mainly on the nitrogen incorporation in the TiO2 lattice. (C) 2009 Elsevier Inc. All rights reserved.
938. Kinetics and optical properties of the silver nanoparticles in aqueous L64 block copolymer solutions
Authors:
Angelescu, DG; Vasilescu, M; Somoghi, R; Donescu, D; Teodorescu, VS
Published: AUG 20 2010, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 366, 162, DOI: 10.1016/j.colsurfa.2010.06.001
Silver nanoparticles were prepared by the chemical reduction of silver nitrate, AgNO3, with excess of sodium borohydride, NaBH4, in dilute aqueous solutions containing triblock copolymers poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-poly(ethylene oxide) (PEO) Pluronic L64. The synthesis was completed in similar to 24h and produced highly stable particle dispersion. The growth of nanoparticles was assessed by combining Mie theory, UV-vis spectroscopy and dynamic light scattering, and the average particle size was determined from transmission electron microscopy. The silver nanoparticles were sterically stabilised as a result of the block copolymer adsorption onto the nanoparticle surface. Besides the stabilizing character, the copolymer affected the kinetics of particle growth, the size and optical properties of as-synthesized Ag nanoparticles. It was revealed that the particle formation took place in two distinct stages. The first step was dominated by Ag ion reduction and growth driven by accretion, while in the second stage coagulated clusters of nanoparticles were obtained obtained. The as-synthesized particles were polydisperse, the individual ones had a size of similar to 7.6 nm as given by transmission electron microscopy, and the hydrodynamic radius of clusters amounted to 60 nm. The silver nanoparticles exhibited broad and structured emission bands centered at 300 and 330 nm for excitation wavelengths in two different ranges, 220-240 nm and 260-290 nm, respectively. This process may be assigned to two emission components corresponding to two different excitation wavelength domains. (C) 2010 Elsevier B.V. All rights reserved.
939. Photocatalytic activity of pulsed laser deposited TiO2 thin films in N-2, O-2 and CH4
Authors:
Socol, G; Gnatyuk, Y; Stefan, N; Smirnova, N; Djokic, V; Sutan, C; Malinovschi, V; Stanculescu, A; Korduban, O; Mihailescu, IN
Published: JUN 1 2010, THIN SOLID FILMS, 518, 4653, DOI: 10.1016/j.tsf.2009.12.051
We report on pulsed laser deposition of TiO2 films on glass substrates in oxygen, methane, nitrogen and mixture of oxygen and nitrogen atmosphere. The nitrogen incorporation into TiO2 lattice was successfully achieved, as demonstrated by optical absorption and XPS measurements. The absorption edge of the N-doped TiO2 films was red-shifted up to similar to 480 nm from 360 nm in case of undoped ones. The photocatalytic activity of TiO2 films was investigated during toxic Cr(VI) ions photoreduction to Cr(III) state in aqueous media under irradiation with visible and UV light. Under visible light irradiation, TiO2 films deposited in nitrogen atmosphere showed the highest photocatalytic activity, whereas by UV light exposure the best results were obtained for the TiO2 structures deposited in pure methane and oxygen atmosphere. (C) 2009 Elsevier B.V. All rights reserved.
940. Study of the Kramers rare earth ions ground multiplet with a large orbital contribution by multifrequency EPR spectroscopy: Ce3+ in PbWO4 scintillator
Authors:
Popescu, FF; Bercu, V; Barascu, JN; Martinelli, M; Massa, CA; Pardi, LA; Stefan, M; Nistor, SV; Nikl, M
Published: MAR 2010, OPTICAL MATERIALS, 32, 575, DOI: 10.1016/j.optmat.2009.11.015
A multifrequency Electron Paramagnetic Resonance (EPR) investigation of Ce3+ impurities in PbWO4 single-crystals at the conventional microwave frequency (CMF) (X-band: 9.43 GHz) and at the high frequencies/fields (HF) 95, 190 and 285 GHz was carried out. The resulting spectra are well described at all frequencies by an axial spin-Hamiltonian corresponding to an effective spin one-half system in a tetragonal site symmetry. The diagonal values of the effective g matrix of the lowest doublet of the ground multiplet, g(parallel to) and g_, are frequency dependent at high fields. For the magnetic field perpendicular to the tetragonal axis, the g_-parameter exhibits also a small azimuthal angular dependence, which is frequency dependent, corresponding to the tetragonal S-4 symmetry. These HF effects are associated with the mixing by the large Zeeman interaction of some of the upper-lying doublets of the ground multiplet into the lowest-lying doublet states. The CMF and multifrequency HF-EPR analysis gives a good description of the magnetic properties and allows an estimation of the crystal field splitting of the ground multiplet of Ce3+ ions with tetragonal symmetry S-4 in the PbWO4 scintillator. (c) 2009 Elsevier BM. All rights reserved.
941. Tunable spin currents in a biased Rashba ring
Authors:
Moldoveanu, V; Tanatar, B
Published: JAN 2010, PHYSICAL REVIEW B, 81, DOI: 10.1103/PhysRevB.81.035326
The effect of Rashba spin-orbit coupling on the spin interference in a noninteracting one-dimensional ring connected to two leads is studied theoretically within the nonequilibrium Greens' function formalism. We compute the charge and spin currents and analyze their Aharonov-Bohm oscillations. The geometry of the system is conveniently described by the angle delta between the two leads. We show that for delta=180 degrees (i.e., for symmetrically coupled leads), a good filtering of up-or down-spin orientation is obtained around half-integer multiples of Phi/Phi(0). These particular flux values are degeneracy points for clockwise and counterclockwise propagating states, corresponding to the same spin orientation in the local spin frame of the ring. In contrast, for the asymmetric coupling, i.e., delta=135 degrees, the filter efficiency is maximum around integer multiples of Phi/Phi(0). The numerical results suggest that the spin filtering is obtained when the clockwise or counterclockwise states interfere destructively. It turns out that the spin filtering regime is stable against variations in the bias applied on the system. The quasiperiodic oscillations of the charge current, as a function of the Rashba strength, are obtained and discussed.
942. Barium magnesium tantalate thin films deposited by RF-magnetron sputtering from a stoichiometric target
Authors:
Braic, V; Kiss, A; Ioachim, A; Toacsan, M; Nedelcu, L; Braic, M
Published: DEC 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 2385, DOI:
Barium magnesium tantalate thin films are attractive materials for high-performance dielectric ceramics for microwave devices, exhibiting a high dielectric constant, a low loss and a near-zero temperature coefficient. We report on the successful deposition of polycrystalline barium magnesium tantalate thin films by RF magnetron sputtering method. The structural and morphological characterization data are presented.
943. Martensitic transformation and accompanying magnetic changes in Ni-Fe-Ga-Co alloys
Authors:
Sofronie, M; Tolea, F; Kuncser, V; Valeanu, M
Published: JUN 1 2010, JOURNAL OF APPLIED PHYSICS, 107, DOI: 10.1063/1.3429231
Two series of cobalt substituted Ni-Fe-Ga ferromagnetic shape memory alloys with lower gallium content (< 27 at. %) were studied by differential scanning calorimetry, x-ray diffraction, and thermomagnetic measurements. Co substitution for Fe or Ni promotes an increase in the Curie temperatures and a variation in the martensitic transformation (MT) temperatures, in accord with the alloy valence electron concentration change. For alloys with MTs below room temperature, a field dependent thermomagnetic hysteresis was evidenced and discussed in connection with the effect of cobalt substitution, on the magnetic hardness of the martensite phase. A direct interpretation of the evolution of the thermomagnetic hysteresis versus the applied field was provided. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3429231]
944. Surface topography and optical properties of nitrogen doped ZnO thin films formed by radio frequency magnetron sputtering on fused silica substrates
Authors:
Nicolescu, M; Anastasescu, M; Preda, S; Calderon-Moreno, JM; Stroescu, H; Gartner, M; Teodorescu, VS; Maraloiu, AV; Kampylafka, V; Aperathitis, E; Modreanu, M
Published: JUN 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 1349, DOI:
We report here on the nitrogen doped ZnO (ZnO:N) thin films deposited by radio frequency (rf) magnetron sputtering using ZnN target (99.9% purity) on, unintentionally heated, fused silica substrates. After deposition Rapid Thermal Annealing (RTA) at 400 and 550 degrees C for 1min in N-2 ambient have been performed on the ZnO:N thin films. The RTA impact on the optical and microstructural properties of ZnO:N thin films have been investigated by X-ray diffraction, Atomic Force Microscopy, Scanning and Transmission Electron Microscopy coupled with Energy Dispersive X-ray analysis, UV-VIS-NIR spectrophotonnetry and UV-VIS-NIR-Far IR Spectroscopic Ellipsometry. XRD and AFM results revealed an improvement in the crystalline state of ZnO:N and a reduction in the films surface roughness following RTA. The EDX spectrum showed the presence of the nitrogen in small quantities in the ZnO structure (nitrogen/oxygen=1/8). The optical constants of ZnO:N from UV down to Far IR spectral range together with the infrared active modes for ZnO:N are also reported.
945. N,N-dimethylbiguanide complexes displaying low cytotoxicity as potential large spectrum antimicrobial agents
Authors:
Olar, R; Badea, M; Marinescu, D; Chifiriuc, MC; Bleotu, C; Grecu, MN; Iorgulescu, EE; Lazar, V
Published: JUL 2010, EUROPEAN JOURNAL OF MEDICINAL CHEMISTRY, 45, 3034, DOI: 10.1016/j.ejmech.2010.03.033
The new complexes M(DMBG)(2)(ClO(4))(2) (M:Mn, Ni, Cu and Zn; DMBG: N,N-dimethylbiguanide) have been synthesized and characterized by IR, EPR, (1)H NMR, (13)C NMR as well as electronic spectroscopy data. Complex [Ni(DMBG)(2)](ClO(4))(2)center dot 2DMF (DMF: N,N-dimethylformamide) crystallizes in the monoclinic P2 (1)/c space group while [Cu(DMBG)(2)](ClO(4))(2) adopt monoclinic P21/c space group as X-ray single crystal data indicate. The redox behavior of complexes was investigated by cyclic voltammetry. The metal-free N, N-dimethylbiguanide and complexes exhibit specific anti-infective properties as demonstrated the low MIC values, a large antimicrobial spectrum and also inhibit the ability of Pseudomonas aeniginosa and Staphylococcus aureus strains to colonize the inert surfaces. The complexes exhibit also a low cytotoxicity levels on HeLa cells. (c) 2010 Elsevier Masson SAS. All rights reserved.
946. Improved critical current densities in thick YBa2Cu3O7-delta multilayer films interspaced with non-superconducting YBa2Cu3Ox nanodots
Authors:
Sarkar, A; Dang, VS; Mikheenko, P; Kechik, MMA; Abell, JS; Crisan, A
Published: NOV 1 2010, THIN SOLID FILMS, 519, 879, DOI: 10.1016/j.tsf.2010.08.102
We have fabricated and studied quasi-multilayered thick YBa2Cu3O7-delta (YBCO) films composed of several YBCO layers Interspaced with quasi-layers of non-superconducting YBa2Cu3Ox nanodots grown by Pulsed Laser Deposition on SrTiO3 (100) substrates Magnetization J(c)(B) at 773 K for these thick films showed significant improvement as compared to pure YBa2Cu3O7-delta films of same or even smaller thickness A high J(c)(B) in our quite thick films (1 mu m to 6 mu m) provides a very high total critical current per centimetre of the film width Ic-w Critical current as high as 830 A per cm width in self field and 77 3 K was achieved in 5 mu m thick quasi-multilayer film with non-superconducting YBa2Cu3Ox nanodots Frequency-dependent susceptibility measurements showed also an increase in the pinning potential The angular dependence of Ic-w at 86 5 K in 3 T shows a clear indication of anisotropic pinning centres aligned along the c-direction (C) 2010 Elsevier B V All rights reserved
947. Study of magnetic nanovectors by Wet-STEM, a new ESEM mode in transmission
Authors:
Maraloiu, VA; Hamoudeh, M; Fessi, H; Blanchin, MG
Published: DEC 15 2010, JOURNAL OF COLLOID AND INTERFACE SCIENCE, 352, 392, DOI: 10.1016/j.jcis.2010.08.066
Many nanovectors used for therapy (drug targeting radiation therapy) or diagnostic such as Magnetic Resonance Imaging (MRI) have a composite structure consisting of an organic core or organic coverage encapsulating magnetic nanoparticles and they are commonly dispersed in liquid suspensions for intravenous injection Here is presented the application of a new Environmental Scanning Electron Microscopy (ESEM) mode in transmission so called Wet-STEM for transmission imaging of droplets of such suspensions This is illustrated by Wet-STEM images from PLLA/Re nanospheres (about 100-300 nm in diameter) loaded with magnetite nanoparticles (about 10 nm in diameter) and from iron oxide core (about 5 nm in size) MRI contrast agents both examples in aqueous suspensions It is shown that the Wet STEM mode allows both the collective behavior of such nanovectors in suspension to be characterized and the inner composite structure of individual vectors to be revealed Such experimental results are discussed by comparison with Monte Carlo computer simulations of the distribution of the electrons scattered through the samples in rather large solid angles (between 20 degrees and 47 degrees) corresponding to the detection conditions (C) 2010 Elsevier Inc All rights reserved
948. Mesoporous Tin-Triflate Based Catalysts for Transesterification of Sunflower Oil
Authors:
Verziu, M; El Haskouri, J; Beltran, D; Amoros, P; Macovei, D; Gheorghe, NG; Teodorescu, CM; Coman, SM; Parvulescu, VI
Published: JUL 2010, TOPICS IN CATALYSIS, 53, 772, DOI: 10.1007/s11244-010-9468-x
Unimodal porous system (denoted as SnTf-MCM-41) and bimodal porosity (denoted as SnTf-UVM-7) were prepared in a two-step synthesis. The triflic acid was incorporated into previously synthesized Sn-containing porous silicas. Chemical analysis was carried out by electron probe microanalysis (EPMA), textural properties were determined by transmission electron microscopy (TEM) and from nitrogen adsorption-desorption isotherms (77 K), while structural characterization by X-ray absorption near-edge structure (XANES), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) measurements. The structural characterization provided evidences on the direct interaction of triflate with incorporated tin species. The acidity of these catalysts was determined from the ammonia chemisorption measurements. The catalysts have been tested for transesterification of sunflower oil under both microwave and ultrasound activation. These experiments showed a direct reaction between the acidity of the catalysts and catalytic performances. No leaching of the triflate species or catalyst deactivation have been detected over several runs.
949. Integrated nanotechnology of pinning centers in YBa2Cu3Ox films
Authors:
Mikheenko, P; Dang, VS; Tse, YY; Kechik, MMA; Paturi, P; Huhtinen, H; Wang, Y; Sarkar, A; Abell, JS; Crisan, A
Published: DEC 2010, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 23, DOI: 10.1088/0953-2048/23/12/125007
A controlled pinning change from the ab-plane dominant to the c-axis dominant has been achieved in a novel method of nanostructured YBa2Cu3Ox (YBCO) growth. The method is a synchronous self-assembly of BaZrO3 (BZO) and Ag-assisted YBCO nanothreads. The formation of entangled nanothreads increases the critical current density while keeping the critical temperature close to that in pure YBCO films. The nanothreads extend through the whole thickness of thick films, making the method suitable for increasing total critical current density per centimeter of width (Ic-w). Two growth mechanisms, the formation of BZO nanorods and YBCO nanocolumns, complement each other, form a coherent structure and produce samples with strong correlated pinning. In addition to the increase in Ic-w, correlated pinning leads to an increase in vortex melting temperature in a wide range of magnetic fields. The films grown by this method have high Ic-w both in low magnetic fields along the c axis and high magnetic fields in the ab plane of YBCO. Such a superconductor would be suitable for both cable and magnet applications.
950. TEMPERATURE DEPENDENCE OF CAPTURE COEFFICIENTS IN TRAPPING PHENOMENA
Authors:
Lepadatu, AM; Stavarache, I; Lazanu, S; Iancu, V; Mitroi, MR; Nigmatulin, RR; Ciurea, ML
Published: 2010, 2010 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 374, DOI:
The temperature dependence of the capture coefficients in trapping phenomena is investigated. It is proved that, besides the dependence induced by the thermal velocity of the carriers, the stress-induced traps at the interfaces of the multi-layered structures present a supplementary temperature dependence. This dependence is found to be of Gaussian type and is in a good agreement with the experimental results.
951. Nanodots induced columnar growth of YBa2Cu3Ox films
Authors:
Mikheenko, P; Tanner, JL; Bowen, J; Sarkar, A; Dang, VS; Abell, JS; Crisan, A
Published: DEC 2010, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 470, S236, DOI: 10.1016/j.physc.2009.11.064
We report columnar growth of YBa2Cu3Ox (YBCO) films by pulsed laser deposition using nanodots of Au, Ag and Pd deposited on SrTiO3 substrate prior to the growth of the film. The nanodots initiate formation of densely packed YBCO columns with c-axis along the length of the columns. The obtained columnar structure offers enhanced pinning of magnetic flux and provides high critical current density in a magnetic field directed along the c-axis of YBCO while keeping high critical current density for other directions of magnetic field. The evidence of columnar structure is given by the planar and cross-sectional atomic force microscopy, transmissional election microscopy and rotational transport measurements of critical current. By creating the columnar structure, an improvement of critical current up to about 200% is achieved comparable to the reference samples without nanodots in a wide range of magnetic field and thickness of the samples. The largest increase in critical current is observed in magnetic fields close to the matching field calculated from the density of nanoparticles or density of YBCO columns. (C) 2009 Elsevier BM. All rights reserved.
952. Coulomb interaction and transient charging of excited states in open nanosystems
Authors:
Moldoveanu, V; Manolescu, A; Tang, CS; Gudmundsson, V
Published: APR 15 2010, PHYSICAL REVIEW B, 81, DOI: 10.1103/PhysRevB.81.155442
We obtain and analyze the effect of electron-electron Coulomb interaction on the time-dependent current flowing through a mesoscopic system connected to biased semi-infinite leads. We assume the contact is gradually switched on in time and we calculate the time-dependent reduced density operator of the sample using the generalized master equation. The many-electron states (MES) of the isolated sample are derived with the exact-diagonalization method. The chemical potentials of the two leads create a bias window which determines which MES are relevant to the charging and discharging of the sample and to the currents, during the transient or steady states. We discuss the contribution of the MES with fixed number of electrons N and we find that in the transient regime there are excited states more active than the ground state even for N=1. This is a dynamical signature of the Coulomb-blockade phenomenon. We discuss numerical results for three sample models: short one-dimensional chain, two-dimensional (2D) lattice, and 2D parabolic quantum wire.
953. Novel Pd heterogeneous catalysts for cycloisomerisation of acetylenic carboxylic acids
Authors:
Neatu, F; Protesescu, L; Florea, M; Parvulescu, VI; Teodorescu, CM; Apostol, N; Toullec, PY; Michelet, V
Published: DEC 2010, GREEN CHEMISTRY, 12, 2149, DOI: 10.1039/c0gc00258e
The Pd-TPPTS complex (TPPTS - trisodium salt of 3,3',3 ''-phosphanetriyl benzenesulfonic acid) and PdCl42- salt heterogenised onto Zn2AlNO3 layered double hydroxide (LDH) using an ion-exchange procedure, have been shown to be efficient green catalysts in the cycloisomerisation reaction of acetylenic carboxylic acids to the corresponding 5-membered heterocycles.
954. Increased critical current density and pinning in thick Ag/YBa2Cu3O7-x multilayers
Authors:
Dang, VS; Mikheenko, P; Sarkar, A; Kechik, MMA; Abell, JS; Crisan, A
Published: NOV 1 2010, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 470, 1241, DOI: 10.1016/j.physc.2010.05.083
We have investigated the superconducting properties of Ag/YBa2Cu3O7-x thick multilayers grown by Pulsed Laser Deposition, and found that the artificial pinning centres induced by Ag nanodots lead to a significant increase in critical current, especially in high applied magnetic fields. Transmission Electron Microscopy showed a columnar growth of YBa2Cu3O7-x, induced by Ag nanodots, while angle-dependent transport measurements revealed the existence of strong, both isotropic and c-axis correlated, artificial pinning centres. (C) 2010 Elsevier B.V. All rights reserved.
955. Inter layer magnetic coupling in exchange bias and spin valve structures with Fe-Mn and Ir-Mn antiferromagnetic layers
Authors:
Kuncser, V; Keune, W; von Horsten, U; Schinteie, G
Published: JUN 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 1393, DOI:
Exchange bias AF/Fe and spin valve AF/Fe/Cu/Fe (AF=Fe50Mn50 and Ir50Mn50) multilayer systems have been prepared by molecular beam epitaxy. Thin tracer layers enriched in the Fe-57 isotope were artificially grown at the AF/Fe interface and the phase composition of the ferromagnetic layer, as well as the interfacial atomic diffusion were observed via Fe-57 conversion electron Mossbauer spectroscopy. The dependence of the magnetization reversal process on training and temperature associated effects was studied by low temperature vibrating sample magnetometry, whereas the interlayer magnetic coupling was analyzed via longitudinal magneto-optic Kerr effect.
956. Correlated time-dependent transport through a two-dimensional quantum structure
Authors:
Gudmundsson, V; Tang, CS; Jonasson, O; Moldoveanu, V; Manolescu, A
Published: MAY 15 2010, PHYSICAL REVIEW B, 81, DOI: 10.1103/PhysRevB.81.205319
We use a generalized master equation (GME) to describe the nonequilibrium magnetotransport of interacting electrons through a broad finite quantum wire with an embedded ring structure. The finite quantum wire is weakly coupled to two broad leads acting as reservoirs of electrons. The mutual Coulomb interaction of the electrons is described using a configuration interaction method for the many-electron states of the central system. We report some nontrivial interaction effects both at the level of time-dependent filling of states and on the time-dependent transport. We find that the Coulomb interaction in this nontrivial geometry can enhance the correlation of electronic states in the system and facilitate it's charging in certain circumstances in the weak coupling limit appropriate for the GME. In addition, we find oscillations in the current in the leads due to the correlations oscillations caused by the switched-on lead-system coupling. The oscillations are influenced and can be enhanced by the external magnetic field and the Coulomb interaction.
957. The influence of chemical composition on initial permeability frequency spectra of cobalt ferrites
Authors:
Vilceanu, V; Feder, M; Boutiuc, L; Dumitru, I; Caltun, OF
Published: JUN 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 811, DOI:
In order to study the influence of the cations substitution on permeability of cobalt ferrites four series of samples with different chemical composition were prepared by conventional ceramic method. The calcined powders and sintered samples were characterized by X-ray diffraction and vibrating samples magnetometer. The microstructure of the samples was analyzed by surface electron microscopy. The initial permeability spectra at room temperature were plotted using the torus standard method. Chemical composition and the microstructure influence the magnetic properties and the initial permeability spectra of the cobalt ferrites samples. Small amount of manganese ions decreases the Curie temperature, increase the initial permeability and saturation magnetization and decreases the coercive magnetic field, thus improving the performances of cobalt ferrites for magnetostrictive sensors applications.
958. RHENIUM-188 LABELLED ALBUMIN MICROSPHERES FOR THERAPY OF LIVER TUMORS
Authors:
Borza, VN; Neacsu, E; Mustaciosu, C; Luca, A; Barna, C; Popescu, N; Mercioniu, I; Albert, P; Hurduc, A; Moldovan, L; Savi, GP; Savi, I; Matei, L
Published: MAY 15 2010, JOURNAL OF LABELLED COMPOUNDS & RADIOPHARMACEUTICALS, 53, 471, DOI:
959. Redox behavior of hemin at p-GaAs(1 0 0) electrode
Authors:
Toader, AM; Volanschi, E; Lazarescu, MF; Lazarescu, V
Published: DEC 30 2010, ELECTROCHIMICA ACTA, 56, 866, DOI: 10.1016/j.electacta.2010.09.083
Electrochemical behavior of hemin on p-GaAs(1 0 0) electrodes was examined by cyclic voltammetry (CV) and impedance spectroscopy (EIS) in phosphate buffer solutions (PBS) at pH 7.45. CV investigations in 0.6 mM hemin in PBS revealed a pair of reversible peaks at -0.44 and -0.32 V vs. SCE resulting in stable adsorbed species. EIS spectra analysis pointed out that these adsorbed species bring significant changes in the semiconductor surface state population and the potential drop distribution between the semiconductor space charge region and the Helmholtz layer. (C) 2010 Elsevier Ltd. All rights reserved.
960. Dynamic correlations induced by Coulomb interactions in coupled quantum dots
Authors:
Moldoveanu, V; Manolescu, A; Gudmundsson, V
Published: AUG 11 2010, PHYSICAL REVIEW B, 82, DOI: 10.1103/PhysRevB.82.085311
Time-dependent transport through two capacitively coupled quantum dots is studied in the framework of the generalized master equation. The Coulomb interaction is included within the exact diagonalization method. Each dot is connected to two leads at different times, such that a steady state is established in one dot before the coupling of the other dot to its leads. By appropriately tuning the bias windows on each dot we find that in the final steady state the transport may be suppressed or enhanced. These two cases are explained by the redistribution of charge on the many-body states built on both dots. We also predict and analyze the transient mutual charge sensing of the dots.
961. One-Pot Synthesis of Menthol Catalyzed by a Highly Diastereoselective Au/MgF2 Catalyst
Authors:
Negoi, A; Wuttke, S; Kemnitz, E; Macovei, D; Parvulescu, VI; Teodorescu, CM; Coman, SM
Published: 2010, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 49, 8138, DOI: 10.1002/anie.201002090
962. Porous Au-TiO2 aerogels nanoarchitectures for photodegradation processes
Authors:
Peter, A; Baia, L; Baia, M; Indrea, E; Toderas, F; Danciu, V; Cosoveanu, V; Diamandescu, L
Published: MAY 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 1077, DOI:
Porous nanoarchitectures based on TiO2 aerogel and colloidal gold particles have been obtained by different synthesis routes: impregnation of TiO2 aerogel with Au colloid, impregnation of TiO2 gel with Au colloid and preparation of TiO2 gel in the presence of Au colloid. The as prepared composites have been thermal treated at 500 degrees C and their structural and morphological properties were investigated. The Raman spectra and XRD data demonstrated the anatase structure of the composite obtained by impregnation of TiO2 aerogel with Au colloid and the mixed anatase-brookite structure of those obtained by impregnation of TiO2 gel with Au colloid and by preparation of TiO2 gel in the presence of Au colloid, respectively. TEM analyses suggest that the Au particles on the TiO2 surface as individual particles, as well as clusters are present. The photocatalytic performances of the synthesized composites were tested in the salicylic acid photodecomposition process and it was found that they are strongly influenced by both anatase - brookite TiO2 structure and Au nanoparticles dispersion on the TiO2 surface.
963. Polymer-microporous host interactions probed by photoluminescence spectroscopy
Authors:
Tiseanu, C; Parvulescu, VI; Cojocaru, B; Lorenz-Fonfria, VA; Kumke, M; Gessner, A; Enculescu, I
Published: 2010, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 12, 3037, DOI: 10.1039/b922591a
Zeolites NaY and ZSM-5 were used as hosts for styrene polymerization after ion-exchange with europium ions. The parent and hybrid, polystyrene coated Eu-NaY (Eu-NaY/PS) and Eu-ZSM-5 (Eu-ZSM-5/PS) zeolites were investigated by using thermal analysis, SEM, PXRD, FT-IR, DR-UV/Vis, steady state and time-resolved photoluminescence spectroscopy. FT-IR spectra evidenced for the interaction between the zeolitic hosts and polystyrene while the PXRD spectra supported for the presence of the polymer inside the channels/pores of Eu-NaY/PS and Eu-ZSM-5/PS materials. The optical properties of Eu-NaY/PS and Eu-ZSM-5/PS were significantly changed relative to those of the parent zeolites, giving further evidence for the presence of polymer inside zeolites. An interesting case is presented by NaY zeolite: following styrene polymerization, the polymer interacted selectively with one of the two main species co-existing inside zeolite while for ZSM-5 a similar effect was not observed.
964. Temperature induced change in the hysteretic behavior of the capacitance-voltage characteristics of Pt-ZnO-Pb(Zr0.2Ti0.8)O-3-Pt heterostructures
Authors:
Pintilie, L; Dragoi, C; Radu, R; Costinoaia, A; Stancu, V; Pintilie, I
Published: JAN 4 2010, APPLIED PHYSICS LETTERS, 96, DOI: 10.1063/1.3284659
Pt-ZnO-Pb(Zr0.2Ti0.8)O-3-Pt (PZT-ZnO) heterostructures were fabricated by using a sol-gel process. Capacitance-voltage measurements performed on a wide temperature range (20-450 K) have revealed the presence of a hysteresis that undergo a change of direction from clockwise at temperatures below 350 K to counter-clockwise at higher temperatures. In the first case, the hysteresis is produced by charge injection, similar to the case of classical metal-oxide-semiconductor capacitors. In the last case, the hysteresis is the fingerprint of polarization reversal, as reported for metal-ferroelectric-semiconductor (MFS) structures based on n-Si. The memory window at 450 K is about 6 V. This result suggests that PZT-ZnO MFS heterostructures can be used for memory devices working at elevated temperatures, in which the ZnO plays the role of the semiconductor.
965. Quantum Confinement in Nanometric Structures
Authors:
Ciurea, ML; Iancu, V
Published: 2010, NEW TRENDS IN NANOTECHNOLOGY AND FRACTIONAL CALCULUS APPLICATIONS, +, DOI: 10.1007/978-90-481-3293-5_5
This paper discusses the quantum confinement effects in nanometric structures that form low dimensional systems. In such systems, each surface/interface acts like a potential barrier, i.e. the wall of a quantum well, generating new energy levels. These levels are computed in a model that uses the approximation of the infinite rectangular quantum wells. The model is adapted for 2D, 1D and 0D systems, respectively. Different applications are discussed. The differences between the model results and the experimental data are proved to be of the same order of magnitude as the differences between the levels computed within the frame of infinite and finite quantum well approximations.
966. OPTIMIZATION OF THERMIONIC VACUUM ARC PLASMA USED FOR MULTILAYER GMR/TMR FILMS PREPARATION
Authors:
Jepu, I; Porosnicu, C; Mustata, I; Lungu, CP; Kuncser, V; Miculescu, F
Optical and electrical behavior of Giant Magnetoresistivc (GMR)/Tunneling Magnetoresistive (TMR) multilayer thin films were controlled adjusting thermionic vacuum arc plasma parameters. Smooth, dense and adherent films were prepared using optimized plasma conditions. A new setup for simultaneous depositions of pure materials was made, having inside the vacuum chamber three simultaneous discharges. To obtain the discharge all of the tungsten filaments of the thermionic vacuum arc guns were heated by a 45-55 A current. The emitted electrons were focused on a tungsten coated carbon crucible anode, filled with Cu, and the others crucible anodes filed with MgO, Co and Ag, respectively. The anode applied voltages for Cu, MgO Co and Ag were up to 1500 V, 1700V 1800V and 820V respectively. An optimization of the geometrical parameters as the distance between the cathode and the anode, and of the external parameters as the discharge voltage and the heating current of tungsten current filament was performed. Structural and morphological properties of the prepared films were analyzed by scanning electron microscopy (SEM). The behavior of the obtained films was first analyzed in a Magneto-Optical Kerr Effect (MOKE) experiment. The electrical resistance behavior of the prepared films was determined in a magnetic field which values varied from 0.4 T to 0.4 T. The important changes in the values of the electrical resistance of the films were observed and correlated to the plasma conditions.
967. Spin splitter regime of a mesoscopic Rashba ring
Authors:
Moldoveanu, V; Tanatar, B
Published: DEC 1 2010, PHYSICS LETTERS A, 375, 191, DOI: 10.1016/j.physleta.2010.10.047
Using the non-equilibrium Greens' function formalism we calculate the spin currents in a one-dimensional ring coupled to three leads and in the presence of perpendicular magnetic flux (1) and Rashba spin-orbit coupling. A finite bias is applied between the input lead and the other two output leads. We show that the spin-orbit coupling allows one to operate this system as a spin splitter, i.e. the output leads deliver spin-polarized currents with different orientations. We find that the spin splitter operation can be tuned at integer multiples of phi/phi(0). Its efficiency depends not only on the value of the Rashba coupling but also on the bias applied between the input and output leads. The selected spin orientation of the output leads can be reversed by a slight change of their contact position. We discuss as well the connection between the spin splitter operation and the spectral properties of the ring. (C) 2010 Elsevier B.V. All rights reserved.
968. Structural and photoluminescence characterization of mesoporous silicon-phosphates
Authors:
Tiseanu, C; Parvulescu, V; Parvulescu, V; Cotoi, E; Gessner, A; Kumke, M; Simon, S; Vasiliu, F
Published: SEP 5 2010, JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, 215, 24, DOI: 10.1016/j.jphotochem.2010.07.015
Two different types of mesoporous silicon-phosphate supports using different surfactants (a mixture of (CH3)(3)C13H27NBr with an organophosphorus coupling molecule (HO-PO(i-C3H7)(2)) and with a co-surfactant ((C2H5)(3)(C6H5)PCl), respectively) were synthesized. Trivalent europium (Eu) ions were immobilized via ion-exchange on these supports. The resulting materials were characterized using nitrogen adsorption isotherms at -196 degrees C, thermogravimetric analysis, SEM, TEM, FT-IR, PXRD, CP/MAS. (HSi)-H-1-Si-29 and P-31 NMR, DR-UV-vis as well as steady-state and time-resolved photoluminescence spectroscopy. The results evidenced that the co-polymerization of silicon and phosphorous yielded a unique morphology in these materials. Following calcination at 450 and 900 degrees C europium-exchanged silicon-phosphates with great surface area (BET=600-705 m(2) g(-1)) and 3.4 nm sized mesopores were obtained. The differences among the optical properties of the non-calcined europium materials such as the emission lifetimes, local environment at the europium sites or the relative contribution of the upper excited levels to the total photoluminescence were assigned to the surfactants used in the synthesis. Calcination of the silicon-phosphates at higher temperatures than 450 degrees C did not induce major changes in the structural properties: in contrast, photoluminescence properties of europium were markedly improved in terms of intensity and average lifetime. (C) 2010 Elsevier B.V. All rights reserved.
969. Artificial pinning in thick YBCO films: Pinning potential and c-axis correlation
Authors:
Crisan, A; Mikheenko, P; Sarkar, A; Dang, VS; Kechik, MMA; Abell, JS; Paturi, P; Huhtinen, H
Published: OCT 1 2010, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 470, 843, DOI: 10.1016/j.physc.2010.02.033
We have introduced artificial pinning centres in thick (>1 mu m) YBCO films grown by Pulsed Laser Deposition using substrate decoration, quasi-multilayers, and target doping approaches. We have found that the frequency dependence of critical current density is consistent with a logarithmic dependence of pinning potential on current density. For most of materials used as nano-dots, artificially-induced pinning centres have a larger potential than natural ones. From angle-dependent in-field transport measurements and from Transmission Electron Microscopy we have found evidence of c-axis correlated pinning centres. (C) 2010 Elsevier B.V. All rights reserved.
970. Preparation and patterning of nanoscale hybrid materials for micro-optics
Authors:
Obreja, P; Cristea, D; Teodorescu, VS; Dinescu, A; Obreja, AC; Comanescu, F; Rebigan, R
Published: OCT 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 2013, DOI:
The refractive index of organic polymers can be modified by incorporation of inorganic nanoparticles with higher or lower refractive index. The paper presents our experimental results regarding the preparation of hybrid nanocomposite films with controlled refractive index for micro-optics and integrated optics. These materials were obtained by chemical routes and sol-gel processes from commercial polymers (PMMA, PVA), metal (Ag), metal oxide nanoparticles (TiO2, ZrO2) or organic materials (Rhodamine, Alq3). The properties of these materials depend on the composition, metal/oxide concentration, particle size and dispersion homogeneity. The hybrid nanocomposite films were characterized using spectroellipsometry, UV-VIS spectroscopy, AFM, TEM and the optical properties were correlated with processing parameters. Micro/nano pattering techniques based on combination of electron beam lithography and replication techniques have been developed to obtain structures with applications in micro-optics. Components like micro-lenses, diffractive optical elements and optical waveguides have been obtained and characterized using SEM and AFM.
971. Fabrication and Electric Transport in MgB2 Doped with Nanosized Carbon-Based Core-Shell Structures
Authors:
Sandu, V; Aldica, G; Popa, S; Cimpoiasu, E; Dumitrache, F; Sandu, E
Published: 2010, OPTOELECTRONIC MATERIALS, PTS 1AND 2, 663-665, +, DOI: 10.4028/www.scientific.net/MSF.663-665.871
We present the fabrication and electric properties of MgB2 ceramic samples doped with nanosized spheres, 4-8 nm, of graphite with a metallic core. The samples were prepared using the spark plasma sintering technique. The size of the additive is comparable to the superconducting coherence length. The short processing time limits the diffusion of the carbon while keeping the core intact. Therefore, in addition to the doping with carbon, the metallic core, which has the size smaller than the superconducting coherence length, create pinning centers which might improve the dissipationless electric transport. The results are analyzed in the framework of different pinning models.
972. Inelastic transitions and counterflow tunneling in double-dot quantum ratchets
Authors:
Moldoveanu, V; Tanatar, B
Published: NOV 10 2010, PHYSICAL REVIEW B, 82, DOI: 10.1103/PhysRevB.82.205312
The ratchet regime of unbiased double quantum dots driven out of equilibrium by an independently biased nearby detector has been theoretically studied using the nonequilibrium Keldysh formalism and the random-phase approximation for the Coulomb effects. When the detector is suitably biased the energy exchange between the two systems removes the Coulomb blockade on the double dot via inelastic interdot tunneling. The energy detuning determines whether the current flows in the same direction as the driving current (positive flow) or in the opposite direction (electronic counterflow). In both cases the intradot transitions lead to negative-differential conductance. Besides the ratchet contribution to the current we also single out a Coulomb drag component.
973. The influence of shape and potential barrier on confinement energy levels in quantum dots
Authors:
Lepadatu, AM; Stavarache, I; Ciurea, ML; Iancu, V
Published: FEB 2010, JOURNAL OF APPLIED PHYSICS, 107, DOI: 10.1063/1.3284083
The influence of the shape of silicon quantum dots embedded in an amorphous silica matrix on the quantum confinement energy levels, as well as that of the Si/SiO2 potential barrier, are studied. The energy levels are computed using both the infinite and finite rectangular quantum well models for spherical quantum dots and the infinite rectangular quantum well for prolate spheroidal quantum dots. The results are compared with each other and also with the experimental activation energies obtained from the temperature dependence of the dark current. These activation energies are identified with the differences between the quantum confinement energies, subject to the selection rules. The finite rectangular quantum well model takes into account the experimental value of the finite potential barrier and the matrix-to-dot electron mass ratio. The energy levels are smaller than those for the infinite rectangular quantum well case; they decrease when the potential barrier decreases and the mass ratio increases. Different aspects of the models are discussed. All the errors are less than about 4%. The spheroidal shape lifts the degeneracy on the magnetic quantum number. The energy levels can decrease or increase with eccentricity as a consequence of the different quantum confinement effects along the major and minor axes. The supplementary information on the magnetic quantum number is beneficial for optical applications.
974. Magnetoelectric properties of multiferroic cobalt ferrite and soft piezoelectric PZT particulate composites
Authors:
Miclea, C; Tanasoiu, C; Amarande, L; Miclea, CF; Plavitu, C; Cioangher, M; Trupina, L; Miclea, CT; Tanasoiu, T; Susu, M; Voicu, I; Malczanek, V; Ivanov, A; David, C
Published: FEB 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 276, DOI:
Multiferroic composite materials, consisting of piezoelectric and piezomagnetic phases, show electric polarization in the presence of a magnetic field and magnetization on applying an electric field, i.e. piezomagnetic phase causes polarization while piezoelectric phase causes changes in magnetization. The figure of merit of such multiferroic particulate composites is the magnetoelectric voltage coefficient representing the amount of polarization induced by a given magnetic field. In the present investigation we prepared and studied the properties of bulk particulate composites made from cobalt ferrite (COF) and a soft piezoelectric material (PZT). Composite samples, according to the formula xCOF center dot(1-x)PZT with 0 <= x <= 1 were prepared by mixing the COF and PZT powders, pressing them as discs and then sintered at 1200 degrees C for 3 hours. Structural, magnetic, piezoelectric and magnetoelectric characteristics of the sintered composites were determined as a function of the mass fraction of COF into PZT and magnetic field. The ME coefficient shows a maximum value of about 70 mV/cm.Oe for composites containing 40 % COF and 60 % PZT, in a DC magnetic field of 3 kOe at a frequency of 1 KHz of the ac magnetic field. Some of the dielectric and piezoelectric properties of the composite samples, as a function of the mass fraction x, were also determined.
975. RPA APPROACH TO NON-LINEAR TRANSPORT IN QUANTUM DOTS
Authors:
Tanatar, B; Moldoveanu, V
Published: 2010, CONDENSED MATTER THEORIES, VOL 24, +, DOI: 10.1142/9789814289153_0040
An accurate theoretical treatment of electron-electron interactions in mesoscopic systems is available in very few cases and approximation schemes are developed in most of the applications, especially for many-level quantum dots. Here we present transport calculations within the random-phase approximation for the Coulomb interaction using the Keldysh Green's functions formalism. We describe the quantum dot systems by a tight-binding Hamiltonian. Our method is similar to the one used by Faleev and Stockman [Phys. Rev. B 66 085318 (2002)] in their study of the equilibrium properties of a homogeneous 2D electron gas. The important extension at the formal level is that we combine the RPA and the Keldysh formalism for studying non-linear transport properties of open quantum dots. Within the Keldysh formalism the polarization operator becomes a contour-ordered quantity that should be computed either from the non-interacting Green functions of the coupled quantum dot (the so-called G(0)W approximation) either self-consistently (GW approximation). We performed both non-selfconsistent and self-consistent calculations and compare the results. In particular we recover the Coulomb diamonds for interacting quantum dots and we discuss the charge sensing effects in parallel quantum dots.
976. SiO2 nanospheres and tubes obtained by sol-gel method
Authors:
Anastasescu, C; Anastasescu, M; Teodorescu, VS; Gartner, M; Zaharescu, M
Published: OCT 1 2010, JOURNAL OF NON-CRYSTALLINE SOLIDS, 356, 2640, DOI: 10.1016/j.jnoncrysol.2010.03.038
Multifunctional nanomaterials with one-dimensional structure have become very attractive because of their potential applications in biochemistry (bioseparation and biointeraction), drug delivery, catalysis, nanotechnology (optical sensors). In this work we report on the synthesis of SiO2 nanospheres and tubes, in a solution of tartaric acid (TTA), pure water and absolute ethanol, starting with tetraethyl orthosilicate (TEOS) via the addition of ammonium hydroxide. In order to characterize the obtained material, transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), thermogravimetric and thermodifferential analysis (DTA/TGA), FT-IR spectroscopy and spectroellipsometry (SE) were used. The tubes have an outer diameter of 0.1-0.2 mu m and length of some microns containing also spherical nanoparticles. The dimensions of the obtained nanotubes are tunable, their diameter and length depending on the synthesis conditions. In the presence of meso-tartaric acid no hollow tubes but nanospheres are obtained. The SiO2 tubes and nanospheres have similar structure but very different morphologies. The large surface area and the distinctive inner and outer surfaces represent a great advantage of the nanotubes over conventional nanoparticles, making these materials suitable for doping and differential functionalization. (C) 2010 Elsevier B.V. All rights reserved.
977. Interfacial atomic diffusion in AF/Fe/Cu/Fe (AF=Fe50Mn50 and Ir50Mn50) multilayer systems
Authors:
Kuncser, V; Keune, W; von Hoersten, U; Schinteie, G; Stefan, N; Palade, P; Filoti, G
Published: AUG 31 2010, THIN SOLID FILMS, 518, 5985, DOI: 10.1016/j.tsf.2010.05.100
Spin valve like AF/Fe/Cu/Fe (AF = Fe50Mn50 and Ir50Mn50) multilayer systems have been prepared by molecular beam epitaxy. Thin tracer layers enriched in the Fe-57 isotope were artificially grown at the AF/Fe and Fe/Cu interfaces and the interfacial atomic diffusion was observed via Fe-57 conversion electron Mossbauer spectroscopy. The results show that the atomic interdiffusion at all involved interfaces is lower in the IrMn based structures as compared to the FeMn based ones. (C) 2010 Elsevier B.V. All rights reserved
978. Magnetism and transport properties of gamma-irradiated polymer-CrO2 composites
Authors:
Sandu, V; Popa, S; Ivan, I; Sandu, E; Hurduc, N; Nor, I
Published: MAY-JUN 2010, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 322, 1408, DOI: 10.1016/j.jmmm.2009.09.045
The transport properties of the gamma-irradiated CrO2-polymer composites were investigated. The resistance R is strongly current I dependent, except at high temperature where it displays a semiconductor-like temperature dependence for all currents. At low currents, I <= 10 mu A, as the temperature decreases far below the ferromagnetic transition, the resistance decreases first, then reaches a minimum, and at last increases again toward a second peak. At even lower temperatures, the second peak is followed by a metallic-like temperature dependence of R that ends at a cusp point marking the metal-insulator transition. The increase of the current shifts the cusp toward lower temperatures and the first minima toward higher temperatures. The resistance increases with the increase in current for all currents in the range 0.2 <= I <= 10 mu A. For I >= 50 mu A, the resistance increases monotonically with the decrease in temperature in the whole temperature range but obeys different laws at low and high temperatures. An explanation attempt in terms of spin transport, disorder, and thermal effects is proposed. (C) 2009 Elsevier B.V. All rights reserved.
979. Iron Oxide-Based Nanoparticles with Different Mean Sizes Obtained by the Laser Pyrolysis: Structural and Magnetic Properties
Authors:
Morjan, I; Alexandrescu, R; Dumitrache, F; Birjega, R; Fleaca, C; Soare, I; Luculescu, CR; Filoti, G; Kuncer, V; Vekas, L; Popa, NC; Prodan, G; Ciupina, V
Published: FEB 2010, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 10, 1234, DOI: 10.1166/jnn.2010.1863
Nano-sized iron oxide-based particles have been directly synthesized by the laser induced pyrolysis of a mixture containing iron pentacarbonyl/air (as oxidizer)/ethylene (as sensitizer). In this paper we further demonstrate the possibility to vary the chemical composition and the nanoparticle dimensions of the iron oxide-based materials by handling the oxidation procedure in the frame of the laser pyrolysis process. Thus, nanoparticles with major maghemite/magnetite content may change composition into mixtures with variable amounts of three components: major gamma-Fe2O3/Fe3O4 iron oxide, metallic Fe and cementite Fe3C. By X-ray diffraction (XRD) it is found that the relative proportion of these phases differs in function of the reaction temperature (laser power). As revealed by transmission electron microscopy (TEM), mean particle sizes between about 4 nm and 6 nm and between about 9 and 11 nm may be prepared by varying the oxidation procedure and the laser power, respectively. By the controlled heating of samples (maximum temperature 185 degrees C), increased crystallinity for the gamma-Fe2O3/Fe3O4 oxide phase was found as well as an increase of the mean particle diameters. The examination of the magnetization curves for samples obtained for different laser powers indicates notable differences in the magnetic behavior and parameters. The temperature dependent Mossbauer measurements confirm the formation of larger particles at higher laser power densities as well as the presence of inter-particle magnetic interactions. On this basis, the estimation of phase composition for the different representative samples is given.
980. Development Of Magnetic Fe@C Nanocomposites Obtained Via The Laser Pyrolysis: Structural And Disaggregation Properties
Authors:
Morjan, I; Alexandrescu, R; Dumitrache, F; Fleaca, C; Birjega, R; Soare, I; Luculescu, CR; Prodan, V; Kuncser, V; Filoti, G; Xu, H; Wang, D
Published: 2010, BONSAI PROJECT SYMPOSIUM: BREAKTHROUGHS IN NANOPARTICLES FOR BIO-IMAGING, 1275, +, DOI: 10.1063/1.3505074
Fe@C) nanoparticles have been successfully synthesized using the laser pyrolysis method and variable nozzle geometries. At large nozzle diameters, XRD and SAED analysis clearly identified distinct alpha-Fe and Fe3C phases. TEM and HRTEM indicated that these Fe-based nanoparticles have an average grain size of 3.5-10.2 nm. Temperature dependent Mossbauer spectra further confirm their distinct nanophases. By using a multi-step reduction procedure, Fe@C powders can be disaggregated into stable, water soluble nanoparticles.
981. INFLUENCE OF PREPARATION METHOD ON STRUCTURAL PROPERTIES OF GeSiO NANOSYSTEMS
Authors:
Stavarache, I; Lepadatu, AM; Teodorescu, V; Stoica, T; Pasuk, I; Stan, G; Iancu, V; Ciurea, ML
Published: 2010, 2010 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 80, DOI: 10.1109/SMICND.2010.5650255
GeSiO nanosystems were obtained using two different preparation methods, sol-gel and magnetron-sputtering. Transmission electron microscopy measurements were performed to investigate the films structure. Amorphous and crystalline Ge dots embedded in amorphous silicon dioxide were observed. The Ge concentration in the GeSiO films was by Energy-dispersive X-ray spectroscopy.
982. Passivation effects of 4,4'-thio-bis-benzenethiolate adsorbed layers on semiconducting electrodes
Authors:
Lazarescu, V; Scurtu, R; Lazarescu, MF; Toader, AM; Volanschi, E
Published: NOV 30 2010, ELECTROCHIMICA ACTA, 55, 8301, DOI: 10.1016/j.electacta.2010.02.004
The effects of the self-assembled layers formed by adsorption of 4 4'-thio-bis-benzenethiol from ethanol solutions on p-S1(111) and p-GaAs(1 00) electrodes were examined by EIS AFM and XPS investigations All the experimental data led to the conclusion that the thio-bis-benzenethiolate film spontaneously formed on Si and GaAs surfaces brings about chemical passivation both in air and in solution as well as strong adsorbate-substrate interactions which affect the semiconductor surface state population and the field effects operating in the interfacial region Semiempirical PM3 molecular orbital calculations showed that electronic interaction of the thiolate film with the two semiconducting electrodes can be understood in terms of changes in the local density of the electronic states at the surface (C) 2010 Elsevier Ltd All rights reserved
983. Synthesis and properties of poly(methyl methacrylate-2-acrylamido-2methylpropane sulfonic acid)/PbS hybrid composite
Authors:
Preda, N; Rusen, E; Musuc, A; Enculescu, M; Matei, E; Marculescu, B; Fruth, V; Enculescu, I
Published: AUG 2010, MATERIALS RESEARCH BULLETIN, 45, 1012, DOI: 10.1016/j.materresbull.2010.04.002
The synthesis of a new hybrid composite based on PUS nanoparticles and poly( methyl methacrylate-2acrylamido-2-methylpropane sulfonic acid) [P(MMA-AMPSA)] copolymer is reported. The chemical synthesis consists in two steps: (i) a surfactant-free emulsion copolymerization between methyl methacrylate and 2-acrylamido-2-methylpropane sulfonic acid and (ii) the generation of PbS particles in the presence of the P( MMA-AMPSA) latex, from the reaction between lead nitrate and thiourea. The composite was studied by scanning electron microscopy (SEM), X-ray diffraction, FTIR spectroscopy, thermogravimetric analysis and differential scanning calorimetry. The microstructure observed using SEM proves that the PbS nanoparticles are well dispersed in the copolymer matrix. The X-ray diffraction measurements demonstrate that the PbS nanoparticles have a cubic rock salt structure. It was also found that the inorganic semiconductor nanoparticles improve the thermal stability of the copolymer matrix. (C) 2010 Elsevier Ltd. All rights reserved.
984. Structural and electrochemical characterization of TiO2/Pt hybrid catalyst system for direct bio-ethanol fuel cell
Authors:
Banu, A; Spataru, N; Teodorescu, VS; Maraloiu, AV; Voiculescu, I; Marcu, AM; Spataru, T
Published: MAY 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 1193, DOI:
This paper is focused on preparation and microstructure and electrochemical characterization of carbon-TiO2/Pt catalyst used as electrode in fuel cells applications. The platinum deposition was comparatively studied on graphitized carbon substrate and carbon substrate covered with titanium oxide. A strong influence on the platinum deposition, depending of the TiO2 presence, was found. The platinum nanoparticles about 5 nm in size are dispersed in aggregates of 50 to 100 nm on the catalyst surface. This dispersion is strongly affected by the titanium oxide and the substrate porosity. The Pt/TiO2/G and Pt/G electrodes were tested for their catalytic activity in the oxidation of ethanol. The prepared Pt/TiO2/G electrode show higher active surface area than for the Pt/G electrode, this increase in the surface area could be explained to be due to a spreading of wetting or the formation of new active sites at the Pt/oxide interface.
985. Polymer-like thin films obtained by RF plasma polymerization of pentacyclic monomers
Authors:
Satulu, V; Mitu, B; Galca, AC; Aldica, GV; Dinescu, G
Published: MAR 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 636, DOI:
Plasma polymerization has been carried out in a parallel plate RF discharge reactor in mixtures of argon with pentacyclic precursors, namely thiophene, furan and pyrrole. The plasma characterization showed the presence of emission bands peculiar to each monomer. The deposition of highly transparent films with partial conservation of the pentacyclic structure, inclusion of various oligomers, roughness and surface energy depending on the precursor nature was demonstrated by material investigations results. The material conductivity is significantly improved upon iodine doping in the case of polythiophene and polypyrrole-like films, while an opposite behavior was observed for the polyfuran-like films.
986. LOW POWER LASER INDUCED OPTICAL NONLINEARITIES IN ORGANIC MOLECULES
Authors:
Dancus, I; Vlad, VI; Petris, A; Frunza, S; Beica, T; Zgura, I; Nicolescu, FA; Jerca, VV; Vuluga, DM
Experimental demonstration of low power laser induced optical nonlinearities in two different types of specially designed materials: dye doped liquid crystals and copolymers with new pendant azobenzene moieties, is presented. Saturation of the nonlinear refractive index change is observed for some of the samples. The origin of the huge nonlinearity and its saturation in the continuous wave laser regime and at low power levels are analyzed.
987. Soft type PZT material used to fabricate a high intensity air siren
Authors:
Miclea, C; Iuga, A; Tanasoiu, C; Trupina, L; Cioangher, M; Miclea, CT; Malczanek, V; Susu, M; Voicu, I
Published: FEB 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 281, DOI:
A high quality soft type PZT material was designed and produced in order to be used as sensor for a high intensity air siren, Two thin disks from this material were assembled into a parallel bimorph type sensor with an intermediate metallic plate for the siren. This assembly behaves like an acoustic resonator in the high frequency audio range. This structure transforms the radial mode of vibration into a flexural one, with a much lower frequency. A mechanical impedance adapter was used in order to assure a good match between the oscillating ceramic and the surrounding air. A theoretical approach was outlined, which allows the evaluation of the resonance frequency for the working transducer. The theoretical and experimental data agree to a satisfactory degree up to the input errors assumed by the model. Acoustical and impedance measurements were made in order to appreciate the influence of the metallic plate on the frequency. The bimorph necessary for making the siren was designed as a parallel structure and the corresponding transducer was measured and evaluated. In order to increase the acoustic emission a frontal cardboard horn was added to the resonator.
988. About the complex relation between short-circuit photocurrent, imprint and polarization in ferroelectric thin films
Authors:
Pintilie, L; Stancu, V; Vasile, E; Pintilie, I
Published: JUN 1 2010, JOURNAL OF APPLIED PHYSICS, 107, DOI: 10.1063/1.3445877
The short-circuit photocurrent was measured in ferroelectric capacitors of polycrystalline and epitaxial quality. The interest was to study the possible relation between photocurrent and back-switching phenomena due to ferroelectric polarization imprint, as suggested by Pintilie [J. Appl. Phys. 101, 064109 (2007)]. An interesting relation between the shape of the ferroelectric hysteresis loop and the shape of the photocurrent spectral distribution was found. In polycrystalline samples, the shape of spectral distribution and the sign of photocurrent are changing in time, although the hysteresis is almost symmetrical. However, the hysteresis is not rectangular as in the case of epitaxial films. This behavior suggests a subtle relation between polarization back-switching and photocurrent. In epitaxial samples a peculiar dependence between photocurrent and polarization imprint was found. All these are explained assuming the presence of an internal field, possibly generated by charged defects, which can change its direction and magnitude under illumination, with consequence on the orientation and magnitude of the ferroelectric polarization, and on the sign/shape of the short-circuit photocurrent spectral distribution. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3445877]
989. Prospects for new antimicrobials based on N,N-dimethylbiguanide complexes as effective agents on both planktonic and adhered microbial strains
Authors:
Olar, R; Badea, M; Marinescu, D; Chifiriuc, CM; Bleotu, C; Grecu, MN; Iorgulescu, EE; Bucur, M; Lazar, V; Finaru, A
Published: JUL 2010, EUROPEAN JOURNAL OF MEDICINAL CHEMISTRY, 45, 2875, DOI: 10.1016/j.ejmech.2010.03.009
Metal-free N,N-dimethylbiguanidium acetate and novel complexes M(DMBG)(2)(CH(3)COO)(2)center dot nH(2)O (M: Mn (II), Ni(II), Cu(II) and Zn(II)) were screened for their antimicrobial properties against Gram-positive (Bacillus subtilis, Listeria monocytogenes, Staphylococcus aureus), Gram-negative (Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa) bacteria and fungal (Candida albicans) strains. The ability of compounds to inhibit the microbial adherence ability to the inert substratum as well as their cytotoxicity was also assessed. Our results are demonstrating that some of the tested compounds are exhibiting potent antimicrobial activity accompanied by low cytotoxicity on HeLa cells. The complexes were characterized using microanalytical, IR, EPR, (1)H NMR as well as UV-vis methods. The redox behaviour of complexes was investigated by cyclic voltammetry. The new derivative (HDMBG)(CH(3)COO) crystallizes in the monoclinic P2(1)/n space group as X-ray single-crystal data indicate. (C) 2010 Elsevier Masson SAS. All rights reserved.
990. Magnetic Configuration and Relaxation in Iron Based Nano-Particles: A Mossbauer Approach
Authors:
Kuncser, V; Schinteie, G; Alexandrescu, R; Morjan, I; Vekas, L; Filoti, G
Published: 2010, TRENDS IN NANOPHYSICS: THEORY, EXPERIMENT AND TECHNOLOGY, 314, DOI: 10.1007/978-3-642-12070-1_13
The difficulty to stabilize a definite crystalline structure or phase, due to a large gradient of defects along the particle diameter, is unfortunately specific to particles of nanometer size. Therefore, atypical spin configurations and magnetic anisotropies as well as enhanced magnetic relaxations via thermal excitations are expected in systems of fine nano-particles. The actual work reports on various possibilities for a comprehensive characterization of the magnetic configuration and magnetic relaxation mechanisms of nano-particles, by corroborating the powerful method of Mossbauer spectroscopy with complementary magnetic and structural techniques. The capabilities of temperature and field dependent Mossbauer spectroscopy to provide valuable information about spin blocking temperatures, effective anisotropy constants, amount of uncompensated spins inside of particle and magnetic phase composition are critically discussed for both powder like systems and nano-particles dispersed in different solvents.
991. Cobalt-doped ZnO prepared by electrochemistry: Chemistry, morphology, and magnetism
Authors:
Matei, E; Enculescu, I; Vasilache, V; Teodorescu, CM
Published: NOV 2010, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 207, 2522, DOI: 10.1002/pssa.200925378
ZnO:Co thin films are prepared by electrochemical deposition at different overpotentials and investigated by scanning electron microscopy, optical spectroscopy, and cathodoluminescence, X-ray photoelectron spectroscopy and Kerr magnetometry (MOKE). An increase of structural disorder and crystallite reorientation are observed for cobalt-doped samples. MOKE magnetometry revealed room-temperature ferromagnetic behavior only for ZnO: Co deposited at -850 mV. These are the samples with the lower cobalt content and lowest structural perturbation of the ZnO matrix by cobalt. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
992. Ferroelectric Schottky diode behavior from a SrRuO3-Pb(Zr0.2Ti0.8)O-3-Ta structure
Authors:
Pintilie, L; Stancu, V; Trupina, L; Pintilie, I
Published: AUG 18 2010, PHYSICAL REVIEW B, 82, DOI: 10.1103/PhysRevB.82.085319
A single ferroelectric Schottky diode was obtained on a SrRuO3-Pb(Zr0.2Ti0.8)O-3-Ta (SRO-PZT20/80-Ta) structure in which the SRO-PZT20/80 interface is the rectifying contact and the PZT20/80-Ta interface behaves as a quasiohmic contact. Both the capacitance-voltage (C-V) and the current-voltage (I-V) characteristics show the memory effect due to the ferroelectric polarization. However, retention studies had revealed that only the "down" orientation of ferroelectric polarization is stable in time (polarization oriented from top to bottom contact). The analysis of the experimental results suggests that the PZT20/80 is n type and that the stable orientation of polarization is related to the presence of a depletion region at the SRO-PZT20/80 Schottky interface.
993. HIGH PERFORMANCE COMPUTING INFRASTRUCTURE FOR MATERIALS SCIENCE
Authors:
Chihaia, V; Slusanschi, E; Herisanu, A; Palade, P; Tapus, N
Published: NOV-DEC 2010, REVUE ROUMAINE DE CHIMIE, 55, +, DOI:
Computer Material Science is a branch of material sciences that uses theoretical concepts and models from chemistry, physics, geology, mineralogy, as well as biology and includes them into software applications in order to calculate the structure and the properties of molecules, gases, liquids, soft and condensed matter. This paper presents the estimated performances of the HPC-ICF cluster of the Institute of Physical Chemistry "Ilie Murgulescu" of the Romanian Academy and the NCIT-UPB Cluster developed by the Computer Science Department of the University Politehnica of Bucharest, with the run in the parallel mode on these systems of the HPL - High Performance Linpack Benchmark as well as of the electronic structure codes GAMESS and ONETEP. The results of the study show that both clusters break the Teraflop barrier, thus making available a valuable tool for the Romanian scientific community in Computing Materials Science.
994. INVESTIGATION OF ELECTRICAL PROPERTIES OF CARBON NANOTUBES
Authors:
Ciurea, ML; Stavarache, I; Lepadatu, AM; Iancu, V; Dragoman, M; Konstantinidis, G; Buiculescu, R
Published: 2009, CAS: 2009 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, +, DOI: 10.1109/SMICND.2009.5336593
This paper presents the investigation of electrical properties of carbon nanotubes (CNT). A sandwich configuration, quartz substrate/Cr/Al/CNT (partially immersed in SiN)/Cr/Al was investigated. The CNT are mainly oriented parallel with the electrodes. Current - voltage characteristics were taken at 20 K and room temperature and a current - temperature characteristic was taken at constant voltage (20 mV). The I - V characteristics are almost linear, while the G - V characteristics present some peaks and dips, interpreted as voltage percolation thresholds. The I - T and R - T characteristics are also linear (except at low temperatures). The investigated structures have a high electrical polarizability.
995. Efficient 1.34-mu m laser emission of Nd-doped vanadates under in-band pumping with diode lasers
Authors:
Pavel, N; Dascalu, T; Vasile, N; Lupei, V
Published: JAN 2009, LASER PHYSICS LETTERS, 6, 43, DOI: 10.1002/lapl.200810099
We describe the output performance of the 1.34-mu m F-4(3/2)-> I-4(13/2) transition in Nd-doped vanadates under in-band pumping with diode lasers at the 0.88-mu m wavelength, directly into the F-4(3/2) emitting level. An end-pumped Nd:YVO4 crystal yielded 3.4 W of continuous-wave (CW) output power for 9.3 W of absorbed pump power. The slope efficiency with respect to the absorbed pump power was 0.43. To the best of our knowledge this is the first domonstration of such a laser system. Comparative results obtained for the pump with diode laser at 0.81 mu m, into the highly-absorbing F-4(5/2) level, are given in order to prove the advantages of the in-band pumping.
996. Structure and properties of (Cu Ca Bi) doped KNN lead-free piezoceramics
Authors:
Miclea, C; Tanasoiu, C; Miclea, CF; Trupina, L; Cioangher, M; Miclea, CT; Malczanek, V; Susu, M; Voicu, I; Ivanov, A
Published: SEP 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 946, DOI:
Lead free ceramics in the system (1-x)KNN x(Bi2O3,CaO,CuO) with 0.0 <= x <= 0.1 were synthesized by the usual solid state reaction and their structural and piezoelectric properties were investigated Dense samples with densities of about 4 68 g/cm(3) were prepared by sintering at an optimum temperature of 1150 degrees C for 6 h Only perovskite phase was detected by X-ray investigation in all samples A typical MPB where orthorombic-tetragonal phases coexist was detected for a doping level of 0.06 where the piezoelectric parameters showed maximum values Planar coupling factor, as much as 0.46, piezoelectric charge constant of 270 pC/N and mechanical quality factor Q(m) of 75 were recorded for the samples situated within the MPB.
997. Fe- and Eu-doped TiO2 Photocatalytical Materials Prepared by High Energy Ball Milling
Authors:
Vasiliu, F; Diamandescu, L; Macovei, D; Teodorescu, CM; Tarabasanu-Mihaila, D; Vlaicu, AM; Parvulescu, V
Published: JUN 2009, TOPICS IN CATALYSIS, 52, 556, DOI: 10.1007/s11244-009-9192-6
TiO2 nanopowders, doped with Fe3+ and Eu3+ were obtained by high-energy ball milling and their physical properties were investigated as a function of the doping content and ball milling time. A noticeable red shift and high photoactivity in the degradation and catalytic oxidation reactions of styrene and phenol were found for all doped specimens.
998. Magnetostructural correlations in the tetranuclear series of {Fe(3)LnO(2)} butterfly core clusters: Magnetic and Moumlssbauer spectroscopic study
Authors:
Bartolome, J; Filoti, G; Kuncser, V; Schinteie, G; Mereacre, V; Anson, CE; Powell, AK; Prodius, D; Turta, C
Published: JUL 2009, PHYSICAL REVIEW B, 80, DOI: 10.1103/PhysRevB.80.014430
Six tetranuclear complexes [Fe(III)(3)Ln(mu(3)-O)(2)(CCl3COO)(8)(H2O)(THF)(3)]center dot THF center dot C7H16 [Ln=Gd(III) (1), Tb(III) (2), Dy(III) (3), Ho(III) (4), Y(III) (5), and Lu(III) (6)] have been studied by magnetic susceptibility and Moumlssbauer spectroscopy. These isostructural molecules have a "butterfly" structure core consisting of two Fe(2)Ln(mu(3)-O) triangular "wings" which share a common Ln-Fe "body"; the dihedral angle between the wings is ca. 148 degrees. The coordination spheres of the iron ions are essentially distorted octahedral. The lanthanides are eight-coordinate with coordination polyhedra that may be described as distorted tetragonal bipyramids. Variable-temperature solid-state magnetic susceptibility in the temperature range 1.8-300 K and magnetization at 1.8 K for compounds 1-6 were measured. The spin state of Fe is S=5/2 in all cases. In compounds 5 and 6, where Ln(III) (Y and Lu, respectively) is diamagnetic, the three Fe atoms form an obtuse isosceles triangle with antiferromagnetic interactions J(Fe-Fe)=-50 K between the wing-tip Fe-w and body Fe-b atoms, and negligible interaction between the Fe-w's, resulting in a ground state of effective spin S=5/2 per cluster. In the complexes with paramagnetic lanthanide ions, the interaction between the Fe-3 triangle and the Ln(III) center is described by an effective exchange constant which is antiferromagnetic and 1 order of magnitude weaker. Besides, at 3 K incipient spin blocking, characteristic of single molecule magnets, was found to occur in the out-of-phase component of the ac susceptibility in {Fe3TbO2}, {Fe3DyO2}, and {Fe3HoO2}. The activation energy of a Debye process describing the magnetization reversal has been determined to be, E-a approximate to 8, 9, and 10 K for the Ln=Tb, Dy, and Ho, respectively, and the prefactor tau(0)approximate to 10(-7) s. The high spin states of the Fe(III) centers were confirmed by the Moumlssbauer spectra, in which two distinguishable Fe sites could be resolved above 80 K, corresponding to the Fe-w and Fe-b sites, respectively. Relatively larger values of the quadrupole splitting of the Moumlssbauer spectra were observed for the Fe-w pair as compared with that for the Fe-b, and both quadrupole splittings diminished with increasing temperature. At 3 K the Moumlssbauer spectra showed a state with blocked spins (sextets) for the {Fe3TbO2} and {Fe3DyO2} cases. From the E-a and tau(0), determined in the ac susceptibility, the relaxation time at 3 K is estimated as tau approximate to 10(-5)-10(-6) s much longer than the time window of Moumlssbauer spectroscopy and compatible with the single molecule magnet behavior. In the presence of a strong magnetic field the moments of the Ln(III) cation and the Fe-3 triangle are polarized. For some compounds at low temperature a magnetic pattern (sextet) for each of the three Fe sites appeared, and the antiferromagnetic coupling within the Fe-3 cluster was directly proved by the opposite trend of the field dependence of the two Fe-w sextets as compared with the Fe-b third one.
999. Spin configurations and interfacial diffusion in exchange bias and spin valve systems with Ir-Mn antiferromagnetic pinning layers
Authors:
Kuncser, V; Schinteie, G; Palade, P; Mustata, I; Lungu, CP; Stefan, N; Chiriac, H; Vladoiu, R; Filoti, G
Published: 2009, ISIAME 2008, +, DOI: 10.1007/978-3-642-01369-0_62
Exchange bias and spin valve structures with Fe as ferromagnetic layers selectively enriched in Fe-57 and Ir-Mn of different compositions as antiferromagnetic pinning layers have been prepared by r.f. sputtering. Conversion Electron Mossbauer Spectroscopy and Magneto Optic Kerr Effect have shown that the local structure and interactions in the whole ferromagnetic layers, with direct influence on their magnetic reversal processes, depend on growing order of the layers and composition of the AF layer. Interfacial atomic diffusion is the main reason of perturbing the local structure of the ferromagnet. Mossbauer Spectroscopy is a powerfool tool which allows a detailed analysis of local configurations, in order to optimize the magnetic and giant magnetoresistive parameters of such multilayers of important technological applications.
1000. Carbon nanotubes from ethanol on Fe-Co/MgO catalysts and related interface phenomena
Authors:
Lupu, D; Biris, AR; Baltog, I; Baibarac, M; Kuncser, V; Schinteie, G; Valeanu, M; Lefrant, S; Biris, AS; Misan, I; Filoti, G
Published: MAR 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 347, DOI:
Mossbauer spectroscopy studies of Fe-Co/MgO catalysts proved that a high dispersion degree of Fe may be achieved for catalysts containing Fe/Co in a ratio close to 1. During materials processing. the presence of hydrogen at high temperatures, even for short time, induced an increased particle size of the catalytic Fe. The evaluation of various iron species from their areas in the Mossbauer spectra revealed the dependence of the nanotube amount on (FeCo alloy + Fe2+) content in the catalyst, in good agreement with literature mechanisms. The Raman spectra show that carbon nanotubes synthesized from ethanol in argon flow on 4.5%Fe:4.5%Co/MgO are richer in low diameter (0.7-1.0nm) tubes than those obtained at low ethanol pressure, in agreement with the effects of hydrogen reported in literature. The close similarity with the Raman spectra of Aldrich double-walled carbon nanotubes and from literature, recommends the syntheses in argon flow as better conditions for double-walled carbon nanotube growth.
1001. Time-dependent transport via the generalized master equation through a finite quantum wire with an embedded subsystem
Authors:
Gudmundsson, V; Gainar, C; Tang, CS; Moldoveanu, V; Manolescu, A
Published: NOV 4 2009, NEW JOURNAL OF PHYSICS, 11, DOI: 10.1088/1367-2630/11/11/113007
In this paper, we apply the generalized master equation to analyze time-dependent transport through a finite quantum wire with an embedded subsystem. The parabolic quantum wire and the leads with several subbands are described by a continuous model. We use an approach originally developed for a tight-binding description selecting the relevant states for transport around the bias-window defined around the values of the chemical potential in the left and right leads in order to capture the effects of the nontrivial geometry of the system in the transport. We observe a partial current reflection as a manifestation of a quasi-bound state in an embedded well and the formation of a resonance state between an off-set potential hill and the boundary of the system.
1002. Ceramic laser materials and the prospect for high power lasers
Authors:
Lupei, V
Published: MAR 2009, OPTICAL MATERIALS, 31, 706, DOI: 10.1016/j.optmat.2008.04.007
The paper discusses the possibilities for enhancement of laser emission parameters and power scaling of Nd-doped transparent ceramic materials. It is shown that by a correlated approach that accounts for the properties of the laser material, pumping conditions and details of laser design, the direct diode laser pumping of these lasers into the emitting level F-4(3/2) enables additional power scaling in the range of 50-60% compared with the traditional 800 nm pumping in F-4(5/2).(.) (C) 2008 Elsevier B.V. All rights reserved.
1003. c-Axis correlated extended defects and critical current in YBa2Cu3Ox films grown on Au and Ag-nano dot decorated substrates
Authors:
Mikheenko, P; Sarkar, A; Dang, VS; Tanner, JL; Abell, JS; Crisan, A
Published: JUL 15 2009, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 469, 804, DOI: 10.1016/j.physc.2009.05.001
We report measurements of critical current in YBa2Cu3Ox films deposited on SrTiO3 substrates decorated with silver and gold nanodots. An increase in critical current in these films, in comparison with the films deposited on non-decorated substrates, has been achieved. We argue that this increase comes from the c-axis correlated extended defects formed in the films and originated from the nanodots. Additionally to creating extended defects, the nanodots pin them and prevent their exit from the sample during the film growth, thus keeping a high density of defects and providing a lower rate of decrease of the critical current with the thickness of the films. The best pinning is achieved in the samples with silver nanodots by optimising their deposition temperature. The nanodots grown at a temperature of a few hundred degrees C have a small diameter of a few nanometres and a high surface density of 10(11)-10(12) particles/cm(2). We give evidence of c-axis correlated extended defects in YBa2Cu3Ox films by planar and cross-sectional atomic force microscopy, transmission electron microscopy and angle-dependent transport measurements of critical current. (C) 2009 Elsevier B.V. All rights reserved.
1004. Nitridation and crystallization of titanium oxynitride by thermal treatment of TiO2-anatase films in NH3
Authors:
Trapalis, C; Calderon-Moreno, JM; Todorova, N; Teodorescu, VS; Stoica, M; Nicolescu, M; Anastasescu, M; Gartner, M; Zaharescu, M
Published: NOV 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 1814, DOI:
Nitrogen is often used for doping TiO2 films to improve their photocatalytic properties in visible light. Multilayer TiO2 anatase films were deposited by sol-gel method on quartz substrate and thermally treated in O-2 and NH3 flow in 500-800 degrees C range. The effect of the annealing treatment (temperature and atmosphere) on the structural properties of TiO2 films was studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Nitridation causes the amorphization of the anatase tetragonal phase at 600 degrees C. The film re-crystallization into the cubic oxynitride phase is observed at 800 degrees C. EDX results confirms that the incorporation of nitrogen into the amorphous films takes place before thermally activated growth of the oxynitride phase and demonstrates that the relative O:N composition in the crystalline phase is dependent on the temperature of the thermal treatment.
1005. Fabrication and Transport Properties of Manganite-Polyacrylamide-Based Composites
Authors:
Sandu, V; Popa, S; Ivan, I; Plapcianu, C; Sandu, E; Mihailescu, C; Doroftei, F
Published: 2009, JOURNAL OF NANOMATERIALS, 2009, DOI: 10.1155/2009/429430
We present the fabrication and transport properties of a series of composites made of La2/3Sr1/3MnO3 and acrylamide-based copolymers. The most important result is the very narrow transition, of only 27 K, displayed by the peak that appears around the metal-insulator transition of the composites made with poly(acrylamide-vinylacetate). Although the amount of polymer is rather low, different copolymers change drastically the electric transport characteristics. Copyright (C) 2009
1006. Characterization of magnetic nano-fluids via Mossbauer spectroscopy
Authors:
Filoti, G; Kuncser, V; Schinteie, G; Palade, P; Morjan, I; Alexandrescu, R; Bica, D; Vekas, L
Published: 2009, ISIAME 2008, +, DOI: 10.1007/978-3-642-01369-0_50
The laser pyrolysis became a useful tool, providing various ways, in production of nano materials. The iron Mossbauer spectroscopy is one very accurate method in evidencing the physical properties and related processes in the nano scale compounds. The effect of pressure, laser spot area and induced combustion, of gas mixture and laser power on the phase composition and inside particle distribution, grain size as well as the related phenomena were investigated by temperature dependent Mossbauer spectroscopy. A selection of most relevant properties is presented and discussed in details.
1007. The synthesis, structural characterization, magnetochemistry and Mossbauer spectroscopy of [Fe(3)LnO(2)(CCl3COO)(8)H2O(THF)(3)] (Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Lu and Y)
Authors:
Mereacre, V; Prodius, D; Turta, C; Shova, S; Filoti, G; Bartolome, J; Clerac, R; Anson, CE; Powell, AK
Published: SEP 23 2009, POLYHEDRON, 28, 3025, DOI: 10.1016/j.poly.2009.06.025
The new tetranuclear complexes [Fe(3)Ln(mu(3)-O)(2)(CCl3COO)(8)(H2O)(THF)(3)]center dot THF (Ln = Ce-III (1), Pr-III (2), Nd-III (3)) and [Fe(3)Ln(mu(3)-O)(2)(CCl3COO)(8)(H2O)(THF)(3)]center dot THF center dot C7H16 (Ln = Sm-III (4), Eu-III (5), Gd-III (6), Tb-III (7), Dy-III (8), Ho-III (9), Lu-III (10) and Y-III (11)) have been prepared. All compounds were prepared by the reaction between [Fe2BaO(CCl3COO)(6)(THF)(6)] and the corresponding Ln(III) nitrate salt. The crystal structures of 1-4, 8 and 9 have been determined; these isostructural molecules have a non-planar {Fe(3)Ln(mu(3)-O)(2)} "butterfly" core. Magnetic susceptibility measurements show dominant intramolecular antiferromagnetic exchange interactions for all the complexes. Fe-57 Mossbauer spectroscopy shows three different environments for the Fe-III metal ions, all in their high-spin state S = 5/2 (confirming that no electron transfer from Ce-III to Fe-III occurs in 1). At the time scale of the Mossbauer spectroscopy (about 10(-7) s), evidence of magnetization blocking, i.e. slow relaxation of the magnetization, is observed below 3 K for 7, which was confirmed by ac susceptibility measurements. (C) 2009 Elsevier Ltd. All rights reserved.
1008. Iron containing 3d-4f compounds: Effect of alternative processing on local interactions and storage properties
Authors:
Filoti, G; Palade, P; Lupu, D; Stromberg, F; Schinteie, G; Ardelean, O; Kuncser, V
Published: JUL 1 2009, JOURNAL OF ALLOYS AND COMPOUNDS, 480, 160, DOI: 10.1016/j.jallcom.2008.10.008
Samples of LaNi5-xFex were prepared by arc melting and subsequent melt spinning procedure. Structural, magnetic and Mossbauer investigations were performed for physical characterization while the hydrogen storage properties were carefully analyzed. Detailed discussions concerning the sample's quality, the site assignment, the effect of temperature and applied fields on hyperfine parameters and the related Debye temperatures were provided. (C) 2008 Elsevier B.V. All rights reserved.
1009. Fabrication of submicrometer periodic structures using interference lithography and two-layer chalcogenide photoresist
Authors:
Indutnyi, IZ; Popescu, M; Lorinczi, A; Sava, F; Min'ko, VI; Shepeliavyi, PE; Dan'ko, VA
Published: DEC 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 1971, DOI:
Technological process of interference lithography using two-layer chalcogenide photoresist were investigated. Top As(40)S(30)Se(30) layer is photoresist with a high selectivity and can be used for recording of interference pattern and formation of first lithographic mask. Second, more thick As(4)Ge(30)S(66) layer, almost is not sensitive to light, but dissolves in weak (0.05%) water solution of KOH. That, optimizing the etchant solutions for both layers, exposure and time of etching it is possible to carry out the technological process of formation of the lithographic mask with high modulation and with the groove form close to rectangular. This technology has been used for the fabrication of one- and two-dimensional periodic structures. Using two layer As(40)S(30)Se(30)-As(4)Ge(30)S(66) photoresist, we have fabricated the diffraction gratings and two-dimensional periodic structures with elements of submicron size. Relief parameters and diffractions properties of the obtained structures and their dependence on etching time are studied.
1010. Sol-gel doped TiO2 nanomaterials: a comparative study
Authors:
Raileanu, M; Crisan, M; Dragan, N; Crisan, D; Galtayries, A; Braileanu, A; Ianculescu, A; Teodorescu, VS; Nitoi, I; Anastasescu, M
Published: SEP 2009, JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 51, 329, DOI: 10.1007/s10971-009-2017-z
Among the great number of sol-gel prepared nanomaterials, TiO2 has attracted significant interest due to its high photocatalytic activity, excellent functionality, thermal stability and non-toxicity. The photocatalytic degradation of pollutants using un-doped and doped TiO2 nanopowders or thin films is very attractive for applications in environmental protection, as a possible solution for water purification. The present work describes a comparative structural and chemical study of un-doped TiO2 and the corresponding S- and Ag-doped materials. The photocatalytic activity was established by testing the degradation of organic chloride compounds from aqueous solutions. Sol-gel Ag-doped TiO2 coatings, prepared by co-gelation and sol-gel Ag-doped TiO2 coatings obtained from nanopowders were also compared. Their structural evolution and crystallization behaviour (lattice parameters, crystallite sizes, internal strains) with thermal treatment were followed by thermal analysis, X-ray diffraction, transmission electron microscopy, atomic force microscopy and specific surface areas measurements. X-ray photoelectron spectroscopy analyses were performed to characterize the surface composition and S or Ag speciation, which was used to interpret the catalytic data.
1011. Total oxidation of toluene on ferrite-type catalysts
Authors:
Florea, M; Alifanti, M; Parvulescu, VI; Mihaila-Tarabasanu, D; Diamandescu, L; Feder, M; Negrila, C; Frunza, L
Published: MAR 30 2009, CATALYSIS TODAY, 141, 366, DOI: 10.1016/j.cattod.2008.05.005
Ferrite catalysts were prepared following two routes, i.e. the hydrothermal one and the calcination of an oxide mixture. In the first route sodium hydroxide, ferrous sulfate and the sulfate of the substituting ion (Mn, Ni) were used. The ferrites obtained using this route was NixFe3-xO4 (x = 0.5) and MnxFe3-xO4 (x similar to 0.65). Following the second route were prepared three samples: NiFe2O4, Ni0.5Zn0.5Fe2O4 and MnFe2O4. Two of them contain the corresponding ferrites while the latter is a presintered oxide mixture (Fe2O3-Mn2O3). All the samples were fully characterized using chemical analysis, X-ray fluorescence spectroscopy and EDX, nitrogen adsorption-desorption isotherms at -196 degrees C, X-ray diffraction (XRD), FTIR, scanning electron microscopy and XPS. The catalytic activity evaluation was made using a mixture of 1700 ppm vol. of toluene and air flowing at 100 ml min(-1) raising the temperature up to 600 degrees C in steps of 25 degrees C. Among these systems the sample representing the presintered Fe2O3-Mn2O3 mixture showed the highest activity. (C) 2008 Elsevier B.V. All rights reserved.
1012. Critical current density and pinning potential in YBa2Cu3O7-delta thick films ablated from a BaZrO3-doped nanocrystalline target
Authors:
Crisan, A; Kechik, MMA; Mikheenko, P; Dang, VS; Sarkar, A; Abell, JS; Paturi, P; Huhtinen, H
Published: APR 2009, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 22, DOI: 10.1088/0953-2048/22/4/045014
We report on the pulsed laser deposition and characterization of thick (1.27 mu m) films ablated from a nanocrystalline YBa2Cu3O7-delta (YBCO) target doped with 4 wt% BaZrO3 (BZO), nYBCO/BZO. DC magnetization measurements have shown a four-to five-fold increase in the critical current density J(c) and a three- to four-fold increase in the maximum pinning force in comparison with 1 mu m thick films grown from a commercial microcrystalline YBCO target, at both 77.3 and 65 K. We have found that the frequency-dependent critical current densities J(c)(f(0)/f) estimated from susceptibility measurements are linear in a double-logarithmic plot ( where f is the frequency of the AC field and f(0) is a macroscopic attempt frequency of about 10(6) Hz), consistent with a logarithmic dependence of the pinning potential on the current density, and are again several times higher in nYBCO/BZO thick films. From the slopes of the J(c)(f(0)/f) dependences we have also estimated the values of pinning potentials in fields between 3 and 5 T.
1013. Cobalt doped ZnO prepared by electrochemistry: chemistry, morphology, and magnetism
Authors:
Enculescu, I; Matei, E; Vasilache, V; Teodorescu, CM
Published: 2009, NANOTECH CONFERENCE & EXPO 2009, VOL 3, TECHNICAL PROCEEDINGS: NANOTECHNOLOGY 2009: BIOFUELS, RENEWABLE ENERGY, COATINGS FLUIDICS AND COMPACT MODELING, +, DOI:
ZnO:Co thin Films are prepared by electrochemical deposition at different overpotentials and investigated by scanning electron microscopy, X-ray photoelectron spectroscopy and Kerr magnetometry (MOKE). Increse of structural disorder and crystallite re-orientation are observed for cobalt doped samples (especially for those obtained at - 750 and at - 800 mV overpotentials). MOKE magnetometry revealed room temperature ferromagnetic behaviour only for ZnO:Co deposited at - 850 mV. These are the samples with the less cobalt content and lowest structural perturbation of the ZnO matrix by cobalt.
1014. Nonmonotonic flux flow in inhomogeneous superconductors above the percolation threshold
Authors:
Sandu, V
Published: FEB 1 2009, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 469, 128, DOI: 10.1016/j.physc.2008.12.010
Flux flow resistivity above critical temperature is analyzed based on the increased evidences that high temperature superconductors are intrinsically inhomogeneous, and local nonpercolating superconducting domains persist high above the critical temperature. It was found that above a certain field, the resistivity originated in the flow Of flux motion starts to decrease with increasing field, due to the predominance of the suppression of the superconducting droplets over the increase of vortex core density. (C) 2008 Elsevier B.V. All rights reserved.
1015. The Influence of the Electrode Type on the Electric-Ferroelectric Properties of Sandwich PbZr0.2Ti0.8O3-BiFeO3-PbZr0.2Ti0.8O3 Structure
Authors:
Pintilie, L; Dragoi, C; Stancu, V; Pintilie, I
Published: 2009, FERROELECTRICS, 391, 66, DOI: 10.1080/00150190903001235
PbZr0.2Ti0.8O3-BiFeO3-PbZr0.2Ti0.8O3 (PZT-BFO-PZT) structure was prepared by sol-gel method on Pt/Si wafers. Three metals were tested as top electrod: Au, Cu, and Pt. A double hysteresis loop was observed in all cases, suggesting an antiferroelectric-like behavior. The values for remnant polarization and coercive field are about 3 mu C/cm(2) and 115 kV/cm, respectively. The saturation polarization is about 22 mu C/cm(2). Capacitance and leakage current show significant dependence on the top metal electrode. The results were explained considering the presence of a Schottky-type contact at the PZT-metal interface.
1016. Coprecipitated Cobalt Ferrite for Sensors
Authors:
Boutiuc, LM; Dumitru, I; Caltun, OF; Feder, M; Vilceanu, V
Published: JUN 2009, SENSOR LETTERS, 7, 246, DOI: 10.1166/sl.2009.1067
In order to determine the influence of the sintering temperature on the performances of the magnetostrictive materials based sensor for stress, three series of cobalt ferrite (CoFe2O4) samples were prepared by coprecipitation method. These samples were sintered at 1050 degrees C, 1100 degrees C, 1150 degrees C. The spinel structure and the presence of the residual phases were investigated by X-ray diffractometry, scanning electron microscopy and vibrating sample magnetometry. Magnetostrictive properties of the samples were measured by strain gauge technique, in a direction which is parallel to the direction of the applied field. This study was focused on the influence of sintering temperature on magnetic properties and on magnetostriction coefficients. The study reveals that the increase of the sintering temperature increased the magnetostriction coefficients but decreased the strain derivative. Cobalt ferrite obtained by this method can be good candidates for sensors.
1017. Improvement of Pinning Force and Critical Current Density in Thick YBa (2) Cu (3) O (7-delta) Films Grown on SrTiO (3) Substrates Decorated with LaNiO (3) Nanodots
Authors:
Crisan, A; Sarkar, A; Mikheenko, P; Dang, VS; Kechik, MMA; Abell, JS
Published: OCT 2009, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 22, 636, DOI: 10.1007/s10948-009-0452-2
We have investigated by DC magnetization measurements and frequency-dependent AC susceptibility the critical current density (J (c)), pinning force (F (p)) and pinning potential in thick (1.3-1.6 mu m) YBa2Cu3O7-delta (YBCO) films grown by Pulsed Laser Deposition on SrTiO3 substrates decorated with LaNiO3 nanodots deposited by a few (5-15) laser pulses, in comparison with those of a 1 mu m thick YBCO reference sample. Experiments show that the highest improvement of superconducting properties was achieved for films grown on substrates decorated with 10 laser pulses on the LaNiO3 target, which have, at 77.3 K, a J (c) of 40-125% higher than in pure YBCO in fields between 1 and 2 T, and F (p) increased by 40%. These results could be important for further improvement of current-carrying capability of coated conductors for in-field power applications.
1018. Coulomb drag in parallel quantum dots
Authors:
Moldoveanu, V; Tanatar, B
Published: JUN 2009, EPL, 86, DOI: 10.1209/0295-5075/86/67004
We study theoretically the electronic transport in parallel few-level quantum dots in the presence of both intradot and interdot long-range Coulomb interaction. Each dot is connected to two leads and the steady-state currents are calculated within the Keldysh formalism using the random-phase approximation for the interacting Green functions. Due to the momentum transfer between the two systems it is possible to get a nonvanishing current through an unbiased Coulomb-blockaded dot, if the other dot is set in the nonlinear transport regime. The transitions between the levels of the passive dot reduce the drag current and lead to negative differential conductance. We also discuss the dependence on temperature and the role of the lead-dot coupling. Copyright (C) EPLA, 2009
1019. Fano effect in a double T-shaped interferometer
Authors:
Moldoveanu, V; Dinu, IV; Tanatar, B
Published: JAN 2009, EUROPEAN PHYSICAL JOURNAL B, 67, 238, DOI: 10.1140/epjb/e2009-00012-0
We study the coherent transport in a one-dimensional lead with two side-coupled quantum dots using the Keldysh's Green function formalism.The effect of the interdot Coulomb interaction is taken into account by computing the firstand second order contributions to the self-energy.We show that the Fano interference due to the resonance of one dotis strongly affected by the fixed parameters that characterize the second dot. If the second dot is tuned close to resonance an additionalpeak develops between the peak and dip of the Fano line shape of the current. In contrast, when the second dotis off-resonance and its occupation number is close to unity the interdot Coulomb interaction merely shifts the Fano line and no other maxima appear.The system we consider is more general than the single-dot interferometer studied experimentally by Kobayashi et al. [Phys. Rev. B 70, 035319 (2004)] and may be used for controlling quantum interference and studying decoherence effects in mesoscopic transport.
1020. RPA APPROACH TO NON-LINEAR TRANSPORT IN QUANTUM DOTS
Authors:
Tanatar, B; Moldoveanu, V
Published: AUG 20 2009, INTERNATIONAL JOURNAL OF MODERN PHYSICS B, 23, 4421, DOI: 10.1142/S0217979209063560
An accurate theoretical treatment of electron-electron interactions in mesoscopic systems is available in very few cases and approximation schemes are developed in most of the applications, especially for many-level quantum dots. Here we present transport calculations within the random-phase approximation for the Coulomb interaction using the Keldysh Green's functions formalism. We describe the quantum dot systems by a tight-binding Hamiltonian. Our method is similar to the one used by Faleev and Stockman [Phys. Rev. B 66 085318 (2002)] in their study of the equilibrium properties of a homogeneous 2D electron gas. The important extension at the formal level is that we combine the RPA and the Keldysh formalism for studying non-linear transport properties of open quantum dots. Within the Keldysh formalism the polarization operator becomes a contour-ordered quantity that should be computed either from the non-interacting Green functions of the coupled quantum dot (the so-called G(0)W approximation) either self-consistently (GW approximation). We performed both non-selfconsistent and self-consistent calculations and compare the results. In particular we recover the Coulomb diamonds for interacting quantum dots and we discuss the charge sensing effects in parallel quantum dots.
1021. Geometrical effects and signal delay in time-dependent transport at the nanoscale
Authors:
Moldoveanu, V; Manolescu, A; Gudmundsson, V
Published: JUL 7 2009, NEW JOURNAL OF PHYSICS, 11, DOI: 10.1088/1367-2630/11/7/073019
Nonstationary and steady-state transport through a mesoscopic sample connected to particle reservoirs via time-dependent barriers is investigated by the reduced density operator method. The generalized master equation is solved via the Crank-Nicolson algorithm by taking into account the memory kernel which embodies the non-Markovian effects that are commonly disregarded. The lead-sample coupling takes into account the match between the energy of the incident electrons and the levels of the isolated sample, as well as their overlap at the contacts. Using a tight-binding description of the system, we investigate the effects induced in the transient current by the spectral structure of the sample and by the localization properties of its eigenfunctions. In strong magnetic fields, the transient currents propagate along edge states. The behavior of populations and coherences is discussed, as well as their connection to the tunneling processes that are relevant for transport.
1022. Potential-Induced Conformational Changes in an alpha-CN-terthiophene Thiolate Film on GaAs(110)
Authors:
Lazarescu, V; Scurtu, R; Lazarescu, MF; Toader, AM; Volanschi, E; Santos, E; Jones, H; Gotz, G; Bauerle, P
Published: JUN 2 2009, LANGMUIR, 25, 6531, DOI: 10.1021/la900043k
Second harmonic generation (SHG) investigations on alpha-CN-terthiophene-thiolate-covered GaAs(110) electrodes in 1 N H2SO4 solution revealed significant changes in the rotational anisotropy of the SH response. The enhancement of the 1- and the 3-fold contributions around -250 mV suggests changes in the symmetry properties of the delocalized electron system due to an alteration of the adsorption geometry induced by the applied potentials. The analysis of the EIS data showed that in the potential region where the SH signal exhibits the more important changes the Mott-Schottky plot undergoes a pronounced shift to more negative potentials as a result of the charging of the surface states grouped about 1.06 eV below the conduction band edge. Semiempirical MO calculations suggest that the most energetically favorable interaction implies electron transfer from the semiconductor conduction band to the lowest unoccupied molecular orbital of the organic molecule with epsilon(LUMO) = -1.707 eV. Such a chemisorption bond bringing the organic molecule to a quasi-planar position is well supported by the major changes in the XPS spectra of the electrochemically biased samples with respect to the as-prepared ones. Two distinct N Is species instead of one and a shift of 1.6 eV to higher BE of the terthiophene S 2s core level are strong evidence for a potential-induced change in the adsorption geometry. Taking into account that the acceptor-like surface state group located close to the semiconductor valence edge (E-C,E-S = -1.06 eV) may correspond to the LUMO level (shifted downward by the adsorption process), we assume that the organic molecule, initially adsorbed by the thiolate end, undergoes a conformational change from a tilted to an almost flat position when the applied potential brings the semiconductor Fermi level into its neighborhood. This assumption is in a very good agreement with the potential-induced variation in the thiol thickness estimated from the thiol capacitance.
1023. Transesterification of vegetable oils on basic large mesoporous alumina supported alkaline fluorides-Evidences of the nature of the active site and catalytic performances
Authors:
Verziu, M; Florea, M; Simon, S; Simon, V; Filip, P; Parvulescu, VI; Hardacre, C
Published: APR 1 2009, , DOI: 10.1016/j.jcat.2009.01.012
1024. Q-switched Nd lasers pumped directly into the F-4(3/2) emitting level
Authors:
Pavel, N; Dascalu, T; Salamu, G; Sandu, O; Leca, A; Lupei, V
Published: DEC 15 2009, OPTICS COMMUNICATIONS, 282, 4754, DOI: 10.1016/j.optcom.2009.08.067
The influence of the direct pumping into the F-4(3/2) emitting level on the output characteristics of continuous-wave (CW) pumped, passively or actively (acoustooptic, AO) Q-switched Nd lasers is discussed. In case of passive Q-switching by Cr4+: YAG saturable absorber (SA) crystal, the change of pumping wavelength from 0.81 mu m into the highly-absorbing F-4(5/2) level to 0.88 mu m into the F-4(3/2) level of Nd does not modify the energy of the Q-switch pulse, but increases the pulse repetition rate and the laser average power for the same absorbed pump power. This is demonstrated with 0.81 and 0.88 gm CW laser diode-pumped Nd:YAG and Nd-vanadate lasers with average output power in the watt-level range at 1.06 mu m. The effect is explained by the control of passive Q-switching by the intracavity photon flux that is influenced by the pump wavelength and by the initial transmission of the SA crystal. On the other hand, it is discussed and experimentally proved that due to the possibility to control externally the frequency of switching, in case of the AO Q-switched Nd laser the change of the pump wavelength from 0.81 to 0.88 pm increases the pulse energy for a fixed frequency, leading to a corresponding increase of the average laser power. (C) 2009 Elsevier B.V. All rights reserved.
1026. Surface states- and field-effects at p- and n-doped GaAs(111)A/solution interface
Authors:
Scurtu, R; Ionescu, NI; Lazarescu, M; Lazarescu, V
Published: 2009, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 11, 1770, DOI: 10.1039/b817045b
We have investigated the behaviour of n- and p-doped GaAs(111) A electrodes in sulfuric acid solution by electrochemical impedance spectroscopy (EIS) and second harmonic generation (SHG) measurements. The potential dependence of the SHG response was found to be closely related to the changes in the surface state population, as revealed by analysis of the impedance data. The nature of the majority of carriers turned out to be a key factor in shaping the surface state- and field-effect on the second harmonic generation process.
1027. Efficient Laser Emission of Nd-vanadates on the 1.34-mu m (4)F(3/2)->(4)I(13/2) Transition under Pumping with Diode Lasers Directly into the Emitting Level
Authors:
Pavel, N; Dascalu, T; Vasile, N; Lupei, V
Published: 2009, 2009 CONFERENCE ON LASERS AND ELECTRO-OPTICS AND QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (CLEO/QELS 2009), VOLS 1-5, 2604, DOI:
Efficient 1.34-mu m laser emission is realized in Nd-vanadates under pumping with diode lasers at 0.88 mu m. A Nd:YVO(4) crystal yielded 3.4-W output power for 9.3-W absorbed pump power, at a slope efficiency of 0.43. (C) 2009 Optical Society of America
1028. Polymer functionalization with manganites
Authors:
Sandu, V; Popa, S; Ivan, I; Plapcianu, C; Sandu, E; Hurduc, N; Nor, I
Published: 2009, SECOND INTERNATIONAL CONFERENCE ON SMART MATERIALS AND NANOTECHNOLOGY IN ENGINEERING, 7493, DOI: 10.1117/12.843221
We investigated the transport properties of a series of composites made of La2/3Sr1/3MnO3 and different copolymers. The temperature dependence of the electrical resistance of the samples is strongly dependent on the nature of the polymers. We found four types of temperature dependences of the electrical resistance: i) simple current dependence of resistivity for poly(methyl-methacrylate-co-styrene) copolymers, ii) single peaked characteristics for poly(acryl amide-co-vinyl acetate), iii) multipeaked dependence found in poly(methyl-methacrylate-co-butadiene) and star type polysiloxane-g-styrene, and iv) current independent characteristics visible in the samples made with linear polysiloxane-based composites.
1029. Enhancing critical current in YBCO thick films: Substrate decoration and quasi-superlattice approach
Authors:
Sarkar, A; Mikheenko, P; Dang, VS; Abell, JS; Crisan, A
Published: AUG-OCT 2009, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 469, 1553, DOI: 10.1016/j.physc.2009.05.242
For power applications of superconducting films. the critical current density (J(c)) and the thickness of the film (d) should be as high as possible. Since J(c) decreases with both thickness and magnetic field, artificial pinning centres in addition to natural ones are required to keep J(c) high. The earliest cost-effective method used for introducing artificial pinning centres was the so-called substrate decoration, i.e., growing nanoscale islands (nano-dots) of certain materials on the substrate prior to the deposition of the superconducting thin film. Later on another version of this approach proved to be successful: building up a layered distribution of a second phase using a multilayer deposition (quasi-superlattices). Several materials have been used for the Creation of artificial pinning centres. Here we report on the artificial pinning centres induced in YBCO thick films by substrate decoration and quasi-superlattice approaches using nano-dots of Pd and non-superconducting YBCO. The cross-sectional AFM images show evidence of c-axis correlated columnar defects. These defects significantly contribute to the pinning of magnetic flux and increase critical current in the films. We observed an important shift of the position of the maximum in the thickness dependence of J(c)(B) towards higher thicknesses compared with pure YBCO films by both approaches. A high J(c)(B) in our quite thick films provides a very high total critical current per cm of the film width. Critical current as high as 800 A/cm width was achieved in a 2.4 mu m thick quasi-superlattice film with non-superconducting YBCO nano-dots. (C) 2009 Elsevier B.V. All rights reserved.
1030. Synthesis, Mechanism, and Gas-Sensing Application of Surfactant Tailored Tungsten Oxide Nanostructures
Authors:
Pokhrel, S; Simion, CE; Teodorescu, VS; Barsan, N; Weimar, U
Published: JUN 9 2009, ADVANCED FUNCTIONAL MATERIALS, 19, 1774, DOI: 10.1002/adfm.200801171
Widely applicable nonaqueous solution routes have been employed for the syntheses of crystalline nanostructured tungsten oxide particles from a tungsten hexachloride precursor. Here, a systematic study on the crystallization and assembly behavior of tungsten oxide products made by using the bioligand deferoxamine mesylate (DFOM) (product I), the two chelating ligands hexadecyltrimethylammoniumbromide (CTAB) (II) and poly(alkylene oxide) block copolymer (Pluronic P123) (III) is presented. The mechanistic pathways for the material synthesis are also discussed in detail. The tungsten oxide nanomaterials and reaction solutions are characterized by Fourier transform IR, H-1, and C-13 NMR spectroscopies, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and selected-area electron diffraction. The indexing of the line pattern suggests WO3 is in its monoclinic structure with a=0.7297nm, b=0.7539nm, c=0.7688nm, and beta=90.91 degrees. The nanoparticles formed have various architectures, such as chromosomal shapes (product I) and slates (II), which are quite different from the mesoporous one (III) that has internal pores or mesopores ranging from 5 to 15 nm. The nanoparticles obtained from all the synthetic procedures are in the range of 40-60 nm. The investigation of the gas-sensing properties of these materials indicate that all the sensors have good baseline stability and the sensors fabricated from material III present very different response kinetics and different CO detection properties. The possibility of adjusting the morphology and by that tuning the gas-sensing properties makes the preparation strategies used interesting candidates for fabricating gas-sensing materials.
1031. Nanostructured Ferrite Formation in Borosilicate Glass
Authors:
Sandu, V; Popa, S; Pasuk, I; Enculescu, I; Nicolescu, MS; Radicescu, S
Published: 2009, MULTI-FUNCTIONAL MATERIALS AND STRUCTURES II, PTS 1 AND 2, 79-82, +, DOI: 10.4028/www.scientific.net/AMR.79-82.445
We present the preparation, structural, and magnetic properties of a series of Fe-containing borosilicate glasses as a function of the ratio SiO2/Fe2O3 which is ranging from 1.49 to 2.68. The role of nucleators (Cr2O3 and P2O5) was also investigated. X-Ray diffraction has revealed the formation of magnetite as the major or unique crystalline phase. As SEM micrographs have revealed, the addition of P2O5 give rise to a finer structure as compared with Cr2O3. In addition, the same oxide decreases the temperature of structural transition with almost 100 degrees C. The magnetization data reveal a two step transition at low temperatures: a high temperature transition at T-v = 128 K, which we attribute to the Verwey transition, and a low temperature transition at T-s = 48 K which, most likely, is the result of change in the dynamic of the domain motion.
1032. Upconversion emission of RE3+ in Sc2O3 ceramic under 800 nm pumping
Authors:
Lupei, A; Lupei, V; Gheorghe, C; Ikesue, A; Osiac, E
Published: MAR 2009, OPTICAL MATERIALS, 31, 749, DOI: 10.1016/j.optmat.2008.02.008
The infrared (800 nm range) radiation conversion to visible in Er3+ doped or (Nd, Yb, Tm) co-doped Sc2O3 transparent ceramics was investigated. The green upconversion (H-2(11/2) -> S-4(3/2)) -> I-4(15/2) emission in Er - 3 (at low Er content) under pulsed pumping into (I-4(15/2) -> I-4(19/2)) absorption lines shows a competition between ESA (excited state absorption) (I-4(15/2) -> I-4(19/2)) + (I-4(19/2) -> H-2(9/2)) and ETU (energy transfer upconversion) (I-4(11/2) -> I-4(15/2)) +(I-4(11/2) -> F-4(7/2)) two-step processes, function on the excitation wavelength. The upconversion transfer rates were estimated. The features of the blue (1)G(4) -> H-3(6) Tm3+ upconversion emission in (Tm, Nd, Yb):Sc2O3 ceramic, under pumping at 808.3 nm were also analyzed. At this wavelength both Nd3+ and Tm3+ present ground state absorption. The data suggest that the population of Tm3+ (1)G(4) emitting level is achieved by the energy transfer processes Nd(F-4(3/2) -> I-4(11/2)) + Tm(H-3(4) -> (1)G(4)), or the chain Nd(F-4(3/2) -> I-4(19/2)) + Yb(F-2(1/2) -> F-2(5/2)) followed by the Yb(F-2(5/2) -> F-2(7/2)) + Tm(H-3(4) -> (1)G(4)), function on Yb3+ content. (C) 2008 Elsevier B.V. All rights reserved.
1033. Current dependent angular magnetoresistance in strongly Pr-doped Y Ba2Cu3O7-delta single crystal
Authors:
Sandu, V; Gyawali, P; Katuwal, T; Almasan, CC; Taylor, BJ; Maple, MB
Published: 2009, 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5: SUPERCONDUCTIVITY, 150, DOI: 10.1088/1742-6596/150/5/052222
We report a strong dependence of the angular magneto resistance (AMR) on the current density in Y0.47Pr0.53Ba2Cu3O7-delta single crystal above the critical temperature T-c = 13 K for any applied field up to 14 T. We estimated the current dependence from the angular dependence of the top resistance R-top, as measured on the face where the current is applied, and the bottom resistance R-bot as measured on the opposite face. At any temperature, both below and above T-c, R-top decreases as the field becomes parallel to the current and ab-plane with an angle dependence that suggests an important contribution arising from the vortex flow. R-bot evolves from a monotonic to nonmonotonic angle dependence with three minima and two maxima in the angle range 0 - 180 degrees as the temperature increases. For less Pr-doped samples, Y0.58Pr0.42Ba2Cu3O7-delta (T-c = 39 K) and Y0.68Pr0.32Ba2Cu3O7-delta (T-c = 55 K), where the interplane resistivity is much lower, both R-top and R-bot follow the same monotonic angle dependence in all temperature and field range.
1034. Pinning Centers Induced in YBCO Films by Nano-Dots in Substrate Decoration and Quasi-Superlattice Approaches
Authors:
Mikheenko, P; Sarkar, A; Dang, VS; Tanner, JL; Kechik, MMA; Abell, JS; Crisan, A
Published: JUN 2009, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 19, 3494, DOI: 10.1109/TASC.2009.2018307
For power applications of superconducting films, the critical current density (J(c)) and the thickness of the film (d) should be as high as possible. Since J(c) decreases with both thickness and magnetic field, artificial pinning centers in addition to natural ones are required to keep J(c) high. The earliest cost-effective method used for introducing artificial pinning centers was the so-called substrate decoration, i.e., growing nanoscale islands (nano-dots) of certain materials on the substrate prior to the deposition of the superconducting thin film. Later on other two approaches proved to be successful: building up a layered distribution of a second phase using a multilayer deposition (quasi-superlattices) and distributing a secondary phase in the film from a compositionally changed target. Several materials have been used for the creation of artificial pinning centers. Here we report on the artificial pinning centers induced in YBCO thick films by substrate decoration and quasi-superlattice approaches using nano-dots of Ag, Au, Pd or non-superconducting YBCO. The cross-sectional AFM images show evidence of c-axis correlated columnar defects. These defects significantly contribute to the pinning of magnetic flux and increase critical current in the films.
1035. Fabrication and characterization of nano-structured ferromagnetic Ti1-xFexO2 thin films
Authors:
Apetrei, R; Negrila, C; Macovei, D; Dascaleanu, V; Teodorescu, CM; Mardare, D; Luca, D
Published: 2009, NANOTECH CONFERENCE & EXPO 2009, VOL 1, TECHNICAL PROCEEDINGS: NANOTECHNOLOGY 2009: FABRICATION, PAR, DOI:
Nanostructured intrinsic and doped titania materials have long been subject to both basic and applied research, in connection with environment and energy related applications. Apart from beneficial effects. such as widening the wavelength range for surface photocatalytic activation, doping TiO2 materials with 3d ferromagnetic cations is a main route to develop ail important class of diluted semiconductors, with potential applications in spintronics. In all the previous investigations the concentration of the ferromagnetic dopant was limited to a few percents. Here, we initiate ail extended investigation of Ti1-xFexO2 within a, wider iron composition range (x = 0 - 0.55) and discuss the magnetic and optical properties of these materials in thin films in relation with their elemental composition, nano-structure and local atomic ordering.
1036. Study of the ground multiplet of Kramers rare earth ions in solid matrices by multifrequency electron paramagnetic resonance spectroscopy: Nd3+ in PbWO4 single-crystals
Authors:
Popescu, FF; Bercu, V; Barascu, JN; Martinelli, M; Massa, CA; Pardi, LA; Stefan, M; Nistor, SV; Nikl, M; Bohacek, P
Published: JUL 21 2009, JOURNAL OF CHEMICAL PHYSICS, 131, DOI: 10.1063/1.3180697
A multifrequency electron paramagnetic resonance (EPR) investigation of Nd3+ impurities in PbWO4 single-crystals at the conventional microwave frequency (MF) 9.43 GHz, and at the 95, 190, and 285 GHz high frequencies was carried out. The resulting spectra are well described at all frequencies by an axial spin-Hamiltonian corresponding to an effective electron spin of one-half and to a tetragonal symmetry. For the magnetic field along the tetragonal axis, the g(-)factor and the hyperfine constant A of the lowest doublet of the ground multiplet decreases with frequency increase. For the magnetic field perpendicular to the tetragonal axis, the g(perpendicular to)-factor exhibits a small azimuthal angular dependence that increases with increasing the frequency due to the S-4 site symmetry. The azimuthal angular dependence allows to clearly distinguish between different local axial symmetries. These properties are interpreted as high field/frequency (HF) effects associated with the mixing by the large Zeeman interaction of some of the upper-lying doublets of the ground multiplet into the lowest-lying doublet states. We show that from the combined analysis of the multifrequency MF- and HF-EPR spectra and of the optical data, an accurate description of the ground multiplet of the Kramers rare earth ions in solid matrices can be derived.
1037. TiO2-CeO2 Nanometric Powders Prepared by Sol-Gel Method
Authors:
Zaharescu, M; Wittmar, A; Teodorescu, V; Andronescu, C; Wittmar, M; Veith, M
Published: 2009, ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 635, +, DOI: 10.1002/zaac.200900186
Nanometric powders in the TiO2-CeO2 System were synthesized using sol-gel methods aiming at corrosion inhibitor preparation. The precursors employed were Ti(OiPr)(4) as TiO2 source and Ce(NO3)(3)center dot 6H(2)O or Ce(CH3CO2)(3)center dot xH(2)O as CeO2 source. Several parameters were varied, like the cerium precursor (cerium nitrate or cerium acetate) and the TiO2:CeO2 molar ratios. For both cerium sources binary powders with TiO2:CeO2 = 4:1 or 1:1 molar ratios were prepared. The obtained materials were dried 12 h in an oven at 100 degrees C and then thermally treated for 1 h at 400 degrees C with a heating rate of 1 degrees C.min(-1) in order to eliminate the water and organic residues. In all cases, nanometric - predominantly amorphous - powders have been obtained which crystallized after the I h thermal treatment at 400 degrees C. The only exception was recorded for the TiO2:CeO2 = 4:1 composition prepared from the Ce(NO3)(3)-6H(2)O precursor which remained amorphous after the thermal treatment. Even though the primary particle sizes were similar to 4-5 nm, the material is constituted from aggregates larger than 50 nm. The desired presence of cerium in two valence states, necessary in active corrosion protection, was achieved and it was put into evidence by XPS and DTA/TGA for the TiO2:CeO2 = 4:1 binary compositions. Future studies have to be performed in order to reduce the agglomeration of the material.
1038. Films and crystalline powder of PbI2 intercalated with ammonia and pyridine
Authors:
Preda, N; Mihut, L; Baibarac, M; Baltog, I; Ramer, R; Pandele, J; Andronescu, C; Fruth, V
Published: JAN 2009, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 20, 470, DOI: 10.1007/s10854-008-9681-6
Thin films and crystalline powder of PbI2 intercalated with ammonia or pyridine have been studied by optical absorption, Raman scattering, photoluminescence, FTIR spectroscopy and thermo-gravimetric analysis. Ammonia intercalated PbI2 shows an increased optical band gap, of about 0.6 eV, with an intense broad emission band peaking at about 2.3 eV as signature in the photoluminescence spectrum. The intercalation of PbI2 with ammonia is noticed in the Raman spectrum by the appearance of new lines situated in low frequency range. The D-3d coordination geometry of Pb2+ in the PbI2 crystal is reduced by compression to orthorhombic one, the distribution of the electronic states in valence band is also changed. Thus, the top of the valence band undergo a deformation inducing a weakness of the interaction between the lead and iodine ions within a layer. Also the PbI2 intercalated with pyridine is featured by optical and vibration properties different that of pure crystalline powder. Finally, the intercalation of PbI2 with different molecules changes the basic semiconducting properties of the crystal. Thermal analyses and infrared absorption spectra have been used to study the desorption of guests species from PbI2 in order to evaluate the stability range and morphological changes with temperature.
1039. Magnetic properties of MgB2-Fe sandwiches produced by Field-Assisted-Sintering Technique
Authors:
Aldica, G; Sandu, V; Plapcianu, C; Badica, P; Groza, JR
Published: 2009, 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5: SUPERCONDUCTIVITY, 150, DOI: 10.1088/1742-6596/150/5/052006
Superconducting SiC and B4C-doped MgB2 samples containing up to three layers of pure Fe have been prepared by Field-Assisted-Sintering Technique (FAST). The adhesion between the Fe and doped-MgB2 layers is excellent due to the enhanced local interdiffusion and increased solubility of Fe into MgB2 grains that are typical for the non-equilibrium processes. Magnetic measurements showed the largest irreversibility, hence, the largest critical current density in the B4C-doped sandwich with one Fe foil. Additionally, the drawback of flux jumps at low temperatures is almost absent for one Fe-layer sandwiches. However, the irreversibility is smaller than in pure MgB2 and SiC-doped MgB2 samples prepared by the same technique, but without the insertion of Fe foil. When the number of Fe foils is increased to three and an excess of 5 % wt. Mg is added, the SiC-doped sandwiches show almost similar irreversibility values and field dependence (at 5 K and at 20 K) as the pristine MgB2 samples without Fe. But, the flux jump is recovered at the same level found for the pristine MgB2 without Fe. An explanation in terms of doping dependence of the ratio between the thermal and magnetic diffusion constants is proposed.
1040. Synthesis, structural characterization, and photocatalytic properties of iron-doped TiO2 aerogels
Authors:
Popa, M; Diamandescu, L; Vasiliu, F; Teodorescu, CM; Cosoveanu, V; Baia, M; Feder, M; Baia, L; Danciu, V
Published: JAN 2009, JOURNAL OF MATERIALS SCIENCE, 44, 364, DOI: 10.1007/s10853-008-3147-3
Fe(III)-doped TiO2 aerogels are prepared by acid catalyzed sol-gel method followed by supercritical drying, and then heat treatment. Raman spectra together with X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns of the iron-doped TiO2 aerogel samples revealed the existence of both anatase and brookite crystalline phases. It was found that the brookite phase formation is favored by the increase of the iron content in the dried samples. XRD measurements show that the lattice constant c of anatase phase decreases with the dopant addition, while the value of a remains essentially unchanged. The microstructure of the investigated samples is relatively compact with small mesopores as revealed from transmission electron microscopy (TEM). The most enhanced photocatalytic activity was exhibited by the TiO2 aerogel sample with 1.8 at.% Fe(III) whose apparent rate constant of the salicylic acid photodegradation was found to be of almost six times higher than that of Degussa P25.
1041. Preparation and characterization of nitrogen-doped TiO2 nanoparticles by the laser pyrolysis of N2O-containing gas mixtures
Authors:
Alexandrescu, R; Scarisoreanu, M; Morjan, I; Birjega, R; Fleaca, C; Luculescu, C; Soare, I; Cretu, O; Negrila, CC; Lazarescu, N; Ciupina, V
Published: MAR 1 2009, APPLIED SURFACE SCIENCE, 255, 5377, DOI: 10.1016/j.apsusc.2008.08.046
Nitrogen-doped TiO2 nanoparticles have been prepared by the IR laser pyrolysis technique. A sensitized mixture of TiCl4 (vapors) and N2O was used as titanium and nitrogen precursors, respectively. The structural properties of the resultant N-doped nanoparticles such as the phase formation and the average particle size and distributions were investigated by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The phase composition varied from almost pure anatase to mixtures of rutile and anatase. A decrease of the mean particle diameters from about 18 nm in case of the almost pure anatase sample to about 13 nm in case of the anatase-rutile mixture is observed. XPS analysis suggests and interstitial character of the doping process. (C) 2008 Elsevier B. V. All rights reserved.
1042. Synthesis of narrow diameter distribution carbon nanotubes on ZnO supported catalysts
Authors:
Lupu, D; Biris, AR; Watanabe, F; Li, ZR; Dervishi, E; Saini, V; Xu, Y; Biris, AS; Baibarac, M; Baltog, I
Published: MAY 12 2009, CHEMICAL PHYSICS LETTERS, 473, 304, DOI: 10.1016/j.cplett.2009.03.069
Multiwall carbon nanotubes, as indicated by electron microscopy and spectroscopy, were grown over a novel Co(5 wt.%)/ZnO catalyst by using a cold wall radio-frequency catalytic chemical vapor deposition method. The nanotubes were found to have a rather narrow diameter distribution, which can be explained by the formation over the ZnO support particles of uniform Co clusters, as shown by high resolution transmission electron microscopy studies. The growth of carbon nanotubes over such a support could represent a fast and reliable method to develop in one step 3D ZnO-CNTs heterogeneous composites of any size or shape, for use in advanced applications. (c) 2009 Elsevier B.V. All rights reserved.
1043. Theoretical investigation of modulated currents in open nanostructures
Authors:
Moldoveanu, V; Manolescu, A; Gudmundsson, V
Published: NOV 2009, PHYSICAL REVIEW B, 80, DOI: 10.1103/PhysRevB.80.205325
We investigate theoretically the transport properties of a mesoscopic system driven by a sequence of rectangular pulses applied at the contact to the input (left) lead. The characteristics of the current which would be measured in the output (right) lead are discussed in relation with the spectral properties of the sample. The time-dependent currents are calculated via a generalized non-Markovian master equation scheme. We study the transient response of a quantum dot and of a narrow quantum wire. We show that the output response depends not only on the lead-sample coupling and on the length of the pulse but also on the states that propagate the input signal. We find that by increasing the bias window the new states available for transport induce additional structure in the relaxation current due to different dynamical tunneling processes. The delay of the output signal with respect to the input current in the case of the narrow quantum wire is associated to the transient time through the wire.
1044. Fast and Simple Specimen Preparation for TEM Studies of Oxide Films Deposited on Silicon Wafers
Authors:
Teodorescu, VS; Blanchin, MG
Published: FEB 2009, MICROSCOPY AND MICROANALYSIS, 15, 19, DOI: 10.1017/S1431927609090011
We present a fast and simple method to prepare specimen,, for transmission electron microscopy Studies of oxide thin films deposited oil silicon Substrates. The method consists of scratching the film surface using I pointed diamond tip, in a special manner. Small and thin fragments are then detached front the film and its substrate. Depending oil the scratching direction, the fragments call be used for plan-view or cross-section imaging. High-resolution images call be also obtained from thin edges of the film fragments. The method is demonstrated in the Case Of HfO2 sol-gel films deposited on [100] Si wafer substrates.
1045. Characterization of magnetic nano-fluids via Mossbauer spectroscopy
Authors:
Filoti, G; Kuncser, V; Schinteie, G; Palade, P; Morjan, I; Alexandrescu, R; Bica, D; Vekas, L
Published: JUN 2009, HYPERFINE INTERACTIONS, 191, 60, DOI: 10.1007/s10751-009-9952-5
The laser pyrolysis became a useful tool, providing various ways, in production of nano materials. The iron Mossbauer spectroscopy is one very accurate method in evidencing the physical properties and related processes in the nano scale compounds. The effect of pressure, laser spot area and induced combustion, of gas mixture and laser power on the phase composition and inside particle distribution, grain size as well as the related phenomena were investigated by temperature dependent Mossbauer spectroscopy. A selection of most relevant properties is presented and discussed in details.
1046. Artificial pinning centres in YBa2Cu3O7-delta thin films by Gd2Ba4CuWOy nanophase inclusions
Authors:
Kechik, MMA; Mikheenko, P; Sarkar, A; Dang, VS; Babu, NH; Cardwell, DA; Abell, JS; Crisan, A
Published: MAR 2009, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 22, DOI: 10.1088/0953-2048/22/3/034020
Artificial pinning centres produced by Gd2Ba4CuWOy (2411W) nanophase inclusions in YBa2Cu3Oy (YBCO) thin films grown by pulsed laser deposition (PLD) using a YBCO target containing 1 mol% 2411W have been investigated. For comparison, YBCO thin films have been grown under the same conditions using a pure (commercial) YBCO target. The resulting films were characterized by AC susceptibility (superconducting transition) and SQUID magnetometry (critical current density, J(c)), and by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive x-ray (EDX) spectroscopy and atomic force microscopy (AFM) (structure, morphology and chemical composition). J(c) of the film grown from the composite target is practically the same as that measured for the reference sample at 5 K over the whole range of applied field up to 4.5 T. For temperatures higher than 50 K, however, the presence of the nano-inclusions leads to increased J(c). The relative enhancement in J(c) increases with further increase in temperature. J(c) of the film containing nanophase inclusions is between two and three times higher than that of the reference sample at 77.3 K and 1.5 T. This can be explained by considering the dimensions of nanophase inclusions compared with the temperature-dependent coherence length. Susceptibility measurements reveal that, apart from a large and sharp transition at about 91 K, there is a secondary, smaller and broader transition between 88 and 84 K in the YBCO film containing nanophase inclusions. This can be explained by substitutions of compatible atoms between YBCO and the 2411W phase (Gd with Y), which might also create additional pinning centres of delta T-c-type.
1047. Study of the ground multiplet of Kramers rare earth ions in solid matrices by multifrequency electron paramagnetic resonance spectroscopy: Nd3+ in PbWO4 single-crystals (vol 131, 034505, 2009)
Authors:
Popescu, FF; Bercu, V; Barascu, JN; Martinelli, M; Massa, CA; Pardi, LA; Stefan, M; Nistor, SV; Nikl, M; Bohacek, P
Published: DEC 28 2009, JOURNAL OF CHEMICAL PHYSICS, 131, DOI: 10.1063/1.3280223
1048. Physical Properties of Manganite-Polysiloxanes Composites Obtained by Co-Precipitation
Authors:
Sandu, V; Popa, S; Plapcianu, C; Sandu, E; Hurduc, N; Nor, I
Published: 2009, ADVANCED MATERIALS AND NANOTECHNOLOGY, PROCEEDINGS, 1151, +, DOI:
We report the fabrication of composites made of La2/3Sr1/3MnO3 and two comb-type polysiloxane-based copolymers, polysiloxane-g-styrene and polysiloxane-g-(styrene-co-butyl-acrylate), in an attempt to improve the elastic properties of the polymer-based composites. The composites were obtained by the co-precipitation of a polymer solution mixed with the lanthanum manganite followed by sintering at appropriate temperatures. The rheological properties of the composites before as well as the magnetic and transport properties after sintering process are presented.
1049. Coulomb drag effect in parallel quantum dots
Authors:
Tanatar, B; Moldoveanu, V
Published: 2009, TRANSPORT AND OPTICAL PROPERTIES OF NANOMATERIALS, 1147, +, DOI:
We study theoretically the electronic transport in parallel few-level quantum dots in the presence of both intradot and interdot long-range Coulomb interaction. Each dot is connected to two leads and the steady-state currents are calculated within the Keldysh formalism using the random-phase approximation for the interacting Green functions. Due to the momentum transfer mechanism between the two systems it is possible to get a nonvanishing current through an unbiased Coulomb-blockaded dot if the other dot is set in the nonlinear transport regime. The transitions between the levels of the passive dot reduce the drag current and lead to negative differential conductance.
1050. Structural investigations of ITO-ZnO films grown by the combinatorial pulsed laser deposition technique
Authors:
Craciun, D; Socol, G; Stefan, N; Miroiu, M; Mihailescu, IN; Galca, AC; Craciun, V
Published: MAR 1 2009, APPLIED SURFACE SCIENCE, 255, 5291, DOI: 10.1016/j.apsusc.2008.07.120
Mixtures of transparent and conductive oxides such as ITO-ZnO have been grown by a combinatorial pulsed laser deposition technique from two targets that were located 15 mm apart. The films were deposited on (1 0 0) Si and quartz substrates that were heated at temperatures from 300 to 500 degrees C. Measurements of the In to Zn ratios along the transversal axis of the substrates, which passes through the maximum thickness points corresponding to each target position were performed using energy dispersive X-ray spectroscopy and spectroscopic ellipsometry. From simulations of the X-ray reflectivity spectra, collected with a 2 mm mask on different locations along the transversal axis of the samples, the density and thickness of the deposited films were calculated and then the In to Zn ratios. The crystalline structure and electrical properties of the deposited films were also investigated along the same axis. Changes in the ratio of In/Zn along this axis resulted in changes of the film lattice constant and texture. (C) 2008 Elsevier B. V. All rights reserved.
1051. Exchange bias and spin valve systems with Fe-Mn antiferromagnetic pinning layers, obtained by the thermo-ionic vacuum arc method
Authors:
Kuncser, V; Valeanu, M; Schinteie, G; Filoti, G; Mustata, I; Lungu, CP; Anghel, A; Chiriac, H; Vladoiu, R; Bartolome, J
Published: JUL 2008, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 320, E230, DOI: 10.1016/j.jmmm.2008.02.054
Exchange bias and spin valve systems with Fe-Mn antiferromagnetic layers of different Fe concentrations were obtained by the thermo-ionic vacuum arc method. The adherence of the multilayer system to the Si substrate depends on the Fe-Mn composition. The overall roughness depends on the growing order of the antiferromagnetic/ferromagnetic layers. Very low blocking temperatures for exchange bias were observed for the considered compositions of the Fe-Mn layer. The coercive forces of both the pinned and the free layers of spin valve structures can be considerably modified along a large set of samples simultaneously prepared. (C) 2008 Elsevier B.V. All rights reserved.
1052. Characteristics of arc plasma deposited TiAlZrCN coatings
Authors:
Balaceanu, M; Braic, V; Kiss, A; Zoita, CN; Vladescu, A; Braic, M; Tudor, I; Popescu, A; Ripeanu, R; Logofatu, C; Negrila, CC
Published: MAY 15 2008, SURFACE & COATINGS TECHNOLOGY, 202, 3987, DOI: 10.1016/j.surfcoat.2008.02.005
TiAlZrCN superhard coatings, in which Ti and Al were additions to ZrCN base compound, were prepared by the cathodic arc method. The films were deposited on Si, plain carbon steel and high-speed steel substrates in a mixture of N-2 and CH4 gases. Elemental and phase composition, chemical bondings, texture, surface roughness, hardness, adhesion, tribological characteristics and erosive-corrosive resistance were investigates as a function of gas composition and total gas flow rate, using XPS, GDOES and XRD techniques, surface profilometry, microhardness and scratch adhesion measurements, tribological and erosive tests. It was shown that the properties and performance of the coatings were strongly dependent on the CH4/(CH4+N-2) flow rate and also on the total gas flow. The tribological and anti-erosive characteristics of the TiAlZrCN coatings were found to be superior to those of reference films (ZrN, ZrC, ZrCN, and TiAlCN). Maximum hardness values (42-45 GPa) were obtained for the films prepared at CH4/(CH4+N2) ratios ranging from 0.2 to 0.4. (c) 2008 Elsevier B.V. All rights reserved.
1053. PIT method for obtaining of MgB(2) wires with SiC powder added
The most popular process of MgB(2) wire fabrication is the so-called in situ powder-in-tube (PIT) process, which is characterized by filing metallic tubes with Mg and B mixed powder, drawing and rolling the material into wires and, finally, by applying a heat treatment. X-ray diffraction analyses were carried out for MgB(2) cores and SiC-added wires. XRD patterns reveal that nearly single-phase MgB(2) was obtained. Also, in this paper are presented the obtained magnetization curves.
1054. Rapidly solidified ferromagnetic shape memory alloys
Authors:
Craciunescu, CM; Ercuta, A; Mitelea, I; Valeanu, M; Teodorescu, VS; Lupu, N; Chiriac, H
Published: MAY 2008, EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS, 158, 165, DOI: 10.1140/epjst/e2008-00670-6
Ferromagnetic shape memory alloys have been manufactured by various techniques involving rapid solidification. Bulk alloys have been obtained by extracting the melted alloy in especially designed copper molds; glass coated wires have been obtained by drawing the melt from glass recipients followed by water cooling and ribbons have been fabricated by melt-spinning. Microstructural observations show particular solidification aspects of fractured areas, while ferromagnetic behavior has been detected in glass coated wires obtained by rapid solidification. The martensitic microstructure was observed on Co-Ni-Ga rapid solidified bulk alloys and Fe-Pd ribbons. The memory effect was detected using a Vibran system that allows the detection of the phase transition for the ribbons and by visual observation for other specimens. The conclusions of the observations are related to the comparison between the ferromagnetic behaviors of shape memory alloys solidified using different techniques.
1055. Interference lithography using chalcogenide inorganic photoresist
Authors:
Indutnyy, IZ; Popescu, M; Lorinczi, A; Sava, F; Min'ko, VI; Shepeliavyi, PE
Published: DEC 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3192, DOI:
There was investigated the application of inorganic photo-resist based on three-component chalcogenide films for fabrication of submicrometer periodic relief on silicon wafers using interference lithography. For this purpose. technological process of resistive two-layer chalcogenide-Cr mask formation on a silicon surface was developed, and silicon anisotropic etching was optimized, too. This technology has been used for the fabrication of diffraction gratings and two-dimensional periodic structures on Si (100) surface. The obtained relief patterns were used to form photonic structures by oblique deposition of silicon monoxide in vacuum.
1056. Antiferroelectric-like behavior in polycrystalline Pb(Zr0.2Ti0.8)O-3-BiFeO3 multilayers prepared by sol-gel method
Authors:
Pintilie, L; Stancu, V; Dragoi, C; Vlaicu, M
Published: NOV 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3149, DOI:
Pb(Zr0.2Ti0.8)O-3-BiFeO3 (PZT-BFO) multilayer structures were realized by sol-gel on Pt/Si substrate and their electrical properties were investigated using top Pt, Au and Cu electrodes. All multilayers start and end with PZT films. The polarization-voltage and current-voltage hysteresis loops resemble to those encountered in case of antiferroelectric (AFE) films, although component materials are both ferroelectric (FE). The AFE-like behavior is more clearly visible in the case of three-layer structures of PZT-BFO-PZT type, and it is not dependent of the metal used as top electrode. After fatigue cycling the polarization hysteresis apparently changes from characteristic AFE double-loop to FE single loop, although the four switching current peaks characteristic for an AFE behavior are still present in the current hysteresis. These results suggest the presence of an AFE interfacial coupling between the PZT and BFO layers.
1057. Synthesis and characterization of star and brush grafted polysiloxanes, obtained by atom transfer radical polymerization
Star- and brush-polysiloxanes were synthesized via living radical polymerization using two different catalytic systems. The new compounds were characterized by H-1-NMR, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) techniques. CuCl and 2,2'-bipyridyl proved to be the most efficient catalytic system. The type of catalytic system and the reaction conditions control the number of arms for star polymers or the grafted-chain density for brush polymers. The use of chloromethyl styrene as monomer or co-monomer yields homogeneous star- or brush-polysiloxanes, although chloromethyl styrene is an inimer system. The homogeneity of materials was verified by GPC and DSC (TOPEM) methods. For linear grafted polysiloxanes the molecular simulations reflect a tendency of chains to adopt globular conformation for high values of the branching density. The polysiloxanes grafted with styrene/chloromethyl styrene were modified with azobenzene in order to obtain systems able to react to the light stimuli. Rheological behavior of the polymer solutions were evaluated before and after irradiation with UV light. After the UV irradiation a significant viscosity increase was evidenced.
1058. Morphology of Si nanocrystallites embedded in SiO2 matrix
Authors:
Teodorescu, VS; Ciurea, ML; Iancu, V; Blanchin, MG
Published: NOV 2008, JOURNAL OF MATERIALS RESEARCH, 23, 2995, DOI: 10.1557/JMR.2008.0358
The nanostructure of Si-x(SiO2)(1-x) films deposited on quartz substrate, where x varies from 0 to 1, was determined by high-resolution transmission electron microscopy in the sample regions with x approximate to 0.1, 0.2. 0.5. and 0.75. In the Si-0.5(SiO2)(0.5) region, the formation of a Si nanocrystallite network was established. At high concentrations of Si nanocrystallites, nanotwins and stacking faults occurred in the crystallites. Large Si crystallites appeared at x >= 0.5 in the quartz Substrate under the interface, while the film presented nanopores over the interface. The mechanisms for the formation of the nanocrystallites were discussed and correlated with the film properties.
1059. Spectroscopic characteristics of Tm3+ in Tm and Tm, Nd, Yb : Sc2O3 ceramic
Authors:
Lupei, V; Lupei, A; Gheorghe, C; Ikesue, A
Published: MAY-JUN 2008, JOURNAL OF LUMINESCENCE, 128, 904, DOI: 10.1016/j.jlumin.2007.12.012
The spectroscopic investigation of Tm3+ or (Nd, Yb, Tm)-doped Sc2O3 transparent ceramics, as laser-active media for visible and IR emission, was performed. The spectra are dominated by Tm3+ ions in sites of C-2 symmetry and an energy level scheme and other spectral parameters were determined. The strong concentration quenching of H-3(4) level emission in Tm:Sc2O3 at 300 K is discussed by considering the resonant cross-relaxation (H-3(4)-> F-3(4))-(H-3(6)-> F-3(4)) process and multipolar interactions of various orders. The main energy-transfer processes leading to the blue upconversion emission from the (1)G(4) Tm3+ level in (Tm, Nd, Yb):Sc2O3 ceramic, under pulsed pumping at 808.3 nm were evidenced. (c) 2008 Elsevier B.V. All rights reserved.
1060. Fe-catalyzed carbon nanotubes growth on fluidized powders by remote radiofrequency plasma beam
Authors:
Vizireanu, S; Stoica, D; Birjega, R; Ghica, C; Teodorescu, V; Nistor, L; Ganea, R; Dinescu, G
Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2060, DOI:
The paper reports the application of a new method combining the Plasma Assisted Chemical Vapour Deposition with the Fluidized Bed Reactor principles for the production of carbon nanotubes on powdered catalysts. An argon plasma beam injected with acetylene in presence of hydrogen was used as fluidized environment for targeting, smashing and mixing the catalytic powder located on the bottom of a cylindrical quartz reactor. The described technique generated plate-like or fibrous like carbon nanostructures on fine Fe particles and carbon nanotubes with 5-10 nm diameters on Fe supported ZSM-5 zeolite.
1061. Transient magnetotransport through a quantum wire
Authors:
Gudmundsson, V; Thorgilsson, G; Tang, CS; Moldoveanu, V
Published: JAN 2008, PHYSICAL REVIEW B, 77, DOI: 10.1103/PhysRevB.77.035329
We consider an ideal parabolic quantum wire in a perpendicular magnetic field. A simple Gaussian-shaped scattering potential well or hill is flashed softly on and off with its maximum at t=0, mimicking a temporary broadening or narrowing of the wire. By an extension of the Lippmann-Schwinger formalism to time-dependent scattering potentials, we investigate the effects on the continuous current that is driven through the quantum wire with a vanishingly small forward bias. The Lippmann-Schwinger approach to the scattering process enables us to investigate the interplay between geometrical effects and effects caused by the magnetic field.
1062. Nanospinel mixed oxides obtained by self-propagating combustion. Blue cobalt aluminate
Authors:
Suciu, C; Mindru, I; Marinescu, G; Patron, L; Carp, O; Teodorescu, VS
Published: OCT 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2707, DOI:
Blue cobalt aluminate was obtained by self-propagating combustion from the system 2Al(NO3)(3)center dot 9H(2)O : 1Co(NO3)(2)center dot 6H(2)O : nNH(2)CH(2)COOH. The precursor was characterized by elemental chemical analysis, IR and UV-Vis spectra and thermal analysis. The CoAl2O4 spinel was characterized by the X-ray diffraction, TEM, IR and UV-Vis spectra.
1063. Polypyrrole - porous silicon nanocomposites
Authors:
Popa, C; Turcu, R; Craciunescu, I; Nan, A; Ciurea, ML; Stavarache, I; Iancu, V
Published: SEP 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2324, DOI:
In this work we report the synthesis and characterization of the polypyrrole - porous silicon nanocomposites. Our main goal is to control the growth of conducting polypyrrole into the alveolar pores of porous silicon, in order to get a functionalized nanocomposite with the required properties for application as electrode in microfluidic devices. Porous silicon was electrochemically etched from (100) p-type silicon wafers. Different silicon resistivities (from 1.8 to 11 Omega cm) and preparation conditions (different electrolyte concentrations and current densities) were used. The electrodeposition of polypyrrole into porous silicon was carried out galvanostatically, at a constant current density 2.5 mA/cm(2) from a solution containing acetonitrile, the monomer, pyrrole and p-toluensulfonic acid as electrolyte. The polymerization time was varied in order to investigate the growing process of polypyrrole into the pores. The morphology and of the as-prepared nanocomposites was investigated by SEM. The existence of PPY into porous silicon is evidenced by the EDX spectra of the nanocomposite. The electrical characterization evidences the relative contributions of the polypyrrole and the substrate resistivity, respectively.
1064. Smart soluble grafted polysiloxanes with potential applications in waterborne paints
Authors:
Nor, I; Moleavin, I; Ibanescu, C; Sandu, V; Hurduc, N
Published: MAY-JUN 2008, ENVIRONMENTAL ENGINEERING AND MANAGEMENT JOURNAL, 7, 342, DOI:
The synthesis of some grafted polysiloxane and azo-polysiloxanes with potential applications as rheology modifiers or surfactants for waterborne paints is reported. Nowadays it became very important to design environmentally friendly systems exhibiting the best end-uses properties. Due to their complex architecture and their sensitivity to UV radiation the studied polymeric systems exhibit very interesting rheological properties. All the polymers containing the azobenzenic groups in the side chains tire able to interact with the UV/VIS light, due to the photo-isomerization processes. Due to this property, the azo-based polymers are able to generate photo-stimuli response accomplished by strong supramolecular properties modifications.
1065. Capacitance-voltage characteristics of heterostructures with high leakage currents
Authors:
Goldenblum, A; Stancu, V; Buda, M; Iordache, G; Pintilie, I; Negrila, C; Botila, T
Published: MAR 1 2008, JOURNAL OF APPLIED PHYSICS, 103, DOI: 10.1063/1.2844210
Leakage currents determine bumps in the capacitance-voltage characteristics of metal-oxide-semiconductor-type heterostructures with capacitance values larger than the insulator capacitance. A nearly parallel shift with frequency is also observed. These aspects are connected with the presence of a high density of interface states. We illustrate these effects for the case of nano-PbS/SiO2/Si heterostructures. The phenomena were simulated and we propose a method to quickly estimate the interface state density level of a heterostructure when leakage channels are present. (C) 2008 American Institute of Physics.
1066. Vortex imaging with varying temperature revealed by SHPM on Bi(2)Sr(2)CaCu(2)O8+y
Authors:
Mihalache, V; Dede, M; Oral, A; Sandu, V
Published: APR 1 2008, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 468, 836, DOI: 10.1016/j.physc.2007.11.059
Scanning Hall probe microscopy with an effective spatial resolution of similar to 1 mu m has been used to investigate the vortex structures in superconducting Bi2Sr2CaCu2O8+delta single crystals in the temperature range 77.3-81.3 K and zero applied field (in the presence of the earth field). The vortex images were obtained in real time mode as the temperature increased slowly for 3.36 h. At 77.3 K, the vortices were arranged in a chain structure. With the increase of the temperature, two jumps in the vortex array occur at 77.3 K, immediately when the temperature starts to rise, and at 79.2 K with a good stability between jumps. The second jump is accompanied by the jump in the average magnetic induction when bundles of 4-5 additional vortices enter the scanning area and the vortex array get disordered. These directly visualized transitions in the vortex lattice are consistent with a vortex creep over the surface barriers at high temperatures. A short movie is presented. (c) 2008 Elsevier B.V. All rights reserved.
1067. Characterization of high performance PbS photodetectors
Authors:
Buda, M; Iordache, G; Stantcu, V; Botila, T
Published: FEB 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 310, DOI:
Dark noise plays an important role in electronic devices, especially in detectors. Performance of infrared detectors is reflected by parameters such as detectivity and specific detectivity, strongly related to the noise spectral density. This work summarizes the results on characterization of high-performance PbS photo detectors, using a certification pending method developed by the laboratory, in agreement to the standard ISO/CEI 17025:2005. The method is validated for a resistor of known resistance, by comparing the Johnson thermal noise using two different methods: first, the fast Fourier transform measured with a Stanford Research Systems SR785 Spectrum Analyzer and second using a Stanford SR830 lock-in amplifier which measures the rms noise for a certain frequency. We studied the influence of physical dimensions on the performance of thin film polycrystalline PbS photoresistors in the planar geometry. Measurements were performed to compare the dark noise of PbS photoresistors with that in high quality metal thin film resistors. The laboratory setup used for the measurements is appropriate to accurately determine typical parameters of infrared detectors such as spectral responsivity, blackbody responsivity, specific detectivity, and noise spectral density.
1068. ELECTROCATALYSTS AND ELECTRODE DESIGN FOR BIFUNCTIONAL OXYGEN/AIR ELECTRODES
Authors:
Nikolova, V; Iliev, P; Petrov, K; Vitanov, T; Zhecheva, E; Stoyanova, R; Valov, I; Stoychev, D
Published: 2008, FUNCTIONALIZED NANOSCALE MATERIALS, DEVICES AND SYSTEMS, +, DOI: 10.1007/978-1-4020-8903-9_22
Electrocatalysts and appropriate electrode designs have been Studied with respect to the development of Bifunctional Air/Oxygen Electrode (BAE). Three groups of catalysts have been prepared: (i) CUxCo3-xO4; (ii) thin films of Co-Ni-Te-O and Co-Te-O and (iii) CoxOv/ZrO2 films. Different catalysts deposited on classical and originally designed GDE were compared by their electrochemical performances.
1069. Comparison between PZT thin films deposited on stainless steel and on platinum/silicon substrate
Authors:
Stancu, V; Sava, F; Lisca, M; Pintilie, L; Popescu, M
Published: 2008, INTERFACIAL NANOSTRUCTURES IN CERAMICS: A MULTISCALE APPROACH, 94, DOI: 10.1088/1742-6596/94/1/012012
Pb(Zr1-xTix)O-3 (PZT) thin films were prepared by sol-gel method on stainless steel (SS) and on platinum-coated silicon substrate (Pt/Si). The structure revealed by X-ray diffraction shows strong crystallographic orientation: (110) and (100), respectively. The crystallite size shows significant differences: d((00l))((SS))= 27.1 nm, d((h00))((Pt)) = 88 nm. The tetragonal splitting is (Delta c/c)((ss))=3.55 % and (Delta c/c)((pt))=3.32 %. The ferroelectric hysteresis loop in the static mode is characterized by remanentpolarization of 25 mu C/cm(2) and coercive field of 45 kV/cm for SS substrate, while for Pt/Si substrate the values are 10 mu C/cm(2) and 39 kV/cm, respectively. The leakage current is about 3 orders of magnitude lower in the PZT film deposited on SS. The better properties of the PZT deposited on SS are explained by the presence of large single crystal-like crystallites, which make the film closer to epitaxial ones. The results show the potential of growing epitaxial films on low-price substrates such as stainless-steel.
1070. Correlational analysis of superconducting mixed copper oxides
Authors:
Zarioiu, C; Lascu, VG; Petrova, L; Novac, A
Published: 2008, MATHEMATICS AND COMPUTERS IN BIOLOGY AND CHEMISTRY, +, DOI:
A unifying structural scheme of all layered superconducting cuprates is proposed. The paper is a review based on a three level correlational analysis of the behaviour of one compound, of a homologous series and a third interseries analysis, revealing multiple correlation between the critical temperature value and different bond lengths via the oxygen content.
1071. Structural and photocatalytic properties of iron- and europium-doped TiO2 nanoparticles obtained under hydrothermal conditions
Authors:
Diamandescu, L; Vasiliu, F; Tarabasanu-Mihaila, D; Feder, M; Vlaicu, AM; Teodorescu, CM; Macovei, D; Enculescu, I; Parvulescu, V; Vasile, E
Published: NOV 15 2008, MATERIALS CHEMISTRY AND PHYSICS, 112, 153, DOI: 10.1016/j.matchemphys.2008.05.023
Iron- and europium-doped (<= 1 at.%)TiO2 nanoparticles powders have been synthesized by a hydrothermal route at 200 degrees C, starting with TiCl4, FeCl3 center dot 6H(2)O and EuCl3 center dot 6H(2)O. The structure, morphology and optical peculiarities were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS), Mossbauer spectroscopy and UV-vis measurements. The photocatalytic performance was analysed in the photodegradation reaction of phenol. Rietveld refinements of XRD patterns reveal that the as-prepared samples consist in iron- and europium-doped TiO2 in the tetragonal anatase structural shape, with particle size as low as 15 nm. By means of Mossbauer spectroscopy on both Fe-57 and Eu-151 isotopes as well as by EXAFS analyses, the presence of Fe3+ and/or Eu3+ ions in the nanosized powders has been evidenced. It was found that iron and europium ions can substitute for titanium in the anatase structure. From the UV-vis reflection spectra, by using the transformed Kubelka-Munk functions, the band gap energy (E-g) of the hydrothermal samples has been determined in comparison with that of Degussa P-25 photocatalyst. A decrease of E-g from 2.9eV found for Degussa photocatalyst to 2.8 eV for the titania doped with 1 at.% Fe has been evidenced, indicating a valuable absorption shift (similar to 20 nm) towards visible light region. However, the best photocatalytic activity in the photodegradation reaction of phenol was evidenced for the hydrothermal sample, TiO2: 1 at.% Fe, 0.5 at.% Eu, in both UV and visible light regions. The photocatalytic activities of iron-doped and iron-europium-codoped samples are high and practically the same only in visible light. The photocatalytic properties in Correlation with the structural and optical peculiarities of the hydrothermal samples are discussed. (C) 2008 Elsevier B.V. All rights reserved.
1072. The CMS experiment at the CERN LHC
Authors:
Chatrchyan, S; Hmayakyan, G; Khachatryan, V; (...) Lungu, GA; (...) Onengut, G (CMS Collaboration)
Published: AUG 2008, JOURNAL OF INSTRUMENTATION, 3, S08004, DOI: 10.1088/1748-0221/3/08/S08004
The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron Collider (LHC) at CERN. It was conceived to study proton-proton (and lead-lead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 10(34)cm(-2)s(-1) (10(27)cm(-2)s(-1)). At the core of the CMS detector sits a high-magnetic-field and large-bore superconducting solenoid surrounding an all-silicon pixel and strip tracker, a lead-tungstate scintillating-crystals electromagnetic calorimeter, and a brass-scintillator sampling hadron calorimeter. The iron yoke of the flux-return is instrumented with four stations of muon detectors covering most of the 4 pi solid angle. Forward sampling calorimeters extend the pseudo-rapidity coverage to high values (vertical bar eta vertical bar <= 5) assuring very good hermeticity. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m and a total weight of 12500 t.
1073. Capacitance spectroscopy study of InGaAs/GaAs quantum dot structures
Authors:
Buda, M; Iordache, G; Mokkapati, S; Tan, HH; Jagadish, C; Stancu, V; Botila, T
Published: FEB 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 326, DOI:
Self assembled InGaAs/GaAs quantum dots (QD) have a great potential for high performance optoelectronic devices such as low threshold laser diodes, infrared detectors, modulators, memories. In order to characterize the behavior of the QD system, we use two p(+)-n structures grown epitaxially on GaAs under similar conditions. The first structure acts as reference while in the second structure a single QD self-assembled layer is introduced in the middle of the n-GaAs matrix layer. The structure is designed such that for OV applied bias the QD layer lies outside the depleted region. When the reverse bias is increased, the charge from the QD system is removed and the depletion layer moves further into the GaAs matrix material. The electronic structure of the QD is investigated using two methods: photoluminescence, in order to characterize the transition energies between electron and hole levels in the QD system and capacitance spectroscopy in order to study the electron levels in the conduction band only. In addition, admittance spectroscopy spectra are measured in order to characterize the carrier transport mechanism. There is no evident step in the capacitance versus frequency behavior at room temperature in the range 1 Hz-1 MHz, indicating a large carrier cross section caption and/or a low activation energy for the carrier transport between the dot system and the wetting layer and GaAs barriers. The plateau in the C-V behavior, due to charging or discharging of the QD system is modeled using the solution of a Poisson equation and the resulting energy of the electron states within the conduction band and QD size distribution are correlated with results from photoluminescence studies, which involve transitions between energy levels both from the conduction and valence bands.
1074. Investigation of nanocrystalline Pbs/n-Si heterostructures for optoelectronic applications
Authors:
Buda, M; Stancu, V; Iordache, G; Pintilie, L; Pintilie, I; Buda, M; Botila, T
Published: FEB 15 2008, MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 147, 288, DOI: 10.1016/j.mseb.2007.09.070
The nano-crystalline PbS/n-Si heterostructure was studied using photocurrent spectra, I-V and C-V characteristics and admittance spectroscopy. The frequency dependent junction capacitance and conductance measurements show the presence of two contributions: first, a defect related mechanism which we attribute to a deep trap level with a large cross-section in nano-crystals with smaller sizes around 5 nm at the interface with Si and a second mechanism with an activation energy of about 250 meV, attributed to carrier transport in relatively large PbS grains of about 15 nm in size. (c) 2007 Elsevier B.V. All fights reserved.
1075. Surfactant involved in Copper Sulfide Nanocrystallites Synthesis
Authors:
Simonescu, CM; Teodorescu, VS; Capatina, C
This paper presents the obtaining of copper sulfide CuS (covelite) from Cu(CH3COO)(2)center dot H2O and thioacetamide (TAA) system. The reaction was conducted in presence or absence of sodium-bis(2-ethylhexyl) sulfosuccinate (Na-AOT). The effects of various reaction parameters on the size and on the shape of nanoparticles have been examined. CuS obtained was characterized by X ray diffraction, IR spectroscopy, TEM - transmission electron microscopy and SAED selected area electron diffraction. The influence of surfactant to the shape and size of CuS (covellite) nanocrystals was established. The size of the nanocrystals varied from 10-60 nm depending on the reaction conditions such as quantity of surfactant.
1076. Concentration dependence of luminescence properties in praseodymium and praseodymium/ytterbium-doped lutetium double phosphates
Authors:
Legendziewicz, J; Guzik, M; Cybinska, J; Stefan, A; Lupei, V
Published: JUL 2008, OPTICAL MATERIALS, 30, 1671, DOI: 10.1016/j.optmat.2007.11.004
In this paper we present a comparative optical study of praseodymium and praseodymium/ytterbium-doped lutetium double phosphates in the wide spectral range (VUV-IR) and for various concentrations of the activators. The absorption and emission spectra of Na3Lu(PO4)(2):Pr3+ and Na3Lu(PO4)(2):Pr3+, Yb3+ were measured at room and low temperatures. It was shown that spectroscopic properties of investigated systems strongly depend on the concentration ratio of the Pr3+ and Yb3+ ions. (c) 2007 Published by Elsevier B.V.
1077. Investigation of metal-oxide semiconductor field-effect transistor-like Si/SiO2/(nano)crystalline PbS heterostructures
Authors:
Stancu, V; Buda, M; Pintilie, L; Pintilie, I; Botila, T; Iordache, G
Published: APR 30 2008, THIN SOLID FILMS, 516, 4306, DOI: 10.1016/j.tsf.2007.11.116
The influence of the gate voltage on photoconductivity in P-Si/SiO2/(nano)crystalline PbS, Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET)-like structures is investigated. The effect on the photo-signal in the wavelength range 500-1180 nm is opposite compared to the effect in the wavelength range 1600-2500 nm: a negative gate voltage increases the signal in the short wavelength range and decreases it for the long wavelength range. The opposite is valid for a positive gate bias. An on-off ratio better than 85 times is obtained for the spectral range 500-1180 nm, corresponding to the absorption in p-Si and better than 3.5 times for the spectral range 1600-2500 nm corresponding to the absorption in the (nano)crystal line PbS region, respectively. (c) 2007 Elsevier B.V. All rights reserved.
1078. InN Thin Films Deposition by rf Magnetron Sputtering
Authors:
Braic, MT; Zoita, CN; Braic, VT; Toacsan, MI; Ioachim, AT
Published: 2008, 2008 33RD INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER AND TERAHERTZ WAVES, VOLS 1 AND 2, +, DOI:
InN thin films were grown by reactive magnetron sputtering in a UHV system, using Ar and N-2 as working gases. Electrical and optical investigations of the films were correlated with their structural and morphological characteristics in order to obtain good quality films for THz applications.
1079. Magnetoresistiviiy and upper critical field in superconductor Mo3Sb7
Authors:
Tran, VH; Bauer, E; Galatanu, A; Bukowski, Z
Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1632, DOI:
Magnetotransport data on a single crystal of the superconducting Mo3Sb7 are reported for temperatures down to 0.4 K and in magnetic fields up to 12 T. The magnetoresistance data are analyzed in terms of the Ginzburg-Landau fluctuation theory. From the experimental data the upper critical field H-c2(0) and Ginzburg-Landau coherent length xi(O) are determined to be similar to 2.3 T and 12 nm, respectively. The H,2(0) value agrees with that inferred from the Werthamer, Helfand, Hohenberg, and Maki theories for conventional type-II superconductors.
1080. A way to increase the critical current in high temperature superconductors: neutron irradiation
Authors:
Sandu, V
Published: NOV 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3123, DOI:
Neutron irradiation is a promising method for a spectacular enhancement of the critical current density of the high temperature superconductors. The suppression of the mechanisms responsible for superconductivity under irradiation are analyzed and put side by side with the effects on the flux line lattice dynamics. Additionally, the evolution of the creation/generation balance of the defects of the crystal structure is connected to the evolution of the response of the vortex system with an emphasis on the ceramic materials.
1081. Excited states dynamics of Er3+ in Sc2O3 ceramic
Authors:
Lupei, A; Lupei, V; Gheorghe, C; Ikesue, A
Published: MAY-JUN 2008, JOURNAL OF LUMINESCENCE, 128, 920, DOI: 10.1016/j.jlumin.2007.11.032
The spectral characteristics of Er3+ in Sc2O3 transparent ceramics are presented. The Er3+ visible spectra in the ceramics, prepared by solid-state synthesis, show only lines that could be assigned to C-2 sites. The Stark energy levels, cross-sections and emission kinetics of levels involved in the green upconversion emission under infrared excitation in the 800 nm range were determined. The green upconversion emission (H-2(11/2), S-4(3/2)) -> I-4(15/2) characteristics under excitation with a pulsed Ti:sapphire laser in (I-4(15/2)-> I-4(9/2)) absorption were analyzed. The emission kinetics reveal a competition of two-step (I-4(15/2)-> I-4(9/2)) + (I-4(9/2)-> H-2(9/2)) excited state absorption (ESA) and (I-4(11/2), I-4(15/2)) -> (I-4(11/2), F-4(7/2)) energy transfer upconversion (ETU) processes function on the excitation wavelength. (c) 2007 Elsevier B.V. All rights reserved.
1082. Doped MgB2 prepared by field assisted sintering technique
Authors:
Aldica, G; Sandu, V; Badica, P; Nishijima, G; Awaji, S; Watanabe, K
Published: 2008, 8TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS'07), 97, DOI: 10.1088/1742-6596/97/1/012079
Field-assisted-sintering technique (FAST) has been employed to obtain polycrystalline MgB2 samples, pristine and doped with 5 mol % SiC and B4C, using commercial MgB2 powder. The mass density of the samples is around 90% of the theoretical value. The response in magnetic field shows that the upper critical field and the irreversibility field are depressed by comparison with pristine MgB2. The latter has an upper critical field H-c2=14.37 T close to the values reported for the single crystals. Scaling analysis of the field dependence of the pinning force suggests that both addition of SiC and B4C stabilizes two well defined pinning regimes in FAST-processed MgB2. At low temperatures, T < 24 K (H <= 5T), the pinning occurs at the grain boundaries whereas at higher temperatures there is a mixed pinning. These effects are supposed to be the combined result of relatively low level of C diffusion into the lattice of MgB2, specific features in formation of the grain boundaries during FAST processing and the influence of the added materials on morphology. At high fields (above 8.5T) and 4.2K, doped samples are superior to the pristine one from the critical current density viewpoint.
1083. Thermal behaviour study of some sol-gel TiO2 based materials
Authors:
Crisan, M; Braileanu, A; Crisan, D; Raileanu, M; Dragan, N; Mardare, D; Teodorescu, V; Ianculescu, A; Birjega, R; Dumitru, M
Published: APR 2008, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 92, 13, DOI: 10.1007/s10973-007-8720-5
Among the great number of sol-gel materials prepared, TiO2 holds one of the most important places due to its photocatalytic properties, both in the case of powders and coatings. Impurity doping is one of the typical approaches to extend the spectral response of a wide band gap semiconductor to visible light. This work has studied some un-doped and Pd-doped sol-gel TiO2 nanopowders, presenting various surface morphologies and structures. The obtained powders have been embedded in vitreous TiO2 matrices and the corresponding coatings have been prepared by dipping procedure, on glass substrates. The relationship between the synthesis conditions and the properties of titania narrosized materials, such as thermal stability, phase composition, crystallinity, morphology and size of particles, and the influence of dopant was investigated. The influence of Pd on TiO2 crystallization both for supported and unsupported materials was studied (lattice parameters, crystallite sizes, internal strains). The hydrophilic properties of the films were also connected with their structure, composition and surface morphology. The methods used for the characterization of the materials have been: simultaneous thermogravimetry and differential thermal analysis, powder X-ray diffraction, electron microscopy (TEM, SAED) and AFM.
1084. Direct measurement of depth-dependent Fe spin structure during magnetization reversal in Fe/MnF2 exchange-coupled bilayers
Authors:
Macedo, WAA; Sahoo, B; Eisenmenger, J; Martins, MD; Keune, W; Kuncser, V; Rohlsberger, R; Leupold, O; Ruffer, R; Nogues, J; Liu, K; Schlage, K; Schuller, IK
Published: DEC 2008, PHYSICAL REVIEW B, 78, DOI: 10.1103/PhysRevB.78.224401
We measured directly the depth-dependent Fe spin rotation upon magnetization reversal in exchange-coupled Fe/MnF2 bilayers using nuclear resonant scattering of synchrotron radiation from an Fe-57-probe layer buried at different depths within the Fe film. Our results show that the exchange-biased ferromagnetic layer develops a noncollinear spin structure along the film normal direction, reminiscent of a partial domain wall parallel to the Fe/MnF2 interface. This is contrary to most theoretical models of exchange bias which assume a collinear spin structure in the ferromagnetic layer.
1085. Structure and dielectric properties of HfO2 films prepared by a sol-gel route
Authors:
Blanchin, MG; Canut, B; Lambert, Y; Teodorescu, VS; Barau, A; Zaharescu, M
Published: AUG 2008, JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY, 47, 172, DOI: 10.1007/s10971-008-1758-4
Mono- and multilayer HfO2 sol-gel thin films have been deposited on silicon wafers by dip-coating technique using a solution based on hafnium ethoxide as precursor. The densification/crystallization process was achieved by classical annealing between 400 and 600 degrees C for 0.5 h (after drying at 100 degrees C). Systematic TEM studies were performed to observe the evolution of the thin film structure depending on the annealing temperature. The overall density of the films was determined from RBS spectrometry correlated with cross section (XTEM) thickness measurements. After annealing at 450 degrees C the films are amorphous with a nanoporous structure showing also some incipient crystallization. After annealing at 550 degrees C the films are totally crystallized. The HfO2 grains grow in colonies having the same crystalline orientation with respect to the film plane, including faceted nanopores. During annealing a nanometric SiO2 layer is formed at the interface with the silicon substrate; the thickness of this layer increases with the annealing temperature. Capacitive measurements allowed determining the value of the dielectric constant as 25 for four layer films, i.e. very close to the value for the bulk material.
1086. Optica and structural properties of polythiophene-like films deposited by plasma polymerization
Authors:
Galca, AC; Satulu, V; Ionita, MD; Bercu, M; Barna, E; Dumitru, M; Mitu, B; Dinescu, G
Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2037, DOI:
Polymer-like organic thin films obtained by plasma techniques are of wide interest for various applications. Polythiophene-like thin films were deposited by plasma polymerization in a parallel plate radiofrequency reactor starting from thiophene vapors. The optical properties of the films were obtained from spectroscopic ellipsometry, in the 250-1250 nm range. The calculated band gap is in agreement with a polythiophene-like material consisting of cross-linking of oligomers. The presence of functional groups and film stability against oxidation is analyzed by FTIR spectrometry. The monitoring of functional groups incorporation during the film deposition was done by analyzing the integral intensities of specific absorption bands and led to the conclusion that homogeneous films are obtained whatever the process duration.
1087. Transport and magnetic properties of CrO2-polymer magnetic composites
Authors:
Sandu, V; Popa, S; Plapcianu, C; Sandu, E; Hurduc, N; Nor, I
Published: 2008, MULTI-FUNCTIONAL MATERIALS AND STRUCTURES, PTS 1 AND 2, 47-50, +, DOI: 10.4028/www.scientific.net/AMR.47-50.326
We report the transport and magnetic properties of sintered CrO2-polymer composites. In order to improve the elastic properties of the CrO2-based composites, we investigated two types of styrene-based copolymers: poly(methyl methacrylate)-styrene (9/1 and 5/5) and linear polysiloxane-g-styrene as well as poly(methyl methacrylate)-butadiene 9/1. The electric transport and magnetoresistance are consistent with the spin tunneling model at low temperatures but the contribution of spin independent channels becomes important at high temperature and high fields. All composites display ferromagnetism at room temperature with saturation at low fields and a slightly temperature-dependent coercive field for the samples grafted either with butadiene or with styrene except for CrO2-polysiloxane-g-styrene composite where it exponentially decreases with increasing temperature.
1088. Electrical properties of electrodeposited CdS nanowires
Authors:
Ghenescu, M; Ion, L; Enculescu, I; Tazlaoanu, C; Antohe, VA; Sima, M; Enculescu, M; Matei, E; Neumann, R; Ghenescu, O; Covlea, V; Antohe, S
Published: MAY 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 2488, DOI: 10.1016/j.physe.2007.09.188
A template method was used to obtain cadmium sulfide (CdS) nanowires. Polymer ion tracks foils (30 mu m tick) were used as templates, after etching with solutions containing NaOH and methanol. CdS nanowires were electrochemically grown in the resulting pores. The nanowires were contacted by sputtering a gold layer on top of the membrane, and the electrical properties were recorded in the temperature range 40-300K. An activated electrical resistance was observed, with activation energy of 0.27eV at temperatures larger than 180 K. I-V characteristics show a symmetric, non-linear shape, in the voltage range used in this experiment. (C) 2007 Elsevier B.V. All rights reserved.
1089. Investigations of conduction mechanism in Cr2O3 gas sensing thick films by ac impedance spectroscopy and work function changes measurements
Authors:
Pokhrel, S; Simion, CE; Quemener, V; Barsan, N; Weimar, U
Published: JUL 28 2008, SENSORS AND ACTUATORS B-CHEMICAL, 133, 83, DOI: 10.1016/j.snb.2008.01.054
This paper investigates the conduction mechanism in Cr2O3 gas sensing thick films. A citrate combustion method was used for the preparation of the metal oxide and ethanol vapour as a test gas. The manner in which surface reactions induced electrical changes are affecting the sensor signals inputs was explored by simultaneous dc and work function changes (Kelvin probe method). The identification of the contributions to conduction of the different sensing layer elements was made possible by ac impedance spectroscopy measurements. A conduction model, which qualitatively explains the experimental findings, was elaborated on the basis of the acquired experimental data and the information provided in literature. The model validity should apply, besides Cr2O3, to all p-type metal oxides used as gas sensitive materials. (C) 2008 Elsevier B.V. All rights reserved.
1090. Coherent and incoherent transport through T-shaped double quantum dots
Authors:
Moldoveanu, V; Tolea, M; Tanatar, B
Published: MAR 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 1104, DOI: 10.1016/j.physe.2007.08.012
We investigate the measurement induced dephasing of the Fano effect in the electronic transport through a double quantum dot mesoscopic interferometer coupled to a charge detector. The current and the differential conductance are computed within the Keldysh formalism, taking into account of the inelastic processes due to the dot-detector interaction. We show that the visibility of the Fano lineshape is reduced by applying a finite bias on the charge detector. (C) 2007 Elsevier B.V. All rights reserved.
1091. Transparent polycrystalline ceramic laser materials
Authors:
Lupei, V; Lupei, A; Ikesue, A
Published: JUL 2008, OPTICAL MATERIALS, 30, 1786, DOI: 10.1016/j.optmat.2008.03.003
High-resolution spectroscopy of the rare earth ions in transparent ceramics of garnets and sesquioxides produced by solid-state synthesis indicate that the variety, nature and structure of the centers formed by the doping ions, their quantum states (energy levels, transition probabilities) and interionic interactions as well as the distribution of the doping ions at the available lattice sites is similar to those of the corresponding single crystals. Moreover, the increased compositional versatility of ceramics enables tailoring of new or improved laser materials. It is inferred that from spectroscopic point of view, the transparent polycrystalline ceramics can substitute the single crystal and extend their capabilities. (c) 2008 Elsevier B.V. All rights reserved.
1092. Correlation between the method of preparation and the properties of the sol-gel HfO2 thin films
Authors:
Zaharescu, M; Teodorescu, VS; Gartner, M; Blanchin, MG; Barau, A; Anastasescu, M
Published: JAN 15 2008, JOURNAL OF NON-CRYSTALLINE SOLIDS, 354, 415, DOI: 10.1016/j.jnoncrysol.2007.07.097
This work describes the preparation of HfO2. thin films by the sol-gel method, starting with different precursors such as hafnium ethoxide, hafnium 2,4-pentadionate and hafnium chloride. From the solution prepared as mentioned above, thin films on silicon wafer substrates have been realized by 'dip-coating' with a pulling out speed of 5 cm min(-1). The films densification was achieved by thermal treatment for 10 min at 100 degrees C and 30 min at 450 degrees C or 600 degrees C, with a heating rate of 1 degrees C min(-1). The structural and optical properties of the films are determined employing spectroellipsometric (SE) measurements in the visible range (0.4-0.7 mu m), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The main objective of this paper was to establish a correlation between the method of preparation (precursor, annealing temperature) and the properties of the obtained films. The samples prepared from pentadionate and ethoxide precursors are homogenous and uniform in thickness. The samples prepared starting from chloride precursor are thicker and proved to be less uniform in thickness. Higher non-uniformity develops in multi-deposition films or in crystallized films. A nano-porosity is present in the quasi-amorphous films as well in the crystallized one. For the samples deposited on silicon wafer, the thermal treatment induced the formation of a SiO2 layer at the coating-substrate interface. (C) 2007 Elsevier B.V. All rights reserved.
1093. Nanostructured PZT type thin films prepared by thermonic vacuum arc method
Authors:
Rasleanu, D; Ionescu, V; Prodan, G; Ciupina, V; Lungu, CP; Surdu-Bob, C; Osiac, M; Pompilian, O; Badulescu, M; Lungu. AM; Ticos, C; Zaroschi, V; Trupina, L; Miclea, C
Published: NOV 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3047, DOI:
PZT type films were prepared using the thermionic vacuum arc (TVA) method; a crucible filled PZT type powder (PbO/ZrO/TiO) was heated by a thermo-electron beam emitted by the circular cathode of the TVA gun. Applying high voltage potential (3000 +/- 200V) on the anode from a regulated HEINZINGER high voltage power supply the thermo-electrons were accelerated toward the anode crucible, evaporating the anode materials and initiating a plasma discharge. The morphology and the structure of the prepared films analyzed by transmission electron microscopy, (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy, showed nanostructured, smooth thin films with specific PZT stoichiometry.
1094. Doping dependence of vortex regimes in Y1-xPrxBa2CU3O7-delta single crystals
Authors:
Gyawali, P; Sandu, V; Almasan, CC; Taylor, BJ; Maple, MB
Published: MAY 2008, PHYSICAL REVIEW B, 77, DOI: 10.1103/PhysRevB.77.174504
Magnetic relaxation measurements on a series of Y1-xPrxBa2CU3O7-delta (x=0.13, 0.34, and 0.47) single crystals were performed over a large field and temperature range in order to investigate the characteristics of the vortex matter across the second magnetization peak (SMP). The magnitude of the SMP varies nonmonotonically with Pr concentration, i.e., the irreversible magnetization normalized by its value at the onset field H-on displays a maximum for the x=0.34 single crystal. The two characteristic fields, H,,, and H,,, follow different temperature T dependences: H-on proportional to T-nu on and H-sp proportional to [1-(T/T-c)(2)](nu sp). The extracted values of the apparent activation energy U* and the creep exponent mu display a maximum at a field H-on < H* < H-sp. Their field dependences point toward the coexistence of both elastic and plastic creep for H > H-on. The degree of participation of each creep mechanism is determined by the charge carrier density, which controls both the elastic properties of the vortex matter and the pinning potential.
1095. Flux-creep activation energy for pure and SiC doped MgB2 by ac-susceptibility measurements
Authors:
Mihalache, V; Sandu, V; Aldica, G; Groza, JR
Published: 2008, 8TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS'07), 97, DOI: 10.1088/1742-6596/97/1/012166
ac susceptibility measurements were performed on pure and SiC-doped MgB2 prepared by field assisted sintering technique in the temperature range between 5 and 50 K. The activation energy for flux-creep U for both samples was determined at dc-fields of 0, 0.5, and 5 T, respectively, from the frequency dependence of the imaginary part of the ac-susceptibility chi '' data measured in the range 17-9997 Hz. It was found that at 0 and 0.5 T, the activation energy of the SiC-doped sample is almost half the energy of the pristine sample whereas at 5 T the activation energies of the two samples become almost equal. A similar behaviour show the H-p(T) lines as obtained from susceptibility data in the range 0-9 T. For fields lower than 7.5 T, the H-p field of the doped sample is lower than for the undoped MgB2. At similar to 7.5 T, the H-p(T) for SiC doped MgB2 crosses over the H-p(T) of pure MgB2 and for higher fields the doped samples exhibits a higher irreversibility H-p. This field dependence was extracted from the evolution of the. chi(1)''(T) data. This behaviour is a consequence of the morphology of the sample with a large spread in grain size.
1096. Photocatalytic and structural properties of mixed titania and zirconia aerogels
Authors:
Danciu, V; Baia, L; Cosoveanu, V; Baia, M; Vasiliu, F; Diamandescu, L; Teodorescu, CM; Feder, M; Popp, J
Published: 2008, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 2, 80, DOI:
A series of TiO2-ZrO2 aerogels with different ZrO2 contents (3-10 %) were prepared by an acid catalyzed sol-gel method followed by low-temperature supercritical drying and heat treatment. The structure and morphology of mixed aerogels were studied by means of Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), xenon sorption and elemental analysis. XRD spectra refinements show that the calcined TiO2-ZrO2 aerogels consist mainly in anatase phase accompanied by a small fraction of tetragonal ZrO2. The Raman spectra proof that the network of the calcined mixed aerogels mainly preserves an anatase structure similar to that of the calcined TiO2 aerogel. The TEM images reveal that the anatase particles present round shapes with a highly homogeneous size (about 3-8 nm). Areas containing chains of amorphous tetragonal zirconia were also identified by the TEM investigations. The addition of zirconia to titania significantly increased the surface area and stabilized the anatase phase of titania. The best catalytic efficiency for the salicylic acid photodecomposition was obtained for the aerogel with 9.39% zirconia that exhibited an apparent rate constant of about three times higher than that of the pure titania aerogel.
1097. Luminescence and EPR study of ZnO : Mn : Cu nanowire array
Authors:
Sima, M; Enculescu, I; Grecu, MN; Secu, M; Sima, M; Matei, E; Vasile, V
Published: MAY 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 2498, DOI: 10.1016/j.physe.2007.08.075
We report on photoluminescence studies on manganese and copper-doped ZnO nanowire array prepared by template method. The ZnO:Mn:Cu semiconductor grown using the electrochemical technique was characterized by electron paramagnetic resonance (EPR) and optical reflection measurements. Morphology and the structure were observed by SEM and X-ray diffraction. The photoluminescence of this system was correlated with manganese and copper concentration in the ZnO matrix. (C) 2007 Elsevier B.V. All rights reserved.
1098. Cationic disorder effects in complex oxide laser materials and phosphors
Authors:
Lupei, A; Lupei, V; Gheoghe, C; Gheorghe, L; Aka, G; Vivien, D
Published: JUL 2008, OPTICAL MATERIALS, 30, 1681, DOI: 10.1016/j.optmat.2007.11.009
A comparative analysis of the high-resolution spectra of the Nd3+ and Pr3+ in strontium lanthanum hexa-aluminates, charge compensated with magnesium Sr1-x(Nd,Pr)(y)Lax-yMgxAl12O19, on a large composition range is presented. The spectra are mainly dependent on the composition parameter x and show two families of centers for x < 0.5 and three for x >= 0.8, with distinct spectral characteristics. Based on spectral data, composition dependence and crystal structure, tentative structural models for the these centers are proposed. It is inferred that this complex picture results from the interplay between the effects determined by the anionic coordination of the centers and the perturbative effects caused by the multiple occupation of specific sites by cations of different valence. (c) 2007 Elsevier B.V. All rights reserved.
1099. WO(x)-CeO(2) and WO(x)-Nb(2)O(5) catalysts deactivation during hexane isomerization
Authors:
Mamede, AS; Payen, E; Granger, P; Florea, M; Parvulescu, VI
Published: MAY 2008, , DOI: 10.1002/aic.11468
1100. PLD and RF-PLD synthesis of Ba0.6Sr0.4TiO3 ferroelectric thin films for electrically controlled devices
Authors:
Nedelcu, L; Ioachim, A; Toacsan, MI; Banciu, MG; Pasuk, I; Buda, M; Scarisoreanu, N; Ion, V; Dinescu, M
Published: NOV 2008, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 93, 679, DOI: 10.1007/s00339-008-4694-9
Ba0.6Sr0.4TiO3 (BST) bulk ceramic synthesized by solid state reaction was used as target for thin films grown by pulsed laser deposition (PLD) and radiofrequency beam assisted PLD (RF-PLD). The X-ray diffraction patterns indicate that the films exhibit a polycrystalline cubic structure with a distorted unit cell. Scanning Electron Microscopy investigations showed a columnar microstructure with size of spherical grains up to 150 nm. The capacitance-voltage (C-V) characteristics of the BST films were performed by applying a DC voltage up to 5 V. A value of 280 for dielectric constant and 12.5% electrical tunability of the BST capacitor have been measured at room temperature.
1101. MODELING OF TRAP DISCHARGING PROCESSES IN MULTIPLE QUANTUM WELL STRUCTURES
Authors:
Ciurea, ML; Iancu, V; Stavarache, I; Lepadatu, AM; Rusnac, E
Published: 2008, CAS: 2008 INTERNATIONAL SEMICONDUCTOR CONFERENCE, PROCEEDINGS, +, DOI: 10.1109/SMICND.2008.4703332
The paper presents the modeling of trap discharging processes in Multiple Quantum Well nanostructures. The coupling between trapping and detrapping phenomena, due to the CaF2 buffer layers is discussed. The relative role of tunneling and displacement currents is also analyzed. The model allows the determination of trap parameters that are not directly measurable. The results are in good agreement with the experimental data.
1102. Shape memory and associated properties in Fe-Mn-Si-based ribbons produced by melt-spinning
Authors:
Valeanu, M; Filoti, G; Kuncser, V; Tolea, F; Popescu, B; Galatanu, A; Schinteie, G; Jianu, AD; Mitelea, I; Schinle, D; Craciunescu, CM
Published: JUL 2008, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 320, E167, DOI: 10.1016/j.jmmm.2008.02.105
Four Fe-Mn-Si alloys, Fe(62)Mn(32)Si(6), Fe(62)Mn(20)Si(5)Cr(8)Ni(5), Fe(62)Mn(16)Si(5)Cr(12)Ni(5) and Fe(65)Mn(9)Si(7)Cr(10)Ni(9), were obtained by the melt-spinning method. The samples were structurally, magnetic and shape memory effect (SME) investigated, both ''as quenched'' and thermally treated. The Mn-rich compositions show different phase, magnetic behavior and SME in comparison with Mn-poor compositions. The thermal treatments generate transformation between the two existing majority phases (alpha and gamma), related magnetization and SME behavior. The features are derived from the corroboration of structural, magnetic interaction and magnitude of SME data. (c) 2008 Elsevier B.V. All rights reserved.
1103. Peculiar structural effect of Sr2FeMoO6 perovskite type compounds
Authors:
Valsangiacom, C; Plapcianu, C; Stoica, L; Aldica, G; Kuncser, V
Published: APR 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 848, DOI:
Double perovskite Sr2FeMoO6 type compounds show special properties, such as magnetoresistance response at relatively small-applied fields and at rather high temperatures (ca. 400 K). Perovskite precursors were obtained unconventionally, in liquid phase, using oxalic acid as complexing agent, in the presence of ethylene glycol as polymerization agent. Ordering control concerning the magnetic properties is predictable to be strongly influenced by the synthesis route. The thermal stability of the precursors and the phase transitions of the oxide samples were analyzed by thermal analysis method, IR spectroscopy, Mossbauer spectroscopy, X-ray diffraction method and magnetic measurements. The experimental data for the perovskite compounds prepared by using oxalic acid as complexing agent revealed a double perovskite structure of analyzed samples, convenient magnetorezistive response (3.51 mu(B)/f.u), in good agreement with the Mossbauer spectra. Moreover, Mossbauer spectreoscopy allows the distinction between the ordered and the disordered phases of the perovskite structure and put in evidence the strong dependence of the structural and magnetic characteristics of the double perovskites on the synthesis route.
1104. A study of patch antennas on ZST substrate
Authors:
Avadanei, OG; Ioachim, A; Gasner, P; Pascariu, GN; Pascariu, V
Published: MAR 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 644, DOI:
Compactness of microstrip antennas has made them very attractive for applications in communication systems. As the need for antenna miniaturization continues, a possible solution is offered by the utilization of high dielectric constant materials as substrate. The purpose of this paper is the study of patch antennas on high permittivity dielectric substrates (Zr-0.8 Sn-0.2)TiO4 - ZST. A comparative investigation of different types of patch and arrays was performed Two substrate thickness h(1)=1 mm and h(2)=2 mm at a frequency of f=1090 MHz was considered. The main advantage of ZST material as a dielectric substrate for patch antennas is the miniaturization of the antennas as well as a high stability with the temperature. For each case we presented the radiation pattern, the efficiency and the input impedance of the patch antennas. The patch antennas were designed using an improved cavity model (a further improved Richards cavity model). The radiation pattern for rectangular array with n = 4, 16, 32 are also presented. The numbers are imposed by the feeding system of the array, which must ensure the same phase for all the patches. A discussion on the suitability of patch antennas with high permittivity substrate is done.
1105. The influence of chemical composition on magnetic properties and magnetostriction coefficient of cobalt ferrites
Authors:
Caltun, O; Dumitru, I; Feder, M; Diamandescu, L; Bibicu, I; Vasiliu, F; Lupu, N; Vilceanu, V
Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1778, DOI:
Four series of cobalt ferrites were prepared by conventional ceramic method. Calcined powders were analyzed by X-ray diffraction and Mossbauer spectroscopy to characterize the crystal structure. Green bodies were sinterized at temperatures between 1250 degrees-1300 degrees C, in air, for 5 hours. Chemical composition of samples and sintering parameters have a strong influence on the magnetic and magnetostrictive properties of the sintering bodies.
1106. Spectroscopic ellipsometry study of amorphous SrxBa1-xNb2O6 thin films obtained by pulsed laser deposition
Authors:
Ion, V; Galca, AC; Scarisoreanu, ND; Filipescu, M; Dinescu, M
Published: 2008, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 5, NO 5, 5, +, DOI: 10.1002/pssc.200777818
Optical properties of amorphous Strontium Barium Niobate (a-SBN) thin film are investigated using spectroscopic ellipsometry. Since the SBN can be applied to optoelectronic devices, the dispersion of refractive index is desirable. The films are obtained by Pulsed Laser Deposition (PLD) onto MgO and Si substrates by targeting a SBN:60 monocrystal: The dielectric function of a-SBN is approximated using a single Tauc-Lorentz oscillator model. Thicknesses of the films and of their rough layer are in agreement with SEM and AFM results. The dispersion of the refractive index is presented in the 1 - 5 eV range.
1107. A simple and efficient route to active and dispersed silica supported palladium nanoparticles
Authors:
Barau, A; Budarin, V; Caragheorgheopol, A; Luque, R; Macquarrie, DJ; Prelle, A; Teodorescu, VS; Zaharescu, M
Published: AUG 2008, CATALYSIS LETTERS, 124, 214, DOI: 10.1007/s10562-008-9465-x
Various mesoporous silica supported Pd materials were prepared by different methodologies in order to control and optimize the metal nanoparticle sizes for catalytic applications. The catalytic activities (conversion, mol% and selectivity to methyl-cinnamate) of the supported palladium catalysts were investigated in the Heck reaction under microwave irradiation using various haloarenes. Pd materials prepared by co-precipitation exhibited a very poor activity in the Heck reaction compared to that of Pd impregnated samples. Impregnated materials prepared without the use of a specific reducing agent had comparable activities to those of APTS-NaBH4 reduced Pd materials, validating the simplicity of the methodology. High selectivities to methylcinnamate were obtained for all materials.
1108. Structure and sensing properties of 0.1SnO(2)-0-9 alpha-Fe2O3 system
Authors:
Sorescu, M; Diamandescu, L; Tomescu, A; Tarabasanu-Mihaila, D; Teodorescu, V
Published: JAN 15 2008, MATERIALS CHEMISTRY AND PHYSICS, 107, 131, DOI: 10.1016/j.matchemphys.2007.06.062
The mixed oxide system 0.1SnO(2)-0-9 alpha-Fe2O3 (Sn1) was synthesized using the hydrothermal method and characterized using X-ray diffraction (XRD), Mossbauer spectroscopy and transmission electron microscopy (TEM). Sensing properties in both CH4 and CO were recorded as a function of temperature, humidity and concentration. The results were compared with those obtained for SnO2 (Sn10). It has been observed that Sn1 displays superior stability and sensitivity for methane as compared to Sn10. For both Sn1 and Sn10, the sensitivity to methane and carbon monoxide is influenced by temperature. In contradistinction to Sn10, Sn1 presents a reduced sensitivity to water vapors. A model based on the simultaneous evaluation of the electrical resistance and workfunction was elaborated to describe the selectivity of Sn1. (c) 2007 Elsevier B.V. All rights reserved.
1109. PIT method for obtaining of MgB2 wires with SiC powder added
Authors:
Alecu, G; Aldica, V; Voina, A; Hodorogea, S
Published: NOV 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2984, DOI:
The most popular process of MgB2 wire fabrication is the so-called in situ powder-in-tube (PIT) process, which is characterized by filing metallic tubes with Mg and B mixed powder, drawing and rolling the material into wires and, finally, by applying a heat treatment. X-ray diffraction analyses were carried out for MgB2 cores and SiC-added wires. XRD patterns reveal that nearly single-phase MgB2 was obtained. Also, in this paper are presented the obtained magnetization curves.
1110. Electrical characterization of thiols self-assembled layers on GaP (111) structures
Authors:
Ghita, RV; Lazarescu, V; Logofatu, C; Negrila, CC; Lazarescu, MF
Published: OCT 2008, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 11, 397, DOI: 10.1016/j.mssp.2008.11.012
The experimental studies on III-V semiconductor compounds surface passivation phenomena are mainly dedicated to solve some technological problems as those regarding the ways to keep the chemical stability of native oxides on surfaces. Self-assembled monolayers (SAMs) provide a simple way to produce relatively ordered structures at a molecular scale, which seems to be capable to protect the clean surface against the evolution of oxidation process. In this respect, thin films of SAMs of aliphatic thiol (dodencanthiol-CH3(CH2)(11)SH) and aromatic thiol (4, 4' tiobisbenzenthiol-S (C6H4SH)(2) have been deposited on the surface of Gap (111) samples. The electrical properties measurements of some structures based on GaP compound was performed. There were recorded current-voltage (I-V) characteristics for complex structures AuGeNi/R-SH/GaP and AuGeNi/Ar-SH/GaP in darkness and also exposed to a Xe lamp. In dark and in "reverse bias" way, the I-V characteristics present the feature of a Zenner diode for GaP/Ar-SH and a gradual increase of current for GaP/R-SH. In dark and "in forward bias" way, the current increases as for a normal diode for both GaP/Ar-SH and GaP/R-SH structures. The complex structures (e.g.: In/AuGeNi/R-SH/GaP/R-SH/AuGeNi/In) are less sensitive to light. The SEM analysis performed on a GaP/R-SH surface shows a continuous packed up layer while GaP/Ar-SH looks like an inhomogeneous deposition of layers with different thickness regions. The diodes' ideality factors determined from I-V characteristics are unusually high (n >> 2) as a possible result of inhomogeneous Schottky contacts or due to ageing effects, in the field of degradation. (C) 2009 Elsevier Ltd. All rights reserved.
1111. Quasi-2D characteristics in the ac susceptibility response of polycrystalline (Bi,Pb)SrCaCuO/2223 multiphase systems
Authors:
Mihalache, V; Cosereanu, L; Miu, L
Published: JAN 1 2008, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 468, 96, DOI: 10.1016/j.physc.2007.10.019
Fundamental and third harmonic ac susceptibility measurements as a function of temperature T, ac magnetic field, and dc magnetic field have been performed on Bi(Pb)SrCaCuO/2223 bulk samples consisting of both Bi2Sr2Ca2Cu3O10+delta (2223) and Bi2Sr2CaCu2O8+delta (2212) phases. Since the chi(1)''(T) peak corresponding to the losses in the weak links between the grains shifts rapidly to lower T and its amplitude is strongly suppressed with increasing the dc magnetic field H-dc, the other peaks related to the losses in the grains become visible. For the samples consisting of single phase 2223, these intragranular peaks are situated near 38 K, 58 K, and 80-88 K (depending on the sample), whereas for the samples consisting of single phase 2212, they are situated near 20 K, 43 K, and 77 K. For H-dc >= 1 kOe, the temperature positions of the intragranular peaks are weakly field dependent. This shows that the transition line determined from the loss peaks behaves like the melting line in two-dimensional (213) systems. Also, as the field increases, the amplitude of the loss peaks can decrease up to their disappearance, suggesting a layer decoupling process. In this way, we show that, above a crossover field of similar to 1 kOe, the vortex lattice in the superconducting grains of polycrystalline samples reproduces the behaviour of the vortex lattice in a quasi-2D object consisting of a set of separated "thin films" with one-, two-, and three-effective-layer thicknesses. For the samples consisting of both 2223 and 2212 phases, three additional peaks were observed, situated near 28 K, 50 K and 75-80 K (depending on the sample). These peaks were attributed to the regions in which the 2212 and 2223 layers alternate. (c) 2007 Elsevier B.V. All rights reserved.
1112. Coulomb effects in open quantum dots within the random-phase approximation
Authors:
Moldoveanu, V; Tanatar, B
Published: MAY 2008, PHYSICAL REVIEW B, 77, DOI: 10.1103/PhysRevB.77.195302
The effect of electron-electron interactions on coherent transport in quantum dot systems is theoretically investigated by adapting the well-known random-phase approximation (RPA) to the nonequilibrium GreenKeldysh formalism for open mesoscopic systems. The contour-ordered polarization operator is computed in terms of the Green functions of the noninteracting system. We apply the proposed RPA-Keldysh scheme for studying Coulomb-modified Fano lines and dephasing effects in interferometers with side-coupled many-level dots. Our method allows us to treat on equal footing the decoherence induced by the intradot interaction and that by the Coulomb coupling to a nearby system. In the case of a single interferometer, we show that the intradot Coulomb interaction leads to a reduction of-the Fano line amplitude. From the analysis of the interaction self-energy, it follows that this effect originates in inelastic scattering processes in which electron-hole pairs are involved. The interplay between the interdot and the intradot interactions in decoherence is discussed for two nearby identical T-shaped interferometers. We also show that the intradot interaction does not prevent the observation of controlled dephasing due to a nearby charge detector, as long as the latter is subjected to a sufficiently large bias.
1113. Photochemistry aspects of the laser pyrolysis addressing the preparation of oxide semiconductor photocatalysts
Authors:
Alexandrescu, R; Morjan, I; Dumitrache, F; Scarisoreanu, M; Soare, I; Fleaca, C; Birjega, R; Popovici, E; Gavrila, L; Prodan, G; Ciupina, V; Filoti, G; Kuncser, V; Vekas, L
Published: 2008, INTERNATIONAL JOURNAL OF PHOTOENERGY, 2008, DOI: 10.1155/2008/604181
The laser pyrolysis is a powerful and a versatile tool for the gas-phase synthesis of nanoparticles. In this paper, some fundamental and applicative characteristics of this technique are outlined and recent results obtained in the preparation of gamma iron oxide (gamma-Fe2O3) and titania (TiO2) semiconductor nanostructures are illustrated. Nanosized iron oxide particles (4 to 9 nm diameter values) have been directly synthesized by the laser-induced pyrolysis of a mixture containing iron pentacarbonyl/air (as oxidizer)/ethylene (as sensitizer). Temperature-dependent Mossbauer spectroscopy shows that mainly maghemite is present in the sample obtained at higher laser power. The use of selected Fe2O3 samples for the preparation of water-dispersed magnetic nanofluids is also discussed. TiO2 nanoparticles comprising a mixture of anatase and rutile phases were synthesized via the laser pyrolysis of TiCl4- (vapors) based gas-phase mixtures. High precursor concentration of the oxidizer was found to favor the prevalent anatase phase (about 90%) in the titania nanopowders. Copyright (C) 2008 R. Alexandrescu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1114. Tunneling magneto-resistance granular thin films deposited by thermo-ionic vacuum arc technique
Authors:
Mustata, I; Anghel, A; Lungu, CP; Pompilian, O; Kuncser, V; Schinteie, G
Published: 2008, PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIEN, 100, 082026, DOI: 10.1088/1742-6596/100/8/082026
Co-MgO granular films presenting TMR effects were prepared by thermo-ionic vacuum arc (TVA) method with the simultaneous ignition of plasma in Co and MgO vapors, respectively. The processing method is suitable for the simultaneous preparation of films of different relative content of Co in the MgO insulating matrix. Morphologic, structural and magnetic behaviors were analyzed in as prepared and annealed samples. The influence of the Co content on the magnetic properties of the prepared films was analyzed, in correlation with tunneling magneto-resistance effects. The tunneling magneto-resistance effect is maximal for certain Co content. This behavior was interpreted by the contrary effects of decreasing the average size of the magnetic grains, and hence the average inter-grains distance at higher Co relative content, and the enhanced magnetic disorder in very fine grains dispersed in the insulating matrix. This mechanism was suggested by the comportment of as prepared and thermally annealed samples.
1115. Eu-151-Mossbauer spectroscopic study on ceramics beloging to ZrO2-Eu2O3-Y2O3 system
Authors:
Volceanov, E; Plapcianu, C; Kuncser, V; Volceanov, A; Matovic, B; Motoc, S
Published: APR 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 895, DOI:
In the last years the ternary stabilized zirconia ceramics have attracted a considerable attention as a source of materials for structural ceramics. In present paper, the simultaneous influence of Eu3+ and Y3+ cations on zirconia powders (obtained by co-precipitation of aqueous salts solutions) on stabilization process in conjunction with the structural characteristics was investigated. A conventional sintering method (in electric furnace) at 1350 degrees C temperature range was applied. SEM+EDAX and XPS (X-ray Photoelectron Spectroscopic) analysis were performed. The Eu3+ Mossbauer parameters: isomer shift and quadrupole splitting have been obtained for 21.6 keV radiation of Eu-151 are in good agreement with the XPS and XRD-obtained crystallographic data of the studied compositions.
1116. Defects in silicon: From bulk crystals to nanostructures
Authors:
Ciurea, ML; Iancu, V; Lazanu, S; Lepadatu, AM; Rusnac, E; Stavarache, I
Defects in silicon are studied as function of the dimensionality of the investigated structures. Defects produced by strong irradiation in bulk crystals, like vacancies or interstitial defects, induce other defects, so that the irradiated devices are irreversibly damaged. Defects in nanostructures are shown to be produced mainly by surface/interface states and strains, and are therefore specific to the investigated structure. The modeling of the experimental methods allows the determination of defect parameters that are not directly measurable. The carriers capture on quantum confinement levels in OD systems has a similar behavior with the trapping phenomena.
1117. Iron oxide colloids and their heterogenization by silica sol-gel entrapment: Catalytic and magnetic properties
Authors:
Neatu, F; Kraynov, A; D'Souza, L; Parvulescu, VI; Kranjc, K; Kocevar, M; Kuncser, V; Richards, R
Published: AUG 31 2008, APPLIED CATALYSIS A-GENERAL, 346, 35, DOI: 10.1016/j.apcata.2008.04.024
Fe3O4 colloids modified by the chiral ligand cinchonidine were prepared with the goal of obtaining a magnetic and catalytic nano-material and were subsequently embedded in silica to form a heterogeneous catalyst. The systems were characterized by TEM and XRD measurements, while the Mossbauer technique was applied for measuring the magnetic properties of the Fe3O4 colloids. The hyperfine magnetic field distribution was consistent with one type of Fe oxide, namely, the magnetite (Fe304). These colloids, both as 'quasi-homogenous catalysts' (or soluble heterogeneous catalysts) and embedded in silica (heterogeneous catalysts) were employed in the selective hydrogenolysis of complex bicyclo[2.2.2]oct-7-enes (bicyclo[2.2.2]oct-2-enes when unsubstituted). (C) 2008 Published by Elsevier B.V.
1118. Measurement-induced decoherence in electronic interferometry at nanoscale
Authors:
Moldoveanu, V; Tanatar, B; Tolea, M
Published: SEP 29 2008, PHYSICS LETTERS A, 372, 6196, DOI: 10.1016/j.physleta.2008.07.079
We introduce a theoretical formalism describing a wide class of 'Which Path' experiments in mesoscopic/nanoscopic transport. The physical system involves a mesoscopic interferometer (e.g. an Aharonov-Bohm ring with embedded dots or a side-coupled quantum dot) which is electrostatically coupled to a nearby quantum point constriction. Due to the charge sensing effect the latter acts as a charge detector. Therefore the interference pattern can be monitored indirectly by looking at the current characteristics of the detector as shown in the experimental work of Buks et al. [E. Buks, R. Schuster, M. Heiblum, D. Mahalu, V. Umansky, Nature (London) 391 (1998) 871]. We use the non-equilibrium Green-Keldysh formalism and a second order perturbative treatment of the Coulomb interaction in order to compute the relevant transport properties. it is shown that in the presence of the Coulomb interaction the current through the detector exhibits oscillations as a function of the magnetic field applied on a single-dot AB interferometer. We also discuss the dependence of the visibility of the Aharonov-Bohm oscillations on the gate potential applied to the dot. (C) 2008 Elsevier B.V. All rights reserved.
1119. Assessment of the distribution of the Yb3+ ions in Sc2O3 ceramics from cooperative absorption and emission
Authors:
Lupei, V; Lupei, A; Boulon, G; Jouini, A; Ikesue, A
Published: FEB 28 2008, JOURNAL OF ALLOYS AND COMPOUNDS, 451, 181, DOI: 10.1016/j.jallcom.2007.04.170
The paper reports the first observation of cooperative optical absorption and emission processes in Yb3+:Sc2O3 transparent laser ceramics. The intensity of cooperative processes in highly transparent ceramics Yb3+:Sc2O3 with up to 30 at.% Yb scales well with the data existing on single crystals and indicates that the distribution of the Yb3+ ions is random, without regions of agglomeration. (c) 2007 Published by Elsevier B.V.
1120. Carbon nanowalls growth by radiofrequency plasma-beam-enhanced chemical vapor deposition
Authors:
Vizireanu, S; Nistor, L; Haupt, M; Katzenmaier, V; Oehr, C; Dinescu, G
Published: APR 4 2008, PLASMA PROCESSES AND POLYMERS, 5, 268, DOI: 10.1002/ppap.200700120
We report the remote growth of carbon nanowalls in a plasma beam sustained by an expanding argon radiofrequency discharge and injected with a small amount of acetylene in the presence of hydrogen as active gas. The growth process was investigated by varying the mass flow rates, ratio and nature of gases (argon, ammonia/hydrogen, and acetylene), the substrate temperature, and the radiofrequency power. Scanning and transmission electron microscopy, Raman spectroscopy, and electron diffraction methods were used for the investigation of the deposited material. We found that although materials with various morphologies can be generally obtained, nanostructured carbon material with a 2D morphology is obtained with a specific range of parameter values.
1121. Magnetic characterization of some nanometric iron oxides
Authors:
Grecu, VV; Constantinescu, S; Grecu, MN; Olar, R; Badea, M; Turcu, R
Published: APR 2008, HYPERFINE INTERACTIONS, 183, 214, DOI: 10.1007/s10751-008-9753-2
Nanosized magnetite particles embedded in polypyrrole matrix have been studied by Mossbauer and electron magnetic resonance spectroscopy. Comparison with as grown magnetite is made. Hyperfine fields distribution is determined and line shape of resonance curves are discussed in terms of composite structure, sizes and treatments.
1122. Comparative Study on the Microstructural and Magnetic Properties of Cobalt Ferrites Synthesized by Ceramic and Oxidation Wet Methods
Authors:
Feder, M; Diamandescu, L; Bibicu, I; Caltun, OF; Dumitru, I; Boutiuc, L; Chiriac, H; Lupu, N; Vilceanu, V; Vilceanu, M
Published: NOV 2008, IEEE TRANSACTIONS ON MAGNETICS, 44, 2939, DOI: 10.1109/TMAG.2008.2002200
CoFe2O4 and CoMn0.2Fe1.8O4 ferrites were synthesized using standard solid state phase ceramic method and coprecipitation and oxidation method. X-ray diffraction, Mossbauer spectroscopy, and surface electron microscopy were used to characterize the samples' microstructures. Vibrating sample measurement and strain gauge technique were used to characterize the magnetic and magnetostrictive properties of both powders and sintered samples, respectively. The specific magnetization increased from 55 emu/g for stoichiometric ferrite samples obtained by conventional method to 179 emu/g for coprecipitated ferite powders respectively. In the manganese substituted cobalt ferrite case the specific magnetization increased only twice, from 77 emu/g to 168 emu/g. The maximum magnetostrictive coefficient of coprecipitated samples of 145 ppm is smaller compared to that of solid state phase ceramic samples of 195 ppm. The most important benefit in the case of the coprecipitated and oxidized samples is the four fold increase of the maximum strain derivative compared to solid state phase ceramic samples.
1123. A SOLID STATE NANO-GENERATOR: CONCEPT, DESIGN AND THEORETICAL ESTIMATIONS
Authors:
Vopsaroiu, M; Cain, MG; Kuncser, V; Blackburn, J
Published: 2008, FUNCTIONALIZED NANOSCALE MATERIALS, DEVICES AND SYSTEMS, +, DOI: 10.1007/978-1-4020-8903-9_44
Nano-technology is a very attractive area of research and innovation because it allows the current trends in miniaturization to continue. The transition from micro scale to nano scale devices has already taken place in many applications such as electronics, magnetic recording and nano-biophysics. However, as we scale down the size of the structures and devices, it becomes obvious that the classical behavior will break down at the nano-scale and an interesting superposition of classical and quantum effects will emerge. Therefore, the validity of classical physics is questioned and many aspects of physics are now being revisited from the point of view of nano-technologies. In line with the new developments in miniaturization and nano-technologies, we propose in this letter a simple mechanism that applies the Faraday effect at the nano-scale in order to create a possible solid-state energy nano-generator device. The proposed nano-generator functionality is based oil what we shall call the Super-Paramagnetic Electromotive Force (SPEF) effect. This has the potential to produce a very small voltage on short time scales by converting directly thermal energy at room temperature to electromotive energy Without the need for external work or mechanical motion.
1124. Combinatorial pulsed laser deposition of thin films
Authors:
Craciun, V; Craciun, D; Mihailescu, IN; Socol, G; Stefan, N; Miroiu, M; Galca, AC; Bourne, G
Published: 2008, HIGH-POWER LASER ABLATION VII, PTS 1-2, 7005, DOI: 10.1117/12.782589
Pulsed Laser Deposition (PLD) is an ideal technique to be used for combinatorial approaches. By simply changing the deposition targets one can obtain alternating layers with different periodicities both vertically and laterally, along the substrate surface. By changing the laser impact area location and the number of pulses on each target used for ablation, one can grow films with a continuous variation of the chemical composition, which will be a function of the location on the substrate. To illustrate the advantages and versatility of this Combinatorial PLD (C-PLD) technique, several examples of films used in applications where more than one property should be tailored or optimized are presented. Investigations of thermo-chemical stability, chemical bonding and crystalline structure of thin films of mixtures of HfO2 and Al2O3 that are used as high-k dielectric layers in advanced C-MOS transistors is the first example, followed by a study of structural, mechanical, optical and electrical properties of mixtures of indium tin oxide and doped or pure zinc oxide that are used as transparent and conductive layers. The third example is from the deposition of multilayers of ZrC and ZrN with variable thicknesses to obtain hard coatings.
1125. FexOy nanoparticles embedded in sol-gel vitreous silica. The effect of the catalyst nature
Authors:
Raileanu, M; Crisan, M; Braileanu, A; Dragan, N; Zaharescu, M; Stan, C; Predoi, D; Kuncser, V; Marinescu, VE; Hodorogea, SM
Published: JAN 15 2008, JOURNAL OF NON-CRYSTALLINE SOLIDS, 354, 631, DOI: 10.1016/j.jnoncrysol.2007.07.070
This work reports on recently investigated structural and magnetic properties of three FexOy-SiO2 nanocomposites prepared by the alkoxide route of the sol-gel method. Depending on the presence or absence of catalyst and on its nature (acidic or basic), important differences among the samples have been observed from the point of view of their structure and properties. (c) 2007 Elsevier B.V. All rights reserved.
1126. Influence of bilayer period on the characteristics of nanornetre-scale ZrN/TiAIN multilayers
Authors:
Vladescu, A; Kiss, A; Popescu, A; Braic, M; Balaceanu, M; Braic, V; Tudor, I; Logofatu, C; Negrila, CC; Rapeanu, R
Published: FEB 2008, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 8, 721, DOI: 10.1166/jnn.2008.D218
in the last decade, considerable research effort was directed to the deposition of multilayer films with layer thicknesses in the nanometer range (superlattice coatings), in order to increase the performance of various cutting tools and machine parts. The goal of the present work was to investigate the main microstructural, mechanical and wear resistance characteristics of a superlattice coating, consisting of alternate multilayer ZrN/TiAIN films, with various bilayer periods (5 divided by 20 nm). The coatings were deposited by the cathodic arc method on Si, plain carbon steel and high speed steel substrates to be used as wear resistance surfaces. The multilayer structures were prepared by using shutters placed in front of each cathode (Zr and Ti + Al). The characteristics of multilayer structures (elemental and phase composition, texture, Vickers microhardness, thickness, adhesion, and wear resistance) were determined by using various techniques (AES, XPS, XRD, microhardness measurements, scratch, and tribological tests). A comparison with the properties of ZrN and TiAIN single-layer coatings was carried out.
1127. Extrinsic tunneling magnetoresistance in thick films of CrO2-polystyrene composite
Authors:
Sandu, V; Aldica, G; Sandu, E
Published: 2007, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 1, 76, DOI:
Polystyrene-CrO2 composite films with extrinsic tunneling magnetoresistance have been obtained. The electric conduction is 2D Mott variable range hopping in the temperature range 77-300 K. The magnetoresistance is negative when the field is aligned parallel to the current (in-plane geometry) and is due to the spin dependent intergrain tunneling of the charge carriers. It reaches a value MR = -10.6 % at room temperature and a magnetic field of 1T. When the field is applied in-plane but perpendicular to the current the magnetoresistivity is positive and has the average value MR = 3.56 %.
1128. Electric and magnetic response of Li-doped YBa2Cu3O7(LiF)(x) under neutron irradiation
Authors:
Sandu, V; Aldica, G; Sandu, E; Nita, P
Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3836, DOI:
We investigate the effect of neutron irradiation on the electric and magnetic properties, including the enhancement of the critical current density, of ceramics YBa2Cu3O7(LiF)(x) samples. The most important finding has been that the level of Li-doping is crucial for the postirradiation response. The irreversibility increases for more than two times in the samples with x <= 0.04 after neutron irradiation at 5 x 10(17) neutron S/cm(2) but less for higher concentrations. The effects of the irradiation on the electric transport and ac-susceptibility suggest a self-organization of the defects at low Li content and a uniformly space distribution for x >= 0.08.
1129. Optical characterization of the phosphate glasses containing pair transition ions
Authors:
Elisa, M; Grigorescu, C; Vasiliu, I; Bulinski, M; Kuncser, V; Predoi, D; Filoti, G; Meghea, A; Iftimie, N; Giurginca, M; Onose, C
Published: MAR 2007, OPTICAL AND QUANTUM ELECTRONICS, 39, 531, DOI: 10.1007/s11082-007-9097-1
The paper deals with optical and electronic properties of the aluminophosphate glasses containing Fe-Mn and Fe-Cr ion pairs in different concentration. The influence of the mixed alkali ions over the electronic properties has been investigated. The optical behavior (optical transmission) of the glass samples has been studied by UV-VIS spectroscopy and the refractive index dependency on wavelength has been discussed. The transmission spectra show features specific for the doping transition ions (TM), revealing different oxidation states of iron (Fe2+/Fe3+), manganese (Mn2+/Mn3+) and chromium (Cr3+/Cr6+) in the vitreous network. Mossbauer spectroscopy offers information regarding the TM oxidation states, redox processes and the iron coordination symmetry in the vitreous network. In the case of Fe-Mn doped glasses, the percentage of Fe2+ is about 40% and a doubled iron content leads to an increasing of Fe2+ percentage up to 53%. The replacing of lithium ions by natrium ions (mixed alkali effect) provides an increasing of the Fe2+ percentage up to 56%. The occurrence of the tetrahedral or octahedral symmetry of Fe(2+)supercript stop ions bonded by O2- ions depends on the transition ion nature and Li+/Na+ ratio. Infrared absorption spectra of the pair transition ions-doped aluminophosphate glasses reveal optical phonons specific for the phosphate glass matrix.
1130. Study of non catalytic oxidehydrogenation of isobutane in an integral reactor
Authors:
Grecu, MN; Burducea, G; Grecu, V; Moldovan, R; Beica, T; Zgura, I
Published: MAR 2007, REVUE ROUMAINE DE CHIMIE, 52, 281, DOI:
X-band ESR spectra of the calamitic and discotic lyotropic nematic phases in sodium dodecyl sulphate (SDS)/decanol/water system, doped with paramagnetic nitroxide free radicals are analyzed in this paper. The studied temperature range was chosen to include phase transitions of the lyotropic systems. The variation of the surfactant hydrocarbon chains ordering versus temperature is determined by the hyperfine splitting tensor (,4) and the spectroscopic splitting tensor ((g) under bar) anisotropies. The temperature dependence of the molecular order parameters for both lyotropic systems and the corresponding angular fluctuations are presented and discussed.
1131. Sequence of phases in the hydrothermal synthesis of zinc-doped magnetite system
Authors:
Sorescu, M; Diamandescu, L; Tarabasanu-Mihaila, D; Teodorescu, V
Published: DEC 15 2007, MATERIALS CHEMISTRY AND PHYSICS, 106, 278, DOI: 10.1016/j.matchemphys.2007.06.001
Hydrothermal techniques have been used to synthesize samples of ZnxFe3-O-x(4) (x = 0.0-1.0) starting with ZnSO4 center dot 7H(2)O/FeSO4 center dot 7H(2)O aqueous solution. The sequence of phases, structural and magnetic properties were followed by X-ray diffraction (XRD), Mossbauer spectroscopy and transmission electron microscopy (TEM). Refinement of the XRD spectra yielded the dependence of the lattice parameters of zinc-doped magnetite and zinc ferrite phase as function of the Zn molar concentration x. As well, the particle diameter was derived and represented as a function of Zn content x. As a function of Zn concentration, the phase content of hydrothermally synthesized samples was found to consist of zinc-doped magnetite, goethite and zinc ferrite. Consistent with the XRD results, Mossbauer spectroscopy data indicate the presence of magnetite and goethite at x <= 0.2, magnetite and zinc ferrite at x <= 0.9 and pure zinc ferrite only at high zinc concentrations. The presence of different magnetite phases was confirmed by TEM and particles with a size of 50 nm were identified. Our results show that zinc ferrite is formed at high zinc concentration by the hydrothermal method and an acicular component of goethite-magnetite is obtained at low zinc content. (C) 2007 Elsevier B.V. All rights reserved.
1132. Flux dynamic changes by neutron irradiation in BISCCO: High harmonics AC susceptibility analysis
Authors:
Di Gioacchino, D; Tripodi, P; Vinko, JD; Mihalache, V; Popa, S
Published: JUN 2007, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 17, 3678, DOI: 10.1109/TASC.2007.898227
High harmonics ac susceptibility measurements joint with neutron irradiations on quasi-bi-dimensional high temperature superconductor (quasi-2D-HTSC) are good tools to study the flux dynamics and its interaction with pinning processes in these superconductors. Flux neutron intensity of 5 * 10(17) n * cm(-2) shows a deep change in the flux pinning dynamics in Bi-Sr-Ca-Cu-O (BSCCO) system. Third harmonic susceptibility signal increases in amplitude after the neutron irradiation, followed by a rise of the pinning and critical current. Moreover, after the irradiation, the measurements underline the demise of the anomalous peak effect (PE) associated with a three-dime.nsional/two-dimensionaI (3D/2D) flux lattice transition.
1133. A. comparative study of micro crystalline and nanocrystalline lead sulfide based PbS/SiO2/Si heterostructures
Authors:
Stancu, V; Pentia, E; Goldenblum, A; Buda, M; Iordache, G; Botila, T
Published: 2007, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 10, 66, DOI:
The PbS micro-crystalline and nano-crystalline films were obtained using the Chemical Bath Deposition method. We investigated comparatively the structural, electrical and photoconductive properties of these films deposited on glass. PbS/SiO2/Si heterostructures made with nanocrystalline PbS layers present interesting peculiarities. Their C-V curves show hysterezis. In a field effect arrangement it is possible to control the photoconductive short and long wavelength ratio response. The heterostructure properties were explained by taking into account the interface charged traps.
1134. Irreversible magnetization above critical temperature in superconducting Y0.47Pr0.53Ba2Cu3O7-delta
Authors:
Sandu, V; Gyawali, P; Katuwal, T; Amasan, CC; Taylor, BJ; Maple, MB
Published: 2007, SIX INTERNATIONAL CONFERENCE OF THE BALKAN PHYSICAL UNION, 899, +, DOI:
Using magnetization measurements, we report the existence of an irreversibility in the magnetization in Y0.47Pr0.53Ba2Cu3O7-delta single crystals above the critical temperature (T-c = 13 K) that is visible up to 200 K. Magnetization vs temperature displays irreversibility up to an applied field of 500 Oe. We noticed a weak irreversibility at high temperatures and a stronger one at low temperatures. In the weak irreversibility regime, both zero-field- and field-cooled magnetization follow similar Curie-Weiss (C-W) dependences, with slightly different parameters. The C-W parameters, decrease fast with increasing field. The C-W temperature is negative, suggesting that the average interaction between spins is antiferromagnetic. All these data suggest that the paramagnetic state is in fact a free spin liquid containing floating antiferromagnetic clusters as well as superconducting phase fluctuations.
1135. Ge dots embedded in silicon dioxide using sol-gel deposition
Authors:
Stoica, TF; Gartner, M; Teodorescu, VS; Stoica, T
Published: OCT 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3274, DOI:
A versatile method, that of sol-gel deposition was used to produce Si1-xGexO2 films on Si substrates. Samples after annealing at different temperatures are investigated by different techniques including high-resolution transmission electron microscopy and spectral ellipsometry. It was revealed that, by annealing at high temperatures, Ge accumulates in small clusters (5-10nm) inside of the oxide layer. By ellipsometric investigations, valuable data about the temperature evolution of the composition and optical constants were obtained.
1136. Synthesis and characterization of spinelic ferrites obtained from coordination compounds as precursors
Authors:
Culita, DC; Patron, L; Teodorescu, VS; Balint, L
Published: APR 25 2007, JOURNAL OF ALLOYS AND COMPOUNDS, 432, 216, DOI: 10.1016/j.jallcom.2006.05.104
Cobalt ferrite and magnetite nanoparticles were obtained by "the complexation method" belonging to soft chemistry, in which cholic acid sodium salt acts as complexation agent. The precursors were characterized by IR, UV-vis spectra and magnetic measurements. X-ray diffraction spectra and transmission electron inicroscopy proved the nanocrystalline structure of the spinelic ferrites. (c) 2006 Elsevier B.V. All rights reserved.
1137. New perturbed Pb--aggregate centers in electrolytically colored KBr : Pb2+ + (Ca, Ba) crystals
Authors:
Polosan, S; Topa, V; Apostol, E; Tsuboi, T
Published: JAN-APR 2007, JOURNAL OF LUMINESCENCE, 122, 948, DOI: 10.1016/j.jlumin.2006.01.364
New luminescent centers with a large near-infrared emissions were obtained by unusual electrolytic coloration method (low temperature and high electric field) in the KBr:Pb2+ crystals co-doped with alkali-earth ions (Ca2+, Sr2+, Ba2+). These so-called Tx centers involve Pb--negative metal ions and the presence of at least one alkali-earth ion, which enhances the photoluminescence properties of those centers. The formation of these new centers is due to the presence of F-centers created in the process of electrolytical coloration. The photoluminescence properties, together with the magnetic circular dichroism spectra, prove the existence of at least one paramagnetic luminescent center. (c) 2006 Elsevier B.V. All rights reserved.
1138. Influence of geometrical properties on light emission of ZnO nanowires
Authors:
Enculescu, I; Sima, M; Enculescu, M; Enache, M; Vasile, V; Neumann, R
Published: SEP 2007, OPTICAL MATERIALS, 30, 75, DOI: 10.1016/j.optmat.2007.01.002
The present paper deals with the preparation and study of optical properties of ZnO nanowires. Nanoporous ion track polycarbonate foils were used as templates for ZnO nanowires growth by electrochemical deposition. The growth was performed using an aqueous electrochemical bath at a temperature of 70 degrees C. SEM and TEM were employed to study the morphological properties of the nanowires. Electron diffraction was employed for structural characterization. Reflection and photoluminescence spectroscopy were used for optical characterization. A comparison between the properties of electrodeposited thin films and nanowires of ZnO was made from the point of view of photoluminescence properties. (c) 2007 Elsevier B.V. All rights reserved.
1139. Thickness oscillation effect in photoexpansion and photocontraction of amorphous selenium
Authors:
Popescu, M; Sava, F; Shimakawa, K; Ikeda, Y; Babin, V
Published: NOV 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3562, DOI:
Thickness oscillations under light irradiation or by switching-off the light have been revealed in amorphous selenium films. The explanation was given in the frame of a theory that takes into account the balance between the expansion of the inter-chain distance due to electrical charging and better ordering of chains due to freedom of chains to accommodate into the structure as a result of the diminishing or increasing of the spatial hindrance.
1140. Why the energy levels observed in electrical transport, phototransport and photoluminescence are different?
Authors:
Ciurea, ML; Iancu, V
Published: 2007, CAS 2007 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, +, DOI: 10.1109/SMICND.2007.4519643
The paper presents an analysis of the electrical transport, phototransport and photoluminescence measurements performed on silicon-based nanocrystalline systems. The experimental results are discussed within the frame of a quantum confinement model. It is proved that the differences between the energy levels identified in the measurements are related to the quantum selection rules specific to each process. It is also proved that, at nanometric scale, the nature of the atoms composing the nanocrystal represents a first order correction, while the size represents a zero order factor.
1141. Electrolytic reduction of Tl+ ions in KCl crystals
Authors:
Polosan, S; Tsubi, T; Apostol, E; Topa, V
Published: SEP 2007, OPTICAL MATERIALS, 30, 97, DOI: 10.1016/j.optmat.2006.11.006
Electrolytic coloration has been made for KCl crystals doped with Tl+ ions and doped with Tl+ and Ca2+ ions. Intensity decrease of the Tl+ absorption bands is observed in the two colored crystals, while several new absorption and emission bands are observed. They are attributed to Tl- ions which were converted from Tl+ ions by electron injection during electrolytic coloration. Different absorption and emission bands are observed for KCI:TI and KCI:T1 + Ca crystals. Sharp absorption band appears at 285 nm in the colored KCl:Tl and at 400 and 503 nm in the colored KCLTl + Ca. Infrared emission bands are observed at 1470, 1600 and 2185 nm in colored KCI:Tl, while at 1630 and 1900 nm in colored KCl:Tl + Ca. It is suggested that the absorption and emission bands in KCl:Tl + Ca are due to Tl- ions perturbed by Ca2+ or vacancy at the nearest neighbor. (c) 2006 Elsevier B.V. All rights reserved.
1142. Memory effects in Si/SiO2/nano-crystalline PbS reterostructures
Authors:
Buda, M; Stancu, V; Pentia, E; Botila, T
Published: 2007, 2006 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, +, DOI:
The mechanism of charge storage in p Si/SiO2 /nano-crystalline PbS heterostructures is investigated using capacitance - voltage (C-V) and conductance-voltage (G-V) measurements at different frequencies. The nano-crystalline thin PbS films were obtained using the Chemical Bath Deposition method with a shorter reaction time and without doping element in the reducing bath. The C-V curves show hysterezis indicating charge storage with a maximum charge density of 3x10(11) cm(-2) for the highest measurement frequency of 100 kHz. The charge storage capacity is enhanced in the rase of using a nano-crystalline PbS thin film instead of a standard macro-crystalline film.
1143. Controlled dephasing in single-dot Aharonov-Bohm interferometers
Authors:
Moldoveanu, V; Tolea, M; Tanatar, B
Published: JAN 2007, PHYSICAL REVIEW B, 75, DOI: 10.1103/PhysRevB.75.045309
We study the Fano effect and the visibility of the Aharonov-Bohm oscillations for a mesoscopic interferometer with an embedded quantum dot in the presence of a nearby second dot. When the electron-electron interaction between the two dots is considered the nearby dot acts as a charge detector. We compute the currents through the interferometer and detector within the Keldysh formalism and the self-energy of the nonequilibrium Green's functions is found up to the second order in the interaction strength. The current formula contains a correction to the Landauer-Buttiker formula. Its contribution to transport and dephasing is discussed. As the bias applied on the detector is increased, the amplitude of both the Fano resonance and Aharonov-Bohm oscillations are considerably reduced due to controlled dephasing. This result is explained by analyzing the behavior of the imaginary part of the interaction self-energy as a function of energy and bias. We emphasize as well the role of the ring-dot coupling. Our theoretical results are consistent with the experimental observation of Buks [Nature 391, 871 (1998)].
1144. Spectroscopic characteristics of RE3+: Sc2O3 ceramics
Authors:
Lupei, V; Lupei, A; Gheorghe, C; Ikesue, A; Stefan, A; Ciupina, V; Prodan, A
Published: 2007, ROMOPTO 2006: EIGHTH CONFERENCE ON OPTICS, 6785, DOI: 10.1117/12.755967
The spectroscopic investigation of the highly transparent rare earth (Pr3+, Nd3+, Ho3+, Er3+ Tm3+, Yb3+) doped Sc2O3 ceramics produced by the solid-state synthesis technique indicate that these materials could substitute the single crystals in construction of solid-state lasers. These studies indicate also that the rare earth doped transparent ceramics could extend considerably the variety and performances (new active systems, wavelength ranges or emission schemes) of these lasers.
1145. Quantum confinement model for phototransport processes in nanocrystalline porous silicon
Authors:
Ciurea, ML; Stavarache, I; Iancu, V
Published: 2007, 2006 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, +, DOI:
The paper presents a quantum confinement model which describes the phototransport processes in nanocrystalline porous silicon. The model supposes that the nanocrystallites surface/interface acts as the walls of an infinite rectangular quantum well, introducing discrete confinement energy levels. This model is proved able to also describe the photoluminescence and the temperature dependence of the dark current in the same samples. Its results are in agreement with the Microstructure investigations.
1146. Interfacial titanium oxide between hydroxyapatite and TiAlFe substrate
Authors:
Nelea, V; Morosanu, C; Bercu, M; Mihailescu, IN
Published: DEC 2007, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 18, 2354, DOI: 10.1007/s10856-007-3135-1
The interface between nano-crystalline hydroxyapatite (HA) thin films and a titanium alloy (Ti5Al2.5Fe) has been studied by means of Fourier transform infrared spectrophotometry and X-ray diffraction at grazing incidence. The HA thin films were deposited by radio-frequency magnetron sputtering in low pressure dry argon on substrates kept at low temperature or heated at 550 degrees C. The effect of film treatment by sputtering and annealing in humid air, as a simple, effective way of restoring the crystallinity and stoichiometry of the HA bulk, was studied in correlation with the development of a titanium oxide layer at the film-substrate interface. An interfacial TiO2 film grew at the interface during annealing in moist air, while a TiO2 layer diffused into the HA films when directly sputtered at 550 degrees C. The formation of an interfacial titanium oxide layer was inhibited by the insertion of a crystalline TiN buffer interlayer between the substrate and the HA film. Separately, the mechanical characteristics of the different HA films were monitored by nanoindentation to find out how they had been affected.
1147. The influences of the packing ligand on spin state and magnetic interactions in new oxalates with 3d-transition metals
Authors:
Filoti, G; Bartolome, J; Kuncser, V; Mindru, I; Patron, L
Published: MAR 2007, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 310, 1454, DOI: 10.1016/j.jmmm.2006.10.465
Two new hetero tri-nuclear oxalates (NH4)(8)[Fe2CO(C2O4)(8)]-6H(2)O and [Fe2Co(C2O4)(2)(OH)(4)]center dot 2H(2)O have been synthesized. The compound presented opposite behaviour in ac-susceptibility measurements, different frustration level and spin-orbit coupling in magnetization ones. The Mossbauer approach pointed to local interactions governed by metal-oxalate strongly coupled unit. The data were interpreted in terms of role of positive (NH4) or negative (OH) bridging ligands on general magnetic properties. (c) 2006 Published by Elsevier B.V.
1148. Development of space instabilities of defect distribution at high fluences in neutron irradiated YBa2CU3O7-delta ceramics
Authors:
Sandu, V; Popa, S; Sandu, E; Di Gioacchino, D; Tnipodi, P
Published: 2007, SIX INTERNATIONAL CONFERENCE OF THE BALKAN PHYSICAL UNION, 899, 647, DOI:
We investigated the behaviour of YBa(2)CU(3)o(7-delta) ceramics by multiharmonic ac-susceptibility. We have found an unexpected improvement of the intragranular response at the highest fluence 9.98 10(17) neutrons/cm(2). However, this fact is accompanied with a continuous suppression of the intergranular properties. We assume that this behavior is the result of the change of the nature of defect distribution at high fluence, when the uniform distribution of defects starts to develop space instabilities as a result of the subtle interplay of the in-cascade rate of interstitial loops production, cascade collapse of the vacancy loops, and the excess network bias.
1149. Electrical characteristics of nano-PbS/SiO2/Si heterostructures obtained by chemical bath method
Authors:
Goldenblum, A; Stancu, V; Buda, M; Iordache, G; Botila, T; Negrila, C
Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3802, DOI:
The PbS/SiO2/Si structures show a clockwise hysteresis of capacitance-voltage (C-V) characteristics. The loop width increases with temperature and sweep time. The conductance-voltage (G-V) characteristics also present a hysteresis effect with two bumps. Both characteristics show a strong shift with frequency. We show that these effects are determined by the positive mobile ions injected in the oxide region during the chemical bath deposition of PbS and by the high concentration Of Si/SiO2 interface states. The corresponding C-V and G-V characteristics are simulated and the main peculiarities of the experimental results are well reproduced by the modeled curves.
1150. Magnetic interactions in water based ferrofluids studied by Mossbauer spectroscopy
Authors:
Kuncser, V; Schinteie, G; Sahoo, B; Keune, W; Bica, D; Vekas, L; Filoti, G
Published: JAN 10 2007, JOURNAL OF PHYSICS-CONDENSED MATTER, 19, DOI: 10.1088/0953-8984/19/1/016205
Various samples of ferrofluids consisting of colloidal suspensions of surfacted cobalt ferrite or magnetite nanoparticles in water were studied by x-ray diffraction and temperature dependent Mossbauer spectroscopy. Information about the particle mean size, the size dispersion and the effective magnetic anisotropy energy was obtained for each sample. The results are consistent with the formation of a magnetic dead layer at the particle surface, whose thickness depends on the surfactant - ferrite combination. The magnetic relaxation processes are faster in the colloidal suspensions of magnetite particles as compared with the suspensions of cobalt ferrite particles. The type of the surfactant also influences the magnetic relaxation behaviour, and hence the macroscopic properties of the ferrofluid at ambient temperature.
1151. Nonadiabatic transport in a quantum dot turnstile
Authors:
Moldoveanu, V; Gudmundsson, V; Manolescu, A
Published: OCT 2007, PHYSICAL REVIEW B, 76, DOI: 10.1103/PhysRevB.76.165308
We present a theoretical study of the electronic transport through a many-level quantum dot driven by time-dependent signals applied at the contacts to the leads. If the barriers oscillate out of phase, the system operates like a turnstile pump under a finite constant bias, as observed in the experiments of Kouwenhoven [Phys. Rev. Lett. 67, 1626 (1991)]. The time-dependent currents and their averages over successive pumping periods are computed from the Keldysh formalism for tight-binding models. The calculation considers a sudden application of the pumping potentials at t=0, which leads to transient features of the time-dependent and averaged currents during the first pumping cycles which turn out to be important in the high-frequency regime. We show that in the transient regime, the efficiency of the system as a pump is rather poor because it mainly absorbs charge from both leads in order to fill the levels located below the bias window. Under a finite bias and a low-frequency pumping signal, the charge transferred across the system depends on the number of levels located within the bias window. The internal charge dynamics and the role of energy sidebands are investigated. The so-called satellite peaks of the averaged current are also observed in the transient regime.
1152. Synthesis of Bi(Pb)-2223 from two different precursors with the same stoichiometry
Authors:
Mihalache, V; Aldica, G; Badica, P
Published: JUN 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1771, DOI:
Samples of (Bi,Pb)(2)Sr2Ca2Cu3O10 (Bi(Pb)-2223) phase have been fabricated from two different oxide precursors with the same stoichiometry, synthesized by solid state reaction in the air at 815 degrees C for 20 h. The first precursor was prepared by mixing Bi2O3, PbO, SrCO3, CaCO3 and CuO powders, while the second one through mixing Bi2O3 and PbO with Sr2Ca2Cu3Ox produced from SrCO3, CaCO3 and CuO powders. Pellets from the two precursors were prepared in the same conditions; heat treatment time was varied and intermediate grindings were applied. Although the maximum attained Bi(Pb)2223 phase amount was about 50% and above 90% in the samples from the two precursors, respectively, the samples from the first precursor have generally shown better superconducting properties such as the critical temperature from resistivity measurements and intragrain critical current J(cg) from magnetic susceptibility measurements. For our particular case the influence of the final heat treatment is relatively low and at the same time the precursor plays a major role in controlling growth processes and final superconducting properties. Lower room-temperature Seebeck coefficient of the thermoelectric power for the samples fabricated from the first precursor suggests that one mechanism through which this control is realized might be the modification of the oxygenation level in the samples produced from different precursors. It was also found that for the samples prepared from the two precursors, intermediate grinding after 110h or more of heat treatment enhances density, almost does not influence J(cg) (or slightly improves it), decreases T-c, and does not influence significantly the amount of Bi(Pb)-2223 phase.
1153. Electrical conduction in initial field assisted sintering stages
Authors:
Aldica, G; Khodash, V; Badica, P; Groza, JR
Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3870, DOI:
Field Activated Sintering Techniques (FAST) are increasingly used to consolidate metal and ceramic powders. They combine application of a pulsed electrical current with external pressure to activate the densification process. The nature of electrical field/current interaction with powder systems is not clear yet. In this regard, in-situ transport measurements and microstructural analyses were carried out during pulsed current application in the FAST processing of Ni powders. Our experimental results were compared with existing electrical conduction theories and observed effects were relatively well explained qualitatively within these theories. Under electrical field it was confirmed that no voltage-current phase-shift occurs at elevated operating interfacial temperatures. For the field situation a higher applied pressure is decreasing the contact instability among particles contacts and of the sintering onset temperature. Microstructural investigations of the FAST-sintered samples indicate rather distribution of the higher density regions and a considerable increase of neck formation above 340 degrees C.
1154. T-c behaviour of 2212 and 2223 phases in (Bi,Pb)Sr(Ca2-xYx)CuO/2223
Authors:
Mihalache, V; Aldica, G
Published: APR 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 922, DOI:
The critical temperature, T-c, for (Bi,Pb)Sr(Ca2-x, Y-x)CuO/2223, with x between 0 and 0.45, polycrystalline samples have been investigated. T-c of (Bi,Pb)(2)Sr2Ca2-xYxCu3O10+delta phase, 2223, found in samples with x < 0.05, decreases whereas Tc of (Bi,Pb)(2)Sr2Ca1-xYxCu2O8+delta phase, 2212, found in samples with x > 0.05, displays a parabolic dependence with the increase of Y content. The change of T-c for 2223 originates mainly from the increase of x. The variation of both x and oxygen content, delta, influences the T-c of 2212. The doping state of 2212 and 2223 in Y substituted samples suggests that, generally, in the samples consisting of both superconducting phases, 2212 is in over-doped state whereas 2223 is in under-doped state. The last affirmation suggests that 2212 could bring a significant contribution in the transport parameters of (Bi,Pb)SrCaCuO/2223 samples.
1155. Mesoscopic Fano effect in an Aharonov-Bohm interferometer Coulomb-coupled to a nearby quantum dot
Authors:
Tolea, M; Moldoveanu, V; Tanatar, B
Published: 2007, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4, NO 2, 4, +, DOI: 10.1002/pssc.200673304
Motivated by the pionieering experiments of Buks et al. [Nature 391, 871 (1998)] we investigate the visibility of the Fano effect in a single-dot Aharonov-Bohm interferometer which is Coulomb-coupled to a nearby quantum dot. The latter acts as a 'Which Path Detector' and is coupled to two leads on which a finite bias is applied. Using the non-equilibrium Keldysh-Green function formalism we compute the currents through the detector and the interferometer. We take into account the first two contributions to the interaction self energy and emphasize the correction to the Landauer formula which appears beyond the single-particle approximation. Particular attention is given to the coherence properties of the interferometer in the presence of the electron-electron interaction between the embedded dot and the detector. We show that when the detector is subjected to a finite bias the amplitude of Aharonov-Bohm oscillations of the current through the interferometer decreases. The Fano line is in turn rather stable under interaction. Our results generalize an earlier work of Silva and Levit [Phys. Rev. B 63, 201309 (2001)] and complement the existing description of the controlled dephasing. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
1156. Structure of PZT thin films deposited on stainless steel and on platinum/silicon substrate
Authors:
Stancu, V; Sava, F; Lisca, M; Pintilie, L; Popescu, M
Published: SEP 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 2969, DOI:
Pb(Zr1-xTix)O-3 (PZT) thin films were prepared by sol-gel method on stainless steel (SS) and on platinum-coated silicon substrate (Pt/Si). The structure revealed by X-ray diffraction shows strong crystallographic orientation: (110) and (100), respectively. A small amount of pyrochlore phases (Pb-2(Zr,Ti)(2)O6-delta is formed in the films deposited on SS substrate. The crystallite size shows significant differences: d((00l))((SS)) = 27.1 nm, d((h00))((Pt)) = 88 nm. The tetragonal splitting is (Delta c/c)((SS)) = 3.55 % and (Delta c/c)((Pt)) = 3.32 %.
1157. Effects of porosity on ferroelectric properties of Pb(Zr0.2Ti0.8)O-3 flims
Authors:
Stancu, V; Lisca, M; Boerasu, I; Pintilie, L; Kosec, M
Published: JUN 4 2007, THIN SOLID FILMS, 515, 6561, DOI: 10.1016/j.tsf.2006.11.165
The sol-gel deposition method has been successfully applied to obtain Pb(Zr0.2Ti0.8)03 thin films on platinized silicon wafers. Addition of different amounts (7-15 wt.%) of organic macromolecular polyvinylpyrrolidone in the precursor solution prior to spin coating proves to be an excellent method for obtaining porous films. The crystal structure of as deposited films was analyzed by X-ray diffraction. The porous films show perovskite phase after annealing at 650 degrees C. The surface morphology has been studied by Atomic Force Microscopy and Scanning Electron Microscopy. The surface profile indicates a roughness of the film of 5 nm and no microcracks on the surface. The ferroelectric behavior was proved for each film, by hysteresis loops and by the "butterfly" shape of the capacitance-voltage characteristics. The remnant polarization and the coercive field decrease while the amount of added PVP increases. (C) 2006 Elsevier B.V. All rights reserved.
1158. TiO2-based nanopowders obtained from different Ti-alkoxides
Authors:
Crisan, M; Braileanu, A; Raileanu, M; Crisan, D; Teodorescu, VS; Birjega, R; Marinescu, VE; Madarasz, J; Pokol, G
Published: APR 2007, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 88, 176, DOI: 10.1007/s10973-006-8125-x
Pure TiO2 and S-doped TiO2 sol-gel nanopowders were prepared by controlled hydrolysis-condensation of titanium alkoxides. The influence of different Ti-alkoxides (tetraethyl-, tetraisopropyl- and tetrabutyl-orthotitanate) used in obtaining TiO2 porous materials in similar conditions (water/alkoxide ratio, solvent/alkoxide ratio, pH and temperature of reaction) has been investigated. The relationship between the synthesis conditions and the properties of titania nanosized powders, such as thermal stability, phase composition, crystallinity, morphology and size of particles, BET surface area and the influence of dopant was investigated. The nature of the alkyl group strongly influences the main characteristics of the obtained oxide powders, fact which is pointed out by thermal analysis, X-ray diffraction, TEM and BET surface area measurements.
1159. Tunneling magneto-resistance granular thin films deposited by thermo-ionic vacuum arc technique
Authors:
Mustata, I; Anghel, A; Lungu, CP; Pontilian, O; Kuncser, V; Schinteie, G
Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3820, DOI:
Co-MgO granular films presenting TMR effects were prepared by thermo-ionic vacuum arc method with the simultaneous ignition of plasma in Co and MgO vapors. Morphologic, structural and magnetic behaviors were analyzed in as prepared and annealed samples. The influence of the Co content on the magnetic properties of the prepared films was analyzed, in correlation with tunneling magneto-resistance effects. The tunneling magneto-resistance effect is maximal for certain Co content. This behavior was interpreted by the contrary effects of decreasing the average size of the magnetic grains, and hence the average inter-grains distance at higher Co relative content, and the enhanced magnetic disorder in very fine grains dispersed in the insulating matrix.
1160. Plasma-assisted catalysis total oxidation of trichloroethylene over gold nano-particles embedded in SBA-15 catalysts
Authors:
Magureanu, M; Mandache, NB; Hu, JC; Richards, R; Florea, M; Parvulescu, VI
Published: NOV 15 2007, , DOI: 10.1016/j.apcatb.2007.05.030
1161. Acylation of different amino derivatives with fatty acids on UL-MFI-type catalysts
Authors:
Musteata, M; Musteata, V; Dinu, A; Florea, M; Hoang, VT; Trong-On, D; Kaliaguine, S; Parvulescu, VI
Published: NOV 2007, , DOI: 10.1351/pac200779112059
1162. Optical studies of TiO2 films deposited on different substrates
Authors:
Cotirlan, C; Vasile, V; Ungureanu, F
Published: 2007, ROMOPTO 2006: EIGHTH CONFERENCE ON OPTICS, 6785, DOI: 10.1117/12.756805
Titanium dioxide thin films prepared by sol-gel method and deposited on p-Si (111), n-GaAs (100) and glass have been investigated by Raman spectrometry and photoluminescence analysis. The films were annealed in the temperature range (500-800)degrees C in air. Raman scattering studies reveal the presence of Raman active modes in the calcinated TiO2 films related to anatase phase of titania. The photo luminescence spectrum presents prominent red shifted peaks (e.g. at 400 nm for TiO2/glass), where the maximum is related to the presence in titania films of defect levels corresponding to oxygen vacancies.
1163. Metal-triflate ionic liquid systems immobilized onto mesoporous MS41 materials as new and efficient catalysts for N-acylation
Authors:
Coman, SM; Florea, M; Parvulescu, VI; David, V; Medvedovici, A; De Vos, D; Jacobs, PA; Poncelet, G; Grange, P
Published: JUL 25 2007, , DOI: 10.1016/j.jcat.2007.04.022
1164. Resistive sensor for water salinity
Authors:
Popescu, M; Lorinczi, A; Sava, F; Savu, V; Savastru, D
Published: DEC 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3956, DOI:
A simple electrical resistance sensor for monitoring of the coastal marine waters has been developed. The good sensitivity and reproducibility of the measurements make this sensor attractive for using in the research of the mixing of sweet (river) waters with the marine water, as well as the variation in the depth of the sea of the water salinity. Another advantage of the sensor is the possibility to monitor the water salinity by simply tracing the electrical resistance when the sensor is drawn at the surface or vertically in the sea and ocean waters.
1165. Ceria-based oxides as supports for LaCoO3 perovskite; catalysts for total oxidation of VOC
Authors:
Alifanti, M; Florea, M; Parvulescu, VI
Published: JAN 31 2007, , DOI: 10.1016/j.apcatb.2005.10.037
1166. Trapping phenomena in silicon-based nanocrystalline semiconductors
Authors:
Ciurea, ML; Iancu, V; Mitroi, MR
Published: OCT 2007, SOLID-STATE ELECTRONICS, 51, 1337, DOI: 10.1016/j.sse.2007.07.002
In this paper, the trapping phenomena in silicon-based nanocrystalline semiconductors are studied. We propose a general and complete model for optical charging spectroscopy measurements, which takes into account the trapping-detrapping-retrapping processes and all the types of discharge currents that can occur in a nanocrystalline system. The model was applied to the measurements performed on multi-quantum well structures, (nc-Si/CaF2)(50), as well as on nanocrystalline porous silicon. This way, the trap parameters that are not directly measurable were determined. (C) 2007 Elsevier Ltd. All rights reserved.
1167. Field-activated sintering of skutterudites
Authors:
Kodash, VY; Groza, JR; Aldica, G; Toprak, MS; Li, S; Mamoun, M
Published: SEP 2007, SCRIPTA MATERIALIA, 57, 511, DOI: 10.1016/j.scriptamat.2007.05.032
Skutterudite (Co0.92Ni0.08)(4) Sb11.88Te0.12 powder has been consolidated under an applied electrical field using a field-assisted sintering technique (FAST). The low FAST sintering temperature and relatively high heating rate considerably reduce grain growth during sintering. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
1168. Phototransport and photoluminescence in nanocrystalline porous silicon
Authors:
Iancu, V; Ciurea, ML; Stavarache, I; Teodorescu, VS
Published: AUG 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 2643, DOI:
The paper presents the phototransport and photoluminescence investigations on nanocrystalline porous silicon. Spectral dependence curves of the phototransport and photoluminescence were taken at room temperature. A typical phototransport curve presents several maxima and shoulders, while the photoluminescence curves present only one maximum. The temperature dependence of the phototransport was measured in the 85 - 250 K range for different wavelengths. All these curves present only one activation energy on the whole temperature interval. The experimental results are interpreted taking into account a quantum confinement model. Previous microstructure investigations proved that the studied nanocrystalline porous silicon is formed by a nanowire network. Then, the electron Hamiltonian can be split into the sum of a 1D longitudinal Bloch part and a 2D transversal part, the nanowire wall acting like a potential well. Thus, a number of discrete energy levels will appear into the band gap. Both phototransport and photoluminescence maxima are due to the transitions between these levels, corresponding to a mean nanowire diameter of 3.2 nm, in good agreement with the previous microstructure and electrical transport investigations. On the contrary, the temperature dependence of the phototransport is determined by the surface states located on the internal surface and/or the interface between nanocrystallites.
1169. Extrinsic tunneling magnetoresistance in thick films of CrO2-polystyrene composite
Authors:
Sandu, V; Aldica, G; Sandu, E
Published: JUL 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 2124, DOI:
Polystyrene-CrO2 composite films with extrinsic tunneling magnetoresistance have been obtained. The electric conduction is 2D Mott variable range hopping in the temperature range 77-300 K. The magnetoresistance is negative when the field is aligned parallel to the current (in-plane geometry) and is due to the spin dependent intergrain tunneling of the charge carriers. It reaches a value MR = -10.6 % at room temperature and a magnetic field of 1T. When the field is applied in-plane but perpendicular to the current the magnetoresistivity is positive and has the average value MR = 3.56 %.
1170. Transient regime in nonlinear transport through many-level quantum dots
Authors:
Moldoveanu, V; Gudmundsson, V; Manolescu, A
Published: AUG 2007, PHYSICAL REVIEW B, 76, DOI: 10.1103/PhysRevB.76.085330
We investigate nonstationary electronic transport in noninteracting nanostructures driven by a finite bias and time-dependent signals applied at their contacts to the leads. The systems are modeled by a tight-binding Hamiltonian, and the transient currents are computed from the nonequilibrium Green-Keldysh formalism. The numerical implementation is not restricted to weak coupling to the leads and does not imply the wideband limit assumption for the spectral width of the leads. As an application of the method we study in detail the transient behavior and the charge dynamics in single and double quantum dots connected to leads by a steplike potential, but the method allows as well consideration of nonperiodic potentials or short pulses. We show that when the higher-energy levels of the isolated system are located within the bias window of the leads, the transient current approaches the steady state in a nonoscillatory smooth fashion. At moderate coupling to the leads and fixed bias the transient acquires a steplike structure, the length of the steps increasing with system size. The number of levels inside a finite bias window can be tuned by a constant gate potential. We find also that the transient behavior depends on the specific way of coupling the leads to the mesoscopic system.
1171. Pure and doped lanthanum manganites obtained by combustion method
Authors:
Berger, D; Matei, C; Papa, F; Macovei, D; Fruth, V; Deloume, JP
Published: 2007, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 27, 4398, DOI: 10.1016/j.jeurceramsoc.2007.02.164
Pure and strontium-doped lanthanum manganite nanopowders were obtained by solution combustion method using metal nitrates as oxidants and different organic compounds as fuel (alpha-alanine, glycine, urea and semioxamazide). Different molar ratios, fuel/oxidant, were chosen to study the effect of the fuel content on the phase formation and powder properties. The complex precursors isolated before ignition of the system, were characterized by FT-IR spectroscopy and thermal analysis. After ignition, the as-synthesized powders were calcined at different temperatures for obtaining single phases. Lanthanum manganite powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), specific surface area and magnetic measurements. (c) 2007 Elsevier Ltd. All rights reserved.
1172. Time-resolved luminescence spectroscopy of Eu2+ in BaFCl : Eu2+ X-ray storage phosphor
Authors:
Secu, M; Secu, CE; Vasile, V; Predoi, D; Gazdaru, DM
Published: JUN 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1802, DOI:
Photoluminescence (PL) spectra recorded at room temperature (RT) in polycrystalline BaFCI:Eu2+ X-ray storage phosphor have shown the europium associated luminescences, a broad luminescence band at 385nm (3.22eV) with a 3.3 +/- 0.1 mu s PL lifetime accompanied by a luminescence line at about 368nm (3.37eV). The energy difference Delta EB-L =226cm(-1) between the two excited levels from which the europium associated band and line luminescences took place was computed. An additional broad luminescence band at about 425nm (2.92eV) with 0.7 +/- 0.1 mu s PL lifetime has been attributed to the europium luminescence perturbed by an impurity. Time resolved spectroscopy measurements have shown that no other impurity luminescences (like oxygen-vacancy centres) can be observed at RT except the europium associated ones.
1173. Thermal behaviour of CuS (covellite) obtained from copper-thiosulfate system
Authors:
Simonescu, CM; Teodorescu, VS; Carp, O; Patron, L; Capatina, C
Published: APR 2007, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 88, 76, DOI: 10.1007/s10973-006-8079-z
Thermal behaviour of CuS (covellite) obtained from the Cu(CH3COO)(2)center dot H2O and Na2S2O3 center dot 5H(2)O system, working at different molar ratio (1:6 and 1:4) in presence/absence of NH4VO3, was studied. It was established that the presence of vanadium in the system induces a densification of CuS nodules, but do not change the hexagonal CuS structure. It has an important influence in thermal behaviour of copper sulfide CuS obtained also. The morphological characteristics of CuS play an important role in the thermal stability and the stoichiometry of the thermal decompositions. Also, the possibility to obtain copper sulfides with greater cooper content was investigated.
1174. Investigations of NCPM second harmonic generation and self frequency doubling in Gd1-x-yRxNdyCa4O(BO3)(3) (R = Sc or Lu) crystals
Authors:
Gheorghe, L; Loiseau, P; Aka, G; Lupei, V
Published: SEP 2007, OPTICAL MATERIALS, 30, 46, DOI: 10.1016/j.optmat.2006.10.018
Pure and Nd3+ doped single crystals of Gd1-xRxCa4O(BO3)(3) (R3+ = Sc3+ or Lu3+) with large size and good quality have been grown by the Czochralski pulling technique. By changing the compositional parameter x of Gd1-xRxCa4O(BO3)(3) crystals, their optical birefringence can be controlled in order to achieve non-critical phase matching (NCPM) in the ranges of 790-824 nm along Y-axis and 920963 nm along Z-axis, during second harmonic generations. Nonlinear optical properties of these new biaxial borate crystals are reported. Preliminary investigations of self frequency doubling in NCPM condition in Gd1-x-yRxNdyCa4O(BO3)(3) crystals have been carried out. (c) 2006 Elsevier B.V. All rights reserved.
1175. Composition dependence of Pr3+ spectral characteristics in strontium lanthanum aluminate crystals
Authors:
Lupei, V; Lupei, A; Gheorghe, C; Gheorghe, L; Aka, G; Vivien, D
Published: SEP 2007, OPTICAL MATERIALS, 30, 167, DOI: 10.1016/j.optmat.2006.11.018
An analysis of the high resolution spectra of the Pr3+ in strontium lanthanum aluminates, charge compensated with magnesium Sl(1-x)Pr(y)La(x-y)Mg(x)Al(12)-xO(19), (on a large composition range) is presented. The spectra are mainly dependent on the composition parameter x, and show more Pr3+ centers, two of them stable. Based on composition dependence and polarization data, structural models for the main two centers are proposed. (c) 2006 Elsevier B.V. All rights reserved.
1176. Localized energy levels generated in Magnetic Czochralski silicon by proton irradiation and their influence on the sign of space charge density
Authors:
Scaringella, M; Menichelli, D; Bruzzi, M; Macchiolo, A; Piemonte, C; Zorzi, N; Candelori, A; Eremin, V; Verbitskaya, E; Pintilie, I
Published: JAN 11 2007, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 570, 329, DOI: 10.1016/j.nima.2006.09.033
The microscopic damage produced in diodes made of n-type Magnetic Czochralski (MCz) silicon by 24 GeV and 26 MeV protons, up to the fluence of 1.3 x 10(15) cm(-2) 1 MeV equivalent neutrons, has been investigated and results are compared to the damage produced in devices made of standard Floating Zone (STFZ) silicon. It is found by means of Thermally Stimulated Currents (TSC) that the production of a radiation induced charged defect is enhanced in MCz, and might be in part responsible for the differences observed in the two materials at room temperature. The influence of defects on the sign of the space charge density has been studied by current transients at constant temperature i(T, t) and by Transient Current Technique (TCT). Type inversion is not revealed up to the highest investigated fluence. Full depletion voltage V-dep measurements versus fluence exhibits a minimum close to 2 x 10(14) cm(-2) 1 MeV equivalent neutrons; at the same fluence, V-dep measured as a function of annealing time changes its initial slope from positive to negative. It is shown by numerical simulations that these features can be accounted by the formation of a double junction, even in absence of type inversion. (c) 2006 Elsevier B.V. All rights reserved.
1177. Superconducting properties of iodine-intercalated Bi2Sr2Ca2Cu3O10+x
Authors:
Mihalache, V; Aldica, G; Miu, D
Published: APR 2007, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 20, 272, DOI: 10.1007/s10948-006-0199-y
The superconducting properties of iodine-intercalated high-temperature superconducting Bi2Sr2Ca2Cu3O10+x phase (Bi-2223) were systematically studied. It was found that for samples containing a significant amount of Bi2Sr2CaCu2O8+x , iodine intercalation results in the dramatic decrease of the inter-granular critical current density, as well as a significant decrease of the critical temperature (T-c), the critical current density in the grains (J(cg)), and of the amount of Bi-2223. For samples with a large amount of Bi-2223, T-c changes insignificantly, whereas J(cg) can even increase. We argue that the different behavior of the superconducting parameters is the result of various oxygen concentrations, and we explain the effect of iodine intercalation based on the parabolic dependence between T-c and the number of holes per CuO2 layer. The H(T) curves (determined from the peak position in the loss signal of ac susceptibility) for intercalated samples deviate significantly from the quasi 2D-like behavior, pointing toward an enhancement of the 3D fluctuations of vortices. For the change in the values and dimensionality of the flux pinning in the process of the intercalation, we attempted a qualitative explanation based on the models proposed in literature.
1178. Organic thin film transistors with HfO2 high-k gate dielectric grown by anodic oxidation or deposited by sol-gel
Authors:
Tardy, J; Erouej, M; Deman, AL; Gagnalre, A; Teodorescu, V; Blanchin, MG; Canut, B; Barau, A; Zaharescu, M
Published: FEB-MAR 2007, MICROELECTRONICS RELIABILITY, 47, 377, DOI: 10.1016/j.microrel.2006.01.012
We report here on pentacene based organic field effect transistors (OFETs) with a high-k HfO2 gate oxide. HfO2 layers were prepared by two different methods: anodic oxidation and sol-gel. A comparison of the two processes on the electrical properties of OFETs is given. Ultra thin nanoporous (20 nm) sol-gel deposited oxide films were obtained following an annealing at 450 degrees C. They lead to high mobility and stable devices (mu = 0.12 cm(2)/V S). On the other hand, devices with anodic HfO2 revealed a little bit more leaky and show some hysteresis. Anodization, however, presents the advantage of being a fully room temperature process, compatible with plastic substrates. Stability and response to a bias stress are also reported. (c) 2006 Elsevier Ltd. All rights reserved.
1179. Fe-doped TiO2 thin films
Authors:
Mardare, D; Nica, V; Teodorescu, CM; Macovei, D
Published: SEP 15 2007, SURFACE SCIENCE, 601, 4483, DOI: 10.1016/j.susc.2007.04.139
The reactive sputtering technique was used to obtain undoped and Fe-doped TiO2 thin films deposited on glass substrates. At 250 degrees C substrate temperature, undoped TiO2 films crystallize in a mixed rutile/anatase phase, while Fe-doped films exhibit the rutile phase only. Presence of Fe3+ ions into the TiO2 lattice is suggested by the intensity variation of forbidden 1s -> 3d transitions between the Ti and Fe K-edges. Ti K-edge EXAFS data are assessed to a mixture of the two kinds of surroundings, a rutile-like crystalline phase, identified also by X-ray diffraction, and a nanosized or amorphous anatase-like surrounding. The local atomic order about Fe atoms is quite different and could be related also to an amorphous phase. The Swanepoel method is used to obtain the dispersion of the refractive index below the interband absorption edge. The dispersion energy, the single-oscillator energy and the coordination number of the Ti atoms are evaluated using the single-oscillator model (Wemple-DiDomenico). (C) 2007 Elsevier B.V. All rights reserved.
1180. Rotational fluctuations of water confined to layered oxide materials: Nonmonotonous temperature dependence of relaxation times
Authors:
Frunza, L; Schonhals, A; Frunza, S; Parvulescu, VI; Cojocaru, B; Carriazo, D; Martin, C; Rives, V
Published: JUN 21 2007, JOURNAL OF PHYSICAL CHEMISTRY A, 111, 5175, DOI: 10.1021/jp0717140
The rotational molecular dynamics of water confined to layered oxide materials with brucite structure was studied by dielectric spectroscopy in the frequency range from 10(-2) to 10(7) Hz and in a broad temperature interval. The layered double hydroxide samples show one relaxation process, which was assigned to fluctuations of water molecules forming a layer, strongly adsorbed to the oxide surface. The temperature dependence of the relaxation rates has an unusual saddlelike shape characterized by a maximum. The model of Ryabov et al. (J. Phys. Chem. B 2001, 105, 1845) recently applied to describe the dynamics of water molecules in porous glasses is employed also for the layered materials. This model assumes two competing effects: rotational fluctuations of water molecules that take place simultaneously with defect formation, allowing the creation of free volume necessary for reorientation. The activation energy of rotational fluctuations, the energy of defect formation, a pre-exponential factor, and the defect concentration are obtained as main parameters from a fit of this model to the data. The values of these parameters were compared with those found for water confined to nanoporous molecular sieves, porous glasses, or bulk ice. Several correlations were discussed in detail, such as the lower the value of the energy of defect formation, the higher the number of defects. The pre-exponential factor increases with increasing activation energy, as an expression of the compensation law, and indicates the cooperative nature of the motional process. The involvement of the surface OH groups and of the oxygen atoms of the interlayer anions in the formation of hydrogen bonds was further discussed. For the birnessite sample, the relaxation processes are probably overlaid by a dominating conductivity contribution, which is analyzed in its frequency and temperature dependence. It is found that the conductivity of birnessite obeys the characteristics of semiconducting disordered materials. Especially the Barton/Nakajima/Namikawa relationship is fulfilled. Analyzing the temperature dependence of the direct current (dc) conductivity sigma(0) in detail gives some hint that sigma(0)(T) has also an unusual saddlelike form.
1181. Primary defects in silicon: existence, characteristics, and their role after high fluence irradiation
Authors:
Lazanu, S; Lazanu, I; Ciupina, V; Prodan, G
Published: APR 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 817, DOI:
In this contribution, an extensive analysis of the primary defects in silicon: vacancy, interstitial and Si-FFCD is performed. Irradiation studies are a useful tool to study production, characteristics and annealing of defects. The experimental results obtained after high proton fluence irradiation of silicon detectors are used in this paper to understand aspects related to the existence and proprieties of primary defects. Investigations on possible differences induced by irradiation in the lattice of silicon, using transmission electron microscopy analysis, have been started and some first preliminary results are presented.
1182. First measurement of the nonlinear coefficient for Gd1-xLuxCa4O(BO3)(3) and Gd1-xScxCa4O(BO3)(3) crystals
Authors:
Andersen, MT; Mortensen, JL; Germershausen, S; Tidemand-Lichtenberg, P; Buchhave, P; Gheorghe, L; Lupei, V; Loiseau, P; Aka, G
Published: APR 16 2007, OPTICS EXPRESS, 15, 4901, DOI: 10.1364/OE.15.004893
The effective nonlinear coefficient and temperature acceptance bandwidth of three Lu and Sc co-doped GdCa4O(BO3) 3 type nonlinear crystals were measured. NCPM for SHG in to the blue-UV spectral region can be obtained by controlling the co-dopant concentration. Measurements were based on intra-cavity SHG of a CW Ti: Sapphire laser, and the effective nonlinear coefficients were found to be in the range of 0.5 to 0.6 pm/V for the three crystals used. The FWHM temperature acceptance bandwidth was measured to be more than 35 degrees C using a 6 mm long Gd0.871Lu0.129Ca4O(BO3)(3) crystal. A maximum of 115 mW at 407.3 nm in a single direction was measured using a 6.5 mm long Gd0.96Sc0.04Ca4O(BO3)(3) crystal. (c) 2007 Optical Society of America.
1183. Structural and optical characterization of undoped, doped, and clustered ZnO thin films obtained by PLD for gas sensing applications
Authors:
Ristoscu, C; Caiteanu, D; Prodan, G; Socol, G; Grigorescu, S; Axente, E; Stefan, N; Ciupina, V; Aldica, G; Mihailescu, IN
Published: MAY 30 2007, APPLIED SURFACE SCIENCE, 253, 6503, DOI: 10.1016/j.apsusc.2007.01.051
The synthesis by pulsed laser deposition technique of zinc oxide thin films suitable for gas sensing applications is herein reported. The ZnO targets were irradiated by an UV KrF* (lambda = 248 nm, tau(FWHM) similar to 7 ns) excimer laser source, operated at 2.8 J/cm(2) incident fluence value, whilst the substrates consisted of SiO2(001) wafers heated at 150 degrees C during the thin films growth process. The experiments were performed in an oxygen dynamic pressure of 10 Pa. Structural and optical properties of the thin films were investigated. The obtained results have demonstrated that the films are c-axis oriented. Their average transmission in the visible-infrared spectral region was found to be about 85%. The equivalent refractive indexes and extinction coefficients were very close to those of the tabulated reference values. Doping with 0.5% An and coating with 100 pulses of Au clusters caused but a very slight decrease (with a few percent) of both transmission and refractive index values. The coatings with the most appropriate optical properties as waveguides have been selected and their behavior was tested for butane sensing. (C) 2007 Elsevier B.V. All rights reserved.
1184. The ferroectric-electric characterization of PZT-PbS composites
Authors:
Stancu, V; Buda, M; Pintilie, L; Popescu, M; Sava, F
Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1520, DOI:
A new method for the preparation of PbS/PZT composite materials is proposed. The PZT matrix has been obtained using the sol-gel method on Pt-coated Si substrates. The PbS (nano) crystals were subsequently obtained by dipping the porous PZT matrix in Pb(NO3)(2) and Na2S solutions at room temperature. The XRD spectra show the presence of the tetragonal phase of PZT. The microstructure of the film was analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The size of the PbS (nano)-particles at the sample's surface is about 25 nm, estimated from the AFM analysis. The roughness of the sample's surface is about 5 nm. The porosity of the composite, estimated from the SEM analysis in cross-section is smaller than for the reference PZT porous matrix. The equivalent dielectric constant of the composite increases by a factor of 4-5 in comparison with the porous PZT reference and does not depend on the thickness of the surface PbS (nano)-crystalline layer. The saturated polarization (Ps) value for the PZT-PbS composite is smaller than that corresponding to the bulk PZT but higher than for the reference porous PZT. We attribute these effects to the partial filling of the pores in the PZT matrix with PbS.
1185. Tin nanoclusters obtained in potassium chloride by thermal annealing
Authors:
Apostol, E; Enculescu, M; Polosan, S; Vasile, E; Topa, V
Published: 2007, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4, NO 3, 4, +, DOI: 10.1002/pssc.200673734
Tin nanoclusters were obtained in potassium chloride crystals following the electrolytic coloration of KCl:Sn2+ and KCl:Sn2++Ca2+ crystals and thermal annealing at various temperatures and times. Electrolytic coloration of KCl:Sn2+ crystals produces electronic centers inside of samples, presumably negative metal ions of tin. Optical absorption measurements were performed on as grown sample, colored and thermal annealed samples. The behavior of the samples with Sn colloids was compared with theoretical predictions according to Mie's theory. Tin nanoclusters in KCl exhibit an absorption band with a peak at 215 nm. The structure of the nanoclusters was studied by optical absorption and transmission electron microscopy means. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
1186. Comparative characterization of PbS macro- and nano-crystalline photoresistive detectors
Authors:
Iordache, G; Buda, M; Stancu, V; Botila, T
Published: 2007, CAS 2007 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, 202, DOI: 10.1109/SMICND.2007.4519680
A comparative study of photodetector performance for nano- and micro-crystalline PbS thin layers is presented Both types of PbS films were obtained using the Chemical Bath Deposition method. To prepare nano-crystalline thin films we used a short reaction time with no doping Bi added At low levels of irradiance (0.1 mW/cm(2)) and room temperature (RT), the macro-crystalline PbS outperforms its nano-crystalline counterpart, by a factor of 6 for the value of Delta R/R-dark. However the nano-crystalline photodetectors show significantly lower optical quenching for large values of irradiance (approximate to 500 mW/cm(2)) at RT and better Delta R/R-dark performance at lower temperature, with an optimum temperature Of 150 K. The low frequency noise behavior is a superposition of 1/f flicker noise at low frequency and generation-recombination and thermal noise at higher frequency. The proportionaliiy factor between the 1/f noise and the DC dark current for the series resistor is 1.5 times larger for the nano-crystalline photodetector at room temperature.
1187. Glassiness and superconductivity in strongly Pr-doped YBa2Cu3O7-delta single crystals
Authors:
Sandu, V; Gyawali, P; Katuwal, T; Almasan, CC; Taylor, BJ; Maple, MB
Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1280, DOI:
We present magnetization data on superconducting strongly Pr-doped YBa2Cu3O7-6 showing the existence of irreversibility at temperatures much higher than superconducting critical temperature and Neel temperatures for both planar Cu and Pr systems. A model in terms of cluster glass is proposed.
1188. Stoichiometric arsenic sulphoselenides as testing probes for positron trapping in chalcogenide glasses
Authors:
Hyla, M; Filipecki, J; Shpryuk, O; Popescuc, M; Balitska, V
Published: OCT 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 3181, DOI:
Positron annihilation lifetime (PAL) measurements are performed for stoichiometric glassy arsenic sulphide g-AS(2)S(3) and selenide g-AS(2)Se(3) in order to probe the corresponding model of positron trapping. An ORTEC spectrometer with Na-22 source placed between two sandwiched glass samples was used in our experiments, the obtained spectra being treated with LT computer program. Two identical samples of g-A(2)S(3) and g-AS(2)Se(3) of about similar to 1.5 mm in thickness prepared from high-purity elemental constituents by conventional melt-quenching route and additionally annealed near glass transition to avoid the inner stressed regions were tested. It is shown that two-state positron trapping model is valid for both glasses, the process of positron trapping being saturated in extended free-volume defects like to atomic vacancies and their agglomerates. Despite difference in the character of nanovoid radius distribution estimated theoretically for g-AS(2)S(3) and g-AS(2)Se(3), they have very close average free volumes resulting in the observed similarity of PAL data. But, in contrast to g-AS(2)Se(3), which has at least three sets of nanovoids centered near similar to 1.5 angstrom, similar to 2.3 angstrom and similar to 2.9 angstrom, only two sets of nanovoids centered near similar to 1.3 angstrom and at similar to 2.8 angstrom are proper to g-AS(2)S(3) giving only one variant of fitting.
1189. Preparation of pure and doped MgB2 by the field-assisted sintering technique and superconducting properties
Authors:
Sandu, V; Aldica, G; Badica, P; Groza, JR; Nita, P
Published: AUG 2007, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 20, 842, DOI: 10.1088/0953-2048/20/8/020
High density (more than 90% of the theoretical density) bulk samples with relatively large size (2.0 cm in diameter) of MgB2, pristine and doped with 5 mol% SiC and B4C were obtained by the field-assisted sintering technique (FAST) from commercial MgB2 powder. The superconducting properties in the magnetic field of the doped samples show depressed upper critical field H-c2 and irreversibility field H-irr when compared with pristine MgB2. The reason for better H-c2 and H-irr in the undoped sample is not clear. Most probable is that this is due to the limited diffusion time which restricts the substitution of carbon for boron in this short-time processing method as well as due to the way grain boundaries are formed in the FAST process. However, all our samples have shown higher values of H-c2 and H-irr than the values reported previously for FAST-MgB2 samples. The data were further investigated through scaling analysis. Data suggest that both additions of SiC and B4C stabilize two well defined pinning regimes in FAST-processed MgB2. At low temperatures, the pinning occurs at the grain border whereas at high temperatures, T >= 24 K, there is mixed pinning (H <= 5 T).
1190. Synthesis, structure and properties of heterotrinuclear carboxylate complexes [Fe2M(Ca, Sr, Ba)O(CCl3COO)(6)(THF)n]
Authors:
Prodius, D; Turta, C; Mereacre, V; Shova, S; Gdaniec, M; Simonov, Y; Lipkowski, J; Kuncser, V; Filoti, G; Caneschi, A
Published: JUL 10 2006, POLYHEDRON, 25, 2182, DOI: 10.1016/j.poly.2006.01.019
Three novel mu(3)-oxo trinuclear carboxylates [Fe2CaO(CCl3COO),(THF)(4)] center dot THF (1), [Fe2SrO(CCl3COO)(6)(THF)(6)] center dot 0.5H(2)O center dot 0.5THF (2) and [Fe2BaO(CCl3COO)(6)(THF)(6)] center dot 0.5H(2)O center dot 0.5THF (3) have been synthesised and subsequently characterised by X-ray structure analysis, thermal gravimetry (TG), infra red (IR) spectroscopy and magnetic measurements. Compounds I and 3 are molecular complexes with s- and d-metals displayed in the apexes of isosceles triangles with a triply bridging oxygen atom at its centre. The Ca center dot center dot center dot Fe and Ba center dot center dot center dot Fe separations have the values 3.750(1) and 4.177(1) angstrom, respectively. In comparison with these. Fe center dot center dot center dot Fe separations, 3.229(2) angstrom in 1 and 3.201(1) angstrom in 3, appear much shorter. The molecular complexes obey C-2 symmetry with the twofold axis passing through s metal and mu(3)-oxo atom. The coordination numbers are 6, 7 and 9 for iron. calcium and barium correspondingly. Magnetic studies reveal the presence of an antiferromagnetic exchange in the isosceles triangular skeletons of the trinuclear species. Using the spin Hamiltonian H = -2J(12)[S1S2], the fitting parameters g(Fe) = 2.00. J(Fe-Fe) = -58.90 cm(-1) for 1 and -60.40 cm(-1) for 3; g(Fe) = 2.14, J(Fe-Fe) = -75.40 cm(-1) for 2 have been estimated. (c) 2006 Elsevier Ltd. All rights reserved.
1191. EPR and TEM characterization of electrolurninescent Alq(3)
Authors:
Grecu, MN; Ghica, C; Mirea, A; Grecu, VV; Schwoerer, M
Published: 2006, ADVANCED MATERIALS FORUM III, PTS 1 AND 2, 514-516, 137, DOI: 10.4028/www.scientific.net/MSF.514-516.133
EPR and TEM investigations on sublimated solid Alq(3), [tris(8-hydroxyquinoline)aluminum(Ill)] are reported. Different paramagnetic centers in microcrystalline Alq3 fractions as synthesized and annealed are observed. Their nature, thermal treatment dependence, as well as correlation with the crystal structure are analyzed. The existence of randomly oriented triplets and quartets in annealed Alq3 fractions is evidenced from the temperature dependence of X- and Q-band EPR spectra. The spin Hamiltonian parameters are given and proposals for the model structures are made.
1192. Modification of the sperconducting parameters of Bi-Sr-Ca-Cu-O by iodine intercalation
Authors:
Mihalache, V; Aldica, G; Miu, D
Published: JUN 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 1291, DOI:
We investigated the superconducting parameters of iodine-intercalated BiSrCaCuO high-temperature superconducting materials. While for samples containing a significant amount of Bi2Sr2CaCu2O8+x, (Bi-2212) iodine intercalation results in the dramatic decrease of the superconducting parameters, it was found that for samples with a nearly single Bi2Sr2Ca2Cu3O10-y (Bi-2223) phase these parameters can increase. We argue that this different behavior of the superconducting parameters is the result of a different doping regime, and can be explained based on the parabolic dependence between T, and the number of holes per CuO2 layer. Iodine intercalation appears to be an efficient way to bring the usually under-doped superconductor to its optimal T-c and flux pinning properties.
1193. FexOy-SiO2 nanocomposites studied by Mossbauer spectroscopy
Authors:
Predoi, D; Kuncser, V; Zaharescu, M; Jitianu, A; Crisan, M; Keune, W; Sahoo, B; Filoti, G; Raileanu, M
Published: APR 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 522, DOI:
FexOy-SiO2 nanocomposites were obtained via the sol-gel method, by using three different precursors for the silica matrix. The morphology and the iron phase composition is strongly influenced by the precursors. The presence of magnetically ordered goethite and fayalite is evidenced by low temperature Mossbauer spectroscopy. Subsequent annealing treatments performed on the initial samples have induced the formation of hematite nanoparticles in the silica matrix, mainly on the account of the goethite decomposition. The total amount and the size distribution of the hematite nanoparticles can be controlled via the initial precursors and the subsequent annealing conditions. The simultaneous analysis of the iron phase composition and of the local magnetic interactions in the analysed samples is performed.
1194. Electronic transport in Si-SiO2 nanocomposite films
Authors:
Ciurea, ML; Teodorescu, VS; Iancu, V; Balberg, I
Published: MAY 20 2006, CHEMICAL PHYSICS LETTERS, 423, 228, DOI: 10.1016/j.cplett.2006.03.070
We report experimental investigations and modeling of the electronic transport in Si-SiO2 nanocomposite films. The current-voltage characteristics measured at room temperature are interpreted as due to high field-assisted tunneling. The activation energies from the current-temperature curves,are given by the energy separations between quantum confinement electronic states, determined from a quantum well model. Consequently, the calculated mean diameter of a nanodot (5.2 nm) is in good agreement with the microstructure data (5 nm). Also, the potential barrier between nanocrystalline Si and amorphous SiO2, previously obtained for nanocrystalline oxidized porous Si (2.2 eV), is confirmed. (c) 2006 Elsevier B.V. All rights reserved.
1195. Core-shell effects in granular perovskite manganites
Authors:
Pana, O; Giurgiu, LM; Darabont, A; Iancu, V; Ciurea, M; Grecu, MN; Bot, A
Published: JAN-MAR 2006, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 67, 627, DOI: 10.1016/j.jpcs.2005.10.148
Unusual conductivity behavior, is observed in the semiconducting phase of granular manganites. It is characterized by, at a certain temperature, of a switching process between two activation energies. A core-shell model is developed to explain the presence of the conductivity of the two activation energies. The model suggests that inside the disordered thin outer layer the energy bands are split into isolated energy levels. Additional correlations between paramagnetic behavior and the existence of the two activation energies within the core-shell model are furnished by the ESR spectroscopic technique. (c) 2006 Published by Elsevier Ltd.
1196. Optical properties of low-dimensional PbI2 particles embedded in polyacrylamide matrix
Authors:
Preda, N; Mihut, L; Baltog, I; Velula, T; Teodorescu, V
Published: JUN 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 913, DOI:
Small particles of Pbl(2) embedded in transparent polymer matrix have been studied by Raman scattering, UV-VIS absorption spectroscopy, low temperature photoluminescence (PL) and Scanning Electron Microscopy (SEM). The Pbl(2) crystallites were prepared by two different methods: i) by cooling to the room temperature a boiling saturated aqueous Pbl(2) solution containing polyacrylamide and ii) by chemical reaction of Kl and Pb(NO3)(2) in aqueous polyacrylamide solution. In both cases, beside the hexagonal platelets of Pbl(2) Were identified rods whose luminescence and Raman signature is quite different than of Pbl(2) platelets. Regardless the rods nature, as distinct KPbl(3) particles or lead iodide low-dimensional particles embedded in the polymer matrix, their photoluminescence is featured by an intense green emission (550 nm) appearing at low temperature at excitation wavelengths less then 350 nm.
1198. Crystallite size effect in PbS thin films grown on glass substrates by chemical bath deposition
Authors:
Popa, A; Lisca, M; Stancu, V; Buda, M; Pentia, E; Botila, T
Published: FEB 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 45, DOI:
Nanocrystalline PbS thin films were grown on glass substrates using Chemical Bath Deposition (CBD) method. The presence of nanocrystals was revealed by optical absorption and photocurrent measurements. We have compared the absorption threshold between large size and nanocrystalline PbS. Our study was performed in order to demonstrate that the size of the PbS thin films crystallites affects the photoelectric properties of the material. Using the Scanning Electron Microscopy (SEM) we have determined that the grains inside large size PbS crystallites are 300 nm. From the optical absorption measurements we have determined that the size of PbS nanocrystals is between 5-50 nm. The photoconduction measurements show that large size PbS has a maximum in infrared situated at 2.4 mu m, and in PbS nanocrystalline thin film this maximum is shifted toward smaller wavelengths towards visible and near infrared.
1199. The SANS facility at the Pitesti 14MW TRIGA reactor
Authors:
Ionita, I; Grabcev, B; Todireanu, S; Constantin, F; Shvetsov, V; Anghel, E; Popescu, G; Mincu, M; Datcu, A
Published: 2006, CRYSTALLOGRAPHY REPORTS, 51, S31, DOI: 10.1134/S1063774506070066
The SANS facility existing at the Pitesti 14MW TRIGA reactor is presented. The main characteristics and the preliminary evaluation of the installation performances are given. A monochromatic neutron beam with 1.5 angstrom <= lambda <= 5 angstrom is produced by a mechanical velocity selector with helical slots. A fruitful partnership was established between INR Pitesti (Romania) and JINR Dubna (Russia). The first step in this cooperation consists in the manufacturing in Dubna of a battery of gas-filled positional detectors devoted to the SANS instrument.
1200. Unstressed carbon-metal films deposited by thermionic vacuum arc method
Authors:
Lungu, CP; Mustata, I; Musa, G; Lungu. AM; Brinza, O; Moldovan, C; Rotaru, C; Iosub, R; Sava, F; Popescu, M; Vladoiu, R; Ciupina, V; Prodan, G; Apetroaei, N
Published: FEB 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 77, DOI:
A novel method based on thermo-ionic vacuum arc plasma was developed to grow metal-carbon zero stress films for MEMS applications. The method chosen to prepare metal-carbon films uses an electron beam emitted by an externally heated cathode accelerated by a high anodic voltage. Applying a high voltage (1-6 kV) between cathode and anode bright plasma was ignited in carbon atoms. In order to minimize the internal stress and to get films with increased adherence, interlayer and graded interlayer with Fe, Cr, Al and Ni was deposited. The prepared films were characterized by XPS, XRD, AFM and ellipsometry.
1201. Mesoscopic Fano effect in Aharonov-Bohm rings with an embedded double dot
Authors:
Tanatar, B; Moldoveanu, V; Tolea, M; Aldea, A
Published: 2006, LOW TEMPERATURE PHYSICS, PTS A AND B, 850, +, DOI:
We investigate theoretically in a tight-binding model the transport properties of the Aharonov-Bohm interferometer (ABI) with one dot embedded in each of its arms. For weak interdot coupling the model Hamiltonian describes the system considered in the experiments of Holleitner et al. [Phys. Rev. Lett. 87, 256802 (2001)]. The electronic transmittance of the interferometer is computed within the Landauer-Buttiker formalism while the coexistence of resonant and coherent transport is explicitly emphasized by using the Feschbach formula. The latter produces effective Hamiltonians whose spectral properties describe the tunneling processes through each dot. We reproduce numerically the stability charging diagrams reported in the experiments of Holleitner et al. When the magnetic flux is fixed and one dot is set to resonance the interferometer transmittance shows Fano, lineshapes as a function of the gate voltage applied to the other dot. Our model includes the effect of the magnetic field on the dot levels and explains the change of the asymmetric tail as the magnetic flux is varied. The transmittance assigned to the Fano, dips located in the almost crossing point of the charging diagrams shows Aharonov-Bohm oscillations.
1202. XPS study of Ti/oxidized GaAs interface
Authors:
Grita, RV; Logofatu, C; Negrila, C; Manea, AS; Cernea, M; Ciupina, V; Lazarescu, MF
Published: FEB 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 36, DOI:
X-Ray Photoelectron Spectroscopy (XPS) analysis was performed on Ti/oxidized GaAs. This interface is prepared by chemical etching in a mixture of reagents, followed by a vacuum deposition of a nanometer Ti layer. The surface sensitivity of XPS (typically 40-100 angstrom), makes the technique ideal for the measurements of oxidation states and oxide layer thickness on III-V compounds. The study of Ti/oxidized GaAs put into evidence a lack of stoichiometry at the semiconductor surface due to the presence of a volatile element (As). At the interface Ti/Oxide/n-GaAs common oxides are present: Ga2O3, As2O3 and As2O5, together with titanium oxide. The XPS spectra recorded on the sample surface sputtered with 5 keV Ar+ ions (in two steps: t = 15 min, t = 45 min) were analyzed using SDP subroutines program facilities. The As signal at the interface after t = 15 min plasma etching is related to GaAs, As2O3 and over 40% from a GaAs oxidation complex or due to intermetallic oxide of Ti. After the last plasma etching at the surface of GaAs the stoichiometry was demonstrated: the signal of As and Ga arises commonly from GaAs. It was remarked a broader titanium line profile, which arises from titanium oxide and from different intermediate states at the interface.
1203. Newly developed Fe-Fe2O3/polyoxocarbosilane core-shell nanocomposite prepared by laser pyrolysis: Characterization and sensing properties
Authors:
Morjan, I; Pola, J; Alexandrescu, R; Dumitrache, F; Tomescu, A; Birjega, R; Gavrila-Florescu, L; Soare, I; Voicu, I; Galikova, A; Ciupina, V; Bastl, Z
Published: 2006, NANOSTRUCTURED MATERIALS AND HYBRID COMPOSITES FOR GAS SENSORS AND BIOMEDICAL APPLICATIONS, 915, +, DOI:
Nanocomposites of iron /iron oxide/polyoxocarbosilane were prepared by the IR co-pyrolysis of Fe(CO)(5) and HMDSO. Their morphologies, chemical content and thermal behavior were studied by different analytical techniques. For examining the sensing capabilities of the low-polymer content nanocomposite thick films, the variation of the electrical resistance to CO and CH4 gases was tested. A promising behavior as concerning the sensitivity and the selectivity was found.
1204. Fano interference in mesoscopic rings with quantum dots
Authors:
Moldoveanu, V; Aldea, A; Tolea, M
Published: 2006, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 3, NO 2, 3, +, DOI: 10.1002/pssc.200562736
We propose a general formalism for describing the coexistence of coherent and resonant transport in hybrid mesoscopic structures. The approach is based on Landauer- Buttiker formula for the electronic transmittance and on an old formula of Feshbach. The latter gives the complete Green function of coupled subsystems in terms of effective Green functions of the disconnected parts and provides informations about the individual contributions of each subsystem to transport. Motivated by the experiments of Kobayashi et al.(Phys. Rev. Lett. 88, 256806 (2002)) and Holleitner et al. (Phys. Rev. Lett. 87, 256802 (2001)) we apply the formalism to study transport in Aharonov-Bohm interferometers (ABI) containing one or two coupled two-dimensional quantum dots (QD). In the single dot case, we reproduce and explain the magnetic field control of the Fano interference and investigate the interaction effects in a self-consistent approach. In the double dot case, we obtain the charging diagrams and establish precise criteria for the observation of mesoscopic Fano effect and AB oscillations. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
1205. Mossbauer spectroscopical investigation of the exchange biased Fe/MnF2 interface
Authors:
Sahoo, B; Macedo, WAA; Keune, W; Kuncser, V; Eisenmenger, J; Nogues, J; Schuller, IK; Felner, I; Liu, K; Rohlsberger, R
Published: APR 2006, HYPERFINE INTERACTIONS, 169, 1377, DOI: 10.1007/s10751-006-9453-8
Two different Fe/MnF2 samples have been prepared by e-beam evaporation on MgO(001) substrates. The Fe layer in the samples includes a 10 angstrom thick Fe-57 probe layer either at the Fe/MnF2 interface (interface sample) or 35 angstrom away from the interface (center sample). The samples are characterized by X-ray diffraction, conversion electron Mossbauer spectroscopy (CEMS) and SQUID magnetometry. Fe-57 CEMS has been employed to study the depth dependent hyperfine interactions in Fe/MnF2 as a function of temperature between 18 K to 300 K. The hyperfine field B-hf has been obtained for the interfacial and off-interfacial Fe-57 layers. At the interface, besides B-hf of bcc-Fe, the presence of a component with a distribution P(B-hf ) is observed. The latter is assigned to interfacial Fe-57 atoms, indicating some (similar to 15%, equivalent to similar to 1 Fe atomic layer) intermixing at the Fe/MnF2 interface and a decrease of the average < B-hf > by 21%. The influence of the interface disappears as the Fe-57 probe layer is placed away from the interface. The temperature dependence of the average < B-hf > of the interface has been measured. The Fe spins, at remanence, are found to lie in the film plane.
1206. Second-harmonic generations of blue light in nonlinear optical crystals of Gd1-xLuxCa4O(BO3)(3) and Gd1-xScxCa4O(BO3)(3) through noncritical phase matching
Authors:
Gheorghe, L; Lupei, V; Loiseau, P; Aka, G; Taira, T
Published: AUG 2006, JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, 23, 1634, DOI: 10.1364/JOSAB.23.001630
Nonlinear optical borate crystals of Gd1-xScxCa4O(BO3)(3) and Gd1-xLuxCa4O(BO3)(3) have been grown and characterized. By changing the composition of these crystals, their optical birefringence can be controlled to obtain second-harmonic generations (SHG) in the ranges of 790-824 mn along the Y axis and 920-963 nm along the Z axis through noncritical phase matching (NUM). The refractive indices of grown crystals were measured with a minimum-deviation technique. The experimental results of NCPM conditions for SHG are in good agreement with the theoretical predictions. (c) 2006 Optical Society of America.
1207. Optical properties of ZnO nanocrystallites embedded in a gold-oxide matrix
Authors:
Goldenblum, A; Marian, AB; Teodorescu, V
Published: DEC 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 2132, DOI:
Thin films having ZnO nanocrystallites, with a minimum average size of 2.2 nm, embedded in an amorphous gold oxide matrix have been investigated. These structures do not present a blue-shift of the absorption spectra relative to those corresponding to large ZnO crystallites, a shift which would be expectable for this range of particle size. It was found that the hydrated gold oxide has a much narrower energy gap than ZnO and does not creates quantum wells in the ZnO crystallite region. The Raman spectra present only the confined vibration modes of ZnO. These peculiarities of the mixed system were analyzed by means of an adequate energy band diagram. A Raman resonant effect, determined by interface transitions, has also been detected.
1208. Mossbauer study of Mg-Ni(Fe) alloys processed as materials for solid state hydrogen storage
Authors:
Palade, P; Principi, G; Sartori, S; Maddalena, A; Lo Russo, S; Schinteie, G; Kuncser, V; Filoti, G
Published: FEB 2006, HYPERFINE INTERACTIONS, 168, 1035, DOI: 10.1007/s10751-006-9389-z
Mg-Ni-Fe magnesium-rich intermetallic compounds were prepared following two distinct routes. A Mg88Ni11Fe1 sample (A) was prepared by melt spinning Mg-Ni-Fe pellets and then by high-energy ball milling for 6 h the obtained ribbons. A (MgH2)(88)Ni11Fe1 sample (B) was obtained by high-energy ball milling for 20 h a mixture of Ni, Fe and MgH2 powders in the due proportions. A SPEX8000 shaker mill with a 10:1 ball to powder ratio was used for milling in argon atmosphere. The samples were submitted to repeated hydrogen absorption/desorption cycles in a Sievert type gas-solid reaction controller at temperatures in the range 520 divided by 590 K and a maximum pressure of 2.5 MPa during absorption. The samples were analysed before and after the hydrogen absorption/desorption cycles by X-ray diffraction and Mossbauer spectroscopy. The results concerning the hydrogen storage properties of the studied compounds are discussed in connection with the micro-structural characteristics found by means of the used analytical techniques. The improved kinetics of hydrogen desorption for sample A, in comparison to sample B, has been ascribed to the different behaviour of iron atoms in the two cases, as proved by Mossbauer spectroscopy. In fact, iron results homogeneously distributed in sample A, partly at the Mg2Ni grain boundaries, with catalytic effect on the gas-solid reaction; in sample B, instead, iron is dispersed inside the hydride powder as metallic iron or superparamagnetic iron.
1209. Neutron-irradiated superconducting YBa(2)Cu(3)(Li)(7-delta) with improved irreversibility
Irradiation of YBa(2)Cu(3)(Li)O(7-delta) ceramics with thermal and epithermal neutrons at fluences higher than 10(17) neutrons/cm(2) has led to a spectacular improvement of the intragranular properties. The critical current density has shown a monotonous dependence. The suppression of the critical temperature was below 2% but shows an increase at 9.8x10(17) neutrons/cm(2). This behaviour is consistent with the appearance of self-organized population of defects at high fluence. An analysis of the nature of the defect distribution, which is responsible for these effects, is provided.
1210. Effect of dopant on the physical properties of polymer films for microphotonics
Authors:
Obreja, P; Cristea, D; Budianu, E; Rebigan, R; Kuncser, V; Bulinski, M; Filoti, G
Published: 2006, PROGRESS IN SOLID STATE CHEMISTRY, 34, 109, DOI: 10.1016/j.progsolidstchem.2005.11.051
This paper presents experimental results concerning the influence of the additives on the physical properties of polymer films. Metal oxides/inorganic salts were used as additives in vinyl-polymers solutions. The physical properties of the metal doped polymer films can be significantly modified by the composition of the doping elements and the curing conditions of the polymer. Morphologic, electronic, magnetic and optic properties of the doped polymers were analysed by AFM. SEM. Mossbauer spectroscopy and optical measurements. The film composition and the deposition processes were optimized to allow a better control of the optical parameters (refractive index. transmission). to reduce the processing temperatures and to improve the chemical sensitivity of the films for sensor applications. These compounds can be easily spin coated onto a variety of directly patterned semiconductor substrates. (C) 2005 Elsevier Ltd. All rights reserved.
1211. Magnetic interactions in NdFeB bulk permanent magnets with additions
Authors:
Chiriac, H; Lupu, N; Chiriac, C; Valeanu, M; Kuncser, V
Published: OCT 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 1769, DOI:
NdFeB-based bulk nanocomposite permanent magnets (with Dy and Co partially substituting Nd and Fe, respectively) with additions of Early Transition Metals (ETM = Mo, Ti, Zr, Cu, Nb, V, W), in form of rods with diameters ranging from 0.5 to 0.8 mm, have been prepared by devitrification annealing of amorphous and partly-amorphous precursors produced by injection die casting. A fully amorphous structure was obtained for rods with the diameter as large as 0.6 mm. The as-cast rod samples are magnetically soft and the magnetic hardness develops as the samples are devitrified to the optimum nanostructure. The best-achieved hard magnetic properties have been obtained for the optimum devitrified (15 min at 630 degrees C) Nd(3)Dy(1)F(3)e(66)Co(10)B(20) samples of 0.6 mm in diameter: H-i(c) = 296 kA/m, mu M-0(r) = 0.86 T, Mr/M-max = 0.65 and (BH)(max), = 74 kJ/m. The Mossbauer spectra indicate the coexistence of 4 magnetic phases: 2:14:1, alpha-Fe, Fe3B and a short-range ordered intermetallic Fe-B-type phase.
1212. Model of the interband nonlinear absorption in amorphous chalcogenides: Quasi-linear analytical solutions
Authors:
Babin, V; Popescu, M; Ciobanu, M; Nicolae, ND; Talianu, C; Ciuciu, G
Published: APR 2006, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 17, 314, DOI: 10.1007/s10854-006-6949-6
It is proposed a quasi-linear algorithm for the solving the kinetic equations system, which describes the excitation and relaxation processes in the electronic and phononic subsystems of amorphous chalcogenides. The nonlinear interaction between an optical field and an amorphous chalcogenide medium is analyzed. The nonlinear interaction between an excitation incident optical field and the non-crystalline chalcogenide materials, evidences the specific nonlinear phenomena in amorphous semiconductors, which have no correspondent in the case of crystalline semiconductors. The model is limited to phenomena occurring in chalcogenide semiconductors, simultaneously with the optical field propagation, by neglecting the excitation phenomena.
1213. Neutron-irradiated superconducting YBa2Cu3(Li)(7-delta) with improved irreversibility
Authors:
Sandu, V; Popa, S; Sandu, E; Di Gioacchino, D; Tripodi, P
Published: FEB 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 395, DOI:
Irradiation of YBa2Cu3(Li)O7-delta ceramics with thermal and epithermal neutrons at fluences higher than 10(17) neutrons/cm(2) has led to a spectacular improvement of the intragranular properties. The critical current density has shown a monotonous dependence. The suppression of the critical temperature was below 2% but shows an increase at 9.8x10(17) neutrons/cm(2). This behaviour is consistent with the appearance of self-organized population of defects at high fluence. An analysis of the nature of the defect distribution, which is responsible for these effects, is provided.
1214. The 'in-plane' angular spin distribution in layered systems as obtained by Fe-57 Mossbauer spectroscopy (vol 196, pg 135, 2002)
Authors:
Kuncser, V; Keune, W; Vopsaroiu, M; Bissell, PR
Published: APR 2006, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 245, 542, DOI: 10.1016/j.nimb.2006.01.022
1215. Hydrogen storage in Mg-Ni-Fe compounds prepared by melt spinning and ball milling
Authors:
Palade, P; Sartori, S; Maddalena, A; Principi, G; Lo Russo, S; Lazarescu, M; Schinteie, G; Kuncser, V; Filoti, G
Published: MAY 18 2006, JOURNAL OF ALLOYS AND COMPOUNDS, 415, 176, DOI: 10.1016/j.jallcom.2005.08.017
Magnesium-rich Mg-Ni-Fe intermetallic compounds have been prepared by two different routes: (a) short time ball milling of ribbons obtained by melt spinning; (b) long time ball milling of a mixture of MgH2, Ni and Fe powders. The first type of samples displays an hydrogen desorption kinetics better than the second one. Pressure composition isotherm measurements exhibit for both type of samples two plateaux, the lower and wider corresponding to the MgH2 phase and the upper and shorter corresponding to the Mg2NiH4 phase. The presence of the two types of hydrides is confirmed by X-ray diffraction analysis. Mossbauer spectroscopy shows that in melt spun and subsequently milled samples iron is mainly in a disordered structure and segregates after hydrogenation, while in directly milled powders remains mainly unalloyed. After multiple hydrogen absorption/desorption cycles the main part of iron is in metallic state in samples of both types, those of first type preserving better hydrogen desorption kinetics. (c) 2005 Elsevier B.V. All rights reserved.
1216. High surface area Mo-V-Te-Nb-O catalysts: Preparation, characterization and catalytic behaviour in ammoxidation of propane
Authors:
Florea, M; Mamede, AS; Eloy, P; Parvulescu, VI; Gaigneaux, EM
Published: MAR 15 2006, , DOI: 10.1016/j.cattod.2005.11.080
1217. Effect of LaCoO3 perovskite deposition on ceria-based supports on total oxidation of VOC
Authors:
Alifanti, M; Florea, M; Cortes-Corberan, V; Endruschat, U; Delmon, B; Parvulescu, VI
Published: MAR 15 2006, , DOI: 10.1016/j.cattod.2005.11.017
1218. Spin configurations in exchange coupled magnetic phases studied by Mossbauer spectroscopy
Authors:
Kuncser, V; Keune, W; Stromberg, F; Schinteie, G; Filoti, G
Published: APR 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 517, DOI:
The ability of the Fe-57 Mossbauer technique to reveal the spin structures in exchange coupled magnetic phases containing iron is emphasized. Experimental results obtained on layered exchange-bias systems are presented. The influence of the ferromagnetic top layer on the out-of-plane spin component of the pinning antiferromagnetic-like layer, in both Fe/FeSn2 and Fe/Fe-Gd-B exchange bias systems, is discussed.
1219. Electrical properties of as-grown molecular beam epitaxy high-k gate dielectrics deposited on silicon
Authors:
Goldenblum, A; Pintilie, I; Buda, M; Popa, A; Lisca, M; Botila, T; Teodorescu, V; Dimoulas, A; Vellianitis, G
Published: MAR 15 2006, JOURNAL OF APPLIED PHYSICS, 99, DOI: 10.1063/1.2180428
The carrier transport mechanisms in as-grown LaAlO3 and La2Hf2O7 high-k insulator layers deposited on n- and p-Si were deduced from temperature dependent C-V and I-V characteristics correlated with photoelectric measurements. Large, parallel shifts in the high frequency C-V curves are explained by the presence of a large density of interface states and an approximate analytical formula relating the density of states to the C-V shift is deduced. The space charge limited current is explained by the existence of impurity channels situated energetically near the conduction or valence band of silicon.
1220. Preparation of Mo-V-Te-Nb mixed oxides using the template route
Authors:
Florea, M; Gaigneaux, EM; Parvulescu, VI
Published: 2006, , DOI: 10.1016/S0167-2991(06)80979-1
1221. Mossbauer spectral study of RFe11.3W0.7 compounds (R = Dy, Ho, Er, and Lu)
Authors:
Lazar, DP; Plugaru, N; Kuncser, V; Valeanu, M; Filoti, G; Bartolome, J; Rubin, J
Published: JUL 2006, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 302, 67, DOI: 10.1016/j.jmmm.2005.08.030
The series of compounds RFe11.3W0.7, where R = Dy, Ho, Er, and Lu, has been measured by Mossbauer spectroscopy between 15 and 295 K. A model which takes into account the Wigner-Seitz cell local environment of each iron site, the distribution of tungsten atoms on the 8i site, and the temperature-dependent magnetic structures of the compounds has been used to analyse the spectra. The assignment and the temperature dependencies of the hyperfine fields and the isomer shifts are in complete agreement with the Wigner-Seitz; cell analysis of the three iron sites in RFe11.3W0.7 compounds. The plausible orientations of the iron magnetic moments in the canted magnetic phase of ErFe11.3W0.7 compound have been established by a thorough Mossbauer spectral analysis. The Mossbauer spectra of DyFe11.3W0.7 clearly show the influence of the two spin re-orientations occurring in this compound and indicate the directions of the iron magnetic moments in both canted and planar magnetic arrangements. (c) 2005 Elsevier B.V. All rights reserved.
1222. Quantum confinement modeling of electrical and optical processes in nanocrystalline silicon
Authors:
Ciurea, ML; Iancu, V; Stavarache, I
Published: DEC 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 2160, DOI:
The paper presents a quantum confinement model for the electrical transport, the phototransport and the photoluminescence phenomena in nanocrystalline silicon. The infinite rectangular quantum well was proved to be the best choice for the investigated systems - nanocrystalline porous silicon and silicon nanodots embedded in an amorphous silicon dioxide matrix. Previous microstructure investigations have shown that the nanocrystalline porous silicon is formed by a nanowire network, so that the electron Hamiltonian is the sum of a one-dimensional Bloch-like Hamiltonian and a two-dimensional infinite rectangular quantum well. In the case of the silicon nanodots, the quantum well is three-dimensional. In both cases, the quantum well introduces quantum confinement levels in the band gap, the investigated phenomena being related with transitions between these levels.
1223. Giant magnetoresistive coatings using thermionic vacuum are technology
Authors:
Anghel, A; Luncu, CP; Mustata, I; Zaroschi, V; Lungu. AM; Barbu, I; Badulescu, M; Pompilian, O; Schinteie, G; Predoi, D; Kunkser, V; Filoti, G; Apetroaei, N
Published: 2006, CZECHOSLOVAK JOURNAL OF PHYSICS, 56, B23, DOI: 10.1007/s10582-006-0173-8
Giant magnetoresistive (GMR) coatings on silicon, glass and Kapton were prepared by simultaneous thermionic vacuum are (TVA) discharges in high vacuum conditions. The magnetic metal or alloy (Fe, Co, Ni, Permalloy) together with the noble non magnetic metal were deposited on substrates having different positions relative to the discharges. Local magnetic interactions and Fe-phase composition were obtained by Mossbauer spectroscopy whereas the magnetoresistance effects were measured by a dc method using a four-point configuration with perpendicular to plane magnetic fields up to 0.8 T. The surface morphology of the coatings was characterized by atomic force microscopy (AFM) in contact mode.
1224. In situ structural changes during toluene complete oxidation on supported EuCoO3 monitored with Eu-151 Mossbauer spectroscopy
Authors:
Alifanti, M; Florea, M; Filotti, G; Kuncser, V; Cortes-Corberan, V; Parvulescu, VI
Published: SEP 30 2006, CATALYSIS TODAY, 117, 336, DOI: 10.1016/j.cattod.2006.05.036
Ceria-zirconia supported (10 and 20 wt.% EuCoO3) versus bulk EuCoO3 perovskite were prepared via citrate decomposition at 700 degrees C and tested for toluene complete oxidation. S-BET, XRD, XPS, H-2-TPD and in situ Eu-151 Mossbauer investigations were performed. Electron delocalization processes around the Eu cations are induced by the reaction, as proved via the evolution of the Mossbauer parameters. All characterization data indicate the formation of a well-dispersed EuCoO3 at the surface of Ce0.9Zr0.1O2 for the 10 wt.% loading and larger crystallite formation for 20 wt.% loading. In terms of intrinsic activity for toluene combustion, supported catalysts were more active than bulk EuCoO3. All structural changes during operation time are reversible. (C) 2006 Elsevier B.V. All rights reserved.
1225. CW blue laser emission by second harmonic generation of 900nm oscillation of Nd-doped strontium and lanthanum aluminate (ASL)
Authors:
Varona, C; Loiseau, P; Aka, G; Ferrand, B; Lupen, V
Published: 2006, SOLID STATE LASERS AND AMPLIFIERS II, 6190, DOI: 10.1117/12.662742
Nd-doped strontium and lanthanum (ASL) crystals Sr1-xLax-yNdyMgxAl12-xO19 (0.05 <= x <= 0.5; y = 0.05) were grown by Czochralski pulling technique. Up to 1.67W of 900mn rR output laser power for an absorbed power of 2.53W was obtained under Ti:sapphire pumping at 792nm. Intracavity second harmonic generation experiments led to 320mW of blue laser power at 450mn with a 10mm-long BiB3O6 nonlinear crystal. Other nonlinear crystals were also evaluated such as LBO.
1226. Scaling of conductivity through the critical temperature in Y0.54Pr0.46Ba2Cu3O7
Authors:
Sandu, V; Katuwal, T; Taylor, BJ; Maple, MB; Almasan, CC
Published: 2006, LOW TEMPERATURE PHYSICS, PTS A AND B, 850, +, DOI:
In-plane conductivity sigma(ab) curves of Y0.54Pr0.46Ba2Cu3O7 single crystals, measured at constant temperature T in magnetic fields H tilted with an angle theta relative to the c-axis, were found to map onto a single curve in a sigma(ab) vs Hcos theta plot. This scaling occurs both below and above the critical temperature T-c, maintaining the same convexity, and is consistent with the dissipation caused by the motion of two-dimensional (2D) vortices. This indicates the presence of 2D vortices above T-c. A second scaling sigma(ab)(Hcos theta) takes place at higher T-c with an opposite convexity. This scaling is consistent with the dissipation of quasiparticies. There is a T range between these two regimes where no scaling is found. We attribute the absence of scaling in this intermediate regime to a 2D to 3D crossover in the vortex matter.
1227. Fractal structures of gold obtained by diffusion limited aggregation in alkali halide crystals
Authors:
Enculescu, M; Enculescu, I; Topa, V
Published: JUN 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 1233, DOI:
Nanostructures of gold embedded in potassium chloride matrices were obtained after the doped crystals growth, by electrolytical colouring, and by thermal treatment. When the TEM images of the nanostructures were analyzed using fractal geometry it means was proved that the self assembling of the metallic structures is governed by the diffusion limited aggregation (DLA) mechanism. The values of the fractal dimension, which were in all cases between 1.7 and 1.9, calculated using two methods, sandbox and box-counting, proved the DLA mechanism.
1228. Highly efficient, 0.84 slope efficiency, 901 nm, quasi-two-level laser emission of Nd in strontium lanthanum aluminate
Authors:
Lupei, V; Aka, G; Vivien, D
Published: APR 15 2006, OPTICS LETTERS, 31, 1066, DOI: 10.1364/OL.31.001064
The possibility of using direct pumping into the emitting level of the Nd3+ ion in magnesium-compensated strontium lanthanum. aluminate (Sr1-xLax-yNdyMgxAl12-xO19) to improve 900 nm F-4(3/2) -> I-4(9/2) laser emission is discussed. Selection of the composition parameters x and y for optimization of laser emission and reduction of heat generation is based on the spectroscopic and crystal growth characteristics. Pumping in the 865.5 nm absorption band I-4(9/2)(Z(1)) F-4(3/2)(R-1) transforms the laser process into a quasi-two-level scheme of very low (below 4%) quantum defects. A very high slope efficiency (over 84%) for 901 nm continuous-wave laser emission is demonstrated with Ti:sapphire laser pumping in this band for a crystal with x = 0.4 and y = 0.05. (c) 2006 Optical Society of America.
1229. Optical and electronic properties of (Fe+Sb): PVA for real time holography
Authors:
Kuncser, V; Bulinski, M; Krautwald, S; Franke, H; Wagner, FE; Cristea, D; Palade, P; Plapcianu, C; Filoti, G
Published: JUN 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 1229, DOI:
The electron transfer processes induced by the ultraviolet exposure of the Fe and Sb doped polyvinyl alcohol (PVA) thin films were studied in comparison with those appeared in the correspondent mono (Fe or Sb) doped ones. Samples with different thickness and subjected to different exposures were analysed by optical absorption as well as by Fe-57 and Sb-121 Mossbauer spectroscopy. The influence of each element from the pair on the electronic mechanism activated by the ultraviolet exposure was investigated. Accordingly, the (Fe+Sb) doped PVA presents improved electronic characteristics, in respect to the specific behaviour of single metal doped polymer recording media for real time holography.
1230. Nanostructured carbon growth by an expanding radiofrequency plasma jet
Authors:
Vizireanu, SI; Mitu, B; Birjega, R; Dinescu, G; Teodorescu, V
Published: 2006, CARBON NANOTUBES: FROM BASIC RESEARCH TO NANOTECHNOLOGY, 222, +, DOI:
Carbon deposition from acetylene injection into plasma jet onto sputtered nickel on silicon is investigated. The whole methodology, including the deposition of catalyst, its etching to islands followed by the carbon growth, is implemented in the same reactor. The investigation of structure and morphology shows the formation of nickel particles coated with graphitic layers.
1231. Manganese doped sol-gel materials with catalytic properties
Authors:
Crisan, M; Raileanu, M; Preda, S; Zaharescu, M; Valean, AM; Popovici, EJ; Teodorescu, VS; Matejec, V; Mrazek, J
Published: APR 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 819, DOI:
In the present study manganese doped alumina and silica gels and thin films deposited on different substrates (refractory metals, silicon wafers) were obtained by the alkoxide and aqueous routes of the sol-gel method. The characterization of the films was realized by X-ray diffraction (XRD), and spectroellipsometry (SE) methods. The un-supported gels (obtained by the gelation of the solutions used for the film deposition) were characterized by DTA/TG analysis, IR spectroscopy, transmission electron-microscopy and electron diffraction (TEM and SAED) and BET method (adsorption of krypton at temperature of liquid nitrogen) for surface area and pores volume determination. The sol-gel materials were tested as catalysts for the ozone decomposition.
1232. On the formation and crystal structure of the Pd6B phase
Authors:
Berger, TG; Leineweber, A; Mittemeijer, EJ; Sarbu, C; Duppel, V; Fischer, P
Published: 2006, ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 221, 463, DOI: 10.1524/zkri.2006.221.5-7.450
The crystal structure of the Pd6B phase has been elucidated employing selected-area electron diffraction and X-ray and neutron powder diffraction methods. It is based on a cubic close packed arrangement of Pd with B occupying 1/6 of the interstitial octahedral sites in an ordered way, such that a monoclinic (C2/c) superstructure results. The crystal structure contains isolated [BPd6] octahedral entities providing large distances between nearest neighbour boron atoms. Depending on the way of preparation, the same Pd6B phase can occur for the same composition in two different 'manifestations' having considerably different lattice parameters, which has a microstructural origin. Various phase equilibria between the ordered Pd6B phase and the disordered interstitial solid solution of boron in cubic close packed palladium have been investigated to clarify the corresponding regions in the phase diagram Pd-B.
1233. Highly efficient one-micron laser emission under 885 nm diode laser pumping in Nd : YAG crystals with an extended range of concentrations
Authors:
Lupei, V; Pavel, N
Published: 2006, SOLID STATE LASERS AND AMPLIFIERS II, 6190, DOI: 10.1117/12.662601
The proper selection of the parameters of the laser material parameters for efficient continuous-wave 1064 nm emission under direct diode laser pumping at 885 nm into the emitting level of Nd:YAG is discussed. High slope efficiency (0.8) in absorbed power for 1.1 and 2.5at.%Nd concentrations and the advantage of using concentrated Nd:YAG crystals for improving the absorption efficiency is demonstrated.
1234. High temperature mixed state c-axis dissipation in low carrier density Y0.54Pr0.46Ba2Cu3O7-delta
Authors:
Katuwal, T; Sandu, V; Almasan, CC; Taylor, BJ; Maple, MB
Published: APR 2006, PHYSICAL REVIEW B, 73, DOI: 10.1103/PhysRevB.73.144510
The nature of the out-of-plane dissipation was investigated in underdoped Y0.54Pr0.46Ba2Cu3O7-delta single crystals at temperatures close to the critical temperature. For this goal, temperature- and angle-dependent out-of-plane resistivity measurements were carried out both below and above the critical temperature. We found that the Ambegaokar-Halperin relationship [V. Ambegaokar and B. I. Halperin, Phys. Rev. Lett. 22, 1364 (1969)] depicts very well the angular magnetoresistivity in the investigated range of field and temperature. The main finding is that the in-plane phase fluctuations decouple the layers above the critical temperature and the charge transport is governed only by the quasiparticles. We also have calculated the interlayer Josephson critical current density, which was found to be much smaller than the one predicted by the theory of layered superconductors. This discrepancy could be a result of the d-wave symmetry of the order parameter and/or of the non-BCS temperature dependence of the c-axis penetration length.
1235. Signature of the magnetic transitions in Y0.2Pr0.8Ba2Cu3O7.delta in high field angular magnetoresistivity
Authors:
Sandu, V; Zhang, C; Almasan, CC; Taylor, BJ; Maple, MB
Published: 2006, YAMADA CONFERENCE LX ON RESEARCH IN HIGH MAGNETIC FIELDS, 51, +, DOI: 10.1088/1742-6596/51/1/052
In-plane (ab) and out-of-plane (c-axis) magnetoresistivity display different symmetry crossovers and/or transitions in 14 T magnetic field applied parallel to the CuO2 planes. The in-plane magnetoresistivity crosses over from four-fold symmetry below 6 K to two-fold symmetry at higher temperatures, which becomes dominant at temperatures higher than 40 K. The out-of-plane magnetoresistivity changes at 17 K from four fold symmetry to ordinary sin2 theta at higher temperatures. The behaviour of the c-axis magnetoresistivity can be ascribed to the antiferromagnetic ordering of the Pr spins whereas the symmetry change of the in-plane magnetoresistivity at 6 K might be attributed to commensurate to incommensurate crossovers of the spin subsystems. The antiferromagnetic order of the Cu(2) sublattice seems to have only a week effect on the magnetoresistivity.
1236. Experimental evidence for a dimensional crossover of the vortex ensemble in BSCCO (Bi1.8Pb0.4Sr1.8Ba0.2Ca2Cu3Ox) by multi-harmonic ac susceptibility measurements
Authors:
Mihalache, V; Popa, S; Di Gioacchino, D; Tripodi, P; Vinko, JD
Published: JAN 1 2006, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 433, 233, DOI: 10.1016/j.physc.2005.11.005
We have studied a portion of H-T phase diagram of the anisotropic Bi2223 bulk system using multi-harmonic ac susceptibility measurements (chi(n)). Based on the behavior of the third harmonic modulus,vertical bar chi(3)vertical bar, the irreversibility line (IL) was obtained from the onset of vertical bar chi(3)vertical bar, and an anomalous peak effect (PE) was observed. It has been shown that the anomalous peak is due to the crossover between a three-dimensional (3D) and a quasi-two dimensional (quasi-2D) peculiarity of vortex dynamics, the crossover magnetic field being H-CR approximate to 0.1T. The obtained portion of B-irr(T) is well described by the melting line of the flux lattice. The 3D flux fluctuation part (low field and high temperature) is described by the nearly parabolic temperature dependence B=B-o(Tc/T - 1)" with n = 1.58 (sample 1) and n = 1.48 (sample 2). The other region (high field and low temperature) is well described by the temperature dependence of the quasi-2D flux fluctuations, T-m(H) = T-m(2D)[1 + b/(In B/B-cr )(1/v)] corresponding to the weak interaction between pancake vortices from adjacent planes. The 2D limit temperature was determined as T-m(2D) = 36.7K (sample 1) and T-m(2D) = 27.3K (sample 2). (c) 2005 Elsevier B.V. All rights reserved.
1237. Structural and microstructural properties of porous PZT films
Authors:
Stancu, V; Boerasu, I; Lisca, M; Pintilie, L; Popescu, M; Sava, F
Published: AUG 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 1497, DOI:
PbZr1-XTiXO3 (PZT) film was prepared by addition of polymer polyvinylpirrolidone (PVP) in the PZT precursor and hydrolysis of the PZT precursor sol. Porous thin films were prepared by spin coating on Pt-coated Si substrate. The structure of the films was investigated by X-ray diffraction (XRD). (100)-oriented PZT 20180 film was obtained by hydrolysis of sol. PVP addition leads to the (110)-orientation of the film. The surface microstructure of the films was characterised with Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The surface profile indicates a films roughness of 5 nm. No micro-cracks were observed on film surface. The average remnant polarization and the coercive field were obtained from the hysteresis loop measurements. The ferroelectric behavior has been evidenced by the presence of the butterfly shape of the capacitance-voltage characteristics. Experimental results show that the dielectric constant of the PZT porous film is lower than that of the dense film.
1238. Optical photoinduced phenomena and holographic recording in amorphous As-Se thin films
Authors:
Iovu, MS; Ciorba, VG; Colomeico, EP; Iovu, MA; Nastase, AM; Prisacari, A; Popescu, M; Shpotyuk, OI
Published: OCT 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2339, DOI:
The effect of light-induced photodarkening in amorphous As100-xSex (x=40 divided by 98) thin films for different thickness and film composition was investigated. It was established a strong dependence of the red shift of the absorption edge and refractive index under light irradiation on the film composition and thermal treatment. It was established that the more sensitive films to photodarkening and holographic recording correspond to non-stoichiometric compositions of As55Se45 and As60Se40 glasses. The experimental results are interpreted in terms of structural optical polymerization process, which includes the transformation of As4Se4 and Se-2 structural units in homogenius AsSe3/2 network.
1239. Absorption and photoluminescence properties of Cds : Mn2+: Cu+ nanostructures
Authors:
Sima, M; Enculescu, I; Ghiordanescu, V; Mihut, L
Published: AUG 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 1955, DOI:
A layer of doped CdS nanocrystals was deposited on the surfaces of nanopores of polyethyleneterephtalate (PET) membranes. Optical absorption measurements were used to determine the bandgaps of the nanocrystals; CdS:Mn2+ and CdS:Mn2+:Cu+ show a blue and red shift, respectively, relative to the band gap of nanostructurated CdS. Photoluminescence spectra of the doped and undoped CdS samples exhibit wide bands covering the visible spectrum range.
1240. Mossbauer study of LaNiSn and NdNiSn compounds and their deuterides
Authors:
Palade, P; Principi, G; Spataru, T; Blaha, P; Schwarz, K; Kuncser, V; Lo Russo, S; Dal Toe, S; Yartys, VA
Published: NOV 2005, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY, 266, 556, DOI: 10.1007/s10967-005-0947-7
LaNiSn and NdNiSn compounds and their deuterides have been studied by variable temperature Sn-119 Mossbauer spectroscopy. The hyperfine parameters obtained experimentally are in good agreement with those derived from first principle calculations. The enlargement of quadrupole splitting observed for LaNiSn after deuteration confirms the lower symmetry of electron density around tin atoms indicated by the calculation of partial Sn-p density of states (DOS). Magnetic ordering is observed at low temperature in deuterided NdNiSn.
1241. X-ray diffraction and magnetic measurements of itinerant electron magnetism in the Y3Ni13-xCoxB2 system
Authors:
Plugaru, N; Rubin, J; Bartolome, J; Pop, V
Published: JAN 2005, PHYSICAL REVIEW B, 71, DOI: 10.1103/PhysRevB.71.024433
The crystallographic and magnetic properties of the Y3Ni13-xCoxB2 series of compounds, with the Nd3Ni13B2-type structure and xless than or equal to5, were investigated by powder x-ray diffraction and magnetic measurements. The susceptibility and magnetization data show that Y3Ni13B2 is a weak itinerant antiferromagnet with a Neel temperature T-N=68 K. A weak ferromagnetic component appears at T-N, suggesting uncompensated antiferromagnetic structure. The compounds with x=0.5 and 1, also order antiferromagnetically, with T-N=94 and 106 K, respectively. The intrinsic weak ferromagnetic component increases with the cobalt content and a field-induced transition, from the antiferromagnetic state to a ferromagnetic state, is observed at the critical transition fields 5.6 and 1.6 T, at 5 K for x=0.5 and 1, respectively. A heterogeneous ferromagnetic state and in-plane magnetic anisotropy are determined for the compounds in the 2less than or equal toxless than or equal to5 composition range. The Curie temperature and spontaneous magnetization increase linearly with the cobalt content. Based on the experimental data, the T-x phase diagram is constructed for xless than or equal to5. The effect of spin fluctuations is highlighted in the nickel-rich compounds in the 3:13:2 and related systems.
1242. Surface chemistry of plasma deposited ZrC hard coatings
Authors:
Balaceanu, M; Braic, M; Braic, V; Vladescu, A; Negrila, CC
Published: OCT 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2560, DOI:
X-ray Photoelectron Spectroscopy (XPS) was used to investigate the chemical state of ZrC coatings deposited by cathodic arc method. A chemistry model of the ZrC films has been proposed. It was pointed out that on the films surface a highly oxidized passive layer, containing also carbon and oxygen as contaminants, was formed. The film bulk was composed by a mixture of ZrC (the dominant phase), ZrO2 and free carbon.
1243. The dynamics of one-dimensional Bloch electrons in constant electric fields
Authors:
Bentosela, F; Duclos, P; Moldoveanu, V; Nenciu, G
Published: APR 2005, JOURNAL OF MATHEMATICAL PHYSICS, 46, DOI: 10.1063/1.1870732
We study the dynamics of a one-dimensional Bloch electron subjected to a constant electric field. The periodic potential is supposed to be less singular than the delta-like potential (Dirac comb). We give a rigorous proof of Ao's result that for a large class of initial conditions (high momentum regime) there is no localization in momentum space. The proof is based on the mathematical substantiation of the two simplifying assumptions made in physical literature: the transitions between far away bands can be neglected and the transitions at the quasicrossing can be described by Landau-Zener-type formulas. Using the connection between the above model and the driven quantum ring (DQR) shown by Avron and Nemirovski, our results imply the increase of energy for weakly singular such DQR and appropiate initial conditions. (C) 2005 American Institute of Physics.
1244. Micro-structure and magnetic properties of Fe-Cu nanocomposites for anisotropic permanent magnets
Authors:
Kuncser, V; Valeanu, M; Lifei, F; Predoi, D; Jianu, A; Kappel, W; Codescu, M; Patroi, E; Pasuk, I; Bulinski, M; Filoti, G
Published: MAY 31 2005, JOURNAL OF ALLOYS AND COMPOUNDS, 395, 6, DOI: 10.1016/j.jallcom.2004.11.059
Melt spun ribbons of FexCu100-x were obtained by different procedures, in order to maximize the dispersion of the Fe atoms in the Cu matrix. Subsequent thermal and mechanical treatments were used for a controlled crystallization process of the soft magnetic phase. A detailed analysis of structural aspects and crystallization dynamics and their relation with the magnetic behavior of the Fe-Cu ribbons has been obtained via Mossbauer spectroscopy, X-ray diffraction (XRD) and magnetic measurements. In order to obtain composite permanent magnets with shape anisotropy, the optimal conditions and the suitable processing were established. © 2004 Elsevier B.V. All rights reserved.
1245. Giant magnetoresistance effects in correlation with local magnetic interactions in Fe-Cu and Co-Cu granular thin films prepared by thermionic vacuum arc method
Authors:
Lungu, CP; Mustata, I; Lungu. AM; Brinza, O; Zaroschi, V; Kuncser, V; Filoti, G; Ion, L
Published: OCT 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2512, DOI:
The simultaneous discharge of Fe (or Co) and, respectively, CU metal sources via thermionic vacuum arc (TVA) was used as a new processing method to obtain granular magneto-resistive films. The nano-structured films with thicknesses of 120 +/- 1 nm and 250 +/- 1 nm were obtained in definite conditions and subsequently characterized via electrical measurements at room temperature, in applied magnetic field. The paper reveals the importance of different specific factors (from size and dispersion effects to annealing influence) on the magnetoresistance behavior. A special contribution of the Mossbauer Spectroscopy, concerning the local structure and interactions as well as the magnetic phase characterization, was emphasized.
1246. Microstructural characterization of polycrystalline Alq(3) grown by sublimation
Authors:
Ghica, C; Grecu, MN; Gmeiner, J; Grecu, VV
Published: DEC 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 3003, DOI:
A microstructural investigation on polycrystalline electroluminescent Alq(3) obtained by train sublimation method is reported in the paper. The morphology and crystalline structure of the obtained Alq3 phases have been analyzed by transmission electron microscopy performed on samples collected from 3 different regions along the sublimation tube.
1247. Morphology and shape evolution of the copper monosulfide nanocrystallites with the reaction time
Authors:
Simonescu, CM; Teodorescu, VS; Brezeanu, M; Melinescu, A
Copper monosulfide nanocrystallites have been obtained by reaction between copper acetate and sodium thiosulphate (1:4) at 90 +/- 5 degrees C. The powder was studied by X ray diffraction, IR spectrometry and TEM - transmission electron microscopy and electron diffraction. The copper monosulfide crystallites have been obtained in spherical or discoidal "nodules" which are bonded in much bigger aggregates. The dimensions of the copper monosulfide crystallites are small (10 to 15 nm) near the nucleation center (indicated by an arrow) and bigger at the edges of the spherical nodule (60 to 80 nm). The evolution of the morphology and the shape of the crystallite aggregate with the reaction time allows to propose a nucleation and a crystal growth mechanism for this system.
1248. Fe-Cu granular thin films with giant magnetoresistance by thermionic vacuum arc method: Preparation and structural characterization
Authors:
Kuncser, V; Mustata, I; Lungu, CP; Lungu. AM; Zaroschi, V; Keune, W; Sahoo, B; Stromberg, F; Walterfang, M; Ion, L; Filoti, G
Published: OCT 1 2005, SURFACE & COATINGS TECHNOLOGY, 200, 983, DOI: 10.1016/j.surfcoat.2005.01.031
Simultaneous discharges of Fe and Cu metal sources by thermoionic vacuum arc (TVA) were used as a new procedure for preparation of granular Fe-Cu thin films with sensibly enhanced room temperature giant magnetoresistive effects. The possibilities to produce thin films with a wide range of structural and magneto-transport characteristics are emphasized. The structural aspects of granular Fe-Cu thin films deposited onto Kapton are investigated via X-ray diffractometry, atomic force microscopy and Mossbauer spectroscopy. The magneto-transport properties are strongly related to composition, structure and magnetic interactions inside the films. (c) 2005 Elsevier B.V. All rights reserved.
1249. Recent advancements in the development of radiation hard semiconductor detectors for S-LHC
Authors:
Fretwurst, E; Adey, J; Al-Ajili, A; Alfieri, G; Allport, PP; Artuso, M; Assouak, S; Avset, BS; Barabashi, L; Barcz, A; Bates, R; Biagi, SF; Bilei, GM; Bisello, D; Blue, A; Blumenau, A; Boisvert, V; Bolla, G; Bondarenko, G; Borchi, E; Borrello, L; Bortoletto, D; Boscardin, M; Bosisio, L; Bowcock, TJV; Brodbeck, TJ; Broz, J; Bruzzi, M; Brzozowski, A; Buda, M; Buhmann, P; Buttar, C; Campabadal, F; Campbell, D; Candelori, A; Casse, G; Cavallini, A; Charron, S; Chilingarov, A; Chren, D; Cindro, V; Collins, P; Coluccia, R; Contarato, D; Coutinho, J; Creanza, D; Cunningham, L; Dalla Betta, GF; Dawson, I; de Boer, W; De Palma, M; Demina, R; Dervan, P; Dittongo, S; Dolezal, Z; Dolgolenko, A; Eberlein, T; Eremin, V; Fall, C; Fasolo, F; Ferbel, T; Fizzotti, F; Fleta, C; Focardi, E; Forton, E; Garcia, C; Garcia-Navarro, JE; Gaubas, E; Genest, MH; Gill, KA; Giolo, K; Glaser, M; Goessling, C; Golovine, V; Sevilla, SG; Gorelov, I; Goss, J; Bates, AG; Gregoire, G; Gregori, P; Grigoriev, E; Grillo, AA; Groza, A; Guskov, J; Haddad, L; Harkonen, J; Hauler, F; Hoeferkamp, M; Honniger, F; Horazdovsky, T; Horisberger, R; Horn, M; Houdayer, A; Hourahine, B; Hughes, G; Ilyashenko, I; Irmscher, K; Ivanov, A; Jarasiunas, K; Johansen, KMH; Jones, BK; Jones, R; Joram, C; Jungermann, L; Kalinina, E; Kaminski, P; Karpenko, A; Karpov, A; Kazlauskiene, V; Kazukauskas, V; Khivrich, V; Khomenkov, V; Kierstead, J; Klaiber-Lodewigs, J; Klingenberg, R; Kodys, P; Kohout, Z; Korjenevski, S; Koski, M; Kozlowski, R; Kozodaev, M; Kramberger, G; Krasel, O; Kuznetsov, A; Kwan, S; Lagomarsino, S; Lassila-Perini, K; Lastovetsky, V; Latino, G; Lazanu, I; Lazanu, S; Lebedev, A; Lebel, C; Leinonen, K; Leroy, C; Li, Z; Lindstrom, G; Linhart, V; Litovchenko, P; Litovchenko, A; Giudice, AL; Lozano, M; Luczynski, Z; Luukka, P; Macchiolo, A; Makarenko, LF; Mandic, I; Manfredotti, C; Manna, N; Garcia, SM; Marunko, S; Mathieson, K; Melone, J; Menichelli, D; Messineo, A; Metcalfe, J; Miglio, S; Mikuz, M; Miyamoto, J; Moll, M; Monakhov, E; Moscatelli, F; Naoumov, D; Nossarzewska-Orlowska, E; Nysten, J; Olivero, P; Oshea, V; Palviainen, T; Paolini, C; Parkes, C; Pesseri, D; Pein, U; Pellegrini, G; Perera, L; Petasecca, M; Plemonte, C; Pignatel, GU; Pinho, N; Pintilie, I; Pintilie, L; Polivtsev, L; Polozov, P; Popa, A; Popule, J; Pospisil, S; Pozza, A; Radicci, V; Rafi, JM; Rando, R; Roeder, R; Rohe, T; Ronchin, S; Rott, C; Roy, A; Ruzin, A; Sadrozinski, HFW; Sakalauskas, S; Scaringella, M; Schiavulli, L; Schnetzer, S; Schumm, B; Sciortino, S; Scorzoni, A; Segneri, G; Seidel, S; Seiden, A; Sellberg, G; Sellin, P; Sentenac, D; Shipsey, I; Sicho, P; Sloan, T; Solar, M; Son, S; Sopko, B; Sopko, V; Spencer, N; Stahl, J; Stolze, D; Stone, R; Storasta, J; Strokan, N; Sudzius, M; Surma, B; Suvorov, A; Svensson, BG; Tipton, P; Tomasek, M; Tsvetkov, A; Tuominen, E; Tuovinen, E; Tuuva, T; Tylchin, M; Uebersee, H; Uher, J; Ullan, M; Vaitkus, JV; Velthuis, J; Verbitskaya, E; Vrba, V; Wagner, G; Wilhelm, I; Worm, S; Wright, V; Wunstorf, R; Yiuri, Y; Zabierowski, P; Zaluzhny, A; Zavrtanik, M; Zen, M; Zhukov, V; Zorzi, N
Published: OCT 21 2005, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 552, 19, DOI: 10.1016/j.nima.2005.05.039
The proposed luminosity upgrade of the Large Hadron Collider (S-LHC) at CERN will demand the innermost layers of the vertex detectors to sustain fluences of about 10(16) hadrons/cm(2). Due to the high multiplicity of tracks, the required spatial resolution and the extremely harsh radiation field new detector concepts and semiconductor materials have to be explored for a possible solution of this challenge. The CERN RD50 collaboration "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" has started in 2002 an R&D program for the development of detector technologies that will fulfill the requirements of the S-LHC. Different strategies are followed by RD50 to improve the radiation tolerance. These include the development of defect engineered silicon like Czochralski, epitaxial and oxygen-enriched silicon and of other semiconductor materials like SiC and GaN as well as extensive studies of the microscopic defects responsible for the degradation of irradiated sensors. Further, with 3D, Semi-3D and thin devices new detector concepts have been evaluated. These and other recent advancements of the RD50 collaboration are presented and discussed. (c) 2005 Elsevier B.V. All rights reserved.
1250. Radiation-hard semiconductor detectors for SuperLHC
Authors:
Bruzzi, M; Adey, J; Al-Ajili, A; Alexandrov, P; Alfieri, G; Allport, PP; Andreazza, A; Artuso, M; Assouak, S; Avset, BS; Barabash, L; Baranova, E; Barcz, A; Basile, A; Bates, R; Belova, N; Biagi, SF; Bilei, GM; Bisello, D; Blue, A; Blumenau, B; Boisvert, V; Bolla, G; Bondarenko, G; Borchi, E; Borrello, L; Bortoletto, D; Boscardin, M; Bosisio, L; Bowcock, TJV; Brodbeck, TJ; Broz, J; Brukhanov, A; Brzozowski, A; Buda, M; Buhmann, P; Buttar, C; Campabadal, F; Campbell, D; Candelori, A; Casse, G; Cavallini, A; Chilingarov, A; Chren, D; Cindro, V; Citterio, M; Collins, P; Coluccia, R; Contarato, D; Coutinho, J; Creanza, D; Cunningham, W; Cvetkov, V; Dalla Betta, GF; Davies, G; Dawson, I; de Boer, W; De Palma, M; Demina, R; Dervan, P; Dierlamm, A; Dittongo, S; Dobrzanski, L; Dolezal, Z; Dolgolenko, A; Eberlein, T; Eremin, V; Fall, C; Fasolo, F; Ferbel, T; Fizzotti, F; Fleta, C; Focardi, E; Forton, E; Franchenko, S; Fretwurst, E; Gamaz, F; Garcia, C; Garcia-Navarro, JE; Gaubas, E; Genest, MH; Gill, KA; Giolo, K; Glaser, M; Goessling, C; Golovine, V; Sevilla, SG; Gorelov, I; Goss, J; Gouldwell, A; Gregoire, G; Gregori, P; Grigoriev, E; Grigson, C; Grillo, A; Groza, A; Guskov, J; Haddad, L; Harkonen, J; Harding, R; Hauler, F; Hayama, S; Hoeferkamp, M; Honniger, F; Horazdovsky, T; Horisberger, R; Horn, M; Houdayer, A; Hourahine, B; Hruban, A; Hughes, G; Ilyashenko, I; Irmscher, K; Ivanov, A; Jarasiunas, K; Jin, T; Jones, BK; Jones, R; Joram, C; Jungermann, L; Kalinina, E; Kaminski, P; Karpenko, A; Karpov, A; Kazlauskiene, V; Kazukauskas, V; Khivrich, V; Khomenkov, V; Kierstead, J; Klaiber-Lodewigs, J; Kleverman, M; Klingenberg, R; Kodys, P; Kohout, Z; Korjenevski, S; Kowalik, A; Kozlowski, R; Kozodaev, M; Kramberger, G; Krasel, O; Kuznetsov, A; Kwan, S; Lagomarsino, S; Lari, T; Lassila-Perini, K; Lastovetsky, V; Latino, G; Latushkin, S; Lazanu, S; Lazanu, I; Lebel, C; Leinonen, K; Leroy, C; Li, Z; Lindstrom, G; Lindstrom, L; Linhart, V; Litovchenko, A; Litovchenko, P; Litvinov, V; Lo Giudice, A; Lozano, M; Luczynski, Z; Luukka, P; Macchiolo, A; Mainwood, A; Makarenko, LF; Mandic, I; Manfredotti, C; Garcia, SM; Marunko, S; Mathieson, K; Mozzanti, A; Melone, J; Menichelli, D; Meroni, C; Messineo, A; Miglio, S; Mikuz, M; Miyamoto, J; Moll, M; Monakhov, E; Moscatelli, F; Murin, L; Nava, F; Naoumov, D; Nossarzewska-Orlowska, E; Nummela, S; Nysten, J; Olivero, P; Oshea, V; Palviainen, T; Paolini, C; Parkes, C; Passeri, D; Pein, U; Pellegrini, G; Perera, L; Petasecca, M; Piatkowski, B; Piemonte, C; Pignatel, GU; Pinho, N; Pintilie, I; Pintilie, L; Polivtsev, L; Polozov, P; Popa, AI; Popule, J; Pospisil, S; Pucker, G; Radicci, V; Rafi, JM; Ragusa, F; Rahman, M; Rando, R; Roeder, R; Rohe, T; Ronchin, S; Rott, C; Roy, P; Roy, A; Ruzin, A; Ryazanov, A; Sadrozinski, HFW; Sakalauskas, S; Scaringella, M; Schiavulli, L; Schnetzer, S; Schumm, B; Sciortino, S; Scorzoni, A; Segneri, G; Seidel, S; Seiden, A; Sellberg, G; Sellin, P; Sentenac, D; Shipsey, I; Sicho, P; Sloan, T; Solar, M; Son, S; Sopko, B; Spencer, N; Stahl, J; Stavitski, I; Stolze, D; Stone, R; Storasta, J; Strokan, N; Strupinski, W; Sudzius, M; Surma, B; Suuronen, J; Suvorov, A; Svensson, BG; Tipton, P; Tomasek, M; Troncon, C; Tsvetkov, A; Tuominen, E; Tuovinen, E; Tuuva, T; Tylchin, M; Uebersee, H; Uher, J; Ullan, M; Vaitkus, JV; Vanni, P; Velthuis, J; Verzellesi, G; Verbitskaya, E; Vrba, V; Wagner, G; Wilhelm, I; Worm, S; Wright, V; Wunstorf, R; Zablerowski, P; Zaluzhny, A; Zavrtanik, M; Zen, M; Zhukov, V; Zorzi, N
Published: APR 1 2005, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 541, 201, DOI: 10.1016/j.nima.2005.01.056
An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 1035 cm-2 s-1 has been envisaged to extend the physics reach of the machine. An efficient tracking down to a few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 1016cm-2. The CERN-RD50 project "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit. The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work. 2005 Published by Elsevier B.V.
1251. Microchemical and mechanical characteristics of arc plasma deposited TiAlN and TiN/TiAlN coatings
Authors:
Braic, M; Braic, V; Balaceanu, M; Pavelescu, G; Vladescu, A; Tudor, I; Popescu, A; Borsos, Z; Logofatu, C; Negrila, CC
Published: APR 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 676, DOI:
Single layer TiAlN and alternate TiN/TiAlN multilayered hard coatings were deposited on Si, plain carbon steel and high-speed steel substrates by the cathodic are technique. Chemical composition, phase composition, texture, Vickers microhardness, adhesion, bilayer period, sliding friction coefficient and wear resistance were investigated by XPS, EDX and XRD analyses, microhardness measurements, scratch and tribological tests.
1252. Development of radiation tolerant semiconductor detectors for the Super-LHC
Authors:
Moll, M; Adey, J; Al-Ajili, A; Alfieri, G; Allport, PP; Artuso, M; Assouak, S; Avset, BS; Barabash, L; Barcz, A; Bates, R; Biagi, SF; Bilei, GM; Bisello, D; Blue, A; Blumenau, A; Boisvert, V; Bolla, G; Bondarenko, G; Borchi, E; Borrello, L; Bortoletto, D; Boscardin, M; Bosisio, L; Bowcock, TJV; Brodbeck, TJ; Broz, J; Bruzzi, M; Brzozowski, A; Buda, M; Buhmann, P; Buttar, C; Campabadal, F; Campbell, D; Candelori, A; Casse, G; Cavallini, A; Charron, S; Chilingarov, A; Chren, D; Cindro, V; Collins, P; Coluccia, R; Contarato, D; Coutinho, J; Creanza, D; Cunningham, W; Dalla Betta, GF; Dawson, I; de Boer, W; De Palma, M; Demina, R; Dervan, P; Dittongo, S; Dolezal, Z; Dolgolenko, A; Eberlein, T; Eremin, V; Fall, C; Fasolo, F; Fizzotti, F; Fleta, C; Focardi, E; Forton, E; Fretwurst, E; Garcia, C; Garcia-Navarro, JE; Gaubas, E; Genest, MH; Gill, KA; Giolo, K; Glaser, M; Goessling, C; Golovine, V; Sevilla, SG; Gorelov, I; Goss, J; Bates, AG; Gregoire, G; Gregori, P; Grigoriev, E; Grillo, AA; Groza, A; Guskov, J; Haddad, L; Harkonen, J; Hauler, F; Hoeferkamp, M; Honniger, F; Horazdovsky, T; Horisberger, R; Horn, M; Houdayer, A; Hourahine, B; Hughes, G; Ilyashenko, I; Irmscher, K; Ivanov, A; Jarasiunas, K; Johansen, KMH; Jones, BK; Jones, R; Joram, C; Jungermann, L; Kalinina, E; Kaminski, P; Karpenko, A; Karpov, A; Kazlauskiene, V; Kazukauskas, V; Khivrich, V; Khomenkov, V; Kierstead, J; Klaiber-Lodewigs, J; Klingenberga, R; Kodys, P; Kohout, Z; Korjenevski, S; Koski, M; Kozlowski, R; Kozodaev, M; Kramberger, G; Krasel, O; Kuznetsov, A; Kwan, S; Lagomarsino, S; Lassila-Perini, K; Lastovetsky, V; Latino, G; Lazanu, S; Lazanu, I; Lebedev, A; Lebel, C; Leinonen, K; Leroy, C; Li, Z; Lindstrom, G; Linhart, V; Litovchenko, A; Litovchenko, P; Lo Giudice, A; Lozano, M; Luczynski, Z; Luukka, P; Macchiolo, A; Makarenko, LF; Mandic, I; Manfredotti, C; Manna, N; Marti i Garcia, S; Marunko, S; Mathieson, K; Melone, J; Menichelli, D; Messineo, A; Metcalfe, J; Miglio, S; Mikuz, M; Miyamoto, J; Monakhov, E; Moscatelli, F; Naoumov, D; Nossarzewska-Orlowska, E; Nysten, J; Olivera, P; OShea, V; Palvialnen, T; Paolini, C; Parkes, C; Passeri, D; Pein, U; Pellegrini, G; Perera, L; Petasecca, K; Piemonte, C; Pignatel, GU; Pinho, N; Pintilie, I; Pintilie, L; Polivtsev, L; Polozov, P; Popa, A; Popule, J; Pospisil, S; Pozza, A; Radicci, V; Rafi, JM; Rando, R; Roeder, R; Rohe, T; Ronchin, S; Rott, C; Roy, A; Ruzin, A; Sadrozinski, HFW; Sakalauskas, S; Scaringella, M; Schiavulli, L; Schnetzer, S; Schumm, B; Sciortino, S; Scorzoni, A; Segneri, G; Seidel, S; Seiden, A; Sellberg, G; Sellin, P; Sentenac, D; Shipsey, I; Sicho, P; Sloan, T; Solar, M; Son, S; Sopko, B; Sopko, V; Spencer, N; Stahl, J; Stolze, D; Stone, R; Storasta, J; Strokan, N; Sudzius, M; Surma, B; Suvorov, A; Svensson, BG; Tipton, P; Tomasek, M; Tsvetkov, A; Tuominen, E; Tuovinen, E; Tuuva, T; Tylchin, M; Uebersee, H; Uher, J; Ullan, M; Vaitkus, JV; Velthuis, J; Verbitskaya, E; Vrba, V; Wagner, G; Wilhelm, I; Worm, S; Wright, V; Wunstorf, R; Yiuri, Y; Zabierowski, P; Zaluzhny, A; Zavrtanik, M; Zen, M; Zhukov, V; Zorzi, N
Published: JUL 1 2005, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 546, 107, DOI: 10.1016/j.nima.2005.03.044
The envisaged upgrade of the Large Hadron Collider (LHC) at CERN towards the Super-LHC (SLHC) with a 10 times increased luminosity of 10(35) cm(-2) s(-1) Will present severe challenges for the tracking detectors of the SLHC experiments. Unprecedented high radiation levels and track densities and a reduced bunch crossing time in the order of 10 ns as well as the need for cost effective detectors have called for an intensive R&D program. The CERN RD50 collaboration "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" is working on the development of semiconductor sensors matching the requirements of the SLHC. Sensors based on defect engineered silicon like Czochralski, epitaxial and oxygen enriched silicon have been developed. With 3D, Semi-3D and thin detectors new detector concepts have been evaluated and a study on the use of standard and oxygen enriched p-type silicon detectors revealed a promising approach for radiation tolerant cost effective devices. These and other most recent advancements of the RD50 collaboration are presented. (c) 2005 Elsevier B.V. All rights reserved.
1253. Czochralski growth and characterization of neodymium-doped strontium lanthanum aluminate (ASL : Nd) single crystals
Authors:
Gheorghe, L; Lupei, V; Lupei, A; Gheorghe, C; Varona, C; Loiseau, P; Aka, G; Vivien, D; Ferrand, B
Published: APR 15 2005, JOURNAL OF CRYSTAL GROWTH, 277, 415, DOI: 10.1016/j.jcrysgro.2005.01.085
Nd-doped strontium lanthanum aluminate crystals, Nd:ASL (Sr1-xNdyLax-yMgxAl12-xO19), with an extended composition parameter x (0.05 and 0.5) have been grown by the Czochralski pulling technique. Structural and compositional properties of the as-grown crystals have been studied using X-ray diffraction, chemical microanalysis and optical spectroscopy. The results show that high crystalline perfection and large size crystals of both compositions can be grown. Low-temperature optical absorption spectra of crystals with compositions corresponding to x = 0.5 and 0.05 reveal that such crystals predominantly contain either C-1- or C-2-type Nd3+-centers, respectively. The possibility to thus differentiate between the two types of the dopant structural centers is of utmost importance for laser applications. (c) 2005 Elsevier B.V. All rights reserved.
1254. Fano regime of one-dot Aharonov-Bohm interferometers
Authors:
Moldoveanu, V; Tolea, M; Gudmundsson, V; Manolescu, A
Published: AUG 2005, PHYSICAL REVIEW B, 72, DOI: 10.1103/PhysRevB.72.085338
We use the Landauer-Buttiker formalism to study the mesoscopic Fano effect in Aharonov-Bohm rings with an embedded two-dimensional noninteracting dot. The magnetic field dependence of the dot levels leads to a global shift of the Fano lines which becomes important for small ring/dot area ratios. As the magnetic field is varied the Fano dips move periodically from one side of the peak to the other, as reported by Kobayashi [Phys. Rev. Lett. 88, 256806 (2002)]. We show that this effect appears due to a specific magnetic control of the difference between the phase of the single nonresonant path via the free arm of the ring and the global phase of all trajectories involving resonant tunnelings through the dot.
1255. Unconventional method of obtaining nanocrystallites from copper sulfides
Authors:
Simonescu, CM; Teodorescu, VE; Patron, L; Giurginca, M; Capatina, C
In this article the obtaining and characterization of a mixture of copper sulfide (CuS, Cu9S, CuS2) is presented. The characterization was made by IR Spectroscopy, X-ray Powder Diffraction (XRD) and Transmission Electron Microscopy (TEM). The sulfide mixture represents an aggregate of small particles with an average diameter of 20-30 nm and particles with the diameter of about 500 nm. The smaller particles have the cuboidal morphology and correspond to CuS2; the bigger ones have the hexagonal morphology and correspond to CuS, and Cu9S8.
1256. New exotic negative ions of In and Ga in KCI crystals
Authors:
Topa, V; Apostol, E
Published: AUG 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2132, DOI:
In this paper we present the experimental proofs that in KCl:In+ and KCl:Ga+ crystals, after non-standard electrolytical colouring, all impurity ions are converted in negative species and occupy anionic positions. The optical absorption and emission, electron paramagnetic resonance, thermal treatment in a flux of N-2 or H-2 and the electrons migration from negative metal species of coloured part to uncoloured part drived by an electric field, have been used as experimental methods for the demonstration of the conversion of In+ and Ga+-ions in negative exotic ions. The last two methods are very important for proving the existence of negative metal ions in crystals. The first one was improved by our team in [1], and the second one reported here for the first time, was used as an indubitable test for the evidence of In and Ga negative metal ions in anionic sites, in electrolytical coloured samples.
1257. Fe-coverage-induced out-of-plane spin components of the antiferromagnetic spin structure in exchange-biased Fe/FeSn2 bilayers
Authors:
Stromberg, F; Keune, W; Kuncser, VE; Westerholt, K
Published: AUG 2005, PHYSICAL REVIEW B, 72, DOI: 10.1103/PhysRevB.72.064440
Exchange-coupled Fe/FeSn2(001) bilayer systems consisting of a polycrystalline ferromagnetic Fe layer grown on an epitaxial antiferromagnetic FeSn2 layer have been prepared by molecular beam epitaxy and investigated by Fe-57 conversion electron Mossbauer spectroscopy and superconducting quantum interference device magnetometry. The systems show a significant exchange bias effect at low temperatures. Tracer layers of Fe-57 (in the Fe layer) and (FeSn2)-Fe-57 (in the FeSn2 layer) have been placed in the samples in order to probe the spontaneous spin orientation at different distances from the Fe/FeSn2 interface. The Fe spins in the ferromagnetic layer are preferentially oriented in the interfacial plane. In as-prepared samples the presence of the Fe top layer induces a striking out-of-plane component of the interfacial Fe spins in the antiferromagnetic FeSn2 film. This perpendicular component decreases in magnitude at a larger distance from the interface. A reorientation transition from out-of-plane toward in-plane spin orientation was observed in the interfacial FeSn2 layer with increasing age of the sample. This effect is correlated with an increased magnitude of the exchange bias field for the aged samples.
1258. Experiments on pulsed laser deposition and characterization of epitaxially in-situ grown YBa2Cu3O7-x thin films
Authors:
Branescu, M; Teodorescu, VS; Socol, G; Balasz, I; Ducu, C; Jaklovszky, J
Published: APR 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 972, DOI:
Experimental results concerning the pulsed laser deposition parameters of in-situ epitaxially grown high crystalline quality YBa2Cu3O7-x thin films are reported. The structural and morphological properties of the deposited films analyzed by transmission electron microscopy, selected area electron diffraction, X-ray diffraction, and Raman spectroscopy are also presented. The YBa2Cu3O7-x thin films, predominantly c-axis oriented had required the smallest oxygen pressure during the cool-down time reported to date.
1259. The nature of the hydrogen bond in the LaNiSnH2 and NdNiSnH hydrides
Authors:
Spataru, T; Palade, P; Principi, G; Blaha, P; Schwarz, K; Kuncser, V; Lo Russo, S; Dal Toe, S; Yartys, VA
Published: MAR 22 2005, JOURNAL OF CHEMICAL PHYSICS, 122, DOI: 10.1063/1.1867436
The electronic structure of LaNiSn and NdNiSn compounds and their hydrides has been studied by first principles calculations and variable temperature Sn-119 Mossbauer spectroscopy and the nature of the hydrogen-metal bond is discussed. The analysis of the electronic density of states (DOS) in both compounds before and after hydrogenation indicates an hybridization of the Sn, Ni, and H orbitals. The partial Sn-p DOS of LaNiSnH2 gives evidence for a lower symmetry of electron density around tin atoms compared to LaNiSn, according to the larger quadrupole splitting in the corresponding Mossbauer spectrum. Theoretical and experimental Mossbauer parameters agree very well for all samples.
1260. Evidence for irradiation triggered nonuniform defects distribution in multiharmonic magnetic susceptibility of neutron irradiated YBa2Cu3O7-delta
Authors:
Sandu, V; Popa, S; Di Gioacchino, D; Tripodi, P
Published: AUG 2005, JOURNAL OF SUPERCONDUCTIVITY, 18, 581, DOI: 10.1007/s10948-005-0040-z
Multiharmonic ac-magnetic susceptibility chi(1) chi(2), chi(3), of neutron irradiated Li-doped YBa2CU3O7-x, has revealed a nonmonotonic dependence of all harmonics on the neutron fluence. The irradiation has a strongly depressive influence on the intergrain connection suggesting an increase of the effective thickness of the intergranular Josephson junction at a neutron fluence of 0.98 x 10(17) cm(-2). Less damaged are the intragrain properties. A spectacular enhancement of the superconducting intragranular properties reflected in the characteristics of all harmonics was observed at highest fluence phi = 9.98 X 10(17) cm(-2). We assume that this effect results from the development of a space inhomogeneous distribution with alternating defectless and defect-rich regions.
1261. A(II)B(VI) photoresistances by sintering-sublimation technics
Authors:
Nazarenco, I; Jaklovszky, J; Ghiordanescu, V; Sava, BA; Albeanu, I; Dumitrescu, M; Ulieru, D
Published: AUG 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2118, DOI:
The sintering-sublimation technics was conceived for increasing the reliability of the photoconductive devices, by decreasing the concentration of mobiles donors, which are utilised for photoconductive material sensibilisation. The technics combines three different technics: the vapor phase deposition; the vacuum vaporising; the ceramic sinterisation. This special technics gives stoichiometric layers. The technics avoids dissociation (the flash sublimation technic), sublimates the compounds from two different sources, on heated support, or sublimates the compound, with Cd excess. It was investigated, by mass spectrometry and optical absorption studies, the presence, in gaseous state, of the A(II)B(VI) molecules. The condensation on the substrate of the vapors is difficult because the Cd, Zn and Hg elements have difficulties in the condensation process. The Frenkel model, of the condensation, can be successfully used for describing the process. This model uses the observations concerning the difficulty of the condensation on supports of those elements, at higher temperatures than 90 - 195 K. It is supposed that the support surface is a potential surface, with holes and potential walls, whose dimensions can not overcome the interatomic distances, for polished surfaces.
1262. Characterization of oxygen dimer-enriched silicon detectors
Authors:
Boisvert, V; Lindstrom, JL; Moll, M; Murin, LI; Pintilie, I
Published: OCT 21 2005, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 552, 55, DOI: 10.1016/j.nima.2005.06.005
Various types of silicon material and silicon p(+)n diodes have been treated to increase the concentration of the oxygen dimer (02) defect. This was done by exposing the bulk material and the diodes to 6 MeV electrons at a temperature of about 350 degrees C. FTIR spectroscopy has been performed on the processed material confirming the formation of oxygen dimer defects in Czochralski silicon pieces. We also show results from TSC characterization on processed diodes. Finally, we investigated the influence of the dimer enrichment process on the depletion voltage of silicon diodes and performed 24 GeV/c proton irradiations to study the evolution of the macroscopic diode characteristics as a function of fluence. (c) 2005 Elsevier B.V. All rights reserved.
1263. Supported perovskites for total oxidation of toluene
Authors:
Alifanti, M; Florea, M; Somacescu, S; Parvulescu, VI
Published: SEP 1 2005, , DOI: 10.1016/j.apcatb.2005.02.018
1264. Anomalous splitting of the first penetration peak in the local magnetization of Bi2Sr2CaCu2O8+y single crystals
Authors:
Mihalache, V
Published: DEC 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 3032, DOI:
A scanning Hall probe microscope (SHPM) with an effective spatial resolution of 1 similar to mu m has been used to study the local induction in high quality superconducting Bi2Sr2CaCu2O8+delta single crystals at high temperatures and low magnetic fields. We observed, for the first time to our knowledge, an anomalous splitting of the peak of first full penetration of magnetic field, We discuss the observed splitting, which is connected to the effects of surface and geometrical barriers on the vortex lattice.
1265. Structural phase transition induced in Fe50Rh50 alloys by high pressure
Authors:
Kuncser, V; Nicula, R; Ponkratz, U; Jianu, A; Stir, M; Burkel, E; Filoti, G
Published: JAN 11 2005, JOURNAL OF ALLOYS AND COMPOUNDS, 386, 11, DOI: 10.1016/j.jallcom.2004.04.139
The equiatomic composition of the FeRh alloy was studied by in situ high pressure energy dispersive X-ray experiments. Pressures as high as 19 GPa were generated using a diamond anvil cell. An incomplete bcc --> fcc phase transition was evidenced, both bcc and fcc phases coexisting above 10.0 GPa. The transition is accompanied by a decrease of the lattice parameter of the remaining bcc phase by approx. 1.5%. A substantial low lattice parameter was observed for the newly formed fee phase, reflecting a rather compressed structure. (C) 2004 Elsevier B.V. All rights reserved.
1266. Magnetic properties of iron-modified amorphous carbon
Authors:
Yastrebov, SG; Ivanov-Omskii, VI; Pop, V; Morosanu, C; Slav, A; Voiron, J
Published: 2005, SEMICONDUCTORS, 39, 844, DOI: 10.1134/1.1992645
The structure and magnetic properties of films of iron-modified amorphous carbon (a-C:Fe) prepared by magnetron cosputtering of iron and graphite targets are studied. X-ray diffraction measurements show that iron enters the samples in the form of Fe nanocrystals that are typically about 20 nm in size and also forms nanocrystals of hexagonal iron carbide. The temperature dependences of the magnetization, measured under cooling in zero and nonzero magnetic fields, are studied. At temperatures T less than or similar to 8 K, a magnetic transition, which provides evidence for the onset of magnetic ordering in the material, is observed to occur. The magnetization isotherms obtained in the 8- to 20-K temperature range are in agreement with this observation. It is shown that a modified version of Langevin's formalism adequately describes the observed features of a-C:Fe film magnetization. (c) 2005 Pleiades Publishing, Inc.
1267. Transport through a quantum ring, dot, and barrier embedded in a nanowire in magnetic field
Authors:
Gudmundsson, V; Lin, YY; Tang, CS; Moldoveanu, V; Bardarson, JH; Manolescu, A
Published: JUN 2005, PHYSICAL REVIEW B, 71, DOI: 10.1103/PhysRevB.71.235302
We investigate the transport through a quantum ring, a dot, and a barrier embedded in a nanowire in a homogeneous perpendicular magnetic field. To be able to treat scattering potentials of finite extent in a magnetic field we use a mixed momentum-coordinate representation to obtain an integral equation for the multiband scattering matrix. For a large embedded quantum ring we are able to obtain Aharonov-Bohm type of oscillations with superimposed narrow resonances caused by interaction with quasibound states in the ring. We also employ the scattering matrix approach to calculate the conductance through a semiextended barrier or well in the wire. The numerical implementations we resort to in order to describe the cases of weak and intermediate magnetic field allow us to produce high resolution maps of the "near field" scattering wave functions, which are used to shed light on the underlying scattering processes.
1268. Properties of high-porosity sol-gel derived indium-tin oxide films
Authors:
Stoica, TF; Gartner, M; Stoica, T; Losurdo, M; Teodorescu, VS; Blanchin, MG; Zaharescu, M
Published: OCT 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2358, DOI:
Indium-tin oxide (ITO) sol-gel films have been obtained with the void concentration up to 50%. The films are nanostructured with nanocrystals of In2O3:Sn and nanovoids. The information obtained from derivative thermo-gravimetry was used to design the annealing program for ITO film formation with a high void concentration. Multilayer films were obtained by successive deposition. The thickness of one layer was about 9 nm. By successive depositions, the void density of the film is reduced. Quantitative analysis of the void density has been performed by spectroscopic ellipsometry. The conductivity of the films can be varied in a large range by annealing in vacuum or in air, at temperature higher than 200 degrees C.
1269. Resonant and coherent transport through Aharonov-Bohm interferometers with coupled quantum dots
Authors:
Moldoveanu, V; Tolea, M; Aldea, A; Tanatar, B
Published: MAR 2005, PHYSICAL REVIEW B, 71, DOI: 10.1103/PhysRevB.71.125338
A detailed description of the tunneling processes, within Aharonov-Bohm (AB) rings containing two-dimensional quantum dots is presented. We show that the electronic propagation through the interferometer is controlled by the spectral properties of the embedded dots and by their coupling with the ring. The transmittance of the interferometer is computed by the Landauer-Buttiker formula. Numerical results are presented for an AB interferometer containing two coupled dots. The charging diagrams for a double-dot interferometer and the Aharonov-Bohm oscillations are obtained, in agreement with the recent experimental results of Holleitner et al. [Phys. Rev. Lett. 87, 256802 (2001)] We identify conditions in which the system shows Fano line shapes. The direction of the asymetric tail depends on the capacitive coupling and on the magnetic field. We discuss our results in connection with the experiments of Kobayashi et al. [Phys. Rev. Lett. 88, 256806 (2002)] in the case of a single dot.
1270. The influence of neutron irradiation on (B0.65C0.35)Ba1.4Sr0.6Ca2Cu3Oz superconducting phase: The role of the grain edge
Authors:
Mihalache, V; Totovana, A; Sandu, V; Popa, S; Aldica, G; Iyo, A
Published: AUG 2005, JOURNAL OF SUPERCONDUCTIVITY, 18, 467, DOI: 10.1007/s10948-005-0029-7
Using the transport and magnetization measurements, the influence of neutron irradiation at a fluence of 5 x 10(17) n cm(-2) on (B0.65C0.35)Ba1.4Sr0.6Ca2Cu3Oz has been investigated. The neutron irradiation was found to decrease critical temperature and transport critical current density, increase the residual and normal state resistivity, and improve the intragranular critical current density with 1.6 x 10(5) A/cm(2) (at 77.3 K and in the applied field up to 160 kA m) and Delta M-irr/Delta M-nonirr ratio (up to factor of 3) at highest field used for investigation. The field dependence of this ratio, which is below the unity at very low field but higher than I at high fields, correlated with the shape of the hysteretic loops as well as with the change of the transport parameters after irradiation suggests the role of the irradiation-induced effects on the grain edges. We discuss these effects in the framework of the Bean-Livingstone surface barriers and geometrical barriers.
1271. Magnetically modulated microwave absorption investigation of Bi1.8Pb0.4Sr1.8Ba0.2Ca2Cu3Ox/(LiF)(y) superconducting system
Authors:
Velter-Stefanescu, M; Duliu, OG; Mihalache, V
Published: JUN 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 1561, DOI:
The effect of LiF content on the 2223 phase of the high temperature superconducting system Bi1.8Pb0.4Sr1.8Ba0.2Ca2Cu3Ox/(LiF)(y) (y = 0.02 to 0.15) was investigated by means of magnetically modulated microwave absorption (MAMMA). The experimental results confirmed a two fold increase of the superconducting phase content together with a slight rise (around 2 %) of the critical temperature for y=0.07. At the same time, for y between 0.05 and 0.12 the -Delta T-c(mw)/Delta B ratio was practically constant and equal to (18.5 +/- 1.5) KT-1, a typical value for 2223 superconducting phase.
1272. Mossbauer effect study of correlation between structure and exchange-bias effect in ferromagnetic Fe/antiferromagnetic FeSn2 bilayers
Authors:
Kuncser, VE; Stromberg, F; Acet, M; Keune, W
Published: MAR 15 2005, JOURNAL OF APPLIED PHYSICS, 97, DOI: 10.1063/1.1858879
Antiferromagnetic (AF) FeSn2(001) epitaxial and polycrystalline layers were grown in ultrahigh vacuum under various conditions on clean InSb(001) substrates and covered by polycrystalline ferromagnetic Fe layers, forming a new system with exchange bias. Isotopically enriched Fe-57- and (FeSn2)-Fe-57-tracer layers were placed on either side of the Fe/FeSn2 interface for a microscopic investigation of the spin structure and atomic interdiffusion phenomena in near-interfacial regions by Fe-57 conversion electron Mossbauer spectroscopy (CEMS) at room temperature and T=10 K. Several spectral components, assigned to pure bcc Fe, Sn-containing bcc Fe, AF-ordered FeSn2, and paramagnetic FeSn2 were resolved in the CEM spectra. Evidence is provided for interdiffusion across the interface. The temperature dependence of the exchange-bias field H-E was measured by magnetometry. The CEMS data provide evidence for a correlation between H-E at low T and chemical disorder (defects) in the FeSn2 films via the intensity of the paramagnetic line. These results support the assumption that exchange bias is related to the presence of AF domains formed via magnetic defects in the antiferromagnet. The T dependence of H-E suggests interfacial exchange-coupling energies higher than the AF wall energy. (C) 2005 American Institute of Physics.
1273. PZT-type materials with improved radial piezoelectric properties
Authors:
Dimitriu, E; Iuga, A; Ciupina, V; Prodan, G; Ramer, R
Published: 2005, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 25, 2404, DOI: 10.1016/j.jeurceramsoc.2005.03.070
The goal of this work is to prepare doped PZT-type materials with improved radial piezoelectric properties. Ceramic materials were obtained by solid-state reaction at different sintering temperatures. SAED, bright field TEM and HRTEM methods were used for the microstructure studies. The influence of the composition and nanostructure on the dielectric and piezoelectric properties of the materials is discussed. One of the materials with high coupling constant was used in the construction of a miniature flexural ventilator. Designated to function at an emf of 220 V/50 Hz, this device is characterized by high efficiency, reliability and low energy consumption. (c) 2005 Elsevier Ltd. All rights reserved.
1274. Net current generation in a 1D quantum ring at zero magnetic field
Authors:
Gylfadottir, SS; Nita, M; Gudmundsson, V; Manolescu, A
Published: MAR 2005, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 27, 283, DOI: 10.1016/j.physe.2004.12.002
We study a non-adiabatic excitation of an electron system in a 1D quantum ring radiated by a short terahertz pulse. The response of two models, a continuous and a discrete, is explored. By introducing a spatial asymmetry in the external perturbation, a net current can be generated in the ring at a zero magnetic field. Effect of impurities and ratchets are investigated in combination with symmetric and asymmetric external excitation. (c) 2005 Elsevier B.V. All rights reserved.
1275. Field effects and surface states in second harmonic generation at n-GaAs(h k l) electrodes
Authors:
Lazarescu, V; Scurtu, R; Lazarescu, MF; Santos, E; Jones, H; Schmickler, W
Published: SEP 5 2005, ELECTROCHIMICA ACTA, 50, 4836, DOI: 10.1016/j.electacta.2005.02.069
Second harmonic generation from n-doped GaAs(111)-A, GaAs(111)-B and GaAs(110) electrodes in sulfuric acid solution has been compared at an incident wavelength of 1064 nm over a potential range, where Faradaic process are excluded. In the p-in/p-out polarization configuration, the rotational anisotropy of the SH response reflects the symmetry of the crystal surface. The isotropic part of the response depends significantly on the applied electric field in the space-charge region, suggesting that the dominant part of the SH response is generated in the near-surface depletion region. The effects of the applied potential on the isotropic amplitude of the SH-signal show, however, that the high density of the surface/interface states at the Fermi level, revealed in impedance spectroscopy, may play an important role as well. (C) 2005 Elsevier Ltd. All rights reserved.
1276. Quantum confinement in the photoluminescence of nanocrystalline porous silicon
Authors:
Stavarache, I; Ciurea, ML; Iancu, V
Published: 2005, CAS 2005: INTERNATIONAL SEMICONDUCTOR CONFERENCE, 1-2, 58, DOI:
The paper presents the photoluminescence of nanocrystalline porous silicon. Two maxima were observed for rather fresh samples, one located at the infrared edge of the visible range and the other one in red. After ageing, the first maximum vanishes, suggesting its relation with the surface states, while the red one undergoes a significant blue shift. A simple quantum confinement model allows to correlate the photon energy of the red maximum with a transition between two confinement levels and to interpret the blue shift in terms of size reduction by oxidation. These results are in good agreement with previous microstructure measurements.
1277. Local interactions and electronic phenomena in substituted LaFeO3 perovskites
Authors:
Russo, U; Nodari, L; Faticanti, M; Kuncser, V; Filoti, G
Published: JAN 14 2005, SOLID STATE IONICS, 176, 102, DOI: 10.1016/j.ssi.2004.06.001
Effects of electronic charge disproportionation were observed by Fe-57 Mossbauer spectroscopy at low temperatures in substituted LaFeO3 perovskites as (La1-xCax)FeO3 and La(Fe1-xMgx)O-3 (xless than or equal to0.5). The presence of both Fe3+ and Fe5+ species was evidenced in both series of compounds. Direct evidence for disproportionation was supported by correlating the Mossbauer results with the chemical determination of tetravalent iron at RT. The evolution of hyperfine parameters vs. substitution degree was comparatively analysed for Fe3+ and Fe5+ ions in relation to their electronic microscopic origin. Electron delocalisation processes are discussed in terms of ion distribution and valence state. (C) 2004 Elsevier B.V. All rights reserved.
1278. Optical and electronic properties of the aluminophosphate glasses doped with 3d-transition metal ions
Authors:
Elisa, M; Grigorescu, CEA; Vasiliu, C; Bulinski, M; Kuncser, V; Predoi, D; Filoti, G; Meghea, A; Iftimie, N; Giurginca, M
Published: OCT 2005, REVIEWS ON ADVANCED MATERIALS SCIENCE, 10, 374, DOI:
Aluminophosphate glasses doped with Fe, Mn, and Cr have been obtained by a wet non-conventional method. Structural information was provided by IR absorption spectra in the range 2000-500 cm(-1). The optical behaviour (transmission and refractive index) of the samples has been studied by UV-VIS-NIR spectroscopy. The Fe valence state and the local coordination were also analysed via Fe-57 Mossbauer spectroscopy, whose data revealed the redox equilibrium in the Fe-doped glasses according to the redox potentials of the transition ions.
1279. Photoluminescence of manganese- and copper-doped CdS nanowires
Authors:
Ghiordanescu, V; Sima, M; Enculescu, I; Grecu, MN; Mihut, L; Secu, M; Neumann, R
Published: FEB 2005, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 202, 454, DOI: 10.1002/pssa.200406927
Arrays of US: Mn2+ : Cu+ micro- and nanowires grown in polycarbonate ion-track templates exhibit photoluminescence in the spectral domain ranging from 500 to 800 mn at room temperature. A comparison with similar US and CdS:Mn2+ wire arrays is presented. The individual contributions to the emission spectra of Cu+ and Mn2+ ions in the US matrix are explained using their energy level schemes. Also SEM, EDX and EPR data are given or these wires. (c) 2005 WILEY-VCH Verlag GmbH A Co. KGaA, Weinheim.
1280. YBa2Cu3O7-delta : Li superconductor system investigated by direct microwave absorption method
Authors:
Velter-Stefanescu, M; Duliu, OG; Sandu, V
Published: APR 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 977, DOI:
The influence of thermal neutrons irradiation at different fluencies on the superconductivity properties of Li (2 at. %) doped YBa2Cu3O7-delta system has been investigated by direct microwave absorption method. We have noticed changes of the superconducting properties of the 123 phase that depend on the neutron fluency. By increasing fluency, initially, the phase structure supports a disordering, then a re-ordering accompanied by a significant increase of the average critical temperature T-c to 85.7 K and finally we observed a degradation of the 123 the phase accompanied by a diminishing of T-c. The intragranular dephasing magnetic field B-d, i.e. the direct microwave absorption (DMA) parameter associated with the magnetic field dependence of the critical current density exhibited an opposite tendency, initially decreasing and then increasing at a value close to those of unirradiated samples. We also noticed only on the irradiated samples the presence of a flatness of the DMA curves around 0.5 T, consistent with the expression of a peak effect.
1281. Soft ferrite materials for magnetic temperature transducers and applications
Authors:
Miclea, C; Tanasoiu, C; Miclea, CF; Gheorghiu, A; Tanasoiu, V
Published: APR 2005, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 290, 1509, DOI: 10.1016/j.jmmm.2004.11.561
Soft ferrites in the CuZnTi system, having the formula Cu1-xZnxTiyFe2-4O4, with 0.50 <= x <= 0.60 and 0.00 <= y <= 0.05 were investigated as a function of composition, sintering temperature and cooling speed, in order to obtain materials with controlled T-C and very high change rate of permeability with temperature around their T-C. The effect of Zn and Ti additions was a drastic change of the Curie temperature with about 10-12 degrees C for each atomic percent of Zn and Ti introduced into the spinel lattice while the cooling speed changed the behaviour of magnetic permeability with temperature around the Curie point. An application using such magnetic temperature sensors for a thermostat is presented. (c) 2004 Elsevier B.V. All rights reserved.
1282. Reply to comment on 'magnetic relaxation phenomena and inter-particle interactions in nanosized gamma-Fe2O3 systems'
Authors:
Predoi, D; Kuncser, V; Filoti, G
Published: APR 6 2005, JOURNAL OF PHYSICS-CONDENSED MATTER, 17, 2254, DOI: 10.1088/0953-8984/17/13/N02
1283. Evidence for vortices in the pseudogap region of Y1-xPrxBa2Cu3O7 from angular magnetoresistivity measurements
Authors:
Sandu, V; Cimpoiasu, E; Katuwal, T; Li, S; Maple, MB; Almasan, CC
Published: OCT 22 2004, PHYSICAL REVIEW LETTERS, 93, DOI: 10.1103/PhysRevLett.93.177005
In-plane angular magnetoresistivity Deltarho(ab)(anis) measurements were made on Y1-xPrxBa2Cu3O7-delta single crystals in the pseudogap region. For xgreater than or equal to0.2 single crystals, Deltarho(ab)(anis)(theta) displays a deviation from the typical quasiparticle contribution (proportional tosin(2)theta) for temperatures smaller than a certain value T-phi in the pseudogap region. This deviation is consistent with a flux-flow type contribution to angular magnetoresistivity, indicating the presence of vortexlike excitations above the zero-field critical temperature in the pseudogap region.
1284. Charge transport in spin-textured YBa2Cu3O6.25
Authors:
Sandu, V; Cimpoiasu, E; Almasan, CC; Paulikas, AP; Veal, BW
Published: JUN 2004, JOURNAL OF SUPERCONDUCTIVITY, 17, 458, DOI: 10.1023/B:JOSC.0000034273.20391.59
The electric transport of the charged particles in a spin texture was investigated in a strongly underdoped YBa2Cu3O6.25 single crystal in order to identify the characteristic electrical transport mechanism. The in-plane resistivity revealed three different regimes of charge transport: a chiral 2D VRH regime up to 55 K with a characteristic temperature T(d)approximate to12,400 K, an impurity band conduction regime above 55 K, and a metallic-like regime beyond 170 K. The out-of-plane resistivity has only one crossover at 115 K, but the conduction mechanisms controlling the two regimes are not clear.
1285. Anomalies of AC susceptibility losses in the doped [Bi(Pb)](2)Sr2Ca2CU3Ox superconductor
Authors:
Mihalache, V; Aldica, G; Badica, P; Crisan, A
Published: APR 2004, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 17, 730, DOI: 10.1088/0953-2048/17/4/030
AC susceptibility measurements have been performed on Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox (Bi-2223) samples doped with different Li-based compounds and prepared by the solid-state method. As-prepared samples and/or samples annealed in oxygen or argon, ground or unground, have been investigated in detail in order to understand the occurrence, nature and evolution of the anomalous peaks observed in chi " (T) curves versus the measuring parameters; we have detected up to four peaks instead of the usual two peaks observed in the non-doped samples. It was found that intrinsic physical-chemical properties, such as the melting temperature of the doping compound, are no less important for the final properties of the superconductor than their insertion properties into the crystal lattice of Bi-2223. Doping compounds with melting temperatures below or close to the phase formation temperature of the Bi-2223 phase can act as flux, changing the growth conditions. Intensification of some processes against others (e.g. decomposition-recovery of the BI-2223 phase, solubilization-precipitation of the secondary phases, changes in the properties of the liquid phase, etc) can lead to the formation of the Bi-2223 phase with different properties than for the non-doped superconductor. Generally, when using flux-type doping compounds, anomalous AC losses peaks are detected and the intra-granular critical current density is enhanced.
1286. Paramagnetism and superconductivity in Eu0.7Sm0.3Ba2Cu3O7-delta
Authors:
Sandu, V; Popa, S; Di Gioacchino, D; Tripodi, P
Published: DEC 2004, JOURNAL OF SUPERCONDUCTIVITY, 17, 710, DOI: 10.1007/s10948-004-0830-8
Magnetic properties of sintered Eu0.7Sm0.3Ba2Cu3O7-delta were investigated both in dc and ac magnetic fields. The dc response reflects the interplay between the rare earth ion paramagnetic and the superconducting charge carrier subsystems, respectively. The harmonic susceptibilities exhibit special features: the second harmonic is anomalously high and the third harmonic in zero dc-field has reversed temperature dependence with respect to the theoretical models. The magnetic relaxation at low fields is monotonous and occurs as a two-stage relaxation, each stage obeying logarithmical time dependence with different rates. At high fields, the relaxation is nonmonotonous with a peak at intermediate time suggesting a temporary re-entrance of irreversibility when the flux-line density increases in the center of the sample because of the redistribution of the vortices toward that region.
1287. Hydroxyapatite thin films grown by pulsed laser deposition and radio-frequency magnetron sputtering: comparative study
Authors:
Nelea, V; Morosanu, C; Iliescu, M; Mihailescu, IN
Published: APR 30 2004, APPLIED SURFACE SCIENCE, 228, 356, DOI: 10.1016/j.apsusc.2004.01.029
Hydroxyapatite (HA) thin films for applications in the biomedical field were grown by pulsed laser deposition (PLD) and radio-frequency magnetron sputtering (RF-MS) techniques. The depositions were performed from pure hydroxyapatite targets on Ti-5Al-2.5Fe (TiAlFe) alloys substrates. In order to prevent the HA film penetration by Ti atoms or ions diffused from the Ti-based alloy during and after deposition, the substrates were pre-coated with a thin buffer layer of TiN. In both cases, TiN was introduced by reactive PLD from TiN targets in low-pressure N-2. The PLD films were grown in vacuum onto room temperature substrates. The RF-MS films were deposited in low-pressure argon on substrates heated at 550 degreesC. The initially amorphous PLD thin films were annealed at 550 degreesC for 1 h in ambient air in order to restore the initial crystalline structure of HA target. The thickness of the PLD and RF-MS films were similar to1 mum and similar to350 nm, respectively. All films were structurally studied by scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GIXRD), energy dispersive X-ray spectrometry (EDS) and white light confocal microscopy (WLCM). The mechanical properties of the films were tested by Berkovich nano-indentation. Both PLD and RF-MS films mostly contain HA phase and exhibit good mechanical characteristics. Peaks of CaO were noticed as secondary phase in the GIXRD patterns only for RF-MS films. By its turn, the sputtered films were smoother as compared to the ones deposited by PLD (50 nm versus 250 nm average roughness). The R-F-MS films were harder, more mechanically resistant and have a higher Young modulus. (C) 2004 Elsevier B.V. All rights reserved.
1288. Spectroellipsometric study of the sol-gel nanocrystalline ITO multilayer films
Authors:
Stoica, TF; Gartner, M; Losurdo, M; Teodorescu, V; Blanchin, M; Stoica, T; Zaharescu, M
Published: MAY 1 2004, THIN SOLID FILMS, 455, 512, DOI: 10.1016/j.tsf.2003.11.251
Tin-doped indium oxide (ITO) thin films have been deposited by sol-gel process using 'sols' of indium and tin isopropoxides. The thickness of one deposited ITO layer is approximately 50 nm. The desired thickness was obtained by 1-5 successive depositions. The XTEM cross-sectional view of an ITO sample with five depositions showed a clear delimitation of the layers with an alternating structure dense/porous ITO layers. The void fraction in porous regions varies between 20 and 25%. Cubic bixbyite In2O3 nanocrystals with size of 10-20 nm and no phases separation of tin oxide were observed. The optical properties of the films have been investigated by optical transmission and spectroscopic ellipsometry. Reliable optical constants and porosity are obtained only with the model of internal structure based on XTEM results. (C) 2003 Elsevier B.V. All rights reserved.
1289. Facet oxidation and degradation of AlGaAs/GaAs pulsed laser diodes
Authors:
Ghita, RV; Lazarescu, MF; Manea, AS; Logofatu, C; Vasile, E; Ciupina, V
Published: 2004, ROMOPTO 2003: SEVENTH CONFERENCE ON OPTICS, 5581, 273, DOI: 10.1117/12.582822
Oxide films grow in atmosphere as a result of oxidation reaction and mass transport of the element through the oxide film. In most III-V compounds (as GaAs) semiconductor oxides of III-element and V-element are formed individually. The AlGaAs/GaAs laser diodes were exposed to facet oxidation at mirror surfaces in normal environmental conditions for a storage process. It was observed a decrease of optical output power in the early stage of experiment together with a constancy of the ratio P/P(0) for the long time term (month). We suggest the development at the mirror laser facet of a natural oxide film as Ga2O3 and GaAsO.. We present a SEM (Scanning Electron Microscopy) image of a natural oxide film grown in atmosphere at the surface of AlGaAs as laser facet, as well as a picture of a facet oxidation of a laser device. The EDS (Electron Dispersion Spectrum) of a natural oxide put into evidence the O (Kalpha) signal. Dielectric coating using Al2O3 and a-Si layers protected a part of laser devices, and at the mirror surface a reflectivity of 70% in the emission range of the laser (890nm) was measured. The emitted power for dielectric coated devices was constant, so the rapid degradation process was slowed down.
1290. Local magnetic interactions in Fe/RE2Fe14B nanocomposite systems
Authors:
Kuncser, V; Valeanu, M; Lifei, F; Jianu, A; Kappel, W; Filoti, G
Published: 2004, SECOND SEEHEIM CONFERENCE ON MAGNETISM, PROCEEDINGS, 3506, DOI: 10.1002/pssc.200405491
The Fe spin configurations in both the soft- and hard- magnetic phases of nanocomposite Fe/RE2Fe14B exchange-spring ribbons have been analysed by Mossbauer spectroscopy. New criteria for evaluating the inter-phase exchange-coupling strength are proposed. The coupling strength is discussed in relation to the annealing conditions and the relative content of the soft magnetic phase.
1291. Effect of ytrium substitution on the structure and piezoelectric properties of lead titanate ceramics
Authors:
Miclea, C; Amarande, L; Tanasoiu, C; Miclea, CF; Sandu, V; Gheorghiu, A
Published: 2004, 2004 International Semiconductor Conference, Vols 1and 2, Proceedings, 414, DOI:
Lead titanate (PT) is well known as a good piezoelectric material with high Curie temperature (similar to 490 degrees C) and low dielectric constant (similar to 200). Pure lead titanate cannot be sintered as ceramic bodies, due to its high crystalline anisotropy (c/a=1.064), but dense ceramic bodies can be obtained if small additions of other elements are used. In this regard we investigated the effect of Y addition on the structure and piezoelectric properties of PT ceramics, with general formula (Pb1-3x/2Yx)(Ti0.98Mn0.02)O-3, and x=0.04, 0.06, 0.08 and 0.10. Density and coupling factors were determined as a function of sintering temperatures, and doping level. Temperature dependence of the electromechanical behaviour was also investigated for temperatures as high as 500 degrees C. The Y modified PT ceramics have low dielectric constant (< 140), high Curie point (T-C > 450 degrees C), and large electromechanical anisotropy.
1292. Preparation and characterization of Ce-doped BaTiO3 thin films by pulsed laser deposition
Authors:
Cernea, M; Ianculescu, A; Monnereau, O; Argeme, L; Bley, V; Bastide, B; Logofatu, C
Published: APR 15 2004, JOURNAL OF MATERIALS SCIENCE, 39, 2759, DOI: 10.1023/B:JMSC.0000021450.39778.81
Thin films of BaTiO3 doped with 5.5 mol% CeO2 have been deposited on Pt/Si substrate by pulsed laser deposition. These films crystallize on the tetragonal BaTiO3 structure without any preferential orientation. Ce-doped BaTiO3 films deposited by PLD at 675degreesC in 30 Pa ambient oxygen exhibits a smooth surface: mean surface roughness (Rms) of 48 nm, mean size of grain of similar to40 Angstrom, average size of aggregates of similar to 315 nm. Thin films as prepared presented good dielectric characteristics: dielectric constant and dielectrics loss ( tan delta) at a frequency of 1 KHz were 220 and 0.2, respectively. The temperature dependence of dielectric constant exhibited a diffuse ferroelectric to paraelectric phase transition at about 0 - 10degreesC. The ferroelectric nature of Ce-doped BaTiO3 film was confirmed by the hysteresis of the C-V curves. (C) 2004 Kluwer Academic Publishers.
1293. Structural and magnetic properties of iron species/SiO2 nanocomposites obtained by sol-gel methods
Authors:
Predoi, D; Kuncser, V; Zaharescu, M; Keune, W; Sahoo, B; Valeanu, M; Crisan, M; Raileanu, M; Jitianu, A; Filoti, G
Published: 2004, SECOND SEEHEIM CONFERENCE ON MAGNETISM, PROCEEDINGS, 3510, DOI:
The phase composition, local structure and magnetic interactions were investigated in FexOx-SiO2 nanocomposites obtained by modern sol-gel methods. The very sensitive method of Mossbauer spectroscopy has evidenced the strong influence of the silica matrix precursor on the iron phase composition in the initial composites as well as on the size distribution of the hematite nanoparticles obtained by suitable thermal annealing treatments.
1294. Minority-spin band parameters in a NiMnSb thin film determined by spectral conductivity
Authors:
Grigorescu, CEA; Trodahl, HJ; Strickland, NM; Bittar, A; Manea, SA; Giapintzakis, J; Monnereau, O; Notonier, R; Kennedy, VJ
Published: DEC 1 2004, JOURNAL OF APPLIED PHYSICS, 96, 6424, DOI: 10.1063/1.1811779
NiMnSb is expected to be a ferromagnetic half metal, an expectation that is based in part on band structure calculations. Here we report optical conductivity studies of the band structure for a film prepared by pulsed laser deposition onto a Si substrate held at a relatively low temperature as is required for some device applications-films which are susceptible to site disorder associated with the vacant site in this half-Heusler compound. We demonstrate that the direct interband transitions are essentially unshifted in comparison with bulk material, though they are somewhat broadened. Below the direct-transition absorption edge we report the presence of indirect spin-reversing transitions between the Fermi energy (E-f) and the extrema of the minority-spin valence and conduction bands, providing a measure of the band edge energies. Both of these edges appear closer to E-f than is seen in well-ordered bulk NiMnSb, with the conduction-band minimum showing weight at only 200 cm(-1) above E-f, close enough to have substantial occupation at ambient temperature. (C) 2004 American Institute of Physics.
1295. Magnetic interactions and spin structure in composite Fe/Nd2Fe14B systems
Authors:
Kuncser, V; Valeanu, M; Lifei, F; Predoi, D; Palade, P; Schinteie, G; Crisan, O; Filoti, G
Published: MAY 2004, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272, 799, DOI: 10.1016/j.jmmm.2003.12.1279
Local magnetic interactions and spin configurations in alpha-Fe/Nd2Fe14B composite exchange-spring magnets have been investigated by Mossbauer spectroscopy and the magnetic behaviour was analysed by magnetometry. A new method for the evaluation of the coupling strength between soft and hard magnetic phases is proposed. (C) 2003 Elsevier B.V. All rights reserved.
1296. Hydrothermal synthesis and structural characterization of (1-x)alpha-Fe2O3-xSnO(2) nanoparticles
Authors:
Sorescu, M; Diamandescu, L; Tarabasanu-Mihaila, D; Teodorescu, VS; Howard, BH
Published: MAY 2004, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 65, 1029, DOI: 10.1016/j.jpcs.2003.10.062
Structural and morphological characteristics of (1 - x)alpha-Fe2O3-xSnO(2) (x = 0.0- 1.0) nanoparticles obtained under hydrothermal conditions have been investigated by X-ray diffraction (XRD), transmission Mossbauer spectroscopy, scanning and transmission electron microscopy as well as energy dispersive X-ray analysis. On the basis of the Rietveld structure refinements of the XRD spectra at low tin concentrations, it was found that Sn4+ ions partially substitute for Fe3+ at the octahedral sites and also occupy the interstitial octahedral sites which are vacant in alpha-Fe2O3 corundum structure. A phase separation of alpha-Fe2O3 and SnO2 was observed for x greater than or equal to 0.4 : the alpha-Fe2O3 Structure containing tin decreases simultaneously with the increase of the SnO2 phase containing substitutional iron ions. The mean particle dimension decreases from 70 to 6 DID, as the molar fraction x increases up to x = 1.0. The estimated solubility limits in the nanoparticle system (1 - x)alpha-Fe2O3-xSnO(2) synthesized under hydrothermal conditions are: x less than or equal to 0.2 for Sn4+ in alpha-Fe2O3 and x greater than or equal to 0.7 for Fe3+ in SnO2. (C) 2003 Elsevier Ltd. All rights reserved.
1297. High-T-c phase obtained in the Pb/Sb doped Bi-Sr-Ca-Cu-O system
Authors:
Fruth, V; Popa, M; Ianculescu, A; Stir, M; Preda, S; Aldica, G
Published: 2004, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 24, 1830, DOI: 10.1016/S0955-2219(03)00449-7
Partial replacement of Bi by Pb and Sb produces materials of high-T-c pure phase, with antimony playing an important role in accelerating the formation of the phase with the higher superconductive transition in the Bi-Sr-Ca-Cu-O system. The influence of the antimony precursors on the superconducting phases mechanism formation was examined. Using a solid state reaction route, two nominal compositions Bi(1.6)Pb(0.3)Sb(0.1)Sr(2)Ca(2)Cu(3)Oy and Bi(1.6)Pb(0.4)Sb(0.1)Sr(2)Ca(2)Cu(4)Oy were investigated. The sources of antimony were Sb2O3 alphaSb(2)O(4) and a prepared mixture Bi1.9Sb0.1Ox. The mechanism formation of the phases upon annealing was investigated using X-ray diffraction and simultaneous thermal analysis. Electrical properties of the obtained materials were evaluated. The presence of the antimony ions determined a higher reactivity of the system as well as the promotion of the superconducting high-T-c phase enhancement. (C) 2003 Elsevier Ltd. All rights reserved.
1298. Disorder effects on the properties of two-dimensional finite systems in perpendicular magnetic field: the tight binding approach
Authors:
Aldea, A; Nita, M; Dinu, V; Tolea, M
Published: JUL 2004, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 241, 2096, DOI: 10.1002/pssb.200404781
We review some aspects concerning the disorder effects on the spectral properties of 2D electronic systems with relevance for the transport and orbital magnetism in perpendicular magnetic field. The lattice model and random Anderson disorder are used. The discussion is carried out separately for periodic and hard wall boundary conditions. The degree of localization is evidenced by the calculation of the inverse participation number of the eigenstates of the Hamiltonian and a striking asymmetry of the localization effect of states in the Landau band is reported. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
1299. Conduction mechanisms in silicon-based nanocomposites
Authors:
Iancu, V; Draghici, M; Jdira, L; Ciurea, ML
Published: MAR 2004, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 6, 56, DOI:
Electrical conduction mechanisms in Si-SiO2 nanocomposite films were experimentally investigated and theoretically modelled. The films with silicon volume concentration varying from 0% to 100% were deposited on rectangular quartz substrates. They were prepared by co-sputtering CVD from two targets, one of silicon and one of silicon dioxide. Their middle part is formed by Si nanodots embedded in SiO2. 50 parallel aluminium electrodes were deposited, forming 49 coplanar samples, centred around x = 45% Si concentration. The microstructure investigations proved that the silicon nanodots have diameters between 4 nm (x = 23%) and 36 nm (x = 81%). The current-voltage characteristics were measured at room temperature, in the -25 divided by +25 V interval. The obtained curves are symmetric and superlinear. As the current - voltage characteristic is determined by the maximum resistance met by the carriers in their path, the experimental curve is modelled by the field-assisted tunnelling under Coulomb blockade. The used parameters are correlated with previous results obtained on nanocrystalline porous silicon. The correlation coefficient between the theoretical formula and the experimental data is greater than 99.95%.
1300. Mossbauer study of the RENiSnD (RE : Pr, Nd) monodeuterides
Authors:
Spataru, T; Principi, G; Kuncser, V; Keune, W; Yartys, VA
Published: MAR 10 2004, JOURNAL OF ALLOYS AND COMPOUNDS, 366, 85, DOI: 10.1016/S0925-8388(03)00744-8
NdNiSnD and PrNiSnD monodeuterides have been studied by Sn-119 Mossbauer spectroscopy at variable temperatures between 4.2 and 300 K. Deuterium insertion into the RE3Ni sites induces at low temperatures a magnetic splitting of the tin nuclear levels. Slightly different magnetic ordering temperatures, 25(1) and 20(1) K, were evidenced for the Nd- and Pr-containing deuterides, respectively. The Mossbauer spectra suggest a similar type of local structures for both compounds, with a mutual substitution of Sn and Ni atoms. The magnetic behaviour is discussed in relation to the different spin waves mechanisms. (C) 2003 Elsevier B.V. All rights reserved.
1301. Tunneling properties of quantum dot arrays in a strong magnetic field
Authors:
Moldoveanu, V; Aldea, A; Tanatar, B
Published: AUG 2004, PHYSICAL REVIEW B, 70, DOI: 10.1103/PhysRevB.70.085303
We study the transport properties of coherently coupled quantum dots in the quantum Hall regime within the Landauer-Buttiker formalism which captures and explains the experimentally observed features in terms of the spectral properties of the coupled dot system. The subpeak structure of the transmittance spectrum and the charging stability diagrams are obtained and discussed. The role of the intradot and interdot Coulomb interaction are pointed out. We show the subpeak evolution with the magnetic field and predict a specific oscillatory behavior of the Hall resistance in strong magnetic field which can be experimentally tested.
1302. Third harmonic ac susceptibility measurements in MgB2 bulk: frequency behavior of IL and 3D glass pinning analysis
Authors:
Di Gioacchino, D; Tripodi, P; Gambardella, U; Sandu, V; Popa, S; Miu, L; Vinko, D
Published: AUG 2004, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 408, 122, DOI: 10.1016/j.physc.2004.02.062
The third harmonics of the ac susceptibility chi(3) of MgB2 bulk samples have been measured in the frequency range 61-1070 Hz as a function of the temperature for different applied dc magnetic fields. The irreversibility line (T-irr versus H-dc) deduced from the temperature onsets of chi(3) for each field shows a frequency dependence: The onset temperature increases as the frequency increases. This frequency dependence has been analyzed using the 3D vortex-glass model. Moreover the real versus imaginary components of the chi(3) for each dc magnetic field have been interpreted with a 3D glass creep using a numerical analysis based on a non-linear diffusion equation of the magnetic field. (C) 2004 Elsevier B.V. All rights reserved.
1303. Poly (vinyl-alcohol) films for microphotonics
Authors:
Obreja, P; Cristea, D; Budianu, E; Gavrila, R; Kusko, M; Kuncser, V
Published: 2004, 16TH INTERNATIONAL CONFERENCE ON MICROELECTRONICS, PROCEEDINGS, 679, DOI:
The paper presents experimental results concerning the influence of additives from a solution of the PVA on the optical properties of the polymer. The refractive index of the poly (vinyl-alcohol) was modified through the addition of inorganic materials and showed values between 1.5 and 2 (depending on the compositions and the curing conditions of the polymer. The transmittance indicated values above 80%. The additives we used were metal oxides/inorganic salts. The composition and the deposition processes were optimized to allow a better control of the optical parameters (refractive index, transmittance), to reduce the processing temperatures and to improve photosensitivity. PVA with these new light-sensitive compositions can be easily spin coated onto variety of semiconductor substrate and directly patterned. A process was developed for channel waveguides fabrication.
1304. The first specimen of tetranuclear (Fe-III, Ln(III)) clusters assembled by carboxylate ligands: synthesis, structure, Mossbauer spectra, and magnetic properties of [Fe3EuO2(CCl3COO)(8)H2O(THF)(3)]center dot THF
Authors:
Turta, C; Prodius, D; Mereacre, V; Shova, S; Gdaniec, M; Simonov, YA; Kuncser, V; Filoti, G; Caneschi, A; Sorace, L
Published: APR 2004, INORGANIC CHEMISTRY COMMUNICATIONS, 7, 579, DOI: 10.1016/j.inoche.2004.02.025
The reaction of the neutral cluster [Fe2BaO(CCl3COO)(6)(THF)(6)] with Eu(NO3)(3) . 6H(2)O in methanol affords novel tetra-nuclear Fe-Eu complex [Fe3EuO2(CCl3COO)(8)H2O(THF)(3)] . THF (1), which displays interesting Mossbauer spectra and magnetic behaviour. (C) 2004 Elsevier B.V. All rights reserved.
1305. Carbon material deposition by remote RF plasma beam
Authors:
Mitu, B; Vizireanu, S; Petcu, C; Dinescu, G; Dinescu, M; Birjega, R; Teodorescu, VS
Published: MAR 1 2004, SURFACE & COATINGS TECHNOLOGY, 180, 243, DOI: 10.1016/j.surfcoat.2003.10.147
Hydrogenated and nitrogenated carbon films were obtained by PECVD with carbon species supplied by acetylene gas injected into an argon or argon/nitrogen remote plasma generated by an expanding radiofrequency discharge. The properties of carbon material like the nature of bonds, morphology, surface topography, crystallinity are presented. The reaction pathways linking the precursors with the depositing species, as revealed by emission spectroscopy, are discussed. (C) 2003 Elsevier B.V. All rights reserved.
1306. Spectroscopic bases for efficiency enhancement and power scaling of self-frequency. multiplication and self-sum-frequency mixing emission in Nd-doped nonlinear crystals
Authors:
Lupei, V; Aka, G; Petit, J; Vivien, D
Published: SEP 2004, JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, 21, 1629, DOI: 10.1364/JOSAB.21.001620
The possibility to enhance the self-nonlinear emission characteristics in Nd-activated nonlinear crystals by direct pumping into the emitting level F-4(3/2) is discussed. It is inferred that the reduction of threshold and the increase of the slope efficiency for the intracavity emission at the fundamental frequency caused by the reduction of quantum defect between the pump and the emitted quanta in the case of direct pumping are strongly amplified in the self-nonlinear processes. Moreover, the diminished heat generation could contribute to a more stable emission and to the scaling to a higher power. The possibility to use the direct pumping is determined by the spectroscopic properties of the laser material. This is illustrated for Nd3+ in Ca4GdO(BO3)(3), where, for direct pumping, the thermally activated transition I-4(9/2)(Z(2)) --> F-4(3/2)(R-1) at 887 nm is suitable. Pumping in this band induces an enhancement of the self-doubled emission power at 530 nm by similar to2.5 times for an absorbed power four to five times above threshold as compared with the 811-nm pumping into the level F-4(1/2) of Nd3+. (C) 2004 Optical Society of America.
1307. Field-effect transistor based on nanometric thin CdS films
Authors:
Mereu, B; Sarau, G; Pentia, E; Draghici, V; Lisca, A; Botila, I; Pintilie, L
Published: JUN 15 2004, MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 109, 263, DOI: 10.1016/j.mseb.2003.10.077
Cadmium sulphide (CdS) thin films were deposited by chemical bath deposition (CBD) method on SiC2/Si (n-type) substrates. Approximately, 70 nm thick nano-crystalline CdS layers were obtained. Thin film field effect transistors were realised by deposition of two coplanar electrodes of Au (drain and source) on the US surface. The gate contact is aluminium deposited on the backside of the Si substrate. The drain current-drain voltage characteristics (I-d - V-d) were performed in dark. Normal field effect transistor characteristics are obtained in case of positive gate and drain voltages, the device acting as an n-channel transistor in the accumulation mode. For negative drain voltages the characteristic is dominated by space charge limited currents (SCLC). An on/off current ratio of about 10(2) is reported, this being limited in our case by geometry. (C) 2003 Elsevier B.V. All rights reserved.
1308. Magnetic interactions and spin configuration in FeRh and Fe/FeRh systems
Authors:
Kuncser, V; Keune, W; Sahoo, B; Duman, E; Acet, M; Radu, F; Valeanu, M; Crisan, O; Filoti, G
Published: MAY 2004, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272, 350, DOI: 10.1016/j.jmmm.2003.11.199
The magnetic interactions and the Fe spin structure have been studied in Fe(6 nm)/FeRh systems by magnetometry, magneto-optic Kerr effect and conversion electron Mossbauer spectroscopy. A spin-flop coupling mechanism, with the interfacial spins of the ferromagnetic phase perpendicular to the spins of the antiferromagnetic phase was experimentally proved. (C) 2004 Elsevier B.V. All rights reserved.
1309. Piezoelectric and optical properties of Sr-doped PT-PZ-Pb(Mg1/3Nb2/3)O-3 ceramics
Authors:
Dimitriu, E; Ramer, R; Ghica, C; Iuga, A; Ghiordanescu, V
Published: 2004, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 24, 1708, DOI: 10.1016/S0955-2219(03)00478-3
Ceramics in the ternary system (Pb,Sr)TiO3-PbZrO3-Pb(Mg1/3Nb2/3)O-3, in the ratio 85.976/5.817/8.207 mol%, was prepared by mixed oxide route. With about 13.98 at % Sr+2, as isovalent substitution in A-position of the lead titanate, high-density samples were obtained for the sintering temperatures of about 1220 and 1230 degreesC. Tetragonal phases were identified both by XRD method and selected area electron diffraction pattern (SAED). The lattice parameter ratio, c/a, of about 1.017 indicated a decrease of tetragonal distortion. The typical TEM micrographs showed domains of about 50 nm wide. The reflection spectra were recorded to prove the presence of the transition Ti+4 to Ti+3. The principal mechanical, electrical and electromechanical properties were discussed as a function of the sintering temperature. The variation of the relative constant with the temperature and frequency evidenced a relaxation-like behavior of this ternary system. By combining the ferroelectric and relaxor end member we tried to improve the piezoelectric properties of a ceramic with a high content of lead titanate, and to achieve a material with both piezoelectric and relaxor-like properties. (C) 2003 Elsevier Ltd. All rights reserved.
1310. Microstructure of Si/Sio(2) nanocomposite films
Authors:
Teodorescu, VS; Ciurea, ML; Iancu, V; Blanchin, MG
Published: 2004, 2004 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1AND 2, PROCEEDINGS, 62, DOI: 10.1109/SMICND.2004.1402802
The paper presents the inicrostructure of the Si/SiO2 nanocomposite films prepared by co-sputtering from Si and SiO2 targets. High resolution transmission electron microscopy and electron diffraction were used to reveal and compare the structures with different silicon/oxygen (SiOx, 0 < x < 2) coinposition. Si nanocrystallites have been evidenced clearly in the SiO1.6 areas. Percolation limits between the Si crystallites was observed in the x=1 areas. The morphology of the Si nanocrystallites and the amorphous SiO2 zones were compared in regions with different composition.
1311. Optical and electronic properties of polyvinyl alcohol doped with pairs of mixed valence metal ions
Authors:
Bulinski, M; Kuncser, V; Plapcianu, C; Krautwald, S; Franke, H; Rotaru, P; Filoti, G
Published: SEP 7 2004, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 37, 2441, DOI: 10.1088/0022-3727/37/17/015
The electronic mechanisms induced by the UV exposure of thin films of polyvinyl alcohol doped with pairs of mixed valence metal ions were studied in relation to their optical behaviour by Mossbauer spectroscopy and optical absorption. The results obtained definitely point to the role of each element from the pair in the electronic mechanism involved, with influence on the optical properties regarding applications in real-time holography and integrated optics.
1312. Epoxidation of cyclohexene on silicalite embedded BiOx clusters
Authors:
Parvulescu, VI; Florea, M; Gelbard, G; Centeno, MA; Macovei, D; Lemay, G; Kaliaguine, S
Published: 2004, RECENT ADVANCES IN THE SCIENCE AND TECHNOLOGY OF ZEOLITES AND RELATED MATERIALS, PTS A - C, 154, 2654, DOI:
Silicalite embedded BiOx Clusters were prepared both with and without Na using sodium silicate and tetraethylorthosilicate as silicium precursors. Catalysts with 3 and 5 wt% Bi were obtained. The MFl structure was established from XRD, TEM, and N-2 adsorption measurements. No deterioration of the silicalite framework by bismuth was observed. Bi exists as BiOx clusters as evidenced from XPS and EXAFS characterization. These clusters are localized inside the silicalite channels. Py-FTIR measurements indicated that 5wt% Bi led to the formation of strong Lewis acid sites. Epoxidation of cyclohexene was found to depend oil both Bi and Na content. On 3%Bi-ZSM-5 it occurred with rather good conversion and selectivity to epoxide. No visible leaching was evidenced. The catalysts were reused for several runs.
1313. Deposition of hydroxyapatite thin films by Nd : YAG laser ablation: a microstructural study
Authors:
Nistor, LC; Ghica, C; Teodorescu, VS; Nistor, SV; Dinescu, M; Matei, D; Frangis, N; Vouroutzis, N; Liutas, C
Published: NOV 2 2004, MATERIALS RESEARCH BULLETIN, 39, 2101, DOI: 10.1016/j.materresbull.2004.07.006
Hydroxyapatite (HA) thin films has been successfully deposited by Nd:YAG laser ablation lambda = 532 nm. The morphology and microstructure of the deposited layers was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). Polycrystalline HA films were directly obtained with the substrate at 300 degreesC and without introducing water vapors in the deposition chamber. Electron paramagnetic resonance (EPR) measurements show that the oxygen stoichiometry in the HA films is also maintained. Depositions performed at lambda = 335 nm laser wavelength and 300 degreesC substrate temperature resulted in polycrystalline layers of mixed composition of HA and tricalciumphosphate (TCP). (C) 2004 Elsevier Ltd. All rights reserved.
1314. Spin magnetization of a strongly correlated electron gas confined in a two-dimensional finite lattice
Authors:
Nita, M; Dinu, V; Aldea, A; Tanatar, B
Published: FEB 2004, PHYSICAL REVIEW B, 69, DOI: 10.1103/PhysRevB.69.073106
The influence of disorder and interaction effects on the ground state polarization of the two-dimensional correlated electron gas is studied by numerical investigations of the unrestricted Hartree-Fock approach. With the model of Anderson disorder a continuous increase of the spin magnetization until the fully polarized regime is obtained. The ferromagnetic ground state is found to be favorable when the electron number is lowered and the interaction and disorder parameters are suitably chosen.
1315. FexCu1-x alloys for permanent magnets
Authors:
Kappel, W; Codescu, MM; Pasuk, I; Patroi, E; Kuncser, V; Valeanu, M; Predoi, D; Filoti, G
Published: SEP 2004, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 6, 978, DOI:
New magnetic composite materials, ribbon samples, with nominal compositions FexCu1-x (x=0.2; 0.5; 0.8) were obtained by the melt spinning technique. Various information was provided via X-ray diffraction, Mossbauer and magnetic measurements. The structural aspects: phase composition, size and texture effects, have been corroborated with magnetic properties. Finally, the possibility to choose the adequate composition and the suitable processing in order to obtain desired anisotropic magnetic materials were presented.
1316. Second harmonic generation at the GaAs(111)-B|solution interface
Authors:
Lazarescu, V; Lazarescu, MF; Jones, H; Schmickler, W
Published: JUN 15 2004, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 567, 261, DOI: 10.1016/j.jelechem.2003.12.035
Second harmonic generation from the interface between GaAs(111)-B and an aqueous electrolyte has been investigated at a long wavelength (1064 nm) and at two shorter ones (865 and 815 nm). The signal showed the symmetry of the crystal; the isotropic amplitude was found to vary substantially with the electrode potential, indicating that a major part of the signal is generated near the interface. The potential dependence was stronger at shorter wavelengths. Impedance spectroscopy revealed the existence of surface states, which may affect the magnitude of the signal. (C) 2004 Elsevier B.V. All rights reserved.
1317. Second harmonic generation and impedance spectroscopy at n-GaAs(100) electrodes
Authors:
Lazarescu, V; Lazarescu, MF; Santos, E; Schmickler, W
Published: SEP 30 2004, ELECTROCHIMICA ACTA, 49, 4238, DOI: 10.1016/j.electacta.2004.04.017
Second harmonic generation from n-GaAs(100) electrodes in sulfuric acid solution has been investigated at an incident wavelength of 1064 nm over a potential range where Faradaic processes are excluded. In the p-in/p-out polarization configuration, the rotational anisotropy in the nonlinear response was found to depend both on the doping level and the applied potential. The effects of the applied potential on the isotropic amplitude of the SHG signal turned out to be closely related to the population of surface states as revealed by impedance spectroscopy, indicating that these states could play a significant role in second harmonic generation. (C) 2004 Elsevier Ltd. All rights reserved.
1318. Nanocrystalline rhombohedral In2O3 synthesized by hydrothermal and postannealing pathways
Authors:
Sorescu, M; Diamandescu, L; Tarabasanu-Mihaila, D; Teodorescu, VS
Published: JAN 15 2004, JOURNAL OF MATERIALS SCIENCE, 39, 677, DOI: 10.1023/B:JMSC.0000011529.01603.fc
1319. Effect of Li2CO3 addition on the Bi1.7Pb0.4Sr1.5Ca2.5CU3.6Ox superconducting system
Authors:
Mihalache, V; Aldica, G; Popa, S; Lifei, F; Miu, D
Published: SEP 2004, MATERIALS LETTERS, 58, 3044, DOI: 10.1016/j.matlet.2004.05.037
We have investigated the effect of Li2CO3 addition on the transport and magnetic properties of Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox, samples in connection with the structural changes observed by scanning electronic microscopy (SEM) and X-ray diffraction. In addition to the results reported in literature, we have extracted new information from the magnetic hysteresis loops and AC susceptibility measurements. One such information is the splitting of the AC loss peak corresponding to the dissipation inside the Bi-2223 grains. The results reported here have been compared with those obtained for Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox/(LiF)(y) and Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox/(LiCl)(y) specimens, and the effect of halogen is pointed out. (C) 2004 Elsevier B.V. All rights reserved.
1320. Synthesis and piezoelectric properties of nanocrystalline PZT-based ceramics prepared by high energy ball milling process
Authors:
Miclea, C; Tanasoiu, C; Gheorghiu, A; Miclea, CF; Tanasoiu, V
Published: AUG-SEP 2004, JOURNAL OF MATERIALS SCIENCE, 39, 5434, DOI: 10.1023/B:JMSC.0000039260.82430.f9
Nanocrystalline powders of a soft FeNbLi-doped PZT material have been prepared by a novel mechanochemical process consisting of mixing the stoichiometric oxides in a planetary ball mill for prolonged times up to 80 h. The constituent oxides were reacted in a tungsten carbide vial with balls of 5, 10 and 20 mm in diameter and a ball/powder ratio of 15/1. The chemical reaction between the component oxides was triggered after 20 h of energetic milling and was completed after 80 h. The XRD of the reacted nanopowder showed the well known perovskite structure. Compacted samples of this powder were sintered between 800-1300degreesC for 3 h and the main piezoelectric properties were determined. The density of the sintered samples reached nearly 99% of the theoretical density at 1100degreesC and showed good piezoelectric characteristics: planar coupling factor of 0.66, dielectric displacement constant d(33) of 550 pm/V, mechanical quality factor of 85, and relative dielectric constant of 3800. The possible mechanisms for solid state reaction of mechanically activated nanopowders such as local heating and pressure at collision as well as defects diffusion are discussed. (C) 2004 Kluwer Academic Publishers.
1321. Emission properties of T-a-centres in KCl
Authors:
Topa, V; Tsuboi, T; Polosan, S
Published: AUG-DEC 2004, RADIATION MEASUREMENTS, 38, 734, DOI: 10.1016/j.radmeas.2004.01.021
Electrolytic colouration at about 600degreesC and 350 V/cm, for KCl crystal containing Pb2+ and for KCl:Pb2+ crystals co-doped with Li+, Na+ and Rb+ has been undertaken. Several absorption bands were observed in both doped and co-doped crystals in the visible-UV region. Excitation into these bands gives rise to the same 0.86 eV emission band except for the Li+-co-doped crystal which gives rise to a 0.80 eV emission band. These absorption bands are due to the same T-a-centre related to Pb-. The observed infrared emission intensity of the crystal with F-centres is higher than of without F-centres. (C) 2004 Elsevier Ltd. All rights reserved.
1322. Effects of Zr and Ti substitutions on the crystallization processes of Fe3B/Nd2Fe14B nanocomposite magnetic system
Authors:
Jianu, A; Valeanu, M; Lazar, DP; Lifei, F; Bunescu, C; Pop, V
Published: MAY 2004, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272, 1494, DOI: 10.1016/j.jmmm.2003.12.1005
The influence of Zr and Ti substitutions on the formation of a nanocomposite magnet was studied by high-temperature X-ray diffraction and magnetic measurements. It has been shown that Ti and especially Zr additions favorably change the crystallization temperatures and the sequence of phase transformations which leads to an exchange coupled magnet, even in a composition range that promotes the precipitation of the detrimental Nd2Fe23B3 phase. (C) 2003 Elsevier B.V. All rights reserved.
1323. Structural, electrical, and photoelectrical properties of CdxPb1-xS thin films prepared by chemical bath deposition
Authors:
Pentia, E; Draghici, V; Sarau, G; Mereu, B; Pintilie, L; Sava, F; Popescu, M
Published: 2004, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 151, G733, DOI: 10.1149/1.1800673
CdxPb1-xS (0 less than or equal to x less than or equal to 1) thin films were prepared on glass substrates using the chemical bath deposition method. The structural, electrical, and photoelectrical properties of the films were investigated, and all were dependent on the x value. For x > 0.5 (high Cd content), the films show a poor crystallinity and weak photoconductivity. For x < 0.5 (high Pb content), the films exhibit a good crystallinity, with an average size of the crystallites of 100 nm, and good photoconductivity. The threshold voltage of photoconductivity is shifted to lower wavelengths with increasing Cd content. The experimental results point toward possible ternary deposition on some composition ranges (near pure PbS or CdS); whereas, for the rest, the deposited film is rather a mixture of phases [not CdxPb1-xS but (CdS)(x)(PbS)(1-x)]. (C) 2004 The Electrochemical Society.
1324. Monte Carlo simulation study of magnetic behaviour of core-shell bimetallic nanoparticles
Authors:
Crisan, O; Tornau, EE; Petrauskas, V; Angelakeris, M
Published: 2004, SECOND SEEHEIM CONFERENCE ON MAGNETISM, PROCEEDINGS, 3763, DOI: 10.1002/pssc.200405549
The magnetic properties of core-shell-type nanoparticles with non-magnetic core and ferromagnetic shell are modeled using Monte Carlo simulation. The influence of the surface spin disorder on the magnetization and Curie temperature of magnetic states is studied. Due to competition between exchange coupling and surface anisotropy, rotation of the magnetization axis is observed, as the surface anisotropy of the ferromagnetic shell is increased. It is shown that the exchange coupling at the core-shell interface can influence the shape of the temperature dependence of total magnetization. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1325. Orbital magnetization of single and double quantum dots in a tight-binding model
Authors:
Aldea, A; Moldoveanu, V; Nita, M; Manolescu, A; Gudmundsson, V; Tanatar, B
Published: JAN 15 2003, PHYSICAL REVIEW B, 67, DOI: 10.1103/PhysRevB.67.035324
We calculate the orbital magnetization of single and double quantum dots coupled both by Coulomb interaction and by electron tunneling. The electronic states of the quantum dots are calculated in a tight-binding model, and the magnetization is discussed in relation to the energy spectrum and to the edge and bulk states. We identify effects of chirality of the electronic orbits and of the anticrossing of the energy levels when the magnetic field is varied. We also consider the effects of detuning the energy spectra of the quantum dots by an external gate potential. We compare our results with the recent experiments of Oosterkamp [Phys. Rev. Lett. 80, 4951 (1998)].
1326. Isolated nanocrystals of indium in KCl crystals
Authors:
Polosan, S; Apostol, E; Vasile, E; Topa, V
Published: SEP 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 704, DOI:
Metal nanoparticles embedded in KCl crystals exhibit different forms and distributions, depending on the type of metal. The nanoparticles can be efficiently studied by optical absorption on these structures, calculated from Mie theory and comparison with Transmission Electron Mmicroscopy (TEM) measurements. The TEM images provide the detailed characteristics of the structures under study. Metal crystalline particle obtained by thermal treatments of negative indiurn ions are spherical. The particle size distribution was determined, the standard deviation was found 1.46, and the main statistical characteristics were calculated.
1327. Magnetic properties of gamma-Fe2O3 nanoparticles
Authors:
Predoi, D; Kuncser, V; Nogues, M; Tronc, E; Jolive, JP; Filoti, G; Schinteie, G
Published: MAR 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 216, DOI:
The gamma-Fe2O3 nanoparticles with different surface states are investigated by X-ray Diffraction, Electron Microscopy, Differential Thermal Analysis and magnetic: measurements in low applied field. The influence of the adsorbed species (H2O and sulphate complexes) on the inter-particle magnetic interactions is analysed in relation to both the magnetic states of the surface and the inter-particle distance.
1328. Densification of In2O3: Sn multilayered films elaborated by the dip-coating sol-gel route
Authors:
Daoudi, K; Canut, B; Blanchin, MG; Sandu, CS; Teodorescu, VS; Roger, JA
Published: NOV 24 2003, THIN SOLID FILMS, 445, 25, DOI: 10.1016/S0040-6090(03)01061-7
Indium Tin Oxide (ITO) thin films have been deposited by the Sol-Gel Dip-Coating technique, the starting solutions being prepared from chlorides. These multilayered films were crystallized by means of a classical heat treatment at temperatures ranging from 500 to 600 degreesC. Five stacked layers are necessary to obtain a global electrical resistivity value of 2.9 x 10(-3) Omega cm, for 500 degreesC annealed film. The paper focuses on the study of the structure of such multilayered deposits, and on the densification process, using transmission electron microscopy, Rutherford Back-scattering Spectrometry and electrical resistivity measurements. This analysis reveals structural inhomogeneities and different crystallite growth processes as a function of annealing temperature and number of deposited layers. (C) 2003 Elsevier B.V. All rights reserved.
1329. Surface particularities in pulsed laser ablation/deposition of the ferromagnetic alloy NiMnSb
Authors:
Grigorescu, CEA; Manea, SA; Mitrea, M; Monnereau, O; Notonier, R; Tortet, L; Keschawarz, R; Giapintzakis, J; Klini, A; Zorba, V; Androulakis, J; Fotakis, C
Published: MAY 15 2003, APPLIED SURFACE SCIENCE, 212, 84, DOI: 10.1016/S0169-4332(03)00404-5
In this work we investigate the surface morphology and stoichiometry of the ablated targets employed with pulsed laser deposition (PLD) of thin films of the ferromagnetic half-Heusler alloy NiMnSb. The NiMnSb targets were: a pressed and sintered pellet and, respectively, polycrystalline discs grown by RF melting. The films were deposited using a KrF excimer laser (lambda = 248 nm, tau = 30 ns, 600 mJ/pulse maximum) delivering pulses at a repetition rate of 10 Hz. SEM observations show different morphologies of the ablated surfaces in the two cases, which are further correlated with EDX analyses to explore surface segregation phenomena. The corresponding films are also considered. Apparently, the crystalline targets keep better the initial stoichiometry than the pressed ones, which in principle would indicate higher film stoichiometry and hence enhanced quality. (C) 2003 Elsevier Science B.V. All rights reserved.
1330. Structure and properties of high-temperature annealed CVD diamond
Authors:
Ralchenko, V; Nistor, L; Pleuler, E; Khomich, AV; Vlasov, I; Khmelnitskii, R
Published: OCT-NOV 2003, DIAMOND AND RELATED MATERIALS, 12, 1970, DOI: 10.1016/S0925-9635(03)00214-0
Effects of high temperature, up to 1700 degreesC, annealing in vacuum of CVD diamond on its structure, optical and mechanical properties are investigated. Translucent polycrystalline diamond films of thickness 0.06-1.0 mm were grown by microwave plasma CVD method, and examined with transmission electron microscopy, optical absorption spectroscopy, and three-point bending technique to measure the fracture strength. A progressive darkening of the samples, with appearance of absorption features specific for graphite-like material, was observed upon annealing at temperatures above 1300 degreesC. The formation along grain boundaries of amorphous carbon and/or well crystallized graphite layers, 5-20 nm thick, as well as intra-granular graphite islands, was directly observed with TEM. This internal diamond-graphite transformation process can be described by two activation energies, both values being much less than those known for the surface graphitization of diamond. The fracture strength of the diamond films increases up to 50% with annealing temperature (1460-1640 degreesC), this being ascribed to a build up of compressive stress as a result of local diamond-graphite conversion. (C) 2003 Elsevier Science B.V. All rights reserved.
1331. Transport and magnetic properties of Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox/(LiCl)(y) superconductors
Authors:
Mihalache, V; Aldica, G; Popa, S; Miu, D
Published: JUN 2003, JOURNAL OF SUPERCONDUCTIVITY, 16, 580, DOI: 10.1023/A:1023837508196
We investigated the superconducting critical temperature, the intra- and intergranular critical current density, and the thermopower properties of Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox/(LiCl)(y) samples. All these properties have been compared with those of Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox/(LiF)(y) specimens. It was found that the critical temperature determined from resistive and AC complex susceptibility measurements show a maximum and the transition width shows a minimum for the intermediate values of y. Powder X-ray diffraction studies and the AC complex susceptibility measurements reveal that in our samples the amount of Bi2Sr2Ca2Cu3O10+delta high-temperature superconducting phase is maximum for y approximate to 0: 02: The amount of LiCl in Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox/(LiCl)(y) changes the superconducting properties of the grains as well as of the intergrain matrix. The splitting of the peak in the temperature dependence of the imaginary part of the complex susceptibility, corresponding to the dissipation inside the grains, was also observed.
1332. Modeling of optical charging spectroscopy investigation of trapping phenomena in nanocrystalline porous silicon
Authors:
Iancu, V; Ciurea, ML; Draghici, M
Published: JUL 1 2003, JOURNAL OF APPLIED PHYSICS, 94, 223, DOI: 10.1063/1.1576301
A model for trapping phenomena in nanocrystalline silicon investigated by the optical charging spectroscopy method is proposed. The model takes into account all the possible contributions to the discharge current. The results previously obtained on fresh and passivated porous silicon samples are interpreted within the framework of the model, which provides a good fit to the experimental data. The role played by the different kinds of trapping centers (donors and acceptors, surface and bulk) and the different trap parameters is analyzed. (C) 2003 American Institute of Physics.
1333. Densification and crystallization of SnO2 : Sb sol-gel films using excimer laser annealing
Authors:
Sandu, CS; Teodorescu, VS; Ghica, C; Canut, B; Blanchin, MG; Roger, JA; Brioude, A; Bret, T; Hoffmann, P; Garapon, C
Published: MAR 15 2003, APPLIED SURFACE SCIENCE, 208, 387, DOI: 10.1016/S0169-4332(02)01412-5
We have successfully applied laser annealing to sol-gel deposited SnO2:Sb thin films in order to achieve their crystallization. The as-deposited films are quasi-amorphous and electrically non-conductive. After laser annealing they crystallize and become conductive. This paper presents a comparative study of the laser annealed films and shows the influence of the irradiation parameters on the crystallization process and the electrical behavior of the films. Our results are quite promising in view of applying this kind of treatment to films deposited on thermally sensitive substrates (e.g. polymers). (C) 2002 Elsevier Science B.V. All rights reserved.
1334. Intensification of synthesis and examination of technological parameters influence on the properties and structure of Bi-(Pb)-Sr-Cu-Ca-O ceramics (vol 384, pg 111, 2003)
Authors:
Yurchenko, IA; Alekseev, AF; Yurchenko, DO; Badica, P; Gridasova, TY; Morozov, VV; Nemirovsky, AV; Peklun, VF
Published: MAY 15 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 387, 420, DOI: 10.1016/S0921-4534(03)00703-2
1335. Magnetic properties of Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox/(LiF)(y) superconducting system
Authors:
Mihalache, V; Aldica, G; Popa, S; Crisan, A
Published: FEB 15 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 384, 457, DOI: 10.1016/S0921-4534(02)02018-X
AC complex susceptibility (with and without a superimposed DC field) and DC magnetization measurements on (Bi,Pb)-2223 high-temperature superconductors with various amounts of LiF are presented. The results are discussed in the frame of the critical state model. The values of the intra- and inter-granular critical current density as well as of fields for full penetration are estimated. It can be seen that, in Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox/(LiF)(y), various amounts of LiF change the superconducting properties of both the grains and the inter-grain matrix. The intra-granular critical current density has similar values from both AC susceptibility and DC magnetization measurements, its highest value being attained for y = 0.15. For all LiF-doped samples, a split of the peak corresponding to the dissipation in the grains was observed. (C) 2002 Elsevier Science B.V. All rights reserved.
1336. Dynamic correlation effects on the plasmon dispersion in a two-dimensional electron gas
Authors:
Yurtsever, A; Moldoveanu, V; Tanatar, B
Published: MAR 15 2003, PHYSICAL REVIEW B, 67, DOI: 10.1103/PhysRevB.67.115308
The charge-density oscillations (plasmons) of a low-density two-dimensional uniform electron gas are studied within the framework of finite temperature and frequency dependent (dynamic) version of Singwi, Tosi, Land, and Sjolander theory and compared with the recent experimental results. The use of the Hartree-Fock approximation for the static structure factor leads to a finite temperature dynamical counterpart of the static Hubbard approximation. We observe important differences between dynamic and static local-field factors as well as between the corresponding plasmon dispersion laws. Our calculated plasmon energies that include dynamic correlations are in very good agreement with the recent experimental results.
1337. Numerical simulations of the backscattering from a crystalline lattice
Authors:
Ciobanu, A; Babin, V; Nicolae, DN; Talianu, C; Morosanu, C
Published: SEP 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 660, DOI:
The backscattering of 100, 300, and 500 eV Ar atoms from the {100} and {110} planes of a Al crystalline target is investigated with a computer code based on the Molecular Dynamics(MD) method. The interactions between particles are described by a screened Coulomb type potential. The angular (both azimuthal and radial) distribution of the backscattered particles together with the distribution of the energy and of the energy loss of scattered particles are calculated using the Lindhard-Scharff parameterization. The azimuthal distribution shows high peaks for 300 and 500 eV incident energies and a cvasi-continuum for 100 eV incident energy in the case of {100} plane, and a single peak for the {110} plane. The radial. distribution of backscattered particles evidences the symmetry properties of the crystal. The relative energy loss decrease when increasing incident energy, and is compatible with the backscattered energy distribution. The results do not agree with the Binary Collision Approximation(BCA).
1338. Bar-configuration in hall measurements with GaAs
Authors:
Ghita, RV; Logofatu, C; Negrila, C; Lazarescu, MF; Manea, AS; Ciupina, V
Published: MAR 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 363, DOI:
The electrical and transport properties of GaAs crystals such as resistivity (rho), mobility (mu) and carrier concentration (n) depend on the purity and defects of a particular crystal. These parameters are normally obtained by performing a simple Hall effect analysis in a bar configuration. The technical procedure is connected with the design of appropriate contacts for Hall bar configuration. In order to ensure good ohmic contacts oil GaAs, thin metal layers of Au-Ge-Ni have been deposited in high vacuum followed by heat treatment in low vacuum. Hall effect measurement is important for checking the quality of the GaAs wafers. We analyzed various GaAs wafers with (100) and (110), orientation obtained by LEC and HB methods. The resistivity of the wafers varied from low resistivity, n-type doped crystals (n = 10(18) cm(-3)), to high resistivity crystals (n = 10(14) cm(-3)). This paper presents the data of Hall characterization of wafers cut from GaAs crystals grown by different methods (LEC, HB).
1339. Raman spectroscopy of amorphous carbon modified with iron
Authors:
Yastrebov, SG; Ivanov-Omskii, VI; Dumitrache, F; Morosanu, C
Published: 2003, SEMICONDUCTORS, 37, 476, DOI: 10.1134/1.1568471
Raman spectroscopy has been employed to study spectra of the vibrational frequencies of carbon in the range 1000-1800 cm(-1) in amorphous carbon films modified with iron. The content of iron in a film has been set technologically by varying between the samples the area ratio of the graphite and iron parts of the target and monitored by Rutherford backscattering. Amorphous carbon layers containing 3, 26, 38, and 54 at. % iron have been obtained. The Raman spectra have the form of a broad band with features that are characteristic of amorphous carbon and lie at 1332 cm(-1) (D-band) and 1552 cm(-1) (G-band). At iron content of 38 and 54 at. %, the spectrum breaks up into a number of bands, which points to fragmentation of the matrix of amorphous carbon with increasing iron content. It is shown that the integral amplitude of scattering decreases nonlinearly with increasing iron content in a sample. The effect is analyzed in terms of a model that accounts for the linear dependence of the rate at which the number of atoms contributing to the scattering changes with the atomic fraction of carbon relative to the total number of carbon atoms in the film. (C) 2003 MAIK "Nauka/Interperiodica".
1340. Easy axis distribution in modern nanoparticle storage media: A new methodological approach
Authors:
Kuncser, V; Keune, W; Vopsaroiu, M; Bissell, PR; Sahoo, B; Filoti, G
Published: MAR 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 226, DOI:
Easy axis distribution in metal particle magnetic tapes for linear digital data storage were studied by Mossbauer spectroscopy and magnetometry, for comparison. Qualitative and quantitative agreement between the distribution parameters deduced at room temperature via the two different techniques was found. The proposed methodology based on the interpretation of the Mossbauer data has the advantage that it can be applied at different temperatures and for very thin films. Moreover, angular spin distribution. at low temperatures were obtained by Mossbauer spectroscopy and discussed with respect to the room temperature results. There was evidenced that the room temperature easy axis angular distribution contains both static orientation and dynamical components.
1341. Intensification of synthesis and examination of technological parameters influence on the properties and structure of Bi-(Pb)-Sr-Cu-Ca-O ceramics
Authors:
Yurchenko, IA; Alekseev, AF; Yurchenko, DO; Badica, P; Gridasova, TY; Morozov, VV; Nemirovsky, AV; Peklun, VF
Published: JAN 15 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 384, 124, DOI: 10.1016/S0921-4534(02)01804-X
Application of active technology factors (for example, the introduction of Bi2Sr2Ca2CU3Oy, (2223) phase additive) and corresponding optimization of synthesis parameters of Bi(Pb)-Sr-Ca-Cu-O (BSCCO) ceramics have allowed reducing the time of oxide precursor sintering from 250 to 25 h. Conditions of positive influence of 2223 phase additives have been investigated. Intensification of BSCCO ceramics synthesis was the basic purpose, but the authors have deliberately conducted broader examinations of the influence of technological parameters on the properties and structure of this material. The complex of the obtained effects (similarly to the solution of an equation set with several unknowns) helps increasing the probability of exact comprehension of the system: technology-processes occurring under ceramics synthesis-phase composition and structure-properties of BSCCO. (C) 2002 Elsevier Science B.V. All rights reserved.
1342. Microstructure and mechanical properties of hydroxyapatite thin films grown by RF magnetron sputtering
Authors:
Nelea, V; Morosanu, C; Iliescu, M; Mihailescu, IN
Published: AUG 22 2003, SURFACE & COATINGS TECHNOLOGY, 173, 322, DOI: 10.1016/S0257-8972(03)00729-1
Hydroxyapatite (HA) thin films for applications in bone prosthesis fabrication were obtained by the radio-frequency magnetron sputtering technique. The depositions were performed from pure HA targets on Si and Ti-5AI-2.5Fe alloy substrates. In some experiments a buffer layer of TiN was introduced by pulsed laser deposition before HA coating. The films were deposited in low-pressure argon or Ar-O-2 mixtures at substrate temperatures ranging from 70 to 550 degreesC. We observed that the films grown at temperatures below 300 degreesC were prevalently amorphous and contain a small amount of crystalline material. The initial crystalline structure of the target is reconstructed after 1 h films annealing at 550 degreesC in ambient air. Both the films directly deposited at 550 degreesC and the ones obtained at room temperature and after that annealed at this temperature-mostly contain the HA phase and exhibit good mechanical characteristics. Weaker peaks of CaO secondary phase are visible in the X-ray diffraction patterns of the films directly grown at 550 degreesC. Traces of TiO2 were detected at the interface with the metallic substrate in case of structures grown without the TiN interlayer. All films were smooth, with an average surface roughness of 50 nm. The films grown on TiN interlayer are harder, have higher elasticity modulus values and an increased mechanical resistance at the indenter penetration. (C) 2003 Elsevier Science B.V. All rights reserved.
1343. Coupled confinement effect on the photoluminescence and electrical transport in porous silicon
Authors:
Ciurea, ML; Draghici, M; Iancu, V; Reshotko, M; Balberg, I
Published: MAY 2003, JOURNAL OF LUMINESCENCE, 102, 497, DOI: 10.1016/S2313(02)00589-6
In this paper we report correlations between the structure, the photoluminescence and the transport properties of luminescent porous silicon. These correlations combined with the observed temperature dependence of tunneling characteristics yield quite a wholesome (pea-pod-like) model for this system. (C) 2002 Elsevier Science B.V. All rights reserved.
1344. Preparation and structural investigation of epitaxially grown antiferromagnetic FeSn2(001) thin films on InSb(001)
Authors:
Kuncser, V; Doi, M; Sahoo, B; Stromberg, F; Keune, W
Published: SEP 1 2003, JOURNAL OF APPLIED PHYSICS, 94, 3581, DOI: 10.1063/1.1595144
Antiferromagnetic FeSn2(001) thin films with different thicknesses and relatively low Neel temperatures were grown on InSb(001)(4x2) surfaces by molecular-beam epitaxy. The Neel temperature could be increased to above room temperature by subsequent thermal annealing. In situ structural characterization was performed by high- and low-energy electron diffraction. The degree of the structural (001) texture as a function of the preparation and annealing conditions was investigated by x-ray diffractometry. The local magnetic properties and the spin structure were studied using Fe-57 conversion electron Mossbauer spectroscopy (CEMS) at different temperatures. The epitaxial FeSn2(001) thin films exhibit in-plane Fe spin orientation and appear to be suitable antiferromagnets for studying the interfacial spin structure in exchange-biased bilayers by CEMS. (C) 2003 American Institute of Physics.
1345. Morphology, structure and optical properties of sol-gel ITO thin films
Authors:
Stoica, TF; Teodorescu, VS; Blanchin, MG; Stoica, TA; Gartner, M; Losurdo, M; Zaharescu, M
Published: AUG 15 2003, MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, 101, 226, DOI: 10.1016/S0921-5107(02)00667-0
The alkoxidic route and the spinning deposition were used to prepare monolayer sol-gel indium tin oxide (ITO) films. The morphology and crystalline structure were investigated by cross-section transmission electron microscopy (XTEM) and atomic force microscopy (AFM). The ITO sol-gel mono-layer contains three regions of different porosities. The basic crystalline structure is that of the In2O3 lattice. The optical properties have been studied by optical transmission and spectroscopic ellipsometry. (C) 2003 Elsevier Science B.V. All rights reserved.
1346. Many-body effects in the Coulomb drag between low density electron layers
Authors:
Yurtsever, A; Moldoveanu, V; Tanatar, B
Published: MAR 2003, SOLID STATE COMMUNICATIONS, 125, 579, DOI: 10.1016/S0038-1098(03)00081-4
Recent Coulomb drag experiments in low-density double-layer electron systems have the power of distinguishing various many-body formulations of the effective interactions. In this work we theoretically study the correlation effects on the drag resistivity in these systems within various models. The effective inter-layer interactions are best described by the generalization to the double-layer case of the Kukkonen-Overhauser approach which differs significantly from the self-consistent field approach of Singwi et al. [Phys. Rev. 176 (1968) 589]. Following the formulation of Vignale and Singwi [Phys. Rev. B 32 (1985) 2156] we derive an expression for the effective inter-layer interaction which embodies the many-body correlations through the local-field corrections. The drag resistivity is calculated within this approach together with the Hubbard approximation for the intra-layer local-field factor and a simple model for the inter-layer correlations. Comparison with the recent measurements of Kellogg et al. [Solid State Commun. 123 (2002) 5151 yields very good agreement. Our results are also contrasted with the corresponding drag resistivities given by the Singwi et al. theory, the dynamic random-phase approximation and the Hubbard approximation. The significant differences found between these theories emphasize the strong sensitivity of the drag resistivity to the effective inter-layer interactions. (C) 2003 Elsevier Science Ltd. All rights reserved.
1347. Optical and electronic properties of metal doped polymers for integrated optics
Authors:
Bulinski, M; Kuncser, V; Cristea, D; Plapcianu, C; Krautwald, S; Franke, H; Wagner, FE; Filoti, G
Published: MAR 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 335, DOI:
The electronic mechanism responsible for the optical behavior of the mixed Fe and Sn doped polymers were studied in comparison with the correspondent single doped (Fe or Sn) ones. Optical absorption as well as Fe-57 and Sn-119 Mossbauer measurements were performed on different UV exposed films. The new data provided the role of each element from the pair on the involved electronic mechanism induced by irradiation.
1348. Anomalous suppression of superconductivity in LiCl-doped Bi-2223
Authors:
Mihalache, V; Aldica, G; Badica, P
Published: OCT 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 392, 188, DOI: 10.1016/S0921-4534(03)01102-X
From ac susceptibility measurements of the [Bi(Pb)](2)Ca2Sr2Cu3Oz (Bi-2223) samples doped with LiCl, we have found and report for the first time anomalously suppressed superconductivity (T, is anomalously decreasing) in the slightly under-doped region. For our BPSCCO/(LiCl)(y) samples this region is situated around y = 0.07. Hole concentration (p) per number of Cu-O planes of the Bi-2223 unit cell, determined from room temperature thermopower (S-300 K) measurements, is approximately 0.15 when y is within anomalous region. Literature data shows that for the La-based cuprates, similar suppression of superconductivity was observed at p similar to 0.12 (so-called "1/8 problem"). This discrepancy would appear because charge ordering phenomenon (probably induced by Li known as a pair breaker as e.g. Zn) may be accompanied by changes in oxygen content or oxygen ordering effects. (C) 2003 Elsevier B.V. All rights reserved.
1349. BiOx clusters occluded in a ZSM-5 matrix: preparation, characterization, and catalytic behavior in liquid-phase oxidation of hydrocarbons
Authors:
Dumitriu, D; Barjega, R; Frunza, L; Macovei, D; Hu, T; Xie, Y; Parvulescu, VI; Kaliaguine, S
Published: OCT 25 2003, JOURNAL OF CATALYSIS, 219, 351, DOI: 10.1016/S0021-9517(03)00216-1
A series of Bi-ZSM-5 containing 4.26, 5.54, and 6.64 wt% bismuth oxide was prepared by introducing Bi during ZSM-5 synthesis. For comparison. 5 wt% Bi (expressed as bismuth oxide)-impregnated ZSM-5 samples were also prepared. These samples were characterized by N-2 adsorption-desorption isotherms at 77 K, XRD, XPS, IR spectroscopy in the lattice vibration range and in the presence of chemisorbed pyridine and CO2 and EXAFS. The characterization data confirmed the occlusion of bismuth oxide clusters in the zeolite pores. An intrinsic acidity due to bismuth oxide clusters was evidenced. This consisted, on one hand, in weak Lewis acid sites, ascribed to coordinatively unsaturated bismuth cations, and, on the other hand, in strong Bronsted acid sites, attributed to boundary Bi (. . .) O-Si linkages. These catalysts were tested in the liquid-phase oxidation of benzene, toluene, and cyclohexane using hydrogen peroxide as oxidizing agent. The results showed that Bi-ZSM-5 catalysts are more active than the reported titanium silicalites, but the efficiency of H2O2 use was quite small, an important part of this being nonselectively decomposed. A good selectivity was observed in cyclohexane oxidation. (C) 2003 Elsevier Inc. All rights reserved.
1350. Near-infrared emission spectra of negative metal ions aggregates
Authors:
Topa, V; Apostol, E
Published: DEC 2003, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 5, 833, DOI:
In this review paper we attempt to summarize the achievements of the near infrared emission studies of negative metal ions (Me-) obtained by nonstandard electrolytical colouring. We present the emission characteristics of Pb--ions aggregates in KCl crystals at 300 and 4.2 K by excitation in the UV and visible range of different laser lines. These centres perturbed by Li+, Na+, Rb+, Ca2+, Sr(2+)and Ba2+ cations, Tl- and Tl- + Ca2+- ions aggregates and the negative aggregates of ln(-) and Ga- in KCl crystals are, also, discused.
1351. Magnetization and susceptibility studies on BaZrO3-doped YBa2Cu3O7-(x) bulk superconductors
Authors:
Bradea, I; Popa, S; Aldica, G; Mihalache, V; Crisan, A
Published: AUG 2002, JOURNAL OF SUPERCONDUCTIVITY, 15, 242, DOI: 10.1023/A:1019911311340
We studied the YBa2Cu3O7-x bulk superconductor doped with BaZrO3 up to 50 wt.%, obtained by solid-state reaction powder technology. From DC magnetization loops and low frequency AC susceptibility measurements we determined the influence of the BaZrO3 doping level on the critical temperature, critical current density, field for full penetration, and intergrain lower critical field. The results show that even high content of BaZrO3 does not lead to degradation of the superconducting properties of bulk YBa2Cu3O7-x.
1352. The effect of rare-earth impurity on the photodarkening relaxation in as-evaporated amorphous As2Se3 : Pr and As2Se3 : Dy films
Authors:
Iovu, MS; Shutov, SD; Boolchand, P; Colomeico, EP; Ciorba, VG; Iovu, SM; Popescu, M
Published: DEC 2002, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 4, 861, DOI:
The effect of foreign impurity atoms (Dy and Pr) in as-evaporated amorphous As2Se3 thin films on the photodarkening relaxation was investigated. The photodarkening amplitude depends on the kind and concentration of rare-earth dopant, as well as on the thickness of the sample. The observed variation of photodarkening amplitude with the sample thickness is due on the amount of absorbed photons generating the photodarkening effect. The photodarkening kinetics is described by a stretched exponential function with the dispersion parameter alpha less than or equal to 0.5, which indicates high dispersion of the relaxation process in untreated as-deposited chalcogenide films.
1353. Structural properties of sputtered ZnO : Au films
Authors:
Goldenblum, A; Teodorescu, V; Wagner, FE; Manaila, R; Filoti, G; Deville, JP; Pantelica, D; Negoita, F; Belu-Marian, A; Scantee, N
Published: JAN 2002, PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82, 204, DOI:
ZnO: Au films have been obtained by a reactive rf magnetron sputtering method using pure Zn and Au targets. Layers with a Au- to- Zn ratio of up to 0. 71 have been deposited. They were analysed by Rutherford back- scattering spectroscopy, elastic recoil detection analysis, transmission electron microscopy, high- resolution electron microscopy, selected- area electron diffraction, X- ray diffraction and Mossbauer spectroscopy. The only crystalline phase found for all investigated Au concentrations was that of ZnO. We conclude that some of the Au enters as interstitial atoms in the compact hexagonal lattice of ZnO being bonded with any three O atoms of the structure and the other part forms an amorphous hydrated gold oxide that coexists with the ZnO crystallites.
1354. Synthesis and structure of trinuclear iron acetate [Fe3O(CH3COO)(6)(H2O)(3)][AuCl4]center dot 6H(2)O
Authors:
Turte, KI; Shova, SG; Meriacre, VM; Gdaniec, M; Simonov, YA; Lipkowski, J; Bartolome, J; Wagner, F; Filoti, G
Published: JAN-FEB 2002, JOURNAL OF STRUCTURAL CHEMISTRY, 43, 117, DOI: 10.1023/A:1016082018299
Iron acetate of composition [Fe3O(H3COO)(6)(H2O3)][AuCl4].6H(2)O (1) was synthesized and investigated by X-ray diffraction analysis and Mossbauer spectroscopy. The [Fe3O(CH3COO)(6)(H2O)(3)](+) complex cation has a structure typical for mu(3)-O bridged trinuclear ferric compounds with iron atoms lying at the vertices of a regular triangle with an oxygen atom at the center. The iron atoms are each coordinated by 4 oxygen atoms of the four bridging carboxylic groups, the mu(3)-O bridging atom, and the coordinated water molecule in the trans-position to the tatter. In the trinuclear cation, the Fe(Ill) ions are coupled by antiferromagnetic exchange interactions with the exchange parameter J = -29.0 cm(-1) (HDVV model for D-3h symmetry). The specific role of the solvate water molecules in structure formation is discussed.
1355. Advanced electroceramic materials for electrotechnical applications
Authors:
Miclea, C; Tanasoiu, C; Miclea, CF; Tanasoiu, V
Published: MAR 2002, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 4, 58, DOI:
Advanced electroceramics have played a critical role in the development of new and modem technologies such as computers, telecomunications and aerospace and they will continue to play the leading role in the technology of the future. The present report presents and discusses a number of advanced electroceramic materials with special references to their specific properties that make them indispensable in a large area of applications. The materials discussed include cobalt-mangan oxides used as negative temperature coefficient thermistors, semiconducting doped barium titanate used for positive temperature coefficient thermistors with large applications in thermal protections and piezoelectric electroceramics of PZT type, which find new application as ceramic transducers and sensors in biomedical and aerospace industries or as simply buzzers, filters, igniters, ultrasonic cleaners, towed array sonars, medical imaging system, ink-jet printing heads, camera shuttlers, positioners for optical systems, micromotors and actuators. Such advanced electroceramic materials are extremely useful for the future sophisticated technologies such as heads for magnetic recording, scanning tunneling microscope, sensors for antilock braking systems, ultrasonic bone-healing devices and some other biomedical applications.
1356. Selective hydrogenation of unsaturated aromatic compounds upon Pd-Eu/gamma Al2O3 catalysts
Authors:
Coman, S; Vasiliu, C; Parvulescu, VI
Published: MAR-APR 2002, REVUE ROUMAINE DE CHIMIE, 47, 362, DOI:
Pd-1wt% Eu/gammaAl(2)O(3) catalysts with different palladium loadings (0, 1, 03 and 0.5 wt%) were prepared by the wetness successive impregnation method. The state of the supported particles and their interaction with the support were evidenced by transmission electron microscopy (TEM) and electron diffraction (SAED) measurements. The deposition of palladium and europium was found to result in a heterogeneous surface. These catalysts were tested in the hydrogenation of the unsaturated aromatic compounds (styrene, divinylbenzene, indene) and the catalytic results were correlated with the TEM and SAED data. On the basis of this. correlation it was concluded that the hydrogenation occurs on both metallic palladium particles and mixed aluminium-europium oxides. Onto metallic particles hydrogenation occurs with radicalic hydrogen atoms while on the oxidic sites with hydrogen spilled over from palladium.
1357. Effect of spin ordering on the magnetotransport of YBa2Cu3O6.25
Authors:
Cimpoiasu, E; Sandu, V; Almasan, CC; Paulikas, AP; Veal, BW
Published: APR 1 2002, PHYSICAL REVIEW B, 65, DOI: 10.1103/PhysRevB.65.144505
In-plane and out-of-plane magnetoresistivity (MR) measurements were performed on the same antiferromagnetic (AF)YBa2Cu3O6.25 single crystal using a six-lead configuration, in magnetic fields H applied along the ab plane. We identified three terms contributing to both MRs. The first term is anisotropic with respect to the in-plane field orientation, with a twofold symmetry for the in-plane MR and a fourfold symmetry for the out-of-plane MR. We show that these anisotropic features of the magnetoresistivity tensor can be understood in terms of the coupling between the spin and the elastic degrees of freedom. The second term in both MRs is negative and isotropic upon in-plane H rotation. We ascribe this term to charge-carrier scattering on the AF domain walls. Finally, the third term is positive, quadratic in H and seems to correlate with the AF phase transition.
1358. Calcium phosphate thin film processing by pulsed laser deposition and in situ assisted ultraviolet pulsed laser deposition
Authors:
Nelea, V; Pelletier, H; Iliescu, M; Werckmann, J; Craciun, V; Mihailescu, IN; Ristoscu, C; Ghica, C
Published: DEC 2002, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 13, 1173, DOI: 10.1023/A:1021150207350
Calcium orthophosphates (CaP) and hydroxyapatite (HA) were intensively studied in order to design and develop a new generation of bioactive and osteoconductive bone prostheses. The main drawback now in the CaP and HA thin films processing persists in their poor mechanical characteristics, namely hardness, tensile and cohesive strength, and adherence to the metallic substrate. We report here a critical comparison between the microstructure and mechanical properties of HA and CaP thin films grown by two methods. The films were grown by KrF* pulsed laser deposition (PLD) or KrF* pulsed laser deposition assisted by in situ ultraviolet radiation emitted by a low pressure Hg lamp (UV-assisted PLD). The PLD films were deposited at room temperature, in vacuum on Ti-5Al-2.5Fe alloy substrate previously coated with a TiN buffer layer. After deposition the films were annealed in ambient air at 500-600 C. The UV-assisted PLD films were grown in (10(-2)-10(-1) Pa) oxygen directly on Ti-5Al-2.5Fe substrates heated at 500-600 degreesC. The films grown by classical PLD are crystalline and stoichiometric. The films grown by UV-assisted PLD were crystalline and exhibit the best mechanical characteristics with values of hardness and Young modulus of 6-7 and 150-170 GPa, respectively, which are unusually high for the calcium phosphate ceramics. To the difference of PLD films, in the case of UV-assisted PLD, the GIXRD spectra show the decomposition of HA in Ca2P2O7, Ca2P2O9 and CaO. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, increasing the tensile strength of the film, while the HA structure was destroyed. (C) 2002 Kluwer Academic Publishers.
1359. Stud of Ag-- and Ag-0-type centers in X- and gamma-ray irradiated NaCl : Ag+, KCl : Ag+ and NaCl : Ag+ + Ca2+ crystals
Authors:
Topa, V; Tsuboi, T; Dragusin, M
Published: MAY 2002, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 191, 300, DOI: 10.1016/S0168-583X(02)00579-7
Creation of Ag and Ag-0 centers by irradiation with ionizing radiations has been investigated using NaCl and KCl crystals containing various concentrations of Ag+ ions and using Ca2+-codoped NaCl:Ag+ and KCI:Ag+ crystals. From the absorption spectra, it is observed that Ag- center perturbed by Ca2+ ion is also created besides the Ag- and Ag-0 centers. It is confirmed that Ag- and Ag-0 centers increase with increasing the concentration of doped Ag- ions. It is suggested that there are two kinds of Ag(c)(0)v(a) centers (i.e. Ag-0 accompanied by vacancy at the nearest neighbor) with different site symmetries depending on the location of vacancy. (C) 2002 Published by Elsevier Science B.V.
1360. Non-equilibrium electronic processes in nanocrystalline silicon
Authors:
Ciurea, ML; Iancu, V; Draghici, M; Jdira, L
Published: 2002, ADVANCED TOPICS IN OPTOELECTRONICS, MICROELECTRONICS, AND NANOTECHNOLOGIES, 5227, 273, DOI:
Nanocrystalline silicon is studied with a view to obtaining a new photonic material. Non-equilibrium electronic processes in such materials play a significant role. We have studied trapping phenomena in nanocrystalline porous silicon and nanocrystalline silicon-based Multi-Quantum Wells structures by means of Optical Charging Spectroscopy method, which is a very good and sensitive method. We have also analyzed the modeling of the processes that occur during our measurements. This modeling allows us to separate the relative contribution of the different types of discharge currents that can appear: ohmic conduction currents of either equilibrium or non-equilibrium carriers, displacement currents, diffusion currents and tunneling currents through insulating layers (in Multi-Quantum Wells structures). It also allows us to increase the accuracy of the determination of the experimental trap parameters and to determine parameters that are not directly measurable. The model can be applied to other nanocrystalline semiconductors and can be easily generalized for other high resistivity materials.
1361. Interplay between spin and crystal lattices in antiferromagnetic YBa2Cu3O6.25
Authors:
Sandu, V; Cimpoiasu, E; Almasan, CC; Paulikas, AP; Veal, BW
Published: AUG 30 2002, INTERNATIONAL JOURNAL OF MODERN PHYSICS B, 16, 3211, DOI: 10.1142/S0217979202013973
In-plane rho(ab) and out-of-plane p(c) resistivity measurements were performed on the same antiferromagnetic YBa2Cu3O6.25 single crystal over a wide range of temperatures T. rho(ab)(T) exhibits two crossovers with decreasing T: a crossover from metallic to weak localization behavior at 175 K and a second crossover to two-dimensional chiral variable-range hopping VRH behavior at 115 K. The latter reflects the topologic excitations induced in the spin system. rho(c)(T) displays an exp(-T-2/T-c,h(2)) dependence at high T and a VRH type dependence below 115 K. The T derivative of rho(c)(T) shows a kink at 32.65 K which we attribute to the antiferromagnetic ordering of the Cu( 1) spins.
1362. Negatively charged Pb- ion produced by electrolytical colouration of KCl crystals containing Li+, Na+ and Rb+ ions
Authors:
Tsuboi, T; Polosan, S; Topa, V
Published: AUG 5 2002, JOURNAL OF PHYSICS-CONDENSED MATTER, 14, 7272, DOI: 10.1088/0953-8984/14/30/315
Electrolytic colouration has been undertaken for not only a KCl crystal containing Pb2+ ions but also KCl crystals containing alkali impurity ions (Li+, Na+ and Rb+) besides Pb2+ ions. Absorption spectra of these electrolytically coloured crystals have been studied, together with the emission spectra. Similar spectra were observed among these crystals. Eight weak absorption bands are observed in the 290-700 nm region, while five intense bands are observed in the 200-290 nm region. It is suggested-that these bands arise from Pb- ions with tetragonal crystal field symmetry. The energy-level assignment for these absorption bands is made using the energy-level diagram of the isoelectronic Bi-0 atom with C-4v crystal field symmetry. It is suggested that an off-centre position effect of the Li+ ion is observed in the kCl crystal codoped with Li+ ions.. Broad emission bands at 1530 and 1580 nm have been. observed in electrolytically coloured KCl containing Pb2+ ions and KCl containing Li+ and Pb2+ ions, irrespectively.
1363. Properties of titanium based hard coatings deposited by the cathodic arc method I. Microchemical and microstructural characteristics
Authors:
Balaceanu, M; Braic, M; Macovei, D; Genet, MJ; Manea, A; Pantelica, D; Braic, V; Negoita, F
Published: MAR 2002, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 4, 114, DOI:
TiN, TiC and Ti(C,N) hard coatings were deposited on Si substrates by a cathodic are system. Various investigation techniques (ERDA, XPS, and XRD) were used to analyze the microchemical and microstructural characteristics of the films (surface chemistry, chemical composition, texture) prepared under different deposition conditions.
1364. Nondestructive testing techniques and piezoelectric ultrasonics transducers for wood and built in wooden structures
Authors:
Tanasoiu, V; Miclea, C; Tanasoiu, C
Published: DEC 2002, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 4, 957, DOI:
A survey of the main NDT methods used to evaluate the quality and properties of wood and wooden structures is given. Among the most important ones there arc visual inspection, sonic and ultrasonic stress wave. Some other methods include: deflection, electrical, isotope and Xray methods. The ultrasonic methods seem to be the most suitable ones in many cases especially for quality control purposes, but these methods depend on the quality of the piezoelectric transducers. Consequently, the construction and characteristics of a new type of piezoelectric transducer are reported. The new transducer is a composite type transducer, consisting of a sandwich type piezoactive element and a steel cylinder glued together. The sandwich piezoactive element was made of five thinner discs of 20 mm diameter and 2 mm thickness. The whole construction has the resonant frequency at 60 kHz, proper to wood investigation. The transducer can be successfully used for NDT of wood, either in the trough transmission or pulse-echo arrangements. The transducers were tested for sound velocity measurements in different wood samples.
1365. Reactivity and magnetism of Fe/InAs(100) interfaces
Authors:
Teodorescu, CM; Chevrier, F; Brochier, R; Richter, C; Ilakovac, V; Heckmann, O; De Padova, P; Hricovini, K
Published: AUG 2002, EUROPEAN PHYSICAL JOURNAL B, 28, 313, DOI: 10.1140/epjb/e2002-00234-6
Interface reaction and magnetism of epitaxially-grown Fe on InAs(100) are studied by core-level photoemission (As 3d and In 4d) and Fe 2p X-ray magnetic circular dichroism using synchrotron radiation. The reactivity of Fe/InAs(100) is relatively low compared to that of other interfaces involving deposition of 3d metals on III-V semiconductors. As a consequence, we observe a magnetic signal at Fe L-2,L-3 edges for the lowest thicknesses studied (1 ML). The atomic magnetic moment reaches a value close to that of the bulk alpha-Fe (2.2 mu(B)) for Fe coverages exceeding 5 ML. A ferromagnetic compound with approximate stoichiometry of FeAs is formed at the interface. The orbital magnetism represents between 12 and 20% of the total momentum, due to 3d density of states depletion and to crystal-field modification of the electronic levels. These properties make the Fe/InAs(100) interface very promising for spin-tunneling devices.
1366. RE3+ emission in garnets: multisites, energy transfer and quantum efficiency
Authors:
Lupei, V
Published: FEB-MAR 2002, OPTICAL MATERIALS, 19, 107, DOI: 10.1016/S0925-3467(01)00206-3
The connection between the high-resolution spectral disordering of the rare earth-doped garnets and the manifestation or the energy transfer in the global or selective emission decay is discussed. It is shown that the identification of the pair satellites and the investigation of their decay properties are important for determination or verification of the mechanisms of interaction that determine the energy transfer in simply activated or in sensitized crystals. The competition of various energy transfer processes in de-excitation of the metastable levels such as down-conversion and up-conversion in Nd: YAG under high intensity pump is discussed. It is shown that the energy transfer parameters determined from the emission decay could give a consistent description of data on quantum efficiency or heating effects. (C) 2002 Elsevier Science B.V. All rights reserved.
1367. The "in-plane" angular spin distribution in layered systems as obtained by Fe-57 Mossbauer spectroscopy
Authors:
Kuncser, V; Keune, W; Vopsaroiu, M; Bissell, PR
Published: NOV 2002, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 196, 147, DOI: 10.1016/S0168-583X(02)01274-0
A practical approach for in-plane angular spin distributions in layered systems, as obtained by Mossbauer spectroscopy, is discussed. The line intensity ratio R-23 of a Mossbauer pattern is expressed versus particular distribution parameters in unidirectional, step-shaped and ellipse-type models. The distribution parameters are deduced from experimental spectra taken by rotating the sample in its own plane. Three-dimensional spin distributions with small out-of-plane components can be analysed using the same method. The procedure is exemplified on four samples containing metallic nano-particles. The in-plane angular magnetic moment distributions derived with this method are compared with the results from bulk vector vibrating sample magnetometry in order to prove the accuracy of the described technique. (C) 2002 Elsevier Science B.V. All rights reserved.
1368. Fractal patterns formed by thermal treatment in alkali halide crystals
Authors:
Enculescu, M; Enculescu, I; Topa, V; Vasile, E
Published: NOV-DEC 2002, PHYSICA B-CONDENSED MATTER, 324, 392, DOI: 10.1016/S0921-4526(02)01451-5
We have succeeded in growing nanocrystals of Ag structured like fractals in several solid matrices (NaG, KBr and KCl). These are shown to be diffusion-limited aggregates when fractal dimensions were evaluated. Depending upon the crystal in which the fractal structures were obtained, the fractal dimensions of the Ag nanoclusters were found to be between 1.73 and 1.81. (C) 2002 Elsevier Science B.V. All rights reserved.
1369. Silver nanoclusters in potassium halides obtained from Ag--ions by electron detachment
Authors:
Enculescu, M; Topa, V; Vasile, E
Published: MAY 2002, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 191, 436, DOI: 10.1016/S0168-583X(02)00587-6
We studied by means of optical absorption and transmission electron microscopy the formation of Ag nanoclusters from Ag--ions in three different potassium halides (KCl, KI and KBr). By stepwise UV illumination at a suitable temperature, the electrons of Ag--ions were detached and the controlled formation and growth of Ag nanoclusters from Ago-atoms take place. At the same time, the detached electrons are captured by K+-ions, proved by the appearance of K-colloid bands. The kinetics of the conversion Ag- + hv + U --> Ag nanoclusters was followed by monitoring the Ag--ions and Ag nanoclusters absorption. The temperatures of illumination are different, depending on the matrix in which Ag nanoclusters are formed (220 degreesC for KCl, 160 degreesC for KBr and 140 degreesC for KI). By optical absorption and TEM we proved that the nanoclusters of Ag obtained by our method are separated, spherical and ovoidal, with average diameters between 7.5 and 50 nm. (C) 2002 Elsevier Science B.V. All rights reserved.
1370. Nanocapsules of biodegradable polymers: preparation and characterization by direct high resolution electron microscopy
Authors:
Guinebretiere, S; Briancon, S; Fessi, H; Teodorescu, VS; Blanchin, MG
Published: SEP 1 2002, MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, 21, 142, DOI: 10.1016/S0928-4931(02)00073-5
In the field of pharmaceutical applications relying on encapsulation of drug by polymer coating, capsules based on biodegradable polymers with mean size of about 500 nm have been obtained by a patented emulsion-diffusion method. The morphology, size and structure of the nanocapsules (NC) control their pharmaceutical properties, especially release of the drug. Here is reported a decisive contribution of transmission electron microscopy (TEM) in revealing the controlled form and size of the NC: mean size values measured by TEM do agree with data obtained by laser granulometry. Moreover, the TEM magnification allows an estimation of the membrane thickness. (C) 2002 Elsevier Science B.V. All rights reserved.
1371. Enhanced magnetization at integer quantum Hall states
Authors:
Meinel, I; Grundler, D; Heitmann, D; Manolescu, A; Gudmundsson, V; Wegscheider, W; Bichler, M
Published: SEP 15 2001, PHYSICAL REVIEW B, 64, DOI: 10.1103/PhysRevB.64.121306
We report on enhancements in the magnetization of two-dimensional electron systems in the quantum Hall regime. The observed discontinuities in the magnetization exceed the predictions for interacting electrons calculated in the Hartree-Fock approximation where only the exchange enhancement of the energy gaps is taken into account. We attribute the further enhancement to many-body correlation effects, i.e., filling factor dependent screening within the screened Hartree-Fock approximation. With this, the discontinuities in the magnetization no longer reflect the discontinuities of the chemical potential, but its behavior in the vicinity of integer filling factors.
1372. Non-Heisenberg magnetic behavior of a triangular bridged heterometallic Fe-2(III)Co(II) complex: Evidence of strong orbital contributions
Authors:
Tsukerblat, BS; Palii, AV; Mirovitskii, VY; Ostrovsky, SM; Turta, K; Jovmir, T; Shova, S; Bartolome, J; Evangelisti, M; Filoti, G
Published: NOV 22 2001, JOURNAL OF CHEMICAL PHYSICS, 115, 9535, DOI: 10.1063/1.1413988
We report the synthesis, magnetization and ac susceptibility of the triangular mu (3)-oxo-bridged heterometallic complex [Fe2CoO(CH3COO)(6)(3-Cl-Py)(3)], in powder form. The model Hamiltonian is elaborated involving isotropic exchange interactions Fe(III)-Fe(III) and Co(II)-Fe(III) dealing with the real spins of high-spin Co(II) and Fe(III) ions, and also spin-orbit coupling and low-symmetry crystal field (C-2v) acting within the T-4(1g) ground manifold of Co(II) ion. The outlined general model takes into account strong anisotropic orbital contribution to the magnetic characteristics of the whole system arising from Co(II) ion with unquenched orbital angular momentum. The treatment of the Hamiltonian is performed with the use of the irreducible tensor operator technique. The influence of the exchange and spin-orbital interactions on the magnetic properties of Fe-2(III)Co(II) clusters is revealed. The result of calculations in the framework of the isotropic model (neglecting low-symmetry crystal field) are in a good agreement with the experimentally observed magnetization versus magnetic field, as well as with the unusual temperature behavior of the magnetic susceptibility of the powder samples (1.8-250 K). The states of the system are enumerated by the quantum number of the total angular momentum J, these hybrid states are combined from the sets of full and intermediate spins of Fe2Co triangle and orbital angular momentum of Co(II), (with fictious L=1). The best fit to the experimental data is achieved for the exchange parameters J(Fe-Fe)=-87.5 cm(-1), J(Fe-Co)=-17 cm(-1) and orbital reduction factor for Co(II) ion kappa =0.93. The ground state and the first excited one are found to possess total angular momentum J=1/2, Effective g-factors for the ground- and first-excited states calculated using the hybrid spin-orbital functions prove to be 4.3 and 0.75, that are distinctly different from the pure spin value 2 peculiar for the Heisenberg model. The comparison of the magnetic measurements with the theory clearly demonstrates the insufficiency of a simple Heisenberg spin-coupling model as evidenced by the discovered strong orbital magnetic contribution. (C) 2001 American Institute of Physics.
1373. Influence of LiF addition on the superconducting properties of Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox high-temperature superconducting oxide
Authors:
Mihalache, V; Aldica, G; Giusca, C; Miu, L
Published: OCT 2001, JOURNAL OF SUPERCONDUCTIVITY, 14, 579, DOI: 10.1023/A:1012983831008
We investigated the superconducting critical temperature, transport critical-current density and the thermo-power properties of Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox/(LiF)(y) samples. It was found that the midpoint critical temperature increases with increasing y, attaining approximate to 119.5 K for y = 0.15. The transition width shows a minimum and the critical temperature (zero electrical resistance) exhibits a maximum as a function of y. The observed behavior is correlated with the SEM analysis. Powder X-ray diffraction studies reveal that in our samples the amount of Bi2Sr2Ca2Cu3O10+delta high-temperature superconducting phase is maximal (70-78%) for y = 0.05-0.07.
1374. Optical properties of polyaniline/CdS nanocrystals composite film
Authors:
Ghiordanescu, V; Sima, M; Nedelcu, M; Giubelan, M
Published: MAR 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 93, DOI:
The optical spectra of CdS nanocrystals embedded in polyaniline matrix have been studied. The presence of surface states is revealed both in absorption and emission spectra. The polymer matrix determines a shift of the absorption edge of CdS nanocrystals, towards higher energies.
1375. The influence of BaZrO3 on the transport properties of the (Bi,Pb)2223 superconducting system
Authors:
Mihalache, V; Aldica, G; Crisan, A
Published: MAY 2001, JOURNAL OF MATERIALS SCIENCE LETTERS, 20, 891, DOI: 10.1023/A:1010912429361
1376. In situ transmission electron microscopy study of Ni silicide phases formed on (001) Si active lines
Authors:
Teodorescu, V; Nistor, L; Bender, H; Steegen, A; Lauwers, A; Maex, K; Van Landuyt, J
Published: JUL 1 2001, JOURNAL OF APPLIED PHYSICS, 90, 174, DOI: 10.1063/1.1378812
The formation of Ni silicides is studied by transmission electron microscopy during in situ heating experiments of 12 nm Ni layers on blanket silicon, or in patterned structures covered with a thin chemical oxide. It is shown that the first phase formed is the NiSi2 which grows epitaxially in pyramidal crystals. The formation of NiSi occurs quite abruptly around 400 degreesC when a monosilicide layer covers the disilicide grains and the silicon in between. The NiSi phase remains stable up to 800 degreesC, at which temperature the layer finally fully transforms to NiSi2. The monosilicide grains show different epitaxial relationships with the Si substrate. Ni2Si is never observed. (C) 2001 American Institute of Physics.
1377. Aggregate centres of Ag- ions in KCl : Na crystals
Authors:
Tsuboi, T; Zota, S; Topa, V
Published: JAN 2001, PHYSICA B, 293, 337, DOI: 10.1016/S0921-4526(00)00551-2
Not only (Ag-)(2) and Ag-(Na+) centres but also various Ag--Na+ aggregate centres have been produced in Ag+-,Na+- and Ca2+-codoped KCl crystals by unusual electrolytic colouration such as colouration at a relatively low temperature of 280 degreesC and a high electric field of 5000 V/cm. Absorption and magnetic circular dichroism spectra due to these centres have been investigated. (C) 2001 Elsevier Science B.V. All rights reserved.
1378. A Mossbauer study of the new phases Th4Fe13Sn5 and ThFe0.22Sn2
Authors:
Principi, G; Spataru, T; Maddalena, A; Palenzona, A; Manfrinetti, P; Blaha, P; Schwarz, K; Kuncser, V; Filoti, G
Published: APR 12 2001, JOURNAL OF ALLOYS AND COMPOUNDS, 317, 572, DOI: 10.1016/S0925-8388(00)01389-X
Two new phases Th4Fe13Sn5 and ThFe0.22Sn2 have been studied by Fe-57 and Sn-119 Mossbauer spectroscopy. The Fe-57 Mossbauer spectra of Th4Fe13Sn5, measured at room temperature and 4.2 Ii without and with applied magnetic field up to 5.5 T, exhibit four sextets. Our measurements prove that all four Ft: sub-lattices are collinear. The Sn-119 Mossbauer spectra of Th4Fe13Sn5 show two sextets with different B-eff, reflecting the influence of ferromagnetic nn iron atoms. The results obtained from full-potential linear augmented plane wave (LAPW) calculations are in agreement with the experimental data and confirm the assignment of Mossbauer spectra, The Mossbauer data for the ThFe0.22Sn compound prove the existence of two different sites both for Fe and Sn, all having icosahedral co-ordination. (C) 2001 Elsevier Science B.V, All rights reserved.
1379. Visible light emission from Cd1-xMnxS nanocrystals
Authors:
Ghiordanescu, V; Sima, M; Grecu, MN; Mihut, L
Published: JUN 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 524, DOI:
The luminescence spectra of some Cd1-xMnxS nanocrystals have been measured at room and liquid nitrogen temperature. The Mn2+ ions give rise to a broad emission band centered at about 580 nm, between the emission bands of CdS host.
1380. Coulomb effects on the transport properties of quantum dots in a strong magnetic field
Authors:
Moldoveanu, V; Aldea, A; Manolescu, A; Nita, M
Published: JAN 15 2001, PHYSICAL REVIEW B, 63, DOI: 10.1103/PhysRevB.63.045301
We investigate the transport properties of quantum dots placed in a strong magnetic field using a quantum-mechanical approach based on the two-dimensional tight-binding Hamiltonian with direct Coulomb interaction and the Landauer-Buttiker formalism. The electronic transmittance and the Hall resistance show Coulomb oscillations and also prove multiple addition processes. We identify this feature as the "bunching" of electrons observed in recent experiments and give an elementary explanation in terms of spectral characteristics of the dot. The spatial distribution of the added electrons may distinguish between the edge and bulk states and it has specific features for bunched electrons. The dependence of the charging energy on the number of electrons is discussed for a strong magnetic field. The crossover from the tunneling to quantum Hall regime is analyzed in terms of dot-lead coupling.
1381. Aspects in HTS laser ablation thin film technology and characterization
Authors:
Branescu, M; Gyorgy, E; Ristoscu, C; Mihailescu, IN; Jaklovsky, J; Mihalache, V
Published: 2001, 11TH INTERNATIONAL SCHOOL ON QUANTUM ELECTRONICS: LASER PHYSICS AND APPLICATIONS, 4397, 313, DOI: 10.1117/12.425154
Thin films of YBa2Cu3O7-x have been obtained on NdGaO3 substrate by pulsed laser deposition with an excimer KrF* (lambda =248 nm, tau (FWHM)greater than or equal to 20 ns) laser source from a stoichiometric target. In the present paper we report details of the technology of pulsed laser deposition of high-temperature superconductor thin films, substrates' requirements and high-temperature superconductor thin film characterisation. The study of some parameters' intercorelations for optimisation of the technology of the pulsed laser deposition of high-temperature superconductor thin films is also analysed Moreover, the contacting technology and techniques of characterisation are described.
1382. Developments for radiation hard silicon detectors by defect engineering - results by the CERN RD48 (ROSE) Collaboration
Authors:
Lindstrom, G; Ahmed, M; Albergo, S; Allport, P; Anderson, D; Andricek, L; Angarano, MM; Augelli, V; Bacchetta, N; Bartalini, P; Bates, R; Biggeri, U; Bilei, GM; Bisello, D; Boemi, D; Borchi, E; Botila, T; Brodbeck, TJ; Bruzzi, M; Budzynski, T; Burger, P; Campabadal, F; Casse, G; Catacchini, E; Chilingarov, A; Ciampolini, P; Cindro, V; Costa, MJ; Creanza, D; Clauws, P; Da Via, C; Davies, G; De Boer, W; Dell'Orso, R; De Palma, M; Dezillie, B; Eremin, V; Evrard, O; Fallica, G; Fanourakis, G; Feick, H; Focardi, E; Fonseca, L; Fretwurst, E; Fuster, J; Gabathuler, K; Glaser, M; Grabiec, P; Grigoriev, E; Hall, G; Hanlon, M; Hauler, F; Heising, S; Holmes-Siedle, A; Horisberger, R; Hughes, G; Huhtinen, M; Ilyashenko, I; Ivanov, A; Jones, BK; Jungermann, L; Kaminsky, A; Kohout, Z; Kramberger, G; Kuhnke, M; Kwan, S; Lemeilleur, F; Leroy, C; Letheren, M; Li, Z; Ligonzo, T; Linhart, V; Litovchenko, P; Loukas, D; Lozano, M; Luczynski, Z; Lutz, G; MacEvoy, B; Manolopoulos, S; Markou, A; Martinez, C; Messineo, A; Mikuz, M; Moll, M; Nossarzewska, E; Ottaviani, G; Oshea, V; Parrini, G; Passeri, D; Petre, D; Pickford, A; Pintilie, I; Pintilie, L; Pospisil, S; Potenza, R; Radicci, V; Raine, C; Rafi, JM; Ratoff, PN; Richter, RH; Riedler, P; Roe, S; Roy, P; Ruzin, A; Ryazanov, AI; Santocchia, A; Schiavulli, L; Sicho, P; Siotis, I; Sloan, T; Slysz, W; Smith, K; Solanky, M; Sopko, B; Stolze, K; Avset, BS; Svensson, B; Tivarus, C; Tonelli, G; Tricomi, A; Tzamarias, S; Valvo, G; Vasilescu, A; Vayaki, A; Verbitskaya, E; Verdini, P; Vrba, V; Watts, S; Weber, ER; Wegrzecki, M; Wegrzecka, I; Weilhammer, P; Wheadon, R; Wilburn, C; Wilhelm, I; Wunstorf, R; Wustenfeld, J; Wyss, J; Zankel, K; Zabierowski, P; Zontar, D
Published: JUN 1 2001, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 465, 69, DOI: 10.1016/S0168-9002(01)00347-3
This report summarises the final results obtained by the RD48 collaboration. The emphasis is on the more practical aspects directly relevant for LHC applications. The report is based on the comprehensive survey given in the 1999 status report (RD48 3rd Status Report, CERN/LHCC 2000-009, December 1999), a recent conference report (Lindstrom et al, (RD48), and some latest experimental results. Additional data have been reported in the last ROSE workshop (5th ROSE workshop, CERN, CERN/LEB 2000-005), A compilation of all RD48 internal reports and a full publication list can be found on the RD48 homepage (http://cern.ch/RD48/). The success of the oxygen enrichment of FZ-silicon as a highly powerful defect engineering technique and its optimisation with various commercial manufacturers are reported. The focus is on the changes of the effective doping concentration (depletion voltage). The RD48 model for the dependence of radiation effects on fluence, temperature and operational time is verified: projections to operational scenarios for main LHC experiments demonstrate vital benefits. Progress in the microscopic understanding of damage effects as well as the application of defect kinetics models and device modelling for the prediction of the macroscopic behaviour was also been achieved but will not be covered in detail. (C) 2001 Elsevier Science B.V. All rights reserved.
1383. Radiation hard silicon detectors - developments by the RD48 (ROSE) collaboration
Authors:
Lindstrom, G; Ahmed, M; Albergo, S; Allport, P; Anderson, D; Andricek, L; Angarano, MM; Augelli, V; Bacchetta, N; Bartalini, P; Bates, R; Biggeri, U; Bilei, GM; Bisello, D; Boemi, D; Borchi, E; Botila, T; Brodbeck, TJ; Bruzzi, M; Budzynski, T; Burger, P; Campabadal, F; Casse, G; Catacchini, E; Chilingarov, A; Ciampolini, P; Cindro, V; Costa, MJ; Creanza, D; Clauws, P; Da Via, C; Davies, G; De Boer, W; Dell'Orso, R; De Palma, M; Dezillie, B; Eremin, V; Evrard, O; Fallica, G; Fanourakis, G; Feick, H; Focardi, E; Fonseca, L; Fretwurst, E; Fuster, J; Gabathuler, K; Glaser, M; Grabiec, P; Grigoriev, E; Hall, G; Hanlon, M; Hauler, F; Heising, S; Holmes-Siedle, A; Horisberger, R; Hughes, G; Huhtinen, M; Ilyashenko, I; Ivanov, A; Jones, BK; Jungermann, L; Kaminsky, A; Kohout, Z; Kramberger, G; Kuhnke, M; Kwan, S; Lemeilleur, F; Leroy, C; Letheren, M; Li, Z; Ligonzo, T; Linhart, V; Litovchenko, P; Loukas, D; Lozano, M; Luczynski, Z; Lutz, G; MacEvoy, B; Manolopoulos, S; Markou, A; Martinez, C; Messineo, A; Mikuz, M; Moll, M; Nossarzewska, E; Ottaviani, G; Oshea, V; Parrini, G; Passeri, D; Petre, D; Pickford, A; Pintilie, I; Pintilie, L; Pospisil, S; Potenza, R; Raine, C; Rafi, JM; Ratoff, PN; Richter, RH; Riedler, P; Roe, S; Roy, P; Ruzin, A; Ryazanov, AI; Santocchia, A; Schiavulli, L; Sicho, P; Siotis, I; Sloan, T; Slysz, W; Smith, K; Solanky, M; Sopko, B; Stolze, K; Avset, BS; Svensson, B; Tivarus, C; Tonelli, G; Tricomi, A; Tzamarias, S; Valvo, G; Vasilescu, A; Vayaki, A; Verbitskaya, E; Verdini, P; Vrba, V; Watts, S; Weber, ER; Wegrzecki, M; Wegrzecka, I; Weilhammer, P; Wheadon, R; Wilburn, C; Wilhelm, I; Wunstorf, R; Wustenfeld, J; Wyss, J; Zankel, K; Zabierowski, P; Zontar, D
Published: JUL 1 2001, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 466, 326, DOI: 10.1016/S0168-9002(01)00560-5
The RD48 (ROSE) collaboration has succeeded to develop radiation hard silicon detectors. capable to withstand the harsh hadron fluences in the tracking areas of LHC experiments. In order to reach this objective, a defect engineering technique was employed resulting in the development of Oxygen enriched FZ silicon (DOFZ), ensuring the necessary O-enrichment of about 2 x 10(17) O/cm(3) in the normal detector processing. Systematic investigations have been carried out on various standard and oxygenated silicon diodes with neutron, proton and pion irradiation up to a fluence of 5 x 10(14)cm(-2) (1 MeV neutron equivalent). Major focus is on the changes of the effective doping concentration (depletion voltage). Other aspects (reverse current, charge collection) are covered too and the appreciable benefits obtained with DOFZ silicon in radiation tolerance for charged hadrons are outlined. The results are reliably described by the "Hamburg model": its application to LHC experimental conditions is shown, demonstrating the superiority of the defect engineered silicon. Microscopic aspects of damage effects are also discussed. including differences due to charged and neutral hadron irradiation. (C) 2001 Elsevier Science B.V. All rights reserved.
1384. Trapping levels in (nc-Si/CaF2)(n) multi-quantum wells
Authors:
Ioannou-Sougleridis, V; Nassiopoulou, AG; Ciurea, ML; Bassani, F; d'Avitaya, FA
Published: AUG 20 2001, MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, 15, 47, DOI: 10.1016/S0928-4931(01)00215-6
Trapping levels which govern the vertical transport in (nc-Si/CaF2)(n) multi-quantum wells were investigated using two different techniques: (a) the temperature dependence of the dark current and (b) the thermally stimulated depolarization current technique (TSDC). Measurements by the first technique showed that the conduction mechanism was thermally activated above 200 K with activation energies of 0.35-0.7 eV, These activation energies were found to increase with increasing electric field. TSDC measurements showed also the existence of at least one broad peak above 200 K with estimated activation energies in the range of 0.4-0.45 eV. Analysis of the peak by the fractional heating method showed a continuous distribution of defect states from 0.3 to 0.83 eV. (C) 2001 Elsevier Science B.V. All rights reserved.
1386. Kinetics of silver structures growth by electrodiffusion in quartz crystals
Authors:
Enculescu, I; Iliescu, B; Teodorescu, V
Published: JAN 2001, SOLID STATE IONICS, 138, 321, DOI: 10.1016/S0167-2738(00)00794-3
Silver layers were grown in quartz crystals by electrodiffusion from an anodic layer of AgNO3. Different experimental arrangements were employed in order to obtain such layers in a reproducible way. We performed DC ionic conductivity measurements on Z-cut and X-cut samples as a function of temperature in the heating up phase and as a function of time at the electromigration temperature. The metal structures and the quartz samples were analyzed by electron microscopy and electron diffraction. Based on the experimental results and on the observations a model, for the metal structure formation is proposed. (C) 2001 Elsevier Science B.V. All rights reserved.
1387. The influence of the h-BN morphology and structure on the c-BN growth
Authors:
Nistor, L; Teodorescu, V; Ghica, C; Van Landuyt, J; Dinca, G; Georgeoni, P
Published: MAR-JUL 2001, DIAMOND AND RELATED MATERIALS, 10, 1356, DOI: 10.1016/S0925-9635(00)00377-0
The morphology and structure of hexagonal graphitic BN (h-BN) powders with graphitization indices GI <5, used as precursors for the synthesis of cubic BN (c-BN) crystals, has been investigated by transmission electron microscopy in diffraction contrast and high resolution. We show that besides the GI, which is a general parameter for controlling the structural quality of h-EN ponders, some other microstructural features strongly influence the synthesis of c-BN. In our opinion, the high reactivity of some h-BN powders results from the presence of some nucleation centers for c-BN, observed at the edges of the h-BN particles. They are formed by a rearrangement of the graphitic (0002) planes by bending back, joining in pairs and forming locally nanoarches (half nanotubes). In these particular places, the nature of bonding locally turns towards sp(3), as in the case of c-BN, (C) 2001 Elsevier Science B.V. All rights reserved.
1388. The influence of BaZrO3 on the magnetic response of (Bi,Pb): 2223 high-temperature superconductors
Authors:
Mihalache, V; Aldica, G; Popa, S; Nita, P; Crisan, A
Published: JUN 2001, JOURNAL OF SUPERCONDUCTIVITY, 14, 386, DOI: 10.1023/A:1011174321955
DC magnetization and AC complex susceptibility measurements on (Bi,Pb) : 2223 high-temperature superconductors impurified with various amounts of BaZrO3 are presented. The results are discussed in the frame of the critical state model. and the values of the inter- and intragranular critical current density as well as of the field for full penetration are estimated. The values of the intergranular critical current density are consistent with those obtained from transport measurements. The intragranular critical current density and the field for full penetration have similar values from both DC magnetization and AC susceptibility measurements. It was shown that, in the (Bi,Pb) : 2223 system. BaZrO3 impurification changes only the properties of the intergrain matrix, while the superconducting properties of the grains are not modified.
1389. Internal structure of the nanosized sol-gel ITO thin films
Authors:
Stoica, TF; Teodorescu, VS; Blanchin, MG; Stoica, TA; Gartner, M; Zaharescu, M
Published: 2001, 2001 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOL 1 & 2, PROCEEDINGS, 66, DOI:
The alkoxide route and the spinning deposition were used to prepare sol gel ITO films. The morphology and crystalline structure were investigated by Cross-section Transmission Electron Microscopy and Atomic Force Microscopy. The inside of the ITO layer has three regions of different porosity and the basic crystalline structure is that of the In2O3 lattice. Three types of surface morphological structures were found from AFM images.
1390. Sintering behaviour of piezoceramic powders prepared by conventional ceramic and mechanical activation process
Authors:
Miclea, C; Tanasoiu, C; Gheorghiu, A; Miclea, CF; Tanasoiu, V
Published: 2001, 2001 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOL 1 & 2, PROCEEDINGS, 300, DOI: 10.1109/SMICND.2001.967469
Conventional and mechanical activation techniques were used to prepare a soft PZT type piezoceramic material. The resulting powders exhibit micro and nanostructures, respectively as indicated by X-ray and electron microscopy. Average crystallite sizes of 1 mu and 50 nm respectively were estimated for the powders. The sintered behavior of pressed samples from the two types of powders was investigated within the 8001300 degreesC temperature range and the densities, structural morphology and dielectric and piezoelectric properties were investigated. Optimum sintering temperature were about 100 degreesC lower for samples made from mechanical activated powder compared to the conventionally ones. Sintered samples from this powder exhibited also enhanced properties compared to those made from the conventionaly prepared powder. It is concluded that the mechanical activation technique is a reliable and simple method to prepare high quality PZT type materials.
1391. Transmission electron microscopy study of silicon nitride amorphous films obtained by reactive pulsed laser deposition
Authors:
Teodorescu, VS; Nistor, LC; Popescu, M; Mihailescu, IN; Gyorgy, E; Van Landuyt, J; Perrone, A
Published: OCT 1 2001, THIN SOLID FILMS, 397, 16, DOI: 10.1016/S0040-6090(01)01408-0
In situ decomposition of silicon nitride films was observed by high-resolution electron microscopy. The films, which were produced by reactive pulsed laser deposition from Si wafer targets at 50-100 Pa ammonia pressure, had a prevalent content of hydrogen-doped, amorphous, non-stoichiometric silicon nitride. A layered morphology of the film, consisting of a density variation in the amorphous structure, developed under electron beam irradiation. This morphology became evident only in cross-sectional observation and was related to the stress-relaxation effect, based on a rearrangement of the bonds, We presume that the stress field anisotropy in the amorphous structure must be related to the presence of some bond texture in the as-grown, amorphous film. (C) 2001 Elsevier Science B.V. All rights reserved.
1392. Advanced technology for making PZT type ceramics by fast firing
Authors:
Miclea, C; Tanasoiu, C; Miclea, CF; Amarande, L; Iorgulescu, R; Tanasoiu, V; Moscu, S
Published: MAR 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 87, DOI:
Densification and piezoelectric performances of some fast fired lead zirconate-titanate ceramics were investigated in comparison with those made by conventionally sintering technique. Micro and nano PZT powders were used as initial powders for the compacts subjected to the Cast and conventionally sinterings. Density maxims of about 98 % of the theoretical density, were obtained for nanopowder compacts fast fired at 1350 degreesC for 20 minutes. The piezoelectric properties of the fast fired and conventionally sintered compacts were determined. Significant increase for d(33) piezoelectric charge constant was observed in the case of fast fired samples compared to conventionally sintered ones. The electromechanical planar coupling factor k(p) was also increased From 0.62 to 0.65 for fast fired samples. The densification mechanism was discussed in terms of a predominantly transient stresses induced during the initial stage of densification by the rather high temperature gradient of the fast fired samples.
1393. Ru-MCM-41 catalysts for diastereoselective hydrogenation
Authors:
Florea, M; Sevinci, M; Parvulescu, VI; Lemay, G; Kaliaguine, S
Published: JUN 2001, , DOI: 10.1016/S1387-1811(01)00224-4
1394. Influence of the deposition configuration on the composition, structure and morphology of La0.6Y0.07Ca0.33Mn3-delta thin films obtained by pulsed laser deposition
Authors:
Ghica, C; Valeanu, M; Nistor, LC; Teodorescu, V; Sandu, C; Ristoscu, C; Mihailescu, IN; Werckmann, J; Deville, JP
Published: DEC 2001, INTERNATIONAL JOURNAL OF INORGANIC MATERIALS, 3, 1256, DOI: 10.1016/S1466-6049(01)00153-2
We present a structural and morphological study on La0.6Y0.07Ca0.33MnO3-delta (LYCMO) thin films deposited by laser ablation onto MgO-buffered silicon wafers using two deposition configurations named on-axis and off-axis. All thin films have been deposited at high temperatures in an oxygen atmosphere. A comparative study between the on-axis and off-axis samples is performed by transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. The films are polycrystalline and show a columnar morphology. The off-axis sample shows a better crystalline texture, although slight compositional variations have been found. (C) 2001 Elsevier Science Ltd. All rights reserved.
1395. Mechanically alloyed Cu-Fe studied by Mossbauer spectroscopy
Authors:
Principi, G; Spataru, T; Gupta, R; Enzo, S; Kuncser, V; Filoti, G
Published: AUG 9 2001, JOURNAL OF ALLOYS AND COMPOUNDS, 326, 192, DOI: 10.1016/S0925-8388(01)01301-9
Recent studies of mechanically alloyed Fe-Cu powder mixtures have suggested differences in the local magnetic environment of iron atoms. For a more accurate definition of this point, ball-milled Cu70Fe30 and Cu50Fe50 alloys were investigated by Mossbauer spectroscopy in the, temperature range 4.2-300 K. The low temperature Mossbauer spectra exhibit a broad magnetic pattern. typical of a defect structural configuration. The magnetic splitting strongly decreases with increasing temperature, especially in the case of Cu70Fe30 alloy. But even for this composition there is, at room temperature, an unresolved magnetic pattern. Applying a magnetic field of 3 T, parallel to gamma rays, at 4.2 K a rotation of all magnetic moments along the external field is observed. The samples behave as an alloy with continuously distributed local fields. (C) 2001 Elsevier Science BY. All rights reserved.
1396. Spectroscopy and laser emission under hot band resonant pump in highly doped Nd : YAG ceramics
Authors:
Lupei, V; Taira, T; Lupei, A; Pavel, N; Shoji, I; Ikesue, A
Published: AUG 1 2001, OPTICS COMMUNICATIONS, 195, 232, DOI: 10.1016/S0030-4018(01)01278-0
The high resolution spectroscopic and emission decay properties of Nd:YAG ceramics with up to 9 at.% Nd show that no major changes from the single crystals other than those induced by the increased Nd concentration occur and indicate that these materials can be used for construction of efficient and high power lasers. The laser emission of a 3.8 at.% Nd ceramic laser component under hot band resonant pump at 885 nm with a Ti:sapphire laser is demonstrated. (C) 2001 Elsevier Science B.V. All rights reserved.
1397. Ionoluminescence in CVD diamond and in cubic boron nitride
Authors:
Manfredotti, C; Vittone, E; Lo Giudice, A; Paolini, C; Fizzotti, F; Dinca, G; Ralchenko, V; Nistor, SV
Published: MAR-JUL 2001, DIAMOND AND RELATED MATERIALS, 10, 573, DOI: 10.1016/S0925-9635(00)00604-X
Using the new ion beam-induced luminescence (IBIL) apparatus in National Legnaro Laboratories, Italy, a series of measurements concerning both wide-area luminescence spectra and monochromatic luminescence maps with a space resolution of a few mum has been carried out on several CVD diamond and c-BN samples. Protons of 2 MeV with a penetration depth of approximately 25 mum have been used in order to investigate the materials in the bulk. These measurements have been correlated with particle-induced X-ray emission (PIXE) and EPR data. The measurements have been performed at increasing proton doses in order to also investigate the radiation hardness of luminescence peaks. The results indicate that ionoluminescence of CVD diamond is dominated by three bands at approximately 2, 2.4 and 2.9 eV, with the intermediate band being very radiation-hard, and the other two radiation-weak. The band at 2 eV is correlated with N content, and is particularly high in samples with poor electronic properties. IBIL in c-BN is also dominated by three bands, one at approximately 2 eV, and the other two at higher energies with respect to CVD diamond. All these three bands seem to be relatively radiation-hard with respect to CVD diamond, and to be related to defects induced by doping. (C) 2001 Elsevier Science B.V. All rights reserved.
1398. Traps in (nc-Si/CaF2)(50) nanostructures
Authors:
Draghici, M; Jdira, L; Iancu, V; Ioannou-Sougleridis, V; Nassiopoulou, A; Ciurea, ML
Published: 2001, CAS: 2002 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, 122, DOI:
Traps in Multi-Quantum Wells (nc-Si/CaF2)(50) nanostructures using Optical Charging Spectroscopy method were investigated. Three maxima and a final abrupt increase were found in the discharge current versus temperature characteristics. The relative contributions of the tunneling and displacement currents through the insulating calcium fluoride were analyzed.
1399. Formation of amorphous carbon and graphite in CVD diamond upon annealing: A HREM, EELS, Raman and optical study
Authors:
Nistor, L; Ralchenko, V; Vlasov, I; Khomich, AV; Khmelnitskii, R; Potapov, P; van Landuyt, J
Published: JUL 23 2001, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 186, 214, DOI: 10.1002/1521-396X(200108)186:2<207::AID-PSSA207>3.0.CO;2-U
Polycrystalline diamond thick films were subjected to annealing in vacuum at temperatures of 1350-1450 degreesC. The films were examined by optical absorption, Raman spectroscopy, transmission electron microscopy and electron energy loss spectroscopy. The formation of amorphous carbon and/or of well-crystallized graphite layers up to 20 nm thick was evidenced along grain boundaries. Intra-granular nanometer-sized graphite islands were also observed, sometimes as transformed micro-twin bands. The diamond-to-graphite transition occurs in such a way that three (111) diamond planes transform into two (0002) graphitic sheets. The internal graphitization causes a severe degradation of the optical quality of the diamond films.
1401. Nanoscale science and engineering in Romania
Authors:
Dascalu, D; Topa, V; Kleps, I
Published: DEC 2001, JOURNAL OF NANOPARTICLE RESEARCH, 3, 352, DOI: 10.1023/A:1012555023738
In spite of difficult working conditions and with very low financial support, many groups from Romania are involved in emerging fields, such as the nanoscale science and technology. Until the last years, this activity was developed without a central coordination and without many interactions between these research groups. In the year 2000, some of the institutes and universities active in the nanotechnology field in Romania founded the MICRONANOTECH network. The aim of this paper is to emphasize the main activities and results of the Romanian groups working in this novel domain. Most of the groups are deal with the nanomaterial technology anti only few of them have activities in nanostructure science and engineering, in new concepts and device modeling and technology. This paper describes the nanotechnology research development in two of the most significant institutes from Romania: Centre for Nanotechnologies from National Institute for Research and Development in Microtehnologies (IMT-Bucharest) and from National Institute for Research and Development in Materials Physics (INCD-FM), Magurele. The Romanian research results in nanotechnology field were presented in numerous papers presented in international conferences or published in national and international journals. They are also presented in patents, international awards and fellowships. The research effort and financial support are outlined. Some future trends of the Romanian nanoscale science and technology research are also described.
1402. SEM, EDS and WAXD microstructural characterization of a new enamel used as a protective and thermal barrier
Authors:
Pencea, I; Manoliu, V; Vasiliu, F; Britchi, M; Olteanu, M
Published: 2001, INTERNATIONAL JOURNAL OF MATERIALS & PRODUCT TECHNOLOGY, 16, 668, DOI: 10.1504/IJMPT.2001.001287
A new enamel has been developed to be used as a protective and thermal barrier coating of aircraft engine components subjected to thermal shocks and corrosion. This enamel is based upon the oxide system SiO2-BaO CaO-Cr2O3 and can stand about 1100 degreesC without losing its adherence and main protective characteristics. The microstructural element concentration and crystalline phases have been studied using scanning electronic microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and wide angle X-ray diffraction (WAXD) in order to offer a better understanding of the enamel characteristics.
1403. Relative abundance of single and vacancy-bonded substitutional nitrogen in CVD diamond
Authors:
Vlasov, II; Ralchenko, VG; Khomich, AV; Nistor, SV; Shoemaker, D; Khmelnitskii, RA
Published: SEP 16 2000, PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, 181, 90, DOI: 10.1002/1521-396X(200009)181:1<83::AID-PSSA83>3.0.CO;2-6
Relations between the concentrations of neutral (N-0) and charged (N+) single-substitutional nitrogen and of nitrogen-vacancy (N-V) complexes in chemical vapour deposited diamond films of approximate to 0.2 mm thickness with nitrogen impurity concentration levels of 10 ppm are studied. For this purpose the films were subjected to 8 MeV electron irradiation at room temperature and subsequent annealing at 800 degrees C. The samples were analysed by micro-photoluminescence; visible and IR absorption, and Electron Spin Resonance techniques. It was found that the concentration of nitrogen in the (N-V) and N+ forms, in as-grown films, is less than 0.1% and 10% of the neutral substitutional nitrogen N-0, respectively.
1404. Nitrogen and hydrogen in thick diamond films grown by microwave plasma enhanced chemical vapor deposition at variable H-2 flow rates
Authors:
Nistor, SV; Stefan, M; Ralchenko, V; Khomich, AV; Schoemaker, D
Published: JUN 15 2000, JOURNAL OF APPLIED PHYSICS, 87, 8746, DOI: 10.1063/1.373604
The presence and concentration of nitrogen and hydrogen impurities in thick diamond films grown by microwave plasma chemical vapor deposition at various H-2 gas flow rates, keeping a constant [CH4]:[H-2]=2.5% concentration ratio, have been determined by electron spin resonance and optical absorption spectroscopy. The relative concentration of both impurities, present as paramagnetic atomic species with different relaxation properties, has been found by ESR measurements to decrease exponentially with the increase in the H-2 gas flow rate. Moreover, the resulting values were proportional to the content of substitutional nitrogen and CHx groups obtained from infrared and ultraviolet-visible optical absorption measurements, respectively. The decrease in the concentration of both impurities with an increase in the quality of the studied diamond films, early observed from high resolution electron microscopy studies on the same samples, strongly suggests that the incorporation of both impurities, as paramagnetic atomic species, is directly related to the concentration of the extended lattice defects. (C) 2000 American Institute of Physics. [S0021- 8979(00)08611-4].
1405. Structural investigation of a La0.6Y0.07Ca0.33MnO3 thin film by high resolution transmission electron microscopy
Authors:
Ghica, C; Nistor, LC; Teodorescu, VS; Valeanu, M; Ristoscu, C; Mihailescu, IN; Deville, JP; Werckmann, J
Published: MAR 2000, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 2, 72, DOI:
The morphology and structure of a La0.6Y0.07Ca0.33MnO3 thin film is studied by transmission electron microscopy. The film was grown by pulsed laser deposition (PLD) on an MgO-buffered silicon <100> wafer. The as-deposited films are polycrystalline and show a columnar morphology. We present a detailed high-resolution transmission electron microscopy structural study concerning a possible monoclinic distortion of the orthorhombic LYCMO crystal cell. (Received February 22, 2000; accepted March 10, 2000).
1406. Sr-ferrite thin films grown on sapphire by pulsed laser deposition
Authors:
Koleva, ME; Zotova, S; Atanasov, PA; Tomov, RI; Ristoscu, C; Nelea, V; Chiritescu, C; Gyorgy, E; Ghica, C; Mihailescu, IN
Published: DEC 15 2000, APPLIED SURFACE SCIENCE, 168, 113, DOI: 10.1016/S0169-4332(00)00612-7
High-quality epitaxial strontium-hexaferrite (SrFe12O19) thin films were grown by pulsed laser deposition (PLD) on c-cut sapphire using KrF* excimer laser at a fluency of 2 J/cm(2) and substrate temperature of 800 degreesC in 100 mTorr oxygen environment. The X-ray diffraction (XRD) and morphology analyzes showed films with excellent crystalline structure and Aat surface. The thickness was found to influence considerably the surface morphology and magnetic properties of the as-deposited films. The highest orientation and the best morphology with smooth surface and fine grain structure was obtained for the him having a thickness of 750 nm. The highest coercive force of 1453 Oe was measured for this film in perpendicular to the plane direction. (C) 2000 Elsevier Science B.V. All rights reserved.
1407. Optical and structural differences between RF and DC AlxNy magnetron sputtered films
Authors:
Dumitru, V; Morosanu, C; Sandu, V; Stoica, A
Published: JAN 24 2000, THIN SOLID FILMS, 359, 20, DOI: 10.1016/S0040-6090(99)00726-9
AlN films have been deposited by RF (1.78 MHz) and DC reactive magnetron sputtering (argon and nitrogen) on glass substrates at low temperatures (< 150 degrees C) and with 16, 21 and 30% nitrogen ratios. We have found optically and structurally distinguishable characteristics for films (both opaque and transparent), obtained using these two experimental methods. We suggest that these differences are due to plasma effects in the substrate during growth, resulting from the different ionic bombardment rates of the two sputtering modes. (C) 2000 Elsevier Science S.A. All rights reserved.
1408. Mossbauer spectroscopy study of Ti-Zr-Ni-Fe icosahedral and approximant phases
Authors:
Nicula, R; Kuncser, V; Jianu, A; Filoti, G; Burkel, E
Published: DEC 15 2000, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 294, 541, DOI: 10.1016/S0921-5093(00)01160-6
Quaternary Ti53Zr21Ni13Fe13 alloys were prepared by melt-spinning using peripheral wheel speeds omega =19.5, 24.2 and 30m/s. The icosahedral (i-) phase formation was studied using high resolution synchrotron radiation powder diffraction. An amorphous phase component is present irrespective of the rapid solidification conditions, its volume fraction decreasing towards lower quenching speed values. The amorphous phase coexists with a b.c.c. rational approximant phase (W-phase). For omega below 20 m/s the formation of an i-phase was also noticed. Transmission Fe-57 Mossbauer spectroscopy measurements indicate that the number of asymmetrical Fe positions decreases with decreasing w in agreement with the improved structural perfection of the W-phase and with the formation of an additional i-phase. (C) 2000 Elsevier Science B.V. All rights reserved.
1409. Optical properties and defect structure of CVD diamond films annealed at 900-1600 degrees C
Authors:
Khomich, AV; Ralchenko, V; Nistor, L; Vlasov, I; Khmelnitskiy, R
Published: SEP 16 2000, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 181, 44, DOI: 10.1002/1521-396X(200009)181:1<37::AID-PSSA37>3.0.CO;2-T
Optical absorption evolution is studied for 150-800 mu m thick diamond films grown by microwave plasma enhanced CVD technique and annealed in vacuum at temperatures 900-1600 degrees C. A noticeable internal degradation (darkening) of the films takes place at T > 1300 degrees C. Changes in the concentration of different CH, groups are revealed from the IR spectra starting at T > 1000 degrees C. Up to 25% of the total amount of hydrogen in as-grown films is found to be unbonded. An interesting effect of reduced absorption in UV range due to the formation of new C-H bonds by reaction of primarily unbonded hydrogen is observed. The diamond darkening correlating with the bonded hydrogen loss process, is ascribed to the appearance of a graphite-like phase (being under a high stress) presumably at grain boundaries, that is revealed by the appearance of a specific absorption peak in UV spectra.
1410. Influence of the Jahn-Teller effect on the linewidth of the Mossbauer spectra of natural spinels
Authors:
Kuncser, V; Russo, U; Graziani, R; Della Giusta, A; Filoti, G
Published: FEB 21 2000, JOURNAL OF PHYSICS-CONDENSED MATTER, 12, 1460, DOI: 10.1088/0953-8984/12/7/326
The temperature dependence of the Mossbauer doublet linewidth of tetrahedrally coordinated Fe2+ ions, distorted by the Jahn-Teller effect, was analysed by means of a new mathematical approach. The idea was that the linewidth depends on a distribution of quadrupole splittings that are in turn dependent on temperature. The variation of the quadrupole splitting was supposed to be connected with the temperature dependent population of the ground state E-g orbitals, split by the local Jahn-Teller effect. The model was applied to three sets of experimental data. The barrier splitting Delta between the two E-g electronic states as well as their widths, delta Delta, were obtained.
1411. The Pb(2+)(Li) and Pb(2+)(Na) centres in KCl crystals
Authors:
Tsuboi, T; Polosan, S; Topa, V
Published: FEB 2000, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 217, 980, DOI: 10.1002/(SICI)1521-3951(200002)217:2<975::AID-PSSB975>3.0.CO;2-U
Emission, absorption and magnetic circular dichroism spectra have been studied on Li(+)- and Pb(2+)-codoped KCl crystals. Two emission bands (one is the A(T)-like emission and the other the A(X)-like emission) have been observed at 350 and 453 nm at room temperature, respectively These emissions have been observed by excitation in the absorption bands with peaks at 270 and 281 nm. These emission bands are attributed to the Pb(2+)(Li) centre, where a Pb(2+) ion has a Li(+) ion at one of the six nearest neighbouring cation sites. Measurements have been also made on Na(+)- and Pb(2+)-codopcd KCl crystals. Unlike the Pb(2+)(Li) centre, only the A(T)-like emission band with a peak at 347 nm due to the Pb(2+)(Na) centre has been observed. It is suggested that such a difference is due to a difference in the position of the impurity alkali ion substituted for the K(+) ion.
1412. Electrical properties of nanocrystalline porous silicon
Authors:
Ciurea, ML; Iancu, V
Published: 2000, 2000 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, CAS 2000 PROCEEDINGS, 64, DOI: 10.1109/SMICND.2000.890188
Conduction properties as well as trapping phenomena in nanocrystalline porous silicon films are investigated in relation to their microstructure. Theoretical models to describe the phenomena are proposed. The main results presented in this paper are: the two-scale porosity of our porous silicon films, the decisive role of the quantum confinement to the conduction phenomena and the prominent part played by the oxidation on the surface effects.
1413. Rapid synthesis of polycrystalline CuGa1-xInxTe2 compounds
Authors:
Gaburici, D; Lazarescu, MF; Manea, A; Sandu, V
Published: 2000, CRYSTAL RESEARCH AND TECHNOLOGY, 35, 270, DOI: 10.1002/1521-4079(200003)35:3<265::AID-CRAT265>3.0.CO;2-9
A series of CuGa1-xInxTe2 bulk quatemary compounds (x=0.17, 0.33, 0.50, 0.67, 0.83) has been synthesized from the corresponding stoichiometric melts by a rapid cooling procedure. The same procedure was used to obtain the ternary bulk compounds CuGaTe2 and CuInTe2 with the aim to compare, according the Vegard law, the match between molar fraction of the indium (x) and the lattice parameters for the aforementioned quatemary compounds. The nature of the crystalline phases, the local structure homogeneity and stoichiometry of these compounds have been investigated by x-ray diffraction (XRD) and scanning electron microscopy (SERI) techniques. The analysis revealed the presence of the chalcopyritic structure for all the samples.
1414. Pulsed laser deposition of hydroxyapatite thin films on Ti-5A1-2.5Fe substrates with and without buffer layers
Authors:
Nelea, V; Ristoscu, C; Chiritescu, C; Ghica, C; Mihailescu, IN; Pelletier, H; Mille, P; Cornet, A
Published: DEC 15 2000, APPLIED SURFACE SCIENCE, 168, 131, DOI: 10.1016/S0169-4332(00)00616-4
We present a method for processing hydroxyapatite (HA) thin films on Ti-5Al-2.5Fe substrates. The films were grown by pulsed laser deposition (PLD) in vacuum at room temperature, using a KrFdouble dagger excimer laser. The amorphous as-deposited HA films were recrystallized in ambient air by a thermal treatment at 550 degreesC. The best results have been obtained when inserting a buffer layer of ceramic materials (TiN, ZrO2 or Al2O3) The films were characterized by complementary techniques: grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), cross-section transmission electron microscopy (XTEM), SAED, energy dispersive X-ray spectroscopy (EDS) and nanoindentation. The samples with buffer interlayer preserve the stoichiometry are completely recrystallized and present better mechanical characteristics as compared with that without buffer interlayer. (C) 2000 Published by Elsevier Science B.V.
1415. Trapping levels in nanocrystalline porous silicon
Authors:
Ciurea, ML; Draghici, M; Lazanu, S; Iancu, V; Nassiopoulou, A; Ioannou, V; Tsakiri, V
Published: MAY 22 2000, APPLIED PHYSICS LETTERS, 76, 3069, DOI: 10.1063/1.126581
Trapping levels in fresh (one month) and naturally aged (one year) nanocrystalline porous silicon have been investigated using the optical charging spectroscopy method. Four significant maxima and/or shoulders were observed for fresh samples and five for aged ones. They have been attributed to five and six trapping levels, respectively. The trapping centers corresponding to the most shallow four levels are situated at or nearby the internal surface of the porous silicon films. (C) 2000 American Institute of Physics. [S0003-6951(00)01621-1].
1416. Fish-tail effect and its evolution under neutron irradiation in Li-doped YBa2Cu3O7-x
Authors:
Sandu, V; Oussena, M; de Groot, PAJ
Published: AUG 2000, JOURNAL OF SUPERCONDUCTIVITY, 13, 528, DOI: 10.1023/A:1007860431003
The evolution of the critical current density of Li-doped YBa2Cu3O7-x polycrystalline samples submitted to neutron irradiation is investigated as function of magnetic field (0 less than or equal to B less than or equal to 6 T) temperature (5 less than or equal to T less than or equal to 85 K) and neutron fluence (0 less than or equal to Phi less than or equal to 9.98 x 10(17) cm(-2)). At fluences lower than 10(17) cm(-2), a second peak in j(s) vs. B dependence is present (fish-tail effect). Its magnitude decreases with increasing the fluence. Above 10(17) cm(-2), the second peak of current density completely disappears; instead, the logarithmic susceptibility shows a second peak at a certain field B-infi. A dependence of B-infi on fluence is proposed.
1417. Oxidation-induced modifications of trap parameters in nanocrystalline porous silicon
Authors:
Draghici, M; Miu, M; Iancu, V; Nassiopoulou, A; Kleps, I; Angelescu, A; Ciurea, ML
Published: NOV 2000, PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, 182, 243, DOI: 10.1002/1521-396X(200011)182:1<239::AID-PSSA239>3.0.CO;2-K
The changes produced by anodic and natural oxidation upon the trap parameters in nanocrystalline porous silicon were compared. To put them in evidence, we used optical charging spectroscopy The same trapping It levels (with the same activation energies) were observed after both oxidation processes. In comparison with flesh samples, a new trapping level (the deepest one) appears and the concentrations of the surface traps strongly diminish.
1418. Microstructural characterization of diamond films deposited on c-BN crystals
Authors:
Nistor, L; Buschmann, V; Ralchenko, V; Dinca, G; Vlasov, I; Van Landuyt, J; Fuess, H
Published: APR-MAY 2000, DIAMOND AND RELATED MATERIALS, 9, 273, DOI: 10.1016/S0925-9635(99)00246-0
The morphology and structure of diamond films, deposited on cubic boron nitride (c-BN) crystals by microwave-plasma-enhanced chemical vapor deposition, is studied by high-resolution scanning electron microscopy and micro-Raman spectroscopy. The c-BN crystals, with sizes of 200 to 350 mu m and grown by a high-temperature/high-pressure technique, were embedded in a copper holder, and used as substrates in deposition runs of 15 min to 5 h. The nucleation centers for diamond appear as well-shaped cuboctahedral crystallites, having diameters of approximately 100 nm. With increasing deposition time the diamond crystallites grew larger, forming islands on the c-BN faces. In some cases, epitaxial growth was observed on the (111) c-BN faces where coalesced particles gave rise to very smooth regions. A number of diamond crystals with peculiar shapes are observed, such as a pseudo five-fold symmetry due to multiple twinning. Moreover, both randomly distributed carbon tubes, about 100 nn in diameter and 1 mu m in length, and spherically shaped features are observed in samples prepared under the typical conditions of diamond deposition, this effect being ascribed to the influence of plasma-sputtered copper contamination. Quite unusual diamond crystals with a deep, pyramidal-shaped hole in the middle grew on the copper substrate between the c-BN crystals. (C) 2000 Elsevier Science S.A. All rights reserved.
1419. Lanthanum chromites doped with divalent transition metals
Authors:
Jitaru, I; Berger, D; Fruth, V; Novac, A; Stanica, N; Rusu, F
Published: 2000, CERAMICS INTERNATIONAL, 26, 196, DOI: 10.1016/S0272-8842(99)00039-5
Heteropolynuclear complex compounds isolated in Cr2O3. xH(2)O-La(NO3)(3)-M(NO3)(2)-A-NH3, (A = CH3COO-,C2O42-; M = Cu, Ni) systems were used as precursors for LaCr1-xMxO3. The perovskite structure of doped lanthanum chromites was determined by XRD analysis. The unit cell volumes, specific surface areas and magnetic properties were investigated. The proposed methods offer new, simple, less expensive procedures for obtaining doped lanthanum chromites. (C) 2000 Elsevier Science Ltd and Techna S.r.l. All rights reserved.
1420. Experimental investigation of the nonlinear optical response in Fe : PVA
Authors:
Bulinski, M; Iova, I; Belea, A; Kuncser, V; Filoti, G
Published: JAN 2000, JOURNAL OF MATERIALS SCIENCE LETTERS, 19, 28, DOI: 10.1023/A:1006739412409
1421. Recrystallisation phenomena during high energy ball milling
Authors:
Nicoara, G; Popescu-Pogrion, N; Husar, V
Published: 2000, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 2, 633, DOI:
The structural and morphological evolution of the NiZn ferrite during mechanical activation has been investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM) and chemical analysis. During the milling process an important amount of metallic phases due to the vials and balls contaminates the ferrite powder and functions as co-participant to the mechanical activation. The XRD- spectra of the as-milled powders showed the presence of the metallic contribution up to 200 hours of milling. For longer intervals of time the extralines intensities due to the presence of metallic phases decrease and only a spinel phase is observed after 400 hours of total milling. The TEM image revealed, after 200 hours, spheroidal nanometric particles in the range 30-80 nm, alongside of some needle type particles. When the milling time was increased, some big plate monocrystals appear and grow. After 400 hour milling, polyhedral crystals 250 divided by 1000 nm size could be observed in the powder.
1422. Hysteresis effect due to the exchange Coulomb interaction in short-period superlattices in tilted magnetic fields
Authors:
Manolescu, A; Gudmundsson, V
Published: MAR 15 2000, PHYSICAL REVIEW B, 61, R7860, DOI: 10.1103/PhysRevB.61.R7858
We calculate the ground state of a two-dimensional electron gas in a shea-period lateral potential in magnetic field, with the Coulomb electron-electron interaction included in the Hartree-Fock approximation. For a sufficiently short period the dominant Coulomb effects are determined by the exchange interaction. We find numerical solutions of the self-consistent equations that have hysteresis properties when the magnetic field is tilted and increased, such that the perpendicular component is always constant. This behavior is a result of the interplay of the exchange interaction with the energy dispersion and the spin splitting. We suggest that hysteresis effects of this type could be observable in magnetotransport and magnetization experiments on quantum-wire and quantum-dot superlattices.
1423. Structural comparison between La0.60Y0.07Ca0.33MnO3-delta bulk and pulsed laser deposited thin films
Authors:
Teodorescu, VS; Nistor, LC; Valeanu, M; Ghica, C; Sandu, C; Mihailescu, IN; Ristoscu, C; Deville, JP; Werckmann, J
Published: MAR 2000, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 211, 60, DOI: 10.1016/S0304-8853(99)00713-1
This work is a comparative study of the structural and magneto-transport properties of La0.60Y0.07Ca0.33MnO3-delta (LYCMO) as bulk and thin film. The bulk samples were prepared by solid-state reaction between the corresponding metallic oxides mixed in stoichiometric ratios. The thin film was deposited by pulsed laser deposition on an MgO single crystal using an excimer laser. We show that the structure and stoichiometry of the bulk target are perfectly reproduced in the thin film. We measured the magnetoresistive effect on both the LYCMO pellet and the thin film by using the four-probe technique. The maximum of the MR effect is 680% on the polycrystalline thin film in a 2T magnetic field. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
1424. Finite-size effects in the magnetization of periodic mesoscopic systems
Authors:
Erlingsson, SI; Manolescu, A; Gudmundsson, V
Published: FEB 2000, PHYSICA E, 6, 766, DOI: 10.1016/S1386-9477(99)00198-8
We calculate the orbital magnetization of a confined 2DEG as a function of the number of electrons in the system. Size effects are investigated by systematically increasing the area of the confining region. The results for the finite system are compared to an infinite one, where the magnetization is calculated in the thermodynamic limit. In all calculations the electron-electron interaction is included in the Hartree approximation. (C) 2000 Elsevier Science B.V. All rights reserved.
1425. The inhibition of the corrosion of Armco iron in HCl solutions in the presence of surfactants of the type of N-alkyl quaternary ammonium salts
Authors:
Branzoi, V; Branzoi, F; Baibarac, M
Published: AUG 15 2000, MATERIALS CHEMISTRY AND PHYSICS, 65, 297, DOI: 10.1016/S0254-0584(00)00260-1
The polarization behaviour of Armco iron in aqueous solutions of HCl with and without inhibitors has been studied by the potentiostatic method. At lower overvoltage values, the dissolution process is controlled by activation, while at higher overvoltage values, the dissolution process is controlled by diffusion. The inhibition of this metal corrosion in the aqueous solutions of HCl has been studied using four surfactants. Under the critical micelle concentration (CMC), the inhibition of these four surfactants is negligible. At a concentration higher than the CMC, the inhibiting action of tetradecyl trimethyl ammonium iodide (TTAI), tetradecyl trimethyl ammonium bromide (TTAB), hexadecyl trimethyl ammonium bromide (HTAB) and dodecyl trimethyl ammonium bromide (DTAB) increases rapidly. The process of inhibition was attributed to the formation of adsorbed film on the metal surface, that protects the metal against corrosive agents. Protection efficiency improved when the inhibitor concentration and the length of the alkyl chain were increased. The four quaternary ammonium salts tested were adsorbed on the Armco iron surface according to a Langmuir isotherm. (C) 2000 Elsevier Science S.A. All rights reserved.
1426. Magnetization in short-period mesoscopic electron systems
Authors:
Gudmundsson, V; Erlingsson, SI; Manolescu, A
Published: FEB 15 2000, PHYSICAL REVIEW B, 61, 4843, DOI: 10.1103/PhysRevB.61.4835
We calculate the magnetization of the two-dimensional electron gas in a short-period lateral superlattice, with the Coulomb interaction included in Hartree and Hatree-Fock approximations. We compare the results for a finite, mesoscopic system modulated by a periodic potential, with the results for the infinite periodic system. In addition to the expected strong exchange effects, the size of the system, the type and the strength of the lateral modulation leave their fingerprints on the magnetization.
1427. Properties of metal clusters embedded in KCl matrix
Authors:
Polosan, S; Apostol, E; Topa, V
Published: 2000, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 2, 642, DOI:
The characterization of nanocrystals embedded in alkali halide crystals concerning shape and size distribution has been performed. Optical absorption, transmission electron microscopy (TEM), x-ray diffraction (XRD) and electron spin resonance (RES) methods has been used. The experimental results are in good agreement with the theoretical considerations concerning absorption and scattering of light by the metal clusters.
1428. Jahn-Teller configurations in natural spinels
Authors:
Kuncser, V; Russo, U; Graziani, R; Della Giusta, A; Palade, P; Bulinski, M; Filoti, G
Published: DEC 1999, PHYSICS AND CHEMISTRY OF MINERALS, 27, 102, DOI: 10.1007/s002690050245
The local configurations and related hyperfine interactions of the tetrahedrally coordinated Fe2+ in two natural spinels were investigated. A special fitting procedure of the Mossbauer spectra is proposed in order to cover the involved mechanisms over the whole temperature range. The behavior of the quadrupole splitting vs temperature was successfully explained in terms of the split of the electronic 3d ground state doublet under a non-cooperative Jahn-Teller effect also providing estimates of the splitting energy for each configuration.
1429. On the lead determination in alkali halides by spectroscopic method
Authors:
Dan, C; Topa, V; Lazarescu, MF
Published: 1999, CRYSTAL RESEARCH AND TECHNOLOGY, 34, 895, DOI: 10.1002/(SICI)1521-4079(199908)34:7<891::AID-CRAT891>3.3.CO;2-B
The octahedral complex [PbX6](4,) (X=Cl, Br) in natrium/potassium chloride or bromide monocrystals as well as in the concentrated solutions of these alkali halides, impurified by lead, shows a characteristic absorption in the region 250-300 nm. Using the height of this absorption band, a quantitative method for determination of lead in the range 8'10(14) - 3.2'10(16) atoms/cm(3) of halide monocrystals or 0.5 20 mg/ml of solutions respectively, was elaborated. Standard graphs of the peak extinction of [PbX6](4) in natrium/potassium chloride and bromide as function of the lead concentration have been obtained.
1430. ESR of paramagnetic atom defects in CVD-grown diamond
Authors:
Nistor, SV; Stefan, M; Ralchenko, V; Goovaerts, E; Schoemaker, D
Published: 1999, RADIATION EFFECTS AND DEFECTS IN SOLIDS, 149, 307, DOI: 10.1080/10420159908230172
ESR measurements in the 9 and 94 GHz microwave frequency bands were performed on thick free-standing polycrystalline diamond films grown by microwave plasma enhanced CVD from CH4/H-2 mixtures under variable deposition conditions. An exponential decrease in the concentration of the N-0 centres with increase in the H-2 flow rate was found. Neither H1 nor H2 centres could be detected.
1431. Memorization of short-range potential fluctuations in Landau levels
Authors:
Manolescu, A; Gudmundsson, V
Published: FEB 15 1999, PHYSICAL REVIEW B, 59, 5430, DOI: 10.1103/PhysRevB.59.5426
We calculate energy spectra; of a two-dimensional electron system in a perpendicular magnetic field and periodic potentials of short periods. The Coulomb interaction is included within a screened Hartree-Fock approximation. The electrostatic screening is poor, and the exchange interatcion amplifies the energy dispersion We obtain, by numerical iterations, self-consistent solutions that have a hysteresislike property. With increasing amplitude of the external potential, the energy dispersion and the electron density become periodic, and they remain stable when the external potential is reduced to zero. We explain this property in physical terms, and speculate that a real system could memorize short-range potential fluctuations after the potential has been turned off.
1432. XTEM study of Al doped TiO2 anatase epitaxial films deposited on MgO by pulsed laser deposition
Authors:
Teodorescu, VS; Blanchin, MG; Garapon, C; Champeaux, C
Published: NOV 1999, JOURNAL OF MATERIALS SCIENCE, 34, 5476, DOI: 10.1023/A:1004796008417
Al doped TiO2 anatase films epitaxially grown by Pulsed Laser Deposition (PLD) on MgO single crystal substrates have been studied by cross-section transmission electron microscopy. The main structural features of such films are the columnar morphology of the anatase grains and the formation of a spinel buffer layer at the TiO2/MgO interface. The spinel layer is Al rich and displays a steep gradient in Mg composition. Correlation between the microstructure and the optical properties of the films is presented also. (C) 1999 Kluwer Academic Publishers.
1433. Transmission electron microscopy study of thin films and surface implanted wafers of LiNbO3
Authors:
Teodorescu, VS; Ghica, C; Blanchin, MG; Moretti, P
Published: JUN 1999, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 1, 48, DOI:
Thin films prepared by pulsed laser deposition and single crystal implanted LiNbO3 wafers used in optoelectronic technology were studied by transmission electron microscopy. The use of high electron beam density for high resolution imaging induced a decomposition effect in the implanted LiNbO3 lattice. It is shown that the most probable decomposition leads to the formation of NbO2 nuclei by a topotactic solid state reaction along the pseudo-cubic directions of the lithium niobate matrix. It is also shown that powdered LiNbO3 specimens or samples obtained by preparation of cross section of LiNbO3 thin films are more stable in the electron beam, compared with the samples obtained from implanted LiNbO3 wafers.
1434. Silver nanocrystals obtained by the ionization of Ag--ions in KCl
Authors:
Vasile, E; Datcu, M; Polosan, S; Apostol, E; Topa, V
Published: MAR 1999, JOURNAL OF CRYSTAL GROWTH, 198, 810, DOI: 10.1016/S0022-0248(98)01112-9
This paper discusses the formation of "corals" arranged silver nanocrystals in a KCl matrix starting from Ag- ions ( similar to 10(17) ions/cm(3)) by subsequent thermal annealing at temperatures between 400-700 degrees C and 250 degrees C. In the last case only, by illumination with total radiation of a 100W Xe-lamp, spherical separated silver clusters were obtained. The stepwise annealing processes were followed by the recording of the optical absorption spectra at 20 degrees C. The sizes of silver clusters were determined through transmission electron microscopy. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
1435. Influence of He, Ne and Kr addition in reactive Ar/N-2 dc magnetron plasma on TiN deposition
Authors:
Braic, M; Zoita, CN; Braic, V; Kiss, A; Popescu, M; Musa, G
Published: MAY 1999, VACUUM, 53, 45, DOI: 10.1016/S0042-207X(98)00419-9
A reactive DC magnetron discharge produced in a TIN deposition system was investigated using optical emission spectroscopy. The influence of He, Ne and Kr addition into an Ar + N-2 working atmosphere was investigated. Addition of small percentages of He or Ne in the working atmosphere of Ar + N-2, caused a decrease of the N-2(+) (B)/N-2(C) ratio, whle with Kr addition the ratio increased. The known decrease of the relative intensity of Ti lines for N-2 addition was also observed for He addition, while it increases when Ne and Kr are added. XRD analysis of TiN thin films revealed that He addition determines the same effect as N-2. This behavior is explained by N and N+ density increase for He addition. (C) 1999 Elsevier Science Ltd. All rights reserved.
1436. An XPS and XRD study of physical and chemical homogeneity of Pb(Zr,Ti)O-3 thin films obtained by pulsed laser deposition
Authors:
Verardi, P; Craciun, F; Mirenghi, L; Dinescu, M; Sandu, V
Published: JAN 1999, APPLIED SURFACE SCIENCE, 138, 556, DOI: 10.1016/S0169-4332(98)00577-7
Pb(Zr,Ti)O-3 (PZT) oriented films deposited by laser ablation on Bu(lll)/Si(lll) have been tested by different techniques for their physico-chemical homogeneity. The samples have been divided in different zones, in order to verify the existence of chemical and structural differences between different regions. Few techniques like X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) have been employed for characterization. XRD analyses showed differences regarding the crystallographic content and the degree of orientation between zones subjected to the plasma arriving at different angles of incidence on the sample surface. In the same zones XPS studies have been performed by a VG ESCALAB 210 Spectrometer, using a non-monochromatic AlKalpha X-ray source (300 W) in the five channel hemispherical analyzer. Wide scans in the binding energy scale 0-1200 eV, at 50 eV analyzer pass energy, were collected both from the as received surface and after sputter cleaning in order to put into evidence all the constituents of the film. Narrow scans of Ti 2p, Zr 3d, Pb 4f and O 1s is were also acquired at 20 eV and 0.1 eV/channel pass energy and 100 ms of dwell time in order to give a better insight into the chemical bonds form and a semiquantitative analyze of the present chemical species. The piezoelectric properties of different zones were also measured, (C) 1999 Published by Elsevier Science B.V. All rights reserved.
1437. Structural aspects of CVD diamond wafers grown at different hydrogen flow rates
Authors:
Nistor, L; Van Landuyt, J; Ralchenko, V
Published: JUL 16 1999, PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, 174, 9, DOI: 10.1002/(SICI)1521-396X(199907)174:1<5::AID-PSSA5>3.0.CO;2-C
Microstructural modifications of thick diamond films grown by microwave plasma CVD at different reactant gas now rates have been studied by transmission electron microscopy. A strong degradation of the diamond quality was observed at low hydrogen flow rates, while the layer grown at the highest hydrogen flow rate was almost defect free. The abundance of various defects observed, mostly microtwins, stacking faults, dislocations and even amorphous regions, clearly correlates with the gas flow rate. Illustrations of typical defects are given and, in particular, planar defect intersections are characterized at atomic resolution in specimens where their density was high.
1438. Fe-57 Mossbauer study of Pr-m(Fe, MO)(n) compounds with m : n=2 : 17 and 1 : 12
Authors:
Morariu, M; Lazar, DP; Galatanu, A; Plugaru, N; Kuncser, V; Filoti, G; Hilscher, G; Kottar, A
Published: MAR 30 1999, JOURNAL OF ALLOYS AND COMPOUNDS, 285, 47, DOI: 10.1016/S0925-8388(98)01055-X
The effects of Mo substitution in Pr2Fe17-xMox and PrFe12-xMox compounds were investigated by X-ray diffraction, magnetic measurements and Mossbauer spectroscopy. Different fitting procedures, using magnetic sextets at low temperature, magnetic sextets and quadrupole doublets at room temperature and paramagnetic doublets well above the Curie points, had to be considered in order to analyze the Mossbauer spectra. The Mossbauer data obtained on the Mo-containing compounds stand for distributions of the hyperfine fields due to the random distributions of Mo over the 6c sites in the 2:17 and 8i sites in the 1:12 compounds. The variations in the isomer shifts and hyperfine fields with composition are discussed in relationship to the local environment details at the different iron sites. Site-specific information on the electronic effects due to Fe(Sd)-Mo(4d) states hybridization are derived. (C) 1999 Elsevier Science S.A. All rights reserved.
1439. Surface quantum wells in hydrogen implanted ZnO
Authors:
Bogatu, V; Goldenblum, A; Many, A; Goldstein, Y
Published: MAR 1999, PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 212, 96, DOI: 10.1002/(SICI)1521-3951(199903)212:1<89::AID-PSSB89>3.3.CO;2-1
Low energy hydrogen ion implantation in ZnO creates an accumulation layer near the surface, giving rise to a quantum well. The corresponding self-consistent Hartree problem is solved by taking into account the donor distribution resulting from the implantation process. The values of the surface potential as a function of repelled away electron concentration are derived. The resulting data are compared with experimental values obtained from space-charge capacitance measurements. A comparative study between the semi-classical and self-consistent quantum treatments is presented.
1440. Multilayer structures deposited by laser ablation
Authors:
Dinescu, M; Stanciu, C; Ghica, D; Dinu, R; Sandu, V; Nastase, N; Balucani, M; Bondarenko, V; Frachina, L; Lamedica, G; Ferrari, A
Published: APR 20 1999, SENSORS AND ACTUATORS A-PHYSICAL, 74, 30, DOI: 10.1016/S0924-4247(98)00331-8
TiN/Si structures were deposited on Si wafers by pulsed laser deposition technique. The highly conductive TiN films were grown on heated (100) Si substrates by laser ablation of a high purity Ti target in nitrogen reactive atmosphere. Subsequently, the Si layer was deposited by laser ablation of a Si target in vacuum (down to 10(-6) mbar) or in low pressure inert gas. The nitrogen gas pressure and the substrate temperature were found to strongly influence the TiN film structure and orientation. The degree of crystallinity of the Si layer grown on the TiN film was found to depend on Si/TiN collector temperature. Values below 550 degrees C (the threshold of TiN oxidation activation) were used in the experiments. Techniques as X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), High Resolution Transmission Electron Microscopy (HRTEM), Scanning Force Microscopy (SFM) have been used to characterize the deposited structures. The TiN/Si structure rectifying properties were tested. The obtained Si/TiN/Si structure could be suitable for the building of Permeable Base Transistor (PBT, vertical MESFET) devices. (C) 1999 Elsevier Science S.A. All rights reserved.
1441. DFT investigation of the adsorption of atomic hydrogen on a cluster-model graphite surface
Authors:
Jeloaica, L; Sidis, V
Published: JAN 29 1999, CHEMICAL PHYSICS LETTERS, 300, 162, DOI: 10.1016/S0009-2614(98)01337-2
The H-graphite interaction is studied for the first time in the framework of density functional theory. A coronene-like model of the (0001) graphite surface is considered. LSD and LSD + GGA results are presented for both a planar substrate and for considering substrate relaxation. Two adsorption regions separated by a barrier are found: a physisorption region around 3 Angstrom from the surface and a chemisorption region around 1.5 Angstrom. The former is site-independent and compatible with a high mobility of the H atoms parallel to the surface. The latter is located exclusively on top of a carbon atom and requires a significant surface relaxation. (C) 1999 Elsevier Science B.V. All rights reserved.
1442. Surface quantum wells in hydrogen implanted ZnO (vol 212, pg 89, 1999)
Authors:
Bogatu, V; Goldenblum, A; Many, A; Goldstein, Y
Published: APR 1999, PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 212, 397, DOI: 10.1002/(SICI)1521-3951(199904)212:2<397::AID-PSSB397>3.0.CO;2-#
1443. Intermediate frustration in [Fe3O(CH3COO)(6)(H2O)(3)] NO3 center dot 4(H2O) trinuclear cluster
Authors:
Filoti, G; Bartolome, J; Dickson, DPE; Rillo, C; Prisecaru, I; Jovmir, T; Kuncser, V; Turta, C
Published: MAY 1999, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 196, 563, DOI: 10.1016/S0304-8853(98)00825-7
The frustration of the trinuclear clusters with antiferromagnetic intracluster interaction was investigated at low temperature and in applied magnetic field, by Mossbauer, susceptibility and magnetisation measurements. The spin configuration and the electronic state are described as a function of the temperature and the intensity of the applied field. The values of the exchange integrals are provided. (C) 1999 Elsevier Science B.V. All rights reserved.
1444. Colloidal sol-gel ITO films on tube grown silicon
Authors:
Stoica, TF; Stoica, TA; Vanca, V; Lakatos, E; Zaharescu, M
Published: JUL 6 1999, THIN SOLID FILMS, 348, 278, DOI: 10.1016/S0040-6090(99)00136-4
Electrical and optical properties of colloidal PTO sol-gel films on glass substrates have been investigated. The optical gap of 3.14 eV and room temperature conductivity of 4 Ohm(-1) cm(-1) were obtained on ITO layers of about 500 Angstrom thickness. Heterostructures of ITO/n-Si have been obtained by colloidal sol-gel deposition of ITO. In this deposition method, the oxidation of silicon during the heterostructure formation can be avoided. The silicon substrates were cut out of silicon tubes. Electrical and photoelectric properties of these structures have been studied in comparison with those of p-n tube-Si junctions obtained by thermal boron diffusion. On ITO/n-Si heterojunctions, the spectral quantum efficiency has a maximum value of about two times higher and a blue shift of the maximum position from 0.75 to 0.6 mu m, than those for p-n junctions. A theoretical investigation of the I-V curves for ITO/n-Si heterojunctions under various illumination levels has been performed and contribution of the tunneling and series resistance phenomena were evaluated. (C) 1999 Elsevier Science S.A. All rights reserved.
1445. Microstructural aspects related to carriers transport properties of nanocrystalline porous silicon films
Authors:
Ciurea, ML; Teodorescu, VS; Nistor, LC; Blanchin, MG
Published: SEP 1999, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, 146, 3521, DOI: 10.1149/1.1392507
A microstructural investigation of porous silicon films, related with a study of carriers transport. is presented. Scanning electron microscopy and conventional transmission electron microscopy with selected area electron diffraction were performed. The films show a double scale porosity: the macroporosity forms an alveolar structure at a micrometric scale and the nanoporosity forms a silicon nanowires network in the alveolar walls and at their surface. Current-voltage characteristics in the -5 to +5 V range and the temperature dependence of dark current in the 150-330 K interval at low voltage were measured. The transport properties are explained by means of a simplified quantum confinement model. Two symmetries of the nanowires, cylindrical and square, are investigated and the differences between them are shown to be insignificant. (C) 1999 The Electrochemical Society. S0013-4651(98)12-109-2. All rights reserved.
1446. High-resolution electron microscopy and electron spin resonance studies on cubic boron nitride crystals made by high-pressure/high-temperature synthesis
Authors:
Nistor, L; Nistor, S; Dinca, C; van Landuyt, J; Schoemaker, D; Copaciu, V; Georgeoni, P; Arnici, N
Published: MAR 1999, DIAMOND AND RELATED MATERIALS, 8, 742, DOI: 10.1016/S0925-9635(98)00282-9
Cubic boron nitride (c-BN) crystals synthesised at high pressures and temperatures are analysed by optical microscopy, transmission electron microscopy, electron diffraction and electron spin resonance. For various growth conditions, the results of these studies indicate that the c-BN crystals contain defects and impurities. This is the first time that dislocation cores have been revealed in c-BN at the atomic level. Atomic resolution at extended dislocations allows us to determine the stacking-fault energy in c-BN, yielding a mean value of 191+/-15 mJ m(-2). This value, which is reported for the first time for c-BN, is of the same order of magnitude as in diamond. (C) 1999 Elsevier Science S.A. All rights reserved.
1447. Irradiation damage in LiNbO3 crystals studied by transmission electron microscopy
Authors:
Teodorescu, VS; Blanchin, MG
Published: 1999, RADIATION EFFECTS AND DEFECTS IN SOLIDS, 150, 184, DOI: 10.1080/10420159908226227
Transmission electron microscopy of Er implanted LiNbO3 crystals reveals a structural modification due to the electron bi am irradiation, which consists of the decomposition of LiNbO3 in niobium oxide nanometric size domains. The corresponding electron diffraction patterns do fit at best with the NbO2 simple tetragonal phase. The orientation of the oxide nuclei is along the pseudo-cubic directions of the lithium niobate.
1448. Pulsed laser deposition of multilayer TiN/Pb(ZrxTi1-x)O-3 for piezoelectric microdevices
Authors:
Verardi, P; Dinescu, M; Craciun, F; Dinu, R; Sandu, V; Tapfer, L; Cappello, A
Published: APR 20 1999, SENSORS AND ACTUATORS A-PHYSICAL, 74, 44, DOI: 10.1016/S0924-4247(98)00342-2
Multilayer Pb(ZrTi)O-3 (PZT)/TiN/Si structures were grown by two subsequent laser ablation processes in reactive atmosphere. First, a fee-oriented TiN film was deposited by laser ablation of a Ti target in high-purity nitrogen reactive gas. Subsequently, a crystalline, piezoelectric PZT film was grown by reactive ablation of a PZT target in oxygen atmosphere. Both deposition processes were conducted at quite low Si(100) substrate temperature: 350 degrees C for TiN and 370 degrees C for PZT, in the same experimental setup (Nd-YAG laser, lambda = 1060 nm, energy/pulse 0.3 J, t(FWHM) = 10 ns). TiN film properties were analyzed by XRD and electric measurements. After the deposition of the PZT layer, the obtained structure was first characterized by XRD, SEM and SIMS techniques. Testing measurements performed after the deposition by thermal evaporation of an Al layer as top electrode on the PZT/TiN/Si structure confirm that they can be used as sensor transducer element. The TiN (as high conductive nitride) layer replaces the former Au layer used as bottom electrode. In this way, the Au diffusion inside the Si substrate, as well as in the deposited layer, is avoided, as could be observed from a comparative study of the SIMS spectra recorded for PZT/TiN/Si and PZT/Au/Si configurations. (C) 1999 Elsevier Science S.A. All rights reserved.
1449. Physico-chemical properties and X-ray study of trinuclear carboxylate [Fe3O(CH3COO)(6)(H2O)(3)](2)[PtCl6]center dot 8H(2)O
Authors:
Turta, C; Shova, S; Meriacre, V; Cadelnic, I; Gdaniec, M; Simonov, YA; Filoti, G
Published: APR 1999, POLISH JOURNAL OF CHEMISTRY, 73, 618, DOI:
Trinuclear carboxylate compound [Fe3O(CH3COO)(6)(H2O)(3)](2)[PtCl6].8H(2)O has been studied by Mossbauer spectroscopy, magnetochemistry, thermal analysis and X-ray crystallography. Crystal data: monoclinic, space group P2(1)/n a = 10.505(2), b = 14.278(3), c = 19.885(4) Angstrom, beta = 96.00(3)degrees and Z = 2. The final R-value is 0.027 for 4606 reflections with I greater than or equal to 2 sigma(I). The crystal consists of the complex [Fe3O(CH3COO)(6)(H2O)(3)](+) cations, centrosymmetric [PtCl6](2-) anions and water molecules. The [Fe3O(CH3COO)(6)(H2O)(3)](+) cation has the typical structure of a trinuclear iron(III) compound with mu(3)-O bridge. All crystal components are connected via a system of hydrogen bonds into a 3D network. Mossbauer spectrum displays at room temperature a single quadrupole doublet with an isomer shift of 0.70 mm/s and quadrupole splitting of 0.48 mm/s, consistent with high-spin Fe(III). mu(eff) per Fe atom (3.25 mu(B) at 293 K and 2.23 mu(B) at 120 K), indicate the antiferromagnetic coupling between the paramagnetic iron ions with J = -31 cm(-1).
1450. Low metal loading Ru-MCM-41 stereocontrolled hydrogenation of prostaglandin intermediates
Authors:
Coman, S; Florea, M; Cocu, F; Parvulescu, VI; Jacobs, PA; Danumah, C; Kaliaguine, S
Published: NOV 7 1999, , DOI: 10.1039/a907119i
1451. Reducibility of ruthenium in relation with zeolite structure
Authors:
Parvulescu, VI; Coman, S; Palade, P; Macovei, D; Teodorescu, CM; Filoti, G; Molina, R; Poncelet, G; Wagner, FE
Published: MAR 1999, APPLIED SURFACE SCIENCE, 141, 176, DOI: 10.1016/S0169-4332(98)00619-9
Ru-zeolites prepared via deposition of aqueous solution of ruthenium chloride on X, L, ZSM-5 and APO-54 were investigated. The impregnated solids were characterized by the following techniques: N-2 sorption, H-2 chemisorption, TPR, XRD, XPS, EXAFS and Mossbauer spectroscopy. It was found that deposition of Ru is influenced by the pore structure and the chemical composition of the supports, in particular the concentration and strength of the protonic sites, with the formation of the different species. The packing of Ru as well as the degree of the reduction and the metal particle size are different according to the penetration depth of the metal and the nature of the zeolite. The amount of chlorine possibly remaining as adatoms of Ru is very low or inexistent. In calcined and reduced catalysts no chloride peak could be evidenced by XPS. The experiments confirmed that the use of large amounts of Ru chloride precursor leads to rather large metal particles. (C) 1999 Elsevier Science B.V. All rights reserved.
1452. Electron spin resonance in gamma-Fe2O3 nanoparticles dispersed in a polymer matrix
Authors:
Prodan, D; Grecu, VV; Grecu, MN; Tronc, E; Jolivet, JP
Published: SEP 1999, MEASUREMENT SCIENCE AND TECHNOLOGY, 10, L43, DOI: 10.1088/0957-0233/10/9/101
gamma-Fe2O3 nanoparticles dispersed in a polymer matrix have been characterized by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The electron paramagnetic resonance (EPR) in 64 Angstrom particles of gamma-Fe2O3 dispersed in a polymer matrix has been investigated in the range 136-286 K.
1453. Nanostructure and phase distributions in (Cu0.80Fe0.20)(100-x)B-x melt spun ribbons studied by Mossbauer spectroscopy
Authors:
Kuncser, V; Rosenberg, M; Yavari, AR; Filoti, G
Published: JUL 20 1999, JOURNAL OF ALLOYS AND COMPOUNDS, 289, 276, DOI: 10.1016/S0925-8388(99)00163-2
The analysis of the Mossbauer spectra of (Cu0.8Fe0.2)(100-x))B-x the melt spun ribbons taken at several temperatures between 4.2 K and room temperature allowed us to identify the occurring Fe-containing phases: alpha-Fe, gamma-Fe and <(Cu)under bar>Fe solid solutions. The presence of B inhibits the phase transformation from fee to bcc Fe. For x = 0 and 1, the amount of Fe in the <(Cu)under bar>Fe solid solution is close to 3 at.% solubility limit, while for x=3 besides crystalline Fe3B, a supersaturated phase of 9.7 at.% Fe in the <(Cu)under bar>Fe solid solution was found, showing a strong deviation from the binary equilibrium phase diagram. (C) 1999 Elsevier Science S.A. All rights reserved.
1454. On the characterization of molecular sieve cavities by the fluorescence of test molecules
Authors:
Frunza, L; Ghiordanescu, V; Kosslick, H; Fricke, R
Published: NOV-DEC 1999, REVUE ROUMAINE DE CHIMIE, 44, 1060, DOI:
Information about guest-host interaction concerning the incorporation of large complexes in molecular sieve was obtained using rhodamine 6 G as test molecule. We embedded the dye in samples of MCM-41 and EMT type molecular sieves and observed that high concentrations can be reached without undesirable dye aggregation. The excitation peak at 520 nm with shoulder at 528 nm shows that our molecular sieves behave as a hydroxylic, relatively polar environment, a little more polar than water.
1455. Growth of carbon nickel multilayer for X-ray-UV optics by RF reactive magnetron sputtering
Authors:
Georgescu, G; Nelea, V; Ulmeanu, M; Ghica, C; Nastase, N
Published: JUL 1999, APPLIED SURFACE SCIENCE, 148, 146, DOI: 10.1016/S0169-4332(99)00219-6
Amorphous C/Ni superlattice films designed as normal-incidence reflector for 5 nm have been grown on float-glass substrates by magnetron sputter deposition in Ar discharge. A comprehensive set of characterization techniques has been applied: grazing X-ray reflection (0.154 nm), atomic force microscopy and transmission electron microscopy in order to determine the quality of the structure. By comparing the results, it could be concluded that RF-magnetron sputtering technique is a good choice for growing such layered synthetic microstructures. (C) 1999 Elsevier Science B.V. All rights reserved.
1456. Weak localization effects in ZnO surface wells
Authors:
Goldenblum, A; Bogatu, V; Stoica, T; Goldstein, Y; Many, A
Published: AUG 15 1999, PHYSICAL REVIEW B, 60, 5838, DOI: 10.1103/PhysRevB.60.5832
Hall effect, magnetoresistance, and electrical conductivity measurements, carried out on ZnO surface wells created by a large variety of methods, are analyzed in the frame of the weak-localization theory. The ZnO surface wells have some unique features that allow the investigation of the weak-localization effects: ZnO has a single valley conduction band; the Thouless length is much larger than the elastic mean-free path even at room temperature; the well accumulates the largest surface electron concentration obtained up to now in a surface quantum well; there are a large variety of preparation methods, some of them making it possible to modify independently both the width and the depth of the surface wells. These features allowed us to investigate: the presence of the weak-localization effect in the largest range of temperatures(1.6-300 K) reported up to now for a quantum well; the influence on the transport properties of the increase in the number of subbands in the well; the effect of the presence of more inelastic scattering mechanisms and their weights in the entire scattering process; and the passage from a quasi-two-dimensional system to a three-dimensional one. [S0163-1829(99)01932-3].
1457. Contribution to the failure analysis of AlGaAs GaAs laser diodes
Authors:
Ghita, RV; Cengher, D; Lazanu, S; Cimpoca, V
Published: 1999, LASER-INDUCED DAMAGE IN OPTICAL MATERIALS: 1998, 3578, 369, DOI: 10.1117/12.344435
High power laser diodes are of interest due to their potential use in medicine and military applications. This paper presents a systematic study of rapid degradation on our AlGaAs/GaAs large optical cavity devices. The increase of normalized threshold current vs. time was experimentally studied. An evaluation for normalized threshold current vs. absorption coefficient for different reflectivities is presented. For the optical output vs. time curve an abnormal increase of light characteristics was experimentally observed. The variation of the optical power was correlated to material parameters during operation and this behavior has been proposed as a practical criterion to select devices that are on their route to rapid degradation. The output optical power vs. electron fluence curve was measured for irradiated devices and a dislocation climb motion was assumed.
1458. Electronic structure of (001) AlAs-InAs-GaAs multilayer structures
Authors:
Velasco, VR; Fernandez-Alvarez, L; Aldea, A; Vlaev, S; Monsivais, G; Garcia-Moliner, F
Published: SEP 3 1998, SURFACE SCIENCE, 412-13, 404, DOI: 10.1016/S0039-6028(98)00458-0
The electronic structure of different (001) (AlAs)(m)(InAs)(1)(GaAs)(m) multilayer structures is studied. We have thus seen the influence of the relative thicknesses of the constituent materials and of the positions of the InAs principal layers in the multilayer structures on the energy eigenstates and on their spatial localization. The calculations are based on an sp(3)s* empirical tight-binding model and on the surface Green function matching method. (C) 1998 Elsevier Science B.V. All rights reserved.
1459. GaN thin films deposition by laser ablation of liquid Ga target in nitrogen reactive atmosphere
Authors:
Dinescu, M; Verardi, P; Boulmer-Leborgne, C; Gerardi, C; Mirenghi, L; Sandu, V
Published: MAY 1998, APPLIED SURFACE SCIENCE, 127, 563, DOI: 10.1016/S0169-4332(97)00705-8
GaN thin films were deposited by laser ablation of liquid Ga target in nitrogen reactive atmosphere. An Nd-YAG laser (lambda = 1.06 mu m, tau(FWHM) = 10 ns) of 0.35 J energy/pulse was used as laser source. The nitrogen pressure was varied in the range of 10(-2) to 10(-1) mbar. As substrates, we used (0001) sapphire plates and (100) Si wafers, coated or uncoated with ZnO as buffer layers, and heated below 300 degrees C. Different analysis techniques evidenced the characteristics of the deposited films. SIMS profiles corresponding to N and Ga in-depth distribution carried out the presence of layers of the order of 130-150 nm, with uniform distribution of Ga and N inside the layer. XPS studies evidenced the Ga-N bonding. The Nls signal contains as main peak the one centered at 397.3 eV and corresponding to Ga-N bond. From the distance between the photoelectron Ga 3d peak and the Auger Ga LMM peak, the calculated Auger parameter of 1083.9 eV corresponds to the one reported in literature for GaN compound (1084.05 eV). Both techniques evidenced an oxygen contamination below 5%. XRD recorded spectra show the presence of a peak assigned to (002) GaN crystalline orientation. Optical absorption spectroscopy studies in the UV-visible range evidenced a high transparency (over 80% transmission) for the deposited films. The energy band gap obtained from the absorption spectra was found to be larger than 3.6 eV. (C) 1998 Elsevier Science B.V.
1460. Iron-oxide-based nanoparticles produced by pulsed infrared laser pyrolysis of Fe(CO)(5)
Authors:
Alexandrescu, R; Morjan, I; Crunteanu, A; Cojocaru, S; Petcu, S; Teodorescu, V; Huisken, F; Kohn, B; Ehbrecht, M
Published: SEP 1 1998, MATERIALS CHEMISTRY AND PHYSICS, 55, 121, DOI: 10.1016/S0254-0584(98)00145-X
The synthesis of nanosized (1-100 nm) particles is an active research field in chemical processing technologies. The process may be of particular relevance in the case of the widely used iron-based materials. In this paper, we report on the preparation and characterization of ultrafine powders produced by pulsed infrared laser pyrolysis of iron pentacarbonyl, Fe(CO)(5), in sensitized mixtures. The synthesis is performed in a flow reactor, at rather high pressure (400 mbar) and high laser fluence (similar to 5 J cm(-2)). The average diameter of the particles is 30 nm. Different characterization methods of the fine powder aged in atmosphere indicate the presence of a substantial oxidic portion, identified as the beta-Fe2O3 . H2O form. Some experimental observations suggest the possibility of iron-oxides formation during synthesis in the flow reactor. The relevant mechanisms for this reaction route are discussed. (C) 1998 Elsevier Science S.A. All rights reserved.
1461. The influence of lithium halides on the superconducting properties of YB2Cu3O7-x
Authors:
Sandu, V; Jaklovszky, J; Cimpoiasu, E; Bunescu, MC
Published: DEC 1998, JOURNAL OF SUPERCONDUCTIVITY, 11, 661, DOI: 10.1023/A:1022664300837
The effects of addition to YBa2Cu3O7-x Of lithium halides (YBa2Cu3O7-x (LIF)(gamma) and YBa2Cu3O7-x (LiCl)(gamma)) on the structural, electric, magnetic, and transport properties are analyzed. Both structural and superconducting properties depend weakly on the lithium content up to gamma=0.10. The critical temperature keeps on a value well above 91 K for a small amount of lithium halide (reaching 93.48 K for gamma=0.02 in YBa2Cu3O7-x (LiF)(gamma) and 91.30 K in YBa2Cu3O7-x (LiCl)(gamma)), but for higher concentration of Li it rapidly decreases (81.68 K for gamma=0.20). The same behavior is exhibited in the lower intragranular critical field. The intragranular critical current density depends on the magnetic field as a power law: j(c)proportional to B-alpha, with a lithium-concentration-dependent a. The voltage-current characteristics follow a law typical for granular superconductors, V proportional to(I-I-c(B, T))(n(B,T)). The dependence of the intergranular critical current, I-c, and of the exponent, n, on temperature, magnetic field, and concentration is analyzed.
1462. Magnetic properties and cation distribution in iron containing pyrochlores
Authors:
Filoti, G; Rosenberg, M; Kuncser, V; Seling, B; Fries, T; Spies, A; Kemmler-Sack, S
Published: MAR 27 1998, JOURNAL OF ALLOYS AND COMPOUNDS, 268, 21, DOI: 10.1016/S0925-8388(97)00621-X
Iron-containing pyrochlores, having ions with various valencies on the B-sites, were investigated by magnetic measurements and Mossbauer spectroscopy. The influence of the ionic radius and of the valence state of the different cations accommodated on A or B sites on the super-exchange interactions and local distortions was emphasized. Three local configurations of iron were given as evidence in agreement with a model based on a random distribution of ions over the B-sites. (C) 1998 Elsevier Science S.A.
1463. On the passivation of the metallic surfaces from the nuclear plant water circuits
Authors:
Filoti, G; Kuncser, V; Palade, P; Micu, IF; Crisan, O
Published: 1998, HYPERFINE INTERACTIONS, 112, 38, DOI: 10.1023/A:1011063905776
Samples obtained from the hot conditioning and hot performance procedures have been investigated by GEMS. Various types of substrates were considered. The surface phases were assigned to magnetite, alpha-Fe, wustite and to spinel solid solutions. The data have been analyzed taking into account the compound stoichiometry, the number of iron unequivalent positions appeared in each identified phase and the relative ratio of the formed products.
1464. Electrical behaviour of fresh and stored porous silicon films
Authors:
Ciurea, ML; Baltog, I; Lazar, M; Iancu, V; Lazanu, S; Pentia, E
Published: JUL 18 1998, THIN SOLID FILMS, 325, 277, DOI: 10.1016/S0040-6090(98)00429-5
We have measured I-V and C-V characteristics, the temperature dependence of dark currents, and thermally stimulated depolarisation currents on fresh and stored samples of photoluminescent porous silicon, By storage in ambient, the low rectifying I-V curves become strong rectifying, and C-V curves become MIS-like. I-T characteristics for fresh samples have only one activation energy, in the 0.49-0.55 eV range. After storage, a slightly modified value, of about 0.50-0.60 eV is observed at low temperatures only. At about 280 K, the activation energy suddenly changes to 1.20-1.80 eV. Also, both the number and the positions of maxima in thermally stimulated depolarisation currents change by storage. The annealing at about 50 degrees C induces small reversible changes in I-T characteristics and strong irreversible ones in thermally stimulated depolarisation currents, both for fresh and stored samples. A simplified quantum confinement model is proposed to explain the main aspects of the electrical behaviour of porous silicon films. The surface and/or interface contributions are observed especially in thermally stimulated depolarisation currents. The changes induced by storage are attributed to the oxidation process of the internal surface of porous silicon films. (C) 1998 Elsevier Science S.A. All rights reserved.
1465. The role of radiation damage structure and fine scale precipitation in the pinning improvement of thermal neutron irradiated lithium fluoride-doped YBa2Cu3O7-x
Authors:
Vasiliu, F; Sandu, V; Nita, P; Popa, S; Cimpoiasu, E; Bunescu, MC
Published: JUL 20 1998, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 303, 219, DOI: 10.1016/S0921-4534(98)00254-8
The improvement of intragranular critical current density, j(c), and flux pinning obtained by thermal neutron irradiation (fluences between 10(16) - 10(18) neutrons/cm(2)) in YBa2Cu3O7,(-x) doped with 8 mol% lithium fluoride (LiF) (YBCO-LIF) is explained by the occurrence of various irradiation defects (point defect clusters, dislocation loops, stacking faults) observed by transmission electron microscopy (TEM), A twin fading process is also revealed accompanied by a lowering of the orthorhombicity index. At higher irradiation fluences (similar to 5 x 10(17) 10(18) neutrons/cm(2)), a new mechanism related to the dispersion of fine Cu2O precipitates in the superconducting YBCO-LiF matrix could explain the enhancement of up to eight times obtained for j(c) values. A good agreement between the dependence of the measured j(c) values on the applied magnetic field and the calculated curves, j(c) = f(B), derived from a theoretical model, previously proposed for the pinning contribution of fine particles dispersed in YBCO matrix, is obtained. The role of thermal neutron irradiation for the flux pinning improvement by introducing of strong pinning centers (irradiation defects and Cu2O microdispersoids) is also discussed. (C) 1998 Elsevier Science B.V. All rights reserved.
1466. Degradation effects in pulsed AlGaAs large optical cavity (LOC) structure laser diodes
Authors:
Ghita, RV; Vasile, E; Cimpoca, V; Baltateanu, N
Published: 1998, FIFTH CONFERENCE ON OPTICS (ROMOPTO '97), PTS 1 AND 2, 3405, 80, DOI: 10.1117/12.312670
High power pulsed laser diodes are of interest due to their potential use in medicine and peculiar applications. This paper presents failure analysis for catastrophic damage in GaAs/AlGaAs LOC pulsed laser devices. There is presented failure decrease of optical power as Ig (P/P-0) = f(t) where Po is initial power, P actual power, t-operating time. The damaged devices were investigated by optical and scanning electron microscopy (SEM) and there was performed a electron dispersion spectroscopy (EDS) analysis These experiments advanced the idea of dividing catastrophic degradation in three types, respectively: 1-catastrophic optical mirror damage (COMD), 2- catastrophic damage due to major mechanic defects (CDMMD), 3-catastrophic damage due to metal migration (e.g. Au) (CDMM). There was established an experimental criterion to characterise catastrophic damage.
1467. Microwave spectroscopy in YBCO superconductors: Influence of neutron irradiation on the 123 phase
Authors:
Velter-Stefanescu, M; Totovana, A; Sandu, V
Published: JUN 1998, JOURNAL OF SUPERCONDUCTIVITY, 11, 330, DOI: 10.1023/A:1022619128787
The high-T-c superconducting system YBa2Cu3Odelta:Li (123) was investigated by microwave absorption. The effect of neutron irradiation on the 123 phase as well as the dependence of the resulting modification both on the neutron fluence and on the doping behavior with Li are discussed. The results show a significant improvement of the superconducting characteristics: critical temperature, phase homogeneity, and critical current densities for a certain neutron fluence. We have found that the optinum neutron fluence for irradiation is 4.98 x 10(21) m(-2).
1468. Influence of the surface treatment of the substrate in the LCVD of CNx films
Authors:
Crunteanu, A; Cireasa, R; Alexandrescu, R; Morjan, I; Nelea, V; Mihailescu, IN; Andrei, A; Vasiliu, F
Published: MAR 1998, SURFACE & COATINGS TECHNOLOGY, 100, 179, DOI: 10.1016/S0257-8972(97)00610-5
Carbon nitride (CNx) films have been prepared by UV (at 248 nm) laser-induced chemical vapor deposition using different materials (alumina, laser-activated alumina, pre-deposited Ti layers on alumina, sapphire and quartz) as deposition substrates. A mixture of ethylene. nitrous oxide and ammonia was chosen as the gas-phase precursor. The changes induced in the gas-phase composition by the irradiation in different experimental conditions were determined by IR transmission measurements. The film composition and morphology were studied by X-ray photoerectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron diffraction (TED). The degree of chemical content modification, especially its dependence on the nature of the substrate, is described for the first time. Depending on the substrate nature, the specific nucleation and growth morphology of crystallites were observed. The electron diffraction data agree well with experimental results obtained in previous works and theoretical data referring to crystalline alpha- and B-C3N4 phases. (C) 1998 Elsevier Science S.A.
1469. Electrical and optical characterization of PbTiO3/Si heterostructures for applications in optoelectronics
Authors:
Dragoi, V; Pintilie, L; Pintilie, I; Petre, D; Boerasu, I; Alexe, M
Published: 1998, FIFTH CONFERENCE ON OPTICS (ROMOPTO '97), PTS 1 AND 2, 3405, 851, DOI: 10.1117/12.312674
The ferroelectric/semiconductor heterostructures were fabricated by sol-gel deposition of lead titanate (PT) thin films on a single-crystalline p-type Si wafers. The ETT films were crystallyzed by a conventional thermal annealing for 30 min at temperatures ranging from 575 degrees C to 675 degrees C. Current-voltage and capacitance-voltage characteristics show a hysteresis which can be due to the spontaneous polarization of PbTiO3. The current-voltage characteristics exhibit a diode behaviour while the capacitance-voltage exhibits a large memory window, up to 3.5 V, for the films annealed at 600-650 degrees C. At the illumination with modulated light, a.c. photovoltage was detected on a broad range of wavelengths (0.35+4 mu m) for all samples. The spectral distribution of the photoelectric signal in the UV-Vis-IR domain shows two local maxima. A model is proposed to explain the observed experimental results.
1470. Quantum confinement model for electric transport phenomena in fresh and stored photoluminescent porous silicon films
Authors:
Iancu, V; Ciurea, ML
Published: OCT 1998, SOLID-STATE ELECTRONICS, 42, 1896, DOI: 10.1016/S0038-1101(98)00160-9
A quantum confinement model is proposed to explain the electrical transport properties in fresh and stored porous silicon (PS) films. In the present paper, the model is verified for the temperature dependence of the dark current. The studied samples are Formed mainly by a network of nanowires, suggesting the separation of the electron Hamiltonian into a longitudinal and a transversal part. The last one can be well described by a two-dimensional (2D) cylindrical infinite quantum well? whose levels determine the dark current activation energies. The storage oxidation induces modifications both in the number and the values of the activation energies, which are in excellent agreement with our model. (C) 1998 Elsevier Science Ltd. All rights reserved.
1471. Far-IR absorption of short-period quantum wires and the transition from one to two dimensions
Authors:
Manolescu, A; Gudmundsson, V
Published: JAN 15 1998, PHYSICAL REVIEW B, 57, 1673, DOI: 10.1103/PhysRevB.57.1668
We investigate the far-IR absorption of short-period parallel quantum wires in a perpendicular quantizing magnetic field. The external rime-dependent electric field is linearly polarized along the wire modulation. The mutual Coulomb interaction of the electrons is treated self-consistently in the ground state and in the absorption calculation within the Hartree approximation. We consider the effects of a metal gate grating coupler, with the same or with a different period as the wire modulation, on the absorption. The evolution of the magnetoplasmon in the nonlocal region where it is split into several Bernstein modes is discussed in the transition from narrow to broad wires and isolated to overlapping wires. We show that in the case of narrow and not strongly modulated wires the absorption can be directly correlated with the underlying electronic band structure.
1472. Theoretical model for carriers transport in nanocrystalline porous silicon films
Authors:
Ciurea, ML; Iancu, V; Pavelescu, G; Baltog, I
Published: 1998, CAS'98 PROCEEDINGS - 1998 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 21ST EDITION, VOLS 1 AND 2, 112, DOI:
A quantum confinement model is proposed to explain the carriers transport in a nanowire network of porous silicon. The electron Hamiltonian is written as the sum of the longitudinal and the transversal contributions. The last one corresponds to a two-dimensional infinite cylindrical quantum well, whose energy levels determine the activation energies observed in the temperature dependence of the dark current. The model is in excellent agreement with the experimental data.
1473. Energy-band structure of spin-Peierls crystal CuGeO3
Authors:
Syrbu, NN; Revcolevschi, A; Tsopa, N; Chebotar', VZ
The absorption spectrum of CuGeO3 crystals is measured in the transmittance region and at the fundamental edge, The reflection spectrum is studied in the range 3-6 eV, The identified transitions are interpreted in the context of band-structure calculations.
1474. Silicon linear image sensors for photometry
Authors:
Cimpoca, V; Cengher, D; Crisan, C; Olariu, N; Oros, C; Cimpoca, M
Published: 1998, CAS'98 PROCEEDINGS - 1998 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 21ST EDITION, VOLS 1 AND 2, 70, DOI:
The paper describes a new linear image sensor for photometry by applying bipolar technology (Standard Buried Collector-SEC) to the manufacture of self-scanning linear photodiode arrays. On a monolithic chip we have designed 128 to 1024 linear photodiodes, demultiplexing system and signals processing system. A dynamic simulation and a real-time measurement have been implemented, that allow to take into account every operational phase of detection. The dialogue between the various functions is established by message's transmission, using common data areas stored on disks or in central memory of PC compatible computer.
1475. Nonmonotonous variation of the superconducting parameters of neutron irradiated Li-doped YBa2Cu3O7-x
Authors:
Sandu, V; Popa, S; Jaklovszky, J; Cimpoiasu, E
Published: APR 1998, JOURNAL OF SUPERCONDUCTIVITY, 11, 251, DOI: 10.1023/A:1022627800159
The effect of thermal and epithermal neutron irradiation on the superconducting critical temperature and critical current density of some Li-doped YBa2Cu3O7-x, samples was studied. The critical temperature exhibits a peak and the critical current density a valley in their dependence on neutron fluence, for moderate dose. A simple model, based on the Van Hove scenario and the kinetics of the defect production, is used to describe both phenomena.
1476. A Mossbauer spectroscopy and magnetic study of FeRh
Authors:
Rosenberg, M; Kuncser, V; Crisan, O; Hernando, A; Navarro, E; Filoti, G
Published: JAN 1998, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 177, 136, DOI: 10.1016/S0304-8853(97)00662-8
A Mossbauer and magnetic study of FeRh has been undertaken in order to understand better the remarkable properties of both melt-spun BCC and ball-milled FCC-phases of the anti-invar FeRh alloy. (C) 1998 Elsevier Science B.V. All rights reserved.
1477. Cobalt-manganese oxide thin films thermistors obtained by MOD
Authors:
Dragoi, V; Alexe, M
Published: 1998, CAS'98 PROCEEDINGS - 1998 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 21ST EDITION, VOLS 1 AND 2, 300, DOI:
Co1.4Mn1.6O4 (CMO) thin films were deposited onto silicon by Metalorganic Decomposition (MOD) method. Structure, composition and morphology were investigated by Electron Dispersive X-Ray Spectroscopy (EDX) and X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Electrical measurements showed possible applications as negative temperature coefficient (NTC) thermistors.
1479. Mossbauer spectroscopy applied to radioactive waste processing
Authors:
Filoti, G; Kuncser, V; Prisecaru, I; Rotaru, P; Turcanu, CN
Published: 1998, HYPERFINE INTERACTIONS, 112, 204, DOI: 10.1023/A:1011076522131
Two original evaluations of the embedding process and of the hydration promotion in cements using only Mossbauer data have been proposed. Quantitative factors connected with the Mossbauer parameters and describing the hydration degree, the quality of the precipitate bonds in the cement matrix, as well as the influence of the additional organic components on the hydration process were found.
1480. The diffraction efficiency in Fe : PVA explained by Mossbauer spectroscopy
Authors:
Kuncser, V; Filoti, G; Podgorsek, R; Biebricher, M; Franke, H
Published: SEP 21 1998, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 31, 2318, DOI: 10.1088/0022-3727/31/18/017
The UV exposure of Fe:PVA thin films induces modifications of both the refractive index and the absorption coefficient. M-line spectroscopy showed the variation of the refractive index while Mossbauer measurements present the Fe2+/Fe3+ ratio versus the exposure energy. The diffraction efficiency experimental data were satisfactorily explained in correlation with the Fe2+/Fe3+ ratio.
1481. Hydrothermal synthesis and structural characterization of some substituted magnetites
Authors:
Diamandescu, L; Mihaila-Tarabasanu, D; Teodorescu, V; Popescu-Pogrion, N
Published: DEC 1998, MATERIALS LETTERS, 37, 348, DOI: 10.1016/S0167-577X(98)00117-7
A hydrothermal method has been used to obtain polycrystalline substituted magnetites, Fe3-xMxO4, (M = Cr, Mn, Co, Ni, Cu; 0 less than or equal to x less than or equal to 0.375) starting with ferrous-hi hydroxide mixtures at temperatures up to 300 degrees C. Well-defined magnetite crystallites, 0.2-0.3 mu m in size have been obtained. The appearance of the intermediate phase alpha-FeOOH during hydrothermal transformation into magnetite has been evidenced and discussed. By means of Fe-57 Mossbauer spectroscopy, the distribution of different incorporated cations in the magnetite lattice has been analysed. (C) 1998 Elsevier Science B.V. All rights reserved.
1482. Electrochemical performance and chemical properties of oxidic cathode materials for 4 V rechargeable Li-ion batteries
Authors:
Ott, A; Endres, P; Klein, V; Fuchs, B; Jager, A; Mayer, HA; Kemmler-Sack, S; Praas, HW; Brandt, K; Filoti, G; Kunczer, V; Rosenberg, M
Published: MAR 30 1998, JOURNAL OF POWER SOURCES, 72, 8, DOI: 10.1016/S0378-7753(97)02772-9
The systems Li1-xMn2-xO4-delta acid Li1-xNi1+xO2 were studied as oxidic cathode materials for 4 V rechargeable Li-ion cells. From a comparison of the results it follows that the spinel system can be subdivided into three regions: in region I (0 less than or equal to x < 0.05) the electrochemical performance is unsatisfying due to a large volume reduction of about 7.5%, inducing stress, multiphase materials and capacity fading. Region II (0.05 less than or similar to x less than or similar to 0.2) contains the best cathode material with a composition near x = 0.1. The spinel framework is stable against Li extraction. In region III (0.2 less than or equal to x less than or equal to 1/3) the capacity is too low for an application in the 4 V region. In the system Li1-xNi1+xO2 the highest capacity is observed for LiNiO2 with x = 0. Experimental difficulties during material synthesis were overcome by suppression of the decomposition of LiNiO2 into Li1-xNi1+xO2, Li2O and O-2. (C) 1998 Elsevier Science S.A. All rights reserved.
1483. Collective modes and the far-infrared absorption of the two-dimensional electron gas in a periodic quantizing magnetic field
Authors:
Manolescu, A; Gudmundsson, V
Published: 1998, SUPERLATTICES AND MICROSTRUCTURES, 23, 1180, DOI: 10.1006/spmi.1997.0557
We investigate the far-infrared (FIR) absorption of a two-dimensional electron gas in a periodically modulated quantizing magnetic field. The magnetic field varies along only one spatial direction and the external time-dependent electric field is linearly polarized along that axis. The mutual Coulomb interaction of the electrons is treated self-consistently in the ground state and in the absorption calculation within the Hartree approximation. The effects of the magnetic material on top of the heterostructure as a grating coupler is included in the time-dependent incident FIR electric field. We show that, similar to an electric modulation, the absorption can be directly correlated to the underlying electronic energy bands. In addition, the magnetic modulation leads to absorption spectra with a richer structure due to the quite different static response of the electron density to the modulation. (C) 1998 Academic Press Limited.
1484. The inhibition of the corrosion of Armco iron in hydrochloric acid solutions by organic surfactants
Authors:
Branzoi, V; Branzoi, F; Baibarac, M; Popa, MV
Published: JUN 1998, REVUE ROUMAINE DE CHIMIE, 43, 513, DOI:
The polarization behaviour of Armco iron in solutions of HCl with and without inhibitors has been studied by potentiostatic method. At lower overvoltage values the dissolution process is controlled by activation, while at higher overvoltage values the dissolution process is controlled by diffusion. The inhibition of this metal corrosion in the aqueous solutions of HCl has been studied using three surfactants. Under the critical micelle concentration the inhibition of those three surfactants is negligible. At a concentration higher than critical micelle concentration, the inhibiting action of surfactants increases rapidly. The process of inhibition was attributed to the formation of the adsorbed film on the metal surface, that protects the metal against the corrosive agents.
1485. Syntheses and structural study of trinuclear iron acetates [Fe3O(CH3COO)(6)(H2O)(3)]Cl center dot 6H(2)O and [Fe3O(CH3COO)(6)(H2O)(3)][FeCl4]center dot 2CH(3)COOH
Authors:
Shova, SG; Cadelnic, IG; Gdaniec, M; Simonov, YA; Jovmir, TC; Meriacre, VM; Filoti, G; Turta, CI
Published: SEP-OCT 1998, JOURNAL OF STRUCTURAL CHEMISTRY, 39, 761, DOI: 10.1007/BF02903548
The structure of two trinuclear iron acetates [Fe3O(CH3COO)(6)(H2O)(3)]Cl . 6H(2)O (I) and [Fe3O(CH3COO)(6)(H2O)(3)][FeCl4]. 2CH(3)COOH (II) was determined by X-ray diffraction analysis. Crystals I and II are ionic and belong to the orthorhombic system with parameters a = 13.704(3), b = 23.332(5), c = 9.167(2) Angstrom, R = 0.0355, space group P2(1)2(1)2 for I and a = 10.145(4), b = 15.323(6), c 22.999(8) Angstrom, R = 0.0752, space group Pbc2(1) for II. The complex cation [Fe3O(CH3COO)(6)(H2O)(3)](+) has a mu(3)-O-bridged structure typical for trinuclear iron(III) compounds. As shown by Mossbauer spectroscopy, the iron(III) ions are in the high-spin state. In trinuclear cations, antiferromagnetic exchange interaction takes place between the Fe(III) ions with the exchange parameter J = -26.69 cm(-1) for N (Heisenberg-Dirac-Van Vleck model for D-3h symmetry).
1486. Electrical properties of sandwich structures with aluminum nitride layers
Authors:
Tanase, M; Morosanu, C; Dumitru, V; Tugulea, L; Tomozeiu, N
Published: 1998, CAS'98 PROCEEDINGS - 1998 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 21ST EDITION, VOLS 1 AND 2, 224, DOI:
Electrical properties of adherent, low stressed aluminum nitride films prepared by magnetron sputtering have been studied. Arrhenius plots in the 100 degrees-170 degrees C range of temperature and transient current curves with different bias steps (af room temperature and 150 degrees C) have been performed. The conduction activation energy has been found and ifs dependence on subsequent annealings has been studied. A phenomenological conduction model at the ITO-AIN interface based on the shape of the transient curves has been elaborated The conditions of behaviour of AlN as a highly insulating layer (sputtering conditions, thicknesses, anealing temperatures) have been established.
1487. Hyperfine fields and Fe magnetic moments in Fe-Rh alloys: a Mossbauer spectroscopy study
Authors:
Filoti, G; Kuncsea, V; Navarro, E; Hernando, A; Rosenberg, M
Published: AUG 21 1998, JOURNAL OF ALLOYS AND COMPOUNDS, 278, 68, DOI: 10.1016/S0925-8388(98)00591-X
The Mossbauer spectra of the melt-spun and subsequently intensively ball-milled Fe65Rh35, Fe50Rh50 and Fe26Rh74 alloys with fee structure are characterized at 4.2 K by broad hyperfine field distributions. The magnetic critical temperatures are 60(5) for the first one and, respectively, 85(5) K for the second and the latter composition, in good agreement with recent magnetic susceptibility studies. The distributions arise as result of the chemical disorder, local strains and atomic displacements, owing to the drastic ball-milling process. The values of the Fe magnetic moments at the peaks of the hyperfine field distributions reached 1.1, 1.6 and 1.9 mu(B) with decreasing iron concentration in semi-quantitative agreement with earlier experimental and recent theoretical evaluations of Fe moments in gamma-Fe and fee Fe50Rh50. Above 400 K an irreversible transformation to the bcc structure occurs for the two Fe-rich alloys with three types of Fe sites in the Fe richest alloy and two different Fe sites in the partially disordered Fe50Rh50. Our analysis allowed us to describe the nn atomic arrangements around these sites. (C) 1998 Elsevier Science S.A. All rights reserved.
1488. Three-dimensional memory effect in fluorescent photosensitive glass activated by europium and cerium
Authors:
Pavel, E; Mihailescu, IN; Hening, A; Vlad, VI; Tugulea, L; Diamandescu, L; Bibicu, I; Chipara, M
Published: AUG 15 1998, OPTICS LETTERS, 23, 1306, DOI: 10.1364/OL.23.001304
The persistent extinction of fluorescence emission of Eu(3+) in glasses activated with europium and cerium is reported for the first time to the authors' knowledge. The glass samples containing EU(3+) and Ce(3+) were initially colorless and transparent and exhibited intense emission peaks at 592 ana 612 nm assigned to the (5)D0-(7)F(1,2) transitions of EU3+. Th, complete extinction of the Eu(3+)-ion emission was obtained as an effect of multipulse excimer-UV-laser (lambda = 248 nm, tau(FWHM) greater than or equal to 20 ns) irradiation of the glass samples. Fluorescence microscopy, Mossbauer spectrometry, and electron spin resonance were applied for investigation of the modifications induced by the laser treatment. As a decisive proof of the extinction of fluorescence me succeeded in recording three-dimensional fluorescent photographic patterns within the activated samples. (C) 1998 Optical Society of America.
1489. Relaxation effects in the Mossbauer spectra of iron complexes with fatty acids
Authors:
Filoti, G; Meriacre, VM; Mateescu, E; Kuncser, V; Turta, KI
Published: 1998, HYPERFINE INTERACTIONS, 116, 136, DOI: 10.1023/A:1012637830809
Six new mu 3-oxo trinuclear iron(III) complexes of the type [Fe3O(R-COO)(6)(H2O)(3)] . X, where X = NO3- or Cl- and R = C-5, C-7, C-8, C-9 were synthesized and investigated by Infra Red, Mossbauer Spectroscopy and magnetic measurements. The data pointed to a high spin state (S = 5/2) for iron and for antiferromagnetic interactions. The asymmetrical shape of the Mossbauer doublet and its temperature dependence was treated using the Plume relaxation model. The relaxation process is influenced by both X and R components.
1490. Optical and Mossbauer study of the real time holographic organometallic material Fe:PVA
Authors:
Kuncser, V; Avramescu, A; Filoti, G; Rotaru, P; Podgorsek, R; Biebricher, M; Franke, H
Published: JUL 5 1997, JOURNAL OF ALLOYS AND COMPOUNDS, 256, 275, DOI: 10.1016/S0925-8388(96)03111-8
The Fe:PVA thin films were studied by optical and Mossbauer spectroscopy. Both the absorption and Mossbauer spectra are dependent on the PVA dilution and ferric chloride concentration. A strong correlation between the optical and Mossbauer results was found, indicating the major role of the iron electronic local levels in the optical phenomena. A relation between the various absorption probabilities and also indirect information about the Debye temperatures were obtained. (C) 1997 Elsevier Science S.A.
1491. The effect of LiOH addition to the superconducting properties of YBa2Cu3O7-x
Authors:
Sandu, V; Jaklovszky, J; Cimpoiasu, E; Bunescu, MC
Published: JUN 1997, JOURNAL OF SUPERCONDUCTIVITY, 10, 239, DOI: 10.1007/BF02770557
The effect of LiOH addition to YBa2Cu3O7-x is presented. The crystal structure remains orthorhombic, but the orthorhombic splitting decreases from 0.0171 at 2 at. % Li to 0.0158 at 50 at. % Li. The critical temperature exhibits a decrease from 91-.18 to 83.79 K in the same range of lithium concentrations. From the magnetization curves were obtained the lower critical fields and the intragranular critical current density. The latter exhibits a negative power law, j(c) proportional to B-alpha, with alpha approximate to 1/2. V-I characteristics are typical for grained superconducting materials: V proportional to(I-I-c)(n(B,T)). The transport critical current dependence on temperature and magnetic field is also presented.
1492. Investigation of some phase transformations induced by CO2-laser irradiation in some rare-earth oxides
Authors:
Vasiliu, F; Sarbu, C; Parvulescu, VI
Published: FEB 1997, SOLID STATE IONICS, 95, 112, DOI: 10.1016/S0167-2738(96)00553-X
Binary rare-earth ceria-ytterbia and ceria-dysprosia and pure CeO2 have been subjected to CO2-laser irradiation. All the samples have been prepared by precipitation and controlled drying. Irradiated samples as well as the samples calcinated at 1273 K have been studied using TG-DTA, TEM and SAED, WAXS and FT-IR. Introduction of a second rare-earth oxide, like ytterbia or dysprosia led to an important increase of 'stability' towards the CO2-laser irradiation. Thermal investigation of these samples revealed in fact a 'metastability' because, for the temperatures of about 500 K, a release of oxygen has been observed. This behaviour could recommend CO2-laser irradiation as a possible alternative for activation of the oxidation catalysts.
1493. Indirect enhancement of PbS photoconductivity by ferroelectric field effect in a PbS/PbTiO3/Si heterostructure
Authors:
Pintilie, I; Pintilie, L; Dragoi, V; Petre, D; Botila, T
Published: AUG 25 1997, APPLIED PHYSICS LETTERS, 71, 1106, DOI: 10.1063/1.119740
A lead sulphide/lead titanate/silicon (PbS/PbTiO3/Si) heterostructure was manufactured by successive deposition of PbTiO3 and PbS thin film on a single crystalline, p-type Si substrate. Chemical methods were used for deposition. A three electrode configuration was used to control the photoconductivity of PbS thin film by field effect, through the ferroelectric PbTiO3 thin film. The spectral distribution of the photoconductive signal shows two maxima, situated at 1.1 and 2.45 mu m. It was found that the photoconductive signal at 1 mu m varies of about eight times when the voltage applied on the Si substrate is varied between -1 and +1 V. At 2 mu m the photoconductive signal is almost independent of the applied voltage on the Si substrate. The observed results are explained considering a ferroelectric field effect by which the photogenerated carriers in Si influence the photoconductive signal in the PbS thin film. (C) 1997 American Institute of Physics.
1494. Temperature induced surface transitions in liquid crystal planar-tilted hybrid cells
Authors:
Moldovan, R; Frunza, S; Beica, T; Tintaru, M; Ghiordanescu, V
Published: 1997, CRYSTAL RESEARCH AND TECHNOLOGY, 32, 675, DOI: 10.1002/crat.2170320510
Temperature induced surface transitions in liquid crystal hybrid cells with asymmetrical anchoring, planar to one surface and tilted to the other, are experimentally studied. The results are theoretically explained by an elastic theory and the resulting values for the effective splay-bend elastic constant for a given liquid crystal, as well as the parameters characterising the anchoring on the boundary surface with tilted anchoring are compared with data from previous experiments, with good agreement.
1495. Radiation damage effects on X- and gamma-ray N+PP+ silicon detectors
Authors:
Cimpoca, V; Petris, M; Ruscu, R; Moraru, R; Breten, M; Cimpoca, M
Published: 1997, CAS '97 PROCEEDINGS - 1997 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 20TH EDITION, VOLS 1 AND 2, 518, DOI:
The paper describes some results concerning technology and behaviour of X-and gamma-ray N+PP+ silicon defectors used in physics research, industrial and medical radiography and non-destructive testing. Devices manufactured under this technology proved to be stable alter an exposure in high intensity the dose range of 10 krad-5 Mrad. Nuclear radiation resistance was studied by irradiation with Co-60 gamma source (1.17, 1.33 MeV) at dose rates of 59 krad/hour and 570 krad/hour.
1496. Radiation-specific free radicals in biological systems: detection and applications
Authors:
Grecu, VV; Duliu, OG; Pascanu, S; Oproiu, C; Georgescu, R; Chipara, MI
In the biological effect of ionizing radiation, a very important process is the production of free radicals and their reactions with one another and with other biomolecules. Electron Spin Resonance (ESR) spectroscopy is an appropriate method to detect the free radicals produced by irradiation and also to estimate their concentration. The samples were irradiated at a linear electron accelerator, The ESR measurements were performed using X-band spectrometers. The resonance spectra of irradiated complex biological materials are presented and discussed. Interesting applications of the ESR method in the field of radiation treatment of biological material are outlined.
1497. Site occupation and Fe-57 Mossbauer spectra of RE6Fe14-xMx with RE=Nd, Pr and M=Ga, Al
Authors:
Kuncser, V; Rosenberg, M; Buschow, KHJ; Filoti, G
Published: JUN 20 1997, JOURNAL OF ALLOYS AND COMPOUNDS, 255, 66, DOI: 10.1016/S0925-8388(96)02851-4
A Mossbauer spectroscopy study of the intermetallics RE6Fe14-xMx where RE=Nd or Pr, M=Ga or Al and x=1 or 2 was undertaken. A comparative analysis of the Mossbauer spectra showed that the second Al or Ga atom substitutes preferentially for the Fe atoms located at the 161 sites. The reduction of the hyperfine fields in Nd6Fe12M2, as compared with Nd6Fe13M, mainly at the 16k, 161, and 161(2) and the corresponding decrease of the average Fe moment gives rise to a total magnetic moment of 41 mu(B) per formula unit in excellent agreement with previous saturation magnetisation measurements.
1498. Hydrogen implantation in polycrystalline ZnO thin films
Authors:
Bogatu, V; Goldenblum, A; Logofatu, B
Published: 1997, CAS '97 PROCEEDINGS - 1997 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 20TH EDITION, VOLS 1 AND 2, 52, DOI:
The paper presents the first results obtained on-the hydrogen ion implantation in polycrystalline ZnO thin films. The ion implantation was carried out with a Kaufman type ion source. The results obtained after the experimental determination of the penetration depth are very close to the ones computed on the basis of the usual theory for monocrystals.
1499. X- and gamma-ray N+PP+ silicon detectors with high radiation resistance
Authors:
Cimpoca, V; Petris, M; Ruscu, R; Breten, M; Moraru, R
Published: 1997, HARD X-RAY AND GAMMA-RAY DETECTOR PHYSICS, OPTICS, AND APPLICATIONS, 3115, 271, DOI: 10.1117/12.277693
The paper describes some results concerning technology and behaviour of X-and gamma-ray N+PP+ silicon detectors used in physics research, industrial and medical radiography and non-destructive testing. These detectors work at the room-temperature and can be used individually to detect X-and soft gamma-rays, or coupled with scintillators for higher incoming energies. Electrical characteristics of these photodiodes, their modification after exposure to radiation and results of spectroscopic X-and gamma-ray measurements are discussed Devices manufactured under this technology proved to be stable after an exposure in high intensity gamma field with the dose range of 10 krad-5 Mrad: Nuclear radiation resistance was studied by irradiation with Co-60 gamma source (1.17, 1.33 MeV) at dose rates of 59 krad/hour and 570 krad/hour. Results indicate that proposed structures enable the development of reliable silicon detectors to be used in a high gamma-radiation environments encountered in a lot of applications.
1500. Corrosion control of steel components exposed to thermal cycling using radioactive tracers
Authors:
Popa-Simil, L; Clapon, V; Racolta, PM; Alexandreanu, B; Rosu, I
Published: OCT-DEC 1997, APPLIED RADIATION AND ISOTOPES, 48, 1519, DOI: 10.1016/S0969-8043(97)00149-8
The aim of the experiments presented in this paper was to choose from the project-recommended types of steel, the most suitable one for manufacturing the inner surfaces of the fire tube of an inert gas generator (IGG). Typically, such generators are used on oil tankers for maintaining an inert gas cushion above the oil's surface in order to prevent accidental combustion. For this approach, we employed the Thm Layer Activation (TLA) technique. Several steel samples have been activated either by 14 MeV proton or 8.5-12.5 MeV deuteron beams. The principle of measuring method, including the calibration procedure for transforming the resulted decreases in radioactivity into material loss data, have been presented in detail in the paper. The real working conditions-exposure to H(2)O, CO(2), and SO(x) compounds (ca. 1-2.5% in regular Diesel oil) having temperatures up to 700 degrees C were assured by mounting the steel samples in a similar tube to the one used offshore. For high accuracy results, the experiment required a dedicated calibration set-up, designed particularly for this application. The main outcome of the experiment was a classification of the different kinds of steels used (brands and/or manufacturers will not be specified in the paper) in accordance with the resistance to erosive corrosion induced by fuel-oil burning products. (C) 1997 Elsevier Science Ltd. All rights reserved.
1501. Electrical properties of porous silicon stabilised by storage in ambient
Authors:
Ciurea, ML; Lazar, M; Lazanu, S; Pentia, E; Dragoi, V
Published: 1997, CAS '97 PROCEEDINGS - 1997 INTERNATIONAL SEMICONDUCTOR CONFERENCE, 20TH EDITION, VOLS 1 AND 2, 180, DOI:
The electrical transport of stabilised porous silicon layers was investigated. The samples were stored in ambient for 1,5-2 years, A MIS-like C-V characteristic, a strong rectifying I-V curve and I-T dependence with two activation energies were obtained, Thermally stimulated depolarization currents have an activation energy of 0.81-0.87 eV. The electrical properties are discussed in the frame of a quantum confinement model, keeping into account the surface component.
1502. Hydrogenation of vinylbenzenes on Pd-Tm/Al2O3 and Tm/Al2O3 catalysts
Authors:
Parvulescu, VI; Parvulescu, V; Macovei, D; Frunza, L
Published: MAY 7 1997, JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS, 93, 1835, DOI: 10.1039/a607928h
Pd-Tm/gamma-Al2O3 catalysts containing 0.1% Pd-1% Tm, 0.3% Pd-1% Tm and 0.5% Pd-1.% Tm, respectively have been obtained by successive impregnation of gamma-Al2O3, first with palladium and then with thulium. Introduction of Tm leads to an increase in the conversion of vinylbenzenes compared to that with monometallic Pd/gamma l-Al2O3 catalysts. For monocomponent Pd/gamma-Al2O3 catalysts, turnover frequency (TOF) is unchanged. For bicomponent Pd-Tm/gamma-Al2O3 catalysts, if one considers that the reaction occurs only on the Pd particles, then introduction of Tm seems to increase the TOF. However, by taking Tm into consideration when calculating the TOF, then the bicomponent catalysts are seen to behave as the monocomponent catalysts. This behaviour is highlighted also by using the Koros-Nowak criterion. If Tm is not considered to be an active species, vinylbenzene hydrogenation appears to be controlled by mass transfer processes. However, the texture characteristics of the bicomponent catalysts are not sufficiently modified by Tm introduction to support such a hypothesis. On the contrary, by considering the Tm participation in the reaction, the slope of the Koros-Nowak dependence is included in a range typical for kinetically controlled reactions.
1503. Variable rate spin freezing and long range antiferromagnetic order in Bi2FeRhO6
Authors:
Filoti, G; Kuncser, V; Rosenberg, M; Schinzer, C; KemmlerSack, S
Published: JUL 5 1997, JOURNAL OF ALLOYS AND COMPOUNDS, 256, 91, DOI: 10.1016/S0925-8388(96)03110-6
A magnetic susceptibility and Mossbauer spectroscopy study of the perovskite Bi2FeRhO6 was undertaken. A freezing start temperature around 270 K was evidenced by both methods. Unlike homogeneous magnetic systems the freezing occurs by involving continuously more and more Fe spins with decreasing temperature over the whole interval down to 4.2 K. At low temperature some evidence for long range antiferromagnetic interactions was found. The Mossbauer data allowed a satisfactory description of the peculiar temperature dependence of the magnetic susceptibility as a superposition of a slain glass antiferromagnetic component and a paramagnetic one. The gradual spin freezing and the absence of percolation derived from the strong influence of the short range interactions, their strengths reflecting the random distribution of the Fe and Rh ions over the B sites of the ABO(3) perovskite. (C) 1997 Elsevier Science S.A.
1504. Spillover effects induced by rare-earth metals on Pd/gamma-Al2O3 in vinylbenzenes hydrogenation
Authors:
Parvulescu, V; Coman, S; Frunza, L; Macovei, D; Sandulescu, I; Parvulescu, VI
Published: 1997, SPILLOVER AND MIGRATION OF SURFACE SPECIES ON CATALYSTS, 112, 170, DOI: 10.1016/S0167-2991(97)80835-X
Pd-Ln/gamma-Al2O3 (Ln = Sm, Gd, Dy, Ho, Tm) catalysts containing 0.1%Pd -1%Ln, 0.3%Pd -1% Ln and respectively, 0.5% Pd -1% Ln (percentage in wt.%) were investigated. Introduction of Ln leads to an increase of the vinylbenzenes conversion comparatively with monometallic Pd/gamma-Al2O3 catalysts. The turnover frequency (TOF) calculus of the latter catalysts suggests that there are no differences among these. In the case of bicomponent Pd-Ln/gamma-Al2O3 catalysts, if one considers that the reaction occurs only on the palladium particles, then introduction of Ln seems to increase the TOF and vinylbenzenes hydrogenation seems to be controlled by the mass transfer processes as indicated by the Koros-Nowak criterion. However, by taking Ln into consideration when calculate the TOF, it results that bicomponent catalysts behave like those monocomponent and the slope of the Koros-Novak dependence is included in a range typical for kinetically controlled reactions. This behavior could be associated to direct participation of Ln to reaction using hydrogen spilled over from the palladium particles.
1505. Diastereoselective hydrogenation of a prostaglandin intermediate over Ru supported on different molecular sieves
Authors:
Cocu, F; Coman, S; Tanase, C; Macovei, D; Parvulescu, VI
Published: 1997, HETEROGENEOUS CATALYSIS AND FINE CHEMICALS IV, 108, 214, DOI:
Hydrogenation of a prostaglandin intermediate has been carried out on some Ru-molecular sieves prepared via deposition of RuCl3. Characterization of these catalysts using different tools like WAXS, XPS or EXAFS indicated differences due to both the different metal loading and the different structure and topology of the investigated molecular sieves (L, APO-34 and ZSM-5). The prostaglandin intermediate has two kinds of unsaturation, a double C=C bond and a prochiral C=O bond. Therefore hydrogenation could imply two different selectivities. On simple Ru-molecular sieves, hydrogenation occurs with different reaction rates and selectivities as a function of the catalysts characteristics. Thus, d.e. of about 100% for a selectivity to the alcohol of 99% were obtained for Ru(12wt.%)-L. However, on these catalysts only the epi configuration was obtained. Modification of the catalysts using L(+) tartaric acid leads to the increase of the reaction rate and the decrease of the d.e. Adding of the pivalic acid to the reaction mixture determined a supplementary increase of the reaction rate. More important in this case is the change of the stereoselectivity, the main product becoming the natural configuration.
1506. Microhardness and elastic properties of bulk glasses and thin films of the GexSb40-xS60 family
Authors:
Pamukchieva, V; Savova, E; Popescu, M
Published: OCT 1997, PHYSICS AND CHEMISTRY OF GLASSES, 38, 262, DOI:
The microhardness (H) of bulk glasses and thin films of the GexSb40-xS60 family has been measured. The volume of the micro-voids (Vh), their formation energy (Eh) and the modulus of elasticity (E) have been calculated. It is assumed that the bulk glasses and thin films have different elasticity levels due to the deformation of specific chemical bonds.
1507. Investigation of the light induced refractive index changes in Fe:PVA
Authors:
Kuncser, V; Filoti, G; Avramescu, A; Podgorsek, R; Biebricher, M; Franke, H
Published: JUL 25 1997, JOURNAL OF ALLOYS AND COMPOUNDS, 257, 292, DOI: 10.1016/S0925-8388(97)00021-2
The light induced modifications in thin films of Fe:PVA were studied by optical and Mossbauer spectroscopy. Under the UV exposure both the refractive index and the absorption coefficient are changing. The real part of the refractive index is measured using m-line Spectroscopy. As a function of UV exposure, the optical absorption as well as the Mossbauer spectra were measured. A correlation between the optical and the measured Fe2+/Fe3+ ratio is discussed. (C) 1997 Elsevier Science S.A.
1508. Comparison between DC and RF magnetron sputtered aluminum nitride films
Authors:
Morosanu, C; Dumitru, V; Cimpoiasu, E; Nenu, C
Published: 1997, DIAMOND BASED COMPOSITES AND RELATED MATERIALS, 38, 132, DOI:
C-axis oriented and disordered aluminum nitride layers have been deposited by RF, respectively DC magnetron reactive sputtering mode. The same deposition conditions were used for gas flow and pressure. The differences between the two growing modes are explained by the influence of ion bombardment upon the growing layers, which is stronger in the RF mode in comparison with the DC one, at the same deposition rate.
1509. Preparation and structure of ordered films of iron carboxylate complexes
Authors:
Popescu, M; Turta, C; Meriacre, V; Zubareva, V; Gutberlet, T; Bradaczek, H
Published: MAR 1996, THIN SOLID FILMS, 274, 146, DOI: 10.1016/0040-6090(95)07080-X
Several iron complexes containing a tri-iron-oxo-cation linked to short chain fatty acids have been used in the preparation of films by self-assembling from solution on glass slides via two procedures: direct evaporation and dragging out. The ordered lamellar structure thus obtained has been investigated by X-ray diffraction. A relation between the lamellar spacing and the disorder in the film has been obtained from the X-ray diffraction data.
1510. Influence of pyrolization temperature on final characteristics of BSCCO ceramic produced by spray-frozen, freeze drying method
Authors:
Badica, P; Aldica, G; Alexeev, AF; Gridasova, TY; Morozov, VV
Published: FEB 1 1996, JOURNAL OF MATERIALS SCIENCE LETTERS, 15, 188, DOI: 10.1007/BF00274446
1511. Optical and microstructural properties of TiO2(Ni2+) thin films
Authors:
Parlog, C; Gartner, M; Osiceanu, P; Teodorescu, V; Moise, F; Ianculescu, A
Published: 1996, CERAMICS INTERNATIONAL, 22, 99, DOI: 10.1016/0272-8842(95)00062-3
Coloured TiO2(Ni2+) thin coatings doped with transitional metals (Ni) were deposited on different substrates (silicon wafers, glass, aluminum) by the sol-gel dip coating process. Complementary techniques (XPS, SE, TEM, XRD, Absorption Spectroscopy) were used to characterize the surface stoichiometry and optical properties, as well as the structure and texture of the thermally treated gels. The presence of fully oxidized film in the outer layers, crystallization in heat treatment to anatase and rutile, formation of porous and coloured films due to the influence of the dopant and the reaction with the substrate, as well as a decrease by three orders of magnitude of the resistivity of Ni-doped films, are reported.
1512. The influence of sintering environment and intermediate grounding on the scattering of the superconducting characteristics in BSCCO ceramic produced by spray-frozen, freeze drying method
Authors:
Badica, P; Aldica, G; Morozov, VV; Popa, S; Mandache, S
Published: DEC 1996, APPLIED SUPERCONDUCTIVITY, 4, 589, DOI:
The effect of intermediate grounding and sintering environment (air or sintered powder) on the superconducting characteristics of Bi(Pb)-Sr-Ca-Cu-O hulk ceramics obtained by spray-frozen freeze drying technique was investigated by X-ray diffraction, electric and magnetic measurements. Intermediate grounding leads to higher scattering coefficients of the superconducting characteristics. This result does not depend on sintering environment. Improved results are obtained when sintering is performed by immersing pellets "in powder" rather than placing them "on powder". The powder used as sintering environment was pyrolized precursor powder calcinated in air for 100 h. (C) 1998 Elsevier Science Ltd. All rights reserved.
1513. Amorphous phase in electrochemically oxidized porous silicon
Authors:
Popescu, MA; Chumash, VN; Cojocaru, I; Jain, VK; Gupta, A
Published: JUN 1996, PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 73, 1731, DOI: 10.1080/01418619608243009
An amorphous phase has been demonstrated in porous silicon prepared by anodization of silicon wafers. The radial distribution function has been calculated on the basis of the X-ray diffraction pattern recorded from a typical sample. There was revealed an amorphous phase of composition SiO1.6.
1514. Coherent dissociation O-16->4 alpha in photoemulsion at an incident momentum of 4.5 GeV/c per nucleon
Authors:
Andreeva, NP; Anzon, ZV; Bubnov, VI; Gaitinov, AS; Eligbaeva, GZ; Eremenko, LE; Kalyachkina, GS; Kanygina, EK; Seitimbetov, AM; Chasnikov, IY; Shakhova, TI; Krasnov, SA; Maksimkina, TN; Tolstov, KD; Chernov, GM; Salmanova, NA; Salomov, DA; Khushvaktova, A; Avetyan, FA; Marutyan, NA; Sarkisova, LT; Sarkisyan, VF; Vokal, S
Published: JAN 1996, PHYSICS OF ATOMIC NUCLEI, 59, 108, DOI:
First searches for the coherent dissociation of relativistic oxygen nuclei into four alpha particles are reported. It is shown that reactions of this type are characterized by a significantly lower decay temperature than the conventional multifragmentation of residual projectile nuclei. The momentum spectra and correlations of alpha particles are not reproduced by the simple statistical model of direct fragmentation. The possibility that the oxygen nucleus undergoing fragmentation acquires a nonzero angular momentum in the collision process is discussed.
1515. Fluctuation conductivity in Li-doped YBa2Cu3O7-delta
Authors:
Sandu, V; Popa, S; Cimpoiasu, E
Published: OCT 1996, JOURNAL OF SUPERCONDUCTIVITY, 9, 492, DOI: 10.1007/BF00723520
The paraconductivity of Li-doped YBa2Cu3O7-x was measured. We have found that the character of the fluctuation changes as lithium content increases: instead of a crossover from 2D to 3D behavior (D is the dimensionality), as we have observed for a low doping level, a double crossover to the 2D percolative and 3D percolative regimes becomes manifest by increasing the lithium content.
1517. On the particles transport between embedded clusters
Authors:
Despa, F; Topa, V
Published: AUG 1996, ZEITSCHRIFT FUR PHYSIK D-ATOMS MOLECULES AND CLUSTERS, 38, 70, DOI: 10.1007/s004600050065
Diffusional interactions within the Ostwald Ripening process are analyzed in the present paper. An off-centre diffusion approach is performed to point out the direct correlation between the size of clusters. Herein the diffusion solution is derived as a function of both the growing and shriniking cluster sizes. Also, it is shown that the frequency transfer of particles between the shrinking cluster and the growing one may acquire high values due to the medium polarization. As a result, the temporal power law of the cluster growth derived in this theoretical model differs from that predicted by the LSW theory. Experimental data for Ag clusters embedded in a KCl matrix are analyzed both by the present theory and by the LSW theory.
1518. Annealing effects in amorphous Fe77Gd3B20 ribbons
Authors:
Mihalca, I; Ercuta, A; Zaharie, I; Jianu, A; Kuncser, V; Filoti, G
Published: MAY 1996, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 157, 162, DOI: 10.1016/0304-8853(95)01143-9
The crystallization kinetics of the amorphous alloy Fe77Gd3B20 were examined under isothermal flash annealing conditions both in air and in a vacuum. Magnetic measurements were used to determine the reaction order (n) and activation energy (E(a)), and Mossbauer spectroscopy (MS) was used to identify some resulting crystalline phases.
1519. Structural modifications of superconducting phases in Bi(Pb)-Sr-Ca-Cu-O system
Authors:
Badica, P; Aldica, G; Alexeev, AF; Gridasova, TY; Morozov, VV
Published: MAR 1 1996, PHYSICA C, 259, 96, DOI: 10.1016/0921-4534(96)00021-4
Bi-Pb-Sr-Ca-Cu-O samples were produced by the spray-frozen, vacuum-freeze drying method from nitrate solutions. Structural modifications of crystallites during sintering were investigated in agreement with bulk density, phase structure of the samples, critical temperature T-c and critical current density j(c). A model for morphology changes of (2223) crystallites during sintering was proposed. Maximum j(c) in a zero magnetic field is reached on samples sintered for 200-250 h.
1520. Crystallization behaviour and phase coexistence at morphotrophic phase boundaries in PZT thin films prepared by sol-gel processing
Authors:
Ontalus, V; Cobianu, C; Vasiliu, F; Parlog, C
Published: JUL 15 1996, JOURNAL OF MATERIALS SCIENCE, 31, 3642, DOI: 10.1007/BF00352771
Pb(Zr0.53Ti0.47)O-3 (PZT) thin films, prepared by sol-gel techniques and deposited on to Si/SiO2/Ti/Pt substrates, have been subjected to thermal annealing in a range of temperatures from 550-800 degrees C. The crystallization behaviour and phase coexistence (tetragonal and rhombohedral) were studied by X-ray diffraction. According to the values of the {110} peak intensity and {110} peak values, the crystallization full-width at half-maximum was more complete at higher temperatures (750, 800 degrees C). At a fixed Zr/Ti ratio close to the morphotropic phase boundary, the lattice parameters of the two phases changed with the annealing temperature. However, the tetragonality degree had relatively low values and the angular rhombohedral distortion was associated with a narrow angular range. The phase coexistence and the variation of the lattice parameters could be explained by the titanium diffusion through the platinum layer. Thus the formation of a {011} titanium rich layer at Pt-PZT interface will supply a titanium excess for the nucleation and growth of textured PZT grains.
1521. A study of hydrogenated amorphous silicon (a-Si:H)/electrolyte interface by means of impedance spectroscopy
Authors:
Dragoe, D; Maracine, L; Popescu, V; Popescu, C
Published: SEP-OCT 1996, REVUE ROUMAINE DE CHIMIE, 41, 748, DOI:
The a-Si:H/electrolyte interface was studied using impedance spectroscopy (IS) method. The measurements were made in the frequency range of 100 Hz - 300 kHz and the potential range of -0.6 V - +0.8 V. The equivalent circuit suggested by the experimental curves allowed us to calculate the main parameters which characterize the interface and the mechanism through which the space charge region supplies carriers to the interface.
1522. Spectroellipsometric studies on TiNx films
Authors:
Pavelescu, G; Braic, M; Braic, V; Melinte, L; Melinte, D
Published: MAY 1996, OPTICAL ENGINEERING, 35, 1342, DOI: 10.1117/1.600625
TIN, films are deposited on glass in a modified de planar three-magnetron geometry. The ellipsometric and reflectance measurements reveal the influence of the substrate bias and of the Ar:N-2 partial pressure ratio on the stoichiometry and optical properties of the films. The stoichiometric structure is obtained for only certain bias voltage and Ar:N, ratio values. The value of the plasma energy omega(p) confirmed the film stoichiometry, as determined from x-ray diffractometry. (C) 1996 Society of Photo-Optical instrumentation Engineers.
1523. NEUTRON-IRRADIATION OF LI-DOPED YBA2CU3O7-DELTA
Authors:
SANDU, V; ALDICA, G; JAKLOVSZKY, J; POPA, S; CIMPOIASU, E; GARLEA, C; GARLEA, I
Published: JUN 1995, JOURNAL OF SUPERCONDUCTIVITY, 8, 340, DOI: 10.1007/BF00728168
The effects of neutron irradiation on the critical temperature and critical current density at 77 K and zero magnetic field of high-temperature superconductors was studied in Li-doped YBa2Cu3O7-x. Damage and thermal neutron reactions with Li produce an insignificant increase of the critical temperature for Li inserted as flame-melted Li2CuO2 while for the others it remains nearly unaffected. The critical transport current density of the sintered YBa2Cu3O7-x remains unaffected for samples with Li2CuO2 and shows a decrease for LiF-doped samples.
1524. ACIDIC AND TEXTURAL PROPERTIES OF H-ZSM-5 IMPREGNATED WITH GALLIUM, INDIUM OR THALLIUM
Authors:
PARVULESCU, VI; FRUNZA, L; CATANA, G; RUSSU, R; PARVULESCU, V
Published: JAN 5 1995, APPLIED CATALYSIS A-GENERAL, 121, 79, DOI: 10.1016/0926-860X(95)85011-2
ZSM-5 samples with a silicon-to-aluminium atomic ratio of 25 were impregnated with gallium, indium or thallium salts. The acidic and textural properties of the samples were determined either before or after reduction. The acidity was investigated by infrared spectroscopy using pyridine (Py) as test molecule, titration with KOH or Py as well as ammonia adsorption. Differences were revealed concerning the dispersion of impregnated species and the distribution of the acidic sites. The sites containing ionic thallium were spectroscopically identified; the other sites were indirectly evidenced. Under our impregnation conditions, gallium species seem to enter inside the zeolite to a higher extent than was reported for similar samples. The contribution of indium to the sample acidity was reduced because it is deposited as a distinct phase onto the external surface. An adsorption mechanism operating during impregnation was proposed on the basis of electrochemical measurements; it was used to account for the acidity data. The textural properties were interpreted in terms of the deposition of the impregnation species near the pore mouth, hindering the entrance of the test molecules.
1525. THE KINETICS OF THE LASER-INDUCED STRUCTURAL-CHANGES IN AS2S3 AMORPHOUS FILMS
Authors:
BERTOLOTTI, M; MICHELOTTI, F; CHUMASH, V; CHERBARI, P; POPESCU, M; ZAMFIRA, S
Published: DEC 1995, JOURNAL OF NON-CRYSTALLINE SOLIDS, 193, 660, DOI: 10.1016/0022-3093(95)00429-7
The intensity dependent complex character of the photodarkening of virgin As2S3 samples exposed to continuous wave (CW) and pulsed laser radiation has been measured. Excitation in the CW and pulsed (picosecond) regime for the same irradiation doses leads to significant differences in the photodarkening curves. It is shown that the kinetics of the photodarkening can be decomposed into several processes related to structural transformations in As2S3: defect elimination and stabilization, polymerization of the structural entities, decomposition followed by arsenic clustering and arsenic oxidation.
1526. Fast diffusion of the off-center impurities Cu+ and Li+ in the KCl lattice
Authors:
Despa, F; Topa, V
Published: 1995, RADIATION EFFECTS AND DEFECTS IN SOLIDS, 137, 1529, DOI:
In this work, we perform a study of the off-center effect: on the diffusion coefficient and we propose a new mechanism for fast diffusion. The model assumes that the equilibrium positions of the cationic impurities are noncentral and that the diffusion proceeds by hopping across the potential barrier along the nonlinear paths with the highest probability [1]. The nonlinear paths between two consecutive positions characterize even the selfdiffusion and furthermore, in the off-center diffusion this path is appropriate. The main results is that the off-center position considerably enhances the diffusion. The theoretical diffusion coefficients have been obtained by modeling the potential barrier. Changes of the configuration entropy and the vibration spectra due to the presence of the noncentral impurity are included in the model. We emphasize the good agreement of the model with the experimental data for KCl:Cu+ and show that if the impurity is placed close to the central site, the appropriate diffusion coefficient is close to that for the cationic self-diffusion: We proceeded in the Li+ cation case as in the case of Cu+ cation.
1528. OPTICAL INDUCED MODIFICATIONS IN THIN-FILMS OF FE-PVA
Authors:
FILOTI, G; KUNCSER, V; FRANKE, H; KARDINAL, T; MANIVANNAN, G
Published: MAR 1995, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY-ARTICLES, 190, 320, DOI: 10.1007/BF02040006
The ferric chloride doped polymers change their refractive index under UV irradiation. The Fe:PVA is sensitive to ferric chloride concentration, molecular weight of PVA, and recording beam power. By Mossbauer investigations we tried to correlate the Fe2+ / Fe3+ ratio, as well as the temperature dependence of the energetical parameters with the assumed mechanisms which involve both the valence state of iron and a cross-linking reaction of PVA matrix.
1529. QUASI-REVERSIBLE TRANSFORMATIONS IN THE ((BI,PB)O)(2)SR2-XCAXBIN-1FENO3N+1+Z (X=0 AND X=1) SYSTEM AND THEIR INFLUENCE ON THE IRON DISTRIBUTION AND MAGNETIC-PROPERTIES OF THE ARISING PHASES
Authors:
FILOTI, G; ROSENBERG, M; SPANU, V; KEMMLERSACK, S; STEUDTNER, C
Published: AUG 1 1995, JOURNAL OF ALLOYS AND COMPOUNDS, 226, 99, DOI: 10.1016/0925-8388(95)01602-3
A phase analysis of the components resulting from a complex program of reactions for the preparation of ((Bi, Pb)O)(2)-Sr2-xCaxBin-1 FenO3n+1+z with x = 0, x = 0 and n = 1, n = 2, using Fe-57 Mossbauer spectroscopy, was performed. Whereas for the phases with n=1 only relatively slight differences in the values of the Neel temperature between 207 and 250 K were found, the phases with n = 2 presented stronger differences, the magnetic ordering temperatures ranging for different conditions of reactions between 205 and 512 K. The two-phase sample with n=2 ordered magnetically below 60 K. An increase in the duration and/or temperature of reaction resulted in compounds with a high degree of inhomogeneity in the vicinity of the Fe sites leading to a distribution of Fe spin freezing temperatures. All the phases studied with n=1 exhibited a Morin spin reorientation transition, with the spins parallel to the c-axis at low temperatures and perpendicular to it above 100-150 K. In all the samples studied about 4%-11% Fe in the form of high spin Fe4+ was present, the corresponding Mossbauer sextet vanishing at higher temperatures because of faster electron hopping.
1530. STRUCTURAL MODIFICATIONS IN IRON HYDRATED OXIDES INDUCED BY FOREIGN CATION
Authors:
SPANU, V; TURCANU, CN; FILOTI, G
Published: MAR 1995, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY-ARTICLES, 190, 380, DOI: 10.1007/BF02040015
The aqueous radioactive wastes are chemical systems as consequence of the variety of the contained cations. The chemical systems precipitated from FeSO4 and FeCl3 simulating the aqueous radioactive waste treatment have been investigated by Mossbauer spectroscopy. Mg2+, Ca2+ and Ba2+ were used as foreign cations, the calcium being among the main components of aqueous radioactive waste. The results showed the ion radius influence varying from Mg2+ and Ba2+ in the case of the precipitation from FeSO4. For the precipitation from ferric chloride the influences are not so evident.
1532. Modified ruthenium exchanged zeolites for enantioselective hydrogenation
Authors:
Parvulescu, VI; Parvulescu, V; Coman, S; Radu, C; Macovei, D; Angelescu, E; Russu, R
Published: 1995, PREPARATION OF CATALYSTS VI: SCIENTIFIC BASES FOR THE PREPARATION OF HETEROGENEOUS CATALYSTS, 91, 570, DOI:
Preparation of modified ruthenium molecular sieves has been investigated in two steps deposition of ruthenium and modifying of ruthenium molecular sieves in presence of ligands. As support sieve there were used two molecular sieves with large pore apertures and low acidity strength (zeolite L and APO-34). Correlation of in situ W-VIS ruthenium deposition measurements with catalyst characterisation revealed that ruthenium deposition takes place not only through ionic exchange but also through adsorption of ruthenium hydrolysed species. Modifying of the ruthenium molecular sieves catalysts with ligands has as effect a diminution of electronic charge on metal. The experimental data indicate that the presence of ligand favours an enantioselective hydrogenation of D-fructose to D-mannitol even if the yields are not very high.
1533. INFLUENCE OF INITIAL CONDITIONS ON THE OPTICAL AND ELECTRICAL CHARACTERIZATION OF SILLENITE-TYPE CRYSTALS
Authors:
HAMRI, A; SECU, M; TOPA, V; BRIAT, B
Published: JAN 1995, OPTICAL MATERIALS, 4, 201, DOI: 10.1016/0925-3467(94)00101-4
We compare a set of results concerning our measurement of the optical absorption (OA), photoconductivity (PC), thermally stimulated currents (TSC) and thermally stimulated luminescence (TSL) on the same crystal. We also investigate the effects of various preillumination treatments at room or liquid nitrogen temperature. We conclude that illumination with infrared light (rather than solely red) plays an important role which has been underestimated in the past.
1534. Magnetic circular dichroism and absorption study of photochromism in Mn-doped Bi12GeO20
Authors:
Ramaz, F; Hamri, A; Briat, B; Topa, V; Mitroaica, G
Published: 1995, RADIATION EFFECTS AND DEFECTS IN SOLIDS, 136, 102, DOI: 10.1080/10420159508218800
We report on the first simultaneaous investigation of the behavior of ligand field and charge transfer bands in doped Bi12GeO20 (BGO) under various illumination and thermal conditions. This was made possible through MCD measurements in both the near IR and the visible spectral regions. The [MnO4](3-) ion is clearly identified in the thermally bleached state. Illumination with blue light leads to the reduction of Mn5+ while the antisite (Bi-Ge(3+) + h) defect is formed. Finally EGO is an interesting host for the popular d(2) ions in a tetrahedral site.
1535. ANION INFLUENCE ON THE HYDRATED OXIDES FORMED BY FE3+ AND FE2+ PRECIPITATION
Authors:
SPANU, V; TURCANU, CN
Published: MAR 1995, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY-ARTICLES, 190, 374, DOI: 10.1007/BF02040014
The anion influence on the hydrated oxides formed by Fe3+ and Fe2+ precipitation simulating the aqueous radioactive waste treatment has been investigated by Mossbauer spectroscopy. Fe-3(SO4)(2), Fe(NO3)(3). FeCl3, FeSO4 and FeCl2 were used as iron sources and neutralized by NaOH. The obtained products contain several kinds of amorphous and/or poorly crystallized hydrated oxides, depending on the anion type which exists in solution and on the initial iron valence. The pH influence on the final precipitate is taken into account.
1536. TIME BEHAVIOR OF CURRENTS IN ZNS-MN METAL-INSULATOR-SEMICONDUCTOR-INSULATOR-METAL STRUCTURES
Authors:
GOLDENBLUM, A; OPREA, A; BOGATU, V
Published: MAY 15 1994, JOURNAL OF APPLIED PHYSICS, 75, 5185, DOI: 10.1063/1.355765
An experimental and theoretical investigation is made on the current pulse evolution, from a very low amplitude toward the steady-state shapes, if a sequence of alternative voltage pulses is applied to a ZnS:Mn metal-insulator-semiconductor-insulator-metal structure. The influence on this evolution of the voltage pulse maximum amplitude, of its rising slope, of pulse shape, and of the frequency is investigated. A quantitative model is developed which explains the current pulse evolution taking into account the competition between the multiplication of the carriers in the ZnS layer, and their recombination involving deep hole traps. The model describes the shapes of current pulse evolution and their peculiarities corresponding to different experimental conditions.
1537. MAGNETIC AND MOSSBAUER STUDIES OF TI4+-SUBSTITUTED SOFT MN-ZN FERRITES
Authors:
NEAMTU, J; SPINU, V; FILOTI, G
Published: MAY 1994, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 133, 483, DOI: 10.1016/0304-8853(94)90601-7
The present work reports the magnetic properties and Mossbauer spectra of soft ferrites MnaZnbFe1-a-b2+Fe23+O4 with Ti4+ substitutions. The addition of Ti4+ to manganese-zinc ferrites induces considerable improvements of properties such as the linear dependence of permeability versus temperature, and small disaccommodation of the permeability. Samples with Mn0.57Zn0.34Fe0.09+x2+TixFe2-2x3+O4 composition (where x = 0.00, 0.02, 0.04, 0.06, 0.08, 1.00) were prepared by the usual ceramic technology. The presence of Ti ions strongly influences the magnetic anisotropy, as evidenced by the temperature dependence of the permeability. A sublattice assigned to Ti4+Fe2+ pairs appeared in the Mossbauer spectra, which also gave information on the local surroundings of iron ions. The appearance of a secondary maximum of permeability (SMP) at negative temperatures or a constant slope over a wide temperature range is typical for mu(i)(t) curves. Increasing Ti4+ contents shift the SMP to higher temperatures because of a positive contribution to K1 of the Ti4+Fe2+ pairs at octahedral sites, in agreement with the hyperfine magnetic fields observed for ferrites with large titanium substitutions.
1538. STEREOSELECTIVITY OF CYCLOOLEFIN POLYMERIZATION WITH WCL6-BASED CATALYTIC-SYSTEMS
Authors:
DIMONIE, M; COCA, S; TEODORESCU, M; POPESCU, L; CHIPARA, M; DRAGUTAN, V
Published: MAY 24 1994, JOURNAL OF MOLECULAR CATALYSIS, 90, 124, DOI: 10.1016/0304-5102(93)E0311-4
The stereochemistry of ring-opening metathesis polymerization of several cycloolefins (cyclopentene, cyclooctene, 1,5-cyclooctadiene, cyclododecene) in the presence of WCl6-based catalysts (WCl6/iBu3Al/epichlorohydrin, WCl6/iBu3Al/Chloranil, WCl6/phenylacetylene, WCl6/Ph4Sn, WCl6/allyl4Si, WCl6/iBu2AlOAliBu2) has been carefully examined. The product stereoselectivity and polymer microstructure were greatly dependent on the nature of the catalytic system and reaction conditions; the nature of the cycloolefin also influenced the steric course of the reaction. An important stereochemical consequence was that the cis and trans content of the polyalkenamer greatly depended on the oxidation state of the W-atom, catalyst activity and reaction temperature. The relationship between the microstructure of several polyalkenamers (polypentenamer, polyoctenamer, polydodecenamer) obtained with the above catalytic systems and cycloolefin reactivity or catalyst nature is fully illustrated. The role of the ligand as well as of the cocatalyst and activator is also shown. The particular stereochemical behaviour of cycloolefins in the presence of the studied WCl6-based catalytic systems is discussed in terms of the metallacarbene-metallacyclobutane mechanism. The steric effects induced by the coordinating cycloolefin and the existing ligands at the transition metal are also considered.
1539. ESR INVESTIGATIONS ON ION-BEAM IRRADIATED POLYCARBONATE
Authors:
CHIPARA, MI; GRECU, VV; NOTINGHER, PV; ROMERO, JR; CHIPARA, MD
Published: JUN 1994, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 88, 422, DOI: 10.1016/0168-583X(94)95393-7
Electron spin resonance (ESR) investigations with a polycarbonate solid state nuclear detector, irradiated with oxygen ions, are reported. The nature of the paramagnetic defects induced by irradiation is discussed. The temperature dependence of resonance line parameters is studied. From the experimental data, obtained by ESR, spectroscopy, the activation energy for defect recombination, the average isotropic exchange integral between paramagnetic defects as well as the average distance between defects, are estimated. Correlations with latent tracks structure are discussed.
1540. TRIVALENT CE2O3 AND CEO2-X INTERMEDIATE OXIDES INDUCED BY LASER IRRADIATION OF CEO2 POWDERS
Authors:
VASILIU, F; PARVULESCU, V; SARBU, C
Published: APR 15 1994, JOURNAL OF MATERIALS SCIENCE, 29, 2101, DOI: 10.1007/BF01154685
A strong non-stoichiometry of pure f c c CeO2 was induced by laser irradiation. The increase of laser power and/or energy density had a saturable effect on particle size growth. The possibility of CeO2 reduction to A-Ce2O3 by laser irradiation was demonstrated. Particles of stable Ce7O12 phase were observed in all specimens irradiated at low laser-power densities. An epitaxial relationship between triclinic Ce11O20 and cubic Ce12O22 phases was found. The controversial C-Ce2O3 Phase was detected at the limits of a b c c particle. An unknown b c c phase of acicular morphology, strongly related to C-Ce2O3, was also registered. The dose dependence of CeO2 structural modifications obtained by laser irradiation as a function of laser energy density variation could be explained by a simple defect aggregation model implying lattice defects (oxygen vacancies and Ce3+ ions).
1541. LAALO3 THIN-FILMS DEPOSITED ON SILICON AND SAPPHIRE AS BUFFER LAYERS FOR YBA2CU3O7-X
Authors:
SANDU, V; JAKLOVSZKY, J; MIU, D; DRAGULINESCU, D; GRIGORIU, C; BUNESCU, MC
Published: AUG 15 1994, JOURNAL OF MATERIALS SCIENCE LETTERS, 13, 1225, DOI: 10.1007/BF00241019
1542. RESISTIVITY AND MAGNETORESISTANCE-ELASTORESISTANCE OF POLYCRYSTALLINE NI-SI THIN-FILMS
Authors:
BELUMARIAN, A; SERBANESCU, MD; MANAILA, R; TEODORESCU, V; IVANOV, I
Published: FEB 1 1994, THIN SOLID FILMS, 238, 317, DOI: 10.1016/0040-6090(94)90072-8
The temperature dependence of the resistivity and magnetoresistance-elastoresistance of r.f.-sputtered Ni-Si thin films with variable silicon content (0-24 at.%) (determined by Rutherford backscattering spectroscopy) annealed to 300 degrees C was measured. The films, investigated by X-ray diffraction and transmission electron microscopy, exhibit a polycrystalline structure of the Ni f.c.c. type with a disorder degree which increases with the silicon content and a metallic-type conduction mechanism. The ferromagnetic properties of Ni are still preserved in the Ni-Si thin films up to 8.8 at.% silicon content.
1543. HYPERFINE FIELDS AND MAGNETIC-ANISOTROPY IN FE100-XGDX THIN-FILMS AND FE80-XGDXB20 (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-24) THIN-FILMS AND RIBBONS
Authors:
KUNCSER, V; FILOTI, G; SERBANESCU, MD; JIANU, A; CRISTEA, L; DORMANN, JL; NOGUES, M; MAKNANI, J
Published: 1994, HYPERFINE INTERACTIONS, 94, 2326, DOI: 10.1007/BF02063782
Mossbauer measurements performed on Fe100-xGdx thin films and on Fe80-xGdxB20 both as thin films and ribbons show a dependence of the spins orientation and [H-hyp] versus temperature, Gd content and preparation conditions. Increasing the Gd content, the initial low anisotropy disappears and [H-hyp] decreases. A sharp increase of the anisotopy with temperature in ribbons with low Gd concentration is evidenced.
1544. DYNAMICAL EVOLUTION OF THE SURFACE MICRORELIEF UNDER MULTIPLE-PULSE-LASER IRRADIATION - AN ANALYSIS BASED ON SURFACE-SCATTERED WAVES
Authors:
BARBORICA, A; MIHAILESCU, IN; TEODORESCU, VS
Published: MAR 15 1994, PHYSICAL REVIEW B, 49, 8395, DOI: 10.1103/PhysRevB.49.8385
We introduce a theoretical analysis of the temporal and spatial evolution of the surface topography of solids following interference between incident and scattered pulsed laser beams. The essential role played by the nonlinear delayed feedback in the laser-radiation-surface system is considered. We show that it finally determines the surface topography evolution from pulse to pulse. In order to complete the analysis, numerical calculations have been conducted under the hypothesis of strong attenuation of laser radiation into the sample and of a limited heat diffusion during the action of a laser pulse. We predict an evolution from very simple to complex (chaotic) structures under multiple-pulse-laser irradiation of solid surfaces. This evolution is determined by some key irradiation parameters; initial surface microrelief, incident laser intensity, and the number of applied laser pulses. Experiments were performed in order to check the main predictions of the theoretical analysis. The system of transversal excited atmospheric pressure-CO2 laser radiation (lambda = 10.6 mum)-interacting with fused silica was chosen as appropriate for performing test experiments. Optical microscopy studies of laser-treated zones evidenced special modifications of the surface topography in good accordance with the conclusions following from the theoretical analysis. The theoretical analysis is also in good agreement with some available data from the literature, at the same time providing a coherent interpretation of previously unexplained behaviors.
1545. PROPERTIES AND HYDROGENATION ACTIVITY OF PD-DY GAMMA-AL2O3 AND DY GAMMA-AL3O2 CATALYSTS .1. PREPARATION AND CHARACTERIZATION
Authors:
PARVULESCU, V; VASILIU, F; SIRBU, C; PARVULESCU, V; ANGELESCU, E
Pd-Dy/gamma-Al2O8 and Dy/gamma-Al2O3 catalysts were prepared using the wet impregnation method. As supports was used Pd/gamma-Al2O3 and gamma-Al2O3. BFETM, TED and SAED analysis of these catallysts revelead the presence of the rare earth element as aluminate, oxide or unidentified forms. The rare earth compounds synthesis is controlled by the palladium percents on gamma-Al2O3.
1546. LUMINESCENCE, ABSORPTION AND MAGNETIC CIRCULAR-DICHROISM OF PB- CENTERS IN KCL CRYSTALS
Authors:
TOPA, V; BRIAT, B; RIVOAL, JC; PEDRINI, C; MOINE, B
Published: APR 1994, JOURNAL OF LUMINESCENCE, 60-1, 606, DOI: 10.1016/0022-2313(94)90228-3
We demonstrate that several kinds of colored T centers can be prepared by an electrical coloring of Pb-doped KCl crystals. Ta is diamagnetic and it contains predominantly the [Pb-]2 species. Te is paramagnetic and we tentatively assign it to [Pb2]- units perturbed by Ca2+. Oxygen centers are thought to occur in Tb.
1547. RADIOACTIVE-WASTE TREATMENT PRODUCTS STUDIED BY MOSSBAUER-SPECTROSCOPY .2. IRON HYDROXIDE PRECIPITATION SYSTEMS
Authors:
SPANU, V; TURCANU, CN
Published: JUN 1994, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY-ARTICLES, 181, 200, DOI: 10.1007/BF02037559
Different iron hydroxide precipitation processes simulating radioactive waste treatment have been investigated by Mossbauer spectroscopy at room temperature and at 80 K. Magnetic oxides (hematite or magnetite) partially affected by superparamagnetic relaxation have been observed. The crystallization degree and the particle size depend on the concentration and the addition order of chemicals. Much smaller particles were precipitated with Ca(OH)2 than with NaOH as neutralization reagent.
1548. AN EMISSION AND KINETIC-STUDY OF THE IMPURITY-TRAPPED EXCITON IN CDCL2-PB2+
Authors:
MOINE, B; PEDRINI, C; GHIORDANESCU, V
Published: MAY 30 1994, JOURNAL OF PHYSICS-CONDENSED MATTER, 6, 4098, DOI: 10.1088/0953-8984/6/22/008
We have studied the spectroscopic properties of Pb2+ in a CdCl2 host crystal. By excitation in the absorption band due to the 1A1g --> 3T1u (P-3(1)) transition, two emission bands are observed. At very low temperature a strong uv luminescence with a very long lifetime (2.5 ms) is detected, As the temperature increases, the lifetime of the uv emission drastically decreases to a few nanoseconds at 100 K, and the uv intensity declines. Meanwhile a strong green fluorescence appears. It is assumed that this emission is of the impurity-trapped exciton type, as in the case of CdCl2:Cu+ and BaF2:Eu2+. A detailed study of the kinetics of both fluorescences is presented.
1549. LINIO2 - QUANTUM LIQUID OF CONCENTRATED SPIN-GLASS
Authors:
ROSENBERG, M; STELMASZYK, P; KLEIN, V; KEMMLERSACK, S; FILOTI, G
Published: MAY 15 1994, JOURNAL OF APPLIED PHYSICS, 75, 6815, DOI: 10.1063/1.356816
From the magnetic and Mossbauer spectroscopy study of LiNi1-xFexO2 With x = 0, 0.01, 0.05, and 0.10 evidence for strong ferromagnetic correlations and spin freezing at low temperatures was found, reminding many characteristic features of spin glass behavior in variance with models describing the ground state of LiNiO2 as a quantum liquid.
1550. ESR INVESTIGATION OF ION-BEAM IRRADIATED POLYETHYLENE
Authors:
CHIPARA, MI; IFRIM, A; GRECU, VV; TOACSAN, MI; POPESCUPOGRION, N; IONESCU, A; CHIPARA, MD; ROMERO, JR
Published: 1994, POLYMER DEGRADATION AND STABILITY, 43, 169, DOI: 10.1016/0141-3910(94)90065-5
Electron spin resonance (ESR) investigations of polyethylene, irradiated with accelerated sulphur ions, are reported- The temperature dependence of resonance line parameters in the range 20-260-degrees-C, has been studied. Additional ESR data on polyethylene irradiated with neutrons as well as on polyethylene thermally degraded in air are presented. The nature of the free radicals induced by irradiation is discussed.
1551. EVIDENCE FOR SPIN FREEZING AND FERROMAGNETIC SHORT-RANGE CORRELATIONS IN FE-57-DOPED LINIO2
Authors:
FILOTI, G; ROSENBERG, M; STELMASZYK, P; ZHOU, R; KEMMLERSACK, S; KLEIN, V
Published: 1994, HYPERFINE INTERACTIONS, 88, 95, DOI: 10.1007/BF02068706
Evidence for a frozen spin ground state and a mixed magnetic ordered and paramagnetic state at intermediate temperatures was found in Fe-57-doped LiNiO2, using Mossbauer spectroscopy. The magnetic measurements, in agreement with Mossbauer data, suggest short-range ferromagnetic correlations at low temperatures and the occurrence of a paramagnetic phase below the spin freezing temperature.
1552. EXAFS CHARACTERIZATION OF DY AND PD-DY ON ALUMINA CATALYSTS
Authors:
MACOVEI, D; PARVULESCU, V; TEODORESCU, CM
Published: APR 1994, REACTION KINETICS AND CATALYSIS LETTERS, 52, 86, DOI: 10.1007/BF02129853
Two Pd-Dy/gamma-Al2O3 catalysts, with 1 wt.% Dy and various Pd loadings (0.1 and 0.5 wt.%) have been investigated by EXAFS at the Dy L(III)-edge, and compared with 1 % Dy/gamma-Al2O3. The Dy-carrier interaction was found to change with the Pd dispersity.
1553. STYRENE HYDROGENATION ON SUPPORTED PD, FE AND PD-FE GAMMA-AL2O3 CATALYSTS
Authors:
PARVULESCU, VI; FILOTI, G; PARVULESCU, V; GRECU, N; ANGELESCU, E; NICOLESCU, IV
Published: MAY 6 1994, JOURNAL OF MOLECULAR CATALYSIS, 89, 282, DOI: 10.1016/0304-5102(93)E0312-5
Bimetallic Pd-Fe/gamma-Al2O3 catalysts with different concentration of palladium and 1 wt.% of iron were prepared via impregnation of Pd/gamma-Al2O3 catalysts with Fe (NO3)3 solution and compared with corresponding monometallic Pd and Fe catalysts. The state of the supported components was studied by hydrogen chemisorption, ESR and Mossbauer spectroscopy; hydrogenation of styrene was also used as a test reaction. The hydrogenation was shown to proceed selectively to ethylbenzene on monometallic Pd catalysts and unselectively to the mixture of ethylbenzene and ethylcyclohexane on the Fe catalysts. Presence of 0.1 wt.% of palladium in the Pd-Fe catalysts directed the hydrogenation exclusively to ethylbenzene while selectivity drops again upon increasing Pd loading to 0.3 and 0.5 wt.%. Possible reasons for such a non-trivial effect from the second metal are discussed.
1554. THEORETICAL AND EXPERIMENTAL-STUDY OF CYLINDRICAL GAS-FLOW CEMS DETECTORS
Authors:
KUNCSER, V; FILOTI, G
Published: JUL 1993, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 82, 191, DOI: 10.1016/0168-583X(93)95100-J
The operational range of the gas counters used in conversion electron Mossbauer spectroscopy (CEMS) is at the limit between the proportional counter and Geiger Muller domains. Starting from the theory of phenomena in gas detectors under space charge conditions, a general expression for the multiplication factor was obtained. The theoretical results, presented graphically, are discussed in connection with experimental data.
1555. SELECTIVE HYDROGENATION OF STYRENE ON PD-HO/GAMMA-AL2O3 AND PD/GAMMA-AL2O3 CATALYSTS
Authors:
PARVULESCU, VI; PARVULESCU, V; FRUNZA, L; GRECU, N; ENACHE, C; ANGELESCU, E
Published: JUN 1993, BULLETIN DES SOCIETES CHIMIQUES BELGES, 102, 399, DOI:
Pd-Ho/gammaAl2O3 catalysts exhibit higher activity for styrene hydrogenation than Pd/gammaAl2O3 ones. The addition of holmium to Pd catalysts changes the place of the palladium impregnation front depending on the state of the supported palladium. As a consequence of the interaction between holmium and Pd/gammaAl2O3 support, oxidized forms as holmium aluminate were formed. These forms are catalytically inactive but represent adsorption centers for styrene. On holmium containing catalysts, hydrogenation takes place between the styrene adsorbed on basic centers and the hydrogen spilled over from palladium particles.
1556. PROMOTION OF HIGH-TC PHASE IN B-DOPED (BI,PB)2SR2CA2CU3OY SUPERCONDUCTORS PREPARED BY THE MELT-QUENCHING METHOD
Authors:
FRUTH, V; ZAHARESCU, M; ALDICA, G
Published: MAR-JUN 1993, APPLIED SUPERCONDUCTIVITY, 1, 707, DOI: 10.1016/0964-1807(93)90280-F
We prepared superconducting Bi1.6Pb0.4-xBxSr2Ca2CU3Oy (x=0, 0.1, 0.2, 0.3 and 0.4) ceramics by the melt-quenching method and examined the effect of B addition on the formation of the high-Tc phase.The temperatures and sequence of formation of the superconducting phases within this composition were determined using simultaneous differential thermal analysis (DTA) and thermogravimetric analysis (TGA), X- ray powder diffraction (XRD). It was found that the bulk ceramics with x=0.1 and 0.2 exhibited superconductivity with a critical temperature range of 95-100 K. The lowering of the partial melting temperature caused by the coexistence of Pb and B elements is effective for the formation mechanism of the high-Tc phase.
1557. ELECTRON-IRRADIATION EFFECT ON VACUUM-EVAPORATED CDS THIN-LAYERS
Authors:
CRISTEA, P; SPANULESCU, I; SECAREANU, I; RUXANDRA, V; SPANULESCU, S; BALTATEANU, N
Published: SEP 15 1993, JOURNAL OF MATERIALS SCIENCE LETTERS, 12, 1469, DOI: 10.1007/BF00591610
1558. SPECTROSCOPY OF MN-2+ IONS IN CDCL2
Authors:
GHIORDANESCU, V; VODA, M; PEDRINI, C
Published: APR 16 1993, CHEMICAL PHYSICS LETTERS, 205, 414, DOI: 10.1016/0009-2614(93)87143-Q
An investigation of ultraviolet absorption and excitation spectra of Cd1-xMnCl2 Crystals is reported. At lower temperatures, T < 77 K, it is shown that a number of lines are associated with the manganese ions. No assignments are given for room temperature excitation spectra because the Mn2+ states are in the fundamental absorption edge.
1559. SIO2-SM2O3 VITREOUS FILMS VIA THE SOL-GEL METHOD
Authors:
ZAHARESCU, M; PIRLOG, C; GARTNER, M; MOISE, F; TEODORESCU, V
Published: AUG 15 1993, JOURNAL OF MATERIALS SCIENCE, 28, 4441, DOI: 10.1007/BF01154953
SiO2-Sm2O3 vitreous films 120 nm thick were obtained via the sol-gel method. Infrared, energy-dispersive analysis of X-rays, spectroscopic ellipsometry and absorption spectroscopy showed a total inclusion of samarium in the silica matrix, which remains amorphous up to 1000-degrees-C. The inclusion of the samarium ion increases the porosity. The optical properties of films were investigated by spectro-ellipsometry, and the parameters obtained were compared with those obtained by other techniques.
1560. EFFECT OF THERMAL-TREATMENT AND SWEEPING ON THE ELECTRICAL-CONDUCTIVITY OF QUARTZ CRYSTALS
Authors:
ILIESCU, B; TOPA, V; TANASE, AT
Published: 1993, CRYSTAL RESEARCH AND TECHNOLOGY, 28, 1168, DOI: 10.1002/crat.2170280822
The effect of thermal treatment and sweeping at different temperatures on the current peaks occurring during the heating-up phase of the electrodiffusion runs are studied. Arrhenius plots of swept synthetic quartz are discussed.
1561. IR SPECTROSCOPIC MEASUREMENTS OF CRYSTALLINITY AND PHASE PURITY OF ZSM-5 SAMPLES
Authors:
FRUNZA, L; DINCA, V; VAGAON, M; CRISAN, D; FLORESCU, I; MANOIU, D; CRISAN, M; RAGAN, N
Published: MAR 1993, REVUE ROUMAINE DE CHIMIE, 38, 246, DOI:
The use of IR spectroscopic method to choose the best batches of ZSM-5 zeolites. is discussed. The crystallinity and the particle size were estimated from IR spectra and by XRD and electron microscopy measurements.
1562. MAGNETIC-PROPERTIES OF FE100-XGDX THIN-FILMS AND FE80-XGDXB20 THIN-FILMS AND RIBBONS (0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-20)
Authors:
FILOTI, G; KUNCSER, V; SERBANESCU, MD; JIANU, A; CRISTEA, L; NOGUES, M; DORMANN, JL; MAKNANI, J
Published: NOV 1993, IEEE TRANSACTIONS ON MAGNETICS, 29, 3125, DOI: 10.1109/20.280879
Magnetic and Mossbauer experiments were performed on Fe100-xGdx thin films and on Fe80-xGdxB20 both in thin films and ribbons for x less-than-or-equal-to 20. The ferrimagnetic order is perturbed by the presence of B and Fe-interactions are.different. For small Gd content, the low anisotropy is in the film plane, while for greater Gd the anisotropy goes out of the plane giving typical features of hysteresis loops and strong decrease of Mossbauer hyperfine fields.
1563. SUPERCONDUCTIVITY IN YBA2CU3O7-DELTA AND (BIPB)2SR2CA2CU3OX
Authors:
DOLOCAN, V; MIU, L; ALDICA, G
Published: FEB 1992, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 104, 610, DOI: 10.1016/0304-8853(92)90947-M
Using a new method, based on nanosecond-pulse reflection, we measured the temperature dependence of the permeability of the superconducting samples. The transition temperature and the superconducting phase content were determined.
1564. PREPARATION OF PURE AND DOPED CDF2 SINGLE-CRYSTALS
Authors:
VODA, M; NISTOR, SV; GHIORDANESCU, V
Published: MAY 1992, JOURNAL OF CRYSTAL GROWTH, 119, 344, DOI: 10.1016/0022-0248(92)90689-G
This paper describes the growth of CdF2 single crystals using the Bridgman method. Unwanted vapour reactions are avoided by using an argon atmosphere and glassy carbon crucibles. The installation for the growth of CdF2 single crystals is described in detail. Optical absorption of CdF2 crystals is shown for wavelengths of 200 to 800 nm. Transmission spectrum in the 2.5-10-mu-m range shows a low level of impurities which do not affect the optical qualities.
1565. SPECTROSCOPY, FLUORESCENCE MECHANISMS AND ENERGY TRANSFERS IN CADMIUM CHLORIDE DOUBLY DOPED WITH COPPER AND MANGANESE
Authors:
VODA, M; GHIORDANESCU, V; PEDRINI, C
Published: AUG 24 1992, JOURNAL OF PHYSICS-CONDENSED MATTER, 4, 7152, DOI: 10.1088/0953-8984/4/34/014
We have observed and identified the optical excitation and emission spectra of Mn2+ ions in the doubly doped CdCl2:Mn:CU system between 77 and 300 K. A comparison is made with the singly doped CdCl2 system. The temperature dependence of the absorption strength is explained by vibrational electronic interaction, and the quantum efficiency is close to unity for low-Mn2+-concentration crystals. In CdCl2 the 1E(g) state of Cu+ lies in the conduction band. By excitation in the main absorption band, 1A1g --> 1E(g), of Cu+ in CdCl2:Mn:Cu crystals an energy transfer to Mn2+ ions takes place through intermediate metastable states (excimer-like species) which form in the lattice near the Cu+ centres. Because these states thermally ionize, the energy transfer rate decreases when the temperature increases and above 100 K the photoionization of Cu+ centres becomes dominant.
1566. CONTRIBUTION TO THE STUDY OF FORMATION MECHANISM OF THE COMPOUNDS IN THE BI2O3-(SR,CA)O-CUO SYSTEM
Authors:
ZAHARESCU, M; BRAILEANU, A; MANAILA, R; FRUTH, V; TANASE, G
Published: APR 1992, MATERIALS RESEARCH BULLETIN, 27, 498, DOI: 10.1016/0025-5408(92)90027-W
The formation mechanism of definite compounds, under non-isothermal conditions, in binary and pseudobinary systems of the type Bi2O3-MO and CuO-MO, where M = Sr, Ca and Sr + Ca and in the pseudoternary system Bi2O3-(Sr,Ca)O-CuO has been studied. It has been established that the components of systems containing Bi2O3 and CaO exhibit much higher reactivity than those of the systems containing SrO and CuO. In the pseudoternary system superconducting phases are formed at low temperature with preferential participation of calcium. with increasing temperature incorporation of Sr and Cu in a preformed network takes place.
1567. SELECTIVE HYDROGENATION OF STYRENE UPON PD-SM/GAMMA-AL2O3 CATALYSTS .1. PREPARATION AND CHARACTERIZATION OF THE CATALYSTS
Authors:
PARVULESCU, V; BIRJEGA, M; PARVULESCU, V; MACOVEI, D; ANDREI, A; ANGELESCU, E; NICOLESCU, IV
Published: MAR 1992, REVUE ROUMAINE DE CHIMIE, 37, 344, DOI:
In the paper the properties of some Pd-Sm/gamma Al2O3 catalysts with different contents of palladium obtained by the successive method of impregnation have been studied. The metallographic microscopy determinations showed that by impregnating samarium upon a Pd/gamma Al2O3 supported catalyst a penetrating front, mostly different from the one of samarium, has resulted depending on the existent concentration of palladium upon the support and also a different migration front of the platinic metal. From the electronic microscopy determinations, electronic diffraction and EXAF3, the state in which the samarium is found after impregnation and after the drying and reduction, respectively, was established. Based on these determinations a mechanism of samarium impregnation was suggested.
1568. RADIOACTIVE-WASTE TREATMENT PRODUCTS STUDIED BY MOSSBAUER-SPECTROSCOPY
Authors:
SPANU, V; TURCANU, CN; FILOTI, G
Published: NOV 2 1992, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY-LETTERS, 166, 320, DOI: 10.1007/BF02163837
Mossbauer effect was used for the characterization of the radioactive waste treatment products, e.g. precipitate formed during the treatment of LLAW (Low Level Active Waste) using iron compounds and their conditioned matrix obtained by cementation.
1569. STRUCTURAL-CHANGES IN MORDENITES REVEALED BY 2-DIMENSIONAL FOURIER SYNTHESIS OF X-RAY-POWDER DIFFRACTION PATTERNS
Authors:
STOICA, AD; TARINA, V; RUSSU, R; GHEORGHE, G
Published: JUL-AUG 1992, ZEOLITES, 12, 709, DOI: 10.1016/0144-2449(92)90119-A
It is shown that X-ray powder diffraction patterns of mordenites can be used to reveal, by 2D Fourier mapping, structural changes due to chemical or thermal effects. During dealumination, a preferential localization of the structural defects at the tetrahedral groups of type 1 was observed. For different degrees of dealumination and cation contents, the localization of cations and/or water molecules inside the mordenite channels can be seen.
1570. CONDUCTION CONCENTRATION RELATIONSHIP IN CHEMORESISTIVE THICK-FILM SNO2 GAS SENSORS
Authors:
IONESCU, R; VASILESCU, V; VANCU, A
Published: MAY 1992, SENSORS AND ACTUATORS B-CHEMICAL, 8, 154, DOI: 10.1016/0925-4005(92)80172-T
The steady-state conductance G of thick-film SnO2 chemoresistive gas sensors is measured for different CO concentrations c in air, in the 0-300 ppm range, at 0 and 100% relative humidity. The conductances G0 at 0 and G at 120 ppm CO in normal air are measured as a function of time in non-steady-state conditions, during the first two hours of stabilization, after keeping the sensors unheated (out of operation) for seven days. The time dependence of the conductance at sudden changes of the CO concentration between c = 0 and c not-equal 0 in normal air is also measured. Experimental results indicate that the ratio (G2-G0(2))/G0 depends almost linearly on c down to very low values (about 1 ppm), it is fairly independent of humidity in the steady state, and of time during the stabilization stage. This can offer a possibility for using SnO2 sensors not only for the detection, but also for the quantitative measurement, of small concentrations of a combustible gas in air.
1571. MAGNETIC-PROPERTIES OF GDCO4-XMXB COMPOUNDS WHERE M = FE OR NI
Authors:
BURZO, E; POP, V; PLUGARU, N
Published: JUN 1991, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 97, 151, DOI: 10.1016/0304-8853(91)90174-9
The GdCo4-xNi(x)B alloys, for x less-than-or-equal-to 3 and GdCo4-xFe(x)B alloys for x less-than-or-equal-to 1.5 crystallize in a hexagonal structure of CeCo4B-type. The magnetic measurements performed in the temperature range 4.2-900 K show that GdCo4-xM(x)B compounds (M = Fe or Ni) are ferrimagnetically ordered. The mean cobalt moments increase when cobalt is substituted by iron and decrease when it is replaced by nickel. Above the Curie temperatures, the reciprocal susceptibilities for GdCo4-xNi(x)B alloys show a nonlinear temperature dependence. The exchange fields acting on cobalt atoms were evaluated. The variations of the cobalt moments are proportional to those of the exchange fields.
1572. NON-ARCHIMEDEAN MODEL FOR THE RELAXATION PROCESS OF THE PHOTOINDUCED DARKENING IN AMORPHOUS-CHALCOGENIDE FILMS
Authors:
POPESCU, M; ANDRIESH, A; CHUMASH, V; ENACHI, N; COJOCARU, I; GROZESCU, A
Published: DEC 1991, JOURNAL OF NON-CRYSTALLINE SOLIDS, 137, 976, DOI: 10.1016/S0022-3093(05)80283-2
The relaxation of the darkening induced by nanosecond laser pulses in amorphous chalcogenide thin films (AsSe and As2Se3) was modelled on the basis of a non-archimedean (ultrametric) approach. While for AsSe only a single time scale of evolution was evidenced (tentatively related to the simple, molecular structure of the glass) in As2Se3 three time scales were evidenced and discussed in the frame of a complex hierarchical structure of the glass with layer fragments, clusters of layers (amorphites) and, possibly, bigger domains.
1573. ON THE LIMITING FACTORS OF THE CRITICAL CURRENT-DENSITY IN HIGH-TC SUPERCONDUCTING CERAMICS
Authors:
MIU, L; CRISAN, A; POPA, S; SANDU, V; NISTOR, L
Published: DEC 1990, JOURNAL OF SUPERCONDUCTIVITY, 3, 394, DOI: 10.1007/BF00617464
The temperature dependence of the critical current density at high temperatures and in weak applied magnetic field for YBa2Cu3O7-y ceramic samples with a pronounced granular character is analyzed. The experimental results can be explained in terms of thermally activated motion of the intergrain Josephson vortices at grain boundaries, which may be an indication that the actual limiting factor for the critical current density in ceramic samples results from a weak pinning force density for the intergrain vortices rather than from the weak-link quenching.
1575. MOSSBAUER INVESTIGATIONS OF THE FE-CU-MN CATALYSTS FOR FISCHER-TROPSCH SYNTHESIS
Authors:
SPANU, V; FILOTI, G; ILIE, I; ZAMFIRESCU, E
Published: JUL 1990, HYPERFINE INTERACTIONS, 57, 2113, DOI: 10.1007/BF02405772
1576. LOCAL MAGNETIC-INTERACTIONS AND SHORT-RANGE ORDER IN AMORPHOUS GDXFE1-X FILMS
Authors:
MANAILA, R; FILOTI, G; FLORESCU, V; SERBANESCU, MD; DRINCIU, C
Published: MAY 1990, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 86, 288, DOI: 10.1016/0304-8853(90)90133-B
1577. A CONCEPT FOR EARTHQUAKE PROTECTION OF THE BUCHAREST TANDEM ACCELERATOR
Authors:
MARINESCU, L; ZORAN, V; DOBRESCU, S; PASCOVICI, G; SEMENESCU, G; MARMUREANU, G; SANDI, H; SIRETEANU, T
Published: FEB 1 1990, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 287, 131, DOI: 10.1016/0168-9002(90)91782-7
1578. A MOSSBAUER STUDY OF THE COBALT COATED HEMATITE
Authors:
LUO, HL; SPANU, V; CHEN, GM; DAI, SY; HUANG, XC; FILOTI, G
Published: JUL 1990, HYPERFINE INTERACTIONS, 54, 602, DOI: 10.1007/BF02396096
1579. SMALL-FIELD BEHAVIOR OF THE CRITICAL CURRENT IN BI2.8PB1.2CA4SR4CU7.2OX CERAMIC SAMPLES ABOVE LIQUID-NITROGEN TEMPERATURE
Authors:
MIU, L; ALDICA, G; CRUCEANU, E; TEODORESCU, V
Published: MAY 1990, JOURNAL OF MATERIALS SCIENCE LETTERS, 9, 534, DOI: 10.1007/BF00725868
1580. DISTRIBUTION FUNCTION OF PRECIPITATED TIO2 PARTICLE VOLUMES
Authors:
MANOLESCU, A; MANAILA, R; MEZINCESCU, GA; NISTOR, L; TEODORESCU, V; SERBAN, S; IOVITA, V
The distribution function of precipitated particles in relation to their volume is modelled by a function reproducing the three moments of the real function. The time evolution of the distribution is simulated by the numerical solving of a non-linear differential equation system for the moments, resulting from the rate equation which describes the growth of the particles.
1581. MAGNETIC-PROPERTIES AND STRUCTURE OF RARE-EARTH TRANSITION-METAL THIN-FILMS IMPLANTED WITH AR+ IONS
Authors:
FLORESCU, V; SERBANESCU, MD; MANAILA, R; GRANT, WA
Published: NOV 1990, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 92, 142, DOI: 10.1016/0304-8853(90)90690-R
1585. ON THE TRANSITION-METAL QUASISUBLATTICE IN ICOSAHEDRAL AL-CR-FE PHASES
Authors:
MANAILA, R; FLORESCU, V; JIANU, A; RADULESCU, O
Published: NOV 1989, PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES, 60, 599, DOI: 10.1080/13642818908206041
1586. TEA-CO2 LASER-DEPOSITED YBA2CU3O7 SUPERCONDUCTING THIN-FILMS
Authors:
SANDU, V; CRISAN, A; GRIGORESCU, D; MIU, L; CHIS, I; ALDICA, G; CRUCEANU, E; GRIGORIU, C; DRAGULINESCU, D
Published: MAY 1989, JOURNAL OF MATERIALS SCIENCE LETTERS, 8, 510, DOI: 10.1007/BF00720279
1587. THE CONVERSION OF ELECTRONIC CENTERS INTO U-CENTERS AND OH-CENTERS
Authors:
TOPA, V; IOAN, A; ILIESCU, B; MITROAICA, G
Published: MAR 1989, PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 152, 59, DOI: 10.1002/pssb.2221520105
1589. MAGNETIC-PROPERTIES AND DEFECTS IN POLYCRYSTALLINE NICKEL FILMS .2. EFFECTS OF ION-IMPLANTATION
Authors:
DINCA, G; MANAILA, R; BELUMARIAN, A; NISTOR, LC; TEODORESCU, V; MIU, L
Published: JAN 1 1989, THIN SOLID FILMS, 168, 9, DOI: 10.1016/0040-6090(89)90683-4
1591. MAGNETIC-PROPERTIES AND DEFECTS IN POLYCRYSTALLINE NICKEL FILMS .1. MICROSTRUCTURE-RELATED MAGNETIC-ANISOTROPY
Authors:
BELUMARIAN, A; MANAILA, R; NISTOR, LC; TEODORESCU, V; DINCA, G; SERBANESCU, D
Published: DEC 15 1988, THIN SOLID FILMS, 167, 12, DOI: 10.1016/0040-6090(88)90476-2
1592. ICOSAHEDRAL PHASES IN THE AL-FE-CR ALLOY SYSTEM
Authors:
MANAILA, R; FLORESCU, V; JIANU, A; BADESCU, A
Published: SEP 16 1988, PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, 109, 66, DOI: 10.1002/pssa.2211090105
1593. EFFECTS OF ION-IMPLANTATION ON MAGNETIC AND STRUCTURAL-PROPERTIES OF AMORPHOUS GD-CO THIN-FILMS
Authors:
FLORESCU, V; ALTAMIMI, Z; SERBANESCU, MD; MANAILA, R; GRANT, WA
Published: MAR 1988, IEEE TRANSACTIONS ON MAGNETICS, 24, 1737, DOI: 10.1109/20.11586
1596. TEMPERATURE-DEPENDENCE OF THE ELECTRICAL-RESISTIVITY IN SOME AMORPHOUS FERROMAGNETIC-ALLOYS
Authors:
DOLOCAN, V; DOLOCAN, E
Published: MAR 1988, IEEE TRANSACTIONS ON MAGNETICS, 24, 1834, DOI: 10.1109/20.11617
1598. THE GAUGE-THEORY AND THE TOPOLOGICAL DISORDER
Authors:
COHEN, V; POPESCU, M
Published: FEB 1987, JOURNAL OF NON-CRYSTALLINE SOLIDS, 90, 68, DOI: 10.1016/S0022-3093(87)80385-X
1600. STRUCTURAL STUDIES ON SOME IRON 8-OXI-QUINOLINATES USING MOSSBAUER-SPECTROSCOPY
Authors:
BARB, D; MORARIU, M; COZAR, O; ZNAMIROVSCHI, V; SEMENIUC, R
Published: AUG 5 1986, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY-LETTERS, 106, 26, DOI: 10.1007/BF02164987
1602. PREPARATION OF BARIUM HEXAFERRITE BY A HYDROTHERMAL METHOD - STRUCTURE AND MAGNETIC-PROPERTIES
Authors:
BARB, D; DIAMANDESCU, L; RUSI, A; TARABASANUMIHAILA, D; MORARIU, M; TEODORESCU, V
Published: APR 1986, JOURNAL OF MATERIALS SCIENCE, 21, 1122, DOI: 10.1007/BF00553240
1604. ODMR IN TRIPLET EXCITED-STATES OF NS2 IONS IN ALKALI-HALIDE CRYSTALS
Authors:
BARANOV, PG; VETROV, VA; ROMANOV, NG; TOPA, V
Published: AUG 1986, PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 136, 707, DOI: 10.1002/pssb.2221360238
1606. SEM, SAED, AND TEM INVESTIGATION OF DOMAIN-STRUCTURE IN PZT CERAMICS AT MORPHOTROPIC PHASE-BOUNDARY
Authors:
LUCUTA, PG; TEODORESCU, V; VASILIU, F
Published: 1985, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 37, 242, DOI: 10.1007/BF00614823
1607. ELECTRON-SPIN-RESONANCE INVESTIGATION OF THE INTERACTION BETWEEN WCL6-BASED CATALYSTS AND CYCLO-OLEFINS
Authors:
CEAUSESCU, E; CORNILESCU, A; NICOLESCU, E; POPESCU, M; COCA, S; BELLOIU, C; OPRESCU, C; DIMONIE, M; HUBCA, G; DRAGUTAN, V; CHIPARA, M
Published: 1985, JOURNAL OF MOLECULAR CATALYSIS, 28, 357, DOI: 10.1016/0304-5102(85)87040-1
1608. NEW ASPECTS OF THE RING-OPENING POLYMERIZATION OF CYCLOOLEFINS
Authors:
CEAUSESCU, E; DIMONIE, M; CORNILESCU, A; CHIPARA, M; GHEORGHIU, M; DRAGUTAN, V
Published: 1985, JOURNAL OF MACROMOLECULAR SCIENCE-CHEMISTRY, A22, 876, DOI: 10.1080/00222338508056640
1610. NEW ASPECTS OF THE MECHANISM OF THE RING-OPENING POLYMERIZATION OF CYCLO-OLEFINS
Authors:
CEAUSESCU, E; CORNILESCU, A; NICOLESCU, E; POPESCU, M; COCA, S; BELLOIU, C; DIMONIE, M; GHERORGHUI, M; DRAGUTAN, V; CHIPARA, M
Published: 1985, JOURNAL OF MOLECULAR CATALYSIS, 28, 349, DOI: 10.1016/0304-5102(85)87039-5
1613. WAVELENGTH-DEPENDENT ABSOLUTE REFLECTIVITIES AND EFFECTIVE MOSAIC WIDTHS OF SINGLE-CRYSTAL NEUTRON MONOCHROMATORS
Authors:
GRABCEV, B; TODIREANU, S; CIOCA, V
Published: 1985, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 228, 481, DOI: 10.1016/0168-9002(85)90295-5
1614. THE PRESENCE OF TI-3+ IN LITIZN FERRITES
Authors:
NICOARA, G; GHIORDANESCU, V
Published: 1984, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 84, K142, DOI: 10.1002/pssa.2210840255
1618. HYPERFINE FIELD DISTRIBUTION IN METGLASSES
Authors:
NISTOR, CI; SPANU, V; MANDACHE, S; FILOTI, G; FLORESCU, V
Published: 1984, PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, 86, 529, DOI: 10.1002/pssa.2210860209
1621. PERIPHERAL AND CENTRAL NUCLEUS-NUCLEUS COLLISIONS AT 4.2 GEV/C PER NUCLEON
Authors:
AGAKISHIEV, HN; ABDINOV, OB; MEKHDIEV, RR; SULEIMANOV, MK; AHABABIAN, N; BAATAR, T; BALDIN, AM; BARTKE, J; BOGDANOWICZ, J; CHEPLAKOV, AP; GASPARIAN, AP; GRISHIN, VG; IVANOVSKAYA, IA; KANAREK, T; KLADNITSKAYA, EN; KONDOR, E; KOPYLOVA, DK; KOWALSKI, M; KVATADZE, RA; LYUBIMOV, VB; NIKITINA, VF; SOLOVIEV, MI; TONEEV, VD; CHASNIKOV, IY; IZBASAROV, MI; VINITSKY, AK; BACKOVIC, S; DAMIANOVIC, V; DRNDAREVIC, S; KRMPOTIC, D; KRPIC, D; SIMIC, L; BALEA, E; BALEA, O; BOLDEA, V; HACMAN, S; PONTA, T; GUDIMA, KK; KELOGLU, YP; ANOSHIN, AI; EROFEEVA, IN; DIDENKO, LA; LYUTOV, SI; MELNIKOVA, NN; MURZIN, VS; POPOVA, VM; SARYCHEVA, LI; SHCHEGLOVA, LM; SMIRNOVA, LN; SOLOMIN, AN; TONEEVA, GP; KORBEL, Z; TRKA, Z; TRKOVA, Y; ISMATOVA, FA; MUMINOV, MM; SUVONOV, I; ANGELOV, N; GREKOVA, LD; KERACHEV, P; SEMERDZHIEV, H; TEMNIKOV, PP; AZIMOV, SA; EDGOROV, SO; INOGAMOV, SV; YULDASHEV, AA; YULDASHEV, BS; AMAGLOBELI, NS; GRIGALASHVILI, NS; DASAEVA, MA; METREVELI, ZV; TEVZADZE, YV; TOPURIDZE, MV; TUVDENDORZH, D; SHARKHU, G; ARMUTLIJSKY, D; KOCHNEV, N; PROKOPIEVA, S; BIALKOWSKA, H; ARAKELIAN, SG; GULKANIAN, GR; KIRAKOSIAN, ZA; KORCHAGIN, SA; RAVINOVICH, IM; VARTANIAN, VA
Published: 1983, ZEITSCHRIFT FUR PHYSIK C-PARTICLES AND FIELDS, 16, 317, DOI: 10.1007/BF01577098
1623. EPITAXIAL-GROWTH OF THIN GOLD-FILMS ONTO PURE AND DOPED NACL AND KCL SUBSTRATES
Authors:
BIRJEGA, MI; POPESCUPOGRION, N; TOPA, V
Published: 1982, THIN SOLID FILMS, 94, 73, DOI: 10.1016/0040-6090(82)90031-1
1625. MAGNETIC HYPERFINE FIELD DISTRIBUTION IN ANNEALED AMORPHOUS GLASSES
Authors:
NISTOR, CI; SPANU, V; MANDACHE, S; FILOTI, G; FLORESCU, V
Published: 1982, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH, 199, 229, DOI: 10.1016/0167-5087(82)90205-8
1627. DIRECT MEASUREMENT OF THE TRANSVERSE RESISTIVITY OF MULTIFILAMENTARY SUPERCONDUCTING COMPOSITES
Authors:
DROBIN, VM; DYACHKOV, EI; KHUKHAREVA, IS; LUPPOV, VG; NICHITIU, A
Published: 1982, CRYOGENICS, 22, 119, DOI: 10.1016/0011-2275(82)90106-0
1629. MAGNETOELECTRIC EFFECT IN THE HETEROGENEOUS SYSTEM NIZN FERRITE-PZT CERAMIC
Authors:
BUNGET, I; RAETCHI, V
Published: 1981, PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, 63, K57, DOI: 10.1002/pssa.2210630163
1631. MACROSCOPIC BEHAVIOR OF A CHARGED BOLTZMANN GAS
Authors:
BANYAI, L; GARTNER, P; PROTOPOPESCU, V
Published: 1981, PHYSICA A, 107, 178, DOI: 10.1016/0378-4371(81)90030-3
1635. TL- CENTERS IN KCL CRYSTALS
Authors:
IOAN, A; TOPA, V
Published: 1980, PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 101, 388, DOI: 10.1002/pssb.2221010140
1638. PLASMA-TARGET COUPLING IN THE CASE OF TEA-CO2 LASER-PRODUCED BREAKDOWN IN FRONT OF A SOLID TARGET
Authors:
URSU, I; APOSTOL, I; DINESCU, M; MIHAILESCU, IN; MOLDOVAN, M; PROKHOROV, AM; AGEEV, VP; KONOV, VI; SILENOK, AV; CHAPLIEV, MI
Published: 1980, OPTICS COMMUNICATIONS, 35, 99, DOI: 10.1016/0030-4018(80)90367-3
1640. COALESCENCE BEHAVIOR OF GOLD PARTICLES VACUUM EVAPORATED ONTO DOPED ALKALI-HALIDE SUBSTRATES
Authors:
BIRJEGA, MI; POPESCUPOGRION, N; TEODORESCU, V; TOPA, V
Published: 1979, THIN SOLID FILMS, 57, 269, DOI: 10.1016/0040-6090(79)90161-5
1641. TOTAL THERMAL-NEUTRON CROSS-SECTIONS OF AL, SI, CU, ZN, GE, PB AND BI SINGLE-CRYSTALS
Authors:
GRABCEV, B; TODIREANU, S; CIOCA, V
Published: 1979, JOURNAL OF APPLIED CRYSTALLOGRAPHY, 12, 400, DOI: 10.1107/S0021889879012784
1643. PARTICULARITIES IN THE GROWTH-BEHAVIOR OF VACUUM-EVAPORATED CHROMIUM THIN-FILMS
Authors:
BIRJEGA, MI; POPESCUPOGRION, N; SARBU, C; TOPA, V
Published: 1979, THIN SOLID FILMS, 58, 221, DOI: 10.1016/0040-6090(79)90240-2
1651. NEW COLOR-CENTERS IN KCL - (TL++CA2+) AND KCL - (TL++SR2+) CRYSTALS
Authors:
IOAN, A; TOPA, V; GIURGEA, M
Published: 1978, PHYSICA STATUS SOLIDI B-BASIC RESEARCH, 89, 520, DOI: 10.1002/pssb.2220890221
1661. STRUCTURE OF GOLD THIN-FILMS EVAPORATED ONTO ALKALI-HALIDE SUBSTRATES WITH COLLOIDAL CENTERS
Authors:
BIRJEGA, MI; TOPA, V; TEODORESCU, V
Published: 1976, THIN SOLID FILMS, 32, 211, DOI: 10.1016/0040-6090(76)90292-3
1662. IMPORTANCE OF COULOMB EFFECTS IN TRANSPORT PHENOMENA ON LOCALIZED STATES
Authors:
ALDEA, A; BANYAI, L; CAPEK, V
Published: 1976, CZECHOSLOVAK JOURNAL OF PHYSICS, 26, 720, DOI: 10.1007/BF01589602
1668. CHARACTERISTICS OF A UHF DISCHARGE USED AS ATOMIC SOURCE FOR A MASER
Authors:
GHEORGHIU, OC; GHEORGHE, VN
Published: 1975, INTERNATIONAL JOURNAL OF ELECTRONICS, 39, 335, DOI: 10.1080/00207217508920490
1669. Insight on Ni(II) and Cu(II) complexes of biguanide derivatives developed as effective antimicrobial and antitumour agents
Authors:
Badea, M; Grecu, MN; Chifiriuc, MC; Bleotu, C; Popa, M; Iorgulescu, EE; Avram, S; Uivarosi, V; Munteanu, AC; Ghica, D; Olar, R
Published: , APPLIED ORGANOMETALLIC CHEMISTRY, e6155, DOI: 10.1002/aoc.6155
Six compounds of the types [M(dmbg)(2)]center dot nH(2)O ((1) M: Ni, n = 0; (4) M: Cu, n = 1; Hdmbg: N,N '-dimethylbiguanide) and, respectively, [ML]center dot nH(2)O (where (2) M: Ni, L: L-1, n = 0; (3) M: Ni, L: L-2, n = 0; (5) M: Cu, L: L-1, n = 0 and (6) M: Cu, L: L-2, n = 3, H2L1: ligand resulted from the condensation of (1) with ammonia and formaldehyde and H2L2: ligand resulted from the condensation of (4) with hydrazine and formaldehyde) were characterized as mononuclear species through information provided by NMR, electronic paramagnetic resonance (EPR) and UV-Vis spectroscopy as well as cyclic voltammetry. All data are consistent with macrocyclic formation by condensation. The complexes adopt a distorted square planar geometry resulting from the chelating behaviour of the corresponding ligands. The EPR spectra recorded after the addition of Cu(II) complexes into the corresponding Ni(II) complexes show a well resolved hyperfine structure with the superhyperfine pattern corresponding to four nitrogen atom donors. The cathodically shift of E-pc2 for both series can be correlated with the increased stability of the M(I) species through macrocyclic ligands. Geometry optimization studies for complexes (2), (3), (5) and (6) have further confirmed the experimental data. The pharmacokinetic computational results indicate that the complexes exhibit medium to low intestinal absorption and slow blood-brain barrier permeability but low toxicity. Their predictive pharmacodynamic profiles show that the compounds present the ability to inhibit protease activity. By corroborating the results of the in silico analysis with the experimental ones, the most promising complexes for antimicrobial applications are (1) and (2) and, respectively, (4) and (6) for the development of novel antitumour strategies.
1671. STUDIES ABOUT STRUCTURAL AND THERMAL INVESTIGATIONS ON Ti50Ni30Cu20 ALLOYS OBTAINED BY DIFFERENT TECHNOLOGICAL PROCESSES
Authors:
Cirstea, CD; Lucaci, M; Valeanu, M; Sofronie, M; Bujoreanu, LG; Lungu, MV; Tsakiris, V; Cucos, A; Talpeanu, D; Enescu, E
Published: , ROMANIAN JOURNAL OF PHYSICS, 2021, DOI: 601
The paper presents the research results in the field of TiNiCu shape memory alloys processed by powder metallurgy techniques. The powders mixtures used to synthesize Ti50Ni30Cu20 alloys were obtained by blended constitutive elemental powders or by mechanical alloying of powder mixtures for 10 and 20 hours, respectively. Finally, a subsequent annealing process was carried out, followed by a rapid cooling in ice water. All experiments were performed under 99.9% argon atmosphere. At room temperature, the obtained materials contained monoclinic and orthorhombic martensite type. The structural and thermal investigation of these materials were discussed in view of the potential development of actuators.
1672. Multilevel Memristive GeTe Devices
Authors:
Velea, A; Dumitru, V; Sava, F; Galca, AC; Mihai, C
Published: , PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, 2000475, DOI: 10.1002/pssr.202000475
Phase-change memories have reached an advanced degree of maturity, although, to be able to meet the increasing storage demand, multilevel capability is needed. A GeTe memristor is obtained in an amorphous state and it is subjected to a specific thermal treatment which initiates the transition toward the crystalline state. It is found that this crystalline state initialization process is highly beneficial for subsequently obtaining a large number of intermediate resistive states between the high and low resistive states. Multiple resistance levels are achieved by operating the devices in both DC sweeps and rectangular pulse modes in the low-voltage subthreshold regime. The conduction is modeled using a space charge limited conduction model, showing three distinct conduction regions in the high resistive state which merge toward a single conduction region as the low resistive state is approached. The obtained memristors can be used as multilevel nonvolatile memories or as synapses in neuromorphic computing.
1673. Sonogashira Synthesis of New Porous Aromatic Framework- Entrapped Palladium Nanoparticles as Heterogeneous Catalysts for Suzuki-Miyaura Cross-Coupling
Authors:
Cata, L; Terenti, N; Cociug, C; Hadade, ND; Grosu, I; Bucur, C; Cojocaru, B; Parvulescu, VI; Mazur, M; Cejka, J
Palladium nanoparticles entrapped in porous aromatic frameworks (PAFs) or covalent organic frameworks may promote heterogeneous catalytic reactions. However, preparing such materials as active nanocatalysts usually requires additional steps for palladium entrapment and reduction. This paper reports as a new approach, a simple procedure leading to the self-entrapment of Pd nanoparticles within the PAF structure. Thus, the selected Sonogashira synthesis affords PAF-entrapped Pd nanoparticles that can catalyze the C-C Suzuki-Miyaura cross-coupling reactions. Following this new concept, PAFs were synthesized via Sonogashira cross-coupling of the tetraiodurated derivative of tetraphenyladamantane or spiro-9,9 '-bifluorene with 1,6-diethynylpyrene, then characterized them using powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy, high-resolution scanning transmission electron microscopy, and textural properties (i.e., adsorption-desorption isotherms). The PAF-entrapped Pd nanocatalysts showed high catalytic activity in Suzuki-Miyaura coupling reactions (demonstrated by preserving the turnover frequency values) and stability (demonstrated by palladium leaching and recycling experiments). This new approach presents a new class of PAFs with unique structural, topological, and compositional complexities as entrapped metal nanocatalysts or for other diverse applications.
1674. Pyrolysis and combustion of polystyrene composites based on graphene oxide functionalized with 3-(methacryloyloxy)-propyltrimethoxysilane
Authors:
Anghel, I; Lisa, G; Sofran, IE; Mitroi-Symeonidis, FC; Rusu, MM; Baia, M; Baia, L; Magyari, K; Danciu, V; Cotet, LC; Stroe, M; Baibarac, M
Published: , JOURNAL OF POLYMER ENGINEERING, 2021, 626, DOI:
In this study, polystyrene composites (PS-GO(f)) with variable concentration (0.5; 1; 2; 3; 4; and 5 wt%) of GO(f) were obtained through the in-situ polymerisation of the styrene in the presence of benzoyl peroxide and graphene oxide(GO) functionalized with 3-(methacryloyloxy)-propyltrimethoxysilane(gamma-MPTS). For determining the morphological and structural particularities of polymeric composites transmission electron microscopy (TEM) measurements were performed. The influence of functionalized GO on thermal and combustion properties of polystyrene (PS)-based composite materials was determined through several methods: Thermogravimetry (TGA); derived thermogravimetry (DTG); microscale combustion calorimetry analysis (MCC); and chemical kinetic studies through TGA and MCC determinations at similar heating rates.
1675. A nanoscale continuous transition from the monoclinic to ferroelectric orthorhombic phase inside HfO2 nanocrystals stabilized by HfO2 capping and self-controlled Ge doping
Authors:
Palade, C; Lepadatu, AM; Slav, A; Cojocaru, O; Iuga, A; Maraloiu, VA; Moldovan, A; Dinescu, M; Teodorescu, VS; Stoica, T; Ciurea, ML
Published: , JOURNAL OF MATERIALS CHEMISTRY C, DOI: 10.1039/d1tc02921e
1676. SOME ASPECTS REGARDING PRECIPITATES IN THE NiTi SHAPE MEMORY MATERIALS
Authors:
Cirstea, CD; Tolea, F; Patroi, D; Cirstea, V; Tsakiris, V
Published: , ROMANIAN JOURNAL OF PHYSICS, 2022, DOI: 903
NiTi cylindrical materials were obtained by spark plasma sintering at 850??C or 900??C from high purity Ni and Ti powders. These mixtures were previously processed by mechanical alloying for 8 and 15 hours. In order to increase the alloy homogeneity, the NiTi materials were subjected to post aging treatment in protective atmosphere at constant temperature 400??C and cooling in water with ice. All samples were characterized by optical microscopy, differential calorimetry (DSC), X-ray measurements (XRD) and micro/nanoindentation measurements. The results demonstrate that the NiTi materials obtained by this preparation route have good mechanical properties and can serve as a quantitative reference for the microstructure design of shape memory materials for various applications, such as the biomedical ones.
1677. An antibody-based amperometric biosensor for 20S proteasome activity and inhibitor screening dagger
Authors:
Barsan, MM; Diculescu, VC
Published: , ANALYST, DOI: 10.1039/d0an02426k
The 20S proteasome enzyme complex is involved in the proteolytic degradation of misfolded and oxidatively damaged proteins and is a focus of medical research for the development of compounds with pharmaceutical properties, which are active in cancer cells and/or neurodegenerative diseases. The present study aims to develop a biosensor for investigating the 20S proteasome activity and inhibition by means of electrochemical methods. The 20S proteasome is best immobilized at the electrode surface through bio-affinity interactions with antibodies that target different subunits on the 20S proteasome, enabling the investigation of the effect of an enzyme's orientation on biosensor response. The enzymatic activity is analyzed by fixed potential amperometry with the highest sensitivity of 24 mu A cm(-2) mM(-1) and a LOD of 0.4 mu M. The detection principle involves the oxidation of an electroactive probe that is released from the enzyme's substrates upon proteolysis. The most sensitive biosensor is then used to study the multicatalytic activity of the 20S proteasome, i.e. the caspase-, trypsin- and chymotrypsin-like activity, by analyzing the biosensor's sensitivity towards different substrates. The behavior of the immobilized 20S proteasome is investigated as a function of substrate concentration. The kinetic parameters are derived and compared with those obtained when the enzyme was free in solution, with K-0.5 values being one to two orders of magnitude lower in the present case. Two 20S inhibitors, epoxomicin and bortezomib, are investigated by analyzing their influence on the 20S biosensor response. The proposed analytical method for proteasome activity and inhibitor screening has the main advantage of being cost-effective compared to the ones typically employed.
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