NIMP| Monica ENCULESCU, Author at NIMP

Projects

1. Molecularly imprinted nanofluidic biosensors for the detection of human derived proteins

Project Type: MANUNET, Start Date: 2020-05-01 End Date: 2022-05-01

2. Plasmon enhancement of dye-doped polymer nanofibers’ light emissions

Project Type: IFA-CEA, Start Date: 2017-06-20 End Date: 2019-06-20

3. Quasi one-dimensional photonic crystals based on refractive index control of polymer nanofibers

Project Type: TE, Start Date: 2011-10-01 End Date: 2014-10-01

Publications

1. PEDOT:PSS based electrospun nanofibres used as trigger for fibroblasts differentiation

Authors: Beregoi, M; Enache, TA; Oprea, D; Enculescu, M; Ciobotaru, IC; Busuioc, C; Enculescu, I

Published: JAN 1 2024, SMART MATERIALS AND STRUCTURES, 33, 015009, DOI: 10.1088/1361-665X/ad10bf

Electrospun nanofibres based on poly(styrene sulfonate) doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) were fabricated using a straightforward procedure which combines electrospinning, sputtering deposition and electrochemical synthesis. In general, electrospun fibre meshes based on conducting polymers are prepared by mixing the conducting polymer with a carrier polymer or chemically coverage of the fibres. In contrast, freestanding nylon 6/6 nanofibre webs were prepared through electrospinning and were coated by sputtering with gold in order to make them conductive. Further, a PEDOT:PSS layer was electrochemically deposited onto the metalized nanofibre meshes and the synthesis parameters were chosen in such a way to preserve the high active area of the fibres. The prepared material was morphologically characterized and the formation of PEDOT:PSS was also demonstrated. The PEDOT:PSS coated nanofibres revealed remarkable electrical properties (sheet resistance of about 3.5 Omega cm(-2)), similar to those of metalized nanofibres (sheet resistance around 3 Omega cm2). The in vitro studies using L929 fibroblast mouse cells showed that the bioactive material has no cytotoxic effect and allows proliferation. Moreover, after 72 h of incubation, the fibroblasts shrunk their nuclei and spread suggesting that a differentiation in myofibroblast occurs without application of any kind of external stimuli. These results will be helpful for developing efficient materials for wound healing applications that work without energy consumption.

2. Albumin-Rutin Nanoparticles: Design, Characterization, and Biophysical Evaluation

Authors: Chilom, CG; Balan, AE; Enache, TA; Oprea, D; Enculescu, M; Florescu, M; David, M

Published: FEB 2024, COATINGS, 14, 220, DOI: 10.3390/coatings14020220

The bioavailability of the administered drugs that reach the systemic circulation is the first point in resolving the pathology of patients. Albumin-based nanoparticles represent an increasingly used strategy to deliver cancer drugs into cells that otherwise cannot overcome biological barriers. In this work, rutin (Ru), a flavonoid with anticancer and antioxidant potential, was incorporated into bovine serum albumin nanoparticles (BSA-Ru NPs), developed using the desolvation method, and the entire system was characterized and evaluated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-Vis absorption spectroscopy. The results showed that BSA and BSA-Ru NPs are uniformly distributed, have relatively large sizes, and have a time stability of more than 60%. Furthermore, the effect of these nanohybrids on the thermal stability of liposomal membranes was evaluated by surface plasmon resonance (SPR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The viability evaluation was assessed by the tetrazolium salt (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) (MTS) protocol in the fibroblast L929 line and a high level of biocompatibility, confirmed by SEM results, was found.

3. Reduced graphene oxide-functionalized zinc oxide nanorods as promising nanocomposites for white light emitting diodes and reliable UV photodetection devices

Authors: Boukhoubza, I; Derkaoui, I; Basyooni, MA; Achehboune, M; Khenfouch, M; Belaid, W; Enculescu, M; Matei, E

Published: SEP 15 2023, MATERIALS CHEMISTRY AND PHYSICS, 306, 128063, DOI: 10.1016/j.matchemphys.2023.128063

We present a breakthrough in the development of novel nanocomposites based on reduced graphene oxide (RGO)-functionalized zinc oxide (ZnO) nanorods that hold exceptional promise for their use in white light emitting diodes (LEDs) and reliable UV photodetection. The nanorods had a pristine hexagonal wurtzite struc-ture, as confirmed by XRD analysis. SEM images revealed sandwich-like nanocomposites with ZnO nanorods coated in reduced graphene oxide and embedded between two layers of RGO. The study also confirmed the hybridization and interactions between the layers using Raman measurements. The resulting nanocomposites displayed a lower band gap energy than ZnO and exhibited unique photoluminescence spectra with a white PL light. The photodetector based on RGO/ZnO/RGO sandwich structures demonstrated exceptional photoresponse, with higher photocurrent under UV illumination, making it highly promising for a wide range of optoelectronic applications. Overall, this study offers a novel and powerful approach to create nanocomposite structures with enhanced optical characteristics.

4. Kinetics and the Effect of Thermal Treatments on the Martensitic Transformation and Magnetic Properties in Ni49Mn32Ga19 Ferromagnetic Shape Memory Ribbons

Authors: Tolea, F; Popescu, B; Bartha, C; Enculescu, M; Tolea, M; Sofronie, M

Published: JAN 2023, MAGNETOCHEMISTRY, 9, 7, DOI: 10.3390/magnetochemistry9010007

In our work, the kinetics of martensitic transformations and the influence of thermal treatments on martensitic transformations, as well as the related magnetic properties of the Ni49Mn32Ga19 ferromagnetic shape memory melt-spun ribbons, have been investigated. Thermal treatments at 673 K for 1, 4 and 8 h can be considered an instrument for fine-tuning the performance parameters of alloys. One-hour thermal treatments promote an improvement in the crystallinity of these otherwise highly textured ribbons, reducing internal defects and stress induced by the melt-spinning technique. Longer thermal treatments induce an important magnetization rise concomitantly with a slight and continuous increase in martensitic temperatures and transformation enthalpy. The activation energy, evaluated from differential scanning calorimeter experimental data with a Friedman model, significantly increases after thermal treatments as a result of the multi-phase coexistence and stabilization of the non-modulated martensitic phase, which increases the reverse martensitic transformation hindrance.

5. Structural, Frequency and Temperature Dependent Dielectric Properties of Zn2+ Substituted Ni-Co Based Spinel Ferrite (ZnxNi0.8-xCo0.2Fe2O4)

Authors: Oumezzine, M; Iuga, A; Enculescu, M; Galca, AC

Published: MAY 1 2023, ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY, 12, 053008, DOI: 10.1149/2162-8777/acd6bb

Zinc substituted nickel-cobalt ferrites, i.e., ZnxNi0.8-xCo0.2Fe2O4 (x = 0.0, 0.05, 0.10 and 0.20) with average crystallite size 100 nm were synthesized by citrate-gel auto-combustion method to investigate effects of Zn2+ substitution on the structural and dielectric properties. Both X-ray diffraction (XRD) and IR spectroscopy studies confirms the formation of pure cubic spinel structure. Variation of lattice parameter infers Vegard's law linear dependence with the addition of Zn2+ concentration. The temperature-dependent behavior of dielectric and modulus spectra has been studied within the frequency range 100 Hz-100 kHz for different temperatures between 100 K and 400 K. It was concluded that the dielectric responses of ZnxNi0.8-xCo0.2Fe2O4 are found to be frequency dependent and thermally activated. Also, In the Zn doped ferrites variations of dielectric loss (tan d) and the imaginary part of electric modulus (M") show the presence of the non-Debye type of dielectric relaxation. Rise in Zinc concentration leads to a decrease in dielectric constant (e (r)) due to the declining of Fe3+-O-M2+ conducting network (M is Co or Ni). Here, we report a low loss tangent factor of the order of 8x10-3 0.6Zn(0.2)Co(0.2)Fe(2)O(4) make this composition suitable for high frequency-applications at room temperature. The activation energy is calculated from electric modulus formalism and DC electrical conductivity and found to increase with further substitution of Zn2+ concentration.

6. Organic Light-Emitting Diodes with Electrospun Electrodes for Double-Side Emissions

Authors: Ciobotaru, IC; Enculescu, M; Polosan, S; Enculescu, I; Ciobotaru, CC

Published: MAR 2023, MICROMACHINES, 14, 543, DOI: 10.3390/mi14030543

Transparent conductive electrodes (TCE) obtained by the electrospinning method and gold covered were used as cathodes in the organic light-emitting diodes (OLEDs) to create double side-emission. The electro-active nanofibers of poly(methyl methacrylate) (PMMA) with diameters in the range of several hundreds of nanometers, were prepared through the electrospinning method. The nanofibers were coated with gold by sputtering deposition, maintaining optimal transparency and conductivity to increase the electroluminescence on both electrodes. Optical, structural, and electrical measurements of the as-prepared transparent electrodes have shown good transparency and higher electrical conductivity. In this study, two types of OLEDs consisting of indium tin oxide (ITO)/ poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT-PSS)/ Ir(III) complex (8-hydroxyquinolinat bis(2-phenylpyridyl) iridium-IrQ(ppy)(2) 20 wt% embedded in N, N '-Dicarbazolyl-4,4 '-biphenyl (CBP) sandwich structure and either gold-covered PMMA electrospun nanoweb (OLED with electrospun cathode) were fabricated together with a similar structure containing thin film gold cathodes (OLED with thin film cathode). The luminance-current-voltage characteristics, the capacitance-voltage, and the electroluminescence properties of these OLEDs were investigated.

7. 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.

8. Kinetics and the Effect of Thermal Treatments on the Martensitic Transformation and Magnetic Properties in Ni₄₉Mn₃₂Ga₁₉ Ferromagnetic Shape Memory Ribbons

Authors: Tolea, F; Popescu, B; Bartha, C; Enculescu, M; Tolea, M; Sofronie, M

Published: JAN 2023, MAGNETOCHEMISTRY, 9, 7, DOI: 10.3390/magnetochemistry9010007

9. 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.

10. Thermoelectric properties of p-type Mg2Si0.3Sn0.7 doped with silver and gallium

Authors: Assahsahi, I; Popescu, B; El Bouayadi, R; Zejli, D; Enculescu, M; Galatanu, A

Published: MAY 25 2023, JOURNAL OF ALLOYS AND COMPOUNDS, 944, 169270, DOI: 10.1016/j.jallcom.2023.169270

Structure, composition, and transport properties of Mg2-xAgx(Si0.3Sn0.7)1-yGay (x = {0, 0.021, y = {0, 0.02, 0.04, 0.061) solid solutions produced by melting followed by spark plasma sintering are investigated. The preparation method is adjusted to control sample stoichiometry and phase composition. Doping with two types of dopants at different sites, while employing synthesis methods which generate a small amount of secondary phase, is an uncommon approach in this materials, expected to enhance their thermoelectric performance. An enhanced carrier concentration but diminished mobility is observed in the samples with higher amounts of dopant, which leads to the highest values of the power factor, for Mg1.98Ag0.02Si0.27Sn0.67Ga0.06 in a narrow temperature range (575-675 K) around the peak value, of 9.10-4 Wm-1 K-2 at 625 K. The two types of dopants have opposing effects on the thermal conductivity, with Ag promoting strong phonon scattering and decreasing its values while Ga increases them because of its en-hanced carrier concentration. The rather high thermal conductivity values of the double doped compounds produce low values of the ZT without exceeding 0.29 at 627 K for Mg1.98Ag0.02Si0.3Sn0.7 sample.(c) 2023 Elsevier B.V. All rights reserved.

11. 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.

12. Preparation of 82Se thin films with trigonal hexagonal crystal structure for in-beam nuclear structure experiments

Authors: Florea, NM; Nita, CR; Sotty, C; Marginean, RM; Bacalum, M; Enculescu, M; Marginean, N; Matei, E; Mereuta, P; Mihai, C; Vasilca, S

Published: SEP 2023, VACUUM, 215, 112250, DOI: 10.1016/j.vacuum.2023.112250

We report a novel approach in producing and characterizing enriched isotopic selenium-82 (82Se) thin films with trigonal hexagonal crystal structure (t-82Se), the most thermodynamically stable form of the element. The ob-tained t-82Se thin films are used as targets in accelerator based nuclear structure experiments. Several 82Se thin films with thicknesses around 5 mg/cm2 (10.4 & mu;m) were deposited on 5 mg/cm2 (3 & mu;m) tantalum (Ta) foils by vacuum evaporation-condensation method. The condensed 82Se films exhibit unstable amorphous structure (a-82Se), therefore were converted to t-82Se by means of an appropriate vacuum heat treatment developed in the target laboratory of IFIN-HH. After the thermal treatment, the microstructure, morphology and composition of the 82Se films were evaluated before and after the vacuum thermal treatment using Fourier Transform Raman Spectroscopy (FT-Raman), X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Mi-croscopy (SEM) and Energy-Dispersive X-Ray Spectroscopy (EDX) techniques. Furthermore, an in-beam & gamma;-spectroscopy experiment performed at the 9-MV tandem accelerator of IFIN-HH confirmed that the ther-mally treated t-82Se films possess high durability and high purity with no detectable contamination and no mass loss.

13. COMPARATIVE STUDY ON TiO2 NANOPARTICLES OBTAINED BY PRECIPITATION AND SOL-GEL

Authors: Alecu, AE; Girjoaba, SA; Enculescu, MM; Busuioc, C

Published: 2023, UNIVERSITY POLITEHNICA OF BUCHAREST SCIENTIFIC BULLETIN SERIES B-CHEMISTRY AND MATERIALS SCIENCE, 85, DOI:

The purpose of the work is the synthesis and characterization of TiO2 nanoparticles. These were obtained by two different methods, precipitation and sol-gel, starting from titanium(IV) isopropoxide and calcining at 500 degrees C for 2 h. The compositional, structural, morphological and optical properties of the resulting powders were investigated by energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, reflectance spectroscopy and photoluminescence spectroscopy. The thermally treated samples contain TiO2 as single phase with tetragonal structure, known as anatase. SEM analysis showed quasi-spherical particles with a diameter of few nanometres for the calcined samples, while the optical studies revealed band gap values of 3.04 and 3.17 eV, as a function of the preparation route.

14. Microengineering Design for Advanced W-Based Bulk Materials with Improved Properties

Authors: Galatanu, M; Enculescu, M; Galatanu, A; Ticos, D; Dumitru, M; Ticos, C

Published: MAR 2023, NANOMATERIALS, 13, 1012, DOI: 10.3390/nano13061012

In fusion reactors, such as ITER or DEMO, the plasma used to generate nuclear reactions will reach temperatures that are an order of magnitude higher than in the Sun's core. Although the plasma is not supposed to be in contact with the reactor walls, a large amount of heat generated by electromagnetic radiation, electrons and ions being expelled from the plasma will reach the plasma-facing surface of the reactor. Especially for the divertor part, high heat fluxes of up to 20 MW/m(2) are expected even in normal operating conditions. An improvement in the plasma-facing material (which is, in the case of ITER, pure Tungsten, W) is desired at least in terms of both a higher recrystallization temperature and a lower brittle-to-ductile transition temperature. In the present work, we discuss three microengineering routes based on inclusions of nanometric dispersions, which are proposed to improve the W properties, and present the microstructural and thermophysical properties of the resulting W-based composites with such dispersions. The materials' behavior after 6 MeV electron irradiation tests is also presented, and their further development is discussed.

15. Development and Characterization of Electrospun Composites Built on Polycaprolactone and Cerium-Containing Phases

Authors: Plocon, C; Evanghelidis, A; Enculescu, M; Isopencu, G; Oprea, O; Bacalum, M; Raileanu, M; Jinga, S; Busuioc, C

Published: SEP 2023, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 24, 14201, DOI: 10.3390/ijms241814201

The current study reports on the fabrication of composite scaffolds based on polycaprolactone (PCL) and cerium (Ce)-containing powders, followed by their characterization from compositional, structural, morphological, optical and biological points of view. First, CeO2, Ce-doped calcium phosphates and Ce-substituted bioglass were synthesized by wet-chemistry methods (precipitation/coprecipitation and sol-gel) and subsequently loaded on PCL fibres processed by electrospinning. The powders were proven to be nanometric or micrometric, while the investigation of their phase composition showed that Ce was present as a dopant within the crystal lattice of the obtained calcium phosphates or as crystalline domains inside the glassy matrix. The best bioactivity was attained in the case of Ce-containing bioglass, while the most pronounced antibacterial effect was visible for Ce-doped calcium phosphates calcined at a lower temperature. The scaffolds were composed of either dimensionally homogeneous fibres or mixtures of fibres with a wide size distribution and beads of different shapes. In most cases, the increase in polymer concentration in the precursor solution ensured the achievement of more ordered fibre mats. The immersion in SBF for 28 days triggered an incipient degradation of PCL, evidenced mostly through cracks and gaps. In terms of biological properties, the composite scaffolds displayed a very good biocompatibility when tested with human osteoblast cells, with a superior response for the samples consisting of the polymer and Ce-doped calcium phosphates.

16. Structural, Frequency and Temperature Dependent Dielectric Properties of Zn²⁺ Substituted Ni-Co Based Spinel Ferrite (Zn_xNi_0.8-xCo_0.2Fe₂O₄)

Authors: Oumezzine, M; Iuga, A; Enculescu, M; Galca, AC

Published: MAY 1 2023, ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY, 12, 053008, DOI: 10.1149/2162-8777/acd6bb

17. 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.

18. TiO₂ Phase Ratio's Contribution to the Photocatalytic Activity

Authors: Stepanova, A; Tite, T; Ivanenko, I; Enculescu, M; Radu, C; Culita, DC; Rostas, AM; Galca, AC

Published: OCT 25 2023, ACS OMEGA, 8, DOI: 10.1021/acsomega.3c05890

Photocatalysis is one of the approaches for solving environmental issues derived from extremely harmful pollution caused by industrial dyes, medicine, and heavy metals. Titanium dioxide is among the most promising photocatalytic semiconductors; thus, in this work, TiO2 powders were prepared by a hydrothermal synthesis using titanium tetrachloride TiCl4 as a Ti source. The effect of the hydrochloric acid (HCl) concentration on TiO2 formation was analyzed, in which a thorough morpho-structural analysis was performed employing different analysis methods like XRD, Raman spectroscopy, SEM/TEM, and N-2 physisorption. EPR spectroscopy was employed to characterize the paramagnetic defect centers and the photogeneration of reactive oxygen species. Photocatalytic properties were tested by photocatalytic degradation of the rhodamine B (RhB) dye under UV light irradiation and using a solar simulator. The pH value directly influenced the formation of the TiO2 phases; for less acidic conditions, the anatase phase of TiO2 crystallized, with a crystallite size of approximate to 9 nm. Promising results were observed for TiO2, which contained 76% rutile, showing a 96% degradation of RhB under the solar simulator and 91% under UV light after 90 min irradiation, and the best result showed that the sample with 67% of the anatase phase after 60 min irradiation under the solar simulator had a 99% degradation efficiency.

19. A Nanocomposite Sol-Gel Film Based on PbS Quantum Dots Embedded into an Amorphous Host Inorganic Matrix

Authors: Elisa, M; Sava, BA; Eftimie, M; Nicoara, AI; Vasiliu, IC; Rusu, MI; Bartha, C; Enculescu, M; Kuncser, AC; Oane, M; Aguado, CE; López-Torres, D

Published: NOV 2023, MATERIALS, 16, 7105, DOI: 10.3390/ma16227105

In this study, a sol-gel film based on lead sulfide (PbS) quantum dots incorporated into a host network was synthesized as a special nanostructured composite material with potential applications in temperature sensor systems. This work dealt with the optical, structural, and morphological properties of a representative PbS quantum dot (QD)-containing thin film belonging to the Al2O3-SiO2-P2O5 system. The film was prepared using the sol-gel method combined with the spin coating technique, starting from a precursor solution containing a suspension of PbS QDs in toluene with a narrow size distribution and coated on a glass substrate in a multilayer process, followed by annealing of each deposited layer. The size (approximately 10 nm) of the lead sulfide nanocrystallites was validated by XRD and by the quantum confinement effect based on the band gap value and by TEM results. The photoluminescence peak of 1505 nm was very close to that of the precursor PbS QD solution, which demonstrated that the synthesis route of the film preserved the optical emission characteristic of the PbS QDs. The photoluminescence of the lead sulfide QD-containing film in the near infrared domain demonstrates that this material is a promising candidate for future sensing applications in temperature monitoring.

20. Bulk MgB2 superconductor for levitation applications fabricated with boron processed by different routes

Authors: Savaskan, B; Ozturk, UK; Guner, SB; Abdioglu, M; Bahadir, MV; Acar, S; Somer, M; Ionescu, AM; Locovei, C; Enculescu, M; Badica, P

Published: OCT 25 2023, JOURNAL OF ALLOYS AND COMPOUNDS, 961, 170893, DOI: 10.1016/j.jallcom.2023.170893

Bulk MgB2 discs were prepared by an in situ route from mixtures of magnesium and boron powders. The boron powders were produced by two methods. The first one consisted of a self-propagating high tem-perature magnesiothermic synthesis (SHS) process followed by acid and fluorine cleaning and a heat treatment in inert atmosphere. This approach produced boron with purities between 86 % and 97 %, where the main impurity was Mg. Depending on the final heat treatment, these boron powders were amorphous or crystalline. In the second route, high purity nano powders (99 %) of boron were obtained by a diborane pyrolysis process. Bulks of MgB2 were characterized by structural, microstructural, and magnetic mea-surements. Critical current density, pinning force aspects and levitation force (including guiding force) details were assessed. Amorphous lower purity boron (86-97 %) obtained by the first processing route was found to promote the largest levitation forces of the MgB2 bulks and, among these samples, the best le-vitation results were recorded when using boron with a purity of 95-97 %. Use of a lower purity boron that decreases the cost of MgB2 promotes large scale production at industrial level of bulk MgB2 super-conducting magnets for levitation applications and enhances the applicability potential of MgB2 super-conductor. The relationship between levitation force and specific features of the samples such as pinning force details are discussed.& COPY; 2023 Elsevier B.V. All rights reserved.

21. Nanostructured PbS-Doped Inorganic Film Synthesized by Sol-Gel Route

Authors: Nicoara, AI; Eftimie, M; Elisa, M; Vasiliu, IC; Bartha, C; Enculescu, M; Filipescu, M; Aguado, CE; Lopez, D; Sava, BA; Oane, M

Published: SEP 2022, NANOMATERIALS, 12, 3006, DOI: 10.3390/nano12173006

IV-VI semiconductor quantum dots embedded into an inorganic matrix represent nanostructured composite materials with potential application in temperature sensor systems. This study explores the optical, structural, and morphological properties of a novel PbS quantum dots (QDs)-doped inorganic thin film belonging to the Al2O3-SiO2-P2O5 system. The film was synthesized by the sol-gel method, spin coating technique, starting from a precursor solution deposited on a glass substrate in a multilayer process, followed by drying of each deposited layer. Crystalline PbS QDs embedded in the inorganic vitreous host matrix formed a nanocomposite material. Specific investigations such as X-ray diffraction (XRD), optical absorbance in the ultraviolet (UV)-visible (Vis)-near infrared (NIR) domain, NIR luminescence, Raman spectroscopy, scanning electron microscopy-energy dispersive X-ray (SEM-EDX), and atomic force microscopy (AFM) were used to obtain a comprehensive characterization of the deposited film. The dimensions of the PbS nanocrystallite phase were corroborated by XRD, SEM-EDX, and AFM results. The luminescence band from 1400 nm follows the luminescence peak of the precursor solution and that of the dopant solution. The emission of the PbS-doped film in the NIR domain is a premise for potential application in temperature sensing systems.

22. Investigations Regarding the Addition of ZnO and Li2O-TiO2 to Phosphate-Tellurite Glasses: Structural, Chemical, and Mechanical Properties

Authors: Elisa, M; Iordache, SM; Iordache, AM; Stefan, CR; Vasiliu, IC; Cristea, D; Ursutiu, D; Samoila, C; Sava, BA; Boroica, L; Dinca, MC; Filip, AV; Eftimie, M; Enculescu, M

Published: MAR 2022, MATERIALS, 15, 1644, DOI: 10.3390/ma15051644

Phosphate and tellurite glasses can be used in optics, optoelectronics, magneto-optics, and nuclear and medical fields. Two series of phosphate-tellurite glasses, (50-x)ZnO-10Al(2)O(3)-40P(2)O(5)-xTeO(2) and (40-x)Li2O-10Al(2)O(3)-5TiO(2)-45P(2)O(5)-xTeO(2) (x = 5, 10), were synthesized by a non-conventional wet-route, and the mechanical properties as key performance measures for their application in optoelectronics were investigated. X-ray Diffraction (XRD) measurements revealed the vitreous nature of the investigated materials. Instrumented indentation tests allowed the calculation of hardness (H) and Young's modulus (E) using the Oliver and Pharr model. The influence of increasing the TeO2 content, as well as the substitution of ZnO by Li2O-TiO2, on the variation of hardness, Young's modulus, penetration depth (PD), and fracture toughness (FT) was evaluated in both series. As a general trend, there is a decrease in the hardness and Young's modulus with increasing penetration depth. The addition of Li2O and TiO2 instead of ZnO leads to improved hardness and elastic modulus values. Regarding the H/E ratio, it was found that the samples with lower TeO2 content should be significantly more crack-resistant compared to the higher TeO2 content samples. The H-3/E-2 ratio, being lower than 0.01, revealed a poor resistance of these glasses to plastic deformation. At the same time, a decrease of the fracture toughness with increasing TeO2 content was noticed for each glass series. Based on dilatometry measurements, the thermal expansion coefficient as well as the characteristic temperatures of the glasses were measured. Field Emission Scanning Electron Microscopy-Energy Dispersive X-ray analysis (FESEM-EDX) revealed a uniform distribution of the elements in the bulk samples. The mechanical properties of these vitreous materials are important in relation to their application as magneto-optical Faraday rotators in laser cavities.

23. The inclusion of ceramic carbides dispersion in In and Yb filled CoSb3 and their effect on the thermoelectric performance

Authors: Popescu, B; Galatanu, M; Enculescu, M; Galatanu, A

Published: FEB 10 2022, JOURNAL OF ALLOYS AND COMPOUNDS, 893, DOI: 10.1016/j.jallcom.2021.162400

In this work, thermoelectric properties of the nanocomposite materials produced via ball milling followed by spark plasma sintering from In0.2Yb0.2Co4Sb12 double filled skutterudite (SKT) with silicon and tungsten carbide inclusions are investigated. The nanocomposites with low volume ratios of beta-SiC and '-WC have a significantly increased power factor, while the lattice thermal conductivity is lowered only for beta-SiC composites. The power factor enhancement in '-WC/SKT composite compensates the increase of its thermal conductivity, and as a consequence, the maximum value of the figure of merit, 0.97, is attained for 0.33 v% 'WC at 450 degrees C, with 15% higher than that of the simple skutterudite sample. (c) 2021 Elsevier B.V. All rights reserved.

24. Influence of the synthesis parameters on the transport properties of Mg2Si0.4Sn0.6 solid solutions produced by melting and spark plasma sintering

Authors: Assahsahi, I; Popescu, B; Enculescu, M; Galatanu, M; Galca, AC; El Bouayadi, R; Zejli, D; Galatanu, A

Published: APR 2022, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 163, DOI: 10.1016/j.jpcs.2021.110561

In this work, the influence of the preparation route on the structural, morphological, and thermoelectric properties of the Mg2Si0.4Sn0.6 solid solutions is investigated. The synthesis based on melting the constituent elements in a closed graphite crucible followed by spark plasma sintering allows mixing elements with a large difference of their melting temperatures and a good control of sample stoichiometry. The optimized synthesis route is validated by the doped V and Sb samples, which yield good thermoelectric performance. The n-type doping leads to two orders of magnitude increase of the carrier concentration, and thus a subsequent increase of the electrical conductivity, which, in turn, augments greatly the power factor of the Mg1.98V0.02Si0.385Sn0.6Sb0.015 to 42.61 x10(-4) Wm(-1)K 2 at 650K. Although doping slightly enlarges the thermal conductivity, a peak value of the figure of merit ZT similar to 1.15 is obtained at 723K, which is 20 times higher than the ZT of un-doped material.

25. 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.

26. MICROSTRUCTURE, MAGNETIC AND MAGNETOSTRICTIVE BEHAVIOUR IN RAPIDLY QUENCHED OFF-STOICHIOMETRIC Ni-Mn-Ga FERROMAGNETIC SHAPE MEMORY ALLOYS

Authors: Sofronie, M; Tolea, F; Enculescu, M; Pasuk, I; Popescu, B

Published: 2022, ROMANIAN REPORTS IN PHYSICS, 74, 503, DOI:

This work reports the effect of the rapid solidification technique and thermal treatment on the martensitic transformation (MT), magnetic and magnetostrictive properties on the off-stoichiometric Ni49Mn31Ga20 and Ni51Mn28Ga21 ferromagnetic shape memory ribbons. The samples were investigated by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, magnetic and magnetostrictive measurements. The temperature dependence of the X-ray phases analysis shows the presence of martensite structures, both tetragonal and monoclinic, at room temperature and allowed to study their evolution through MT. The thermal treatment induces changes in the microstructure with implications in MT and Curie temperatures evolution. The competition between the magnetization orientation and twin boundary motion within martensitic variants under magnetic field evidenced in the magnetic-strain curves was discussed and correlated with the magnetic data.

27. 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: JUL 2022, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 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.

28. Charge transport mechanisms in free-standing devices with electrospun electrodes

Authors: Ciobotaru, IC; Polosan, S; Enculescu, M; Nitescu, A; Enculescu, I; Beregoi, M; Ciobotaru, CC

Published: SEP 24 2022, NANOTECHNOLOGY, 33, 395203, DOI: 10.1088/1361-6528/ac7ac1

Embedding electronic and optoelectronic devices in common, daily use objects is a fast developing field of research. New architectures are needed for migrating from the classic wafer- based substrates. Novel types of flexible PMMA/Au/Alq(3)/LiF/Al structures were obtained starting from electrospun polymer fibers. Thus, using an electrospinning process poly (methyl metacrylate) (PMMA) nanofibers were fabricated. A thin Au layer deposition rendered the fiber array conductive, this being further employed as the anode. The next steps consisted of the thermal evaporation of tris(8-hydroxyquinolinato) aluminum (Alq(3)) and aluminum deposition as the cathode. The Au covered PMMA nanofiber layer had a similar behavior with an indium tin oxide film i.e. low sheet resistance 10.6 omega/sq and high transparency. The low electrode resistivities allow an electron drift mobility of about 10(-6) cm(2) V-1 s(-1) at a low applied field, similar to the counterpart structures based on thin films. Concerning the relaxation processes in these structures, the Cole-Cole plots exhibit a slightly deformed semicircle, indicating a more complex equivalent circuit for the processes between metal electrodes and the active layer. This equivalent circuit includes reactance equivalent processes at the anode, cathode, in the active layer and most probably originates from the roughness of the metallic electrodes.

29. Microwave and Terahertz Properties of Spark-Plasma-Sintered Zr0.8Sn0.2TiO4 Ceramics

Authors: Nedelcu, L; Burdusel, M; Grigoroscuta, MA; Geambasu, CD; Enculescu, M; Badica, P; Banciu, MG

Published: FEB 2022, MATERIALS, 15, 1258, DOI: 10.3390/ma15031258

Zr0.8Sn0.2TiO3 (ZST) powders synthesized by solid-state reaction were subject to processing by spark plasma sintering (SPS). A single-phase ceramic with a high relative density of 95.7% and 99.6% was obtained for sintering temperatures of 1150 degrees C and 1200 degrees C, respectively, and for a dwell time of 3 min. In order to reduce the oxygen vacancies, as-sintered discs were annealed in air at 1000 degrees C. The dielectric loss of the annealed samples, expressed by the Q x f product, measured in the microwave (MW) domain, varied between 35 THz and 50 THz. The intrinsic losses (Q x f ~ 60 THz) were derived by using terahertz time-domain spectroscopy (THz-TDS).

30. 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.

31. 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%.

32. Electrochemical Deposition of ZnO Nanowires on CVD-Graphene/Copper Substrates

Authors: Boukhoubza, I; Matei, E; Jorio, A; Enculescu, M; Enculescu, I

Published: AUG 2022, NANOMATERIALS, 12, 2858, DOI: 10.3390/nano12162858

ZnO nanostructures were electrochemically synthesized on Cu and on chemical vapor deposited (CVD)-graphene/Cu electrodes. The deposition was performed at different electrode potentials ranging from -0.8 to -1.2 V, employing a zinc nitrate bath, and using voltametric and chronoamperometric techniques. The effects of the electrode nature and of the working electrode potential on the structural, morphological, and optical properties of the ZnO structures were investigated. It was found that all the samples crystallize in hexagonal wurtzite structure with a preferential orientation along the c-axis. Scanning electron microscopy (SEM) images confirm that the presence of a graphene covered electrode led to the formation of ZnO nanowires with a smaller diameter compared with the deposition directly on copper surface. The photoluminescence (PL) measurements revealed that the ZnO nanowires grown on graphene/Cu exhibit stronger emission compared to the nanowires grown on Cu. The obtained results add another possibility of tailoring the properties of such nanostructured films according to the specific functionality required.

33. Growth and characterization of 3.5 at.% Nd:LGSB bifunctional crystal

Authors: Broasca, A; Greculeasa, M; Voicu, F; Stanciu, G; Hau, S; Gheorghe, C; Brandus, CA; Pavel, N; Enculescu, M; Gheorghe, L

Published: JAN 2022, OPTICAL MATERIALS, 123, 111832, DOI: 10.1016/j.optmat.2021.111832

The performances of 3.5 at.% Nd:LGSB bifunctional laser and nonlinear optical (NLO) crystal were investigated. A high-quality single crystal with incongruent melting, having dimensions of about 12 mm in diameter and 35 mm in length, was grown along the c-axis by the Czochralski technique. The phase-matching curve for type I second harmonic generation (SHG) was determined. Efficient laser emission at 1062 nm, along the phase-matching direction for SHG of 1062 nm radiation, was obtained under the pump at 807 nm with a fiber-coupled laser diode. The Nd:LGSB laser operated with a high slope efficiency of eta(sa) = 0.56 (with respect to the absorbed pump power), delivering the highest output power of 2.1 W for 4.04 W of absorbed pump power. Preliminary SFD experiments resulted in achieving a maximum green output power of 48 mW at 3.94 W absorbed pump power.

34. Structural, morphological and optical properties of Cu-Fe-Sn-S thin films prepared by electrodeposition at fixed applied potential

Authors: El Khouja, O; Galca, AC; Nouneh, K; Zaki, MY; Touhami, ME; Taibi, M; Matei, E; Negrila, CC; Enculescu, M; Pintilie, L

Published: MAR 1 2021, THIN SOLID FILMS, 721, DOI: 10.1016/j.tsf.2021.138547

Cu-Fe-Sn-S films were obtained on indium tin oxide / glass substrates by a low-cost electrodeposition using an aqueous solution of CuSO4, FeSO4, SnSO4, and Na2S2O3 at room temperature followed by high-temperature sulfurization (500 degrees C) in argon flow. A range of cathodic potentials have been used for electrodeposition, those being chosen after a preliminary cyclic voltammetry study. The coatings were characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray Photoelectron Spectroscopy and conventional spectroscopy (diffuse reflectance and specular transmission). The results are discussed with respect to the used applied potential.

35. 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, 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.

36. 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, 2184, 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.

37. Pulsed Laser Deposition Films Based on CdSe-Doped Zinc Aluminophosphate Glass

Authors: Elisa, M; Iordache, SM; Iordache, AM; Rusu, MI; Socol, G; Filipescu, M; Bartha, C; Enculescu, M

Published: FEB 2021, JOM, 73, 503, DOI: 10.1007/s11837-020-04150-3

A composite material with applications in optoelectronics has been investigated. Pulsed laser deposition CdSe-doped glass film was prepared by the combinatorial deposition from two targets, namely pure CdSe and glass belonging to the 20Li(2)O-10Al(2)O(3)-7BaO-2La(2)O(3)-2ZnO-59P(2)O(5)system. Exciton peaks in the Vis domain, related to electron-hole pairs transitions from the valence band to the conduction band, were revealed in the optical absorption spectra of the CdSe-doped film. CdSe quantum dots (QDs) band gap energy depends on the CdSe quantum confinement effect. CdSe-doped film photoluminescence exhibits peaks in the red domain assigned to CdSe transitions from the excited state to the ground state. The size of CdSe nanoclusters, determined from x-ray diffraction is correlated with scanning electron microscopy-energy dispersive x-ray spectroscopy and atomic force microscopy results. Vibration modes specific both to CdSe QDs and to the vitreous network have been evidenced by Fourier transform infrared and Raman spectroscopy.

38. Effect of starting materials and sintering temperature on microstructure and optical properties of Y2O3:Yb(3+)5 at% transparent ceramics

Authors: Yavetskiy, RP; Balabanov, AE; Parkhomenko, SV; Kryzhanovska, OS; Doroshenko, AG; Mateychenko, PV; Tolmachev, AV; Li, J; Jiang, N; Gheorghe, L; Enculescu, M

Published: FEB 2021, JOURNAL OF ADVANCED CERAMICS, 10, 61, DOI: 10.1007/s40145-020-0416-3

Y2O3:Yb(3+)5 at% ceramics have been synthesized by the reactive sintering method using different commercial yttria powders (Alfa-Micro, Alfa-Nano, and ITO-V) as raw materials. It has been shown that all Y(2)O(3)starting powders consist from agglomerates up to 5-7 mu m in size which are formed from 25-60 nm primary particles. High-energy ball milling allows to significantly decreasing the median particle sizeD(50)below 500 nm regardless of the commercial powders used. Sintering experiments indicate that powder mixtures fabricated from Alfa-Nano yttria powders have the highest sintering activity, while (Y0.86La0.09Yb0.05)(2)O(3)ceramics sintered at 1750 degrees C for 10 h are characterized by the highest transmittance of about 45%. Y2O3:Yb(3+)ceramics have been obtained by the reactive sintering at 1750-1825 degrees C using Alfa-Nano Y(2)O(3)powders and La2O3+ZrO(2)as a complex sintering aid. The effects of the sintering temperature on densification processes, microstructure, and optical properties of Y2O3:Yb(3)(+)5 at% ceramics have been studied. It has been shown that Zr(4)(+)ions decrease the grain growth of Y2O3:Yb(3+)ceramics for sintering temperatures 1750-1775 degrees C. Further increasing the sintering temperature was accompanied by a sharp increase of the average grain size of ceramics referred to changes of structure and chemical composition of grain boundaries, as well as their mobility. It has been determined that the optimal sintering temperature to produce high-dense yttria ceramics with transmittance of 79%-83% and average grain size of 8 mu m is 1800 degrees C. Finally, laser emission at similar to 1030.7 nm with a slope efficiency of 10% was obtained with the most transparent Y2O3:Yb(3+)5 at% ceramics sintered.

39. Screen-Printed Carbon Electrodes Modified with Double-Walled Carbon Nanotubes Functionalized with Polypyrrole and Their Electrochemical Processes in the Presence of Folic Acid

Authors: Daescu, M; Baibarac, M; Enculescu, M; Serbschi, C

Published: APR 2021, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 21, DOI: 10.1166/jnn.2021.18973

In this work, the electrochemical polymerization of pyrrole in the presence of H3PMo12O40 onto the screen-printed carbon electrodes (SPCE) modified with double-walled carbon nanotubes (DWNTs) is reported. The influence of the pyrrole and H3PMo12O40 concentration as well as a scan rate used to recording of cyclic voltammograms that describe the electrochemical synthesis of polypyrrole (PPY) onto the DWNTs surface is assessed. Using scanning electron microscopy (SEM) we demonstrate that the electrosynthesis of PPY doped with H3PMo12O40 heteropolyanions (PPY-PMo12) results in the generation of a globular morphology. Considering the variations induced of DWNTs in the IR and Raman spectra of PPY doped with H3PMo12O40 heteropolyanions, a functionalization process of carbon nanotubes with macromolecular compound is invoked. According to SEM investigations, DWNTs allow the realization of connections between the globular structures of the macromolecular compound. The changes induced of folic acid (FA) during the oxidation-reduction processes at the interface of the DWNTs functionalized with PPY doped with H3PMo12O40 heteropolyanions (SPCE-DWNT/PPY-PMo12) with electrolyte solution are reported.

40. Intrinsic Dielectric Loss in Zr0.8Sn0.2TiO4 Ceramics Investigated by Terahertz Time Domain Spectroscopy

Authors: Nedelcu, L; Geambasu, CD; Enculescu, M; Banciu, MG

Published: JAN 2021, MATERIALS, 14, DOI: 10.3390/ma14010216

Terahertz time-domain spectroscopy (THz-TDS) was employed for estimation of intrinsic dielectric loss of Zr0.8Sn0.2TiO4 (ZST) ceramics. Single-phase ZST dielectric resonators (DRs) with various synthesis parameters and, consequently, different extrinsic losses, were prepared by conventional ceramic technology. Even though the DRs exhibit a similar microstructure, their quality factor (Q is the inverse of dielectric loss tangent) measured in microwave (MW) domain at 6 GHz varies between 2500 and 8400. On the other hand, it was found that the THz dielectric loss is less sensitive to the sample preparation. The intrinsic losses (Q x f similar to 60 THz) of the ZST ceramics have been derived from THz data.

41. Magnetic and Magnetostrictive Properties of Ni50Mn20Ga27Cu3 Rapidly Quenched Ribbons

Authors: Sofronie, M; Tolea, M; Popescu, B; Enculescu, M; Tolea, F

Published: SEP 2021, MATERIALS, 14, DOI: 10.3390/ma14185126

The influence of the rapid solidification technique and heat treatment on the martensitic transformation, magnetic properties, thermo- and magnetic induced strain and electrical resistivity is investigated for the Cu doped NiMnGa Heusler-based ferromagnetic shape memory ribbons. The martensitic transformation temperatures are unexpectedly low (below 90 K-which can be attributed to the disordered texture as well as to the uncertainty in the elements substituted by the Cu), preceded by a premartensitic transformation (starting at around 190 K). A thermal treatment slightly increases the transformation as well as the Curie temperatures. Additionally, the thermal treatment promotes a higher magnetization value of the austenite phase and a lower one in the martensite. The shift of the martensitic transformation temperatures induced by the applied magnetic field, quantified from thermo-magnetic and thermo-magnetic induced strain measurements, is measured to have a positive value of about 1 K/T, and is then used to calculate the transformation entropy of the ribbons. The magnetostriction measurements suggest a rotational mechanism in low fields for the thermal treated samples and a saturation tendency at higher magnetic fields, except for the temperatures close to the phase transition temperatures (saturation is not reached at 5 T), where a linear volume magnetostriction cannot be ruled out. Resistivity and magnetoresistance properties have also been measured for all the samples.

42. Structural, magnetic and magnetostrictive properties of the ternary iron-palladium-silicon ferromagnetic shape memory ribbons

Authors: Sofronie, M; Popescu, B; Enculescu, M

Published: FEB 5 2021, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 127, DOI: 10.1007/s00339-021-04315-0

The influence of the partial substitution of Fe by Si and thermal treatments on the structural, magnetic and magnetostrictive properties of the Fe67.5Pd30.5Si2 rapidly solidified ribbons has been investigated. A remarkable decrease in the martensite transformation temperature, with similar to 65 K lower than that of the Fe-Pd archetype alloy, is observed in the as-prepared ribbons. The thermal treatments shift the martensite transformation temperatures upward, with approximately 13 K for the higher thermal treatment. Also, these induce an improvement in the crystallinity in these ribbons with high texture and an increase in the crystallite size as a result of reducing the internal defects and stress. The thermodynamic considerations discussed in the frame of the Clapeyron-Clausius relation by using the calorimetric and thermomagnetic measurements (up to 7 T) reveal a weak influence of the magnetic fields on the martensitic transformation temperatures (similar to 0.5 K/T). The magnetostriction decrease with temperature under small magnetic fields was discussed, beside an unusual behaviour in the technically saturated domain. This behaviour is based on the coexistence of the ordinary and forced magnetostrictions, the last one increasing faster with the temperature decreasing.

43. Cytotoxicity, Antioxidant, Antibacterial, and Photocatalytic Activities of ZnO-CdS Powders (vol 13, 182, 2020)

Authors: Zgura, I; Preda, N; Enculescu, M; Diamandescu, L; Negrila, C; Bacalum, M; Ungureanu, C; Barbinta-Patrascu, ME

Published: DEC 2021, MATERIALS, 14, DOI: 10.3390/ma14247713

44. The Physico-Chemical Properties and Exploratory Real-Time Cell Analysis of Hydroxyapatite Nanopowders Substituted with Ce, Mg, Sr, and Zn (0.5-5 at.%)

Authors: Chirica, IM; Enciu, AM; Tite, T; Dudau, M; Albulescu, L; Iconaru, SL; Predoi, D; Pasuk, I; Enculescu, M; Radu, C; Mihalcea, CG; Popa, AC; Rusu, N; Nita, S; Tanase, C; Stan, GE

Published: JUL 2021, MATERIALS, 14, DOI: 10.3390/ma14143808

Cation-substituted hydroxyapatite (HA), standalone or as a composite (blended with polymers or metals), is currently regarded as a noteworthy candidate material for bone repair/regeneration either in the form of powders, porous scaffolds or coatings for endo-osseous dental and orthopaedic implants. As a response to the numerous contradictions reported in literature, this work presents, in one study, the physico-chemical properties and the cytocompatibility response of single cation-doped (Ce, Mg, Sr or Zn) HA nanopowders in a wide concentration range (0.5-5 at.%). The modification of composition, morphology, and structure was multiparametrically monitored via energy dispersive X-ray, X-ray photoelectron, Fourier-transform infrared and micro-Raman spectroscopy methods, as well as by transmission electron microscopy and X-ray diffraction. From a compositional point of view, Ce and Sr were well-incorporated in HA, while slight and pronounced deviations were observed for Mg and Zn, respectively. The change of the lattice parameters, crystallite size, and substituting cation occupation factors either in the Ca(I) or Ca(II) sites were further determined. Sr produced the most important HA structural changes. The in vitro biological performance was evaluated by the (i) determination of leached therapeutic cations (by inductively coupled plasma mass spectrometry) and (ii) assessment of cell behaviour by both conventional assays (e.g., proliferation-3-(4,5-dimethyl thiazol-2-yl) 5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay; cytotoxicity-lactate dehydrogenase release assay) and, for the first time, real-time cell analysis (RTCA). Three cell lines were employed: fibroblast, osteoblast, and endothelial. When monophasic, the substituted HA supported the cells' viability and proliferation without signs of toxicity. The RTCA results indicate the excellent adherence of cells. The study strived to offer a perspective on the behaviour of Ce-, Mg-, Sr-, or Zn-substituted HAs and to deliver a well-encompassing viewpoint on their effects. This can be highly important for the future development of such bioceramics, paving the road toward the identification of candidates with highly promising therapeutic effects.

45. 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, 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.

46. Secondary phases and their influence on optical and electrical properties of electrodeposited Cu2FeSnS4 films

Authors: El Khouja, O; Galca, AC; Zaki, MY; Talbi, A; Ahmoum, H; Nouneh, K; Touhami, ME; Taibi, M; Matei, E; Enculescu, M; Pintilie, L

Published: NOV 2021, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 127, DOI: 10.1007/s00339-021-05038-y

Cu-Fe-Sn-S have been electrodeposited on indium tin oxide coated glass (ITO/glass) substrates, varying only the deposition time, followed by sulfurization in argon atmosphere at a temperature of 500 degrees C. X-ray diffraction patterns confirmed the formation of polycrystalline CFTS and other secondary phases. The Raman spectroscopy results confirm the formation of stannite phase, by the existence of the most intense peak at 330 cm(-1) corresponding to A-symmetry vibrational mode, while the SnS2 surface phase reduces upon increasing deposition time. The inferred bandgaps by specular transmission are in 1.4-1.7 eV range, influenced by the detected orthorhombic Cu4SnS4 and rhodostannite secondary phases. The electrical measurements confirm the p-type nature of the films, while density of free carriers is relatively high (similar to 10(19) cm(-3)), leading to extremely low resistivity in the Omega cm range.

47. 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, 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.

48. Fabrication of ZnO and TiO2 Nanotubes via Flexible Electro-Spun Nanofibers for Photocatalytic Applications

Authors: Enculescu, M; Costas, A; Evanghelidis, A; Enculescu, I

Published: MAY 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11051305

Web-like architectures of ZnO and TiO2 nanotubes were fabricated based on a three-step process of templating polymer nanofibers produced by electrospinning (step 1). The electrospun polymer nanofibers were covered by radio-frequency magnetron sputtering with thin layers of semiconducting materials (step 2), with FESEM observations proving uniform deposits over their entire surface. ZnO or TiO2 nanotubes were obtained by subsequent calcination (step 3). XRD measurements proved that the nanotubes were of a single crystalline phase (wurtzite for ZnO and anatase for TiO2) and that no other crystalline phases appeared. No other elements were present in the composition of the nanotubes, confirmed by EDX measurements. Reflectance spectra and Tauc plots of Kubelka-Munk functions revealed that the band gaps of the nanotubes were lower than those of the bulk materials (3.05 eV for ZnO and 3.16 eV for TiO2). Photocatalytic performances for the degradation of Rhodamine B showed a large degradation efficiency, even for small quantities of nanotubes (0.5 mg/10 mL dye solution): similar to 55% for ZnO, and similar to 95% for TiO2.

49. Multifunctional GaFeO3 Obtained via Mechanochemical Activation Followed by Calcination of Equimolar Nano-System Ga2O3-Fe2O3

Authors: Diamandescu, L; Tolea, F; Feder, M; Vasiliu, F; Mercioniu, I; Enculescu, M; Popescu, T; Popescu, B

Published: JAN 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11010057

The equimolar oxide mixture beta-Ga2O3-alpha-Fe2O3 was subjected to high-energy ball milling (HEBM) with the aim to obtain the nanoscaled GaFeO3 ortho-ferrite. X-ray diffraction, Fe-57 Mossbauer spectroscopy, and transmission electron microscopy were used to evidence the phase structure and evolution of the equimolar nano-system beta-Ga2O3-alpha-Fe2O3 under mechanochemical activation, either as-prepared or followed by subsequent calcination. The mechanical activation was performed for 2 h to 12 h in normal atmosphere. After 12 h of HEBM, only nanoscaled (similar to 20 nm) gallium-doped alpha-Fe2O3 was obtained. The GaFeO3 structure was obtained as single phase, merely after calcination at 950 degrees C for a couple of hours, of the sample being subjected to HEBM for 12 h. This temperature is 450 degrees C lower than used in the conventional solid phase reaction to obtain gallium orthoferrite. The optical and magnetic properties of representative nanoscaled samples, revealing their multifunctional character, were presented.

50. EFFECT OF Mn SUBSTITUTION ON THE STRUCTURAL, MAGNETIC AND MAGNETOSTRICTIVE PROPERTIES OF Fe-Pd FERROMAGNETIC SHAPE MEMORY RIBBONS

Authors: Sofronie, M; Enculescu, M; Crisan, AD; Tolea, F

Published: 2020, ROMANIAN REPORTS IN PHYSICS, 72, DOI:

This work reports the effect of the Mn substitution, rapid solidification technique and heat treatments on the martensitic transformation, magnetic and magnetostrictive properties on the Fe70-xPd30Mnx (x = 1, 3) ferromagnetic shape memory ribbons. The samples were investigated by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, magnetic and magnetostrictive measurements. The thermal treatments induce significant changes in the microstructure and magnetocrystalline anisotropy of the martensitic phase, for Fe67Pd30Mn3 compared to Fe69Pd30Mn1. The competition between the magnetization orientation and twin boundary motion within martensitic variants under magnetic field evidenced in the magnetic-strain curves was discussed and correlated with the magnetic data.

51. Cytotoxicity, Antioxidant, Antibacterial, and Photocatalytic Activities of ZnO-CdS Powders

Authors: Zgura, I; Preda, N; Enculescu, M; Diamandescu, L; Negrila, C; Bacalum, M; Ungureanu, C; Barbinta-Patrascu, ME

Published: JAN 1 2020, MATERIALS, 13, DOI: 10.3390/ma13010182

In this work, ZnO-CdS composite powders synthesized by a simple chemical precipitation method were thoroughly characterized. The morphological, structural, compositional, photocatalytical, and biological properties of the prepared composites were investigated in comparison with those of the pristine components and correlated with the CdS concentration. ZnO-CdS composites contain flower-like structures, their size being tuned by the CdS amount added during the chemical synthesis. The photocatalytic activity of the composites was analyzed under UV irradiation using powders impregnated with methylene blue; the tests confirming that the presence of CdS along the ZnO in composites can improve the dye discoloration. The biological properties such as antioxidant capacity, antibacterial activity, and cytotoxicity of the ZnO, CdS, and ZnO-CdS composites were evaluated. Thus, the obtained composites presented medium antioxidant effect, biocidal activity against Escherichia coli, and no toxicity (at concentrations less than 0.05 mg/mL for composites with a low CdS amount) for human fibroblast cells. Based on these results, such composites can be used as photocatalytic and/or biocidal additives for photoactive coatings, paints, or epoxy floors, which in their turn can provide a cleaner and healthier environment.

52. Biomorphic 3D fibrous networks based on ZnO, CuO and ZnO-CuO composite nanostructures prepared from eggshell membranes

Authors: Preda, N; Costas, A; Enculescu, M; Enculescu, I

Published: JAN 15 2020, MATERIALS CHEMISTRY AND PHYSICS, 240, DOI: 10.1016/j.matchemphys.2019.122205

Three-dimensional (3D) fibrous networks based on metal oxides were obtained by a bio-inspired approach: the replication of an ecological daily-waste, the eggshell membrane (ESM). The biomorphic process consists in the immersion of the ESM into aqueous solutions containing the metal salt precursors followed by the calcination of the metal ions impregnated ESM. Biomorphic ZnO, CuO and ZnO-CuO composite networks were obtained, their morphological, structural, compositional, optical, photocatalytical and electrical properties being evaluated. The scanning electron microscopy investigations proved that the hierarchical structure of the original organic template is perfectly replicated into inorganic architectures consisting of interconnected fibers containing metal oxide nanoparticles as building blocks. The photocatalytical properties of the metal oxide networks under solar simulator irradiation were tested through the degradation of methylene blue. Using Si/SiO2 patterned with interdigitated metallic electrodes as substrates during the calcination step, the electrical properties of the selfcontacted metal oxide networks were investigated. Thus, by replicating the unique architecture of the ESM, 3D metal oxide interwoven meshwork can be easily developed for various applications in fields such as photocatalysis, sensing, optoelectronic devices, etc.

53. 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, 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.

54. Synthesis of Core-Double Shell Nylon-ZnO/Polypyrrole Electrospun Nanofibers

Authors: Beregoi, M; Preda, N; Costas, A; Enculescu, M; Negrea, RF; Iovu, H; Enculescu, I

Published: NOV 2020, NANOMATERIALS, 10, DOI: 10.3390/nano10112241

Core-double shell nylon-ZnO/polypyrrole electrospun nanofibers were fabricated by combining three straightforward methods (electrospinning, sol-gel synthesis and electrodeposition). The hybrid fibrous organic-inorganic nanocomposite was obtained starting from freestanding nylon 6/6 nanofibers obtained through electrospinning. Nylon meshes were functionalized with a very thin, continuous ZnO film by a sol-gel process and thermally treated in order to increase its crystallinity. Further, the ZnO coated networks were used as a working electrode for the electrochemical deposition of a very thin, homogenous polypyrrole layer. X-ray diffraction measurements were employed for characterizing the ZnO structures while spectroscopic techniques such as FTIR and Raman were employed for describing the polypyrrole layer. An elemental analysis was performed through X-ray microanalysis, confirming the expected double shell structure. A detailed micromorphological characterization through FESEM and TEM assays evidenced the deposition of both organic and inorganic layers. Highly transparent, flexible due to the presence of the polymer core and embedding a semiconducting heterojunction, such materials can be easily tailored and integrated in functional platforms with a wide range of applications.

55. Performant Composite Materials Based on Oxide Semiconductors and Metallic Nanoparticles Generated from Cloves and Mandarin Peel Extracts

Authors: Zgura, I; Enculescu, M; Istrate, C; Negrea, R; Bacalum, M; Nedelcu, L; Barbinta-Patrascu, ME

Published: NOV 2020, NANOMATERIALS, 10, DOI: 10.3390/nano10112146

In this work, the metal and semiconducting nanoparticles (AgNPs, ZnONPs and AgZnONPs) were phyto-synthesized using aqueous vegetal extracts from: Caryophyllus aromaticus L. (cloves) and Citrus reticulata L. (mandarin) peels. The morphological, structural, compositional, optical and biological properties (antibacterial activity, and cytotoxicity) of the prepared composites were investigated. The most effective sample proved to be AgZnONPs, derived from cloves, with a minimum inhibitory concentration (MIC) value of 0.11 mg/mL and a minimum bactericidal concentration (MBC) value of 2.68 mg/mL. All the other three composites inhibited bacterial growth at a concentration between 0.25 mg/mL and 0.37 mg/mL, with a bactericidal concentration between 3 mg/mL and 4 mg/mL. The obtained composites presented biocidal activity against Staphylococcus aureus, and biocompatibility (on human fibroblast BJ cells) and did not damage the human red blood cells. Additionally, an important result is that the presence of silver in composite materials improved the bactericidal action of these nanomaterials against the most common nosocomial pathogen, Staphylococcus aureus.

56. Novel Ecogenic Plasmonic Biohybrids as Multifunctional Bioactive Coatings

Authors: Barbinta-Patrascu, ME; Ungureanu, C; Badea, N; Bacalum, M; Lazea-Stoyanova, A; Zgura, I; Negrila, C; Enculescu, M; Burnei, C

Published: JUL 2020, COATINGS, 10, DOI: 10.3390/coatings10070659

The objective of the present study is the valorization of natural resources and the recycling of vegetal wastes by converting them into novel plasmonic bio-active hybrids. Thus, a "green" approach was used to design pectin-coated bio-nanosilver. Silver nanoparticles were generated from two common garden herbs (Mentha piperitaandAmaranthus retroflexus), and pectin was extracted from lemon peels. The samples were characterized by the following methods: Ultraviolet-visible (UV-Vis) absorption spectroscopy, Fourier Transform Infrared (FT-IR), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), dynamic light scattering (DLS), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM)-Energy-dispersive X-ray Spectroscopy (EDX), and zeta potential measurements. Microscopic investigations revealed the spherical shape and the nano-scale size of the prepared biohybrids. Their bioperformances were checked in terms of antioxidant and antibacterial activity. The developed plasmonic materials exhibited a strong ability to scavenge short-life (96.1% divided by 98.7%) and long-life (39.1% divided by 91%) free radicals. Microbiological analyses demonstrated an impressive antibacterial effectiveness of pectin-based hybrids againstEscherichia coli. The results are promising, and the obtained biomaterials could be used in many bio-applications, especially as antioxidant and antimicrobial biocoatings.

57. Reticulated Mesoporous TiO2 Scaffold, Fabricated by Spray Coating, for Large-Area Perovskite Solar Cells

Authors: Tomulescu, AG; Stancu, V; Besleaga, C; Enculescu, M; Nemnes, GA; Florea, M; Dumitru, V; Pintilie, L; Pintilie, I; Leonat, L

Published: JAN 2020, ENERGY TECHNOLOGY, 8, DOI: 10.1002/ente.201900922

Development of reproducible, low-cost fabrication technologies that are readily adaptable to large-scale production, is one of the main challenges in the field of perovskite solar cells (PSCs). So far, for all the other layers in a solar cell, large-area deposition methods have been adapted, except for mesoporous fabrication. Herein, the fabrication of mesoporous TiO2 scaffolds using a large-area deposition technique, such as spray coating, is shown. Moreover, this technique induces the formation of a very specific reticulated structure with well-delimited, oval-shaped cavities. The cavities have irregular dimensions, with diameters in the range of 3-7 mu m, approximate to 350 nm height, resulting in an overall increase in roughness of one order of magnitude, compared with the spin-coated mesoporous scaffold. Using this rough structured mesoporous TiO2 in PSCs not only does not affect the efficiency of solar cells but actually improves it from an average of 10% to 12% in comparison with the devices containing a spin-coated mesoporous scaffold.

58. 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, DOI: 10.1016/j.jallcom.2020.155546

59. Graphene Oxide Concentration Effect on the Optoelectronic Properties of ZnO/GO Nanocomposites

Authors: Boukhoubza, I; Khenfouch, M; Achehboune, M; Leontie, L; Galca, AC; Enculescu, M; Carlescu, A; Guerboub, M; Mothudi, BM; Jorio, A; Zorkani, I

Published: AUG 2020, NANOMATERIALS, 10, DOI: 10.3390/nano10081532

In this work, the effects of graphene oxide (GO) concentrations (1.5 wt.%, 2.5 wt.%, and 5 wt.%) on the structural, morphological, optical, and luminescence properties of zinc oxide nanorods (ZnO NRs)/GO nanocomposites, synthesized by a facile hydrothermal process, were investigated. X-ray diffraction (XRD) patterns of NRs revealed the hexagonal wurtzite structure for all composites with an average coherence length of about 40-60 nm. A scanning electron microscopy (SEM) study confirmed the presence of transparent and wrinkled, dense GO nanosheets among flower-like ZnO nanorods, depending on the GO amounts used in preparation. Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-Vis) absorption spectroscopy, and photoluminescence (PL) measurements revealed the impact of GO concentration on the optical and luminescence properties of ZnO NRs/GO nanocomposites. The energy band gap of the ZnO nanorods was independent of GO concentration. Photoluminescence spectra of nanocomposites showed a significant decrease in the intensities in the visible light range and red shifted suggesting a charge transfer process. The nanocomposites' chromaticity coordinates for CIE 1931 color space were estimated to be (0.33, 0.34), close to pure white ones. The obtained results highlight the possibility of using these nanocomposites to achieve good performance and suitability for optoelectronic applications.

60. Spectroscopic investigations of Pr3+ ions doped CNGG and CLNGG single crystals

Authors: Hau, S; Gheorghe, C; Gheorghe, L; Voicu, E; Greculeasa, M; Stanciu, G; Broasca, A; Enculescu, M

Published: AUG 30 2019, JOURNAL OF ALLOYS AND COMPOUNDS, 799, 301, DOI: 10.1016/j.jallcom.2019.05.154

Spectroscopic characteristics of Pr3+ ions doped CNGG and CLNGG single crystals were investigated in order to assess their potential as laser materials for visible emission. The Judd-Ofelt intensity parameters for the f-f transitions of Pr3+ ions were used to determine spectroscopic and laser emission features. The temperature dependence of the absorption spectra for the H-3(4) -> P-3(0) transition was used to highlight the multicenter structure, different Stark levels, hot bands, and also the connection between the vibronic and electronic lines. The presence of electron-phonon interaction was also observed in the emission spectra corresponding to the P-3(0) -> H-3(4) transition under different excitation wavelengths. Based on low temperature absorption and emission spectra, partial energy level diagrams of Pr3+ ions doped in CNGG and CLNGG single crystals were obtained. The emission cross-sections for different transitions of Pr3+ ions were evaluated by the Fuchtbauer-Ladenburg formula. The fluorescence decay curve of the D-1(2) level was measured under selective excitation at different concentrations and temperatures. The concentration quenching process for the D-1(2) state was also studied. (C) 2019 Elsevier B.V. All rights reserved.

61. Development of W-monoblock divertor components with embedded thermal barrier interfaces

Authors: Galatanu, M; Cioca, M; Ighigeanu, A; Ruiu, G; Enculescu, M; Popescu, B; Galatanu, A

Published: SEP 2019, FUSION ENGINEERING AND DESIGN, 146, 1354, DOI: 10.1016/j.fusengdes.2019.02.074

In the case of DEMO fusion reactor, the divertor should be able to extract a steady heat flux of about 10 MW/m(2). A promising concept is the W-monoblock which should be connected to a CuCrZr or an advanced Cu ODS alloy pipe passing through the W component. Taking into account the optimum operating temperature windows for W and existing Cu-based alloys and the thermal expansion coefficients mismatch of these two materials, a "thermal barrier" interface material is inserted in between in order to mitigate the thermal stresses and to optimize the heat flow through divertor components. In this work we investigate the feasibility to realize such divertor components using materials produced by FAST (field assisted sintering technology). This powder metallurgy technique was used firstly to produce W or W-based composites and the thermal barriers in an almost final shape and then to join the materials in realistic divertor mock-ups. The thermal barrier materials are various Cu-based composites which are included both as single material or as functionally graded components. The interface quality between different materials is investigated by scanning electron microscopy and the heat flow through components is evaluated using simulations.

62. Prototype Orthopedic Bone Plates 3D Printed by Laser Melting Deposition

Authors: Chioibasu, D; Achim, A; Popescu, C; Stan, GE; Pasuk, I; Enculescu, M; Iosub, S; Duta, L; Popescu, A

Published: MAR 19 2019, MATERIALS, 12, DOI: 10.3390/ma12060906

Laser melting deposition is a 3D printing method usually studied for the manufacturing of machine parts in the industry. However, for the medical sector, although feasible, applications and actual products taking advantage of this technique are only scarcely reported. Therefore, in this study, Ti6Al4V orthopedic implants in the form of plates were 3D printed by laser melting deposition. Tuning of the laser power, scanning speed and powder feed rate was conducted, in order to obtain a continuous deposition after a single laser pass and to diminish unwanted blown powder, stuck in the vicinity of the printed elements. The fabrication of bone plates is presented in detail, putting emphasis on the scanning direction, which had a decisive role in the 3D printing resolution. The printed material was investigated by optical microscopy and was found to be dense, with no visible pores or cracks. The metallographic investigations and X-ray diffraction data exposed an unusual biphasic alpha+beta structure. The energy dispersive X-ray spectroscopy revealed a composition very similar to the one of the starting powder material. The mapping of the surface showed a uniform distribution of elements, with no segregations or areas with deficient elemental distribution. The in vitro tests performed on the 3D printed Ti6Al4V samples in osteoblast-like cell cultures up to 7 days showed that the material deposited by laser melting is cytocompatible.

63. PCL-ZnO/TiO2/HAp Electrospun Composite Fibers with Applications in Tissue Engineering

Authors: Jinga, SI; Zamfirescu, AI; Voicu, G; Enculescu, M; Evanghelidis, A; Busuioc, C

Published: NOV 2019, POLYMERS, 11, DOI: 10.3390/polym11111793

The main objective of the tissue engineering field is to regenerate the damaged parts of the body by developing biological substitutes that maintain, restore, or improve original tissue function. In this context, by using the electrospinning technique, composite scaffolds based on polycaprolactone (PCL) and inorganic powders were successfully obtained, namely: zinc oxide (ZnO), titanium dioxide (TiO2) and hydroxyapatite (HAp). The novelty of this approach consists in the production of fibrous membranes based on a biodegradable polymer and loaded with different types of mineral powders, each of them having a particular function in the resulting composite. Subsequently, the precursor powders and the resulting composite materials were characterized by the structural and morphological point of view in order to determine their applicability in the field of bone regeneration. The biological assays demonstrated that the obtained scaffolds represent support that is accepted by the cell cultures. Through simulated body fluid immersion, the biodegradability of the composites was highlighted, with fiber fragmentation and surface degradation within the testing period.

64. Thermophysical and mechanical properties of W-Cu laminates produced by FAST joining

Authors: Galatanu, A; Galatanu, M; Enculescu, M; Reiser, J; Sickinger, S

Published: SEP 2019, FUSION ENGINEERING AND DESIGN, 146, 2374, DOI: 10.1016/j.fusengdes.2019.03.193

W-laminates are multi layered composites realized from alternately stacked W and a second metal foils. Such materials are promising candidates for W-based structural materials for fusion reactors like DEMO or beyond concepts, due to the fact that cold-rolled ultrafine-grained thin W foils show exceptional properties in terms of ductility, toughness and ductile to brittle transition (DBT), in contrast to classic bulk W materials. Therefore, different routes to transfer the W foils properties to bulk materials have been investigated. In this work we present the results obtained for W-Cu laminates produced via a FAST (Field Assisted Sintering Technique) joining route. The main advantages of FAST resides in the short processing time, with subsequent lower recrystallization detrimental effects. Structural and thermophysical properties show that the best materials are obtained for about 100 mu m thick W foils and 50-100 mu m thick Cu foils, while tensile and Charpy impact tests results show that the FAST processed W-Cu laminates are similar to the W-Cu laminates obtained by diffusion bonding.

65. Effect of high gamma radiations on physical properties of In2S3 thin films grown by chemical bath deposition for buffer layer applications

Authors: Souli, M; Bensalem, Y; Secu, M; Bartha, C; Enculescu, M; Mejri, A; Kamoun-Turki, N; Badica, P

Published: JUN 2019, RESULTS IN PHYSICS, 13, DOI: 10.1016/j.rinp.2019.02.051

Polycrystalline In2S3 thin films have been grown on SnO2/glass substrates by chemical bath deposition technique and irradiated at different high gamma doses 3, 7, 15 and 40 kGy. X-ray diffraction, Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), Spectrophotometer, Photoluminescence and Thermoluminescence were used to investigate physical properties of In2S3 thin films induced by gamma irradiation. After being irradiated, structural properties of In2S3 thin films have shown that preferred orientation has been moved from (4 0 0) plan at 2 theta(1)=33.42 degrees to a new created orientation at 2 theta(2)=38.06 degrees for 40 kGy gamma dose. EDS analysis has shown that atomic percentage (S/In) has been strongly varied for 40 kGy which indicate significant changes in stoichiometry. Thermoluminescence of irradiated In2S3 thin films has revealed a good sensitivity toward absorbed gamma dose. After irradiation, optical transmittance of In2S3 thin films has been increased from 50% to a maximum value of 70% in the visible range for 15 kGy dose. Band gap energy E-g has been slightly decreased. Other optical parameters such absorption and extinction coefficients, refractive index and permittivity have been determined. These experimental results show that gamma radiations can be used for tuning physical properties of In2S3 thin films for photovoltaic applications.

66. Highly transparent Yb:Y2O3 ceramics obtained by solid-state reaction and combined sintering procedures

Authors: Stanciu, G; Gheorghe, L; Voicu, F; Hau, S; Gheorghe, C; Croitoru, G; Enculescu, M; Yavetskiy, RP

Published: FEB 15 2019, CERAMICS INTERNATIONAL, 45, 3222, DOI: 10.1016/j.ceramint.2018.10.224

(Y0.87-xLa0.1Zr0.03Ybx)(2)O-3 (x = 0.02, 0.04, 0.05) transparent ceramics were obtained by solid-state reaction and combined sintering procedures with La2O3 and ZrO2 as sintering additives. A method based on two-step intermediate sintering in air followed by vacuum sintering was applied in order to control the densification and grain growth of the samples during the final sintering process. The results indicate that La2O3 and ZrO2 co-additives can improve the microstructure and optical properties of Yb:Y2O3 ceramics at relatively low sintering temperature. On the other hand, the addition of Zr4+ ions leads to the formation of dispersed scattering volumes in the ceramic bodies. Transmittance of 78.8% was measured for the 2.0 at% Yb:Y2O3 ceramic sample at the wavelength of 1100 nm. The spectroscopic properties of Yb:Y2O3 ceramics were investigated at room temperature. The obtained results show that the absorption cross-section at 978 nm is in the range of 2.08 x 10(-20) to 2.36 x 10(-20) cm(2), whereas the emission cross-section at 1032 nm is similar to 1.0 x 10(-20) cm(2).

67. Physical properties investigation of samarium doped calcium sulfate thin films under high gamma irradiations for space photovoltaic and dosimetric applications

Authors: Souli, M; Reghima, M; Secu, M; Bartha, C; Enculescu, M; Mejri, A; Kamoun-Turki, N; Badica, P

Published: FEB 2019, SUPERLATTICES AND MICROSTRUCTURES, 126, 119, DOI: 10.1016/j.spmi.2018.12.021

This research work is dedicated to study structural, morphological, optical and photoluminescence properties of samarium doped calcium sulfate (CaSO4) thin films after exposure to high gamma radiations. Polycrystalline doped CaSO4 thin films have been grown on glass substrates by spray pyrolysis technique and irradiated at different high gamma doses 3, 7, 15 and 40 kGy. Physical characterization of irradiated thin films has been made by X-ray diffraction, Spectrophotometer, Scanning Electron Microscope, Energy Dispersive Spectroscopy, Fluorescence Spectrometer and Thermoluminescence. The most remarkable result, as shown by structural analysis, is the increase of grain size from 52 to a maximum value of 93 nm for 15 kGy gamma dose which indicates a clear enhancement in crystal structure by gamma irradiation. Moreover, the preferred orientation has been immediately changed from (102) plan to (100) just after the first 3 kGy gamma dose. SEM micrographs of irradiated thin layers show deep modifications in surface morphology. Optical transmission spectra have shown a sharp and intense peak at 350 nm wavelength. Band gap energy has been slightly decreased from 3.9 eV before irradiation to 3.6 eV for 40 kGy. A new and strong energy level noted E r , has been emerged and created due to high gamma irradiations in addition to the principal one relative to band gap energy. Other parameters like absorption and extinction coefficients and refractive index have been determined. Thermoluminescence data show a high sensibility to gamma radiations doses which offer opportunities for dosimetry applications. These experimental results suggest the use of irradiated samarium doped calcium sulfate as optical window for space photovoltaic devices where gamma rays are abundant. These results are also helpful for researchers using CaSO4 thin films near nuclear apparatus (nuclear reactors and particle accelerators) or those interested in studying interaction between radiations and condensed matter.

68. 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.

69. Hierarchical functionalization of electrospun fibers by electrodeposition of zinc oxide nanostructures

Authors: Matei, E; Busuioc, C; Evanghelidis, A; Zgura, I; Enculescu, M; Beregoi, M; Enculescu, I

Published: NOV 15 2018, APPLIED SURFACE SCIENCE, 458, 563, DOI: 10.1016/j.apsusc.2018.06.143

Electrospun sub-micrometer polymer fiber mats represent an interesting substrate which can be employed as a transparent conducting electrode. Functionalization by using nanostructures represents a convenient way of increasing the range of applications. The present paper describes an electrodeposition process which can be applied for preparing ZnO nanostructures covered fibers in a straightforward manner. Poly(methyl methacrylate) fiber mats were obtained by electrospinning using metal frame collectors. Subsequent metallization by DC sputtering was used, these microstructured electrodes being thermally transferred onto glass substrates and further employed as working electrodes for the electrochemical deposition of ZnO. The transparency of the metal covered webs, a function of fiber density, is comparable to that of conventional transparent conductive oxides electrodes such as ITO. The same enhanced control of the ZnO electrodeposition process was observed for the case of the web electrodes as for the classic case of deposition on transparent conducting oxides or on metallic substrates. Structural, optical, morphological and wetting properties were investigated and correlated with the electrodeposition conditions. The photocatalytic properties of ZnO covered fibers were tested through the decomposition of methylene blue thin films under UV irradiation.

70. 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.

71. High temperature thermo-physical properties of SPS-edW-Cu functional gradient materials

Authors: Galatanu, M; Enculescu, M; Galatanu, A

Published: FEB 2018, MATERIALS RESEARCH EXPRESS, 5, DOI: 10.1088/2053-1591/aaa860

The divertor of a fusion reactor like DEMO requires materials able to withstand high heat fluxes and neutron irradiation for several years. For the water cooling concept of this essential part of the reactor, the most likely plasma facing material will be W, while the heatsink material considered is CuCrZr or an improved version of such a Cu-based alloy. To realize W-Cu alloy joints able to withstand thousands of thermal cycles can be difficult due to the difference between the thermal expansion coefficients of these materials. In this work we investigate the possibility to realize such joints by using W-Cu functional gradient materials (FGMs) produced from nanometric and micrometric metallic powders mixtures and consolidated by spark plasma sintering at about 900 degrees C. Morphological and thermal properties investigations, performed for typical compositions, shows that the best results are obtained using powders with micrometric dimensions. A resulting 1 mm thick, 3 layers W-Cu FGM produced by this simple method shows a remarkable almost constant thermal conductivity value of 200 W m(-1) K-1, from room temperature up to 1000 degrees C.

72. White-Light Emission of Dye-Doped Polymer Submicronic Fibers Produced by Electrospinning

Authors: Enculescu, M; Evanghelidis, A; Enculescu, I

Published: JUL 2018, POLYMERS, 10, DOI: 10.3390/polym10070737

Lighting and display technologies are evolving at tremendous rates nowadays; new device architectures based on new, microscopic building blocks are being developed. Besides high light-emission efficiencies, qualities including low cost, low environmental impact, flexibility, or lightweightness are sought for developing new types of devices. Electrospun polymer fibers represent an interesting type of such microscopic structures that can be employed in developing new functionalities. White-light-emitting fiber mats were prepared by the electrospinning of different dye-doped polymer solutions. Two approaches were used in order to obtain white-light emissions: the overlapping of single-dye-doped electrospun fiber mats, and the electrospinning of mixtures of different ratios of single-dye-doped polymer solutions. Scanning electron microscopy (SEM) was used to investigate the morphologies of the electrospun fibers with diameters ranging between 300 nm and 1 mu m. Optical absorption and photoluminescence (PL) were evaluated for single-dye-doped submicronic fiber mats, for overlapping mats, and for fiber mats obtained from different compositions of mixtures. Depending on the ratios of the mixtures of different dyes, the luminance was balanced between blue and red emissions. Commission Internationale de L'Eclairage (CIE) measurements depict this fine-tuning of the colors' intensities, and the right composition for white-light emission of the submicronic fiber mats was found.

73. 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.

74. Yellow laser potential of cubic Ca-3(Nb,Ga)(5)O-12:Dy3+ and Ca-3(Li,Nb,Ga)(5)O-12:Dy3+ single crystals

Authors: Gheorghe, C; Hau, S; Gheorghe, L; Voicu, F; Greculeasa, M; Enculescu, M; Belikov, KN; Bryleva, EY; Gaiduk, OV

Published: MAR 30 2018, JOURNAL OF ALLOYS AND COMPOUNDS, 739, 816, DOI: 10.1016/j.jallcom.2017.12.259

Spectroscopic investigation of Dy3+ doped Ca-3(Nb,Ga)(5)O-12 (CNGG) and Ca-3(Li,Nb,Ga)(5)O-12 (CLNGG) single crystals were performed in order to assess their potential as laser materials for yellow emission. Dy: CNGG and Dy: CLNGG single crystals were grown by the Czochralski method and investigated by high-resolution spectroscopic measurements for the first time. The Judd-Ofelt intensity parameters for the f-f transitions of Dy3+ in CNGG and CLNGG single crystals, were used to determine radiative transition rates A(r), branching ratios beta, and radiative lifetime tau(r) of the fluorescent Dy3+ levels. Based on low temperature absorption and emission spectra, partial energy levels diagram of Dy3+ doped CNGG and CLNGG single crystals were obtained. The emission cross-sections for the F-4(9/2) -> H-6(13/2) transition of special interest for laser application were determined. The room temperature decay curves were analyzed through the framework of Inokuti-Hirayama (I-H) model and the results shows that electric dipole-dipole interaction are responsible for the energy transfer processes between Dy3+ ions in CNGG and CLNGG single crystals. (c) 2017 Elsevier B.V. All rights reserved.

75. Wet chemical synthesis of ZnO-CdS composites and their photocatalytic activity

Authors: Zgura, I; Preda, N; Socol, G; Ghica, C; Ghica, D; Enculescu, M; Negut, I; Nedelcu, L; Frunza, L; Ganea, CP; Frunza, S

Published: MAR 2018, MATERIALS RESEARCH BULLETIN, 99, 181, DOI: 10.1016/j.materresbull.2017.11.013

The present study is focused on the wet chemical synthesis and the characterization of ZnO-CdS composites. The X-ray diffraction shows that the composites contain ZnO in hexagonal wurtzite structure and CdS in cubic phase. The scanning/transmission electron microscopy images reveal flower-like structures with different sizes depending on the CdS content. The optical investigations on composites reveal that the reflectance spectra disclose two thresholds of similar to 370 nm and similar to 460 nm associated with the ZnO and CdS, respectively. The photocatalytic activity measurements evidenced that the degradation efficiency of RhB in the presence of composites is higher comparatively with pristine ZnO, depending on the catalyst morphology, which varies with CdS content and the pH value of RhB solution. The electron paramagnetic resonance revealed the presence of the paramagnetic point defects in the samples. Thus, the wet chemical approaches are suitable for a large scale production of such ZnO-CdS composites having enhanced photocatalytic activity.

76. 1532 nm sensitized luminescence and up-conversion in Yb,Er:YAG transparent ceramics

Authors: Vorona, I; Yavetskiy, RP; Dobrotvorskaya, MV; Doroshenko, AG; Parkhomenko, SV; Tolmachev, AV; Kosyanov, DY; Gheorghe, L; Gheorghe, C; Hau, S; Enculescu, M

Published: MAR 2018, OPTICAL MATERIALS, 77, 225, DOI: 10.1016/j.optmat.2018.01.038

Luminescent properties of Yb,Er:YAG transparent ceramics containing 5 at% Yb3+ and 0.5, 1 and 1.5 at%, respectively, Er3+ ions have been studied. It has been found that increasing of erbium ions concentration increases both efficiency of nonradiative energy transfer Yb3+ -> Er3+ (which reaches 72% for 1.5 at% Er3+) and the luminescence in the range of 650-700 nm associated with F-4(9/2), (11/2) -> I-4(15/2) transitions of Er3+ ions. It was also determined that the concentration quenching of sensitized luminescence of Er3+ ions at 1532 nm is associated with secondary excitation of metastable energy level of Er3+ followed by up conversion emission. (C) 2018 Elsevier B.V. All rights reserved.

77. Effects of a surfactant on the morphology and photocatalytic properties of polycrystalline Fe-doped ZnO powders

Authors: Diamandescu, L; Cernea, M; Trusca, R; Enculescu, M; Tanase, L; Baibarac, M; Feder, M; Nicoara, AI; Popescu, T

Published: OCT 2018, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 121, 328, DOI: 10.1016/j.jpcs.2018.05.041

In this study, we compared the structural, morphological, and optical properties of a series of Zn1-xFexO (x = 0.00, 0.01, and 0.03) powders synthesized via a hydrothermal route with and without cetyltrimethylammonium bromide as a cationic surfactant. Our results highlighted the critical effects of the surfactant and the iron concentration on the structure, morphology, and optical properties of ZnO. X-ray diffraction, Mossbauer spectroscopy, and X-ray photoelectron spectroscopy analyses indicated the presence of a single phase comprising ZnO with a hexagonal wurtzite structure in all samples and a single oxidation state (+3) for the iron (Fe3+) that replaced Zn2+ in the ZnO structure. Morphological investigations by scanning electron microscopy showed that the surfactant and Fe3+ dopant greatly affected the shape of the ZnO grains, which varied between sheets and rod-like flowers. We found that the morphological and photocatalytic properties of the two series of samples comprising iron-doped ZnO with and without the surfactant were in opposition. We propose a possible growth mechanism for the ZnO polycrystalline grains in the presence of the Fe dopant and/or surfactant. The photocatalytic properties increased for the samples prepared with surfactant as the iron content increased, which was confirmed by ultraviolet-visible reflection measurements. The photocatalytic activities of the samples prepared without surfactant decreased in both the ultraviolet and visible spectral regions as the iron content increased in the samples.

78. A Comparative Study of Ge-Based Organometallic Additions to MgB2

Authors: Batalu, D; Nakamura, T; Enculescu, M; Popa, S; Pasuk, I; Aldica, G; Ionescu, AM; Badica, P

Published: JUN 2018, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 28, DOI: 10.1109/TASC.2018.2808366

Four Ge-based organometallic (OM = C6H10 Ge2O7) polymers with similar chemical composition were used as additions for MgB2. MgB2 (OM) 0.0014 dense samples with a relative density higher than 97% were obtained by ex situ spark plasma sintering. The critical current density and the irreversibility magnetic field of the added samples are slightly improved at high magnetic fields by repagermanium (Alfa Aesar) addition when compared to the pristine reference sample. Addition of Ge-straight-chain polymer shows some improvement of the maximum volume pinning force, F-p (max). There is no significant Ge substitution in the crystal lattice of MgB2, while C substitutes for B. Pinning mechanism is mainly of a point pinning type, with the grain boundary pinning mechanism strengthening at lower temperatures and when additives are not used. A relatively high amount of carbon in the samples washes out the Ge effects on pinning-force-related parameters. The structure and morphology of the polymer additive play an important role in dispersion when mixing, impacting the quality of the superconducting properties. The nanosize dimension of the pristine MgB2 powder shows also some drawbacks in mixing and sintering.

79. Thermophysical properties of Cu-ZrO2 composites as potential thermal barrier materials for a DEMO W-monoblock divertor

Authors: Galatanu, M; Enculescu, M; Galatanu, A

Published: FEB 2018, FUSION ENGINEERING AND DESIGN, 127, 184, DOI: 10.1016/j.fusengdes.2018.01.011

DEMO fusion reactor divertor is expected to extract a heat flux of about 10 MW/m(2). One of the most promising concept design for it is the W-monoblock, which should be connected to a CuCrZr or an advanced Cu ODS alloy pipe passing through the W component. Since the optimum operating temperature windows for W and existing Cu alloys are far away from overlapping, a suited interface is needed to keep the adjacent materials as close as Possible to their respective temperature operating windows. The interface material should therefore have a low enough thermal conductivity to act as a thermal barrier and a thermal expansion coefficient suited to protect the W-pipe joint from stresses induced by the different thermo-mechanical properties of W and Cu-alloys. As interface materials we have considered Cu-ZrO2 composites produced by powder metallurgy route. Such materials can be realized in an unexpected large compositional range (up to at least 90% ZrO2 volume concentration) and be easily further joined to both W and Cu-alloys by an electrical field assisted technology. We analyse their microstructure and thermo-physical properties both as single materials and included in W-thermal barrier-CuCrZr 3-layers systems in comparison to those of previously produced Cu-ased composites and commercially available Cu foams.

80. CERAMIC THIN FILMS DEPOSITED BY SPIN COATING AS COATINGS FOR METALLIC IMPLANTS

Authors: Busuioc, C; Constantinoiu, I; Enculescu, M; Beregoi, M; Jinga, SI

Published: 2018, REVISTA ROMANA DE MATERIALE-ROMANIAN JOURNAL OF MATERIALS, 48, 406, DOI:

Ceramic thin films belonging to SiO2-P2O5-CaO-MgO-ZnO-CaF2 system were obtained by combining the sol-gel approach with the spin coating technique. Titanium plates were employed as substrates. The deposited coatings were characterized in terms of composition, structure and morphology with the help of the following methods: X-ray diffraction, Fourier - transform infrared spectroscopy and scanning electron microscopy coupled with energy - dispersive X-ray spectroscopy. In order to assess the bioactivity of a potential metallic implant covered with such layers, the samples were immersed in simulated body fluid for 14 days and their surface was investigated. The results showed that the thin films calcined at a lower temperature have a better biological response due to the vitroceramic nature.

81. 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.

82. (Fe, Nd) codoped ZnO micro- and nanostructures with multifunctional characteristics like photocatalytic activity, optical and ferromagnetic properties

Authors: Diamandescu, L; Cernea, M; Tolea, F; Secu, EC; Trusca, R; Secu, M; Enculescu, M

Published: DEC 1 2018, CERAMICS INTERNATIONAL, 44, 21975, DOI: 10.1016/j.ceramint.2018.08.310

Zn1-x-yFexNdyO, x = 0.02 and y = 0.00-0.05 were successfully synthesized via a hydrothermal method at 200 degrees C. XRD and Mossbauer spectroscopy indicated that (Fe, Nd) codoped ZnO, calcined at 700 degrees C, 3 h in air, contains hexagonal ZnO phase as main phase and traces of ZnFe2O4; no phase containing neodymium was observed. In this study, a strong powder morphology dependence on Nd concentration and calcination temperature was evidenced by SEM. The photocatalytic properties were found to depend on the sample morphology and Nd content. Thermoluminescence signal is weak compared to the undoped ZnO and the curves shape was almost independent on the doping level and dependent on the calcination temperature and was related to the structural defects induced by the synthesis and calcination. Photoluminescence spectra showed that the green-yellow band due to the oxygen related defects, decreases by Fe and Nd-codoping. Thermo-magnetization curves measured in low applied fields and the magnetic hysteresis loops recorded in the temperature range 5-380 K, indicate two superimposed magnetic regimes, one predominant above 100 K the other below 100 K. The observed magnetic order is not directly related to the dopant Fe or Nd ions, but to different type of defects.

83. Annealing-Induced High Ordering and Coercivity in Novel L1(0) CoPt-Based Nanocomposite Magnets

Authors: Crisan, AD; Vasiliu, F; Mercioniu, I; Bartha, C; Enculescu, M; Crisan, O

Published: JUN 2018, METALS, 8, DOI: 10.3390/met8060466

A novel class of quaternary intermetallic alloys based on CoPt is investigated in view of their interesting magnetic properties induced by the presence of hard magnetic L1(0) phase. A Co48Pt28Ag6B18 alloy has been prepared by rapid solidification from the melt and subjected to various isothermal annealing procedures. The structure and magnetism of both as-cast and annealed samples as well as the phase evolution with temperature are investigated by means of thermal analysis, X-ray, and selected area electron diffraction, scanning and high-resolution electron microscopy, and magnetic measurements. The X-ray diffraction (XRD) analysis shows that both the as-cast alloy and the sample annealed at 400 degrees C (673 K) have a nanocrystalline structure where fcc CoPt phase predominates. Annealing at 473 degrees C promotes the formation of L1(0) phase triggered by the disorder-order phase transformation as documented in the differential scanning calorimetry results. The sample annealed at 670 degrees C (943 K) shows full formation of L1(0) CoPt as revealed by XRD. Magnetic measurements showed coercivity values ten times increased compared to the as-cast state. This confirms the full formation of L1(0) CoPt in the annealed samples. Moreover, detailed atomic resolution HREM images and SAED patterns show the occurrence of the rarely seen (003) superlattice peaks, which translated into a high ordering of the L1(0) CoPt superlattice. Such results spur more interest in finding novel classes of nanocomposite magnets based on L1(0) phase.

84. Enhanced near-infrared response of a silicon solar cell by using an up-conversion phosphor film of Yb/Er - co-doped CeO2

Authors: Grigoroscuta, M; Secu, M; Trupina, L; Enculescu, M; Besleaga, C; Pintilie, I; Badica, P

Published: SEP 1 2018, SOLAR ENERGY, 171, 46, DOI: 10.1016/j.solener.2018.06.057

Co-doped CeO2 thin films were grown from a bulk target with starting composition Ce0.95Yb0.04Er0.01O2 by pulsed laser deposition (PLD) on a p(+)-n-n(+) single crystal silicon diode. The PLD laser fluence was varied between 1.7 J/cm(2) and 3.7 J/cm(2). The device with the film grown for a laser fluence of 2.3 J/cm(2) delivers the highest performance taking advantage of the up conversion (UC) effect provided by this film. Namely, the increase in the relative power conversion efficiency of the device is 12.1% and 39.2% for illumination under 1 and 2.1 sun, respectively, and its relative external quantum efficiency is 8.2% when illuminated with 980 nm light. The film grown for the optimum 2.3 J/cm(2) fluence shows good target-film composition transfer and a granular morphology with a low roughness. The UC mechanism consists of efficient energy transfer between spatially separated Yb3+ and Er3+ ions, i.e. the absorption of infrared light photons by the Yb3+ ions (F-2(7/2) -> F-2(5/2) transition) is followed by a two-step energy transfer process to neighboring Er3+ ions and by their characteristic luminescent emissions ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and (F-4(9/2) -> I-4(15/2)).

85. Physical-chemical characterization and biological assessment of simple and lithium-doped biological-derived hydroxyapatite thin films for a new generation of metallic implants

Authors: Popescu, AC; Florian, PE; Stan, GE; Popescu-Pelin, G; Zgura, I; Enculescu, M; Oktar, FN; Trusca, R; Sima, LE; Roseanu, A; Duta, L

Published: MAY 1 2018, APPLIED SURFACE SCIENCE, 439, 735, DOI: 10.1016/j.apsusc.2018.01.008

We report on the synthesis by PLD of simple and lithium-doped biological-origin hydroxyapatite (HA) films. The role of doping reagents (Li2CO3, Li3PO4) on the morphology, structure, chemical composition, bonding strength and cytocompatibility of the films was investigated. SEM investigations of the films evidenced a surface morphology consisting of particles with mean diameters of (5-7) mu m. GIXRD analyses demonstrated that the synthesized structures consisted of HA phase only, with different degrees of crystallinity, mainly influenced by the doping reagent type. After only three days of immersion in simulated body fluid, FTIR spectra showed a remarkable growth of a biomimetic apatitic film, indicative of a high biomineralization capacity of the coatings. EDS analyses revealed a quasi-stoichiometric target-to-substrate transfer, the values inferred for the Ca/P ratio corresponding to a biological apatite. All synthesized structures displayed a hydrophilic behavior, suitable for attachment of osteoblast cells. In vitro cell viability tests showed that the presence of Li2CO3 and Li3PO4 as doping reagents promoted the hMSC growth on film surfaces. Taking into consideration these enhanced characteristics, corroborated with a low fabrication cost generated by sustainable resources, one should consider the lithium-doped biological-derived materials as promising prospective solutions for a next generation of coated implants with rapid osteointegration. (C) 2018 Elsevier B.V. All rights reserved.

86. Photocatalytic activity of wool fabrics deposited at low temperature with ZnO or TiO2 nanoparticles: Methylene blue degradation as a test reaction

Authors: Frunza, L; Diamandescu, L; Zgura, I; Frunza, S; Ganea, CP; Negrila, CC; Enculescu, M; Birzu, M

Published: MAY 15 2018, CATALYSIS TODAY, 306, 259, DOI: 10.1016/j.cattod.2017.02.044

Different amounts of TiO2 and ZnO particles were deposited upon wool fabrics, which are among the less studied textiles. The materials were get from industry or were home made. Model samples for these oxide deposition and properties were also considered. Either sputtering or chemical sol-gel/electro less technique was respectively applied. The coated samples were then characterized structurally and morphologically, by XRD, SEM and XPS and were checked for photocatalytic properties. Both UV and vis light beams were used for irradiation. The photocatalytic experiments were performed by photodegradation of methylene blue in the PCC2 checker apparatus. The fabrics were firstly impregnated with the dye solution and then dried: self cleaning of the wool fabric samples took in fact place. Reflectance data in the visible spectral range of highest absorption band served for direct analysis of MB degradation. The photocatalytic properties of the coated fabrics increased much in comparison with the raw materials. The photocatalytic decolorization of methylene blue follows up a simple apparently first order kinetic equation in many studied cases. Thus it was demonstrated that MB decolorization can serve as a test reaction at least for self cleaning of fabrics. (C) 2017 Elsevier B.V. All rights reserved.

87. Dwell Time Influence on Spark Plasma-Sintered MgB2

Authors: Aldica, G; Popa, S; Enculescu, M; Pasuk, I; Ionescu, AM; Badica, P

Published: FEB 2018, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 31, 325, DOI: 10.1007/s10948-017-4236-9

Samples of MgB2 with relative density above 95% were obtained by spark plasma sintering (SPS) at 1150 A degrees C for a heating time of 100 A degrees C/min and a maximum pressure of 95 MPa. Dwell time was of 1, 4, 7, 10, and 20 min. Samples show that dwell time has a low influence on superconducting characteristics. However, small differences were observed and they are discussed from the viewpoint of density, structural, microstructural, critical current density, irreversibility field, and pinning type. The dominant contribution for all investigated samples is given by point and delta T (c) pinning.

88. Effect of mixing complexing agents on the properties of electrodeposited CZTS thin films

Authors: Zaki, MY; Nouneh, K; Touhami, ME; Belakhmima, RA; Galca, AC; Pintilie, L; Enculescu, M; Baibarac, M; Taibi, M

Published: SEP 2018, OPTICAL MATERIALS, 83, 256, DOI: 10.1016/j.optmat.2018.06.030

This work involves the synthesis and characterization of Cu2ZnSnS4 (CZTS) layers. The films were prepared on ITO/glass substrate by ecofriendly and simple single-step electrodeposition method followed by sulfurization and annealing at 500 degrees C under Argon flow. By using two different complexing agents, the electrodeposition process can give better results. Therefore, the effect of combining the trisodium citrate - TC to multiple cornplexing agents (cetyl trimethyl ammonium bromide - CTAB, ethylene diamine tetra acetic acid - EDTA, Boric Acid - BA, Glutamic Acid - GA and Tartaric Acid - TA) is investigated. The characterization of the absorber films was done by X-ray diffraction (XRD) analysis, Raman spectroscopy, Scanning Electron Microscopy and Diffuse Reflectivity. The combination of TC and CTAB is suggested to be the best pair of complexing agents within the combinations used in this work.

89. Compressive properties of pristine and SiC-Te-added MgB2 powders, green compacts and spark-plasma-sintered bulks

Authors: Badica, P; Batalu, D; Burdusel, M; Grigoroscuta, MA; Aldica, GV; Enculescu, M; Gabor, RA; Wang, ZY; Huang, RX; Li, PF

Published: JUN 15 2018, CERAMICS INTERNATIONAL, 44, 10191, DOI: 10.1016/j.ceramint.2018.03.008

Pristine and (SiC + Te)-added MgB2 powders, green and spark plasma sintered (SPS) compacts were investigated from the viewpoint of quasi-static and dynamic (Split-Hopkinson Pressure Bar, SHPB) compressive mechanical properties The amount of the additive (SiC + Te) was selected to be the optimum one for maximization of the superconducting functional parameters. Pristine and added MgB2 show very similar compressive parameters (tan delta, fracture strength, Vickers hardness, others) and fragment size in the SHPB test. However, for the bulk SPSed samples the ratio of intergranular to transgranular fracturing changes, the first one being stronger in the added sample. This is reflected in the quasi-static K-IC that is higher for the added sample. Despite this result, sintered samples are brittle and have roughly similar fragmentation behavior as for brittle engineering ceramics. In the fragmentation process, the composite nature of our samples should be considered with a special focus on MgB2 blocks (colonies) that show the major contribution to fracturing. The Glenn-Chudnovsky model of fracturing under dynamic load provides the closest values to our experimental fragment size data.

90. Optical properties of Sm3+ doped Ca-3(Nb,Ga)(5)O-12 and Ca-3(Li,Nb,Ga)(5)O-12 single crystals

Authors: Gheorghe, C; Hau, S; Gheorghe, L; Voicu, F; Greculeasa, M; Achim, A; Enculescu, M

Published: JUN 2017, JOURNAL OF LUMINESCENCE, 186, 182, DOI: 10.1016/j.jlumin.2017.02.036

Sm3+ doped partially disordered calcium-niobium-gallium -garnet (CNGG) and calcium-lithium-niobium-gallium -garnet (CLNGG) single crystals were grown by the Czochralski method. Spectroscopic characteristics of Sm:CNGG and Sm:CLNGG single crystals were obtained by high-resolution absorption and emission spectra and emission dynamics measurements. Partial energy levels of Sm3+ doped CNGG and CLNGG were extracted from the measured spectra. The Judd-Ofelt theory has been applied to evaluate the Omega(t)(t=2,4, 6) intensity parameters, radiative transition rates A(r) branching ratios beta, and radiative lifetime tau(r), of the fluorescent Sm3+ (4)G(5/2) level. The emission cross-sections for the (4)G(5/2)-> H-6(J) (J=5/2, 7/2, 9/2) transitions of special interest for visible laser application were obtained by the Fucht-bauer - Ladenburg equation. The interaction between Sm3+ ions is dipole-dipole type and the C-DA, microparameter for both crystals was calculated based on Inokuti-Hirayama model. (C) 2017 Elsevier B.V. All rights reserved.

91. Cu-based composites as thermal barrier materials in DEMO divertor components

Authors: Galatanu, M; Enculescu, M; Ruiu, G; Popescu, B; Galatanu, A

Published: NOV 2017, FUSION ENGINEERING AND DESIGN, 124, 1134, DOI: 10.1016/j.fusengdes.2017.02.031

For DEMO fusion reactor an expected heat flux of about 10MW/m(2) should be extracted by the divertor which will have, most likely, an armour part made of W and a following heat sink part made of Cu, or ODS Cu alloy. Unfortunately, for these materials the optimum operating temperature windows do not overlap. Thermal barrier materials are interface materials included in such components, aiming to keep the temperatures of both armour and heat sink parts in the corresponding operating windows, and to mitigate the effects of their different thermomechanical properties. Here we propose a simple spark plasma sintering route to create Cu-based composites with a high content (10-40 vol%) of various dispersed materials (Al or Y oxides, C, SiC), allowing a fine tuning of the content and a large pool of predefined shapes and dimensions. The resulting specimens can be further joined to armour and heatsink components via a similar electrical field assisted technology. Micro-structural and thermal properties are investigated for these materials allowing to select the most suited materials in view of their thermal conductivity and thermal expansion coefficients. (C) 2017 The Authors. Published by Elsevier B.V.

92. CHARACTERIZATION OF CdS-DOPED GLASS FILMS OBTAINED BY PULSED LASER DEPOSITION

Authors: Iordanescu, CR; Elisa, M; Epurescu, G; Filipescu, M; Enculescu, M; Monteiro, RCC; Constantin, L

Published: 2017, REVISTA ROMANA DE MATERIALE-ROMANIAN JOURNAL OF MATERIALS, 47, 65, DOI:

In the present work we study the optical, struc-tural and morphological properties of CdS-doped glass films, deposited by Pulsed Laser Deposition (PLD) method. The glass target used for ablation was prepared by conventional melt-quenching technique and the semiconductor dopant, CdS powder, was embedded in the borosilicate melt glass host by continuous stirring. In order to improve the properties of the films, the laser wavelength was modified. Photoluminescence emission (PL) of CdSdoped glass films revealed a broad band located in the visible range. The structural analysis was carried out by micro-Raman spectroscopy, pointing out specific vibration modes for Si-O-Si bonds as well as for CdS dopant. The morphology and the chemical characterization of the films were investigated by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX) and Atomic Force Microscopy (AFM).

93. 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.

94. MORPHOLOGICAL AND OPTICAL PROPERTIES OF ELECTROSPUN SnO2 FIBERS

Authors: Busuioc, AD; Ciovica, I; Stoleriu, S; Enculescu, M; Evanghelidis, A; Visan, T

Published: OCT-DEC 2017, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 12, 1105, DOI:

The electrospinning technique was employed for the preparation of SnO2 fibers starting from a precursor solution consisting of a tin salt, polyvinylpyrrolidone as carrier polymer and N,N-dimethylformamide as dispersion medium. In order to achieve single-phase crystalline structures, the as-spun fibers were calcined at 500, 700 or 900 degrees C, with two different heating rates of 1 or 10 degrees C/min. The thermally treated samples were characterized in terms of structure, morphology and bandgap by employing X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and UV-Vis spectroscopy. A fine tuning of the bandgap width was attained through the selection of different values for the electrospinning and calcination parameters.

95. 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.

96. 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.

97. From an Anomalous Peak Effect to a Second Magnetization Peak in Nb-rich Nb-Ti Alloys

Authors: Ionescu, AM; Ivan, I; Enculescu, M; Grigoroscuta, M; Miu, D; Valeanu, M; Badica, P; Miu, L

Published: APR 2017, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 30, 1108, DOI: 10.1007/s10948-016-3670-4

We investigated the evolution of the DC magnetic hysteresis curves of Nb0.89Ti0.11 alloys thermo-mechanically processed by intermediate heat treatments at 900 degrees C in vacuum and cold rolling (similar to 50% thickness reduction). Starting with a rectangular piece (similar to 0.4 mm thick) cut from the as-grown alloy, after the first thermo-mechanical treatment, the specimen exhibits over a wide temperature T interval a peak effect not far from the DC irreversibility line. With a supplemental thermo-mechanical treatment, the peak effect disappears and is substituted by a second magnetization peak ( where the characteristic fields are significantly lower) induced by pinning enhancement. The second magnetization peak was clearly seen at high temperatures only, due to the occurrence of thermo-magnetic instabilities in the low-T domain. In both cases, analysis of magnetic relaxation evidences a crossover towards plastic vortex creep accompanying the maximum in the effective critical current density. These results suggest a common nature of the observed effects, related to the disordering of the vortex system induced by pinning.

98. Interfacial mechanisms of novel laser-irradiated L1(0)-based nanocomposite magnets

Authors: Crisan, O; Crisan, AD; Enculescu, M

Published: APR 2016, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 122, DOI: 10.1007/s00339-016-9947-4

In melt-spun FePtB-based ribbons, the addition of Ag has been proven to decrease the temperature of phase transformation from the A1 fcc FePt phase to the hard magnetic tetragonal L1(0) phase. Alloys with 6 and 9 at.% Ag added to the initial FePtB have been synthesized by rapid solidification from the melt. The samples have been laser irradiated and submitted to nitriding procedure. This procedure has been proven beneficial for inducing complete transformation of A1 to L1(0) phase and a strong (001) texturing. Ag segregation combined to mechanisms of creation of vacancies and diffusion of N give rise to the formation of an intergranular disordered region and due to an improved interfacial coupling between FePt grains, enhanced coercivity and two-phase magnetic behavior is obtained.

99. STRUCTURAL AND MAGNETIC PROPERTIES OF Sr2FeMoO6 OBTAINED AT LOW TEMPERATURES

Authors: Bartha, C; Plapcianu, C; Crisan, A; Enculescu, M; Leca, A

Published: JUL-SEP 2016, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 11, 780, DOI:

The double-perovskite Sr2FeMoO6 has been obtained by solid state method at low temperature (1060 degrees C) and a very short time of synthesis (up to 4h). Both, X-ray diffraction and scanning electron microscopy (SEM) confirmed the formation of Sr2FeMoO6 oxide with grain sizes around 160 mm, and a small amount of SrMoO4 as an impurity. Mossbauer spectroscopy revealed a mixed site population with Fe and Mo ions generating a structure type with population inversion. This structure has a critical influence on the magnetic properties, as confirmed by the magnetization and TC values, i.e 3.56 mu(B)/f.u and 415 K, respectively. The Sr2FeMoO6 behavior was interpreted in terms of ferrimagnetic couplings generated by the various distributions of local interactions between Fe and Mo neighbors while comparing the ideal structure should show antiferromagnetic coupling between the two sublattices.

100. Effect of polyhedral oligomeric silsesquioxane nanoreinforcement on the properties of epoxy resin/monoglycidylether-terminated poly(dimethylsiloxane) nanocomposites

Authors: Florea, NM; Lungu. A; Balanuca, B; Badica, P; Craciun, L; Damian, CM; Enculescu, M; Ionescu, C; Tihan, G; Iovu, H

Published: AUG 2016, HIGH PERFORMANCE POLYMERS, 28, 734, DOI: 10.1177/0954008315595447

This article reports the synthesis and characterization of several types of organic-inorganic nanocomposites based on epoxy resin/monoglycidylether-terminated poly(dimethylsiloxane) reinforced with 2, 5, or 10 wt% polyhedral oligomeric silsesquioxanes (POSS) bearing one glycidyl (1GE-POSS) or eight glycidyl(8GE-POSS) groups. The morphological features of the studied samples were established through atomic force microscopy, contact angle measurements, X-ray photoelectron spectroscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy, and it was demonstrated that 8GE-POSS is well dispersed within the polymer matrix, while 1GE-POSS exhibits a high tendency to form aggregates. Differential scanning calorimetry (DSC) and Fourier transform infrared resonance (FTIR) measurements are used to follow the curing behavior and to study the polymerization kinetics of epoxy groups. As evidenced by DSC and FTIR results, the inclusion of 8GE-POSS within the polymer matrix leads to a lower epoxy polymerization rate of the resulted nanocomposites than those reinforced with 1GE-POSS. The dynamic mechanical analysis results revealed that the thermomechanical properties are gradually improved with increasing of 8GE-POSS content due to the higher cross-linking density.

101. 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.

102. 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.

103. STRUCTURAL AND MORPHOLOGICAL EVOLUTIONS INDUCED BY THE ANNEALING OF CaF2 NANOCRYSTALLINE POWDERS BY USING Eu3+ ION PROBE LUMINESCENCE

Authors: Polosan, S; Secu, M; Enculescu, M

Published: APR-JUN 2016, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 11, 624, DOI:

Eu-doped CaF(2)nanocrystalline powders have been prepared by using co-precipitation technique. Structural and morphological modifications induced by annealing are followed by using Eu3+-ion probe. Theluminescence properties are changing gradually together with the morphology of doped CaF2 nanoparticles accompanied by anEu(3+)-> Eu2+ conversion. Cathodoluminescence measurements show uniform distribution of the europium dopant ions in the annealed samples accompanied by a strong increase of the integral photoluminescence signal. During annealing the cubic structure of CaF2 nanoparticles is altered going to the spherical morphology due to the Eu3+ ions incorporation. In the annealed samples Eu3+ ions are incorporated as Eu3+-O dimer centres with the coordination symmetry (C-2 nu); in the sintered samples there are two non-equivalent Eu3+ sites. The thermoluminescence peaks have been assigned to the recombination of the Eu3+ related traps in these sites.

104. 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

Published: 2016, ROMANIAN REPORTS IN PHYSICS, 68, 269, DOI:

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.

105. Influence of metallic and semiconducting nanostructures on the optical properties of dye-doped polymer thin films

Authors: Enculescu, M; Matei, E

Published: SEP 1 2016, THIN SOLID FILMS, 614, 35, DOI: 10.1016/j.tsf.2015.12.021

Dye-doped polymer thin films were obtained by spin-coating of 8% polyvinylpyrrolidone (PVP) solutions (in ethanol). Ni or ZnO nanowires were incorporated in Rhodamine 6G doped polymer films (10(-4) M dye concentration). Optical and morphological properties of simple dye-doped polymer films and films containing metallic or semiconducting nanostructures were investigated. Optical microscopy and scanning electron microscopy were used to image the nanowires. The presence of Ni nanowires induces a small shift (2-3 nm) to longer wavelengths on the emission band of Rh 6G doped PVP film. The ZnO nanowires' presence was confirmed by X-ray diffraction measurements. An enhancement of the emission of the dye doped polymer is induced by the semiconducting structures. (C) 2015 Elsevier B.V. All rights reserved.

106. Electrical properties of templateless electrodeposited ZnO nanowires

Authors: Matei, E; Costas, A; Florica, C; Enculescu, M; Pintilie, I; Pintilie, L; Enculescu, I

Published: FEB 2016, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING, 42, 372, DOI: 10.1016/j.mssp.2015.11.007

Electrochemical deposition allows the preparation of ZnO nanostructures with precisely controlled morphology and properties, by finely tuning the process parameters. ZnO nanowires were deposited onto gold substrates by electrodeposition from a low concentration zinc nitrate bath Photolithography was employed for patterning interdigitated electrode systems onto silicon/silicon dioxide substrates and ZnO electrodeposition lead to wires connected to each other by bridging neighboring interdigits allowing electronic transport characterization. Optical measurements, i.e. reflection and photoluminescence spectroscopy, were performed and the results were correlated to electronic transport data. We found that we deal with a system for which one can apply a model of space charge limited currents with different traps energy distribution as a consequence of electrodeposition rate. Current versus temperature measurements show different behavior for lower and higher range of temperatures. Such nanowires, fabricated and contacted in a straightforward way, allow a wide area of applications ranging from conductometric bio- or chemo-sensors to optoelectronic devices. (C) 2015 Elsevier Ltd. All rights reserved.

107. 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.

108. 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.

109. 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.

110. ELECTROSPRAYING OF ZnO MICROSTRUCTURES FOR ELECTRICAL CONTACTING

Authors: Costas, A; Florica, C; Evanghelidis, A; Enculescu, M; Preda, N; Enculescu, I

Published: OCT-DEC 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 1188, DOI:

ZnO complex microstructures were deposited onto interdigitated metallic electrodes by electrospraying. Simple methods, such as wet chemical precipitation and optical lithography, were used for the synthesis of flower-like and snowflake-like ZnO structures and for the preparation of interdigitated metallic electrodes, respectively. The electrosprayed ZnO particles preserve the structural, optical and morphological properties of the chemically synthesized ZnO powders. During the electrospraying process, the ZnO microstructures form bridges between the interdigitated metallic electrodes leading to electrical contacting. Changes in the electron transport through the ZnO microstructures are evidenced by their exposure to ammonia or their passivation with poly(methyl methacrylate). Merging such easy-scalable and low-cost techniques, devices based on electrosprayed complex ZnO structures can be designed.

111. 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.

112. The influence of heating rate on superconducting characteristics of MgB2 obtained by spark plasma sintering technique

Authors: Aldica, G; Burdusel, M; Popa, S; Enculescu, M; Pasuk, I; Badica, P

Published: DEC 15 2015, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 519, 189, DOI: 10.1016/j.physc.2015.10.004

Superconducting bulks of MgB2 were obtained by the Spark Plasma Sintering (SPS) technique. Different heating rates of 20, 100, 235, 355, and 475 degrees C/min were used. Samples have high density, above 95%. The onset critical temperature T-c, is about 38.8 K. There is an optimum heating rate of similar to 100 degrees C/min to maximize the critical current density J(c0), the irreversibility field H-irr, the product (J(c0) x mu H-0(irr)), and to partially avoid formation of undesirable flux jumps at low temperatures. Significant microstructure differences were revealed for samples processed with low and high heating rates in respect to grain boundaries. (C) 2015 Elsevier B.V. All rights reserved.

113. Microbial colonization of biopolymeric thin films containing natural compounds and antibiotics fabricated by MAPLE

Authors: Cristescu, R; Surdu, AV; Grumezescu, AM; Oprea, AE; Trusca, R; Vasile, O; Dorcioman, G; Visan, A; Socol, G; Mihailescu, IN; Mihaiescu, D; Enculescu, M; Chifiriuc, MC; Boehm, RD; Narayan, RJ; Chrisey, DB

Published: MAY 1 2015, APPLIED SURFACE SCIENCE, 336, 239, DOI: 10.1016/j.apsusc.2014.11.145

Although a great number of antibiotics are currently available, they are often rendered ineffective by the ability of microbial strains to develop genetic resistance and to grow in biofilms. Since many antimicrobial agents poorly penetrate biofilms, biofilm-associated infections often require high concentrations of antimicrobial agents for effective treatment. Among the various strategies that may be used to inhibit microbial biofilms, one strategy that has generated significant interest involves the use of bioactive surfaces that are resistant to microbial colonization. In this respect, we used matrix assisted pulsed laser evaporation (MAPLE) involving a pulsed KrF* excimer laser source (lambda = 248 nm, tau = 25 ns, nu = 10 Hz) to obtain thin composite biopolymeric films containing natural (flavonoid) or synthetic (antibiotic) compounds as bioactive substances. Chemical composition and film structures were investigated by Fourier transform infrared spectroscopy and X-ray diffraction. Films morphology was studied by scanning electron microscopy and transmission electron microscopy. The antimicrobial assay of the microbial biofilms formed on these films was assessed by the viable cell counts method. The flavonoid-containing thin films showed increased resistance to microbial colonization, highlighting their potential to be used for the design of anti-biofilm surfaces. (C) 2014 Elsevier B.V. All rights reserved.

114. Titanium dioxide layer deposited at low temperature upon polyester fabrics

Authors: Zgura, I; Frunza, S; Frunza, L; Enculescu, M; Florica, C; Ganea, CP; Negrila, CC; Diamandescu, L

Published: JUL-AUG 2015, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17, 1063, DOI:

TiO2 deposition by sputtering or sol-gel techniques was applied onto less thermal stable polyester textiles and onto a related poly(lactic acid) material. The temperature of deposition and of the further treatment was low enough as allowed by the support nature. Structural and spectroscopic characterization of the raw and coated samples has been performed. TiO2 coated particles are amorphous as indicated by X-ray diffraction and scanning electron microscopy. Sputtered layers consist in aggregates randomly distributed on the substrate while the sol gel layers show a uniform coverage of nanoparticles having a mosaic-like structure. The morphology of the sputtered layers depends on the deposition pressure as well. The loading degree estimated on the basis of the thermogravimetric data is rather low (ca. 2%), but the fabric properties are much influenced by the deposition. Photocatalytic activity also present on the coated surfaces was evaluated in the methylene blue degradation. TiO2 layer is quite adherent as checked by an ultra-sonication method.

115. OPTICAL AND PHOTOCATALYTIC PROPERTIES OF ELECTROSPUN ZnO FIBERS

Authors: Busuioc, C; Evanghelidis, A; Enculescu, M; Enculescu, I

Published: JUL-SEP 2015, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 10, 965, DOI:

ZnO nanofibers were obtained by electrospinning a solution of zinc acetate dihydrate and polyvinylpyrrolidone in N, N-dimethylformamide, followed by calcination at 500, 650 or 800 degrees C for 1 h. X-ray diffraction, selected area electron diffraction, scanning electron microscopy, transmission electron microscopy, reflectance spectroscopy and photoluminescence spectroscopy were used for the characterization of the resulting fibers. The thermally treated samples exhibit ZnO single phase with polycrystalline hexagonal structure. The morphological investigation revealed an accentuated contraction process during calcination, as well as the increase of the crystallite size and the appearance of a breaking tendency with the calcination temperature enhancement. Both UV and Visible emissions under excitation at 350 nm were showed by the optical studies, which also led to band gap values slightly lower than those reported for similar one-dimensional nanostructures. In order to assess the photocatalytic activity of ZnO fibers, the photodegradation of methylene blue in aqueous medium (10(-3) M) under UV irradiation (368 nm) was analyzed.

116. Novel nanocornposites based on epoxy resin/epoxy-functionalized polydimethylsiloxane reinforced with POSS

Authors: Florea, NM; Lungu. A; Badica, P; Craciun, L; Enculescu, M; Ghita, DG; Ionescu, C; Zgirian, RG; Iovu, H

Published: JUN 15 2015, COMPOSITES PART B-ENGINEERING, 75, 234, DOI: 10.1016/j.compositesb.2015.01.043

The purpose of the present study is to develop novel nanocomposites based on diglycidylether of bisphenol A (DGEBA) combined with diglycidylether-terminated polydimethylsiloxane (DG-PDMS), reinforced with 10 wt.% (mono-/octa) epoxy POSS nanocages (MEP or OEP-POSS). DG-PDMS and POSS compounds were covalently incorporated into DGEBA resin via copolymerization of epoxy groups. The effect of both DG-PDMS and POSS nanoparticles on the curing reaction, glass transition temperature (T-g), thermal stability, hardness and morphology of DGEBA/DG-PDMS +/- POSS nanocomposites were studied by DSC, FTIR, DMA, TGA, SEM/EDX, AFM and contact angle measurements. SEM/EDX and AFM results prove that OEP-POSS is well dispersed within DGEBA/DG-PDMS polymer matrix, while MEP-POSS forms large POSS aggregates. The thermo-mechanical properties of POSS based nanocomposites are also in good correlation with morphology features. MEP-POSS based nanocomposite with heterogeneous dispersion of FOSS aggregates exhibits lower T-g value and thermal stability in comparison with OEP-POSS nanocomposite which exhibits a nanoscale dispersion of the PUSS cages. The obtained T-g of OEP-POSS based nanocomposite increases with 31 degrees C in comparison with the unreinforced matrix. Moreover, this nanocomposite shows the highest storage modulus (E') and hardness. (C) 2015 Elsevier Ltd. All rights reserved.

117. Ge-Added MgB2 Superconductor Obtained by Ex Situ Spark Plasma Sintering

Authors: Batalu, D; Aldica, G; Burdusel, M; Popa, S; Enculescu, M; Pasuk, I; Miu, D; Badica, P

Published: FEB 2015, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 28, 534, DOI: 10.1007/s10948-014-2705-y

Spark plasma sintering (SPS) was applied for fabrication of dense (relative density > 97 %) bulk MgB2 samples added with Ge. Mixtures of MgB2 and Ge powders with starting compositions (MgB2) Ge (x) , x=0.005, 0.01, and 0.03 were used. Added samples show enhancement of the critical current density at high magnetic fields when compared to a pristine reference sample. The optimum composition is for x=0.005 and for this sample J (c)(20 K) =10(2)A/cm (2) is obtained at 5 T, while for the reference sample is obtained at 3.9 T. Ge does not substitute in the crystal lattice of MgB2 and T (c,onset) or T (c,midpoint) from magnetization measurements scatter within 0.15 or 0.3 K, respectively.

118. Zinc oxide electroless deposition on electrospun PMMA fiber mats

Authors: Preda, N; Evanghelidis, A; Enculescu, M; Florica, C; Enculescu, I

Published: JAN 1 2015, MATERIALS LETTERS, 138, 242, DOI: 10.1016/j.matlet.2014.10.021

ZnO crystallites were grown by electroless deposition on poly(methyl methacrylate) (PMMA) fiber mats prepared by an electrospinning technique. The electroless deposition involves three steps: sensitization, activation and deposition, which were performed by subsequently dipping the PMMA fiber mats in the appropriate solutions. After the deposition the PMMA fibers are uniformly coated with ZnO prisms which show hexagonal wurtzite structure and optical signatures (band-gap value and emission bands) typical for this semiconductor. By combining electroless deposition and electrospinning, different semiconductor coated polymer fibers can be obtained for a wide range of applications. Both methods are appropriate for large scale production, being scalable, cheap, efficient and suitable for large-area covering techniques. (C) 2014 Elsevier B.V. All rights reserved.

119. DEPOSITION OF TITANIUM DIOXIDE LAYERS UPON POLYESTER TEXTILE MATERIALS: CHECKING THE ADHERENCE BY ULTRA-SONICATION

Authors: Zgura, I; Frunza, S; Enculescu, M; Florica, C; Cotorobai, F

Published: 2015, ROMANIAN JOURNAL OF PHYSICS, 60, 494, DOI:

An important parameter of deposited thin films is their adhesion to the substrate materials, we focused on the adhesion of TiO2 layer by sol-gel or sputtering onto textile substrate as checked by an ultra-sonication method. The characterization-made prior and after the tests have shown a good adherence of the nanoparticles, despite the low deposition temperature.

120. Superior biofunctionality of dental implant fixtures uniformly coated with durable bioglass films by magnetron sputtering

Authors: Popa, AC; Stan, GE; Enculescu, M; Tanase, C; Tulyaganov, DU; Ferreira, JMF

Published: NOV 2015, JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS, 51, 327, DOI: 10.1016/j.jmbbm.2015.07.028

Bioactive glasses are currently considered the suitable candidates to stir the quest for a new generation of osseous implants with superior biological/functional performance. In congruence with this vision, this contribution aims to introduce a reliable technological recipe for coating fairly complex 3D-shaped implants (e.g. dental screws) with uniform and mechanical resistant bioactive glass films by the radio-frequency magnetron sputtering method. The mechanical reliability of the bioactive glass films applied to real Ti dental implant fixtures has been evaluated by a procedure comprised of "cold" implantation in pig mandibular bone from a dead animal, followed by immediate tension-free extraction tests. The effects of the complex mechanical strains occurring during implantation were analysed by scanning electron microscopy coupled with electron dispersive spectroscopy. Extensive biocompatibility assays (MTS, immunofluorescence, Western blot) revealed that the bioactive glass films stimulated strong cellular adhesion and proliferation of human dental pulp stem cells, without promoting their differentiation. The ability of the implant coatings to conserve a healthy stem cell pool is promising to further endorse the fabrication of new osseointegration implant designs with extended lifetime. (C) 2015 Elsevier Ltd. All rights reserved.

121. Exciton-phonon interaction in PbI2 revealed by Raman and photoluminescence studies using excitation light overlapping the fundamental absorption edge

Authors: Baibarac, M; Smaranda, I; Scocioreanu, M; Mitran, RA; Enculescu, M; Galatanu, M; Baltog, I

Published: OCT 2015, MATERIALS RESEARCH BULLETIN, 70, 772, DOI: 10.1016/j.materresbull.2015.06.012

Enhancement at low temperatures of the Raman scattering excited by laser light situated near the edge of the fundamental absorption band is often encountered when studying nanoscale structures. Theory devoted to this phenomenon has established that it originates in an exciton-phonon interaction process, known as the Frohlich interaction, Such a phenomenon was observed in PbI2. The experimental data conclude that the enhancement of the Raman emission results from: (i) an optical excitation near edge of fundamental absorption band; (ii) it is conditioned by the existence of excitonic PL; (iii) its occurrence is different over stokes and anti-stokes Raman branches as result of the different overlapping of the Raman spectral range and the excitonic PL band profile; and (iv) it appears more intense in micrometric powders or in bulk crystalline material. These data are interpreted as stimulated Raman effect resulting from the mixing of the pump laser light and the excitonic light. (C) 2015 Elsevier Ltd. All rights reserved.

122. Fabrication of magnetite-based core-shell coated nanoparticles with antibacterial properties

Authors: Grumezescu, AM; Cristescu, R; Chifiriuc, MC; Dorcioman, G; Socol, G; Mihailescu, IN; Mihaiescu, DE; Ficai, A; Vasile, OR; Enculescu, M; Chrisey, DB

Published: MAR 2015, BIOFABRICATION, 7, DOI: 10.1088/1758-5090/7/1/015014

We report the fabrication of biofunctionalized magnetite core/sodium lauryl sulfate shell/antibiotic adsorption-shell nanoparticles assembled thin coatings by matrix assisted pulsed laser evaporation for antibacterial drug-targeted delivery. Magnetite nanoparticles have been synthesized and subsequently characterized by transmission electron microscopy and x-ray diffraction. The obtained thin coatings have been investigated by FTIR and scanning electron microscope, and tested by in vitro biological assays, for their influence on in vitro bacterial biofilm development and cytotoxicity on human epidermoid carcinoma (HEp2) cells.

123. 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.

124. 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.

125. 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.

126. Polysaccharide-assisted crystallization of ZnO micro/nanostructures

Authors: Preda, N; Enculescu, M; Enculescu, I

Published: JAN 15 2014, MATERIALS LETTERS, 115, 260, DOI: 10.1016/j.matlet.2013.10.081

ZnO micro/nanostructures with complex morphology were synthesized by a simple chemical reaction between zinc nitrate and hexamethylenetetramine in the presence of polysaccharides. X-ray diffraction analysis showed that all obtained samples are of wurtzite structure. The reflectance and room temperature photoluminescence spectra have been used to investigate the optical properties of the ZnO structures. The scanning electron microscopy images reveal that the ZnO morphology (star, double-jellyfish, double-raspberry and edelweiss-flower) can be easily changed by varying the polysaccharides: sodium alginate, gum arabic and chitosan. The polysaccharide-assisted crystallization method could provide a facile approach to synthesize other desired compounds with controllable morphology. (C) 2013 Elsevier B.V. All rights reserved.

127. Significant enhancement of the critical current density for cubic BN addition into ex situ spark plasma sintered MgB2

Authors: Badica, P; Aldica, G; Burdusel, M; Popa, S; Negrea, RF; Enculescu, M; Pasuk, I; Miu, L

Published: SEP 2014, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 27, DOI: 10.1088/0953-2048/27/9/095013

High density (above 93%) superconducting bulks of MgB2 with addition of hexagonal BN (h-BN) and cubic BN (c-BN) with compositions ((MgB2) + (BN)(x), x = 0.01, 0.03, 0.05) were obtained by ex situ spark plasma sintering. All the investigated samples have the critical temperature T-c = 38.8 K. The variation of the critical current density J(c) with the external magnetic field H for h-BN added sample is almost overlapping the J(c)(H) dependence for the pristine MgB2 sample. On the other hand, J(c) for the samples added with c-BN is larger at high magnetic fields, while the decrease of J(c) at low H is very small. At T = 20 K, a J(c) of 10(2) A cm(-2) is determined for the sample with x(c-BN) = 0.005 at H = 58 kOe, and for the sample with x(c-BN) = 0.01 at 54 kOe. Magnetic relaxation measurements indicate a significant flux pinning enhancement in MgB2 samples added with c-BN. It is proposed that the disorder at the interface caused by the convenient lattice matching relationship between the lateral plane of the MgB2 crystal prism and the face of the c-BN crystal cube is responsible for the observed vortex pinning increase.

128. Addition of Ho2O3 of different types to MgB2 in the ex-situ Spark Plasma Sintering: Simultaneous control of the critical current density at low and high magnetic fields

Authors: Aldica, G; Popa, S; Enculescu, M; Batalu, D; Miu, L; Ferbinteanu, M; Badica, P

Published: AUG 14 2014, MATERIALS CHEMISTRY AND PHYSICS, 146, 323, DOI: 10.1016/j.matchemphys.2014.03.030

Two different types of Ho2O3 powders (showing a much different morphology) were added to MgB2 in the ex-situ Spark Plasma Sintering (SPS). In the 5-25 K range, the first Ho2O3 powder type does not significantly suppress the critical current density J(c) at low magnetic fields and the second one enhances it at high fields, while their mixture simultaneously controls J(c) at both small and high magnetic fields so that the decrease is small at low fields and there is a notable enhancement at high fields when compared to pristine sample. The control of J(c)(H) is discussed versus specific characteristics of the raw powders, the resulting microstructure of the added SPS-ed samples and pinning details from magnetic relaxation measurements. (C) 2014 Elsevier B.V. All rights reserved.

129. 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.

130. Cell Adhesion Response on Femtosecond Laser Initiated Liquid Assisted Silicon Surface

Authors: Ulmeanu, M; Sima, LE; Ursescu, D; Enculescu, M; Bazan, X; Quintana, I

Published: MAR 2014, CURRENT TOPICS IN MEDICINAL CHEMISTRY, 14, 629, DOI: 10.2174/1568026614666140118204946

Silicon substrates were irradiated at normal incidence with a femtosecond Ti:sapphire laser (Quatronix, 90 fs pulse duration, 1 kHz repetition rate, M-2 similar to 1.2, maximum energy peak 350 mJ) operating at a wavelength of 400 nm and focused via a microscope objective (Newport; UV Objective Model, 37x 0.11 N.A.). The laser scanning was assisted by liquids precursors media such as methanol and 1,1,2-trichlorotrifluoroethane. By altering the processing parameters, such as incident laser energy, scanning speed, and different irradiation media, various surface structures were produced on areas with 1 mm 2 dimensions. We analyzed the dependence of the surface morphology on laser pulse energy, scanning speed and irradiation media. Well ordered areas are developed without imposing any boundary conditions for the capillary waves that coarsens the ripple pattern. To assess biomaterial-driven cell adhesion response we investigated actin filaments organization and cell morphological changes following growth onto processed silicon substrates. Our study of bone cell progenitor interaction with laser nanoprocessed silicon lines has shown that cells anchor mainly to contact points along the nanostructured surface. Consequently, actin filaments are stretched towards the 15 mu m wide parallel lines increasing lateral cell spreading and changing the bipolar shape of mesenchymal stem cells.

131. DEPENDENCE ON THE DYE'S TYPE AND CONCENTRATION OF THE EMISSIVE PROPERTIES OF ELECTROSPUN DYE-DOPED BEADED NANOFIBERS

Authors: Enculescu, M; Evanghelidis, A; Busuioc, C; Florica, C; Costas, A; Oancea, M; Preda, N; Matei, E; Enculescu, I

Published: APR-JUN 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 816, DOI:

Luminescent polymer fibers were obtained by electrospinning solutions of 8% (in ethanol) polyvinylpyrrolidone (PVP) doped with three different dyes (coumarin 6, rhodamine 6G and sulforhodamine 101). Using the same parameters for the electrospinning process, nanofibers with diameters between 200 and 800 nm and different sizes and distributions of the beads were obtained as proven by scanning electron microscopy (SEM). We assessed the dependence of their emissive properties (intensity and wavelength) on the type of dye using photoluminescence (PL) spectra for the same concentration of the dopand dye (10(-3)M). Moreover, employing 4 different concentrations for coumarin 6 and rhodamine 6G (from 10(-3) to 10(-6) M) we evaluated the dependence with the concentration of the dye on the emissive properties of the electrospun dye-doped PVP nanofibers.

132. Superhydrophobic ZnO networks with high water adhesion

Authors: Florica, C; Preda, N; Enculescu, M; Zgura, I; Socol, M; Enculescu, I

Published: AUG 8 2014, NANOSCALE RESEARCH LETTERS, 9, DOI: 10.1186/1556-276X-9-385

ZnO structures were deposited using a simple chemical bath deposition technique onto interdigitated electrodes fabricated by a conventional photolithography method on SiO2/Si substrates. The X-ray diffraction studies show that the ZnO samples have a hexagonal wurtzite crystalline structure. The scanning electron microscopy observations prove that the substrates are uniformly covered by ZnO networks formed by monodisperse rods. The ZnO rod average diameter and length were tuned by controlling reactants' concentration and reaction time. Optical spectroscopy measurements demonstrate that all the samples display bandgap values and emission bands typical for ZnO. The electrical measurements reveal percolating networks which are highly sensitive when the samples are exposed to ammonia vapors, a variation in their resistance with the exposure time being evidenced. Other important characteristics are that the ZnO rod networks exhibit superhydrophobicity, with water contact angles exceeding 150 degrees and a high water droplet adhesion. Reproducible, easily scalable, and low-cost chemical bath deposition and photolithography techniques could provide a facile approach to fabricate such ZnO networks and devices based on them for a wide range of applications where multifunctionality, i.e., sensing and superhydrophobicity, properties are required.

133. High magnetic field enhancement of the critical current density by Ge, GeO2 and Ge2C6H10O7 additions to MgB2

Authors: Batalu, D; Aldica, G; Popa, S; Miu, L; Enculescu, M; Negrea, RF; Pasuk, I; Badica, P

Published: JUL 1 2014, SCRIPTA MATERIALIA, 82, 64, DOI: 10.1016/j.scriptamat.2014.03.024

Ge, GeO2 and Ge2C6H10O7 additions to MgB2 obtained by ex situ spark plasma sintering significantly enhance the critical current density J(c) in high magnetic fields. A J(c)(T = 20 K) of 102 A cm(-2) is obtained at 3.9 T in the pristine sample and at 5.8 T in the MgB2(Ge2C6H10O7)(0.0014) sample. The decrease in the critical temperature for added samples is less than 1 K and T-c(20 K, H = 0) shows a small decrease from 5.5 x 10(5) A cm(-2) in the pristine sample to 3.9 x 10(5) A cm(-2) in MgB2(Ge2C6H10O7)(0.0014) sample. Ge does not substitute into the MgB2 lattice. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

134. Zinc Oxide and Polysaccharides: Promising Candidates for Functional Nanomaterials

Authors: Preda, N; Enculescu, M; Zgura, I; Socol, M; Florica, C; Evanghelidis, A; Matei, E; Enculescu, I

Published: 2014, SIZE EFFECTS IN NANOSTRUCTURES: BASICS AND APPLICATIONS, 205, 136, DOI: 10.1007/978-3-662-44479-5_5

Recently, ZnO and natural polysaccharides have received more and more attention as interesting components for designing complex functional nanomaterials, key elements being their high occurrence and low-cost. In this chapter are presented possibilities for tailoring the ZnO properties by using polysaccharides in the synthesis process as well as reports on the functionalization of cellulose-based natural fabrics with ZnO. In both cases, in the preparation step were used only simple and scalable wet chemical methods. The resulting materials with suitable characteristics, e.g. dependence of the ZnO nanostructures optical properties on their morphology or high-UV blocking and superhydrophobicity for ZnO-functionalized fabrics, can find applications in domains where such qualities are required.

135. Micropatterned ZnO rod arrays prepared by Au-catalyzed electroless deposition

Authors: Florica, C; Preda, N; Enculescu, M; Enculescu, I

Published: JUL 2014, PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, 8, 652, DOI: 10.1002/pssr.201409089

Micropatterned ZnO was synthesized by an electroless deposition process using Au stripes as catalytic surfaces. The Au-patterned electrodes were prepared on SiO2/Si wafers using photolithography. The site-selective deposition of patterned ZnO hexagonal rod arrays is confirmed by scanning electron microscopy. The ZnO micropatterned surface revealed a conversion of wettability from hydrophilic to super-hydrophobic depending on the deposition reaction parameters. The electrical measurements carried out at room temperature before and after exposure to ammonia vapors of the patterned ZnO arrays show a resistance variation with exposure time. Highly reproducible, easy scalable and low-cost, photolithography and electroless deposition techniques could provide a facile approach to fabricate functionalized micropatterns, for a wide range of applications. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

136. 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.

137. Polyester fabrics coated with SiOx nanoparticles by vacuum deposition at small angle. Structural characterization and wetting properties

Authors: Frunza, L; Zgura, I; Enculescu, M; Frunza, S; Ganea, CP; Rasoga, O; Cotorobai, F; Dorogan, A

Published: JAN-FEB 2014, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 16, 181, DOI:

Vacuum deposition at small angle was successfully applied in deposition of SiOx particles onto polyester textile materials; this deposition is here presented in comparison with that upon other materials made from poly(lactic acid), polyamide or hemp. Structural and spectroscopic characterization of deposited samples has been performed and compared with that of the raw materials. The deposited particles are amorphous. Contact angle measurement by the sessile drop method, was used to study the wettability behavior of the investigated composite systems. The hierarchical roughness structure generates hydrophylic properties onto polyester fabrics and the other functionalized samples after deposition. The deposition technique was proven to be highly reproducible, easy scalable and cheap, allowing a wide range of applications.

138. Influence of morphology on the emissive properties of dye-doped PVP nanofibers produced by electrospinning

Authors: Enculescu, M; Evanghelidis, A; Enculescu, I

Published: DEC 2014, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 75, 1371, DOI: 10.1016/j.jpcs.2014.07.008

Dye-doped polymer micro- and nanofibers with tailored light emission properties have great potential for applications in optical, optoelectronic, or photonic devices. In this study, these types of structures were obtained by electrospinning rhodamine 6 G-doped polyvinylpyrrolidone (PVP) using a polymer solution of 10% (mass) concentration in ethanol. Polymer nanofibers with different morphologies (smooth and beaded) and diameters of about 500 nm were obtained using different electrospinning conditions with the same solutions. Fluorescence optical microscopy observations showed that the dye was distributed uniformly in the doped PVP nanofibers. Different shifts were observed when we compared the wavelength of the dye emission band peak of the smooth nanofibers (566 nm) and the wavelength of the dye emission band peak of the beaded fibers (561.5 nm) produced by electrospinning in different conditions with the wavelength of the emission band peak for transparent thin films produced by spin coating (558 nm) using the same polymer solution. This demonstrates that it is possible to tune the optical properties of electrospun dye-doped polymer nanofibers simply by modifying the morphology of the material, i.e., the parameters of the electrospinning process. (C) 2014 Elsevier Ltd. All rights reserved.

139. Te and SiC co-doped MgB2 obtained by an ex situ spark plasma sintering technique

Authors: Aldica, G; Popa, S; Enculescu, M; Badica, P

Published: MAR 2013, SCRIPTA MATERIALIA, 68, 431, DOI: 10.1016/j.scriptamat.2012.11.011

Ex situ spark plasma sintering was used to obtain dense MgB2 co-doped with SiC and Te. The composition (MgB2) + (SiC)(0.025) + Te-0.01 shows critical current densities J(c)(20 K, 5 T) of 3.5 x 10(2) A cm(-2) and J(c)(5 K, 9 T) of 2 x 10(3) A cm(-2). These values are higher than for pristine samples or those separately doped with Te or SiC. They are also comparable at high fields and temperatures with the best reported values for the co-doped MgB2 bulks produced by conventional in situ methods. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

140. Single bath electrodeposition of samarium oxide/zinc oxide nanostructured films with intense, broad luminescence

Authors: Matei, E; Enculescu, M; Enculescu, I

Published: APR 15 2013, ELECTROCHIMICA ACTA, 95, 178, DOI: 10.1016/j.electacta.2013.02.044

Electrochemical deposition from a solution containing zinc and samarium ions, leads to a samarium oxide/zinc oxide sandwich-like structure with an intense, visible, broad luminescence peak centered at 550 nm. The successive deposition of the two materials is related to the bath composition and overpotential, taking place for values higher than a certain threshold. The zinc oxide film, first one to be deposited, presents typical hexagonal prism morphology while samaria coating films present a porous, nanowall like structure. The photoluminescence emission is at least 10 times more intense than in the case of typical electrodeposited ZnO films of similar thickness and does not appear in Sm2O3 films electrodeposited from solutions containing only Sm ions. Samples prepared in different conditions were characterized from the point of view of composition, structure, morphology and optical properties. The characteristics of the emission spectra of the films make them interesting for solid state lightning applications. (c) 2013 Elsevier Ltd. All rights reserved.

141. Polymer Sphere Array Assisted ZnO Electroless Deposition

Authors: Preda, N; Enculescu, M; Enculescu, I

Published: JAN 1 2013, SOFT MATERIALS, 11, 464, DOI: 10.1080/1539445X.2012.693147

ZnO uniform films were deposited on polymer sphere arrays by an electroless technique. The low-dimensional ZnO particles were grown from an aqueous solution of zinc nitrate and dimethylamineborane. The X-ray diffraction studies demonstrate that the ZnO crystallites have a hexagonal wurtzite structure. The scanning electron microscopy images prove that ZnO hexagonal prisms are synthesized with a fairly uniform diameter of around 200 nm. From the contact angle measurements it was found that the electroless deposition on polymer sphere arrays of semiconductor hexagonal prisms leads to an improvement of ZnO hydrophobic properties.

142. Periodic arrays of nanostructures in silicon and gallium arsenide by near-field enhanced laser irradiation in liquid precursors

Authors: Ulmeanu, M; Anghel, I; Filipescu, M; Luculescu, C; Enculescu, M; Zamfirescu, M

Published: FEB 5 2013, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 418, 51, DOI: 10.1016/j.colsurfa.2012.11.002

A simple approach to fabricate periodic arrays of ring bumps, disk and convex bumps or holes on silicon and gallium arsenide substrates is reported. In the process, a mono or double layer of 700 nm diameter silica colloidal particles were self-assembled on the substrates and a single pulse from a 200 fs laser at 387 nm wavelength was applied. The surfaces were irradiated at normal incidence by immersing the substrates in a glass container filled with acetone, carbon tetrachloride and 1,1,2-trichlor-trifluorethan liquid precursors. The influence of the medium on the near-field interactions for both substrates is investigated. (C) 2012 Elsevier B.V. All rights reserved.

143. Antimicrobial activity of biopolymer-antibiotic thin films fabricated by advanced pulsed laser methods

Authors: Cristescu, R; Popescu, C; Dorcioman, G; Miroiu, FM; Socol, G; Mihailescu, IN; Gittard, SD; Miller, PR; Narayan, RJ; Enculescu, M; Chrisey, DB

Published: AUG 1 2013, APPLIED SURFACE SCIENCE, 278, 213, DOI: 10.1016/j.apsusc.2013.01.062

We report on thin film deposition by matrix assisted pulsed laser evaporation (MAPLE) of two polymer-drug composite thin film systems. A pulsed KrF* excimer laser source (lambda = 248 nm, tau = 25ns, nu = 10 Hz) was used to deposit composite thin films of poly(D,L-lactide) (PDLLA) containing several gentamicin concentrations. FTIR spectroscopy was used to demonstrate that MAPLE-transferred materials exhibited chemical structures similar to those of drop cast materials. Scanning electron microscopy data indicated that MAPLE may be used to fabricate thin films of good morphological quality. The activity of PDLLA-gentamicin composite thin films against Staphylococcus aureus bacteria was demonstrated using drop testing. The influence of drug concentration on microbial viability was also assessed. Our studies indicate that polymer-drug composite thin films prepared by MAPLE may be used to impart antimicrobial activity to implants, medical devices, and other contact surfaces. (C) 2013 Elsevier B.V. All rights reserved.

144. MORPHOLOGY-CONTROLLED SYNTHESIS OF ZnO STRUCTURES BY A SIMPLE WET CHEMICAL METHOD

Authors: Preda, N; Enculescu, M; Florica, C; Costas, A; Evanghelidis, A; Matei, E; Enculescu, I

Published: OCT-DEC 2013, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 8, 1600, DOI:

Zinc oxide particles were synthesized by a simple wet chemical method. Using zinc nitrate and various precipitating agents, like KOH, NaOH and (CH2)(6)N-4, particles with different morphologies were obtained. Also, the addition of a structure-directing agent, like gum arabic - a highly branched biopolymer, leads to a decrease in the ZnO particles size (for KOH and NaOH) and to a dramatical change of the ZnO particle shape in the case of (CH2)(6)N-4. The X-ray diffraction analysis showed that all obtained samples are of wurtzite structure. The reflectance and photoluminescence spectra have been used to investigate the optical properties of the ZnO structures. The morphologies observed by scanning electron microscopy reveal snowflake-like, flower-like, star-like and double-raspberry-like structures. A possible formation mechanism for ZnO micro/nanostructures with different morphologies was proposed. The biopolymer-assisted crystallization method could provide a facile approach to synthesize other desired compounds with controllable morphology.

145. MgB2 with Addition of Bi2O3 Obtained by Spark Plasma Sintering Technique

Authors: Burdusel, M; Aldica, G; Popa, S; Enculescu, M; Pasuk, I; Badica, P

Published: MAY 2013, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 26, 1556, DOI: 10.1007/s10948-012-2015-1

Bi2O3 and Bi-metal powders were mixed with MgB2 powder. Starting compositions were (MgB2)(Bi2O3) x, x = 0.0025, 0.005, 0.015, and (MgB2)(Bi)(y), y = 0.01. Mixtures were processed by Spark Plasma Sintering (SPS) technique. As obtained composite samples show high density, above 94 % of the theoretical density. Samples with Bi2O3 for x = 0.0025 and 0.005 show higher critical current densities, J(c), at high fields and at 20 K than for the pristine sample. Their irreversibility field, H-irr, is also higher. On the other hand, sample added with Bi-metal has lower J(c) and H-irr at any temperature than for the pristine sample.

146. 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.

147. Silicon bump arrays by near-field enhanced femtosecond laser irradiation in fluorine liquid precursors

Authors: Ulmeanu, M; Anghel, I; Jipa, F; Filipescu, M; Enculescu, M; Zamfirescu, M

Published: AUG 1 2013, APPLIED SURFACE SCIENCE, 278, 304, DOI: 10.1016/j.apsusc.2013.01.050

A simple approach to fabricate periodic arrays of conical bumps on silicon (Si) substrate is reported. In the process, a single pulse from a 200 fs laser at 387 nm wavelength was applied on a self-assembled monolayer of 700 nm and 390 nm diameter silica spheres on a n-doped Si (1 0 0) wafer. The surface was irradiated at normal incidence by immersing the silicon substrates in a glass container filled with 1, 1, 2 trichlor-trifluorethan liquid precursors. After laser irradiation, at laser fluences in the range from 1 to 40 J/cm(2), a regular array of conical Si bumps was fabricated. The density of the Si bumps can be varied by varying the particle size diameter. The influence of the medium on the near-field interactions for both sizes silica particles layer is investigated. (C) 2013 Elsevier B.V. All rights reserved.

148. Direct sintering of SiC-W composites with enhanced thermal conductivity

Authors: Galatanu, M; Popescu, B; Enculescu, M; Tiseanu, I; Craciunescu, T; Galatanu, A

Published: OCT 2013, FUSION ENGINEERING AND DESIGN, 88, 2602, DOI: 10.1016/j.fusengdes.2013.05.036

Different types of SiC-W composites have been realized by spark plasma sintering in a single step process starting with beta SiC nanometric powder, W nanometric and micrometric sized powders, and W foils. SEM, EDX, XRD and X-ray tomography have been used to analyze the sample morphology while the thermal properties of the resulting materials have been investigated up to 1000 degrees C using a LFA thermal analyzer. The results show the possibility to produce dense W-SiC composites, with enhanced thermal conductivity using a relatively simple route. (C) 2013 Elsevier B.V. All rights reserved.

149. Functionalized magnetite silica thin films fabricated by MAPLE with antibiofilm properties

Authors: Mihaiescu, DE; Cristescu, R; Dorcioman, G; Popescu, CE; Nita, C; Socol, G; Mihailescu, IN; Grumezescu, AM; Gudovan, D; Enculescu, M; Negrea, RF; Ghica, C; Chifiriuc, C; Bleotu, C; Chrisey, DB

Published: MAR 2013, BIOFABRICATION, 5, DOI: 10.1088/1758-5082/5/1/015007

We report on the fabrication of magnetite/salicylic acid/silica shell/antibiotics (Fe3O4/SA/SiO2/ATB) thin films by matrix-assisted pulsed laser evaporation (MAPLE) to inert substrates. Fe3O4-based powder have been synthesized and investigated by XRD and TEM. All thin films were studied by FTIR, SEM and in vitro biological assays using Staphylococcus aureus and Pseudomonas aeruginosa reference strains, as well as eukaryotic HEp-2 cells. The influence of the obtained nanosystems on the microbial biofilm development as well as their biocompatibility has been assessed. For optimum deposition conditions, we obtained uniform adherent films with the composition identical with the raw materials. Fe3O4/SA/SiO2/ATB thin films had an inhibitory activity on the ability of microbial strains to initiate and develop mature biofilms, in a strain-and antibiotic-dependent manner. These magnetite silica thin films are promising candidates for the development of novel materials designed for the inhibition of medical biofilms formed by different pathogenic agents on common substrates, frequently implicated in the etiology of chronic and hard to treat infections.

150. Luminescent micro- and nanofibers based on novel europium phthalate complex

Authors: Enculescu, M; Preda, N; Matei, E; Enculescu, I

Published: SEP 14 2012, MATERIALS CHEMISTRY AND PHYSICS, 136, 58, DOI: 10.1016/j.matchemphys.2012.06.018

We synthesized by wet chemical route a novel europium-potassium phthalate complex Eu3+K+[(COO)(2)(C6H4)](2). The compound is a white powder insoluble in water. X-ray diffraction evaluation shows that we obtained a new crystalline compound with no traces of the starting materials (potassium hydrogen phthalate and europium chloride). Scanning electron microscopy reveals that the powder consists of fiber-shaped structures with sizes larger than 250 nm in diameter. Energy dispersive X-ray analysis proves that the compound has a 1:1 europium-potassium ratio. Fourier transform infrared spectroscopy confirms the presence of the phthalate in the new compound. Photoluminescence and cathodoluminescence measurements show that the fiber-shaped structures are intensely luminescent with emission bands corresponding to the D-5(0) -> F-7(J) (J = 1-4) Eu (III) ion's transitions in the region between 580 nm and 700 nm, the most intense maximum being observed around 615 nm. Up-converted luminescence with a maximum at 315 nm was recorded. (c) 2012 Elsevier B.V. All rights reserved.

151. Synthesis and characterization of bead-like particles based on chitosan and vinyl polymers

Authors: Preda, N; Enculescu, M

Published: SEP 2012, JOURNAL OF POLYMER RESEARCH, 19, DOI: 10.1007/s10965-012-9963-9

Styrene, methyl methacrylate and glycidyl methacrylate vinyl monomers were grafted onto chitosan by surfactant-free emulsion copolymerization using potassium persulfate as initiator. The grafted compounds were characterized by X-ray diffraction, FTIR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and zeta potential measurements. X-ray diffraction showed changes in the crystallinity pattern of chitosan after the copolymerization reaction. Evidence of grafting was confirmed by FTIR spectroscopy. From zeta potential measurements it is found that the surfaces of graft copolymers latex particles have positive charges resulting from the cationic chitosan molecules. The morphology evaluated by SEM, TEM and AFM proves that in the absence of chitosan, latexes of vinyl homopolymers contain quasi-monodispersed spheres with average diameter of about 400 nm or 250 nm while the graft copolymers latexes are formed by clustered irregular beads with average diameter around 100 nm.

152. TILT c AXIS CRYSTALLITE GROWTH OF ALUMINIUM NITRIDE FILMS BY REACTIVE RF-MAGNETRON SPUTTERING

Authors: Stan, GE; Pasuk, I; Trinca, LM; Galca, AC; Enculescu, M; Miculescu, F

Published: JAN-MAR 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 50, DOI:

The article reports on the tilted growth of textured aluminium nitride thin films obtained by radio-frequency magnetron sputtering onto 50 mm diameter Si (111) wafers, in reactive atmosphere, in a planar sputtering system without tilting the substrate and with no additional sputtering geometry alterations. The films were investigated using, X-ray diffraction, spectroscopic ellipsometry and scanning electronic microscopy, done by local measurements on the wafer surface, at different distances from the centre. A progressive increase of the tilt angle when moving away from the sample centre has been found. The maximum tilt angle of the columnar AlN crystallites, obtained near the edges of the wafer, is about 7 degrees. The results showed also that tilting is associated with smaller thickness and larger dispersion of the c axis orientation. Synthesizing inclined c axis AlN films should allow the fabrication of surface acoustic wave devices based on shear waves for liquid sensor applications.

153. Large scale microstructuring on silicon surface in air and liquid by femtosecond laser pulses

Authors: Ulmeanu, M; Jipa, F; Radu, C; Enculescu, M; Zamfirescu, M

Published: SEP 15 2012, APPLIED SURFACE SCIENCE, 258, 9317, DOI: 10.1016/j.apsusc.2011.08.110

Large-scale microstructures were imprinted on the surface of silicon with dimensions of 1 mm x 1 mm by femtosecond laser line-by-line scanning irradiation. The scanning was made under air and under chlor/hydrogen based liquid layers. Scanning electron microscope investigations evidenced homogeneous surface microstructures, such as: ripples with sub-wavelengths dimensions, Si pillars and directional oriented bacilliform structures. The dependence of the surface morphology on laser energy, scanning speed and irradiation media was analyzed. In air, the microstructure changes from directional-arranged bacilliform structures to well-known ripple structures with a width of about 525 nm. When using the liquid media, we observe ripple structures with a width of about 370 nm and an overlapping of those that evolve in certain regions into Si pillars. The surfaces show interesting gradient topography behaviour which could be used as model scaffolds for the systematic exploration of the role of 3D micro/nano morphology on cell adhesion and growth. By using chlor and hydrogen based liquids we were able to explore the microstructuring of the silicon by line-by-line irradiation process using the femtosecond laser. (C) 2011 Elsevier B. V. All rights reserved.

154. COMBINATORIAL PULSED LASER DEPOSITION OF AG-CONTAINING CALCIUM PHOSPHATE COATINGS

Authors: Socol, G; Socol, M; Sima, L; Petrescu, S; Enculescu, M; Sima, F; Miroiu, M; Popescu-Pelin, G; Stefan, N; Cristescu, R; Mihailescu, CN; Stanculescu, A; Sutan, C; Mihailescu, IN

Published: APR-JUN 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 576, DOI:

Embedding silver (Ag) into CaPs one could expect the enhancement of the antimicrobial performances of coatings for load bearing implants. The aim of this research was to evaluate whether the cellular morphology is influenced by the variation of Ag content, as well as by the solubility and morphological features of Ag-containing CaP coatings obtained by combinatorial pulsed laser deposition technique. In this view, we developed compositional libraries of either Ag and hydroxyapatite (HA) or Ag and beta-tricalcium phosphate (beta-TCP). The Ag content along the length of the combinatorial CaP coatings increased up to a maximum of similar to 1 at.%. SEM and AFM images evidenced the abundant presence of particulates typical for CaP coatings deposited by PLD. AFM histograms showed that the samples were rough with RMS values within 61-209 nm range. Ag content values up to 0.6 at. % into HA coatings were found nontoxic for mesenchymal stem cell (MSC) growth.

155. Sm3+-doped Sc2O3 polycrystalline ceramics: Spectroscopic investigation

Authors: Gheorghe, C; Lupei, A; Voicu, F; Enculescu, M

Published: SEP 15 2012, JOURNAL OF ALLOYS AND COMPOUNDS, 535, 82, DOI: 10.1016/j.jallcom.2012.04.083

Sm3+-doped Sc2O3 translucent polycrystalline ceramics were fabricated by solid-state reaction method in order to evaluate its potential for visible emission. The optical spectra in the UV-IR range of Sm3+ in these samples, at different temperatures (10-300 K), were performed. A series of data on Sm: Sc2O3 system not investigated previously were obtained from the analysis of the absorption and visible emission spectra as well as the emission kinetics: an extended energy level scheme, absorption cross sections for different bands, lifetimes, etc. Additional spectroscopic parameters were evaluated in the frame of the Judd-Ofelt (J-O) theory: J-O intensity parameters, oscillator strengths, radiative transitions probabilities, radiative lifetimes, branching ratios, and the cross sections (by Fuchtbauer-Ladenburg) of the main three visible emissions: (4)G(5/2) -> H-6(5/2) (yellow), (4)G(5/2) -> H-6(7/2) (orange) and (4)G(5/2) -> H-6(9/2) (red). (C) 2012 Elsevier B.V. All rights reserved.

156. MgB2 with addition of Sb2O3 obtained by spark plasma sintering technique

Authors: Burdusel, M; Aldica, G; Popa, S; Enculescu, M; Badica, P

Published: APR 2012, JOURNAL OF MATERIALS SCIENCE, 47, 3836, DOI: 10.1007/s10853-011-6238-5

Superconducting bulks of MgB2 with addition of Sb2O3 and Sb with different stoichiometric compositions ((MgB2) + (Sb2O3) (x) , x = 0.0025, 0.005, 0.015, and (MgB2) + (Sb)(y), y = 0.01) were obtained by the Spark Plasma Sintering (SPS) technique. All added samples have high density, above 95% and critical temperature, T (c), of 38.1-38.6 K. This result and XRD data suggest that Sb does not enter the lattice of MgB2. Impurity phases are Mg3Sb2, MgO, and MgB4. The optimum addition is Sb2O3 for x = 0.005. This sample shows the critical current density, J (c)(5 K, 0 T) = 4 x 10(5) A/cm(2) and J (c)(5 K, 7 T) = 6 x 10(2) A/cm(2), while the irreversibility field, H (irr) (5 K, 100 A/cm(2)) = 8.23 T. Indicated values of J (c) and H (irr) are higher than for the pristine sample. The mechanism of J (c) and H (irr) increase in the Sb2O3 added samples is complex and composed of opposite effects most probably involving morphology elements, the presence of nano metric MgB4 and the indirect influence of oxygen or oxygen and Sb. Crystallite size of MgB2 is decreasing when Sb-based additions are introduced and the effect is stronger for the Sb-metal addition. The sample with Sb-metal addition does not improve J (c) and H (irr) when compared with pristine sample.

157. ZnO morphological, structural and optical properties control by electrodeposition potential sweep rate

Authors: Matei, E; Enculescu, M; Preda, N; Enculescu, I

Published: JUN 15 2012, MATERIALS CHEMISTRY AND PHYSICS, 134, 993, DOI: 10.1016/j.matchemphys.2012.03.101

ZnO films were electrodeposited from an aqueous nitrate bath on ITO/glass substrates. The process was performed not by the usual potentiostatic approach but by using potential ramps with different sweep rates. We tested these ramps in both directions i.e. either towards electronegative (direct) or electropositive (inverse) potential. As expected, the samples prepared in different deposition conditions show different morphology, different quality of crystalline structure and different optical properties. By employing inverse ramps we prepared films with high quality structural and optical properties. We assume that in these conditions the growth is followed by an etching process which preferentially removes the areas with high defect concentration and leads to the formation of hollow hexagonal prisms. (c) 2012 Elsevier B.V. All rights reserved.

158. Synthesis of CdS nanostructures using template-assisted ammonia-free chemical bath deposition

Authors: Preda, N; Enculescu, M; Gherendi, F; Matei, E; Toimil-Molares, ME; Enculescu, I

Published: SEP 2012, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 73, 1089, DOI: 10.1016/j.jpcs.2012.05.003

CdS micro- and nano-structures (micro/nanotubes and nanostructured films) were obtained by ammonia-free chemical bath deposition using polymer templates (ion track-etched polycarbonate membranes and poly(styrene-hydroxyethyl methacrylate) nanosphere arrays). The semiconductor structures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), optical absorption, photoluminescence and electrical measurements. The diameters of CdS tubes are between 300 nm and few microns and the lengths are up to tens of micrometers. The SEM images prove that the CdS films are nanostructured due to the deposition on the polymer nanosphere arrays. For both CdS structures (tubes and films) the XRD patterns show a hexagonal phase. The optical studies reveal a band gap value of about 2.5 - 2.6 eV and a red luminescence at similar to 1.77 eV. A higher increase of conductivity is observed for illuminating the CdS nanostructured film when compared to the simple semiconductor film. This is a consequence of the periodic patterning induced by the polymer nanosphere array. (C) 2012 Elsevier Ltd. All rights reserved.

159. Optical and electrical properties of arylenevinylene compounds thin films prepared by vacuum evaporation

Authors: Rasoga, O; Vacareanu, L; Grigoras, M; Enculescu, M; Socol, M; Stanculescu, F; Ionita, I; Stanculescu, A

Published: JAN 2012, SYNTHETIC METALS, 161, 2617, DOI: 10.1016/j.synthmet.2011.10.001

This paper discusses the properties of two arylenevinylene oligomers thin films deposited by vacuum evaporation on different substrates. The morphology of the thin films was investigated by scanning electron microscopy and atomic force microscopy, and the optical properties by UV-Vis and fluorescence spectroscopy. The optical nonlinear phenomenon of two-photon absorption induced fluorescence has been evidenced in the thin films of these compounds. We have also investigated the electrical properties of semiconductor/insulator/semiconductor (ITO/oligomer/Si) heterostructures in correlation with the contact energetic barriers, morphological and structural properties of the layers. (C) 2011 Elsevier B.V. All rights reserved.

160. Enhancement of critical current density and irreversibility field by Te or TeO2 addition to MgB2 bulk processed by spark plasma sintering

Authors: Aldica, G; Popa, S; Enculescu, M; Badica, P

Published: APR 2012, SCRIPTA MATERIALIA, 66, 573, DOI: 10.1016/j.scriptamat.2012.01.006

Te metal or TeO2 were added to MgB2 ((MgB2) (A)(x), x = 0.005, 0.01, 0.03, A = addition). The mixtures were processed by spark plasma sintering. The critical current density J(c), of the samples containing the Te/TeO2 additions is enhanced at high fields and at temperatures up to 20K. The curve of J(c)(5 K, H) for the sample with optimum x(Te) = 0.01 shows no accelerated decrease up to 8 T (J(c)(5 K, 8 T) = 1.8 x 10(3) A cm(-2)). The irreversibility field of the samples containing the Te/TeO2 additions is also enhanced. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

161. Effect of aqueous comonomer solubility on the surfactant-free emulsion copolymerization of methyl methacrylate

Authors: Preda, N; Matei, E; Enculescu, M; Rusen, E; Mocanu, A; Marculescu, B; Enculescu, I

Published: JAN 2011, JOURNAL OF POLYMER RESEARCH, 18, 30, DOI: 10.1007/s10965-009-9387-3

Surfactant-free emulsion copolymerization was used to prepare methyl methacrylate-hydroxyethyl methacrylate (MMA-HEA) and methyl methacrylate-hydroxypropyl methacrylate (MMA-HPMA) latex particles. Also, glycidyl methacrylate (GMA) was grafted onto the surface of the preformed MMA-HPMA latex particles by seeded surfactant-free emulsion copolymerization. The copolymerization reactions were conducted at 75 A degrees C using a water-soluble initiator, potassium persulfate (KPS). The morphologies of copolymer latex particles were observed using Scanning electron microscopy (SEM). The influence of different reactions parameters (the MMA saturation concentration (Sr), the KPS concentration and the aqueous solubility of the comonomers (HEA or HPMA)) on the particles average diameter and particles size dispersity was investigated. The experimental results showed that the increase of initiator concentration induces in all investigated cases the increase of particles average diameter, while the presence of HEA or HPMA as comonomers in the copolymerization reaction of MMA (1,000% Sr) lead to a decrease of particles average diameter. At small KPS concentration the latex is monodisperse, the increase of the initiator concentration leading to the formation of polydisperse latex. In the case of grafting reaction of GMA onto the monodisperse preformed MMA-HEA latex particles, although the average diameter of the final particles doubles the latex remains quasi-monodisperse.

162. Silicon structuring by etching with liquid chlorine and fluorine precursors using femtosecond laser pulses

Authors: Radu, C; Simion, S; Zamfirescu, M; Ulmeanu, M; Enculescu, M; Radoiu, M

Published: AUG 1 2011, JOURNAL OF APPLIED PHYSICS, 110, DOI: 10.1063/1.3619856

The aim of this study is to investigate the micrometer and submicrometer scale structuring of silicon by liquid chlorine and fluorine precursors with 200 fs laser pulses working at both fundamental (775 nm) and frequency doubled (387 nm) wavelengths. The silicon surface was irradiated at normal incidence by immersing the Si (111) substrates in a glass container filled with liquid chlorine (CCl(4)) and fluorine (C(2)Cl(3)F(3)) precursors. We report that silicon surfaces develop an array of spikes with single step irradiation processes at 775 nm and equally at 387 nm. When irradiating the Si surface with 400 pulses at 330 mJ/cm(2) laser fluence and a 775 nm wavelength, the average height of the formed Si spikes in the case of fluorine precursors is 4.2 mu m, with a full width at half maximum of 890 nm. At the same irradiation wavelength chlorine precursors develop Si spikes 4 mu m in height and with a full width at half maximum of 2.3 mu m with irradiation of 700 pulses at 560 mJ/cm(2) laser fluence. Well ordered areas of submicrometer spikes with an average height of about 500 nm and a width of 300 nm have been created by irradiation at 387 nm by chlorine precursors, whereas the fluorine precursors fabricate spikes with an average height of 700 nm and a width of about 200 nm. Atomic force microscopy and scanning electron microscopy of the surface show that the formation of the micrometer and sub-micrometer spikes involves a combination of capillary waves on the molten silicon surface and laser-induced etching of silicon, at both 775 nm and 387 nm wavelength irradiation. The energy-dispersive x-ray measurements indicate the presence of chlorine and fluorine precursors on the structured surface. The fluorine precursors create a more ordered area of Si spikes at both micrometer and sub-micrometer scales. The potential use of patterned Si substrates with gradient topography as model scaffolds for the systematic exploration of the role of 3D micro/nano morphology on cell adhesion and growth is envisaged. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3619856]

163. 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.

164. Luminescent Dye-Doped KAP Nanorods Obtained by Template Assisted Crystallization

Authors: Enculescu, M; Neumann, R

Published: MAY 2011, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 11, 3948, DOI: 10.1166/jnn.2011.3832

Luminescent nanorods of potassium acid phthalate (KAP) doped with rhodamine 6G (Rh 6G) dye molecules were grown by template assisted crystallization. Pores with diameters ranging from tens of nanometers to few micrometers were obtained in polycarbonate foils after heavy-ion irradiation and subsequent chemical etching of the damage trails along the ion trajectories. Crystallization from solution was employed for filling of the pores with the dye-doped KAP rods. These nanostructures were characterized using scanning electron microscopy, optical absorption spectroscopy and photoluminescence detection. X-ray diffraction was used for structural analysis. The luminescence of the dye-doped rods undergoes a redshift when the diameter of the structures decreases. This shift is probably caused by increasing dye concentration in the rods with decreasing pore diameter. The luminescence originating from the Rh 6G presence is up-converted due to the second-harmonic generation in KAP.

165. 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.

166. Polymer-assisted crystallization of low-dimensional lead sulfide particles

Authors: Preda, N; Rusen, E; Enculescu, M; Matei, E; Marculescu, B; Enculescu, I

Published: AUG 2011, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 43, 1832, DOI: 10.1016/j.physe.2011.06.019

PbS micro- and nanoparticles were synthesized by a simple precipitation reaction of lead nitrate with thioacetamide in hydrosoluble polymer water solutions. The effects of four water soluble polymers: polyacrylamide (PAM), polyvinyl alcohol (PVA), polyethylene glycol (PEG) and poly-N-vinyl pyrrolidone (PVP) on the PbS crystallites morphology and structural properties were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that for the PbS particles obtained in the PVA. PEG and PVP, the (2 0 0) diffraction peak of the nanocrystals becomes dominant. The highest texture in the [2 0 0] direction was observed for the crystallites obtained in the presence of PVP. Polydisperse PbS particles with cubic morphology and size ranging from 100 nm to several microns are obtained in the case of PAM and PEG. Monodisperse cubic PbS crystallites with an average size of 200 nm are formed in the presence of PVA and PVP. (C) 2011 Elsevier B.V. All rights reserved.

167. Hydrogen Generation from Photocatalytic Silver vertical bar Zinc Oxide Nanowires: Towards Multifunctional Multisegmented Nanowire Devices

Authors: Maijenburg, AW; Rodijk, EJB; Maas, MG; Enculescu, M; Blank, DHA; ten Elshof, JE

Published: OCT 4 2011, SMALL, 7, 2713, DOI: 10.1002/smll.201101198

168. Temperature-dependent refractive index of potassium acid phthalate (KAP) in the visible and near-infrared

Authors: Moutzouris, K; Stavrakas, I; Triantis, D; Enculescu, M

Published: APR 2011, OPTICAL MATERIALS, 33, 816, DOI: 10.1016/j.optmat.2010.12.021

We report an investigation of the temperature-dependence of the refractive index of potassium acid phthalate (KAP) crystal. Refractive index measurements are based on a refractometer setup operating in a temperature range from 25 degrees C to 200 degrees C and using five different laser wavelengths in the visible and near-infrared. Temperature-dependent dispersion relations are proposed, with an average fitting quality that exceeds experimental accuracy, and compared to previous room-temperature Sellmeier equations. Consequently, the new relations are employed for the calculation of various linear and nonlinear optical properties of KAP. (C) 2011 Elsevier B.V. All rights reserved.

169. THE INFLUENCE OF SYNTHESIS PARAMETERS ON SIZE AND MORPHOLOGY OF POLY(STYRENE-HYDROXYETHYL METHACRYLATE) COLLOIDS

Authors: Preda, N; Enculescu, M; Matei, E; Enculescu, I

Published: OCT-DEC 2010, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 5, 1065, DOI:

Poly(styrene-hydroxyethyl methacrylate) [P(ST-HEMA)] latex particles were prepared by surfactant-free emulsion copolymerization. As water-soluble initiator was used potassium persulfate (KPS). The influence of different reactions parameters, such as the reaction temperature, the both monomers (ST and HEMA) concentrations and the KPS concentration on the particles average diameter and particles size dispersion was investigated. Generally monodisperse spherical particles are synthesized, but we also obtained stable large three-dimensional colloidal aggregates. These are formed by the agglomeration of monodispersed spheres in certain polymerization conditions. The P(ST-HEMA) monodispersed spheres with 350 nm average diameter were assembled into colloidal crystals using dip-coating technique. Colloidal crystals with different thickness were obtained by modifying two experimental factors, the colloidal concentration and the substrate lifting speed. The morphologies of copolymer latex particles and colloidal crystals were observed using scanning electron microscopy (SEM). The optical properties of colloidal crystals films were also investigated by transmission spectroscopy.

170. MAPLE preparation and characterization of benzil thin films

Authors: Socol, M; Socol, G; Rasoga, O; Stanculescu, F; Stanculescu, A; Mihailescu, I; Ionita, I; Preda, N; Enculescu, M; Antohe, S

Published: NOV 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1806, DOI:

In this study the Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique was used to prepare thin films from a low melting point (< 100 degrees C) organic compound (benzil). Optical properties of the films have been investigated by UV-VIS, FTIR and PL spectroscopy. Details about crystallinity were obtained by XRD measurements. FTIR spectra have confirmed the preservation of the chemical structure of the compound during the deposition process. SEM and AFM investigation have evidenced a topography of the MAPLE deposited films characterized by different grain size depending on the deposition conditions. Second harmonic generation measurements have revealed that the MAPLE deposited benzil films have preserved the optical nonliniar properties of the bulk crystalline benzil.

171. Luminescence of dye-doped KAP and KDP nanorods

Authors: Enculescu, M; Trautmann, C

Published: MAR-JUL 2010, RADIATION MEASUREMENTS, 45, 604, DOI: 10.1016/j.radmeas.2009.11.015

Rods of potassium acid phthalate (KAP) and potassium dihydrogen phosphate (KDP) doped with rhodamine 6G (Rh 6G) were grown using the template approach. Pores of hundreds of nanometers in diameter were obtained in polycarbonate (PC) foils after heavy ions irradiation and subsequent chemical etching. Crystallization from solution was used for filling the pores and the nanostructures were characterized using scanning electron microscopy and photoluminescence spectroscopy studies. SEM images of micro- and nano-rods (300 nm and 2.5 mu m diameter) indicate a crystalline growth tendency. When exciting the PC foils containing rods of 100 nm diameter emission bands appear at 581 nm for Rh 6G doped KAP and at 602 nm for Rh 6G doped KDP. A shift of the emission bands towards red was observed when the luminescent properties of the rods with diameters of 100 nm were compared with the luminescent properties of the bulk crystals and of the micrometrical sized rods. (C) 2009 Elsevier Ltd. All rights reserved.

172. SEQUENTIAL DEPOSITION OF MULTISEGMENT NANOWIRES

Authors: Matei, E; Preda, N; Enculescu, M; Ansermet, JP; Molares, MET; Enculescu, I

Published: OCT-DEC 2010, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 5, 1076, DOI:

Electrochemical replication of nanoporous membranes represents a facile approach towards the fabrication of nanostructures with tailored properties. By the template method we prepared multisegment nanowires with tailored structure. The first step of the process was the fabrication of the nanoporous template by swift heavy ion irradiation and subsequent selective etching of the ion track. The next step was to fill the pores with the desired combination of materials. In this manner, by sequential electrodeposition steps of metal and semiconductor we prepared Ni - CdTe and Ni - ZnO - Ni nanowires.

173. Nano and micro-morphology modifications of Si (100) substrate induced by femtosecond laser pulse irradiations in air, water, CCl4 and C2Cl3F3

Authors: Ionel, L; Cristescu, CP; Jipa, F; Enculescu, M; Radoiu, M; Dabu, R; Zamfirescu, M; Ulmeanu, M

Published: NOV 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1924, DOI:

The aim of this study is to investigate the influence of the different media, e.g. air, water, CCl4 (carbon tetrachloride) and C2Cl3F3 (tricloro-trifluoro-ethane), when irradiating a Si (100) substrate, with a 200 femtosecond (fs) laser pulses of a Ti:sapphire laser operating at 775 nm. Various micro and nanomorphologies could be achieved by changing the media, the laser pulse energy and the number of pulses. It is shown that the resulting Si (100) surface presents a regulated morphology in air consisting of parallel ripples and the formation of regular arrays of submicrometer spikes on Si (100) in CCl4 and C2Cl2F3, respectively. Irradiation of a Si (100) substrate immersed in water creates a regularly structured surface but it doesn't facilitate the spikes formation. The potential use of the patterned Si substrates as model scaffolds for the systematic exploration of the role of 3D micro/nano morphology on cell adhesion and growth is envisaged.

174. Morphological and optical properties of doped potassium hydrogen phthalate crystals

Authors: Enculescu, M

Published: SEP 1 2010, PHYSICA B-CONDENSED MATTER, 405, 3727, DOI: 10.1016/j.physb.2010.05.074

Potassium hydrogen phthalate (KAP) crystals doped with rhodamine 6G (Rh 6G) and polyvinylpyrrolidone (PVP) were grown by solution evaporation technique. Nucleation occurred without the use of seeds and optically transparent crystals were obtained. The grown crystals were characterized by XRD measurements performed on crystals and their powders, optical transmission and photoluminescence measurements. The influence of the dopants on the structural, morphological and optical properties of the KAP crystals was analysed. Dopants do not change the structure of the single crystals while the addition of PVP changes the morphology of crystals from pseudo-hexagonal to rhomb. Three new XRD reflections are observed in all single-crystal and powder XRD spectra and are probably (0 3 0), (0 4 0) and (0 5 0) lines. The UV cut-off and transparency of the crystals are not changed by doping. Dye-doped KAP crystals exhibit a strong emission band centred at 550 nm excited with 480 nm wavelength. For the dye-doped crystals the up-conversion was investigated and its second harmonic origins are proved using photoluminescence measurements. (C) 2010 Elsevier B.V. All rights reserved.

175. 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.

176. Optical properties of CdS electrodeposited nanowires

Authors: Matei, E; Preda, N; Enculescu, M; Sima, M; Sima, M; Enculescu, I

Published: OCT 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 1022, DOI:

Electrochemical deposition was performed in order to prepare CdS nanowires. The method employed for preparation of such high aspect ratio nanostructures was template replication. Ion track polycarbonate membranes were used as templates. The nanowires were studied by scanning electron microscopy (morphology characterization), energy dispersive X ray analysis (composition) and optical spectroscopy. Optical reflection spectroscopy was performed in order to determine the band gap value while photoluminescence spectroscopy was used for getting information regarding the point defects in the material.

177. Influence of dye concentration on optical properties of rhodamine 6G doped KAP crystals

Authors: Enculescu, M; Matei, E; Preda, N; Enculescu, I

Published: NOV 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 1212, DOI:

Crystals of potassium acid phthalate (KAP) doped with rhodamine 6G (Rh 6G) were grown by slow evaporation method from aqueous solutions. Crystals of good optical quality suitable for optical applications were obtained. Different concentrations of rhodamine 6G (10(-5) M, 2x10(-5) M, 5x10(-5) M and 10(-4) M in the growth solutions) were used in order to tune the optical properties of the crystals. Depending of the dye concentration, the absorption spectra of the dye-doped crystals show several bands in the range between 360 nm and 526 nm. The photoluminescence of the KAP crystals induced by the dye-doping reveals two emission bands peaking at 540 nm and 560 nm.

178. Growth and optical characteristics of coumarin 6 doped potassium hydrogen phthalate (KAP) crystals

Authors: Enculescu, M

Published: DEC 2009, OPTICAL MATERIALS, 32, 285, DOI: 10.1016/j.optmat.2009.08.002

Single-crystals of potassium hydrogen phthalate (KAP) doped with coumarin 6 (C6) were grown by solution evaporation technique. Powder X-ray diffraction. optical transmission and luminescence measurements were performed. The structure and morphology of the KAP crystals are not changed with the incorporation of the dye. Transparency of the dye-doped crystals is suited for non-linear optical (NLO) applications and UV cut-off is not changed when compared with the pure KAP crystals. The dye-doped crystals present an absorption band at 350 nm while the growth solution exhibits a peak at 400 nm. The doped crystals have a strong emission band at 450 nm that is excited at 350 nm and the second harmonic generating (SHG) properties are demonstrated using luminescence measurements. (C) 2009 Elsevier B.V. All rights reserved.

179. Transport properties of electrodeposited ZnO nanowires

Authors: Tazlaoanu, C; Ion, L; Enculescu, I; Sima, M; Enculescu, M; Matei, E; Neumann, R; Bazavan, R; Bazavan, D; Antohe, S

Published: MAY 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 2507, DOI: 10.1016/j.physe.2007.07.013

ZnO nanowires were electrodeposited by using a template approach. Ion track polycarbonate foils (30 mu m thick) were used as templates. Current-voltage (I-V) characteristics were recorded in the temperature range 40-300 K. I-V characteristics show a symmetric, non-linear shape, at temperatures greater than 240 K and voltages greater than 15 V. At lower temperatures, linear characteristics were recorded for the voltage range used. The temperature dependence of the electrical resistance is activated, with activation energy of 0.42 eV at temperatures greater than 240 K. (C) 2007 Elsevier B.V. All rights reserved.

180. Potassium hydrogen phthalate (KAP) micro- and nano-rods prepared by a template approach

Authors: Enculescu, M

Published: JUN 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1504, DOI:

Micro and nanorods of potassium acid phthalate (KAP) with diameters ranging from a hundred nanometers to tens of microns were obtained by solution growth in polycarbonate (PC) ion track templates. The ion track templates were produced by swift heavy ion irradiation of PC foils (e.g. U with 11.4 MeV/nucleon specific energy) and subsequently etching. After the growth the host templates were partially dissolved in dichlormethane and imagined by scanning electron microscopy. The template approach allows the fabrication of arrays of uniform nanostructures with a controlled morphology.

181. Influence of polyvinylpyrolidone as an additive in electrochemical preparation of ZnO nanowires and nanostructured thin films

Authors: Enculescu, I; Matei, E; Sima, M; Enculescu, M; Sima, M; Ghica, C

Published: MAR-APR 2008, SURFACE AND INTERFACE ANALYSIS, 40, 560, DOI: 10.1002/sia.2749

Preparation of ZnO in different nano-morphological forms became a hot topic during the last few years. This tendency was motivated by the wide field of potential applications ranging from optics to electronics and spintronics. In the present work, we deal with the preparation of ZnO nanowires and nanostructured thin films using electrochemical deposition. ZnO nanowires were grown using the template approach, namely by replicating the nanopores of polycarbonate ion track membranes. The method yields uniform arrays of nanowires with the morphology controlled by the shape and size of the templates pores. Adding polyvinylpyrolidone as an additive in the growth bath became a necessity due to the fact that polycarbonate ion track membranes are usually hydrophobic and thus filling of the nanopores with the growth electrolyte is rather difficult. In order to better understand the influence of the additive on the electrochemical deposition of such nanostructures, similar experiments were performed for the deposition of ZnO thin films. Scanning electron microscopy, X-ray diffraction and optical spectroscopy measurements were performed for characterization of the deposited structures. Copyright (c) 2008 John Wiley & Sons, Ltd.

182. Effect of additives on nickel nanowires electrochemical deposition

Authors: Matei, E; Enculescu, I; Enculescu, M; Neumann, R

Published: MAR 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 511, DOI:

The paper presents the effect of additives on nickel nanowires preparation by employing a template approach. The nanostructures were obtained by electrochemical deposition in ion track nanoporous membranes. The main goal was to find a wetting agent which increases the pores filling efficiency. Due to the fact that the polycarbonate nanoporous membranes used as templates are strongly hydrophobic problems appear when filling the nanopores with the aqueous electrochemical baths. We found that polyvinylpyrrolidone (PVP) added in the bath improves membrane wetting, thus increasing the deposition efficiency up to 80%. Electrochemical polarization and chronoamperometry were employed for identifying and studying the processes which take place in the case of cathodic deposition of nickel nanowires. Scanning electron microscopy was employed for nanostructure morphology characterization.

183. Optical spectroscopy and thermoluminescence of electrolytically colored KCl:Tl+ crystals

Authors: Polosan, S; Enculescu, M; Secu, M; Apostol, E

Published: NOV 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3011, DOI:

The paper presents the spectroscopic properties of electrolytic colored KCl:Tl and KCI:Tl+Ca crystals and the assignments of the new defects which are formed during electron injection process. The new formed defects Tl-0 and Tl-0+Ca2+ with the metal in the anionic sites, presents very high photoluminescence properties in the near infrared region. Together with those centers, the F-centers, their aggregates and the holes centers are formed during electrolytic coloring process. Their properties were studied by optical absorption (OA), photoluminescence (PL) and thermoluminescence (TL) measurements and compared with those obtained by ionizing irradiation in uncolored KCl:Tl crystals. The results suggest a more efficient Tl+-> Tl-0 process in the case of Ca2+ codoped samples due to the prolonged time of electrons injection, low temperature and high electric field.

184. Optical spectroscopy of Yb2+ ions in YbF3-doped CaF2 crystals

Authors: Nicoara, I; Lighezan, L; Enculescu, M; Enculescu, I

Published: APR 2008, JOURNAL OF CRYSTAL GROWTH, 310, 2032, DOI: 10.1016/j.jcrysgro.2007.11.183

Transparent colorless Ca1-xYbxF2+x (X = 0-0007-0.016) crystals were grown using the vertical Bridgman technique. In order to obtain efficient Yb3+-Yb2+ conversion in the as-grown crystals, a special procedure has been developed. Room temperature optical absorption spectra reveal the characteristic UV absorption bands of the Yb2+ ions in the as-grown crystals, with intensities more than 10 times higher than those reported by other authors using various conversion procedures. The influence of YbF3 content and of codoping with Pb2+ ions on the absorption and emission spectra has been studied. Room temperature emission bands in the near UV (not reported before) and in the visible spectral domain have been observed. The emission intensity depends on the dopant concentration. A comparison of our results with those obtained by other authors is also given. (c) 2007 Elsevier B.V. All rights reserved.

185. 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.

186. Nickel nanotubes prepared by electroless deposition in ion track templates

Authors: Enculescu, I; Sima, M; Enculescu, M; Matei, E; Molares, MET; Cornelius, T

Published: MAR 2008, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 2, 136, DOI:

Nickel nano- and micro- tubes were prepared by electroless deposition in ion track template membranes. By choosing the appropriate etching conditions membranes with cylindrical or conical pores were obtained allowing the preparation of cylindrical or conical tubules. The activation of the membranes was a two step process. The bath used for deposition was an acidic one. Typically for acidic bath deposition, by energy dispersive X ray analysis, a phosphorous content of up to 10 % was found in the deposit.

187. Fractal characteristics of metal clusters self-assembled in alkali halide matrices

Authors: Enculescu, M; Enculescu, I

Published: 2007, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4, NO 3, 4, +, DOI: 10.1002/pssc.200673716

Metal nanoclusters of Ag and An were obtained in alkali halide crystals (NaCl, KBr and KCl). The fractal character of the structures is proved by the fractal dimensions calculated using a home made computer program. The self aggregation of the metallic structures is governed in both cases (Ag and Au) by the DLA mechanism. This is proved by the values of the fractal dimension calculated using two methods, sandbox and box-counting, which are between 1.7 and 1.8 for Ag and for Au between 1.7 and 1.9. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

188. Preparation of metallic nanowires with magnetic properties using the template method

Authors: Enculescu, I; Sima, M; Enculescu, M; Ghica, C; Enache, M; Neumann, R

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1470, DOI:

Metallic nanowires with magnetic properties were prepared by electrochemical deposition in nanoporous ion track membranes. Thus, we prepared Co-Cu alloy and Co/Cu multilayered nanowires. The technique allows the preparation of uniform arrays of parallel nanowires with desired properties. The process of electrochemical deposition of metals in nanoporous membranes was studied by means of cyclic voltammetry and impedance spectroscopy. The influences of deposition conditions such as bath composition, temperature and deposition potential on the morphological, structural and compositional properties of the nanowires were systematically studied.

189. 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.

190. Micro and nanorods of alkali halides grown in polymer templates

Authors: Enculescu, M; Enculescu, I; Sima, M; Neumann, R; Trautmann, C

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1563, DOI:

Porous membranes containing cylindrical pores with diameters ranging from a few tens of nanometers to a few tens of micrometers were prepared by using the ion track technique. Swift heavy ions (e.g. Au with 11.4 MeV/nucleon specific energy) were used for creating the ion tracks in polycarbonate foils. Etching was performed using an aqueous solution of NaOH containing methanol. The growth of the alkali-halides micro- and nanorods was performed by evaporation from a saturated solution. The rods were imaged using scanning electron microscopy. The method opens up the possibility of growing nanostructures with applications as nanolaser media or nanoscintillators.

191. Deposition and properties of CdTe nanowires prepared by template replication

Authors: Enculescu, I; Sima, M; Enculescu, M; Enache, M; Ion, L; Antohe, S; Neumann, R

Published: MAY 2007, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 244, 1611, DOI: 10.1002/pssb.200675109

We used the template method to prepare CdTe wires with diameters ranging from 80 nm to 1 mu m. As templates we used polycarbonate and polyethilene tereplitalate ion track membranes and as the method of filling the pores of such membranes we employed electrochemical deposition. The conditions (i.e. bath composition and deposition potential) necessary to obtain the stoichiometric composition of the semiconductor were found. Scanning and transmission electron microscopy were employed for morphological characterization of the nano and microwires. Energy dispersive X-ray analysis was employed for determining the Cd/Te ratio. Selected area electron diffraction was employed for structural measurements. Reflection spectroscopy measurements were performed on nanowire arrays for determining the band gap of the deposited nanostructures. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

192. SiOx-P2O5 films: promising components in photonic structure

Authors: Vasiliu, I; Gartner, M; Anastasescu, M; Todan, L; Predoana, L; Elisa, M; Grigorescu, C; Negrila, C; Logofatu, C; Enculescu, M; Moldovan, A; Pavelescu, G; Zaharescu, M

Published: MAR 2007, OPTICAL AND QUANTUM ELECTRONICS, 39, 521, DOI: 10.1007/s11082-007-9096-2

We intend to prepare periodic multilayered structures for photonic applications. With this goal we have performed a study of some characteristics of SiO (x) -P2O5 films deposited by the sol-gel method on glass and ITO (InSnO (x) )-coated glass. The as prepared films were annealed to different temperatures (150 and 200 degrees C). The chemical composition of the samples was determined by X-ray Photoelectron Spectroscopy (XPS). The XPS results revealed the presence of P in the as-deposited films. The structural an optical properties were examined by Fourier Transform Infrared Spectroscopy (FTIR), Spectroellipsometry (SE) and UV Transmission Spectroscopy. IR spectra of the deposited films attest the interaction of an amorphous SiO2 with the H3PO4 used as a P-precursor. Refractive indices for individual SiO (x) -P2O5 determined from SE measurements show a densification of the layer structure with the increasing temperature in the thermal treatment. The UV transmission spectra revealed a lower transmission for the sol-gel SiO (x) -P2O5 films as compared to ITO/glass substrate. AFM images proved the densification of the films with annealing in agreement with the ellipsometric results.

193. 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.

194. 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.

195. Heavy ion induced damage in NaCl and KCl crystals

Authors: Enculescu, M; Schwartz, K; Trautmann, C; Toulemonde, M

Published: APR 2005, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 229, 405, DOI: 10.1016/j.nimb.2004.12.131

NaCl and KCI single crystals were irradiated with swift heavy ions (An, Ph, Bi and U) of energy between 560 and 2640 MeV. The damage induced by the ions was studied using optical absorption spectroscopy, chemical etching and small-angle X-ray scattering. The damage in the tracks is dominated by the creation of simple color centers (F and V-3 centers). Their concentration increases as a function of fluence, saturating when single tracks overlap. The F-center containingly track zone extends up to several tens of nanometers. In addition to this large track halo, there exists also a much smaller region (1-2 nm) close to the ion trajectory in which defect aggregates are formed. Indications for this track core are given by the preferential chemical etchability of ion tracks and also by the anisotropic pattern produced by small-angle X-ray scattering. This halo-core track structure is very similar as in LiF, however given by the higher mobility of the primary hole centers in NaCl and KCl, recombination with electrons is facilitated resulting in a lower efficiency for defect creation. (c) 2005 Elsevier B.V. All rights reserved.

196. Swift heavy ion irradiation effects on doped alkali halides

Authors: Enculescu, M

Published: DEC 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 3056, DOI:

The effects produced by heavy ion irradiation in KBr:Ag and KCl:Ag crystals are investigated using optical spectroscopy. For KCl, the results are compared with the effects obtained in the pure crystals. After irradiation with heavy ions up to 11.2 MeV/u specific energy, the absorption bands suffer a series of changes, related to the structure of defects and also to their dimensions. In the high Ag concentrated samples, the Ag+ ions are changing their valence to Ag- while in the samples containing Ag nanoclusters the irradiation induces changes in the nanocluster size.

197. A model for structures growth by sodium electrodiffusion in quartz crystals

Authors: Enculescu, I; Iliescu, B; Enculescu, M; Covalcica, I

Published: 2002, CRYSTAL RESEARCH AND TECHNOLOGY, 37, 874, DOI: 10.1002/1521-4079(200208)37:8<868::AID-CRAT868>3.0.CO;2-J

Dendritic structures were grown inside the quartz crystal by electrodiffusion of sodium ions from a NaCl layer at the anode. The electric field was applied along the optical axis Z and the structures were grown in the xy plane. An experimental arrangement using a pointed cathode and a graphite plate anode was employed. X ray diffraction analysis shows that the structures' chemical composition is a mixture of sodium silicates. To explain the structures' growth a model is proposed. The model is a bidimensional one. The transport of the particles along the Z axis structural channels by the electric field was taken into account by introducing a probability of generating the particles in the growth plane as a function of the distance to the cathode. The computer generated results and the experimental ones were compared and a good correlation was found.

198. 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.

199. 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.

200. Optical absorption of Ag- centres in KCl: line shape calculation

Authors: Zota, S; Enculescu, M

Published: FEB 2000, PHYSICA B, 275, 343, DOI: 10.1016/S0921-4526(99)00762-0

The line shapes of the absorption spectra of KCl: Ag- are calculated at several temperatures in the range 80-300 K and are compared with the experimental results. The complete 12 x 12 Hamiltonian matrix of the system, which includes the linear electron-lattice interaction, was diagonalized directly and the integration has been performed by the Gaussian quadrature method. The results explain most of the characteristic features experimentally observed. (C) 2000 Elsevier Science B.V. All rights reserved.

201. Pulsed Laser Deposition Films Based on CdSe-Doped Zinc Aluminophosphate Glass

Authors: Elisa, M; Iordache, SM; Iordache, AM; Rusu, MI; Socol, G; Filipescu, M; Bartha, C; Enculescu, M

Published: , , DOI: 10.1007/s11837-020-04150-3

202. MICROSTRUCTURE, MAGNETIC AND MAGNETOSTRICTIVE BEHAVIOUR IN RAPIDLY QUENCHED OFF-STOICHIOMETRIC Ni-Mn-Ga FERROMAGNETIC SHAPE MEMORY ALLOYS

Authors: Sofronie, M; Tolea, F; Enculescu, M; Pasuk, I; Popescu, B

Published: , ROMANIAN REPORTS IN PHYSICS, 2022, DOI: 503

203. Effect of starting materials and sintering temperature on microstructure and optical properties of Y2O3:Yb(3+)5 at% transparent ceramics

Authors: Yavetskiy, RP; Balabanov, AE; Parkhomenko, SV; Kryzhanovska, OS; Doroshenko, AG; Mateychenko, PV; Tolmachev, AV; Li, J; Jiang, N; Gheorghe, L; Enculescu, M

Published: , , DOI: 10.1007/s40145-020-0416-3

Dr. Monica ENCULESCU

Scientific Researcher I

Projects

1. Molecularly imprinted nanofluidic biosensors for the detection of human derived proteins

2. Plasmon enhancement of dye-doped polymer nanofibers’ light emissions

3. Quasi one-dimensional photonic crystals based on refractive index control of polymer nanofibers

Publications

1. PEDOT:PSS based electrospun nanofibres used as trigger for fibroblasts differentiation

2. Albumin-Rutin Nanoparticles: Design, Characterization, and Biophysical Evaluation

3. Reduced graphene oxide-functionalized zinc oxide nanorods as promising nanocomposites for white light emitting diodes and reliable UV photodetection devices

4. Kinetics and the Effect of Thermal Treatments on the Martensitic Transformation and Magnetic Properties in Ni49Mn32Ga19 Ferromagnetic Shape Memory Ribbons

5. Structural, Frequency and Temperature Dependent Dielectric Properties of Zn2+ Substituted Ni-Co Based Spinel Ferrite (ZnxNi0.8-xCo0.2Fe2O4)

6. Organic Light-Emitting Diodes with Electrospun Electrodes for Double-Side Emissions

7. Influence of on-off pulsed current pattern on processes during spark plasma sintering of MgB2 superconductor

8. Kinetics and the Effect of Thermal Treatments on the Martensitic Transformation and Magnetic Properties in Ni49Mn32Ga19 Ferromagnetic Shape Memory Ribbons

9. Growth and characterization of Cu-Ni-Sn-S films electrodeposited at different applied potentials

10. Thermoelectric properties of p-type Mg2Si0.3Sn0.7 doped with silver and gallium

11. Carbon Inks-Based Screen-Printed Electrodes for Qualitative Analysis of Amino Acids

12. Preparation of 82Se thin films with trigonal hexagonal crystal structure for in-beam nuclear structure experiments

13. COMPARATIVE STUDY ON TiO2 NANOPARTICLES OBTAINED BY PRECIPITATION AND SOL-GEL

14. Microengineering Design for Advanced W-Based Bulk Materials with Improved Properties

15. Development and Characterization of Electrospun Composites Built on Polycaprolactone and Cerium-Containing Phases

16. Structural, Frequency and Temperature Dependent Dielectric Properties of Zn2+ Substituted Ni-Co Based Spinel Ferrite (ZnxNi0.8-xCo0.2Fe2O4)

17. Burdock-Derived Composites Based on Biogenic Gold, Silver Chloride and Zinc Oxide Particles as Green Multifunctional Platforms for Biomedical Applications and Environmental Protection

18. TiO2 Phase Ratio's Contribution to the Photocatalytic Activity

19. A Nanocomposite Sol-Gel Film Based on PbS Quantum Dots Embedded into an Amorphous Host Inorganic Matrix

20. Bulk MgB2 superconductor for levitation applications fabricated with boron processed by different routes

21. Nanostructured PbS-Doped Inorganic Film Synthesized by Sol-Gel Route

22. Investigations Regarding the Addition of ZnO and Li2O-TiO2 to Phosphate-Tellurite Glasses: Structural, Chemical, and Mechanical Properties

23. The inclusion of ceramic carbides dispersion in In and Yb filled CoSb3 and their effect on the thermoelectric performance

24. Influence of the synthesis parameters on the transport properties of Mg2Si0.4Sn0.6 solid solutions produced by melting and spark plasma sintering

25. Monodispersed nanoplatelets of samarium oxides for biosensing applications in biological fluids

26. MICROSTRUCTURE, MAGNETIC AND MAGNETOSTRICTIVE BEHAVIOUR IN RAPIDLY QUENCHED OFF-STOICHIOMETRIC Ni-Mn-Ga FERROMAGNETIC SHAPE MEMORY ALLOYS

27. MgB2 with Addition of Cubic BN and Ge2C6H10O7 Obtained by Spark Plasma Sintering Technique

28. Charge transport mechanisms in free-standing devices with electrospun electrodes

29. Microwave and Terahertz Properties of Spark-Plasma-Sintered Zr0.8Sn0.2TiO4 Ceramics

30. Bulk and surface characteristics of co-electrodeposited Cu2FeSnS4 thin films sulfurized at different annealing temperatures

31. Effect of chlorine and bromine on the perovskite crystal growth in mesoscopic heterojunction photovoltaic device

32. Electrochemical Deposition of ZnO Nanowires on CVD-Graphene/Copper Substrates

33. Growth and characterization of 3.5 at.% Nd:LGSB bifunctional crystal

34. Structural, morphological and optical properties of Cu-Fe-Sn-S thin films prepared by electrodeposition at fixed applied potential

35. Redox Mechanism of Azathioprine and Its Interaction with DNA

36. MgB2 powders and bioevaluation of their interaction with planktonic microbes, biofilms, and tumor cells

37. Pulsed Laser Deposition Films Based on CdSe-Doped Zinc Aluminophosphate Glass

38. Effect of starting materials and sintering temperature on microstructure and optical properties of Y2O3:Yb(3+)5 at% transparent ceramics

39. Screen-Printed Carbon Electrodes Modified with Double-Walled Carbon Nanotubes Functionalized with Polypyrrole and Their Electrochemical Processes in the Presence of Folic Acid

40. Intrinsic Dielectric Loss in Zr0.8Sn0.2TiO4 Ceramics Investigated by Terahertz Time Domain Spectroscopy

41. Magnetic and Magnetostrictive Properties of Ni50Mn20Ga27Cu3 Rapidly Quenched Ribbons

42. Structural, magnetic and magnetostrictive properties of the ternary iron-palladium-silicon ferromagnetic shape memory ribbons

43. Cytotoxicity, Antioxidant, Antibacterial, and Photocatalytic Activities of ZnO-CdS Powders (vol 13, 182, 2020)

44. The Physico-Chemical Properties and Exploratory Real-Time Cell Analysis of Hydroxyapatite Nanopowders Substituted with Ce, Mg, Sr, and Zn (0.5-5 at.%)

45. Antibacterial composite coatings of MgB2 powders embedded in PVP matrix

46. Secondary phases and their influence on optical and electrical properties of electrodeposited Cu2FeSnS4 films

47. Influences of Dispersions' Shapes and Processing in Magnetic Field on Thermal Conductibility of PDMS-Fe3O4 Composites

48. Fabrication of ZnO and TiO2 Nanotubes via Flexible Electro-Spun Nanofibers for Photocatalytic Applications

49. Multifunctional GaFeO3 Obtained via Mechanochemical Activation Followed by Calcination of Equimolar Nano-System Ga2O3-Fe2O3

50. EFFECT OF Mn SUBSTITUTION ON THE STRUCTURAL, MAGNETIC AND MAGNETOSTRICTIVE PROPERTIES OF Fe-Pd FERROMAGNETIC SHAPE MEMORY RIBBONS

51. Cytotoxicity, Antioxidant, Antibacterial, and Photocatalytic Activities of ZnO-CdS Powders

52. Biomorphic 3D fibrous networks based on ZnO, CuO and ZnO-CuO composite nanostructures prepared from eggshell membranes

53. Adsorption, wicking behavior and photodegradation tests of Rhodamine B solution upon wool substrates

54. Synthesis of Core-Double Shell Nylon-ZnO/Polypyrrole Electrospun Nanofibers

55. Performant Composite Materials Based on Oxide Semiconductors and Metallic Nanoparticles Generated from Cloves and Mandarin Peel Extracts

56. Novel Ecogenic Plasmonic Biohybrids as Multifunctional Bioactive Coatings

57. Reticulated Mesoporous TiO2 Scaffold, Fabricated by Spray Coating, for Large-Area Perovskite Solar Cells

58. Magneto-functionalities of La 1-x A x MnO 3 (A = K; Ba) synthesized by flash combustion method

59. Graphene Oxide Concentration Effect on the Optoelectronic Properties of ZnO/GO Nanocomposites

60. Spectroscopic investigations of Pr3+ ions doped CNGG and CLNGG single crystals

61. Development of W-monoblock divertor components with embedded thermal barrier interfaces

62. Prototype Orthopedic Bone Plates 3D Printed by Laser Melting Deposition

63. PCL-ZnO/TiO2/HAp Electrospun Composite Fibers with Applications in Tissue Engineering

64. Thermophysical and mechanical properties of W-Cu laminates produced by FAST joining

65. Effect of high gamma radiations on physical properties of In2S3 thin films grown by chemical bath deposition for buffer layer applications

66. Highly transparent Yb:Y2O3 ceramics obtained by solid-state reaction and combined sintering procedures

67. Physical properties investigation of samarium doped calcium sulfate thin films under high gamma irradiations for space photovoltaic and dosimetric applications

68. Nanostructured palladium doped nickel electrodes for immobilization of oxidases through nickel nanoparticles

69. Hierarchical functionalization of electrospun fibers by electrodeposition of zinc oxide nanostructures

70. Effect of green body annealing on laser performance of YAG:Nd3+ ceramics

71. High temperature thermo-physical properties of SPS-edW-Cu functional gradient materials

72. White-Light Emission of Dye-Doped Polymer Submicronic Fibers Produced by Electrospinning

73. Magneto-optical properties of Ce3+ and Tb3+-doped silico-phosphate sol-gel thin films

8. Kinetics and the Effect of Thermal Treatments on the Martensitic Transformation and Magnetic Properties in Ni₄₉Mn₃₂Ga₁₉ Ferromagnetic Shape Memory Ribbons

16. Structural, Frequency and Temperature Dependent Dielectric Properties of Zn²⁺ Substituted Ni-Co Based Spinel Ferrite (Zn_xNi_0.8-xCo_0.2Fe₂O₄)

18. TiO₂ Phase Ratio's Contribution to the Photocatalytic Activity