NIMP| Elena MATEI, Author at NIMP

Projects

1. Metal-oxide-metal nanowires for sensors development

Project Type: PCE, Start Date: 2021-01-04 End Date: 2023-12-31

Publications

1. Palladium-Coated Submicron Electrospun Polymeric Fibers with Immobilized Uricase for Uric Acid Determination in Body Fluids

Authors: Leote, RJB; Crisan, DN; Matei, E; Enculescu, I; Diculescu, VC

Published: 2024 FEB 12 2024, ACS APPLIED POLYMER MATERIALS, 6, DOI: 10.1021/acsapm.3c02811

This work describes the development of a flexible uric acid (UA) biosensor based on palladium-coated submicrometer electrospun poly(methylmethacrylate) (PMMA) fibers metalized with gold and attached to polyethylene terephthalate substrate (Pd/Au/PMMA/PET). The morphological characterization conducted by scanning electron microscopy revealed nanoscale Pd dendritic structures. Electrochemical investigations in the absence and in the presence of redox probes demonstrated that these Pd nanostructures are responsible for a six-fold increase in the electroactive area and enhanced electron transfer kinetics when compared to the gold-coated electrospun fibers. The UA biosensor obtained by immobilizing the uricase enzyme (UrOx) onto the Pd/Au/PMMA/PET electrode surface, allowed UA detection with a sensitivity of 431 mu A cm(-2) mM(-1) and a limit of detection of 12 mu M. Investigation of the redox reactions of hydrogen peroxide (a product of the enzymatic oxidation of UA by UrOx) at the Pd/Au/PMMA/PET electrode demonstrated that the working principle of the biosensor is based on the reduction of PdO produced at the electrode surface during the spontaneous reduction of hydrogen peroxide on Pd. This allows a biosensor operating potential of -0.05 V (vs Ag/AgCl) with high selectivity. The UrOx/Pd/Au/PMMA/PET biosensor was applied for UA detection in body fluids (sweat, urine, and blood serum) with recovery values between 98 and 105%, which were validated by high-performance liquid chromatography analysis. The stability of the device was evaluated over a period of 3 months, retaining 78% of the initial sensitivity, and reproducibility with RSD = 4.9% was achieved. The analytical performance of the biosensor under harsh mechanical deformations and at physiological temperatures demonstrated the potential applications of the device to wearable sensing platforms.

2. Optical characterization of Sm3+doped phosphate glasses for potential orange laser applications

Authors: Bayoudhi, D; Bouzidi, C; Matei, E; Secu, M; Galca, AC

Published: JAN 2024, JOURNAL OF LUMINESCENCE, 265, 120204, DOI: 10.1016/j.jlumin.2023.120204

Undoped and Sm3+doped 45P2O5-45Na2O-2Al2O3-8BaO glasses were synthesized by the melt-quenching technique. The glass structure and luminescence properties were investigated by using Raman spectroscopy, scanning electron microscopy (SEM), spectroscopic ellipsometry, Judd-Ofelt theory and photoluminescence. Electron microscopy showed the homogeneity of samples. Raman spectroscopy revealed that the overall struc-ture of the glass was unaffected by the doping of Sm3+ and ellipsometry was used to measure the optical constants. Judd-Ofelt (JO) analysis was performed on the absorption bands of Sm3+ (4f5) and the three phenomenological parameters (omega 2, omega 4, and omega 6) were computed and then used to determine radiative properties such as the radiative transition probability (Ar), the fluorescent branching ratio (beta r), the stimulated emission cross-section (sigma e) and the radiative lifetime (tau rad). Photoluminescence (PL) spectrum showed the typical four transitions of Sm3+ at wavelengths of 564, 600, 645 and 703 nm corresponding to 4G5/2 -> 6H5/2, 6H7/2, 6H9/2 and 6H11/2, respectively. The spectroscopic quality factors omega 4/omega 6, the predicted lifetime (tau rad) calculated using the JO method and the experimentally lifetime (tau exp) for the 4G5/2level were calculated and discussed. The glass color purity is as high as 98%, which makes it a potential candidate for laser emission.

3. Antimicrobial and Antioxidant Properties of Polyvinyl Alcohol Biocomposite Films Containing Ferulic Acid and Cellulose Extracted from Robinia Pseudoacacia Pods

Authors: Marinas, IC; Oprea, E; Gaboreanu, DM; Matei, E; Nedelcu, L; Zgura, I; Angheloiu, M; Chifiriuc, MC

Published: DEC 31 2024, JOURNAL OF NATURAL FIBERS, 21, 2355297, DOI: 10.1080/15440478.2024.2355297

4. Palladium-Coated Submicron Electrospun Polymeric Fibers with Immobilized Uricase for Uric Acid Determination in Body Fluids

Authors: Leote, RJB; Crisan, DN; Matei, E; Enculescu, I; Diculescu, VC

Published: FEB 12 2024, ACS APPLIED POLYMER MATERIALS, 6, DOI: 10.1021/acsapm.3c02811

5. Atomically Thin MoS₂ Layers Selectively Grown on Mo Patterned Substrates for Field-Effect-Controlled Photosensors

Authors: Stavarache, I; Palade, C; Slav, A; Dascalescu, I; Lepadatu, AM; Trupina, L; Matei, E; Ciurea, ML; Stoica, T

Published: FEB 28 2024, ACS APPLIED NANO MATERIALS, 7, DOI: 10.1021/acsanm.3c05809

Selective growth of 2D MoS2 layers on patterned substrates is highly desired for easy fabrication of devices. Selectively grown 2D MoS2 on Mo patterned substrates for the formation of intimate metallic contact was obtained by a Mo-CVD method in which MoO2 from an oxidized Mo pattern and S powder are the growth precursors. Mo films were deposited by magnetron sputtering on SiO2(300 nm)/c-Si substrates and patterned by photolithography techniques for obtaining Mo strips and finger contact structures, with the gap between the strips and finger varied from 5 to 20 mu m. The filling of the gap by selectively grown atomically thin MoS2 plates of 1-2 monolayers (MLs) was demonstrated by scanning electron microscopy and atomic force microscopy imaging. Field effect devices for the characterization of the photosensitivity of selectively grown MoS2 have been fabricated from finger contact structures. The dark current is drastically reduced from 10(-9) to 10(-13)-10(-14) A by varying the gate voltage from +7 to -7 V, showing the n-type semiconductor behavior of the selectively grown 2D MoS2. High photosensitivity of 10(5) (%) was obtained for 4.5 x 10(-4) mW/cm(2) at 650 nm wavelength illumination. The spectral responsivity reaches values of 15-25 A/W at 600 nm wavelength and shows an energy onset of 1.72-1.77 eV corresponding to about 2 ML MoS2. The carrier-trapping effect responsible for the slow part of the device response can be caused by structural defects and also by adsorbed molecules like in gas sensors.

6. Structural and magneto-optical investigations of citrate sol-gel derived barium hexaferrite nanocrystalline powder

Authors: Secu, M; Secu, CE; Matei, E; Negrilla, C; Turchenko, V; Radu, C; Polosan, S

Published: MAY 5 2024, JOURNAL OF ALLOYS AND COMPOUNDS, 983, 173897, DOI: 10.1016/j.jallcom.2024.173897

Magneto-optical measurements enable the identification of Fe2+ and Fe3+ in the R and S blocks of BaFe12O19 Mhexaferrite powder obtained by sol -gel processing, followed by thermal annealing at 900 C for 3 hours. The ferromagnetic phase is evidenced by the spin-majority configuration (Fe3+) due to their unpaired electrons between d -d orbitals, while the Fe2+ in the low spin possesses diamagnetic behavior strongly dependent on the surrounded crystal field. Additionally, the irradiation with gamma rays changes the ratio between Fe2+/Fe3+, mainly on the surface of BaFe12O19 nanocrystals. These changes were confirmed by X-ray Photoelectron Spectroscopy measurements, in which the concentration of Fe2+ increased from 69% to 82%, while the one of Fe3+ decreased from 31% to 18%. he thermoluminescent measurements reveal the same changes of Fe3+ in Fe2+ by electron capturing during irradiation, which is released as a red emission after recombination processes. The changes are explained by the increasing of some Fe-O bonds along the c-axis, mainly due to breaking a part of these bonds. The X-ray analysis confirms the changing of the parameters for the BaFe12O19 hexagonal structure.

7. GRAPHENE FOR ELECTRONIC DEVICES - SYNTHESIS AND CHARACTERIZATION

Authors: Apostol, M; Enache, A; Diculescu, V; Tite, T; Onea, M; Enculescu, I; Matei, E; Andronescu, E

Published: 2024, UNIVERSITY POLITEHNICA OF BUCHAREST SCIENTIFIC BULLETIN SERIES B-CHEMISTRY AND MATERIALS SCIENCE, 86, DOI:

In this paper, graphene was obtained on a copper substrate using the CVD method, and then it was transferred to various substrates such as glass and SiO2/Si patterned with metallic interdigitated electrodes. The graphene thus obtained was characterized using Raman spectroscopy, scanning electron microscopy (SEM), current-voltage measurements, and electrochemical methods, in order to be used for sensing applications.

8. Abundant Catalytic Edge Sites in Few-Layer Horizontally Aligned MoS₂ Nanosheets Grown by Space-Confined Chemical Vapor Deposition

Authors: Velea, A; Buruiana, AT; Mihai, C; Matei, E; Tite, T; Sava, F

Published: JUN 2024, CRYSTALS, 14, 551, DOI: 10.3390/cryst14060551

Recently, a smart strategy for two-dimensional (2D) materials synthesis has emerged, namely space-confined chemical vapor deposition (CVD). Its extreme case is the microreactor method, in which the growth substrate is face-to-face stacked on the source substrate. In order to grow 2D transition metal dichalcogenides by this method, transition metal oxides, dispersed in very small amounts on the source substrate, are used as source materials in most of the published reports. In this paper, a colloidal dispersion of MoS2 in saline solution is used and MoS2 nanosheets with various shapes, sizes (between 5 and 60 mu m) and thicknesses (2-4 layers) have been synthesized. Small MoS2 flakes (regular or defective) are present on the surface of the nanosheets. Catalytic sites, undercoordinated atoms located at the edges of MoS2 flakes and nanosheets, are produced in a high number by a layer-plus-island (Stranski-Krastanov) growth mechanism. Several double-resonance Raman bands (at 147, 177, 187, 225, 247, 375 cm(-1)) are assignable to single phonon processes in which the excited electron is elastically scattered on a defect. The narrow 247 cm(-1) peak is identified as a topological defect-activated peak. These findings highlight the potential of defect engineering in material property optimization, particularly for solar water splitting applications.

9. Two-step process for the fabrication of direct FLG\MoS₂ heterostructures

Authors: Buruiana, AT; Bocirnea, AE; Sava, F; Matei, E; Tite, T; Mariana, A; Simandan, ID; Galca, AC; Velea, A

Published: AUG 1 2024, MATERIALS CHEMISTRY AND PHYSICS, 322, 129530, DOI: 10.1016/j.matchemphys.2024.129530

MoS2 has proven its efficacy in flexible electronics, transistor devices, and various biological and chemical applications. However, it is still challenging to achieve large-area MoS2 monolayers with desired material quality and electrical properties to fulfill the requirement for practical applications. Moreover, the main strategy for the preparation of a 2D heterostructure it is based on the sequential stacking of the layered materials using wet or dry transfer methods which introduces many defects. This paper presents an economically viable and straightforward two-step methodology to obtain MoS2 thin films, encompassing magnetron sputtering deposition of Mo and subsequent annealing in a sulfur-rich environment. This approach successfully yielded MoS2 thin films on Si\SiO2 substrates. Additionally, heterostructures consisting of few layer graphene (FLG) and MoS2 were directly obtained using the same method. The utilization of grazing incidence X-ray diffraction verified the formation of the hexagonal MoS2 phase, a finding further confirmed by Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) investigations revealed the successful sulfurization process, with surface-bound oxides forming only subsequent to air exposure. Comprehensive assessment involving X-ray reflectivity, atomic force microscopy and XPS collectively inferred the fabrication of thin films comprised of a small number of MoS2 layers covering the entire substrate. Electrical assessments exhibited an electrical hysteresis, demonstrating its potential for memristor applications. Overall, this study outlines a cost-effective fabrication method for producing nanoscale MoS2 thin films with excellent properties, avoiding the use of toxic gases such as H2S. These findings contribute to the potential development of cutting-edge applications.

10. Biocompatible and antimicrobial chitosan/PVP/PEO/PAA/AgNP composite hydrogels synthesized by e-beam cross-linking

Authors: Demeter, M; Calina, I; Scarisoreanu, A; Mitran, V; Popa, M; Cîmpean, A; Chifiriuc, MC; Micutz, M; Matei, E; Mitu, B

Published: MAR 2024, RADIATION PHYSICS AND CHEMISTRY, 216, 111391, DOI: 10.1016/j.radphyschem.2023.111391

Novel biocompatible composite hydrogels with good elastic and antimicrobial properties have been fabricated by e-beam cross-linking using chitosan and water-soluble polymers mixed with commercial silver nanoparticles (AgNP). Hydrogels having different formulations were characterized by rheological, swelling, FTIR, SEM, and biodegradation measurements. The network structure, biocompatibility, and antimicrobial properties were evaluated as well. The composite hydrogels showed higher stability and absorb large amounts of fluids specific to an infected wound without losing structural integrity. The rheological, SEM, and network structure results demonstrate that at above 0.1 mg/mL AgNP, hydrogels with high cross-linking density are obtained. The in vitro response of fibroblasts proved the high biocompatibility of the hydrogel's composites. The antimicrobial activity is directly influenced by the amount of AgNP and cross-linking degree of the hydrogel. Significant antimicrobial activity was recorded against Gram-negative bacteria, while for the Gram-positive ones, the growth inhibition seems to require a decrease of the cross-linking degree.

11. Physico-chemical and pro-wound healing properties of microporous cellulosic sponge from Gleditsia triacanthos pods functionalized with Phytolacca americana fruit extract

Authors: Marinas, IC; Pircalabioru, GG; Oprea, E; Geana, EI; Zgura, I; Romanitan, C; Matei, E; Angheloiu, M; Brincoveanu, O; Georgescu, M; Chifiriuc, MC

Published: NOV 2023, CELLULOSE, 30, DOI: 10.1007/s10570-023-05491-3

This study aimed to exploit two invasive plant species to develop a novel, multifunctional, bioactive wound dressing based on a microporous cellulosic sponge (CS) from Gleditsia triacanthos pods and functionalizing them with Phytolacca americana fruit extract. The CS was functionalized, lyophilized, and characterized by Attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, contact angle, water absorption, and retention capacity. In addition, two parameters were evaluated in temporal dynamics: controlled release of phenolic compounds and antioxidant activities. The hemolytic index, blood clotting kinetics, lactate dehydrogenase release, and wound scratch assays proved their hemo- and bio-compatibility, as well as their ability to promote cell proliferation and migration promoting-activity and to inhibit microbial growth. Furthermore, the obtained spongious material exhibited an anti-inflammatory effect by modulating the macrophages' secretion profile of IL-6 and IL-10. In conclusion, the microporous cellulosic sponge obtained from G. triacanthos could be used as a vehicle to ensure the controlled release of bioactive principles with pro-wound healing activities extracted from invasive plants. [GRAPHICS] .

12. 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.

13. Hydroxyapatite Thin Films of Marine Origin as Sustainable Candidates for Dental Implants

Authors: Dorcioman, G; Grumezescu, V; Stan, GE; Chifiriuc, MC; Gradisteanu, GP; Miculescu, F; Matei, E; Popescu-Pelin, G; Zgura, I; Craciun, V; Oktar, FN; Duta, L

Published: APR 2023, PHARMACEUTICS, 15, 1294, DOI: 10.3390/pharmaceutics15041294

Novel biomaterials with promising bone regeneration potential, derived from rich, renewable, and cheap sources, are reported. Thus, thin films were synthesized from marine-derived (i.e., from fish bones and seashells) hydroxyapatite (MdHA) by pulsed laser deposition (PLD) technique. Besides the physical-chemical and mechanical investigations, the deposited thin films were also evaluated in vitro using dedicated cytocompatibility and antimicrobial assays. The morphological examination of MdHA films revealed the fabrication of rough surfaces, which were shown to favor good cell adhesion, and furthermore could foster the in-situ anchorage of implants. The strong hydrophilic behavior of the thin films was evidenced by contact angle (CA) measurements, with values in the range of 15-18 degrees. The inferred bonding strength adherence values were superior (i.e., similar to 49 MPa) to the threshold established by ISO regulation for high-load implant coatings. After immersion in biological fluids, the growth of an apatite-based layer was noted, which indicated the good mineralization capacity of the MdHA films. All PLD films exhibited low cytotoxicity on osteoblast, fibroblast, and epithelial cells. Moreover, a persistent protective effect against bacterial and fungal colonization (i.e., 1- to 3-log reduction of E. coli, E. faecalis, and C. albicans growth) was demonstrated after 48 h of incubation, with respect to the Ti control. The good cytocompatibility and effective antimicrobial activity, along with the reduced fabrication costs from sustainable sources (available in large quantities), should, therefore, recommend the MdHA materials proposed herein as innovative and viable solutions for the development of novel coatings for metallic dental implants.

14. Optical and Structural Properties of Composites Based on Poly(urethane) and TiO2 Nanowires

Authors: Stroe, M; Burlanescu, T; Paraschiv, M; Lorinczi, A; Matei, E; Ciobanu, R; Baibarac, M

Published: FEB 2023, MATERIALS, 16, 1742, DOI: 10.3390/ma16041742

This article's objective is the synthesis of new composites based on thermoplastic polyurethane (TPU) and TiO2 nanowires (NWs) as free-standing films, highlighting their structural and optical properties. The free-standing TPU-TiO2 NW films were prepared by a wet chemical method accompanied by a thermal treatment at 100 degrees C for 1 h, followed by air-drying for 2 h. X-ray diffraction (XRD) studies indicated that the starting commercial TiO2 NW sample contains TiO2 tetragonal anatase (A), cubic Ti0.91O (C), and orthorhombic Ti2O3 (OR), as well as monoclinic H2Ti3O7 (M). In the presence of TPU, an increase in the ratio between the intensities of the diffraction peaks at 43.4 degrees and 48 degrees belonging to the C and A phases of titanium dioxide, respectively, is reported. The increase in the intensity of the peak at 43.4 degrees is explained to be a consequence of the interaction of TiO2 NWs with PTU, which occurs when the formation of suboxides takes place. The variation in the ratio of the absorbance of the IR bands peaked at 765-771 cm(-1) and 3304-3315 cm(-1) from 4.68 to 4.21 and 3.83 for TPU and the TPU-TiO2 NW composites, respectively, with TiO2 NW concentration equal to 2 wt.% and 17 wt.%, indicated a decrease in the higher-order aggregates of TPU with a simultaneous increase in the hydrogen bonds established between the amide groups of TPU and the oxygen atoms of TiO2 NWs. The decrease in the ratio of the intensity of the Raman lines peaked at 658 cm(-1) and 635 cm(-1), which were assigned to the vibrational modes E-g in TiO2 A and E-g in H2Ti3O7 (ITiO2-A/I-H2Ti3O7), respectively, from 3.45 in TiO2 NWs to 0.94-0.96 in the TPU-TiO2 NW composites, which indicates that the adsorption of TPU onto TiO2 NWs involves an exchange reaction of TPU in the presence of TiO2 NWs, followed by the formation of new hydrogen bonds between the -NH- of the amide group and the oxygen atoms of TixO2x-mn, Ti2O3, and Ti0.91O. Photoluminescence (PL) studies highlighted a gradual decrease in the intensity of the TPU emission band, which is situated in the spectral range 380-650 nm, in the presence of TiO2 NW. After increasing the TiO2 NW concentration in the TPU-TiO2 NW composite mass from 0 wt.% to 2 wt.% and 17 wt.%, respectively, a change in the binding angle of the TPU onto the TiO2 NW surface from 12.6 degrees to 32 degrees and 45.9 degrees, respectively, took place.

15. Photocatalytic Activity of the Blends Based on TiO2 Nanoparticles and Reduced Graphene Oxide for Degradation of Acetaminophen

Authors: Daescu, M; Chivu, M; Matei, E; Negrila, C; Cramariuc, O; Baibarac, M

Published: JUN 4 2023, MOLECULES, 28, 4546, DOI: 10.3390/molecules28114546

The aim of this work is to highlight the influence of blends based on TiO2 nanoparticles and reduced graphene oxide (RGO) on the photodegradation of acetaminophen (AC). To this end, the catalysts of TiO2/RGO blends with RGO sheet concentrations equal 5, 10, and 20 wt. % were prepared by the solid-state interaction of the two constituents. The preferential adsorption of TiO2 particles onto the RGO sheets' surfaces via the water molecules on the TiO2 particle surface was demonstrated by FTIR spectroscopy. This adsorption process induced an increase in the disordered state of the RGO sheets in the presence of the TiO2 particles, as highlighted by Raman scattering and scanning electron microscopy (SEM). The novelty of this work lies in the demonstration that TiO2/RGO mixtures, obtained by the solid-phase interaction of the two constituents, allow an acetaminophen removal of up to 95.18% after 100 min of UV irradiation. This TiO2/RGO catalyst induced a higher photodegradation efficiency of AC than TiO2 due to the presence of RGO sheets, which acted as a capture agent for the photogenerated electrons of TiO2, hindering the electron-hole recombination. The reaction kinetics of AC aqueous solutions containing TiO2/RGO blends followed a complex first-order kinetic model. Another novelty of this work is the demonstration of the ability of PVC membranes modified with Au nanoparticles to act both as filters for the removal of TiO2/RGO blends after AC photodegradation and as potential SERS supports, which illustrate the vibrational properties of the reused catalyst. The reuse of the TiO2/RGO blends after the first cycle of AC photodegradation indicated their suitable stability during the five cycles of pharmaceutical compound photodegradation.

16. Multi-analytical characterization of the white inlaid decoration on the prehistoric pottery from southern Romania

Authors: Secu, M; Matei, E; Secu, C; Bartha, C; Buruiana, T; Rostas, AM; Popescu, AD; Boroneant, A; Bajenaru, R

Published: JUN 2023, SOLID STATE SCIENCES, 140, 107193, DOI: 10.1016/j.solidstatesciences.2023.107193

Complex physico-chemical investigations have been performed on white inlaid substance used in the orna-mentation of prehistoric clay artefacts from southern Romania ceramics from the Early Chalcolithic, up to the Middle/Late Bronze Age. Structural and morphological investigations of the white pigments have showed hundreds of nm up to microns size particles with calcite and hydroxyapatite (ash bone) as dominant components. The calcite was found on Early Chalcolithic pigment vessels while those where hydroxyapatite was dominant from the Middle/Late Bronze Age. FTIR spectra revealed the biogenic source of the hydroxyapatite (i.e. cremated animal bone) and the crystallinity degree values agrees with the expected temperatures of firing of the ancient furnaces; the calcite-based pigments were supposed to be filled post firing. The EPR was not able to able to provide a clear assignment of the cremated animal bones but thermoluminescence showed various sources of calcite.

17. 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.

18. 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.

19. Photocatalytic Activity of the Blends Based on TiO₂ Nanoparticles and Reduced Graphene Oxide for Degradation of Acetaminophen

Authors: Daescu, M; Chivu, M; Matei, E; Negrila, C; Cramariuc, O; Baibarac, M

Published: JUN 4 2023, MOLECULES, 28, 4546, DOI: 10.3390/molecules28114546

20. Physico-chemical and pro-wound healing properties of microporous cellulosic sponge from Gleditsia triacanthos pods functionalized with Phytolacca americana fruit extract

Authors: Marinas, IC; Pircalabioru, GG; Oprea, E; Geana, EI; Zgura, I; Romanitan, C; Matei, E; Angheloiu, M; Brincoveanu, O; Georgescu, M; Chifiriuc, MC

Published: 2023 SEP 22 2023, CELLULOSE, DOI: 10.1007/s10570-023-05491-3

21. Optical and Structural Properties of Composites Based on Poly(urethane) and TiO₂ Nanowires

Authors: Stroe, M; Burlanescu, T; Paraschiv, M; Lorinczi, A; Matei, E; Ciobanu, R; Baibarac, M

Published: FEB 2023, MATERIALS, 16, 1742, DOI: 10.3390/ma16041742

22. Hybrid nanostructures based on vertically graphenes decorated with tungsten oxide nanoparticles for enhanced capacitive performance

Authors: Coman, LG; Marcu, M; Acsente, T; Vizireanu, S; Satulu, V; Dinescu, G; Matei, E; Spataru, T; Spataru, N; Preda, L

Published: NOV 2023, DIAMOND AND RELATED MATERIALS, 139, 110316, DOI: 10.1016/j.diamond.2023.110316

Herewith, we investigated the capacitive properties of hybrid nanometric architectures consisting of tungsten oxide nanoparticles deposited on graphite (WOx/G) and graphite coated with highly-porous carbon nanowall layers (WOx/CNW/G). The deposition of the nanostructured oxide was performed by a plasma-assisted sublimation, vapor transport and condensation technique. The samples containing the CNW interlayer show superior areal capacitances making this architecture and its fabrication route promising approaches for supercapacitor applications. Thus, areal capacitances of WOx/CNW/G and WOx/G, estimated from galvanostatic chargedischarge tests (GCD) at an applied density current of 1 mA cm-2, are 1247.2 mF cm-2 and 527.3 mF cm-2, respectively. From SEM and XPS investigations, it was observed that CNW promotes the formation of a high amount of small tungsten oxide particles, homogeneously distributed on electrode surface, and facilitates the formation of highly conductive tungsten nitride species, resulting in electrodes with remarkable charge-storage capacity.

23. Pulsed laser deposited V2O3 thin-films on graphene/aluminum foil for micro-battery applications

Authors: Tite, T; Ungureanu, C; Buga, M; Stavarache, I; Matei, E; Negrila, CC; Trupina, L; Spinu-Zaulet, A; Galca, AC

Published: MAR 15 2023, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 933, 117290, DOI: 10.1016/j.jelechem.2023.117290

The development of new thin-film cathodes triggered a recent research interest in energy storage applications. Over the past years, vanadium oxides have been extensively explored as promising electrodes for batteries owing to their rich valence states and remarkable electrochemical properties. Herein, we report on the synthe-sis of undoped and Sn doped V2O3 thin-films on graphene (G)/Al foil by pulsed laser deposition followed by rapid thermal annealing in N2 at low temperature (similar to 430 degrees C). The obtaining V2O3 phase on graphene/Al foil (G/Al) has been confirmed by X-ray diffraction and Raman and X-ray photoelectron spectroscopy analyses. The synthesized vanadium oxide films were tested as cathodes in coin cells. The electrochemical properties have been systematically investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge discharge (GCD) measurements. A superior electrochemical performance was observed for the V2O3 on G/Al structures, with an initial capacity of around 300 mAh g-1, with respect to the bare G/Al electrode. The use of the Sn-doped (5 mol%) V2O3 thin-films improved slightly the initial capac-ity up to a value of ca. 311 mAh g-1. Both V2O3/G/Al and Sn-doped V2O3/G/Al exhibited excellent cycling performances after 40 cycles with a capacity maintenance at a C-rate C/20 of 317 mAh g-1. Long-term cycling test (up to 200 cycles) showed that the Sn doping could be an excellent strategy to improve the stability of the electrodes, which yielded a capacity loss of only 0.128% per cycle. Possible mechanisms are presented and dis-cussed. This work could serve as point of reference for future developments in the field of batteries employing vanadium oxide-based thin-films deposited by physical vapor deposition techniques.

24. WO₃ layer sensitized with BiVO₄ and MIL-101(Fe) as photoanode for photoelectrochemical water oxidation

Authors: Sima, M; Vasile, E; Preda, N; Matei, E; Sima, A; Negrila, C

Published: OCT 2023, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 181, 111472, DOI: 10.1016/j.jpcs.2023.111472

Thick tungsten oxide layers were prepared electrophoretically in order to be used as photoanodes in photoelectrochemical water oxidation applications. The highest photocurrent density was obtained for a WO3 layer with thickness of similar to 900 nm. Additionally, WO3/BiVO4 and WO3/BiVO4/MIL-101(Fe) heterojunctions have been fabricated using WO3 layer as substrate. WO3/BiVO4 shows an increased value of the electrochemical active surface area indicating that more sites of this photoanode are activated through the formation of the heterojunction. The small V5+ signals observed in the V 2p XPS spectra of these heterojunctions were attributed to the substitution of V5+ atoms with W6+ atoms on the surface of BiVO4. Excessive W doping of the BiVO4 film determined the decrease of the photoelectrochemical performance of WO3/BiVO4 photoanode. The significant improvement of the photoconversion efficiency of the sample decorated with MIL-101(Fe) indicated that this cocatalyst provides sites more efficiently in the photoelectrochemical process. This performance was correlated with the reduced value of the charge transfer resistance at electrode/electrolyte interface obtained from electrochemical impedance spectroscopy investigation.

25. An improved balanced replicated sampling design for preliminary screening of the tailings ponds aiming at zero-waste valorization. A Romanian case study

Authors: Pencea, I; Turcu, RN; Popescu-Arges, AC; Timis, AL; Priceputu, A; Ungureanu, C; Matei, E; Nedelcu, L; Petrescu, MI; Niculescu, F

Published: APR 1 2023, JOURNAL OF ENVIRONMENTAL MANAGEMENT, 331, 117260, DOI: 10.1016/j.jenvman.2023.117260

The scope of this study consists of setting up of an integrated cost-effective sampling & laboratory analyses procedure which delineates sampling, sub-sampling and analytical uncertainties in case of fine-grained extractive waste deposits. This procedure is designed to support the decision makers towards fine-grained waste deposits upcycling and land reclamation. This procedure consists of a balanced replicated sampling design (BRSD) coupled with a three split levels ANOVA data processing. The paper provides the readership with the mathematical backgrounds of the three split level ANOVA analysis (3L-ANOVA) and an Excel algorithm for its implementation. Also, the paper presents an example of implementation of the developed methods in the case of a Romanian iron ore tailings (IOT) old pond. The findings of the paper consist of: a) argues, based on OM, SEM-EDS, XRFS and XRD observations, that classical TOS is ineffective for fine-grained waste deposits; b) BRSD in conjunction with 3L-ANOVA analysis is the only approach fit for reliable characterization of the fine-grained stockpiles; c) sampling uncertainty is the critical factor of the uncertainty budget of the analyte concentration; d) Lilliefors approach is adequate for the hypothesis testing where or not the measurand is normal distributed; e) The outcomes of the BRDSD&3L-ANOVA investigations carried on Teliuc tailings, estimated at circa 5.5* 106 m3, consist mainly of mineral quantification at lot level i.e. quartz-54% (+/- 7%), hematite-15% (+/- 3%), calcite-11% (+/- 3%), MgO 3% (+/- 1%), Al2O3 9% (+/- 2%). The concentrations of some CRMs like Ti, V, Ba, Y, W were found at ACE limits and their associated relative expanded uncertainties overpass 50%. Thus, the expanded uncertainties clearly depict the reliability of acquired data for the decision makers regarding waste valorization. f) The IOT into Teliuc can be upcycled as minerals for cement and ceramic industries as well as for geopolymer manufacture. Also, IOT can be downcycles as filler in road construction and mine closure. Finally, the Teliuc yard can be rehabilitated with zero-waste left behind. The data exactness provided by this procedure can be increased to any desirable level through increasing the number of collected items, but the cost of sampling and analyses increases proportionally. In such circumstances, the posted approach can be tailored at the stakeholder request as to safely underpin the decision to turn fine-grained by-products into valuable secondary resources, facilitating a greater circularity of the mining industry.

26. In vitro analysis of the cytotoxic effect of two different sizes ITER-like tungsten nanoparticles on human dermal fibroblasts

Authors: Carpen, LG; Acasandrei, MA; Acsente, T; Matei, E; Lungu, I; Dinescu, G

Published: MAR 2023, HELIYON, 9, e13849, DOI: 10.1016/j.heliyon.2023.e13849

Background: Based on the current configuration of the International Thermonuclear Experimental Reactor, tungsten (W) was chosen as the armour material. Nevertheless, during operation, the expected power and temperature of plasma can trigger the formation of W dust in the plasma chamber. According to the scenario for a Loss Of Vacuum Accident (LOVA), in the case of confinement failure dust is released, which can lead to occupational or accidental exposure.Methods: For a first evidence of potential risks, fusion devices relevant W dust has been produced on purpose, using a magnetron sputtering gas aggregation source. We aimed to assess the in vitro cytotoxicity of synthesized tungsten nanoparticles (W-NPs) with diameters of 30 and 100 nm, on human BJ fibroblasts. That was systematically investigated using different cytotoxic endpoints (metabolic activity, cellular ATP, AK release and caspase-3/7 activity) and by direct observation with optical and scanning electron microscopy.Results: Increasing concentrations of W-NPs of both sizes induced cell viability decrease, but the effect was significantly higher for large W-NPs, starting from 200 mu g/mL. In direct correlation with the effect on the cell membrane integrity, high concentrations of large W-NPs appear to increase AK release in the first 24 h of treatment. On the other hand, activation of the cellular caspase 3/7 was found significantly increased after 16 h of treatment solely for low concentra-tions of small W-NPs. SEM images revealed an increased tendency of agglomeration of small W -NPs in liquid medium, but no major differences in cells development and morphology were observed after treatment. An apparent internalization of nanoparticles under the cell membrane was also identified.Conclusion: These results provide evidence for different toxicological outputs identified as mechanistic responses of BJ fibroblasts to different sizes of W-NPs, indicating also that small W -NPs (30 nm) display lower cytotoxicity compared to larger ones (100 nm).

27. Raman Spectroscopy as Spectral Tool for Assessing the Degree of Conversion after Curing of Two Resin-Based Materials Used in Restorative Dentistry

Authors: Gatin, E; Iordache, SM; Matei, E; Luculescu, CR; Iordache, AM; Grigorescu, CEA; Ilici, RR

Published: AUG 2022, DIAGNOSTICS, 12, 1993, DOI: 10.3390/diagnostics12081993

(1) Background: The treatment of dental cavities and restoration of tooth shape requires specialized materials with specific clinical properties, including being easy to model, light-cured, having a natural color, reduced shrinkage, a hardness similar to hydroxyapatite, and no leakage. The dimensional stability of resin composite materials is affected by polymerization shrinkage, degree of conversion (number of pi carbon bonds converted into sigma ones), thermal contraction and expansion, and interactions with an aqueous environment. (2) Methods: The materials used in our investigation were two composite resins with similar polymer matrices, but different filler (micro/nano filler). To evaluate the properties of samples, we employed the pycnometer technique (pycnometer from Paul Marienfeld Gmbh, Lauda-Konigshofen, Germany), RAMAN spectroscopy technique (MiniRam Equipment from B&W Tek Inc., Plainsboro Township, NJ, USA; 785 nm laser source), SEM and EDX (FEI Inspect S.). (3) Results: The size of the filler plays an important role in the polymerization: for the pycnometric results, the larger particle filler (Sample 1) seems to undergo a rapid polymerization during the 45 s curing, while the nanoparticle filer (Sample 2) needs additional curing time to fully polymerize. This is related to a much larger porosity, as proved by SEM images. The lower degree of conversion, as obtained by Raman spectroscopy, in the same geometry means that the same volume is probed for both samples, but Sample 1 is more porous, which means less amount of polymer is probed for Sample 1. (4) Conclusions: For the two composites, we obtained a degree of conversion of 59% for Sample 1 and 93% for Sample 2, after 45 s of curing.

28. 'Put variety in White': Multi-analytical investigation of the white pigments inlaid on Early Chalcolithic pottery from Southern Romania

Authors: Opris, V; Velea, A; Secu, M; Rostas, AM; Buruiana, AT; Simion, CA; Mirea, DA; Matei, E; Bartha, C; Dimache, M; Lazar, C

Published: APR 2022, JOURNAL OF ARCHAEOLOGICAL SCIENCE-REPORTS, 42, 103402, DOI: 10.1016/j.jasrep.2022.103402

The current study aims to present and discuss the results obtained by complementary archaeometric methods applied for the first time on white pigments inlaid on excised pottery of the Boian-Vidra tradition (Early Chalcolithic, c. 4900-4600 BCE). The samples came from three settlements located in Southern Romania (Sultana-Ghetarie, Vidra, and Vladiceasca). They were selected considering that the pottery was produced in approximately contemporary sites, located relatively close to each other in the same geographical region, namely the Romanian Plain. The experimental part included the analysis of local samples of carbonate concretions and prehistoric animal bone ash as reference materials. Archaeometric investigations consisted in applying "in-air" PIXE and EDX methods for the chemical composition, XRD and FTIR for mineralogical data, SEM for microstructure observation, and EPR for the characterisation of the paramagnetic centres. Calcite, bone ash, and silica rich sediments were identified as the primary decorating pigments. The mixtures of calcite and bone-ash observed in 13 samples were specific to the sites at Vidra and Vladiceasca. Silica-rich sediments from distant sources were the main whitening materials in two samples from Vladiceasca, while for the samples from Sultana-Ghetarie, calcite was the only whitening mineral. The results show with a high degree of confidence the use of both local (i.e., carbonate neo-formations and bone ash) and exotic (silica-rich sediments) raw materials to obtain the white pigment applied to Boian-Vidra pottery. Thus, the current data show the adaptability of the potters with respect to the surrounding resources and also provide new evidence for a vast trade network of raw materials and/or finished products in the Lower Danube area during the Early Chalcolithic. The deliberate mixing of two whitening materials from different sources could be a technological choice and may highlight complex symbolic behaviours.

29. ZnS stacking order influence on the formation of Zn-poor and Zn-rich Cu2ZnSnS4 phase

Authors: Zaki, MY; El Khouja, O; Nouneh, K; Touhami, ME; Matei, E; Azmi, S; Rusu, MI; Grigorescu, CEA; Briche, S; Boutamart, M; Badica, P; Burdusel, M; Secu, M; Pintilie, L; Galca, AC

Published: MAY 2022, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 33, DOI: 10.1007/s10854-022-08160-6

This paper reports the synthesis and characterization of Cu2ZnSnS4 (CZTS) absorber films, prepared by a two-step electrodeposition of a ZnS (zinc sulfide) binary and a CZT (copper, zinc and tin) ternary precursors on Mo/Ti/Si substrates. The as-electrodeposited ZnS/CZT and CZT/ZnS stacks were thermally treated in a tubular furnace in sulfur environment at 550 degrees C. The role of the ZnS buffer layer is to provide a zinc and sulfur reservoir, needed to complete the formation of kesterite phase. X-ray diffraction and Raman analyses revealed the formation of the CZTS phase. The surface morphology and chemical composition of the films were studied using a scanning electron microscope. The bandgap values inferred from diffuse reflectance data, are discussed with respect to the stoichiometry which is considerably affected by the order of the stacks. Room-temperature photoluminescence of the CZT/ZnS sample showed a board PL band of 1.51 eV. It was found that the film with a ZnS layer on top is preferred for the formation of a Zn-rich single CZTS phase.

30. 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.

31. ZnS stacking order influence on the formation of Zn-poor and Zn-rich Cu2ZnSnS4 phase

Authors: Zaki, MY; El Khouja, O; Nouneh, K; Touhami, ME; Matei, E; Azmi, S; Rusu, MI; Grigorescu, CEA; Briche, S; Boutamart, M; Badica, P; Burdusel, M; Secu, M; Pintilie, L; Galca, AC

Published: APR 2022, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, DOI: 10.1007/s10854-022-08160-6

32. 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.

33. Structural and transport properties of Cu2CoSnS4 films prepared by spray pyrolysis

Authors: El Khouja, O; Assahsahi, I; Nouneh, K; Touhami, ME; Secu, M; Talbi, A; Khaaissa, Y; Matei, E; Stancu, V; Galatanu, A; Galca, AC

Published: NOV 1 2022, CERAMICS INTERNATIONAL, 48, DOI: 10.1016/j.ceramint.2022.07.185

In the present work, stannite Cu2CoSnS4 (CCTS) films were elaborated using spray pyrolysis method on soda-lime glass, at different deposition temperatures (T-d = 250, 300, and 350 degrees C), followed by different chosen sulfurization temperatures (T-s = 450, 500, and 550 degrees C). X-ray diffraction (XRD) revealed the nearly single-phase formation of CCTS films at 300 degrees C deposition temperature. After sulfurization in argon flow, the XRD lines become narrower, the average crystallite size expanding above 70 nm. The Raman spectroscopy analysis confirmed the stannite structure formation, as well as the presence CoS2 secondary phases, which reduces at higher sulfurization temperature (550 degrees C). The energy dispersive spectroscopy results indicated atomic ratios of Cu/Co/Sn/S close to the ideal stoichiometric ratio 2:1:1:4. The room temperature photoluminescence emission is recorded with maximum in the 1.35-1.40 eV range. Thermoelectric properties are measured up to 130 degrees C, the films show poor power factor as a result of small positive Seebeck coefficients 10-45 Of K -1 and low electrical conductivity despite of having relatively high carrier concentration (similar to 10(20) cm(-3)).

34. The Synergistic Effect of the Laser Beam on the Thermionic Vacuum Arc Method for Titanium-Doped Chromium Thin Film Deposition

Authors: Vladoiu, R; Mandes, A; Dinca, V; Ciupina, V; Matei, E; Polosan, S

Published: APR 2022, COATINGS, 12, 470, DOI: 10.3390/coatings12040470

Laser-Induced Thermionic Vacuum Arc (LTVA) provides a better way to produce uniform metallic thin films than the classical Thermionic Vacuum Arc (TVA) method. In Ti-doped chromium thin films produced using LTVA, the amorphous chromium is superimposed with small bcc chromium nanoparticles. These amorphous/crystalline structures with small crystallites induce lower roughness and electrical resistivity, reducing electron-phonon scattering and increasing charge transport across LTVA thin films. A significant shift in resistivity for the LTVA samples is observed due to electron scattering on the phonon-crystalline structures in the TVA samples which exhibit larger crystallites. Meanwhile, the wettability measurements reveal a higher contact angle, resulting in a lower surface free energy and consecutively lower dissociation energy for the LTVA-produced thin films than the TVA samples.

35. Structural and Optical Characterization of Silica Nanospheres Embedded with Monodisperse CeO2-Eu3+ Nanocrystals

Authors: Secu, C; Bartha, C; Matei, E; Radu, C; Secu, M

Published: FEB 2022, MAGNETOCHEMISTRY, 8, 22, DOI: 10.3390/magnetochemistry8020022

Luminescent nanocrystals embedded into silica microspheres were shown to be useful for silica labeling for biological applications, ensuring mechanical and chemical stability, nontoxicity, biocompatibility and optical properties. We used sol-gel technology to prepare silica nanospheres embedded with fluorescent and magnetic Eu3+(1 mol%)-doped CeO2 nanocrystals. The X-ray diffraction pattern analysis and transmission electron microscopy investigations showed CeO2:Eu3+(1 mol%) nanocrystals of about 9 nm size and Ce3+ ions substitution by the Eu3+ ions; the nanocrystals dispersed inside the nanosized silica spheres of about 400 nm diameters. The photoluminescence spectra recorded under UV-light excitation showed Eu3+ ions luminescence peaks (D-5(0)-F-7(J), J = 0-4) accompanied by a weaker 425 nm luminescence due to the silica matrix; the quantum yield was 0.14. The weak hysteresis loop and magnetization curves recorded up to 20,000 Oe showed dominantly paramagnetic behavior associated with the silica matrix; a slight opening of the hysteresis loop to a very small magnetic field (about 0.005 Oe) was due to the presence of the two rare earth ions. The photonic crystal properties of SiO2-CeO2:Eu3+(1 mol%) silica nanospheres deposited as films on quartz plates were revealed by the two weak attenuation peaks at 420 and 500 nm and were associated with the reflection from different planes. The SiO2-CeO2:Eu3+(1 mol%) nanospheres are attractive potential candidates for photonics-related applications or for multifunctional bio-labels by combining the luminescence and magnetic properties of the nanocrystals.

36. 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.

37. Capacitive Photodetector Thin-Film Cells of Cu-As2S3-Cu as Revealed by Dielectric Spectroscopy

Authors: Ganea, P; Socol, G; Zamfira, S; Cretu, N; Matei, E; Lorinczi, A

Published: FEB 2022, SENSORS, 22, 1143, DOI: 10.3390/s22031143

The As2S3-Cu interface was studied by dielectric spectroscopy measurements on Cu-As2S3-Cu thin film heterostructure samples to assess the charge carriers' contribution to the electrical properties of such an interface. Three-dimensional printed masks ensured good reproducibility during the PLD deposition of heterostructure samples. The samples were tested for electrical conductivity and AC photoconductivity by dielectric spectroscopy measurements. DC bias voltages and light were applied to the samples. The electrical capacity of the thin film heterostructure can be modified electrically and optically. We observed long-term photoconductivity with a time dependency that was not exponential, and a quick change of the electrical capacity, indicating the potential of the heterostructure cells as photodetector candidates.

38. Layered SnSe nanoflakes with anharmonic phonon properties and memristive characteristics

Authors: Buruiana, AT; Bocirnea, AE; Kuncser, AC; Tite, T; Matei, E; Mihai, C; Zawadzka, N; Olkowska-Pucko, K; Kipczak, L; Babinski, A; Molas, MR; Velea, A; Galca, AC

Published: OCT 15 2022, APPLIED SURFACE SCIENCE, 599, 153983, DOI: 10.1016/j.apsusc.2022.153983

Understanding the phonon anharmonicity and temperature-dependent behavior of phonons that affect the thermal transport properties in 2D materials is crucial for developing efficient thermoelectric and memristor devices. SnSe has attracted significant interest because of its potential applications for developing such novel devices. Here, orthorhombic SnSe nanoflakes with a thickness of less than 100 nm and oriented along the [100] crystal axis were obtained using physical vapor transport at atmospheric pressure. Polarization-resolved Raman spectroscopy of SnSe nanoflakes was performed at a temperature of 5 K. Temperature-dependent frequencies and linewidths of Raman modes in tin selenide were fitted according to the anharmonic phonon coupling theory. The results indicate that both two and three order processes are responsible for the phonon decay in tin selenide. The memristive property was confirmed by electrical measurements of SnSe devices. SnSe memristors have an operating current of 10-4 A, similar to other transition-metal dichalcogenide memristors, but are more energy efficient than memristors based on defect migration, with a threshold voltage of 3 V.

39. Temperature-induced phase transition and tunable luminescence properties of Ce3+-Mn2+-Zr4+ tri-doped LaPO4 phosphor

Authors: AitMellal, O; Oufni, L; Messous, MY; Matei, E; Rostas, AM; Galca, AC; Secu, M

Published: JUL 2022, OPTICAL MATERIALS, 129, 112567, DOI: 10.1016/j.optmat.2022.112567

Tunable blue-white-orange emitting LaPO4:Ce3+/Mn2+/Zr4+(LPCMZ) phosphors have been synthesized by co precipitation followed by calcination. The X-ray diffraction (XRD) shows the phase transition from hexagonal to monoclinic between 600 and 700 ?C, accompanied by the increase of average nanocrystallites size from 8 to 64 nm. The Raman measurements revealed the vibrational modes associated with the LPCMZ crystalline phases, where the band positions and the full width at half maximum values depend on the structural parameters and nanocrystals size. For low-temperature calcination of 500 ?C, scanning electron microscopy (SEM) revealed nanoclusters composed of thinner nanoneedles, which developed into a rod-like self-assembly shape for higher calcination temperatures at around 900 ?C. Electron paramagnetic resonance (EPR) spectroscopy reveals a broad isotropic EPR signal, assigned to agglomerated/clustered Mn2+ ions, which are dispersed only at high temperatures above 900 ?C. The photoluminescence spectra recorded under UV-excitation of Ce3+ ions showed the Mn2+ green/red (546, 630 nm) emissions due to an energy transfer (ET) between Ce3+ and Mn2+. Depending on the calcination temperature, the Mn2+ emission color can be finely adjusted from blue to white and orange.

40. New Chalcogenide Glass-Ceramics Based on Ge-Zn-Se for IR Applications

Authors: Velea, A; Sava, F; Badica, P; Burdusel, M; Mihai, C; Galca, AC; Matei, E; Buruiana, AT; El Khouja, O; Calvez, L

Published: JUL 2022, MATERIALS, 15, 5002, DOI: 10.3390/ma15145002

The consumer market requests infrared (IR) optical components, made of relatively abundant and environmentally friendly materials, to be integrated or attached to smartphones. For this purpose, three new chalcogenides samples, namely Ge23.3Zn30.0Se46.7 (d_GZSe-1), Ge26.7Zn20.0Se53.3 (d_GZSe-2) and Ba4.0Ge12.0Zn17.0Se59.0I8.0 (d_GZSe-3) were obtained by mechanical alloying and processed by spark plasma sintering into dense bulk disks. Obtaining a completely amorphous and homogeneous material proved to be difficult. d_GZSe-2 and d_GZSe-3 are glass-ceramics with the amount of the amorphous phase being 19.7 and 51.4 wt. %, while d_GZSe-1 is fully polycrystalline. Doping with barium and iodine preserves the amorphous phase formed by milling and lowers the sintering temperature from 350 degrees C to 200 degrees C. The main crystalline phase in all of the prepared samples is cubic ZnSe or cubic Zn0.5Ge0.25Se, while in d_GZSe-3 the amorphous phase contains GeSe4 clusters. The color of the first two sintered samples is black (the band gap values are 0.42 and 0.79 eV), while d_GZSe-3 is red (E-g is 1.37 eV) and is transparent in IR domain. These results are promising for future research in IR materials and thin films.

41. Hybrid Nanostructures Obtained by Transport and Condensation of Tungsten Oxide Vapours onto CNW Templates

Authors: Carpen, LG; Acsente, T; Satulu, V; Matei, E; Vizireanu, S; Bita, BI; Dinescu, G

Published: APR 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11040835

We present hybrid nanomaterial architectures, consisting of carbon nanowalls (CNW) templates decorated with tungsten oxide nanoparticles, synthesized using a mechanism based on tungsten oxide sublimation, vapor transport, followed by vapor condensation, in the absence or presence of plasma. The key steps in the decoration mechanism are the sublimation of tungsten oxides, when are exposed in vacuum at high temperature (800 degrees C), and their redeposition on colder surfaces (400-600 degrees C). The morphology and chemical composition of the hybrid architectures, as obtained from Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy, are discussed with respect to substrate nature and the physical conditions of synthesis. We pointed out that the decoration process is strongly dependent on the temperature of the CNW templates and plasma presence. Thus, the decoration process performed with plasma was effective for a wider range of template temperatures, in contrast with the decoration process performed without plasma. The results are useful for applications using the sensing and photochemical properties of tungsten oxides, and have also relevance for fusion technology, tungsten walls erosion and material redeposition being widely observed in fusion machines.

42. Design of highly transparent conductive optical coatings optimized for oblique angle light incidence

Authors: Nedelcu, N; Chiroiu, V; Munteanu, L; Girip, I; Rugina, C; Lorinczi, A; Matei, E; Sobetkii, A

Published: AUG 2021, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 127, DOI: 10.1007/s00339-021-04726-z

In this paper, three deposition techniques are combined to create a window material with high average transmission at oblique angles of incidence. Spectrophotometry and ellipsometry measurements, respectively, yield the optical constants n and k. In contrast with other analyses on the subject, a high average transmission, higher than 91% in the 450-900 nm spectral range, is obtained at incident angles of 20-25 degrees. The refractive index and extinction coefficient are determined by the Swanepoel method. The iterative optimization performed using the OpenFilters software leads to an antireflection (AR) multilayer with low reflection and high transmission. The surface quality of the films was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), which revealed compact, continuous, and smooth films.

43. 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.

44. Optical Properties of Composites Based on Poly(o-phenylenediamine), Poly(vinylenefluoride) and Double-Wall Carbon Nanotubes

Authors: Baibarac, M; Daescu, M; Matei, E; Nastac, D; Cramariuc, O

Published: AUG 2021, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, 22, DOI: 10.3390/ijms22158260

In this work, synthesis and optical properties of a new composite based on poly(o-phenylenediamine) (POPD) fiber like structures, poly(vinylidene fluoride) (PVDF) spheres and double-walled carbon nanotubes (DWNTs) are reported. As increasing the PVDF weight in the mixture of the chemical polymerization reaction of o-phenylenediamine, the presence of the PVDF spheres onto the POPD fibers surface is highlighted by scanning electron microscopy (SEM). The down-shift of the Raman line from 1421 cm(-1) to 1415 cm(-1) proves the covalent functionalization of DWNTs with the POPD-PVDF blends. The changes in the absorbance of the IR bands peaked around 840, 881, 1240 and 1402 cm(-1) indicate hindrance steric effects induced of DWNTs to the POPD fiber like structures and the PVDF spheres, as a consequence of the functionalization process of carbon nanotubes with macromolecular compounds. The presence of the PVDF spheres onto the POPD fiber like structures surface induces a POPD photoluminescence (PL) quenching process. An additional PL quenching process of the POPD-PVDF blends is reported to be induced in the presence of DWNTs. The studies of anisotropic PL highlight a change of the angle of the binding of the PVDF spheres onto the POPD fiber like structures surface from 50.2 degrees to 38 degrees when the carbon nanotubes concentration increases in the POPD-PVDF/DWNTs composites mass up to 2 wt.%.

45. The effect of fullerene layer on the aggregates formation in amyloid beta Langmuir-Blodgett films

Authors: Breazu, C; Rasoga, O; Socol, M; Ganea, P; Tite, T; Matei, E; Stanculescu, F; Stanculescu, A

Published: JAN 30 2021, APPLIED SURFACE SCIENCE, 537, DOI: 10.1016/j.apsusc.2020.147800

The investigation of the effect of carbon nanomaterials and lipids on the aggregation particularities of the amyloid beta/A beta(1-42) layers is important for understanding the generation mechanism of neuronal disorder and how it can be inhibited. Additionally, amyloids are nanomaterials with a wide area of potential applications from nanotechnology to biotechnology. This paper presents a study about the preparation of A beta(1-42) layer by two different methods, Langmuir-Blodgett (L-B) and drop cast (DC), on Si and Si covered by a layer of Buckminster fullerene, C-60, and on the effect of fullerene layer or/and cholesterol (Ch) on the generation of A beta(1-42) secondary structure forms, relevant for specific applications. AFM, SEM FTIR and Raman analysis offered details about the layer surface topography, morphology and particularities of the secondary structure generated in the process of A beta(1-42) molecules aggregation. This study showed that the presence of Ch inhibited the formation of fibrils in A beta(1-42) film deposited by L-B on Si covered by C-60 The structures developed during aggregation were correlated with the topography and roughness of the films. The presence of Ch determined a decrease in roughness for L-B film and increase in roughness for DC film deposited on Si covered by C-60 layer.

46. Hard/soft effects of multivalence co-dopants in correlation with their location in PZT ceramics

Authors: Amarande, L; Cioangher, MC; Toma, V; Miclea, CF; Stefan, M; Pasuk, I; Iuga, AR; Negrila, C; Matei, E; Palici, AM; Joita, AC

Published: DEC 1 2021, CERAMICS INTERNATIONAL, 47, 33389, DOI: 10.1016/j.ceramint.2021.08.243

Piezoelectric hard/soft effects of multivalence co-dopants (Sb and Mn) in correlation with their location in the lattice, were investigated in PZT ceramics, prepared by conventional ceramic technology, with the following compositions: Pb0.98Sr0.02 ((Ti0.49Zr0.51)(1-0.015-x)Mn0.015Sbx)O-3 with x = 0, 0.005, 0.01, 0.02, 0.03, where antimony was initially assumed to substitute for Ti/Zr ions. The antimony valence state was found to be +3 in all samples by X-ray Photoelectron Spectroscopy investigations. The Electron Paramagnetic Resonance spectra evidenced a steep enhancement of the Mn2+ concentration upon increasing antimony doping level, explained by a charge compensation mechanism, between the Sb3+ ions substituting Pb2+ at the A-sites and the Mn2+ ions, localized at the B-sites. The incorporation of Sb3+ at the A-site of the PZT lattice is also supported by the variation of the lattice parameters, determined by X-ray Diffraction, with the increasing Sb concentration. The investigation of the dielectric, electromechanical and ferroelectric properties evidenced a hard piezoelectric behavior, mainly attributed to the presence of large sized Mn2+ ions, localized at B-sites. Our results prove that the piezoelectric hard/soft response is decisively influenced by the interplay between multiple valence states and locations of the co-dopants, on one hand, and the charge compensation mechanisms, on the other hand. This provides indirect information about the location of some co-dopants which can substitute for both cationic sites in the PZT based ceramics.

47. Azathioprine Electrochemical Adsorption onto the Reduced Graphene Oxide Sheets in Absence and in the Presence of Polyaniline

Authors: Udrescu, A; Toulbe, N; Matei, E; Baibarac, M

Published: APR 2021, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 21, DOI: 10.1166/jnn.2021.18974

The azathioprine (AZA) electrochemical adsorption onto the screen-printed carbon electrodes (SPCE) modified with the reduced graphene oxide (RGO) sheets in the absence and in the presence of polyaniline-emeraldine salt (PANI-ES) is reported in this work. Using cyclic voltammetry(CV), in the case of the SPCE modified with the RGO sheets non-functionalized and functionalized with PANI-ES, respectively, an irreversible process at the electrode/electrolyte interface is highlighted to take place. In the case of the SPCE modified with the non-functionalized RGO sheets(SPCE-RGO), the oxidation-reduction processes induce an up-shift of the AZA Raman lines from 856 and 1011 cm(-1) to 863 and 1020 cm(-1), respectively. These variations indicate an AZA adsorption onto the surface of the SPCE modified with the RGO sheets that takes place throughtthe imidazole and pyrimidine cycles of mercaptopurine, when the generation of the pi-pi(*) bonds between the mercaptopurine structure and hexagonal carbon cycles of RGO occurs. The electrochemical functionalization of the RGO sheets with PANI-ES is proved bythe appearance of the Raman lines at 1165, 1332-1371, 1496 and 1585 and 1616 cm(-1). The oxidation-reduction processes induced at the interface of the SPCE modified with PANI-ES functionalized RGO sheets and the electrolyte consisting into a phosphate buffer (PB) and AZA lead to thegeneration of new positive charges onto the PANI macromolecular chain and the adsorption of the drug on the working electrode surface that takes place via the pi-pi(*) bonds established between the benzene/quinoide rings of PANI and the imidazole/ purine cyclesof AZA. These results indicate that the SPCE modified with the PANI-ES functionalized RGO sheets shows potential applications in the field of sensors for AZA detection.

48. Mixture of Graphene Oxide/Phosphoric Acid/Melamine as Coating for Improved Fire Protective Performance and Enhancement of Surface Electrical Properties on Wood Chipboard

Authors: Cotet, LC; Cadar, C; Mihis, A; Magyari, K; Muresan-Pop, M; Pop, LC; Mihaila, A; Szekely, I; Dragan, S; Dudescu, M; Zgura, I; Matei, E; Baia, M; Baibarac, M; Anghel, I; Baia, L

Published: APR 2021, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 21, DOI: 10.1166/jnn.2021.18959

Looking for multifunctional materials, an assessment of the performances both as fire retardant and generator of electrically conductive surfaces for a three component mixture of graphene oxide, phosphoric acid and melamine applied on wood chipboard was performed. A simple approach was used to investigate the intumescent char formation and quantify the loss mass during vertical burning tests, in which the prepared samples were exposed for a certain time interval to a flame generated by an ethanol lamp in ambient conditions. Moreover, mass loss evolution and structural changes that occur during the burning process were more comprehensive investigated by differential thermal and thermogravimetric (DTA/TGA) techniques. By comparing the performances between the wood chipboard samples without any coverage and those covered with one or multiple component mixture, an increase of protection against the fire action was noticed when the three component mixture was used. Also, an improvement of the electrical properties was observed, after flame exposure of the samples covered with multiple layers (i.e., two and three), when the three component mixture was used. Morphological and structural investigations by microscopy (optical and electronic-SEMEDX), X-ray diffraction (XRD) and spectral (Raman, FTIR) methods are described. An assessment of market potential is also discussed.

49. Vibrational and Photoluminescence Properties of Composites Based on Double-Walled Carbon Nanotubes, Poly(o-phenylenediamine) and Poly(ethylene oxide)

Authors: Daescu, M; Oprica, M; Smaranda, I; Matei, E; Nastac, D; Cramariuc, O; Cramariuc, B; Baibarac, M

Published: APR 2021, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 21, DOI: 10.1166/jnn.2021.18975

Chemical polymerization of o-phenylenediamine (OPD) in the presence of poly(ethylene oxide), double-wall carbon nanotubes (DWNTs) and ferric chloride is carried out in order to obtain composites based on the poly(o-phenylenediamine)-poly(ethylene oxide) (POPD-PEO) fibres covered and interconnected with DWNTs. Vibrational and photoluminescence properties of these composite materials as well as their morphologies are shown by infrared (IR) spectroscopy, Raman scattering, photoluminescence (PL) and scanning electron microscopy (SEM). An adsorption of DWNTs onto the POPD rods surface in the absence and in the presence of. PEO is highlighted by SEM. The vibrational changes reported by Raman scattering and IR spectroscopy prove a covalent functionalization of DWNTs with the macromolecular compound POPD which is doped with FeCl4- T ions. New hydrogen bonds are generated between POPD covalently functionalized DWNTs and hydroxyl groups of PEO according to IR spectroscopic studies. The two macromolecular compounds, POPD and POPD-PEO, show a complex emission band with maxima at 572 and 566 nm, having a shoulder at 667 nm. A significant change in the profile of the PL bands of POPD and POPD-PEO is induced in the DWNTs presence. We show that DWNTs induce (i) a diminution in the POPD PL band intensity peaked between 525-600 nm simultaneous with the increase in the intensity of the PL band situated in the 600-800 nm spectral range and (ii) an enhancement process of the emission band localized in the 475-800 nm spectral range in the case of POPD-PEO.

50. Gold coated electrospun polymeric fibres as new electrode platform for glucose oxidase immobilization

Authors: Aldea, A; Leote, RJB; Matei, E; Evanghelidis, A; Enculescu, I; Diculescu, VC

Published: JUN 2021, MICROCHEMICAL JOURNAL, 165, 106108, DOI: 10.1016/j.microc.2021.106108

Fibres of poly(methyl methacrylate) were obtained by electrospinning, subjected to coating with a gold layer and then attached on a thin polyethylene terephthalate substrate in order to obtain flexible electrodes for biosensing applications. The morphology of these electrodes, investigated by scanning electron microscopy showed multilayers of random oriented fibres of approx. 400 nm diameter. The electrochemical characterization of these flexible electrodes was performed by cyclic voltammetry and electrochemical impedance spectroscopy in acid and neutral media, in the absence and in the presence of redox probes, proving their superior performance (e.g. 5fold current density value) when compared to planar gold electrodes obtained on silicon wafers. The electrodes obtained from conductive electrospun polymeric fibres nets were tested by cyclic voltammetry and amperometry for the detection of hydrogen peroxide with a sensitivity of 0.84 mA cm-2 mM-1 and a detection limit of 20.40 ?M. The immobilization of the model enzyme glucose oxidase at the surface of the gold-coated electrospun polymeric fibres electrode was investigated and the obtained biosensor was applied for glucose determination in aqueous solutions by fixed potential amperometry with a sensitivity of 3.10 ?A cm-2 mM-1, a detection limit of 0.33 mM, and reduced interferences. Also, the practical applicability of the biosensor was tested for the detection of glucose in artificial sweat and serum samples.

51. Micrometer Sized Hexagonal Chromium Selenide Flakes for Cryogenic Temperature Sensors

Authors: Buruiana, AT; Sava, F; Iacob, N; Matei, E; Bocirnea, AE; Onea, M; Galca, AC; Mihai, C; Velea, A; Kuncser, V

Published: DEC 2021, SENSORS, 21, DOI: 10.3390/s21238084

Nanoscale thermometers with high sensitivity are needed in domains which study quantum and classical effects at cryogenic temperatures. Here, we present a micrometer sized and nanometer thick chromium selenide cryogenic temperature sensor capable of measuring a large domain of cryogenic temperatures down to tenths of K. Hexagonal Cr-Se flakes were obtained by a simple physical vapor transport method and investigated using scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray photoelectron spectroscopy measurements. The flakes were transferred onto Au contacts using a dry transfer method and resistivity measurements were performed in a temperature range from 7 K to 300 K. The collected data have been fitted by exponential functions. The excellent fit quality allowed for the further extrapolation of resistivity values down to tenths of K. It has been shown that the logarithmic sensitivity of the sensor computed over a large domain of cryogenic temperature is higher than the sensitivity of thermometers commonly used in industry and research. This study opens the way to produce Cr-Se sensors for classical and quantum cryogenic measurements.

52. 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.

53. Water oxidation at photoanodes based on hematite films and nanowire arrays

Authors: Sima, M; Matei, E; Vasile, E; Sima, A; Preda, N; Logofatu, C

Published: APR 30 2021, THIN SOLID FILMS, 724, DOI: 10.1016/j.tsf.2021.138626

In this paper we report the results of a photoelectrochemical study performed on photoanodes based on hematite nanowire arrays and films prepared on fluoride-doped tin oxide coated glass (FTO) and FTO/TiO2 substrates, respectively by hydrothermal and spray pyrolysis methods. The hematite nanowires grown on FTO/TiO2 substrate are more stable mechanically, longer (1 ?m) and their density on substrate is higher. Hematite film obtained on FTO substrate has a thickness of 92 nm covering uniformly the substrate. X-ray photoelectron spectroscopy measurements showed that hematite samples synthesized on FTO/TiO2 substrate have lower content of oxygen vacancies. The photoelectrochemical performances of the prepared photoanodes are in close connection with the presence or absence of the TiO2 underlayer, with oxygen vacancies content and with their morphological characteristics. Electrochemical impedace spectroscopy was used to investigate the charge transfer kinetics at electrode/electrolyte interface and Mott-Schottky analysis was performed to estimate the flatband potential and the carrier density. TiO2 underlayer led to the formation of defects on the samples surface which induced a positive shift of the flatband potentials compared to that of the bare hematite film. The results showed that the best density photocurrent was obtained with a photoanode of hematite nanowires grown on FTO/TiO2 substrate.

54. Silicon Metalens Fabrication from Electron Beam to UV-Nanoimprint Lithography

Authors: Baracu, AM; Avram, MA; Breazu, C; Bunea, MC; Socol, M; Stanculescu, A; Matei, E; Thrane, PCV; Dirdal, CA; Dinescu, A; Rasoga, O

Published: SEP 2021, NANOMATERIALS, 11, DOI: 10.3390/nano11092329

This study presents the design and manufacture of metasurface lenses optimized for focusing light with 1.55 mu m wavelength. The lenses are fabricated on silicon substrates using electron beam lithography, ultraviolet-nanoimprint lithography and cryogenic deep reactive-ion etching techniques. The designed metasurface makes use of the geometrical phase principle and consists of rectangular pillars with target dimensions of height h = 1200 nm, width w = 230 nm, length l = 354 nm and periodicity p = 835 nm. The simulated efficiency of the lens is 60%, while the master lenses obtained by using electron beam lithography are found to have an efficiency of 45%. The lenses subsequently fabricated via nanoimprint are characterized by an efficiency of 6%; the low efficiency is mainly attributed to the rounding of the rectangular nanostructures during the pattern transfer processes from the resist to silicon due to the presence of a thicker residual layer.

55. Rhodamine B Photodegradation in Aqueous Solutions Containing Nitrogen Doped TiO2 and Carbon Nanotubes Composites

Authors: Udrescu, A; Florica, S; Chivu, M; Mercioniu, I; Matei, E; Baibarac, M

Published: DEC 2021, MOLECULES, 26, DOI: 10.3390/molecules26237237

In this work, new results concerning the potential of mixtures based on nitrogen doped titanium dioxide (TiO2:N) and carbon nanotubes (CNTs) as possible catalyst candidates for the rhodamine B (RhB) UV photodegradation are reported. The RhB photodegradation was evaluated by UV-VIS absorption spectroscopy using samples of TiO2:N and CNTs of the type of single-walled carbon nanotubes (SWNTs), double-wall carbon nanotubes (DWNTs), multi-wall carbon nanotubes (MWNTs), and single-walled carbon nanotubes functionalized with carboxyl groups (SWNT-COOH) having various concentrations of CNTs. The best photocatalytic performance was obtained for sample containing TiO2:N and 2.5 wt.% SWNTs-COOH, when approx. 85% of dye removal was achieved after 300 min. of UV irradiation. The reaction kinetics of RhB aqueous solutions containing TiO2:N/CNT mixtures followed a complex first-order kinetic model. The TiO2:N/CNTs catalyst induced higher photodegradation efficiency of RhB than TiO2:N due to the presence of CNTs, which act as adsorbent and dispersing agent and capture the photogenerated electrons of TiO2:N hindering the electron-hole recombination.

56. Effect of ferroelectric poling on the photoelectrochemical activity of hematite-BaTiO3 nanowire arrays

Authors: Sima, M; Vasile, E; Preda, N; Sima, A; Matei, E; Logofatu, C

Published: OCT 22 2021, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 46, 36244, DOI: 10.1016/j.ijhydene.2021.08.152

Ferroelectric alpha-Fe2O3/BaTiO3 photoanodes (hematite/BT) were fabricated on FTO and FTO/TiO2 substrates using a hydrothermal process and spin coating along with thermal treatments. The prepared hematite nanowires had length under 1 mu m and the BT film was about 18 nm thick. SEM, TEM and XPS investigations prove the formation of alpha-Fe2O3/BaTiO3 heterojunction structure. The ferroelectric poling of hematite/BT heterojunction was conducted both in propylene carbonate and in air. The photoelectrochemical performance of hematite/BT photoanodes is strongly influenced by the direction of ferroelectric polarization. The positive poling of the hematite/BT prepared on FTO/TiO2 substrate produces a 40.4% photocurrent density enhancement, in comparison with not poled version of the sample. Electrochemical impedance spectroscopy measurements provided usefull information regarding the effect of ferroelectric polarization on the charge transfer kinetics at the photoanode/electrolyte interface. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

57. Poly(Vinyl Chloride) Spheres Coated with Graphene Oxide Sheets: From Synthesis to Optical Properties and Their Applications as Flame-Retardant Agents

Authors: Baibarac, M; Stingescu, L; Stroe, M; Negrila, C; Matei, E; Cotet, LC; Anghel, I; Sofran, IE; Baia, L

Published: FEB 2021, POLYMERS, 13, DOI: 10.3390/polym13040565

A new method to obtain poly(vinyl chloride) (PVC) spheres, which consists of an interaction between commercial PVC grains and hexyl ethyl cellulose and lauroyl peroxide at a temperature of 60 degrees C, is reported. The addition of the graphene oxide (GO) sheets dispersed in dimethylformamide to the reaction mixture leads to the generation of composites made of PVC spheres coated with GO sheets. Scanning electron microscopy studies have demonstrated that this method allows for the transformation of PVC grains with sizes between 75 and 227 mu m into spheres with sizes varying from 0.7 to 3.5 mu m when the GO concentration in the PVC/GO composite mass increases from 0.5 to 5 wt.%. Our studies of Raman scattering and FTIR spectroscopy highlight a series of changes that indicate the appearance of ClCH=CH-, CH2=CCl-, and/or -CH=CCl- units as a result of PVC partial dehydrogenation. New -COO- and C-OH bonds on the GO sheet surfaces are induced during the preparation of PVC spheres coated with GO sheets. A photoluminescence (PL) band with a maximum at 325 nm is reported to characterize the PVC spheres. A PVC PL quenching process is demonstrated to be induced by the increase in the concentration of the GO sheets in the PVC/GO composite mass. The perspectives regarding the use of this composite as a flame-retardant material are also reported.

58. Combining Fluorinated Polymers with Ag Nanoparticles as a Route to Enhance Optical Properties of Composite Materials

Authors: Satulu, V; Mitu, B; Ion, V; Marascu, V; Matei, E; Stancu, C; Dinescu, G

Published: AUG 2020, POLYMERS, 12, DOI: 10.3390/polym12081640

Polymer-based nanocomposites have recently received considerable attention due to their unique properties, which makes them feasible for applications in optics, sensors, energy, life sciences, etc. The present work focuses on the synthesis of nanocomposites consisting of a polytetrafluorethylene-like matrix in which metallic nano-silver are embedded, by using multiple magnetron plasmas. By successively exposing the substrate to separate RF magnetrons using as combination of target materials polytetrafluorethylene (PTFE) and silver, individual control of each deposition process is insured, allowing obtaining of structures in which silver nanoparticles are entrapped in-between two PTFE layers with given thicknesses. The topographical and morphological characteristics investigated by means of Scanning Electron Microscopy and Atomic Force Microscopy techniques evidenced the very presence of Ag nanoparticles with typical dimension 7 nm. The chemical composition at various depositing steps was evaluated through X-ray Photoelectron Spectroscopy. We show that the presence of the top PTFE layer prevents silver oxidation, while its thickness allows the tailoring of optical properties, as evidenced by spectroellipsometry. The appearance of chemical bonds between silver atoms and PTFE atoms at interfaces is observed, pointing out that despite of pure physical deposition processes, a chemical interaction between the polymeric matrix and metal is promoted by plasma.

59. Oxidation of chalcopyrite in air-equilibrated acidic solution: Inhibition with phenacyl derivatives

Authors: Chirita, P; Duinea, MI; Sarbu, LG; Birsa, LM; Baibarac, M; Sava, F; Matei, E

Published: JUL 2020, TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 30, 1942, DOI: 10.1016/S1003-6326(20)65351-1

The effects of 4-(2-hydroxyphenyl)-2-(morpholin-4-yl)-1,3-thiazole (Pr02), 1-(3,5-dibromo-2-hydroxyphenyl)-1-oxoethan-2-yl-N,N-diethyldithiocarbamate (Pr04) and 1-(5-bromo-2-hydroxy-3-methylphenyl)-1-oxoethan-2-yl-O- ethyl xanthate (Pr06) on the aqueous oxidation of chalcopyrite (CuFeS2) in air-equilibrated solution at a temperature of 25 degrees C and a pH of 2.5 were studied. The effects were investigated by using potentiodynamic polarization, electro-chemical impedance spectroscopy (EIS), scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) analysis, aqueous batch experiments, Fourier transform infrared (FTIR) spectroscopy, Raman scattering and quantum chemical calculations. It is found that the anodic current densities decrease in the order of EtOH Pr02 > Pr04 > Pr06. These results, along with those of the EIS measurements, show that Pr02, Pr04 and Pr06 are effective anodic inhibitors of chalcopyrite aqueous oxidation. Both Raman scattering and FTIR spectroscopy indicate that the elemental sulfur, polysulfide and ferric oxyhydroxides that form on the surface of the mineral are not responsible when it comes to the aqueous oxidation inhibition of chalcopyrite. Quantum chemical calculations show that the adsorption of the tested compounds on the chalcopyrite surface is energetically favorable and so, it can explain the inhibiting effects that were observed.

60. Synthesis and characterization of conducting aniline and o-anisidine nanocomposites based on montmorillonite modified clay

Authors: Kenane, A; Galca, AC; Matei, E; Yahiaoui, A; Hachemaoui, A; Benkouider, AM; Bartha, C; Istrate, MC; Galatanu, M; Rasoga, O; Stanculescu, A

Published: JAN 2020, APPLIED CLAY SCIENCE, 184, DOI: 10.1016/j.clay.2019.105395

A study on clay mineral polymer nanocomposites (CPN), namely polyaniline/montmorillonite-cetyltrimethylammonium bromide (PANI/Mt-CTAB), poly o-anisidine/montmorillonite-cetyltrimethylammonium bromide (poly(o-ANIS)/Mt-CTAB) and poly o-anisidine-co-aniline/montmorillonite-cetyltrimethylammonium bromide (poly(o-ANIS-co-ANI)/Mt-CTAB), synthesized by oxidative chemical polymerization method is presented. The nanocomposites have been characterized by Fourier transform infrared spectroscopy, UV-vis spectroscopy, and cyclic voltammetry, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and thermogravimetry and differential scanning calorimetry analysis. By UV-vis measurements different electronic transitions for the CPNs were pointed out. The voltammograms indicate that the synthetized materials are electroactive. The FTIR analysis reveals the characteristic bands of the polymers and of the Mt-CTAB. The shift of the bands to higher/lower wavenumbers demonstrate the interaction between the pristine polymers macromolecular chains and the montmorillonite (Mt). The intercalation of the polymers inside the mineral clay was confirmed by the increased interlayer distance connected with the position of the 011 diffraction plane of the Mt., and the intercalation and exfoliation states were highlighted in the scanning and transmission electron microscopy images. The obtained results are encouraging in respect with the purpose to use them in the field of photovoltaic applications.

61. Simple and clean method for obtaining Sn nanoparticles for hydrophobic coatings

Authors: Buruiana, AT; Sava, F; Matei, E; Zgura, I; Burdusel, M; Mihai, C; Velea, A

Published: NOV 1 2020, MATERIALS LETTERS, 278, DOI: 10.1016/j.matlet.2020.128419

Sn nanoparticles (NPs) are usually obtained by difficult chemical routes in several steps followed by thermal treatments. Here, a simple and clean method, to obtain Sn NPs directly on the substrate, is developed based on a vapor transport technique. The method is versatile, thus can be easily adjusted to obtain Sn NPs of different size, areal density and morphology, by controlling the deposition conditions. NPs are grown on Si/SiO2 substrate and characterized. Water contact angle measurements show that Sn nanoparticles increase the surface hydrophobicity by 20%. Thus, NPs cleanly obtained from a low-cost, earth-abundant, and environmentally friendly material, can be used to modulate the wettability of surfaces. (C) 2020 Elsevier B.V. All rights reserved.

62. Towards phase pure kesterite Cu2ZnSnS4 absorber layers growth via single step free sulfurization electrodeposition under a fix applied potential on Mo substrate

Authors: Azmi, S; Moujib, A; Layachi, OA; Matei, E; Galca, AC; Zaki, MY; Secu, M; Rusu, MI; Grigorescu, CEA; Khoumri, EM

Published: NOV 25 2020, JOURNAL OF ALLOYS AND COMPOUNDS, 842, DOI: 10.1016/j.jallcom.2020.155821

This work presents a new synthesis and characterization of Kesterite Cu2ZnSnS4 films by one step electrodeposition with free sulfurization annealing treatment at different applied potentials. This study highlights the effect of applied potential and annealing treatment on the properties of CZTS deposited films. X-ray Diffraction and Raman spectroscopy were employed to assess the structure and composition of the films elaborated at -1V, -1.1V, and -1.2V vs Saturated Calomel Electrode (SCE). The morphological and optical properties were studied using Scanning Electron microscopy and photoluminescence spectroscopy (PL), respectively. The structural properties are improved by annealing treatment, while -1.1V vs SCE was found to be the optimum applied potential to prepare the Kesterite CZTS thin film with a bandgap around 1.5 eV. (C) 2020 Elsevier B.V. All rights reserved.

63. Epitaxial GeSn Obtained by High Power Impulse Magnetron Sputtering and the Heterojunction with Embedded GeSn Nanocrystals for Shortwave Infrared Detection

Authors: Dascalescu, I; Zoita, NC; Slav, A; Matei, E; Iftimie, S; Comanescu, F; Lepadatu, AM; Palade, C; Lazanu, S; Buca, D; Teodorescu, VS; Ciurea, ML; Braic, M; Stoica, T

Published: JUL 29 2020, ACS APPLIED MATERIALS & INTERFACES, 12, 33886, DOI: 10.1021/acsami.0c06212

GeSn alloys have the potential of extending the Si photonics functionality in shortwave infrared (SWIR) light emission and detection. Epitaxial GeSn layers were deposited on a relaxed Ge buffer on Si(100) wafer by using high power impulse magnetron sputtering (HiPI-MS). Detailed X-ray reciprocal space mapping and HRTEM investigations indicate higher crystalline quality of GeSn epitaxial layers deposited by Ge HiPI-MS compared to commonly used radio frequency magnetron sputtering (RF-MS). To obtain a rectifying heterostructure for SWIR light detection, a layer of GeSn nanocrystals (NCs) embedded in oxide was deposited on the epitaxial GeSn one. Embedded GeSn NCs are obtained by cosputtering deposition of (Ge1-xSnx)(1-y)(SiO2)(y) layers and subsequent rapid thermal annealing at a low temperature of 400 degrees C. Intrinsic GeSn structural defects give p-type behavior, while the presence of oxygen leads to the n-character of the embedded GeSn NCs. Such an embedded NCs/epitaxial GeSn p-n heterostructure shows superior photoelectrical response up to 3 orders of magnitude increase in the 1.2-2.5 mu m range, as compared to performances of diode based only on embedded NCs.

64. Secondary Crystalline Phases Influence on Optical Properties in Off-Stoichiometric Cu2S-ZnS-SnS2 Thin Films

Authors: Sava, F; Diagne, O; Galca, AC; Simandan, ID; Matei, E; Burdusel, M; Becherescu, N; Becherescu, V; Mihai, C; Velea, A

Published: OCT 2020, MATERIALS, 13, DOI: 10.3390/ma13204624

Cu2ZnSnS4 (CZTS) is an economically and environmentally friendly alternative to other toxic and expensive materials used for photovoltaics, however, the variation in the composition during synthesis is often followed by the occurrence of the secondary binary and ternary crystalline phases. These phases produce changes in the optical absorption edge important in cell efficiency. We explore here the secondary phases that emerge in a combinatorial Cu2S-ZnS-SnS2 thin films library. Thin films with a composition gradient were prepared by simultaneous magnetron sputtering from three binary chalcogenide targets (Cu2S, SnS2 and ZnS). Then, the samples were crystallized by sulfurization annealing at 450 degrees C under argon flow. Their composition was measured by energy dispersive X-ray spectroscopy (EDX), whereas the structural and optical properties were investigated by grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy and optical transmission measurements. As already known, we found that annealing in a sulfur environment is beneficial, increasing the crystallinity of the samples. Raman spectroscopy revealed the presence of CZTS in all the samples from the library. Secondary crystalline phases such as SnS2, ZnS and Cu-S are also formed in the samples depending on their proximity to the binary chalcogenide targets. The formation of ZnS or Cu-S strongly correlates with the Zn/Sn and Cu/Zn ratio of the total sample composition. The presence of these phases produces a variation in the bandgap between 1.41 eV and 1.68 eV. This study reveals that as we go further away from CZTS in the composition space, in the quasi-ternary Cu2S-ZnS-SnS2 diagram, secondary crystalline phases arise and increase in number, whereas the bandgap takes values outside the optimum range for photovoltaic applications.

65. Ionophore- Nafion (TM) modified gold-coated electrospun polymeric fibers electrodes for determination of electrolytes

Authors: Aldea, A; Matei, E; Leote, RJB; Rau, I; Enculescu, I; Diculescu, VC

Published: DEC 10 2020, ELECTROCHIMICA ACTA, 363, 137239, DOI: 10.1016/j.electacta.2020.137239

The present work describes the electrochemical properties of ionophores immobilized at the surface of electrodes obtained from electrospun polymeric fibers, in order to develop sensors for the analysis of electrolytes. Poly(methyl methacrylate) submicrometer fibers were prepared by electrospinning, coated with a gold layer by magnetron sputtering and then transferred on polyethylene terephthalate (PET) in order to obtained flexible electrodes. The ionophores were immobilized at the surface of these electrodes by drop-casting a ionophore-Nafion mixed solution. The sensor surface was investigated by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy in order to understand the morphology and distribution of a model Ca2+ ionophore over the electrode surface. Also, Fourier-transformed infrared spectroscopy was performed and demonstrated that the model Ca2+ ionophore can be immobilized in the nafion matrix maintaining its conformation, while cyclic voltammetry and electrochemical impedance spectroscopy demonstrated that the Ca2+ ionophore allows the diffusion of target ions through this this type of membrane. In order to prove the concept of ionophore-based sensors for the analysis of some electrolytes, Ca2+, NH4+, Cl- and H+ ionophore immobilized in a nafion matrix at the surface of these flexible electrodes were tested and the determination of the target ions performed by potentiometry in different media including artificial sweat. Finally, sensitivities, limits of detection, selectivity coefficients were determined. (C) 2020 Elsevier Ltd. All rights reserved.

66. SnSe2-Zn-Porphyrin Nanocomposite Thin Films for Threshold Methane Concentration Detection at Room Temperature

Authors: Lorinczi, A; Fagadar-Cosma, E; Socol, G; Mihailescu, A; Matei, E; Sava, F; Stefan, M

Published: DEC 2020, CHEMOSENSORS, 8, DOI: 10.3390/chemosensors8040134

Nanocomposite thin films, sensitive to methane at the room temperature (25-30 degrees C), have been prepared, starting from SnSe2 powder and Zn(II)-5,10,15,20-tetrakis-(4-aminophenyl)- -porphyrin (ZnTAPP) powder, that were fully characterized by XRD, UV-VIS, FT-IR, Nuclear Magnetic Resonance (H-1-NMR and C-13-NMR), Atomic Force Microscopy (AFM), SEM and Electron Paramagnetic Resonance (EPR) techniques. Film deposition was made by drop casting from a suitable solvent for the two starting materials, after mixing them in an ultrasonic bath. The thickness of these films were estimated from SEM images, and found to be around 1.3 mu m. These thin films proved to be sensitive to a threshold methane (CH4) concentration as low as 1000 ppm, at a room temperature of about 25 degrees C, without the need for heating the sensing element. The nanocomposite material has a prompt and reproducible response to methane in the case of air, with 50% relative humidity (RH) as well. A comparison of the methane sensing performances of our new nanocomposite film with that of other recently reported methane sensitive materials is provided. It is suitable for signaling gas presence before reaching the critical lower explosion limit concentration of methane at 50,000 ppm.

67. Optical Properties of Composites Based on Graphene Oxide and Polystyrene

Authors: Stroe, M; Cristea, M; Matei, E; Galatanu, A; Cotet, LC; Pop, LC; Baia, M; Danciu, V; Anghel, I; Baia, L; Baibarac, MA

Published: MAY 2020, MOLECULES, 25, DOI: 10.3390/molecules25102419

In this work, new optical properties of composites based on polystyrene (PS) microspheres and graphene oxide (GO) are reported. The radical polymerization of styrene in the presence of benzoyl peroxide, pentane and GO induces the appearance of new ester groups in the PS macromolecular chains remarked through an increase in the absorbance of the infrared (IR) band at 1743 cm(-1). The decrease in the GO concentration in the PS/GO composites mass from 5 wt.% to 0.5 wt.% induces a diminution in the intensities of the D and G Raman bands of GO simultaneous with a down-shift of the D band from 1351 to 1322 cm(-1). These variations correlated with the covalent functionalization of the GO layers with PS. For the first time, the photoluminescent (PL) properties of PS/GO composites are reported. The PS microspheres are characterized by a PL band at 397 nm. Through increasing the GO sheets' concentration in the PS/GO composite mass from 0.5 wt.% to 5 wt.%, a PS PL quenching process is reported. In addition, in the presence of ultraviolet A (UVA) light, a photo-degradation process of the PS/GO composite having the GO concentration equal to 5 wt.% is demonstrated by the PL studies.

68. Influence of boric acid concentration on the properties of electrodeposited CZTS absorber layers

Authors: Zaki, MY; Nouneh, K; Touhami, ME; Matei, E; Badica, P; Burdusel, M; Negrila, CC; Baibarac, M; Pintilie, L; Galca, AC

Published: MAY 2020, PHYSICA SCRIPTA, 95, DOI: 10.1088/1402-4896/ab6afd

This work involves the synthesis and characterization of Cu2ZnSnS4 (CZTS) layers. The films were prepared on Mo/glass substrates by single-step electrodeposition method followed by sulfurization at 500 degrees C under argon flow. The effect of boric acid concentration on the crystallographic structure, compositional and morphological properties of CZTS films was investigated, with the objective to understand the growth behavior and to enhance the film properties. Cyclic Voltammetry was used in order to estimate the adequate deposition potential for the CZT alloy. The x-ray diffraction analysis showed the formation of the kesterite phase in all the samples. The Raman and x-ray photoelectron spectroscopy studies confirmed the existence of the CZTS phase. The scanning electron microscopy was employed to inspect the films structure. The results indicated that increasing the concentration of boric acid affects the physico-chemical properties of the films.

69. Morphological and structural investigation of the poly(Vinyl chloride) / graphene oxide composites

Authors: Stingescu, L., Cadar, C., Cotet, L.C., Baia, L., Saszet, K., Magyari, K., Mihis, A.G., Fort, C.I., Stroe, M., Matei, E., Nila, A., Anghel, I., Baia, M., Baibarac, M., Danciu, V.

Published: 2020, , DOI: 10.24193/subbchem.2020.3.19

The morphological and structural properties of the poly(vinyl chloride)/graphene oxide (PVC/GO) composites are reported. By the mixture of the two constituents, the PVC/GO composite membranes with a concentration of the GO sheets varying from 0 wt.% to 0.5, 1, 2, 3, 4 and 5 wt.% were prepared. Using scanning electron microscopy (SEM) and the analysis of the atomic force microscopy (AFM) images we observed that as increasing the GO concentration in the PVC mass from 0 wt.% to 5 wt.%, the average surface roughness decreases from 235 µm to 227 µm. Using Raman scattering, we report that as increasing the GO concentration in the PVC mass, the ratio between the relative intensities of the Raman glines situated in the spectral ranges 600- 650 and 2850-3000 cm-1 (I600-650/I2850-3000) increases as a consequence of the change of GO carbon atoms hybridization from sp2 to sp3. An increase in the number of C-C bonds, simultaneous with the appearance of O-C=O bonds and the decrease of the chlorine concentration, when the GO concentration increases in the PVC weight is reported by X-ray photoelectron spectroscopy (XPS). The down-shift of the main diffraction signal from 24° to 26° when the GO concentration increases in the PVC/GO composite mass from 0 wt.% to 5 wt.%, confirms the incorporation of GO in the polymeric matrix and the modification of the original PVC sample structure. Using transmission electron microscopy (TEM), no agglomerations of the GO structures within the PVC/GO matrix contrast limit were observed. © 2020, Universitatea Babes-Bolyai, Catedra de Filosofie Sistematica. All rights reserved.

70. Towards a Correlation between Structural, Magnetic, and Luminescence Properties of CeF3:Tb(3+)Nanocrystals

Authors: Bartha, C; Secu, C; Matei, E; Negrila, C; Leca, A; Secu, M

Published: JUL 2020, MATERIALS, 13, DOI: 10.3390/ma13132980

In this study, we report on the structural, magnetic, and optical properties of Tb3+-doped CeF(3)nanocrystals prepared via a polyol-assisted route, followed by calcination. X-ray diffraction analysis and electron microscopy investigations have shown the formation of a dominant Ce(0.75)F(3)nanocrystalline phase (of about 99%), with a relatively uniform distribution of nanocrystals about 15 nm in size. Magnetization curves showed typical paramagnetic properties related to the presence of Ce(3+)and Tb(3+)ions. The magnetic susceptibility showed a weak inflexion at about 150 K, assigned to the cerium ions' crystal field splitting. Under UV light excitation of the Ce(3+)ions, we observed Tb(3+)green luminescence with a quantum yield of about 20%.

71. MORPHOLOGICAL AND STRUCTURAL INVESTIGATION OF THE POLY(VINYL CHLORIDE)/GRAPHENE OXIDE COMPOSITES

Authors: Stingescu, L; Cadar, C; Cotet, LC; Baia, L; Saszet, K; Magyari, K; Mihis, AG; Fort, CI; Stroe, M; Matei, E; Nila, A; Anghel, I; Baia, M; Baibarac, M; Danciu, V

Published: 2020, STUDIA UNIVERSITATIS BABES-BOLYAI CHEMIA, 65, 258, DOI: 10.24193/subbchem.2020.3.19

The morphological and structural properties of the poly(vinyl chloride)/graphene oxide (PVC/GO) composites are reported. By the mixture of the two constituents, the PVC/GO composite membranes with a concentration of the GO sheets varying from 0 wt.% to 0.5, 1, 2, 3, 4 and 5 wt.% were prepared. Using scanning electron microscopy (SEM) and the analysis of the atomic force microscopy (AFM) images we observed that as increasing the GO concentration in the PVC mass from 0 wt.% to 5 wt.%, the average surface roughness decreases from 235 mu m to 227 mu m. Using Raman scattering, we report that as increasing the GO concentration in the PVC mass, the ratio between the relative intensities of the Raman lines situated in the spectral ranges 600-650 and 2850-3000 cm(-1) (I600-650/I2850-3000) increases as a consequence of the change of GO carbon atoms hybridization from sp(2) to sp(3). An increase in the number of C-C bonds, simultaneous with the appearance of O-C=O bonds and the decrease of the chlorine concentration, when the GO concentration increases in the PVC weight is reported by X-ray photoelectron spectroscopy (XPS). The down-shift of the main diffraction signal from 24 degrees to 26 degrees when the GO concentration increases in the PVC/GO composite mass from 0 wt.% to 5 wt.%, confirms the incorporation of GO in the polymeric matrix and the modification of the original PVC sample structure. Using transmission electron microscopy (TEM), no agglomerations of the GO structures within the PVC/GO matrix contrast limit were observed.

72. Electrochemical Sensor for Carbonyl Groups in Oxidized Proteins

Authors: Enache, TA; Matei, E; Diculescu, VC

Published: FEB 5 2019, ANALYTICAL CHEMISTRY, 91, 1927, DOI: 10.1021/acs.analchem.8b03969

The interaction of proteins with free radicals leads, among other types of damages, to the production of stable carbonyl groups, which can be used as a quantification of oxidative stress at proteins level. The aim of this study was the development of an electrochemical sensor for the detection of carbonyl groups in proteins oxidized by reactive oxygen species. Its working principle is based on the redox properties of dinitrophenylhydrazine (DNPH). BSA was used as a model protein and its oxidation achieved through Fenton reactions. Using differential pulse voltammetry at glassy carbon electrode, the electrochemical behavior of DNPH and of the native and oxidized BSA was investigated in solution. It has been shown that the hydrazine moiety of the DNPH is the electroactive center and is responsible for carbonyl complexation. Special attention was paid to the immobilization of the DNPH in order to retain its redox properties, and this was achieved on a mixed 4-styrenesulfonic acid-nafion matrix. The sensor's surface characterization and the detection of carbonyl groups in oxidized protein were performed by voltammetry, Fourier-transformed infrared spectroscopy and scanning electron microscopy while the voltammetric results were confirmed by surface plasmon resonance measurements. It has been shown that upon interaction with carbonyl groups of the oxidized protein, the oxidation peak of the hydrazine moiety of DNPH decreases as a function of incubation time and protein concentration. The sensor sensitivity was 0.015 nmol carbonyl per mg of oxidized protein and detection limits of 50 mu g oxidized BSA and 0.75 pmol carbonyls.

73. Direct Immobilization of Biomolecules through Magnetic Forces on Ni Electrodes via Ni Nanoparticles: Applications in Electrochemical Biosensors

Authors: Barsan, MM; Enache, TA; Preda, N; Stan, G; Apostol, NG; Matei, E; Kuncser, A; Diculescu, VC

Published: JUN 5 2019, ACS APPLIED MATERIALS & INTERFACES, 11, 19877, DOI: 10.1021/acsami.9b04990

The present work describes a new simple procedure for the direct immobilization of biomolecules on Ni electrodes using magnetic Ni nanoparticles (NiNPs) as biomolecule carriers. Ni electrodes were fabricated by electroplating, and NiNPs were chemically synthesized. The chemical composition, crystallinity, and granular size of Ni electrodes, NiNP, and NiNP-modified Ni electrodes (NiNP/Ni) were determined by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS). The electrochemical characterization of Ni electrodes by cyclic voltammetry and electrochemical impedance spectroscopy confirmed the existence of nickel oxides, hydroxides, and oxohydroxide films at the surface of Ni. Magnetic characterization and micromagnetic simulations were performed in order to prove that the magnetic force is responsible for the immobilization process. Further, Ni electrodes were employed as amperometric sensors for the detection of hydrogen peroxide because it is an important performance indicator for a material to be applied in biosensing. The working principle for magnetic immobilization of the enzyme-functionalized NiNP, without the use of external magnetic sources, was demonstrated for glucose oxidase (GOx) as a model enzyme. XPS results enabled to identify the presence of GOx attached to the NiNP (GOx-NiNP) on Ni electrodes. Finally, glucose detection and quantification were evaluated with the newly developed GOx-NiNP/Ni biosensor by amperometry at different potentials, and control experiments at different electrode materials in the presence and absence of NiNP demonstrated their importance in the biosensor architecture.

74. Structural and optical properties of ZnO thin films grown by rapid atmospheric mist chemical vapor technique

Authors: Derbali, S; Nouneh, K; Galca, AC; Touhami, ME; Secu, M; Matei, E; Leonat, LN; Pintilie, L; El Harfaoui, N; Fahoume, M

Published: JUL 2019, OPTICAL AND QUANTUM ELECTRONICS, 51, DOI: 10.1007/s11082-019-1937-2

In this work, the effect of deposition time on the structural and optical properties of ZnO films deposited by Ultrasonic Spray Mist-CVD was studied aiming the application in perovskite solar cells, as holes blocking layer. Crystallinity, surface morphology and optical properties of the ZnO films were investigated by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), conventional and Photoluminescence (PL) spectroscopies, respectively. The XRD measurement proves the existence of the hexagonal wurtzite phase and a high degree of crystallinity with [001] preferential orientation. The SEM study shows that the films possess a compact structure. Smooth and homogenous surface was confirmed also by AFM. The obtained results indicate that ZnO films deposited by a simple, safe and cost-effective method present a great potential for application in perovskite solar cells.

75. The influence of the nanocrystals size and surface on the Yb/Er doped LaF3 luminescence properties

Authors: Secu, CE; Matei, E; Negrila, C; Secu, M

Published: JUN 30 2019, JOURNAL OF ALLOYS AND COMPOUNDS, 791, 1104, DOI: 10.1016/j.jallcom.2019.03.267

Up-conversion luminescence and thermoluminescence properties of LaF3 nanocrystals, with sizes of about 20 nm, were studied and discussed in relation to -size and surface related effects. XPS spectra have evidenced the presence of oxidized Er and La ions within a thin layer (of about 1 nm thickness) at the nanocrystals surface, as well as Yb ions bonded with fluorine ions. The green ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and red (F-4(9/2) -> I-4(15/2)) up-conversion emissions of Er3+ ions are influenced by the relative dominance of Erions that reside within the thin oxidized layer. The broad thermoluminescence curves are assigned to the recombination of trap defects associated with surface states and within the oxidized surface layer. (C) 2019 Elsevier B.V. All rights reserved.

76. Gd3+ co-doping influence on the morphological, up-conversion luminescence and magnetic properties of LiYF4:Yb3+/Er3+ nanocrystals

Authors: Secu, CE; Bartha, C; Matei, E; Negrila, C; Crisan, A; Secu, M

Published: JUL 2019, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 130, 241, DOI: 10.1016/j.jpcs.2019.03.003

The influence of the Gd3+ co-dopant on the structure, morphology and up-conversion luminescence/magnetic properties of the LiYF4:Gd3+/Yb3+/Er3+ nanocrystals was investigated and compared to those of Gd-free samples. Electron microscopy has indicated an inhibiting effect of the agglomeration and collapsing process of the nanocrystals compared to the Gd-free powder samples. The surface analysis of nanocrystals have not shown oxygen-metal bonds related to the metal oxidation within the surface nanometric layer. The paramagnetic properties are related to the magnetic moment of the Gd3+ ions. The up-conversion luminescence of the LiYF4:Gd3+/Yb3+/Er3+ nanocrystals is about six times stronger than in LiYF4:Yb3+/Er3+ nanocrystals; the enhancement effect is most probably due to the lattice distortion induced by the Gd co-doping.

77. 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.

78. 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.

79. Magnetism and magnetoresistance of single Ni-Cu alloy nanowires

Authors: Costas, A; Florica, C; Matei, E; Toimil-Molares, ME; Stavarache, I; Kuncser, A; Kuncser, V; Enculescu, I

Published: AUG 30 2018, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 9, 2355, DOI: 10.3762/bjnano.9.219

Arrays of magnetic Ni-Cu alloy nanowires with different compositions were prepared by a template-replication technique using electrochemical deposition into polycarbonate nanoporous membranes. Photolithography was employed for obtaining interdigitated metallic electrode systems of Ti/Au onto SiO2/Si substrates and subsequent electron beam lithography was used for contacting single nanowires in order to investigate their galvano-magnetic properties. The results of the magnetoresistance measurements made on single Ni-Cu alloy nanowires of different compositions have been reported and discussed in detail. A direct methodology for transforming the magnetoresistance data into the corresponding magnetic hysteresis loops was proposed, opening new possibilities for an easy magnetic investigation of single magnetic nanowires in the peculiar cases of Stoner-Wohlfarth-like magnetization reversal mechanisms. The magnetic parameters of single Ni-Cu nanowires of different Ni content have been estimated and discussed by the interpretation of the as derived magnetic hysteresis loops via micromagnetic modeling. It has been theoretically proven that the proposed methodology can be applied over a large range of nanowire diameters if the measurement geometry is suitably chosen.

80. Inhibitory effect of three phenacyl derivatives on the oxidation of sphalerite (ZnS) in air-equilibrated acidic solution

Authors: Chirita, P; Duinea, MI; Sandu, AM; Birsa, LM; Sarbu, LG; Baibarac, M; Sava, F; Popescu, M; Matei, E

Published: JUL 1 2018, CORROSION SCIENCE, 138, 162, DOI: 10.1016/j.corsci.2018.04.017

Three phenacyl derivatives have been investigated as potential inhibitors for the aqueous oxidation of sphalerite (ZnS) in air-equilibrated solutions of HCl (pH 2.5 and 25 degrees C) using potentyodynamic polarization, aqueous batch experiments, scanning electron microscopy coupled with energy dispersive X-ray (SEM/EDX) analysis, Fourier transform infrared (FTIR) spectroscopy, Raman scattering and quantum chemical calculations. Findings show that the studied phenacyl derivatives are inhibitors of sphalerite aqueous oxidation. Quantum chemical calculations indicate that the adsorption of phenacyl derivatives on ZnS is energetically favorable and accounts for the observed inhibiting effects.

81. On the properties of organic heterostructures prepared with nano-patterned metallic electrode

Authors: Breazu, C; Socol, M; Preda, N; Matei, E; Rasoga, O; Girtan, M; Mallet, R; Stanculescu, F; Stanculescu, A

Published: JUN 15 2018, APPLIED SURFACE SCIENCE, 443, 602, DOI: 10.1016/j.apsusc.2018.02.103

This paper presents a comparative study between the properties of the heterostructures realized with single/multi layer organic (zinc phthalocyanine or/and fullerene) prepared on Si substrate between flat or patterned aluminum (Al) layer metallic electrode and multi layer ZnO/Au/ZnO transparent conductor electrode (TCE). The UV-Nanoimprint Lithography was used for the realization of a 2D array of nanostructures (holes/pillars) characterized by a periodicity of 1.1 mu m and cylindrical shape: diameter = 400 nm and depth/height = 300 nm. The effect of the electrode patterning on the properties of the organic heterostructures was analyzed. For the samples with patterned Al electrode was remarked a slight red shift of the peaks in the reflection spectra determined by an increased interaction between the organic molecules in the delimited region of the patterned holes. The shape of the emission spectra at excitation with UV light showed a narrow intense peak around 500 nm associated with the intense resonance phenomena between the energy of the incident light and the surface plasmons in the patterned Al layer. The TCE followed the morphology of the organic film on which it was deposited. The significant differences between the morphology of the top layer in the heterostructures realized on flat and patterned Al are correlated with the total thickness of the successively deposited layers and with the particularities of the molecular arrangement, leading to the preservation or deleting of patterning. An injection contact behavior was evidence for most heterostructures built on flat and patterned Al. The slight increase in current at an applied bias <1 V in the heterostructure Si/Al/ZnPc/TCE is attributed to the larger interfacial area between the patterned Al electrode and ZnPc layer compared to the interface area between flat Al and ZnPc. A buffer layer of 1,4,5,8-naphthalen-tetracarboxylic dianhydride (NTCDA), sandwiched between the flat metallic electrode and organic film in the heterostructure Si/Al/C60/ZnPc/TCE has determined an increase in the current at low applied voltages. (C) 2018 Elsevier B.V. All rights reserved.

82. Synthesis and characterization of dextran-coated iron oxide nanoparticles

Authors: Predescu, AM; Matei, E; Berbecaru, AC; Pantilimon, C; Dragan, C; Vidu, R; Predescu, C; Kuncser, V

Published: MAR 2018, ROYAL SOCIETY OPEN SCIENCE, 5, DOI: 10.1098/rsos.171525

Synthesis and characterization of iron oxide nanoparticles coated with a large molar weight dextran for environmental applications are reported. The first experiments involved the synthesis of iron oxide nanoparticles which were coated with dextran at different concentrations. The synthesis was performed by a co-precipitation technique, while the coating of iron oxide nanoparticles was carried out in solution. The obtained nanoparticles were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectrometry, Fourier transform infrared spectroscopy and superconducting quantum interference device magnetometry. The results demonstrated a successful coating of iron oxide nanoparticles with large molar weight dextran, of which agglomeration tendency depended on the amount of dextran in the coating solution. SEM and TEM observations have shown that the iron oxide nanoparticles are of about 7 nm in size.

83. Effect of heavy ions irradiation on the properties of benzil crystals

Authors: Stanculescu, F; Socol, M; Matei, E; Stanculescu, A

Published: AUG 2017, CRYSTAL RESEARCH AND TECHNOLOGY, 52, DOI: 10.1002/crat.201700047

Thick slices mechanically polished cut from a pure benzil ingot grown from melt in a modified Bridgman-Stockbarger configuration were irradiated with Ni ions having a specific energy of 11.4 MeV/u at different fluences. The effect of radiation on the properties of bulk benzil has been investigated. The chemical structure was not substantially affected as shown by infrared spectrum. The changes induced on the disorder degree have been evaluated from the Urbach law and X Ray Diffraction measurements. The morphology and surface topography have been analyzed emphasising a decrease in the size of granules and an increase in the surface roughness by irradiation. No effect of irradiation on the photoluminescence emission and optical nonlinear properties has been evidenced. These results recommend benzil as candidate for applications in space technology.

84. Tungsten nanoparticles with controlled shape and crystallinity obtained by magnetron sputtering and gas aggregation

Authors: Acsente, T; Negrea, RF; Nistor, LC; Matei, E; Grisolia, C; Birjega, R; Dinescu, G

Published: AUG 1 2017, MATERIALS LETTERS, 200, 124, DOI: 10.1016/j.matlet.2017.04.105

We report the synthesis of tungsten nanoparticles with two distinct shapes, concave hexapods and faceted cube-octahedral nanocrystals. These types of nanoparticles were obtained with a cluster source based on magnetron sputtering and gas aggregation, by supplying the magnetron discharge with continuous or pulsed wave radiofrequency power. Detailed morphological and microstructural studies were performed. The hexapod particles present a dendritic growth while the faceted ones have a single crystal structure. The alpha-W and beta-w crystalline phases are present in both types of nanoparticles; nevertheless, the beta-W structure is dominant for the hexapod ones. Although the beta-w phase is usually metastable, we observed its unexpected long term preservation in hexapod nanoparticles. The results, added to previously reported nanoflower-like particles, point out the ability to control the shape and structure of the tungsten nanoparticles using the magnetron sputtering gas aggregation technique. (C) 2017 Elsevier B.V. All rights reserved.

85. ONE SIDE POLYANILINE COATED FIBERS BASED ACTUATOR

Authors: Beregoi, M; Evanghelidis, A; Ganea, P; Iovu, H; Matei, E; Enculescu, I

Published: 2017, UNIVERSITY POLITEHNICA OF BUCHAREST SCIENTIFIC BULLETIN SERIES B-CHEMISTRY AND MATERIALS SCIENCE, 79, 130, DOI:

In this study, one side aligned PANI coated micro-fibers were fabricated in order to develop a novel actuator configuration. Thus, electrospun PMMA fibers were coated only on one side with a thin gold layer guiding in this way the deposition of PANI (only on the side with gold considering an adequate PANI deposition time). Further, the half-metalized fibers were employed as working microelectrodes for electrochemical deposition of PANI. The prepared PANI coated fibers present actuation properties when they are in contact with an electrolyte like 1 M H2SO4. By switching the potential between +1.4 and -0.2 V, the fiber strips move due to the swelling/shrinking and anisotropic deposition of PANI film.

86. MAPLE prepared heterostructures with oligoazomethine: Fullerene derivative mixed layer for photovoltaic applications

Authors: Stanculescu, A; Rasoga, O; Socol, M; Vacareanu, L; Grigoras, M; Socol, G; Stanculescu, F; Breazu, C; Matei, E; Preda, N; Girtan, M

Published: SEP 30 2017, APPLIED SURFACE SCIENCE, 417, 195, DOI: 10.1016/j.apsusc.2017.03.053

Mixed layers of azomethine oligomers containing 2,5-diamino-3,4-dicyanothiophene as central unit and triphenylamine (LV5) or carbazol (LV4) at both ends as donor and fullerene derivative, [6,6]-phenylC61 butyric acid butyl ester ([C60] PCB-C4) as acceptor, have been prepared by Matrix Assisted Pulsed Laser Evaporation (MAPLE) on glass/ITO and Si substrates. The effect of weight ratio between donor and acceptor (1: 1; 1: 2) and solvent type (chloroform, dimethylsulphoxide) on the optical (UV-vis transmission/absorption, photoluminescence) and morphological properties of LV4 (LV5): [C60] PCB-C4 mixed layers has been evidenced. Dark and under illumination I-V characteristics of the heterostructures realized with these mixed layers sandwiched between ITO and Al electrodes have revealed a solar cell behavior for the heterostructures prepared with both LV4 and LV5 using chloroform as matrix solvent. The solar cell structure realized with oligomer LV5, glass/ITO/LV5: [C60] PCB-C4 (1: 1) has shown the best parameters. (C) 2017 Elsevier B.V. All rights reserved.

87. Crystallization kinetics mechanism investigation of sol-gel-derived NaYF4:(Yb,Er) up-converting phosphors

Authors: Bartha, C; Secu, CE; Matei, E; Secu, M

Published: SEP 14 2017, CRYSTENGCOMM, 19, 5000, DOI: 10.1039/c7ce01265a

The crystallization mechanism of sol-gel-derived NaYF4:(Yb, Er) up-converting phosphors has been studied by differential scanning calorimetry analysis using both model-free and model fitting approaches. Structural and optical data have shown that the hexagonal NaYF4:(Yb, Er) phase crystallization process occurs at around 315 degrees C as a result of the thermal decomposition of the metal trifluoroacetates. As the annealing temperature increases, sphere-like microcrystals of about 1-2 mu m size (at 300 degrees C) break up into smaller ones (400-500 nm size) and finally collapse at higher temperatures (600 degrees C); the up-conversion luminescence signal intensity increases due to the crystallinity improvement and dehydration process. The crystallization process can be described as an autocatalytic-type reaction where the accompanying cubic NaYF4 phase played a catalytic role by reducing the energy barrier against the crystallization of the hexagonal NaYF4 phase, causing its fast self-accelerated crystallization. The energy resulting from the disintegration process of the initial NaYF4 microcrystals contributed to the growth and agglomeration processes and finally the collapse of the crystalline fragments with increasing temperature.

88. Polyaniline based microtubes as building-blocks for artificial muscle applications

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

Published: DEC 2017, SENSORS AND ACTUATORS B-CHEMICAL, 253, 583, DOI: 10.1016/j.snb.2017.06.128

Morphology is a key element in the functionality of low dimensional structures including here electroactive polymers, especially when applications such as muscle like actuators are sought. The reason is that morphology in the context of a high specific surface object strongly influences specific parameters such as ionic diffusion, conductivity and consequently the actuation capability of the system. In the present work a new architecture for microtube-based actuating elements is presented. Free-standing fibrillar microtubes with diameter in the range of micrometers and with a core-shell polyaniline/gold structure are fabricated through a scalable approach. Aligned electrospun poly(methyl methacrylate) fibers are coated with gold and are further employed as microstructured electrodes for the electrochemical deposition of polyaniline. Further the poly(methyl methacrylate) core was dissolved, leading to a tubular structure. The polyaniline/gold microtubes show complex, rapid and reversible movement patterns, with great stability and consistency over repeated actuation cycles. Thus, when the potential is swept between -0.2 and 1 V at different rates, the microtubes move, this movement being associated with the morphological and structural characteristics of the deposited polyaniline layer, a mechanism based on the expansion/contraction and conformational changes of the polymer chains due to the insertion/expulsion of ions. The response time of these electroactive microstructures during one cycle is in the range of seconds, a consequence of their low dimensionality and specific structure. Moreover the actuation takes place in different electrolytes including simulated gastric fluid, which enables a wide range of applications. (C) 2017 Elsevier B.V. All rights reserved.

89. Templateless electrodeposition ZnO nanowires for charge transport optimization in OLED structures

Authors: Polosan, S; Matei, E; Ciobotaru, IC; Ciobotaru, CC

Published: OCT 2016, MATERIALS RESEARCH EXPRESS, 3, DOI: 10.1088/2053-1591/3/10/105018

Passivated zinc oxide nanowires (NW) were used to improve the charge injection in organic lightemitting diode (OLED) structures. Conducting polymers, deposited on the well-dispersed ZnO NW, were used to modify the electrical conductivity across the OLED structure because the charge transport is influenced by the interface interactions. Passivation with polymers improves the transport characteristics of the device due to the interaction between ZnONWand PEDOT:PSS polymer. The hole current density increases with the ZnO NW concentration, which made the current injection more balanced and therefore enhanced the electroluminescence efficiency. A templateless electrochemical deposition method was used to grow zinc oxide nanowires on an ITO/glass substrate because parameters such as the densities and dimensions of the nanowires can be controlled to produce thin and well dispersed structures.

90. INVESTIGATIONS ON THE PROPERTIES OF A TWO-DIMENSIONAL NANOPATTERNED METALLIC FILM

Authors: Breazu, C; Preda, N; Socol, M; Stanculescu, F; Matei, E; Stavarache, I; Iordache, G; Girtan, M; Rasoga, O; Stanculescu, A

Published: OCT-DEC 2016, Digest Journal of Nanomaterials and Biostructures, 11, 1229, DOI:

This paper presents some investigations of the effect of nanopatterning on the properties of aluminum layer deposited by sputtering. UV-Nanoimprint Lithography technique has been used for the realization of a 2D array of nanostructures (pillars) in aluminum film characterized by cylindrical shape and the following structural parameters: diameter between 400 nm and 490 nm, depth between 320 nm and 420 nm and periodicity of 1.1 mu m, which have been revealed by SEM and AFM measurements. The UV-Vis transmission, reflection and photoluminescence measurements have evidenced the effect of the nanopatterning on the optical properties of the A1 layer.

91. SOL-GEL TEMPLATE ASSISTED SYNTHESIS AND UP-CONVERSION PROPERTIES OF (Yb-Er) DOPED SiO2-LiYF4 GLASS CERAMIC RODS

Authors: Secu, CE; Matei, E

Published: APR-JUN 2016, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 11, 494, DOI:

Up-conversion properties of the glass-ceramics microrods containing (Er3+, Yb3+)-doped LiYF4 nanocrystals have been studied. Under 980 nm laser light pumping, both Yb3+/Er3+ co-doped LiYF4 samplesshow green ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and red (F-4(9/2) -> I-4(15/2)) up-conversion luminescences explained by a two-photon processes. The luminescence decay time of the green luminescence is much shorter in the glass-ceramics microrods (0.9 mu s) compared to the bulk powder (15 mu s) indicating the enhancement of the non-radiative relaxation rate due to the cross-relaxation effects between Er3+-ions. The quantum efficiencies were estimated for the green luminescence being much smaller in the glass-ceramic rods (eta = 0.15%) compared the bulk powder (eta = 2%) or pellet (eta = 46%).

92. Electrochromic properties of polyaniline-coated fiber webs for tissue engineering applications

Authors: Beregoi, M; Busuioc, C; Evanghelidis, A; Matei, E; Iordache, F; Radu, M; Dinischiotu, A; Enculescu, I

Published: AUG 30 2016, INTERNATIONAL JOURNAL OF PHARMACEUTICS, 510, 473, DOI: 10.1016/j.ijpharm.2015.11.055

By combining the electrospinning method advantages (high surface-to-volume ratio, controlled morphology, varied composition and flexibility for the resulting structures) with the electrical activity of polyaniline, a new core-shell-type material with potential applications in the field of artificial muscles was synthesized. Thus, a poly(methylmethacrylate) solution was electrospun in optimized conditions to obtain randomly oriented polymer fiber webs. Further, a gold layer was sputtered on their surface in order to make them conductive and improve the mechanical properties. The metalized fiber webs were then covered with a PANI layer by in situ electrochemical polymerization starting from aniline and using sulphuric acid as oxidizing agent. By applying a small voltage on PANI-coated fiber webs in the presence of an electrolyte, the oxidation state of PANI changes, which is followed by the device color modification. The morphological, electrical and biological properties of the resulting multilayered material were also investigated. (C) 2015 Elsevier B.V. All rights reserved.

93. Characterization of hydrogenated and deuterated silicon carbide films codeposited by magnetron sputtering

Authors: Pantelica, D; Ionescu, P; Petrascu, H; Dracea, MD; Statescu, M; Matei, E; Rasoga, O; Stancu, C; Marascu, V; Ion, V; Acsente, T; Dinescu, G

Published: MAR 15 2016, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 371, 326, DOI: 10.1016/j.nimb.2015.10.060

In this work we present the deposition of amorphous SiC thin films by radiofrequency dual magnetron sputtering. The dependence of the deposited films properties over the discharges electrical power and the effect of hydrogenous species (H-2 and/or D-2) addition to main discharge gas (Ar) were investigated. Accurate elemental analysis of the samples, including detection of hydrogen and deuterium, was performed by ion beam analysis (IBA) techniques: RBS (Rutherford Backscattering Spectrometry) and ERDA (Elastic Recoil Detection Analysis). SiCx thin films with thicknesses between 1700 and 4500 angstrom and C/Si ratio between 0.2/1 and 1.25/1 were obtained in different deposition conditions. The results prove that thin films of amorphous SiC with well controlled properties can be produced using radiofrequency dual magnetron sputtering. (C) 2015 Elsevier B.V. All rights reserved.

94. 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.

95. 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.

96. Amorphous thin films in the gallium-chalcogen system

Authors: Popescu, M; Sava, F; Lorinczi, A; Velea, A; Simandan, ID; Galca, AC; Matei, E; Socol, G; Gherendi, F; Savastru, D; Miclos, S

Published: JUN 2016, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 253, 1037, DOI: 10.1002/pssb.201552551

Thin amorphous films based on gallium-chalcogen (Ga-Ch), namely Ga2S3, Ga2Se3, Ga2Te3, and GaTe have been prepared by pulsed laser deposition (PLD). The films were characterized by X-ray diffraction, extended X-ray absorption fine structure (EXAFS), energy-dispersive X-ray spectroscopy (EDX), optical transmission spectroscopy, ellipsometry, and electrical measurements. Structural measurements showed that Ga is threefold coordinated, except the Te-based alloys were, it seems, only twofold coordinated, while the chalcogen is usually twofold coordinated. In all the compositions, layered and chain-like structures are assumed. The bandgaps range between 1.09 eV for Ga2Te3 and 2.21 eV for Ga2Se3. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

97. Electrical properties of single CdTe nanowires

Authors: Matei, E; Florica, C; Costas, A; Toimil-Molares, ME; Enculescu, I

Published: FEB 12 2015, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 6, 450, DOI: 10.3762/bjnano.6.45

Ion track, nanoporous membranes were employed as templates for the preparation of CdTe nanowires. For this purpose, electrochemical deposition from a bath containing Cd and Te ions was employed. This process leads to high aspect ratio CdTe nanowires, which were harvested and placed on a substrate with lithographically patterned, interdigitated electrodes. Focused ion beam-induced metallization was used to produce individual nanowires with electrical contacts and electrical measurements were performed on these individual nanowires. The influence of a bottom gate was investigated and it was found that surface passivation leads to improved transport properties.

98. Inhibition of troilite (FeS) oxidative dissolution in air-saturated acidic solutions by O-ethyl-S-2-(2-hydroxy-3,5-diiodophenyl)-2-oxoethylxantogenate

Authors: Chirita, P; Constantin, CA; Badica, CE; Duinea, MI; Birsa, LM; Matei, E; Baltog, I

Published: MAY 1 2015, MATERIALS CHEMISTRY AND PHYSICS, 157, 107, DOI: 10.1016/j.matchemphys.2015.03.021

The inhibiting action of O-ethyl-S-2-(2-hydroxy-3,5-diiodophenyl)-2-oxoethylxantogenate (EHDO) on the oxidation of FeS in air-saturated solutions at pH 1.3 and 25 degrees C was studied using potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The uninhibited and inhibited surfaces were characterized by scanning electron microscopy, energy dispersive X-ray analysis and Raman spectroscopy. It was found that EHDO acts as an anodic inhibitor. Also, it was found that the corrosion of Fe(0) is slower than the oxidative dissolution of uninhibited FeS but faster than the oxidative dissolution of inhibited FeS. This behavior makes EHDO a potential inhibitor of the corrosion of Fe(0) when covered by FeS. (C) 2015 Elsevier B.V. All rights reserved.

99. Synthesis of flower-like tungsten nanoparticles by magnetron sputtering combined with gas aggregation

Authors: Acsente, T; Negrea, RF; Nistor, LC; Logofatu, C; Matei, E; Birjega, R; Grisolia, C; Dinescu, G

Published: JUN 23 2015, EUROPEAN PHYSICAL JOURNAL D, 69, DOI: 10.1140/epjd/e2015-60097-4

We present the synthesis of tungsten nanoparticles using a gas aggregation cluster source based on a magnetron sputtering discharge. The nanoparticles have sizes between 70 and 100 nm and a dendritic morphology, with branches emerging from the center and evolving in a flower-like pattern. Structural investigations revealed the presence of alpha-W and residual beta-W crystalline phases. Post deposition oxidation of the nanoparticles is also investigated.

100. Ceramics and amorphous thin films based on gallium sulphide doped by rare-earth sulphides

Authors: Popescu, M; Sava, F; Lorinczi, A; Velea, A; Simandan, ID; Badica, P; Burdusel, M; Galca, AC; Matei, E; Preda, N; Secu, M; Socol, G; Jipa, F; Zamfirescu, M; Balan, A

Published: APR 2015, SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 30, DOI: 10.1088/0268-1242/30/4/044001

Bulk ceramics of Ga2S3 and rare-earth sulfides (EuS, Gd2S3, Er2S3) as well as combinations thereof have been prepared by spark plasma sintering (SPS). The disk-shaped ceramics were used as targets for pulsed laser deposition (PLD) experiments to obtain amorphous thin films. The properties of these new bulks and amorphous thin films have been investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), optical transmission spectroscopy, and atomic force microscopy (AFM). In order to test the photoexpansion effect in Gd2S3 and the possibility to create planar arrays of microlenses, the film was irradiated with femtosecond laser pulses at different powers. For low laser power pulses (up to 100mW power per pulse) a photoexpansion effect was observed, which leads to formation of hillocks with a height of 40-50 nm. EuS doped Gd2S3 thin film shows luminescence properties, which recommend them for optoelectronic applications.

101. 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.

102. Field Effect Transistor with Electrodeposited ZnO Nanowire Channel

Authors: Florica, C; Matei, E; Costas, A; Molares, MET; Enculescu, I

Published: AUG 10 2014, ELECTROCHIMICA ACTA, 137, 297, DOI: 10.1016/j.electacta.2014.05.124

ZnO nanowires were prepared by electrochemical deposition in polycarbonate ion track templates. After the deposition process the polymer templates were dissolved in dichloromethane and the nanowires were harvested by ultrasonication in isopropyl. A droplet of nanowire suspension was placed on a Si/SiO2 substrate patterned with interdigitated electrodes. By means of electron beam lithography single nanowires were selected and provided with electrical contacts. We found that in order to obtain reliable electrical contacts and typical field effect characteristics the electrode deposition process needs to be adapted to the 3 D shape of the wires and that annealing and passivation treatments are necessary. (C) 2014 Elsevier Ltd. All rights reserved.

103. Effects of substrate and ambient gas on epitaxial growth indium oxide thin films

Authors: Nistor, M; Seiler, W; Hebert, C; Matei, E; Perriere, J

Published: JUL 15 2014, APPLIED SURFACE SCIENCE, 307, 460, DOI: 10.1016/j.apsusc.2014.04.056

Indium oxide thin films were grown by pulsed electron beam deposition method at 500 Con c-cut sapphire and (0 0 1) oriented LaAlO3 single crystal substrates in oxygen or argon gas. The effects of ambient gas and substrate symmetry on the growth of indium oxide thin films were studied. Stoichiometric In2O3 films are formed in oxygen, while oxygen deficient In2O2.5 films are grown in argon, with In metallic nanoclusters embedded in a In2O3 matrix (nanocomposite films). In both cases, epitaxial In2O3 films having the bixbyite phase were grown with various orientation relationships, depending upon the substrate symmetry and gas ambient (oxygen or argon). Domain matching epitaxy was used to describe the precise in-plane epitaxial film-substrate relationships. The differences in film texture were correlated to the differences in growth conditions, while the differences in the film properties were correlated to the film oxygen composition. (c) 2014 Elsevier B.V. All rights reserved.

104. Synthesis and Raman scattering of multiferroic Fe-Pb(Zr0.2Ti0.8)O-3 core-shell wire arrays

Authors: Baibarac, M; Sima, M; Matei, E; Pasuk, I; Mihut, L

Published: JAN 2014, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 211, 205, DOI: 10.1002/pssa.201330062

A new method to fabricate an Fe-PZT core-shell wire arrays developed in three steps is reported in this paper. This involves the electrochemical growth of an iron wire array by template method, deposition by spin coating of the PZT precursor prepared by sol-gel technique on the iron wires surface and annealing treatment to obtain Fe-PZT core-shell structures. The structure of the Fe-PZT core-shell wire array was characterized by scanning electron microscopy (SEM) and Raman scattering. Raman lines situated at 372 and 575cm(-1) indicate the formation of the FeO particles on the Fe wires surface as a result of the use of an aqueous solution for electrochemical synthesis. An upshift of Raman lines of Fe decorated with FeO wires was observed after formation of Fe-PZT core-shell structure. The annealing treatment of this structure involves a partial transformation of the FeO into Fe2O3 particles both with structure rhombohedral and cubic that were evidenced by Raman lines peaked at 243 and 497cm(-1), respectively. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

105. Biocatalytic designs for the conversion of renewable glycerol into glycerol carbonate as a value-added product

Authors: Tudorache, M; Ghemes, G; Nae, A; Matei, E; Mercioniu, I; Kemnitz, E; Ritter, B; Coman, S; Parvulescu, VI

Published: DEC 2014, CENTRAL EUROPEAN JOURNAL OF CHEMISTRY, 12, 1270, DOI: 10.2478/s11532-014-0547-x

A comparative study of two different biocatalytic models, e.g. enzyme immobilized on magnetic particles (EIMP) and cross-linking enzyme aggregates onto magnetic particles (CLEMPA) was performed. The first model was designed as enzyme-immobilized on the magnetic particles surface (EIMP). The second model was constructed as a network structure with the enzyme aggregates and magnetic particles placed into the nodes and polyglutaraldehyde cross-linker as the network ledges. The design was called cross-linking enzyme aggregates onto magnetic particles (CLEMPA). The biocatalysts were prepared using lipase enzyme from Aspergillus niger for catalyzing the glycerol (Gly) conversion to glycerol carbonate (GlyC). The biocatalyst characteristics for both designs (EIMP and CLEMPA) were evaluated using scanning electron microscopy (SEM), laser light scattering (LLS) and UV-Vis techniques. The EIMP model was strongly influenced by the composition of the polymeric layer covering the particles surface, while the size of the magnetic particles affected mostly the CLEMPA design. Also, the biocatalytic capacity of the tested models was evaluated as maximum 52% Gly conversion with 90% GlyC selectivity for EIMP, and 73% Gly conversion with 77% GlyC selectivity for CLEMPA. Both biocatalytic models were successfully used to prepare GlyC from "crude" glycerol collected directly from the biodiesel process (e.g. 49% Gly conversion with 91% GlyC selectivity for EIMP and 70% Gly conversion with 80% GlyC selectivity for CLEMPA).

106. Covalent Functionalization of Graphene Oxide with Cisplatin

Authors: Ciobotaru, CC; Damian, CM; Matei, E; Iovu, H

Published: MAR 2014, MATERIALE PLASTICE, 51, 80, DOI:

The objective of this study was to obtain graphene oxide starting from graphite and to covalently functionalize this nanomaterial with Cisplatin. The presence of the drug was pointed out using different methods like FTIR Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), Thermogravimetric analysis (TGA), RAMAN Spectroscopy, X-Ray Diffraction and Scanning electron microscopy (SEM).

107. COVALENT FUNCTIONALIZATION OF SINGLE WALLED CARBON NANOTUBES WITH DOXORUBICIN FOR CONTROLLED DRUG DELIVERY SYSTEMS

Authors: Ciobotaru, CC; Damian, CM; Polosan, S; Matei, E; Iovu, H

Published: JAN-MAR 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 422, DOI:

The objective of this study was to obtain nanocomposites based on SWCNTs functionalized with carboxyl groups and doxorubicin (DOX) as a chemotherapeutic drug through covalent bonds formed by carboxyl groups from SWCNTs and amino groups from DOX. The formation of these nanocomposites was proved by using different characterization methods like Fourier transform Infrared spectroscopy and X-ray photoelectron spectroscopy (XPS). Also thermogravimetrical analysis was employed to study the thermal behavior of our nanocomposites. X-ray diffraction and Raman spectroscopy revealed that the surface was modified by the covalent bonding of DOX to SWCNTs. The in vitro drug release was studied by using UV-VIS Spectroscopy.

108. BaFBr:Eu2+ nanophosphor-SiO2 hybrid entrapped in Anodise Alumina membrane pores array

Authors: Secu, CE; Matei, E; Secu, M; Damian, V

Published: SEP 2014, RADIATION MEASUREMENTS, 68, 41, DOI: 10.1016/j.radmeas.2014.07.001

Sol-gel template method has been used to prepare BaFBr:Eu2+ nanophosphor-SiO2 hybrid entrapped within the nanopores array (of about 200 nm size) of a comercial anodized alumina (AA) membrane. Structural and morphological measurements using electron microscopy (SEM) and X-ray diffraction (XRD) have shown the presence of the BaFBr:Eu2+ nanophosphor in the silica xerogel entrapped within the nanopores array; photoluminescence and X-ray excited luminescence measurements have shown Eu2+ luminescence at 395 nm accompanied by a broad band due to AA membrane. The method assures a relatively uniform spreading of the BaFBr nanophosphor into the AA membrane pores array without the nanoparticles agglomeration. Preliminary imaging tests have shown a spatial resolution in the micrometer range and even in the submicrometer range can be expected. As BaFBr:Eu2+ is a very efficient Xray phosphor the material might be used as X-ray micro-imaging detector. (C) 2014 Elsevier Ltd. All rights reserved.

109. 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.

110. POLYESTER FABRICS COVERED WITH ZNO PARTICLES: PARTICLE INTERACTION WITH THE SURFACE SHOWN BY DIELECTRIC PROPERTIES

Authors: Ganea, CP; Frunza, L; Zgura, I; Preda, N; Matei, E; Frunza, S

Published: OCT-DEC 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 1503, DOI:

Polyester fabrics modified with ZnO particles by electroless deposition were investigated by broadband dielectric spectroscopy in a parallel capacitor between 10(-2) and 10(7) Hz in a temperature interval from ca. 123 to 473 K. Textile samples were routinely characterized for the structure and interaction of the ZnO particles with the fiber surface. Since a textile fabric material is a mixture of air and fibers, the parameters taken into consideration should be called as effective ones. The deposition of ZnO particles lead to complex dielectric spectra and to the temperature dependence of the decomposed peaks following Arrhenius law.

111. Characterization of hydrogenated and deuterated thin carbon films deposited by magnetron sputtering

Authors: Pantelica, D; Ionescu, P; Petrascu, H; Nita, CR; Matei, E; Rasoga, O; Acsente, T; Dinescu, G

Published: JUL 15 2014, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 331, 124, DOI: 10.1016/j.nimb.2014.01.029

Thin films of C layers were deposited by radiofrequency magnetron sputtering on silicon substrates using three gaseous atmospheres: pure Ar, Ar + H-2 and Ar + D-2 mixtures. Scanning Electron Microscopy investigations showed that addition of D-2 or H-2 to main sputtering gas (Ar) leads to the enhancement of the deposition rate while the layer morphology remained columnar. Fourier Transform Infrared Spectroscopy measurements revealed the presence of D-C or H-C chemical bonds in the samples. Ion beam analysis measurements performed by simultaneous recording of the recoiled H and D ions, and of backscattered He-4 confirmed the incorporation of hydrogen and deuterium in the deposited carbon thin films. (C) 2014 Elsevier B.V. All rights reserved.

112. 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.

113. Cu codoping control over magnetic precipitate formation in ZnCoO nanowires

Authors: Granville, S; Matei, E; Enculescu, I; Toimil-Molares, ME

Published: DEC 22 2014, APPLIED PHYSICS LETTERS, 105, DOI: 10.1063/1.4904987

Using electrodeposition, we have grown nanowires of ZnCoO with Cu codoping concentrations varying from 4-10 at. %, controlled only by the deposition potential. We demonstrate control over magnetic Co oxide nano-precipitate formation in the nanowires via the Cu concentration. The different magnetic behavior of the Co oxide nano-precipitates indicates the potential of ZnCoO for magnetic sensor applications. (C) 2014 AIP Publishing LLC.

114. Embedding of IrQ(ppy)(2) organometallic compounds in polypyrrole conducting polymer for OLED's applications

Authors: Ciobotaru, IC; Matei, E; Ciobotaru, CC; Polosan, S

Published: DEC 2014, SYNTHETIC METALS, 198, 328, DOI: 10.1016/j.synthmet.2014.10.041

Conducting polypyrrole:IrQ(ppy)(2) thin films were obtained by electrochemical method which ensure uniform dispersion of the organometallic in the polymer matrix. A thin layer of about 50 nm polypyrrole: IrQ(pPY)(2) thin films were deposited on the ITO/glass substrate and used for spectroscopic, structural, and electric characterization. The photoluminescence spectrum of polypyrrole:IrQ.(ppy)2 have shown the two main emissions of IrQ(ppy)(2) at 2.44 eV (508 nm) and 2 eV (620 nm) besides of the polypyrrole weak emission centered at 2.55 eV (485 nm). The electric conductivity of the doped polypyrrole thin layer has almost the same conductivity with the undoped polypyrrole thin film suggesting an homogenous polypyrrole:IrQ(ppy)(2) composite which can be used as emissive layer in the OLED's structures. (C) 2014 Elsevier B.V. All rights reserved.

115. Influence of 2,2 '-bipyridine on oxidative dissolution of iron monosulfide

Authors: Chirita, P; Badica, CE; Constantin, CA; Birsa, LM; Matei, E; Baibarac, M

Published: OCT-NOV 2014, SURFACE AND INTERFACE ANALYSIS, 46, 846, DOI: 10.1002/sia.5459

The 2,2'-bipyridine effects on iron monosulfide (FeS) oxidative dissolution rates have been examined by potentiodynamic polarization and electrochemical impedance spectroscopy. The adsorption of 2,2'-bipyridine to synthetic FeS was investigated by batch adsorption experiments, SEM, energy-dispersive X-ray analysis and Raman spectroscopy. The experiments were performed in air-saturated solutions at pH 5, 25 degrees C and an ionic strength of I = 0.004 M NaCl. Correlation between oxidative dissolution rates and 2,2'-bipyridine adsorption suggests that FeS oxidative dissolution is the result of two antagonistic processes: (i) the inhibiting adsorption of 2,2'-bipyridine on mineral surface and (ii) the promoting effect of 2,2'-bipyridine on the iron dissolution from FeS surface. Copyright (C) 2014 John Wiley & Sons, Ltd.

116. Magnetic configurations of Ni-Cu alloy nanowires obtained by the template method

Authors: Matei, E; Enculescu, I; Toimil-Molares, ME; Leca, A; Ghica, C; Kuncser, V

Published: AUG 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1863-3

High aspect ratio nanowires of Ni-Cu alloys have been synthesized by potentiostatic electrochemical deposition in etched ion-track membranes. The nickel-to-copper ratio in the nanowires was controlled via the deposition potential and electrochemical bath composition. We present a detailed study of nanowire properties including morphology, composition, and magnetic behavior. We report the magnetic configurations measured as function of the nanowire composition and discuss domain formation, anisotropy aspects, and local easy axis distributions.

117. 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.

118. Maghemite and poly-DL-alanine based core-shell multifunctional nanohybrids for environmental protection and biomedicine applications

Authors: Covaliu, CI; Paraschiv, G; Biris, SS; Jitaru, I; Vasile, E; Diamandescu, L; Velickovic, TC; Krstic, M; Ionita, V; Iovu, H; Matei, E

Published: NOV 15 2013, APPLIED SURFACE SCIENCE, 285, 95, DOI: 10.1016/j.apsusc.2013.08.059

This paper deals with the synthesis of two nanohybrid materials based on maghemite (gamma-Fe2O3) and poly-DL-alanine using a two-step procedure consisting of maghemite nanoparticles synthesis by microemulsion method and nanohybrids obtaining by coating of maghemite nanoparticles with poly-DL-alanine biopolymer in two different molar ratios (H1:5 and H1: 15). The maghemite and their corresponding nanohybrids were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoemission spectroscopy, Mossbauer spectroscopy, Transmission electron microscopy, High resolution transmission electron microscopy with selected area electron diffraction and Atomic absorption spectroscopy. The two nanohybrids under the investigation have the average particle sizes of 22 nm and 23 nm. The Fourier transform infrared spectroscopy spectra and X-ray photoemission spectroscopy data indicate the existence of some interactions between the maghemite nanoparticles and poly-DL-alanine shell. The saturation magnetization values for maghemite and the two nanohybrids determined by a Vibrating Sample Magnetometer correspond to a typical superparamagnetic behavior suitable for applying in biomedical field. Also, with respect of biomedical application the biological activity of maghemite and its corresponding nanohybrids was investigated on healthy human cells (PBMC) and cancerous cells (HeLa). Furthermore, in order to support the multifunctionality of the gamma-Fe2O3 sample and nanohybrids we also investigated their wastewater treatment properties by measuring the removal efficiency of heavy metal Cd (II) ions. (C) 2013 Elsevier B. V. All rights reserved.

119. Synthetic fabrics coated with zinc oxide nanoparticles by electroless deposition: Structural characterization and wetting properties

Authors: Frunza, L; Preda, N; Matei, E; Frunza, S; Ganea, CP; Vlaicu, AM; Diamandescu, L; Dorogan, A

Published: OCT 1 2013, JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, 51, +, DOI: 10.1002/polb.23346

Electroless deposition was successfully applied in developing crystalline particles of zinc oxide onto polyester textile materials; this deposition is here presented in comparison with other materials made from poly(lactic acid), polyamide or hemp. Structural and spectroscopic characterization of the raw and deposited samples has been performed. The structure of zinc oxide particles was that of wurtzite type as indicated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Crystallites were 20-500 nm in diameter and up to 1 mu m in length. The grown particles cover the fibers not only on the fabric surface but in the textile depth. 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 superhydrophobic properties onto polyester fabrics, for which water contact angles exceed 150 degrees. The other functionalized samples also become more hydrophobic after deposition. Cassie-Baxter model was found suitable to describe the behavior, though the fraction of surface occupied by the water-solid interface is high enough. The electroless deposition technique applied previously for cotton fabrics was once more proven to be highly reproducible, easy scalable, and cheap, allowing a wide range of applications. (c) 2013 Wiley Periodicals, Inc.

120. 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.

121. 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.

122. 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.

123. COMPARATIVE SURVEY OF THE MOST USED SELF ADHESIVE DENTAL CEMENTS BASED ON RESIN COMPOSITES

Authors: Gatin, E; Matei, E; Pirvu, D; Galbinasu, B; Iordache, S

Published: JAN-MAR 2012, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 7, 214, DOI:

The present study is dedicated to the investigation of self-adhesive cements, based on resin composites (RBC). Reported cases of dental restorations decays, are influenced by interface/surface quality and marginal adaptation to dentin and enamel. The influence is given by organic and inorganic (filler) phase as well. Regarding the organic phase, this is involved in bonding with dentin remains and enamel. Differences were noticed between the investigated materials; results from EDX patterns reveal major differences between inorganic phase (filler) in specimens and a non homogenous state for all samples. Results are confirmed by the mapping patterns. Low discontinuity areas for samples specimen were remarked for Biscem and RelyXU100 samples, then for MaxcemElite dental cement. Regarding mechanical properties, those are dramatically influenced by the filler. The major determination is given by the particles size and state of homogeneity for a given specimens composition. SEM results revealed a textured structure with a small filler particles size for RelyX U100 than other samples (less than, d - 1 mu m). A stirring method is recommended for all samples before application for an improved homogeneity.

124. 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.

125. Interaction of NaYF4:Er:Yb Nanoparticles with Phospholipid Monolayers as Models of Biological Membranes

Authors: Petrescu, L; Cinteza, O; Voiculescu, AM; Rosu, T; Enculescu, I; Matei, E; Georgescu, S; Birjega, R; Avram, S; Mihailescu, D

Published: SEP 2012, REVISTA DE CHIMIE, 63, 961, DOI:

Given the evolution of imaging techniques in the biomedical field is becoming more necessary to develop sensitive markers, less toxic and not least more economical. Upconverting luminescent nanocrystals doped with rare earth ions, excited in infrared and emitting in visible, are considered real concurrent to classical fluorescent markers, featuring a number of advantages in rapport with them. The aim of this study is to prepare NaYF4 nanoparticles doped with erbium and ytterbium for biological applications in bioimaging techniques. After synthesis, upconverting nano particles were coated with SiO2 for surface sealing and passivation. The nano particles were characterized by X-ray diffraction, luminescence spectroscopy, electronic microscopy and dynamic light scattering. The interaction of the nanoparticles with mimicking cell membrane models was studied. NaYF4 nanoparticles showed a good size distribution and good emission efficiency. The uncoated nanoparticles increase the fluidity of the lipid monolayer, while the effect of the silica coated nanoparticles is substantially reduced.

126. 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.

127. Electrodeposited ZnO films with high UV emission properties

Authors: Matei, E; Enculescu, I

Published: NOV 2011, MATERIALS RESEARCH BULLETIN, 46, 2154, DOI: 10.1016/j.materresbull.2011.04.025

We report here our results in the preparation of ZnO films with high UV band to band characteristic luminescence emission by potentiostatic electrodeposition. Zinc nitrate aqueous baths with different concentration and additives were employed for the preparation of the films on platinum substrates. We focused our research in determining how the electrodeposition bath composition, i.e. zinc nitrate concentration and addition of KCI or polyvinyl pyrolidone and applied overpotential influence the morphological and optical properties of the oxide films. Scanning electron microscopy was employed for characterizing the films in terms of morphology. Optical reflection, photoluminescence spectroscopy and cathodoluminescence were used for determining the optical characteristics of the samples. The morphology of the deposit varies from hexagonal prisms to platelets as a function of the deposition rate. This experimental parameter also influences the luminescence properties. We found that at low deposition rates high UV luminescent material is obtained. (C) 2011 Elsevier Ltd. All rights reserved.

128. 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.

129. Electrochemical Growth of Eosin Y/Manganese Doped ZnO as Hybrid Films and Nanowires

Authors: Sima, M; Visan, T; Matei, E; Ungureanu, F; Enculescu, I; Sima, M

Published: 2011, ZEITSCHRIFT FUR PHYSIKALISCHE CHEMIE-INTERNATIONAL JOURNAL OF RESEARCH IN PHYSICAL CHEMISTRY & CHEMICAL PHYSICS, 225, 339, DOI: 10.1524/zpch.2011.0042

The electrodeposition process of Eosin Y/ZnO:Mn as films and nanowires performed using a solution containing zinc and manganese nitrates + lactic acid mixture was studied by linear voltammetry. The films and wires grown by polarization at -1.1 V/SCE electrode potential were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). Additionally, the Eosin Y presence was evidenced by optical measurements as absorption and photoluminescence spectroscopy. The manganese content in films depends on the nature of support electrode used. On the other hand, the presence of Eosin Y species in the deposition bath increased significantly the manganese concentration in the ZnO:Mn nanowires electrodeposited at -1.1 V/SCE.

130. Upconversion luminescence of Er, Yb - doped nanolanganite powders synthesized by a citrate sol-gel method

Authors: Voiculescu, AM; Georgescu, S; Toma, O; Nastase, S; Birjega, R; Petrescu, L; Enculescu, I; Matei, E

Published: NOV 2011, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 1173, DOI:

Langanite nanopowders doped with erbium and ytterbium were prepared by a citrate sol-gel method and annealed in air at various temperatures between 700 degrees C and 1000 degrees C. For annealing temperatures 900 degrees C and 1000 degrees C, part of the langanite transforms in perovskite (LaGaO(3)), as evidenced in XRD spectra. The reddish color of the powders due to color centers associated to oxygen defects intensifies with increasing annealing temperature. Green and red luminescence was obtained for IR (933 nm) pumping and only green for UV pump. The mechanisms involved in luminescence and energy transfer processes are presented and discussed.

131. 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.

132. Thin films of arylenevinylene oligomers prepared by MAPLE for applications in non-linear optics

Authors: Stanculescu, A; Vacareanu, L; Grigoras, M; Socol, M; Socol, G; Stanculescu, F; Preda, N; Matei, E; Ionita, I; Girtan, M; Mihailescu, IN

Published: APR 1 2011, APPLIED SURFACE SCIENCE, 257, 5302, DOI: 10.1016/j.apsusc.2010.11.094

This paper discusses two arylenevinylene oligomers with optical nonlinear properties. Their trans molecular structure was confirmed by Fourier Transform Infrared Spectroscopy and Nuclear Magnetic Resonance. Second Harmonic Generation and two-photon fluorescence have been observed on Matrix Assisted Pulsed Laser Evaporation-deposited thin films. We have seen two local maxima in UV-Vis spectra and a red shift of the photoluminescence peak for carbazole-based oligomer, which can be correlated with a higher conformational flexibility and with strong polarization interactions in the solid state. Scanning Electron Microscopy and Atomic Force Microscopy images have revealed a grainy morphology of the film deposited on titanium and a higher roughness for carbazole-based oligomer. Second harmonic measurements have shown nearly equal values of the second-order nonlinear optical coefficient for the triphenylamine and carbazole-based oligomers for P-laser < 100 mW. z-Scan and x-scan representations of the carbazole-based oligomer film have shown strong two-photon fluorescence intensity inside the sample confirming a volume process, and a strong second harmonic at the surface of the sample determined by the surface morphology. (C) 2010 Elsevier B.V. All rights reserved.

133. 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.

134. LASER INDUCED CRYSTALLIZATION IN SPUTTERED FeSiB THIN FILMS

Authors: Tolea, F; Stoica, M; Matei, E; Cristescu, CP

Published: 2010, UNIVERSITY POLITEHNICA OF BUCHAREST SCIENTIFIC BULLETIN-SERIES A-APPLIED MATHEMATICS AND PHYSICS, 72, 256, DOI:

Thin films with nominal composition Fe(78)Si(9)B(13) generated by radio-frequency (rf) sputtering on Si substrates with (100) orientation were irradiated with an eyeliner laser with 130mJ/cm(2) fluence. Information on the induced structural changes were obtained by X-ray diffraction and scanning electron microscopy, while the magnetization curves were determined by the magneto-optical Kerr effect. The effects of the irradiation consist in the growing of crystallites,appearence of melted and ultra-fast frozen zones, surface oxidation and changes in the magnetic properties of the thin films.

135. STRUCTURAL DETAILS OF THE Ag-As2S3 INTERFACE OBTAINED BY VACUUM THERMAL EVAPORATION FOLLOWED BY GREEN LASER IRRADIATION

Authors: Lorinczi, A; Velea, A; Matei, E; Simandan, ID; Popescu, M

Published: NOV 2010, CHALCOGENIDE LETTERS, 7, 612, DOI:

As2S3 on Ag heterostructures deposited onto microscope glass substrates have been prepared. The quality of the hetero-structures has been investigated by careful analysis of the scanning electron microscope pictures taken on the native cross-sections, produced after the vacuum deposition sequence and various green laser irradiation times. The As2S3 layer is not uniformly grown, but reveals a columnar-like structure and multi-scale aggregation.

136. Semiconductor Hybrid Structure: Nanowires Embedded in a Matrix from the Same Material

Authors: Sima, M; Vasile, E; Sima, M; Matei, E

Published: 2010, SEMICONDUCTORS, METAL OXIDES, AND COMPOSITES: METALLIZATION AND ELECTRODEPOSITION OF THIN FILMS AND NANOSTRUCTURES, 25, 161, DOI: 10.1149/1.3318514

Hybrid systems obtained by incorporation of a nanostructurated material into a matrix from the same thermoelectric (TE) material are predicted to show an increased TE efficiency compared to classical bulk materials. The authors have synthesized Bi1.95Te2.7Se0.35 submicron wires by electrodeposition into a polycarbonate membrane; after polymer membrane dissolution, the wire array supported on a metallic film was electrochemically embedded in a Bi2Te2.65Se0.35 film in order to prepare a hybrid structure. Wires and hybrid structure were analyzed by scanning electron microscopy (SEM), energy X-ray spectrometry (EDX) and X-ray diffraction (XRD).

137. 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.

138. Optical and morphologic properties of YVO4:Eu phosphor

Authors: Georgescu, S; Voiculescu, AM; Cotoi, E; Toma, O; Gheorghe, L; Achim, A; Matei, C; Enculescu, I; Matei, E; Osiac, M

Published: 2010, ROMOPTO 2009: NINTH CONFERENCE ON OPTICS: MICRO- TO NANOPHOTONICS II, 7469, DOI: 10.1117/12.866769

In this paper we present new results concerning the optical and morphologic properties of YVO4:Eu red nanophosphor prepared by a precipitation method and subsequently annealed in air at various temperatures. We monitored the morphologic changes induced by the thermal treatments using the optical spectroscopy (reflectance and luminescence spectra), XRD and electron microscopy. The annealing leads to an increase of the particle size and improvement of the order of the crystalline lattice of YVO4. The annealing at 800 degrees C produces the sample with the highest luminescence intensity.

139. Multisegment CdTe nanowire homojunction photodiode

Authors: Matei, E; Ion, L; Antohe, S; Neumann, R; Enculescu, I

Published: MAR 12 2010, NANOTECHNOLOGY, 21, DOI: 10.1088/0957-4484/21/10/105202

Electrochemical deposition in nanoporous ion track membranes is used for the preparation of multisegment CdTe-homojunction diode nanowires. Our study is based on the fact that the deposition overpotential strongly influences the composition of the compound semiconductor nanowires. Therefore, the transport behavior of the nanowire devices can be tailored by appropriately choosing a certain sequence of electrodeposition potentials. The wires were characterized using scanning electron microscopy, energy dispersive x-ray analysis, optical spectroscopy and x-ray diffraction. The current-voltage characteristics measured prove that, by appropriately choosing the voltage pulse pattern, one can fabricate nanowires with ohmic or rectifying behavior. The semiconducting nanowires are sensitive to light, their spectral sensitivity being characteristic of CdTe. The preparation of functional nanostructures in such a simple approach provides, as a major advantage, an increase in the process reproducibility and opens a wide field of potential optoelectronic applications.

140. Structure and properties of silver doped SnSe2 and Ge2Sb2Te5 thin films prepared by pulsed laser deposition

Authors: Popescu, M; Velea, A; Sava, F; Lorinczi, A; Tomescu, A; Simion, C; Matei, E; Socol, G; Mihailescu, IN; Andonie, A; Stamatin, I

Published: MAR 2010, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 207, 520, DOI: 10.1002/pssa.200982900

Amorphous thin films of SnSe2 and Ge2Sb2Te5 doped by different amount of silver (0.1, 0.2, 0.5 and 1 Ag atoms per formula unit) have been prepared by pulsed laser deposition (PLD) starting from solid polycrystalline targets. The films were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The good gas sensing properties for CO, as well as the sensitivity for CH4 and NO of the Ag; doped SnSe2 films have been demonstrated in the composition SnSe2Ag0.2. The structural effect of silver introduced in Ge2Sb2Te5 matrix has been investigated. The freshly deposited thin films doped by various amount of Ag develop three phases: an amorphous one, and two crystalline phases consisting of a major fcc cubic phase of AgSbTe2 and a minor cubic phase of composition Ag2Te. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

141. Synthesis of Eu-doped bismuth germanate nano-ceramic powder

Authors: Polosan, S; Matei, E; Logofatu, C

Published: OCT 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1508, DOI:

Europium doped Bi(4)Ge(3)O(12) nanocrystals were successfully obtained by solid state reaction between precursor oxides at 800 degrees C. The XRD and XPS measurements shows an increasing of the lattice constant in the case of Eu:BGO nanocrystals, due to the electropositive character of Eu(III) ions compared with the host cations, which induces an ionic character for Eu-O bound and a more covalent one for the Ge-O bounds. The photoluminescence of Eu:BGO due to (5)D(0) -> (7)F(2) transition have a lower splitting compared with Eu:BGO monocrystals suggesting a lower crystal field in the sintered nanocrystals, due to a mixing between the crystalline and amorphous phases.

142. 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.

143. Cobalt-doped ZnO prepared by electrochemistry: Chemistry, morphology, and magnetism

Authors: Matei, E; Enculescu, I; Vasilache, V; Teodorescu, CM

Published: NOV 2010, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 207, 2522, DOI: 10.1002/pssa.200925378

ZnO:Co thin films are prepared by electrochemical deposition at different overpotentials and investigated by scanning electron microscopy, optical spectroscopy, and cathodoluminescence, X-ray photoelectron spectroscopy and Kerr magnetometry (MOKE). An increase of structural disorder and crystallite reorientation are observed for cobalt-doped samples. MOKE magnetometry revealed room-temperature ferromagnetic behavior only for ZnO: Co deposited at -850 mV. These are the samples with the lower cobalt content and lowest structural perturbation of the ZnO matrix by cobalt. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

144. 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.

145. Magnetic properties of NiCu thin films obtained by electrodeposition

Authors: Bazavan, D; Bazavan, R; Enculescu, I; Matei, E; Necula, C; Ion, L; Antohe, S

Published: MAY 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 488, DOI:

Using an electrochemical method have been produced NiCu thin films for magnetic applications. The recent development of first-order reversal curve (FORC) diagrams has allowed the detailed investigation of coercivity spectra, interaction and domain states of magnetic thin films. Their magnetic properties have been investigated by Micro Mag (TM) 3900 Vibrating Sample Magnetometer (VSM) and are discussed.

146. Cobalt doped ZnO prepared by electrochemistry: chemistry, morphology, and magnetism

Authors: Enculescu, I; Matei, E; Vasilache, V; Teodorescu, CM

Published: 2009, NANOTECH CONFERENCE & EXPO 2009, VOL 3, TECHNICAL PROCEEDINGS: NANOTECHNOLOGY 2009: BIOFUELS, RENEWABLE ENERGY, COATINGS FLUIDICS AND COMPACT MODELING, +, DOI:

ZnO:Co thin Films are prepared by electrochemical deposition at different overpotentials and investigated by scanning electron microscopy, X-ray photoelectron spectroscopy and Kerr magnetometry (MOKE). Increse of structural disorder and crystallite re-orientation are observed for cobalt doped samples (especially for those obtained at - 750 and at - 800 mV overpotentials). MOKE magnetometry revealed room temperature ferromagnetic behaviour only for ZnO:Co deposited at - 850 mV. These are the samples with the less cobalt content and lowest structural perturbation of the ZnO matrix by cobalt.

147. 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.

148. Chalcogenide photonic structures

Authors: Popescu, M; Savastru, D; Popescu, A; Miclos, S; Lorinczi, A; Sava, F; Velea, A; Baschir, L; Ciobanu, M; Matei, E; Socol, G; Mihailescu, IN; Niciu, H

Published: SEP 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 859, DOI:

Chalcogenide glasses can be tailored for getting special configurations with photonic crystal properties A review on the advances in chalcogenide glass photonics is given Several methods to prepare two-dimensional photonic As-S glass and three-dimensional packing have been developed, and the photonic structures have been characterized Numerical simulations have also been performed The chalcogenide photonic structures fabricated by micro-technological procedures are described and tuned to work in the far infrared region of the electromagnetic spectrum

149. Titanium oxide thin films produced by pulsed laser deposition

Authors: Sima, C; Grigoriu, C; Viespe, C; Pasuk, I; Matei, E

Published: JUN 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 830, DOI:

The structural peculiarities of titanium oxide films formed by pulsed laser deposition have been investigated. A pure titanium target was irradiated by a Nd:YAG laser (355 and 532 nm). The work studied the influence of the beam wavelength, and oxygen pressure (20, 40, 80, and 160 mTorr) upon the layer structure. The films deposited at room temperature were partly crystalline. The crystalline fraction was a mixture of titanium sub-oxides. The 532 nm wavelength seems to favour the oxidation of titanium leading to TiO(2) formation even at room temperature. After annealing, crystalline TiO(2-) anatase formed at both irradiation wavelengths, but only at low oxygen pressures (20 and 40 mTorr). The best crystallization occurs in the layers deposited at the lowest oxygen pressure (20 mTorr), at both laser beam wavelengths; most anatase formed in the sample obtained at 20 mTorr, 532 nm. At 20 mTorr the films were compact, for both wavelengths, but also tilted or randomly distributed columnar grains were observed at higher pressure. The films deposited with 355 nm, were thinner than those with 532 nm; at 355 nm the thickness decreased at higher pressure, while at 532 nm the dependence was opposite.

150. 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.

151. 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.

152. 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.

153. Preparation and Properties of Cobalt Doped ZnO Nanowires

Authors: Enculescu, I; Matei, E; Sima, M; Neumann, R; Granville, S; Ansermet, JP

Published: NOV 2008, IEEE TRANSACTIONS ON MAGNETICS, 44, 2680, DOI: 10.1109/TMAG.2008.2003242

The template method was used for preparing Zn1-xCoxO nanowires with x ranging from 0.01 to 0.05. Thus, electrochemical deposition was employed for filling up the pores of polycarbonate ion track nanoporous membranes with the desired material. The method allows a good control over the morphology and composition of the deposited nanowires, as evidenced by scanning electron microscopy (SEM) and energy dispersive X ray analysis (EDX). Measurements of the magnetic properties showed a paramagnetic behavior of the nanowire arrays for the whole set of temperatures and Co concentrations.

154. 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.

155. Phase-change electrical memory elements and devices

Authors: Popescu, M; Lorinczi, A; Sava, F; Velea, A; Matei, E; Socol, G; Mihailescu, IN

Published: OCT 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2621, DOI:

Electrical memory elements based on Ge-Sb-Te pure and doped by Sn-Se have been obtained by pulsed laser deposition on special substrates covered by gold as well as on common glass. A set of electrical memory elements in a 4x4 matrix structure on the glass substrate has been produced. Devices with 3 and 10 memory elements have been constructed and tested for their memory properties. The special features of the voltage-current characteristics have been revealed.

156. Luminescence and EPR study of ZnO : Mn : Cu nanowire array

Authors: Sima, M; Enculescu, I; Grecu, MN; Secu, M; Sima, M; Matei, E; Vasile, V

Published: MAY 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 2498, DOI: 10.1016/j.physe.2007.08.075

We report on photoluminescence studies on manganese and copper-doped ZnO nanowire array prepared by template method. The ZnO:Mn:Cu semiconductor grown using the electrochemical technique was characterized by electron paramagnetic resonance (EPR) and optical reflection measurements. Morphology and the structure were observed by SEM and X-ray diffraction. The photoluminescence of this system was correlated with manganese and copper concentration in the ZnO matrix. (C) 2007 Elsevier B.V. All rights reserved.

157. Structural and morphological properties of NiCu magnetic thin films

Authors: Bazavan, D; Bazavan, R; Enculescu, I; Matei, E; Ion, L; Antohe, S

Published: NOV 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3057, DOI:

NiCu thin films for magnetic applications have been produced by using an electrochemical method. Their structural and morphological properties have been investigated by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM and EDX) and are discussed in correlation with the growth conditions.

158. 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.

159. Electrochemical growth and characterization of nanostructured ZnO thin films

Authors: Ghica, C; Enculescu, I; Nistor, LC; Matei, E; Van Tendeloo, G

Published: DEC 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3240, DOI:

ZnO is a wide band-gap (ca. 3.4 eV) semiconductor, piezoelectric, pyroelectric, biocompatible, transparent in the visible spectrum and UV light emitting material. The fabrication in 2001 of the first nanobelts of semiconductor oxide materials lead to a rapid expansion of researches concerning one dimensional nanostructures (nanotubes, nanowires, nanobelts), given their possible application in optics, optoelectronics, piezoelectricity, catalysis. Researches carried on up to date evidenced the possibility to obtain an extraordinary variety of ZnO nanostructures, in function of the experimental parameters and the used growth methods. In this work we present morphostructural results on nanostructured ZnO layers obtained by electrochemical deposition. The films have been grown on gold covered glass plates and Si wafers, in various experimental conditions such as: nature of the wetting agents, electrical polarization of the substrate (continuous, pulsed). The influence of the growth conditions on the crystalline structure and morphology of the films is revealed by scanning and transmission electron microscopy studies. The films show a variety of growth morphologies, from entangled-wires-like to honeycomb-like layers. These large-specific-surface layers will be tested as nanostructured substrates for photovoltaic cells with improved efficiency.

Dr. Elena MATEI

Scientific Researcher I