2. Articole
Permanent URI for this collectionhttps://msuir.usm.md/handle/123456789/47
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Item PREPARATION AND CHARACTERIZATION OF Ga 2O 3 AND GaN NANOPARTICLES(SPIE, 2015) Rusu, Emil; Ursachi, Veaceslav; Raevschi, Simion; Vlazan, PaulinaIn this communication, we present results on preparation of GaN nanoparticles by conversion of Ga 2O 3 nanocrystals in a flow of NH 3 and H 2. The monoclinic Ga2O 3 nanoparticles have been prepared by hydrothermal method with gallium nitrate and sodium hydroxide as precursors. Ga2O 3 nanowires are produced with increasing the duration of the hydrothermal process up to 24 hours. The production of β-phase Ga2O 3 has been confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. According to XRD, Raman and FTIR spectra, wurtzite type GaN nanocrystals with an average size of 28.6 nm are obtained by nitridation of Ga2O3 nanoparticles. Doping of Ga2O 3 nanomaterial with Eu 3+ ions in the hydrothermal process is demonstrated, and the emission spectra of this Eu-doped nanomaterial are compared with those of Eu-doped nanoparticles prepared previously by solid state reactions.Item PHOTOLUMINESCENCE STUDY OF Eu-DOPED Ga2O3 AND GaN NANOWIRES AND NANOPARTICLES PRODUCED BY HYDROTHERMAL GROWTH(Editura "Tehnica-UTM", 2015-05-20) Rusu, Emil; Ursachi, Veaceslav; Culeac, Ion; Raevschi, Simion; Vlazan, PaulinaWe present results on preparation of Eu doped GaN nanoparticles and nanowires on the basis of Ga2O3 nanomaterial produced by hydrothermal growth. The monoclinic Ga2O3 nanoparticles and nanowires have been prepared with gallium nitrate and sodium hydroxide as precursors. nanomaterial produced by hydrothermal growth. The monoclinic Ga2O3 nanoparticles and nanowires have been prepared with gallium nitrate and sodium hydroxide as precursors. The geometrical form on the nanomaterial is determined by the duration of the hydrothermal process. The Ga2O3 nanomaterial is transformed unto GaN nanoparticles and nanowires by nitridation in a flow of NH3 and H2. The photoluminescence properties Eu doped Ga2O3 and GaN nanomaterial are investigated under pulsed and continuum wave excitation. The produced material is also investigated by means of XRD analysis, Raman scattering and Fourier transform infrared (FTIR) spectroscopy.Item SYNTHESIS AND PROPERTIES OF AL-DOPED ZnO THIN FILMS FOR PHOTOVOLTAICS(Institute of Electrical and Electronics Engineers Inc., 2018-11-27) Potlog, Tamara; Lungu, Ion; Botnariuc, Vasile; Gorceac, Leonid; Raevschi, Simion; Taku, Miyake; Worasawat, Suchada; Mimura, HidenoriPolycrystalline undoped and Al-doped ZnO thin films were deposited by spray pyrolysis using oxygen and argon atmospheres. The influence of postdeposition vacuum annealing on the structure, morphology and optical properties was studied by X-ray diffraction, atomic force microscopy and UV–VIS spectroscopy. The thermal vacuum annealing induces structural and morphological changes, especially in Al-doped ZnO thin films synthetized in oxygen atmosphere. Further on, the electrical conductivity in dependence of the nature of gas atmosphere and Al concentration is discussed.Item THE CARACTERIZATION OF THE CdS-BASED SOLAR CELL HETEROJUNCTIONS(Institute of Electrical and Electronics Engineers Inc., 2010-10-11) Potlog, Tamara; Botnariuc, Vasile; Gorceac, Leonid; Spalatu, Nicolae; Maticiuc, Natalia; Raevschi, SimionThe CdS-based solar cell heterojunctions (HJ) have been obtained by growth of CdS at relatively lower temperature using the close space sublimation method(CSS). Investigation of the photovoltaic characteristics shows an efficiency of about 12 % for InP/CdS and 9.6 % for CdS/CdTe solar cell HJ. The analysis of the forward dark current-voltage and the capacitance-voltage characteristics indicate a tunnelling recombination current which flows through states near or at the interfaces of a thermal energy of about 0.62 eV for CdS/CdTe and 0.42 eV for InP/CdS solar cell heterojunctions. The solar energy conversion efficiency is influenced by the interface states through the open circuit voltage and the fill factor.Item ABOUT THE EDGE LUMINESCENCE OF CADMIUM SULPHIDE THIN LAYERS GROWN ON MOLYBDENUM(Institute of Electrical and Electronics Engineers, 1995-11-11) Raevschi, Simion; Gorceac, Leonid; Coval, Andrei; Chetruș, PetruCdS layers on to molybdenum were synthesized from separate elements in an open flowing hydrogen set. The surface micromorphology and some electrical and photoluminescent properties were investigated. The nature of layers edge photoluminescence peaks are discussed in the frames of the excitated exciton model.Item THIN AlN FILMS GROWTH ON Si (III) BY HYDRIDE VAPOR PHASE EPITAXY(2008) Raevschi, Simion; Davydov, Valerii; Zhilaev, Yurii; Gorceac, Leonid; Botnariuc, VasileThin AlN layers have been grown on Si (111) by hydride vapor phase epitaxy (HVPE) method in a horizontal quartz reactor. The surface of layers has been studied by scanning electron microscopy and by the Raman spectroscopy method and found to have the structured morphology. It has been determined that the layers have high specific electrical resistance and are strained in the plane of the substrate.Item EFFECT OF CARRIER GAS AND VACUUM ANNEALING ON THE PHYSICAL PROPERTIES OF ZnO THIN FILMS DOPED WITH GALLIUM BY CHEMICAL SPRAY PYROLYSIS(Editura "Tehnica-UTM", 2018-05-24) Potlog, Tamara; Lungu, Ion; Botnariuc, Vasile; Raevschi, Simion; Worasawat, Suchada; Mimura, Hidenori; Gorceac, LeonidStructural, optical and electrical properties of zinc oxide thin films doped with 2% Ga, annealed in the vacuum at the same temperature and obtained onto glass substrates by the chemical spray pyrolysis method in the different gas atmospheres were investigated by X-ray Diffraction (XRD), UV-VIS spectrophotometry and Hall measurements, respectively. XRD studies revealed that all films were polycrystalline in nature, with a hexagonal wurtzite crystal structure and a predominant (002) c-axis orientation. All ZnO:Ga thin films had higher than 80 % transmittances in the visible region. Doping with 2% Ga led to a decrease in the optical band gap indifferent of the nature of the carrier gas. The synthesis of ZnO thin films with 2% Ga doping and annealing in the same conditions in Ar and O2 atmospheres led to the lower conductivity with electron concentration of 1016 cm−3.Item THE INTERACTION BETWEEN ENDOTHELIAL CELLS AND GALLIUM NITRIDE NANOPARTICLES(2019) Braniste, Tudor; Andree, Birgit; Benecke, Nils; Raevschi, Simion; Plesco, Irina; Cebotari, Serghei; Haverich, Axel; Tighineanu, Ion; Hilfiker, AndresIn this study, human umbilical vein endothelial cells (HUVECs) were investigated in direct contact with Gallium Nitride (GaN/Fe) based nanoparticles. GaN is a compound semiconduc- tor material, with remarkable characteristics including piezoelectric properties, high thermal stability, radiation hardness and excellent chemical inertness, which make it promising for biomedical applications. There is, however, limited knowledge about the biocompatibility of nanostructured GaN and the impact of GaN nanoparticles on living cells. We report on growth and characterization of GaN/ZnFe2O4 multifunctional piezoelectric and magnetic nanoparticles as well as on their assimilation and interaction with HUVECs. Thin GaN layers were grown on ZnFe2O4 nanoparticles with sizes up to 100 nm, using Hydride Vapor Phase Epitaxy (HVPE). After GaN growth, the sacrificial core of nanoparticles was decomposed at high temperatures in hydrogen flow, the final composition of nanoparticles corresponding to GaN:Fe. The resulted nanoparticles were incubated with human umbilical vein endothelial cells in order to remotely influence the cells activity through nanoparticles. By cultivating cells in medium supplemented with different concentrations of nanoparticles, we show that HUVECs tolerate GaN nanoparticles. The obtained results show that, being uptaken by the cells, the GaN nanoparticles are deposited into vesicles and thus can be used as guiding elements for controlled transportation or designed spatial distribution of cells in a magnetic field, which represent a step forward towards application in cellular therapy.Item STANAT DE CADMIU OBŢINUT PRIN METODA PULVERIZĂRII(CEP USM, 2013-09-26) Botnariuc, Vasile; Gorceac, Leonid; Coval, Andrei; Inculeţ, Ion; Chetruş, Petru; Raevschi, SimionItem TERAHERTZ SHIELDING PROPERTIES OF AERO-GaN(IOP Publishing Ltd, 2019) Braniste, Tudor; Dragoman, Mircea; Alyabyeva, Liudmila; Zhukov, Sergey; Ciobanu, Vladimir; Aldrigo, Martino; Raevschi, Simion; Dragoman, Daniela; Iordanescu, Sergiu; Shree, Sindu; Gorshunov, Boris; Adelung, Rainer; Tiginyanu, IonThe electrodynamic properties of the first aero-material based on compound semiconductor namely of Aero-GaN, in the terahertz frequency region are experimentally investigated. Spectra of complex dielectric permittivity, refractive index, surface impedance are measured at frequencies 4–100 cm−1 and in the temperature interval 4–300 K. The shielding properties are found based on experimental data. The aero-material shows excellent shielding effectiveness in the frequency range from 0.1 to 1.3 THz, exceeding 40 dB in a huge frequency bandwidth, which is of high interest for industrial applications. These results place the aero-GaN among the best THz shielding materials known today.
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