2. Articole

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Author: search.filters.author.Ursachi, Veaceslav

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    MORPHOLOGY AND LUMINESCENCE PROPERTIES OF ZnO LAYERS PRODUCED BY MAGNETRON SPATTERING
    (Technical University of Moldova, 2011-07-07) Rusu, Emil; Ghițu, Irina; Prilepov, Vladimir; Zamalai, Victor; Ursachi, Veaceslav
    We show that the morphology and the luminescence properties of ZnO layers produced by magnetron sputtering can be controlled by technological parameters of sputtering, particularly by the ratio of argon to oxygen gases in the gas flow during the growth process. Smooth and flat layers were produced with a high Ar/O ratio, while porous layers with various morphologies were obtained with a low Ar/O ratio. The layers produced with O/Ar ration equal to 10 exhibit extremely high near-bandgap luminescence intensity even higher in comparison with bulk ZnO single crystals. The free carrier density estimated from the analysis of photoluminescence spectra is also very high in these samples suggesting that these technological conditions promote both optical and electrical activation of the doping Al impurity. The samples grown with high Ar/O ratios exhibit strong visible emission which is controlled by the technological conditions.
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    PREPARATION AND CHARACTERIZATION OF Ga 2O 3 AND GaN NANOPARTICLES
    (SPIE, 2015) Rusu, Emil; Ursachi, Veaceslav; Raevschi, Simion; Vlazan, Paulina
    In 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.
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    AERO-TiO2 PREPARED ON THE BASIS OF NETWORKS OF ZnO TETRAPODS
    (2022) Ciobanu, Vladimir; Ursachi, Veaceslav; Lehmann, Sebastian; Braniște, Tudor; Raevschi, Simion; Zamalai, Victor V.; Monaico, Eduard V.; Colpo, Pascal; Nielsch, Kornelius; Tighineanu, Ion
    In this paper, new aeromaterials are proposed on the basis of titania thin films deposited using atomic layer deposition (ALD) on a sacrificial network of ZnO microtetrapods. The technol-ogy consists of two technological steps applied after ALD, namely, thermal treatment at different temperatures and etching of the sacrificial template. Two procedures are applied for etching, one of which is wet etching in a citric acid aqua solution, while the other one is etching in a hydride vapor phase epitaxy (HVPE) system with HCl and hydrogen chemicals. The morphology, composition, and crystal structure of the produced aeromaterials are investigated depending on the temperature of annealing and the sequence of the technological steps. The performed photoluminescence analysis suggests that the developed aeromaterials are potential candidates for photocatalytic applications.
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    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, Paulina
    We 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.