Facultatea de Fizică şi Inginerie / Faculty of Physics and Engineering
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Item Magnetotransport properties of ultrathin LaMnO3 layers [Articol](Technical University of Moldova, 2011-07-07) Șapoval, Oleg; Belenciuc, Alexandr; Zasavițchi, Efim; Canțer, Valeriu; Moșneaga, VasiliiWe report the transport and magnetic properties of La-deficient ultrathin films of La1-MnO3 (LMO) grown on SrTiO3 (STO) and engineered by using different interfacial layers. LMO layer and adjusting interface oxide (LaO-STO and SMO) layers were grown by a metalorganic aerosol deposition technique with monolayer accuracy. The role of LaO-TiO2 interface in the formation of ferromagnetic metallic state in very thin LMO films was demonstrated. Ferromagnetic metallic ground state in LMO films with the thickness down to 6 monolayers is stabilized by a combination of a La-deficiency and the interface-induced doping.Item Ultrathin manganite layers [Articol](2011) Șapoval, OlegEpitaxial La-deficient ultrathin films of La1-MnO3 (LMO) were grown by a metalorganic aerosol deposition technique with monolayer accuracy on SrTiO3 (STO) substrates and engineered by using different interfacial layers. The role of LaO-TiO2 interface in the formation of the ferromagnetic metallic state in very thin LMO films was demonstrated. The ferromagnetic metallic ground state in LMO films with the thickness down to 6 monolayers is stabilized by a combination of a La-deficiency and the interface-induced doping.Item Thin layer photovoltaic modules based on CdS-CdTe heterojunctions [Articol](2011) Fiodorov, Vladimir; Gașin, Petru; Gagara, Ludmila; Chetruș, PetruA technology of thin layer photovoltaic modules with dimensions of 65 x 80 mm2 based on CdS-CdTe heterojunctions prepared via the quasi-closed volume technique was developed. The modules were made on a single glass plate; each element was positioned along the given plate so that the resulting module contains nine solar cells with an area of 3 cm2. The design of the module made it possible to study the energy parameters of each solar cell as well as the entire module. The study of the photovoltaic module based on CdS-CdTe heterojunctions showed the following parameters: short circuit current Isc = 270 mA; open circuit voltage Ucd = 0.786 V; FF =0.46, power discharged in the load Pmax ≈ 100 mW, and efficiency η ≈ 8.2% at the radiation power of 53 mW/cm2.Item Nanolamellar structures of Oxide-AIIIBVI: Cd semiconductors type for use as detectors of radiation in the UV spectral region [Articol](Technical University of Moldova, 2011-07-07) Dmitroglo, Liliana; Untila, Dumitru; Chetruș, Petru; Evtodiev, Igor; Caraman, Iuliana; Lazăr, Gabriel; Nedeff, ValentinIn the paper, optical and photoelectrical properties of GaSe and InSe single crystal films of 10-5÷10-7 m submicron thickness and of semiconductor-native oxide structures obtained by annealing at (450÷700)°C in a normal atmosphere, are studied. The absorption spectrum of InSe lamella as well as of GaSe lamella in the energetic range from the red threshold up to 4,5 eV contains three bands with a rapid increase of the absorption coefficient which varies in the limits of (100÷106) cm-1 At the energies higher than 1,25 eV and 2,01 eV for InSe and GaSe respectively the light absorption are determined by the direct optical transitions in the centre of the Brillouin zone and at the energies higher than. At the absorption coefficients of (100÷102)cm-1 the indirect optic transitions are present. 3,0 eV also by the direct optical transitions in the points of the bands high symmetry. The resistive photosensitivity bands cover the spectral range Eg≤ hν ≤ 4,5 eV for lamellar photoresistors in which electric field EC6. The resistive photosensitivity band width could be controlled by the lamella thickness for d ≥1μm. The open circuit voltage spectral distribution is analysed from which results that at the oxidation temperature of 700°C in GaSe layer at the heterojunction interface the defects are formed on which the charge carriers, collected in the junction, are dissipated. The noneequilibrium charge carrier free path is of 0,8 μm.Item Electrical properties of thermally annealed CdS thin films obtained by chemical bath deposition [Articol](Institute of Electrical and Electronics Engineers Inc., 2011-10-17) Scorțescu, Dumitru; Maticiuc, Natalia; Nicorici, Valentina; Spalatu, Nicolae; Potlog, Tamara; Hiie, Jaan; Valdna, VelloElectrical conductivity and the Hall-effect are investigated in the temperature interval (80-400) K on thermally annealed in H 2 CdS thin films obtained by chemical bath deposition. Different characters of the temperature dependence of conductibility are observed in the CdS films annealed at different temperatures. The Hall measurements allow calculating the values of the NA , N D , n ex and ED . According to Hall measurements the CdS films show several donor levels at different energetic depths in dependence of the annealing temperature. The sample annealed at high temperatures than 350oC proves to be compensated with a sharply decreasing electrical conductivity with the temperature decrease.Item Morphology and luminescence properties of ZnO layers produced by magnetron spattering [Articol](Technical University of Moldova, 2011-07-07) Rusu, Emil; Ghițu, Irina; Prilepov, Vladimir; Zamalai, Victor; Ursachi, VeaceslavWe 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.Item The caracterization of the CdS-based solar cell heterojunctions [Articol](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 Absorption and photoconductivity of PbMoO4 crystals [Articol](2011) Mușinschi, Valeriu; Caraman, Mihail; Mușinschi, CameliaSpectral characteristics of the fundamental absorption coefficient and photoconductivity of PbMoO4 crystals with two polarizations in a temperature range of 77 to 300 K are investigated. The measurements of light transmitted in the polarized radiation for both orientations ( E|| C4 and E ┴ C4, C4 is the [001] crystallographic direction corresponding to the optical axis) of crystals are carried out. Spectral dependence of the absorption coefficient at the edge absorption (λ ≈ 0.3-0.5 μm) shows that the edge absorption is determined by indirect assisted by phonons transitions. The measured spectral dependence of the absorption coefficient at two orientations of polarization of light and the known theoretical dependence were combined and compared for determination the types of optical transitions in the fundamental absorption of PbMoO4 crystals. Limited energies Egind and Egdir for E|| C4 and E ┴ C4 were found. A detailed investigation of the fundamental absorption of PbMoO4 crystals is presented. A simple model of band structure of crystals is proposed. The photoconductivity of PbMoO4 single crystals is investigated on E|| C4 and E ┴ C4 at 300 K in the fundamental absorption spectral region of 2.8 to 5.0 eV. The spectral dependence of the photoconductivity is studied and discussed in conjunction with reported optical data. The monopolar character of the photoconductivity was confirmed by investigation time-of-flight motion of carriers. The present study reveals only the intrinsic photoconductivity in PbMoO4 pure single crystals. Spectral responses of the photocurrent through PbMoO4 crystals showed one spectral band in a range of 3.1 to 5.0 eV with maximums at 3.45 and 3.73 eV for E|| C4 and E ┴ C4, respectively. A good correlation of the photoconductivity bands at E|| C4 and E ┴ C4 with absorption bands at also polarizations has been demonstrated. The unipolar time-of flight motion of carriers was analyzed, and drift mobility of electrons and its temperature dependence were determined.Item Şcoala doctorală – element-cheie în organizarea ştiinţei moderne [Articol](Academia de Ştiinţe a Moldovei, 2011) Paladi, FlorentinItem Porous InP as piezoelectric component in magneto-electric composite sensors [Articol](io, 2011) Gerngross, M.-D.; Sprincean, Veaceslav; Leisner, M.; Carstensen, J.; Föll, H.; Tiginyanu, IonWe report on the fabrication of cheap piezoelectric porous InP templates by electrochemical etching and additional purely chemical post-etching and on the galvanic filling of the resulting nanopore array with Ni-Fe using a highly viscous electrolyte. The d14 component of porous InP is found to be around a stunning |60| pm/V. The deposited Ni-Fe shows a very narrow hysteresis loop with low coercive field strength (170 G) and very low remanence (0.005 emu).