2. Articole
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Item HOT WALL BEAM EPITAXIAL GROWTH OF PbTe LAYERS ON BaFdCaFdSi(llI) SUBSTRATES(Institute of Electrical and Electronics Engineers Inc., 2000-10-10) Belenciuc, AlexandrPbTe(III) thin films were grown by the hot wall beam epitaxy (HWBE) technique on Si( III ) substrates using intermediate BaF2/CaF2 buffers grown by MBE. The best PbTe layers exhibit the high resolution X-ray rocking curve linewidth of about 130 arcsec,the low temperature Hall mobility of 8 x l d cm2Ns, and an excellent surface morphology with the roughness of a few angstrom as it was determined by the atomic force microscopy (AFM). The results indicate that high-quality PbTe films can be obtained on fluoride covered Si(III ) substrates by simple and cheap HWBE method.Item CHARACTERIZATION OF GEOMETRICALLY FRUSTRATED Zn1−xMnxAl2O4 THIN FILMS PREPARED BY METALORGANIC AEROSOL DEPOSITION(2009) Sanchez, Rodolfo; Saleta, Martin Eduardo; Șapoval, Oleg; Gehrke, Kai; Moșneaga, Vasilii; Samwer, KonradWe present the results on the structure and magnetoelectric properties of Zn1−xMnxAl2O4 thin films (0 ≤ x ≤ 1), prepared by metalorganic aerosol deposition (MAD) technique. The films have been grown epitaxially on MgO(100) substrates and characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis (EDX), magnetization, electron paramagnetic resonance (EPR) and capacitance as a function of temperature and magnetic field. For large x values (x = 0.75 and 1), we observed a deviation of the magnetization from a Curie-Weiss law below 40K, indicating the expected magnetic ordering of the spinel. In the proximity of this magnetic characteristic temperature the capacitance as a function of temperature shows a peak, which infers a multiferroic character of these spinels.Item X-RAY DIFFRACTION ANALYSIS OF PbTe/SnTe SUPERLATTICES GROWN ON Si(III) SUBSTRATES(2009) Șapoval, Oleg; Belenciuc, Alexandr; Fiodorov, Alexandr; Canțer, Valeriu; Zasavițchi, EfimThe 50 period PbTe/SnTe superlattices (SLs) were grown on Si (111) substrates by hot-wall beam epitaxy (HWBE) using an intermediate fluoride buffer. The SL period varied from 6.6 to 24.0 nm with PbTe:SnTe thickness ratios of 2:1 and 1:1. The structural analysis was performed by X-ray diffraction and reflection measurement techniques. The resolution up to 8 orders of SL satellite diffraction peaks indicates well-formed SLs with sharp interfaces and long range ordering. The processing of X-ray spectra on the basis of dynamical theory of diffraction was used for estimation of individual layer thicknesses and residual strains. The differences in lattice parameters both between SL components and relative to the substrate, as well as the thermal expansion coefficient mismatch of A 4 B 6 compounds with regard to the substrate, are the reasons for the strains appearing in this SL structure. Fitted parameters of the normal lattice mismatch revealed that the SnTe layers are equally strained independent of thickness, whereas the stress of PbTe layers is progressively decreasing with thickness. In spite of residual lattice mismatch strain, the SL structures exhibited ability to full relax of the thermal mismatch strains as in the case of earlier investigated single layers of A 4 B6 grown on Si (111) coated with fluoride buffer. Our results indicate the possibility to fabricate high efficient thermoelectric coolers based on PbTe/SnTe SLs directly integrated with Si chips.Item GIANT NEGATIVE PHOTOCONDUCTIVITY IN La 0.7Ca0.3MnO3 THIN FILMS(2004) Moșneaga, Vasilii; Giske, Arnold; Samwer, Konrad; Mișina, Elena; Tamura, Takehisa; Nakabayashi, Seiichiro; Belenciuc, Alexandr; Șapoval, Oleg; Culiuc, LeonidThe increase of the resistance up to two orders of magnitude under laser illumination (l5760 nm) was observed in La0.7Ca0.3MnO3 ~LCMO! epitaxial thin films in ferromagnetic state.Optical absorption also increases by 10–15 % and the magnetic second-harmonic generation signal decreases down to zero under the irradiation. The light induced changes are reversible with decreases down to zero under the irradiation. The light induced changes are reversible with characteristic relaxation times t;1 – 30 s. Magnetic field, B54 T, suppresses the photoconductivity and decreases its relaxation time. Photoinduced effects are caused by the injection of a large number of extra carriers, which change the ~antiferromagnetic! AFM/FM phase balance in LCMO, favoring the insulating AFM state.Item METODE EXPERIMENTALE DE STUDIERE A STĂRILOR DE SUPRAFAȚĂ ÎN COMPUŞII STRATIFICAȚI DE TIP AIII BVI(Tipografia Universității de Stat „Alecu Russo” din Bălți, 2005-10-05) Blaj, Octavian; Scurtu, Roman; Evtodiev, IgorItem LUMINESCENT PROPERTIES OF ZnS SINGLE CRYSTAL ANNEALED IN THE V th GROUP ELEMENTS MELT(2006) Sobolevscaia, Raisa; Corotcov, Vadim; Bruc, Leonid; Sușchevici, Constantin; Chetruș, PetruThe influence of ZnS single crystal annealing in the media based on V-group elements Bi and Sb on its photoluminescent (PL) properties was studied. The following media: Bi, Sb, Bi+Zn, Sb+Zn, Bi+S, Sb+As and Bi+Al were used for the annealing.Two types of the starting crystals were used: I) low resistivity ZnS; II) high resistivity ZnS. The annealing was carried out in the vacuumed silica ampoules at the temperatures of 1400 K (I) and 1200 K (II) during 100hrs. The obtained results show that ZnS crystals annealing in Bi and Sb melts leads to the analogical reorganization of radiation centers based on the native and impurity defects generated by interphase interaction at ZnS-melt interface. These defects are responsible for the appearance of the green radiation having the feature of intracentred transitions. The high value of green band half-width indicates that it is a superposition of a few bands. These could be a PL bands related to the oxygen presence, the impurity centers of the V group elements and to V S .Item (BENZOYLFORMALDEHYDE OXIMATO-j2N,O)- (BENZOYLFORMALDEHYDE OXIME-jN)- CHLORIDOPLATINUM(II)(2007) Cucușchin, Nicolae; Chetruș, Petru; Haukka, MattiIn the title complex, [Pt(C 8H 6NO 2 )Cl(C 8H 7NO 2)], the Pt II centre is coordinated by a monodentate and an N,O-chelating deprotonated benzoylformaldehyde oxime and a Cl atom. There is an intramolecular N—OH—O hydrogen-bonding system between the oxime OH group and the oximate O atom.Item ELECTRICAL AND PHOTOELECTRICAL PROPERTIES OF HETEROJUNCTIONS ON THE BASE OF Cu(InGa)Se2(2005) Chetruș, Petru; Gașin, Petru; Nicorici, Valentina; Suman, VictorCdS films deposited by hot wall technique on mica were used as substrates for Cu(InGa)Se2 deposition. Two methods were used for the deposition of Cu(InGa)Se2 films: a) vacuum thermal evaporation from a single source and b) “flash” evaporation. The obtained films were of p-type conductivity with hole concentration varied from 2×1018 cm-3 to 6×1020 cm-3 depending on the fabrication method. The structures Cu(InGa)Se2–CdS were divided into two groups: the structures of type I having the CdS film thickness from 1.6 m to 2.8 m and the structures of type II having the CdS film thickness from 0.6 m to 0.8 m. It was established that the direct/reverse current ratio is 8-16. For the first type heterostructures the diffusion potential is 1.2–1.8 V and for the second type is 0.2–0.34 V. The Cu(InGa)Se2–CdS fotosensitivity is situated in the wavelength region from 0.51 m to 1.1 m and is determined by the electron-hole pair generation in both materials.Item CHEMICAL METHOD FOR THE GALLIUM ARSENIDE RECTIFICATION STRUCTURE DIVIDE INTO CRYSTALS(UTM, 2009-10-01) Baranov, Simion; Cinic, Boris; Dudca, Tudor; Suman, VictorThis investigations are referred to power semiconductor devices (PSD) area manufactured by gallium arsenide (GaAs) advanced technology. The work’s objective is excluding the break-down effect on the p-n junction surface of high voltage devices, which is advance progressed with diminishing the crystal dimensions in the dividing process of the semiconductor structures. We propose the method of the GaAs deep etching by a mixture utilizing concentrated acids as nitric and hydrochloric acids in equal rates. After 30 min of mixing up the solution formation is consorted of the endothermic reaction, bound up by nitrosyl chloride (NOCl) formation, which dissolves the GaAs decomposed product in solution by arsenic oxidation up to As(V), forming ortoarsenic acid and gallium chloride. This method is used for dividing semiconductor structure of GaAs with 0.4-0.6 mm of thickness in small dimensioned crystals. The advantages of this technology are the great speed of GaAs dissolving, low costs of manufacturing and profitableness.Item METHOD OF STUDY GALLIUM AND ARSENIC LOSSES IN TECHNOLOGY OF GALLIUM ARSENATE OBTAINED FROM WASTES(2005) Baranov, Serghei; Redwing, Joan; Bogdevici, Oleg; Cinic, Boris; Izmailov, DenisHaving the goal to recover gallium (Ga) and arsenic (As) from technological wastes derived from the process of growing epitaxial gallium arsenide structures, it is proposed to extract gallium arsenate (GaAsO4) by precipitation and filtration of the sediment. In this paper it is proposed to measure the concentrations of Ga and As by means of the atomic absorption spectrometer AAnalyst 800 directly in the filtrate solution. We compare the results obtained by two methods of elemental Ga and As atomization: flame and thermal atomization. The values of Ga and As concentrations in filtrate are function of pH for solutions containing 1- 680 mg/1 of Ga and 55-880 mg/1 of As. The developed method can be used to study and further optimize the technological process.