2. Articole
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Item EPITAXIAL RELATIONS IN BaF2 FILMS GROWN BY MBE ON Si(III) SUBSTRATES(Institute of Electrical and Electronics Engineers Inc., 1995-10-11) Belenciuc, Alexandr; Fiodorov, Alexandr; Zencenco, Vladimir; Lucaș, Victor; Vasiliev, AlexandrThe dependence of the epitaxial orientations of the films in BaFdSi(III) heterostructures on growth conditions and the influence of heat treatment on the stability of epitaxial relations in such structures are investigated. The correlations between the types of epitaxial relations and structures of interface are also discussed.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 SECONDARY ION MASS SPECTROSCOPY OF ZINC SELENIDE CRYSTALS WITH PHOTOCONDUCTIVITY SPECTRAL MEMORY(2017) Belenciuc, Alexandr; Ilinykh, Nicolai; Kovalev, LeonidItem 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 INTERFACE-CONTROLLED MAGNETISM AND TRANSPORT OF ULTRATHIN MANGANITE FILMS(2013) Șapoval, Oleg; Huhn, Sebastian; Verbeeck, Johann; Jungbauer, Markus; Belenciuk, Alexandr; Moșneaga, VasiliiWe report ferromagnetic, T C ¼ 240 K, and metallic, T MI ¼ 250 K, behaviors of a three unit cell thick interface engineered lanthanum manganite film, grown by metalorganic aerosol deposition technique on SrTiO 3(100) substrates. Atomically resolved electron microscopy and chemical analysis show that ultrathin manganite films start to grow with La-O layer on a strongly Mn/Ti-intermixed interface, engineered by an additional deposition of 2 u.c. of Sr-Mn-O. Such interface engineering results in a hole-doped manganite layer and stabilizes ferromagnetism and metallic conductivity down to the thickness of d ¼ 3 u.c. The films with d ¼ 8 u.c. demonstrate a metallic conductivity down to the thickness of d ¼ 3 u.c. bulk-like transport behavior with TMI T C ¼ 310330 K.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 MAGNETOTRANSPORT PROPERTIES OF ULTRATHIN LaMnO3 LAYERS(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 DEVELOPMENT OF MATERIALS FOR THERMOELECTRIC GENERATORS: SUPERLATTICE Ca3Co4O9-Sr3Co4O9(Editura "Tehnica-UTM", 2015-05-20) Șapoval, Oleg; Belenciuc, Alexandr; Jooss, Christian; Roddatis, Vladimir; Moșneaga, VasiliiWe have prepared multilayered structures composed from misfit layered Ca- and Sr- cobaltates by Metalorganic Aerosol Deposition technique. X-ray and Transmission Electron Microscopy analyzes confirms the forming superlattice along c direction from common CoO2 interlayers and alternating Ca2CoO3 and Sr2CoO3 layers with periodicity of 4-6 unit cell. Our results indicate the possibility to fabricate artificial material on the base of layered cobaltates for thermoelectric applications.Item ULTRATHIN MANGANITE LAYERS(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.