Facultatea de Fizică şi Inginerie / Faculty of Physics and Engineering
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Item Characterization of geometrically frustrated Zn1-xMn xAl2O4 thin films prepared by metalorganic aerosol deposition [Articol](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 [Articol](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 (Benzoyl-formaldehyde oximato-κ2 N,O)(benzoyl-formaldehyde oxime-κN) chloridoplatinum(II) [Articol](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 Chemical method for the gallium arsenide rectification structure divide into crystals [Articol](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 Mecanismul de transport al curentului şi luminescenţa structurilor Pd-ZnSe [Articol](UTM, 2009-10-01) Scurtu, Roman; Gașin, Petru; Covali, AndreiAu fost analizate proprietăţile electrice şi de luminescenţă ale structurilor Schottky ZnSe-Pd obţinute pe baza monocristalelor de ZnSe cu rezistivitatea de 0.78 Ω•cm şi concentraţia electronilor 1.82 10 16 cm-3 . S-a determinat mecanismul de transport al purtătorilor de sarcină prin structură. La polarizări directe curentul depinde exponenţial de tensiunea aplicată şi este determinat de emisia electronilor. La polarizări inverse dependenţa curentului de tensiune este descrisă de o funcţie de putere, cu factorul m=3÷6. Cu mărirea temperaturii curentul invers creşte exponenţial, ceea ce indică faptul că în mecanismul de transport predomină procesele de tunelare. La polarizări directe şi temperaturi ~80 K structurile Pd-ZnSe iradiază lumină în regiunea albastră a spectrului cu maximul de luminescenţă la 2.7 eV.Item Study of multiple record of the optical information on photothermoplastic mediums (PTPM) in the holographic way [Articol](SPIE, 2007) Goglidze, Tatiana; Dementiev, Igor; Cortiucova, Iulia; Mațcova, NataliaIn the given work results of experiments on carrying out of cyclic record on PTPM are resulted by holographic way. The optical scheme is resulted, allowing automating process of record of elementary holograms in the form of diffraction gratings on PTPM and their definitions diffraction efficiency. The mechanism of occurrence of "parasitic" memory PTPM due to photostructural transformations into thin layers CGS is considered.Item The electrical transport mechanism in the (nCdS–рAs2Se3) heterojunctions [Articol](2008) Goglidze, Tatiana; Dementiev, Igor; Dmitriev, Serghei; Nasedchina, Nadejda; Mațcova, NataliaIn the given paper we present results of I-V characterization of thin film heterojunctions on the basis of (nCdS)–(рAs 2 Se3 ). Structures have been obtained via spray pyrolysis deposition of polycrystalline nCdS layers on glass substrate and consecutive thermal vacuum deposition of the amorphous рAs 2 Se3 layers. The possible mechanisms of the current passing through obtained structure are discussed on the basis of results of I-V measurements performed at the different polarities and electrical field intensities in the heterojunction.Item Thin AIN films growth on Si (III) by hydride vapor phase epitaxy [Articol](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 New photoluminophore nanocomposite based on organic compound with Eu3+ ions and copolymer styrene-butylmethacrilate [Articol](2009) Iovu, Mihail; Andrieș, Andrei; Buzurniuc, Svetlana; Verlan, Victor; Turta, Constantin; Zubareva, Vera; Caraman, MihailNew nanocomposite (NC) material on the base of thenoyltrifluoroacetone (TTA) coordinated with triva- lent europium ions and structured with phenantroline (Eu(TTA)3Phen) and copolymer from styrene and butylmethacrylate (1:1) (SBMA) was prepared. The visible photoluminescence spectra of composites excited with N2-laser (k = 0.337 lm) at room and T = 78 K temperatures were studied. For the Eu(TTA)3- Phen/SBMA nanocomposite material emission bands located at 578, 590, 612, 675 and 705 nm can be attributed to the spin forbidden f–f transitions 5D0 ? 7Fi (i = 0,1,2,3 and 4), respectively. The more inten- sive luminescence band situated at 612 nm with the half width of 3 nm is connected to the Eu3+ ion elec- tronic transition 5D0 ? 7F2. It was shown that the maximum intensity of photoluminescence occurs at the concentration of 15% of the Eu(TTA)3Phen in the SBMA polymer matrix.Item Photoelectrical properties of layered GaS single crystals and related structures [Articol](2008) Caraman, Mihail; Chiricenco, Valentina; Leontie, Liviu; Rusu, Ioan I.The photoconductivity of pure and Cu-doped layered gallium monosulfide (GaS) single crystals, and of Ni–GaS(Cu)–In and GaS(Cu)–ZnO structures, is investigated. The activation energies of surface states were found as 0.10 eV, 0.40 eV and 17 meV, 400 meV for GaS and GaS(Cu), respectively. Cu acceptor levels are localized at 0.44 eV and 0.52 eV above the valence band of GaS. ZnO–GaS(Cu) heterojunctions show remarkable photosensitivity in the wavelength range of 250–700 nm.