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 Metode experimentale de studiere a stărilor de suprafaţă în compuşii stratificaţi de tip AIII BVI [Articol](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 [Articol](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 (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 Electrical and photoelectrical properties of heterojunctions on the base of Cu(InGa)Se2 [Articol](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 [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 Method of study gallium and arsenic losses in technology of gallium arsenate obtained from wastes [Articol](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.Item Gallium arsenate removal from waste waters [Articol](2005) Baranov, Serghei; Cinic, Boris; Redwing, Joan; Stăvilă, VitalieThe aim of this paper is to study the loss of gallium (Ga) and arsenic (As) loss during the sedimentation of gallium arsenate (GaAsO4 ) from waste solutions of GaAs epitaxial production by chloride method. The solid wastes of this semiconductor manufacturing process are removed from technological equipment by dissolution in an acidic etching solution. In order to recover valuable Ga and very toxic As from these waste solutions we proposed to precipitate them as gallium arsenate. Experiments have been conducted to determine the migration of the two elements in filtrate and washing solutions as a function of pH for both model and real industrial wastes. It has been determined the optimal interval of pH for sedimentation, the losses of Ga and As present 0,01-0,053%. For model solutions the sedimentation is optimal in the range of pH from 3,2 to 4,3, while in the case of real waste solution this interval is 3,6-5,0. Comparative evaluation of the precipitation efficiency revealed that for model solutions the arsenic loss during the precipitation is higher (0,5%), and this can be explained by a different ratio of initial Ga3+ and AsO43- in model and real solutions. The results described in this paper provide important guidelines for the sedimentation of gallium arsenate from acidic waste solutions and indicate an overall efficiency of the process that could lead to savings in cost and process time for industrial effluent treatment technologies.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.