National Institute Of Materials Physics - Romania

Publications

5840 articles found

4541. Properties of titanium based hard coatings deposited by the cathodic arc method I. Microchemical and microstructural characteristics

Authors: Balaceanu, M; Braic, M; Macovei, D; Genet, MJ; Manea, A; Pantelica, D; Braic, V; Negoita, F

Published: MAR 2002, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 4, 114, DOI:

TiN, TiC and Ti(C,N) hard coatings were deposited on Si substrates by a cathodic are system. Various investigation techniques (ERDA, XPS, and XRD) were used to analyze the microchemical and microstructural characteristics of the films (surface chemistry, chemical composition, texture) prepared under different deposition conditions.

4542. Bi2-xSbxTe3 thick thermoelectric films obtained by electrodeposition from hydrochloric acid solutions

Authors: Nedelcu, M; Sima, M; Manea, AS; Lazarescu, MF; Ghita, RV; Craciunoiu, F; Visan, T

Published: MAR 2002, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 4, 106, DOI:

A method to produce composition modulated Bi2-xSbxTe3 alloys by electrodeposition has been developed. The electrolyte, which consists in a HCl 6M (pH = 0) aqueous solution, allows for the co-deposition of bismuth, antimony and tellurium to be accomplished at room temperature on glassy carbon, platinum or nickel electrode. The composition of the films, their crystal structures and morphology were studied as function of electrochemical parameters and bath composition. It is shown that the electrodeposits are monophasic and exhibit a polycrystalline state. The electrical resistivity was of the order of 7-10 mOmegacm, whereas the electrodeposition rate value was 30-50 mum/h for the films with good thermoelectric properties.

4543. Microstrip filters using new compact resonators

Authors: Banciu, MG; Ramer, R; Ioachim, A

Published: FEB 28 2002, ELECTRONICS LETTERS, 38, 229, DOI: 10.1049/el:20020174

Compact two-pole and four-pole passband filters in 900 MHz frequency band using novel square microstrip resonators are presented. The measured filters' responses demonstrate the feasibility of selective filters using these new resonators.

4544. Magnetic properties of nanocrystalline materials: A Monte Carlo simulation

Authors: Crisan, O; Labaye, Y; Berger, L; Greneche, JM

Published: FEB 23 2002, PHYSICA STATUS SOLIDI A-APPLIED RESEARCH, 189, 848, DOI: 10.1002/1521-396X(200202)189:3<845::AID-PSSA845>3.0.CO;2-#

The magnetic properties of interfacial regions between ferromagnetic nanograins and the residual matrix in nanocrystalline materials, are modelled using Monte Carlo simulation. The exchange coupling between matrix and nanograin influences differently the nanograin surface and the interface between nanograin and matrix. This behaviour has been explained in terms of a polarisation mechanism of the interfacial zones leading to magnetic correlation between spins of nanograin surface and core.

4545. Decomposition of Ca : Cu=1 : 1 nitrate powder: thermal analysis and structural studies

Authors: Badica, P; Aldica, G; Crisan, A

Published: FEB 1 2002, JOURNAL OF MATERIALS SCIENCE, 37, 594, DOI: 10.1023/A:1013777826319

Thermal decomposition processes in mixtures of Ca : Cu = 1 : 1 nitrate powders produced by a conventional technique and by freeze drying method have been investigated by thermal analysis and X-ray diffraction. Results have been compared with literature values and data obtained by our investigations of individual calcium and copper nitrates. Temperatures at which decomposition processes occur change with by +/-30degreesC and depend also on the level of mixing of the nitrates. An exemption is the temperature for CuO phase formation, which was determined for the Cu-nitrate and for both 1 : 1-nitrate powders to be at 266degreesC. The domains of stability for different phases are shown to be variable. Also, for 1 : 1-powders, alpha-type and beta-type Ca(NO3)(2) . 2H(2)O phases coexist, while in Ca-nitrate only the alpha-type phase was observed. (C) 2002 Kluwer Academic Publishers.

4546. Preparation of BaTi4O9 from oxalates

Authors: Cernea, M; Chirtop, E; Neacsu, D; Pasuk, I; Iordanescu, S

Published: FEB 2002, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 85, 503, DOI:

A barium titanate precursor with a barium:titanium ratio of 1:4 was prepared by controlled coprecipitation of mixed barium and titanium species with an ammonium oxalate aqueous solution at pH 7. The results of thermal analysis and IR measurement show that the obtained precursor is a mixture of BaC2O4.0.5H(2)O and TiO(OH)(2).1.5H(2)O in a molar ratio of 1:4. Crystallized BaTi4O9 was obtained by the thermal decomposition of a precipitate precursor at 1300degreesC for 2 h in air. The dimensions of the powder calcined at 1000degreesC are between 100 and 300 nm. The grain dimensions of the sintered sample for 2 h at 1300degreesC are of the order of 10 to 30 mum. Dielectric properties of disk-shaped sintered specimens in the microwave frequency region were measured using the TE011 mode. Excellent microwave characteristics for BaTi4O9-epsilon = 38 +/- 0.5, Q = 3800-4000 at 6-7 GHz and tau(f) = 11 +/- 0.7 ppm/degreesC-were found.

4547. Thermally stimulated current method applied to highly irradiated silicon diodes

Authors: Pintilie, I; Tivarus, C; Pintilie, L; Moll, M; Fretwurst, E; Lindstroem, G

Published: JAN 11 2002, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 476, 657, DOI: 10.1016/S0168-9002(01)01654-0

We propose an improved method for the analysis of Thermally Stimulated Currents (TSC) measured on highly irradiated silicon diodes. The proposed TSC formula for the evaluation of a set of TSC spectra obtained with different reverse biases leads not only to the concentration of electron and hole traps visible in the spectra but also gives an estimation for the concentration of defects which not give rise to a peak in the 30-220 K TSC temperature range (very shallow or very deep levels). The method is applied to a diode irradiated with a neutron fluence of phi(n) = 1.82 x 10(13) n/cm(2). (C) 2002 Published by Elsevier Science B.V.

4548. Structural properties of sputtered ZnO : Au films

Authors: Goldenblum, A; Teodorescu, V; Wagner, FE; Manaila, R; Filoti, G; Deville, JP; Pantelica, D; Negoita, F; Belu-Marian, A; Scantee, N

Published: JAN 2002, PHILOSOPHICAL MAGAZINE A-PHYSICS OF CONDENSED MATTER STRUCTURE DEFECTS AND MECHANICAL PROPERTIES, 82, 204, DOI:

ZnO: Au films have been obtained by a reactive rf magnetron sputtering method using pure Zn and Au targets. Layers with a Au- to- Zn ratio of up to 0. 71 have been deposited. They were analysed by Rutherford back- scattering spectroscopy, elastic recoil detection analysis, transmission electron microscopy, high- resolution electron microscopy, selected- area electron diffraction, X- ray diffraction and Mossbauer spectroscopy. The only crystalline phase found for all investigated Au concentrations was that of ZnO. We conclude that some of the Au enters as interstitial atoms in the compact hexagonal lattice of ZnO being bonded with any three O atoms of the structure and the other part forms an amorphous hydrated gold oxide that coexists with the ZnO crystallites.

4549. Reactive-field-assisted-sintering of freeze-dried powders in the BSCCO system

Authors: Badica, P; Aldica, G; Groza, JR; Bunescu, MC; Mandache, S

Published: JAN 2002, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 15, 42, DOI: 10.1088/0953-2048/15/1/307

The reactive-field-assisted-sintering technique (RFAST) has been applied to freeze-dried decomposed precursor powders with a starting cation composition of Bi:Pb:Sr:Ca:Cu = 1.7:0.3:2.0:2.5:3.5. A short time (< 15 min) RFAST treatment at 800-900degreesC did not lead to the formation of Bi2Sr2Ca2Cu3O10+x, (2223-phase). But RFAST was favourable to Bi2Sr2CaCu2O8+y, (2212-phase) formation particularly in samples with a low content of the 2212-phase in the precursor powder. Heat treatment (HT) after RFAST showed that the 2223 phase could form more rapidly than in freeze-dried pressed and sintered pellets produced by the traditional technique. The resultant ceramics after 70 h of annealing contain 75% 2223-phase and have T-c(R=0) = 100.7 K, T-c = 109.5 K and DeltaT(c) = 22.4 K.

4550. Plasmons and the drag effect in a strong magnetic field

Authors: Manolescu, A; Tanatar, B

Published: JAN 2002, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 13, 88, DOI: 10.1016/S1386-9477(01)00227-2

We study the effect of magnetoplasmons on the drag resistance in a strong magnetic field, at finite temperatures, The typical magnetic field is about 1 T, and the temperature is up to 10 K. The Landau levels are broadened by disorder, but well separated in energy. We discuss intra-Landau level magnetoplasmons, with low frequencies, below omega(c), and inter-Landau level magnetoplasmons (also called Bernstein modes), with high frequencies, close to multiples of omega(c). We compare the temperature dependence of the minima and maxima of the Shubnikov-de Haas oscillations of the transresistance. (C) 2002 Published by Elsevier Science B.V.