National Institute Of Materials Physics - Romania

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5781 articles found

4371. (Ca,Ba)CuO2 films grown by MOCVD: surface morphology and structural studies

Authors: Endo, K; Badica, P; Itoh, J

Published: APR 15 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 386, 322, DOI: 10.1016/S0921-4534(02)02147-0

Thin films of (Ca1-xBax)CuO2 (x = 0-1) have been grown on (0 0 1) SrTiO3 by metal organic chemical vapor deposition. These films are potential candidates as barrier layer for SIS and/or SNS Josephson junctions. For this purpose, the films should be flat and smooth. In this regard we have investigated the possibility of decreasing the films roughness by the control of the Ba/Ca ratio, the substrate temperature and oxygen partial pressure during the growth of the film. The minimum mean square root roughness and regular morphology are obtained for the x = 0.3-0.5. In the samples with x = 0.5 the highest intensity of the X-ray diffraction peaks for the (Ca0.5Ba0.5)CuO2 phase and the lowest for the impurity phases were attained at a substrate temperature of 750-780 degreesC and oxygen partial pressure of 15 Torr. (C) 2002 Published by Elsevier Science B.V.

4372. Preparation and characterization of (001) SmBa2Cu3Oy thin films by MOCVD

Authors: Endo, K; Badica, P; Itoh, J

Published: APR 15 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 386, 326, DOI: 10.1016/S0921-4534(02)02149-4

Superconducting (0 0 1) thin films of SmBa2Cu3Oy have been grown by MOCVD on (0 0 1) SrTiO3 and (0 0 1) LaAlO3 substrates. The films on both substrates are smooth with RMS of 1.428 and 1.037 nm respectively, but have different morphology (revealed by atomic force microscopy) for the same synthesis conditions. The films grown on SrTiO3 have shown rectangular- or square-type terraces. The height between the neighboring terraces was corresponding to the c-axis length of one unit dell. This type of morphology is due to the two-dimensional nucleation and growth mechanism. In the case of the films on the LaAlO3 the surface morphology consisted of irregular grains (close to spherical). For both situations we have not found any evidence for a spiral growth mechanism. Therefore, our films are suitable for electronics applications of integrate type and not only. The as-grown films were oxygen deficient and due to this exhibited rather poor superconducting properties. Oxygen annealing at temperatures of 500-600 degreesC increased T-c(R=0) up to 87.8 K. (C) 2002 Published by Elsevier Science B.V.

4373. Competition between ferroelectric and semiconductor properties in Pb(Zr0.65Ti0.35)O-3 thin films deposited by sol-gel

Authors: Boerasu, I; Pintilie, L; Pereira, M; Vasilevskiy, MI; Gomes, MJM

Published: APR 15 2003, JOURNAL OF APPLIED PHYSICS, 93, 4783, DOI: 10.1063/1.1562009

Asymmetric metal-ferroelectric-metal (MFM) structures were manufactured by sol-gel deposition of a lead zirconate-titanate (PZT with Zr/Ti ratio 65/35) film on Pt-coated Si, with a Au top electrode. The average remnant polarization of 9 muC/cm2 and the coercive field of 39 kV/cm were obtained from the hysteresis loop measurements. A detailed analysis of the polarization-electric field (P-E), capacitance-voltage (C-V), and current-voltage (I-V) measurement results allowed us to estimate the near-electrode space-charge region thickness (roughly half of the film thickness at zero voltage), net doping concentration (around 10(18) cm(-3)), built-in potential (in the 0.4-0.8 V range, depending on the injecting electrode), and dynamic dielectric constant (5.2). The current logarithm-voltage dependence for the field-enhanced Schottky emission obeys a "1/4" law. The spectral distribution of the short circuit current measured under continuous light illumination in the 290-800 nm range exhibits a cutoff wavelength at 370 nm and a maximum sensitivity at about 340 nm. The estimated band-gap energy of the PZT material is 3.35 eV. The MFM structure is discussed in terms of two back-to-back Schottky diodes with a ferroelectric material in between. It is concluded that the semiconductor properties of the films are not negligible and, in certain conditions, are dominating over the ferroelectric ones. (C) 2003 American Institute of Physics.

4374. AFM observation of as-grown (119) Bi-2223 and (103) Y-123 thin films by MOCVD

Authors: Endo, K; Badica, P; Itoh, J

Published: APR 15 2003, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 386, 295, DOI: 10.1016/S0921-4534(02)02136-6

In high temperature superconductors (HTS) the coherence length along non-c-axis directions is longer. This feature can be useful when designing electronics devices based on HTS. Therefore, growth and characterization of non-c-axis oriented thin HTS films is of great interest. In this paper we present our comparative results on preparation by MOCVD and characterization by atomic force microscopy, X-ray diffraction and transport measurements of as-grown (119) Bi-2223 and (103) Y-123 thin films on (110) SrTiO3. The films have shown the same type of surface morphology (grains with mountain-range shape, aligned in parallel chains to the [001] substrate's azimuth). This morphology is the result of the orientation relationship between the (119) Bi-2223 or (10 3) Y-123 and (110) SrTiO3. The transport measurements with temperature revealed strong anisotropy of the films in the normal state region when the measuring current has been applied in-plane, parallel and perpendicular to the edges (from the basal plane) of the mountain-range grains. Higher values for T-c0 have been obtained for the Y-123 films (42 K) than for the Bi-2223 ones (31 K). The both films are as-grown and non-oxygenated ones. (C) 2002 Published by Elsevier Science B.V.

4375. Electronic properties of gold-aluminium intermetallic compounds

Authors: Palade, P; Wagner, FE; Jianu, AD; Filoti, G

Published: APR 7 2003, JOURNAL OF ALLOYS AND COMPOUNDS, 353, 32, DOI: 10.1016/S0925-8388(02)01203-3

The intermetallic compounds in the Au-Al system were studied by Au-197 Mossbauer spectroscopy. The observed isomer shifts and electric quadrupole splittings are compared with the electron densities and electric field gradients at the gold nuclei obtained by LAPW calculations using the WIEN97 computer code. This provides insights into the electronic structure of Au-Al alloys and yields values for the groundstate quadrupole moment of Au-197 and for the change of the nuclear charge radius for the 77 keV transition of Au-197. (C) 2002 Elsevier Science B.V. All rights reserved.

4376. Au-induced perpendicular magnetization in Fe films grown on Si(001)

Authors: Zavaliche, F; Wulfhekel, W; Przybylski, M; Bodea, S; Grabowski, J; Kirschner, J

Published: APR 7 2003, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 36, 784, DOI: 10.1088/0022-3727/36/7/302

We report on Fe films grown on Au-buffered Si(001) showing perpendicular magnetization at ambient temperatures. The in-plane magnetization in ultra-thin Fe films grown at 150 K reorients irreversibly out-of-plane as a result of annealing close to room temperature. A Au cap layer which is expected to segregate to the top of the Fe film may be responsible for this behaviour. This hypothesis is based on the observation of an in-plane to out-of-plane reorientation of magnetization upon the growth of an ultra-thin Au cap layer on a slightly thicker Fe film. The origin of such a strong out-of-plane anisotropy of Fe induced by Au is discussed.

4377. ESR studies on collagen irradiated with protons

Authors: Chipara, M; Romero, JR; Ignat, M; Constantinescu, B; Secu, C

Published: APR 2003, POLYMER DEGRADATION AND STABILITY, 80, 49, DOI: 10.1016/S0141-3910(02)00381-6

Electron spin resonance investigations on collagen irradiated with protons are reported. The resonance spectra were assigned to a convolution of lines due to similar toCH(2)-CH2. residues and peroxy radicals. Raising the temperature of the sample (in air), the concentration of similar toCH(2)-CH2. residues decreases while, the concentration of peroxy radicals increases due to the denaturation induced enhancement of the oxidation process. An increase in the apparent intensity of the recorded spectrum has been observed around 100 degreesC and ascribed to the release of adsorbed water molecules. (C) 2003 Elsevier Science Ltd. All rights reserved.

4378. New class of catalysts for the propane ammoxidation process based on vanadium aluminum oxynitrides

Authors: Florea, M; Prady-Silvy, R; Grange, P

Published: APR 2003, , DOI: 10.1023/A:1022857211248

4379. Second-order generation of point defects in gamma-irradiated float-zone silicon, an explanation for "type inversion"

Authors: Pintilie, I; Fretwurst, E; Lindstrom, G; Stahl, J

Published: MAR 31 2003, APPLIED PHYSICS LETTERS, 82, 2171, DOI: 10.1063/1.1564869

Radiation-induced defects in silicon diodes were investigated after exposure to high doses of Co-60-gamma irradiation using the thermally stimulated current method. We have found that, for high irradiation doses, a second-order defect can be detected. This defect is largely suppressed in oxygen-enriched material while it is the main cause for the space charge sign inversion effect observed in standard float-zone material. (C) 2003 American Institute of Physics.

4380. Densification and crystallization of SnO2 : Sb sol-gel films using excimer laser annealing

Authors: Sandu, CS; Teodorescu, VS; Ghica, C; Canut, B; Blanchin, MG; Roger, JA; Brioude, A; Bret, T; Hoffmann, P; Garapon, C

Published: MAR 15 2003, APPLIED SURFACE SCIENCE, 208, 387, DOI: 10.1016/S0169-4332(02)01412-5

We have successfully applied laser annealing to sol-gel deposited SnO2:Sb thin films in order to achieve their crystallization. The as-deposited films are quasi-amorphous and electrically non-conductive. After laser annealing they crystallize and become conductive. This paper presents a comparative study of the laser annealed films and shows the influence of the irradiation parameters on the crystallization process and the electrical behavior of the films. Our results are quite promising in view of applying this kind of treatment to films deposited on thermally sensitive substrates (e.g. polymers). (C) 2002 Elsevier Science B.V. All rights reserved.