National Institute Of Materials Physics - Romania

Annealing effect of the irreversibility fields (H-irr) in (Cu,C)Ba2Ca2Cu3Oy ((Cu,C)-1223) and (Cu,C)Ba2Ca3Cu4Oy ((Cu,C)-1234) have been investigated. The samples prepared under high pressure were post-annealed in nitrogen gas in the temperature range of 400-500degreesC. H-irr of (Cu,C)-1234 was improved after annealing at 450degreesC while T-c remained almost constant. This suggests that carrier density of five-coordinated CuO2 planes or conductivity of charge reservoir layers is changed by annealing while keeping that of four-coordinated CuO2 planes almost constant. Both samples show H-irr similar or equal to 4 T at 90 K by the post-annealing, which is quite attractive for practical application. (C) 2003 Elsevier Science B.V. All rights reserved.

To enhance or improve critical currents density (J(c)) and irreversibility field (H-irr) of (Cu,C)Ba2Ca3Cu4O10.5-delta ((Cu,C)-1234), pinning centers were introduced by heavy-ion irradiation. The polycrystalline samples were irradiated with An(15+) ions (240 MeV energy) at various fluence of 1 x 10(11), 2.5 x 10(11) and 5 x 10(11) ions/cm(2). J(c) and H-irr were determined for the irradiated samples as well as unirradiated samples. J(c) (77 K, 1 T) increase from 3.9 x 10(4) A/cm(2) to 4.1 x 10(6) A/cm(2) for at fluence of 1 x 10(11) ions/cm(2) of heavy-ion irradiated sample and decreases with further increase of fluence. These results indicate the possibility of further enhancement of Jc and of achieving a very high H-irr of (Cu,C)-1234 below a fluence of 1 x 10(11) ions/cm(2). (C) 2003 Elsevier Science B.V. All rights reserved.

Complex semiconducting ceramic compositions were prepared. Structure, crystallite morphology, hardness and electrical conduction were investigated. After annealing at 150 degreesC a distinct crystalline phase was obtained and the ceramic became compact, hard, of higher resistivity, while preserving the basic semiconducting properties (C) 2002 Elsevier Science Ltd. All rights reserved.

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.

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.

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.

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.

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.

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.

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.