Publications

The subject of magnetic anisotropy in nanostructured materials is of considerable interest from both experimental and theoretical points of view. Systems that consist of either isolated or interacting nanoparticles are shown to exhibit different magnetic properties of the nanoparticle surface than those of the bulk. This altering of magnetic behavior is mainly related to surface spins structure cot-related with finite size effects, providing that the nanoparticles are sufficiently small so that the surface-to-volume atomic ratio would be high enough. This work reports on both the simulation and experimental approach on the magnetic behavior of ferromagnetic nanoparticles. We investigate the competition between surface and bulk magnetocrystalline anisotropy in small magnetic particles. The experimentally obtained magnetic data for ferromagnetic core-shell-type AgCo nanoparticles are interpreted consistently with the results of Monte Carlo simulation of the magnetic behavior of single domain nanoparticles.

In this review paper we attempt to summarize the achievements of the near infrared emission studies of negative metal ions (Me-) obtained by nonstandard electrolytical colouring. We present the emission characteristics of Pb--ions aggregates in KCl crystals at 300 and 4.2 K by excitation in the UV and visible range of different laser lines. These centres perturbed by Li+, Na+, Rb+, Ca2+, Sr(2+)and Ba2+ cations, Tl- and Tl- + Ca2+- ions aggregates and the negative aggregates of ln(-) and Ga- in KCl crystals are, also, discused.

Indium Tin Oxide (ITO) thin films have been deposited by the Sol-Gel Dip-Coating technique, the starting solutions being prepared from chlorides. These multilayered films were crystallized by means of a classical heat treatment at temperatures ranging from 500 to 600 degreesC. Five stacked layers are necessary to obtain a global electrical resistivity value of 2.9 x 10(-3) Omega cm, for 500 degreesC annealed film. The paper focuses on the study of the structure of such multilayered deposits, and on the densification process, using transmission electron microscopy, Rutherford Back-scattering Spectrometry and electrical resistivity measurements. This analysis reveals structural inhomogeneities and different crystallite growth processes as a function of annealing temperature and number of deposited layers. (C) 2003 Elsevier B.V. All rights reserved.

The influence of oxygen in silicon on bulk damage effects induced by Co-60-gamma irradiation has been studied in a dose range between 0.2 and 900 Mrad. The detector processing and oxygen enrichment were carried out in a common project by the Institute of Micro-sensors CiS using n-type high-resistivity FZ silicon (3-6 kOmega cm) with and orientation. Different oxygen concentrations were achieved by diffusion at 1150degreesC for 24, 48 and 72 h. This report on bulk damage effects is focussed on the observed changes in the reverse current, the effective space charge density N-eff extracted from C/V measurements and investigations using the transient current technique. A substantial improvement of radiation hardness concerning the development of the macroscopic properties was found for detectors manufactured on oxygenated material compared to standard material. It will be demonstrated that the change of the effective space charge density as well as the increase of the reverse current can be attributed to the creation of two deep acceptor levels and a shallow donor level. (C) 2003 Elsevier B.V. All rights reserved.

In this contribution, the production of defects in radiation fields and their evolution toward equilibrium in silicon for detector uses has been modelled. In the quantitative model developed, the generation rate of primary defects is calculated starting from the projectile-silicon interaction and from recoil energy redistribution in the lattice. Vacancy-interstitial annihilation, interstitial migration to sinks, divacancy and vacancy-impurity complex (VP, VO, V2O, CiOi and CiCs) formation are considered. The results of the model support the experimental available data. The correlation between the initial material parameters, temperature, irradiation and annealing history is established. The model predictions could be a useful clue in obtaining harder materials for detectors at the new generation of accelerators or for space missions. (C) 2003 Elsevier B.V. All rights reserved.

We performed flux-creep annealing experiments on disordered (overdoped) Bi2Sr2CaCu2O8+delta and La2-xSrxCuO4 single crystals in remnant magnetic field at T = 10 K, where, as generally accepted, the vortex creep process is thermally activated, and at T = 2 and 1.8 K, in the putative quantum creep regime. A simple data analysis shows that the variation of the creep barrier U with the current density J remains qualitatively the same, regardless of T. In the case of La2-xSrxCuO4 single crystals in remnant field U(J) diverges in the low-J limit, and flux-creep annealing considerably reduces the normalized relaxation rate S at low T. We emphasize that the relatively large "residual" S values appearing below a certain crossover temperature in "standard" magnetization relaxation experiments are mainly due to the usually fixed relaxation time window in the conditions of a strong U(J) nonlinearity. (C) 2003 Published by Elsevier B.V.

Radiation-induced defects in silicon diodes were investigated after exposure to high doses of Co-60 gamma irradiation, using Deep Level Transient Fourier Spectroscopy and Thermally Stimulated Current methods. The main focus was on differences between standard and oxygen-enriched material and the impact of the observed defect generation on the diode properties. Two close to mid gap trapping levels and a bi-stable donor level have been found to be responsible for the main macroscopic changes both in standard and oxygen-enriched float zone diodes. (C) 2003 Elsevier B.V. All rights reserved.

The glassy composition As25Te35Si40 was investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), Raman spectroscopy, and infrared absorption (IR) measurements. X-ray diffraction patterns at room temperature and at temperatures around T-g were recorded and the radial distribution functions have been calculated. A continuous random network model for the ideal homogeneous glass structure has been proposed.

The replication of single-ion track templates opens up the possibility of accessing electrical properties of nanowires without using lithographic techniques. Polycarbonate foils of 30-mum thickness were irradiated with single swift heavy ions (e.g. An 11.4 or Xe 8.3 MeV/nucleon). By controlled one-sided etching of the damage trail caused by the ion, templates containing a single conical pore were prepared. The narrow pore openings had diameters down to 25 nm and opening angles up to 2degrees. By electrochemical deposition of copper, single conical wires were obtained. The electric current recorded during electrodeposition reflects the geometry of the pore. The wires were provided with electrical contacts. Current-voltage measurements confirmed that their resistance was ohmic. The wires could withstand a maximum current density above 10(8) A/cm(2).

The inhibiting effect of ETU has been studied regarding the corrosion of carbon-steel in NH4Cl 0.1 M solution at 25degreesC and 50degreesC. The effects of the inhibitor have been demonstrated using weight loss and electrochemical measurements as well as Mossbauer spectrometry. The efficiency of ETU increases with the raise of the concentration, but lowers with the temperature. An activation energy was determined using the Arrhenius equation. The experimental data characterize a Langmuir type adsorption isotherm and the results were correlated to the adsorption of the inhibitor Mossbauer spectrometry shows the formation of a superficial film on the surface of the corroded sample in the presence of ETU. This film provides a good corrosion protection for the sample.