Publications

The microstructure of the Cr/CrN and Ti/TiN multilayers coatings deposited with the pulsed laser deposition (PLD) technique was studied using transmission electron microscope Philips CM20 TWIN (200 kV). It was found that the metallic buffer layers are characterized by the smallest columnar crystallite size and the highest defect density; this might rise their hardness but compromise the coating adhesion. The intermediate metallic layers showed a larger and less defected columnar structure as compared with the nitride layers, what should improve the coatings toughness. The scratch test performed with a Rockwell penetrator of 200 gm diameter loaded from 0.03 N up to 20 N indicated that the switching from a single layer to a multilayered metal/nitride coating of the same thickness improved the resistance to scratch test in case of Ti/TiN from 16.4 N for a TiN single layered to 22.9 N for a 32 layered coating and Cr/CrN from 4.4 N for a CrN single layered to 6.6 for a 32 layered ones. (c) 2005 Elsevier B.V. All rights reserved.

A review of the evolution of the amorphous chalcogenide field of research from early times up to the present state of the art is presented. On the basis of recent achievements a bright future for these materials is predicted. (c) 2006 Elsevier B.V. All rights reserved.

The intermediate, self-organized phase, in the As-Se system has been modeled on the basis of clusters with one or more selenium-selenium bridges. The X-ray diffraction patterns of the glass models at the limits of the 'floppy phase-stressed rigid phase' window have been calculated. The structural and optical anisotropy in a matrix of clusters containing Se-Se bonds is supposed to be a consequence of breaking and re-linking the broken clusters in the direction of the polarized light beam that acts upon the chalcogenide material. (c) 2006 Elsevier B.V. All rights reserved.

We investigated the superconducting parameters of iodine-intercalated BiSrCaCuO high-temperature superconducting materials. While for samples containing a significant amount of Bi2Sr2CaCu2O8+x, (Bi-2212) iodine intercalation results in the dramatic decrease of the superconducting parameters, it was found that for samples with a nearly single Bi2Sr2Ca2Cu3O10-y (Bi-2223) phase these parameters can increase. We argue that this different behavior of the superconducting parameters is the result of a different doping regime, and can be explained based on the parabolic dependence between T, and the number of holes per CuO2 layer. Iodine intercalation appears to be an efficient way to bring the usually under-doped superconductor to its optimal T-c and flux pinning properties.

Small particles of Pbl(2) embedded in transparent polymer matrix have been studied by Raman scattering, UV-VIS absorption spectroscopy, low temperature photoluminescence (PL) and Scanning Electron Microscopy (SEM). The Pbl(2) crystallites were prepared by two different methods: i) by cooling to the room temperature a boiling saturated aqueous Pbl(2) solution containing polyacrylamide and ii) by chemical reaction of Kl and Pb(NO3)(2) in aqueous polyacrylamide solution. In both cases, beside the hexagonal platelets of Pbl(2) Were identified rods whose luminescence and Raman signature is quite different than of Pbl(2) platelets. Regardless the rods nature, as distinct KPbl(3) particles or lead iodide low-dimensional particles embedded in the polymer matrix, their photoluminescence is featured by an intense green emission (550 nm) appearing at low temperature at excitation wavelengths less then 350 nm.

In-plane current-voltage (I-V) characteristics of high-temperature superconductors in a zero applied magnetic field exhibit intrinsic two-dimensional (2D) behavior at relatively high transport-current densities. This allowed us an accurate determination of the temperature variation of the zero-field I-V exponent a(T) (V proportional to I-a) at the superconducting (CuO2)(2) layer level in the case of highly anisotropic Bi2Sr2CaCu2O8+delta films in the vicinity of the Kosterlitz-Thouless-Berezinskii transition temperature T-KT. The mean-field critical temperature and T-KT were determined from the zero-field resistive transition in the framework of the 2D Coulomb gas model. It was found that a(T-KT)approximate to 3, pointing toward a dynamic critical exponent z(T-KT)=2. The a(T) dependence observed by us is in good agreement with Langevin simulations of the 2D Coulomb gas model.

Band-pass filters with dielectric resonators of (Zr-0.8, Sn-0.2)TiO4 ceramic materials (ZST) were developed for X-band applications. The ZST materials exhibit a dielectric constant of about 36.8 and low loss in microwave range. A Qxf product higher than 50,000 was achieved for the ZST samples with 0.2 % wt NiO sintering addition. The external coupling was performed using microstrip lines on a substrate of 9.22 dielectric constant and 0.635 mill height. Filters with a minimum insertion loss between 0.46 dB and 1.74 dB, the bandwidth between 40 MHz and 170 MHz and with the central frequency around 10 GHz were manufactured.

This paper presents the investigation of the optical properties of bisphenol A polycarbonate organic matrix/CdS clusters composite material in correlation with the method for the films' preparation using as precursors cadmium acetate (Cd(CH3COO)(2)), respectively ammonium thiocyanate (NH4CNS), and as general solvent for all the components, is dimethyformamide. The effect of the heat treatment temperature (90 degrees C or 150 degrees C) on the position and shape of the fundamental absorption edge was investigated for given substrate, drying conditions and duration (1.5 h or 0.5 h) of the heat treatment. A large blue shift of the absorption edge was evidenced in films prepared in vertical configuration and thermally treated at 90 degrees C for 1.5 h, which can be associated with a small dimension of the CdS crystallites and in consequence with quantum confinement effects. Using the effective mass theory we have deduced a crystallite dimension in the range 8.8-15 nm. We also have studied the interaction of the light with this composite material evaluating an optical band gap between 2.92 and 3.69 eV (depending on the preparation and annealing conditions) and an absorption mechanism in CdS clusters closer to an indirect transition and deviated from the normal direct absorption process in bulk CdS semiconductor.

Optical transmittance studies were carried out on some doped titanium dioxide thin films, obtained by r.f. magnetron reactive sputtering, using glass and ITO/glass substrates. We have observed that, while TiO2 films have a good transparency till about 2000 nm, the ensemble TiO2 and ITO (indium tin oxide) films gives a decrease of the optical transmittance in near infraread region, being still transparent in the visible range. The mentioned decrease depends on the dopant used. This is an important observation, since TiO2 films are already used as coatings for many buildings. So, for economic reasons, the necessary energy used for the inside cooling of the air can be reduced, by getting a good visible transparent window, together with a NIR shielding.