Publications

Multilayers made of alternative layers of composition SnSe2 and tellurium (three pairs) have been prepared by pulsed laser deposition (PLD). The complex films have been investigated by X-ray diffraction. After a special annealing in oxygen fluence at various temperatures, up to 620 degrees C, the films were investigated both by X-ray diffraction and for gas sensing. Gas sensing properties were tested for water vapours, carbon monoxide (CO) and methane (CH4). After annealing at high temperature, the structure of the multilayer samples show oxide phases like TeO2, SnO2 and a mixed oxide ternary phase SnTe3O8. The annealed multilayers show good sensing properties to water vapours and CO gas.

This work is aimed at providing a better understanding of the biocompatibility of 316L stainless steel in the human body, where various biomolecules are able to bind metal ions and convey them from the surface of orthopaedic implant to various parts of the body. The passivation behavior of orthopaedic 316L implant was studied by associating the electrochemical methods (Differential Pulse Voltammetry and Cyclic Voltammetry) with the surface M(Mossbauer spectroscopy as a function of type of physiological media; glucydic, proteic and lipidic. Was studied the electrochemical behaviour of steel in three artificial media: Aminosteryl, Intralipid and Kabiven in the concentrations corresponding to the administration dosages. The results were discussed in the context of the formation of passive film which stability strongly depends on the corrosive activity of the physiological media in the order: Aminosteryl < Kabiven < Intralipid.

ITO films of composition (In2O3)(0.9) - (SnO2)(0.1) have been prepared by pulsed laser deposition (PLD).The films were found to be amorphous. The structure and evolution of the films during annealing in air, oxygen atmosphere and reducing atmosphere (CO2) have been investigated by X-ray diffraction. The films annealed in ambient atmosphere start to crystallize under 250 degrees C annealing temperature. The films treated in oxygen atmosphere crystallize at higher temperature (similar to 300 degrees C).

We investigated MOCVD growth of c-axis two-layer and three-layer stacked heterostructures on (100) SrTiO3 of SI, IS or SIS type. S denotes high temperature superconductor thin films of YBa2Cu3O7 (Y-123), Bi2Sr2Ca2Cu3O10 (Bi-2223) or Bi2Sr2CaCu2O8 (Bi-2212), while I stands for insulating thin films of (Ba, Ca) CuO2 or (Sr, Ca) CuO2. X-ray diffraction, atomic force microscopy and measurements of resistivity versus temperature were performed after the deposition of each layer. The best results, suitable for further device fabrication, were obtained for the SIS structure (100) SrTiO3/Bi-2223/(Sr, Ca) CuO2/Bi-2212. Similar structures with I = (Ba, Ca) CuO2 have shown higher impurity phases and lower superconducting quality of the top superconducting layer. For two-layer or three-layer structures, Bi-2223 as a top layer could not be obtained and, instead, a phase with Bi-2212 formed. Structures with (100) SrTiO3/Y-123/(Sr, Ca) CuO2/Y-123 or (100) SrTiO3/Y-123/(Ba, Ca) CuO2/Y-123 were also promising, but a current leak often occurred due to greater roughness. Structures with Y-123 are less sensitive to growth temperature than those with BSCCO.

This paper presents some investigations on the electrical transport properties of ITO/single (double) layer organic semiconductor (m-DNB, benzil, PTCDA, Alq3) contacts in SIS-like (ITO/organic/Si) and MIS-like (ITO/organic/metal) heterostructures. The I-V characteristics have emphasised the injection properties of different contacts and the effect of space charge limited currents in correlation with the type and preparation conditions of the contacts. We have studied the influence of the type of contact (In/ITO; In/Al) on the electrical conduction in Alq3/PTCDA/Si/In heterostructure. In a planar grid contact configuration for In/Al/PTCDA/Al/In structure we have observed the effect of the low electric field on the shape of the I-V characteristic. (c) 2007 Elsevier B.V All rights reserved.

We report here on the characteristics of RF-sputtered 300 nm thick films of TiO2-2xNx prepared on glass substrates at 350 degrees C, by adjusting the N-2:Ar partial pressure ratio in the deposition chamber between 0.00 and 0.33. XRD, XPS, AFM and contact angle data were used to derive film structure, elemental composition and oxidation state of Ti, surface morphology and hydrophilicity, respectively. The band gap was derived from spectral data in the 350-450 nm range. Film structure and composition were changed by adjusting the partial pressure of the reactive gases during sputtering and by post-deposition annealing at 400 degrees C in air, for 90 min. The values of the contact angle of films' surface with de-ionized water and of surface free energy per unit area show that films are super-hydrophilic for high-nitrogen content. Correlations are made between film structure, elemental composition, electronic and wettability properties. (c) 2007 Elsevier B.V. All rights reserved.

In-plane zero-magnetic-field current-voltage (I-V) characteristics of oxygen-deficient YBa2Cu3O7-delta films (7-delta similar to 6.5, 6.55, and 6.65) were thoroughly investigated. A good agreement with the quasi two-dimensional (2D) vortex-antivortex unbinding scenario was observed, similar to the behaviour of highly anisotropic Bi2Sr2CaCu2O8+delta films. The temperature variation of the I-V exponent allows the determination of the Berezinskii-Kosterlitz-Thouless transition temperature T-KT at the superconducting Cu-O layer level, and the mean-field critical temperature T-c0. We found that both T-KT and T-c0 increase with increasing doping, and T-c0 remains in the region of the electrical resistivity drop. These results do not support the vortex fluctuation scenario for the superconducting transition in underdoped cuprates. (C) 2007 Elsevier B.V. All rights reserved.

A first sharp diffraction peak (FSDP) is the most sensitive characteristic to medium range order in non-crystalline solids with speculative origin up to now. The compositional trends in the FSDP position and full width at half maximum are tested on the example of pseudo-binary Sb2S3-As2S3 and Sb2S3-GeS2 systems of chalcogenide glasses. The FSDP-related correlations are found for the investigated materials and considered in terms of packing factor of amorphous layers and experimental density of glass.

A versatile method, that of sol-gel deposition was used to produce Si1-xGexO2 films on Si substrates. Samples after annealing at different temperatures are investigated by different techniques including high-resolution transmission electron microscopy and spectral ellipsometry. It was revealed that, by annealing at high temperatures, Ge accumulates in small clusters (5-10nm) inside of the oxide layer. By ellipsometric investigations, valuable data about the temperature evolution of the composition and optical constants were obtained.