Publications

We modeled the equilibrium structure, at 0 K temperature, of some spherical As(2)S(3) molecules with only 12 rings of ten member (alternating As and S atoms) and 20 triangular faces: As(60)S(90) (like C(60)), As(140)S(210) (like C(140)), As(320)S(480) (like C(320)), grown on carbon fullerene and As(20)S(30) (like C(20)). We used a Monte-Carlo relaxation procedure in the frame of valence force fields theory. The onion-like configurations of the arsenic sulphide was demonstrated as possible. The deposited films of As(2)S(3) seen in the cross-section prove the presence of onion-like configurations even in pure As(2)S(3) material.

Photo-diffusion of silver across an As2S3 thin film layer is studied, as continuing some earlier work about surface morphology modifications in double-layer structures of Ag and As2S3, and some qualitative preliminary results on lateral Ag diffusion in As2S3 thin films. An estimation of the Ag film's dissolution rate and the diffusion front's advancement rate in As,S3 is given based on crosssection measurements. In order to understand better the diffusion mechanism of Ag in As2S3, a structural model of the As2S3 matrix is used to estimate the amount of silver which might be hosted by an As2S3 layer in terms of molar ratio, and an interaction mechanism of the Ag with the chalcogenide matrix is proposed. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Green house gases, carbon dioxide, ozone, nitrous oxide and chlorofluorocarbons, result inevitably from fossil fuels combustion. The capture of CO2 from flue gases is an effective way to prevent the threat of global warming. The usage of flue gases with low CO2 content in the synthesis of precipitated calcium carbonate, a valuable mineral compound, seems to be an interesting solution for CO2 permanent removal. The quality of the solid product obtained (pure polymorphic phase and narrow particle size distribution in micron and sub-micron domain), can increase the value of the process due to the various applications of calcium carbonate (as filler in paper industry, pharmaceuticals, plastic materials and rubber). The present paper analyzes the chemical absorption of CO2 from flue gases in a waste lime solution. The important advantage of this process over conventional technologies of CO2 removal is that it provides a mineral product with many industrial uses, the fine crystallized CaCO3. Based on experimental results a mathematical model including the chemical process and the precipitation of solid phase was developed. The CO2 absorption was modeled using the general model for mass transfer with chemical reaction. The crystallization steps were modeled in the frame of population balance equation. The kinetic parameters corresponding to the crystallization process including nucleation, particle growth and agglomeration were estimated by nonlinear regression using experimental particle size distribution data.

The electrodeposition process of Eosin Y/ZnO:Mn as films and nanowires performed using a solution containing zinc and manganese nitrates + lactic acid mixture was studied by linear voltammetry. The films and wires grown by polarization at -1.1 V/SCE electrode potential were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). Additionally, the Eosin Y presence was evidenced by optical measurements as absorption and photoluminescence spectroscopy. The manganese content in films depends on the nature of support electrode used. On the other hand, the presence of Eosin Y species in the deposition bath increased significantly the manganese concentration in the ZnO:Mn nanowires electrodeposited at -1.1 V/SCE.

Trapping aspects in two typical silicon-based nanostructures are investigated. Both 1D nanocrystalline porous silicon structures and 2D (nc-Si/CaF2)50 multilayered structures are considered. The curves of relaxation current versus temperature were obtained using the thermally stimulated currents method without external bias. Two types of maxima (rather broad maxima and spikes) were experimentally evidenced. The spikes are due to the stress-induced traps and their parameters are temperature dependent. To describe the trapping-detrapping-retrapping processes, a general model was proposed. The temperature dependence of stress-induced trap concentrations was described by a power law and the corresponding temperature dependence of cross-sections by a Gaussian law. The model was successfully applied on available experimental data.

Fe(3)O(4) nanoparticles were synthesized by a wet chemical method using Fe(III)/Fe(II) - hydrazine dihydrochloride systems. The structure, morphology, and magnetic properties of magnetite were examined by X-ray powder diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), Mossbauer spectroscopy and superconducting quantum interference device (SQUID). Almost all the particles exhibit superparamagnetic like properties at room temperature. This behavior can be correlated with the size of the particles which ranged between 20-70 nm.

Percolation phenomena are investigated and discussed in three kinds of nanostructures: first two are nanocrystalline silicon-based systems, Si nanodots embedded in amorphous SiO2 matrix and porous silicon formed by an oxidized nanowire network, and the third consisting of a multi-walled carbon nanotube network embedded in amorphous SiN. The current-voltage characteristics measured on first two systems present voltage percolation thresholds with the same shape - a saturation plateau region of the current, followed by an abrupt increase. The current-voltage and conductance-voltage curves measured on multi-walled carbon nanotube network embedded in amorphous SiN present non-periodic and temperature independent oscillations. These oscillations are interpreted as voltage percolation thresholds.

The effect of Fe, respective Cu, additions as substitute for Ni in NiTi shape memory alloys (SMAs) on the delaying of its phase transition and narrowing hysteresis are well known, NiTi-Fe and NiTi-Cu SMAs having applications especially to the actuators that require such properties. These SMAs are currently produced by conventional melting methods, which are energo-intensive and impose very severe processing conditions to avoid contamination. The results of researches presented in this paper prove the possibility of these SMAs obtaining by powder metallurgy via reactive sintering - more advantageous from both technical and economic point of view. A beneficial effect on both sintering and homogeneity of the obtained SMAs proved to have a controlled mechanical alloying applied to powder mixture before compacting and sintering.