Publications

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.

Smooth, transparent and highly oriented nanostructured ZnO films were synthesized by RF-magnetron sputtering onto Si(100) substrates. A mild-pressed zinc oxide powder target was used for all depositions. The sputtering parameters were varied in order to obtain structures with good adherence and crystallinity. The depositions were carried out in inert argon atmosphere at four sputtering pressures (0.2 Pa, 0.25 Pa, 0.3 Pa and 0.45 Pa). ZnO films were deposited at 150 degrees C. The films were characterized from structural (XRD) and morphological (AFM) point of view. The influence of each sputtering parameter on the morphological and structural properties is discussed.

In this study, copper sulfide CuS (covellite) was obtained, starting from the Cu(CH3COO)(2)center dot H2O and thiourea ((NH2CSNH2) system, and working in presence or absence of sodium-bis(2-ohylhexyl) sulfosuccinate (Na-AOT). Samples obtained from Cu(CH3COO)(2)center dot H2O:NH2CSNH2:Na-AOT system were deposited as thin films on the glass substrates. CuS samples obtained were characterized by X ray diffraction, IR spectroscopy, TEM transmission electron microscopy and SAED - selected area electron diffraction. The influence of surfactant on the shape and size of CuS (covellite) nanocrystals was established.

Indium Zinc Oxide compositional libraries were fabricated by combinatorial pulsed laser deposition technique on glass substrate at room temperature. Two pairs of targets with In atomic concentrations, In/(In+Zn), of 28 at.% and 56 at.% or 42 at.% and 70 at.% were employed. A high transparency was observed for all the coatings with transmittance values better than 95%. The maximum thicknesses of the samples, inferred by spectroscopic ellipsometry, were within the 174-310 nm range for the simple PLD films, whereas in case of combinatorial PLD coatings were 341 or 467 nm. Energy dispersive X-ray spectroscopy revealed that In content in the combinatorial films was in the 27-52 at. % range. From atomic force microscopy histograms we evidenced a decrease of the RMS roughness down to 1 nm with the increase of the In content. As a result of the compositional library studies two minimum values of the electrical resistivity were identified at 2.3x10(-3) Omega.cm and 8.6 x 10(-4) Omega.cm, which correspond to 28.8-29.5 at.% and 44-49 at% range of Indium content.