Publications

Comparative studies of gate oxides on a N+ pre-implanted area (N-interface similar to 1x10(19)cm(-3)) and on a virgin Si face 4H-SiC material (N-interface similar to 1x10(16)cm(-3)) have been undertaken by means of Capacitance-Voltage (C-V) characteristics, performed at different temperatures and frequencies, and Thermal Dielectric Relaxation Current technique. In the non implanted samples, the stretch out of the C-V curves get larger as the temperature is lowered to 150K, while for lower temperatures the C-V characteristics become steeper and some discontinuities occur. These discontinuities are specific for the non-implanted sample and are associated with charging of the fast near interface states (NIToxfast) via a tunneling from the shallow interface states (D-it). The tunneling from the shallow D-it to NIToxfast supress the a.c. response of D-it, which is recovered only after most of the NIToxfast are charged with electrons.

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.

Non-linear phenomena have been observed in the Ag(paint)-As2S3 system. This behaviour is useful in rectifier devices and in dynamical switching devices based on chalcogenides.

Nanostructured thermoelectric semiconductors are a promising material to convert waste heat to electricity for energy regeneration due to improvement of Seebeck coefficient and thermal conductivity reducing. Among various thermoelectric materials, bismuth telluride based alloys are the most used in the fabrication of TE devices. The processes associated with the electrodeposition of (Bi,Sb)(2)Te-3 nanowires and films are reported along with an analysis of the composition, morphology and structure of resulting materials. Electrochemical behavior was examined using cyclic and linear voltammetry and electrochemical impedance spectroscopy techniques.

A derivative of p-aminoazobenzene-epoxy resin was studied. Visually examination between crossed polarizers does not show birefringence but it can be optically induced. Changing the polarization direction of the irradiating light leads to the changing of the privileged direction of the induced birefringence. The birefringence value was evaluated and compared with liquid crystals as anisotropic compounds.

The aim of this paper is the preparation and characterization of hydroxyapatite doped with europium (Eu3+, Eu:Hap). The nanopowders were obtained by coprecipitation method and analyzed through infrared spectroscopy (FT-IR) and Fourier transform Raman spectroscopy (FT-Raman). The preliminary results reveal the nanometric dimension of the particles and indicate that Eu3+ has been introduced into the framework of HAp. The Eu concentration effects of nano Eu: HAp were studied on human osteoblast MG 63 cells in vitro. Our results demonstrate that cell proliferation is not related to the Eu concentration in the HAp particles. This work provides an interesting view of the role of nano Eu: HAp as ideal biomedical materials in future clinical applications.

The electrical conductivity of new nanocomposite systems liquid-ctystal/montmorillonite clay is performed using impedance spectroscopy. The dependence of the electrical conductivity on the frequency, temperature and bias voltage is obtained. The results referring to the alternative voltage influence allow getting more information on the conduction mechanism than the previous ones obtained under frequency and temperature influence. An important role has the polarization at the electrode-sample interface, both in continuous and alternative current. The electrode polarization effect on the electrical conductivity in dependence on the above mentioned parameters is also examined.

Electrical and photoconductive properties of films consisting of amorphous Ge nanoparticles uniformly distributed in amorphous SiO2 were studied. These films were prepared by sol-gel method and treated by rapid thermal annealing technique. Measurements of current-voltage and conductance-temperature characteristics, spectral and bias dependences of the photocurrent on samples with coplanar geometry of electrodes, were performed. The current-voltage characteristics have a weak rectifying behaviour. The variable range hopping transport mechanism, described by the Mott law, in amorphous materials, in the absence of dominant Coulomb interactions, was evidenced in the temperature dependence of the dark current. The samples exhibit very good photoconductive properties, explained by taking into account the Ge clusters and defects, produced by the rapid thermal annealing.

GeSiO nanostructures obtained by using two different preparation methods, sol-gel and magnetron-sputtering were studied. They are formed from Ge nanoparticles dispersed in amorphous matrix, with different morphology depending on the preparation method. Electrical investigations (current-voltage and current-temperature measurements) were performed and experimental results were modelled. It was shown that preparation conditions induce the electrical behaviour of GeSiO films, so that the electrical transport in sputtered films is governed by a hopping mechanism, while in sol-gel ones it is dominated by the junction formed at the interface with Si substrate. Also, the temperature dependence of current shows different hopping mechanisms.

High quality granular ferromagnetic thin films on glass and silicon wafer substrates were obtained using the original thermionic vacuum arc (TVA) method developed at National Institute for Laser, Plasma and Radiation Physics. We report obtaining of 77-200 nm thick Cu/Ni/Fe structures. An experimental set-up, with three simultaneously discharges, was made to obtain the desired thin film composition and thickness. The structural and morphological properties of the prepared nanostructured films were analyzed by AFM (Atomic Force Microscopy), XRD (X-ray Diffraction) and SEM (Scanning Electron Microscopy). Magneto-Optical Kerr Effect studies were made in order to infer the changes in polarization of an optical radiation due to the magnetic field influence. In order to obtain concluding electrical measurements results, cooper electrodes were deposited using the same method before and after the actual three material thin structures. In this way significant changes in the electrical resistance behavior were noticed and were correlated with TVA plasma parameters used for film preparation.