Publications

Electrochemical polymerization of indole in a LiClO4/CH3CN solution on a single-walled carbon nanotubes (SWNTs) film was studied by cyclic voltammetry, Raman scattering and FTIR spectroscopy. Comparing the cyclic voltammograms recorded on a blank Pt electrode with those obtained when carbon nanotubes films were previously deposited onto the Pt electrode, a down-shift of the indole reduction peak potential in the latter case was observed. Raman spectroscopy studies indicate that the electrochemical deposition of polyindole (PIN) onto the SWNT film results in a breaking of SWNT bundles into individual tubes. A covalent functionalization of SWNTs with PIN in the doped state is demonstrated by FTIR spectroscopy, when an increase in the intensity of the absorption band at 1045 cm(-1) is observed. Besides, Raman and FTIR studies performed on samples electrochemically prepared and thereafter post-chemically reacted with an NH4OH solution, indicate both a roping process of individual tubes with PIN as a binding agent and a strong steric hindrance effect. (C) 2009 Elsevier B.V. All rights reserved.

The knowledge of the effects of radiation in semiconductor devices, in particular in detectors, represents an important and active field of research. The influence of isovalent impurities, carbon and germanium, on the radiation damage of silicon for detectors is investigated in the frame of a quantitative phenomenological model for defect kinetics, developed previously by the authors. The concentrations of defects induced by irradiation in materials with different doping levels are calculated, as well as the leakage current and effective carrier concentrations in p-n junction detectors made from these materials. The beneficial effect of Ge on the radiation damage of silicon is deduced.

This work focuses on the investigation of radiation-induced defects responsible for the degradation of silicon detector performance. Comparative studies of the defects induced by irradiation with Co-60-gamma rays, 6 and 15 MeV electrons, 23 GeV protons and reactor neutrons revealed the existence of point defects and cluster-related centers having a strong impact on damage properties of Si diodes. The detailed relation between the "microscopic" reasons as based on defect analysis and their "macroscopic" consequences for detector performance is presented. In particular, it is shown that the changes in the Si device properties (depletion voltage and leakage current) after exposure to high levels of Co-60-gamma doses can be completely understood by the microscopically investigated formation of two point defects, a deep acceptor and a shallow donor, both depending strongly on the oxygen concentration in the silicon bulk. Specific for hadron irradiation are the annealing effects which decrease (increase) the originally observed damage effects as seen by the changes of the depletion voltage and these effects are known as "beneficial" and "reverse" annealing, respectively. A group of three cluster-related defects, revealed as deep hole traps, proved to be responsible specifically for the reverse annealing. Their formation is not affected by the oxygen content or silicon growth procedure suggesting that they are complexes of multi-vacancies located inside extended disordered regions. (C) 2009 Elsevier B.V. All rights reserved.

The fabrication and characterisation of surface acoustic wave resonators operating in the gigahertz frequency range are presented. The devices were fabricated on thin AlN layers deposited by magnetron sputtering on high resistivity (100) oriented silicon substrates. Using direct writing e-beam lithography, well defined interdigital transducers with 300 nm finger width and spacing have been obtained. On-wafer microwave measurements have demonstrated a narrow bandstop frequency characteristic with high rejection at approximately 5 GHz and an electromechanical coupling coefficient of 0.53%.

In this paper, we apply the generalized master equation to analyze time-dependent transport through a finite quantum wire with an embedded subsystem. The parabolic quantum wire and the leads with several subbands are described by a continuous model. We use an approach originally developed for a tight-binding description selecting the relevant states for transport around the bias-window defined around the values of the chemical potential in the left and right leads in order to capture the effects of the nontrivial geometry of the system in the transport. We observe a partial current reflection as a manifestation of a quasi-bound state in an embedded well and the formation of a resonance state between an off-set potential hill and the boundary of the system.

Composites based on carbon nanotubes and ZnO particles with needle shapes were prepared for applications in energy storage. Depending on the temperature (85 or 25 degrees C) at which the reaction between NaOH and ZnCl(2) was carried out, particles with two different morphologies: needle-shaped (NS) and double-pyramid-shaped (DPS), respectively, are obtained. Scanning electron microscopy, photoluminescence, UV-Vis absorption spectroscopy, x-ray diffraction and Raman light scattering studies reveal that the NS and DPS particles belong to ZnO with wurtzite (WZ) structure and epsilon-Zn(OH)(2) as precursors of ZnO, respectively. Using the ZnO/carbon nanotube composite as a negative electrode and an electrolytic solution containing LiPF(6), the charge-discharge characteristics of rechargeable lithium ions cells were determined. Additional information concerning the electrochemical reactions at the interface of the two electrodes was obtained by cyclic voltammetry.

A method for building photonic structures in As2S3 amorphous chalcogenide films has been developed. 2-D photonic configurations characterized by a regular assembly of rods (triangular lattice) or gratings with traces of micrometer period have been obtained. A femto-second laser has been used in photonic crystal registration. The simulation performed on these photonic configuration shows that the obtained chalcogenide structures could be efficient for operation in the infrared range around several micrometers wavelength.

Nitrogen is often used for doping TiO2 films to improve their photocatalytic properties in visible light. Multilayer TiO2 anatase films were deposited by sol-gel method on quartz substrate and thermally treated in O-2 and NH3 flow in 500-800 degrees C range. The effect of the annealing treatment (temperature and atmosphere) on the structural properties of TiO2 films was studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Nitridation causes the amorphization of the anatase tetragonal phase at 600 degrees C. The film re-crystallization into the cubic oxynitride phase is observed at 800 degrees C. EDX results confirms that the incorporation of nitrogen into the amorphous films takes place before thermally activated growth of the oxynitride phase and demonstrates that the relative O:N composition in the crystalline phase is dependent on the temperature of the thermal treatment.

The heterostructure Ag/As2S3 was deposited on glass substrate in two configurations: Ag/As2S3/glass and As2S3/Ag/glass. The effect of light emitted by a halogen lamp has been investigated by optical microscopy and X-ray diffraction. Particular morphological and structural aspects were revealed. Lateral diffusion rate of Ag has been determined.