National Institute Of Materials Physics - Romania

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.

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).

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.

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.

The structure of the chalcogenide glass films of composition As2S3-GeS2 has been investigated bu X-ray diffraction. The relation between the quasi-distance as evidenced from the first sharp diffraction peak, and the composition ration has been estabilished. The Boolchand (intermediate) phase was found ro be characterized by large structuro-compositional fluctuations.

The present paper deals with the preparation and study of optical properties of ZnO nanowires. Nanoporous ion track polycarbonate foils were used as templates for ZnO nanowires growth by electrochemical deposition. The growth was performed using an aqueous electrochemical bath at a temperature of 70 degrees C. SEM and TEM were employed to study the morphological properties of the nanowires. Electron diffraction was employed for structural characterization. Reflection and photoluminescence spectroscopy were used for optical characterization. A comparison between the properties of electrodeposited thin films and nanowires of ZnO was made from the point of view of photoluminescence properties. (c) 2007 Elsevier B.V. All rights reserved.

Pb(Zr1-xTix)O-3 (PZT) thin films were prepared by sol-gel method on stainless steel (SS) and on platinum-coated silicon substrate (Pt/Si). The structure revealed by X-ray diffraction shows strong crystallographic orientation: (110) and (100), respectively. A small amount of pyrochlore phases (Pb-2(Zr,Ti)(2)O6-delta is formed in the films deposited on SS substrate. The crystallite size shows significant differences: d((00l))((SS)) = 27.1 nm, d((h00))((Pt)) = 88 nm. The tetragonal splitting is (Delta c/c)((SS)) = 3.55 % and (Delta c/c)((Pt)) = 3.32 %.

In order to prepare poly(N-vinyl carbazole) (PVK) and carbon nanotube (CNs) based composites, electrochemical polymerization of N-vinyl carbazole (NVK) was studied by cyclic voltammetry (CV) in LiClO4/acetonitrile solutions. Cyclic voltammograms recorded on a blank Pt electrode and those obtained when single or multi-walled carbon nanotubes (SWNTs or MWNTs) films were previously deposited onto the Pt electrode show a down-shift of the VK reduction peak potential in the latter case. The influence of monomer concentration and supporting electrolyte on the polymerization conditions and electrochemical properties of these composite materials were also investigated. Morphologic aspects as well as the photoluminescence properties of the PVK/CNs composite were also investigated. A covalent functionalization of carbon nanotubes with PVK is suggested on the basis of infrared (IR) spectroscopic studies. Using the PVK/CN composite as a positive electrode and an electrolytic solution containing LiPF6, a higher specific discharge capacity of the rechargeable lithium cells, similar to 45 and 115 mA h g(-1), are reported for PVK functionalized SWNTs and MWNTs, respectively. (c) 2007 Elsevier Ltd. All rights reserved.

Thin films of composition GeSb2Te4 and (GeSb2Te4)(90)(SnSe2)to have been prepared by pulsed laser deposition and characterized by X-ray diffraction and scanning electron microscopy. The electrical switching was revealed in both compositions.

The structure of amorphous silicon and amorphous hydrogenated silicon has been investigated starting from a large model of amorphous silicon (2052 atoms). The modifications induced in a-Si model by when hydrogen is introduced have been revealed. The diffusion of hydrogen leads to a nanostructuring effect in the continuous random network of amorphous silicon. The effect of hydrogen on the distributed distortion defects in silicon network has been modelled. The most strained bonds have been broken and hydrogen wasd attached to the dangling bonbds on silicon. A free energy relaxation process was carried out in the frame of a Monte - Carlo - Metropolis procedure. There was demonstrated that, by nanostructuring, the total free energy of the model decreases. The variation of the bond stretching and bond bending energy as a function of the number of broken bonds indicated a dominant contribution of the bond bending term. The modelling shows, undoubtedly, the disappearance of many structural defects that probably are related to the deep electronic states in the gap of amorphous silicon.