Origin of giant photocontraction in obliquely deposited amorphous Ge_xSe_{1-x} thin- films and the intermediate phase

Obliquely deposited amorphous Ge_xSe{1-x} thin-films at several compositions in the 0.15 < x < 0.333 range, and at several obliqueness angles in the 0 < alpha < 80 range at each x were evaporated on Si and glass substrates. Here alpha designates the angle between film normal and direction of vapor transport. Raman scattering, ir reflectance and optical absorption measurements were undertaken to characterize the vibrational density of states and optical band gaps. Edge views of films in SEM confirm the columnar structure of obliquely (alpha = 80) deposited films. Films, mounted in a cold stage flushed with N2 gas, were irradiated to UV radiation from a Hg-Xe arc lamp, an

Crystallization kinetics of SbxSe100-x thin films

The crystallization kinetics in SbxSe100-x films with 39≤x≤58 is studied by monitoring the optical transmission of the films during both isothermal and constant rate heatings. The structure of the films upon crystallization and at certain intermediate stages is studied by electron microscopy techniques. The results are analyzed in the frame of the Johnson-Mehl-Avrami theory in order to determine the kinetic parameters (Avrami exponent, activation energy and frequency factor) in addition to the crystallization temperature. The results show that film crystallization is always preceeded by a relaxation process which modifies substantially the optical properties of the amorphous material. Amorphous films with compositions close to the stoichiometric compound (Sb2Se3) are found to show the highest activation energy for crystallization.This work is partially supported by CICYT (Spain) under project TIC 93-0125.Peer Reviewe

An experimental approach for synthesis of Fe-Al-O multiferroic fibrous material

peer reviewedBasic principles of the electro-hydrodynamics are applied for synthesis of solid state Fe-Al-O multi-ferroic fibrous material. For that purpose stable blend spinning solutions comprised of a high molecular assisting organic polymer and salts of iron and aluminum are developed. These solutions are tested under electrospinning conditions and synthesis of homogeneous as spun non-woven mats characterized by fibre mean diameters in the microand nano-size range is successfully demonstrated. Multi-step thermal procedure is applied for the consecutive solvent evaporation, polymer pyrolisis and final fibre calcination. Electronoptical imaging technique and XRD are applied for revealing the sample morphology and the phase composition correspondingly. The results obtained outline the wide possibilities for fabrication of multi-ferroics fibrous nano-materials on the basis of Fe-Al-O

Mixing kinetics and write-once optical recording characteristics of Sb/Se bilayer films

Bilayer Sb/Se films are irradiated with 12 ns pulses from an ArF laser (extended areas) and from a focused Ar+ laser (micron-sized areas). Real-time reflectivity measurements are used to determine if the process occurs within the solid or liquid phase and the transformation time, in addition to measure the optical contrast and the medium sensitivity. Transmission electron microscopy is used to analyze the structure of the transformed areas and the medium resolution. The results show that mixing is initiated by preferential melting at the gram boundaries and an amorphous phase is produced upon irradiation a high energy densities. Finally, the characteristics of the mixing process in Sb/Se films as a write-once optical recording mechanism are discussed in terms of the sensitivity and resolution of the recorded spots and the time required for recording.This work has been partially supported by CICYT (Spain) under TIC-93 program.Peer Reviewe

Structure and properties of nanosized electron beam deposited zirconia thin films

Thin films of amorphous zirconium oxide are deposited in high vacuum via the electron gun evaporation of pure ZrO2 within a large scale of vapour incidence angles. A nanosized grain surface structure and columnar growth morphology are revealed by electron optical methods. It is demonstrated that the oblique deposition results in both column inclination and anisotropy of the column cross section that are related to the vapour beam incidence. The revealed structure is found to influence the Knoop microhardness, DC conductivity and the effective refractive index by inducing in-plane anisotropy, which is most pronounced at high vapour incidence angles. The dependence of these properties on the vapour incidence is explained with the nanodimensionality of the film morphological features. Finally, it is shown how an excimer laser processing modifies both the structure and properties of the zirconia films. (C) 2001 Elsevier Science B.V. All rights reserved

Laser assisted modification and chemical metallization of electron-beam deposited ceria thin films

Excimer laser processing is applied for tailoring the surface morphology and phase composition of CeO2 ceramic thin films. E-beam evaporation technique is used to deposit samples on stainless steel and silicate glass substrates. The films are then irradiated with ArF* excimer laser pulses under different exposure conditions. Scanning electron microscopy, optical spectrophotometry, X-ray diffractometry and EDS microanalysis are used to characterize the non-irradiated and laser-processed films. Upon UV laser exposure there is large increase of the surface roughness that is accompanied by photo-darkening and ceria reduction. It is shown that the laser induced changes in the CeO2 films facilitate the deposition of metal nano-aggregates in a commercial copper electroless plating bath. The significance of laser modification as a novel approach for the production of CeO2 based thin film catalysts is discussed. © 2009 Elsevier B.V. All rights reserved.This work has been performed in the frame of the Bulgarian-Spanish Scientific Cooperation Agreement, supported by the Bulgarian Academy of Sciences and the National Research Council of Spain (CSIC).Peer Reviewe

Phase transitions in excimer laser irradiated zirconia thin films

In the present work, excimer laser irradiation below the ablation threshold is successfully applied as a tool for surface modification of vapor grown amorphous zirconia (ZrO2) thin films. Characterization of virgin and laser processed areas was performed by optical spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED), low angle X-ray diffraction (LAXRD) and reflection high energy electron diffraction (RHEED). The occurrence of phase transitions to orthorhombic or monoclinic modification of amorphous zirconia on laser parameters dependency is established. Separation of a new Zr phase is detected in parallel to the formation of crystalline zirconia phases. The observed structure transformations strikingly coincide with some polymorphic transitions in zirconia powders and sintered ceramics. The results obtained demonstrate the necessity for applying both surface and in-depth analytical techniques in characterizing excimer laser induced changes in thin ZrO2 films. (C) 2001 Elsevier Science B.V. All rights reserved