Search

Bulk materials of Sb2Se3-xSx solid solutions (x = 0, 1, 2 and 3) have been synthesized by fusion of the constituent elements in the stoichiometric ratios in vacuum-sealed silica tubes. The materials compositions were confirmed by using energy dispersive analysis of X-rays (EDAX). X-ray powder diffraction measurements were performed for all the prepared samples at 300 K. The analysis of X-ray data has indicated that all the prepared materials are polycrystalline of single-phase and belonging to the orthorhombic system with space group Pbnm (62). The crystal structural parameters were refined by Rietveld method using the FullProf program. The influence of the S-content in the ternary compounds on the structural properties was discussed. It was verified that the investigated compositions are formed of infinite puckered chains of stoichiometric composition indefinitely extended in the plane parallel to the c-axis. These larger chains are, in turn, bonded into sheets roughly perpendicular to the b-axis through sets of Sb-Se/S bonds, weaker than that within the chain. Finally, the sheets are held together to make the crystalline solid. [ABSTRACT FROM AUTHOR]

AgGa0.5In0.5Te2 thin films were deposited, by thermal evaporation of presynthesised bulk ingot material, onto a Corning 7095 glass substrates. EDXS studies on the prepared films show that the as-deposited films are nearly stoichiometric. Also, XRD studies on the as-deposited and annealed films revealed an amorphous-to-crystalline phase transition at Ta ≈ 473 K. The optical constants (n, k) of the amorphous and crystalline AgGa0.5In0.5Te2 films, were determined from the transmittance and the reflectance data at normal incidence in the spectral range 400-2500 nm. The high frequency dielectric constant and the carrier concentration and the effective mass ratio were determined from the analysis of the refractive index at long wavelengths. The analysis of the absorption spectra of the investigated films revealed non-direct energy gaps, characterizing the amorphous films, in contrary to the crystalline films which exhibited only direct energy gaps. [ABSTRACT FROM AUTHOR]

Nanocrystalline thin films of Sb37.07Mn1.95Se60.98 with different thickness (7, 20, 40, and 80 nm) were successfully prepared via inert gas condensation technique. As-deposited films showed amorphous structure by grazing incident in-plane X-ray diffraction (GIIXD) technique. All films of different thicknesses were heat treated at 433 K for 90 min. The GIIXD pattern of annealed films showed nanocrystalline orthorhombic structure. The effect of thickness of annealed films on the structure and optical properties was studied. Calculated particle sizes are 20.67 and 24.15 for 40 and 80 nm thickness of heat treated film. High resolution transmission electron microscope HRTEM images and their diffraction patterns proved that 40 nm film thickness annealed at different temperature has nanocrystalline nature with observed (high) crystallinity that increases with annealing temperature. Blue shift of optical energy gap was observed from 1.68 to 2 eV with decreasing film thickness from 80 to 7 nm. Film thickness of 40 nm was exposed to different heat treated temperatures from 353 to 473 K to detect its effect on structure and optical and electrical properties. Blue shift from 1.73 to 1.9 eV was observed in its optical band gap due to direct transition as heat treatment temperature decreasing from 473 to 353 K. Electrical conductivity was studied for different heat treated films of thickness 40 nm, and intrinsic conduction mechanism is dominant. The activation energy Ea was affected by heat treatment process. [ABSTRACT FROM AUTHOR]

The regeneration is one of the most important phenomena in forest ecosystems and the most important factor of development and sustainability of forests. Assessment of the regeneration is one of the best criteria for monitoring forest function stability. The aim of this study was to investigate the spatial variability of regeneration diversity and its relationship with tree species diversity in Zagros Forests, Kermanshah (Gahvareh).This study was conducted at 70 hectares of Gahvareh forests. In this area, 67 sample plots (400 m2) were used in a 100 × 100 m sampling grid. In each plot, total number and species of trees and all seedlings which had diameter less than 7.5 cm were recorded. We also recorded asexual regeneration in 1/4 plots (100 m2). Then the spatial continuity was described using geostatistics (variogram and cross- variogram). The variograms of variables revealed the presence of spatial autocorrelation except evenness index (Sheldon) of trees and sexual regeneration. They had spatial dependence at large ranges that showed the large distance of dependency and homogeny of condition. In addition, cross-variograms indicated a strong spatial relationship between diversity of sexual regeneration and tree diversity and between diversity and richness of asexual regeneration and tree abundance. [ABSTRACT FROM AUTHOR]