Results 1 - 10 of 391
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[en] Ab initio calculations with the RHF/6-311G* basis set are used for geometrical optimization of regular pyramidal and defect quasi-tetrahedral clusters in binary As-S glasses. It is shown that quasi-tetrahedral S=AsS3/2 structural units are impossible as main network-building blocks in these glasses.
[en] The main objective of this work was to combine the positive characteristics of transparent photopolymers and light-sensitive chalcogenide glasses, with aim to improve the amplitude–phase modulation characteristics of in situ optically recorded photonic elements on the surface, and in the bulk of thick composite layer on a given substrate. The positive results were obtained due to the developed technology routes of nanocomposite (NC) fabrication by intermixing selected, optically tunable, VIS–NIR transparent and high refractive index As-S (Se) nanoparticles (NPs) produced by chemical dissolution, and acrylate monomers with initiators. Subsequent photopolymerization of such nanocomposite occurs during optical recording photonic elements and is supplemented by mass-transport processes, which enhance relief parameters. Structure, optical parameters of the new light-sensitive media and conditions of one step recording of optical elements in it were investigated.
[en] Ultrafast differential scanning calorimetry (DSC) was employed to investigate the glass transition kinetics of As2S3 and As2Se3. By using the Arrhenius method, a fragility index of ∼22 can be estimated in both As2S3 and As2Se3. However, when the scanning rate is more than , non-Arrhenius behavior can be observed in such “strong” liquids where the Vogel–Fulcher method is more accurate to describe the glass transition kinetics. The fragilities of As2S3 and As2Se3 glasses are thus extrapolated as 28.3 ± 1.94 and 23.7 ± 1.80, respectively. This indicates that, As2Se3 glass has a better structural stability and it is a better candidate for device applications. (paper)
[en] AsS2 single crystals have been obtained for the first time from an As2S3 melt at pressures above 6 GPa and temperatures above 800 K in the As2S3 → AsS + AsS2 reaction. The monoclinic structure of the new high-pressure phase is solved by X-ray diffraction analysis and compared to the structure of high-pressure AsS phase, which was studied previously.
[en] The invention relates to the electro photography and allows to improve the quality of the medium by reducing the darkness decay. On the electro conducting base it is applied a vitreous photo conductor of the germanium selenide and a photoconductor layer of arsenic sulphide
[en] A near-field scanning optical microscopic analysis is performed on As2S3 film gratings in order to simultaneously collect index and topography images with sub-micrometre resolution. This technique makes it possible to unambiguously study the correlation between photodarkening and photoexpansion at the local scale. The development of a positive index change concomitantly with expansion or contraction in films of different thermal histories suggests that homopolar bonds are not a major contributor to the darkening effect. Photodarkening is instead associated with structurally stable defects that appear to be largely decoupled from the volume change mechanism. While photoexpansion and photodarkening follow the same growth kinetic during irradiation of annealed films with band-gap light, it is clearly shown that their structural origin is different. These results have relevance for grating fabrication since both the relief and the index patterns contribute to the grating efficiency, yet they appear to have distinct behaviour during processing or long-term stability.
[en] The photo-stimulated interdiffusion within chalcogenide based nano-layered structures (NLS) produces large changes in properties, which have potential application in optical pattern recording. The mechanism of these changes is investigated for two NLS consisting of 100 alternate layers of antimony and As2S3, but of different relative thicknesses, by high-resolution X-ray photoelectron spectroscopy. The results suggest the formation of Sb-S bonds at the expense of As-S bonds, with a consequent increase in the refractive index but minimal change in thickness. The role of oxygen in photoinduced transformations, especially in the top layers, is characterized and discussed.
[en] Paper presents the results of analysis of several experimentally obtained physical parameters of Bix(As2S3)100−x glassy system from the topological point of view. The dependence on composition of the glass transition temperature was explained with increase in total number of mechanical constraints and based on Tanaka′s relation. The compound with the highest content of Bi showed an exception from observed behavior due to its structural complexity. Its heterogenity also reflected on the flow of thermal decomposition process. The reduction of the optical band gap was correlated with the decrease of system cohesive energy. The observed minimum of compactness for the compound with x = 5 at.% of Bi is probably caused by Tanaka’s 2D → 3D transformations. The decrease of the mean bond energy was interpreted as a consequence of formation of weaker Bi-S bonds instead of As-S bonds, and the formation of homopolar bonds between residual As atoms in excess. (paper)