Evolution of Chemical Structure During Silver Photodiffusion into Chalcogenide Glass Thin Films

The change of chemical structure resulting after X–ray and photo-induced silver diffusion into chalcogenide glass (ChG) thin films is monitored by high resolution X-ray photoelectron spectroscopy (XPS). As40S60 and Ge30Se70 thin films, which are based on pyramids and tetrahedral structural units, are investigated as model materials. Survey, core level (As 3d, S 2p, Ge 3d, Ge 2p, Se 3d, Ag 3d5/2, O 1s, C 1s) and valence band spectra have been recorded and analyzed. Reference point for the binding energy is established by the subsequent deposition of thin gold film on top of the measured samples. The chemical structure gradually changes during diffusion of silver in all the samples. The mechanism of change depends on the chemical composition, thickness of the diffused silver layer and conditions of irradiation. It is revealed that surface oxygen can play important role in the Ag photodiffusion process, leading to phase separation on the surface of the films. Photodiffusion of Ag into As40S60 film leads to the formation of a uniform ternary phase and arsenic oxides on the surface. The formation of ethane-like Ge2(S1/2)6 units together with germanium oxidation are the main outcomes of X-ray induced Ag diffusion into Ge30Se70 film

Chemical order in GexAsySe1-x-y glasses probed by high resolution X-ray photoelectron spectroscopy

We have measured high-resolution x-ray photoelectron spectra of Ge xAsySe1-x-y glasses with a mean coordination number (MCN) from 2.2 to 2.78. The valence band spectra showed that a number of Se–Se–Se trimers can be found in Se-rich samples, whilst multiband features induced by phase separation can be observed in extremely Se-poor samples. When the Ge, As, and Se 3d spectra were decomposed into several doublets, which correspond, respectively, to different chemical environments, the perfect AsSe₃/₂ pyramidal and GeSe₄/₂ tetrahedral structures in Se-rich samples gradually evolved into defect structures, including As–As and Ge–Ge homopolar bonds, with increasing Ge and As concentrations. Two transition-like features were found at MCN = 2.5 and 2.64–2.72 that correspond first to the disappearance of Se-chains in the glass network and, subsequently, destruction of the perfect GeSe₄/₂ tetrahedral structures, respectively.This research was supported by Australian Research Council through its Centres of Excellence, and Discovery Programs. R.P.W acknowledges support from U.S. National Science Foundation through International Materials Institute for New Functionality in Glass and the Australian Academy of Sciences through its Scientific Visits to North America program

High-resolution XPS for determining the chemical order in chalcogenide network glasses

The power of X-ray photoelectron spectroscopy (XPS) measurements and analysis is demonstrated to establish the structure of network glasses using the examples of binary As-Se, As-S, Ge-Se and Ge-S series. Short-range chemical order in these materials is established, and main building blocks of their structurally-disordered glass network are identified throughout respective glass-forming compositional domains. The XPS fitting procedure is correlated with disproportionality analysis based on the conditions of chemically-ordered bond network model and uniform distribution of constituent chemical elements. The structure of binary As-based glasses (As-Se and As-S) is shown to be adequately described by the terms of ‘chain-crossing’ model, while ‘outrigger raft’ model has to be additionally used to build a network of Ge-based glasses (Ge-Se and Ge-S)

Effect of Photo-Oxidation on the Photodiffusion of Silver in Germanium Chalcogenide Glasses

We report results on photoinduced changes in Ge-chalcogenide glasses, which occur in ultra high vacuum (UHV) vs. in air. They demonstrate the important role of oxygen that determines the magnitude and the type of the photoinduced effects. To observe photodiffusion without the presence of oxygen, Ag/glass thin films were prepared, subjected to photodiffusion, and chemically analyzed, all within the chamber of high resolution X-ray Photoelectron Spectroscopy (XPS) equipment. Under these oxygen-free conditions, Ag is introduced in the Ge-Se hosting network. The results show that the diffusion product is homogeneous, comprising of Ge-chalcogen tetrahedra and ethane-like units (GeSe3)2 with Ag+ ions attached to them. In oxygen containing ambient, Ge rich glasses oxidize more easily than the chalcogen rich glasses, since oxygen reacts primarily with Ge. Under these experimental conditions, which are likely to exist in practical applications, a higher concentration of Ag can be introduced, with the formation of Ag containing products like α and β Ag2Se and Ag8GeSe6. Raman spectroscopy reveals that because of interaction between Ge and oxygen, the initially Ge-rich chalcogenide network becomes chalcogen-rich after the oxidation of Ge

Modified Positron Annihilation Model for Glassy-Like As2\text{}_{2}Se3\text{}_{3}

An approach to structural characterization of chalcogenide glasses based on the study of void distribution is discussed. The results of positron annihilation lifetime spectra measurements for glassy-like g-As$\text{}_{2}$Se$\text{}_{3}$ are compared with nano-void distribution data obtained from Monte Carlo simulation. In this consideration perspectives to involve the parameters of nano-voids calculated from the first sharp diffraction peak in the framework of known Elliott's model are analyzed

Modified Positron Annihilation Model for Glassy-Like As 2

An approach to structural characterization of chalcogenide glasses based on the study of void distribution is discussed. The results of positron annihilation lifetime spectra measurements for glassy-like g-As$\text{}_{2}$Se$\text{}_{3}$ are compared with nano-void distribution data obtained from Monte Carlo simulation. In this consideration perspectives to involve the parameters of nano-voids calculated from the first sharp diffraction peak in the framework of known Elliott's model are analyzed

OVERVIEW OF ADVANCED SET OF COMPONENTS SET FOR TRAFFIC CONTROL AND SAFETY OF TRAINS

The article gives a brief overview of the advanced set of equipment for traffic control and safety of trains, used on Russian railways, principles implemented in such equipment have been identified, the problems associated with the use of such equipment in emergencies have been identified. The article also deals with problems that should be included in the key priority tasks to determine the future development of the set of equipment for control and safety of trains traffic on the railways of the Russian Federation

WIRELESS SYSTEM OF INTERVAL REGULATION OF TRAINS TRAFFIC ON THE LINE

The article deals with the device and operation of wireless system of central interval regulation of trains traffic designed for rapid short-term train traffic on lines between railway stations, repaired from destructions caused by man-made accidents, natural disasters or combat operations, on lines between stations for a time period required for repair of standard interval control systems