A simulation of the cluster structures in Ge-Se vitreous chalcogenide semiconductors

A structure of germanium selenide glasses is simulated by the featured clusters built from the tetrahedral GeSe4 units up to the clusters with six germanium atoms (Ge6Se16H4 and Ge6Se16H8). Quantum chemical calculations at the DFT level with effective core potentials for Ge and Se atoms for the clusters of different composition reveal their relative stability and optical properties.Comment: 5 pages, 3 Figures include

Positron Trapping Processes in Temperature-Sensitive Thick- film Structures

Positron trapping processes in so-called “free” thick-film structures based on spinel-type Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics are studied. The observed positron trapping can be fully defined within the two-state positron trapping model. The defect-related component in the fit of the experimentally measured positron lifetime spectra for thick films and bulk ceramics testifies to similarity of positron trapping processes in spinel-based materials. It is shown that in some cases the size of free-volume entities in thick films can rise due to redistribute space of their inner structure at addition glasses and other compounds. But positrons are trapped more strongly in bulk ceramics due to more ramified their grain/pores structure

Positronium Characterization of Nanopores in Technologically Modified MgO-Al2O3 Ceramics

It is established that positron annihilation lifetime spectroscopy can be successful used as porosimetry method to study of nanopores size and transformation of free volume in humidity-sensitive MgO-Al2O3 ceramics in adsorption-desorption cycles using lifetimes of ortho-positronium-related components. It is shown that the fourth component gives information about water-free volume or nanopores size, while the third component reflects positronium trapping both in nanopores and in water “bubbles”

Peculiarities of Ga and Te incorporation in glassy arsenic selenides

International audienceEffect of simultaneous Ga and Te addition on the structure of As2Se3 glasses is studied using X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) and Raman techniques. It is shown that most of As, Se and Te atoms build a covalent network according to their main valences. Three-fold coordinated As atoms form pyramidal structural units, which are connected via bridges of two-fold coordinated chalcogen atoms (Se, Te). On the other hand, coordination of Ga in glassy samples is found to be greater than three, as expected from its valence, increasing with Te content. Some of the As atoms appear to be converted into four-fold coordinated state at low Te concentration, while a fraction of Te and, possibly, Se atoms are thought to exist in a singly-coordinated (terminal) state in the vicinity of Ga in the samples with higher Te concentration

'Cold' crystallization in nanostructurized 80GeSe 2 -20Ga 2 Se 3 glass

International audience'Cold' crystallization in 80GeSe 2-20Ga 2 Se 3 chalcogenide glass nanostructurized due to thermal annealing at 380°C for 10, 25, 50, 80, and 100 h are probed with X-ray diffraction, atomic force, and scanning electron microscopy, as well as positron annihilation spectroscopy performed in positron annihilation lifetime and Doppler broadening of annihilation line modes. It is shown that changes in defect-related component in the fit of experimental positron lifetime spectra for nanocrystallized glasses testify in favor of structural fragmentation of larger free-volume entities into smaller ones. Nanocrystallites of Ga 2 Se 3 and/or GeGa 4 Se 8 phases and prevalent GeSe 2 phase extracted mainly at the surface of thermally treated samples with preceding nucleation and void agglomeration in the initial stage of annealing are characteristic features of cold crystallization

Positronics of radiation-induced effects in chalcogenide glassy semiconductors

Using As2S3 and AsS2 glasses as an example, the principal possibility of using positron annihilation spectroscopy methods for studying the evolution of the free volume of hollow nanoobjects in chalcogenide glassy semiconductors exposed to radiation is shown. The results obtained by measurements of the positron annihilation lifetime and Doppler broadening of the annihilation line in reverse chronological order are in full agreement with the optical spectroscopy data in the region of the fundamental absorption edge, being adequately described within coordination defect-formation and physical-aging models