Deformation of a chalcogenide glass film under optical modulated excitation

International audienceWe report a significant thinning of an amorphous chalcogenide film (at least 5% of its initial thickness) from the Ge-Sb-Se system deposited by RF magnetron sputtering method on a borosilicate substrate, namely a BK7. This phenomenon is due to a resonant symmetric vibration mode at a low frequency, in the tens of Hertz range. By exciting the material with modulated near-infrared light (lambda = 1.55 mu m), we observe three transmission peaks of a probing light at slightly different frequencies of modulation. We assign these resonances to the air/chalcogenide, chalcogenide/BK7 and BK7/air interfaces. Under the effect of the optical modulated radiation pressure, the mechanical deformations of these interfaces show the contribution of associated surface tensions

Effect of rare-earth doping on the free-volume structure of Ga-modified Te20As30Se50 glass

International audienceBy exploring the positron-electron annihilation technique in positron lifetime measuring mode, it is shown that principal rare-earth (RE) induced structural reconfiguration in Ga-codoped TAS-235 glass (that is a glassy Te20As29Ga1Se50 alloy) is related to occupation of intrinsic free-volume voids by embedded RE ions tightly connected with Ga-based tetrahedrons via strong covalent RE-Se/Te-Ga links. A gradual decrease in the intensity of the second component of two-term decomposed lifetime spectra of annihilating positrons accompanied with a detectable increase in the defect-related positron lifetime (thus inducing essentially a depressed rate in positron trapping) is evidenced by the example of Pr3+ ions added homogeneously to Te20As29Ga1Se50 glass in the amount of 500 ppmw. Observed changes in positron lifetime spectra are explained in terms of the competitive contribution of different occupancy positions in Ga-codoped glass available for RE ions and trapped positrons

Positron annihilation probing of crystallization effects in TAS-​235 glass affected by Ga additions

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Struktura skel Ge-Sb-S na atomární úrovni: chemické uspořádání na krátkou vzdálenost a dlouhé vazby Sb-S

The structure of Ge20Sb10S70, Ge23Sb12S65 and Ge26Sb13S61 glasses was investigated by neutron diffraction (ND), X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) measurements at the Ge and Sb K-edges as well as Raman scattering. For each composition, large scale structural models were obtained by fitting simultaneously diffraction and EXAFS data sets in the framework of the reverse Monte Carlo (RMC) simulation technique. Ge and S atoms have 4 and 2 nearest neighbors, respectively. The structure of these glasses can be described by the chemically ordered network model: Ge-S and Sb-S bonds are always preferred. These two bond types adequately describe the structure of the stoichiometric glass while S-S bonds can also be found in the S-rich composition. Raman scattering data show the presence of Ge-Ge, Ge-Sb and Sb-Sb bonds in the S-deficient glass but only Ge-Sb bonds are needed to fit diffraction and EXAFS datasets. A significant part of the Sb-S pairs has 0.3-0.4 angstrom longer bond distance than the usually accepted covalent bond length (similar to 2.45 angstrom). From this observation it was inferred that a part of Sb atoms have more than 3 S neighbors.Struktura skel Ge20Sb10S70, Ge23Sb12S65 a Ge26Sb13S61 byla zkoumána měřeními neutronové difrakce (ND), rentgenové difrakce (XRD), extended X-ray absorption fine structure (EXAFS) na Ge a Sb K-hranách a Ramanovým rozptylem. Pomocí současně fitovaných dat z difrakce a EXAFS v rámci reverzní Monte Carlo (RMC) simulační techniky byly pro všechna složení získány strukturní modely ve velkém měřítku. Ge a S atomy mají 4 a 2 nejbližší sousedy. Struktura těchto skel může být popsána chemicky uspořádaných modelem sítě: Ge-S a Sb-S vazby jsou vždy preferovány. Tyto dva typy vazeb adekvátně popisují strukturu stechiometrických skel, zatímco vazby S-S mohou být nalezeny u složení bohatého S. Data Ramanova rozptylu ukazují přítomnost vazeb Ge-Ge, Ge-Sb a Sb-Sb ve sklech s deficitem S, ale pouze vazby Ge-Sb jsou nutné pro fitování difrakčních a EXAFS dat. Významná část párů Sb-S má o 0.3-0.4 angstromu delší vazby než obvykle akceptovaná délka kovalentní vazby (ca 2.45 angstromu). Na základě tohoho pozorování bylo vyvozeno, že část atomů Sb má více než 3 sousední atomy S