S.R. Elliott

A unified model for reversible photostructural effects in chalcogenide glasses

Abstract A general mechanism is proposed for the production of reversible photo-induced changes in chalcogenide glasses in terms of the scission of bonds, both inter-molecular and intra-molecular. Which mechanism is dominant is determined by several factors, in particular the type of chalcogen atom present in the material. The consequences of the various bond-breaking models are examined in detail for the cases of photo-induced changes in the structural, optical and mechanical properties of such materials.

Extended X-ray absorption fine-structure spectroscopy study of photostructural changes in amorphous arsenic chalcogenides

Abstract Extended X-ray absorption fine-structure spectroscopy (EXAFS) measurements have been performed on amorphous arsenic sulphide, in both bulk-glass and thin-film forms, in order to probe the changes in local order accompanying the photostructural changes which occur in such materials. The irreversible photo-induced changes occurring in the thin films are associated with changes in the first coordination shell; these are ascribed to the conversion of As-As bonds to As-S bonds. In contrast, no significant changes in the first coordination shell, as revealed by EXAFS, appear to accompany the reversible photo-induced changes observed in glassy As2S3. Instead, changes in the region of the second shell are observed, and these are ascribed to either an increase in (bond-angle) disorder, or to an increase in inter-molecular distances, occurring on illumination.

A numerical phasing technique for application to one-dimensional NMR spectra

Une methode d« auto-etalonnage a ete adaptee a partir de lalgorithme de Cornwell et Wilkinson utilise en radio astronomie pour mettre en phase numeriquement les formes de raies RMN a 1 dimension

Quantitative interpretation of exponentially broadened solid-state NMR signals

Abstract It is demonstrated that the application of an exponential line-broadening function to the free induction decay of magic-angle spinning solid-state NMR spectra can give rise to substantial errors in the areas of individual Gaussian component peaks subsequently fitted to the spectra obtained by Fourier transformation of the FID. Various procedures are discussed which can give quantitatively accurate results when fitting component peaks to line-broadened spectra. In addition “window” functions multiplying the FID can give rise to severe distortion of the Fourier-transformed spectrum. The application of the numerical algorithm CLEAN to the MAS NMR spectrum to remove the effects of both line broadening and “windowing” of the FID is also described.

EXAFS and neutron scattering studies of reversible photostructural changes in bulk germanium chalcogenide glasses

Abstract EXAFS and neutron scattering studies of bulk GeS 2 and GeSe 2 glasses provide evidence that the reversible photostructural change in these materials is associated with changes in the first and second coordination spheres of both the germanium and chalcogen atoms. The germanium is seen to over-coordinate while the chalogen under-coordinates, with respect to the annealed glassy state, upon illumination.

A.C. conductivity in a-P thin films

Abstract A.C. and d.c. conductivity measurements are reported for sputtered a-P films. As-deposited films exhibit a relatively large temperature dependence of σ(ω) and of its frequency exponent, s, as well as a T − 1 4 temperature dependence of σ(0): annealing, or hydrogenation during deposition, decreases the temperature dependence of σ(ω) and s, as well as suppressing the variable-range hopping d.c. conduction. The results are discussed in terms of the correlated barrier hopping model for a.c. conduction, and it is concluded that paramagnetic, neutral defects predominate in the as-deposited films, whereas diamagnetic, charged defects are predominant in annealed and hydrogenated films.

ODMR in glow-discharge deposited silicon nitride

Abstract We report optically detected magnetic resonance (ODMR) measurements on glow-discharge deposited a-SiNx:H in the range 0