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

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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.