In situ high-resolution X-ray photoelectron spectroscopy of light-induced changes in As-Se glasses

To establish the mechanism of reversible photoinduced changes such as in th e recently discovered opto-mechanical effect in chalcogenide glasses, we ha ve measured the effect of He-Ne laser light on the electronic structure of As-Se glasses using high-resolution X-ray photoelectron spectroscopy (XPS). We present the first results during in situ irradiation of As-Se bulk glas s and amorphous films in the spectrometer, as well as after ex situ exposur e in air. The nonreversible light-induced changes are due to the segregatio n of Se on the surface, increased homogeneity for As, and a greater heterog eneity in the chemical environment of Se. In addition, there are reversible changes in the valence band (VB), indicating transfer of lone-pair states of Se to a new kind of bonding state deeper in the band, which have a small er population in the absence of light. (C) 2000 Elsevier Science B.V. All r ights reserved.