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 the recently discovered opto-mechanical effect in chalcogenide glasses, we have 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 glass and amorphous films in the spectrometer, as well as after ex situ exposure in air. The non-reversible light-induced changes are due to the segregation of Se on the surface, increased homogeneity for As, and a greater heterogeneity 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 smaller population in the absence of light.