REVERSIBLE PHOTO-AMORPHIZATION OF CRYSTALLINE FILMS OF AS50SE50

Crystalline As50Se50 films < 3 mu m can be completely amorphized by illumination with band gap light. It is found that the ability of an amorphous film to crystallize upon thermal annealing, prior to photo-induced amorphization, is influenced by the presence of a substrate. Scraped films or powdered bulk glass do not readily crystallize, by contrast with thin films adhering to silica-glass substrates. Raman scattering spectra of crystalline and photo-amorphized films differ: the (low-temperature) crystal exhibits sharp peaks characteristic of a molecular crystal (As4Se4), whereas the spectrum of the photo-amorphized phase has broad, featureless peaks. These imply that photo-amorphization is caused by photo-induced scission of As-As bonds in the molecular units and subsequent cross-linking.