Photoinduced changes in the surface morphology of As50Se50 chalcogenide glass films

The photoinduced changes in the surface morphology of As50Se50 chalcogenide glass films are observed using atomic force microscopy. The thin film samp les, on single crystal silicon or a microscope glass slide as substrate, we re exposed to laser light of wavelength lambda = 632 or 685 nm. The results show nucleation and gradual growth of micrometer size pyramids that grow w ith laser irradiation, ultimately covering similar to 15% of exposed area i n 20 min. The rate of growth of a given pyramid slows down with time until it ceases to grow on reaching a height of several 100 nm. The maximum heigh t of these faceted pyramids is similar to 1 lm, sometimes even larger than the film thickness, which cannot be understood from the reported photoinduc ed expansion. A photoinduced oxidation is suspected, in which As atoms in t he surface layer move to the sites of pyramids. These observations raise ne w questions about the impact of ambient atmosphere on photodarkening and ot her photoinduced effects in chalcogenide glasses. (C) 2001 Elsevier Science B.V. All rights reserved.