Irreversible thermostructural transformations in amorphousAs2S3films: A light-scattering study

Polarized spectra of evaporated thin films of ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ glass have been recorded before and after annealing at the glass transition temperature and compared with the corresponding spectrum of the bulk glass. The spectra of virgin films consist of several sharp molecular bands superposed on a networklike continuum which is characteristic of the bulk glass, whereas annealed films yield only the bulk glass spectrum albeit with some indication of residual nonstoichiometry. These results are direct evidence that irreversible thermostructural transformations (or equivalent photostructural transformations) in evaporated ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ films proceed through polymerization of a metastable molecular glass as suggested by deNeufville, Moss, and Ovshinsky. The polarized Raman spectra of the vapors over ${\mathrm{As}}_2$ ${\mathrm{S}}_3$ liquid have been obtained and indicate the presence of serveral gaseous molecular species. The molecular constituency of the evaporated amorphous film is also complex but distinct from that of the vapor, an indication that deposition itself introduces some structural alterations.