The structure of vapour-deposited arsenic sulphides prepared using a cooled (78 K) substrate

Amorphous molecular As₄S₄ and non-stoichiometric “As₂S₃” evaporated films have been prepared by condensing onto a substrate at liquid nitrogen temperature in situ in the X-ray diffractometer. The structures of these films are shown to be similar, thus confirming the importance of As₄S₄ (realgar-type) molecules in amorphous films prepared by evaporation of “As₂S₃” glass. The local molecular packing in the as-deposited amorphous As₄S₄ film shows a preference for a packing arrangement similar to that found in the α-crystalline phase. Both as-deposited films contain gross structural defects such as molecular clusters and/or voids which irreversibly reduce in importance as the film structures relax on warming to ambient temperatures. Also, the As₄S₄ film partially devitrifies to the high-temperature β-crystalline phase on warming to ambient, but no devitrification occurs in the non-stoichiometeric film due to the presence of more than one molecular type.