Annealing-induced reduction in nanoscale heterogeneity of thermally evaporated amorphous As2 S3 films

The morphology and structural order of thermally deposited and annealed amorphous As2 S3 films have been investigated using high resolution transmission electron microscopy. It was found that both the as-deposited and annealed films contained sparsely distributed nanocrystallites of the orpiment As2 S3 crystalline phase. However, from selected area electron diffraction both films appeared amorphous. Fluctuation electron microscopy revealed that the as-deposited film contained greater nanoscale inhomogeneity. Low temperature annealing reduced the nanoscale inhomogeneity and resulted in a more homogeneous and energetically favorable network. The reduction in nanoscale inhomogeneity upon low temperature annealing was accompanied by the appearance of a first sharp diffraction peak in the diffraction pattern. This first-sharp diffraction peak has been attributed to chemical ordering of interstitial voids. Our measurements suggest that this chemical short-range ordering is associated with the dissolution of the energetically unfavorable larger correlated structures that contribute to the inhomogeneity of the as-deposited film.