Structure and photoinduced structural changes ina-As2S3films: A study by differential anomalous x-ray scattering

Differential anomalous x-ray-scattering experiments were carried out on two samples, annealed and photodarkened a-${\mathrm{As}}_2$ ${\mathrm{S}}_3$ films of 4 μm in thickness. Two x-ray energies were chosen. One is 11 859 eV, just below the arsenic K edge; the other is 11 700 eV, below the edge by 167 eV. The study of the structure and photoinduced reversible structural changes in the a-${\mathrm{As}}_2$ ${\mathrm{S}}_3$ films show that the first sharp diffraction peak (FSDP) is related to intermediate-range correlations. These correlations extend as far as 7.0 Å. Beyond 7.0 Å, however, the structure in radial distribution function tends to the average atomic density. The FSDP is dominated by the arsenic-related atomic correlations, especially As-As atomic correlation. After photodarkening, the structure overall in both the short and intermediate ranges moves to a more disordered state. The photoinduced structural changes involve changes of the As-As atomic pair correlation in the intermediate range as illustrated by the comparisons of the changes between the annealed and photodarkened a-${\mathrm{As}}_2$ ${\mathrm{S}}_3$ films in the FSDP’s and the differential structure factors.