Reverse Monte Carlo study of structural relaxation in vitreous selenium

Vitreous selenium is used extensively for light detection. Its photoconduct ing properties are altered by structural relaxation near room temperature. X-ray diffraction, densiometry, and calorimetry are used to determine the c hange of the glass state during relaxation. Annealing for 24 h at 300 K inc reases the density by 0.14% and lowers the enthalpy by 105 J/mol. The struc ture factor of cast samples was measured before and after annealing, and re verse Monte Carlo models of the structure of selenium glass were generated to match the data for the quenched and annealed states. Atoms in amorphous selenium are arranged in randomly oriented chains. In the model clusters an nealing effects are found by analyzing inter- and intrachain distances, bon d angle distributions, and dihedral angle distributions. The average bond l ength remains unchanged upon annealing, while the distribution of bond leng ths becomes narrower by 1.2%. Distances between atoms in adjacent chains de crease by about 0.03%, i.e., the selenium chains move closer together, and the distribution of interchain distances becomes narrower. Bond angles with in the chains are affected slightly. The mean bond angle decreases by 0.016 degrees, which indicates a greater folding of the selenium chains and repr esents an evolution towards the angles found in crystalline selenium phases . The bond angle distribution for the annealed state is 0.006 degrees narro wer. (C) 2001 American Institute of Physics.