Study of Ring-to-chain Structural Change of Evaporated Amorphous Selenium by Reverse Monte Carlo Simulation

Abstract

We studied the photoinduced ring-to-chain structural change of amorphous selenium (a-Se) evaporated at room temperature with in situ observation by highly sensitive electron diffraction and Reverse Monte Carlo (RMC) simulation. Although the structure before irradiation (SBI) is a random chain structure containing random rings (RCSR) (30% atoms in relevant number of 1013 network atoms), the structure after irradiation (SAI) is a random chain structure. These are obtained with the RMC simulation of the difference in structure factors from RCSR. The average bond angles for SBI and SAI are 105.1°and 104.3°, respectively. The average dihedral bond angles for SBI and SAI are 101.7°and 100.7°, respectively. Rings that form the initially closed loops in SBI are broken by photoirradiation. Bonds of random rings in SAI are not closed, and change to the random chain structure. These results are similar to those of Roy et al. (Phil. Mag. B, 78, 1, 1998, 87-94.) obtained by extended X-ray absorption fine structure spectroscopy (EXAFS).