Photo-induced volume changes in selenium. Tight-binding molecular dynamics study

Abstract

Tight-binding molecular dynamics simulations of photo-excitations in small Se clusters (isolated Se 8 ring and helical Se chain) and glassy Se networks (containing 162 atoms) were carried out in order to analyze the photo-induced instability in amorphous selenium. In the cluster systems after taking an electron from the highest occupied molecular orbital to the lowest unoccupied molecular orbital a bond breaking occurs. In the glassy networks photo-induced volume expansion was observed and at the same time the number of coordination defects changed significantly due to illumination.

On photoinduced volume change in amorphous selenium: Quantum chemical calculation and Raman spectroscopy

“…4,[23][24][25] Due to illumination covalent bonds became longer and we consider this effect as bond breakings. 4,[23][24][25] Due to illumination covalent bonds became longer and we consider this effect as bond breakings.…”

Ab initio calculations for photo‐darkening and photo‐induced structural changes in As 2 S 3 and GeS 2

“…Therefore photo-induced structural changes can involve significant atomic motions, equivalent to intra-molecular bond scission and the formation of va-lence alternation pair defects that has been reported for Se [7]. In this regard, photo-structural and photodarkening changes in Se persist only as long as the sample is illuminated with band edge photons [14,15]. When the light is removed the materials returns to the pristine state.…”

Modelling of photo-induced changes in chalcogenide glasses: a-Se and a-AsSe

“…For the photo-induced volume change simulations we used our recently developed TB-MD computer code (ATOMDEP program package for C [10], for Si [11], and for Se [12]). Self-consistency was taken into account via the on-site Hubbard term within the TB model [13,14].…”

“…Samples contained 162 atoms and the initial density was 4.33 g/cm 3 . Our 'cook and quench' sample preparation procedure was the following [12]. First, we choose the temperature of the system to be 5000 K for the first 300 MD steps to randomize the atomic positions.…”