Activated mechanisms in amorphous silicon: an activation-relaxation-technique study

At low temperatures, dynamics in amorphous silicon occurs through a sequence of discrete activated events that locally reorganize the topological network. Using the activation-relaxation technique, a data base containing over 8000 such events is generated, and the events are analyzed with respect to their energy barrier and asymmetry, displacement and volume expansion/contraction. Special attention is paid to those events corresponding to diffusing coordination defects. The energetics is not clearly correlated with the displacement, nor with the defect density in well relaxed configurations. We find however some correlation with the local volume expansion: it tends to increase by about 4 eV/\AA$^3$. The topological properties of these events are also studied; they show an unexpectedly rich diversity.