Shrinkage mechanism of nanocavities in amorphous Si under ion irradiation: An in situ study

Nanocavities of diameter <25 nm can be readily formed in Si substrates by H or He implantation followed by thermal annealing. These nanocavities readily interact with both fast-diffusing metal impurities and implantation-induced Si interstitials and under prolonged ion irradiation, nanocavities eventually disappear. In this study, we have measured nanocavity evolution under ion irradiation when the nanocavities were surrounded by amorphous Si. The average nanocavity diameter was monitored by in situ transmission electron microscopy (TEM) observations during irradiation with Ne, Si or As ions at temperatures of 300-600 K. The nanocavity diameter decreased linearly with ion fluence. The shrinkage process is shown to be essentially athermal and controlled by atomic displacements generated close to the nanocavity/matrix interface during ion irradiation. Our in situ results shed new light on possible irradiation-induced nanocavity shrinkage mechanisms