Crystallographic analysis of the amorphization caused by ion irradiation: Self-irradiation

We have examined a mechanism of Si amorphization, by a classical molecular-dynamics, paying attention to whether or not the self-interstitial atom (SIA) clusters were a precursor to amorphization, when a crystalline Si was self-irradiated by several keV ions at a low temperature of 100 K. The pixel mapping (PM) analyzed crystallographically a crystalline to amorphous (CA) transition caused by ion irradiation by means of a set of long-range-order parameters. The spatial distribution of SIAs were also counted by PM. Throughout the sequential self-irradiation, the fraction of isolated SIAs was dominant. Although the fractions were small, we found the significant increase of small SIA clusters, e.g. I2-I4, as the crystalline state was being collapsed. We conclude that those small SIA clusters can be the trigger to enhance the production of more SIAs, and results in CA transition