Crystallographic analysis of extended defects in diamond-type crystals

We examined the geometry of self-interstitial atom (SIA) clusters using the pixel mapping (PM) method, on the output data of MD calculations. Perfect crystalline silicon (c-Si) is amorphized by self-irradiation, and we observe that many SIA are produced. During sequential self-irradiation, the most frequently observed species were isolated SIA, i.e. I1 (monomer). The fractions of SIA clusters decreased as I2 (dimer), I3 (trimer), and I4 (tetramer) clusters, respectively. For I2 clusters, the 〈1 1 0〉 oriented I2's were the dominant I2 species, which agree with previous predictions based on static calculations. Nevertheless, other I2's with different orientations were also significant. Some of them have been proposed as intermediate I2's in forming dislocations. The present results imply that irradiation-induced SIA's play an important role in the triggering of amorphization, and MD combined with PM can reveal the intermediate processes underlying extended-defect formation.