Molecular dynamics simulation of ion focusing and crowdion formation in self-ion-irradiated Fe

We have used molecular dynamics (MD) simulation to investigate damage and defect development in a 〈1 0 0〉 Fe substrate upon 2 keV Fe ion bombardment. The damage cascade formation is accompanied by atomic shifting over a limited distance along the direction of one atomic row, which leads to formation of crowdions aligned with 〈1 1 1〉 direction. At the end of structural relaxation and defect recombination, crowdions lead to formation of dumbbell defects - a type of vacancy-interstitial complexes having one vacancy between a pair of slightly displaced interstitials. The dumbbell defects are initially oriented along 〈1 1 1〉 direction. After a typical period of 0.2 ps, some dumbbell defects rotate towards 〈1 1 0〉 direction. Crowdion and dumbbell defect formation influence the time dependent damage buildups.