Microscopics of Ion Track Formation in the Bulk and at the Surface

Abstract

The formation of ion tracks in the bulk and near-surface regions of various dielectrics have been studied using a multiscale approach combining Monte-Carlo code TREKIS and molecular dynamics simulations. It was demonstrated that the morphology of swift heavy ion tracks in non-amorphizable oxides is determined by recrystallization of the initially disordered region, which, in turn, is governed by the kinetics of the metallic and oxygen sublattices at the crystallization surface. The presence of a free surface can significantly suppress the lattice recovery rate, producing larger structure modified tracks in the near-surface regions. Matching of simulation results with TEM images of crystalline hillocks and tracks in Al2O3 revealed that the recrystallization of sub-surface tracks (~20 nm depth) in this solid requires much longer times in comparison to bulk simulations. The recrystallization processes strongly manifest themselves in the overlapping tracks regime. Overlapping of tracks in non-amorphizable solids could realize in several modes depending on the distance between the tracks: from almost complete structure recovery, to the formation of connected or isolated tracks. In contrast, track interaction in amorphizable targets has almost no effect on the defective region morphology