Molecular dynamics simulations of the structure of latent tracks in quartz and amorphous SiO 2

Abstract

Swift heavy ion irradiation (SHII) can leave a latent ion track around the ion path. Tracks in amorphous silicon dioxide (a-SiO2) and quartz are interesting due to applications in nanofabrication, for example. In recent experiments, a previously unresolved fine structure in latent ion tracks in a-SiO2 was found comprising a lower density core and a higher density shell. We model the formation of latent ion tracks in crystalline quartz and amorphous SiO2 using classical molecular dynamics (MD) to simulate the irradiation at the atomistic level, and compare the results to small angle X-ray scattering (SAXS) experiments on amorphous, 2 μm thick SiO2 layers. Electronic energy deposition of 197 Au ions corresponding to experiments is used in the simulations, to allow direct comparison between simulations and existing experiments. We explain the formation of the experimentally observed cylindrical core-shell structure with the dynamic simulations, and compare the obtained track dimensions and threshold energies with the experiment.