Molecular dynamics simulations of the structure of latent tracks in quartz and amorphous SiO₂

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.