Ultrafast phase transitions in polyamorphic materials triggered by swift heavy ion impacts

Abstract

We report unexpectedly fast phase transitions inside the track as pressure and temperature develop after a swift heavy ion impact. By means of molecular dynamics simulations we reveal the origin of the core-shell fine structure observed in a-${\mathrm{Si}}_{}{\mathrm{O}}_{2}$ and a-${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$, as well as the dense core in a-Si. The fine structure of the track is composed of two distinct amorphous phases that result from the different pressure levels in the core and in the shell during solidification. We link this behavior to the tetrahedral network present in these materials.