Damage along an ion track in diamond: a computer simulation

TL;DR

This study uses computer simulations to investigate how heavy ion impacts create damage in diamond, revealing how thermal spikes induce amorphous regions whose structure depends on temperature and size.

Contribution

It introduces a detailed simulation approach to understand ion-induced damage in diamond and amorphous carbon, highlighting the dependence of damage structure on thermal spike parameters.

Findings

Amorphous regions with threefold carbon bonds form after thermal spikes in diamond.

Damage structure depends strongly on heating temperature and thermal spike size.

Scaling laws relate the fraction of two-fold bonded atoms to spike temperature across different volumes.

Abstract

We present tight-binding molecular dynamics simulations of the structural modifications that result from the "thermal spike" that occurs during the passage of a heavy fast ion through a thin diamond or amorphous carbon layer, and the subsequent regrowth upon cooling. The thermal spike and cooling down are simulated by locally heating and then quenching a small region of carbon, surrounded either by diamond or by a mostly three-fold bonded amorphous carbon network. For the case of the thermal spike in diamond we find that if the ``temperature'' (kinetic energy of the atoms) at the center of the thermal spike is high enough, an amorphous carbon region containing a large fraction of threefold coordinated C atoms (two-fold bonded) remains within the diamond network after cooling. The structure of this amorphous layer depends very strongly on the ``temperature'' of heating and on the dimensions of the thermal spike. Scaling is found between curves of the dependence of the percentage of two-fold bonded atoms in the region of the thermal spike on the heating ``temperature'' for different volumes. When the thermal spike occurs in an initially amorphous sample the structure of the damaged region after cooling exhibits the above dependencies as well as being a function of the structure of the original amorphous carbon layers.