Strong mass effect on ion beam mixing in metal bilayers

TL;DR

This study uses molecular dynamics simulations to reveal that the atomic mass ratio in metal bilayers critically influences ion beam mixing and thermal spike formation during low-energy ion irradiation.

Contribution

It demonstrates that the atomic mass ratio determines the occurrence of thermal spikes and atomic mixing, providing a simple ballistic explanation for experimental observations.

Findings

Mass ratio below 0.33 leads to thermal spikes.

Simulations match experimental data trends.

Ballistic mechanism explains low-temperature phase behavior.

Abstract

Molecular dynamics simulations have been used to study the mechanism of ion beam mixing in metal bilayers. We are able to explain the ion induced low-temperature phase stability and melting behavior of bilayers using only a simple ballistic picture up to 10 keV ion energies. The atomic mass ratio of the overlayer and the substrate constituents seems to be a key quantity in understanding atomic mixing. The critical bilayer mass ratio of $\delta < 0.33$ is required for the occurrence of a thermal spike (local melting) with a lifetime of $\tau > 0.3$ ps at low-energy ion irradiation (1 keV) due to a ballistic mechanism. The existing experimental data follow the same trend as the simulated values.