Space-filling, multi-fractal, localized thermal spikes in silicon, germanium and zinc oxide

TL;DR

This paper investigates thermal spikes as the mechanism behind cluster emission in heavy ion irradiated solids, using fractal thermodynamics to explain experimental observations in silicon, germanium, and zinc oxide.

Contribution

It introduces a fractal thermodynamic model to quantitatively describe thermal spike-induced cluster emission, extending understanding beyond collision cascade theories.

Findings

Thermal spikes exhibit fractal characteristics with a dimension dependent on interatomic potential.

The probability of thermal spike initiation is space-filling and multi-fractal.

Cluster emission ratios depend on surface vacancy formation energies.

Abstract

The mechanism responsible for the emission of clusters from heavy ion irradiated solids is proposed to be thermal spikes. Collision cascade-based theories describe atomic sputtering but cannot explain the consistently observed experimental evidence for significant cluster emission. Statistical thermodynamic arguments for thermal spikes are employed here for qualitative and quantitative estimation of the thermal spike-induced cluster emission from silicon, germanium and zinc oxide. The evolving cascades and spikes in elemental and molecular semiconducting solids are shown to have fractal characteristics. Power law potential is used to calculate the fractal dimension.The fractal dimension is shown to be dependent upon the exponent of the power law interatomic potential. Each irradiating ion has the probability of initiating a space-filling, multi-fractal thermal spike that may sublime a localized region near the surface by emitting clusters in relative ratios that depend upon the energies of formation of respective surface vacancies.