Direct observation of spike effects in heavy-ion sputtering

Abstract

Transmission electron microscopy has been used to study the formation of surface craters by Bi⁺ and Bi₂ ⁺ bombardment of Au in the energy range 10–500 keV. Craters ∼5 nm in diameter were observed in individual displacement cascades of energy 50 keV. The observed energy and energy—density dependence of crater yields, sizes and fine structure indicate that the craters were formed in extra-high-energy—density surface spikes which occur with a low (∼10⁻²) but finite probability due to fluctuations in energy deposition in individual cascades. In light of the present experimental evidence, we propose a modified ‘thermal-spike’ model for the explanation of the quite large deviations from linear cascade theory that have been observed by conventional self-ion and molecular-ion sputtering-yield measurements in heavy metals.