Nanoparticle ejection from gold during ion irradiation

We have used in situ transmission electron microscopy to study the sputtering of gold by inert-gas ions and, in particular, nanoparticles ejected by individual ion impacts. Irradiations were performed at room temperature in transmission geometry with Ne, Ar, Kr and Xe ions at energies between 100 and 600 keV. Nanoparticles result from situations in which ion impacts also give rise to nanometer size craters on the surface. The number of nanoparticles increased linearly with increasing ion dose. The rate of nanoparticle ejection scales with the probability, calculated with standard Monte Carlo techniques, for high-energy deposition events by individual ions in the near-surface region regardless of the irradiation. The percentage of near-surface, high-energy recoils that eject a nanoparticle is high. The rate of nanoparticle ejection depends on energy transfer to the Au lattice and not on the ion that makes the impact or its energy. Ejected nanoparticles account for the nonlinear component of sputtering. Monte Carlo calculations offer a general technique for predicting situations in which nanoparticles can be ejected and thus when the nonlinear contribution to the sputtering yield is likely to be significant.