Mechanistic study of atomic desorption resulting from the keV-ion bombardment of fcc{001} single-crystal metals.

Abstract

Energy-resolved angular distributions of Ni and Rh atoms desorbed by keV ${\mathrm{Ar}}^{+}$ ion bombardment have been measured using multiphoton resonance ionization detection. The experimental spectra were simulated using molecular-dynamics calculations which are based on the molecular-dynamics/Monte Carlo corrected effective-medium interaction potential. Important collision events were identified using a recently developed graphical utility which allows easy visualization of atomic motions subsequent to bombardment. Three major microscopic ejection mechanisms were determined, each of which is categorized into three additional interactions. The features which make up the polar angle spectra are assigned to one of these mechanisms. We find that the majority of particles eject due to a collision with an atom from one layer below (${\mathrm{\ensuremath{\Delta}}}_{1}$ mechanism). A mechanism involving a collision due to an atom from the same layer, however, is responsible for a shift in peak position with energy. This investigation strongly reinforces the view that the inherent registry of the atoms in the crystal lattice is the crucial factor in determining the dominant microscopic sequences of events which lead to ejection as well as the macroscopically observable quantities.