Angular, energy, and population distributions of neutral atoms desorbed by keV ion beam bombardment of Ni{001}

Abstract

Multi-photon resonance ionization, time-of-flight mass spectrometry and imaging techniques have been employed to measure the polar-angle, kinetic energy, and population distributions of Ni atoms desorbed from 5 keV Ar ion bombarded Ni{001}. The measured angle- and energy-resolved intensity maps of the sputtering yield provide a set of data that can be used to examine the detailed interactions between the particles of the solid surface during the sputtering event. The results show a considerable degree of anisotropy associated with both the ejection angle as well as the crystallographic direction. In order to have an understanding of the interactions of the desorbed particles with the surface, molecular dynamics simulations of the ion-induced sputtering event are performed. The agreement between experimental and computer simulation results is excellent. Measurements performed on excited states of sputtered Ni show that the valence electron shell structure is an important factor in determining the angle-integrated kinetic energy distribution while the magnitude of the excitation energy is of secondary importance. Population distribution among different electronic states is obtained through two sets of measurements performed on different instruments. Both measurements employ the same resonant ionization schemes and laser fluences. The results show that the a 3D 3 and a 3D 2 states are more heavily populated than is predicted by a Boltzmann-type distribution.