Band Effects on Ion-Surface Charge Exchange

Abstract

Various aspects of charge exchange between low-energy ions (10 eV–2 keV) and solid surfaces are discussed with particular emphasis placed on the effects of valence orbital hybridization on the electronic transition probabilities, and uniqueness of surface scattering relative to diatomic gas-phase collision is highlighted. Two classes of projectiles are explored, i.e. inert noble-gas ions and a reactive hydrogen ion. One or two core vacancies are created in noble-gas projectiles during collisions with specific target atoms, leading to (re)ionization and autoionization. In contrast to gas-phase collision, it is found that one-electron excitation predominates over simultaneous two-electron excitation. This result is basically ascribed to the band effect of energy-level crossing. Neutralization of the slow hydrogen ion at a surface is rather unique compared to the noble-gas ions and its probability is sensitively dependent upon ionicity of target atoms or the nature of the valence band. This is because a valence electron is captured via a new class of resonance neutralization which is mediated by a short-lived chemisorption state of hydrogen on a surface.