Charge-state distribution of 400 keV He ions scattered from solid surfaces

Abstract

Charge-state distribution of backscattered He ions was investigated when 400 keV He + ions were incident on three different surfaces; clean Si(0 0 1)(2 × 1), SiO 2 (2.5 nm)/Si(0 0 1) and Ag(0.31 ML)/Si(0 0 1). The dependence of the charge state on the exit angle of the scattered ions was obtained by measuring the energy spectra of both the scattered He + and He 2+ ions at various exit angles for each surface. For the Si(0 0 1)(2 × 1) surface, the charge state of the scattered ions shows a considerable dependence on the exit angle, while no dependence is observed for the SiO 2/Si(0 0 1) surface. For the Ag/Si(0 0 1) surface, the He + fractions in the ions scattered from the surface Si and Ag atoms are different significantly from each other at large exit angle from the surface. These dependences are explained by a model including the nonequilibrium charge-exchange process of the exiting ions with the valence electrons at the surface.