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

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 x 1), SiO2(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 He2+ ions at various exit angles for each surface. For the Si(0 0 1)(2 x 1) surface, the charge state of the scattered ions shows a considerable dependence on the exit angle, while no dependence is observed for the SiO2/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. (C) 2004 Elsevier B.V. All rights reserved.