Probing hollow atom states formed during impact of highly charged ions on surfaces: N6,7+ and O7+ on Al(110) and Si(100)

This paper presents spectra obtained from the interaction of slow N7+ and O7+ ions interacting with a Si(100) crystal and from N6+ ions interacting with an Al(110) surface at grazing incidence. The spectra show profound structures which, by means of Hartree-Fock atomic structure calculations, allow us to identify the hollow atom states present at the moment of KLL decay. The velocity dependence of the spectra can be explained by a model in which the projectiles L-shell is filled by direct capture of a single target core electron during consecutive binary collisions between projectile and target atoms. The cross section for this capture process is large and, by its localized nature, yields a velocity dependent L-shell filling rate.