Interaction of slow multicharged ions with solid surfaces: current concepts and new information on slow electron emission

Abstract

Slow multicharged ions (MCI) approaching a solid surface are transiently converted into highly excited complexes, involving a potential energy possibly much larger than the kinetic projectile energy. De-excitation of such complexes proceeds within less than one pico-second via a manifold of interrelated reaction channels, giving rise to characteristic signatures as slow and fast electron emission, and X-ray radiation. For impact on LiF, also potential-energy dependent ejection of neutral and ionized target particles has been observed. Before their close contact with a metal surface, MCI are converted by multiple capture of target electrons into the so-called hollow atoms which rapidly decay by autoionization, at the surface loose outer electrons due to shielding, and eventually become de-excited inside the solid. At insulator surfaces, MCI neutralization and de-excitation is less well understood. Recently measured electron number statistics for MCI impact on clean metal (Au) as well as insulator (LiF) surfaces deliver interesting new information.