Theoretical studies of ion neutralization at a solid surface

Abstract

Calculations are presented of the kinetic-energy distribution of Auger electrons emitted during ion neutralization at Si (111) and H-covered Si (111) surfaces. An expression is derived for the Auger electron kinetic-energy distribution (KED) using an "internal" absorption or radiation formulation of the Auger process. This expression relates the KED spectra to various surface electronic densities of states. It includes nonadiabatic energy transfer broadening, but in other respects it is similar to previously derived expressions for KED spectra. The position-dependent density of states for Si (111) and H-covered Si (111) is calculated using a fully self-consistent surface potential. Using these state densities we show that the experimentally measured KED spectra can be reproduced assuming that the Auger electron originates in a region within the last few planes of atoms, while the ion is neutralized a few angstroms outside the last plane. The importance of electron correlations for narrow half-filled surface-state bands is demonstrated and evidence presented that hole-hole interaction energies can be neglected in the neutralization event.