Role of energy-level shifts on Auger neutralization processes: A calculation beyond the image potential

Abstract

Auger neutralization of slow ${\mathrm{He}}^{+}$ near Al(100) surfaces is analyzed by introducing the effect of the ion on the metal electrons. This is taken into account by including in the calculation the $2s$ and $2p$ levels of He that can be filled by metal electrons when the ion approaches the surface. These levels and the $1s$ level are calculated for short and large distances between the ion and metal atoms. We find that the $1s$ level is completely modified with respect to the image potential shift for short distances, due to the strong interaction among He and Al atoms. Auger neutralization rates are calculated, and we obtain a most probable distance of neutralization of about 3 a.u. between He and the last Al layer. At this distance our theoretical $1s$ level shows an energy shift of about 2 eV, in agreement with experimental findings. We thus conclude that slow ${\mathrm{He}}^{+}$ ions neutralize much closer to the metal surface than previously thought.