ROLE OF ENERGY-LEVEL SHIFTS ON AUGER NEUTRALIZATION PROCESSES - A CALCULATION BEYOND THE IMAGE POTENTIAL

Auger neutralization of slow He+ near Al(100) surfaces is analyzed by introducing the effect of the ion on the metal electrons. This is take n 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 Is level are calculated for short and la rge distances between the ion and metal atoms. We find that the Is lev el is completely modified with respect to the image potential shift fo r short distances, due to the strong interaction among He and Al atoms . Auger neutralization rates are calculated, and we obtain a most prob able distance of neutralization of about 3 a.u. between He and the las t Al layer. At this distance our theoretical Is level shows an energy shift of about 2 eV, in agreement with experimental findings. We thus conclude that slow He+ ions neutralize much closer to the metal surfac e than previously thought.