Low-energy Na+ neutralization on Al(1 1 1) and Cu(1 1 0) surfaces at grazing incidence

Jellium model is well known and used to understand the neutralization of alkali-metal ions on metal surfacesbut we find it cannot explain our experiments for the neutralization of 0.4 keV and 0.8 keV Na⁺ ions on Al(1 1 1) and Cu(1 1 0) surfaces in grazing incidence. As the exit angle increases neutral fractions on Cu(1 1 0) surface decreases first and then increases which is similar to our previous results at large scattering angles. While for the Al(1 1 1) surface we observe opposite characteristics. This anomalous bell-shaped feature cannot be explained by the Jellium model. One possible explanation is the inner 2p electron promotion at smaller exit angles this may cause the Na* excited states to be generated and produce excess Na⁺ ions while the similar electronic excitation process is inefficient for the Cu(1 1 0) surface in the present energy range.