Inner-shell promotions in low-energy Li⁺-Al collisions at clean and alkali-covered Al(100) surfaces

Spectra of scattered ions and ion-induced electron emissions are used to investigate the electronic processes that occur during 0.4–5.0-keV Li⁺ bombardment of clean and alkali-atom-covered Al(100). The results show that Li 1s electrons are promoted during hard Li-Al collisions, but not during Li-K or Li-Na collisions. Consequences of the inner-shell electron promotions are evident in the inelastic loss, neutralization behavior, and electron emissions of the scattered Li particles. Spectra of scattered Li⁺ ions exhibit discrete-loss features, which are resistant to the usual increase in resonant neutralization that accompanies the deposition of alkali atoms on the surface. The loss features are due to Li 1s excitation via electron promotion, while the production of ions away from the surface via autoionization is responsible for their lack of response to alkali-atom adsorption. Spectra of ion-induced electron emissions confirm that Li^*(1s2s²) is produced and that it undergoes autoionization.