The role of atomic collisions in kinetic electron emission from Al surfaces by slow ions

We measured energy distributions of electrons emitted in the interaction of slow Kr+ and Na+ with Al surfaces. The data allow to correlate emission intensities with spectral signatures of electron excitation processes. Our results indicate that electron promotion processes leading to the excitation of Al target atoms plays the dominating role in kinetic electron emission from Al surfaces by slow ions. In the case of Kr+ ions, electron promotion occurs in close atomic collisions between recoiling target atoms. For Na+ projectiles, a significant contribution to Al excitation comes also from a vacancy transfer process in asymmetric collisions involving ions that have survived neutralization in the interaction with the surface.