Dynamics of excited state production in the scattering of inert gas atoms and ions from Mg and Al surfaces

We present results of a detailed study of the production of electronically excited states in the scattering of ionic or neutral inert gas projectiles in the keV energy range at Al and Mg surfaces. The complementary observation of scattered particles (neutrals or ions), secondary electrons and photons leads to a rather complete description of the successive stages of inelastic scattering events. Efficient neutralisation of the incident ions occurs, when they approach the surface. This is clearly demonstrated by the strong similarities between results obtained for incoming ions and incoming ground-state neutrals. The characteristics of the scattered particle distributions, the observation of scattered ions, and also of some excited states by electron and photon spectroscopy, delineates the decisive importance of short-distance binary collisions with atoms of the surface, in the production of these species. A detailed comparison with the “inverse” collisional systems in the gas phase shows that the same kind of primary excitations as described in the quasi-molecular orbital promotion model are operative and allows, for example, predictions about which of projectile and/or target atoms can be excited. Some very strong differences to gas-phase collisions are also demonstrated. They stress the importance of surface-specific effects, such as the role of resonant or Auger electron transfers between the metal surface and the receding particle in defining the final state population. In particular, an interesting surface-induced core rearrangement effect is emphasised, and different rearrangement mechanisms are presented and discussed.