Inelastic inert gas ion collisions with metal targets. Rearrangement and adsorbate effects

Abstract

Results of recent studies of inert gas ion scattering on metal surfaces obtained in this laboratory and elsewhere are briefly reviewed. These have focussed on a study of He, Ne and Ar ion scattering on Na, Mg, Al and Si surfaces for energies in the 500 eV to 15 keV energy range. Measurements of scattered ion and neutral energy and angular distributions, charge fraction determinations and electron and photon spectroscopy results are reported. These demonstrate the role of electronically inelastic “binary” small impact partameter collisions with surface atoms. These are responsible for production of singly and doubly excited states and ionisation. The results of ion solid collisions are analysed and compared to results of gas phase studies of similar collisional systems. Analogies and some major differences are pointed out. The main trends in excitation processes follow the prediction of the molecular orbital prtomotion model, at least insofar as the prediction of the type of excited particle produced: projectile or target. This suggests that the primary orbital promotion mechanism is the same. Significant differences are encountered and have been discussed in terms of electron capture and loss processes involving the excited species resulting from the binary collision. The existence of core rearrangement processes have been shown to exist on the example of Ne 2+ 1D to 3P rearrangement. Models of this core rearrangement process have been proposed. The presence of adsorbates has been shown to modify the outcome of scattering. This is partly due to collisions with both metal target atoms and adsorbate atoms, leading to a modification of the primary excitation process. Further modifications occur due to a change in the secondary electron loss and capture processes leading to a modification of the final state distributions.