SPIN-DEPENDENT STUDIES OF THE DYNAMICS OF HE(2(3)S) ATOM DEEXCITATION AT SURFACES

Electron spin labelling techniques provide a powerful technique with which to probe the dynamics of He(2(3)S) atom deexcitation at surfaces. Studies with a clean Cu(100) surface reveal that deexcitation occurs exclusively through resonance ionization followed by Auger neutralization and that the electrons involved in Auger neutralization are correlated in spin. Model calculations suggest that this can be explained by considering the local perturbation in the surface electronic structure induced by the presence of the (polarized) He+ ion. The calculated induced densities of states are spin dependent and exhibit sharp Kondo-like resonances near the Fermi level. Measurements at an adsorbed Xe film are also described and suggest that electron ejection results both from direct Auger deexcitation (surface Penning ionization) and from resonance ionization of incident atoms, the resulting ions being neutralized through an interaction that involves neighboring Xe atoms in the film. The Xe film data provide an unusual example of a surface at which resonance ionization and Auger deexcitation occur in parallel with comparable rates.