Localization of surface excitations and stimulated desorption

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Abstract
We recently proposed that delocalized surface electronic excitations may localize by inducing lattice distortions, analogous to small-polaron formation in bulk materials. Here we explain this idea and argue that such localization is a necessary condition for desorption via electronic excitations. The idea of a small polaron is briefly reviewed and the similarity to the desorption problem is explored. It is shown that multihole excitations in which the holes hop together move slowly and are coupled strongly to the lattice motion; as a result they rapidly localize. Moreover, single holes or excitonlike states may also localize depending upon the strength of the coupling to the atomic positions and the local lifetime against hopping. A qualitative understanding of the phenomenon is provided and predictive methods explained, illustrated using the results of ab initio calculations on hydrogen: silicon. Future experimental and theortical work is suggested.

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