Localization of surface excitations and stimulated desorption

It is proposed that delocalized surface electronic excitations may localize by inducing lattice distortions, analogous to small polaron formation in bulk materials. It is argued that such localization is a necessary condition for desorption via electronic excitations. It is shown that multi-hole 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 exciton-like states may also localize depending upon the strength of the coupling to the atomic positions and the local life-time 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. The low-lying eigenstates of an electronic excition of a deformable surface are studied within the adiabatic regime, where the electrons follow the atomic motions.