Electron–phonon coupling and lifetimes of excited surface states

Many important chemical and physical phenomena are influenced by inherent dissipative processes, which involve energy transfer between the electrons (electron–electron scattering) and between the electrons and the ionic motion (electron–phonon scattering). The non-adiabatic interaction between the valence electrons and the ion motion in a solid reveals the break down of the Born–Oppenheimer approximation. To pin down the influence of the electron and phonon structure on these scattering processes the two-dimensional surface states are ideal both from an experimental and theoretical point of view. Several experimental techniques presently in use are able to give information about the lifetime of an excited electron or hole in the surface state band. With help from advanced theoretical calculations it is possible to sort out the relative importance of the electron–electron and electron–phonon scattering processes responsible for the quenching of the excitation and to point out the key parameters of the electron and phonon structure.