Scattering of hot electrons by adatoms at metal surfaces.

The scattering of electrons in image-potential states by Cu adatoms on Cu(001) surfaces has been investigated by means of time- and angle-resolved two-photon photoemission. Several interband and intraband-scattering mechanisms have been identified and their contributions to the total decay of the states determined quantitatively. The adsorbates mainly cause quasielastic scattering processes. Inelastic processes in contrast are due to interactions with electrons in the substrate and are not significantly increased by Cu adatoms. Quasielastic scattering into bulk bands contributes significantly to the depopulation of surface states.