Decay and dephasing of image-potential states studied by time-resolved two-photon photoemission

Applying two-photon photoemission spectroscopy with femtosecond time resolution the dynamic behavior of image-potential states on Cu(0 0 1) and Cu(1 1 9) has been studied. Inelastic and quasielastic scattering processes can be separated comparing energy- and time-resolved spectroscopy. Quantum-beat spectroscopy allows to access population decay and dephasing of higher image-potential states. For Cu(0 0 1) the surface order and electronic structure were modified by adsorption of small amounts of CO and Cu homoepitaxy. This reveals that defects influence decay rates and dephasing rates considerably with the branching ratio strongly dependent on the nature of the scattering potential introduced.