FEMTOSECOND PHOTOEMISSION-STUDY OF ULTRAFAST ELECTRON DYNAMICS IN SINGLE-CRYSTAL AU(111) FILMS

The energy-dependent relaxation of photoexcited electrons has been mea sured by time-resolved two-photon photoemission spectroscopy on single -crystal Au(lll) films with thickness ranging from 150 to 3000 Angstro m. It is found that the energy-dependent relaxation does not show any significant thickness dependence, which indicates that electron transp ort is a much slower dynamical process in the near-surface region than expected from bulk properties. Furthermore, lifetimes of the photoexc ited electrons can be fitted well by the Fermi-liquid theory with a sc aling factor plus an effective upper lifetime. This observation enable s separation of electron-electron scattering, and to a lesser extent e lectron-phonon scattering, processes from electron-transport effects o n the surface dynamics. [S0163-1829(98)04840-1].