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

The energy-dependent relaxation of photoexcited electrons has been measured by time-resolved two-photon photoemission spectroscopy on single-crystal Au~111! films with thickness ranging from 150 to 3000 A. It is found that the energy-dependent relaxation does not show any significant thickness dependence, which indicates that electron transport is a much slower dynamical process in the near-surface region than expected from bulk properties. Furthermore, lifetimes of the photoexcited electrons can be fitted well by the Fermi-liquid theory with a scaling factor plus an effective upper lifetime. This observation enables separation of electronelectron scattering, and to a lesser extent electron-phonon scattering, processes from electron-transport effects on the surface dynamics. @S0163-1829~98!04840-1#