Excited electron dynamics of bismuth film grown on Si(1Â 1Â 1) surface by interferometric time-resolved two-photon photoemission spectroscopy

We have carried out studies on the excited-electron dynamics in the single and poly crystalline Bi films by interferometric time-resolved two-photon photoemission spectroscopy (ITR-2PPE). The fast energy relaxation times of the excited electrons due to the electron-electron scattering were observed. The energy relaxation times were less than 15 fs and those of the single crystalline film are faster than those of the poly crystalline film. The faster energy relaxation times of the single crystalline Bi film are attributed to the higher scattering rate induced by the higher densities of states by appearance of the surface states in the vicinity of the Fermi level.