Valence-electron dispersion of close-packed Li determined by photoemissionfrom thin films on Cu(111)

The dispersion of valence electrons in the perpendicular direction of (111) -oriented Li films formed by evaporation of the alkali metal onto Cull (111 ) is studied by photoemission (hv = 4.5 - 26 eV). The conventional bulk ban d mapping method fails at low photon energies when interband transitions ar e expected from states near below E-F. In this energy range the dispersion is instead determined from the energies measured for discrete quantum-well- like overlayer states resolved for 1-17 atomic layers thick Li films. For f ilms thick enough (>30 ML) for saturation of the shape of photoemission spe ctra, the maximum separation between the Fermi edge and the interband emiss ion peak is 2.8 eV. This is an apparent photoemission band width which, acc ording to our estimate is 0-0.4 eV smaller than the actual band width. The quantum well state energies measured for ultrathin films indicate that the Fermi surface is closed with the zone boundary edge 0.1-0.2 eV above the Fe rmi level. [S0163-1829(99)12231-8].