4F-ELECTRONIC AND SURFACE-ELECTRONIC STRUCTURE OF LANTHANIDE METALS

We report recent progress in high-resolution photoemission (PE) from m onocrystalline lanthanide-metal surfaces using synchrotron radiation. Systematic studies of the valence-band structure have shown that a loc alized d-like surface state is an intrinsic property of close-packed l anthanide-metal surfaces. These often partially occupied states are st ill not sufficiently well understood. For close-packed surfaces, relat ively small surface core-level shifts of the 4f PE lines were observed , in good agreement with the results of recent ab initio calculations. By comparing photoemission and inverse photoemission spectra of Gd(00 01), the surface core-level shifts could be separated into initial- an d final-state contributions. This is in accord with recent progress in the theoretical description of surface core-level shifts for lanthani de-metal surfaces with inclusion of final-state effects. We further di scuss thermal broadening of bulk and surface 4fPE lines from Yb(111), and show that cooling of the lanthanide materials to liquid-He tempera tures is needed for achieving the highest resolution.