Surface phenomena on noble and rare earth metals

Abstract

The effect of the vacuum interface on the electronic structure of metals was explored using X-ray photoelectron spectroscopy (XPS). In the noble metal gold a narrowed and shifted surface density of states was isolated and a surface atom core level shift was resolved. The latter is due to reduction of the empty d density of states at the surface. For silver, overlayer experiments demonstrated that in XPS the 3.7 eV plasmon is largely of extrinsic surface origin. The excitation of this plasmon by photoemission from an adsorbate atom core level was also observed in accord with recent theories. A surface phase transition to an intermediate valence state was found on samarium and YbAu 2. It is understood in terms of the narrowing of the 5d band which raises the Fermi energy up to the empty 4f level.