Ballistic-electron-emission microscopy of conduction-electron surface states

Cu/Au, Ag/Au, and Au/Cu/Au bilayer and trilayer (111) films grown on Si(111 ) and Si(100) substrates exhibit a spiral grain topography that, as determi ned by scanning tunneling spectroscopy, yields a high density of conduction -electron surface states on the flat areas of these grains. This results in strong spatial variations in the ballistic-electron-emission microscopy (B EEM) current due to differences in the proportion of electrons which tunnel into bulk as opposed to surface states. This enables BEEM imaging of varia tions in the density of unoccupied surface states and the examination of th e effect of incomplete coverages of adatoms in coupling such surface states to the bulk.