EFFECTS OF SURFACE-FEATURES UPON THE AU(111) SURFACE-STATE LOCAL DENSITY OF STATES STUDIED WITH SCANNING TUNNELING SPECTROSCOPY

The local density of states of the Au(111) surface state on flat planes, monatomic steps, narrow terraces, and in monatomic pits were measured with a scanning tunneling microscope. The experiments were performed on a single-crystal Au(111) sample in ultrahigh vacuum. We measure a decrease in the surface-state intensity by a factor of 2-10 on monatomic steps. The surface-state local density of states for narrow terraces has been found to be relatively unchanged from the value on flat (111) planes. Preliminary results for monatomic-deep sputter pits with diameters of order 25 angstrom show surface-state density of states peak shifts on the order of + 100 meV with respect to the value on flat (111) planes. Our results are consistent with the treatment of steps as a region of weakly repulsive potential with respect to the two-dimensional nearly free-electron-like surface state. A model of surface-state tunneling incorporating this result has been developed and produces reasonable quantitative agreement with the data.