STM STUDIES OF THE INTERACTION OF SURFACE-STATE ELECTRONS ON METALS WITH STEPS AND ADSORBATES

Scanning tunneling microscopy (STM) studies have shown that scattering of surface state electrons by steps and adsorbates leads to long-rang e oscillations in the local density-of-states (LDOS). Here we examine the nature of the states probed in the vicinity of the scatterer. We f ind that at steps, the LDOS primarily reflects the Smoluchowski charge -redistribution process. Perturbation of the surface state by the step extends more than 10 Angstrom from the step-edge and induces bulk-sur face state mixing. Unusually narrow spectra and delocalized images are observed for adsorbed sulfur on Ag(111) and are explained in terms of the electronic structure changes induced by chemisorption.