The roles which were played by surface states and bulk states in screening defects and step edges on close-packed surfaces were determined by studying 2-dimensional Fourier transforms of scanning tunnelling microscopic images. These images, which were obtained at low temperatures using low bias voltages, exhibited wave interference patterns that originated from energy-resolved Friedel oscillations of surface-state electrons that were created by the screening of surface defects. The images also yielded the 2-dimensional surface Fermi-contour. The present results for (111) surfaces revealed the existence of an additional contour in the Fourier transform scanning tunnelling microscopy power spectrum. This contour was related to the so-called neck of the bulk Fermi surface, as accounted for by a simple model. The results provided information on the roles that both bulk and surface-state electrons played in the screening of defects at, or near to, the surface. It was found that that surface-state electrons dominate the screening of step edges on Au(111).

Screening Waves from Steps and Defects on Cu (111) and Au (111) Imaged with STM: Contribution from Bulk Electrons L.Petersen, P.Laitenberger, E.Laegsgaard, F.Besenbacher: Physical Review B, 1998, 58[11], 7361-6