By studying 2-dimensional Fourier transforms of scanning tunnelling microscopy images, information was obtained concerning the roles which were played by surface states and bulk states in the screening of defects and step-edges on close-packed surfaces. The scanning tunnelling microscopic images, obtained at low temperature and a low bias voltage, exhibited wave interference patterns which originated from the energy-resolved Friedel oscillations of surface-state electrons that were created by the screening of surface defects. The Fourier-transform scanning tunnelling microscopy directly yielded images of the 2-dimensional surface Fermi contour. Results were presented here for Cu and Au (111) surfaces. These 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 furnished information concerning the role that bulk and surface-state electrons played in the screening of defects at, or near to, the surface. It was found that the surface-state electrons dominated the screening of step-edges on the Au (111) surface.

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