Surface state electron dynamics of clean and adsorbate-covered metal surfaces studied with the scanning tunnelling microscope

Using low-temperature scanning tunnelling microscopy and spectroscopy we have studied the dynamics of surface state electrons confined to vacancy islands on Ag(1 1 1) and localised at single magnetic and non-magnetic atoms adsorbed on Ag(1 1 1) and Cu(1 1 1). The line width of confined electronic states is found to be only weakly affected by the actual geometry of the vacancy island. A corresponding model shows that lossy boundary scattering is the dominant lifetime-limiting process in the vacancies studied. We present a corrected analysis of the spatial decay of electron interference patterns, leading to a more consistent description of the Ag(1 1 1) surface state lifetime than was previously the case. A scanning tunnelling spectroscopy study of single adsorbed atoms is presented. By means of an extended Newns-Anderson model an observed resonance is interpreted in terms of an adsorbate-induced bound state split off from the bottom of the surface-state band. A preliminary line shape analysis of the bound state indicates that adsorbed atoms can modify the surface-state lifetime.