Modification of the Shockley-type surface state on Ag(1 1 1) by an adsorbed xenon layer

The Shockley-type surface state for the clean and a Xe covered Ag(1 1 1) surface is studied with scanning tunneling microscopy and scanning tunneling spectroscopy at a temperature of 5 K. The minimum of the parabolic dispersion shifts from −67 meV below EF=0 for the clean Ag(1 1 1) surface to +52 meV with one layer of Xe adsorbed, hence the surface state becomes completely unoccupied after Xe adsorption. The dispersion is determined by measuring energy-dependent, locally-resolved, tunneling spectroscopy maps. These show standing wave patterns as local density of states formed by electron scattering at surface steps, which reveal equal effective masses with and without the Xe layer adsorbed. A line width analysis of the energetic onset of the surface state gives a slightly smaller lifetime of the surface state after Xe adsorption, in sharp contrast to the results for image states. We discuss the results and conclude that the wavefunction of the Shockley-type surface state stays close to the metal surface also after Xe adsorption, and that the observed shifts cannot be explained by the simultaneous change of the workfunction, but will be given mainly by the changes of the surface potential on an atomic scale.