The underlayer influence on photoemission and thermal desorption of xenon adsorbed on Ag(111)

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Abstract
Combined UV and x-ray photoelectron spectroscopy, work function, and thermal desorption measurements are presented for the submonolayer to multilayer adsorption of xenon on a Ag(111) surface. The results compliment the detailed LEED studies of this system by Webb and co-workers. Successive layer-by-layer growth up to at least three Xe layers is seen from the variation of the XPS Xe (3d5/2) intensity as a function of exposure. The thermal desorption of xenon from the first and second layer is compatible with zeroth order desorption kinetics. This is suggestive of desorption from 2D solid Xe islands, in agreement with the first order phase transitions during population of the first and second layer observed by Webb et al. The adsorption energies of the first and second layer are estimated to be E1ad=5.2 and E2ad=4.3 kcal/mol, respectively. The dipole moment per xenon atom in the first layer has the coverage independent value of μ1(Xe)=0.2D. Particular emphasis is put on the discussion of the layer dependent photoemission behavior of xenon. The present work includes the first complete set of UPS and XPS electron binding energies for Xe on one and the same metal. Comparison of the layer values with those of other Xe/metal systems as well as their layer dependent shift provide twofold support for the notion that the electron binding energies (with respect to EF) of adsorbed xenon atoms ‘‘float’’ with the local electrostatic surface potential of the respective adsorption site. This is further supported by some measurements for xenon adsorbed on a sputter-roughened Ag surface. Both the adsorption energy as well as the photoemission behavior of xenon are sensitive towards the surface topography, which in turn can be utilized for the characterization of surface defects induced by sputtering.