Influence of Xe adlayer morphology and electronic structure on image-potential state lifetimes of Ru(0001)

The dynamics of image-potential states of clean and Xe-covered Ru(0001) was investigated by means of time-resolved two-photon photoemission. Xe adsorption is found to cause a substantial increase of the lifetime of the first image-potential state from 11 fs for the clean surface to 125 fs for a bilayer of Xe. The lifetimes in the presence of the commensurate and the incommensurate monolayer phases differ distinctly; 36 fs and 52 fs, respectively, were obtained on the two phases. The lifetime of the second image-potential state shows a weaker dependence on Xe coverage. A simple tunneling model and a dielectric continuum model are used to estimate the reduced coupling of the wave function of the image-potential states with the metallic substrate which is responsible for the increased lifetime in the presence of Xe layers. (C) 2000 Published by Elsevier Science B.V. All rights reserved.