Resonances induced by Cs adsorbates on Cu(100): Localization of image potential states

The modifications of the electronic states located in the surface region induced by a Cs adsorbate on a Cu(100) surface are studied using a wave-packet propagation method. Several states localized around the adsorbate are found and can be sorted in two categories: (i) states corresponding to strongly distorted atomic levels and (ii) states with an energy slightly below the image state continuum band bottoms. The latter are attributed to localization inside the two-dimensional image state continua induced by the short-range adsorbate potential. The possibility of observing these states by photoemission is discussed.