Observation of Final-State Screening in Inverse Photoemission from Adsorbed Xenon Layers

Inverse photoemission spectra of xenon layers adsorbed on Au(110) have been recorded. The unoccupied levels of xenon exhibit layer-dependent peak shifts to higher energies. The $6s$ level of the second xenon layer is shifted by 0.65 eV relative to the monolayer energy, with the $6p$ level exhibiting a 0.85-eV shift. These shifts are related to the image-charge screening of the negative-ion inverse-photoemission-spectra final states. This observation demonstrates the influence of screening in inverse photoemission, and provides a test of the different conflicting models put forward in explanation of such shifts.