Two-photon photoemission as a probe of electron interactions with atomically thin dielectric films on metal surfaces

Electrons bound to a metal surface by the image potential are seen to persist in the presence of various adsorbates. A new two-photon photoemission spectrometer with high resolution and sensitivity permits precise measurement of adsorbate-induced changes in image state binding energy and dispersion. This provides a unique probe of electron interaction with thin dielectric films. Monolayer xenon on Ag(111) reduced the electron's effective mass. Spectra of alkane multilayers show rich structure with layer-by-layer shifts in binding energy. Bilayers gave evidence of electron localization.