Femtosecond dynamics of image potential states of C 6F 6/Cu(111) studied with two-photon photoemission

Abstract

The energetics and dynamics of electronic states of C 6F 6/Cu(111) are investigated with time-resolved two-photon photoemission spectroscopy. An unoccupied σ ∗ molecular resonance is observed from submonolayer up to multilayer coverages. For one monolayer (ML) of C 6F 6, image potential states are observed with binding energies of 0.37 and 0.18 eV below the vacuum level, which decrease slightly above 2 ML. The lifetime of the lower-lying image state is only 12±4 fs for 1 ML and 5±4 fs for 2 ML, and thus much shorter than those in other adsorbate–metal systems. This is attributed to an efficient decay from the image state into the σ ∗ molecular resonance of the C 6F 6 layer.