Characterization of the n=1 image state on Ni(111) with two-photon photoemission

Abstract

The binding energy and E(k∥) dispersion of the n=1 image potential state have been measured on Ni(111) using angle-resolved two-photon photoemission. The binding energy, εn=1, is found to be 0.8±0.1 eV. The E(k∥) dispersion relation is well described by an effective mass m*/me, of 1.0±0.1, in disagreement with earlier momentum-resolved inverse photoemission results, but in agreement with theoretical predictions based on a phase analysis of the n=1 image state wave function. Two-photon photoemission spectra were also recorded for Ni(111)-p(2×2)-O, showing the disappearance of the image state and the emergence of a weak, broad, nondispersive feature attributable to two-photon photoemission from states originating near the Fermi level.