IMAGE-POTENTIAL STATES ON NI(111) - A 2-PHOTON-PHOTOEMISSION STUDY

The binding energies of the first three members of the image-state Rydberg series on Ni(111) were determined by two-photon photoemission to be -0.80, -0.25, and -0.10 eV, respectively. The effective mass of the n=1 image state was measured as m*/m=1.12. We demonstrate that the photon energy for resonant excitation from the occupied n=0 surface state to the n=1 image state is k? dependent, and from this we obtain an independent confirmation of the n=0 state dispersion measured previously by photoemission spectroscopy. The experimental data are well reproduced by a model calculation based on the phase-accumulation model for surface states. © 1990 The American Physical Society.