Binding energy of image-potential states: Dependence on crystal structure and material

Abstract

We have measured the binding energy of the image-potential states on Cu(100) and Ag(100) surfaces with two-photon photoemission spectroscopy. We find ${E}_{B}$=0.57 (0.18)\ifmmode\pm\else\textpm\fi{}0.02 eV for Cu(100) and 0.53 (0.16)\ifmmode\pm\else\textpm\fi{}0.02 eV for Ag(100) for the n=1 (n=2) states, respectively. These values are compared with the nearly hydrogenic binding energies of 0.77--0.83 eV obtained for the (111) surfaces of Cu, Ag, and Ni using the same method. The comparison shows that the binding energy does not depend on the material as long as the surface structure remains constant but changes markedly with the crystal orientation.