Spectroscopy of image-potential states with inverse photoemission.

Cu(100), Cu(110), Ag(111},Au(111), and Au(100}), a semimetal [Sb(100}],and a layered compound {1T-TiS2). Data for Au{111) show that image-potential states exist even in the presence of bulk states. The coupling with bulk states is weak as indicated by the narrow {&0.1 eV) width of the image states. The binding energies of the lowest state cluster around 0.7 eV for a variety of metal and semimetal surfaces indicating a universal phenomenon. This value is close to the hydrogenic binding energy of —, 6 Ry -0.85 eV for the n =1 state, which indicates that the simple Coulombic image potential dominates the energy balance.