Image-potential and intrinsic surface states on Ag(100)

Applying $\overrightarrow{\mathrm{k}}$-resolved inverse photoemission spectroscopy to the Ag(100) surface, we have found two different types of unoccupied electronic surface states: (i) Near-normal-incidence, image-potential surface states produce a steplike spectral feature about 0.5 eV below the vacuum level; (ii) near the $\bar{X}$ point of the surface Brillouin zone, an $s$-like Shockley-type surface state appears at $E_F+3.8\mathrm{}$ eV, in agreement with electroreflectance measurements by Kolb et al. Both surface states are quenched by the adsorption of water at 110 K.