Unoccupied Surface State on Ag(110) as Revealed by Inverse Photoemission

By use of the new technique of $k$-resolved inverse photoemission spectroscopy, an unoccupied $s$-like surface state on Ag(110) has been detected, which lies within the projected $L_{2^{\prime }}\to L_1$ gap of the bulk. At the $\overline{X}$ point of the surface Brillouin zone, the energy of the surface state is 1.65 eV above the Fermi level $E_{\mathrm{F}}$, and exhibits a band dispersion $E\left(k_{\parallel }\right)$ towards higher energies. The surface-state emission is immediately quenched when the surface is exposed to very small amounts of oxygen or hydrogen.