Unoccupied bulk and surface states on Ag(111) studied by inverse photoemission.

Abstract

We present k-resolved inverse photoemission spectroscopy (KRIPES) results for Ag(111) in the \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} K\ifmmode\bar\else\textasciimacron\fi{} direction of the surface Brillouin zone. The spectra were taken as a function of electron energy and angle of incidence at a fixed photon energy (9.7 eV) of the emitted radiation. The crystal-induced surface state and the image-potential-induced surface state are observed with final-state electron energies at \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} in good agreement with a recently proposed multiple reflection model and with dispersion characterized by effective masses ${m}^{\mathrm{*}}$=0.7m and ${m}^{\mathrm{*}}$\ensuremath{\approxeq}m, respectively. The measured intensity of the surface state roughly follows a ${\mathrm{cos}}^{2}$\ensuremath{\alpha} dependence, where \ensuremath{\alpha} is the angle between the sample normal and the polarization vector of the detected photons. Transitions into bulk-derived final states are observed, with final-state electron energies ranging from ${E}_{F}$ to ${E}_{F}$+20 eV. The dispersions of these bulk-derived final states agree with very simple ``empty-lattice isochromats'' derived from free-electron bands of proper symmetry, as well as with results of a band-structure calculation based upon a combined interpolation scheme.