Inverse Photoemission Observation of an Unoccupied Surface State on Pd(111)

Abstract

The energy dispersion curve $E\left(k_{\parallel }\right)$ has been measured for an unoccupied $\mathrm{sp}$-like surface state on Pd(111) with $k$-resolved inverse photoemission spectroscopy. At the zone center, $\overline{\Gamma }$, the energy of the surface state is 1.7 eV above the Fermi level, in good agreement with theoretical pseudopotential calculations of Louie, although the energy dispersion away from $\overline{\Gamma }$ is appreciably more rapid than in theory. The work opens up the possibility of probing unoccupied surface states in the same way that angle-resolved photoemission probes occupied surface states.