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

The energy dispersion curve E(k_∥) has been measured for an unoccupied sp-like surface state on Pd(111) with k-resolved inverse photoemission spectroscopy. At the zone center, Γ, 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 Γ 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.