Unoccupied surface resonance on Cu(100) and the effect of vacuum-level pinning

Abstract
We have identified a new unoccupied surface resonance approximately 1.15 eV above the Fermi level on Cu(001) with the use of inverse photoemission. The resonance has to be separated from a nearby intense peak due to a bulk direct transition. This has been done in two ways: (a) varying the photon energy, which causes a shift in the bulk peak, and (2) varying the work function, wich causes a shift in the resonance. The occurrence of the resonance is consistent with a recently proposed phase analysis.