Electronic structure of Pd thin films on Re(0001) studied by high-resolution core-level and valence-band photoemission

The electronic structures of Pd thin films grown epitaxially on a Re(0001) single-crystal surface are investigated with high-resolution photoelectron spectroscopy. A clear splitting of the Pd 3d(5/2) core level is observed as the coverage of Pd increases from submonolayer to multilayer. The peak at higher binding energy is assigned to emission from the Pd layer at the interface with the Re substrate, while the other is from "bulk" Pd. The observed valence-band spectrum of the pseudomorphic Pd monolayer on Re clearly revealed a reduction in the density of states near the Fermi level and shifting of the d-band center to higher binding energy. It is possible to reconcile the seemingly contradictory core level and valence-band shifts based on the charge-density maps from the earlier full-potential linearized augmented-plane-wave band-structure calculation by Wu and Freeman. Filling of the Pd d band by electron donation from the substrate does not occur. Rather, the correct physical picture for the electronic modification is substrate-induced charge polarization in the Pd layer.