Photoelectron spectroscopy studies of the Pd/Ru(0001) and (Cu+Pd)/Ru(0001) interfaces

The electronic structures of Pd and (Cu + Pd) overlayers on Ru(0001) have been studied. Photoelectron emission spectroscopy based on synchrotron radiation and radiation from a Mg Kalpha x-ray source has been used to study the valence band of the surfaces and the Ru 3d, Pd 3d and Cu 2p core levels. The interaction of Pd with Ru(0001) is studied in the coverage range of submonolayer to several monolayers. The core level spectra of the Pd 3d5/2 level show a new component for Pd coverages above 1 ML. In the submonolayer range the binding energy (BE) of the Pd 3d(5/2) level is constant at 335.08 eV. A state characterized as an interface state between the Pd adlayer and the Ru substrate is observed at a BE of 1.22 eV This state, which dominates the valence band for submonolayer Pd coverages, has not been reported earlier and it is seen neither for clean Ru(0001) nor for multilayers of Pd. It is a characteristic that the overlayer d bands are narrower in the low-coverage regime. Deposition of Cu, on a 0.4 ML Pd/Ru(0001) surface up to 1 ML total coverage of Pd and Cu, results in a mixed two-dimensional overlayer.