Core edge energy loss studies of Pd clusters on graphite

Abstract

In order to verify that the d-band of Pd clusters moves towards higher binding energies when the cluster size decreases, we have carried out energy loss measurements of the M4,5 core edge of Pd clusters with different diameters evaporated on polycristalline graphite. Generally the shifts have been attributed in the past both to initial and or final state effects. In the last case one could not observe variations with our technique which probes the partial unfilled density of states. Our experimental results show an enhancement of the absorption and a narrowing of the lineshape with increasing cluster size. We attribute the observed effects to a genuine change in the electronic structure which occurs in the initial state of the cluster. Comparative studies of this effect have been performed following the evolution of the M4,5 VV Auger levels and the collective excitations in the range 0-30 eV far from the elastic peak.