Substrate and morphology effects on photoemission from core-levels in gold clusters

The combination of X-ray photoelectron spectroscopy and spectrophotometry of supported gold clusters on SiO2 reveals the importance of cluster morphology in determining core-electron binding energies. As-deposited films show a discontinuous dependence of the binding energy on gold content, associated with a transition from coagulated or partially coalesced clusters to isolated clusters. In contrast, annealed films exhibit a smooth increase in binding energy down to very low gold content. Comparison of the photoemission from annealed clusters deposited on and embedded in the insulating SiO2, as well as clusters deposited on a conducting ITO substrate, was used to highlight the contributing factors that determine the core-electron binding energy and line-width, namely: (i) initial-state effects relating to the electronic structure, (ii) final-state effects relating to relaxation processes, and (iii) the cluster charge, including the influence of image charge screening.