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 of 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 a very low gold content. Comparison of the photoemission from annealed clusters deposited on and embedded in the insulating SiO2, as well as clisters 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.