Size-dependent XPS spectra of small supported Au-clusters

High resolution XPS spectra (4f) of mass-selected AuN-clusters supported by a thin natural silica layer are presented in the size range N = 1–35 atoms per cluster. The XPS binding energy as well as peak width is found to increase systematically with decreasing cluster size. Furthermore a size-dependent asymmetry is observed on the high energy tail of the photoemission peaks. Analysing the XPS shift and line shape using the dynamic electrostatic model helps to identify initial and final state effects such as negative surface core level shift, inhomogeneous broadening, dynamic final-state screening and chemisorption-like interaction between cluster and support.