Final state effect for Au 4f line from gold-nano-particles grown on oxides and HOPG supports

The effect of a positive charge left to a small metal particle immediately after photoemission, so called the final state effect is studied for Au 4f binding energy (EB) shifts. The size and shape of Au nano-particles were determined by high-resolution medium energy ion scattering combined with scanning electron microscopy of a field emission type. The shape of Au nano-particles is well approximated by a partial sphere with diameter d and height h. It is found that the EB shift is well expressed as number of atoms per particle (nA) and independent of support species. The EB shift changes dramatically at a critical nA value of ∼70 atoms, where metal-nonmetal transition takes place. In the nonmetal region, the EB shift increases steeply almost exponentially with decreasing nA and in contrast, gradually decreases with increasing nA in the metallic region. The effect of the positive charge of an Au 4f vacancy created by photoemission is expressed by the relaxation time τ and the effective charge +α e when the photoelectron just leaves the Au particle surface (e: electron charge, α < 1).