Large noble metal clusters: Electron confinement and band structure effects

Abstract

For the electronic properties of large clusters the interaction of the free electron gas with the ion core lattice may result in additional quantization phenomena which are well known in the area of surface and thin-film physics. We measured the geometric and electronic properties of silver and gold clusters grown in nanopits on graphite with low-temperature scanning tunnelling microscopy and spectroscopy in combination with high-resolution photoemission. With the emergence of a Shockley surface state on the top (111) facets of gold clusters with a size of about 104 atoms, we observed one explicit example for the influence of the ion core lattice. The two-dimensional confinement of the surface state is set into the context of a possible one-dimensional confinement perpendicular to the surface, analogous to quantum well states in thin metal films. The basic mechanisms for the dependence of the electronic structure on the cluster size and the shape are tentatively discussed within a 'bulk limit', introducing the bulk band structure into the description of the clusters.