Uniform Au-clusters supported on well-defined substrate [octanedithiol/Au(111)] were analyzed by tunneling and x-ray photoelectron spectroscopy. Single-electron tunneling effect and the binding-energy shift observed in these spectroscopies exhibit the consistent cluster-size dependency. Au $4f$ core-level shift of the supported clusters can be well explained by the charging energy $e^2/2C,$ where C is the capacitance between a cluster and its surroundings. The main contributions to this C are the self-capacitance of the cluster, the dielectric constant of the octanedithiol layer $\left(\epsilon \sim 3\right)$ and the effect of the substrate. The other possible contributions are attributed to the effect of nearest-neighbor clusters and the electron spillout from the cluster and substrate due to the coupling between the molecular orbital and the conducting electrons.

• Received 8 March 2002

DOI:https://doi.org/10.1103/PhysRevB.66.115410