Scanning tunneling microscopy and spectroscopy of palladium clusters supported on graphite

Abstract

The surface of palladium clusters supported on graphite has been investigated with a scanning tunneling microscope in ultrahigh vacuum. Electron tunneling spectra were measured for clusters of different sizes. The surface density of electronic states at the Fermi energy presents a strong size dependence for small clusters and becomes size independent for clusters larger than a critical volume. This phenomenon has been interpreted in terms of the size-dependent electronic structure of the particles.