HREELS study of alkanethiol passivated gold clusters on graphite

Passivated metal (e.g. gold) nanoclusters consist of a metal particle core surrounded by a ligand coat. We have investigated films of gold particles passivated with alkanethiol (C8H17S) ligands deposited from solution onto a graphite surface using high-resolution electron energy loss spectroscopy (HREELS). Vibrational modes of the CHx groups of the ligands are observed, together with their overtones. Incident energy dependent measurements show an enhancement in intensity of these vibrational modes at a specific energy, ∼10 eV, consistent with a negative ion resonance state. This observation is compared with previous studies of self-assembled monolayers of thiols on the Au (111) surface.