Surface Manipulation of the Electronic Energy of Subnanometer-Sized Gold Clusters: An Electrochemical and Spectroscopic Investigation

Stable undecagold clusters were synthesized and protected with a monolayer of alkanethiolates. The particles were found to exhibit semiconductor electronic characteristics with a band gap of about 1.8 eV, as evaluated from voltammetric and spectroscopic measurements. Photoluminescence in the visible range was also observed from the peak position at 840 nm. The indirect band-gap characteristics indicate that there exist substantial surface trap states in the nanoparticle molecules. Prior to exchange reactions with alkanethiols, however, no luminescence was observed with the gold particles, Au11Cl3(PPh3)7. This was interpreted, at least in part, by the effect of ligand fields on the electronic (band-gap) energy splitting and the resulting electron distributions. These observations strongly suggest that surface chemistry plays a vital role in determining the electronic energy structure of these subnanometer-sized gold particles.