Superior Oxygen Stability of N-Heterocyclic Carbene-Coated Au Nanocrystals: Comparison with Dodecanethiol.

The stability of Au nanocrystals (NCs) coated with different N-heterocyclic carbenes (NHCs) or dodecanethiol (DDT) to oxygen-based treatments was investigated. A dominant effect of the ligand type was observed with a significantly greater oxygen resistance of NHC-coated Au NCs compared to that of the thiol-based analogues. NHC-coated Au NCs are stable to 10 W oxygen plasma etching for up to 180 s whereas the integrity of DDT-coated Au NCs is strongly affected by the same treatment from 60-80 s. In the latter case, the average size of the NCs (from 2.6 to 6.3 nm) and the method of synthesis have no effect on the stability. NHC-coated Au NCs were found to generate of a smaller quantity of ligand-derived species under molecular oxygen treatment, which could account for the increased stability.