Comparative STM studies of mixed ligand monolayers on gold nanoparticles in air and in 1-phenyloctane.

Scanning tunnelling microscopy (STM) studies have found stripe-like domains on gold nanoparticles (NPs) coated with certain binary mixtures of ligand molecules. The majority of these NPs' properties have been investigated for particles in solvents. Yet, most STM studies are for NPs in a dry state. Images of the same particles in air and liquid have not been obtained yet. In this work, a judicious choice of ligand molecules led to NPs with close-to-ideal STM imaging conditions in air and in 1-phenyloctane (PO). Large datasets under both conditions were acquired and rapidly evaluated through power spectral density (PSD) analysis. The result is a quantitative comparison of stripe-like domains in air and PO on the same NPs. PSD analysis determines a characteristic length-scale for these domains of ~1.0 nm in air and in PO showing persistence of striped domains in these two media. A length scale of ~0.7 nm for homoligand NPs was found.