Nanoscale probing of interfaces between nanoparticles and support with atomic force microscopy

Abstract

Shape control of metal nanocrystals has broad applications, including catalysis, plasmonics, and sensing. It was found that controlling the atomic arrangement on metal nanocrystal surfaces affects many properties, including the electronic dipole or work function. Tuning the surface structure of exposed facets of metal nanocrystals was enabled by shape control. We investigated the effect of shape on nanomechanical properties, including friction and adhesion forces. Two nanoparticles systems, cube nanocrystal (NC) with low-index were and hexoctahedral (HOH) NC with high-index (321) surface, were used as model nanoparticle surfaces. Scanning force microscopy was used to probe nanoscale friction and adhesion on the nanoparticle surface. Capping layers on the nanoparticle surface was removed via ethanol washing. While the adhesion on the nanoparticle with capping layer didn’t show shape dependence, after removal of capping layers, the cube Au NC exhibited the higher adhesion force compared to HOH Au NC. Because of the abundant presence of high-density atomic steps and kinks, high-index faceted nanoparticles have the more corrugated surface, than low-index nanoparticles, that results in the lower contact area, and thus lower adhesion. The study shows that the surface structure on the nanoparticle can be directly probed with adhesion and friction mapping with atomic force microscopy.