Modeling the impact of alkanethiol SAMs on the morphology of gold nanocrystals

Self-assembled monolayers (SAMs) are applied to gold nanoparticles to guide growth, increase stability, and provide additional functionality. However, as with any surface coating, the changes to the energetics of the surface can have unanticipated consequences, as well as introducing new opportunities. Understanding the relationship between the efficiency and type of SAMs and the underlying gold nanoparticles is challenging, but can be explored very efficiently using theory and computer simulation. In this paper, the relationship between the density of alkanethiol SAMs with different chain lengths and the shape of gold nanoparticles is reported as a function of size, including the impact of highly under-coordinated sites such as edges and corners. The results show that the most favorable sites for adsorption are on the {111} facets adjacent to the {111}|{111} edges (followed by the corners), but it is the concentration of SAMs on facets themselves that drives variations in the morphology. With the right choice of thiol and control of the SAM efficiency, it will be possible to create gold nanoparticles with a majority of either {111} or {100} facets, as required.