Theoretical description of the role of amine surfactant on the anisotropic growth of gold nanocrystals

Amine molecules are very commonly used surface agents in the shape-controlled synthesis of nanocrystals. In the case of amine-mediated synthesis of Au nanowires, the roles of the amine molecules were studied using theoretical calculation and correspondingly, the mechanism for the anisotropic growth of Au nanowires is discussed. Two features of amine molecules as surfactants in the synthesis system for colloid nanocrystals were found and deeply studied. One feature is the self-assembly of amine molecules induced by the strong interaction between the long carbon-chains. The theoretical calculation result shows that the interaction energy between amine molecules becomes larger when the carbon chain length increases. This result indicates that the amine molecules with longer carbon chains more preferentially self-assembly through their carbon-chains as they adsorb onto nanoparticles. The other feature is the large difference of adsorption energies on the Au (100) and (111) facets. These two features of the oleylamine molecules play important roles on the anisotropic growth of Au nanocrystal along the direction. This study will help to further understand the functions of amine molecules in the synthesis of colloidal nanocrystals. Two functions of oleylamine molecules as surfactants were found and studied, which performed key roles in the anisotropic growth of Au nanowires.