Amidation-Controlled Polymorphism in SnS Nanoparticles

Controlling the functionality of nanoparticles (NPs) requires molecular-level control over their surfaces often achieved by addition of surfactants such as the oleylamine (OLA)/oleic acid (OA) mixture. The surfaces of colloidal SnS NPs synthesized using OLA/OA mixtures have been studied theoretically and experimentally. We show that SnS NPs are capped by oleylamide, resulting from OLA and OA amidation reactions. The role of oleylamide in the synthesis of SnS was elucidated. Density functional theory calculations of ligand binding to the surfaces confirm the stabilization of the metastable cubic SnS by amides. This result indicates the critical role of amidation in this, and probably other, NP syntheses.