Size‐Focusing of Au Nanoparticles through Dissolution–Renucleation Process Imaged with In Situ TEM

The transformation of large polydisperse nanoparticles (NPs) into small monodisperse ones by adding ligands is an important and powerful post-synthesis method for tuning the size and morphology of NPs. However, the mechanism of this widely used process is not well understood. Here, using in situ liquid-phase transmission electron microscopy (TEM), we show that the steps of this transformation are a complete dissolution of the original NPs and a subsequent renucleation and growth of new, smaller, uniformly-sized NPs. This work offers mechanistic insights into the synthesis of monodisperse NPs and highlights the importance of direct imaging in identifying the physical and chemical details of nanoscale processes that occur in a liquid phase.