Copper assisted symmetry and size control of gold nanobars

Shape and size control of metal nanocrystals has become a powerful tool in tuning their physicochemical properties for applications, however, the growth mechanisms controlling shape and size are not fully elucidated. Gold nanocuboids provide a simple nanoparticle system for investigating nanocrystal growth mechanisms. Here, we study the control over size and shape anisotropy of gold nanocuboids by copper additives. We first optimize the synthesis and yield. We find that, in the presence of copper additives, symmetry is broken and anisotropic growth can occur, leading to nanobars, rather than nanocubes, accompanied by a significant reduction in particle size. We show that symmetry breaking is caused by a combination of rapid deposition on {111} facets coupled with the slow surface diffusion rate introduced by surface copper. This reveals a mechanism by which metal additives can cause symmetry breaking and control shape in nanoparticle growth.