Preferential Outward Diffusion of Cu during Unconventional Galvanic Replacement Reactions between HAuCl4 and Surface-Limited Cu Nanocrystals

Metal diffusion in nanoscale materials is of great Interest, yet the detailed kinetic behavior of such diffusion remains elusive. We observe direction-controlled Cu diffusion during unconventional galvanic replacement reactions between surface-limited Cu nanocrystals (NCs) and HAuCl4. Using presynthesized Cu-Cu1.81S hetero-oligomer and Cu-Cu2S heterodimer NCs as templates and reactants, the controlled addition of HAuCl4 leads to the preferential outward diffusion of Cu, visualized by the formation of single-crystalline and straight, or polycrystalline and kinked, CuAu nanowires, respectively. The time dependent growth of these nanowires enables determination of nanoscale diffusion coefficients of Cu during these processes, for the first time.