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 HAuCl(4). Using presynthesized Cu-Cu(1.81)S hetero-oligomer and Cu-Cu(2)S heterodimer NCs as templates and reactants, the controlled addition of HAuCl(4) 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.