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

Abstract

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–Cu_1.81S 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.