On the Atomic Scale Diffusion in Au–Ag Nanoparticles

We reported in situ scanning electron microscopy studies of the diffusion process in individual core–shell Au–Ag particles in the temperature range of 548–723 K. The diameter of the Au core was ∼6 nm, and the thickness of the Ag shell was 6.5 nm. We studied diffusion across defect-free boundaries between the metals with a spatial resolution of 0.11 nm. The activation energy and frequency factor for defect-free particles are E_a = 167 ± 6 kJ/mol and D₀ = (1.8 ± 0.6) · 10^–3 cm²/s, respectively. These values are similar to those for bulk materials. The diffusion coefficient for the particles with boundary defects was shown to be several orders of magnitude higher than that for the defect-free particles. Obtained results allow us to rationally explain all reported results on solid-state diffusion in the Au–Ag systems, mainly that the self-alloying is primarily the result of the defects rather than the size of the particles.