<i>In Situ</i> Observation of Atomic Redistribution in Alloying Gold–Silver Nanorods

The catalytic performance and optical properties of bimetallic nanoparticles critically depend on the atomic distribution of the two metals in the nanoparticles. However, at elevated temperatures, during light-induced heating, or during catalysis, atomic redistribution can occur. Measuring such metal redistribution <i>in situ</i> is challenging, and a single experimental technique does not suffice. Furthermore, the availability of a well-defined nanoparticle system has been an obstacle for a systematic investigation of the key factors governing the atomic redistribution. In this study, we follow metal redistribution in precisely tunable, single-crystalline Au-core, Ag-shell nanorods <i>in situ</i>, both at a single particle and an ensemble-averaged level, by combining <i>in situ</i> transmission electron spectroscopy with <i>in situ</i> extended X-ray absorption fine structure validated by <i>ex situ</i> measurements. We show that the kinetics of atomic redistribution in Au–Ag nanoparticles depend on the metal composition and particle volume, such that a higher Ag content or a larger particle size led to significantly slower metal redistribution. We developed a simple theoretical model based on Fick’s first law that can correctly predict the composition- and size-dependent alloying behavior in Au–Ag nanoparticles, as observed experimentally