What is happening at the atomic level during the seed-mediated growth of copper on gold?

Yan, Yanzi; Li, Kei Kwan; Huang, Xintong; Yu, Xude; Ding, Yong; Xu, Jianhong; Xia, Younan · Sci Adv · 2026

basic_science · Level V

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Abstract

Bimetallic nanocrystals obtained via seed-mediated growth are typically analyzed using conventional electron microscopy and many interesting features at the atomic level are often missed. Here we report the seed-mediated growth of copper (Cu) on gold (Au) nanospheres for the synthesis of Au-Cu bimetallic nanocrystals enclosed by a Janus surface comprised of an ordered intermetallic phase and a disordered alloy. Initially, the abundant Cu(II) precursor enables uniform Cu deposition, followed by inter-diffusion to generate an ultrathin shell made of intermetallic Au<sub>1</sub>Cu<sub>1</sub>. The growth subsequently evolves into an asymmetric mode, where Cu deposition preferentially proceeds at one activated site to generate Au<sub>x</sub>Cu<sub>y</sub> alloy with a graded composition. When tested for nitrate reduction, the Janus nanocrystals show 100% Faradaic efficiency across a wide potential range and a high ammonia yield rate.