Formation of CuO whiskers and facet-controlled oxidation during the oxidation of Au-Cu nanoparticles fabricated by solid-state dewetting

Abstract

The fabrication of cupric oxide (CuO) nanowires from Cu particles via thermal oxidation provides a simple and scalable method to produce hierarchical structures. A stress-induced growth mechanism is believed to account for the nanowire formation while a slow oxidation rate is favored to sustain the driving force. Here, CuO whiskers are grown from Au-Cu nanoparticles because the formation of Au-Cu phases decreases the Cu diffusion rate and in turn slows down the oxidation rate. The driving force for the whisker growth is attributed to the compressive stress imposed by the CuO shell on the Au-Cu core, which is induced by the significantdifference in their linear thermal expansion coefficients. The contribution of the compressive stress is proved by the calculation. Moreover, preferred oxidation is observed and it is related to the crystalline structures of different facets existing on the surface of Au-Cu nanoparticles. The more compact the plane, the slower the diffusion rate through the plane, resulting in the formation of thinner CuO on the relevant facet. The results open a cost-effect way to fabricate hybrid nanostructures consisting of Cu-based core–shell nanoparticles attached with CuO whiskers and bring new insights into the oxidation behaviors of Cu on different crystal planes.