Mixing of Immiscible Components by the Size Effect: A Case Study of Au-Ni Nanostructures

Modern catalysts widely utilize multicomponent nanosized materials and structures, and the interphase interactions in such systems are still unresolved in many aspects. In this work, we present the results of the experimental investigation of interface interactions in Au-Ni bimetallic nanostructures using advanced electron microscopy techniques. Nanoparticles were formed in a vacuum by the sequential condensation of components. The formation of solid solutions was investigated by high-resolution high-angle annular dark-field scanning transmission electron microscopy, electron diffraction, Xray energy-dispersive spectrometry, and electron energy loss spectroscopy methods down to the atomic level while heating Au-Ni nanoparticles in a transmission electron microscope. It has been shown that Au and Ni, which are immiscible in bulk, form a homogeneous solid solution at room temperature upon the reduction of size down to approximate to 2 nm. The resulting solid solution has a random alloy structure and provides long-term stability characteristics to equilibrium alloys. This effect has been analyzed in the framework of available approaches.