Intermetallic nanocrystals are a large family of emerging materials with extensive applications in many fields. Yet, a generalized synthetic method for intermetallic nanocrystals is lacking. Here, we report the development of a colloidal synthesis method based on amalgamation of monometallic nanocrystal seeds with low–melting point metals. We use this approach to achieve crystalline and compositionally uniform intermetallic nanocrystals of Au-Ga, Ag-Ga, Cu-Ga, Ni-Ga, Pd-Ga, Pd-In, and Pd-Zn compounds. We demonstrate both compositional tunability across the phase spaces (e.g., AuGa2, AuGa, Au7Ga2, and Ga-doped Au), size tunability (e.g., 14.0-, 7.6-, and 3.8-nm AuGa2), and size uniformity (e.g., 5.4% size deviations). This approach makes it possible to systematically achieve size- and composition-controlled intermetallic nanocrystals, opening up a multitude of possibilities for these materials.

Gold nanoparticles that are partially or fully covered by metal oxide shells provide superior functionality and stability for catalytic and plasmonic applications. Yet, facile methods for controlled fabrication of thin oxide layers on metal nanoparticles are lacking. Here, we report an easy method to reliably engineer thin Ga2O3 shells on Au nanoparticles, based on liquid-phase chemical oxidation of Au–Ga alloy nanoparticles. We demonstrate that, with this technique, laminar and ultrathin Ga2O3 shells can be grown with ranging thickness from sub- to several monolayers. We show how the localized surface plasmon resonance can be used to understand the reaction process and quantitatively monitor the Ga2O3 shell growth. Finally, we demonstrate that the Ga2O3 coating prevents sintering of the Au nanoparticles, providing thermal stability to at least 250 °C. This approach, building on dealloying of bimetallic nanoparticles by the solution-phase oxidation, promises a general technique for achieving controlled metal/oxide core/shell nanoparticles.

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