Engineering of Oxide Protected Gold Nanoparticles.

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 GaO shells on Au nanoparticles, based on liquid-phase chemical oxidation of Au-Ga alloy nanoparticles. We demonstrate that, with this technique, laminar and ultrathin GaO 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 GaO shell growth. Finally, we demonstrate that the GaO 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.