Engineering of Sub-Nanometer Oxide Shell on Gold Nanoparticles

Metal oxide shells fully or partially covering gold nanoparticles are intensively studied for a wide range of applications in the fields of catalysis and plasmonics. When carefully designed, these coatings enhance the functionality and stability of the nanoparticles. Yet, facile and well controlled fabrication methods of thin metal oxide layers on metal nanoparticles are still lacking. Currently used methods struggle to produce uniform layers below 1 nm. In this work, we show an easy fabrication process to reliably engineer uniform Ga₂O₃ shells on Au nanoparticles with a thickness ranging from sub- to several monolayers. These thin shells are obtained by a liquid-phase chemical oxidation of alloyed Au-Ga nanoparticles. We demonstrate how the plasmonic properties of the nanoparticles can be used to understand the reaction process and quantitatively monitor the Ga₂O₃ shell growth. Finally, we show as a practical application that the Ga₂O₃ coating prevents the sintering of the Au nanoparticles, ensuring thermal stability up to at least 250°C. Dealloying of bimetallic nanoparticles by in-solution oxidation is a promising approach to obtain controlled metal-metal oxide core-shell nanoparticles.