Watching Plasmon-Induced Nanoparticle Ostwald Ripening

Light-absorbing plasmonic nanostructures are used in a variety of applications, including photocatalysis and sensing. Because structure is intricately linked to function and performance, it is essential to understand how the structures of these materials might evolve under light excitation and what are the types and atomic natures of these structural transformations. Using a transmission electron microscope equipped with the capability of laser excitation of the specimen, we monitored the structures of Au–Cu alloy nanoparticles under plasmonic excitation. Plasmonic excitation was found to induce Ostwald ripening of nanoparticles. This process occurs in a switch-like manner distinct from electron-beam-induced coalescence that we also observe. This structural transformation is not induced by heating and is an example of a nonthermal structural transformation induced by plasmonically excited carriers. These results inform us about potential transformations of plasmonic nanostructures that can occur under operating conditions of plasmonic photocatalysis or plasmon-assisted electrocatalysis, where a high areal density of plasmonic nanoparticles supported on a substrate is subjected to continuous light excitation.