Watching Plasmon-Induced Nanoparticle Ostwald Ripening

Light-absorbing plasmonic nanostructures are used ina varietyof applications, including photocatalysis and sensing. Because structureis intricately linked to function and performance, it is essentialto understand how the structures of these materials might evolve underlight excitation and what are the types and atomic natures of thesestructural transformations. Using a transmission electron microscopeequipped with the capability of laser excitation of the specimen,we monitored the structures of Au-Cu alloy nanoparticles underplasmonic excitation. Plasmonic excitation was found to induce Ostwaldripening of nanoparticles. This process occurs in a switch-like mannerdistinct from electron-beam-induced coalescence that we also observe.This structural transformation is not induced by heating and is anexample of a nonthermal structural transformation induced by plasmonicallyexcited carriers. These results inform us about potential transformationsof plasmonic nanostructures that can occur under operating conditionsof plasmonic photocatalysis or plasmon-assisted electrocatalysis,where a high areal density of plasmonic nanoparticles supported ona substrate is subjected to continuous light excitation.