Light-Directed Growth/Etching of Gold Nanoparticles via Plasmonic Hot Carriers

Plasmon-induced hot carriers can be used to control both the growth and the etching behavior of gold nanoparticles (Au NPs) with laser irradiation. Here, the Au NPs placed on Si substrate are irradiated with a continuous wave laser (641 nm) in the presence of HAuCl₄ solution. Irradiation results in growth/etching of Au NPs depending on the power, time, and HAuCl₄ concentration. We reveal that the electronic band structure of the substrate plays a critical role in the growth/etching as it determines the charge transfer process. The growth is realized through the reduction of [AuCl₄]⁻ to Au(0) via hot-electron injection, while the holes are transferred to the substrate to avoid oxidative etching. If the holes are blocked due to the higher energy barriers or charge accumulation, only oxidative etching is observed. We further distinguish the hot-carrier-induced growth from that induced by plasmon-enhanced two-photon chemistry, where the latter is dominant in the Au nanorods/aggregates with large nonlinearity. Our results not only present a clear and in-depth understanding of the hot-carrier chemistry on the nanoparticles’ morphology but also provide a simple, in situ, and precise way to tune the size, shape, and compositions on a single-particle level, which is ready for on-chip fabrication and integration.