d-Band Holes React at the Tips of Gold Nanorods

Abstract

Reactive hot spots on plasmonic nanoparticles have attracted attention for photocatalysis as they allow for efficient catalyst design. While sharp tips have been identified as optimal features for field enhancement and hot electron generation, the locations of catalytically promising d-band holes are less clear. Here we exploit d-band hole-enhanced dissolution of gold nanorods as a model reaction to locate reactive hot spots produced from direct interband transitions, while the role of the plasmon is to follow the reaction optically in real time. Using a combination of single-particle electrochemistry and single-particle spectroscopy, we determine that d-band holes increase the rate of gold nanorod electrodissolution at their tips. While nanorods dissolve isotropically in the dark, the same nanoparticles switch to tip-enhanced dissolution upon illimitation with 488 nm light. Electron microscopy confirms that dissolution enhancement is exclusively at the tips of the nanorods, consistent with previous theoretical work that predicts the location of d-band holes. We, therefore, conclude that d-band holes drive reactions selectively at the nanorod tips.

Recent Developments in Single-Entity Electrochemistry

“…More recently, Landes and co-workers utilized hyperspectral dark field imaging to add spectral information to electrochemical dark field studies. − A recent example on the electrodissolution of gold nanorods (NRs) shows spectral differences between illuminated and nonilluminated NRs during the dissolution process, which is attributed to the involvement of d-electrons . The longitudinal plasmon mode of the nonilluminated NRs red shifts upon dissolution, reflecting an increase in the aspect ratio which is attributed to isotropic etching, while the illuminated NRs blue shift due to a decrease in the aspect ratio attributed to enhanced etching at the tips enabled by hot charge carriers.…”

Photocatalysis of Metallic Nanoparticles: Interband vs Intraband Induced Mechanisms

“…In principle, these interband hot holes should be better used to support the oxidative catalytic pathways in which the metal crystals accept electrons during the course of photocatalysis. This approach has been demonstrated for oxidation reactions or other reactions have the oxidation step as the rate-determining step. − ,,, In this section, we highlight some of those reactions and the catalytic role of “deep” holes from IBs. The term “deep” refers to the very low potential below E F .…”

Atomistic Theory of Hot-Carrier Relaxation in Large Plasmonic Nanoparticles

“…While the aforementioned modeling efforts allowed important insights into the relaxation dynamics of hot-carriers, it is important to note that they all employed highly simplified models of the NP electronic structure: they often use simple spherical well models or assume that the NP’s density of states is the same as that of a bulk-free electron gas. As a consequence, such models cannot capture hot-carriers generated in d bands, describe the dependence of the electronic structure on the exposed facets of the NP, or describe plasmonic heterostructures atomistically, all of which can play a critical role. − …”

“…As a consequence, such models cannot capture hot-carriers generated in d bands, 17 describe the dependence of the electronic structure on the exposed facets of the NP, 18 or describe plasmonic heterostructures atomistically, 19 all of which can play a critical role. 20 − 24 …”