Circular Differential Photocurrent Mapping of Hot Electron Response from Individual Plasmonic Nanohelicoids.

ABSTRACT

Chiral plasmonic nanocrystals have recently attracted increasing attention in circular polarization-dependent photocatalysis driven by hot carriers. While being concealed in traditional ensemble measurements, the individual chiral photocatalytic activity of nanocrystals can exclusively be revealed by directly correlating the circular differential photocurrent response to helical morphologies using single-particle techniques. Herein, we develop a method named circular differential photocurrent mapping (CDPM) and demonstrate that CDPM can be used to characterize the circular differential hot electron (CDHE) response from individual Au nanohelicoids (AuNHs) on a TiO2 photoanode in a photoelectrochemical cell. The single-particle circular differential scattering and CDHE measurements were interpreted with calculations performed on a model in direct correlation to the helical morphologies of the nanocrystal. While CDHE response was found inactive at a dipolar resonance of 750 nm, helicity-convoluted sites of HE generation were identified on the AuNH at a specific higher-order mode of 550 nm, resulting in a significant response of CDHE in association with the handedness of the AuNH. Details of circular differential contributions were further resolved by examining the efficiencies of individual AuNHs in terms of g-factors. Our study provides a powerful microscopic method at the single-particle level for the photocatalytic characterization of chiral nanocrystals, gaining fundamental insights into the photocatalysis of chirality, especially toward plasmon-induced asymmetrical photochemistry or photoelectrochemistry.