Direct Imaging of Surface Plasmon-Driven Hot Electron Flux on the Au Nanoprism/TiO2

Direct measurement of hot electron flux from a plasmonic Schottky nanodiode is important for obtaining fundamental insights explaining the mechanism for electronic excitation on a surface. Here, we report the measurement of photoinduced hot electrons on a triangular Au nanoprism on TiO2 under incident light with photoconductive atomic force microscopy (pc-AFM), which is direct proof of the intrinsic relation between hot electrons and localized surface plasmon resonance. We find that the local photocurrent measured on the boundary of the Au nanoprism is higher than that inside the Au nanoprism, indicating that field confinement at the boundary of the Au nanoprism acts as a hot spot, leading to the enhancement of hot electron flow at the boundary. Under incident illumination with a wavelength near the absorption peak (645 nm) of a single Au nanoprism, localized surface plasmon resonance resulted in the generation of a higher photoinduced hot electron flow for the Au nanoprism/TiO2, compared with that at a wavelength of 532 nm. We show that the application of a reverse bias results in a higher photocurrent for the Au nanoprism/TiO2, which is associated with a lowering of the Schottky barrier height caused by the image force. These nanoscale measurements of hot electron flux with pc-AFM indicate efficient photon energy transfer mediated by surface plasmons in hot electron-based energy conversion.