Mechanistic Analysis of Plasmon-Induced Charge Separation by the Use of Chemically Synthesized Gold Nanorods

Chemically synthesized Au nanorods (AuNRs) with different aspect ratios were used for plasmon-induced charge separation (PICS) at a Au–TiO2 interface to elucidate the dependence of its efficiency on photon energy. To produce good electrical contact between the AuNRs and TiO2, the AuNR–TiO2 electrode was washed with hot ethanol and annealed under reduced pressure to remove the cetyltrimethylammonium bromide that protected the AuNR surface. Each photocurrent action spectrum of the electrode showed two discrete peaks due to transverse and longitudinal modes as did the corresponding absorption spectrum, indicating that the photoresponse was derived from the plasmonic light absorption of the AuNRs. It was found that the internal quantum efficiency of the longitudinal mode was lower than that of the transverse mode. The photocurrent action spectra were reproduced from the absorption spectra on the basis of a model for an external photoelectric effect (hot electron injection) and an interference effect from the interband transition of Au; the threshold of photon energy was estimated to be 0.87 eV.