Surface Plasmon-driven Hot Electron Flow Probed with Metal-semiconductor Nanodiodes

Abstract

A continuous flow of hot electrons that are not at thermal equilibrium with the surrounding metal atoms is generated by the absorption of photons. Here we show that hot electron flow generated on a gold thin film by photon absorption (or internal photoemission) is amplified by localized surface plasmon resonance. This was achieved by direct measurement of photocurrent on a chemically modified gold thin film of metal-semiconductor (TiO2) Schottky diodes. Photons coupled into the modified gold thin film excite surface plasmon resonance, which enhances hot electron flows going over Schottky barrier between the gold film and TiO2. The short-circuit photocurrent obtained with low-energy photons is consistent with Fowler’s law, confirming the presence of hot electron flows. The morphology of the metal thin film was modified to a connected gold island structure after heating such that it exhibits surface plasmon. Photocurrent and optical measurements on the connected island structures revealed the presence of a localized surface plasmon at 550 ± 20 nm. The results indicate an intrinsic correlation between the hot electron flows generated by internal photoemission and localized surface plasmon resonance. We discuss the effect of dye molecules adsorbed on gold film in the efficiency of internal photoemission.