Plasmon-Resonant Enhancement of Photocatalysis on Monolayer WSe2

We report plasmonic enhancement of photocatalysis by depositing 5 nm Au nanoislands onto tungsten diselenide (WSe2) monolayer films. Under 532 nm wavelength illumination, the bare WSe2 film produces a relatively small photocurrent (20 nA). With the addition of Au nanoparticles, we observe enhancements of up to 7x (0.14 mu A) in the measured photocurrent. Despite these relatively small photocurrents, it is remarkable that adequate charge separating fields are generated over just 7.3 angstrom of material. Here, the improvement in the photocatalytic performance is caused by the local electric field enhancement produced in the monolayer WSe2 monolayer by the plasmonic Au nanoislands, as verified by electromagnetic simulations using the finite different time domain (FDTD) method. The near-field optical enhancement increases the electron-hole pair generation rate at the surface of WSe2, thus, increasing the amount of photogenerated charge contributing to increasing the amount of photogenerated charge contributing to photoelectrochemical reactions. Despite reducing the effective surface area of WSe2 in contact with the electrolytic solution by 70%, the plasmonic nanoislands couple the incident light very effectively from the far field to the near field in the plane of the monolayer WSe2, thereby improving the overall photoconversion efficiency from 3.5% to 24.7%.