Ultrahigh Polarization-Sensitive Raman Scattering and Photon Emission in a Plasmonic Au/Biphenyl-4-thiol/Ag Nanowire Nanocavity

Reducing gap distance to the nanometer range exhibits a strong local electric field enhancement, providing a promising platform for exploring light-matter interactions at the nanoscale. Here, we designed and fabricated an anisotropic nanocavity using monolayer biphenyl-4-thiol (BPT) and WSe2 as a barrier and a Ag nanowire and Au film as a cavity, allowing local electric field enhancement by controlling the polarity of incident light. Strong and polarization-dependent Raman scattering of BPT molecules is observed, which may be applied for mid-infrared light detection. Moreover, the BPT monolayer can act as a uniformly distributed nanometer-size barrier layer to prohibit carrier transferring from WSe(2 )to the Au film. The nanometer barrier thickness induced a strong localized electric field that altered the carrier recombination paths in monolayer WSe2. Trion emission intensity is enhanced over 520 times at room temperature, and the dark state is observed at a temperature below 253 K. Below 173 K, a new low energy emission peak quickly outweighs the trion, exciton, and dark state emission and dominate the emission spectrum, which could be related to a strong exciton-plasmon coupling. Therefore, the designed nanocavity is an excellent platform to study the abundant emission phenomenon in transition-metal dichalcogenide and related heterostructures.