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

Abstract

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 WSe 2 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 WSe 2 . 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.