Resonance Coupling in an Individual Gold Nanorod-Monolayer WS2 Heterostructure: Photoluminescence Enhancement with Spectral Broadening

Recently, resonance coupling between plasmonic nanocavity and two-dimensional semiconductors has attracted considerable attention. Most of the previous studies have focused on demonstrating this effect with light scattering or reflection spectroscopy, while the photoluminescence (PL) spectrum can help ascertain the underlying physics. Here, we report on the light-emitting characteristics of a monolayer WS2 flake coupled with a plasmonic gold nanorod. We construct a heterostructure by integrating an individual gold nanorod on top of a small piece of monolayer WS2, where the WS2 area is determined by the projected area of the nanorod. In such a heterostructure, the background PL from the uncoupled WS2 can be suppressed, which allows us to characterize the resonance coupling effect using correlated single-particle dark-field (DF) scattering and PL spectroscopies. Distinct mode splitting and anticrossing dispersion are observed in the scattering spectra, which originate from the resonance coupling between the excitons in the WS2 and plasmon resonance in the gold nanorod. In addition, a 1187-fold enhancement is obtained for the light emitted from the heterostructure relative to that of the pristine monolayer WS2. The emission spectra are broadened with mode-splitting features at room temperature, which can be further decomposed into two resonance modes using a coupled mode analysis. Moreover, two PL modes are polarized along the longitudinal axis of the gold nanorod. These findings show the potential of the designed individual gold nanorod-monolayer WS2 heterostructure as a platform for studying the resonance coupling effect between plasmon resonance and two-dimensional excitons.