Simultaneous Surface-Enhanced Resonant Raman and Fluorescence Spectroscopy of Monolayer MoSe₂: Determination of Ultrafast Decay Rates in Nanometer Dimension

The fact that metallic nanostructures are an excellent light receiver and transmitter connects the underlying principles of two widely applied optical processes: surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF). A comparative study of SERS and SEF can eliminate the typical unknown quantities of the system and reveal important parameters that cannot be accessed by conventional techniques. Here, we use this simultaneous SERS and SEF technique in a monolayer MoSe₂ coupled plasmonic nanocavity. After optimizing the spatial and the spectral overlaps between excitonic and plasmonic resonances, the SERS and SEF enhancement factors can exceed 10⁷ and 6000, respectively, at the same time on the same nanocube. The comparison of the SERS and SEF enhancements allows the estimation of the ultrafast total decay rate of the bright exciton in monolayer MoSe₂ in the nanocavity down to tens of femtoseconds, which is otherwise hard to realize using time-resolved techniques.