Strain and plasmonic field induced modifications of material excitation response in monolayer MoS2

We report Raman and photoluminescence (PL) emission spectroscopy studies on monolayer MoS2/gold micro-disc hybrid structures. The observed frequency shift and broadening of phonon modes of the monolayer MoS2 are mainly the manifestations of the mechanical strain rather than the plasmonic field induced electron doping. We also observe considerable enhancement of the phonon mode intensities as a consequence of the surface enhanced Raman scattering caused by the plasmonic fields. The interaction of localized surface plasmon resonances (LSPRs) excited near the edge of the micro-discs with excitons in the monolayer MoS2 enhances A exciton emission, while suppressing that from B excitons and the trions. The changes in the PL emission near the edge are attributed to the modification of the emission rate via the Purcell effect, whereas the PL quenching on a relatively flat disc surface is due to lower density and the non-radiative nature of LSPRs.