Single Particle Studies on Plasmon Enhanced Photoluminescence of Monolayer MoS2 by Gold Nanoparticles of Different Shapes

Plasmon-exciton interactions between noble metal nanostructures and two-dimensional (2D) transition metal dichalcogenides (TMDCs) have drawn great interest due to significantly enhanced optical properties in these systems. Plasmon resonance of noble metal nanoparticles and plasmon-exciton interactions are strongly dependent on the particle morphology. Single particle spectroscopic studies can overcome the ensemble average effects of sample inhomogeneity to unambiguously reveal the effects of particle morphology. In this work, plasmon modulated emission of MoS2 in various plasmonic-MoS2 hybrid structures has been studied on the single particle level. Gold (Au) nanoantenna of different shapes including nanosphere, nanorod, nanocube, and nanotriangle with similar overall dimensions, which have different sharp tips and contact area with MoS2, have been chosen to explore the particle shape effects. Different extent of enhancement in photoluminescence of MoS2 was observed for Au nanoantenna of different shapes. It was found that Au nanotriangle gave the highest enhancement factor while Au nanosphere gave the lowest enhancement factor. Numerical simulation results show that the dominant contribution arises from increased quantum yield while enhanced excitation efficiency just plays a minor role. The quantum yield enhancement is affected by both the sharp tips and contact mode of Au nanoantenna with MoS2. Polarization of MoS2 emission was also found modulated by plasmon mode of Au nanoantenna. These single particle spectroscopic studies allow us to unambiguously reveal the effects of particle morphology on plasmon enhanced PL in these nano-hybrid to provide better understanding of the plasmon-exciton interactions.