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In the recent decade two-dimensional transition metal dichalcogenides (2D TMDs) has attracted great attention in a variety of optoelectronic applications including photodetectors, optical chemical sensors, light-emitting diodes, lasers, and opto-valleytronic devises because of their high ON/OFF current ratios, low sub-threshold switching, strong photoluminescence, controllable valley polarization and high thermal stability. Despite their excellent optoelectronic properties, their optoelectronic applications are limited by the weak light-matter interaction in 2D TMDs due to the atomic thickness. Because plasmonic metal nanoparticles (NPs) have the capability to concentrate light beyond the diffraction limit, there is an emerging trend of exploiting light-matter interactions in hybrid systems consisting of 2D TMDs and plasmonic metal NPs for boosting the performance of 2D TMD-based optoelectronic devices. Plasmonic metal NPs have been employed to enhance light-matter interactions in quantum emitters including dye molecules and quantum dots through mechanisms such as Fano interference, strong coupling, plasmon-induced resonance energy transfer, and plasmon-enhanced emission. However the understanding and the active control of the interaction between 2D TMD and plasmonic NPs are still limited. So, herein, we report two tunable plasmon-exciton interactions that are novel in hybridized systems consist of 2D TMD and plasmonic NPs: (1) tunable plasmon-induced resonance energy transfer from a single Au nanotriangle (AuNT) to monolayer MoS2; (2) tunable Fano resonance and plasmon-exciton coupling in a single AuNT on monolayer WS2 at room temperature. In the first case, we report the first observation and tuning of plasmon-trion and plasmon-exciton resonance energy transfer (RET) from a single AuNT to monolayer MoS2 at room temperature. We achieved these phenomena by the combination of rational design of hybrid 2D TMD-plasmonic NP systems and single-nanoparticle measurements. By combining experimental measurements with theoretical calculations, we conclude that the efficient RET between SPs of metal NPs and excitons or trions in monolayer MoS2 is enabled by the large quantum confinement and reduced dielectric screening in monolayer MoS2. In the second case, we report tunable Fano resonances and plasmon-exciton coupling in 2D WS2-AuNT hybrids at room temperature. The tuning of Fano resonances and plasmon-exciton coupling was achieved by active control of the WS2 exciton binding energy and dipole-dipole interaction through controlling the dielectric constant of the surround medium. Specially, Fano resonances are controlled by the exciton binding energy or the localized surface plasmon resonance (LSPR) strength through tuning the dielectric constant of surrounding solvents or the dimension of AuNTs. Additionally, we observe a transition from weak to strong plasmon-exciton coupling when increasing the dielectric constant of surrounding solvents. Large coupling strength of 80-100 meV is obtained at room temperature due to the strong field localization of the AuNTs and large transition dipole moment of the WS2 exciton. Our results provide guidance on systematic tuning of the Fano line-shape and Rabi splitting energies at room temperature for 2D TMD-plasmonic NP hybrids.
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