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Transition metal dichalcogenide (TMD) monolayers, with their direct band gaps, have attracted wide attention from the fields of photonics and optoelectronics. However, monolayer semiconducting TMDs generally suffer from low excitation absorption and emission efficiency, limiting their further applications. Here a flip‐over plasmonic structure comprised of silver nano‐disk arrays supporting a WS2 monolayer sandwiched by hexagonal boron nitride (h‐BN) layers is demonstrated. The flip‐over configuration optimizes the optical process with a free excitation/emission path from the top and a strong plasmonic interaction from the bottom. As a result, the photoluminescence from the TMD monolayers can be greatly enhanced more than tenfold by optimizing the metasurface, which can be further improved nearly tenfold by optimizing the thickness of bottom h‐BN. This study shows the advantages of using the flip‐over structure, where the plasmonic interaction between the metasurface and TMDs can be tuned by introducing optimized plasmonic arrays and h‐BN layers with suitable thickness. This hybrid device configuration paves a reliable platform to study the light–matter interaction, achieving highly efficient plasmonic TMD devices. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenide (TMDC) monolayers have enabled important applications in light emitting devices and integrated nanophotonics because of the direct bandgap, spin-valley locking and highly tunable excitonic properties. Nevertheless, the photoluminescence polarization is almost random at room temperature due to the valley decoherence. Here, we show the room temperature control of the polarization states of the excitonic emission by integrating WS2 monolayers with a delicately designed metasurface, i.e. a silver sawtooth nanoslit array. The random polarization is transformed to linear when WS2 excitons couple with the anisotropic resonant transmission modes that arise from the surface plasmon resonance in the metallic nanostructure. The coupling is found to enhance the valley coherence that contributes to ~30% of the total linear dichroism. Further modulating the transmission modes by optimizing metasurfaces, the total linear dichroism of the plasmon-exciton hybrid system can approach 80%, which prompts the development of photonic devices based on TMDCs. Here the authors show that WS2 coupled with a plasmonic sawtooth nanoslit array is an efficient exciton-plasmon hybrid system which enables polarization modulation of the excitonic emission at the nanoscale up to 80% and observation of valley coherence at room temperature. [ABSTRACT FROM AUTHOR]

Two-dimensional transition metal dichalcogenides have already attracted enormous research interest. To understand the dependence of electronic properties on the quality and defect morphology is vital for synthesizing high quality materials and the realization of functional devices. Here, we demonstrate the mapping of the conductive variations by conducting atomic force microscopy (C-AFM) in the monolayer tungsten disulfide (WS2) grown by chemical vapor deposition. The electronic properties are strongly affected by the formation of vacancies in monolayer WS2 during growth, which is also verified by the photoluminescence. This spatial study of defects provides opportunities for optimization of the growth process for enhancing devices performance of TMDs monolayers. [ABSTRACT FROM AUTHOR]

Superconductivity in monolayer tungsten disulfide (2H-WS2) is achieved by strong electrostatic electron doping of an electric double-layer transistor (EDLT). Single crystals of WS2 are grown by a scalable method − chemical vapor deposition (CVD) on standard Si/SiO2 substrate. The monolayers are identified by both AFM and color-coding techniques. The EDLT device based on single-layer WS2 shows ambipolar transfer characteristics indicating a semiconducting nature of the material. Metallic transport on the electron side evolves into superconductivity with critical temperature Tc = 3.15 K. [ABSTRACT FROM AUTHOR]

Superconductivity in monolayer tungsten disulfide (2H-WS2) is achieved by strong electrostatic electron doping of an electric double-layer transistor (EDLT). Single crystals of WS2 are grown by a scalable method − chemical vapor deposition (CVD) on standard Si/SiO2 substrate. The monolayers are identified by both AFM and color-coding techniques. The EDLT device based on single-layer WS2 shows ambipolar transfer characteristics indicating a semiconducting nature of the material. Metallic transport on the electron side evolves into superconductivity with critical temperature Tc = 3.15 K. [ABSTRACT FROM AUTHOR]