The advance in designing arrays of ultrathin two-dimensional optical nano-resonators, known as metasurfaces, is currently enabling a large variety of novel flat optical components. The remarkable control over the electromagnetic fields offered by this technology can be further extended to the active regime in order to manipulate the light characteristics in real-time. In this contribution, we couple the excitonic resonance of atomic thin MoS2 monolayers with gapsurface-plasmon (GSP) metasurfaces, and demonstrate selective enhancement of the excitonplasmon polariton emissions. We further demonstrate tunable emissions by controlling the charge density at interface through electrically gating in MOS structure. Straddling two very transition, to both explore and advance the manipulation of light-matter interactions at the subwavelength dimensions, thus leading to novel nanoscale polaritonic optoelectronic devices.

Accessing the metastable phases in a controlled fashion can further expand the applications of atomically thin transition metal dichalcogenides (TMDs). Although top-down approaches based on ion intercalation exfoliation have shown to be an effective route to transform 2H phase into 1T and/or 1T′ polytype phases, a bottom-up growth strategy could be more suitable for device integration. Herein, we show that by assisting the atmospheric pressure chemical vapor deposition (APCVD) growth with a specific alkali metal halide (AMH), it possible to induce the direct synthesis of 1T phase domains coexisting with 2H phase structure in micrometer-sized MoS2 monolayer flakes. The photoluminescence emission and structural properties of three different AMH (NaCl, KBr and KCl) MoS2 crystals are compared. Both NaCl and KBr assisted MoS2 monolayers displayed the semiconducting 2H-phase. On the other hand, we demonstrate that KCl promotes the formation of a 1T–2H phase mixture. X-ray photoemission spectroscopy and resonant Raman studies performed on KCl–MoS2 monolayers show the emergence of a second chemical state and 1T Raman bands compared to the rest of the samples. High-resolution scanning transmission electron microscope imaging revealed important changes in the atomic arrangement between 2H and 1T domains, providing clear evidence of the presence of the 1T metastable phase in the lattice. Moreover, the growth 1T domains can also be controlled by modifying the deposition temperature. Our experiments show that the introduction of KCl during the APCVD growth result in stable 1T-MoS2 domains, providing a simple and reproducible route towards the polymorphism phase engineering of layered TMDs using a direct bottom-up approach.

Two-dimensional molybdenum disulfide (MoS2) featuring atomically thin thickness and unique electronic structure with favorable bandgap has been widely recognized as an attractive new material for the development of the next generation of ultra-compact, light-weight optoelectronic components. In parallel, the recently emerged metasurfaces have demonstrated exceptional controllability over electromagnetic field within ultra-compact subwavelength dimension offering an unprecedented approach to improve the performance of optoelectronic devices. In this work, we are proposing an integration of metasurfaces with 2D semiconductor materials to achieve polarization sensitive, fast-response photodetectors. The reported devices are among the most compact hybrid MoS2-gap-plasmon metasurface detectors. Relying on the significant electromagnetic field confinement provided by the metasurfaces to enhance light absorption and to reduce the surface states, which generally limit the photo-generated carriers lifetime, we measured enhanced photocurrent and a fast detection speed. Moreover, the strong optical anisotropy introduced by the metasurfaces is used to efficiently control the polarization sensitivity of the photodetector. This work provides a feasible and effective solution to improve the performance of two-dimensional materials based photodetectors.