Research On The Coupling Mechanism Based On Two Dimensional Materials And Plasmon

After entering the information age,with extensive use of optoelectronic devices,there is an increasing requirement of their dimensions.Due to the diffraction limit,the dimensions of optoelectronic devices based on traditional solid materials cannot be scaled down without limit.It is vital to scale down the dimensions of the structures and thus achieve the miniaturization of optoelectronic devices,promoting the development of optoelectronic integration technology.Surface plasmons are evanescent waves generated by the externally electromagnetic field coupled with the collectively oscillation of the free electrons on the surface of a metal material.They can break through the optical diffraction limit and greatly reduce the mode volume.It provides a promising solution to achieve nanophotonic devices.Recently,two-dimensional（2D）materials have attracted extensive attention due to their unique layered structures and excellent optoelectronic properties.Compared with traditional bulk materials,2D materials own atomic thickness,enabling the widespread use in nanophotonic devices.However,the ultrathin thickness severely affects the interaction between 2D materials and light.The tiny volume of surface plasmons is conducive to enhancing the light-matter interaction in 2D materials.The research based on the plasmon coupling mechanism of 2D materials is of great significance to promote the development of nanophotonics.According to this,the coupling mechanism based on surface plasmons in 2D materials are studied here,which is described as follows:1.Absorption enhancement in black phosphorus based on localized surface plasmon resonanceThe localized surface plasmon resonance（LSPR）excited by metal nanostructures breaks through the diffraction limit and realizes the enhancement of light absorption by 2D materials black phosphorus（BP）.Owing to the adjustment of bandgap with the thickness,two different structures based on BP are proposed for visible and mid-to-far infrared bands.The first one is the BP optical absorption structure integrated with nanoscale grating.The absorption characteristics of the BP-nanograting structure are studied by using the finite difference time domain（FDTD）method in the visible light band.The simulation results show that LSPR is produced at the interface between BP layer and the grating.It exhibits a strong ability of field confinement,which greatly enhances the absorption in BP.It is known that LSPR is sensitive to the dimensions of the structure.By optimizing geometric parameters of grating structure,BP light absorption reaches 89.8%.The second one is the hybrid structure composed of BP nanoribbon arrays and metal grating slit.The LSPR effect excited by BP nanoribbon arrays and the extraordinary optical transmission（EOT）effect excited by metal grating slit structure are studied by using FDTD method in the middle and far infrared bands respectively.The maximum absorption of the hybrid structure is as high as 99.92%at the resonance wavelength of 8.9μm.The design strategy of metal nanostructures combined with BP can effectively improve BP light absorption,which further promotes the research of high-performance BP based nano photonic/optoelectronic devices and provides new ideas for composite structure design based on 2D materials.2.Strong coupling of localized surface plasmon mode and monolayer BP exciton modeThe strong coupling is realized by utilizing the ultra-small mode volume of plasmonic nanostructures and the large exciton binding energy of monolayer BP.The localized surface plasmon（LSP）mode is affected by the shape and dimensions of the metal structure.Due to this fact,BP-plasmonic coupling structures are proposed for realizing Rabi splitting in visible bands and Fano resonance in terahertz bands,respectively.The first one is Rabi splitting of coupled structure composed of monolayer BP with silver grating/disk structure at room temperature.The strong coupling mechanism of the structure is studied by establishing the coupled oscillator model（COM）.By employing the FDTD method,the dimensions of the proposed structure and the polarization angle of the incident light are optimized.Simulation results demonstrate that the splitting of reflection peaks occurs in the reflection spectra of the structure,which exhibits anti-crossover behavior on the spectra.The strong coupling between BP exciton mode and LSP mode results in Rabi splitting,with splitting energy up to 250 me V.The second one is the tunable Fano resonance of the coupled structure composed of bowtie BP and gold ring in the terahertz band.By employing the FDTD method,the dimensions of gold ring and the Fermi level of BP are optimized to achieve the dynamic tuning of the Fano resonance amplitude and frequency.Simulation results demonstrate that the Fano resonance is excited by the coherent cancellation of the resonance between the bowtie BP and the gold ring.The frequency sensitivity of the proposed structure is as high as 9.3μm/RIU and figure of merit（FOM）of 69.3.The design strategy of monolayer BP coupled with plasmon nanostructures effectively enhances the coupling strength between multimodes,which provides a new approach for the further development of applications based on strong coupled photons.3.Photoluminescence enhancement in monolayer molybdenum disulfide based on localized surface plasmonBased on the Purcell effect,a highly efficient photoluminescence（PL）coupling structure composed of monolayer molybdenum disulfide（Mo S₂）and the plasmon nanostructures is designed theoretically.The luminescence principle of monolayer Mo S₂ and Purcell enhancement mechanism of the coupling structure are clarified by establishing exciton energy level system.The absorption and PL properties of monolayer Mo S₂ are analyzed by employing the FDTD method.The simulation results show that the absorption and PL efficiency of monolayer Mo S₂ can be improved due to LSP excited by the gold nanoparticle array.Under the optimal structural parameters,the Purcell enhancement factor of the proposed structure is as high as 95.The design strategy of monolayer Mo S₂ coupled plasmon nanostructure provides a very promising platform for the further development of high-efficiency light-emitting devices based on MoS₂.