Study On Theoretical Design And Regulation Mechanism Of Spectral Radiation Characteristics Of Micro/Nano Structures

The research on the regulation of the spectral radiation characteristics of micro/nano structures is a comprehensive subject field combining materials,physics and micro/nano processing.It has a wide range of applications in the fields of radiant cooling,solar desalination and gas detection.How to enhance the interaction between electromagnetic waves and matter has always been a hot research field.Past studies have shown that a variety of abnormal electromagnetic responses supported by sub-wavelength micro/nano structures can be used to control the spectral radiation characteristics of micro/nano structures.Although a lot of work has been done in the direction of spectral radiation characteristics regulation of the micro/nano structures,but it involves how to achieve broadband perfect absorption for a specific band,how to achieve narrowband perfect absorption at the communication wavelength on the basis of reducing the difficulty of processing,how to enhance the interaction of two-dimensional materials with light to improve their localized absorptance,how to use graphene and phase change materials to achieve active regulation of spectral radiation characteristics,etc.,and further research is still needed.This thesis mainly focuses on the following aspects in theory to address the above-mentioned problems:Firstly,based on the localized surface plasmon resonances excited by Au nanoparticles,a monolayer MoS₂-based composite structure is proposed to achieve broadband absorption in the visible band.The localized field in the monolayer MoS₂ is enhanced through the combined action of the Au nanoparticle array and the dielectric Bragg reflector in the composite structure,at the resonance wavelengths of 467.7 nm and 557.8 nm,the localized absorptance of the monolayer MoS₂ is about 3.01 times and 18.43 times higher than that of a suspended monolayer MoS₂,respectively.The proposed monolayer MoS₂-based composite structure can also be used in other transition metal dichalcogenides to achieve broadband absorption.In addition,the infrared broadband perfect absorber needs to achieve broadband absorption to improve energy conversion efficiency.Based on the strong absorption characteristics of indium tin oxide（ITO）nanowires at their ENP（epsilon-near-pole）and ENZ（epsilon-near-zero）resonance wavelengths,it is proposed to use stacked multilayer ITO nanowires with different doping concentrations to achieve broadband perfect infrared absorption.By optimizing the doping concentration,volume filling factor and length of each layer of ITO nanowires,the stacked five-layer ITO nanowires can achieve broadband perfect absorption in the wavelength range of 1.7-8μm.Secondly,based on the Tamm plasmon polaritons（TPPs）mode combined with monolayer WS₂,a monolayer WS₂-based TPPs structure is proposed to achieve perfect absorption in the visible band.Meanwhile,according to the strong field confinement in the spacer layer between the metal and the dielectric Bragg reflector when the TPPs structure excites the TPPs mode,and the coupling enhanced exciton transition localized absorption of monolayer WS₂ is achieved by adjusting the resonance wavelength of the monolayer WS₂-based TPPs structure to match the exciton peak of the monolayer WS₂.Results show that with the help of the monolayer WS₂-based TPPs structure,A exciton transition localized absorptance of 90.2%can be achieved,which is nearly 5 times higher than that of the suspended monolayer WS₂.Thirdly,based on TPPs mode and coupled mode theory,a graphene-based Tamm plasmon polaritons structure is proposed.Results show that its spectral absorptance is about99%at the communication wavelength,and the full width at half-maximum is only 2.5 nm,and the localized absorptance of graphene is about 32.6 times higher than that of a suspended graphene.However,exciting TPPs mode requires a complicated multilayer structure design and exciting guided mode resonance requires a special pattern design,which will greatly increase the manufacturing cost and cause damage to the graphene and affect the performance of the graphene.Therefore,based on Fabry-Pérot（FP）resonance,a graphene-based FP structure that is easier to process is proposed.Results show that its spectral absorptance is about 99.9%at the communication wavelength,the full width at half-maximum is 33 nm,and the localized absorptance of graphene is about 36.2 times higher than that of a suspended graphene.In addition,the chemical potential of graphene can be actively tuned by applying gate voltage.Based on TPPs mode and coupled mode theory,a dual-narrowband near-infrared absorber based on graphene electrical tuning is proposed.In this absorber,FP resonance and guided mode resonance can be excited at the same time under TM polarization,dual-narrowband absorption peaks are obtained;only FP resonance can be excited under TE polarization,one narrowband absorption peak is achieved.Further studies indicate that active tuning of the absorption peak can be achieved without changing the FP and guided mode resonance wavelengths by adjusting the chemical potential of graphene.Finally,based on the defect mode of one-dimensional photonic crystal（1DPh C）,single-channel or multi-channel spectral transmission tuning can be achieved in the mid-infrared band by adding single or multiple phase change material Ge₂Sb₂Te₅ defect layers in 1DPh C,and it is used in the design of the optical filter in the non-dispersive infrared spectrum detection technology.In addition,the phase-change material Ge₂Sb₂Te₅and graphene are used to actively tune the hyperbolic phonon polaritons of h BN and realize tunable multi-channel spontaneous emission rate enhancement of h BN.