Enhanced Near-field Thermal Radiation Based On Coupled Surface Resonance Modes

Micro/nano optoelectronic devices have attracted much attention because of their small structure and high integration.When the dimension reaches hundreds of nanometers or even tens of nanometers,the thermal conductivity efficiency of heat conduction decreases significantly,which affects the working efficiency and life of the device.As one of the three channels of heat transfer,thermal radiation does not depend on molecular collision and surface contact.Micro-nano devices are expected to conduct heat away through near-field thermal radiation(NFTR)to achieve the purpose of rapid cooling.In the near field,due to the participation of evanescent wave,NFTR between two objects can be greatly enhanced.When some surface resonance mode and the coupling mode are excited on the surface of the object,higher photon state density and photon tunneling probability could be supported,which helps to further break through the Planck's blackbody(BB)limit.This thesis mainly introduces the enhancement effect of surface plasmon polaritons(SPPs),surface phonon polaritons(SPhPs),hyperbolic phonon polaritons(HPPs),magnetic polaritons(MPs)and their coupling modes on NFTR.The enhancement mechanism of SPP-SPhP coupling modes to NFTR is discussed experimentally.Firstly,this thesis proposes a NFTR enhancement based on the coupling of multiple SPP and HPP modes.An infinite layer heterostructure of graphene-hexagonal boron nitride(hBN)is designed.Through the coupling of graphene SPPs and HPPs of hBN,the heterostructures supports a continuous and near-unity photon tunneling probability during the mid-and far-infrared bands,which exceeds the BB limit by four order of magnitude at a gap distance of 10 nm.Besides,with the assistance of graphene SPPs,combined with SPhPs of SiO2 and HPPs of hBN,using the complementarity of excitation frequencies of two phonon modes,more surface resonance modes can be excited in different frequency ranges.Finally,only three layers of the heterostructures are used to achieve 97%of thermal radiation energy of the infinite layer heterostructure.The effect of graphene Fermi level on NFTR is discussed.Secondly,this thesis proposes a NFTR enhancement based on multiple MPs coupling.Based on rigorous coupled-wave analysis(RCWA)and an equivalent LC circuits,the excitation process of the MPs is demonstrated when the graphene layer gradually approaches the silicon grating.It is proved that the interaction between graphene and silicon grating can excite MPs and dominate most of the heat transfer.The coupling mechanism of multiple MPs in G/Si grating multilayer heterostructures and the enhancement effect on NFTR are analyzed.Thirdly,the enhancement effect of SPP-SPhP coupling modes on NFTR is verified experimentally for the first time.Using the coupling of graphene SPPs and amorphous quartz SPhPs,high photon tunneling probability is constructed in a broad band of mid-far infrared.Emitter and receiver based on graphene-amorphous quartz are prepared.A three-dimensional high-precision nanometer displacement and a deflection system are used to measure the NFTR of millimeter-scale plates with a gap distance range from 170 nm to 1200 nm.The BB limit is broken by 64 times in the experiment(other groups in the world only reach 10?28 times at a similar spacing).This experimental result establishes the experimental record of NFTR enhancement at similar spacing.The mechanism of NFTR between dissimilar objects is analyzed.It is demonstrated that pattern matching is a necessary condition for NFTR enhancement,which is verified by experiments on two dissimilar graphene-amorphous quartz plates.