Research On Graphene Plasmon And Its Application In Near-field Thermal Radiation

Possessing unique electronic structure with excellent properties,graphene yielded into great interest to researchers and has been widely used in many fields such as physics,chemistry and material science.The tunable properties of graphene exhibited great potential for the applications of integrated electronic components.In optics,surface plasmon polariton could be excited in graphene at wide frequency ranges from terahertz to mid-infrared.Furthermore,graphene holds surpassing local field enhancement which makes its extensive usage in the terahertz region to design and fabricate optoelectronic devices.Near-field thermal radiation is heat transfer phe-nomenon and exists between two objects having distance less than the thermal wavelength.Since graphene plasmon reposes in highly overlapping region with thermal radiation spectrum and fi-nally provides strong coupling,which can significantly increase the near-field thermal radiation.In addition,composite structures based graphene could further improve the near-field thermal ra-diation and enhanced thermal radiation intensity.In this work,properties of graphene plasmon and its application in near-field thermal radiation were studied,main research results could be summarized as follows:We gave detail research on three kinds of graphene-hyperbolic materials,namely(hexago-nal boron nitride,aluminum nitride and zinc oxide)heterostructures.It was found that graphene plasmon could be coupled to hyperbolic phonon polaritons in a way to create a new kind of elec-tromagnetic oscillation mode.Moreover,by exploiting dispersion relation and the corresponding field distribution,we then presented the analysis on typical features of electromagnetic oscillation modes.In addition,loss,propagation velocity and decay time of these modes were also obtained by numerical method.Our results showed that the hybrid polaritons merged tunable property of graphene plasmon as well as low-loss of hyperbolic phonon polaritons.In the following work,near-field thermal radiation between monolayer graphene was ana-lyzed and it was concluded that graphene plasmon excited range was compatible with the range of the thermal radiation spectrum.It was found that the surface plasmon between graphene played a pivotal role in near-field heat radiation.The distribution of the transmission probability was interlinked with the graphene plasmon in near-field.For this purpose,different parameters such as graphene' s Fermi level,graphene's relaxation time and the temperature difference between graphene,which influenced the transmission were then discussed and analyzed.On these basis,near-field thermal radiation between graphene-hexagonal boron nitride hetero-structure was calcu-lated.Results showed that in the presence of hybrid polaritons,near-field thermal radiation gained significant improvement in comparison with graphene and hexagonal boron nitride especially at higher Fermi levels.Next,we used Derjaguin approximation method to study the enhancement of near-field heat radiation between micro sphere and plate.We noticed that when micro sphere and plate were covered by graphene simultaneously,then it yielded in an ample improvement in near-field thermal conductivity between them.We found that near-field heat radiation mainly contributed by a small area in sphere near the plate and provided guidance for the experimental im-plementation.Finally,near-field heat transfer of graphene composite structure for long-distance by using intermediate layer was explored.The results were compared and explained while using different kinds of intermediate layers.In addition,influencing factors were also discussed.Moreover,we studied the application of near-field thermal radiation in two types of ther-mophotovoltaic cells.In the p-n junction thermophotovoltaic cell,near-field tunneling of surface plasmon polariton was significantly enhanced when a hyperbolic metamaterial was used as the source in near field thermal radiation and thus greatly improved the efficiency as well as output power of thermophotovoltaic cell.For graphene-based Schottky junction thermophotovoltaic cell,our results showed strong resonance of graphene plasmon modes which improved near-field ther-mal radiation between the source and Schottky junction for different barriers in a sense to surpass their photoelectric conversion power and efficiency even at high temperatures.