Modulating Of Plasmon In Graphene Nanoribbons And Transformation Of Plasmon In Graphene Hole Arrays

Graphene is the first found 2D material,it has linear energy-momentum dispersion,and the carriers in graphene are massless Dirac fermions,providing a good platform for the research of low-dimensional material system.Surface plasmon is a kind of elementary excitation in metal,it is bonded to the surface of metal and leads to huge enhancement of electric field,playing important role in fields such as surface-enhanced Raman scattering,et.al.The combination of graphene and surface plasmons,namely graphene plasmons,makes up for the shortcomings of surface plasmons in metal such as massive loss and weak confinement in low frequencies,and can easily tune the Fermi surface,becomes a research hotspot in condensed matter physics.Graphene is a kind of single-layer material and the plasmonic property of graphene is sensitive to the surrounding dielectric environment,so how to modulate graphene plasmons by changing its dielectric environment is an important research direction.Owing to the surface plasmons,we can observe extraordinary optical transmission in thick metal hole arrays and suppressed transmission in thin metal hole arrays because of the coupling of plasmons in upper surface and lower surface,so what will the transmission spectrum look like in graphene hole arrays which are single-layer material?How is the energy of plasmons transferred in such structure?The dissertation study the influence of dielectric environment on graphene plasmons and the transformation of plasmon in graphene hole arrays by using commercial software--COMSOL.The dissertation is composed of three parts:In the first chapter,we introduce crystal structure,energy band structure and optical properties of graphene.Then we introduce surface plasmon polariton and localized surface plasmon in metal.The dispersion and excitation of graphene plsmons is discussed at last.In the second chapter,we study the influence of graphene edge's dielectric environment on graphene plasmons by numerical simulation and graphene is regarded as surface current.We find that compared with graphene nanoribbons(GNRs)on flat silicon substrate,the dispersion curve of GNRs in the groove of silicon substrate shifts down.On the contrary,dispersion curve of GNRs on the protruding platform of silicon substrate shifts up.Such observations reveal that dispersion curve of graphene plasmons will shift down when increasing the volume fraction of silicon substrate surrounding the edge of GNRs.Then we replace silicon with silicon dioxide and find that when increasing the volume fraction of silicon dioxide substrate,dispersion curve of graphene plasmons will shift down and the coupling between graphene plasmon and phonon of substrate will be enhanced.Additionally,maximum absorptivity for two dispersion curve branches at low frequency will be improved.In the third chapter,we study graphene hole arrays in vacuum by numerical simulation.The transmission spectrum of graphene hole arrays is similar to thin metal hole arrays,we can see obvious valley.But we can not give the conclusion directly that there is only short range surface plasmon mode in graphene hole arrays,because the transmissivity of graphene is very close to 1.The reflectance spectrum of graphene hole arrays reveals that the reflectivity increase when graphene plasmons are motivated.The reason may be that graphene plasmons are transferred to photon or graphene plasmon interact with photon.In addition,we prepare graphene hole arrays sample by electron beam lithography and reactive ion etching.