Investigation Of The Tunable Electromagnetic Property Based On Graphene Plasmonic Molecules

Surface plasmon polariton(SPP)is one kind of electromagnetic wave on the metal surface which can break through the diffraction limit.Akin to atom and molecule system,plasmonic molecule(PM)is one common nanostructure through the interaction between individual plasmonic unities based on SPP.PM is usually made of noble metal like gold or silver and many different structures of PM have been widely studied in recent years.However,the PM made of noble metal has a lot of serious disadvantages.For example,PMs made of conventional metals suffer from large ohmic loss.More importantly,PMs supported by metals are deficient in flexibility,and are hardly optimized in the frequency regimes of interest as long as geometric construction is determined.Graphene is one of new type materials and is able to support SPP with low ohmic loss and high confinement.Moreover,graphene has the decisive advantage of continuous tunable property via manipulation of its chemical potential.So the electromagnetic behaviors of graphene PMs can be further tuned in a fixed structure.Although PMs composed of graphene have great potential,limited attention has been paid to the PMs composed of graphene.This paper utilizes the commercial software to investigate the electromagnetic characters of PMs composed of different graphene oligomers.The main research work and results are as follow:1.We propose a graphene tetramer and a graphene pentamer composed of coupled graphene nanodisks.These graphene oligomers are able to form PMs due to the strong interaction between graphene nanodisks.The transformation from the isolated to the collective modes of the proposed structure is investigated by analyzing the whispering gallery modes and extinction spectra with various inter-nanodisk gap distances.In addition,the effect of introducing a central nanodisk into the tetramer on the extinction spectra is explored,which leads to Fano resonance.Furthermore,the refractive index sensing properties of the proposed graphene plasmonic oligomer have been demonstrated.2.We construct a graphene hexamer and show that line shape of Fano resonance is modulated by changing the parameters of graphene hexamer.A flexible method for optimizing Fano resonance is the description of Fano resonance in extinction spectra by separate resonances given by several subgroups modes.An appropriate increase in size of the central nanodisk is a practical method to enhance the quality of Fano resonance.Increase of chemical potential of central graphene nanodisk has completely opposite effect on the ring mode and central mode,leading to the change of the relative height of the two peaks in extinction spectra.Increase of momentum relaxation time effectively modifies the robustness of Fano resonance in graphene hexamer.On the basis of these optimizations,the Fano resonance can reach high quality and a stable state.3.We build complex graphene oligomers with 13 graphene nanodisks and investigate the effect of local chemical potential change on graphene PMs and effect mechanism.The results show that the electromagnetic response of graphene PMs can be substantially modified by the modification of the local chemical potential,strengthening or reducing the intrinsic plasmonic modes.The graphene oligomers with different symmetry have the same effect mechanism.As a consequence,the advances of flexibility in graphene molecules will be widely applied in prospect and boost the improvement of nanodevices.