Graphene Plasmon And Its Infrared Optical Properties

Plasmon is the collective oscillation of free electrons in materials induced by external electric field disturbances,with the characteristics of strong energy confinement and electric field enhancement,which has great application potential in the fields of biosensing,photoelectric detection and communication,and photocatalysis.Recently,the science of two-dimensional materials,including graphene,Mo S2 and black phosphorus and so on,develops rapidly and shows intriguing optical and electrical properties,which enable the generation and propagation of low-loss plasmons in the infrared and terahertz bands.Compared with the traditional noble metal plasmons,graphene plasmons show stronger field localization and electrical tunability in the infrared band,breaking the dynamic modulation limitation of the metal plasmons whose response depends on structures and facilitating the development of ultra-thin,low-loss,active infrared and terahertz devices.The infrared optical properties of graphene plasmons are the basis for the development of new infrared optoelectronic devices,but the current research on the infrared optical properties of graphene plasmons has not been perfect.Thus,in order to explore the mechanism of graphene-light interaction,the study makes attempts from the aspects of the dielectric environment,the physical parameters,and the structures of graphene,which are significant for the optical properties of graphene plasmons.Specifically,the impacts of low-loss dielectric environment,mobility and stacked structures on the optical properties of graphene plasmons are well studied.The main topics and results of the dissertation are as followed:1.To solve the competition absorption between ion-gel and graphene plasmon,a dielectric interlayer obstructing ion-gel and graphene nanostructures is proposed.The plasmon devices with dielectric-graphene ribbons stack is prepared.It is shown that the device could maintain the electric tunability of graphene and weaken the coupling strength between local electric field and ion-gel layer,improving the absorption of graphene plasmon from 10% to 35% near the spectral position of ion-gel.2.The mobility of graphene is sensitive to the impurities and defects,thus,its experimental value is usually much lower than the ideal situation.However,the influence of mobility on the tunability of graphene plasmon is seldom considered.In order to solve the problem,the optical properties of graphene plasmon with varied mobility are studied.The interaction between the optical resonant cavity and graphene plasmons of different mobilities conditions is simulated.It is found that as the mobility decreases the cavity mode and the plasmon mode,corresponding to the non-resonant component and the resonant component of the electric field at the surface of graphene,respectively,have fixed wavelength and similar absorption.The absorption of two modes with different Fermi levels was also studied.It was found that as Fermi level increases,the peak of cavity mode would show fixed frequency and grow slowly while the peak of plasmon mode would show blue shift and rise considerably.Furthermore,the peak of plasmon device with low mobility would shift from cavity mode to plasmon mode.When the frequency of cavity mode was high than plasmon mode,the peak would show red shift with increasing Fermi level.The graphene dolmen structure with optical cavity is fabricated and the red shift of peak due to reduction of mobility is verified experimentally.3.To solve the tunability lack problems of stacked graphene structures,a graphene-dielectric-graphene structure is proposed.The graphene plasmon device with stacked structure was fabricated.Compared with traditional structures with multilayer graphene stacked directly,the dielectric in proposed structure could enrich the alignment of graphene ribbons in different layers.The plamson devices with vertical and parallel ribbon stacks are prepared.It is shown that the vertical stack could achieve a full polarization absorption of more than 35% and the full width at half-maximum of the parallel stack's absorption spectrum could reach 3.5 ?m with the maximum absorption rate exceeding 50%.Consequently,the dynamic modulation of the stacked structure is realized,and the polarization insensitivity and absorption bandwidth of the plasmon is improved through the vertical and parallel graphene stacks,respectively.4.The influences of physical parameters and dielectric environment on the reflectivity of graphene plasmon are studied by simulation.The reflection coefficient of graphene ribbons with varied Fermi levels and incident frequencies is analyzed.With the variation of graphene Fermi level,it is shown that the reflectance of metasurface could maintain high and the range of the reflected phase could exceed 5 rad during a wide frequency range.The application potential of graphene plasmons is explored and a tunable far-infrared metasurface is proposed.Through manipulation of Fermi level in each cell of the metasurface,the plane reflection focusing is realized,with the same phase of light at the focus reflected from each cell.Compared with traditional metallic metasurface lens,the profile of phase in graphene metasurface could vary with Fermi level.By tuning the Fermi level of each graphene ribbon in the array,the frequency and focus of the metasurface lens could be manipulated.Simulation results show that the lens based on graphene ribbon performed quite remarkably with responding tunable frequency from 4 THz to 6 THz and the moving range of focus could reach to 200 ?m.