Modulation Of Graphene Carrier Density By A Mixed Doping Route And Experiment Investigation Of Suspended Graphene Plasmon

Graphene is a two-dimensional carbon nanomaterial with sp2 hybrid orbitals,which is hexagonal honeycomb lattice.It exhibits a linear dispersion relationship,that is,the energy E is proportional to the momentum k.The unique structure results in many outstanding properties,such as the quantum anomalous Hall effect in electron transport and Klein tunneling.As the earliest discovered Dirac semimetal,graphene has a significant advantage that its carrier density can be easily tuned.Various methods for controlling carrier density have been developed,like electrostatic gating,ionic liquid,chemical doping,surface adsorption,light etc.Among them,gate tuning is the most widely used one.However,in practical applications,gate tuning also has some limitations.For example,some designed circuits and test instruments cannot stand high voltages over hundreds or even tens of volts.In the tapping mode AFM or SNOM tests,high gate voltages will prevent the tip from approaching the sample surface.Recently,a method of doping with electron beam irradiation has appeared,which can change the graphene carrier density locally and continuously,but the tuning range is small.Here,we report a new mixed doping route combining HNO3 doping and electron beam doping,which shows greater ability to tuning the carrier density continuously in a larger range.By analyzing the results of the scanning near-field optical microscope(SNOM)and electrical transport,we can find this mixed doping route adjusts the graphene carrier density from 2.08×1013 cm-2 to-1.49×1012 cm-2 that the tuning effect be equivalent to 321 V for gate tuning of the 300 nm silicon oxide.In addition,graphene can be writed into pre-designed nano patterns via local electron beam irradiation,which is expected to be applied into many regions.In addition,we performed the experimental research on the plasmon of suspended graphene.The main content is the following three parts:In Part 1,we first introduced the research history of graphene,its lattice and band structure,and its transport properties.Then we discussed the preparation and characterization of graphene.Finally,we gave a brief introduction of graphene plasmons,including dispersion relations of plasmons,near-field excitation,modulation,real-space imaging and propagation.In Part 2,we described in detail a method that can precisely and precisely tune the density of graphene carriers:HNO3 and electron beam irradiation.We first obtained p-type doping graphene with nitric acid vapor,then different doses of electron beams were irradiated onto graphene to achieve different n-type doping,after that electrical transportation and scanning near-field optical microscopy(SNOM)tests were performed to characterize the tuning effect.HNO3 doped graphene can be pre-designed for micro-nano patterns through local electron beam irradiation.Focusing the electron beam on a small area makes it possible to directly write logic circuits into a single graphene,bringing benefits to the future applications of graphene and other two-dimensional materials-based electronic and optoelectronic devices.In Part 3,we introduced the device preparation and near-field optical testing of suspended graphene.First,we introduce the micro-nano processing including electron beam lithography(EBL),ultraviolet lithography,electron beam evapour deposition and reactive ion etching(RIE).Then systematically introduced the method of preparing suspended graphene of others,focusing on the method of preparing suspended graphene of us,and tested Atomic Force Microscope(AFM)and Near Field Scanning Optical Microscope(SNOM).Finally,conclude the problems during the experiment and propose the possible solutions.