| Graphene,as a two-dimensional material with single atomic layer,has excellent electrical and thermal conductivity,high specific surface area,high chemical stability and other properties,which provides wide application prospects including new energy batteries,hydrogen storage materials and other fields.Meanwhile,the advantages of high aspect ratio,high electron mobility and high transmittance of graphene makes it a potential application for field emission cathode and gate material.Generally,graphene is usually prepared on planar substrates such as eopper and silicon,which ensures the integrity of graphene structure.However,the local electric field and current density decrease remarkably,due to the effect of planar structure,which reduces the field emission properties of graphene while planar graphene is fragile during the transfer process.Moreover,graphene has great field emission properties,which challenges to the application of graphene as a field emission gate.In order to solve the problem above,a method of graphene preparation on nickel sponge substrate was proposed in this paper,which solved the problem of low local electric field and low current density when graphene was applied as field emission cathode.The results were optimized and better field emission performance was obtained.At the same time,it solves the problem that graphene can be damaged and installed hard when it is used as field emission gate.Better electronic transmittance and stability are also achieved.The main contents of this paper are as follows:(1)Graphene foam with three-dimensional structure were prepared on nickel sponge substrates by CVD.The structure and morphology of graphene foam under different reaction time and corrosion time were studied by XRD,Raman Spectra and SEM.It was found that the number of graphene layers increased gradually and graphene grew more uniformly with the increasing reaction time.(2)The field emission properties of graphene foam were tested by diode structure.The effects of different etching time,positive and negative sides and the size of base aperture on the field emission properties of graphene foam were studied.The field emission properties of graphene foam were optimized and improved,and the field emission stability was tested.Less than 1V/?m tum-on field and near 30000 ultrahigh field enhancement factor can be obtained by the experimental results.Meanwhile,it was found that the field emission performance of the negative side was significantly worse than that of the positive side,indicating that graphene deposited preferentially on the front side of the sponge structure.The research of the base aperture shows that the moderate size has effects on the field emission properties of graphene foam.The field emission properties of graphene foam were improved by modifying Au nanoparticles,which shows that the field emission properties of graphene foam can be effectively improved by modifying Au nanoparticles.The maximum current density is three times than that origin,and the field enhancement factor is more than 100,000,which indicates that the modified Au nanoparticles can effectively improve the field emission properties of graphene foam.Finally,the field emission stability experiment shows that current of graphene foam fluctuates obviously,but it remains about 10%,and the overall fluctuation level is still acceptable.(3)The grid modulation characteristics of graphene foam were tested by triode structure.The relationship between grid voltage and grid spacing and electron beam modulation was studied by simulation and the reasons were analyzed.Then the relationship between the grid voltage and the electron transmittance is studied.It is found that the higher the grid voltage,the lower the electron transmittance of the grid,and the balance is reached when the electron transmittance is close to 49%.Finally,the stability of the grid eurrent is studied.The eurrent variation between the anode voltage and the anode current shows that the current stability of graphene sponge grid is better. |
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