Study On Preparation,Growth Mechanism And Secondary Electron Emission Performance Of Vertical Graphene

The secondary electron emission(SEE)that occurs on the solid surface will cause the accumulation of charge on the solid surface and result in an electron cloud effect,which greatly hinders the stability and development of various devices such as particle accelerators,spacecrafts,electric vacuum devices,etc.Therefore,it is crucial to find surface materials with low secondary electron yield(SEY).Studies have shown that graphene has low SEY.Compared with randomly oriented conventional graphene sheets,vertical graphene(VG)has huge application prospects due to its non-stacked morphology.However,the growth parameters and mechanism of plasma enhanced chemical vapor deposition(PECVD)method for the preparation of controllable and large-scale VG are still to be studied,and there is no relevant report on it's SEE emission performance.In view of the above research status,this article takes VG as the research object.After in-depth investigation of the preparation method of VG,PECVD was used to prepare a controllable and large-scale VG through the adjustment of growth parameters,and the growth mechanism was discussed in detail,besides,the SEE characteristics were tested and its launch mechanism was analyzed,including:(1)VG on Ni substrates from CH₄ feedstock are synthesized by PECVD,by optimizing the growth temperature and the ratio of H₂ to CH₄,VG grow uniformly on Ni plate.The as-prepared graphene showes perpendicular growth to the substrate,uniform distribution,moderate density and high degree of graphitization,and the highest height was 10?m.(2)Under the conditions of the optimal parameters obtained in(1),the growth mechanism of VG was revealed by selecting samples of vertical graphene at different growth stages.The growth of VG goes through three stages:dissolution of carbon-bearing species onto Ni,then precipitation and crystallization to form carbon nano-onions(CNOs)at supersaturated condition,and the final growth of VG from the outside of CNOs.The continuous flow of CH₄ and the highly crystalline carbon-dissolved layer serve as the source of VG.(3)Selecting the carbon spheres sample and VG sample obtained under the optimal parameter conditions in(1),Ni substrate and industrial graphite as the comparison to compare the SEE.The maximum SEY(?_m)of VG measured is only 0.70,confirming the significant secondary electron suppression performance of VG,and explaining the mechanism of SEE suppression based on the microstructure of VG.