Study On The Emission Performance Of Coated Cathode Based On Surface State Simulation

A cathode with low temperature,high current,high stability and long life has always been the goal pursued by new cathode research,and it is also an inevitable requirement for the development of high-power and high-frequency vacuum devices in the future.In order to further explore the surface state of coated cathode and the mechanism that affects the emission performance,simulation software is used to carry out the modeling and simulation analysis of the cathode surface structure,and to study the influence of the surface state on the emission performance.With novel graphene-coated cathode sturctures proposed,the surface state and work function of the graphene-coated cathode are simulated and analyzed.And the surface state properties and emission performance of the graphene-coated cathodes are verified through experiments.The contents of this paper are listed as follows:First,the characteristics of different cathodes are introduced,and the characteristics,fabrication,transference,and characterization methods of graphene materials and their applications in electronic devices are summarized.Then,first-principles simulation software is introduced;After that,research for simulation of cathode surface work function is summarized,as well as related theoretical basis for the cathode work function simulation.In terms of simulation,the process of the cathode surface simulation is given.And the surface state of pure metal crystal and barium tungsten cathode are modeled and simulated,with the surface state properties,work function,band structure and density of states analyzed.Based on the analysis of the surface state of the coated cathode,two new types of graphenecoated cathode structures were proposed,and then modeled,simulated and anaylized.The simulation results show that the surface work function of the proposed graphene-coated barium tungsten can be as low as 1.58 e V;and the surface work function of the graphene-coated tungsten cathode can also be as low as 1.746 e V.In terms of experiments,cathode samples were fabricated for the proposed graphenecoated tungsten cathode and graphene-coated barium tungsten cathode respectively.Based on these,the graphene-coated barium tungsten cathode diode was fabricated,with the emission performance of the diode tested and analyzed through experiments.The experimental results show that the equivalent surface work function of the graphene-coated barium tungsten cathode can be as low as 1.16 e V,and at least lower than 1.56 e V,which is much smaller than that of the B-type cathode.The experimental results are close to the simulation results,which preliminarily verifies the correctness of the surface state modeling of the graphene-coated barium tungsten cathode,and demonstrates the effectiveness of the cathode design and emission performance research method based on the surface state modeling and simulation.The work in this paper provide a good reference for the design of new cathode materials based on surface state modeling and simulation analysis.The proposed and fabricated graphene-coated cathode is also expected to be used as a high emission efficiency,low temperature and/or high current density electron emission source in the future.Related work has a good role in promoting the research and development of vacuum electronic devices.