Preparation Technology And Electron Emission Characteristics Of Carbon Nanotube Cold Cathode

Carbon nanotubes(CNTs)have received great attention in the field of electron source applications because of their excellent electron emission properties.Although the research on CNTs cold cathode has been widely studied,it still needs to be further improved in some fields and some aspects.On the one hand,it is necessary to have high emission current density and higher emission current in some situations,such as the application field of high intensity axial point emission electron gun,especially the electron gun of electron beam selective melting equipment.On the other hand,the highly valued CNTs thin film cathode has not solved the problem of poor tolerance in poor working environment because of the limitation of its own properties.In order to solve the above problems,this paper has made some explorations in the cathode structure and preparation technology:As for the point emission cathode,the electron emission ability of the cathode has been improved by increasing the number of emitters in the tip region;As for the area of surface emission cathode,the self-recovery mechanism of CNTs cathode damaged was established by building CNTs/silver bulk composite structure.The point emission cathode were prepared by growing carbon nanotubes on the tip of nickel-plated metal,using iron phthalocyanine pyrolysis.By continuously optimizing the preparation parameters,the field emission performance of the point emission cathode is gradually improved,the opening field strength of the point emission cathode is about 2.0V/?m,at the field strength of 3.4V/?m,the maximum current density is 3.5A/cm~2,and the corresponding current is 1mA,at the constant field strength of 2.6V/?m,the fluctuation amplitude of current density is kept within±16%.Due to the growth of multiple clusters of CNTs in the effective emission area of the point emission cathode tip,the maximum current of the point emission cathode is four orders of magnitude higher than that of the reported about single carbon nanotube cold cathode(500nA).Therefore,the study of point emission cathode can provide a new idea and important reference value for uniaxial electron sources which need large current and power.CNTs/silver bulk cathodes with high density and certain mechanical strength were prepared by hot pressing sintering process with the mixture of CNTs and silver powder obtained by high energy ball milling.By systematically studying temperature parameters,pressure parameters and carbon nanotube content,it is found that the comprehensive performance of the bulk cathode is the best when the sintering temperature is 700?,the sintering pressure is 30MPa and the carbon nanotube content is 5%.The opening field strength is about 2.25V/?m,at the field strength of 3V/?m,the maximum current density measured is 1.2mA/cm~2.Thanks to the advantages of hot pressing sintering process,the bulk cathodes prepared by hot pressing sintering not only improve the field emission performance,compared with thin film cathodes and pressureless sintered bulk cathodes also have certain processability,and can be used to prepare various forms of cathodes.In addition,the current emission stability of the bulk cathode is tested by using the high current pulse emission technology.The experimental results show that the bulk cathode has a certain self-repairing ability and can keep the emission stability for a long time.It is suitable for field emission scenes with high power,high field intensity and high frequency.