Preparation And Electron Emission Properties Of Carbon Nanotubes Bulk Composites

Carbon nanotubes(CNTs)are one of the most promising field emission cathode materials.However,for CNT film cathodes,the resistance to damage,repeatability and stability of CNT film will be adversely affected under severe conditions such as poor vacuum and high electric field;and the film will be susceptibly damaged during device assembling.Both were harmful to the practical application of CNTs cathode.Therefore,in this work,the scheme of bulk carbon nanotube(B-CNT)cathode was proposed to solve these problems.A series of research work,including preparation process of B-CNT cathode and surface treatment for electron emission properties optimization,were proceeded,and some useful results were obtained.The effects of preparation methods(ball milling and ultrasonic stirring),cathode sintering temperature and CNT content on the field emission properties of B-CNT cathodes were investigated systematically,and the field emission performance optimization process of the cathode was also studied.It was found that:1)for dry ball milling,the best emission performance was obtained under the conditions of 700?sintering temperature and 10wt.%of CNT content;2)for wet ball milling,the best emission performance appeared under the conditions of 800?sintering temperature and 15wt.%of CNT content;3)the field emission performance of the cathode was jointly affected by the defect emission of CNT and the screening effect;4)the cathode field emission performance can be improved by two methods,which were carboxylated CNTs and nitric acid corroded the cathode surface,respectively;5)the field emission performance of cathode,which prepared by using ultrasonic stirring dispersion method under the conditions of 800?and 10wt.%,was equivalent to the best performance of ball milling prepared one.The field emission performance of the B-CNT cathode and the film cathode were compared.The initial turn-on electric field of the carbon nanotube film cathode was0.23 V/?m and the maximum emission current density was 5163.76?A/cm~2,but these performance then began to drop sharply.The maximum emission current density of film cathode the second test was equivalent to that of the B-CNT cathode.By the seventh time,the turn-on electric field of film cathode was increased to 1.73 V/?m,and the maximum emission current density dropped to 38.52?A/cm~2,which was only about one-tenth of B-CNT cathode.However,the turn-on electric field and maximum emission current density of the B-CNT cathode maintained high repeatability in multiple consecutive tests:turn-on electric field(2.20±0.07 V/?m)and maximum emission current density(340±50?A/cm~2).Therefore,in terms of practical application of devices,the overall performance of B-CNT cathode was significantly better than that of the film cathode,which may be due to a certain self-recovery ability of bulk cathode.