Study On Field Emission Performance Of Carbon Nanotube Array And Design Of X-ray Tube Electron Gun

As the core component of X-ray tube,the electron gun plays an important role in the fields of industrial inspection and medical imaging.In recent years,many organizations have devoted themselves to the research of field emission electron guns.Among them,the research and exploration of field emission cathode materials is even more important.Carbon nanotubes with a nanometer-scale curvature radius of tip have been recognized as the preferred materials for field emission cathodes.At present,the preparation processes of carbon nanotubes on silicon substrate are relatively mature,but most of them are complicated and the cost is too high.Reducing the growth cost is of great significance for the further development of carbon nanotube field emission cathodes.In addition,it is necessary to grow carbon nanotubes on a suitable metal substrate with more high electrical and thermal conductivity compared to silicon substrate in practical applications.In this paper,the process simplification,modification and field emission performance of carbon nanotubes on silicon substrate and the transfer,direct growth and field emission performance of carbon nanotubes on metal substrate were studied.Finally,the X-ray tube field emission electron gun based on carbon nanotubes was designed using CST software.The main contents and conclusions are as follows:(1).The preparation,modification and field emission performance of carbon nanotube arrays on silicon substrate were studied.We used a simple growth process to inject the catalyst precursor into the reaction chamber through a spray device without the need to pre-deposit a metal catalyst and a metal oxide buffer layer.By this means,the growth process was greatly simplified and the growth cost of carbon nanotubes was reduced.The relationship between the field emission performance and the aspect ratio of carbon nanotubes was obtained.The field shielding effect of carbon nanotubes was reduced by acetone densification,and the field emission performance was further improved.The turned-on electric field and threshold electric field of the densified carbon nanotubes were0.83 V/?m and 2.45 V/?m,and the field enhancement factor was 26588.Finally,the fieldemission current stability of carbon nanotubes was tested.The results showed that the densification process enhanced the field emission stability of carbon nanotubes.(2).The transfer,direct growth and field emission performance of carbon nanotubes on metal substrate were studied.A simple and low-cost transfer method was used to achieve the transfer of carbon nanotubes from a silicon substrate to a metal substrate,while retaining the top structure of the original growth carbon nanotubes.By this way,the field emission performance of carbon nanotubes was not affected during the transfer.After that,we achieved the preparation of carbon nanotubes on metal substrates using the same experimental equipment and process as the silicon substrate.The microstructure and field emission performance of carbon nanotubes grown on three different metal substrates were studied.It was found that carbon nanotubes grown on the high-voltage aluminum alloy substrate had the best field emission performance.The turn-on electric field and threshold electric field were 0.92 V/?m and 2.58 V/?m,and the field enhancement factor was 20930.(3).The application of field emission characteristics of carbon nanotubes in X-ray tube electron gun was studied.Based on the carbon nanotubes prepared in this paper as the cathode material of the field emission,the field emission electron gun was simulated and designed by the electron beam simulation software CST particle studio.By analyzing the effects of characteristic parameters on the performance of carbon nanotube field emission electron gun,the theoretical optimization model of the electron gun was obtained.