Research On CNTs-based Vacuum Channel Electron Source And Electron Optics System Design

Carbon nanotubes(CNTs)have excellent field emission properties with stable physicochemical properties,high aspect ratio and low fugitive work.And it has broad application prospects in field emission electron sources,which are gradually applied in vacuum devices such as X-ray tubes,traveling wave tubes and vacuum ionization meters.The vacuum channel structure proposed in recent years is also a kind of field emission cold cathode,and its channel length is usually very small making the operating voltage low,so the device can be miniaturized,which is expected to realize the integration of field emission electron source.With the deep development of micro and nano processing technology,the combination of the two has become possible.The vacuum channel structure of CNTs was prepared by micro and nano processing process,and the vacuum channel electron source was studied by simulation and experiment,while the electron optical system was designed by electrostatic lens.The main results of this paper are as follows:(1)Using the self-assembly film forming technique,CNTs thin films were successfully prepared,and its surface morphology was uniform.In combination with high-precision patterned UV lithography,CNTs-based vacuum channel structures with a gap length of 10 μm were prepared,and field emission tests were performed by nanomanipulator under an electron microscope.According to the test results,the device has a low turn-on voltage of about 12.5 V and a turn-on electric field strength of about 1.25 V/μm.(2)The vacuum channel structure of gold/CNTs composite was obtained by transferring CNTs in the gold film which deposited by vacuum thermal vapor.Experimental comparison was obtained that the CNTs-based vacuum channel structure with better device performance.The multi-tips cathode structure was designed and optimized by numerical simulations to improve the field emission performance.The effect of vacuum channel length and the number of cathode tips on the field emission performance is also analyzed.The experimental results show that the field emission performance can be improved by optimizing the number of cathode tips under keeping the length of vacuum channel at 10 μm.When the number of cathode tips is increased from 2 to 5,the turn-on field strength decreases from 1.4 V/μm to 0.8 V/μm.In addition,the vacuum channel with longer gap is easier to work and the turn-on field strength is lower.When the gap is 20 μm,the turn-on field strength is only 0.33 V/μm.(3)Numerical simulations were used to study the electron emission mechansim of the vacuum channel electron source and to predict the device performance.Then electron source of multi-tips cathode structure was tested experimentally,the results showed that the current can be collected on the anode above the vacuum channel.The longer the gap,the easier the anode current is extracted.Anode voltage increases to 780 V,the maximum anode current is 581 μA,the emission efficiency exceeds 52%,when the gap is 20 μm and the field emission current is at the m A level.Under the condition of gate voltage is 25 V or 30 V,the full utilization of the emission current can be achieved when the anode voltage is sufficient,in this case,the device has low power consumption and high reliability.In addition,the symmetrical vacuum channel structure is used as the electron emission region,and Einzel lens focused structure are designed according to the electron optics theory to modulate the electron beam and optimize the electron beam spot size on the anode.