| The field emission electron source has the advantages of high beam spot brightness,low energy dissipation,low power consumption and instantaneous start.It is the core component of high-end vacuum electronic devices and determines the performance level as well as application range of vacuum electronics equipment.Due to its excellent electrical conductivity,mechanical properties and ultra-high melting point,the single crystal tungsten tip is the most widely used field emission electron source now.However,because of the large work function of metal tungsten,its open field strength is high,and the beam spot current of the single crystal tungsten field emission electron source is small.Therefore,people have been devoted to the development of new field emission cathode materials.Metal carbide can effectively reduce the work function of the field emission cathode tip and is a very promising class of materials in field emission research.However,there are two major problems in using metal carbide as a field emission cathode material:1)the melting point of metal carbide is very high;2)it is difficult to prepare metal tungsten carbide single crystal tip.This study developed a new preparation method.Using carbon nanocones with unique cone structure as templates and carbon sources,based on micro-operation /scanning electron microscope system,tungsten carbide single crystal tip with nano size was prepared in situ by ultra-fast quenching.With the help of scanning electron microscope morphology analysis,transmission electron microscope high resolution and composition analysis and other analytical testing techniques,its cutting-edge structure and field emission performance were studied preliminaryly.The main research work and results are as follows:(1)Different types of carbon nanocones were used as carbon sources,and the micromanipulation system was used to make them react with the tungsten probe.Theeffects of different types of carbon nanocones and different quenching conditions on the morphology and composition of tungsten carbide tip were studied.Using the original carbon nanocone as a template,slowly increase the applied voltage in 2V/time steps,a tungsten carbide single crystal tip with radius of only 50 nanometers was successfully obtained.And a new method for preparing a solid carbon tungsten compound was developed.(2)The systematic research shows that the voltage during the preparation process plays a vital role in the formation,morphology,crystal form and kinetics of the carbon tungsten compound field emission cathode nanotip.Its emission crystal plane is(200),and the corresponding work function is low.This illustrates its potential application in field emission devices.(3)Electrical tests were performed on the prepared single crystal tungsten carbide field emission cathode nanotips,the magnitude and stability of the emission current were measured.And the relationship between the emission capability and the emitting crystal plane was explored.The results show that the on-site electric field of the tungsten carbide cathode tip is smaller than that of the traditional tungsten cathode tip,and the field emission current fluctuates within 4μA.This will promote the application of tungsten carbide materials in the field emission cathode field. |
