| Various kinds of high-energy accelerators and high-frequency microwave devices often need cathode materials to provide electron beam with high brightness, good quality and high current density. Compared with conventional thermoionic cathode, field emission cathode has many special advantages, such as room-temperature operation without a cathode heater, high current density and start fast. Field emission cathode is an ideal electron source for vacuum devices and varieties of high-energy accelerators, which has become a hot research in recent years. In various cathode materials, LaB6 has excellent field emission properties, but because of its high melting point and good chemical stability, how to design and manufacture a field emission cathode become a very critical issue.To improve the field emission capability of cathode, we designed and fabricated two structures(annular structure and a comb-shaped structure) of polycrystalline LaB6 field emission cathode. we successfully produced a large area polycrystalline LaB6 field emission cathode which has excellent electron emission properties by adjusting the process parameters. The main contents include:1. We use MAGIC to simulate and calculate the surface field and found that changing the emitter structure parameters can improve the surface field strength, which provides a theoretical basis for the subsequent preparation work. Research results that emitter structure and work function of emission materials are the key parameters that affect cathode’s field emission capabilities. The field emission material which has lower work function has better field emission properties.2. In this article, Silicon nitride(SiNx) thin film used as mask layer was deposited on the surface of LaB6 substrate by RF magnetron sputtering mechanism. And research results that with RF power increasing the deposition rate first increases and then decreases. The uniformity and deposition rate of thin film is inversely proportional relationship. The higher the operating pressure, the lower the deposition rate, and they have a linear relationship.3. In this article, polycrystalline La B6 field emission cathode was prepared by electro-chemical etching method. We found that the parameters such as the electrolyte composition, concentration, corrosion liquid, aqueous solvent and the voltage between electrodes can affect the morphology.Compared with phosphoric acid, the hydrochloric acid is more suitable in electrolyte electrochemical etching of polycrystalline LaB6. The higher the proportion of corrosion liquid in electrolyte, the more smooth of the surface; the lower the water content of the solvent, the rougher of the surface and the faster of the etch rate.4. Studies come up with a suitable electro-chemical etching method to prepare the polycrystalline LaB6 field emission cathode of annular structure. The best preparations for its parameters are: photoresist is used as a mask layer, the substrate activation temperature is 180 ℃,the holding time is 3h. Electrolyte ratio is V(HCl):V(C2H5OH):V(H2O)=1mL:20mL:20mL.The voltage between electrodes is 3V.The electro-chemical etching time is 1h. Finally, we successfully prepared an annular polycrystalline LaB6 field emission cathode.5. Field emission measurements of polycrystalline LaB6 field emitters were carried out in diode geometry devised and fabricated by ourselves. The emission performance of comb-shaped structure cathodes is better than annular structure. The turn-on field of comb structures is 6 ~ 8V / μm, the threshold field is 18 ~ 21 V / μm. After testing, the polycrystalline material at low vacuum still exhibit good stability and anti-poisoning ability, exhibiting superior properties as a field emission material. |
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