Study on the Effect of Heating Current on the Emission Characteristics of LaB₆ Cold Cathode

Compared with thermionic and Schottky cathodes, field emission cold cathodes have the advantages of fast response, high current density and low energy spread, which are beneficial for the high resolution and high signal-to-noise ratio for imaging. However, the emission current of cold cathode is not stable due to the varied surface caused by the gas adsorption and desorption. The varying surface with a varied work function results in a fluctuation and decay of the current and the only commercial tungsten field emission source still has a fluctuation of 5%/h and rapid decay of 20%/10 h even under a high vacuum of 10⁻⁹ Pa. Increasing operation temperature can reduce the adsorption of gases on the cathode surface. Maintaining high temperature during the emission process is an effective way to improve the stability, but higher operation temperature will also change the electron emission characteristics of cold cathode, such as an increasing the energy spread, so it is important to study the effect of different heating currents on the emission characteristics of cold cathode for practical applications. In this paper, a single-crystal LaB₆ nanoneedle point electron source was fabricated by focused ion beam （FIB） milling, and its electron emission characteristics were investigated at different heating temperatures. Firstly, the temperatures of the cathode under different heating currents were obtained by COMSOL Multiphysics electro-thermal coupling simulation, and then the experimental study of the stability of the cold field emission current was carried out under different heating temperatures, and the experimental results showed that the field emission stability would be significantly improved with increasing heating current. Finally, theoretical calculations based on electron emission theory reveald that the highest heating current in this experiment corresponds to a temperature of about 1000 K. The emission mechanism is still field emission, and maintains low energy spread and high brightness. This work will serve as a guide for obtaining high-performance cold cathode point electron sources with stable emission.