Currently, the research and development of field emission source engineering is focusing on the main areas below [1]:
        i) Increase the brightness;
        ii) Improve the beam current stability;
        iii) Improve the lifetime;
        iv) Minimize the electron-electron interactions so that the beam spreading and energy spread can be reduced;
        v) Novel emitters, e.g. zirconium coated tips, bare tungsten tips, oxygen processed tips, carbon emitters, carbon coated tungsten emitters and even solid state emitters;
        vi) Develop different types of optical systems for field emission sources, e.g. selecting various magnetic and/or electrostatic lenses at high voltage potentials in UHV systems, and special magnetic lenses just below the anode;
        vii) Develop field emission guns operating at higher accelerating voltages up to MeV.

[1] K. D. van der Mast, Journal of Microscopy, 130(3), 309, (1983).