In-situ uniformity control of field emission beam

Field-emitter array (FEA) cathodes with high emission current are promising for applications that require high beam brightness such as free electron lasers and microwave/THz vacuum electronic amplifiers. Using metallic FEAs fabricated by molding, sub-nanosecond electrical switching in high acceleration electric field up to 30 MV/m and ultrafast near infrared laser-induced field emission with up to 5 pC electron charge pulse were demonstrated recently. However, field emission beam imaging experiments indicated that only a limited number of tips emitted electrons. This is partly because of the distribution of the tip radii of curvature Rtip that demands a procedure to improve it. This is particularly important for high current operation, since, when gate voltage is increased for higher current, current density at sharp emitters that are already switched on at low-voltages, could easily exceed the critical value in the order of 10^7–10^8 A/cm2 and trigger destructive vacuum arc. Aiming at homogenizing the Rtip distribution, we explored the effect of in-situ exposure of FEA tips to low pressure noble gas and studied evolution of beam image and current-voltage (I-V) characteristics.

Fig. FEA beam images: before and after Ar conditioning [1]
Fig. FEA beam images: before and after Ar conditioning [1]
Fig. In-situ uniformity control by Ne conditioning [5]
Fig. In-situ uniformity control by Ne conditioning [5]

[1] S. Tsujino, M. Paraliev, E. Kirk, and H.-H. Braun, Homogeneity improvement of field emission beam from metallic nano-tip array by noble-gas conditioning, Appl. Phys. Lett. 99, 073101 (2011).

[2] S. Tsujino, S. Tsujino, M. Paraliev, E. Kirk, C. Gough, S. Ivkovic, H. Braun, Characterization of all-metallic field emitter arrays in combined diode-RF cavity electron gun, 24th International Vacuum Nanoelectronics Conference (IVNC2011), (Wuppertal, Germany, 18.07-22.07.2011).

[3] S. Tsujino, M. Paraliev, E. Kirk, and H.-H. Braun, Uniformity of field emission electron beam and picosecond field emission from metallic field emitter arrays under high electric field, International Vacuum Electronics and Vacuum Electron Sources Conference (Monterey, CA, 24-26, April 2012).

[4] S. Tsujino, M. Paraliev, P. Helfenstein, and H.-H. Braun, Transverse emittance of single-gate FEAs ~ influence of the beam uniformity, C6, 25st International Vacuum Nanoelectronics Conference (IVNC2012) (Jeju, Korea, 9-13, July, 2012).

[5] S. Tsujino and M. Paraliev, Picosecond electrical switching of single-gate metal nanotip parrays, J. Vac. Sci. Technol. B 32, 02B103 (2014).