Boosting the Electron Beam Transmittance of Field Emission Cathode Using a Self-Charging Gate

The gate-type carbon nanotubes (CNTs) cathodes exhibit advantages in long-term stable emission owing to the uniformity of electrical field on the CNTs, but the gate inevitably reduces the transmittance of electron beam (E-beam), posing challenges for system stabilities. In this work, we introduce an E-beam focusing technique using the self-charging SiNx/Au/Si gate. The surface potential of SiNx is measured to be approximately -60 V quickly after the cathode turning-on, the negative potential can be maintained as the emission goes on. The charged surface generates rebounding electrostatic forces on the following electrons, significantly focusing the E-beam on the center of gate hole and allowing them to pass through with minimal interceptions. An average transmittance of 96.17% is observed during a 550-hour prototype test. We believe that this high-efficiency, long-term stable cathode has great potential for using in neutralizers, solar sails and tethered satellites in the long-term space missions.