Formation of a single nanodimensional emitting protrusion on a surface of a tungsten carbide field emitter

It is of special interest to obtain a single nanodimensional emitting protrusion on the surface of a tungsten carbide emitter, which would serve as an ideal point source of electrons and ions. However, it is difficult to grow a single nanodimensional protrusion on the surface of a tungsten carbide emitter. In this study, the task was solved as follows. In the course of a field crystal growth, each nanoprotrusion reach a stationary state when the stretching electrostatic field forces pressure P_F = F²/8π equal to the compressing surface tension forces pressure P_γ = 2γ/r (γ - the coefficient of surface tension) [5]. The pressure P_F creates a grow and sharpening of a protrusion and the pressure P_γ creates a blunting and disappearance of a protrusion. If the P_F value is gradually decreased (by reducing the applied voltage U), the value of P_γ will became greater than P_F at first for the sharpest nanoprotrusion. As a result, this protrusion will be became blunt and cease to emit. By further reducing the applied voltage U we can gradually eliminate the emission from other protrusions until a single emitting nanoprotrusion survives.