Our EBPG uses the emitter shown in (b), and these days so does every other e-beam system. This electron source is called a “field emitter” because a high field at the tip induces electrons to tunnel out of the metal. It is called a “thermal field emitter” because the tungsten pin is kept hot to keep it clean. Also, the heater allows ZrO to flow down to the sharp end, where it lowers the work function of the metal.