flashing

The cold (cathode) field-emission electron gun (CFEG) is operated only under an electric field without heating the emitter, while the Shottky type electron gun is used by heating the emitter. Thus, the emitter surface of the CFEG suffers gas adsorption and ion sputtering, leading to a decrease of the emission current and an unstable emission current. To remove adsorbed gasses and surface roughness due to ion sputtering, the emitter is heated. This procedure is called “flashing.” In the existing CFEG, immediately after flashing, the work function of the emitter becomes large and the emission current decreases due to gas adsorption onto the clean emitter surface. Thus, the CFEG is usually used after the emission current becomes stable with the emitter surface being is covered with a thin absorbed-gas layer, and is used until its emission current is lowered by absorption of many gasses.
In recent years, a CFEG has been developed, whose pressure of the residual gases in the vicinity of the emitter surface is low. The newly developed CFEG achieves no waiting time after flashing and a stable emission current with less contamination by maintaining the work function small. It provides a high brightness electron beam for a long operation time.

Related Term(s)