thermal (thermally assisted) field-emission electron gun
thermal (thermally assisted) field-emission electron gun
The thermal (thermally assisted) field-emission electron gun (TFEG) emits electrons from a tungsten (W) tip emitter by tunneling the potential barrier (～4.5 eV) where the emitter is heated at ～1600 K in a strong electric field. Compared with the cold cathode type, its emission current is very stable for a long time because the emitter does not adsorb residual gases due to constant heating. Thus the electron gun is more advantageous for micro-area or nano-area analysis than the cold cathode type. The energy spread of the emitted electrons from the TFEG is ～0.7 eV. Its brightness is as high as <8×108 A/cm2.sr at 200 kV. The size of the virtual source produced is >10 nm. This type of gun is not available commercially but has been replaced by a Schottky type gun.
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