cold (cathode) field-emission electron gun

The cold (cathode) field-emission electron gun (CFEG) emits electrons from the tungsten (W) tip emitter by tunneling the potential barrier (～4.5 eV) where the emitter is kept at room temperature in a strong electric field. Since the energy spread of the emitted electrons from the CFEG is narrower (～0.3 eV) than the Schottky type, the CFEG provides a superbly high energy resolution in EELS. Since the size of the virtual source produced is as small as ～10 nm, the electron beam has a high coherence, suitable for electron holography. Its brightness is as high as ～1×10⁹ A/cm².sr at 200 kV. The CFEG can produce a small-sized probe. Since the emitter surface is likely to be contaminated by residual gases, the emission current is likely to fluctuate. It is necessary to flash the emitter tip in a commercially-available CFEG at intervals of about 8 hours. Recently, the stability of the beam current has greatly been improved by acquiring a better vacuum. Thus, the barrier for EELS, EDS and WDS experiments by using CFEG is lowered.

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