Emission characteristics of single-crystal LaB6 electron gun

Characteristics of electron beams emitted from an electron gun employing [100], [110], and [111] axial orientation LaB6 cathodes were investigated over a long period of time. Although the [100] cathode has high initial brightness, emission characteristics are unstable. This instability is caused by vaporization of the (100) plane, which has a low work function, on the cathode top. However, the [110] and [111] cathodes are stable, because the {100} surfaces are formed on the sloping surface of the cathode with time. Therefore, the [110] and [111] cathodes may be more suitable for many applications in spite of a lower initial brightness.