ABSTRACT

This chapter focuses on the properties and emission characteristics of the ZrO/W Schottky cathode. The ZrO/W cathode operated at elevated temperature is considerably less sensitive to residual gas pressures than field emission cathodes operating at room temperature. If one is operating the ZrO/W cathode under conditions where emitter dulling is occurring, the measured rate of net plane collapse is also affected by O2 pressure and emitter temperature. Poly-crystalline and single-crystal LaB6 and CeB6 point cathodes have been used over the past 15 years in a variety of microprobe instruments, but almost exclusively in the crossover mode. Point cathodes are used in electron optical systems to produce high-brightness, submicron, focused electron beams. Virtual source point cathodes are distinguished from the more conventional “crossover mode” thermionic cathodes, which operate near the space charge limit, by the high electric field at the cathode surface.