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For applications with large beam spot sizes, where large total current and current density are required, large, flat crystal faces of LaB6 or CeB6 can be the cathodes of choice.

This regime is unsuitable for point sources such as field emitters, which are unable to provide sufficient total current, and has been thought of as the realm of the dispenser cathode. However, LaB6 and CeB6 may be more suitable, being particularly robust and resistant to chemical poisoning. They have modest vacuum requirements and long shelf life, and need only be brought up to operating temperature to provide emission, eliminating the activation procedure required of dispenser cathodes.

This decreases the life of the cathode. Care must be taken to properly optimize cathode temperature to obtain the required emission without overheating the crystal. CeB6 has another advantage over LaB6 relating to lifetime: its evaporation rate at normal operating temperatures near 1800 K is lower than that of LaB6. So long as care is taken to operate the cathode below 1850 K, CeB6 should maintain an optimum tip shape longer, and therefore last longer.

These trends allow us to tailor our cathodes to the requirements of practically all thermionic cathode applications. For example, SEM and most transmission electron microscope (TEM) applications are best served by a 90° cone angle and a 16 mm flat tip. This combination provides high brightness, a moderate source size, and very good lifetime. High resolution TEMs require a 60° cone and a 5 mm flat tip for very high brightness and a small source size. In applications requiring high total current in a large beam spot, a 310 oriented crystal in a "top hat" configuration may be preferred, providing a slightly lower work function and large emitting surface. We excel at developing specialized cathodes for custom applications and research purposes. Contact us for your custom cathode needs.

The structure of the MVM is amazingly robust, sustaining reasonable impact without deviating from structural specifications. Because the graphite pads shield evaporation of the crystal in the direction of the clamping force, the emitter crystal can be fully utilized without degradation of the mount. Structural failure of the MVM is not a concern when the cathode is operated within the correct temperature and pressure range. Typically, the beam stability of the Mini Vogel Mount cathode exceeds the specifications of the system in which it runs.

They can provide long-term, stable operation at current densities up to 50 A/cm², and may be fabricated in a variety of shapes and with many different heating and mounting configurations. The design of the cathode tip is critical for maximum lifetime and optimum performance.