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Lanthanum hexaboride (LaB₆) and cerium hexaboride (CeB₆) cathodes are ideal for many small spot size applications such as SEM, TEM, surface analysis and metrology, and for high current applications such as microwave tubes, lithography, electron-beam welders, X-ray sources and free electron lasers. Applied Physics Technologies has decades of experience in research, development, and manufacturing of LaB₆ and CeB₆ cathodes. We can provide the cathodes you need for replacement, OEM, and custom applications

The unique properties of hexaboride crystals provide stable electron-emitting media with work functions near 2.65 eV. The low work function yields higher currents at lower cathode temperatures than tungsten, which means greater brightness (or current at the beam focus) and longer cathode life. Typically, these cathodes exhibit 10 times the brightness and more than 10 times the service life of tungsten cathodes. In electron microscope applications, these characteristics translate to more beam current in a smaller spot at the sample, improved resolution, and less frequent cathode replacement.

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. 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.

LaB₆ and CeB₆ are the materials of choice for high current cathodes in a variety of advanced and custom applications. The performance and lifetime of the hexaboride cathode are determined by several factors: vacuum level, cathode temperature, impurity level, crystal orientation, tip shape, and mount design.

Vacuum requirements are more stringent for hexaboride emitters than for tungsten in order to minimize carbon contamination. In laboratory tests, CeB₆ has proven to be more resistant to the negative impact of carbon contamination than LaB₆, which gives it an edge in potential cathode lifetime.

Excessive operating temperatures accelerate evaporation, thus decreasing 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.

A comparison of electron emission characteristics of LaB₆, CeB₆ and tungsten at typical operating temperatures