The design of the cathode tip is critical for maximum lifetime and optimum performance. Tip design must also match the specific application’s requirements for beam current, spot size, and brightness. For electron microscopy, a conical tip with a flat emitting surface at the apex has proven to be the optimum design, and what Applied Physics Technologies likes to refer to as its standard cathode style.


With the flat-tipped cone design, changes in both cone angle and flat diameter affect emission characteristics. In general, the small cone angle (60°) results in higher brightness, but a larger angle (90°) provides longer life and easier alignment. Small flat diameters also result in higher brightness plus a smaller source size, but larger flats provide longer lifetimes and more beam current.


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 90° cone angle and 16 µm 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 µm 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 application and research purposes.


Contact Us for your custom cathode requests.



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1600 NE Miller St. McMinnville, OR 97128


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