6.6: Emission imaging of a single crystal LaB6 cathode surface

LaB₆ cathode is still the emitter of choice in a variable-shape beam (VSB) electron beam lithography tool. In commercial LaB₆ cathodes, the (100) crystalline plane is used as the emissive surface. Typical size of emitter is ~70 μm DIA. Though generally stable, this crystalline plane is sensitive to residual atmosphere, and it may have microscopic defects (inclusions, dislocations, etc.) which appear and evolve over the time. Routine initial microscopic inspection of LaB₆ cathodes gives us an initial optical/SEM image of surface, which may change during cathode life. With a simple technique, we have obtained LaB₆ cathode emission images, which showed features unavailable to optical and electron microscopy. This technique can be used for LaB₆ quality evaluation during standard cathode test runs.