Correlation between single crystal LaB6 cathode optical and emission images

LaB
₆
cathode is the emitter of choice in electron beam lithography tools. In commercial LaB
₆
cathodes, the (100) crystalline plane is used as the emissive surface. Typical size of emitter is ~70 μm DIA. Quality control is usually done by observing (100) surface with a powerful microscope. Emission images of the same cathodes often reveal irregularities practically invisible or barely visible neither in optical microscope nor in SEM. We have obtained emission images of the LaB6 cathodes and compared them to optical and SEM images.