Preparation and performance of LaB₆ cathode for electron microscopes

Lanthanum hexaboride (LaB₆) cathode is widely used as electron source in electron microscopy instruments due to its high brightness, long service life, and stable emission performance. In this study, a highly oriented (100) single-crystal LaB₆ was prepared, exhibiting a work function of approximately 2.67 eV measured at 1800 K. Using this single crystal, a cathode micro-tip with a micrometer-scale radius of curvature was fabricated using a precision grinding and polishing process. A multilayer pyrolytic graphite clamping structure with a rhenium sheet shunt was also designed for the cathode assembly, which reduced the required heating power to 5.04 W at 1800 K. The angular emission pattern displayed a centrally symmetric "four-leaf clover" distribution, indicative of emission contributions from multiple crystallographic planes. The prepared LaB₆ cathode has been successfully applied in the ZEM20 scanning electron microscope, enabling high-quality imaging at 50,000× magnification.