Thermionic emission patterns from a hemispherical LaB6 cathode of <110> orientation were obtained by using an experimental set-up similar to the Martin experiment. The emission pattern from a clean surface clearly indicated that the bright region consisted of a (100) spot surrounded by four (210) spots. This suggested that the bright spots except for the center spot in the cross-over images observed for <100>, <110> and <111> cathodes corresponded to the (210) spots deduced by Oshima et al. Emission patterns under various vacuum conditions showed that a specific emission pattern appeared with good reproducibility.

Direct Observation of Thermionic Emission Pattern of Hemispherical Single-Crystal LaB6. Shimizu, R., Onoda, H., Hagiwara, H., Ishii, S.: Journal of Applied Physics, 1981, 52[10], 6316-21