Oxygen-enhanced thermionic emission pattern of hemispherical single-crystal LaB6

With the application of Martin’s experimental arrangement for direct observation of thermionic emission patterns from a hemispherical single-crystal LaB6 cathode, it has been determined that oxygen-enhanced thermionic emission does occur for the (210) plane at the rather low partial pressure of oxygen, i.e., in the 10−9-Torr region, at sample temperatures of 1050 °C. For further quantitative assessment, work-function measurements by Richardson plots were done for different crystal planes of clean surface by attaching a photomultiplier. The result clearly shows that the values of the work function increases in order from (100), (210), (110), and (111). The measurements were also extended to the oxygen-enhanced surface of the (210) plane and it was found that the results follow, phenomenologically, the Richardson plot as well.