Thermionic emission from single-crystal LaB6 tips with [100], [110], [111], and [210] orientations

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Abstract
Thermionic emission patterns from the single‐crystal LaB6 [100], [110], [111], and [210] tips have been observed under the Schottky condition. The observed emission patterns are interpreted on the basis of a model involving an anisotropic work function of LaB6; the regions around the [111] crystal orientation have a high‐work function, while those around the [210] crystal orientation have a low work function. This model also explains qualitatively the order of the total emission currents from those tips. The observed patterns predominantly consist of the emission from the conical face rather than the top of the tips under this experimental condition. Changes in the emission pattern and cathode surface in operation at 10−4 Torr are also discussed.