Field Emission from Rhenium: Emission Pattern Corresponding to Hexagonal Crystal Structure

Field emission patterns from a clean metal having the hexagonal crystal structure (rhenium) are photographed. The fabrication of rhenium needle-shaped cathodes having tip radii of the order of 5×${10}^{-5\mathrm{}}$ cm is described, and electron microscope shadowgraphs of such emitters are shown. The use of a high-temperature flash in vacuum to smooth and clean the emitter is illustrated. Emission pattern detail is correlated with crystallographic structure; in particular, the crystal faces with low Miller-Bravais indices have reduced current density, resulting, it is assumed, from values of the work function which are higher than the average value. Rhenium is shown to be more resistant to work function change by oxygen adsorption than is tungsten by a direct comparison under identical experimental conditions.