Patch Effect for the Thermionic Emission from Polycrystalline Tantalum

Abstract

The slope modifications for the Schottky line implied by simple patch theory have been obtained at high fields for thermally etched tantalum filaments. For ac‐aged filaments, only the usual low field patch modification was obtained. For dc‐aged filaments an additional anomaly at higher fields was obtained, simultaneous with the appearance of the dc etch pattern on certain faces of the crystal grains. This high field anomaly, consisted of a double break in slope, and appeared at an average patch field about 50 times the patch field due to the distribution of crystal faces.