Crystallographic Variations of Field Emission from Tungsten

A photometric method has been developed and used to measure field‐emission electron currents as a function of the crystallographic directions found in a tungsten single crystal emission point. Data obtained indicate that the appearance of bright and dark areas on the pattern of a field‐emission projection tube can be explained by the differences in the work functions of the various crystallographic directions. The experiments also suggest that the value of the exponent of the work function needed to relate the field‐emission equation to observed data is ($\frac{3}{2}$ ) as predicted by theory. The method of analysis is independent of the need for high accuracy of electric field determination. However, it does depend on a knowledge of the electric field distribution about the surface of the emission point. In these experiments, the field distribution was an assumption based on experimental data. To insure the constancy of the electron emission required for measurement it was necessary to maintain an excellent vacuum. A method is given for the attainment and maintenance of a pressure in the region of 10⁻¹² mm of Hg.