Thermionic Emission Constants and Their Interpretation

A critical review of the procedures used in the measurement and interpretation of thermionic emission with particular reference to nonmetallic cathodes is presented. Definitions are proposed for the terms ``true work function,'' ``effective work function,'' and ``Richardson work function.'' The use of Schottky plots is criticized and the advantages of effective work function plots over the conventional Richardson plots are discussed. Factors relating to the interpretation of the thermionic emission constants which are discussed include reflection coefficients, nonuniform true work functions, temperature dependence of the electron affinity, and temperature dependence of the Fermi energy.