Elements of Thermionics

Recent review papers in this field have provided those engaged in research on thermionic emission with critical review material of an encyclopaedic nature. This article approaches the matter from a different point of view, viz, that of the engineer or research worker in some other field who wishes to acquaint himself with the main experimental features and the principal theoretical developments of the subject. Much the greater part is devoted to the latter. An attempt is made, assuming only undergraduate mathematics, to begin with a simple formulation of statistical mechanics and proceed from there to certain relationships of landmark importance. These include the Richardson equation which is of general validity for all substances, the Schottky equation concerning effects of electric field, and the Fowler equation for emission from a normal impurity semiconductor which is the Richardson equation expressed in terms of a particular semiconductor model. Certain results of quantum mechanics are introduced where needed and no previous mastery of this subject is required.