A Theory of Secondary Electron Emission from Metals

A theory of secondary electron emission from metals is formulated on the basis of the Sommerfeld free-electron model, momentum transfer between electrons and lattice being included by introducing a finite mean free path for elastic scattering. The approach to the problem is similar to that of Kadyschewitsch, but the development is simpler and comparison with experiment is made in more detail. An understanding is reached of the influence of work function and the width of the conduction band, making it clear why, on the average, metals with large work function might be expected to be the best emitters. The observed effect of changing the work function of a given metal by surface layers of foreign atoms is interpreted, an inverse relationship between emission and work function being obtained which is in qualitative agreement with experiment. The theory also accounts for the velocity distribution of the secondaries, giving the general shape of the curve and determining the approximate position of the maximum, and is consistent with the observed angular distribution of the secondaries. The investigation is not carried far enough to give new theoretical information concerning the variation of secondary emission with primary energy. However, the relation of the present theory to some work of Bruining is indicated, and attention directed to an important empirical relationship.