Electron Emission in Intense Electric Fields

1. Introduction .—The main features of the phenomenon of the extraction of electrons from cold metals by intense electric fields are well known, and an approximate theory of the effect was first developed by Schottky. More recently the experimental data have been much improved, notably by Millikan and Eyring, and Millikan and Lauritsen. The theory has been considered afresh by O. W. Richardson and by Houston working with Sommerfeld. It seems to us, however, that there is still room for improvement in the theoretical exposition and its correlation with the experiments. Neither O. W. Richardson nor Houston really treat the theory in the simple straightforward way which is now possible in the new mechanics, using the revived electron theory of metals which we owe to Sommerfeld. Again, while Millikan and Lauritsen seem to have established quite definitely the laws of dependence of the emission on the field strength F, they speak of the implications of their result in a way which is hard to justify and might in certain circumstances prove to be definitely misleading. Millikan and Lauritsen show that a plot of log I, where I is the current, against 1/F yields a good straight line whenever the experimental conditions are sufficiently stable. At ordinary temperatures these currents are completely independent of the temperature. The formula for these current is I = C e ─a /F, (1) Which is, of course, indistinguishable from I = CF2 e ─a /F. (2) Millikan and his associates have also shown that as the higher temperatures, at which ordinary thermionic emission begins, are approached, the strong field emission does become sensitive to temperature and finally blends into the thermionic.