The Use of an Energy Analyser for the Measurement of the Total Energy Distribution of Field-Emitted Electrons from Tungsten

Abstract

A retarding potential analyser designed by Hartwig and Ulmer has been used to determine the variation of the width of the energy distribution of thermionically emitted electrons with beam current. An electron gun was developed which was used with the Hartwig and Ulmer analyser to determine the half-width and shape of the total energy distribution of the electrons field emitted from tungsten at a vacuum of about 10-9Torr. Fowler-Nordheim plots and collector current measurements were obtained for different values of gun parameters and general observations on the nature of field emission were made including the effect of adsorption one mission current. F-N plot results for particular emitters were combined with the half-widths of relevant energy distributions to give a mean value for the work function of tungsten. A techniquew.as developed for making field emitters having a radius of about 250Å as confirmed by scanning electron microscope measurements. Other techniques included a method of computing equipotential values in a system of electrodes with cylindrical symmetry, the measurement of very small currents of about 10-14  A, and the use of a.c. field desorption for the emitter cleaning. Effects seen during emitter cleaning were described. The analyser had three faults (a) the collector current was too small, (b) the lens effect at the entrance of the collector cage limited resolution and (c) it was very difficult to align the, emitted beam with the analyser axis. (a) and (c) were remedied by the construction of a simple analyser with fewer electrodes which were coated with phosphor. Although it was hot attempted to improve the resolution, this might have been done by the use of a grid at the cage entrance. A criticism of the analyser was given.