Off-axis modeling and measurement of emission parameters for the Schottky emitter

Abstract

The optical performance of on-and off-axis emission from the central (001) facet of a Schottky emission (SE) source has been studied using a hybrid experimental and numerical approach, which allows for the simultaneous determination of all key performance measures. A recently developed computer modeling program was instrumental in aiding the discovery of empirical relationships that allow work function (u), b (where field factor b ¼ F=V e for emitter surface field F and extraction voltage V e ), and source brightness (B r ) to be calculated from on-and off-axis experimental angular intensity (I 0 ) data. Emission parameters F, current density (J), and u, were determined from experimental data for off-axis emission angle up to 4 in which energy spread (DE50) and I 0 were directly measured. Also included in this study was the influence of the various end-form shapes of the polyhedral SE source on the various emission parameters. Plots of B r versus DE50 for emitters over a range of b, I 0 , and off-axis angle have been constructed, which allow users of the SE source for electron optical applications to understand the tradeoff between DE50 and B r .