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

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 (phi), beta (where field factor beta 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') data. Emission parameters F, current density (J), and phi, were determined from experimental data for off-axis emission angle up to 4 degrees in which energy spread (Delta E50) and I' 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 Delta E50 for emitters over a range of beta, I', and off-axis angle have been constructed, which allow users of the SE source for electron optical applications to understand the tradeoff between Delta E50 and B-r. (C) 2013 American Vacuum Society.