Total energy distributions of field-emitted electrons at high current density

Abstract

Measurements of the total energy distributions (TED) have been carried out at high current densities ($J={10}^{6} \mathrm{to} {10}^{8}$ A/${\mathrm{cm}}^{2}$) for a high-work-function ($\ensuremath{\varphi}=4.5$ eV) and low-work-function ($\ensuremath{\varphi}=2.5$ eV) field emitter. At high values of $J$, both emitters give values of the full width at half maximum (FWHM) of the TED which exceed the values based on Fowler-Nordheim theory by a few eV. This deviation of the FWHM values increases with $J$, is independent of temperature, and decreases with emitter radius for a specified beam acceptance angle. The study of these anomalous values of FWHM values extends from 84 to 1975 K. It is believed that Coulomb interaction in the vacuum space in front of the emitter can account for these results, although internal electron energy-broadening mechanisms cannot be ruled out.