Broadening of the energy distribution of thermal-field emitted electrons from carbon fibres

Abstract

The energy distribution of electrons thermal-field emitted from carbon fibres and post-accelerated up to 25 keV has been measured. At low total emission currents (of the order of nano-amperes) the energy distribution of the emitted electrons agrees, at room temperature, with the theoretical prediction for the free-electron model, and at elevated temperatures (up to 1520 K) the energy spread is about 0.1 eV higher than predicted. This difference may be explained by assuming that the emission occurs from sharp microfibrils. With increasing current the energy distribution becomes broadened. It is shown that this broadening is independent of the tip temperature and most probably due to Coulomb interaction of the beam electrons in regions of high current density within the electron optical system.