Electron‐Electron Interactions in Finely Focused Beams of Low Energy Electrons

Although low current beams of low energy electrons can be finely focused through the use of retarding field focusing optics, it had been suggested that the reduced axial spacing of the low energy electrons could lead to serious defocusing because of electron-electron interactions. However, the Monte Carlo simulation of such electron-electron interactions in the region between final lens and target plane shows that there are no appreciable differences in energy spread and spot diameter with beam currents up to 5 ..mu..A transported through aperture sizes greater than 0.01 mm in radius at energies of 10 keV, 1 keV, and 100 eV. Preliminary experimental results indicate that current density of 250 A/cm/sup 2/ of 1 keV electrons can be obtained by using hairpin tungsten filaments.