Negative Electron Affinity Photocathodes as High-Performance Electron Sources.Part 1. Achievement of Ultra-High Brightness from an NEA Photocathode

摘要

Brightness, energy spread and emission area are key parameters of electronsources for instruments such as electron microscopes and electron beam lithography tools. In developing transmission mode NEA photocathodes as sources for these applications, these characteristics have been measured in specialized sealed tubes. Average lateral energies were measured at 63 meV for a 1.5 micron thick photocathode, and 83meV for a 0.5 micron thick photocathode, which was known to be emitting 'hot' electrons. A current density of 84l A/cm2 was obtained from a 1.7 micron diameter emission area. This high current density can be explained in terms of lateral drift and diffusion of surface trapped electrons. Combined angular and current density data indicate a brightness of about 10(exp-8)A/cm2-sr at 3kV.