ABSTRACT
Every practical electron beam instrument relies on a stable, long-lived electron source. The most commonly used sources extract electrons from a bulk metal or semiconductor, and accelerate the particles across a vacuum gap using the electric field of an electrode at a positive potential relative to the source. Electron emission is a fundamentally quantum mechanical process. Electrons are free to drift throughout the bulk material, with a net flux incident on the emission surface from within the material. We define the electron affinity as the energy needed in practice to remove a single electron from the emitter. The energy bands of the solid emitter material tend to bend at the interface with the vacuum. The emission current density depends on the temperature and the applied electric field. An electron which has been emitted into the vacuum experiences an electrostatic force which attracts it back toward the emission surface.
