US Patent 7863581 Focused negative ion beam field source

An apparatus for producing negative ions including an emitter coated with an ionic liquid room-temperature molten salt, an electrode positioned downstream relative to the emitter, a power supply that applies a voltage to the emitter with respect to the electrode. The power supply is sufficient to generate a stable high brightness beam of negative ions having minimal chromatic and spherical aberrations in the beam. An electrostatic lens and deflector is used to focus and direct the beam to a target.