Cold field emitter
AssigneeFEI Company
InventorsTheodore Carl Tessner, Gregory A. Schwind, Lynwood W. Swanson
Life of this patent
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Abstract
A stable cold field electron emitter is produced by forming a coating on an emitter base material. The coating protects the emitter from the adsorption of residual gases and from the impact of ions, so that the cold field emitter exhibits short term and long term stability at relatively high pressures and reasonable angular electron emission.
Claims35
A cold field electron source, comprising:
- a base;
- two electrodes extending through the base;
- a filament connected to the two electrodes;
- a metallic emitter attached to the filament, the metallic emitter having an emitter tip on one end;
- and
- a coating on the emitter tip of a second material chemically combined with the metallic material of the tip.
A method of emitting electrons using a cold filed emitter, comprising:
- providing a base;
- providing multiple electrodes extending through the base;
- providing a filament connected to two of the electrodes;
- providing an emitter attached to the filament, the emitter having at one end a single crystal emitter tip of an emitter tip material;
- providing a layer of a coating material on the emitter tip, the layer of coating material including a chemical combination of the material of which the emitter tip is constructed and another material;
- and
- applying an extraction voltage near the emitter tip to extract electrons while maintaining the emitter tip at a temperature such that no significant thermionic emission occurs.
A cold field electron source, comprising:
- an emitter shaft composed of a first material and including a tip;
- a coating of a second material covering the tip, the coated emitter capable of operating at a temperature at which thermionic emission does not contribute significantly to the energy spread among emitted electrons and at a pressure of 10−8 Torr (1.3×10−8 mbar) for a period of 24 hours with less than plus or minus 5% change in beam current without an external feedback control loop, with a beam current of greater than zero nA.
A method of producing a cold field emitter, comprising:
- providing a wire having a portion tapering toward a tip;
- exposing the wire to gas at a low pressure to adsorb gas molecules onto the wire;
- and
- heating the wire after exposing the wire to a gas at a low pressure to a temperature sufficient to react the adsorbed gas molecules with the wire to form a coating improves the stability of the emission at low temperatures.
A method of operating a cold field electron emitter, comprising:
- providing an emitter in a vacuum chamber, the emitter tip including a coating over a base material;
- evacuating the vacuum chamber to a pressure of equal to or greater than about 10−9 Torr (1.3×10−9 mbar);
- and
- providing an electric field at the tip of the emitter to extract electrons, the emitter temperature being below a temperature at which significant thermionic emission occurs, to extract electrons continuously for a period of greater 24 hours with a beam current variation of less than 5% without an external feedback control loop, with a beam current of greater than zero nA.
Dependencies are inferred from the claim text.