Light modulated electron source

A method for modulating an electron beam emitted from a silicon-type field emitter cathode, the method comprising:

• generating an electric field at an emission tip of the field emitter cathode such that a conduction band at the emission tip is maintained above a Fermi level of the field emitter cathode;
• and
• controlling a photon-beam source configured to generate a photon beam including photons having a wavelength shorter than about 1 μm and configured to direct the photon beam toward the field emitter cathode,
• wherein controlling the photon-beam source includes generating said photon beam with a first intensity during a first time period, and generating said photon beam with a second intensity during a second time period, said second intensity being substantially higher than the first intensity such that an emission of electrons from emission tip is minimized during said first time period, and such that, during said second time period, a sufficient number of said photons are absorbed by said field emitter cathode to create photoelectrons in the conduction band, thereby producing a photo-assisted field emission of said electron beam from the emission tip.

A device including an electron source configured to generate a primary electron beam, wherein the electron source comprises:

• a field emitter cathode including a silicon substrate having opposing first and second surfaces, and an emitter protrusion having a base integrally connected to the silicon substrate, a body portion extending from the first surface, and an emission tip disposed at a distal end of the body portion;
• an electrode having an aperture and being maintained at a positive voltage relative to the field emitter cathode, said electrode being configured such that electrons emitted from the emission tip form an electron beam that passes through the aperture;
• a photon-beam source configured to generate a photon beam including photons having a wavelength shorter than about 1 μm and being directed onto the emitter protrusion such that at least some of said photons are absorbed by said field emitter cathode;
• a control circuit configured to modulate an emission current of the electron beam by controlling an intensity of the photon beam transmitted from the photon-beam source and received by the field emitter cathode;
• and
• a dielectric layer disposed on the first surface adjacent to the field emitter protrusion,
• wherein the electrode comprises an extractor disposed on the dielectric layer and maintained at a positive voltage of between about 30 V and 200 V relative to the field emitter cathode, and an anode that is disposed at an offset distance of at least 1 mm from the emission tip and maintained at a positive voltage of at least 500 V relative to the field emitter cathode, and
• wherein the device further comprises electron optics configured to direct the primary electron beam to a sample.