A method is provided for forming a three-dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article, the method comprising the steps of: providing at least one electron beam source emitting an electron beam for at least one of heating or fusing the powder material, where the electron beam source comprises a cathode, an anode, and a Wehnelt cup between the cathode and anode; providing a guard ring between the Wehnelt cup and the anode and in close proximity to the Wehnelt cup, where the guard ring is having an aperture which is larger than an aperture of the Wehnelt cup; protecting the cathode and/or the Wehnelt cup against vacuum arc discharge energy currents when forming the three-dimensional article by providing the guard ring with a higher negative potential than the Wehnelt cup and cathode.

An emitter is configured to emit charged particles. The emitter comprises a body, a metal layer and a charged particle source layer. The body has a point. The metal layer is of a first metal on at least the point. The charged particle source layer is on the metal layer. The point comprises a second metal other than the first metal.

An electron gun comprising a cathode having an electron emitting surface and whose planar shape is circular; a heater; an anode being arranged to oppose the cathode; and a heat resistant member. The anode applies a positive potential relative to the cathode to extract electrons in a predetermined direction. The cathode has, in a central portion thereof, a through hole along a central axis of the cathode. The heat resistant member has a first portion to close the through hole and a second portion being positioned between the cathode and the heater.

An electron gun comprising a cathode having an electron emitting surface and whose planar shape is circular; a heater; an anode being arranged to oppose the cathode; and a heat resistant member. The anode applies a positive potential relative to the cathode to extract electrons in a predetermined direction. The cathode has, in a central portion thereof, a through hole along a central axis of the cathode. The heat resistant member has a first portion to close the through hole and a second portion being positioned between the cathode and the heater.

An external grid-controlled hot cathode array electron gun, including an insulated cathode base, a filament, a plurality of hot cathode emission elements, and a grid-controlled structure is disclosed. In one aspect, the grid-controlled structure includes an insulated grid-controlled structure body and a plurality of through holes. One side of the grid-controlled structure body abuts against the cathode base to clamp the filament between the grid-controlled structure body and the cathode base and the plurality of hot cathode emission elements are inserted into the plurality of through holes respectively.

An electron beam source is provided that includes a vessel forming a chamber, a cathode disposed within the chamber, the cathode comprising a low dimensional electrically conductive material having an anisotropic restricted thermal conductivity, an electrode disposed in the chamber, the electrode being connectable to a power source for applying a positive voltage to the electrode relative to the cathode for accelerating free electrons away from the cathode to form an electron beam when the cathode is illuminated by electromagnetic (EM) radiation such that the cathode thermionically emits free electrons, and an electron emission window in the chamber for passing a generated electron beam out of the chamber. An electron microscope that incorporates the electron beam source is also provided.

An external grid-controlled hot cathode array electron gun, including an insulated cathode base, a filament, a plurality of hot cathode emission elements, and a grid-controlled structure is disclosed. In one aspect, the grid-controlled structure includes an insulated grid-controlled structure body and a plurality of through holes. One side of the grid-controlled structure body abuts against the cathode base to clamp the filament between the grid-controlled structure body and the cathode base and the plurality of hot cathode emission elements are inserted into the plurality of through holes respectively.

An electron emission apparatus, an electron gun, and a method of fabrication of the electron gun are provided. The electron gun includes a cathode, a Wehnelt, and an anode. The cathode is configured to provide an electron beam. The Wehnelt has a bore. The bore is configured to pass the electron beam. The anode is disposed proximate to the cathode. The diameter of the bore of the Wehnelt and the offset between the Wehnelt and the cathode satisfy a predetermined dimensional relationship. The predetermined dimensional relationship is at least a function of a diameter of the bore of the anode and a distance between the Wehnelt and the anode.

An electron beam source is provided that includes a vessel forming a chamber, a cathode disposed within the chamber, the cathode comprising a low dimensional electrically conductive material having an anisotropic restricted thermal conductivity, an electrode disposed in the chamber, the electrode being connectable to a power source for applying a positive voltage to the electrode relative to the cathode for accelerating free electrons away from the cathode to form an electron beam when the cathode is illuminated by electromagnetic (EM) radiation such that the cathode thermionically emits free electrons, and an electron emission window in the chamber for passing a generated electron beam out of the chamber. An electron microscope that incorporates the electron beam source is also provided.

The present invention relates to an electron gun cathode mount adapted at one end to secure a thermionic cathode and at the other end to be connected to an attachment member, wherein the electron gun cathode mount is structured so as to be capable of, when in use, reducing heat transfer from the thermionic cathode to the attachment member, and the material forming the electron gun cathode mount has a thermal conductivity of less than 10 Wm.sup.?1K.sup.?1 at the operating temperature of the thermionic cathode in a direction from the thermionic cathode to the attachment member. The present invention also relates to an electron gun assembly having the electron gun cathode mount installed therein.