Method for reproducibly fabricating and using stable thermal-field emission cathodes

Claim 1

The method of claim 1 in which magnitude of the field is not allowed to exceed a value at which arcing occurs between the tip and the electrode.

Claim 11

A method for fabricating a stable thermal field emission cathode for long-term usage under conditions of high current density emission in a relatively relaxed vacuum environment, the method including the steps of: a. forming a generally conical tip at one end of a Miller indices <100> oriented metal wire composed of a material having a body centered cubic crystalline structure; b. heating the metal wire in a partially evacuated enclosure to a first temperature, which first temperature is sufficiently high to cause the desorption of surface contaminants, including compounds of carbon, while not exceeding a second temperature at which the generally conical tip would undergo substantial geometric deformation; c. heating the metal wire in the partially evacuated enclosure without exceeding a second temperature at which substantially all residual surface oxide of the metal would be desorbed; and d. imposing an electrical potential between the wire tip and an adjacent electrode, the imposed potential being adequate to develop a field of sufficient magnitude at the wire tip to initiate build-up of the (100) planes and to initiate faceting of at least the (110) and (211) planes; steps c and d being performed in overlapping sequence, whereby a stable thermal field emission cathode is formed having an axially disposed, generally tetrahedral, endform, the apex of said endform being characterized by a relatively small effective radius of curvature.

Claim 17

A method for reproducibly fabricating a stable thermal field emission cathode for long-term usage under conditions of high current density emission in a relatively relaxed vacuum environment, the method including the steps of: a. forming a generally conical tip at one end of a Miller indices <100> oriented metal wire composed of a material having a body centered cubic crystalline structure; b. heating said metal wire in a partially evacuated enclosure, to a first temperature sufficiently high to cause the desorption of surface contaminants, including carbon as a volatile oxide thereof, while not exceeding a second temperature at which substantially all residual surface oxide would be desorbed from the wire tip; c. maintaining said metal wire in said partially evacuated enclosure at a third temperature, the third temperature being less than the second temperature but sufficiently high to assure surface mobility at the wire tip responsive to surface tension; and d. imposing an electrical potential between the tip of the metal wire and an adjacent electrode, said potential being of sufficient magnitude to initiate build-up of the (100) planes and to initiate faceting of at least the (110) and (211) planes, said potential being less than that potential at which geometrically destructive vacuum arcing occurs; said imposing step being sequentially interchangeable with said maintaining step; whereby a stable thermal field emission cathode is formed having an axially disposed, generally tetrahedral, endform, the apex of the endform being characterized by a relatively small effective radius of curvature and a correspondingly small effective emission area.

Claim 26

A method for reproducibly fabricating a stable thermal field emission cathode for long-term usage under conditions of high current density emission in a relatively relaxed vacuum environment, the method including the steps of: a. forming a generally conical tip at one end of a Miller indices <100> oriented metal wire composed of a material having a body centered cubic crystalline strucuture; b. heating the metal wire in a partially evacuated enclosure to a first temperature, which first temperature is sufficiently high to bring about the desorption of substantially all surface contaminants, including carbon as a volatile oxide thereof, while not exceeding a second temperature at which the generally conical tip would undergo substantial geometric deformation; c. heating the metal wire in the partially evacuated enclosure to a third temperature, which third temperature is lower than a temperature at which substantially all residual surface oxide of the metal would be desorbed, said metal wire being exposed to a limited partial pressure of oxygen sufficient to assure the presence of oxides on the surface of the metal wire; and d. imposing an electrical potential between the tip of the metal wire and an adjacent electrode, the potential being adequate to develop a field of sufficient magnitude to initiate build-up of the (100) planes and to initiate faceting of at least the (110) and (112) planes, the potential being lower than a potential at which geometrically destructive vacuum arcing occurs; steps c and d being performed in overlapping sequence, whereby a stable thermal field emission cathode is formed having an axially disposed, generally tetrahedral, endform, the apex of which endform is characterized by a relatively small effective radius of curvature and a correspondingly small effective emission area.

Claim 29

A method for reproducibly fabricating a stable thermal field emission cathode for long-term usage under conditions of high current density emission in a relatively relaxed vacuum environment, the method including the steps of: a. forming a generally conical tip at one end of a Miller indices <100> oriented metal wire composed of a material having a body centered cubic crystalline structure; b. heating the metal wire in a partially evacuated enclosure to a first temperature, which first temperature is sufficiently high to bring about the desorption of substantially all surface contaminants, including carbon as a volatile oxide thereof, while not exceeding a second temperature at which the generally conical tip would undergo substantial geometric deformation; c. maintaining the metal wire in the partially evacuated enclosure at a third temperature, which third temperature is lower than a fourth temperature at which substantially all residual surface oxide would be desorbed; d. forming oxides of the metal comprising the wire on the tip surface thereof; and e. imposing an electrical potential between the tip of the metallic wire and an adjacent electrode, the potential being adequate to develop a field of sufficient magnitude to initiate build-up of the (100) planes and to initiate faceting of at least the (110) and (112) planes, said potential being lower than a potential at which geometrically destructive Vacuum arcing occurs; whereby a stable thermal field emission cathode is formed having an axially disposed, generally tetrahedral, endform, the apex of which endform is characterized by a relatively small effective radius of curvature.

Claim 32

A method for reproducibly fabricating a stable thermal field emission cathode for long-term usage under conditions of high current density emission in a relatively relaxed vacuum environment, the method including the steps of: a. forming a conical tip with a generally hemispherical endform at one end of a Miller indices <100> oriented tungsten wire having a diameter in the range of values between 0.005 and 0.010 inches; b. heating the tungsten wire in a partially evacuated enclosure to a first temperature falling in the range of temperatures between 1,400* and 1,900*K, the enclosure having an internal pressure in the range of pressures between 10 7 and 10 9 torr; c. maintaining the tungsten wire in the enclosure at a second temperature falling in the range of temperatures between 1, 200* and 1,900*K; and d. imposing an electrical potential between the tungsten wire and an adjacent electrode, the potential being of sufficient magnitude to cause an initial electrical current flow between the tungsten wire and the electrode in the range of currents between 10 and 20 microamperes; whereby a stable thermal field emission cathode is formed having an axially disposed, generally tetrahedral, endform, the apex of which endform is characterized by a relatively small effective radius of curvature.

Claim 35

A method for reproducibly fabricating a stable thermal field emission cathode for long-term usage under conditions of high current density emission in a relatively relaxed vacuum environment, the method including the steps of: a. forming a conical tip with a generally hemispherical endform at one end of a Miller indices <100> oriented tungsten wire having a diameter in the range of values between 0.005 and 0.010 inches; b. heating the tungsten wire in a partially evacuated enclosure to a first temperature in the range of temperatures between 1, 400*K and 1,900*K, the enclosure having an internal pressure in the range of pressures between 10 7 and 10 9 torr; c. maintaining the tungsten wire in the enclosure at a second temperature falling in the range of temperatures between 1, 200*K and 1,900*K; d. imposing an electrical potential between the tungsten wire and an adjacent electrode, the potential being of sufficient magnitude to cause initial electrical current flow between the tungsten wire and the electrode in the range of currents between 5 and 25 microamperes; e. detecting substantially increased current flow between the tungsten wire and the electrode, the increased current flow being an indicia of (100) plane build-up and the associated facetings of at least the (110) and (112) planes; and f. adjusting the imposed potential to achieve a predetermined current flow rate between the wire and the electrode; whereby a stable thermal field emission cathode is formed having an axially disposed, generally tetrahedral, endform, the apex of which endform is characterized by a relatively small effective radius of curvature.

Claim 38

A method for refabricating during operation a thermal field emission cathode fabricated from <100> oriented starting material, said method including the sequentially interchangeable and overlapping steps of: a. heating the cathode in a partially evacuated enclosure to at least a first temperature, said first temperature being sufficiently high to assure surface mobility at the emission tip of said cathode, while not exceeding a second temperature at which substantially all residual surface oxide would be desorbed; and b. imposing an electrical potential between the cathode and an adjacent electrode, said potential being of sufficient magnitude to initiate build-up of the (100) planes and to initiate faceting of at least the (110) and (112) planes, the potential being lower than a potential at which geometrically destructive vacuum arcing occurs.