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Controlled Method of Melting Lanthanum Hexaboride Cathodes Prior to Fabricating Fine Tips

IP.com Disclosure Number: IPCOM000077128D
Original Publication Date: 1972-Jun-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Blair, WW: AUTHOR [+2]

Abstract

The lanthanum hexaboride (LaB6) rod to be melted is first machined to a rough point and then assembled into a standard rod cathode assembly with heater coil and heat shield, as shown in the drawing. A second assembly with a flat top LaB6 rod cathode, heater coil and heat shield is mounted opposite the first assembly, separated by electrical insulators. This unit is constructed so that the two LaB6 rods are separated by about 0.4 mm.4

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Controlled Method of Melting Lanthanum Hexaboride Cathodes Prior to Fabricating Fine Tips

The lanthanum hexaboride (LaB6) rod to be melted is first machined to a rough point and then assembled into a standard rod cathode assembly with heater coil and heat shield, as shown in the drawing. A second assembly with a flat top LaB6 rod cathode, heater coil and heat shield is mounted opposite the first assembly, separated by electrical insulators. This unit is constructed so that the two LaB6 rods are separated by about 0.4 mm.4

The unit is placed in a vacuum. The upper pointed rod (the one to be melted) is then heated by radiant power from the upper coil. When the tip of the upper rod reaches approximately 1400 degrees C, the lower rod is heated, a switch is closed connecting the positive side of a variable-power supply to the upper rod, and electron emission from the lower rod occurs. Because the upper rod is pointed, this area gets hot first and consequently the point melts. The melting process is observed through a vacuum window and is visually monitored.

The advantage of preheating the pointed rod is that the electron bombardment power required to melt the tip is low enough to be easily controlled, allowing for accurate visual Monitoring. The preheating of the rod assures that the center radius will be melted. The use of the LaB6 rod cathode allows up to 100 Angstroms/cm/2/ of current emission, this facilitates the use of low voltage power supplies.

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