Field Emission from Carbon Fibres: A New Electron Source

Abstract

IN certain electron beam devices, field electron emitting sources possess distinct advantages over thermionic emitters¹. Much effort has been expended to exploit these advantages in instruments such as scanning electron microscopes², microwave amplifiers^1,3, and X-ray generators^1,4. The preferred emitter material in nearly all these devices has been tungsten, which operates only under ultra high vacuum conditions; it is primarily for this reason that field electron emitters have not been widely adopted commercially. Consequently attempts have been made to find materials which will operate in the region 10⁻⁶ to 10⁻⁸ torr^5–7. As field electron emitters silicon carbide “whiskers” were less sensitive to vacuum conditions than tungsten⁸, but a number of practical difficulties—the material varied considerably from sample to sample, it was not easy to make a reliable ohmic contact to the crystal and the etching technique (similar to that of Smith⁹) was somewhat variable in its results—made reproducible operation difficult.