Field Emission from Carbon Fibres: A New Electron Source

IN certain electron beam devices, field electron emitting sources possess distinct advantages over thermionic emitters 1 . Much effort has been expended to exploit these advantages in instruments such as scanning electron microscopes 2 , 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 tungsten 8 , 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 Smith 9 ) was somewhat variable in its results—made reproducible operation difficult.