Background and motivation

Advances in electron sources technology potentially have a profound impact on a whole range of applications, extending from flat panel displays to telecommuni-cations and electric-propulsion systems for spacecraft. Presently, the most widely employed electron source is the bulky thermionic cathode which is used in televi-sion cathode-ray tubes and high power microwave amplifiers. In our never ending quest for miniaturization, recent requirements for electron sources in applications such as flat panel displays, parallel electron beam microscopy and nanolithography, compact microwave amplifiers and portable X-ray tubes have motivated worldwide research into alternative smaller, more efficient source technologies. Field emission (FE) electron sources are candidates for such applications. In contrast to the commonly used thermionic emission based on a hot filament, field emission from an unheated cold cathode occurs by electron tunneling through a field-thinned barrier at room temperature. It is immediately apparent that a field emitter could be more power efficient than a thermionic emitter which requires heat-ing. In addition, field emission sources also offer several attractive characteristic