FIELD-EMISSION FROM HAFNIUM CARBIDE

We report on experiments to determine the feasibility of using refractory transition metal carbides as stable field emission cathodes. Applications of such cathodes could include radiation immune microcircuitry, radio frequency (rf) vacuum microelectronic amplifiers, flat panel displays, e-beam lithography, and other uses where the need is for very high density, small spot size electron sources. Hafnium carbide (HfC) single crystal specimens were prepared by arc floating zone refinement from sintered stock. Field emission patterns from heated HfC emitters were observed, and emission stability measurements were made. Ordering of the work functions of low-index crystal planes was determined through field emission microscopy and comparisons were made with thermionic projection microscopy. An effective thermionic work function of phi{100} = 3.34 eV was obtained for a clean surface. The ability of heated HfC field emitters to operate at pressures above those commonly found for field emission cathodes is demonstrated. Current versus time plots are shown on heated emitters having stable dc currents of 0.5 mA and lifetimes > 2400 h. Pulsed field emission measurements on room-temperature HfC emitters are also reported.