Preparation and characterization of zirconium carbide field emitters

The authors report on experiments to determine the feasibility of using the refractory transition metal carbide ZrC as a stable field-emission cathode. Emphasis is on the preparation and analysis of methods needed to obtain stable electron emission from a cold field-emission cathode. ZrC single-crystal specimens were prepared by arc floating zone refinement from sintered stock, yielding an average bulk stoichiometry of C/Zr=0.913. Due to its brittle nature and the high temperatures required for cleaning of this carbide, new mounting methods were developed. Emitter etching procedures are reported for ZrC, as well as in situ tip sharpening techniques of neon-ion bombardment and temperatures required for thermal cleaning. A temperature of 1500 degrees C is required to remove adsorbates including oxygen. A clean ZrC field-emission pattern is shown. Ordering of work functions of various crystal planes is reported through field-emission microscopy, and comparisons are made with thermionic projection microscopy. Effective thermionic work functions are presented for clean surfaces to support further the ordering obtained. The ability of ZrC field emitters to operate at pressures far above those commonly found for field-emission cathodes is demonstrated.