An investigation of the field emission characteristics of W, Mo and Si emitters with deposited ZrC films

Summary form only as given. We have demonstrated significant improvements in performance of field emitter arrays (FEAs) by depositing ZrC films onto the emitter surfaces. These findings have been made on Mo emitter arrays obtained from SRI and, in a preliminary fashion, on Si emitter arrays obtained from MCNC. The challenge with this approach is to achieve the desired properties (stability and low work function) in the deposited layers. In order to understand the nature of these layers in detail, we have undertaken a fundamental study of ZrC and HfC layers on well-characterized surfaces. We report here the results of carefully controlled studies of the deposition of ZrC onto individual prefabricated W, Mo and Si emitters and of I-V and field emission microscopy (FEM) characterization of the resulting cathodes. Emitters were individually fabricated by electrochemical etching of polycrystalline wire (W and Mo) and single crystals (W and Si). The emitters were cleaned by heating and were characterized in an in situ FEM in the carbide evaporation chamber. Once it was verified that the emitter apex was a single crystal and its clean field emission pattern had been established, a film of carbide was evaporated onto the emitter surface from a high-purity ZrC evaporation source. The deposited film was subjected to a variety of heating treatments, each of which was followed by FEM examination and determination of I-V characteristics. The nature of electron emission changes induced by deposition of the carbide films on the initially clean metal emitters can be inferred using a technique which was developed earlier to study emission changes from single crystal carbide emitters. Fowler-Nordheim slope/intercept data for an emitter, before and after carbide film deposition, are plotted onto a family of curves of constant work function and a family of curves of constant field enhancement factor. Trends in changes of work function or field enhancement factor may then be determined. The results of these experiments indicate that work function reductions of the order of 1 eV can be achieved by the deposition of ZrC films once W or Mo field emitters. Furthermore, a degree of beam confinement has been observed in these individual emitter studies, with the greatest work function lowering effect observed on the (100) planes of individual emitters. The results of these fundamental studies and of studies of ZrC on FEAs will be reported.