The comparison of the emission characteristics of Zr/O/W and Hf/O/W Schottky emission cathodes

Schottky emission (SE) cathodes, mainly the Zr/O/W SE cathode, are being used successfully for several different microprobe applications. The Zr/O/W SE cathode is a source capable of high brightness and high angular intensity values. Practical values for the Zr/O/W SE cathode have been measured as high as 109 A/cm/sup 2/ sr and 5 mA/sr, respectively. Although the Zr/O/W SE cathode has the ability to operate at high current densities for extended periods of time with high stability, it has some limitations for applications that require low angular intensities and low total currents. Initial results show that these limitations can be eliminated by replacing the Zr with Hf. The Hf/O/W SE cathode is another high brightness SE source that is better suited for low angular intensity applications. In this paper, the emission characteristics for the Hf/O/W SE cathode are investigated and compared with the Zr/O/W SE cathode.