Paper TF-ThA7
Low Work Function CsI Coatings for Enhanced Field Emission Properties

Thursday, October 21, 2010, 4:00 pm, Room Ruidoso

The use of CsI coatings on graphite fiber cathodes has been shown to reduce the field strength required for field emission from approximately 10⁴ V/cm to 250 V/cm. Interestingly, the mechanism for enhanced field emission is poorly understood. We have explored the enhancement mechanism by using simulated cathode structures consisting of CsI films deposited (by thermal evaporation and by pulsed laser deposition) onto graphite and Si surfaces; the films were characterized by x-ray photoelectron, Auger electron, ultraviolet photoelectron, and electron energy loss spectroscopy. Two aspects of the enchantment mechanism have been explored. The first, cathode conditioning, was addressed by characterizing the surfaces of CsI-coated cathodes and (stainless steel) anodes before and after conditioning. The results allow us to assess the change in cathode surface chemistry as well as the extent to which material is transferred between electrodes during conditioning. The second aspect concerns the reported observation that CsI coated cathodes, after use, exhibit the disappearance of I and the appearance of a coating that appears to have wetted the cathode surface. We hypothesize that I depletion leaves behind a film of Cs which, with its low melting point, will flow during cathode operation. To test this hypothesis, we have characterized I depletion from CsI by carrying out electron and photon stimulated desorption from CsI surfaces. The talk will conclude with a discussion of our findings and their relevance to the enhancement mechanism.