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Summary form only given. Csl coated carbon fiber cathodes have shown promise as a cold cathode for microwave and x-ray devices. In particular, the cathodes have demonstrated over 1 million shots lifetime at operating voltages at or in excess of 165 kV and current densities greater than 50 A/cm2. Further, the materials have also operated in a DC mode. While the vacuum emission characteristics have been well-studied1, the materials characteristics of the cathodes themselves, particularly after operation have not received great attention. Furthermore, while researchers at University of Wisconsin" have demonstrated a reduction in work function due to the Csl coating, the emission mechanism remains poorly understood. This paper gives results of a series of materials diagnostics investigating the cathode surface morphology as well as the changes in the carbon fiber structure with cathode shot history. We rely principally upon SEM images and Raman microscopy for this data. Finally, we present a basic model for electron emission from Csl coated carbon fibers that begins to satisfy some of the experimental results.