High-temperature processable carbon–silicate nanocomposite cold electron cathodes for miniature X-ray sources

We report on the fabrication, Raman characterization and electron emission behavior of cold electron cathodes that are specifically designed to be used in miniature X-ray sources. The cathodes are fabricated by screen-printing a nanocomposite paste comprising multiwall carbon nanotubes as fillers in a matrix of graphite, glass and bentonite clay. The cathodes can resist high temperatures up to 880 °C and, as such, can survive most high-temperature brazing steps required for vacuum-tight sealing of the sources. We demonstrate peak emission current densities around 300 mA cm−2 at an applied electric field of 175 kV cm−1 and stable emission around 50 mA cm−2 at 125 kV cm−1 for at least 5 hours without significant degradation. X-rays were successfully generated at 3.2 watts of peak power (80 μA, 40 kV) with a commercial X-ray tube modified to accommodate a paste cathode.