Very large cathode current and long term stability of vacuum sealed tubes with engrafted-carbon-nanotube emitters

For the future commercial applications of carbon nanotubes (CNTs) in high power vacuum microwave amplifiers or compact X-ray tubes, we have attempted to fabricate engrafted CNT field emitters on a metallic substrate using both screen printing and chemical vapor deposition. Cobalt nano-grains are doped in the printed CNT paste and act as the catalyst for the engrafted growth of CNTs by the cold wall chemical vapor deposition. Stable cathode current (similar to 30 mA) from a small area (similar to 1.5 mm(2)) of engrafted CNT emitters was measured in a vacuum-sealed diode tube. High current density (>1.6A/cm(2)) has also gotten in the vacuum sealed tube in which the emitters spread about 0.78 mm(2) after an aging process that lasts more than 12 h in DC mode with the water cooling of the anode. (C) 2014 Elsevier B.V. All rights reserved.