A cold cathode X-ray tube was fabricated using a carbon nanotube (CNT) field electron emitter made by a free-standing CNT film which is composed of a highly packed CNT network. A lot of CNT bundles with a sharp tip are vertically aligned at the edge of the thin CNT film with a length of 10 mm and a thickness of 7 μm. The cold cathode X-ray tube using the CNT field emitter presents an extremely high tube current density of 152 A/cm2 (corresponding to tube current of 106.4 mA), the electron beam transmittance of 95.2% and a small focal spot size (FSS) of 0.5 mm. In addition, the cold cathode X-ray tube also shows stable lifetime during 100 000 shots. High emission current density of the cold cathode X-ray tube is mainly attributed to a lot of electron emission sites at an edge of the CNT film. The small FSS is caused by an ensemble of the CNT field electron emitter made by a free-standing thin CNT film and the optimized curve-shape elliptical focusing lens. Based on obtained results, the cold cathode X-ray tube can be widely used for various X-ray applications such as medical diagnosis systems and security check systems in the future.

Graphite nanoplatelet (GNP) paste field emitters fabricated using all-carbon-based materials, such as GNPs, graphite nanoparticles, graphite binders, and a graphite rod substrate have been demonstrated. The GNP field emitters on the graphite rod substrate showed an emission current density of 84.3 mA/cm2 and good emission stability with a degradation rate of less than 10%, indicating higher emission performance than other GNP field emitters. The enhanced field emission performance of the GNP field emitter is attributed to a low work function barrier between carbon materials, low contact resistance between GNPs and the graphite rod substrate, and good GNP paste bulk electrical conductivity. The new approach to fabricate GNP field emitters using all-carbon-based materials can be useful for various field emission devices.