Highly stable carbon nanotube and graphene field emitters for miniature X-ray tubes

Abstract

Carbon nanotube (CNT) field emitters that exhibit extremely high stability against high-voltage arcing has been demonstrated. The CNT emitters were fabricated on a sharp copper tip substrate that produces a high electric field. A metal mixture composed of silver and copper nanoparticles was used as a binder to attach CNTs to the substrate. Due to the strong adhesion of the metal mixture, CNTs were not detached from the substrate even after many intense arcing events. Through electrical conditioning of the as-prepared CNT emitters, vertically-standing CNTs with almost the same heights were formed on the substrate surface and most of loosely-bound impurities were removed from the substrate. Consequently, no arcing was observed during the normal operation of the CNT emitters and the emission current kept constant even after intentionally induced arcing. Additionally, a simple and convenient route was presented to fabricate freestanding graphene nanosheets and large-area/patterned graphene nanofilms by thermal annealing of indium (In) and graphite mixture. In particles mixed with graphite powder catalytically oxidize the graphite powder and produce carbon oxide gases. The carbon oxide gases are then catalytically graphitized to form graphene nanostructures on In. The morphologies of the graphene nanostructures can be controlled by the In geometry: vertically-standing graphene nanosheets are synthesized using In particles and a graphene nanofilm is grown on a thin In layer. In is then completely removed, and thus high-purity graphene is finally produced. The graphene nanosheets exhibited excellent field-emission performance due to high-density edges. In addition, the graphene nanofilms show electrical conductivities comparable to or better than that of reduced graphene oxide. Furthermore, a large-area or a patterned graphene nanofilm is synthesized using a uniform or a pre-patterned In layer, respectively.