The development of diamond–based nano-carbon composite materials for electron field emitters and microplasma cathode application
I-Nan Lin1*
1Department of Physics, Tamkang University, Tamsui, Taiwan
* presenting author:I-Nan Lin,
The invention of fullerene, carbon nanotubes and graphene inspire new chemistry and physics that was followed by thousands of researches, exploring the potential applications of these new carbon materials. Ultrananocrystalline diamond (UNCD) films show overwhelmingly better electrical conductivity and electron field emission (EFE) properties than the microcrystalline diamond (MCD) or nanocrystalline diamond (NCD) films. The UNCD materials possess a unique granular structure, consisting of ultra-small diamond grains with very uniform size (~5 nm) and thick grain boundaries (~0.1 nm). The grain boundaries contain large proportion of trans-ployacetylene (TPA) phase or other kind of carbonaceous materials, rendering the UNCD films more conductive than the MCD (or NCD) films, which contain grain boundaries of negligible thickness. The drawback of the granular structure of the UNCD films is that the grain boundaries are insufficiently conducting that limited the EFF properties attainable for these materials.
The UNCD films are actually carbon composite materials with each of the constituents, the diamond grains and the grain boundaries, of nano-scale. Therefore, the possible route for amending such a deficiency is to use graphene-like materials to replace for the resistive grain boundary materials. However, mixing of the graphene-like materials with the nano-sized diamond particles is not able to achieve a composite material with good enough electrical properties, as the contact between the mechanically mixed graphene and diamond nano-particles are not sufficiently good. The best solution is to convert the amorphous grain boundaries existing in UNCD films into graphene-like phase in-situ.
In this paper, we reported a one-step microwave plasma enhanced chemical vapor deposition (MPE-CVD) process to synthesize a diamond films with needle-like diamond grains embedded in a matrix of graphene-like materials. Such a diamond-based nano-carbon composites (d/NCC) possesses overwhelmingly superior electrical conductivity and EFE properties, with longer lifetime stability, compared with the other kind of carbon materials. Several potential applications, such as flexible EFE emitters, microplasma UV source, EC sensing electrodes will be demonstrated.

Keywords: conductive diamond films, electron field emission, microplasms