Improvement of electron field emission properties of nanocrystalline diamond films by a plasma post-treatment process for cathode application in microplasma devices

Abstract

The electron field emission (EFE) properties of nanocrystalline diamond (NCD) films were markedly enhanced when prepared with a plasma post-treatment on the ultra-small-grain granular-structured diamond films, as compared with conventional NCD films directly grown on Si using CH4/Ar/H2 plasma. Transmission electron microscopy reveals that the primary influence for the improvement of the EFE properties of these films was owing to an induction of the nanographitic phase in the films, while the ultrasmall diamond grains (∼5 nm) coalesced to form large diamond grains (∼hundreds of nanometers) during the plasma post-treatment process. This modification of the granular structure of the NCD films was greatly enhanced when a negative bias voltage (−300 V) was applied during the plasma post-treatment process. Moreover, three-electrode microplasma devices performed overwhelmingly better than two‐electrode devices, exhibiting a higher plasma current density with a longer lifetime stability. These microplasma devices...