Formation of nanocrystalline diamond cones by reactive ion etching in microwave plasma for enhancing field emission

Cone-like nanostructures are formed on nitrogen-incorporated nanocrystalline diamond films by reactive ion etching (RIE) in a moderate-pressure microwave plasma. A thin Au layer is deposited on the film and followed by heating for transformation of an Au layer into Au nanoparticles as the mask for RIE. The diameter and spacing of Au nanoparticles depend upon the heating temperature and the thickness of Au. The smooth film surface is transformed into a number of cone-like protrusions with diameters, heights, and spacings of tens to a few hundreds of nm by RIE in a hydrogen/argon plasma and removal of Au residue in aqua regia. The formation of sharp nanostructures enhances field emission characteristics, so that the current density at high fields is increased largely up to the order of 10−3 A cm−2 and the turn-on field is reduced down to around 1.8 V m−1, comparable to other carbon nanostructures, due to enhancement of local fields.