Ultrananocrystalline diamond for electronic applications

Ultrananocrystalline diamond is a unique form of carbon with grain sizes in the 3-5 nm region. This nanostructure has profound implications on electronic transport, as ~10% of carbon is at the grain boundaries. Thus, this material has significant π bonding which governs the majority of the electrical conductivity due to the lower energy gap of π-π* transitions relative to σ-σ* transitions. The addition of nitrogen into the gas phase during deposition promotes n-type conductivity, due to the increase in the density of states associated with π bonding. This material is not doped in the conventional sense, and its applications lie in the electrode/metallic conductivity region rather than in the more moderately doped active device regime. This review paper aims to describe the origin and behaviour of the conductivity mechanism, as well as briefly review some applications.