On the electrical activity of sp 2 -bonded grain boundaries in nanocrystalline diamond

By means of tight-binding molecular dynamics simulations we find that the ground-state atomic structure of a typical high-energy grain boundary in diamond is highiy disordered with a large fraction of sp 2 bonded atoms. This structure gives rise to localised bands within the band gap. We describe how multiphonon assisted hopping conduction can arise from such electronic states in high-energy grain boundaries, giving in turn a basis for the experimentally observed conductivity and electron field emission in nanocrystalline diamond. Simulated electron-energy-loss spectra indicate correlations between the disordered atomic structure and features of the electronic structure.