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 g round-state atomic structure of a typical high-energy grain boundary in dia mond is highly disordered with a large fraction of sp(2) bonded atoms. This structure gives rise to localised bands within the band gap. We describe h ow multiphonon assisted hopping conduction can arise from such electronic s tates in high-energy grain boundaries, giving in turn a basis for the exper imentally observed conductivity and electron field emission in nanocrystall ine diamond. Simulated electron-energy-loss spectra indicate correlations b etween the disordered atomic structure and features of the electronic struc ture.