ABSTRACT
Some of these changes in the electronic structure are unique to carbon, and result from the fact that graphite is a narrow band overlap semimetal. In the absence of interplanar interactions, graphite would be a zero-gap semiconductor, as a result of symmetry. Thus the small band overlap in graphite results from interactions between planes. These interplanar interactions can be modified, and effectively reduced to zero, by introducing stacking disorder, resulting in turbostratic carbon, where the carbon atom sites on adjacent layers are uncorrelated and where the individual graphene sheets are not explicitly bonded to each other. When long range order in the planes is disrupted, this degeneracy is lifted, and, in effect, a narrow band gap semiconductor results, in which there are localized states in the gap near the band edges. This disorder can be extended continuously to describe amorphous carbon as a limiting case. Experimentally, heat treatment or annealing can be used to increase
the amount of order in a disordered graphite, and ion implantation or neutron irradiation can be used to increase the disorder. The heat treatment temperature ( 7 h t ) at fixed residence time has been used as a rough characterization parameter for the amount of disorder (Oberlin, 1984).
