Diamond-to-graphite conversion in nanodiamond and the electronic properties of nanodiamond-derived carbon system

Heat-treatment-induced conversion of nanodiamond to nanographite is investigated. Graphitization starts at the surface region around a heat-treatment temperature of 900°C, then it proceeds inward in the particle, and finally it is completed around 1600°C, where nanographite particles form a polyhedron with a hollow inside. The change in the electronic feature is subjected to the structural change induced by the heat treatment. In the intermediate stage of graphitization, where graphene sheets are small and defective, charge transfer takes place from graphitic π-band to nonbonding edge states. Electrophoretic deposition of nanodiamond particles provides a technique for fabricating isolated single nanodiamond particles on a substrate. Successive heat treatment at 1600°C converts a nanodiamond particle to a single nanographene sheet laying flat on a highly oriented pyrolytic graphite substrate. Weak interaction between the nanographene sheet and the substrate is expected to give a model system of nanographene, for which theory predicts the presence of nonbonding \gv-electron states of the edge origin and its related unconventional nanomagnetism.