Structure and electronic properties of graphite nanoparticles

We have investigated the structure and electronic properties of graphite nanoparticles prepared by heat treating diamond nanoparticles. The prepared nanographite forms a polyhedron with a hollow in its inside, whose faces comprise a stacking of 3--6 planar graphene sheets with an in-plane size of 7--8 nm and an intersheet distance of 0.353 nm. The large intersheet distance suggests a considerably large reduction in interlayer interaction compared to the case of bulk regular graphite. Electron-spin-resonance and magnetic-susceptibility measurements show that there is a considerable enhancement in the density of states at the Fermi energy, indicating the presence of an additional band superimposed upon the bonding {π} and the antibonding π* bands around the Fermi energy. Taking into consideration the discontinuous shape at an edge line formed by crossing adjacent graphene sheets, graphene sheets in a nanographite particle are considered to have open {π}-bond edges. On the basis of the theoretical suggestion that nonbonding {π} orbitals give edge-inherited surface states depending on the shape of the graphene edge, this is suggestive of the contribution of the edge states to the electronic structure of nanosized graphene having open {π}-bond edges.