Nanocrystalline Graphite Growth on Sapphire by Carbon Molecular Beam Epitaxy

We report the fabrication of nanocrystalline graphite films on sapphire substrates of various cutting directions by using solid carbon source molecular beam epitaxy. Raman spectra show a systematic change from amorphous carbon to nanocrystalline graphite with a cluster diameter of several nanometers, depending on the growth temperature. The symmetry of the substrate seems to have little effect on the film quality. Simulations suggest that the strong bonding between carbon and oxygen may lead to orientational disorders. Transport measurements show a Dirac-like peak and a carrier type change by the gate voltage.