We have grown epitaxial thin sheets of graphene on BC 3 /NbB 2 (0001) and measured phonon dispersion curves of the graphene sheets by means of high-resolution electron energy-loss spectroscopy (HREELS). The phonon dispersion curves have been calculated on the basis of ab initio calculations. The observed curves were in good agreement with theoretical curves. The quality of crystallinity of the graphene layers was high compared with the bulk graphite crystals. In this paper, we demonstrate that the combination of HREELS measurement and ab initio calculations is extremely effective for investigation of honeycomb-structured materials.

The entire phonon-dispersion curves along the Gamma-M direction of a BC3 honeycomb sheet have been determined both experimentally and theoretically for the first time. Most of the observed curves agreed with the theoretical ones calculated on the basis of ab initio theory. From the stretching force constants of the nearest-neighbor C-C and B-C bonds, together with that of the B-B bond, we clarified the characteristic feature of the C-C and B-C bonds. From the experimental and theoretical results, we discussed the possibility of high T(c).

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