▎ 摘　　要

We report on the growth of nanocrystalline graphene on c-plane Al2O3 substrates by molecular beam epitaxy. Graphene films are grown by carbon evaporation from a highly-oriented-pyrolytic-graphite filament and cover the entire surface of two-inch wafers. The structural quality of the material (degree of crystallinity) is investigated in detail by Raman spectroscopy and is revealed to be strongly dependent on the growth temperature and time. We observe that adjacent graphene layers grow parallel to each other and to the substrate surface with domains sizes larger than 30 nm. Transmission electron microscopy confirms the planarity of the nanocrystalline films and X-ray photoelectron spectroscopy proves the predominant se nature of the grown layers. Transport measurements reveal that the layers are p-type doped with mobility values up to 140 cm(2)/Vs at room temperature. The present results demonstrate the potential of molecular beam epitaxy as a technique for realizing the controlled growth of graphene (mono- and few-layer) over large areas directly on an insulating substrate. (C) 2013 Elsevier Ltd. All rights reserved.