OUERGHI ET AL . VOL. XXX ’ NO. XX ’ 000–000 ’ XXXX www.acsnano.org A C XXXX American Chemical Society Large-Area and High-Quality Epitaxial Graphene on Off-Axis SiC Wafers Abdelkarim Ouerghi, †, * Mathieu G. Silly, ‡ Massimiliano Marangolo, § Claire Mathieu, † Mahmoud Eddrief, § Matthieu Picher, † Fausto Sirotti, ‡ Souliman El Moussaoui, ‡ and Rachid Belkhou ‡ † Laboratoire de Photonique et de Nanostructures (CNRS-LPN), Route de Nozay, 91460 Marcoussis, France, ‡ Synchrotron-SOLEIL, Saint-Aubin, BP48, F91192 Gif sur Yvette Cedex, France, and § Institut des NanoSciences de Paris, UPMCCNRS, UMR 7588, 4 Place Jussieu, 75005 Paris, France T he recent discovery of the electronic properties of a graphene layer 13 has fostered the exciting research field of graphene-based materials, in turn stimulat- ing many new discoveries 4 and potential applications. 2 Graphene is a zero band gap material with very unique electronic and optical properties including extremely high carrier mobility, massless Dirac fermions, and quantum Hall effects at room tempera- ture. 3 This has led to a tremendous rise in experimental research on graphene for applications such as ultra-high-speed field- effect transistors, pn junction diodes, ter- ahertz oscillators, optical sensors, and low- noise electronics. 4,5 Up to now, a large number of fundamental studies of gra- phene have been carried out using micro- mechanical cleavage of single-layer flakes from graphite, 2 chemical vapor deposition (CVD) of carbon on single-crystal transition metals, 6,7 or epitaxial growth by thermal decomposition of SiC surfaces. 1 The two latter approaches have already been shown to reach large-scale graphene. For electronic applications, the epitaxial growth of graphene by CVD presents a drawback since it requires transferring the graphene onto an insulating substrate. This transfer step involves heavy chemical ma- nipulation and can result in contamination and limiting of the mobility of the sample. In the case of epitaxial graphene on SiC, the substrate acts already as an insulator, so that intrinsic properties of graphene are preserved. Moreover epitaxial graphene on SiC is suitable for optics, because the substrate is transparent over a very broad frequency spectrum, and for application in high-frequency devices, where losses due to residual conductivity of the substrate have to be minimized by using high-quality insulating materials. Nevertheless, control of the preparation conditions for homo- geneous large-area graphene layers remains a challenge. Indeed, on the on-axis Si-terminated SiC substrate, vacuum annealing leads only to small graphene domains (a few hundred nano- meters) with nonuniform multilayers growing simultaneously. 4,8 It appears that this limitation is mainly due to the high sublimation rate of Si atoms from SiC substrates at elevated temperatures (∼1400 °C). Therefore, homoge- neity can be signi ficantly improved by a better control of the sublimation rate of Si atoms (Figure 1). Recent approaches have been taken toward higher-quality films involving heating under argon at atmospheric pressure 8,9 or supplying an excess of Si in the gas phase. 10 These new approaches enable significant improvements in domain size and in the electronic properties compared to vacuum * Address correspondence to Abdelkarim.Ouerghi@lpn.cnrs.fr. Received for review March 15, 2012 and accepted June 16, 2012. Published online 10.1021/nn301152p ABSTRACT The growth of large and uniform graphene layers remains very challenging to this day due to the close correlation between the electronic and transport properties and the layer morphology. Here, we report the synthesis of uniform large-scale mono- and bilayers of graphene on off-axis 6H-SiC(0001) substrates. The originality of our approach consists of the fine control of the growth mode of the graphene by precise control of the Si sublimation rate. Moreover, we take advantage of the presence of nanofacets on the off-axis substrate to grow a large and uniform graphene with good long-range order. We believe that our approach represents a significant step toward the scalable synthesis of graphene films with high structural qualities and fine thickness control, in order to develop graphene-based electronic devices. KEYWORDS: epitaxial graphene . spectroscopy . vicinal SiC . scanning tunneling microscopy . low-energy electron microscopy . electronic properties ARTICLE