Engineering the electronic structure of epitaxial graphene by transfer doping and atomic intercalation
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troduction The growth of epitaxial graphene (EG) on silicon carbide (SiC) has been established as one of the most promising methods for obtaining large graphene samples (also see the introductory article in this issue, as well as the articles by Ruan et al. and Nyakiti et al.). On the two SiC basal plane surfaces, SiC(0001) and SiC(0001), large crystalline regions of graphene can be prepared with homogeneous thickness and uniform properties. Notably, the two crystal faces are characterized by dramatically different growth modes for graphene. On SiC(0001) (the so-called Si face), graphene layers develop in a well-defined epitaxial relationship to the SiC substrate, and additional layers of graphene emerge with the same rotational orientation, so that both monolayer graphene and electronically coupled few-layer graphene (FLG) slabs can be prepared.1,2 In contrast, on SiC(0001) (the so-called C face), graphene layers exhibit a varying rotational relationship with respect to the substrate, and in particular, subsequent layers typically assume different rotational orientations, so that stacks of graphene monolayers emerge.3 The reason for this difference appears to be the strongly differing strengths of the interactions between EG and the
SiC substrate on the two surfaces. On SiC(0001), the rather weak influence of the substrate leads to almost charge-neutral graphene layers, a fact that has been extensively exploited to investigate the remarkable electronic properties of graphene on a wafer size scale.4 However, it also leads to an undefined rotational orientation of the first grown layer with respect to the substrate and even rotational disorder among different patches of the first graphene layer.5,6 In contrast, on SiC(0001), strong coupling between EG and the substrate fixes the epitaxial angle of each layer.1 This interaction leads to covalent bonds between the topmost silicon atoms of SiC and the initial carbon layer grown. Because of these bonds, this initial carbon layer does not have a delocalized π-band system. The layer is rather electronically inactive and is therefore often called zero-layer graphene (ZLG). When thicker slabs of graphene are grown, the layer closest to the substrate assumes this ZLG structure and serves as a buffer layer for the layers above; it is only for these additional layers that the typical π bands for monolayer graphene (MLG), bilayer graphene (BLG), and so forth appear. Most importantly, the bond configuration of the coupling between ZLG and SiC induces considerable n-doping in the overlying graphene layers.
U. Starke, Max-Planck-Institut für Festkörperforschung, Germany; [email protected] S. Forti, Max-Planck-Institut für Festkörperforschung, Germany; [email protected] K.V. Emtsev, Max-Planck-Institut für Festkörperforschung, Germany; [email protected] C. Coletti, Center for Nanotechnology Innovation, Italian Institute of Technology, Italy; [email protected] DOI: 10.1557/mrs.2012.272
© 2012 Materials Research Society
MRS BULLETIN • VOLUME 37 • DECEMBER 2012 • www.mrs.org/bull
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