Quasifreestanding multilayer graphene films on the carbon face of SiC

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Quasifreestanding multilayer graphene films on the carbon face of SiC

D. A. Siegel, C. G. Hwang, A. V. Fedorov, and A. Lanzara

Phys. Rev. B 81, 241417(R) – Published 30 June 2010

Abstract

The electronic band structure of as-grown and doped graphene grown on the carbon face of SiC is studied by high-resolution angle-resolved photoemission spectroscopy, where we observe both rotations between adjacent layers and $A B$ stacking. The band structure of quasifreestanding $A B$ bilayers is directly compared with bilayer graphene grown on the Si face of SiC to study the impact of the substrate on the electronic properties of epitaxial graphene. Our results show that the C-face films are nearly free standing from an electronic point of view due to the rotations between graphene layers.

Received 4 March 2010

DOI:https://doi.org/10.1103/PhysRevB.81.241417

Authors & Affiliations

D. A. Siegel^1,2, C. G. Hwang², A. V. Fedorov³, and A. Lanzara^1,2,*

¹Department of Physics, University of California, Berkeley, California 94720, USA
²Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
³Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

^*Author to whom correspondence should be addressed; alanzara@lbl.gov

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Vol. 81, Iss. 24 — 15 June 2010

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Images

Figure 1
(Color online) (a) ARPES dispersions taken along the $Γ -K$ direction at $k_{z} = 4.0 Å^{- 1}$ , showing bands that correspond to a superposition of signals from $A B$ -stacked films of different thicknesses. (b) The second derivative of panel (a) enhances the weaker multilayer sidebands. (c) Photon energy or $k_{z}$ dependence of photoemission intensity, at 1 eV binding energy, shows that the bands of panel (a) correspond to different thicknesses of $A B$ -stacked films. (d) Four Lorentzian peaks were fit to ten MDCs to obtain the data in (e). (e) A comparison of the intensity ratios of the bands in (a) to the intensity ratios one should expect from previously measured x-ray data.Reuse & Permissions
Figure 2
(Color online) (a) A cartoon illustrating bilayer graphene grown on the Si face of SiC, including the SiC substrate, carbon-rich buffer layer (horizontal dotted line) and bilayer graphene planes (horizontal solid lines). (b) A cartoon illustrating the stackings in C-face graphene. Arrows mark rotational faults. Layer groups (i)–(iv) correspond to 1 ML, 2 ML, 2 ML, and 1 ML $A B$ -stacked domains, respectively. (c) An $A B$ -stacked bilayer pair. (d) A rotated bilayer pair.Reuse & Permissions
Figure 3
(Color online) (a) ARPES dispersions taken along the $Γ -K$ direction at $k_{z} = 4.5 Å^{- 1}$ for the as-grown sample. Tight-binding dispersions have been added for the bilayer bands as a guide to the eye. The vertical dotted line in panels (a) and (c) give the position of the K point. (b) is a second derivative of (a). (c) ARPES dispersions taken along the $Γ -K$ direction at $k_{z} = 4.5 Å^{- 1}$ , electron doped by 0.0158 electrons per unit cell by potassium deposition. Tight-binding dispersions have been added as a guide to the eye. (d) is a second derivative of (c). The K point in panel (d) has been marked for each of the bilayer bands.Reuse & Permissions
Figure 4
(Color online) (a) Comparison of band energies at the K point [in Fig. 2 these are the energies where bands cross the vertical dotted lines, as marked by Greek letters in panel 2(d)] for bilayer graphene grown on the C face in red (gray) and Si face (black) of SiC, as a function of doping. Si-face data were obtained from Ref. 18. (b) Comparison of $U$ as a function of doping. The error bar for the leftmost data point gives an upper limit from a tight-binding fit. (c) Comparison of $γ_{1}$ as a function of doping.Reuse & Permissions
Figure 5
(Color online) Illustrations of the interlayer potential difference $U$ for bilayer graphene on the carbon and silicon faces of SiC for several dopings. On the Si face, the as-grown junction between bilayer graphene and the SiC substrate forms a Schottky potential and a buildup of charge near the interface, which results in a finite $U$ . On the C face, azimuthal rotations between bilayer graphene and the graphitic substrate result in a much smaller substrate interaction and a smaller $U$ . Electron doping the sample with potassium increases $U$ as indicated.Reuse & Permissions

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