Electronic Structure of Epitaxial Graphene Layers on SiC: Effect of the Substrate

A strong substrate-graphite bond is found in the first all-carbon layer by density functional theory calculations and x-ray diffraction for few graphene layers grown epitaxially on SiC. This first layer is devoid of graphene electronic properties and acts as a buffer layer. The graphene nature of the film is recovered by the second carbon layer grown on both the (0001) and $(000\overline{1})$ 4H-SiC surfaces. We also present evidence of a charge transfer that depends on the interface geometry. Hence the graphene is doped and a gap opens at the Dirac point after three Bernal stacked carbon layers are formed.

Figure 1

Interface geometry: (a) side view; (b) top view of the $\sqrt{3}\times \sqrt{3}R30$ cell for a Si-terminated SiC face.

Figure 2

X-ray ($00l$) reflectivity data from 9 graphene layers grown on the $4\mathrm{H}\mathrm{\text{−}}\mathrm{SiC}(000\overline{1})$ surface. Bulk and graphite Bragg peaks are labeled. Blue (thin) line is the best fit structure with one reconstructed SiC bilayer as described in the text. The wide grey line is a fit with an extended reconstruction of two SiC bilayers.

Figure 3

Dispersion curves for one (a),(b), two (c),(d), and three (e),(f) carbon layers on bulk truncated SiC. Curves (a), (c), and (e) [(b), (d), and (f)] correspond to the Si- (C-)terminated face. The first C layer forms a BL layer with no graphenelike dispersion (a),(b). One C layer on top of the BL shows a linear dispersion (c),(d) characteristic of a single graphene sheet. Two C layers on top of the BL show a splitting of the Dirac bands (e),(f) as expected for a free graphene bilayer.

Figure 4

Dispersion curves for 2 C layers on top of the C-deficient surface. The Diraclike dispersion at the $K$ point is preserved, but the Fermi level is shifted due to charge transfer from the substrate.

Figure 5

Isocharge density contours along $z$ axis for 3 C layers on top of (a) C- and (b) Si-terminated surfaces. The large charge density between the last bulk layer and the first carbon layer indicates strong binding between them.