Interaction, growth, and ordering of epitaxial graphene on SiC{0001} surfaces: A comparative photoelectron spectroscopy study

K. V. Emtsev, F. Speck, Th. Seyller, L. Ley, and J. D. Riley

Phys. Rev. B 77, 155303 – Published 2 April 2008

Abstract

Thermally induced growth of graphene on the two polar surfaces of $6 H − Si C$ is investigated with emphasis on the initial stages of growth and interface structure. The experimental methods employed are angle-resolved valence band photoelectron spectroscopy, soft x-ray induced core-level spectroscopy, and low-energy electron diffraction. On the Si-terminated (0001) surface, the $(6 \sqrt{3} \times 6 \sqrt{3}) R 30 °$ reconstruction is the precursor of the growth of graphene and it persists at the interface upon the growth of few layer graphene (FLG). The $(6 \sqrt{3} \times 6 \sqrt{3}) R 30 °$ structure is a carbon layer with graphene-like atomic arrangement covalently bonded to the substrate where it is responsible for the azimuthal ordering of FLG on SiC(0001). In contrast, the interaction between graphene and the C-terminated $(000 \bar{1})$ surface is much weaker, which accounts for the low degree of order of FLG on this surface. A model for the growth of FLG on SiC{0001} is developed, wherein each new graphene layer is formed at the bottom of the existing stack rather than on its top. This model yields, in conjunction with the differences in the interfacial bonding strength, a natural explanation for the different degrees of azimuthal order observed for FLG on the two surfaces.

Received 11 July 2007

DOI:https://doi.org/10.1103/PhysRevB.77.155303

Authors & Affiliations

K. V. Emtsev, F. Speck, Th. Seyller^*, and L. Ley

Lehrstuhl für Technische Physik, Universität Erlangen-Nürnberg, Erwin-Rommel-Strasse 1, 91058 Erlangen, Germany

J. D. Riley

Department of Physics, La Trobe University, Bundoora, Victoria 3083, Australia

^*Corresponding author; thomas.seyller@physik.uni-erlangen.de; URL: http://www.tp2.uni-erlangen.de

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Vol. 77, Iss. 15 — 15 April 2008

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Images

Figure 1
(Color online) Left: Top view of the CSG model on SiC(0001). The large diamond shows the $(\sqrt{3} \times \sqrt{3}) R 30 °$ unit mesh of the model surface. Note that the structure has one dangling bond per unit mesh due to an unsaturated Si atom. For the CSG model on $Si C (000 \bar{1})$ , the roles of the substrate C and Si atoms are interchanged. Right: A monolayer graphene placed on the bulk-truncated SiC(0001) surface. The large diamond indicates the unit cell of the resulting $6 \sqrt{3}$ coincidence lattice, which contains 169 graphene unit cells and 108 SiC(0001) unit meshes.Reuse & Permissions
Figure 2
(Color online) Photoelectron intensity map vs binding energy and parallel electron momentum of (a) $Si C (0001) - 6 \sqrt{3}$ and (b) 1 ML graphene on top of $Si C (0001) - 6 \sqrt{3}$ $(h ν = 50 eV)$ . The inset shows the direction of $k_{∥}$ within the hexagonal Brillouin zone of graphene. LEED patterns of the (c) $6 \sqrt{3}$ reconstruction and (d) 1 ML graphene on 6H-SiC(0001). The reciprocal lattice vectors of the SiC $(\vec{s_{1}}, \vec{s_{2}})$ and graphene $(\vec{G_{1}}, \vec{G_{2}})$ lattices are indicated. Linear combinations of either $\vec{s_{1}}$ and $\vec{s_{2}}$ only or $\vec{G_{1}}$ and $\vec{G_{2}}$ only lead to the first order diffraction spots S and G of SiC and graphene, respectively. Examples are indicated. The remaining spots can be constructed by linear combinations of $\vec{s_{1}}$ , $\vec{s_{2}}$ , $\vec{G_{1}}$ , and $\vec{G_{2}}$ . These are the diffraction spots characteristic of the $6 \sqrt{3}$ reconstruction.Reuse & Permissions
Figure 3
(Color online) (a) $C 1 s$ core-level spectra of the $Si C (0001) - 6 \sqrt{3}$ reconstruction. (b) Evolution of the $C 1 s$ core-level spectrum upon growth of up to 3.4 layers of graphene (FLG). The inset shows the intensity ratio of component S2 to bulk component SiC for measurements at $h ν = 510 eV$ as a function of FLG thickness. $d = 0$ corresponds to the $6 \sqrt{3}$ reconstruction. (c) EDCs taken at $Γ$ (see Fig. 2) of the $6 \sqrt{3}$ reconstruction, graphene, bilayer graphene, and graphite. The peak corresponds to the maximum of the $σ$ band. Note the energy difference of $(1.0 \pm 0.1) eV$ between the $σ$ -band maximum of the $6 \sqrt{3}$ reconstruction and graphite.Reuse & Permissions
Figure 4
(Color online) [(a)–(d)] Photoelectron intensity map vs binding energy and parallel electron momentum acquired at different stages of FLG growth on $Si C (000 \bar{1})$ starting from the clean $(3 \times 3)$ reconstruction. The graphene overlayer thickness determined from the $C 1 s$ core levels is indicated. The inset in (b) shows the Brillouin zone of graphene with the nominal azimuth marked by the arrow. $σ$ and $π$ mark the $σ$ and $π$ bands, respectively, for the nominal azimuth. $σ^{'}$ and $π^{'}$ indicate the $σ$ and $π$ bands of rotated domains, respectively. SiC in (a) and (b) marks a prominent SiC bulk band. Photon energy was $h ν = 65 eV$ . [(e)–(h)] LEED patterns obtained for various stages of FLG growth. The reciprocal lattice vectors of the SiC $(\vec{s_{1}}, \vec{s_{2}})$ and graphene $(\vec{G_{1}}, \vec{G_{2}})$ lattices are indicated.Reuse & Permissions
Figure 5
(Color online) (a) CIS core-level spectra of the initial stage of graphene formation on the $Si C (000 \bar{1})$ surface with a coverage of 0.15 and 0.5 ML. (b) $C 1 s$ core-level spectra after subsequent growth of up to 4.3 layers of graphene on the C face.Reuse & Permissions

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