Direct Measurement of the Growth Mode of Graphene on SiC(0001) and $\mathrm{SiC}(000\overline{1})$

We have determined the growth mode of graphene on SiC(0001) and $\mathrm{SiC}(000\overline{1})$ using ultrathin, isotopically labeled $\mathrm{Si}{}^{13}\mathrm{C}$ “marker layers” grown epitaxially on the $\mathrm{Si}{}^{12}\mathrm{C}$ surfaces. Few-layer graphene overlayers were formed via thermal decomposition at elevated temperature. For both surface terminations (Si face and C face), we find that the ${}^{13}\mathrm{C}$ is located mainly in the outermost graphene layers, indicating that, during decomposition, new graphene layers form underneath existing ones.

Figure 1

AFM images recorded after annealing (a) $\mathrm{SiC}(0001)\mathrm{\text{−}}6H$, and (b) $\mathrm{SiC}(000\overline{1})\mathrm{\text{−}}6H$, at $1200°\mathrm{C}$ in ${10}^{-6}$ Torr disilane. A uniform step height of 0.8 nm is observed at both surfaces, corresponding to three SiC bilayers. (c) Drift corrected 47 eV bright-field LEEM images recorded before and after CVD growth of $\mathrm{Si}{}^{13}\mathrm{C}$. The initial and final positions of selected steps are shown, indicating downward step flow during growth.

Figure 2

(a) Three epitaxial $\mathrm{Si}{}^{13}\mathrm{C}$ bilayers grown on bulk $\mathrm{Si}{}^{12}\mathrm{C}$. (b) Resulting ${}^{13}\mathrm{C}$ graphene layer that forms upon thermal decomposition of the outer three bilayers. (c,d) Two possible structures for bilayer graphene formed upon further thermal decomposition. (e) Simulated 100 keV MEIS energy spectra for the structures shown in (c). The curves show simulations for ${}^{13}\mathrm{C}$ on top (red) and ${}^{12}\mathrm{C}$ on top (blue). When ${}^{13}\mathrm{C}$ is on top, the ${}^{12}\mathrm{C}$ peak is shifted to lower energy. Conversely, when ${}^{12}\mathrm{C}$ is on top, the ${}^{13}\mathrm{C}$ peak is shifted to lower energy. Dashed lines indicate the deconvolution of the ${}^{12}\mathrm{C}$ spectrum into SiC and interfacial graphene components.

Figure 3

100 keV MEIS energy distributions recorded for graphene grown on (a) SiC(0001) and (b) $\mathrm{SiC}(000\overline{1})$. Symbols are measured data, and curves are simulations results. The color indicates the average graphene thickness. Blue, green, and black correspond to approximately 1.5, 2.5, and 3.5 ML of graphene, respectively. Arrows indicate the energy of protons scattered from ${}^{12}\mathrm{C}$ and ${}^{13}\mathrm{C}$ situated at the surface. The black dashed curve in (a) indicates a model for 2.7 ML of graphene in which the ${}^{13}\mathrm{C}$ graphene is located under the ${}^{12}\mathrm{C}$ graphene rather than above it (see text).