Decoupling graphene from SiC(0001) via oxidation

When epitaxial graphene layers are formed on SiC(0001), the first carbon layer (known as the “buffer layer”), while relatively easy to synthesize, does not have the desirable electrical properties of graphene. The conductivity is poor due to a disruption of the graphene $\pi$ bands by covalent bonding to the SiC substrate. Here we show that it is possible to restore the graphene $\pi$ bands by inserting a thin oxide layer between the buffer layer and SiC substrate using a low temperature, complementary metal-oxide semiconductor-compatible process that does not damage the graphene layer.

Figure 1

(Color online) Electron-energy loss spectra recorded from (a) a thick graphite flake placed on SiC(0001) (black), (b) a graphene buffer layer on SiC(0001) before oxidation (blue/dark gray), and (c) the same buffer layer after oxidation (red/gray). All spectra were recorded using 33 eV electrons.

Figure 2

XPS spectra of the (a) $\text{Si}2p$ and (b) $\text{C}1s$ core levels from a buffer layer grown on SiC(0001). The bottom spectrum in each panel is from the buffer layer before oxidation. The middle spectra are from the buffer layer after oxidation. The top spectra are from a thick graphene film grown on SiC(0001) via high-temperature sublimation.

Figure 3

[(a) and (c)] 28 eV LEED patterns and [(b) and (d)] AFM images recorded from a graphene buffer layer on SiC(0001) [(a) and (b)] before and [(c) and (d)] after oxidation of the SiC substrate. The AFM images are nearly identical while the diffraction patterns show that strong coupling to the SiC lattice is lifted by the oxidation.

Figure 4

(Color online) Medium-energy ion-scattering spectra for graphene/SiC(0001) (a) before and (b) after oxidation. Contributions from carbon, silicon, and oxygen have been shifted and plotted on the same depth scale. After oxidation, the oxygen leading edge occurs deeper than the carbon edge, showing that the oxygen is subsurface.