Effects of Al on epitaxial graphene grown on 6H-SiC(0001)

Aluminum was deposited on epitaxial monolayer-grown graphene on SiC(0001). The effects of annealing up to 1200 °C on the surface and interface morphology, chemical composition, and electron band structure were analyzed in situ by synchrotron-based techniques at the MAX Laboratory. After heating at around 400 °C, Al islands or droplets are observed on the surface and the collected Si 2p, Al 2p, and C 1s core levels spectra indicate Al intercalation at the graphene SiC interface. Also, the original single π-band splits into two, indicating decoupling of the carbon buffer layer and the formation of a quasi-free-standing bilayer-like electronic structure. Further heating at higher temperatures from 700 to 900 °C yields additional chemical reactions. Broader core level spectra are then observed and clear changes in the π-bands near the Dirac point are detected. More electron doping was detected at this stage since one of the π-bands has shifted to about 1.1 eV below the Fermi level. Different ordered phases of (7 × 7), (4 × 4), (1 × 1)_Al, and (1 × 1)_G were also observed on the surface in this temperature range. The original single π-band was restored after heating at ∼1200 °C, although an Al signal was still able to be detected. (papers)