▎ 摘　　要

We report on the conversion of epitaxial monolayer graphene on SiC(0001) into decoupled bilayer graphene by performing an annealing step in air. We prove by Raman scattering and photoemission experiments that it has structural and electronic properties that characterize its quasi-free-standing nature. The (6 root 3 x 6 root 3)R30 degrees buffer layer underneath the monolayer graphene loses its covalent bonding to the substrate and is converted into a graphene layer due to the oxidation of the SiC surface. The oxygen reacts with the SiC surface without inducing defects in the topmost carbon layers. The high-quality bilayer graphene obtained after air annealing is p-doped and homogeneous over a large area. (C) 2012 Elsevier Ltd. All rights reserved.