▎ 摘　　要

We report that graphene grown by molecular beam epitaxy from solid carbon (CMBE) on (0001) SiC in the presence of unintentional oxygen exhibits a small bandgap on the order of tens of meV. The presence of bandgaps is confirmed by temperature dependent Hall effect and resistivity measurements. X-ray photoelectron spectroscopy (XPS) measurements suggest that oxygen incorporates into the SiC substrate in the form of O-Si-C and not into the graphene as graphene oxide or some other species. The effect is independent of the carrier type of the graphene. Temperature dependent transport measurements show the presence of hopping conduction in the resistivity and a concurrent disappearance of the Hall voltage. Interactions between the graphene layers and the oxidized substrate are believed to be responsible for the bandgap. VC 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3697830]