Band-gap tuning of monolayer graphene by oxygen adsorption

We have performed high-resolution angle-resolved photoemission spectroscopy of oxygen-adsorbed monolayer graphene grown on 6H-SiC(0 0 0 1). We found that the energy gap between the π and π∗ bands gradually increases with oxygen adsorption to as high as 0.45 eV at the 2000 L oxygen exposure. A systematic shrinkage of the π∗ electron Fermi surface was also observed. The present result strongly suggests that the oxidization is a useful technique to create and control the band gap in monolayer graphene.