Semiconductor-Metal Transition and Band-Gap Tuning in Quasi-Free-Standing Epitaxial Bilayer Graphene on SiC

We have performed angle-resolved photoemission spectroscopy of quasi-free-standing bilayer graphene epitaxially grown on silicon carbide. Prepared bilayer graphene shows a semiconducting behavior with a finite energy gap at the Fermi level in contrast to the theoretical prediction. We found that potassium-deposition on the sample leads to the semiconductor-to-metal transition together with the enhancement of the gap energy between the pi and pi* bands. The observed controllable tuning of the Fermi-level position and the gap energy provides an important step toward the band-gap engineering with bilayer graphene.