Dirac cone manipulation via bismuth and oxygen intercalation underneath graphene on Re(0001)

This paper reports on an investigation by angle-resolved photoelectron spectroscopy of the graphene on Re(0001) sub- strate, after intercalation by bismuth atoms. Our results demonstrate that intercalation of Bi atoms restores the quasi-free-standing properties of graphene. Thus, the band structure of this system is characterized by a linear π-state dispersion near the K point of the Brillouin zone. The Dirac point shifts toward higher binding energies by approximately 0.4 eV, which is caused by charge transfer from Bi atoms to graphene. Besides we observed a band gap with a width of at least 0.4 eV. The possible reasons of the band gap in the system Gr/Bi/Re(0001) can be caused by hybridization of π-states of graphene with 5d-rhenium states and/or bismuth states or symmetry breaking of the sublattices of graphene. Moreover, the Dirac point position is found to be different depending on the intercalated atoms. Intercalation of the oxygen atoms underneath graphene after exposure to the air results in the appearance of the second π-state branch in the electronic structure. There are two Dirac cones in the ARPES image and for the first one the charge transfer from the Bi atoms leads to the Dirac point position below the Fermi level, i.e. to the n-doping of graphene. For the second one the Dirac point is located above the Fermi level resulting in p-doping that is caused by charge transfer between oxygen and graphene atoms.