Bifunctional effects of the ordered Si atoms intercalated between quasi-free-standing epitaxial graphene and SiC(0001): graphene doping and substrate band bending

Bifunctional effects of the Si atoms intercalated between the n-type 6H-SiC(0001) substrate and the (6 root 3 x6 root 3) R30 degrees zero layer have been disclosed by scanning tunneling microscopy, low-energy electron diffraction, high-resolution synchrotron photoemission spectroscopy and angle-resolved photoemission spectroscopy. As a result of Si intercalation, an ordered Si interfacial layer composed of a Si adlayer and Si adatoms with dangling bonds has been formed under quasi-free-standing epitaxial graphene (EG). It turns out that the SiC(0001) band bending is determined by the Fermi level located close to the lowest states of the upper Hubbard band. The Hubbard bands originate from strong correlation effects of the electrons in the dangling bonds of the Si adatoms ordered on the Si adlayer. The doping level of the decoupled graphene is determined by the amount of charge transferred from the Si adatoms ordered on the Si adlayer to the quasi-free-standing EG.