Selective adsorption and electronic interaction of F₁₆ CuPc on epitaxial graphene

We investigate the electronic coupling between copper hexadecafluoro- phthalocyanine (F₁₆ CuPc) and epitaxial graphene (EG) on 6H-SiC(0001) using a combined approach of low-temperature scanning tunneling spectroscopy and electronic structure calculations. The molecules are preferentially adsorbed on monolayer EG than bilayer EG. Competing molecule-surface and intermolecular van der Waals interactions result in two well-ordered incommensurate phases. We show that the amount of charge transfer from EG to F₁₆ CuPc can be tuned by applied voltage or the thickness of graphene layers. A characteristic feature at ∼0.4eV above the Dirac point is identified in bilayer EG, which indicates its electronic structure is modified via introducing extra unoccupied states upon adsorption.