Structural and Electronic Decoupling of C60 from Epitaxial Graphene on SiC

We have investigated the initial stages of growth and the electronic structure of C-60 molecules on graphene grown epitaxially on SiC(0001) at the single molecule level using cryogenic ultrahigh vacuum scanning tunneling microscopy and spectroscopy. We observe that the first layer of C-60 molecules self-assembles into a well-ordered, close-packed arrangement on graphene upon molecular deposition at room temperature while exhibiting a subtle C-60 superlattice. We measure a highest occupied molecular orbital-lowest unoccupied molecular orbital gap of similar to 3.S eV for the C-60 molecules on graphene in submonolayer regime, indicating a significantly smaller amount of charge transfer from the graphene to C-60 and substrate-induced screening as compared to C-60 adsorbed on metallic substrates. Our results have important implications for the use of graphene device applications that require electronic decoupling between functional molecular adsorbates and substrates.