High-quality PVD graphene growth by fullerene decomposition on Cu foils

We present a new protocol to grow large-area, high-quality single-layer graphene on Cu foils at relatively low temperatures. We use C₆₀ molecules evaporated in ultra high vacuum conditions as carbon source. This clean environment results in a strong reduction of oxygen-containing groups as depicted by X-ray photoelectron spectroscopy (XPS). Unzipping of C₆₀ is thermally promoted by annealing the substrate at 800ºC during evaporation. The graphene layer extends over areas larger than the Cu crystallite size, although it is changing its orientation with respect to the surface in the wrinkles and grain boundaries, producing a modulated ring in the low energy electron diffraction (LEED) pattern. This protocol is a self-limiting process leading exclusively to one single graphene layer. Raman spectroscopy confirms the high quality of the grown graphene. This layer exhibits an unperturbed Dirac-cone with a clear n-doping of 0.77 eV, which is caused by the interaction between graphene and substrate. Density functional theory (DFT) calculations show that this interaction can be induced by a coupling between graphene and substrate at specific points of the structure leading to a local sp³ configuration, which also contribute to the D-band in the Raman spectra.