Nucleation of graphene layers on magnetic oxides: Co 3 O 4 (111) and Cr 2 O 3 (0001) from theory and experiment
We report directly grown strongly adherent graphene on Co 3 O 4 (111) by carbon molecular beam epitaxy (C MBE) at 850 K and density functional theory (DFT) findings that the first graphene layer is reconstructed to fit the Co 3 O 4 surface, while subsequent layers retain normal graphene structure. This adherence to the Co 3 O 4 structure results from partial bonding of half the carbons to top oxygens of the substrate. This structure is validated by X-ray photoelectron spectroscopy and low-energy electron diffraction studies, showing layer-by-layer graphene growth with ~0.08 electrons/carbon atom transferred to the oxide from the first graphene layer, in agreement with DFT. In contrast, for Cr 2 O 3 DFT finds no strong bonding to the surface and C MBE on Cr 2 O 3 (0001) yields only graphite formation at 700 K, with C desorption above 800 K. As a result, strong graphene-to-oxide charge transfer aids nucleation of graphene on incommensurate oxide substrates and may have implications for spintronics.