Graphene Supported on Hematite Surfaces: A Density Functional Study

Structural, electronic, and chemical properties of graphene supported on hematite (alpha-Fe2O3) (0001) surfaces are investigated, employing density functional theory calculations. Apart from pristine surface-graphene systems, also the interaction with various technologically relevant adsorbates is addressed. Both ferryl-terminated (S-O) and single iron-terminated (S-Fe) surfaces of alpha-Fe2O3 are considered. While the graphene sheet is nearly unaltered when in contact with S-Fe, a sizable amount of graphene-to-surface charge transfer is found in the case of S-O. This charge transfer leads to rather strong binding and is accompanied by a remarkable shift of the Fermi energy away from the Dirac point in graphene. In a second step, hydrogen atoms and hydroxyl groups are introduced as adsorbants. A strong site-selectivity behavior for the adsorption is found in S-O-supported graphene (G/S-O), where the presence of adsorbates can lead to the formation of covalent surface-graphene bonds. This is not the case for SEC-supported graphene (G/S-Fe) where no strong site selectivity is observed. The hydrogen dissociation reaction on G/S-O, which is found to be exothermic, is simulated using the nudged elastic band method. The strong electric dipole forming at the G/S-O interface is found to influence strongly the adsorption of water molecules on graphene. Finally, it is shown that upon adsorption of alkali metal atoms on G/S-O, the Fermi level of the system can be shifted back toward the Dirac point of graphene, counteracting the charge transfer effects due to the interaction with the hematite surface.