Nickel Carbide as a Source of Grain Rotation in Epitaxial Graphene

Graphene has a close lattice match to the Ni(111) surface, resulting in a preference for 1 x 1 configurations. We have investigated graphene grown by chemical vapor deposition (CVD) on the nickel carbide (Ni2C) reconstruction of Ni(111) with scanning tunneling microscopy (STM). The presence of excess carbon, In the form of Ni2C, prevents graphene from adopting the preferred 1 x 1 configuration and leads to grain rotation. STM measurements show that residual Ni2C domains are present under rotated graphene. Nickel vacancy islands are observed at the periphery of rotated grains and Indicate Ni2C dissolution after graphene growth. Density functional theory (DFT) calculations predict a very weak (van der Waals type) Interaction of graphene with the underlying Ni2C, which should facilitate a phase separation of the carbide Into metal-supported graphene. These results demonstrate that surface phases such as Ni2C can play a major role in the quality of epitaxial graphene.