Effects of Hydrogen on the Stacking Orientation of Bilayer Graphene Grown on Copper

The development of a synthesis method for bilayer graphene with a specific stacking orientation has become an important goal toward fully exploiting the extraordinary physical properties of bilayer graphene. However, reliable control of the stacking orientation of graphene has not yet been demonstrated because of the lack of understanding of the mechanism that determines the stacking orientation of graphene during its growth stage. Here, we report that the type of edge passivation of growing graphene affects the stacking orientation of bilayer graphene and that the edge configuration can be controlled by adjusting the H2 flow rate during graphene growth. Dangling C atoms at the edge of graphene preferentially interact with surrounding Cu atoms under low H2 flow rates. In this case, the orientation of adlayer graphene is mainly determined by the epitaxial relationship between the adlayer graphene and the Cu surface. Consequently, the formation of a non-Bernal-stacked bilayer graphene is preferred thermodynamically. By contrast, under high H2 flow rates, passivation of graphene edge by hydrogen weakens the interaction between graphene and Cu. Thus, the interaction between graphene layers governs the stacking orientation and leads to Bernal stacking.