Relative stability of armchair, zigzag and reczag graphene edges on the Ru(0001) surface

The relative stability of armchair, zigzag, and the reconstructed zigzag (reczag) graphene edges was studied using density functional theory with the Perdew, Burke, and Ernzerhof (PBE) exchange correlation functional for graphene nanoribbons in vacuo and on the Ru(0001) surface. Although the reczag edge was found to be more stable in vacuo confirming previous predictions of Koskinen et al. [Phys. Rev. Lett. 101 (2008) 115502], the relative stability reverses upon adsorption on the Ru(0001) surface. The zigzag edge is more stable than the reczag edge on the surface by about 0.15 eV/Å and the armchair ribbon was found to be approximately isoenergetic with the zigzag ribbon. For all three types of edges, strong edge–Ru interactions are observed that cause the edges to buckle down. The lowered edge height may facilitate C attachments at graphene edges during graphene synthesis.