The migration of gold atoms attached to single vacancies near the edges of graphene ribbons was studied using density-functional theory calculations. The stable position for a single gold atom was found to be on top of a vacancy, as in an infinite graphene sheet. An energy of 5eV was needed for the Au atom to move through the vacancy to the other side of the sheet, but the Au atom could migrate in lateral direction together with the vacancy, with a migration barrier of about 2.2eV. The sites near the edges of the graphene layer were energetically more favourable for gold-atom-vacancy pairs than sites in the middle of extended graphene layers. The migration barriers for different pathways showed that it was easier for the gold atom to move toward the edge where it could be captured. When the gold atom reaches the edge, it could migrate along the edge with an energy barrier of only 1.4eV. The results explained recent experimental observations and provided information on the dynamics of metal atoms on substitutional sites in graphene as well as on their agglomeration at defects and at edges of graphene ribbons.

Migration of Gold Atoms in Graphene Ribbons: Role of the Edges. W.Zhang, L.Sun, Z.Xu, A.V.Krasheninnikov, P.Huai, Z.Zhu, F.Banhart: Physical Review B, 2010, 81[12], 125425