Abstract
The migration of gold atoms attached to single vacancies near the edges of graphene ribbons is studied using density-functional theory calculations. The stable position for a single gold atom is found to be on top of a vacancy, as in an infinite graphene sheet. An energy of 5 eV is needed for the Au atom to move through the vacancy to the other side of the sheet, but the Au atom can migrate in lateral direction together with the vacancy, with a migration barrier of about 2.2 eV. The sites near the edges of the graphene layer are energetically more favorable for gold-atom-vacancy pairs than sites in the middle of extended graphene layers. The migration barriers for different pathways show that it is easier for the gold atom to move toward the edge where it can be captured. When the gold atom reaches the edge, it can migrate along the edge with an energy barrier of only 1.4 eV. Our results explain recent experimental observations [Y. Gan et al., Small 4, 587 (2008)] and provide 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.
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