Abstract

Metal clusters adsorbed on graphene can give rise to interesting physical properties. Using density-functional theory calculations, we investigate Au-n and Fe-n (n = 1-5) clusters adsorbed on perfect and defected graphene with a single vacancy. With the exception of Fe clusters on defected graphene, clusters are bonded to graphene through an anchor atom. Geometries of clusters on graphene are similar to their free-standing structures except for the Fe-5 cluster on perfect graphene. Compared to Au, Fe clusters are more strongly bonded to graphene. We find that it is important to include long-range van der Waals interactions for Au clusters adsorbed on perfect graphene. An Au-5 cluster becomes parallel to the graphene only when the van der Waals interactions are taken into account. Charge transfer between clusters and graphene shows strong size dependency, and the amount is larger in the presence of the single vacancy on the graphene than a pristine sheet. Perfect graphene is found to be doped for Au clusters with an odd number of atoms and undoped with an even number of atoms. Magnetic moments are also calculated as a function of cluster size and an odd-even oscillation is observed in Au-n-perfect as well as defected graphene system. While Fe-n clusters remain to be magnetic for all n, the spin of a single Fe atom on a defect site is very small due to a covalent bonding to C atoms.