Interaction of graphene with Au (n) clusters: a first-principles study

Abstract

The interaction between Au (n) (n = 1-6) clusters and graphene is studied using first-principles simulations, based on density functional theory. The computed binding energy between Au (n) and graphene depends on the number of atoms in the cluster and lies between -0.6 eV and -1.7 eV, suggesting (weak) chemisorption of the clusters on graphene, rather than physisorption. Overall, the electronic properties, spin-orbit interaction and spin texture, as well as the transport properties of graphene strongly depend on the precise size of the Au (n) clusters. Doping of graphene is predicted for clusters with an odd number of Au atoms, due to overlap between Au s and carbon p(z) states close to the Fermi level. On the other hand, there is no charge transfer between even size Au clusters and graphene, but a gap is formed at the Dirac cone, due to the breaking of the pseudo spin inversion symmetry of graphene's lattice. The adsorbed Au (n) clusters induce spin-orbit interactions as well as spin and pseudo spin interactions in graphene, as indicated by the splitting of the electronic band structure. A hedgehog spin texture is also predicted for adsorbed clusters with an even number of Au atoms. Ballistic transport simulations are performed to study the influence of the adsorbed clusters on graphene's electronic transport properties. The influence of the cluster on the electron transmission across the structure depends on the mixing of the valence orbitals in the transport energy window. In the specific case of the Au-3/graphene system, the adsorbed clusters reduce the transmission and the conductance of graphene. The Au-3 clusters act as 'scattering centers' for charge carriers, in agreement with recent experimental studies.