Adsorption of rare-earth adatoms (Nd, Gd, Eu, Yb) on graphene was studied by first-principles calculations based upon the density-functional theory. The calculations showed that the hollow site of graphene was the energetically favorable adsorption site for all the rare-earth adatoms studied. The adsorption energies and diffusion barriers of Nd and Gd on graphene were found to be larger than those of Eu and Yb. Comparison with scanning tunnelling microscopy experiments for Gd and Eu epitaxially grown on graphene confirmed these calculated adsorption and barrier differences, since fractal-like islands were observed for Gd and flat-topped crystalline islands for Eu. The formation of flat Eu islands on graphene could be attributed to its low diffusion barrier and relatively larger ratio of adsorption energy to its bulk cohesive energy. The interactions between the Nd and Gd adatoms and graphene cause noticeable in-plane lattice distortions in the graphene layer. Adsorption of the rare-earth adatoms on graphene also induces significant electric dipole and magnetic moments.

Adsorption and Growth Morphology of Rare-Earth Metals on Graphene Studied by ab initio Calculations and Scanning Tunneling Microscopy. Liu, X., Wang, C.Z., Hupalo, M., Yao, Y.X., Tringides, M.C., Lu, W.C., Ho, K.M.: Physical Review B, 2010, 82[24], 245408