Evolution of gold nanostructures on graphene.

or exposure to a hydrogen plasma. [ 5 ] Metal–graphene interactions have been much studied theoretically, in terms of the specifi c sites of the metals on the benzene ring, their binding energies etc. So, for example, center-ring positions (H sites) are predicted as preferred locations for most metals (e.g., Ti, Fe), corner sites directly above C atoms (T sites) for Sb, Sn, and Ni, and bridge sites above C–C bonds (B sites) for Pd, Cr, and Pt. [ 6–10 ] Some predictions are even in contradiction with each other because of different approximations for the calculations; the local density and the generalized gradient approximations lead to different binding energies and thereby to different sites. For Au atoms, for example, T sites are predicted by the former and B sites by the latter method. [ 11 ] Furthermore, arbitrary variables used in the calculation, such as cutoff energies [ 12 ] and size of the supercell, [ 13 ] can affect the result of density functional theory (DFT) calculations. Also, some calculations predict gold to dope graphene in an n-type manner, whereas others predict p-type doping effects. [ 11 , 14 , 15 ]