Adsorption and diffusion of the Rh and Au adatom on graphene moire/Ru(0001)

Detailed density functional theory calculations have been performed to investigate the adsorption and diffusion of the Rh and Au adatom on the graphene moire superstructure on Ru(0001). The adsorption energies of each adatom in all of the non-equivalent C-top and C-6 ring center sites on the graphene moire have been calculated. The resulting potential energy surfaces encompass the entire graphene moire unit cell and shows that the adsorption of both Rh-1 and Au-1 is most stable in the fcc region on the graphene moire. The minimum-energy diffusion path between adjacent moire cells is identified to run mostly directly between the fcc and hcp regions for Au-1, but deviates toward the mound region for Rh-1. The global diffusion barrier is estimated to be 0.53 eV for Rh-1 and 0.71 eV for Au-1, corresponding to a hopping rate between adjacent moire cells of similar to 10(3) s(-1) and similar to 1 s(-1) at 298 K, respectively. The consequences of different hopping rates to cluster nucleation have been explored by performing Monte Carlo-based statistical analysis, which suggests that diffusing species other than adatoms need to be taken into account to develop an accurate description of cluster nucleation and growth on this surface. (C) 2013 AIP Publishing LLC.