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

Abstract

Detailed density functional theory calculations have been performed to investigate the adsorption and diffusion of the Rh and Au adatom on the graphene moiré superstructure on Ru(0001). The adsorption energies of each adatom in all of the non-equivalent C-top and C6 ring center sites on the graphene moiré have been calculated. The resulting potential energy surfaces encompass the entire graphene moiré unit cell and shows that the adsorption of both Rh1 and Au1 is most stable in the fcc region on the graphene moiré. The minimum-energy diffusion path between adjacent moiré cells is identified to run mostly directly between the fcc and hcp regions for Au1, but deviates toward the mound region for Rh1. The global diffusion barrier is estimated to be 0.53 eV for Rh1 and 0.71 eV for Au1, corresponding to a hopping rate between adjacent moiré cells of ~10(3) s(-1) and ~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.