Adsorption and diffusion of adatoms on Ru(0 0 0 1): A first-principles study

Using first-principles total energy calculations within density functional theory, we investigated adsorption and diffusion of various elements (S, Ge, Pd, Ag and Pt) on the Ru(0 0 0 1) surface. It was found that the hcp hollow site is the preferred adsorption site for all atoms considered (S, Ge, Pd and Pt) except Ag which has equal probability to be adsorbed at the hcp hollow site, fcc hollow site, and the bridge site. Furthermore, S and Ge addlayers become unstable when the coverage goes beyond 0.25 monolayer (ML) due to the repulsive interaction between adsorbates. In contrary, the binding energies of the metal adsorbates Pd, Ag and Pt increase with coverage, all the way up to full coverage (1 ML). The diffusion barriers of the five adsorbates on Ru(0 0 0 1) are investigated and their relationships with the covalent radii of the adsorbates are discussed.