Structural analyses of ordered rubidium phases on Ru(0001) using low-energy electron diffraction

The adsorption geometries of the p(2×2) and (√3×√3)R30° Rb/Ru(0001) phases at coverages of 0.25 and 0.33, respectively, were investigated using low-energy electron diffraction. The structure analyses revealed that Rb resides in the threefold fcc site in the p(2×2) phase while for the (√3×√3)R30° phase the hcp site is favored. The effective radius of Rb does not change with the Rb coverage within the error bars of this analysis. The concept of ‘‘split positions’’ has been used in order to take the enhanced motion of the adsorbate atoms parallel to the surface properly into account.