Coverage-dependent adsorption sites in the K/Ru(0001) system: a low-energy electron-diffraction analysis
The two ordered phases p(2 \xd7 2) at a coverage \u03b8 = 0.25 and (\u221a3 \xd7 \u221a3)R30\xb0 at \u03b8 = 0.33 of potassium adsorbed on Ru(0001) were analyzed by use of low-energy electron-diffraction (LEED). In the (\u221a3 \xd7 \u221a3)R30\xb0 phase, the K atoms occupy threefold hcp sites, while in the p(2 \xd7 2) phase the fcc site is favoured. In both phases, the K hard-sphere radii are nearly the same and close to the covalent Pauling radius.