Coverage-dependent adsorption sites in the K/Ru(0001) system: a low-energy electron-diffraction analysis
b'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.'