We have used dynamical low-energy electron diffraction (LEED) to determine the adsorption site and the geometry of the surface region for the p(2×2) overlayer of potassium adsorbed on Ni(111). The structure consists of the potassium atoms adsorbed on top of the Ni atoms with vertical reconstructions of Ni atoms in the first and second substrate layers combined with a slight horizontal reconstruction of the first substrate layer. The potassium-nickel bond length is found to be 2.82±0.04 Å corresponding to a rather short effective potassium ‘‘radius’’ of about 1.57 Å.

• Received 22 July 1991

DOI:https://doi.org/10.1103/PhysRevLett.68.2786