Low-energy electron diffraction study of the surface geometry of Ni(100)–(3×3)-K+4O

A dynamical LEED study of the (3×3) structure which forms upon coadsorption of K and O on Ni(100) indicates that this structure is comprised of one K atom and four O atoms per (3×3) unit cell. The K atom is adsorbed in a substitutional site, and surrounded by four O atoms in hollow sites. The four O atoms are displaced by 0.35±0.08 Å from the centers of the hollows, and the average ONi distance is 1.92±0.17 Å. The KO distance is 2.93±0.15 Å and the KNi distance is 3.33±0.12 Å. We propose that the primary driving force for the creation of the vacancies is the reduction of energy when the K atoms move closer to the surface. At a later stage of oxidation, these vacancies may facilitate the formation of NiO by helping to alleviate the strain in the lattice mismatch between the NiO structure and Ni(100).