The adsorption geometry of the (2 × 1)-2O oxygen phase formed on the Co(101̄0) surface

Abstract

The bond geometry of the (2 × 1)-2O-p2mg overlayer on Co(101̄0) was determined by analyzing low-energy electron diffraction (LEED) intensity data. Oxygen occupies the three-fold coordinated hcp site along the densely packed rows on the unreconstructed surface. The O atoms are attached to two atoms in the first Co layer and to one Co atom in the second layer. The strong interaction between O and Co is indicated by the bond lengths of 1.83 ± 0.10 A ̊ and 1.99 ± 0.10 A ̊ to the top-layer Co and the Co atoms in the second layer, respectively. The most striking result of our work is that oxygen adsorption causes a marked expansion (by 25%) of the first Co layer spacing (0.90 Å) with respect to the bulk value of 0.72 Å. This strong expansion might offer diffusion channels for O atoms to penetrate further into the subsurface region.