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Abstract:
The bond geometry of the (2 x 1)-20-p2mg overlayer on Co(101̅̅0) 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 Ǻ. and 1.99±0.10 Ǻ 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 Ǻ) with respect to the bulk value of 0.72 Ǻ. This strong expansion might offer diffusion channels for O atoms to penetrate further into the subsurface region.
