Adsorption and Diffusion of Oxygen Atoms on a Pt(211) Stepped Surface

To clarify the influence of surface steps on the diffusion of adsorbed oxygen atoms on Pt, we have carried out density functional calculations of the adsorption of atomic oxygen on a Pt(211) stepped surface and the diffusion barriers between the adsorbed states. Comparison with Pt(111) and Pt(100) flat surfaces reveals that atomic oxygen is strongly bound at the ledge of the steps and weakly bound at the bottom of the steps. We show that the variation in the adsorption preferences correlates well with the d-band centers of the outermost Pt atoms on a clean Pt(211) surface. Although a high-energy barrier of E diff,⊥ = 1.36 eV is obtained for diffusion perpendicular to the step edge, the barrier lies within the range of experimental values. The energy barrier also depends on whether the O atom is ascending or descending the step, being about 0.3 eV lower in the case of the former. The barrier to diffusion parallel to the edge of E diff,|| = 0.73 eV is also higher compared with the equivalent barrier on a flat Pt(111) surface due to the deeper energy well at the ledge.