LEED spot profile analysis of the structure of electrochemically treated Pt(100) and Pt(111) surfaces
The structures formed by oxidation-reduction cycling of ordered Pt(100) and Pt(111) surfaces in aqueous electrolytes were studied using LEED spot profile analysis. Surfaces cycled to anodic potential limits above 1.0 V (RHE) and emersed at 0.5 V gave LEED spots which varied in width periodically with beam energy. The varying spot widths indicated a type of randomly stepped surface, and mean terrace widths were estimated by comparison with the previously published scattering calculations of Henzler and Lu and Lagally. LEED spots from surfaces cycled to potentials below 1.0 V (RHE) remained sharp at all beam energies. The restructuring resulted from the anodic formation of an amorphous surface oxide phaes involving place exchange of platinum and oxygen followed by a reduction process in which the platinum atoms do not all return to their original positions in the surface lattice. The observed spot profiles changed both with the the number of cycles and with the upper potential limit. Cycling to 1.28-1.58 V produced characteristically different structures than cycling to limits of 1.08-1.28 V. At the higher potentials, a randomly-stepped surface was formed whose mean terrace width and extent of vertical relief were functions of the total anodic charge. Cycling to the lower potential limits produced a type of structure which is intermediate between the classical two-level island and the multi-level randomly-stepped structure. A three-level structure with a high degree of correlation between the first (island-like) and third (hole-like) levels is proposed for the latter.