Coadsorbate Induced Reconstruction of a Stepped Pt(111) Surface by Sulfur and CO: A Novel Surface Restructuring Mechanism Observed by Scanning Tunneling Microscopy

The chemisorption of sulfur and CO was found to have profound effects on the structure of a stepped platinum surface. By itself, sulfur chemisorbs, forming a $p\left(2\ifmmode\times\else\texttimes\fi{}2\right)$ ordered structure, and induces doubling of the terrace widths and step heights. Subsequent coadsorption of CO displaces the sulfur, compressing it to distances of $\sqrt{3}$ times the Pt lattice spacing, and induces surface restructuring. New terraces form which contain exclusively CO and are separated by monatomic steps from the terraces containing the compressed sulfur overlayer. This coadsorbate induced restructuring phenomenon has strong implications in the mechanisms of surface catalyzed reactions.