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 s stepped platinum surface. By itself, sulfur chemisorbs, forming a {ital p}(2{times}2) ordered structure, and destabilizes the step structure by inducing doubling of the terrace widths and step heights. Subsequent coadsorption of CO displaces the sulfur, compressing it to distances of {radical}3 times the Pt lattice spacing. In addition to displacing S, CO enhances Pt atom diffusion from the double heights steps, restructuring the surface by forming new terraces separated by monatomic height steps. These new terraces contain exclusively CO, while the compressed sulfur overlayer is found on the alternating terraces. The segregation of CO and S and their effect on the substrate morphology has strong implications in the mechanisms of surface catalyzed reactions. {copyright} {ital 1996 The American Physical Society.}