Coadsorption of sulfur and carbon monoxide on platinum single-crystal surfaces studied by scanning tunneling microscopy

The spatial distribution of sulfur and carbon monoxide coadsorbed on stepped Pt(lll) surfaces was characterized by low-energy electron diffraction and scanning tunneling microscopy. The formation of a p(2 x 2) sulfur overlayer on the platinum substrate leads to the slow doubling of the original monatomic steps, but subsequent room temperature exposure of that surface to CO removes the reconstruction and induces the formation of approximately 50 Angstrom wide intermediate steps covered with carbon monoxide exclusively. Additional CO dosing causes the development of more complex structures at the edge of the steps, where the excess sulfur is pushed to the bottom of the step while the rest of the terrace becomes covered with CO + S intermixed layers. The implications of these results for catalysis are briefly discussed.