AN IN-SITU STM DETERMINATION OF A KINETIC PATHWAY FOR THE COADSORBATE-INDUCED COMPRESSION OF SULFUR BY CO ON PT(111)

STM has been used to study the interactions between CO and S coadsorbed on Pt(111). At coverages less than or equal to 0.25 monolayers, sulfur forms ordered 2X2 islands. When CO is coadsorbed with sulfur on Pt(111), the sulfur is compressed into ordered structures of higher local coverage. We have observed the steps leading to this compression with both STM and LEED. This paper presents in situ STM evidence suggesting the mechanism by which sulfur is compressed by coadsorbed CO on Pt(111). In this mechanism, sulfur is displaced by CO from the p(2 x 2) site to the next nearest fee hollow site. This displacement initiates a chain reaction by which one-dimensional rows of sulfur atoms separated by root 3 times the Pt-Pt distance are created. The formation of sulfur chains generates new sites for CO adsorption by which the compression phenomenon is further propagated.