SPONTANEOUSLY ORGANIZED MOLECULAR ASSEMBLY OF AN AROMATIC ORGANIC DISULFIDE ON SILVER PLATINUM ALLOY SURFACES - AN ANGLE-DEPENDENT X-RAY PHOTOEMISSION INVESTIGATION/

This article reports an angle dependent X-ray photoemission investigat ion on the formation of a self-assembled monolayer of a small organic disulfide molecule (Naphtho[1,8-cd]-1,2-dithiole) on silver/platinum a lloy surfaces. In addition to the S 2p signal normally associated with thiolate bond formation, a high binding energy S 2p signal was observ ed and is assigned to a sulfonic acid moiety. This is the first such r eport of sulfonic acid formation in disulfide systems and is quite sim ilar to the process occurring on copper and silver surfaces for n-alka ne thiols. The angle dependent intensities of the C Is, S 2p and Ag 3d core levels were used to make a quantitative estimate of the surface composition and thus obtain information on the molecular orientation. The molecule was oriented almost normal to the silver/platinum alloy s urface with the sulfonic acid moiety being closer to the monolayer-air interface than the thiolate sulfur which was very close to the alloy surface. This is explained as arising due to steric effects associated with the larger sulfonic acid group. (C) 1997 Elsevier Science B.V.