title: Surface-enhanced Raman scattering study of the kinetics of self-assembly of carboxylate-terminated n-alkanethiols on silver.
abstract: Adsorption of 11-mercaptoundecanoic acid (MUA) on silver from methanol and aqueous solutions was monitored in situ by surface-enhanced Raman scattering (SRES) spectroscopy. While adsorption of MUA from methanol is a one-step formation of a thiol-bound monolayer, SERS spectra reveal that monolayer formation from aqueous solution involves interactions of both carboxylate and thiol groups of MUA with the silver surface. Several Raman scattering bands, including the ν(C-S), ν(s)(COO(-)), and ν(C-C), were used to investigate the evolution of the structure of adsorbed MUA on silver surfaces. The time-dependent profiles of these bands for assembly from aqueous solution indicate a multistep process, which is initiated by the binding of both carboxylate and thiol groups to silver, producing a mixture of gauche and trans conformations. In a subsequent step, the COO-Ag interactions are displaced by stronger S-Ag bonds, leading to ordering of the resulting monolayer with formation of a complete SAM with all-trans conformations. The results also showed that the adsorption process depended strongly on the solution pH and surface potential of the metal. These factors can significantly affect the participation and displacement of -COO(-) during self-assembly of MUA from aqueous solution.
authors.affiliation: Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112, United States.
authors.forename: Chaoxiong
authors.initials: C
authors.lastname: Ma
authors.forename: Joel M
authors.initials: JM
authors.lastname: Harris
mesh_terms: D000327:Adsorption; D000473:Alkanes / Q000138:chemical synthesis* / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D007700:Kinetics; D012834:Silver / Q000737:chemistry*; D013059:Spectrum Analysis, Raman; D013438:Sulfhydryl Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D013499:Surface Properties
chemical_list: D000473:Alkanes; D002264:Carboxylic Acids; D013438:Sulfhydryl Compounds; D012834:Silver