Comparison of a fluorinated aryl thiol self-assembled monolayer with its hydrogenated counterpart on polycrystalline Ag substrates

Matthew C. Schalnat, Jeanne E. Pemberton

Research output: Contribution to journalArticle

21 Scopus citations

Abstract

The effects of perfluorination of aryl thiols on surface coverage, surface electronic properties, and molecular orientation of self-assembled monolayers of thiophenol (TP) and pentafluorothiophenol (F5TP) on polycrystalline Ag were evaluated using linear sweep voltammetry, ultraviolet photoelectron spectroscopy (UPS), and surface Raman spectroscopy, respectively. Electrochemical reductive desorption by linear sweep voltammetry indicates a surface coverage for the TP monolayer of (5.07 ± 1.29) × 10 -10 mol/cm2, equating to a molecular area of 32.8 ± 8.3 Å2, and a surface coverage for the F5TP monolayer of (1.95 ± 0.59) × 10-10 mol/cm2, equating to an area of 85.2 ± 25.8 Å 2/ molecule. TP-modified Ag exhibits a change in work function (δφ) of -0.64 eV relative to bare Ag, whereas F5TP modified Ag exhibits a δφ of +0.54 eV relative to bare Ag. Quantitative analysis of the UPS and reductive desorption results yields molecular pictures of the proposed interfaces with TP molecules tilted <20° from the surface normal in a herringbone pattern spaced 6.4 Å apart and F5TP molecules in a more disordered arrangement tilted 67° from the surface normal with an intermolecular distance of 10.4 Å. Qualitative surface Raman spectroscopic analysis of in-plane and out-of-plane modes for these systems confirms that TP molecules are oriented more vertical than F5TP molecules in these monolayers.

Original languageEnglish (US)
Pages (from-to)11862-11869
Number of pages8
JournalLangmuir
Volume26
Issue number14
DOIs
StatePublished - Jul 20 2010

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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