Reference

Effect of Ring Substitution Position on the Structural Conformation of Mercaptobenzoic Acid Self-Assembled Monolayers on Au(111)

All Rights Reserved. Effect of Ring Substitution Position on the Structural Conformation of Mercaptobenzoic Acid Self-Assembled Monolayers on Au(111). Lee, Jonathan R. I.; Willey, Trevor M.; Nilsson, Joakim; Terminello, Louis J.; De Yoreo, James J.; van Buuren, Tony (Lawrence Livermore National Laboratory, Livermore, CA 94550, USA). Langmuir, 22(26), 11134-11141 (English) 2006 American Chemical Society. CODEN: LANGD5. ISSN: 0743-7463. DOCUMENT TYPE: Journal CA Section: 22 (Physical Organic Chemistry) Section cross-reference(s): 66, 73, 74 Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, photoemission spectroscopy (PES), and contact angle measurements have been used to examine the structure and bonding of self-assembled monolayers (SAMs) prepd. on Au(111) from the positional isomers of mercaptobenzoic acid (MBA). The isomer of MBA and solvent chosen in SAM prepn. has considerable bearing upon film morphol. Carbon K-edge NEXAFS measurements indicate that the monomers of 2-, 3-, and 4-MBA have well-defined orientations within their resp. SAMs. Monomers of 3- and 4-MBA assume an upright orientation on the Au substrates in monolayers prepd. using an acetic acid in ethanol solvent. The aryl ring and carboxyl group of these mols. are tilted from the surface normal by a colatitudal angle of ~30°. Prepn. of 4-MBA SAMs using pure ethanol solvent, a more traditional means of synthesis, had no appreciable effect upon the monomer orientation.There are some commonly used reagents with their cas registry numbers 4869-59-4 and 1074-36-8 in this article. Nonetheless, S(2p) PES measurements illustrate that it results in extensive bilayer formation via carboxyl group hydrogen-bonding between 4-MBA monomers. In 2-MBA monolayers prepd. using acetic acid/ethanol solvent, the monomers adopt a more prostrate orientation on the Au substrates, in which the aryl ring and carboxyl group of the mols. are tilted ~50° from the surface normal. This configuration is consistent with an interaction between both the mercaptan sulfur and carboxyl group of 2-MBA with the underlying substrate. S(2p) and C(1s) PES expts. provide supporting evidence for a bidentate interaction between 2-MBA and Au(111). .