Effects of Alkyl Chains on the Formation of Self-assembled Monolayers of Thiophenes.

Abstract

A comparative study of the growth processes of self-assembled monolayers (SAMs) of thiophene and alkylthiophene on Au(111) was made by Fourier-transform infrared reflection absorption spectroscopy (FTIR-RAS). Measurements of temporal peak intensity and the time-dependent Langmuir adsorption isotherm revealed two phases with different mo- lecular orientations during SAM growth of thiophene. In the primary stage, thiophene in the SAM orients parallel to the gold surface. In the second stage, the molecule reorients to a standing-up configuration with respect to the surface. Intro- duction of alkyl chain to thiophene ring does not essentially change the growth process, but induces a faster growth rate than that of the thiophene SAM. The intermolecular forces of adsorbate, e.g., van der Waals force, play a role as a rate- limiting factor for the self-assembly of adsorbates on the solid surface.