Time-Resolved IR Studies of Monolayer Self-Assembly on a Gold Substrate Using Planar Array Infrared (PA-IR) Spectroscopy

Abstract

Time-resolved and spatially resolved infrared spectra (line images) of self-assembled monolayers of octadecylthiol (ODT) on gold substrates were investigated by planar array infrared (PA-IR) spectroscopy, with a grazing incidence reflection attachment. It was observed that PA-IR spectra with a good signal-to-noise ratio that is comparable to those obtained from Fourier transform infrared spectroscopy could be acquired with a significantly shorter collection time. Focusing on the peak intensities and peak positions of the CH2 asymmetric stretch (approximately 2918 cm-1) and the CH3 symmetric stretch (approximately 2960 cm-1), respectively, the molecular orientation and organization of the monolayers were determined. The ODT formed a uniform monolayer on the surface of the gold whether it was deposited within 1−2 s or over a 40 h period. Disordered monolayers formed instantly, and with an increase in dipping time, the monolayer became more ordered, becoming highly ordered after dipping times of many (>24) hours.