Self-Assembly Process of Alkanethiol Monolayers

Abstract

To reveal formation of self-assembled monolayers (SAM), we analyzed the molecular orientation of SAMs of alkanethiol and the molecular organization in the Langmuir-Blodgett (LB) and vacuum deposited (VD) films by Fourier-transform infrared reflection absorption spectroscopy (FT-IR-RAS) and X-ray diffraction (XRD). XRD of the LB films suggests that alkanethiol orients normal to a gold substrate. Alkanethiol in the VD films tilts with a larger angle on the gold than on the glass substrates. The FT-IR-RAS spectra revealed that the molecular organization in the SAM on the gold (111) surface is dependent on the immersion time. Alkanethiol in the SAM aligns normal to the substrate, when the molecule undergoes close packing. A stable SAM embedded in a well-ordered monolayer is controlled by the intermolecular interaction of alkanethiol as well as the interaction between sulfur and gold.