Molecular Self-Assembly and Structure of Aromatic Thiols on Au(111)

Abstract

Self-assembled monolayers (SAMs) of organic molecules on metal surfaces are promising systems for application ranging from biomedicine, wetting, corrosion inhibition, molecular sensors, and nanopatterning. SAMs generated from aromatic thiols have attracted significant attention because of their properties compared to alkanethiol SAMs.1-3 Aromatic thiol SAMs have high anisotropy, strong intermolecular interaction, delocalized electron distribution, high conductivity, and ease of synthetic modification. To extend the application of these SAMs, it is essential to understand the surface structure of SAMs as well as to obtain high-quality ordered SAMs. In this study, we have characterized SAMs of organic thiols containing terminal phenyl groups (C6H5(CH2)nSH, n=0-2) on Au(111) using scanning tunneling microscopy. Benzenethiol (BT) SAMs have disordered phases containing bright domains, whereas benzenemethanethiols can form ordered SAMs with no clear domain boundaries. However, we found that the ordered BT SAMs can be obtained by the displacement of precovered cyclohexanethiols by BT molecules or via the adsorption process at a solution temperature of 50 °C. In addition, benzeneethanethiols containing two methylene groups between the sulfur headgroups and benzene ring form very uniform SAMs with long-range ordered domains and a few vacancy islands at a solution temperature of 50 °C.