Formation and Superstructure of Organosulfur Self-Assembled Monolayers on Au(111)

Abstract

The discovery of molecular assemblies by the spontaneous adsorption of organic thiols on gold surfaces has proven to be a major advance for chemists and surface scientists in the research fields ranging from biomedicine, wetting, corrosion inhibition, molecular sensors, and nanopatterning.1-3 SAMs prepared from n-alkanethiols and -functionalized alkanethiols have been extensively studied to date. However, there have been a few studies on the formation of cyclic thiol or thioacetate SAMs on gold surfaces. In order to extend the application of SAMs, it is essential to develop and characterize a new SAM system. It is also very important to understand the nature of the self-assembly processes and the SAM structure. In this study, we have characterized various SAMs samples on Au(111) formed by cyclic thiols or conjugated tolane thioacetates using scanning tunneling microscopy and X-ray photoelectron spectroscopy. Our high-resolution STM study revealed that cyclohexanethiol having a flexible six-membered aliphatic ring on Au(111) can form long-range 2D ordered SAMs, which can be described as the (5 2 10)R48 superstructure. This unique superstructure can be ascribed to two geometrical isomers of CHT molecule, that is, the equatorial and axial chair isomers. On the other hand, the adsorption of cyclopentanethiols on Au(111) leads to the formation of partial ordered SAMs, which can assigned as ( 3.5 5)R25 superstructure. This means that the structural rigidity and size of aliphatic cyclic ring of molecules play a very important role in determining the final SAM structure and the self-assembly processes of molecules. In this presentation, we will overview our research activities related to SAMs and discuss how we can control the structure and properties of organic SAMs.