Structural Control of Tolane Molecular-Rod Self-Assembled Monolayers for Molecular Electronics

Abstract

Self-assembled monolayers (SAMs) formed by conjugated aromatic molecules on gold have drawn much attention due to their potential applications in molecular electronics.1,2 In this study, the surface structures and adsorption conditions of self-assembled monolayers (SAMs) formed by tolane compounds in various solutions were examined by scanning tunneling microscopy (STM) and x-ray photoelectron spectroscopy (XPS). STM imaging revealed that tolane thioacetate (TTA) and tolane methylthioacetate (TMTA) on Au(111) can form two-dimensional ordered SAMs in a NH4OH basic solution (Figure 1). It was also found that a small difference in chemical structure between TTA and TMTA shows large structural variations such as the formation of domains and vacancy islands as well as the adsorption condition of sulfur atoms. In addition, it is also revealed that the solution temperature plays a very important role in determining the surface structures of TTA and TMTA SAMs on Au(111) surface. From XPS measurement, it was confirmed that these SAMs on Au(111) were formed via the Au-S chemical bond during self-assembly processes.