Formation of Ordered Self-Assembled Monolayers of Thioacetyl-terminated Tolane on Au(111)

Abstract

Surface structures and adsorption conditions of self-assembled monolayers (SAMs) on Au(111) prepared by tolane compounds were examined by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). We found that SAM formation by Tolanethioacetate (TTA) on Au(111) strongly depends on experimental conditions for the deprotection of acetyl group. Molecular-scale STM imaging revealed that TTA molecules on Au(111) can form well-ordered SAMs in TBACN catalytic medium compared to in pure solvent. TTA SAMs on Au(111) formed in catalytic TBACN solution contain an unique ordered phase consisting rod-like domains, which can be described as a (2 × √7) R62° structure. We also found that that the concentration of catalytic TBACN strongly affects the formation of two-dimensional TTA SAMs. The SAMs of Tolane disulfide (TDS) and Tolane methyl sulfide (TMS) with different substituent group attacted to the sulfur atom have very unique surface structure. Activity of sulfur headgroup is very important factor for determining the structure of SAMs. In addition, XPS measurements showed a strong S 2p peak at 162 eV for TTA SAMs on Au(111), implying that the SAMs were formed via chemical reactions between the sulfur atoms and gold surfaces.