Formation of Highly Ordered Self-assembled Monolayers by -Conjugated Tolanethioacetates on Au(111)

Abstract

Surface structure and adsorption conditions of tolanethioacetate (TTA) self-assembled monolayers (SAMs) on Au(111) in catalytic tetrabutylammonium cyanide (TBACN) solution were examined by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). We found that SAM formation by adsorption of TTA molecules 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. The adsorption of TTA molecules on Au(111) in catalytic TBACN solution at 50 °C for 24 h led to the formation of long-range ordered phase containing rod-like domains, which can be described as a (2 × √7)R62° structure. On the other hand, the adsorption of TTA molecules on Au(111) at room temperature led to the formation of different packing structure, which can be described as a (√3 × √8)R50° structure. In addition, XPS measurements showed a strong S 2p peak at 162 eV for TTA SAMs on Au(111), implying that TTA SAMs were formed via chemical reactions between the sulfur atoms and gold surfaces.