Molecular Self-Assembly of Thioacetyl-Terminated Tolanes on Au(111)

Abstract

Binding condition, two-dimensional (2D) superstructure, and time-dependant phase transition of self-assembled monolayers (SAMs) formed by thioacetyl-terminated tolane molecules on Au(111) were examined by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). XPS measurements revealed that binding conditions of SAMs formed on Au(111) by tolanethioacetate (TTA) and tolane methyl thioacetate (TMTA) were considerably different from each other, suggesting that the adsorption conditions of tolane SAMs were strongly influenced by a difference in the chemical structure of tolanes. It was found that TTA and TMTA molecules would not form ordered SAMs after immersion of Au(111) substrate in a 0.5 mM N,N`-dimethylformamide solution for 1 day. However, we observed time-dependant phase transitions of TTA and TMTA SAMs from the disordered phase to the ordered phase as a result of long-term structural rearrangement after incubation at room temperature for 10 day. STM imaging also revealed that the adsorption of TTA and TMTA molecules on Au(111) leads to 2D ordered SAMs in a NH4OH solution. Our results here will be very helpful for understanding the formation and binding conditions of thioacetyl-terminated SAMs on Au(111) and controlling 2D SAM structure.