Adsorption of thiophene and 2,5-dimethylthiophene on Au(1 1 1) from ethanol solutions

The formation of thin films by the adsorption of thiophene (TP) and 2,5-dimethylthiophene (DMTP) on Au(1 1 1) in 1 mM ethanol solutions was investigated by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). XPS and STM studies revealed that the adsorption of TP molecules on Au(1 1 1) gives rise to the formation of two-dimensional ordered self-assembled monolayers through chemisorption between the sulfur atom in TP and the gold surface, while the adsorption of DMTP molecules having two methyl groups at 2,5-positions of the TP ring leads to the formation of physisorbed multilayers having a liquid-like phase. These results indicate that two methyl groups at 2,5-positions of the TP ring significantly affect the growth process of the thin film, which strongly reflect that interactions between the sulfur atom in the TP ring and gold play an important role in adsorption process of molecules.