Steric effects on adsorption and desorption behaviors of alkanethiol self-assembled monolayers on Au(111)

Adsorption conditions and desorption processes of self-assembled monolayers (SAMs) formed on Au(111) by propanethiol (PT) and PT-derivatives containing methyl groups on the α-carbon atom were examined by X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). XP spectra showed the formation of S–Au bonds, while adsorption condition depends on the molecular backbone structure. TDS indicated that PT SAM has two desorption fragments, dimer and monomer, at 450 K and 370 K, respectively. By increasing the number of methyl group, the dimerization was significantly suppressed. The monomer desorption peak shifted to a lower temperature, suggesting that the desorption process of alkanethiol SAMs is influenced by side-groups.