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

Abstract

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 alpha-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.