Thermal decomposition processes of self-assembled monolayers (SAMs) on Au (111) composed of various thiol molecules were explored by thermal desorption spectroscopy (TDS).
Desorption as disulfides was always observed for the methanethiol SAMs at any coverage, whereas the desorbed species from the SAMs of n-octanethiol strongly depended on the molecular density. In the case of cyclohexanethiol (cyclohexyl mercaptan), only monomers (thiol) desorbed from the SAM. In the cases of the mixed SAMs comprised of cyclohexylthiol and other thiolates (methanethiol and octanethiol), the desorption of asymmetric disulfides in a small yield was observed. TDS and X-ray photoelectron spectroscopy measurements revealed that these thiols are chemically bound to gold surfaces and that there was no significant difference in the chemical characters of their bonds to the substrates. These results suggest that the structure of a thiol molecule plays a critical role in determining the manner of desorption, thus providing hints for improving the thermal stability of SAMs.
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