Coadsorption self-assembled monolayers of trithiocyanuric acid and 1,3,5-benzenetrithiol on an evaporated silver film

Abstract

Coadsorption self-assembled monolayer (SAM) films of trithiocyanuric acid (TCA) and 1,3,5-benzenetrithiol (BTT) on evaporated silver substrate were investigated using FT-IRAS and Raman Spectroscopy. Additionally, the adsorption structure of BTT was characterized by FT-IRAS and ab initio DFT calculations. Both BTT and TCA have three thiol moieties. Observed IR bands for BTT in a KBr disc and IRAS bands for BTT SAM film on silver film suggest that BTT adsorbs to the surface through two sulfur atoms and is more-or-less normal to the surface. The calculated frequencies of the silver–BTT complexes of thiol form with two silver atoms agreed with the observed IRAS bands of BTT on silver films. The IRAS spectra of a coadsorption SAM film of TCA and BTT, which was prepared from the same molar concentrations of TCA and BTT mixed in a methanol solution, showed only the bands that belong to the adsorbed BTT. A very weak IRAS band from TCA adsorbates appeared only with higher molar concentrations of TCA. The same results were obtained in the Raman spectroscopic experiment. It is evident that BTT strongly inhibits adsorption of TCA to silver films.