Adsorption of 4,4′-thiobisbenzenethiol (4,4′-TBBT) on a colloidal silver surface and a roughened silver electrode surface was investigated by means of surface-enhanced Raman scattering (SERS) for the first time, which indicates that 4,4′-TBBT is chemisorbed on the colloidal silver surface as dithiolates by losing two H-atoms of the S-H bond, while as monothiolates on the roughened silver electrode. The different orientations of the molecules on both silver surfaces indicate the different adsorption behaviors of 4,4′-TBBT in the two systems. It is inferred from the SERS signal that the two aromatic rings in 4,4′-TBBT molecule are parallel to the colloidal silver surface as seen from the disappearance of νC-H band (3054 cm-1), which is a vibrational mode to be used to determine the orientation of a molecule on metals according to the surface selection rule, while on the roughened silver electrode surface they are tilted to the surface as seen from the enhanced signal of νC-H. The orientation of the C-S bond is tilted with respect to the silver surface in both cases as inferred from the strong enhancement of the νC-S. SERS spectra of 4,4′-TBBT on the roughened silver electrode with different applied potentials reveal that the enhancement of 4,4′-TBBT on the roughened silver electrode surface may be related to the chemical mechanism (CM). More importantly, the adsorption of 4,4′-TBBT on the silver electrode is expected to be useful to covalently adsorb metal nanoparticles through the free S-H bond to form two- or three- dimensional nanostructures.
- Chemical mechanism
- Silver surface