Multilayer formation of 1,2-ethanedithiol on gold: Surface-enhanced Raman scattering and ellipsometry study

Abstract

Invoking the fact that surface-enhanced Raman scattering (SERS) is a very sensitive surface-probing technique and that 1,2-ethanedithiol(1,2-EDT) is the simplest alkanedithiol molecule, we have analyzed the SER spectra of 1,2-EDT in aqueous gold sol to confirm spectroscopically the feasibility of multilayered film formation for alkanedithiols on the gold surface. We could clearly identify the S-S stretching band that reveals the formation of multilayers of 1,2-EDT on the colloidal gold surface. Surprisingly, the intermolecular disulfide bond appeared to form even at a submonolayer coverage limit, implying that the adsorption of alkanedithiol on gold does not take place homogeneously from the early stage of self-assembly. A separate ellipsometry measurement performed with vacuum-evaporated gold substrates revealed that up to tetralayers could be assembled on gold by 1,2-EDT in n-hexane while a bilayer formed in ethanol.