Structure and composition of binary monolayers self-assembled from sodium 2-mercaptoetanosulfonate and mercaptoundecanol mixed solutions on silver and gold supports

Abstract

Voltammetric reductive desorption, scanning tunneling microscopy (STM) and surface-enhanced Raman scattering (SERS) were used to determine the composition and structure of mixed, two-component monolayers of sodium 2-mercaptoetanosulfonate (MES) and mercaptoundecanol (MUL) on silver and gold supports. Monolayers were prepared by self assembling from ethanolic solutions of varying composition. Preferred adsorption of MUL was found in the electrochemical experiments on Au(111). The presence of two well-separated reductive desorption peaks in the voltammograms of the mixed monolayers on Au(111) indicated the existence of MES-rich and MUL-rich phases in a wide range of solution compositions. STM imaging confirmed formation of a few-nanometer-wide thiol domains for x_MES greater than 0.5 in the solution used for SAMs preparation. On the contrary, SERS experiments pointed at dominant adsorption of MES on rough Ag and Au substrates. Nearly exclusive adsorption of the MES for x_MES greater than 0.5 was observed on the rough Ag surface.