Grafting Aryl Diazonium Cations to Polycrystalline Gold: Insights into Film Structure Using Gold Oxide Reduction, Redox Probe Electrochemistry, and Contact Angle Behavior

Abstract

The structure and properties of thin organic films electrografted to conducting surfaces by reduction of the corresponding diazonium salts are not well understood. In this work we used electrochemistry and contact angle measurements to characterize multilayer carboxyphenyl and methylphenyl films grafted to Au surfaces. Freshly grafted films contain material that can be readily removed during potential cycling and sonication. Observation of Au oxide surface electrochemistry confirms a porous bulk film structure as previously found for films electrografted to carbon surfaces. The charge associated with Au oxide reduction was used to estimate the upper limit for surface concentration of modifiers directly attached to the surface after careful preparation of the Au surface prior to and after grafting. Values for the surface concentration of the modifier in the range of 3−4 × 10-10 mol cm-2 indicate that the first layer of the films is loosely packed. The close correspondence of surface concentration with that...