Real Time Monitoring of the Electrochemical Transformation of a Ferrocene-Terminated Alkanethiolate Monolayer at Gold via an Adhesion-Based Atomic Force Microscopic Characterization

This paper demonstrates the real time monitoring of the electrochemical transformation of a surface-bound redox species using AFM-based adhesion measurements. The measurements were conducted using a monolayer formed by the chemisorption of 11-mercaptoundecyl ferrocenecarboxylate (FcT) at a Au(111) electrode and a gold-coated probe tip modified with an octadecanethiolate (OT) monolayer. Using this probe tip−sample combination, the one-electron oxidation of the ferrocenyl group of the FcT monolayer results in a decrease in the observed force of adhesion ( F ad ) at the microcontact formed by the two different surfaces. Using surface tension arguments, this change is attributed to the decrease in the effective miscibility at the microcontact as a consequence of the oxidation of the ferrocenyl group to the ferrocenium ion. Issues related to the underlying changes in the interfacial structure that give rise to the differences in F ad are discussed.