Formation of Mixed Monolayers from 11-Mercaptoundecanoic Acid and Octanethiol on Au(111) Single Crystal Electrode under Electrochemical Control

Abstract

The formation process and characterization of mixed layers of 11-mercaptoundecanoic acid (MUA) and octanethiol (OT) on Au(111) single crystal electrodes under electrochemical control from alkaline solutions are analyzed in this work by means of electrochemical techniques such as chronocoulometry, cyclic voltammetry, and electrochemical impedance spectroscopy. The surface composition of the layers differs from the component ratio of bulk solution and is supposed to be directed by both the adsorption potential of the individual molecules and its adsorption behavior. The relative competitive adsorption capacity of the two functional groups in the bifunctional molecules plays an important role in the electrochemical deposition of mixed layers as the second component can occupy the free space that the first molecule liberates during reorganization. Two different mixed layers can be obtained under the experimental conditions of this work: a macroscopically homogeneous layer and a homogeneously mixed layer at higher and lower MUA:OT ratios. The macroscopically mixed layer should be formed by small domains that keep the same energetic as the single-component SAM of the thiol constituents, and the homogeneously mixed should be formed by few MUA molecules diluted in an OT layer.