Interfacial electrochemistry and in situ SEIRAS investigations of self-assembled organic monolayers on Au/electrolyte interfaces

Electrified solid/liquid interfaces offer unique opportunities for the fabrication and characterization of 2D supramolecular nanostructures. The combination of macroscopic electrochemical methods with structure sensitive techniques, such as scanning probe microscopy (SPM) or vibrational spectroscopy enables the development of a detailed knowledge on structure and functionality of the created molecular assemblies. In the present dissertation, the steady state and dynamic properties of self-assembled adlayers of trimesic acid and thioalkylviologens were investigated on gold/electrolyte interfaces employing surface enhanced IR absorbance spectroscopy (SEIRAS) in combination with various electrochemical methods. The double layer properties of the Au/aqueous electrolyte interface were investigated first for massive Au(111) single crystal electrodes and Au(111-20 nm) film electrodes in contact with 0.1 M $H$_{2}SO_{4}$ and 0.1 M HClO$_{4}$. Cyclic voltammetry revealed that the response of the film electrodes resembles that of a massive Au (111) electrode with a low step density. The potential-dependent adsorption of anions and interfacial water was investigated in detail by in situ SEIRAS. As the second topic, the adsorption and phase formation of trimesic acid (TMA) on Au(111) and Au(111-20 nm) electrodes were comprehensively investigated by electrochemical techniques, scanning tunneling microscopy and SEIRAS. Depending on the applied electrode potential, TMA molecules form several highly ordered 2D adlayers: two physisorbed phases, one characterized by a hexagonal honeycomb pattern and the other by close-packed linear-dimers of planar oriented molecules; and one stripe-like chemisorbed adlayer of perpendicularly oriented molecules. Weakly hydrogen-bonded, strongly hydrogen-bonded and isolated water species are coadsorbed. The potential-induced formation of chemisorbed TMA starts with a fast orientation change from planar, physisorbed molecules to tilted and/or perpendicular in a disordered chemisorbed phase. Subsequently, the chemisorbed TMA molecules align slowly into the highly ordered stripe-like structure. Both substrate/adsorbate and intermolecular hydrogen-bonding interactions are strongly dependent on the electrode potentia