Electrochemical and atomic force microscopy investigations of gold nanoparticles and metal oxide surfaces

This dissertation describes electrochemical and atomic force microscopy (AFM) investigations of several nanostructured electrode/electrolyte interfaces. Chapter 1 introduces the fundamental aspects of metal electrodeposition at highly oriented pyrolytic graphite (HOPG) substrates. Chapter 2 describes the electrochemical deposition and re-oxidation of Au at HOPG, and an unusual stabilization of Au nanoparticles on the upper plane of graphite step edges. Scanning electron microscopy (SEM) and AFM show that Au nanoparticles decorate the graphite surface at short deposition times, and that a small percentage of these particles grow into large micrometer-sized crystallites. Subsequent re-oxidation of the deposited metal reveals that the Au crystallites are readily oxidized, but the Au nanoparticles remain stabilized along the upper plane of the graphite step edges.; Chapter 3 introduces the properties of metal/oxide films, including their structure and growth properties. Chapter 4 describes the application of conducting atomic force microscopy (CAFM) to visualize the heterogeneous electronic conductivity of Ti/TiO₂ electrodes. Conductivity through the TiO₂ film was found to preferentially occur at grain boundaries, although large spatial variations in the oxide film conductivity are also observed above topographically featureless regions of grain faces. Chapter 5 discusses cyclic voltammetric investigations of Al/Al₂O₃ film dissolution in the absence and presence of aggressive halide ions (i.e. Cl− and Br−). Computer simulations, based on the high field growth model, have been employed to extract dissolution rates of the oxide film as a function of [Cl−]. It has been shown that an ∼50 fold increase in the dissolution rate of the Al₂O ₃ film occurs when Cl− is added to borate solutions. Chapter 6 describes chronoamperometric studies of Al₂O₃ film dissolution in the presence of halide ions. Also discussed is the relationship between pitting potential of the Al/Al₂O₃ film and the dissolution rate of the oxide film.