Self-Assembled Monolayers Observed Using Electrochemical Scanning Tunneling Microscopy and Cyclic Voltammetry

Electrochemical scanning tunneling microscopy (EC-STM) and cyclic voltammetry (CV) were used to characterize Au(111) surfaces in aqueous electrolyte solutions containing halides, both with and without additional adsorbing molecules: tetrapyridylporphyrin, cobalt (II) tetrapyridylporphyrin, alpha-cyclodextrin and beta-cyclodextrin. Tetrapyridylporphyrin was found to form highly ordered self-assembled monolayers (SAMs) on iodine- and bromine-modified Au(111) at positive potentials where a disorganized SAM would be expected for a bare electrode. The range of electrode potentials at which organized TPyP domains were observed on bromine-modified Au(111) extends over 0.4 V more positive than what has been found previously for iodine-modified Au(111). Bromine modification was performed in situ, however no effect of polybromide adsorption was found. Coupled with the wider potential window of stability, these results find bromine-modified Au(111) to be a superior platform for the formation of ordered organic SAMs at elevated potentials. The adsorption of alpha- or beta-cyclodextrin was found to stabilize the Au(111) - (sqrt(3) x 22) surface structure in the presence of dissolved chloride, bromide, or iodide. Cyclic voltammetry data suggests that the adsorbed cyclodextrins have a significant effect on the kinetics of the anion-induced lifting of the (sqrt(3) x 22) reconstruction.;Beyond investigations of Au(111) electrode surfaces, a new procedure for the fabrication of insulated tungsten STM tips was developed. This procedure uses electrophoretic paint as the insulating coating, and yields tips exhibiting low leakage currents with much greater reproducibility than existing procedures, particularly the most commonly used procedures which employ apiezon wax or nail polish. Finally, the electrochemically driven catalytic oxidation of alcohols by 2,2',6,6'-tetramethylpiperidin-N-oxyl (TEMPO*) was investigated for the first time in a fluorous solvent. Cyclic voltammograms recorded using a Pt microelectrode suggest a unique effect of the fluorous medium on the reaction mechanism.