Tailoring the chemistry of gold surfaces with aryl layers formed by the electrochemical reduction of diazonium cations

The electrochemical reduction of para-substituted aryldiazonium cations is a convenient method of introducing chemical functional groups to a surface. The number of conductive surfaces that have been used for this purpose is rapidly expanding. The body of work presented in this thesis will serve to further investigate this method as it applies to polycrystalline gold surfaces.;Two-component, mixed molecular layers comprised of diazonium-derived NAB and dodecanethiolate (DDT) were prepared using a sequential deposition approach. The aryl component is first deposited electrochemically, followed by immersion in a solution of DDT. We will demonstrate that control over the composition of the layers can be achieved by manipulating the concentration of NAB diazonium cations at the electrochemical grafting step. The mixed layers were characterized by reflection-absorption spectroscopy, atomic force microscopy, electrochemical blocking, and x-ray photoelectron spectroscopy. The electron transfer kinetics of Ru(NH3)63+/2+ were examined at the mixed layer electrodes. The kinetics are highly dependent on the relative proportions of NAB and DDT present and the thickness of the NAB component.;The NAB:DDT mixed films were employed as the molecular layer in molecular electronics junctions. We examined the suitability of Al2O 3/Au top contacts for these junctions. Junctions for which the molecular layer was mostly comprised of DDT showed an increased failure rate.;The stability of diazonium-derived nitroazobenzene (NAB) layers on Au was investigated by subjecting them to a variety of treatments including prolonged exposure to UV radiation, refluxing solvents, ultrasonication, chemical displacement by octadecanethiol (ODT), and the application of negative potentials to -1.5 V vs Ag/AgCl. Infrared reflection-absorption spectroscopy (IRRAS) and electrochemical blocking were used to make the assessments. The films are very resistant to ODT displacement reactions, moderately resistant to ultrasonication and refluxing; but not very resistant to the other treatments. In most cases, quantitative IRRAS measurements indicate that > 50% of the layer resists the treatments. A direct, side-by-side comparison of the stability of nitrobenzene (NB) layers deposited electrochemically from nitrobenzene diazonium cations to self-assembled monolayers (SAMs) of mercaptonitrobenzene was made. Both types of layers are prone to removal by the various treatments. This is likely due to the presence of weakly bound, physisorbed material in addition to more strongly bound material. Immersion in an ODT solution results in complete displacement of the thiol derived nitrobenzene monolayer but does not completely displace the diazonium-derived layer.