Date

2013

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Chemistry

First Adviser

Ferguson, Gregory S.

Other advisers/committee members

Moore, David T.; Roberts, James E.; Chaudhury, Manoj K.

Abstract

The work in this dissertation is focused on the development of methods for spatially controlling the adsorption of self-assembled monolayers (SAMs) on selected gold electrodes in an array. This research draws from synthetic organic and inorganic chemistry, electrochemistry, and surface science to provide a unique solution to the problem of directing the formation of SAMs, which are potentially useful in sensing and photovoltaic applications. To meet this need, we developed a facile electrochemical method that utilizes gold-oxide thin films as protecting layers to allow the selective placement of SAMs on specific gold electrodes. This approach is analogous to the protection-deprotection strategy used successfully by synthetic organic chemists for decades and is potentially applicable for a broad range of chemical functionality. The gold-oxide thin film can easily be added or removed, allowing convenient incorporation into the synthetic scheme. We used a combination of x-ray photoelectron spectroscopy (XPS), variable-angle spectroscopic ellipsometry (VASE) and contact-angle measurements to demonstrate that distinct monolayers can be formed on the neighboring electrodes and microelectrodes with no evidence of cross-contamination.In order to characterize the thin oxide films used in this method, as well as to assess their lability in various chemical environments, we also developed a method for measuring their wavelength-dependent, complex refractive index (n + ik). We first measured the thickness of the thin film independently by angle-resolved XPS. Using that thickness value, we determined the values of n and k by VASE. Using this unique combination of XPS and VASE, we were able to obtain values for the complex refractive index of an electrochemically formed thin film of gold oxide for wavelengths between 350 and 800 nm. Exploratory studies involving silver (I)-thiolate polymers were conducted to examine their possible use as precursors to monolayer films and metallic nanoparticles. X-ray photoelectron spectroscopy (XPS) measurements suggested that these polymers adsorb onto gold surfaces from solution, but decomposition produced surfaces that were not the same as those formed by self-assembly of alkanethiols on gold bearing a submonolayer of underpotential-deposited silver. In separate studies, the silver(I)-thiolate polymers could be decomposed into nanoparticles by thermolysis or photolysis as confirmed by transmission electron microscopy (TEM) and UV/vis spectrophotometry.

Included in

Chemistry Commons

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