Understanding electrically activated processes at electrode-electrolyte interfaces is needed to improve many technologies, including energy conversion, semiconductor devices, bio-sensors, corrosion protection, etc. In-situ spectro-electrochemical studies based on a wide range of spectroscopies are particularly useful. Scanning Transmission X-ray microscopy (STXM) is a synchrotron-based technique which measures near-edge X-ray absorption fine structure (NEXAFS) with high spatial resolution. In addition to information on morphology, STXM also provides chemical state analysis using the X-ray absorption data, which makes in-situ STXM studies of electrochemical process of special interest. This thesis reports ex-situ and in-situ STXM based qualitative and quantitative studies on copper (Cu) electrodeposition and electrostripping. The influence of electrolyte pH on the distribution of Cu(I) and Cu(0) species electrodeposited from aqueous CuSO4 solutions was studied. An instrument capable of performing in-situ flow electrochemical STXM studies was designed and fabricated. The performance of this device was evaluated for in-situ Cu electrodeposition studies. Findings based on ex-situ and in-situ STXM studies are discussed. Suggestions are made for further instrumentation improvements. / Thesis / Master of Science (MSc)

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published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

This dissertation details the effect of underpotentially deposited (UPD) Pb on the surface enhanced Raman scattering (SERS) ability of roughened polycrystalline Ag electrodes. The deposition of monolayer and submonolayer amounts of Pb results in a quenching of the SERS response for pyridine and Cl⁻ adsorbed at Ag electrodes. Various factors which may contribute to the loss of SERS intensity are investigated. The most significant factors include changes in surface roughness features brought about by Pb UPD, changes in surface electronic properties of Pb-modified Ag and changes in a chemical contribution to surface enhancement. Possible changes in surface roughness properties of the Ag electrode due to Pb deposition are examined using scanning electron microscopy (SEM) and SERS reversibility studies. SEMs of roughened Ag electrodes before and after Pb monolayer deposition show no significant change in the morphology of the larger roughness features. However, the deposition and stripping of 60 - 70% of a Pb monolayer results in a loss of ca. 50% of the original SERS intensity for both adsorbate bands. This irreversible loss of SERS intensity is attributed to the destruction of atomic scale roughness (ASR). These results suggest that ca. 50% of the observed SERS response arises from a mechanism involving ASR. In addition, the destruction of ASR is shown to be largely responsible for the quenching of SERS at higher Pb coverages. The morphology of the SERS quenching profiles at lower Pb coverages for pyridine and Cl⁻ varies as a function of excitation wavelength. Experimental quenching profiles are compared with theoretical quenching profiles based on an electromagnetic contribution to SERS. Theoretical quenching profiles are calculated using a model for electromagnetic enhancement at a overlayer-covered ellipsoids proposed by Murray. The experimental results for both adsorbates are in agreement with the theoretical predictions for laser excitation in the blue. Experimental results in the green and red wavelength regions are best explained in terms of photoassisted charge-transfer mechanisms for surface enhancement.

The growing technological application of metallic lithium has produced a greater need to understand its fundamental surface chemical properties. The use of lithium as an anode in high-energy density battery systems represents one application where this knowledge is required to optimize system performance. The surface chemistry of lithium will be discussed in terms of oxidants which represent the reductive half-cell components of these batteries, contaminants present during cell fabrication, and solvents used as the electrolytic medium. These systems have been studied in the low pressure limit ( < 1 millitorr) at atomically clean lithium surfaces using X-ray Photoelectron Spectroscopy (XPS). The lithium/sulfur dioxide system has been singled out for detailed study in order to explore the relationship between gas-phase and solution-phase processes. Electrochemical characterization of the lithium anode has been conducted as a function of controlled surface composition within this system. The ability of lithium to induce corrosion at structural components of these batteries (i.e., glass insulators) has also been investigated. A description of the chemical activity of lithium and its consequence has been developed from these results.

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Electrochemical cycling of Ag surfaces under basic conditions has led to the discovery of a new, simple, rapid and cost effective method for the preparation of nano-structured Ag surfaces with features ranging from 30&ndash;150 nm in diameter. Our results indicated that during cyclic voltammetry, the surface was oxidized, resulting in the formation of soluble Ag complexes which were re-deposited as elemental Ag nanostructures (NSs) on the cathodic scan. The electrochemical properties of the Ag NSs were greatly affected by the presence of organophosphonates and other additives (vide infra), which also influenced the growth of nanostructures. The interaction of these Ag NSs with malathion and paraoxon were explored in more detail using Surface Enhanced Raman Spectroscopy. Results showed that generally smaller nanosized features resulted in high quality surface Raman enhancement. Next, Ag NSs&rsquo; properties in the presence of organophosphonates was investigated in tap water and apple juice in order to address issues related to matrix effects and potential interference from constituents in solution. Electrochemical and localized surface plasmon resonance results demonstrated the ability to detect organophosphonates in real samples, albeit at a lower limit of detections and without any selectivity to any particular organophosphonate. Next, the morphology and corrosion behaviour of Ag surfaces was explored in the absence and presence of surfactants and capping agents. Results demonstrated the protection of Ag surfaces against corrosion in the presence of Tween-20, while potassium citrate presence enhanceed corrosion of silver surfaces, resulting in the formation of a pitted surface with smaller Ag NSs. Lastly, the interactions of 2-cyano-3-(2&prime;-(5&prime;,10&prime;,15&prime;,20-tetraphenyl porphyrinato zinc-(II))yl) acrylic acid-modified Ag NSs with biomolecules were explored using spectro-electrochemical techniques. The photocurrent response of porphyrin-modified Ag NSs was quenched by the addition of adenosine-5&rsquo;-monophosphate (AMP), guanosine-5&rsquo;-monophosphate (GMP) and cytidine5&rsquo;-monophosphate (CMP), with a quenching efficiency of 80%, 68% and 48% for AMP, CMP and GMP, respectively.