The focus of the following research was to (1) understand the chemistry involved in nitriding an organosilicate glass substrate prior to tantalum deposition, as well as the effect nitrogen incorporation plays on subsequent tantalum deposition and (2) the reduction of a native oxide, the removal of surface contaminants, and the etching of a HgCdTe surface utilizing atomic hydrogen. These studies were investigated utilizing XPS, TEM and AFM. XPS data show that bombardment of an OSG substrate with NH3 and Ar ions results in the removal of carbon species and the incorporation of nitrogen into the surface. Tantalum deposition onto a nitrided OSG surface results in the initial formation of tantalum nitride with continued deposition resulting in the formation of tantalum. This process is a direct method for forming a thin TaN/Ta bilayer for use in micro- and nanoelectronic devices. Exposure to atomic hydrogen is shown to increase the surface roughness of both air exposed and etched samples. XPS results indicate that atomic hydrogen reduces tellurium oxide observed on air exposed samples via first-order kinetics. The removal of surface contaminants is an important step prior to continued device fabrication for optimum device performance. It is shown here that atomic hydrogen effectively removes adsorbed chlorine from the HgCdTe surface.

Supplying the global energy demand through renewable sources has never been as accessible as it is now thanks to developments in technology and infrastructure that have enabled low-cost energy production from sources like wind, solar, and hydroelectric power. However, the challenge of integrating variable renewable energy generators into existing grid infrastructure has driven the demand for efficient and inexpensive energy storage technologies to buffer these intermittent energy supplies. Using electrochemical devices like fuel cells and electrolyzers is an attractive approach for both the long- and short-term storage of energy, where excess energy is used to drive the conversion of low energy reactants into high energy, storable fuels which can be consumed when energy supply is low. These devices rely on highly active electrocatalysts in order to drive these reactions efficiently. However, a major challenge for these technologies lies in developing catalysts at commercial scale without compromising their selectivity or lifetime. Several degradation mechanisms like catalyst particle detachment, dissolution, or surface poisoning by undesired species can quickly diminish the activity and selectivity of a given catalyst, and drive up the costs of electrochemical storage systems. Thus, developing catalysts that balance stability, activity, and selectivity is crucial to improve the economic viability of these energy storage devices. One approach towards mitigating the issues of catalyst stability and activity is through adhering a semi-permeable oxide membrane onto the catalyst surface, creating a structure known as an oxide encapsulated electrocatalyst (OEC). These architectures have previously been shown to improve reaction selectivity, poisoning resistance and nanoparticle stability by improving the adhesion of catalyst nanoparticles, preventing poisoning species from reaching the buried catalytic interface, and controlling the local concentrations of reactants as a means of shifting reaction kinetics. Though earlier studies of OECs have demonstrated a wide array of beneficial properties that encapsulated catalyst architectures offer, they have often been based on highly heterogeneous electrodes and been evaluated across a wide range of conditions, which complicates the identification of the mechanisms that underlie these improvements. Currently, little is understood about the governing mechanisms that influence how oxide overlayers interact with – and ultimately affect – the catalyst surface, as well as alter the reactions occurring at the buried interface. Design rules that relate OEC structure to catalytic performance have the potential to greatly accelerate the understanding and development of such architectures, and would allow for more rational, targeted design of OEC structure in a way that would accelerate their application to new electrocatalytic systems.The aim of this dissertation is therefore to systematically investigate the design space of OEC architectures by using well-defined, model planar electrocatalysts in order to draw clear relationships between the structure, composition, and chemical/physical properties of OECs and the resulting effects they have on electrocatalytic performance. Using planar Pt catalysts encapsulated by a thin, highly tunable carbon-modified silicon oxide (SiOₓCy) overlayers, properties like overlayer thickness, carbon concentration, and density can be specifically adjusted during the room temperature photochemical synthesis procedures used for overlayer fabrication. Similarly, changing the composition of the underlying Pt catalyst while keeping overlayer properties constant can provide insights into how catalyst and overlayer materials interact with and influence the structure of one another. Rigorous materials characterization like X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), ellipsometry, and scanning electron microscopy (SEM) coupled with electroanalytical techniques such as cyclic voltammetry and impedance spectroscopy relates observations in the physical and chemical properties of OECs directly to the electrochemical performance of various probe reactions. In Chapter 3, carbon-free, SiO₂-like overlayers of uniform thicknesses were synthesized using a room temperature, Ultraviolet (UV)-ozone photochemical process that allowed for specific control over the resulting overlayer thicknesses, which ranged between 1.8 nm and 18.0 nm. Two different compositions of the planar catalyst substrate were investigated at all thicknesses. The first catalyst investigated was a 50 nm thick, uniform layer of polycrystalline Pt that displayed bulk properties. The second, thinner catalyst substrate was only 3 nm thick, and contained trace quantities of oxophilic Ti species at the buried interface, which migrated to the surface during electrode fabrication. Ultimately it was found that electrodes based on ultrathin, Ti-doped Pt possesses thinner Pt oxide (PtOₓ) interlayers, while exhibiting reduced permeability for Cu²⁺ and H⁺ compared to the bulk Pt species. Thin layer Pt electrodes also demonstrated enhanced retention of the SiOₓ overlayer during stability testing in 0.5 M H₂SO₄, credited in part to the differences in PtOₓ concentration and structure that form at the buried interface as a result of trace Ti concentrations. These observations lead to the study presented in Chapter 4, which sought to assess the impact of chemical and physical overlayer properties on resulting electrochemistry. Compositions of the SiOₓCy overlayer were altered by restricting the exposure of electrodes to the photochemical UV-ozone curing step during synthesis, which was responsible for removing carbonaceous groups in the overlayer’s precursor. Limiting the length of this step between 15 minutes and 120 minutes yielded overlayer with residual carbon concentrations ranging between 30% and 4%, respectively, and demonstrated markedly different physical and chemical properties that impacted species transport through the overlayer. Specifically, the less dense, carbon-rich SiOₓCy layers restricted the flux of H⁺ to the Pt interface during the hydrogen evolution reaction (HER) under transport limited conditions, but displayed high permeability towards dissolved oxygen species for the oxygen reduction reaction (ORR). By contrast, the denser, carbon free SiOx layers blocked oxygen transport almost entirely, but showed limiting current densities for HER that were comparable to an unencapsulated surface. This is believed to occur from the differing transport mechanisms for H⁺ and O₂ through SiOₓ, where the former diffuses through a Grotthuss-type transport mechanism, and the latter through a solution-diffusion mechanism. The high density SiOₓ layers therefore constrain the flux of O₂ due to its lower free volume compared to the carbon rich overlayers, but has a higher concentration of silanol carrier groups that promote H⁺ transport. These results demonstrated the impact that overlayer compositions can have on modulating the local concentrations of reactants, and motivated the further study of OECs on alcohol oxidation reactions (AORs) in Chapter 5. Using the same approach to control overlayer composition detailed above, SiOₓCy overlayers deposited on Pt thin film electrodes were fabricated and their catalytic performance towards the oxidation of carbon monoxide, formic acid, and C₁-C₄ alcohols were assessed. All SiOₓCy - encapsulated electrodes decreased the overpotentials required to oxidize and remove Pt-bound CO species – a poisoning intermediate for a number of AORs, with the largest reductions seen for the carbon poor, SiO₂-like overlayers through a possible Si-OH mediated removal step. Unexpectedly though, electrodes that had the largest reductions in CO oxidation overpotentials showed the least enhancement for AOR activity for all encapsulated samples. These observations suggest that a different rate determining step may be governing the overall reaction rate on encapsulated electrodes over the potential ranges investigated - most likely bond scission of C-H bonds and/or oxidation of formate-based intermediates. Finally, Chapter 6 presents results obtained from state-of-the-art operando ambient pressure X-ray photoelectron spectroscopy (APXPS) studies, which were used to investigate the behavior of SiOₓ overlayers and ions in solution to understand local interactions and electronic effects that arise under wetted, electrochemical operating conditions. It was found that the choice of electrolyte had a clear impact on the overlayer’s response to different applied potentials. Si 1s spectra of the SiOₓ overlayer taken in K₂SO₄ electrolytes showed a slight positive correlation with applied potential that signified a weak electronic interaction between the SiOₓ and the underlying Pt. However, when the anion was switched to Cl⁻, clear, non-linear correlations between the Si 1s binding energy and potential emerged, suggesting a major change in the local chemical and electronic conditions within the overlayer. Analyzing ion concentrations also showed that overlayers demonstrate different distributions and ion rejection properties based on an ion’s valence and size. The mechanism through which these changes manifest is quite complex, as the layers themselves can introduce numerous perturbations in the system by disrupting the electrochemical double layer, introducing steric confinement at the buried interface, or promoting different reaction pathways. Although continued work will be necessary to better de-convolute these effects and develop optimized, concise design rules, the studies presented in this thesis illustrate the unique opportunity that the application of OECs has towards the future customization of electrocatalysts for a wide range of chemistries and applications.

Two projects are presented here. In the first, metal-cyclopentadienyl bond dissociation energies (BDEs) were measured for seven metallocene ions (Cp2M+, Cp = η5-cyclopentadienyl = c-C5H5, M = Ti, V, Cr, Mn, Fe, Co, Ni) using threshold collision-induced dissociation (TCID) performed in a guided ion beam tandem mass spectrometer. For all seven room temperature metallocene ions, the dominant dissociation pathway was simple Cp loss from the metal. Traces of other fragment ions were also detected, such as C10H10+, C10H8+, C8H8+, C3H3+, H2M+, C3H3M+, C6H6M+, and C7H6M+, depending on the metal center. Statistical modeling of the Cp-loss TCID experimental data, including consideration of energy distributions, multiple collisions, and kinetic shifts, allow the extraction of 0 K [CpM+ - Cp] BDEs. These are found to be 4.95 ± 0.15, 4.02 ± 0.14, 4.22 ± 0.13, 3.51 ± 0.12, 4.26 ± 0.15, 4.57 ± 0.15, and 3.37 ± 0.12 eV for Cp2To+, Cp2V+, Cp2Cr+, Cp2Mn+, Cp2Fe+, Cp2Co+, and Cp2Ni+, respectively. The measured BDE trend is largely in line with arguments based on a simple molecular orbital picture, with the exceptions of a reversal in Cp2Mn+ and Cp2Ni+ BDEs (although within uncertainty), and the exceptional case of titanocene, most likely attributable to its bent structure. The new results presented here are compared to previous literature values and are found to provide a more complete and accurate set of thermochemical parameters. In the second project, imaging photoelectron photoion coincidence (iPEPICO) spectroscopy has been used to determine 0 K appearance energies for the unimolecular dissociation reactions of several energy selected 1-alkyl iodide cations n-CnH2n+1I+ → CnH2n+1+ + I, (n = 2-5). The 0 K appearance energies of the iodine-loss fragment ions were determined to be 9.836 ± 0.010, 9.752 ± 0.010, 9.721 ± 0.010, and 9.684 ± 0.010 eV for n-C3H7I, n-C4H9I, n-C5H11I, and n-C6H13I molecules, respectively. Isomerization of then-alkyl iodide structures into 2-iodo species adds complexity to this study. Using literature adiabatic ionization energies, ionic bond dissociation energies were calculated for the four modeled iodoalkyl cations and it was shown that as the alkyl chain length increases, the carbon-halogen bond strength decreases, supporting the suggestions set forth by inductive effects. In the modeling with statistical energy distributions and rate theory, the role of hindered rotors was also evaluated and no strong experimental evidence was found either way. The heaviest species in the series, heptyl iodide (C7H15I) was also measured via iPEPICO and showed to have a greater complexity of fragmentation than the lighter analogs. Sequential dissociation of the first fragment ion, C7H15+ leads to C4H9+, C5H11+, and C3H7+ ions in competitive dissociation processes, dominated at low energies by the C4H9+ cation.

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X-ray photoelectron spectroscopy (XPS) is the most widely used surface analysis technique for chemically probing surfaces. Its popularity stems from the large amount of information that can be gathered about the electronic states of the atoms it probes, including core shell information and valence electron information. Simple qualitative analysis (peak identification) can often be performed, but quantitative analysis is a much more complicated process. Although XPS usage has increased dramatically, so has the amount of erroneous analysis observed in the literature. In my thesis, I first present a perspective on how to improve the quality of surface and material data analysis. This chapter focuses on responsible groups, using population biology models and the Prisoner's Dilemma to describe the situation and the potential changes that must be made to counteract error propagation. I quantify errors in XPS data analysis to provide perspective on the gravity of the situation. Over 400 publications in three journals were analyzed. Additionally, another 900 journals were surveyed to determine the quantity of information in the analysis. The parameters include experimental parameters, e.g., the pass energy, peak fitting parameters, the spot size, X-ray source, and the type of spectrometer. I found that over 40% of the publications had significant errors that could potentially change the conclusions of the publication. About 35% of all papers neglected to note the type of spectrometer used, and 85% did not mention the type of software used for analysis. The latter half of this work focuses on XPS peak fitting. I present a broad overview of peak fitting, including how to determine the appropriate background and peak shapes to use, how to quantify XPS data, and how to account for other phenomena associated with photoemission. The line shape chosen for peak fitting is critical, as it is the synthetic shape that is used to model observed physical phenomena. A detailed review on typical line shapes, including the Voigt and pseudo-Voigt functions is presented, along with how to apply them in peak fitting. How and why asymmetric peak shapes are required is also discussed, including which effects cause asymmetry, and if it is inherent to the material or the method of analysis. Finally, a discussion on using constraints to properly model known effects is presented. These efforts were guided by the findings in the former half of this work. The trends presented here are not unique to XPS. Other fields and techniques have similar reproducibility problems. This work discusses possible solutions and what efforts as a community need to be taken to remedy the reproducibility crisis. Additionally, this work includes guides that have original research to improve approaches to XPS analysis, including peak fitting, constraint parameters, and the appropriate use of line shapes.

Advances in the interconnection technology have played a key role in the continued improvement of the integrated circuit (IC) density, performance and cost. Copper (Cu) metallization, dual damascenes processing and integration of copper with low dielectric constant material are key issues in the IC industries. Chemical mechanical planarization of copper (CuCMP) has emerged as an important process for the manufacturing of ICs. Usually, Cu-CMP process consists of several steps such as the removal of surface layer by mechanical action of the pad and the abrasive particles, the dissolution of the abraded particles in the CMP solution, and the protection of the recess areas. The CMP process occurs at the atomic level at the pad/slurry/wafer interface, and hence, slurries and polishing pads play critical role in its successful implementation. The slurry for the Cu-CMP contains chemical components to facilitate the oxidation and removal of excess Cu as well as passivation of the polished surface. During the process, these slurry chemicals also react with the pad. In the present study, investigations were carried out to understand the effect of hydrogen peroxide (H2O2) as an oxidant and benzotriazole (BTA) as an inhibitor on the CMP of Cu. Interaction of these slurry components on copper has been investigated using electrochemical studies, x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). In the presence of 0.1M glycine, Cu removal rate was found to be high in the solution containing 5% H2O2 at pH 2 because of the Cu-glycine complexation reaction. The dissolution rate of the Cu was found to increase due to the formation of highly soluble Cu-glycine complex in the presence of H2O2. Addition of 0.01M BTA in the solution containing 0.1M glycine and 5% H2O2 at pH 2 exhibited a reduction in the Cu removal rate due to the formation of Cu-BTA complex on the surface of the Cu further inhibiting the dissolution. XPS and SIMS investigations revealed the formation of such Cu-glycine complex, which help understand the mechanism of the Cu-oxidant-inhibitor interaction during polishing. Along with the slurry, pads used in the Cu-CMP process have direct influence an overall process. To overcome problems associated with the current pads, new application specific pad (ASP) have been developed in collaboration with PsiloQuest Inc. Using plasma enhanced chemical vapor deposition (PECVD) process; surface of such ASP pads were modified. Plasma treatment of a polymer surface results in the formation of various functional groups and radicals. Post plasma treatment such as chemical reduction or oxidation imparts a more uniform distribution of such functional groups on the surface of the polymer resulting in unique surface properties. The mechanical properties of such coated pad have been investigated using nanoindentation technique in collaboration with Dr. Vaidyanathan’s research group. The surface morphology and the chemistry of the ASP are studied using scanning electron microcopy (SEM), x-ray photoelectron spectroscopy (XPS), and fourier transform infrared spectroscopy (FTIR) to understand the formation of different chemical species on the surface. It is observed that the mechanical and the chemical properties of the pad top surface are a function of the PECVD coating time. Such PECVD treated pads are found to be hydrophilic and do not require being stored in aqueous medium during the not-in-use period. The metal removal rate using such surface modified polishing pad is found to increase linearly with the PECVD coating time. Overall, this thesis is an attempt to optimize the two most important parameters of the Cu-CMP process viz. slurry and pads for enhanced performance and ultimately reduce the cost of ownership (CoO).

Biomedical implants are commonly made from commercially pure titanium and other metal alloys, which are chosen for their strength and density. To improve the stability and promote bone cell growth into the implant, efforts to bond coatings to metal have been extensively studied. Many coatings used are considered bioactive, which promote the adhesion and growth of the bone cells surrounding the implant [A.1]. Of these, the most commonly investigated coating is a ceramic called hydroxyapatite, which is brittle, leading to flaking and inadequate bone cell growth [A.2]. Alternate bioactive coatings are being examined, including chitosan, the deacetylated form of chitin. Chitin is the second most abundant polymer in nature [A.3] and is found in the exoskeletons of insects and shellfish [A.4]. Chitosan has been proven to have excellent biocompatibility [A.5], be non-toxic [A.3], and promote the adhesion and growth of bone cells [A.6 ? A.7]. In this research, four treatment combinations were developed and tested in an attempt to improve film bonding. These treatment combinations were created using one of two silane molecules, aminopropyltriethoxysilane and triethoxsilylbutyraldehyde, and one of two metal treatments, passivation and piranha treatment. XPS was used to characterize the reaction steps for each of the treatment combinations. A significant decrease in TiO, along with significant increases in SiOx groups, C ? N ? H, and C = O, indicated that the reactions were proceeding as expected. XPS also indicated that, chemically, the chitosan films were not significantly different and were unchanged by the treatment combinations. Following chemical analysis, mechanical testing was performed on the four treatment combinations. No changes to the bulk properties were seen as demonstrated by nano-indentation, further indicating that the four treatment combinations did not change the chemical properties of chitosan. The bulk adhesion of the films was greatly improved for all four treatment combinations, as demonstrated by tensile testing. The highest value from this research, 19.50 ± 1.63 MPa, was significantly higher than the previously published results of 1.6 ? 1.8 MPa [A.10]. Overall, the treatments developed in this study significantly improved the adhesion of the chitosan film on the titanium substrate, without modifying the chemical or structural properties of chitosan. [A.1] Ratner, B. D. and A. S. Hoffman. Biomaterials Science: An Introduction to Materials in Medicine. California: Academic Press, Inc., 1996, Foreword, 1-8. [A.2] S.D. Cook, K.A. Thomas, J.F. Kay. ?Experimental Coating Defect in Hydroxylapatite-Coated Implants.? Clinical Orthopaedics and Related Research, 1992, 265, 280-290. [A.3] A.K. Singla, M. Chawla. ?Chitosan: some pharmaceutical and biological aspects- an update.? Journal of Pharmacy and Pharmacology, 2001, 53, 1047-1067. [A.4] Q. Li, E.T. Dunn, E.W. Grandmaison, M.F.A. Goosen. ?Application and Properties of Chitosan.? Journal of Bioactive and Compatible Polymers, 1992, 7, 370-397. [A.5] M. Prasitsilp, R. Jenwithisuk, K. Kongsuwan, N. Damrongchai, P. Watts. ?Cellular responses to chitosan in vitro: The importance of deacetylation.? Journal of Materials Science: Materials in Medicine, 2000, 11, 773-778. [A.6] R.A.A. Muzzarelli, M. Mattioli-Belmonte, A. Pugnaloni, G. Biagini. ?Biochemistry, histology, and clinical uses of chitins and chitosans in wound healing.? Chitin and Chitinases, ed. P. Jolles, R.A.A. Muzzarelli, Switzerland: Birkhauser Verlag Basel, 1990. [A.7] P. Klokkevold, L. Vandemark, E.B. Kenney, G.W. Bernard. ?Osteogenesis Enhanced by Chitosan (Poly-N-Acetyl Glucosaminoglycan) In Vitro.? Journal of Periodontology, 1996, 67, 1170-1775. [A.8] J.D. Bumgardner, R. Wiser, P.D. Gerard, P. Bergin, B. Chestnutt, M. Marini, V. Ramsey, S.H. Elder, J.A. Gilbert. ?Chitosan: potential use as a bioactive coating for orthopaedic and craniofacial/dental implants.? Journal of Biomaterials Science, Polymer Edition, 2003, 14 (5), 423-438.

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<p>Fabrication of microarrays using sol-gel immobilization has been utilized as an approach to develop high density biosensors. Microarray fabrication using various printing techniques including pin-printing and piezoelectric ink jet printing methods has been demonstrated. However, only limited characterization to understand the encapsulated biomolecule-material interface has been reported. Herein, Chemical characterization using X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) on pin-printed microarrays of sol-gel derived acetylcholinesterase (AChE) microarrays is reported. Furthermore, the <em>in situ</em> fabrication of microarrays following the sol-gel process using piezoelectric ink jet printing methods was explored. Through techniques measuring solution viscosity, surface tension and particle size, important aspects of bio-ink formulation for piezoelectric ink jet printing were identified. Combined, a greater understanding towards the fabrication and characterization of sol-gel derived microarrays was achieved through this exploratory research.</p> / Master of Science (MSc)