Increasing systemic error during copper CMP (Chemical Mechanical Planarization) is due to the uneven surfacetopography generated during the process. A mechanistic model based on a fundamental understanding of the processconstituents was proposed to predict material removal rates and the post CMP topography. Two synergisticmechanisms were proposed: 1) chemically dominant behavior is explained by the repetitive removal and formation ofa protective layer on copper surface and chemical dissolution during the process, 2) mechanically dominant removalmechanism is due to the material behavior of copper at the nano-scale and subsequent oxidation and removal of theplastically deformed copper. As a step forward to optimize the process and the manufacturing system, this model wasextended to explain pattern dependent variability during copper CMP.

Vanadium oxide has emerged as a potential electrochemical capacitor material due to its attractive pseudocapacitive performance; however, it is known to suffer from capacitive degradation upon sustained cycling. In this work, the electrochemical cycling behavior of anodically electrodeposited vanadium oxide films with various surface treatments in aqueous solutions is investigated at different pH. Quantitative compositional analysis and morphological studies provide additional insight into the mechanism responsible for capacitive degradation. Furthermore, the capacitance and impedance behavior of vanadium oxide electrochemical capacitor electrodes is compared for both aqueous and nonaqueous electrolyte-solvent systems. Alkali metal chloride and bromide electrolytes were studied in aqueous systems, and nonaqueous systems containing alkali metal bromides were studied in polar aprotic propylene carbonate (PC) or dimethyl sulfoxide (DMSO) solvents. The preferred aqueous and nonaqueous systems identified in the half-cell studies were utilized in symmetric vanadium oxide whole-cells. An aqueous system utilizing a 3.0 M NaCl electrolyte at pH 3.0 exhibited an excellent 96% capacitance retention over 3000 cycles at 10 mV s^-1. An equivalent system tested at 500 mV s^-1 displayed an increase in capacitance over the first several thousands of cycles, and eventually stabilized over 50,000 cycles. Electrodes cycled in nonaqueous 1.0 M LiBr in PC exhibited mostly non-capacitive charge-storage, and electrodes cycled in LiBr-DMSO exhibited a gradual capacitive decay over 10,000 cycles at 500 mV s^-1. Morphological and compositional analyses, as well as electrochemical impedance modeling, provide additional insight into the cause of the cycing behavior. Lastly, reduced graphene oxide and vanadium oxide nanowire composites have been successfully synthesized using electrophoretic deposition for electrochemical capacitor electrodes. The composite material was found to perform with a higher capacitance than electrodes containing only vanadium oxide nanowires by a factor of 4.0 at 10 mV s^-1 and 7.5 at 500 mV s^-1. The thermally reduced composite material was examined in both symmetric and asymmetric whole cell electrochemical capacitor devices, and although the asymmetric cell achieved both higher energy and power density, the symmetric cell retained a higher capacitance over 50,000 cycles at 200 mV s^-1.

With stringent requirements of copper chemical mechanical planarization (CMP), such as minimized step heights, enhanced uniformity and minimal defects, the CMP process needs to be improved based on a fundamental understanding of the material removal mechanisms. Also, with the stringent requirements, the problems in copper CMP process cannot be resolved solely improving the process itself; rather, systemic understanding of the entire manufacturing processes is necessary, demanding a robust copper CMP model to be implemented to design for manufacturing (DfM) tools. Previous models heavily relied on Preston's equation ( ), which needs to be calibrated for every new set of processing parameters, slowing down the process development. Previous models focused on limited interactions of the consumables and the workpiece during copper CMP, being insufficient at capturing the synergies between chemical and mechanical aspects of copper CMP.

Therefore, a quantitative and physicochemical model of copper CMP that predicts material removal rate (MRR) was proposed while focusing on the interplay of consumables and copper and the synergies between chemical and mechanical aspects of the process. While considering the synergies, two mechanisms of the material removal during copper CMP were suggested: chemically dominant and mechanically dominant mechanisms. The total MRR during copper CMP was determined by summing those two contributions.

The chemically dominant mechanism attributed the material removal during copper CMP to the removal of the protective material formed on the surface of copper and to the chemical dissolution of copper from the surface both at regions occupied and not occupied by the protective material with different rates. The kinetics of the formation of the protective material at the millisecond scale were studied through electrochemical experiments and theoretical analysis where a governing equation for the adsorption of benzotriazole (BTA) was constructed and solved. It was found that the grown protective material (CuBTA) during copper CMP was only a fraction of a monolayer partly occupying the surface of a wafer. This was because the time allowed for the adsorption of BTA on the surface of copper was limited by the time between consecutive asperity and copper interactions, which was only of the order of one millisecond. The formation and the removal of the protective material were assumed to be balanced during CMP, yielding a constant chemically dominant MRR. The removal of the protective material by abrasion with abrasive particles was investigated by in situ electrochemical measurement during polishing. The removal efficiency of a pad asperity where abrasive particles are embedded was evaluated from the measurements and was compared with the theoretical analysis. It showed a good agreement and suggested that the copper during CMP is mostly deformed elastically by the abrasive particles.

The influence of the concentration of copper ions on the kinetics of the formation of the protective material was also investigated using potential-step chronoamperometry using two types of copper microelectrode, namely a three dimensional and a planar electrode. The amount of copper ion may easily build up to a level that exceeds the solubility product of Cu(II)BTA2. Under these conditions, Cu(II)BTA2 can nucleate, consuming the protective material formed on the surface of copper. This phenomenon is highly undesirable as it increases the dissolution rates at the regions where the protective material is removed, worsening the topography after copper CMP.

The mechanically dominant MRR was determined from the volume of a wafer that is plastically deformed by indentation of abrasives that are squeezed between pad asperities and the wafer. The shear stress induced in copper by the force applied on an abrasive is lower than the ideal shear strength of copper, which is the relevant property for plasticity at this length scale. However, the crystallographic defects in the copper crystal may reduce the hardness of the material, allowing the material to be plastically deformed. Especially the roughness of the surface induced by chemical additives in the slurry greatly reduces the resistance to plastic deformation of copper. Because of the localized spatial distribution of those crystallographic defects the plastic deformation occurs only locally. Also, only a part of the plastically deformed material will be detached from the surface, contributing to the MRR. While applying this mechanism, the discrepancy of the MRR behavior with varying size and concentration of abrasives between the prediction and the experimental observations was resolved by proposing a new mechanism that determines the number of abrasives participating in the abrasion of the material. The transport mechanisms of abrasive particles toward a wafer and the electrostatic interactions between abrasives were considered to affect the number of abrasive particles deposited on the surface of a wafer. If the deposition of abrasives on the surface of a wafer is limited by the diffusion of abrasives, the MRR decreases with the size of the abrasives. In contrast, the MRR increases with the size of abrasives if the deposition of the abrasives is limited by the jamming limit of the deposited abrasives at the surface of the wafer. Also, micrometer sized abrasives increases the MRR when the size is increased because the deposition of abrasives is limited by the interception mechanism of the abrasives.

The proposed model successfully captured the synergies between chemical and mechanical aspects and quantitatively predicted the MRR during copper CMP. In the future, the model will be applied to predict the pattern dependent variability of topography of a wafer after CMP. The proposed model quantitatively predicts the local MRR of copper. Along with a robust model for dielectric and barrier materials, the model can predict the topography after CMP, contributing to the optimization of the CMP process.

The decomposition of hydrogen peroxide (H₂O₂) on iron minerals can generate hydroxyl radical (^*OH), a strong oxidant capable of transforming a wide range of contaminants. This reaction is critical to ex situ advanced oxidation processes employed in waste treatment systems, as well as in situ chemical oxidation processes used for soil and groundwater remediation. Unfortunately, the process in the ex situ treatment systems is relatively inefficient at circumneutral pH values. In this research, the development of iron-containing catalysts with improved efficiency was investigated. In addition, little is known about the factors that control the performance of in situ treatment systems. Another aim of this dissertation was to elucidate those factors to provide a basis for improving the efficiency of the remediation method.

Two types of silica- and alumina-containing iron (hydr)oxide catalysts were synthesized by sol-gel processing techniques (Chapter 2). Relative to iron oxides, such as hematite and goethite, these catalysts were 10 to 80 times more effective in catalyzing the production of ^*OH from H₂O₂ under circumneutral conditions. The higher efficiency makes these catalysts promising candidates for ex situ advanced oxidation processes. Moreover, because alumina and silica alter the reactivity of the iron oxides with H₂O₂, understanding the activity of iron associated with natural aluminosilicates and silica-containing minerals in the subsurface is crucial to explaining the variability of ^*OH production observed in in situ treatment systems.

In addition to the sol-gel technique used in Chapter 2, silica-containing iron (hydr)oxide catalysts were synthesized by immobilizing iron oxide onto mesoporous silica supports, such as SBA-15 (Chapter 5). The iron-containing SBA-15 was 10 times more effective than iron oxides in catalyzing the production of ^*OH from H₂O₂. Moreover, this catalyst could be employed for selective oxidation of small organic contaminants based on size exclusion. However, a major drawback of the mesoporous silica-based catalysts is their instability under circumneutral conditions (Chapter 6). The dissolution of mesoporous silica materials raises questions about their use for water treatment, because silica dissolution might compromise the behavior of the material.

To gain insight into factors that control H₂O₂ persistence and ^*OH yield in in situ processes, the decomposition of H₂O₂ and transformation of contaminants were investigated in the presence of iron-containing minerals and aquifer materials (Chapter 3). Consistent with the observation described in Chapter 2, iron-containing aluminosilicates were more effective than iron oxides in converting H₂O₂ into ^*OH. In both iron-containing mineral and aquifer material systems, the yield of *OH was inversely correlated with the rate of H₂O₂ decomposition. In the aquifer material systems, the yield also inversely correlated with the Mn content, consistent with the fact that the decomposition of H₂O₂ on manganese oxides does not produce ^*OH. The inverse correlation between Mn content and H₂O₂ loss rate and ^*OH yield suggests that the amount of Mn in aquifer materials could serve as a proxy for predicting H₂O₂ decomposition rates and contaminant oxidation efficiency.

In addition to the surface and structure properties of iron solids, the presence of solutes, such as dissolved silica, also affected the decomposition of H₂O₂ (Chapter 4). The adsorption of dissolved silica onto mineral surfaces altered the catalytic sites, thereby decreasing the reactivity of iron- and manganese-containing minerals with H₂O₂. Therefore, the presence of dissolved SiO₂ could lead to greater persistence of H₂O₂ in groundwater, which should be considered in the design of in situ H₂O₂-based treatment systems. In addition to in situ treatment, dissolved silica also can affect the reactivity of iron-containing catalysts used in ex situ processes. Therefore, its presence in contaminated industrial wastewater should be considered when ex situ treatment systems are designed.

Nanoparticles have attracted a lot of attention in the past few decades due to their unique, size-dependent properties. In order to use these nanoparticles in devices or sensors effectively, it is important to maintain uniform properties throughout the system; therefore nanoparticles need to have uniform sizes - or monodisperse. In order to achieve monodispersity, an extreme control over the reaction conditions is required during their synthesis. These reaction conditions such as temperature, concentration of reagents, residence times, etc. affect the structure of nanoparticles dramatically; therefore when the conditions vary locally in the reaction vessel, different sized nanoparticles form, causing polydispersity.

In widely-used batch wise synthesis techniques, large sized reaction vessels are used to mix and heat reagents. In these types of systems, it is very hard to avoid thermal gradients and to achieve rapid mixing times as well as to control residence times. Also it is not possible to make rapid changes in the reaction parameters during the synthesis. The other drawback of conventional methods is that it is not possible to separate the nucleation of nanoparticles from their growth; this leads to combined nucleation and growth and subsequently results in polydisperse size distributions.

Microfluidics is an alternative method by which the limitations of conventional techniques can be addressed. Due to the small size, it is possible to control temperature and concentration of reagents precisely as well as to make rapid changes in mixing ratios of reagents or temperature of the reaction zones. There have been several microfluidic reactors - (microreactors) in literature that were designed to improve the size distribution of nanoparticles.

In this work, two novel microfluidic systems were developed for achieving controlled synthesis of nanoparticles. The first microreactor was made out of a chemically robust polymer, polyurethane, and it was used for low temperature nanoparticle synthesis. This microreactor was fabricated by using a CO2-laser printer, which is an inexpensive method for fabricating microfluidic devices and it is a relatively fast way compared to other fabrication techniques. Iron oxide nanoparticle synthesis was demonstrated using this reactor and size distributions with a standard deviation of 10% was obtained.

The second microreactor presented in this work was designed to produce monodisperse nanoparticles by utilizing thermally isolated heated and cooled regions for separating nucleation and growth processes. This microreactor was made out of silicon and it was used to demonstrate the synthesis of TiO2 nanoparticles. Size distributions with less than 10% standard deviation were achieved. This microreactor also provides a platform for studying the effects of temperature and residence times which is very important to understand the reaction kinetics of nanoparticle synthesis.

In this work, two microfluidic techniques for retrieving nanoparticles from the microreactors were also discussed. The first method was based on trapping the aqueous droplet phase inside the microchannel and the second method was utilizing a micropost array to direct droplets from the oil solution to the pure water.

As a final step, a printing technique was used to print nanoparticles synthesized inside the microreactors for future applications. This ability is important for achieving smart surfaces that can utilize the properties of nanoparticles for sensing applications in the future.

Copper CMP is a corrosion-wear process, in which mechanical and chemical-electrochemical phenomena interact synergistically. Existing models generally treat copper CMP as a corrosion enhanced wear process. However, the underlying mechanisms suggest that copper CMP would be better modeled as a wear enhanced corrosion process, where intermittent asperity/abrasive action enhances the local oxidation rate, and is followed by time-dependent passivation of copper. In this work an integrated tribo-chemical model of material removal at the asperity/ abrasive scale was developed. Abrasive and pad properties, process parameters, and slurry chemistry are all considered. Three important components of this model are the passivation kinetics of copper in CMP slurry chemicals; the mechanical response of protective films on copper; and the interaction frequency of copper with abrasives/pad asperities. The material removal rate during copper CMP was simulated using the tribo-chemical model, using input parameters obtained experimentally in accompanying research or from the literature.

Of all the defining characteristics of a material, there are probably none more important than structure. Through a simple change in structure, materials can exhibit vastly different properties due to its influence at length scales from atomic crystal structure to microstructure. In fact, structure is so important in the study of materials science that it is given one of the four coveted spots on the materials science tetrahedron.

From advances in colloidal nanocrystals, materials with well-defined intrinsic characteristics such as composition and phase can now be synthesized reproducibly. However, these materials are often orders of magnitude smaller than actual device length scales. This disparity in length scales, however, is a fertile opportunity space where structural control can be used both to augment the intrinsic properties of nanocrystals and to bridge the length scales between nanocrystal building blocks and that of an actual device. More specifically, it may actually allow independent imposition of a structural motif separate from other parameters like composition and phase: an almost impossible feat from the standpoint of bulk materials processing.

Recent developments in nanocrystal surface chemistry have generated a sub-class of nanocrystals, called ligand-stripped nanocrystals, which are colloidally stable even in the absence of stabilizing ligands. This advancement opens both opportunities to access properties that require access to the nanocrystal surface, and new avenues for assembly that capitalizes on interactions with the nanocrystal surface. In assembly, it opens the question of how one might direct the arrangement of these nanocrystals through the use of a structure-directing agent such as a block copolymer. Initial work in 2012 demonstrated the first assembly of these nanocrystals using an artisanal polystyrene-b-polydimethylacrylamide (PS-PDMA) block copolymer of which the latter block is hypothesized to interact strongly with the nanocrystal surface. Chapter 2 expounds this discovery by investigating the assembly of ligand stripped nanocrystals using PS-PDMA micelles with emphasis on the influence of nanocrystal size and volume fraction on the overall ordering of the assembled structures. Grazing incidence small angle x-ray scattering is employed to quantitatively characterize ordering both at the block copolymer and nanocrystal length scale. The nanocrystal size dependence of ordering is shown such that ordering decreased dramatically for nanocrystal sizes bigger than the PDMA domain size. Similarly, nanocrystal ordering also decreased for nanocrystal volume fractions exceeding the volume fraction of PDMA in the system. Finally, the extreme limits of assembly using PS-PDMA micelles is demonstrated whereby single nanocrystal networks or networks with two length scales of ordering can be generated either at low volume fractions of large nanocrystals or at high volume fractions of small nanocrystals.

Chapter 3 extends the assembly of ligand stripped nanocrystals into block copolymer microphase-separated morphologies using PS-PDMA. Here, the phase separation behavior of PS-PDMA with and without nanocrystals is shown alongside methods used to achieve the final morphologies. Both volume fraction and size studies mirroring the studies in Chapter 2 is conducted to arrive at the maximal nanocrystal size and volume fractions after which assembly is kinetically arrested. Morphological control to access the hexagonal and lamellae phases is demonstrated with either a change in relative block copolymer block lengths or through a co-swelling approach using mixed solvents. Then, the compositional diversity of this assembly paradigm is demonstrated with the successful assembly of different metal oxide, metal chalcogenide, and gold nanocrystals. The nature of this diversity is expanded upon with a Fourier Transform Infrared Spectroscopy (FTIR) study that ultimately suggests that the nature of the interaction between PDMA and the nanocrystal surface is based upon hydrogen bonding. Finally, Chapter 4 discusses future work based on the co-assembly of nanocrystal mixtures, the control of PS-PDMA morphology in solution, and the use of block copolymers beyond PS-PDMA for the directed assembly of ligand stripped nanocrystals.

Moving beyond the context of assembly towards the arena of ion transport properties, ligand free nanocrystal thin films are applied as model systems to investigate the phenomena of intermediate temperature proton conduction between 250 °C and 100 °C: an anomalous phenomenon where porous metal oxide structures exhibit significant protonic conductivity that are traditionally absent in their bulk counterpart. Chapter 5 explores this phenomenon using porous nanocrystal thin films of cerium oxide or titanium oxide. The study establishes the viability of nanocrystals as model systems by demonstrating the influence of nanocrystal size on protonic conductivity for cerium oxide holding other variables such as porosity comparable. Then, capillary condensation is ruled out as the cause of the phenomenon, and an alternate hypothesis built upon metal oxide surface defect chemistry is proposed. This influence of defect chemistry is preliminary studied with emphasis on the oxygen partial pressure dependence of intermediate temperature protonic conductivity. The observed non-dependence of conductivity on oxygen partial pressure for cerium oxide is consistent with prior observations of the poor dependence of cerium oxide surface defect chemistry on oxygen partial pressure. This is in contrast with the clear oxygen partial pressure dependence observed for titanium dioxide. Holding porosity constant, the higher proton conductivity observed for 4 nm cerium oxide compared to that of 9 nm cerium oxide is rationalized by an enrichment of Ce3+ on the surface and corresponding oxygen vacancies for ultra small cerium oxide nanocrystals. Similarly, the higher proton conductivity observed for cerium oxide compared to titanium dioxide is rationalized by the lower enthalpy of formation of oxygen vacancies for cerium oxide. Then, the link between surface defect chemistry and protonic conductivity is proposed: dissociate water adsorption in surface oxygen vacancies may be responsible for the generation of mobile protons on the surface of the metal oxide.

Chapter 6 continues the investigation of intermediate temperature proton conductivity but addresses the stability of the phenomena. Here, time dependent conductivities at all temperatures is presented where a general decrease in conductivity under humidified conditions at temperatures lower than 200 °C is observed. Extended time dependent conductivity measurements at 100 °C show a gradual decrease in conductivity over 2 orders of magnitude over 48 hours for cerium oxide. Detailed FTIR studies reveal the nature of the decrease as passivation of the metal oxide surface due to the formation of cerium hydroxycarbonate consistent with the characteristic instability of rare-earth oxides under ambient or humidified conditions. Thermodynamic analysis further reveal a transition point of 575 °C after which the formation of cerium hydroxycarbonate becomes thermodynamically unfavorable. A reaction for the formation of cerium hydroxycarbonate from cerium oxide, CO2 and H2O is proposed and tested with a time, temperature and oxygen partial pressure dependent conductivity measurement. The results show that the rate of decrease in conductivity is significantly slower for pure oxygen environments. Gallium doping of cerium oxide to reduce the surface affinity toward hydroxycarbonate formation was tested but was found to have little efficacy in enhancing the stability. Thus, an alternate materials selection criteria based upon mineralogy that ultimately suggest titanium dioxide as a stable material under humidified conditions is tested. While the absolute conductivity of porous titanium dioxide nanocrystal systems start lower than that of cerium oxide nanocrystal systems, titanium dioxide appears stable over the tested 48-hour period thus showing the merit of using titanium dioxide over cerium oxide in actual applications due to gains in system stability. The study for titanium dioxide is completed with another detailed FTIR study that shows the formation of bicarbonate species on the surface of titanium dioxide under humidified conditions though the species do not hinder protonic conductivity. The stability of the phenomena for titanium dioxide under pure oxygen environments is also demonstrated. Finally, Chapter 7 discusses future work utilizing in situ FTIR studies to identify the spectroscopic signatures of acidic protons on the oxide surface that result from the aforementioned dissociative water adsorption on surface oxygen vacancies, and tuning of conductivity through manipulation of surface defect concentrations either by acceptor doping or tuning of surface facet termination.

Electrochemical reduction of CO2 (CO2R) to chemical fuels and feedstock via the use of renewable electrical energy is a potential way to mitigate rising atmospheric CO2 emissions. The ultimate goal of this research field is the ability to develop catalysts capable of converting CO2 selectively and efficiently into specific products. Of all the possible products from CO2R, products with 2 or more carbons (C2+ products) such as ethylene and oxygenates (e.g. ethanol) are highly desirable as they are already used as fuels in the existing energy infrastructure or as chemical feedstock in industry. Therefore in this thesis, I explore various catalytic materials to facilitate CO2R to generate these products.

Initially, I was excited by reports in the literature on the use of heteroatom doped carbon materials as catalytic materials. For example, it was claimed that these materials could convert CO2 selectively to CO, formate or even to methane. These materials typically consist of a carbon structure doped with ~1-5% of heteroatoms such as nitrogen, sulfur, phosphorous or even boron. Synthesis of these materials is simple; they usually involve high temperature annealing of a carbon material (e.g. graphene) with a source containing the heteroatom of choice. However, I discovered that these materials can carry various levels of metallic impurities depending on their preparation method. Therefore, the true catalytic activity of these carbon materials can be obscured by these catalytically active impurities. In Chapter 2, I therefore investigate the role of metallic impurities present in different carbon materials during CO2R.

Next, I investigated nanostructured catalysts for CO2R. These catalysts are prepared by electrochemical oxidation and reduction cycling of Cu foil assisted by halide anions in the solution. These halide anions serve to promote the oxidation process of Cu to create Cu2O and subsequent reduction back to metallic Cu0 results in a nanostructured surface. These catalysts have been shown to be more selective towards C2+ products (especially ethylene) compared to flat, polycrystalline Cu. In Chapter 3, I thus examine the effect of different halide anions on the nanostructuring process and its resultant catalytic activity for CO2R.

In the literature, oxide-derived Cu catalysts have been shown to be promising catalysts to facilitate the reduction of CO2 to C2+ products. Typically, these catalysts are synthesized by oxidation of Cu to Cu2O and/or CuO and subsequent reduction back to Cu0. Also, the cation in the electrolyte used for CO2 reduction used in the has been shown to be very important in determining the C2+ selectivity of Cu catalysts. In particular, a larger cation such as Cs+ promotes a higher C2+ selectivity compared to K+. An interesting question is whether oxide-derived Cu catalysts could be combined with Cs+ to yield very high C2+ selectivity. In Chapter 4, I prepare oxide-derived catalysts via 4 different means according to previous reports and I study their catalytic activity for CO2R in aqueous electrolyte containing either K+ or Cs+. I show that a very high faradaic efficiency for formation of C2+ products (~70%) can be achieved by optimizing the roughness factor of these catalysts with Cs+ containing electrolyte.

It has been proposed by various researchers that oxides in oxide-derived Cu catalysts are stable despite the highly reducing conditions applied during CO2 reduction. Therefore, a large amount of residual oxides remain in the catalyst and these have been proposed to be the reason for high C2+ selectivity for oxide-derived Cu catalysts. In chapter 5, I investigated whether oxides are truly stable during CO2 reduction. I fabricated 18O labeled catalysts and used secondary ion mass spectrometry to determine the 18O content before and after CO2 reduction. I found that <1% of the original 18O content remains after CO2 reduction, showing that residual oxides are unstable, as thermodynamically predicted.

The previous chapters all describe catalysts which have ill-defined structures. I therefore sought to obtain greater control over the dimensions and composition of my catalysts and I turned to photolithography to fabricate model catalysts. In Chapter 6, I describe a device which I named the “AuCu device” to investigate a process termed as “CO crossover” in CO2R. CO spillover occurs when a CO producing catalyst produces CO from CO2 and this can then crossover onto Cu sites. This result in an increased production of C2+ oxygenates at the expense of ethylene. The AuCu device which I fabricated consists of interdigitated lines of Au and Cu on an insulating SiO2 substrate. In this device, Au serves to produce CO and the Cu serves to reduce this CO as well as externally supplied CO2 to further reduced products. The lines are designed to be electronically isolated and as such can be independently actuated. Such a system is therefore ideal to study the CO crossover effect.

Additionally, in chapter 6, I describe another catalyst system, which was also fabricated via photolithography. This system, consisting of Cu dots or lines patterned onto a Ag substrate is designed to take full advantage of the CO crossover effect to achieve a high selectivity to oxygenates. Exposed Ag sites serve to produce CO and thus by varying the areal coverage of Cu dots/lines, systematic control of CO spillover can be exercised. This allows me to tune the ratio of oxygenates to ethylene from 0.59 to 2.39. In the best system, an oxygenate selectivity of >40% can be achieved.

In conclusion, I investigated a variety of catalyst systems for CO2R for my graduate studies. My thoughts and future outlook are summarized in Chapter 7. I outline the main challenges in this field and my thoughts on how selectivity and catalyst activity might be improved. I also emphasize the importance of efforts to understand the mechanism of CO2 reduction.