Browsing by Author "Prieto, Amy L., advisor"
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Item Embargo Cu-P-Se nanoparticles: understanding the reaction pathways for the colloidal synthesis of energy conversion and storage materials(Colorado State University. Libraries, 2024) Neisius, Nathan A., author; Prieto, Amy L., advisor; Finke, Richard, committee member; Herrera-Alonso, Margarita, committee member; Paton, Robert, committee memberNanotechnology has garnered considerable interest over the last 40 years, owing to the unique, desirable properties that can be targeted through established synthetic methods for tuning the size of materials at the nanoscale. As no one single material has properties suitable for a wide range of applications, property driven synthesis has been at the forefront of the nanoparticle (NP) field. Particularly, colloidal NP syntheses provide a large synthetic landscape to explore as a result of the vast synthetic tunability to target specific parameters such as, particle size, morphology, composition, and defects. Although significant efforts have been made toward deciphering the transformation processes of unary and binary NPs, traditionally the colloidal NP field has been driven by a top-down approach, driven by trial-and-error methods, limiting the design of desired, complex materials. Thus, to further progress nanoparticle technology, understanding the underlying transformation processes occurring throughout the formation of colloidal nanoparticles is essential to develop novel materials as well as control the structure/property relationships. The copious amounts of both organic and inorganic interactions, as well as the complexity of capturing the transformation from molecular to the solid-state regime, complicates the reaction landscape for more complex, ternary phases. The purpose of the work included and explained in this dissertation is to develop stoichiometric syntheses for both Cu-P-Se ternary phases, Cu3PSe4 and Cu7PSe6, and to then understand the reaction pathways for an improved retrosynthetic analysis and enable translation of the synthetic knowledge to other systems. Cu-P-Se ternary chalcogenide NPs are of particular interest, owing to the synthetic complexity of navigating a rich phase space with thermodynamically stable binary phases close in energy to the desired ternary phases, as well as applicable structural properties for thermoelectrics, photovoltaics, and battery applications. Therefore, to contribute to the progression of the nanoparticle field the general objectives of this study are, (1) analyzing the transformation of commonly employed precursors and solvents (2) capture the influence of precursor reactivity on ternary phase formation, and (3) perform careful characterization of speciation and final nanoparticles, all of which to establish a full scope of Cu-P-Se nanoparticle formation and the impact of individual synthetic parameters on chalcogenide-based precursors. In Chapter 1, the relevant literature for the following chapters is reported and reviewed to provide the essential background information. This chapter is divided into 6 subsections; (1) Need for renewable energy and how nanoparticles provide solutions, (2) State of nanoparticle synthesis field, current limitations, and progress towards developing a better understanding of nanoparticle reaction pathways, (3) Motivation for exploring the Cu-P-Se phase space, (4) Se reactivity in NP syntheses, (5) Cu3P – the required precursor for Cu-P-Se formation, (6) Dissertation overview, publications, and presentations. The first colloidal NP synthesis report on Cu3PSe4 was developed by a previous group member, Dr. Jennifer Lee, which demonstrated that the phase purity of Cu3PSe4 requires the use of Cu3P NPs and selenium powder (Se) in ODE as precursors. Alternate reaction precursors, and therefore pathways, were disproven throughout this study, leading to the working hypothesis that the interactions of Se and ODE were a necessary step to form active species that then react with Cu3P NPs. Although frequently employed in NP research, and heavily characterized, the implications of the Se/ODE solution on Cu3PSe4 phase formation are still misunderstood. Therefore, the studies presented in Chapter 2 are aimed at probing the Cu3PSe4 reaction landscape and the findings are separated into (1) ex situ reactions that are characterized with molecular and solid-state characterization techniques to determine the implications of the solution dynamics on Cu-P-Se NP phase formation, and (2) how different Se/ODE speciation can be isolated and subsequently favor the alternate, metastable Cu-P-Se phase, Cu7PSe6. A persistent limitation to the previous study is that ODE contaminates the final products, making the findings and analysis of Se/ODE rather difficult to interpret, thus requiring a simplified, cleaner reaction to produce phase pure Cu3PSe4. For that reason, Chapter 3 shifts the direction of the Cu3PSe4 synthesis towards a more stoichiometric, atom-economical reaction by eliminating ODE as the solvent. Rather, a long-chain, aliphatic solvent, octadecane (ODA) is employed that proves to be an operationally inert solvent under the standard synthetic conditions and produces cleaner, phase pure Cu3PSe4 NPs as determined by powder X-ray diffraction (PXRD) and transmission electron microscopy (TEM). If ODA was reacting with Se0 powder, the most favorable pathway, commonly cited in literature, is the formation of H2Se and oxidized ODA (alkene). Hence, molecular characterization techniques, nuclear magnetic resonance (NMR, 1H and 13C) and fast-Fourier infrared spectroscopy (FT-IR), were utilized to demonstrate the absence of oxidized ODA species, which is consistent with Se0 preferentially reacting with Cu3P, promoting a more direct reaction pathway. Eliminating the presence of alternate, competing reaction pathways in the ODE synthesis and establishing a near-stoichiometric reaction, allows us to capture the underlying transformation process of Cu3P to Cu3PSe4. From these systematic improvements, we hypothesize that Se0 powder is dispersed in ODA, which promotes a formal eight-electron transfer between Cu3P and 4 Se0. Extracting the synthetic information from the previous chapters to target the metastable Cu-P-Se phase, Cu7PSe6, provides the framework for Chapter 4. Previous methods to isolate Cu7PSe6 are based on traditional, solid-state techniques, where the elemental precursors are ground and subsequently heated to high temperatures (>1000K). Although a colloidal or solution-based synthesis has yet to produce phase-pure Cu7PSe6 particles, attempts explained in Chapter 2 provide a basis on the phase space complexity, where the products consisted of Cu7PSe6 but with thermodynamic byproducts, Cu-Se phases and Cu3PSe4 present. Therefore, an alternate Se precursor, diphenyl diselenide (Ph2Se2), is employed to form the metastable phase, which effectively avoids Cu3PSe4 formation. Importantly, an alternate route to form Cu3PSe4 is with analogous dialkyl diselenide precursor, dibenzyl diselenide, where a key finding is the presence of amorphous phosphorus (P) on Cu1-xSe binaries at low temperatures, which then efficiently reincorporates once the desired 300 ˚C reaction temperature is reached. Thus, in Chapter 4 we investigate why Cu7PSe6 is favored with Ph2Se2 as a precursor, which is predicated on the formation of byproduct species that effectively "trap" P. A proof of concept is explored to further demonstrate the dynamics of P in solution, where the Cu-P-Se phase space can be controllably toggled across by injecting P(5+) species. A drawback for the Cu-P-Se syntheses is the lack of compositional understanding of the pre-synthesized Cu3P NPs, thus further complicating the reaction stoichiometries. Chapter 5 first investigates the previously published synthesis by Liu et al., by thoroughly characterizing the final Cu3P nanoparticles under identical reaction conditions and exploring alternate reaction stoichiometries to reduce the presence of residue precursors. From such, it is determined that the particles substantially deviate from the stoichiometric Cu3P composition, with a Cu:P ratio around 1.5:1.0. Particular focus is also placed on monitoring the degradation of a green phosphorous source, triphenyl phosphite, P(OPh)3. Although triphenyl phosphite (TPOP) has been previously used for transition metal phosphide systems, a lack of systematic investigations leads to questions on the reduction of TPOP en route to forming Cu3P, a formal P(3+) to P(3-) event. Additionally, limited characterization of the final organic byproducts in the original synthesis, begs to question what, if any, byproducts could be contaminating the Cu3P NPs. Therefore, we develop and probe stoichiometric syntheses that isolate phase pure Cu3P NPs to avoid the original 30-fold excess of P. The transformation of hexadecylamine (reductant and ligand) and TPOP were characterized with 1H and 31P NMR to evaluate the role of each en route to forming Cu3P. As this is project is still developing, the necessary future directions are given to systematically approach this problem, with an emphasis on first-step experiments and essential characterization methods to completely grasp the decomposition mechanism of TPOP. Ultimately, this has implications when systematically applying TPOP to alternate transitional metal phosphide NP syntheses, as well as developing more precise Cu-P-Se syntheses. Finally, the work presented herein is summarized in Chapter 6 along with an outlook on the project as a whole. Specifically, future directions and preliminary insight into the underlying reaction pathways and mechanism of Cu3PSe4 formation are explored. Additionally, we explore preliminary data on an analogous material Ag-P-Se, which was plagued for years by the lack of a reproducible Ag-P precursor synthesis that limited our ability to extract the synthetic intuition from the Cu-P-Se system. However, recent literature findings on a potential Ag3P precursor provides promise on synthesizing Ag-P-Se phases in the future, which is critically analyzed to ensure that any bottlenecks in future syntheses are limited. Ultimately, the work provided in the following chapters is aimed at making strides to developing a more in depth understanding of precursor interactions between transition metals and main group elements, as well as properly monitoring such reactions to extract synthetic information to analogous systems. With the knowledge gained on the presented studies, we aspire to contribute to the NP field in order to continually improve NP synthesis and therefore nanomaterials. Finally, this work is supported by NSF Macromolecular, Supramolecular, and Nanochemistry (MSN #2109141).Item Open Access Developing and investigating copper and iron chalcogenide nanoparticle syntheses to elucidate the underlying processes of formation(Colorado State University. Libraries, 2021) Moloney, Lily June, author; Prieto, Amy L., advisor; Sambur, Justin, committee member; Krummel, Amber, committee member; Buchanan, Kristen, committee memberNanoparticle technology is rapidly growing field due to the unique, tunable properties of nanoparticles (NPs) as compared to their bulk counterparts, enabling a wide range of new applications. The key step, however, to applying NP systems to new areas is developing high quality syntheses. Specifically, solution-based methods for synthesizing NPs offer many synthetic handles for tuning structure/property relationships by controlling composition, size, morphology and capping agents. To effectively design syntheses to control the resulting properties, in depth investigation of the underlying fundamental processes are required. Elucidation of these processes would allow trends to be illuminated and a toolkit of synthesis methods could be built. However, a myriad of interactions (organic, inorganic, solid-state) occur during these reactions, and often these interactions are intertwined with each other. Therefore, careful examination of nanoparticle synthesis for various systems are necessary to advance the NP field. In Chapter 1, we review literature reports that exemplify the careful examination of underlying mechanisms and pathways required for developing synthesis methods that allow for control over composition, size, morphology. This chapter is split into two major sections; 1) balancing precursor reactivities and elucidating mechanisms and 2) understanding reaction pathways. The first section is split into anion and cation speciation/reactivity. The anion section focuses on the development of chalcogenide reactivity trends and how these trends have led to advanced nanoparticle control. The cation section considers the use of metal-amide complexes to increase and balance reactivities of cations to produce small, phase pure NPs. In depth mechanism studies of these metal-amide reactions in model unary and binary system led to the utilization of this reagent in more complex ternary systems. The second section focuses on investigation of reaction pathways, discussing how exploration of the reaction phase space as well as determination of intermediates is important for achieving a full picture. We end with a brief discussion on the importance of thorough characterization for describing these reaction mechanisms and pathways accurately. The importance of investigating the reaction pathway was inspiration for the research described in Chapter 2. Few solution-based techniques to synthesize Cu3Si, a material with applications in electronics, batteries, and photovoltaics, exist. This could stem from the limited number of Si precursors viable in solution-based techniques. This led us to explore the reaction between Mg2Si and CuCl2 in oleylamine, as a solution-based metathesis route to form Cu3Si particles. The reaction pathway and the role of the solvent were characterized and elucidated. It was found that the reaction proceeds through a two-step pathway, where a Si matrix, Cu particles, and MgCl2 initially form. Then, the Cu particles diffuse into the Si matrix to form Cu3Si particles encased in a Si matrix (Cu3Si@Si matrix). Additionally, various solvents are tested to understand the importance of the solvent for the reaction to proceed successfully. The coordinating ability of the solvent was important, where an overly non-coordinating or coordinating solvent limited the production of Cu3Si@Si matrix particles. Oleylamine was found to be a “goldy-locks” solvent as the coordination supported both steps of the reaction. In Chapter 3, the mechanistic metal-silylamide studies described in Chapter 1 offered inspiration. Specifically, Rebecca C. Miller in our group was recently able to synthesize Fe2GeS4 by utilizing lithium bis(trimethylsilyl)amide (LiHMDS). The increased understanding of the Fe-Ge-S phase space and the role of the LiHMDS gained from this previous study led to the research presented in Chapter 3. In this chapter, we report the first nanoparticle synthesis of Fe2GeSe4 and Fe2GeS4-xSex (x = 0.8 and 1) via a LiHMDS-assisted hot-injection method. This system allowed the role of LiHMDS in balancing not only the cationic but also anionic species to be investigated. This was done by exploring the synthesis parameters, the pre-injection chalcogen speciation, and the reaction pathways. Finally, in Chapter 4, synthesis methods attempted toward Cu2SiSe3 formation are described and a future direction for this project is proposed. Copper-based chalcogenides have gained much attention due to their exemplary intrinsic and structural properties. Cu2SiSe3 has been theorized to be a potential photovoltaic material, yet a NP synthesis of this material has not been realized. Exploration of hot injection, metathesis, and solvothermal solution phase methods are reported. However, all efforts resulted in binary Cu/Se phases over the formation of the desired ternary. A future direction for this project could be instead focusing on investigating reactivity trends of the group IV elements, Si, Ge, and Sn, using an amide-assisted synthesis of the Cu2IVSe3 materials.Item Open Access Development of a multidisciplinary toolkit for the colloidal nanoparticle synthesis of copper selenophosphate, Cu3PSe4, a promising material for photovoltaics(Colorado State University. Libraries, 2021) Lee, Jennifer M., author; Prieto, Amy L., advisor; Ackerson, Chris J., committee member; Henry, Chuck S., committee member; Buchanan, Kristen S., committee memberTo view the abstract, please see the full text of the document.Item Open Access Electrodeposition and speciation study of different transition metal antimonides for application into lithium ion batteries(Colorado State University. Libraries, 2010) Kershman, Jacob Ray, author; Prieto, Amy L., advisor; Elliott, C. Michael, committee member; Kipper, Matthew J., committee memberSeveral new deposition setups were designed and tested to increase the uniformity of depositions of Cu2Sb. It was shown that the jacketed beaker setup produces the most uniform films compared to other setups used. This setup was used to obtain the average thickness and mass measurements of a triplicate set of films deposited at deposition times of 1, 2.5, 5, 7, and 10 minutes. The thickness (determined by AFM) and weight were both linear and corresponded to a growth rate of 300 nm per minute or 0.2 mg of Cu2Sb per minute. Preliminary battery testing revealed that the thinner films cycled much better than thicker films. Films thicker than ~1 µm did not cycle well at all, and cleaved completely off the surface of the electrode during cycling. Cu2Sb was successfully electrodeposited into commercial alumina filters. The Cu2Sb wires were ordered in a different direction compared to the electrodeposition on planar substrates ([101] versus [001] direction). A two step anodization process was shown to produce self-ordered AAO templates with pore sizes between 30 and 40 nm. It was shown that the mechanical and electrochemical polishing steps are not necessary to obtain the self-ordered templates. Promising results have been shown with multiple methods to break through the barrier layer of these alumina templates. Even when the barrier layer is removed a native oxide is formed within a few seconds on the surface of the aluminum which blocks the electrodeposition of copper. The backside of the template indicated that the breakthrough was only in localized spots. Previously, crystalline Cu2Sb was electrodeposited at single potential through the complexation of the metals in aqueous solution using citric acid at pH 6. This direct electrodeposition is unusual for intermetallic materials and the reason for the Cu2Sb case is not well understood. In order to determine why this material deposits under these solution conditions, a deeper understanding of the speciation in solution must be obtained. To study what metal-ligand complexes are present in the Cu-Sb-Citrate deposition, solution electrospray ionization mass spectrometry (ESI-MS) was employed. ESI-MS results were shown to be a qualitative technique to study the solution chemistry of the Cu2Sb system. These results have been compared to speciation calculations, UV-Vis, titrations, and literature results. The heterometallic species [CuSb(HCit)(Cit)], previously only reported in solids that had been crystallized out of solution, was discovered in solution through ESI-MS. In addition, ESI-MS data pointed to [Sb(HCit)2]- as the most abundant antimony citrate species over previously reported [SbH-1Cit]-. The additional species from ESI-MS gave rise to the development of two new balanced reactions for the deposition of Cu2Sb, in hope of the realization of understanding why Cu2Sb deposits. By understanding the solution chemistry, other transition metal antimonides were electrodeposited from aqueous citrate solutions. It is shown that through the co-deposition reaction, which is dependent on the solution chemistry and the fast interstitial diffusion of metals through antimony diffusion in the solid state, many different intermetallic antimonides can be deposited including: crystalline NiSb, the co-deposition of FeSb, and several copper-rich copper antimonide phases including Cu11Sb3, Cu4Sb, Cu0.95Sb0.05, and possibly other mixed copper antimonide phases. This leads to a better understanding of the electrodeposition of the Cu2Sb system, which can lead to further improvement of the electrodeposition other transition metal antimonides and intermetallics.Item Open Access Energy storage and conversion materials: Part 1, Synthesis and characterization of ruthenium tris-bipyridine based fullerene charge transfer salts as a new class of tunable thermoelectric materials; Part 2, Synthesis and characterization of polymer thin films for use as a lithium ion battery separator(Colorado State University. Libraries, 2013) Bates, Daniel James, author; Elliott, C. Michael, advisor; Prieto, Amy L., advisor; Finke, Richard G., committee member; Van Orden, Alan, committee member; Crans, Debbie C., committee member; Dandy, David S., committee memberTo view the abstract, please see the full text of the document.Item Open Access Exploring phase selectivity and morphological control in Cu-Sb-Se nanoparticle synthesis(Colorado State University. Libraries, 2023) Kale, Amanda R., author; Prieto, Amy L., advisor; Sambur, Justin, committee member; Krummel, Amber, committee member; Ma, Kaka, committee memberNanoparticles are used in a variety of applications, such as optoelectronics, medicine, and energy generation and storage. Different applications necessitate different nanoparticle compositions and morphologies. Thus, developing fine synthetic control over composition, phase, and morphology is of interest to the field. Solution-phase nanoparticle synthesis allows control over particle shape and size, though phase purity is often an issue in ternary syntheses. Often precursor reactivity must be balanced to avoid binary sinks; however, in the Cu-Sb-Se system, the ternaries compete with one another. In this dissertation we explore the knobs of a hot-injection synthesis in oleylamine that can be tuned to favor different Cu-Sb-Se ternary phases and control particle morphologies. In Chapter I we begin with a discussion of the term precursor reactivity and how we define it here. We also address the common frameworks used to explain reactivity, and the specific challenges of balancing reactivity in multinary chalcogenide syntheses. We also discuss how these challenges manifest in the Cu-Sb-Se system, and why the structures and phase space of this material are interesting to study. In Chapter II we discuss a guide for fitting X-ray diffraction data for complex nanomaterial systems, outlining important considerations when working on the nanoscale as well as our sequential approach to refinements and recommended best practices. We also discuss a case study on the refinements of anisotropic, multiphase systems, which we use for the following chapter. The main synthetic work follows in the next two chapters, focusing first in Chapter III on the decomposition of metastable Cu3SbSe3 to thermodynamic CuSbSe2. We investigate how this can be manipulated through the addition of an amide base. In Chapter IV, we explore tuning morphology and specifically nanosheet branching in CuSbSe2, in which we show that we can induce twinning in CuSbSe2 and initial characterization suggests that this occurs in a different manner than in the very similar sulfide system. Finally, in Chapter V we reflect on the considerations and next steps for this work, including preliminary results on the use of soft base ligands to complex Cu, as well as on promising directions of field of nanoparticle synthesis as a whole.Item Open Access Hot injection synthesis and characterization of copper antimony selenide non-canonical nanomaterials toward earth-abundant renewable energy conversion(Colorado State University. Libraries, 2018) Agocs, Daniel B., author; Prieto, Amy L., advisor; Buchanan, Kristen, committee member; Sambur, Justin, committee member; Sites, James R., committee member; Van Orden, Alan, committee memberRenewable and carbon-free energy generation has become a critically important field as the global population continues to increase. Further, the ample supply afforded by natural resources such as sunlight and geothermal heat are attractive options that can be harnessed using technologies like photovoltaics and thermoelectrics. There is a growing interest in searching for novel materials that exhibit high efficiencies in these devices, ideally composed of earth abundant, non-toxic materials. This search is aided by theory, which has identified several families of compounds with interesting structure types that may exhibit properties amenable to incorporation in high efficiency devices. However, many of these materials have not yet been thoroughly evaluated for photovoltaics or thermoelectrics. This dissertation is focused on developing the synthesis and describing the basic characterization of nanoparticles of members of the compounds in the Cu-Sb-Se series, of which syntheses have been developed for Cu3SbSe4 and Cu3SbSe3 and are described in this dissertation. Herein, we describe a hot-injection route for the formation of Cu3SbSe4 and Cu3SbSe3 nanocrystals. In order to place this work in context, the first chapter of this dissertation provides a detailed summary of the literature investigating the Cu-Sb-Se family of compounds. Here, the highest thermoelectric efficiencies have been achieved for Cu3SbSe4 while Cu3SbSe3 is not yet comparable thermoelectrically to Cu3SbSe4 nor as efficient as the photovoltaic material CuSbSe2. The second chapter details the development of a hot injection synthesis of Cu3SbSe4 nanocrystals. In order for these materials to be applied as electronic materials in real devices, their stability and function under ambient conditions is of interest. Therefore, we studied the changes in electronic conductivity as a function of exposure to atmosphere. The conductivity increase was attributed to a hole mobility increase, and this was further correlated to structural oxidations. Chapter 3 details development of a synthesis for phase-pure Cu3SbSe3 nanodiscs. This material has become of interest recently for photovoltaic applications due to its acceptable band gap for solar absorption. While the synthesis of nanoscale Cu3SbSe3 has been reported, these results have not been reproduced, and property measurements among these limited works vary. Therefore, a robust synthesis was developed and initial optical and photoelectrochemical properties were measured and are reported in this dissertation that demonstrate photoactivity in thin films of the Cu3SbSe3 nanodiscs. In the fourth chapter, a more vigorous exploration of the nanodisc morphology observed in Cu3SbSe3 is reported. As a degree of self-assembly is observed in stacks of the nanodiscs, the morphology is investigated to understand how tuning nanocrystal morphology, size, and surface might affect the resulting particle interactions. To this end, a double injection synthesis was developed wherein the products exhibit optoelectronic properties similar to those of the original single injection reaction. Chapter 5 entails the electrochemical investigation of the copper antimony selenide nanostructures. Electrochemical measurements to experimentally elucidate the electronic structure are reported, and a photovoltaic architecture is proposed for a Cu3SbSe3-absorber layer device. Further, the presence of a thiol has been demonstrated to be critical to not only morphology within the Cu3SbSe3 synthesis but also the product phase formation. Therefore, initial measurements and challenges with in-situ electrochemical exploration of precursor reactivity are reported. Finally, chapter 6 briefly emphasizes the major findings within this dissertation. The experimental results for both Cu3SbSe4 and Cu3SbSe3 syntheses are reiterated. Further, additional directions for future work with this system are suggested. These primarily focus on fabrication of a Cu3SbSe3 photovoltaic cell to begin understanding photogenerated carrier transport. This can be extended through applying knowledge gained by understanding disc stacking to improve film deposition and electronic properties within Cu3SbSe3 materials. Finally, development of an electrochemical measurement system for use in oleylamine media would allow a new perspective on investigation of colloidal nanocrystalline formation. These proposed experiments would contribute to their respective fields in the broader context of expanding search criteria for novel photovoltaic materials, addressing the challenge of grain boundary recombination sites in photovoltaic nanocrystals, and providing tools for exploring nanoparticle synthesis.Item Open Access Improvement in dye sensitized solar cell efficiency through functionalization of redox mediators and passivation of the photoanode using a home-built atomic layer deposition system(Colorado State University. Libraries, 2017) Thomas, Joshua D., author; Prieto, Amy L., advisor; Fisher, Ellen R., committee member; Menoni, Carmen S., committee member; Sampath, Walajabad S., committee memberThe efficiency of dye sensitized solar cells (DSSCs) is driven based on the contributions of a vast array of kinetic and thermodynamic processes which must all function in sync with one another. The redox mediator factors into a majority of these processes and thus its proper function is vital to adequate function of the DSSC as a whole. The function of the redox mediator can be altered in two ways: changing the identity of the redox couple used and modifying one of the components which the redox couple is interacting with. Herein, both methods have been performed to optimize the properties and processes involved in efficient DSSC function. Several cobalt bipyridine coordination complex type mediators have been synthesized and differentiated through the modification of the ligand structure. The purpose of the modification was to generate complexes with more positive redox potentials to increase the open circuit voltage of the cells. Subsequently, attempts were made to further modify the ethyl ester substituted ligands which yielded the highest redox potential in order to provide higher stability for the resulting mediator. While the outcome of the synthesis was unsuccessful at this point, promising results have been shown. Further, an apparatus was constructed in order to cheaply perform atomic layer deposition of aluminum oxide on the surface of the mesoporous titanium dioxide photoanodes for DSSCs. Atomic layer deposition has been shown to reduce the rate of recombination with the oxidized mediator. In this case, improvement in the open circuit voltage of the cell was shown. However, the overall improved performance of the DSSCs shown in the literature could not be replicated. It is hoped that more high resolution analytical techniques could be used to elucidate the deficiencies still present in the use of this technique.Item Open Access Low temperature solution synthesis of ZnSb, MnSb, and Sr-Ru-O compounds(Colorado State University. Libraries, 2011) Noblitt, Jennifer Lenkner, author; Prieto, Amy L., advisor; Dandy, David S., committee member; Elliot, C. Michael, committee member; Fisher, Ellen R., committee member; Van Orden, Alan K., committee memberIncreasing energy demands are fueling research in the area of renewable energy and energy storage. In particular, Li-ion batteries and superconducting wires are attractive choices for energy storage. Improving safety, simplifying manufacturing processes, and advancing technology to increase energy storage capacity is necessary to compete with current marketed energy storage devices. These advancements are accomplished through the study of new materials and new morphologies. Increasing dependence on and rising demand for portable electronic devices has continued to drive research in the area of Li-ion batteries. In order to compete with existing batteries and be applicable to future energy needs such as powering hybrid vehicles, the drawbacks of Li-ion batteries must be addressed including (i) low power density, (ii) safety, and (iii) high manufacturing costs. These drawbacks can be addressed through new materials and morphologies for the anode, cathode, and electrolyte. New intermetallic anode materials such as ZnSb, MnSb, and Mn2Sb are attractive candidates to replace graphite, the current industry standard anode material, because they are safer while maintaining comparable theoretical capacity. Electrodeposition is an inexpensive method that could be used for the synthesis of these electrode materials. Direct electrodeposition allows for excellent electrical contact to the current collector without the use of a binder. To successfully electrodeposit zinc and manganese antimonides, metal precursors with excellent solubility in water were needed. To promote solubility, particularly for the antimony precursor, coordinating ligands were added to the deposition bath solutions. This work shows that the choice of coordinating ligand and metal-ligand speciation can alter both the electrochemistry and the film composition. This work focuses on the search for appropriate coordinating ligands, solution pH, and bath temperatures so that high quality films of ZnSb, MnSb, and Mn2Sb may be electrochemically deposited on a conducting substrate. Increasing use of natural resources for energy generation has driven research in the area of energy storage using superconducting materials. To meet energy storage needs the materials must have the following features: (i) safety, (ii) superconductivity at or above liquid nitrogen temperature (77 K), (iii) low cost manufacturing processes, and (iv) robustness. The search for materials that meet all of these criteria is on-going, specifically in the area of high temperature superconductivity. The precise mechanism of superconductivity is not known. A few theories explain some of the phenomenological aspects, but not all. In order to logically select and synthesize high temperature superconductors for industrial applications, the precise mechanism must first be elucidated. Additionally, a synthetic method that yields pure, high quality crystals is required because transition temperatures have been shown to vary depending on the preparation method due to impurities. Before measuring properties of superconductors, the development of a synthesis method that yields pure, high quality crystals is required. Most superconductors are synthesized using traditional solid state methods. This synthesis route precludes formation of kinetically stable phases. Low temperature synthesis is useful for probing thermodynamic verses kinetic stability of compounds as well as producing high quality single crystals. A novel low temperature hydrothermal synthesis of Sr-Ru-O compounds has been developed. These materials are important because of their interesting properties including superconductivity and ferromagnetism. Sr2RuO4 is particularly interesting as it is superconducting and isostructural to La2CuO4, which is only superconducting when doped. Therefore, Sr2RuO4 is a good choice for study of the mechanism of superconductivity. Additionally, new kinetically stable phases of the Sr-Ru-O family may be formed which may also be superconducting. Sr-Ru-O compounds were previously synthesized via the float zone method. There is one report of using hydrothermal synthesis, but the temperatures used were 480-630 °C. In general, hydrothermal methods are advantageous because of the potential for moderate temperatures and pressures to be used. Additionally, the reaction temperature, precursor choice, and reaction time can all be used to tune the composition and morphology of the product. Hydrothermal methods are inexpensive and a one-step synthesis which is very convenient to scale up for industrial application. This work shows how a hydrothermal method at temperatures between 140 °C and 210 °C was developed for the synthesis of the Sr-Ru-O family of compounds.Item Embargo Navigating the thermodynamic landscape in search of synthetic routes to ternary nitrides(Colorado State University. Libraries, 2022) Rom, Christopher Linfield, author; Neilson, James R., advisor; Prieto, Amy L., advisor; Sambur, Justin, committee member; Szamel, Grzegorz, committee member; Buchanan, Kristen, committee memberTernary nitride materials—a class of ceramics composed of two different metals bound with anionic nitrogen (N3-) as a solid—are underexplored because they are difficult to make. Nitrides rarely occur in nature, as the oxygen in the air (O2) is more reactive towards metals than the nitrogen (N2). Consequently, oxide minerals dominate the earth's crust while nitride minerals are extremely rare. Almost all ternary nitrides that have been discovered have synthesized, usually with rigorously air-free conditions. Despite much effort in the past century, the number of known ternary nitrides (approximately 450) pales in comparison to that of ternary oxides (over 4,000). Yet there are world-changing materials within this small number of compounds, like the (In,Ga)N alloys that underpin efficient blue light emitting diodes. Fortunately, recent computational work has predicted a number of theoretically stable ternary nitrides, providing targets for synthesis. This dissertation focuses on the synthesis of new ternary nitrides. Guided by increasingly user-friendly computational tools, these chapters describe syntheses overcome the thermodynamic barriers that often inhibit the formation of new ternary nitrides. Along the way, several new materials are discovered and characterized for promising magnetic and semiconducting properties: MnSnN2, MgWN2 in two structure types, Mg3WN4, MgZrN2, CaZrN2, and CaHfN2. These adventures in synthesis not only report new compounds, but also highlight promising strategies for future explorations of uncharted nitride phase space.Item Open Access Part 1: Synthesis and characterization of magnetic Cr5Te8 nanoparticles. Part 2: Local atomic structure studies using theory to simulate polarons in superconducting cuprates and experiment to analyze alternative energy nanomaterials(Colorado State University. Libraries, 2012) Martucci, Mary B., author; Prieto, Amy L., advisor; Elliott, C. Michael, committee member; Fisher, Ellen R., committee member; Rickey, Dawn, committee member; Patton, Carl E., committee memberThe field of spintronics, the development of spin-based devices that utilize the spin degree of freedom to increase memory capacity, has emerged as a solution to faster more efficient memory storage for electronic devices. One class of materials that has been extensively studied is the half-metallic ferromagnets, compounds that are 100% spin-polarized at the Fermi level. One material in this group that has been investigated is chromium telluride (Cr1-xTe), whose family of compounds is known to exhibit a wide range of interesting magnetic and electronic properties. We have developed a hot injection solution synthesis of Cr5Te8 nanoplatlets which show similar magnetic behavior to the bulk material. It has also been shown that selenium and sulfur analogues can be obtained without changing the reaction conditions, making progress toward a better understanding of the reaction as well as an interesting family of compounds. Using real-space simulations, the effect of polarons in the high-Tc superconducting cuprates has been studied. The simulations demonstrate energetically favorable sites for the defects and show evidence of longer-range pairing interactions. Variations of the stripe show similar energetic results. X-ray absorption fine structure spectroscopy and neutron scattering have been utilized to examine the local structure of Ni-doped Mg nanoparticles, a hydrogen storage material as well as Cu2ZnSnS4 (CZTS) nanoparticles, a photovoltaic material. The Mg-Ni material shows much local disorder upon hydrogen cycling. The CZTS data demonstrate a loss of sulfur from around the copper sites upon annealing, helping to explain the changes observed in the optical absorption properties resulting from the annealing process.Item Embargo Tuning antimony anodes through electrodeposition to inform on the reaction and degradation mechanisms in sodium-ion batteries(Colorado State University. Libraries, 2023) Nieto, Kelly, author; Prieto, Amy L., advisor; Sambur, Justin, committee member; Krummel, Amber, committee member; Bandhauer, Todd, committee memberElectrification of portable devices, transportation, and large grid-level storage necessitate a portfolio of energy storage devices tailored to specific applications. Sodium-ion batteries are a naturally abundant alternative to lithium, but high performing anodes must be developed in order to reach widespread commercialization. Alloy-based anodes such as antimony (Sb) are attractive targets for their high theoretical capacities. However, the electrochemical performance of Sb is poor, and the reaction mechanism is poorly understood. Herein, antimony-based anodes for sodium-ion batteries are explored to elucidate sodiation pathways and investigate the role of electrode fabrication, electrolyte composition, and architecture on the reaction and degradation mechanism. Chapter I describes our research methodology and consists of our synthetic method of electrodeposition, materials characterization, battery assembly, and electrochemical characterization. Through this process, we can develop a better understanding of the electrochemical performance of alloy-based anode materials. The tunability of electrodeposition as a synthetic technique for the fabrication of Sb-based anodes is exploited in Chapter II. The effects of solution additives in the electrodeposition of Sb anodes are investigated and provide insight into how the morphology and crystallinity of the deposited anodes can be tuned. It was revealed that CTAB and SPS could significantly tune the electrodeposition of Sb films by altering the deposition by causing structural changes that either improved cycle life or rate capabilities. In Chapter III, electrodeposited and slurry cast Sb anodes were compared through differential capacity analysis, and it was demonstrated that electrode fabrication can significantly impact the sodiation/desodiation reaction pathway. Additionally, electrodeposited Sb anodes provided valuable insight into the mechanism without having to deconvolute the influences of binders and additives necessary in slurry casting. Chapter IV describes preliminary studies on how electrolyte composition can influence sodiation/desodiation reactions during Sb anode cycling. Traditional battery electrolytes are composed of carbonate species and salts, which are reduced onto the anode surface to form the solid electrolyte interphase (SEI). Due to the inherent volume expansion of Sb anodes when sodiated/desodiated, the SEI is hypothesized to continuously form and affect the cyclability of these anodes. In this investigation, we have found that electrolyte composition can influence the cycle life and sodiation/desodiation pathway, and we describe additional studies to probe how the SEI could hinder sodium ion transport. Chapter V builds upon Chapter II and explores how electrodeposition can be employed to develop three-dimensional (3D) electrodes to enhance the energy and power density of Sb-based anodes. Although we show that experimental parameters can be tuned to obtain uniform coverage, significant challenges in achieving conformal coverage of the current collector while maintaining high active material loading remain. The final chapter, Chapter VI, concludes the dissertation by describing further directions required to deepen the understanding of the degradation mechanism for Sb. We have begun to develop a 3D-printed optical, electrochemical cell that can couple operando optical studies with electrochemical studies to understand how electrode composition, structure, and electrolyte composition affect mechanical stability and ionic/electronic diffusivity in these electrodes. Understanding these fundamental processes and developing tools and characterization techniques to study alloy-based anode materials will lay the foundation for creating earth-abundant energy storage systems with high energy densities and long cycle life.Item Open Access Tuning optoelectronic properties and understanding charge transport in nanocrystal thin films of earth abundant semiconducting materials(Colorado State University. Libraries, 2011) Riha, Shannon C., author; Parkinson, Bruce A., advisor; Prieto, Amy L., advisor; Elliott, C. Michael, committee member; Field, Stuart, committee member; Henry, Charles, committee member; Rappe, Anthony, committee memberWith the capability of producing nearly 600 TW annually, solar power is one renewable energy source with the potential to meet a large fraction of the world's burgeoning energy demand. To make solar technology cost-competitive with carbon-based fuels, cheaper devices need to be realized. Solution-processed solar cells from nanocrystal inks of earth abundant materials satisfy this requirement. Nonetheless, a major hurdle in commercializing such devices is poor charge transport through nanocrystal thin films. The efficiency of charge transport through nanocrystal thin films is strongly dependent on the quality of the nanocrystals, as well as their optoelectronic properties. Therefore, the first part of this dissertation is focused on synthesizing high quality nanocrystals of Cu2ZnSnS4, a promising earth abundant photovoltaic absorber material. The optoelectronic properties of the nanocrystals were tuned by altering the copper to zinc ratio, as well as by introducing selenium to create Cu2ZnSn(S1-xSex)4 solid solutions. Photoelectrochemical characterization was used to test the Cu2ZnSnS4 and Cu2ZnSn(S1-xSex)4 nanocrystal thin films. The results identify minority carrier diffusion and recombination via the redox shuttle as the major loss mechanisms hindering efficient charge transport through the nanocrystal thin films. One way to solve this issue is to sinter the nanocrystals together, creating large grains for efficient charge transport. Although this may be quick and effective, it can lead to the formation of structural defects, among other issues. To this end, using a different copper-based material, namely Cu2Se, and simple surface chemistry treatments, an alternative route to enhance charge transport through nanocrystals thin films is proposed.Item Open Access Understanding the amide-assisted synthesis and olivine structure-directed twinning of Fe₂GeS₄ nanoparticles(Colorado State University. Libraries, 2020) Miller, Rebecca Caroline, author; Prieto, Amy L., advisor; Shores, Matthew P., committee member; Sites, James R., committee member; Ackerson, Christopher J., committee memberThe reality of detrimental anthropogenic effects on the environment requires the development of a number of sustainable practices and technologies. The Prieto Group strives to advance the synthesis and understanding of materials for use in energy conversion and storage. Advances in computational solid-state chemistry have resulted in the identification of a number of earth-abundant, relatively non-toxic compounds as promising photovoltaic absorber materials. However, the synthesis of solids remains a step behind, requiring empirical exploration of precursors and conditions. As reaction intermediates and mechanisms are discovered, general synthetic strategies can be translated from one material system to the next. Inorganic nanoparticle (NP) syntheses rely on the interdisciplinary expertise of solid-state, organometallic, and organic chemistry and show interesting complexity. The work herein has advanced the understanding of amide-assisted NPs syntheses and examined the microstructure of twinned Fe2GeS4 NPs. Chapter 1 presents a history of solution-based, amide-assisted NP reactions. As scientists understand the in situ speciation of precursors, more efficient reactions can be designed. This understanding allows the use of more benign and safe (both in terms of human and environmental) precursors and provides higher synthetic control over the end products. The presence of amide bases has generally provided access to higher NP nucleation rates and accessed smaller, more monodisperse particles. The increased monomer reactivity has also allowed the formation of ternary NPs free from binary or unary impurities by balancing the reactivity of cations of different valency. The most common amide base is LiN(SiMe3)2, and I relate this field to the use of its conjugate acid, hexamethyldisilazane or HMDS, in NP syntheses. Its addition has aided the production of NPs, but its chemical role remains unclear. This chapter was written utilizing a portion of an invited review paper written by myself, Jennifer M. Lee, Lily J. Moloney, and Amy L. Prieto in the Journal of Solid State Chemistry (2019, 273, 243-286.). Section 2.2 of the review outlined the evolution of understanding of amide-assisted NP syntheses and was adapted and expanded upon herein. In Chapter 2, I report the redesign of a Fe2GeS4 NP synthesis. In 2013, the Prieto group was the first to report a NP synthesis for the compound, which had been predicted to be a promising photovoltaic absorber material in 2011. The original reaction relied on HMDS as an additive and employed the highly-reactive S precursor, hexamethyldisilathiane. Herein, I speculate on these precursors' roles and exchange their use for LiN(SiMe3)2 and S powder, eliminating the formation of an Fe1–xS intermediate and reducing the growth time from 24 h to 10 min. I thoroughly map the reaction landscape of this system and provide structural, compositional, and optical characterization of the particles. This work was published in the Journal of the American Chemical Society (J. Am. Chem. Soc. 2020, 142 (15), 7023–7035.). The Fe2GeS4 NPs show an interesting star-shaped morphology, so I examine the microstructure via electron microscopy and identify the presence of crystal twinning in Chapter 3. The particles exist as three sets of stacked nanoplates intersecting at 60˚ angles, which forms a triplet of twins or trillings. In the products, 98% of the particles are twinned. Because crystal twinning, and especially trilling formation, in macroscopic crystals is rare, a synthetic route to a massive collection of twinned particles stands as a valuable resource for understanding the fundamentals of crystal twinning in olivine compounds. I relate the twinning to the underlying hexagonal pseudosymmetry of the orthorhombic, olivine crystal structure. Because of the ratio of the unit cell dimensions (a_Pnma/b_(Pnma )≈√3), the compound is susceptible to forming twins with growth of the [010] direction off the {310} faces. This can occur for other olivine compounds of similar unit cell dimension ratios, so I rank all of the olivine compounds listed in the Inorganic Crystal Structure Database according to this metric in Appendix A. This chapter is a manuscript prepared for submission. Finally, Chapter 4 outlines our recommendations for future work to advance the understanding of amide-assisted NP syntheses and translate this synthetic system to other compounds. I suggest the systematic development of SnS NP reactions utilizing each of the precursors: Sn silylamide, alkali silylamides, and HMDS. I outline a set of complementary techniques to characterize the reaction intermediates and mechanisms. This type of investigation has been done by the Kovalenko group for the formation of unary Sn0 NPs, but the interaction of the chalcogen species remains unknown. Further, no systematic mechanistic study exists for the use of HMDS in NP synthesis. This work would advance the understanding and use of amide-assisted syntheses for all metal chalcogenide compounds. In addition, I present preliminary data in our extrapolation of the Fe2GeS4 NP synthesis to the following solid solutions: Fe2GeS4–xSe (including the end member Fe2GeSe4) and Fe2–xMnxGeS4. One composition of each solid solution was formed and characterized by powder X-ray diffraction, and I present electron microscopy to show twinning in the Fe2GeS4–xSex (x = 0.96, 24 mol% Se) NPs. Lastly, I consider the possibility for twinning in an important olivine compound for battery science, LiFePO4, which is a common cathode material. The crystal structure shows a high degree of hexagonal pseudosymmetry, indicating that the energetics of forming twin domains may be favorable. I discuss the possible ramifications this may have on battery cycling performance. Thus, the scope of this work focuses on one compound, Fe2GeS4, but investigation into its synthesis and microstructure has opened a number of avenues for promising research. This compound itself presents a promising material for both photovoltaic and thermoelectric energy conversion, and the syntheses herein provide a launching point for property measurement and application evaluation. Further, the general examination of twinning in olivine compounds identifies questions for evaluating the function of other compounds useful for a number of applications. Lastly, analogous calculations to the geometrical evaluation done for orthorhombic olivine compounds could be carried out for other crystal structure types with unit cells that exist close to higher orders of symmetry. The advances presented herein on understanding the reactivity and roles of NP precursors are fundamental for progressing the field of NP synthesis. The reproducible formation and structural characterization of these twinned NPs provide a promising system for future explorations in crystal twinning and its effect on material properties.Item Open Access Understanding the solid electrolyte interface (SEI) on alloying anodes: development of a methodology for SEI sample preparation and x-ray photoelectron spectroscopy characterization and studies of the SEI on electrodeposited thin film intermetallic anodes for Li-ion batteries(Colorado State University. Libraries, 2020) Kraynak, Leslie A., author; Prieto, Amy L., advisor; Shores, Matthew, committee member; Strauss, Steven, committee member; Bandhauer, Todd, committee memberThe solid electrolyte interface (SEI) is an important component of Li-ion rechargeable batteries that forms due to the potential stability limits of the organic electrolyte falling within the large operating potential window of the battery. It plays a crucial role in battery performance by passivating the electrode surface; it also affects the safety, Li-ion consumption/inventory, and Li-ion transport rates of the battery. Despite decades of study, there is still much that is unknown about the SEI, especially how to intentionally modify the composition and properties of the SEI in order to obtain better performance as measured by metrics that include reversible capacity and cycle lifetime. The gaps in understanding of the SEI are even more pronounced for alloying anode materials, and the mechanical and chemical instability of electrode surfaces and the SEI formed from conventional secondary battery electrolytes is one of the bottlenecks in the development of next generation battery technologies. The first chapter of this dissertation is an overview of studies from the past two decades concerning the SEI formed on metallic alloying anodes, examining SEI formation, the evolution of the SEI over long term cycling, and improvements to the SEI through the use of additives and novel electrolytes. Compared to the body of literature on the SEI on other anode materials such as graphite, Li metal, and silicon, there has been relatively little published about the SEI on metallic alloying anodes such as tin, antimony, and intermetallics, especially considering the scope of these types of anode materials. However, a comparison of the existing literature concerning the SEI on alloying anodes reveals interesting similarities and difference between the SEI formation and evolution on metallic alloying anodes and highlights some critical gaps in knowledge for the field. The second chapter concerns the development of a methodology to study the SEI formed on alloying anodes, and in particular binder- and additive-free thin film electrodes. The formation, composition, and properties of the SEI are dependent on a number of experimental variables, which makes it difficult understand the factors that affect SEI performance and limits progress towards the goal of more controlled or intentional SEI formation for better battery performance. One of the first steps towards this goal is to be able to make and characterize SEI samples in a reproducible manner. This chapter outlines some of the important considerations for SEI sample preparation that are not widely discussed in the battery community in addition to some of the important considerations for using X-ray photoelectron spectroscopy to characterize the SEI. The third and fourth chapters are about using the methodology described in Chapter 2 to characterize the SEI formed on intermetallic thin film anodes. The third chapter examines the role that vinylene carbonate, a conventional SEI-improving electrolyte additive, plays in passivating the surface and extending the cycle lifetime of Cu2Sb electrodes. The fourth chapter is concerned with understanding what role the SEI plays in the cycle performance of pure phase SnSb thin film electrodes. Studying changes in the SEI on SnSb over different stages of cycling can help elucidate whether the SEI plays a role in the capacity retention and long cycle lifetime of SnSb and whether it ultimately contributes to the failure of the electrode.Item Open Access Using electrochemical methods to synthesize and understand energy dense anodes for lithium-ion and "beyond" battery technologies(Colorado State University. Libraries, 2021) Ma, Jeffrey, author; Prieto, Amy L., advisor; Shores, Matthew, committee member; Finke, Richard, committee member; Weinberger, Chris, committee memberTo view the abstract, please see the full text of the document.