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- Creators: Arizona State University
Description
Photosynthesis, one of the most important processes in nature, has provided an energy basis for nearly all life on Earth, as well as the fossil fuels we use today to power modern society. This research aims to mimic the photosynthetic process of converting incident solar energy into chemical potential energy in the form of a fuel via systems capable of carrying out photo-induced electron transfer to drive the production of hydrogen from water. Herein is detailed progress in using photo-induced stepwise electron transfer to drive the oxidation of water and reduction of protons to hydrogen. In the design, use of more blue absorbing porphyrin dyes to generate high-potential intermediates for oxidizing water and more red absorbing phthalocyanine dyes for forming the low potential charge needed for the production of hydrogen have been utilized. For investigating water oxidation at the photoanode, high potential porphyrins such as, bis-pyridyl porphyrins and pentafluorophenyl porphyrins have been synthesized and experiments have aimed at the co-immobilization of this dye with an IrO2-nH2O catalyst on TiO2. To drive the cathodic reaction of the water splitting photoelectrochemical cell, utilization of silicon octabutoxy-phthalocyanines have been explored, as they offer good absorption in the red to near infrared, coupled with low potential photo-excited states. Axially and peripherally substituted phthalocyanines bearing carboxylic anchoring groups for the immobilization on semiconductors such as TiO2 has been investigated. Ultimately, this work should culminate in a photoelectrochemical cell capable of splitting water to oxygen and hydrogen with the only energy input from light. A series of perylene dyes bearing multiple semi-conducting metal oxide anchoring groups have been synthesized and studied. Results have shown interfacial electron transfer between these perylenes and TiO2 nanoparticles encapsulated within reverse micelles and naked nanoparticles. The binding process was followed by monitoring the hypsochromic shift of the dye absorption spectra over time. Photoinduced electron transfer from the singlet excited state of the perylenes to the TiO2 conduction band is indicated by emission quenching of the TiO2-bound form of the dyes and confirmed by transient absorption measurements of the radical cation of the dyes and free carriers (injected electrons) in the TiO2.
ContributorsBergkamp, Jesse J (Author) / Moore, Ana L (Thesis advisor) / Mariño-Ochoa, Ernesto (Thesis advisor) / Gust, Devens J (Committee member) / Gould, Ian (Committee member) / Arizona State University (Publisher)
Created2013
Description
In recent years we have witnessed a shift towards multi-processor system-on-chips (MPSoCs) to address the demands of embedded devices (such as cell phones, GPS devices, luxury car features, etc.). Highly optimized MPSoCs are well-suited to tackle the complex application demands desired by the end user customer. These MPSoCs incorporate a constellation of heterogeneous processing elements (PEs) (general purpose PEs and application-specific integrated circuits (ASICS)). A typical MPSoC will be composed of a application processor, such as an ARM Coretex-A9 with cache coherent memory hierarchy, and several application sub-systems. Each of these sub-systems are composed of highly optimized instruction processors, graphics/DSP processors, and custom hardware accelerators. Typically, these sub-systems utilize scratchpad memories (SPM) rather than support cache coherency. The overall architecture is an integration of the various sub-systems through a high bandwidth system-level interconnect (such as a Network-on-Chip (NoC)). The shift to MPSoCs has been fueled by three major factors: demand for high performance, the use of component libraries, and short design turn around time. As customers continue to desire more and more complex applications on their embedded devices the performance demand for these devices continues to increase. Designers have turned to using MPSoCs to address this demand. By using pre-made IP libraries designers can quickly piece together a MPSoC that will meet the application demands of the end user with minimal time spent designing new hardware. Additionally, the use of MPSoCs allows designers to generate new devices very quickly and thus reducing the time to market. In this work, a complete MPSoC synthesis design flow is presented. We first present a technique \cite{leary1_intro} to address the synthesis of the interconnect architecture (particularly Network-on-Chip (NoC)). We then address the synthesis of the memory architecture of a MPSoC sub-system \cite{leary2_intro}. Lastly, we present a co-synthesis technique to generate the functional and memory architectures simultaneously. The validity and quality of each synthesis technique is demonstrated through extensive experimentation.
ContributorsLeary, Glenn (Author) / Chatha, Karamvir S (Thesis advisor) / Vrudhula, Sarma (Committee member) / Shrivastava, Aviral (Committee member) / Beraha, Rudy (Committee member) / Arizona State University (Publisher)
Created2013
Description
Cellular redox phenomena are essential for the life of organisms. Described here is a summary of the synthesis of a number of redox-cycling therapeutic agents. The work centers on the synthesis of antitumor antibiotic bleomycin congeners. In addition, the synthesis of pyridinol analogues of alpha-tocopherol is also described. The bleomycins (BLMs) are a group of glycopeptide antibiotics that have been used clinically to treat several types of cancers. The antitumor activity of BLM is thought to be related to its degradation of DNA, and possibly RNA. Previous studies have indicated that the methylvalerate subunit of bleomycin plays an important role in facilitating DNA cleavage by bleomycin and deglycobleomycin. A series of methylvalerate analogues have been synthesized and incorporated into deglycobleomycin congeners by the use of solid-phase synthesis. All of the deglycobleomycin analogues were found to effect the relaxation of plasmid DNA. Those analogues having aromatic C4-substituents exhibited cleavage efficiency comparable to that of deglycoBLM A5. Some, but not all, of the deglycoBLM analogues were also capable of mediating sequence-selective DNA cleavage. The second project focused on the synthesis of bicyclic pyridinol analogues of alpha-tocopherol. Bicyclic pyridinol antioxidants have recently been reported to suppress the autoxidation of methyl linoleate more effectively than alpha-tocopherol. However, the complexity of the synthetic routes has hampered their further development as therapeutic agents. Described herein is a concise synthesis of two bicyclic pridinol antioxidants and a facile approach to their derivatives with simple alkyl chains attached to the antioxidant core. These analogues were shown to retain biological activity and exhibit tocopherol-like behaviour.
ContributorsCai, Xiaoqing (Author) / Hecht, Sidney M. (Thesis advisor) / Gould, Ian R (Committee member) / Hartnett, Hilairy E (Committee member) / Arizona State University (Publisher)
Created2011
Description
Throughout time, compounds from natural sources have provided humans with medicines, and recently become the structural inspiration for semisynthetic drugs. One arena that has benefited greatly from the use of these natural products is the discovery of novel antibacterial agents. Methicillin-resistant Staphylcoccus aureus (MRSA) continues to plague the United States as well as throughout the world, at least in part because of increasing antibiotic resistance. Therefore, scientists continue to scour natural products as potential leads, either directly or indirectly, for antibiotics to treat MRSA. The structure of the indole sesquiterpene, polyalthenol, was discovered in 1976 and recent work shows a 4µg/mL minimum inhibitory concentration (MIC) against a variety of strains of MRSA. Given the unique framework of this natural product and its biological activity against MRSA, the total synthesis becomes the next logical step. Presently a racemic synthesis has successfully afforded an indole ketone with the correct relative stereochemistry of polyalthenol, however, the completion of the total synthesis of polyalthenol presents several challenges. Herein, the work towards the synthesis is described in addition to the proposed completion of the synthesis.
ContributorsReichenberg, Erynn Wright (Author) / Madar, David J (Thesis advisor) / Skibo, Edward (Committee member) / Miller, William (Committee member) / Arizona State University (Publisher)
Created2012
Description
Amphipathic molecules consist of hydrophilic and hydrophobic regions, which make them surface-active molecules. The uniqueness of these compounds results in inducing low surface tension and self-assembly of the molecules inside a solvent which have been exploited in personal care, the oil industry and agriculture industry. Amphipathic molecules are also used in the healthcare industry as drug delivery systems and other bio-nanotechnology applications.
In this thesis, a novel series of grafted siloxanes have been explored for their probable application in the healthcare industry. The siloxanes are grafted with poly(ethylene glycol) (PEG) and quaternary ammonium salt (QUAT). The effects of varying 1) molar ratios of QUAT to PEG and 2) PEG chain length on contact angle, surface tension, critical micelle concentration (CMC), and micelle assembly properties were studied. In contact angle experiments, the hydrophilicity of grafted siloxanes increased by grafting PEG and QUAT. The amphiphilicity increases and CMC decreases as the PEG chain length shortens. Adding QUAT also reduces CMC. These trends were observed in surface tension and Isothermal Titration Calorimetry experiments. A change in self-assembly behaviour was also observed in Dynamic Light Scattering experiments upon increasing the PEG chain length and its ratio relative to the quaternary ammonium in the siloxane polymer.
These polymers have also been studied for their probable application as a sensitive 1H NMR spectroscopy indicator of tissue oxygenation (pO2) based on spectroscopic spin-lattice relaxometry. The proton imaging of siloxanes to map tissue oxygenation levels (PISTOL) technique is used to map T1 of siloxane polymer, which is correlated to dynamic changes in tissue pO2 at various locations by a linear relationship between pO2 and 1/T1. The T1-weighted echo spin signals were observed in an initial study of siloxanes using the PISTOL technique.
The change in the ratio of QUAT to PEG and the varying chain length of PEG have a significant effect on the physical property characteristics of siloxane graft copolymers. The conclusions and observations of the present work serve as a benchmark study for further development of adaptive polymers and for the creation of integrated “nanoscale” probes for PISTOL oximetry and drug delivery.
In this thesis, a novel series of grafted siloxanes have been explored for their probable application in the healthcare industry. The siloxanes are grafted with poly(ethylene glycol) (PEG) and quaternary ammonium salt (QUAT). The effects of varying 1) molar ratios of QUAT to PEG and 2) PEG chain length on contact angle, surface tension, critical micelle concentration (CMC), and micelle assembly properties were studied. In contact angle experiments, the hydrophilicity of grafted siloxanes increased by grafting PEG and QUAT. The amphiphilicity increases and CMC decreases as the PEG chain length shortens. Adding QUAT also reduces CMC. These trends were observed in surface tension and Isothermal Titration Calorimetry experiments. A change in self-assembly behaviour was also observed in Dynamic Light Scattering experiments upon increasing the PEG chain length and its ratio relative to the quaternary ammonium in the siloxane polymer.
These polymers have also been studied for their probable application as a sensitive 1H NMR spectroscopy indicator of tissue oxygenation (pO2) based on spectroscopic spin-lattice relaxometry. The proton imaging of siloxanes to map tissue oxygenation levels (PISTOL) technique is used to map T1 of siloxane polymer, which is correlated to dynamic changes in tissue pO2 at various locations by a linear relationship between pO2 and 1/T1. The T1-weighted echo spin signals were observed in an initial study of siloxanes using the PISTOL technique.
The change in the ratio of QUAT to PEG and the varying chain length of PEG have a significant effect on the physical property characteristics of siloxane graft copolymers. The conclusions and observations of the present work serve as a benchmark study for further development of adaptive polymers and for the creation of integrated “nanoscale” probes for PISTOL oximetry and drug delivery.
ContributorsGupta, Srishti (Author) / Green, Matthew D (Thesis advisor) / Kodibagkar, Vikram (Committee member) / Holloway, Julianne (Committee member) / Arizona State University (Publisher)
Created2018
Description
Layer structured two dimensional (2D) semiconductors have gained much interest due to their intriguing optical and electronic properties induced by the unique van der Waals bonding between layers. The extraordinary success for graphene and transition metal dichalcogenides (TMDCs) has triggered a constant search for novel 2D semiconductors beyond them. Gallium chalcogenides, belonging to the group III-VI compounds, are a new class of 2D semiconductors that carry a variety of interesting properties including wide spectrum coverage of their bandgaps and thus are promising candidates for next generation electronic and optoelectronic devices. Pushing these materials toward applications requires more controllable synthesis methods and facile routes for engineering their properties on demand.
In this dissertation, vapor phase transport is used to synthesize layer structured gallium chalcogenide nanomaterials with highly controlled structure, morphology and properties, with particular emphasis on GaSe, GaTe and GaSeTe alloys. Multiple routes are used to manipulate the physical properties of these materials including strain engineering, defect engineering and phase engineering. First, 2D GaSe with controlled morphologies is synthesized on Si(111) substrates and the bandgap is significantly reduced from 2 eV to 1.7 eV due to lateral tensile strain. By applying vertical compressive strain using a diamond anvil cell, the band gap can be further reduced to 1.4 eV. Next, pseudo-1D GaTe nanomaterials with a monoclinic structure are synthesized on various substrates. The product exhibits highly anisotropic atomic structure and properties characterized by high-resolution transmission electron microscopy and angle resolved Raman and photoluminescence (PL) spectroscopy. Multiple sharp PL emissions below the bandgap are found due to defects localized at the edges and grain boundaries. Finally, layer structured GaSe1-xTex alloys across the full composition range are synthesized on GaAs(111) substrates. Results show that GaAs(111) substrate plays an essential role in stabilizing the metastable single-phase alloys within the miscibility gaps. A hexagonal to monoclinic phase crossover is observed as the Te content increases. The phase crossover features coexistence of both phases and isotropic to anisotropic structural transition.
Overall, this work provides insights into the controlled synthesis of gallium chalcogenides and opens up new opportunities towards optoelectronic applications that require tunable material properties.
In this dissertation, vapor phase transport is used to synthesize layer structured gallium chalcogenide nanomaterials with highly controlled structure, morphology and properties, with particular emphasis on GaSe, GaTe and GaSeTe alloys. Multiple routes are used to manipulate the physical properties of these materials including strain engineering, defect engineering and phase engineering. First, 2D GaSe with controlled morphologies is synthesized on Si(111) substrates and the bandgap is significantly reduced from 2 eV to 1.7 eV due to lateral tensile strain. By applying vertical compressive strain using a diamond anvil cell, the band gap can be further reduced to 1.4 eV. Next, pseudo-1D GaTe nanomaterials with a monoclinic structure are synthesized on various substrates. The product exhibits highly anisotropic atomic structure and properties characterized by high-resolution transmission electron microscopy and angle resolved Raman and photoluminescence (PL) spectroscopy. Multiple sharp PL emissions below the bandgap are found due to defects localized at the edges and grain boundaries. Finally, layer structured GaSe1-xTex alloys across the full composition range are synthesized on GaAs(111) substrates. Results show that GaAs(111) substrate plays an essential role in stabilizing the metastable single-phase alloys within the miscibility gaps. A hexagonal to monoclinic phase crossover is observed as the Te content increases. The phase crossover features coexistence of both phases and isotropic to anisotropic structural transition.
Overall, this work provides insights into the controlled synthesis of gallium chalcogenides and opens up new opportunities towards optoelectronic applications that require tunable material properties.
ContributorsCai, Hui, Ph.D (Author) / Tongay, Sefaattin (Thesis advisor) / Dwyer, Christian (Committee member) / Zhuang, Houlong (Committee member) / Arizona State University (Publisher)
Created2018
Description
Mitochondria produce the majority portion of ATP required in eukaryotic cells. ATP is generated through a process known as oxidative phosphorylation, through an pathway consisting five multi subunit proteins (complex I-IV and ATP synthase), embedded inside the mitochondrial membrane. Mitochondrial electron transport chain dysfunction increases reactive oxygen species in the cell and causes several serious disorders. Described herein are the synthesis of antioxidant molecules to reduce the effects in an already dysfunctional system. Also described is the study of the mitochondrial electron transport chain to understand the mechanism of action of a library of antioxidants. Illustrated in chapter 1 is the general history of research on mitochondrial dysfunction and reported ways to ameliorate them. Chapter 2 describes the design and synthesis of a series of compounds closely resembling the redox-active quinone core of the natural product geldanamycin. Geldanamycin has been reported to confer cytoprotection to FRDA lymphocytes in a dose dependent manner under conditions of induced oxidative stress. A library of rationally designed derivatives has been synthesized as a part of our pursuit of a better neuroprotective drug. Chapter 3 describes the design and synthesis of a library of pyrimidinol analogues. Compounds of this type have demonstrated the ability to quench reactive oxygen species and sustain mitochondrial membrane potential. Described herein are our efforts to increase their metabolic stability and total ATP production. It is crucial to understand the nature of interaction between a potential drug molecule and the mitochondrial electron transport chain to enable the design and synthesis a better therapeutic candidates. Chapter 4 describes a part of the enzymatic
binding studies between a molecular library synthesized in our laboratory and the mitochondrial electron transport chain using sub mitochondrial particles (SMP).
binding studies between a molecular library synthesized in our laboratory and the mitochondrial electron transport chain using sub mitochondrial particles (SMP).
ContributorsDey, Sriloy (Author) / Hecht, Sidney M. (Thesis advisor) / Angell, Charles A (Committee member) / Gould, Ian (Committee member) / Arizona State University (Publisher)
Created2015
Description
The current Li-ion batteries with organic liquid electrolytes are limited by their safety and energy density. Therefore, ceramic electrolytes are proposed in developing next-generation, energy-dense Li-metal batteries by replacing organic liquid electrolytes to improve safety and performance. Among numerous ceramic Li-ion conductors, garnet-based solid electrolyte c-Li7La3Zr2O12 (c-LLZO) is considered one of the most promising candidates to enable Li metal batteries due to its high ionic conductivity, chemical stability, and wide electrochemical stability window against Li metal. However, synthesis and processing of c-LLZO through conventional solid-sate reaction methods requires long periods of calcination (> 6 h) at high reaction temperatures (> 1000 °C). The need for high reaction temperature results to attain cubic-LLZO phase results in large aggerated LLZO particles and causes Li-loss from the garnet structure, making them unfavorable to process further as bulk pellets or thin films. To overcome processing challenges with solid-state reaction method, two novel facile synthesis approaches molten salt (flux growth method), and solution combustion are employed to produce submicron-sized LLZO powders at low reaction temperatures (< 1000 °C) in a short time. In the first case, molten salt synthesis method with LiCl-KCl eutectic mixture is employed to produce sub-micron sized Ta-doped LLZO (LLZTO) powders at low temperatures (900 °C, 4 h). In addition, a detailed investigation on effect of sintering medium and sintering additives on the structural, microstructural, chemical, and Li-ion transport behavior of the LLZTO pellets are investigated. Sintered LLZTO pellets prepared using molten salt synthesis route exhibited high Li-ion conductivity up to 0.6 mS cm-1 and high relative density (> 95 %) using Pt-crucible. In the second case, a facile solution-combustion technique using an amide-based fuel source CH6N4O is utilized to produce submicron-sized Al-doped LLZO (Al-LLZO) powders at low reaction temperatures 600-800 °C in a short duration of 4 h. In addition, effect of fuel to oxidizer ratio on phase purity, particle growth size, and formation mechanism of conductive Al-LLZO are reported and discussed. The Al-LLZO pellets sintered at 1100 °C/ 6 h exhibited high Li-ion conductivity up to 0.45 mS cm-1 with relative densities (> 90 %).
ContributorsBadami, Pavan Pramod (Author) / Kannan, Arunachalandar Mada (Thesis advisor) / Chan, Candace (Thesis advisor) / Song, Kenan (Committee member) / Arizona State University (Publisher)
Created2021
Description
The study of acoustic ecology is concerned with the manner in which life interacts with its environment as mediated through sound. As such, a central focus is that of the soundscape: the acoustic environment as perceived by a listener. This dissertation examines the application of several computational tools in the realms of digital signal processing, multimedia information retrieval, and computer music synthesis to the analysis of the soundscape. Namely, these tools include a) an open source software library, Sirens, which can be used for the segmentation of long environmental field recordings into individual sonic events and compare these events in terms of acoustic content, b) a graph-based retrieval system that can use these measures of acoustic similarity and measures of semantic similarity using the lexical database WordNet to perform both text-based retrieval and automatic annotation of environmental sounds, and c) new techniques for the dynamic, realtime parametric morphing of multiple field recordings, informed by the geographic paths along which they were recorded.
ContributorsMechtley, Brandon Michael (Author) / Spanias, Andreas S (Thesis advisor) / Sundaram, Hari (Thesis advisor) / Cook, Perry R. (Committee member) / Li, Baoxin (Committee member) / Arizona State University (Publisher)
Created2013
Description
Sn-based group IV materials such as Ge1-xSnx and Ge1-x-ySixSny alloys have great potential for developing Complementary Metal Oxide Semiconductor (CMOS) compatible devices on Si because of their tunable band structure and lattice constants by controlling Si and/or Sn contents. Growth of Ge1-xSnx binaries through Molecular Beam Epitaxy (MBE) started in the early 1980s, producing Ge1-xSnx epilayers with Sn concentrations varying from 0 to 100%. A Chemical Vapor Deposition (CVD) method was developed in the early 2000s for growing Ge1-xSnx alloys of device quality, by utilizing various chemical precursors. This method dominated the growth of Ge1-xSnx alloys rapidly because of the great crystal quality of Ge1-xSnx achieved. As the first practical ternary alloy completely based on group IV elements, Ge1-x-ySixSny decouples bandgap and lattice constant, becoming a prospective CMOS compatible alloy. At the same time, Ge1-x-ySixSny ternary system could serve as a thermally robust alternative to Ge1-ySny binaries given that it becomes a direct semiconductor at a Sn concentration of 6%-10%. Ge1-x-ySixSny growths by CVD is summarized in this thesis. With the Si/Sn ratio kept at ~3.7, the ternary alloy system is lattice matched to Ge, resulting a tunable direct bandgap of 0.8-1.2 eV. With Sn content higher than Si content, the ternary alloy system could have an indirect-to-direct transition, as observed for Ge1-xSnx binaries. This thesis summarizes the development of Ge1-xSnx and Ge1-x-ySixSny alloys through MBE and CVD in recent decades and introduces an innovative direct injection method for synthesizing Ge1-x-ySixSny ternary alloys with Sn contents varying from 5% to 12% and Si contents kept at 1%-2%. Grown directly on Si (100) substrates in a Gas-phase Molecular Epitaxy (GSME) reactor, both intrinsic and n-type doped Ge1-x-ySixSny with P with thicknesses of 250-760 nm have been achieved by deploying gas precursors Ge4H10, Si4H10, SnD4 and P(SiH3)3 at the unprecedented low growth temperatures of 190-220 °C. Compressive strain is reduced and crystallinity of the Ge1-x-ySixSny epilayer is improved after rapid thermal annealing (RTA) treatments. High Resolution X-ray Diffraction (HR-XRD), Rutherford Backscattering Spectrometry (RBS), cross-sectional Transmission Electron Microscope (XTEM) and Atomic Force Microscope (AFM) have been combined to characterize the structural properties of the Ge1-x-ySixSny samples, indicating good crystallinity and flat surfaces.
ContributorsHu, Ding (Author) / Kouvetakis, John (Thesis advisor) / Menéndez, Jose (Committee member) / Trovitch, Ryan (Committee member) / Arizona State University (Publisher)
Created2019