Matching Items (157)
Description
This dissertation describes a series of four studies on cognitive aging, working memory, and cognitive flexibility in dogs (Canis lupus familiaris) and their wild relatives. In Chapters 2 and 3, I designed assessments for age-related cognitive deficits in pet dogs which can be deployed rapidly using inexpensive and accessible materials. These novel tests can be easily implemented by owners, veterinarians, and clinicians and therefore, may improve care for elderly dogs by aiding in the diagnosis of dementia. In addition, these widely deployable tests may facilitate the use of dementia in pet dogs as a naturally occurring model of Alzheimer’s Disease in humans.In Chapters 4 and 5, I modified one of these tests to demonstrate for the first time that coyotes (Canis latrans) and wolves (Canis lupus lupus) develop age-related deficits in cognitive flexibility. This was an important first step towards differentiating between the genetic and environmental components of dementia in dogs and in turn, humans. Unexpectedly, I also detected cognitive deficits in young, adult dogs and wolves but not coyotes. These finding add to a recent shift in understanding cognitive development in dogs which may improve cognitive aging tests as well as training, care, and use of working and pet dogs. These findings also suggest that the ecology of coyotes may select for flexibility earlier in development.
In Chapter 5, I piloted the use of the same cognitive flexibility test for red and gray foxes so that future studies may test for lifespan changes in the cognition of small-bodied captive canids. More broadly, this paradigm may accommodate physical and behavioral differences between diverse pet and captive animals. In Chapters 4 and 5, I examined which ecological traits drive the evolution of behavioral flexibility and in turn, species resilience. I found that wolves displayed less flexibility than dogs and coyotes suggesting that species which do not rely heavily on unstable resources may be ill-equipped to cope with human habitat modification. Ultimately, this comparative work may help conservation practitioners to identify and protect species that cannot cope with rapid and unnatural environmental change.
ContributorsVan Bourg, Joshua (Author) / Wynne, Clive D (Thesis advisor) / Aktipis, C. Athena (Committee member) / Gilby, Ian C (Committee member) / Young, Julie K (Committee member) / Arizona State University (Publisher)
Created2022
Description
The application of silicon thin films in solar cells has evolved from their use in amorphous silicon solar cells to their use as passivating and carrier-selective contacts in crystalline silicon solar cells. Their use as carrier-selective contacts has enabled crystalline silicon solar cell efficiencies above 26%, just 3% shy of the theoretical efficiency limit. The two cell architectures that have exceeded 26% are the silicon heterojunction and tunnel oxide passivating contact cell. These two cell architectures use two different forms of silicon thin films. In the case of the silicon heterojunction, the crystalline wafer is sandwiched between layers of intrinsic amorphous silicon, which acts as the passivation layer, and doped amorphous silicon, which acts as the carrier-selective layer. On the other hand, the tunnel oxide passivating contact cell uses a thin silicon oxide passivation layer and a doped polycrystalline silicon layer as the carrier-selective layer. Both cell structures have their distinct advantages and disadvantages when it comes to production. The processing of the silicon heterojunction relies on a low thermal budget and leads to high open-circuit voltages, but the cost of high-vacuum processing equipment presents a major hurdle for industrial scale production while the tunnel oxide passivating contact can be easily integrated into current industrial lines, yet it requires a higher thermal budgets and does not produce as high of an open-circuit voltage as the silicon heterojunction. This work focuses on using both forms of silicon thin films applied as passivating and carrier-selective contacts to crystalline silicon thin films.First, a thorough analysis of the series resistivity in silicon heterojunction solar cells is conducted. In particular, variations in the thickness and doping of the individual
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contact layers are performed to reveal their effect on the contact resistivity and in turn the total series resistivity of the cell. Second, a tunnel oxide passivated contact is created using a novel deposition method for the silicon oxide layer. A 21% efficient proof-of-concept device is presented demonstrating the potential of this deposition method. Finally, recommendations to further improve the efficiency of these cells is presented.
ContributorsWeigand, William (Author) / Holman, Zachary (Thesis advisor) / Yu, Zhengshan (Committee member) / Bertoni, Mariana (Committee member) / Tongay, Sefaattin (Committee member) / Arizona State University (Publisher)
Created2023
Description
Metal-Oxide-Semiconductor (MOS) is essential to modern VLSI devices. In the past decades, a wealth of literature has been created to understand the impact of the radiation-induced charges on the devices, i.e., the creation of electron-hole pairs in the oxide layer which is the most sensitive part of MOS structure to the radiation effect. In this work, both MOS and MNOS devices were fabricated at ASU NanoFab to study the total ionizing dose effect using capacitance-voltage (C-V) electrical characterization by observing the direction and amounts of the shift in C-V curves and electron holography observation to directly image the charge buildup at the irradiated oxide film of the oxide-only MOS device.C-V measurements revealed the C-V curves shifted to the left after irradiation (with a positive bias applied) because of the net positive charges trapped at the oxide layer for the oxide-only sample. On the other hand, for nitride/oxide samples with positive biased during irradiation, the C-V curve shifted to the right due to the net negative charges trapped at the oxide layer. It was also observed that the C-V curve has less shift in voltage for MNOS than MOS devices after irradiation due to the less charge buildup after irradiation.
Off-axis electron holography was performed to map the charge distribution across the MOSCAP sample. Compared with both pre-and post-irradiated samples, a larger potential drop at the Si/SiO2 was noticed in post-irradiation samples, which indicates the presence of greater amounts of positive charges that buildup the Si/SiO2 interface after the TID exposure.
TCAD modeling was used to extract the density of charges accumulated near the SiO2/Si and SiO2/ Metal interface by matching the simulation results to the potential data from holography. The increase of near-interface positive charges in post-irradiated samples is consistent with the C-V results.
ContributorsChang, Ching Tao (Author) / Barnaby, Hugh (Thesis advisor) / Holbert, Keith (Committee member) / Tongay, Sefaattin (Committee member) / Arizona State University (Publisher)
Created2023
Description
My thesis, Design of Hierarchically Porous Materials Containing Covalent Organic Frameworks, focuses on testing the validity of incorporating nanoporous organic materials into macroporous scaffolding to improve the functionality of covalent organic frameworks as materials for filtration applications. The macroporous scaffold was based off of a material recently described in literature and the bulk of the experimentation was focused on the effects of the necessary processing for the creation of the macroporous material on the structure of the covalent organic frameworks. The property primarily investigated was the Brunauer-Emmett-Teller surface area, as the applicability of the frameworks is largely determined by their nanoporous surface area.
ContributorsRidenour, Brian (Author) / Jin, Kailong (Thesis director) / Tongay, Sefaattin (Committee member) / Barrett, The Honors College (Contributor) / Materials Science and Engineering Program (Contributor)
Created2023-05
Description
The recent discoveries of 2D van der Waals (vdW) materials have led to the realization of 2D magnetic crystals. Previously debated and thought impossible, transition metal halides (TMH) have given rise to layer dependent magnetism. Using these TMH as a basis, an alloy composing of Fe1-xNixCl2 (where 0 ≤ x ≤ 1) was grown using chemical vapor transport. The intrigue for this alloy composition stems from the interest in spin canting and magnet moment behavior since NiCl2 has in-plane ferromagnetism whereas FeCl2 has out-of-plane ferromagnetism. While in its infancy, this project lays out a foundation to fully develop and characterize this TMH via cationic alloying. To study the magnetic properties of this alloy system, Vibrating Sample Magnetometry was employed extensively to measure the magnetism as a function of temperature as well as applied magnetic field. Future work with use a combination of X-Ray Diffraction, Raman, Scanning Electron Microscopy, and Energy-Dispersive X-Ray Spectroscopy Mapping to verify homogeneous alloying rather than phase separation. Additionally, ellipsometry will be used with Kramer-Kronig relations to extract the dielectric constant from Fe1-xNixCl2. This work lays the foundation for future, fruitful work to prepare this vdW cationic alloy for eventual device applications.
ContributorsPovilus, Blake (Author) / Tongay, Sefaattin (Thesis director) / Yang, Sui (Committee member) / Barrett, The Honors College (Contributor) / Materials Science and Engineering Program (Contributor)
Created2022-05
Description
Vanadium-dioxide-based devices show great switchability in their optical properties due to its dramatic thermochromic phase transition from insulator to metal, but generally have concerns due to its relatively high transition temperature at 68 °C. Doping the vanadium dioxide with tungsten has been shown to reduce its transition temperature at the cost lower optical property differences between its insulating and metallic phases. A recipe is developed through parametric experimentation to fabricate tungsten-doped vanadium dioxide consisting of a novel dual target co-sputtering deposition, a furnace oxidation process, and a post-oxidation annealing process. The transmittance spectra of the resulting films are measured via Fourier-transform infrared spectroscopy at different temperatures to confirm the lowered transition temperature and analyze their thermal-optical hysteresis behavior through the transition temperature range. Afterwards, the optical properties of undoped sputtered vanadium films are modeled and effective medium theory is used to explain the effect of tungsten dopants on the observed transmittance decrease of doped vanadium dioxide. The optical modeling is used to predict the performance of tungsten-doped vanadium dioxide devices, in particular a Fabry-Perot infrared emitter and a nanophotonic infrared transmission filter. Both devices show great promise in their optical properties despite a slight performance decrease from the tungsten doping. These results serve to illustrate the excellent performance of the co-sputtered tungsten-doped vanadium dioxide films.
ContributorsChao, Jeremy (Author) / Wang, Liping (Thesis advisor) / Wang, Robert (Committee member) / Tongay, Sefaattin (Committee member) / Arizona State University (Publisher)
Created2022
Description
Rare-earth tritellurides (RTe3) are two-dimensional materials with unique quantum properties, ideal for investigating quantum phenomena and applications in supercapacitors, spintronics, and twistronics. This dissertation examines the electronic, magnetic, and phononic properties of the RTe3 family, exploring how these can be controlled using chemical pressure, cationic alloying, and external pressure.The impact of chemical pressure on RTe3 phononic properties was investigated through noninvasive micro-Raman spectroscopy, demonstrating the potential of optical measurements for determining charge density wave (CDW) transition temperatures. Cationic alloying studies showed seamless tuning of CDW transition temperatures by modifying lattice constants and revealed complex magnetism in alloyed RTe3 with multiple magnetic transitions.
A comprehensive external pressure study examined the influence of spacing between RTe3 layers on phononic and CDW properties across the RTe3 family. Comparisons between different RTe3 materials showed LaTe3, with the largest thermodynamic equilibrium interlayer spacing (smallest chemical pressure), has the most stable CDW phases at high pressures. Conversely, CDW phases in late RTe3 systems with larger internal chemical pressures were more easily suppressed by applied pressure.
The dissertation also investigated Schottky barrier realignment at RTe3/semiconductor interfaces induced by CDW transitions, revealing changes in Schottky barrier height and ideality factor around the CDW transition temperature. This indicates that chemical potential changes of RTe3 below the CDW transition temperature influence Schottky junction properties, enabling CDW state probing through interface property measurements.
A detailed experimental and theoretical analysis of the oxidation process of RTe3 compounds was performed, which revealed faster degradation in late RTe3 systems. Electronic property changes, like CDW transition temperature and chemical potential, are observed as degradation progresses. Quantum mechanical simulations suggested that degradation primarily results from strong oxidizing reactions with O2 molecules, while humidity (H2O) plays a negligible role unless Te vacancies exist.
Lastly, the dissertation establishes a large-area thin film deposition at relatively low temperatures using a soft sputtering technique. While focused on MoTe2 deposition, this technique may also apply to RTe3 thin film deposition.
Overall, this dissertation expands the understanding of the fundamental properties of RTe3 materials and lays the groundwork for potential device applications.
ContributorsYumigeta, Kentaro (Author) / Tongay, Sefaattin (Thesis advisor) / Ponce, Fernando (Committee member) / Drucker, Jeffery (Committee member) / Erten, Onur (Committee member) / Arizona State University (Publisher)
Created2023
Description
Janus Transition Metal Dichalcogenides (TMDs) are emerging 2D quantum materials with an asymmetric chalcogen configuration that induces an out-of-plane dipole moment. Their synthesis has been a limiting factor in exploring these systems' many-body physics and interactions. This dissertation examines the challenges associated with synthesis and charts the excitonic landscape of Janus crystals by proposing the development of the Selective Epitaxy and Atomic Replacement (SEAR) technique. SEAR utilizes ionized radical precursors to modify TMD monolayers into their Janus counterparts selectively. The synthesis is coupled with optical spectroscopy and monitored in real-time, enabling precise control of reaction kinetics and the structural evolution of Janus TMDs. The results demonstrate the synthesis of Janus TMDs at ambient temperatures, reducing defects and preserving the structural integrity with the hitherto best-reported exciton linewidth emission value, indicating ultra-high optical quality. Cryogenic optical spectroscopy (4K) coupled with a magnetic field on Janus monolayers has allowed the isolation of excitonic transitions and the identification of charged exciton complexes. Further study into macroscopic and microscopic defects reveals that structural asymmetry results in the spontaneous formation of 2D Janus Nanoscrolls from an in-plane strain. The chalcogen arrangement in these structures dictates two types of scrolling dynamics that form Archimedean or inverted C-scrolls. High-resolution scanning transmission electron microscopy of these superlattices shows a preferential orientation of scrolling and formation of Moiré patterns. These materials' thermodynamically favorable defect states are identified and shown to be optically active. The encapsulation of Janus TMDs with hexagonal Boron Nitride (h-BN) has allowed isolation defect transitions. DFT coupled with power-dependent PL spectroscopy at 4K shows the broad defect band to be a convolution of individual defect states with extremely narrow linewidth (2 meV) indicative of a two-state quantum system. The research presents a comprehensive synthesis approach with insights into the structural and morphological stability of 2D Janus layers, establishing a complete structure-property correlation of optical transitions and defect states, broadening the scope for practical applications in quantum information technologies.
ContributorsSayyad, Mohammed Yasir (Author) / Tongay, Sefaattin (Thesis advisor) / Esqueda, Ivan S (Committee member) / Zhuang, Houlong (Committee member) / Arizona State University (Publisher)
Created2024
Description
Innovative project delivery methods and project management systems have advanced the world of construction engineering and management, yet the benefits of their applications remain not wholly accomplished without accompanying them with the suitable methods of implementation. As integrated delivery methods have arisen from the need for faster project delivery with early teams’ involvement, their benefits are not attained unless they are executed by the most qualified contracting firms for the job and administered following collaborative approaches. More holistically, integrated project management systems support meeting project guidelines while enforcing the social role played by individuals and teams in addressing challenges that influence their technical performance. Thus, the author was one of the 41 team members that developed an innovative IPM framework which is the Integrated Project/Program Management Maturity and Environment Total risk Rating known as IP2M METRR that helps them review their project team environment and levels of system maturity. Like the integrated delivery methods, an IPM framework is not expected to solve challenges on its own unless supported with guidance for practitioners to efficiently implement the framework. Thus, in this dissertation the author aims to address the challenges by studying the implementation of innovative methods for integrated delivery and integrated management in large government-owned engineering construction projects. The objective is to guide the implementation of (1) design-build (D-B) and construction manager-general contractor (CM-GC) methods in the contractor procurement phase and post-award contract administration phase; and (2) earned value management system (integrated project management application) through a paradigm shift in its assessment, using the IP2M METRR, and focusing on the novel sociotechnical aspect. The author studied data from 128 government-owned projects with total worth of about $46.7 U.S. billion, 11 experts, and 215 practitioners; and used mixed-methods research and industry engaging research techniques, including remote research charrettes which the author supported its development and testing and reported on in this dissertation.The contributions of this dissertation include: (1) identifying best practices for D-B and CM-GC contractor procurement, (2) developing D-B and CM-GC contract administration tool selection framework, (3) gauging lessons learned on IP2M METRR application, (4) identifying issues and recommendations in IPM application implementation, (5) validating IP2M METRR framework, and (6) developing and testing industry-engaging research approach.
ContributorsSanboskani, Hala (Author) / El Asmar, Mounir (Thesis advisor) / Grau, David (Thesis advisor) / Gibson, Jr., George E. (Committee member) / Bearup, Wylie (Committee member) / Kaloush, Kamil (Committee member) / Arizona State University (Publisher)
Created2024
Description
The residential building sector accounts for more than 26% of the global energy consumption and 17% of global CO2 emissions. Due to the low cost of electricity in Kuwait and increase of population, Kuwaiti electricity consumption tripled during the past 30 years and is expected to increase by 20% by 2027. In this dissertation, a framework is developed to assess energy savings techniques to help policy-makers make educated decisions. The Kuwait residential energy outlook is studied by modeling the baseline energy consumption and the diffusion of energy conservation measures (ECMs) to identify the impacts on household energy consumption and CO2 emissions.
The energy resources and power generation in Kuwait were studied. The characteristics of the residential buildings along with energy codes of practice were investigated and four building archetypes were developed. Moreover, a baseline of end-use electricity consumption and demand was developed. Furthermore, the baseline energy consumption and demand were projected till 2040. It was found that by 2040, energy consumption would double with most of the usage being from AC. While with lighting, there is a negligible increase in consumption due to a projected shift towards more efficient lighting. Peak demand loads are expected to increase by an average growth rate of 2.9% per year. Moreover, the diffusion of different ECMs in the residential sector was modeled through four diffusion scenarios to estimate ECM adoption rates. ECMs’ impact on CO2 emissions and energy consumption of residential buildings in Kuwait was evaluated and the cost of conserved energy (CCE) and annual energy savings for each measure was calculated. AC ECMs exhibited the highest cumulative savings, whereas lighting ECMs showed an immediate energy impact. None of the ECMs in the study were cost effective due to the high subsidy rate (95%), therefore, the impact of ECMs at different subsidy and rebate rates was studied. At 75% subsidized utility price and 40% rebate only on appliances, most of ECMs will be cost effective with high energy savings. Moreover, by imposing charges of $35/ton of CO2, most ECMs will be cost effective.
The energy resources and power generation in Kuwait were studied. The characteristics of the residential buildings along with energy codes of practice were investigated and four building archetypes were developed. Moreover, a baseline of end-use electricity consumption and demand was developed. Furthermore, the baseline energy consumption and demand were projected till 2040. It was found that by 2040, energy consumption would double with most of the usage being from AC. While with lighting, there is a negligible increase in consumption due to a projected shift towards more efficient lighting. Peak demand loads are expected to increase by an average growth rate of 2.9% per year. Moreover, the diffusion of different ECMs in the residential sector was modeled through four diffusion scenarios to estimate ECM adoption rates. ECMs’ impact on CO2 emissions and energy consumption of residential buildings in Kuwait was evaluated and the cost of conserved energy (CCE) and annual energy savings for each measure was calculated. AC ECMs exhibited the highest cumulative savings, whereas lighting ECMs showed an immediate energy impact. None of the ECMs in the study were cost effective due to the high subsidy rate (95%), therefore, the impact of ECMs at different subsidy and rebate rates was studied. At 75% subsidized utility price and 40% rebate only on appliances, most of ECMs will be cost effective with high energy savings. Moreover, by imposing charges of $35/ton of CO2, most ECMs will be cost effective.
ContributorsAlajmi, Turki (Author) / Phelan, Patrick E (Thesis advisor) / Kaloush, Kamil (Committee member) / Huang, Huei-Ping (Committee member) / Wang, Liping (Committee member) / Hajiah, Ali (Committee member) / Arizona State University (Publisher)
Created2019