Matching Items (108)
Description

Studying the so-called ”hidden” phases of quantum materials—phases that do not exist under equilibrium conditions, but can be accessed with light—reveals new insights into the broader field of structural phase transitions. Using terahertz irradiation as well as hard x-ray probes made available by x-ray free electron lasers (XFELs) provides unique

Studying the so-called ”hidden” phases of quantum materials—phases that do not exist under equilibrium conditions, but can be accessed with light—reveals new insights into the broader field of structural phase transitions. Using terahertz irradiation as well as hard x-ray probes made available by x-ray free electron lasers (XFELs) provides unique capabilities to study phonon dispersion in these materials. Here, we study the cubic peak of the quantum paraelectric strontium titanate (SrTiO3, STO) below the 110 K cubic-to-tetragonal tran- sition. Our results reveal a temperature and field strength dependence of the transverse acoustic mode in agreement with previous work on the avoided crossing occurring at finite wavevector, as well as evidence of anharmonic coupling between transverse optical phonons and a fully symmetric A1g phonon. These results elucidate previous optical studies on STO and hold promise for future studies on the hidden metastable phases of quantum materials.

ContributorsStanton, Jade (Author) / Teitelbaum, Samuel (Thesis director) / Smith, David (Committee member) / Barrett, The Honors College (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Department of Physics (Contributor)
Created2023-05
Description

One of the identified health risk areas for human spaceflight is infectious disease, particularly involving environmental microorganisms already found on the International Space Station (ISS). In particular, bacteria belonging to the Burkholderia cepacia complex (Bcc) which can cause human disease in those who are immunocompromised, have been identified in the

One of the identified health risk areas for human spaceflight is infectious disease, particularly involving environmental microorganisms already found on the International Space Station (ISS). In particular, bacteria belonging to the Burkholderia cepacia complex (Bcc) which can cause human disease in those who are immunocompromised, have been identified in the ISS water supply. This present study characterized the effect of spaceflight analog culture conditions on Bcc to certain physiological stresses (acid and thermal as well as intracellular survival in U927 human macrophage cells). The NASA-designed Rotating Wall Vessel (RWV) bioreactor was used as the spaceflight analogue culture system in these studies to grow Bcc bacterial cells under Low Shear Modeled Microgravity (LSMMG) conditions. Results show that LSMMG culture increased the resistance of Bcc to both acid and thermal stressors, but did not alter phagocytic uptake in 2-D monolayers of human monocytes.

ContributorsVu, Christian-Alexander (Author) / Nickerson, Cheryl (Thesis director) / Barrila, Jennifer (Committee member) / Ott, Mark (Committee member) / Barrett, The Honors College (Contributor) / Harrington Bioengineering Program (Contributor)
Created2023-05
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Description
Hydrogen is considered one of the most potential fuels due to its highest gravimetric energy density with no pollutant emission during the energy cycle. Among several techniques for hydrogen generation, the promising photoelectrochemical water oxidation is considered a long-term solar pathway by splitting water. The system contains a photoanode and

Hydrogen is considered one of the most potential fuels due to its highest gravimetric energy density with no pollutant emission during the energy cycle. Among several techniques for hydrogen generation, the promising photoelectrochemical water oxidation is considered a long-term solar pathway by splitting water. The system contains a photoanode and a cathode immersed in an aqueous electrolyte where charge separation takes place in the bulk of the semiconducting material on light absorption, leading to water oxidation/reduction at the surface of the photoelectrodes/cathode. It is imperative to develop materials that demonstrate high light absorption in the wide spectrum along with photoelectrochemical stability. N-type Monoclinic scheelite bismuth vanadate (BiVO4) is selected due to its incredible light absorption capabilities, direct bandgap (Eg ∼ 2.4-2.5 eV) and relatively better photoelectrochemical stability. However, BiVO4 encounters huge electron-hole recombination due to smaller diffusion lengths and positive conduction bands that cause slow charge dynamics and sluggish water oxidation kinetics. In order to improve the illustrated drawbacks, four strategies were discussed. Chapter 1 describe the fundamental understanding of photoelectrochemical cell and BiVO4. Chapter 2 illustrates details of the experimental procedure and state-of-the-art material characterization. Chapter 3 provide the impact of alkali metal placement in the crystal structure of BiVO4 systematically that exhibited ~20 times more performance than intrinsic BiVO4, almost complete bulk charge separation and enhancement in the diffusion length. Detailed characterization determined that the alkali metal getting placed in the interstitial void of BiVO4 lattice and multiple interbands formation enhanced the charge dynamics. Chapter 4 contains stoichiometric doping of Y3+ or Er3+ or Yb3+ at the Bi3+ site, leading to an extended absorption region, whereas non-stoichiometric W6+ doping at the V5+ site minimizes defects and increased charge carriers. To further enhance the performance, type-II heterojunction with WO3 along p-n junction with Fe:NiO enhance light absorption and charge dynamics close to the theoretical performance. Chapter 5 provides a comprehensive study of a uniquely developed sulfur modified Bi2O3 interface layer to facilitate charge dynamics and carrier lifetime improvement by effectively passivating the WO3/BiVO4 heterojunction interface. Finally, chapter 6 summarized the major findings, conclusion and outlook in developing BiVO4 as an efficient photoanode material.
ContributorsPrasad, Umesh (Author) / Kannan, Arunachala Mada (Thesis advisor) / Azeredo, Bruno (Committee member) / Chan, Candace (Committee member) / Segura, Sergio Garcia (Committee member) / Arizona State University (Publisher)
Created2021
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Description
In this dissertation, the surface interactions of fluorine were studied during atomic layer deposition (ALD) and atomic layer etching (ALE) of wide band gap materials. To enable this research two high vacuum reactors were designed and constructed for thermal and plasma enhanced ALD and ALE, and they were equipped for

In this dissertation, the surface interactions of fluorine were studied during atomic layer deposition (ALD) and atomic layer etching (ALE) of wide band gap materials. To enable this research two high vacuum reactors were designed and constructed for thermal and plasma enhanced ALD and ALE, and they were equipped for in-situ process monitoring. Fluorine surface interactions were first studied in a comparison of thermal and plasma enhanced ALD (TALD and PEALD) of AlF3 thin films prepared using hydrogen fluoride (HF), trimethylaluminum (TMA), and H2-plasma. The ALD AlF3 films were compared ¬in-situ using ellipsometry and X-ray photoelectron spectroscopy (XPS). Ellipsometry showed a growth rate of 1.1 Å/ cycle and 0.7 Å/ cycle, at 100°C, for the TALD and PEALD AlF3 processes, respectively. XPS indicated the presence of Al-rich clusters within the PEALD film. The formation of the Al-rich clusters is thought to originate during the H2-plasma step of the PEALD process. The Al-rich clusters were not detected in the TALD AlF3 films. This study provided valuable insight on the role of fluorine in an ALD process. Reactive ion etching is a common dry chemical etch process for fabricating GaN devices. However, the use of ions can induce various defects, which can degrade device performance. The development of low-damage post etch processes are essential for mitigating plasma induced damage. As such, two multistep ALE methods were implemented for GaN based on oxidation, fluorination, and ligand exchange. First, GaN surfaces were oxidized using either water vapor or O2-plasma exposures to produce a thin oxide layer. The oxide layer was addressed using alternating exposures of HF and TMG, which etch Ga2O3 films. Each ALE process was characterized using in-situ using ellipsometry and XPS and ex-situ transmission electron microscopy (TEM). XPS indicated F and O impurities remained on the etched surfaces. Ellipsometry and TEM showed a slight reduction in thickness. The very low ALE rate was interpreted as the inability of the Ga2O3 ALE process to fluorinate the ordered surface oxide on GaN (0001). Overall, these results indicate HF is effective for the ALD of metal fluorides and the ALE of metal oxides.
ContributorsMessina, Daniel C (Author) / Nemanich, Robert J (Thesis advisor) / Goodnick, Stephen (Committee member) / Ponce, Fernando A (Committee member) / Smith, David (Committee member) / Arizona State University (Publisher)
Created2021
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Description
The silicon-based solar cell has been extensively deployed in photovoltaic industry and plays an important role in renewable energy industries. A more energy-efficient, environment-harmless and eco-friendly silicon production technique is required for price-competitive solar energy harvesting. Silicon electrorefining in molten salt is promising for the ultrapure solar-grade Si production. To

The silicon-based solar cell has been extensively deployed in photovoltaic industry and plays an important role in renewable energy industries. A more energy-efficient, environment-harmless and eco-friendly silicon production technique is required for price-competitive solar energy harvesting. Silicon electrorefining in molten salt is promising for the ultrapure solar-grade Si production. To avoid using highly corrosive fluoride salt, CaCl2-based salt is widely employed for silicon electroreduction. For Si electroreduction in CaCl2-based salt, CaO is usually added to enhance the solubility of SiO2. However, the existence of oxygen in molten salt could result in system corrosion, anode passivation and the co-deposition of secondary phases such as CaSiO3 and SiO2 at the cathode. This research focuses on the development of reusable oxygen-free CaCl2-based molten salt for solar-grade silicon electrorefining. A new multi-potential electropurification process has been proposed and proven to be more effective in impurities removal. The as-received salt and the salt after electrorefining have been electropurified. The inductively-coupled plasma mass spectrometry and cyclic voltammetry have been utilized to determine the impurities removal of electropurification. The salt after silicon electrorefining has been regenerated to its original purity level before by the multi-potential electropurification process, demonstrating the feasibility of a reusable salt by electropurification. In an oxygen-free CaCl2-based salt without silicon precursor, the silicon dissolved from the silicon anode can be successfully deposited at the cathode. The silicon anode has been operated for more than 50 hours without passivation in the oxygen-free system. Silicon ions start to be deposited after 0.17 g of silicon has been dissolved into the salt from the silicon anode. A 180 µm deposit with a silver-luster surface was obtained at the cathode. The main impurities in the silicon anode such as aluminum, iron and titanium were not found in the silicon deposits. No oxygen-containing secondary phases are detected in the silicon deposits. These results confirm the feasibility of silicon electrorefining in the oxygen-free CaCl2-based salt.
ContributorsTseng, Mao-Feng (Author) / Tao, Meng (Thesis advisor) / Kannan, Arunachala Mada (Committee member) / Mu, Linqin (Committee member) / Goryll, Michael (Committee member) / Arizona State University (Publisher)
Created2023
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Description

The current Solid-State Electrolyte (SSE) used in Li-ion batteries are limited by their current production methods (i.e., die-pressing; tape casting), planar geometries and random porosities. This constrains their use for mass production in manufacturing plants. 3D-printing of SSEs, however, is a new, highly-researched method that shows promise in expanding beyond

The current Solid-State Electrolyte (SSE) used in Li-ion batteries are limited by their current production methods (i.e., die-pressing; tape casting), planar geometries and random porosities. This constrains their use for mass production in manufacturing plants. 3D-printing of SSEs, however, is a new, highly-researched method that shows promise in expanding beyond the laboratory to more large-scale industrial production as rapid prototyping takes place. Indeed, laboratory studies to date suggest that SSE technology is safer than current production methods and provides a safe high energy solid-state battery. For SSE technology to become a reality though, it must be scalable and financially feasible. Therefore, this thesis aids to bridge the gap between laboratory studies and commercialization by examining the financial feasibility of adopting this technology for a hypothetical battery manufacturing plant. In doing this, I develop a model of the incremental net cash flows, and subsequently the Net Present Value (NPV), from such an enterprise. If the present value of future cash flows from the enterprise are anticipated to be greater than the investment costs, the NPV is positive and the investment in this new technology would be considered instantaneously value enhancing and thus financially feasible. However, future cash flows are highly uncertain, which brings into question financial feasibility in a risky environment. To address the riskiness of future cash flows, I model three risk factors: the cost of raw materials, the potential growth in battery sales, as well as the potential mark-up (profit margin) of the SSE enterprise. Using Monte Carlo simulation (MCS) I model the incremental cash flows considering these risk factors and derive probabilistic assessments of NPV. My analysis suggests that despite the uncertainty caused by the volatility of raw metal prices, assumptions on price mark-up, and uncertain market demand for Li-ion batteries, there is a high probability of an investment in SSE batteries being financially feasible. Future research should consider the value of real options (optionality embedded in tangible investments) as traditional NPV analysis may underestimate the potential value of an investment in the presence of uncertain cash flows, especially if management has the ability to respond to the uncertainty.

ContributorsFonseca, Nathan (Author) / Manfredo, Mark (Thesis director) / Kannan, Arunachala Mada (Committee member) / Barrett, The Honors College (Contributor) / Engineering Programs (Contributor)
Created2022-05
ContributorsForgey, Sydney (Performer) / Hickman, Miriam, 1955- (Performer) / Smith, David (Performer) / ASU Library. Music Library (Publisher)
Created2020-03-25
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Description
A piezoelectric transducer, comprised of electroded and active pad PZT layer atop a backing PZT layer and protected with an acoustic matching layer, and operating under a pulse-echo technique for longitudinal ultrasonic imaging, acts as both source and detector.

Ultrasonic transducer stacks (modules), which had failed or passed during pulse-echo

A piezoelectric transducer, comprised of electroded and active pad PZT layer atop a backing PZT layer and protected with an acoustic matching layer, and operating under a pulse-echo technique for longitudinal ultrasonic imaging, acts as both source and detector.

Ultrasonic transducer stacks (modules), which had failed or passed during pulse-echo sensitivity testing, were received from Consortium X. With limited background information on these stacks, the central theme was to determine the origin(s) of failure via the use of thermal and physicochemical characterization techniques.

The optical and scanning electron microscopy revealed that contact electrode layers are discontinuous in all samples, while delaminations between electrodes and pad layer were observed in failed samples. The X-ray diffraction data on the pad PZT revealed an overall c/a ratio of 1.022 ratio and morphotropic boundary composition, with significant variations of the Zr to Ti ratio within a sample and between samples. Electron probe microanalysis confirmed that the overall Zr to Ti ratio of the pad PZT was 52/48, and higher amounts of excess PbO in failed samples, whereas, inductively coupled plasma mass spectrometry revealed the presence of Mn, Al, and Sb (dopants) and presence of Cu (sintering aid) in in this hard (pad) PZT. Additionally, three exothermic peaks during thermal analysis was indicative of incomplete calcination of pad PZT. Moreover, transmission electron microscopy and scanning transmission electron microscopy revealed the presence of parylene at the Ag-pad PZT interface and within the pores of pad PZT (in failed samples subjected to electric fields). This further dilutes the electrical, mechanical, and electromechanical properties of the pad PZT, which in turn detrimentally influences the pulse echo sensitivity.
ContributorsPeri, Prudhvi Ram (Author) / Dey, Sandwip (Thesis advisor) / Smith, David (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2018
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Description
Computer assisted language learning (CALL) has become increasingly common as a means of helping learners develop essential skills in a second or foreign language. However, while many CALL programs claim to be based on principles of second language acquisition (SLA) theory and research, evaluation of design and learning outcomes at

Computer assisted language learning (CALL) has become increasingly common as a means of helping learners develop essential skills in a second or foreign language. However, while many CALL programs claim to be based on principles of second language acquisition (SLA) theory and research, evaluation of design and learning outcomes at the level of individual CALL exercises is lacking in the existing literature. The following proposed study will explore the design of computer-based vocabulary matching exercises using both written text and images and the effects of various design manipulations on learning outcomes. The study will use eye-tracking to investigate what users attend to on screen as they work through a series of exercises with different configurations of written words and images. It will ask whether manipulation of text and image features and combinations can have an effect on learners’ attention to the various elements, and if so, whether differences in levels of attention results in higher or lower scores for measures of learning. Specifically, eye-tracking data will be compared to post-test scores for recall and recognition of target vocabulary items to look for a correlation between levels of attention to written forms in-task and post-test gains in scores for vocabulary learning.
ContributorsPatchin, Colleen (Author) / Smith, David (Thesis advisor) / Ross, Andrew (Committee member) / James, Mark (Committee member) / Arizona State University (Publisher)
Created2019
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Description
Despite the safe and effective use of attenuated vaccines for over fifty years, measles virus (MV) remains an insidious threat to global health. Problematically, infants less than one year of age, who are the most prone to severe infection and death by measles, cannot be immunized using current MV vaccines.

Despite the safe and effective use of attenuated vaccines for over fifty years, measles virus (MV) remains an insidious threat to global health. Problematically, infants less than one year of age, who are the most prone to severe infection and death by measles, cannot be immunized using current MV vaccines. For this dissertation, I generated and performed preclinical evaluation of two novel MV vaccine candidates. Based on data from clinical trials that showed increasing the dosage of current MV vaccines improved antibody responses in six-month-old recipients, I hypothesized that increasing the relevant antigenic stimulus of a standard titer dose would allow safe and effective immunization at a younger age. I generated two modified MVs with increased expression of the hemagglutinin (H) protein, the most important viral antigen for inducing protective neutralizing immunity, in the background of a current vaccine-equivalent. One virus, MVvac2-H2, expressed higher levels of full-length H, resulting in a three-fold increase in H incorporation into virions, while the second, MVvac2-Hsol, expressed and secreted truncated, soluble H protein to its extracellular environment. The alteration to the virion envelope of MVvac2-H2 conferred upon that virus a measurable resistance to in vitro neutralization. In initial screening in adult mouse models of vaccination, both modified MVs proved more immunogenic than their parental strain in outbred mice, while MVvac2-H2 additionally proved more immunogenic in the gold standard MV-susceptible mouse model. Remarkably, MVvac2-H2 better induced protective immunity in the presence of low levels of artificially introduced passive immunity that mimic the passive maternal immunity that currently limits vaccination of young infants, and that strongly inhibited responses to the current vaccine-equivalent. Finally, I developed a more physiological infant-like mouse model for MV vaccine testing, in which MV-susceptible dams vaccinated with the current vaccine-equivalent transfer passive immunity to their pups. This model will allow additional preclinical evaluation of the performance of MVvac2-H2 in pups of immune dams. Altogether, in this dissertation I identify a promising candidate, MVvac2-H2, for a next generation measles vaccine.
ContributorsJulik, Emily (Author) / Reyes del Valle, Jorge (Thesis advisor) / Chang, Yung (Committee member) / Blattman, Joseph (Committee member) / Hogue, Brenda (Committee member) / Nickerson, Cheryl (Committee member) / Arizona State University (Publisher)
Created2016