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Description
Most hardware today is based on von Neumann architecture separating memory from logic. Valuable processing time is lost in shuttling information back and forth between the two units, a problem called von Neumann bottleneck. As transistors are scaled further down, this bottleneck will make it harder to deliver performance in computing power. Adding to this is the increasing complexity of artificial intelligence logic. Thus, there is a need for a faster and more efficient method of computing. Neuromorphic systems deliver this by emulating the massively parallel and fault-tolerant computing capabilities of the human brain where the action potential is triggered by multiple inputs at once (spatial) or an input that builds up over time (temporal). Highly scalable memristors are key in these systems- they can maintain their internal resistive state based on previous current/voltage values thus mimicking the way the strength of two synapses in the brain can vary. The brain-inspired algorithms are implemented by vector matrix multiplications (VMMs) to provide neuronal outputs. High-density conductive bridging random access memory (CBRAM) crossbar arrays (CBAs) can perform VMMs parallelly with ultra-low energy.This research explores a simple planarization technique that could be potentially extended to integrate front-end-of-line (FEOL) processing of complementary metal oxide semiconductor (CMOS) circuitry with back-end-of-line (BEOL) processing of CBRAM CBAs for one-transistor one-resistor (1T1R) Neuromorphic CMOS chips where the transistor is part of the CMOS circuitry and the CBRAM forms the resistor. It is a photoresist (PR) and spin-on glass (SOG) based planarization recipe to planarize CBRAM electrode patterns on a silicon substrate. In this research, however, the planarization is only applied to mechanical grade (MG) silicon wafers without any CMOS layers on them. The planarization achieved was of a very high order (few tens of nanometers). Additionally, the recipe is cost-effective, provides good quality films and simple as only two types of process technologies are involved- lithography and dry etching.
Subsequent processing would involve depositing the CBRAM layers onto the planarized electrodes to form the resistor. Finally, the entire process flow is to be replicated onto wafers with CMOS layers to form the 1T1R circuit.
ContributorsBiswas, Prabaha (Author) / Barnaby, Hugh (Thesis advisor) / Kozicki, Michael (Committee member) / Velo, Yago Gonzalez (Committee member) / Arizona State University (Publisher)
Created2021
Description
Realization of efficient, high-bandgap photovoltaic cells produced using economically viable methods is a technological advance that could change the way we generate and use energy, and thereby accelerate the development of human civilization. There is a need to engineer a semiconductor material for solar cells, particularly multijunction cells, that has high (1.6-2.0 eV) bandgap, has relatively inactive defects, is thermodynamically stable under normal operating conditions with the potential for cost-effective thin-film growth in mass production.This work focuses on a material system made of gallium, indium, and phosphorus – the ternary semiconductor GaInP. GaInP based photovoltaic cells in single-crystal form have demonstrated excellent power conversion efficiency, however, growth of single-crystal GaInP is prohibitively expensive. While growth of polycrystalline GaInP is expected to lower production costs, polycrystalline GaInP is also expected to have a high density of electronically active defects, about which little is reported in scientific literature. This work presents the first study of synthesis, and structural and optoelectronic characterization of polycrystalline GaInP thin films.
In addition, this work models the best performance of polycrystalline solar cells achievable with a given grain size with grain-boundary/surface recombination velocity as a variable parameter. The effects of defect characteristics at the surface and layer properties such as doping and thickness on interface recombination velocity are also modeled.
Recombination velocities at the free surface of single-crystal GaInP and after deposition of various dielectric layers on GaInP are determined experimentally using time-resolved photoluminescence decay measurements. In addition, experimental values of bulk lifetime and surface recombination velocity in well-passivated single crystal AlInP-GaInP based double heterostructures are also measured for comparison to polycrystalline material systems.
A novel passivation method – aluminum-assisted post-deposition treatment or Al-PDT – was developed which shows promise as a general passivation and material improvement technique for polycrystalline thin films. In the GaInP system, this aluminum post-deposition treatment has demonstrated improvement in the minority carrier lifetime to 44 ns at 80 K. During development of the passivation process, aluminum diffusivity in GaInP was measured using TEM-EDS line scans. Introduction, development, and refinement of this novel passivation mechanism in polycrystalline GaInP could initiate the development of a new family of passivation treatments, potentially improving the optoelectronic response of other polycrystalline compound semiconductors as well.
ContributorsChikhalkar, Abhinav (Author) / King, Richard R (Thesis advisor) / Honsberg, Christiana (Committee member) / Newman, Nathan (Committee member) / Tongay, Sefaattin (Committee member) / Arizona State University (Publisher)
Created2021
Description
Corrosion is one of the key failure modes for stainless steel (SS) piping assets handling water resources managed by utility companies. During downtime, the costs start to incur as the field engineer procures its replacement parts. The parts may or may not be in stock depending on how old, complex, and common the part model is. As a result, water utility companies and its resilience to operate amid part failure are a strong function of the supply chain for replacement piping. Metal additive manufacturing (AM) has been widely recognized for its ability to (a) deliver small production scales, (b) address complex part geometries, (c) offer large elemental metal and alloy selections, (d) provide superior material properties. The key motive is to harvest the short lead time of metal AM to explore its use for replacement parts for legacy piping assets in utility-scale water management facilities. In this paper, the goal was to demonstrate 3D printing of stainless steel (SS) 316L parts using selective laser melting (SLM) technology. The corrosion resistance of 3D printed SS 316L was investigated using (a) Chronoamperometry (b) Cyclic Potentiodynamic Polarization (CPP) and Electrochemical Impedance Spectroscopy (EIS) and its improved resistance from wrought (conventional) part was also studied. Then the weldability of 3D printed SS 316L to wrought SS 316L was illustrated and finally, the mechanical strength of the weld and the effect of corrosion on weld strength was investigated using uniaxial tensile testing. The results show that 3D printed part compared to the wrought part has a) lower mass loss before and after corrosion, (b) higher pitting potential, and (c) higher charge transfer resistance. The tensile testing of welded dog bone specimens indicates that the 3D printed parts despite being less ductile were observed to have higher weld strength compared to the wrought part. On this basis, metal AM holds great value to be explored further for replacement piping parts owing to their better corrosion resistance and mechanical performance.
ContributorsSampath, Venkata Krishnan (Author) / Azeredo, Bruno (Thesis advisor) / Torres, Cesar (Committee member) / Mu, Bin (Committee member) / Arizona State University (Publisher)
Created2021
Description
Anecdotally, native Mandarin speakers have difficulty distinguishing between the “s” (as in sink) and the “th” (as in think) sounds as well as between the “a” (as in dad) and “ea” (as in dead) sounds. Here, 29 native English speakers, 52 native Mandarin speakers who live in China, and 34 native Mandarin speakers who have been living in an English language dominant environment were recruited to serve as participants. To assess the phoneme contrasts that may occur in native Mandarin speakers in China, and possible improvement in native Mandarin speakers living in an English environment, relative to Native English speakers living in America, a phoneme discrimination test was administered, three paired phonemes were used in the current study: /b/ paired with /p/ as a control pair, /æ/ paired with /ɛ/, and /θ/ paired with /s/. The results showed that native English speakers have significantly higher accuracy rates for the three paired phoneme discrimination tasks than the native Mandarin speakers who live in China. But there was no significant difference between the native English speakers and native Mandarin speakers who have lived in an English environment on the phonemes or words discriminations tasks.
ContributorsChen, Hao (Author) / Nanez, Jose (Thesis advisor) / Horne, Zachary (Thesis advisor) / Holloway, Steven (Committee member) / Arizona State University (Publisher)
Created2021
Description
This study aimed to develop a measurement model for executive function (EF) in middle childhood for a low-income Mexican American sample and to elucidate dynamic change processes among measurable developmental correlates of EF during infancy and early toddlerhood as predictors of later higher-order EF abilities. Drawing from developmental theory and a model of neurovisceral integration, surges in neurocognitive regulatory abilities may be supported by both previous and concurrent changes in physiological functioning and engagement in reciprocal social relationships. Utilizing recent methodological innovations, the current study moved beyond traditional growth models to evaluate possible points of attenuation and acceleration in dyadic reciprocity and vagal functioning over time as well as dynamic associations between these unfolding developmental processes. Data were collected from 322 low-income Mexican American children in the home at 24 weeks and in a laboratory space at ages 1, 1.5, 2, 3, and 6 years. A parent-report measure of executive function also was collected over the phone between child age 7.5 and 9 years. Results suggested that, in this sample, EF was best modeled at child age 6 years as a unidimensional construct. Findings also supported the importance of earlier dyadic reciprocity for later EF, but there was a lack of evidence supporting the theorized link between EF and earlier vagal functioning and codevelopment of vagal functioning and dyadic reciprocity. This study highlights the importance of including dyadic measures of parent-child contingencies in studies of EF development and, from a clinical perspective, the potential use of relationship-based, dyadic intervention and prevention models to support crucial development of EF skills central to everyday adaptive functioning.
ContributorsWinstone, Laura (Author) / Luecken, Linda J (Thesis advisor) / Spinrad, Tracy (Committee member) / O'Rourke, Holly (Committee member) / Friedman, Lauren (Committee member) / Arizona State University (Publisher)
Created2022
Description
In the legal system, the prediction of a person’s risk of committing a crime has mostly been based on expert judgment. However, newer techniques that employ machine learning (ML)—a type of artificial intelligence—are being implemented throughout the justice system. Yet, there is a lack of research on how the public perceives and uses machine learning risk assessments in legal settings. In two mock-trial vignette studies, the perception of ML-based risk assessments versus more traditional methods was assessed. Study 1 was a 2 (severity of crime: low, high) x 2 (risk assessment type: expert, machine learning) x 2 (risk outcome: low, high) between-subjects design. Participants expressed ethical concerns and discouraged the use of machine learning risk assessments in sentencing decisions, but punishment recommendations were not affected. Study 2 was a within-subjects design where participants were randomly assigned read through one of three crime scenarios (violent, white-collar, sex offense) and one of three risk assessment techniques (expert, checklist, machine learning). Consistent with Study 1, participants had ethical concerns and disagreed with the use of machine learning risk assessments in bail decisions, yet their own decisions and recommendations did not reflect these concerns. Overall, laypeople express skepticism toward these new methods, but do not appear to differentially rely on ML-based versus traditional risk assessments in their own judgments.
ContributorsFine, Anna (Author) / Schweitzer, Nicholas (Thesis advisor) / Salerno, Jessica (Committee member) / Smalarz, Laura (Committee member) / Arizona State University (Publisher)
Created2021
Description
Concussion, or mild traumatic brain injury (mTBI), is a frequent cause of brain damage among youth and, therefore, represents a major public health problem. While most youth recover from concussion within 2 to 4 weeks, some concussed children and adolescents endure prolonged symptoms, along with mood disturbance sequelae for months. Few studies have assessed mood disturbance and concussion in pediatric populations. Additional research is necessary to understand pediatric concussion recovery and mood disturbance better, to guide early intervention efforts, and to improve pediatric concussion care. The purpose of this study was to examine how symptoms of mood disturbance (i.e., anxiety, depression, anger) and somatization relate to the odds of concussion recovery in male and female youth 12 to 17 years of age, who presented for neuropsychological evaluation after head injury. Significantly fewer females were deemed recovered at initial neuropsychological evaluation compared to males. Bivariate analyses of mood disturbance and somatization predictors revealed significant group differences in symptom burden between those determined recovered from concussion and those who had not recovered. Logistic regressions of each mood disturbance variable and somatization on concussion recovery suggested a modest decline in the odds of recovery as symptoms of mood disturbance or somatization increase. A multivariable logistic regression model of mood disturbance predictors, somatization, gender, and age was significant and explained over a quarter of the variance in concussion recovery; however, after a backward variable selection procedure, only depression and somatization symptoms were significant in the final model and accounted for a modest decline in the odds of concussion recovery at initial evaluation. Results replicate and extend research findings in pediatric concussion.
ContributorsBarros, Kathleen (Author) / Kinnier, Richard (Thesis advisor) / Kurpius, Sharon (Committee member) / Lavoie, Michael (Committee member) / Arizona State University (Publisher)
Created2021
Description
The objective of this research was to develop Aluminophosphate-five (AlPO4-5, AFI) zeolite adsorbents for efficient oxygen removal from a process stream to support an on-going Department of Energy (DOE) project on solar energy storage. A molecular simulation study predicted that substituted AlPO4-5 zeolite can adsorb O2 through a weak chemical bond at ambient temperature. Substituted AlPO4-5 zeolite was successfully synthesized via hydrothermal crystallization by following carefully designed procedures to tailor the zeolite for efficient O2 adsorption. Synthesized AlPO4-5 in this work included Sn/AlPO-5, Mo/AlPO-5, Pd/AlPO-5, Si/AlPO-5, Mn/AlPO-5, Ce/AlPO-5, Fe/AlPO-5, CuCe/AlPO-5, and MnSnSi/AlPO-5. While not all zeolite samples synthesized were fully characterized, selected zeolite samples were characterized by powder x-ray diffraction (XRD) for crystal structure confirmation and phase identification, and nitrogen adsorption for their pore textural properties. The Brunauer-Emmett-Teller (BET) specific surface area and pore size distribution were between 172 m2 /g - 306 m2 /g and 6Å - 9Å, respectively, for most of the zeolites synthesized. Samples of great interest to this project such as Sn/AlPO-5, Mo/AlPO-5 and MnSnSi/AlPO-5 were also characterized using x-ray photoelectron spectroscopy (XPS) and energy-dispersive x-ray spectroscopy (EDS) for elemental analysis, scanning electron microscopy (SEM) for morphology and particle size estimation, and electron paramagnetic resonance (EPR) for nature of adsorbed oxygen. Oxygen and nitrogen adsorption experiments were carried out in a 3-Flex adsorption apparatus (Micrometrics) at various temperatures (primarily at 25℃) to determine the adsorption properties of these zeolite samples as potential adsorbents for oxygen/nitrogen separation. Experiments showed that some of the zeolite samples adsorb little-to-no oxygen and nitrogen at 25℃, while other zeolites such as Sn/AlPO-5, Mo/AlPO-5, and MnSnSi/AlPO-5 adsorb decent but inconsistent amounts of oxygen with the highest observed values of about 0.47 mmol/ g, 0.56 mmol/g, and 0.84 mmol/ g respectively. The inconsistency in adsorption is currently attributed to non-uniform doping of the zeolites, and these findings validate that some substituted AlPO4-5 zeolites are promising adsorbents. However, more investigations are needed to verify the causes of this inconsistency to develop a successful AlPO4-5 zeolite-based adsorbent for oxygen/nitrogen separation.
ContributorsBuyinza, Allan Smith (Author) / Deng, Shuguang (Thesis advisor) / Varman, Arul M (Committee member) / Jin, Kailong (Committee member) / Arizona State University (Publisher)
Created2021
Description
The prevalence of autonomous technology is advancing at a rapid rate and is becoming more sophisticated. As this technology becomes more advanced, humans and autonomy may work together as teammates in various settings. A crucial component of teaming is trust, but to date, researchers are limited in assessing trust calibration dynamically in human-autonomy teams. Traditional methods of measuring trust (e.g., Likert scale questionnaires) capture trust after the fact or at a specific time. However, trust fluctuates, and determining what causes this might give machine designers insight into how machines can be improved upon so that operator’s trust towards the machines is more properly calibrated. This thesis aimed to assess the validity of an interaction-based metric of trust: anticipatory pushing of information. Anticipatory pushing of information refers to teammate A anticipating the needs of teammate B and pushing that information to teammate B. It was hypothesized there would be a positive relationship between the frequency of anticipatory pushing and self-reported trust scores. To test this hypothesis, text chat data and self-reported trust scores were analyzed in a previously conducted study in two different sessions (routine and degraded). Findings indicate that the anticipatory pushing of information and the self-reported trust scores between the human-human pairs in the degraded sessions were higher than the routine sessions. In degraded sessions, the anticipatory pushing of information between the human-human pairs was associated with human-human trust.
ContributorsBhatti, Shawaiz (Author) / Cooke, Nancy (Thesis advisor) / Chiou, Erin K (Committee member) / Gutzwiller, Robert (Committee member) / Arizona State University (Publisher)
Created2021
Description
Individuals with psychogenic non-epileptic seizures (PNES) show signs of emotion-related dysfunction and disrupted interpersonal relationships. Affectionate touch is an important form of non-verbal communication in relationships that may foster emotion regulation and emotional awareness. The present online survey study included 62 individuals with PNES and 80 seizure-free trauma-exposed controls high (n=40) or low (n=40) in overall symptoms of psychopathology. As hypothesized, PNES individuals reported experiencing less frequent affectionate touch and less interoceptive awareness than either control group. They also reported more somatic symptoms, more emotion regulation difficulties, and less positive emotion than the low psychopathology group. Unexpectedly, there were no group differences in emotional awareness difficulties, nor in initiation of affectionate touch. Across participants, lower interoceptive awareness was associated with lower affectionate touch frequency, indicating that if one has difficulty understanding and being aware of their own body, affectionate touch sensations may not necessarily be understood as pleasant and may be minimized or avoided. Emotional awareness difficulties surprisingly were associated with greater affectionate touch frequency among PNES (versus the expected pattern of awareness difficulties associated with less affectionate touch, as found among controls), suggesting affectionate touch may be used as an attempt to try and understand one’s own feelings, or to compensate for, or even mask a lack of understanding. Findings indicate a distinct difference in physical affection frequency and interoceptive awareness among PNES individuals even when matched to a group similar in psychiatric distress/psychopathology. These findings offer insight into the relationships between interoceptive awareness, affectionate touch, and emotion regulation more broadly.
ContributorsVillarreal, Lucia (Author) / Roberts, Nicole A (Thesis advisor) / Burleson, Mary H (Committee member) / Duran, Nicholas (Committee member) / Arizona State University (Publisher)
Created2021