Matching Items (183)
Description
Interdigitated back contact (IBC) solar cells have achieved the highest single junction silicon wafer-based solar cell power conversion efficiencies reported to date. This thesis is about the fabrication of a high-efficiency silicon heterojunction IBC solar cell for potential use as the bottom cell for a 3-terminal lattice-matched dilute-nitride Ga (In)NP(As)/Si monolithic tandem solar cell. An effective fabrication process has been developed and the process challenges related to open circuit voltage (Voc), series resistance (Rs), and fill factor (FF) are experimentally analyzed. While wet etching, the sample lost the initial passivation, and by changing the etchant solution and passivation process, the voltage at maximum power recovered to an initial value of over 710 mV before metallization. The factors reducing the series resistance loss in IBC cells were also studied. One of these factors was the Indium Tin Oxide (ITO) sputtering parameters, which impact the conductivity of the ITO layer and transport across the a-Si:H/ITO interface. For the standard recipe, the chamber pressure was 3.5 mTorr with no oxygen partial pressure, and the thickness of the ITO layer in contact with the a-Si:H layers, was optimized to 150 nm. The patterning method for the metal contacts and final annealing also change the contact resistance of the base and emitter stack layers. The final annealing step is necessary to recover the sputtering damage; however, the higher the annealing time the higher the final IBC series resistance. The best efficiency achieved was 19.3% (Jsc = 37 mA/cm2, Voc = 691 mV, FF = 71.7%) on 200 µm thick 1-15 Ω-cm n-type CZ C-Si with a designated area of 4 cm2.
ContributorsMoeini Rizi, Mansoure (Author) / Goodnick, Stephen (Thesis advisor) / Honsberg, Christina (Committee member) / Goryll, Michael (Committee member) / Smith, David (Committee member) / Bowden, Stuart (Committee member) / Arizona State University (Publisher)
Created2022
Description
The future will be replete with Artificial Intelligence (AI) based agents closely collaborating with humans. Although it is challenging to construct such systems for real-world conditions, the Intelligent Tutoring System (ITS) community has proposed several techniques to work closely with students. However, there is a need to extend these systems outside the controlled environment of the classroom. More recently, Human-Aware Planning (HAP) community has developed generalized AI techniques for collaborating with humans and providing personalized support or guidance to the collaborators. In this thesis, the take learning from the ITS community is extend to construct such human-aware systems for real-world domains and evaluate them with real stakeholders. First, the applicability of HAP to ITS is demonstrated, by modeling the behavior in a classroom and a state-of-the-art tutoring system called Dragoon. Then these techniques are extended to provide decision support to a human teammate and evaluate the effectiveness of the framework through ablation studies to support students in constructing their plan of study (\ipos). The results show that these techniques are helpful and can support users in their tasks. In the third section of the thesis, an ITS scenario of asking questions (or problems) in active environments is modeled by constructing questions to elicit a human teammate's model of understanding. The framework is evaluated through a user study, where the results show that the queries can be used for eliciting the human teammate's mental model.
ContributorsGrover, Sachin (Author) / Kambhampati, Subbarao (Thesis advisor) / Smith, David (Committee member) / Srivastava, Sidhharth (Committee member) / VanLehn, Kurt (Committee member) / Arizona State University (Publisher)
Created2022
Description
Written corrective feedback (WCF) has received considerable attention in secondlanguage (L2) writing research. The conducive role of WCF in developing L2 writing and
second language acquisition has been corroborated by a number of theoretical frameworks,
and the findings of empirical studies, meta-analyses, and research syntheses. WCF research
has predominantly addressed its effectiveness in improving learners’ syntactic, lexical, and
orthographic knowledge. This dissertation project extends the scope of this line of research
to formulaic aspects of language and investigates the relative effectiveness of WCF
targeting formulaic vs. non-formulaic constructions in L2 writing. The text-analytic
descriptive aspect of this research design aimed at investigating the extent of L2 learners’
non-target-like use of formulaic vs. non-formulaic forms in L2 writing and writing
teachers’ WCF treatment of non-target (non)formulaic language use. A total of 480 first
drafts of essays written by 33 advanced adult English-as-a-foreign language (EFL) learners
during one semester and 480 drafts of essays corrected through WCF by three EFL teachers
constituted the corpus in this study. Advancing the field of learner corpus research, the
findings demonstrated that whereas learners’ non-target formulaic forms outnumbered that
of non-formulaic ones in their writing assignments, all three teachers provided WCF more
often for erroneous use of non-formulaic forms. The quasi-experimental aspect of the
research design attempts to add new empirical evidence on the L2 learning potential of
accessing and processing WCF provided for formulaic vs. non-formulaic constructions in
L2 writing. To this end, a total of 66 EFL learners in a Test of English as a Foreign
Language preparation course participated in a pretest-posttest design, with 5 experimental groups (those who were provided with direct, indirect, direct plus metalinguistic, and
indirect plus metalinguistic WCF) and a control group (those who were not provided with
WCF). Maintaining a division between formulaic vs. non-formulaic forms, the findings
provide empirical evidence on the interactions between types of WCF, types of linguistic
targets, and the effectiveness of WCF in terms of enhancing L2 learners’ accuracy and
acquisition in their revised writing and new writings in the short and long term.
ContributorsGholami, Leila (Author) / Smith, David (Thesis advisor) / Matsuda, Paul K (Committee member) / James, Mark A (Committee member) / Arizona State University (Publisher)
Created2022
Description
Transitioning into civilian life after military service is a challenging prospect. It can be difficult to find employment and maintain good mental health, and up to 70 percent of veterans experience homelessness or alcoholism. Upon discharge, many veterans pursue higher education as a way to reintegrate into civilian society. However, many studies have shown that veterans encounter multiple challenges during their attempt to reintegrate into civilian life, including anxiety, a lack of relevant skills, post-traumatic stress disorder (PTSD), and other issues that may lead to communication and interaction challenges in the higher education environment. Student veterans also face challenges in the lack of common language and culture clashes due to differences between military and college culture. This study used a mixed-methods approach to examine the challenges military veterans face related to language use in civilian life. The data was collected from 149 student veterans who completed a questionnaire and 11 student veterans who participated in interviews. Detailed analysis of collected data showed that student veterans experienced some challenges in language use, especially when they initially enrolled in their courses, but they seemed to have overcome challenges after spending time in the university setting. The veterans who had prior college education before joining the military seemed to have a slight advantage, having had experience using the academic language. The study also explored how student veterans chose to share their veteran status with other people in their university community. The findings showed that they strongly identified with their veteran identity and was comfortable sharing their status with others, but they also sometimes were reluctant to share their military experience in details because they were afraid that their peers would not understand.
ContributorsObaid, Naji (Author) / Matsuda, Aya (Thesis advisor) / Smith, David (Committee member) / James, Mark (Committee member) / Arizona State University (Publisher)
Created2022
Description
Climate change is a threat to food security and food system stability, especially towards small islands. Climate change is increasing the frequency of extreme weather events, further putting island rural farming communities at greater risk for reduced crop yields and food insecurity. Puerto Rico’s dependence on food imports exacerbates vulnerabilities during natural disasters including reduced food quality, rural impoverishment, and periodic food insecurity. Despite these vulnerabilities, Puerto Rican farmers serve as cultural emblems within their community, providing fresh foods in times of disaster when federal aid was not available. There is very limited research focusing on how the informal social structures of these rural communities contribute to community-level disaster preparedness and mitigation strategies. Since the devastating Hurricane Maria in 2017, there has been little literature focusing on increasing rural farming community resilience against natural disasters like hurricanes in Puerto Rico. Using literature mapping software, this scoping review identifies a very limited existing set of research concerning adaptive capacity strategies in rural farming communities in Puerto Rico since 2017, discusses the strengths and weaknesses of aid organizations like the Southern Sustainable Agricultural Research and Education grant in Utuado, Puerto Rico, and suggests value in additional focused research specific to identifying how communities implement disaster preparedness and mitigation strategies.
ContributorsCastro, Andrea (Author) / Brundiers, Katja (Thesis director) / Wutich, Amber (Committee member) / Barrett, The Honors College (Contributor) / School of Sustainability (Contributor) / School of Human Evolution & Social Change (Contributor)
Created2023-05
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 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
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
Description
Given increasing frequency and intensity of extreme weather events and disparities in socio-economic conditions, managing flood risks has become ever more challenging. Building a community flood resilience becomes an essential strategy to reduce flood risks and achieve sustainable development. However, enhancing community flood resilience presents numerous obstacles and potential downsides. To address such a challenge, this dissertation investigates the interactions among natural, built environment, and actor systems using a case study of flooding in Jakarta, Indonesia, focusing on the Ciliwung river watershed. The study first develops a conceptual framework for community flood resilience by integrating concepts from disaster, flood, and community resilience research to represent how water, structural elements, and actors are connected and can contribute to hazards and vulnerabilities. Building on the framework, the study utilizes a mixed-methods approach, combining stakeholder interviews with network and heatmap analysis to identify the roles and interconnections of relevant actors in Jakarta’s flooding. Next, the study employs a hybrid of agent-based and system dynamics modeling to explore the complex interactions among the watershed’s physical and actor systems. The model evaluates how the level of collaboration among government agencies affects flood management interventions and community resilience under various scenarios concerning weather patterns and land-use change.
The research provides an exploratory tool and a strategic guide for enhancing community flood resilience. The stakeholder analysis reveals the complexity of stakeholder relationships and challenges such as imbalance in resource allocation, authority overlap, and low engagement. These insights highlight the need for trust-building, community involvement, and strategic alignment in flood management efforts. Systems modeling to derive policy recommendations bridges the gap between theoretical frameworks and governance challenges, offering empirical evidence of the critical role of governmental collaboration in reducing exposure to floods. The systems modeling results suggest that under conditions of uncertainties, enhancing community flood resilience requires a coordinated approach among stakeholders.
ContributorsSulistyo, Sinta Rahmawidya (Author) / Agusdinata, Datu Buyung (Thesis advisor) / Aggarwal, Rimjhim (Committee member) / Brundiers, Katja (Committee member) / Arizona State University (Publisher)
Created2024
Description
Extreme heat is an increasingly major issue for urban areas worldwide due to the effects of climate change. There are a variety of actions that can be taken to combat this heat, with the most beneficial being sustainable heat actions. These actions address extreme heat, and also aim to be long-lasting, equitable and just for people and nature. Teaching future generations of professionals about extreme heat issues and solutions approaches to address them prepares these individuals for their future roles in society. To teach these solutions to future professionals, a two week long study abroad program focusing on urban heat adaptation and sustainable solutions has been created for students at Arizona State University. The city of study used for this curriculum is Freiburg, Germany, a city well-known for its sustainable actions and policy. This curriculum is broken down into pre-course modules and abroad modules. The pre-course modules occur online prior to the course while the abroad modules take place in Freiburg. There are 23 modules included in this curriculum in total. These modules give students an introduction to the city, introduce types of heat actions, provide examples of sustainable heat solutions, and culminate with a final presentation comparing the city of Freiburg, Germany with students' home city, Tempe, Arizona. This curriculum can be used by schools and universities worldwide to study sustainable heat solutions in the context of Freiburg, Germany. Due to the ease with which Tempe-based sections can be switched out, the course is adaptable to multiple learning scenarios. The curriculum is highly place-based in relation to the city of Freiburg and the course is an untested program intended to act as a two week course, providing some limiting factors and considerations. A final learning reflection highlights the main findings from the curriculum writing process.
ContributorsVanLare, Alexandra (Author) / Brundiers, Katja (Thesis director) / Ramey, Alex (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor) / School of Sustainability (Contributor) / Department of Information Systems (Contributor)
Created2024-05
Description
The continued rise of temperatures and extreme heat events globally is contributing to increases in mortality and morbidity in every region of the world. Urban areas are experiencing the combined effects of anthropogenic climate change and the urban heat island effect, exacerbating the risks associated with heat for urban residents. In response, cities must make every effort to adapt, pursuing engagement in high-quality planning processes and implementing robust sets of strategies to mitigate and manage the heat. Cities are shaped by networks of plans, however, the process of systematically evaluating these plans has focused on individual plans or plan types when assessing their quality. This study combines qualitative plan quality evaluation and semi-structured interviews to assess how Vienna’s network of plans addresses heat. Two clear divides emerge when analyzing the plan network; direction-setting principles are included more often than others, and mitigation strategies are more prevalent than management strategies. These results, which are consistent across the broader plan quality evaluation literature, illuminate a clear path for Vienna to continuously improve their planning process and effectively respond to heat.
ContributorsLeyba, Bryan (Author) / Meerow, Sara (Thesis advisor) / Damyanovic, Doris (Committee member) / Hondula, David (Committee member) / Arizona State University (Publisher)
Created2023