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- All Subjects: STEM
- Creators: Oliver, Jill
Description
HgCdTe is the dominant material currently in use for infrared (IR) focal-plane-array (FPA) technology. In this dissertation, transmission electron microscopy (TEM) was used for the characterization of epitaxial HgCdTe epilayers and HgCdTe-based devices. The microstructure of CdTe surface passivation layers deposited either by hot-wall epitaxy (HWE) or molecular beam epitaxy (MBE) on HgCdTe heterostructures was evaluated. The as-deposited CdTe passivation layers were polycrystalline and columnar. The CdTe grains were larger and more irregular when deposited by HWE, whereas those deposited by MBE were generally well-textured with mostly vertical grain boundaries. Observations and measurements using several TEM techniques showed that the CdTe/HgCdTe interface became considerably more abrupt after annealing, and the crystallinity of the CdTe layer was also improved. The microstructure and compositional profiles of CdTe(211)B/ZnTe/Si(211) heterostructures grown by MBE was investigated. Many inclined {111}-type stacking faults were present throughout the thin ZnTe layer, terminating near the point of initiation of CdTe growth. A rotation angle of about 3.5° was observed between lattice planes of the Si substrate and the final CdTe epilayer. Lattice parameter measurement and elemental profiles indicated that some local intermixing of Zn and Cd had taken place. The average widths of the ZnTe layer and the (Cd, Zn)Te transition region were found to be roughly 6.5 nm and 3.5 nm, respectively. Initial observations of CdTe(211)B/GaAs(211) heterostructures indicated much reduced defect densities near the vicinity of the substrate and within the CdTe epilayers. HgCdTe epilayers grown on CdTe(211)B/GaAs(211) composite substrate were generally of high quality, despite the presence of precipitates at the HgCdTe/CdTe interface. The microstructure of HgCdSe thin films grown by MBE on ZnTe/Si(112) and GaSb(112) substrates were investigated. The quality of the HgCdSe growth was dependent on the growth temperature and materials flux, independent of the substrate. The materials grown at 100°C were generally of high quality, while those grown at 140°C had {111}-type stacking defects and high dislocation densities. For epitaxial growth of HgCdSe on GaSb substrates, better preparation of the GaSb buffer layer will be essential in order to ensure that high-quality HgCdSe can be grown.
ContributorsZhao, Wenfeng (Author) / Smith, David J. (Thesis advisor) / McCartney, Martha (Committee member) / Carpenter, Ray (Committee member) / Bennett, Peter (Committee member) / Treacy, Michael J. (Committee member) / Arizona State University (Publisher)
Created2011
Description
STEM has increasingly become a buzz word in the world of education. According to Briener, et. al. (2012), the most common perspective of STEM education is teaching the integrated disciplines of science, technology, engineering, and mathematics as "one cohesive entity" instead of as separate subjects (p. 5). Prioritizing a STEM focus is a tactic many schools are beginning to adapt and one the United States government is financially backing, contributing significantly to the popularity of the movement (Briener, et.al., 2012). Across the nation, schools are making strides towards incorporating more STEM activities, and many school districts are designating entire schools as STEM schools. These STEM schools distinguish themselves with consistent commitment and attention to aspects of the STEM fields within instruction, including research opportunities for students, 21st Century skills, and a variety of learning environments. Bridges Elementary is one such identified STEM school that exemplifies these criteria, amongst others, setting a precedent for STEM schools to come.
ContributorsFefolt, Molly Lynn (Author) / Walters, Molina (Thesis director) / Oliver, Jill (Committee member) / Division of Teacher Preparation (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
As a Country, the United States is continually falling behind academically when compared to other Nations. Therefore, the purpose of my Honors Thesis is to enlighten others on the importance of incorporating science, technology, engineering, and mathematics (STEM) into our classrooms. When students have the chance to partake in hands on, inquiry based lessons, their new knowledge for the subject increases drastically. However, completing STEM lessons in the classroom is a challenging task. For this reason, I have designed a unit's worth of lesson plans, where the unit encompasses science, technology, engineering, and mathematics. These STEM lessons are inquiry-based so that students get an understanding that science is a learning process, not just a group of facts to be memorized. The lessons are written in the 5E format, as this format is based on the way human beings learn. I wanted to make this as easy as possible for teachers to bring inquiry-based STEM learning into the classroom. When students are allowed to take control of their own learning and make discoveries for themselves, they are going to realize the excitement that comes with STEM. This will lead more students to pursue STEM careers, thus helping bring the United States back to a competitive level academically.
ContributorsPiatak, Mary Frances (Author) / Oliver, Jill (Thesis director) / Walters, Molina (Committee member) / Division of Teacher Preparation (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
This project examined the need for Science, Technology, Engineering, and Math (STEM) activities within a specific modality (centers) and their potential influence on elementary students with a particular emphasis on gender. STEM is an interdisciplinary curriculum that seeks to seamlessly incorporate science, technology, engineering, and math. Due to the increasing demand for STEM professions and proficiency within each aspect, the education system and individual educators require lessons and modalities that motivate learning in each of these areas. Administrators and teachers need creative ways to provide effective STEM implementation. Currently, the education system as a whole lacks creative and motivating material for these four domains. Not only this, but there has been a misunderstanding in regard to what effective STEM implementation entails, as well as a dearth of classroom ready lessons for educators. As a result, this thesis project developed a way to implement STEM through the use of learning centers. Learning centers are defined as designated areas within a classroom that allow easy access to a variety of learning materials. Within these centers are activities that reinforce concepts by using inquiry-based learning. Learning centers are effective in developing additional concepts or providing students with a greater breadth of knowledge on a concept. This thesis project developed three STEM learning center activity boxes and two STEM learning center outlines. Creating effective STEM learning centers and outlines was a multistep process. The first step was to develop a 3E lesson plan for each activity. Once the lesson plans were revised and complete, the creation of the three activity boxes was next. To create the activity boxes, all the required materials and worksheets were gathered and printed. From there, the next step was to implement the learning centers in a classroom to observe the results and propose any modifications. Afterwards, a reflection detailing the results and modifications was made. In the end, the goal of this project was to develop easily implemented STEM activities for my future classroom. Coming up with a creative way to get kids curious and excited about STEM is key in building STEM awareness. Not only did my project create STEM activities I can implement, but it also allowed me the opportunity to share my activities with other teachers. As a result, influencing the spread of STEM amongst future and current teachers.
ContributorsSchott, Nicole Elizabeth (Author) / Walters, Molina (Thesis director) / Oliver, Jill (Committee member) / Division of Teacher Preparation (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
The research described in this dissertation involved the use of transmission electron microscopy (TEM) to characterize II-VI and III-V compound semiconductor quantum dots (QDs) and dilute-nitride alloys grown by molecular beam epitaxy (MBE) and intended for photovoltaic applications. The morphology of CdTe QDs prepared by the post-annealing MBE method were characterized by various microscopy techniques including high-resolution transmission electron microscopy (HR-TEM), and high-angle annular-dark-field scanning transmission electron microscopy (HAADF-STEM). Extensive observations revealed that the of QD shapes were not well-defined, and the QD size and spatial distribution were not determined by the amount of CdTe deposition. These results indicated that the formation of II-VI QDs using a post-annealing treatment did not follow the conventional growth mechanism for III-V and IV-IV materials. The structural properties of dilute-nitride GaAsNx films grown using plasma-assisted MBE were characterized by TEM and HAADF-STEM. A significant amount of the nitrogen incorporated into the dilute nitride films was found to be interstitial, and that fluctuations in local nitrogen composition also occurred during growth. Post-growth partial relaxation of strain resulted in the formation of {110}-oriented microcracks in the sample with the largest substitutional nitrogen composition. Single- and multi-layered InAs QDs grown on GaAsSb/GaAs composite substrates were investigated using HR-TEM and HAADF-STEM. Correlation between the structural and optoelectronic properties revealed that the GaAsSb barrier layers had played an important role in tuning the energy-band alignments but without affecting the overall structural morphology. However, according to both XRD measurement and electron microscopy the densities of dislocations increased as the number of QD layers built up. An investigation of near-wetting layer-free InAs QDs incorporated with AlAs/GaAs spacer layers was carried out. The microscopy observations revealed that both embedded and non-embedded near-wetting layer-free InAs QDs did not have well-defined shapes unlike conventional InAs QDs. According to AFM analysis and plan-view TEM characterization, the InAs QDs incorporated with spacer layers had smaller dot density and more symmetrical larger sizes with an apparent bimodal size distribution (two distinct families of large and small dots) in comparison with conventional InAs QDs grown without any spacer layer.
ContributorsTang, Dinghao (Author) / Smith, David J. (Thesis advisor) / Crozier, Peter A. (Committee member) / Liu, Jingyue (Committee member) / Mccartney, Martha R (Committee member) / Arizona State University (Publisher)
Created2014