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- All Subjects: STEM
- Creators: Division of Teacher Preparation
- Creators: Bennett, Peter
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
The energy band gap of a semiconductor material critically influences the operating wavelength of an optoelectronic device. Realization of any desired band gap, or even spatially graded band gaps, is important for applications such as lasers, light-emitting diodes (LEDs), solar cells, and detectors. Compared to thin films, nanowires offer greater flexibility for achieving a variety of alloy compositions. Furthermore, the nanowire geometry permits simultaneous incorporation of a wide range of compositions on a single substrate. Such controllable alloy composition variation can be realized either within an individual nanowire or between distinct nanowires across a substrate. This dissertation explores the control of spatial composition variation in ternary alloy nanowires. Nanowires were grown by the vapor-liquid-solid (VLS) mechanism using chemical vapor deposition (CVD). The gas-phase supersaturation was considered in order to optimize the deposition morphology. Composition and structure were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD). Optical properties were investigated through photoluminescence (PL) measurements. The chalcogenides selected as alloy endpoints were lead sulfide (PbS), cadmium sulfide (CdS), and cadmium selenide (CdSe). Three growth modes of PbS were identified, which included contributions from spontaneously generated catalyst. The resulting wires were found capable of lasing with wavelengths over 4000 nm, representing the longest known wavelength from a sub-wavelength wire. For CdxPb1-xS nanowires, it was established that the cooling process significantly affects the alloy composition and structure. Quenching was critical to retain metastable alloys with x up to 0.14, representing a new composition in nanowire form. Alternatively, gradual cooling caused phase segregation, which created heterostructures with light emission in both the visible and mid-infrared regimes. The CdSSe alloy system was fully explored for spatial composition variation. CdSxSe1-x nanowires were grown with composition variation across the substrate. Subsequent contact printing preserved the designed composition gradient and led to the demonstration of a variable wavelength photodetector device. CdSSe axial heterostructure nanowires were also achieved. The growth process involved many variables, including a deliberate and controllable change in substrate temperature. As a result, both red and green light emission was detected from single nanowires.
ContributorsNichols, Patricia (Author) / Ning, Cun-Zheng (Thesis advisor) / Carpenter, Ray (Committee member) / Bennett, Peter (Committee member) / Smith, David (Committee member) / Arizona State University (Publisher)
Created2012
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 creative project created and implemented a seven-day STEM curriculum that ultimately encouraged engagement in STEM subjects in students ages 5 through 11. The activities were incorporated into Arizona State University's Kids' Camp over the summer of 2017, every Tuesday afternoon from 4 to 6 p.m. with each activity running for roughly 40 minutes. The lesson plans were created to cover a myriad of scientific topics to account for varied student interest. The topics covered were plant biology, aerodynamics, zoology, geology, chemistry, physics, and astronomy. Each lesson was scaffolded to match the learning needs of the three age groups (5-6 year olds, 7-8 year olds, 9-11 year olds) and to encourage engagement. "Engagement" was measured by pre- and post-activity surveys approved by IRB. The surveys were in the form of statements where the children would totally agree, agree, be undecided, disagree, or totally disagree with it. To more accurately test engagement, the smiley face Likert scale was incorporated with the answer choices. After implementation of the intervention, two-tailed paired t-tests showed that student engagement significantly increased for the two lesson plans of Aerodynamics and Chemistry.
ContributorsHunt, Allison Rene (Co-author) / Belko, Sara (Co-author) / Merritt, Eileen (Thesis director) / Ankeny, Casey (Committee member) / Division of Teacher Preparation (Contributor) / Harrington Bioengineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2017-12
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
Clean and accessible drinking water is a crucial and limited resource. As the world's population grows and demand increases, water resources will become more limited. This project aims to educate students on water resources, drinking water, and how biomimicry can allow society to improve its water usage. The project consists of a ten day unit plan which addresses several water topics such as: the various uses of water, water distribution, where drinking water comes from, the water treatment process, and more. After establishing background knowledge on water and surrounding issues, the students will be challenged to design a water bottle using biomimicry. Biomimicry is looking at nature to draw and inspire solutions to human problems. This unit has been optimized for use by elementary teachers. The ten day unit consists of a lesson summary, objectives, standards, and recommended activities for each day. Of the ten days, three lesson plans were fully developed using the 5E format. The research supporting this project is compiled in the following report.
ContributorsSalik, Rachael (Co-author) / Burke, Aurora (Co-author) / Walters, Molina (Thesis director) / Larson, Kelli L. (Committee member) / Civil, Environmental and Sustainable Engineering Programs (Contributor) / Division of Teacher Preparation (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
In recent education trends, an emphasis has been placed on teaching students in STEM (Science, Technology, Engineering, and Mathematics) disciplines. Many researchers have advocated for integrating Arts education as well, changing STEM education to STEAM (STEM + Arts) education. This paper describes an original 8th Grade physics curriculum integrating Science, Technology, Engineering, Arts, and Mathematics (STEAM). The curriculum was designed to teach core science concepts through inquiry and dance activities. The curriculum uses the 5E inquiry format, specifically using dance and movement activities to elaborate on the learned science content. The unit curriculum is designed to be implemented in an 8th Grade science classroom based on best practices in Science Instruction and Dance Education. The curriculum was not implemented as a research study this year, but is designed to support research in the future. The curriculum was however presented to Term 6 Pre-service Teachers in Mary Lou Fulton Teacher's College at ASU, whom evaluated the effectiveness of the lessons and offered feedback. This paper includes a review of current literature on STEAM education and dance integration, rationale for the curriculum's 5E Format and dance integration, the entire physics unit curriculum in 5E format, Pre-service Teacher feedback, and implications for a future research study with the unit curriculum.
ContributorsHarris, Carson Donald (Author) / Chen, Ying-Chih (Thesis director) / Atkinson, Laura (Committee member) / Division of Teacher Preparation (Contributor) / School of Film, Dance and Theatre (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
The research of this dissertation has primarily involved using transmission electron microscopy (TEM) techniques to study several semiconductor materials considered promising for future photovoltaic device applications.
Layers of gallium phosphide (GaP) grown on silicon (Si) substrates were characterized by TEM and aberration-corrected scanning transmission electron microscopy (AC-STEM). High defect densities were observed for samples with GaP layer thicknesses 250nm and above. Anti-phase boundaries (APBs) within the GaP layers were observed at interfaces with the Si surfaces which were neither atomically flat nor abrupt, contradicting conventional understanding of APB formation.
Microcrystalline-Si (μc-Si) layers grown on crystalline-Si (c-Si) substrates were investigated. Without nanoparticle seeding, an undesired amorphous-Si (a-Si) layer grew below the μc-Si layer. With seeding, the undesired a-Si layer grew above the μc-Si layer, but μc-Si growth proceeded immediately at the c-Si surface. Ellipsometry measurements of percent crystallinity did not match TEM images, but qualitative agreement was found between TEM results and Ultraviolet Raman spectroscopy.
TEM and Xray spectroscopy were used to study metal-induced crystallization and layer exchange for aluminum/ germanium (Al/Ge). Only two samples definitively exhibited both Ge crystallization and layer exchange, and neither process was complete in either sample. The results were finally considered as inconclusive since no reliable path towards layer exchange and crystallization was established.
Plan-view TEM images of indium arsenide (InAs) quantum dots with gallium arsenide antimonide (GaAsSb) spacer layers revealed the termination of some threading dislocations in a sample with spacer-layer thicknesses of 2nm, while a sample with 15-nm-thick spacer layers showed a dense, cross-hatched pattern. Cross-sectional TEM images of samples with 5-nm and 10-nm spacer-layer thicknesses showed less layer undulation in the latter sample. These observations supported photoluminescence (PL) and Xray diffraction (XRD) results, which indicated that GaAsSb spacer layers with 10-nm thickness yielded the highest quality material for photovoltaic device applications.
a-Si/c-Si samples treated by hydrogen plasma were investigated using high-resolution TEM. No obvious structural differences were observed that would account for the large differences measured in minority carrier lifetimes. This key result suggested that other factors such as point defects, hydrogen content, or interface charge must be affecting the lifetimes.
Layers of gallium phosphide (GaP) grown on silicon (Si) substrates were characterized by TEM and aberration-corrected scanning transmission electron microscopy (AC-STEM). High defect densities were observed for samples with GaP layer thicknesses 250nm and above. Anti-phase boundaries (APBs) within the GaP layers were observed at interfaces with the Si surfaces which were neither atomically flat nor abrupt, contradicting conventional understanding of APB formation.
Microcrystalline-Si (μc-Si) layers grown on crystalline-Si (c-Si) substrates were investigated. Without nanoparticle seeding, an undesired amorphous-Si (a-Si) layer grew below the μc-Si layer. With seeding, the undesired a-Si layer grew above the μc-Si layer, but μc-Si growth proceeded immediately at the c-Si surface. Ellipsometry measurements of percent crystallinity did not match TEM images, but qualitative agreement was found between TEM results and Ultraviolet Raman spectroscopy.
TEM and Xray spectroscopy were used to study metal-induced crystallization and layer exchange for aluminum/ germanium (Al/Ge). Only two samples definitively exhibited both Ge crystallization and layer exchange, and neither process was complete in either sample. The results were finally considered as inconclusive since no reliable path towards layer exchange and crystallization was established.
Plan-view TEM images of indium arsenide (InAs) quantum dots with gallium arsenide antimonide (GaAsSb) spacer layers revealed the termination of some threading dislocations in a sample with spacer-layer thicknesses of 2nm, while a sample with 15-nm-thick spacer layers showed a dense, cross-hatched pattern. Cross-sectional TEM images of samples with 5-nm and 10-nm spacer-layer thicknesses showed less layer undulation in the latter sample. These observations supported photoluminescence (PL) and Xray diffraction (XRD) results, which indicated that GaAsSb spacer layers with 10-nm thickness yielded the highest quality material for photovoltaic device applications.
a-Si/c-Si samples treated by hydrogen plasma were investigated using high-resolution TEM. No obvious structural differences were observed that would account for the large differences measured in minority carrier lifetimes. This key result suggested that other factors such as point defects, hydrogen content, or interface charge must be affecting the lifetimes.
ContributorsBoley, Allison (Author) / Smith, David J. (Thesis advisor) / McCartney, Martha R. (Thesis advisor) / Liu, Jingyue (Committee member) / Bennett, Peter (Committee member) / Arizona State University (Publisher)
Created2020