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Title:Spatial confinement of metallodielectric eutectic alloys and related outreach curriculum studies
Author(s):Tyler, Kaitlin I
Director of Research:Braun, Paul V.
Doctoral Committee Chair(s):Braun, Paul V.
Doctoral Committee Member(s):Bellon, Pascal; Krogstad, Jessica A.; Shoemaker, Daniel P.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Directional solidification
Abstract:This thesis is split into two major sections; one focused on eutectic solidification control for optical applications and the second focused on outreach curriculum understanding for increased female engagement in STEM fields. Spatial Confinement of Metallodielectric Eutectic Alloys There is a large drive to develop new fabrication techniques for metamaterials; a subclass of materials with unique structure-driven properties that are not found in nature. Traditional methods include time-consuming and complex techniques such as lithography and focused ion beam (FIB) milling. A new push in utilizing eutectic alloys for these applications due to their spontaneous phase separation and microstructure control capabilities has emerged. This work investigated the use of an aluminum based metallodielectric eutectic systems, Germanium-Aluminum (GeAl), with an anomalous faceted/non-faceted growth mechanism for optical metamaterial applications in the near infrared (NIR) region. Aluminum in particular was chosen due to its plasmonic properties, which germanium was chosen for its dielectric properties and faceted growth mechanism which would give the final microstructures atomically smooth interfaces. These interfaces are key in reducing the scattering of the aluminum plasmons in the final application. In this study, a thermally isolated Macor ceramic fixture was used to directionally solidify GeAl samples at various thermal gradients and draw rates. This Macor fixture allowed for both thermal isolation and sample confinement at three different thicknesses. Both the surface and internal 3D order of the samples was investigated to see the effects of thermal isolation and confinement. Long range surface order was achieved with thermal gradients of 9 deg C/mm and a draw rate of 321um/s. This order was confirmed via 2D Fast Fourier Transform image analysis. Electron Backscatter Diffraction confirmed that a unique microstructure has formed in the highly ordered regions of the sample, suggesting an unseen orientation relationship between Ge and Al. This orientation relationship seems to allow for local cooperative phase growth, similar to that seen in normal eutectic or non-faceted/non-faceted systems. Preliminary optical analysis of this material was performed on ordered regions. To see the surface order optical effects, reflectance measurements using a polarizer were conducted. The material behaved as expected given the degree of order and the quality of the material surface, proving this was a good ideal system to investigate. For the 3D order, FIB cross sections were performed on three different sample thicknesses in ordered regions. There was a clear trend for increasing order and decreasing thickness. This was to be expected based on other research on spatially confined eutectic materials and how they can force said alloys to solidify in non-equilibrium ways. Transmission optical microscopy was also performed on samples with Ge removed to show that lamellar regions of the sample can propagate through the depth of the sample, further helping understand the internal microstructure. In the future, more work should be done to investigate this possible orientation relationship found in ordered areas of the material. Additional EBSD, alongside TEM and Nano CT, would help improve the understanding of the crystallographic orientations and overall internal sample morphology. Thermal simulations of the samples during solidification can provide additional information of the local thermal environment at the solid/liquid interface. The combination of this information would help provide a more robust explanation of why these ordered regions occur and why they are sporadic within the sample. Investigation of Engineering Outreach Curriculum Effects on Participant Self-Confidence It is well known that women are a minority in STEM, particularly engineering. Many researchers are have commented on the need for young women to have a high self-confidence in their skills in engineering from a young age. To help improve this self-confidence, universities host outreach camps. These camps showcase engineering in a fun and safe environment with the overall goal of increasing the number of women in STEM. The impact of how these outreach events are structured and the incorporation of engineering design, something stressed highly in college curriculums, is not well understood. To attempt and understand this complex problem, a materials science outreach camp for high school girls called Girls Learning About Materials (GLAM) was investigated. Initial camper feedback on this camp led the researchers to believe the current structure was causing confusion amongst participants. Fearing the long term effect this confusion would have, a complete camp curriculum restructuring occurred. By including a design project and an overarching theme to unify the diverse field, we were able to improve internal camper feedback. Due to a lack of pre- and post- change survey data, we were unable to make broad claims about the effectiveness of these changes on participant self-confidence. Therefore, to try and understand the larger impact of the camp restructuring, three outreach camps were compared in a more rigorous study investigating the self-confidence changes in participants. These three camps had varying levels of design (Design-focused, design-incorporated, and design-absent) to focus the outcomes of the study to the impact of design alone. GLAM served as the design-incorporated camp. The results show that design alone does have a large impact on improving participant outcomes, but the way design is incorporated throughout the week also is important. Based on these results, the design-incorporated (GLAM) camp had the best overall outcome. While these findings are quite promising, they also highlighted the need for a complete and deep understanding of the motivations behind camp curriculums. Otherwise, one cannot fully understand if the quantitative survey results reflect the camp itself. A future study has begun to provide this complex analysis via a multicase study of four outreach camps through surveys, interviews, and video observations.
Issue Date:2018-12-05
Rights Information:Copyright 2018 Kaitlin I. Tyler. All Rights Reserved
Date Available in IDEALS:2019-02-07
Date Deposited:2018-12

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