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Title:Solidification of eutectics utilizing directional solidification and confining templates for optical metamaterial applications
Author(s):Kohanek, Julia B.
Director of Research:Braun, Paul V.
Doctoral Committee Chair(s):Braun, Paul V.
Doctoral Committee Member(s):Bellon, Pascal; Maass, Robert; Shoemaker, Daniel P.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
directional solidification
silver chloride
potassium chloride
silicon pillar
template solidification
eutectic solidification
copper electrodeposition
lead tin eutectic
AgCl KCl eutectic
eutectic metamaterials
eutectic optics
Abstract:Fabrication of optical metamaterials, or structured materials with unique optical responses not found in the original material, requires complex and time-consuming methods such as e-beam photolithography, microscale 3D printing, ion beam milling etc. A possible new way to fabricate these unique structures is utilizing self-assembly techniques such as the phase separation found in eutectic solidification. Due to the periodic nature of eutectics, these materials are a great choice for applications in optical metamaterials. The goal of this thesis is to understand and apply directional solidification of eutectics to form unique structures with structural motifs, which behave as optical meta-materials. Solid templates are used to further finely tune the structure and shape of the eutectic phases, producing distinctive optical properties with potential for new applications in photonics. This work investigated three different binary eutectic systems consisting of Pb-Sn, AgCl-KCl, and (d)-camphor-biphenyl. The Pb-Sn system is a well-studied eutectic system and provides large optical responses due to the plasmonic effect naturally found in metals. AgCl-KCl was used due to the ability to easily form a very uniform lamellar eutectic microstructure in most solidification experiments. Finally, the (d)-camphor-biphenyl eutectic was studied as a model eutectic system for metallodielectric eutectic systems that can produce interesting optical responses such as Ge-Al. The camphor solidifies in a similar manner to aluminum and the biphenyl solidifies in a similar manner to germanium. The Pb-Sn eutectic was directionally solidified at different speeds using a 2D solidification apparatus and investigated for possible applications in diffraction gratings. From there both the AgCl-KCl and Pb-Sn eutectics were directionally solidified through confining pillar templates and the microstructures analyzed. In the pillar templates, depending on the height and width of the pillars, the eutectic lamella change orientation by 90 degrees. If the eutectic is kept as a thin layer in relation to the height of the pillars the solidification is kept vertical. In these cases, the pillar template has more of an effect on the surface microstructure, and the microstructure begins to deviate from the naturally occurring lamellar microstructure. The direction of solidification, the solidification speed, and the surface energies of the two phases all play a role in what the final microstructure shapes looks like. At certain solidification speeds and pillar spacings, these eutectic microstructures begin to resemble the structure of the optical metamaterial referred to as a split ring resonator. The (d)-camphor and biphenyl binary eutectic was used as a model system and directionally solidified using a 2D directional solidification apparatus under a microscope to better analyze the solidification of this non-faceted/faceted eutectic system. The transparent nature of the eutectic allowed for visualization of the solid liquid interface under the microscope. As a result, a transition from faceted to non-faceted solidification could be observed when the thermal gradient was increased. Applying this knowledge to metallodielectric eutectics such as Al-Ge could lead to better solidification control of these optically interesting microstructures. In addition to this work, the binary phase diagram for the (d)-camphor and biphenyl system was determined. The final portion of this thesis looks into the preliminary work of electrodeposition of copper into a copper inverse opal for integrated electronic cooling devices.
Issue Date:2019-04-16
Rights Information:Copyright 2019 Julia Kohanek
Date Available in IDEALS:2019-08-23
Date Deposited:2019-05

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