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Description
Solid-state lithium-ion batteries are a major area of research due to their increased safety characteristics over conventional liquid electrolyte batteries. Lithium lanthanum zirconate (LLZO) is a promising garnet-type ceramic for use as a solid-state electrolyte due to its high ionic conductivity. The material exists in two dierent phases, one that is cubic in structure and one that is tetragonal. One potential synthesis method that results in LLZO in the more useful, cubic phase, is electrospinning, where a mat of nanowires is spun and then calcined into LLZO. A phase containing lanthanum zirconate (LZO) and amorphous lithium occursas an intermediate during the calcination process. LZO has been shown to be a sintering aid for LLZO, allowing for lower sintering temperatures. Here it is shown the eects of internal LZO on the sintered pellets. This is done by varying the 700C calcination time to transform diering amounts of LZO and LLZO in electrospun nanowires, and then using the same sintering parameters for each sample. X-ray diraction was used to get structural and compositional analysis of both the calcined powders and sintered pellets. Pellets formed from wires calcined at 1 hour or longer contained only LLZO even if the calcined powder had only undergone the rst phase transformation. The relative density of the pellet with no initial LLZO of 61.0% was higher than that of the pellet with no LZO, which had a relative density of 57.7%. This allows for the same, or slightly higher, quality material to be synthesized with a shorter amount of processing time.
ContributorsLondon, Nathan Harry (Author) / Chan, Candace (Thesis director) / Tongay, Sefaattin (Committee member) / Department of Physics (Contributor) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
The standard theory of indirect gap optical absorption in semiconductors predicts an unphysical divergence when the photon energy reaches the direct band gap. Current theoretical efforts to eliminate this divergence require experimental validation with measurements covering a spectral region that exceeds the direct band gap. For transmittance and reflectance measurements needed in examining the absorption in a material like Ge, the needed film thicknesses are too small for the samples to be mechanically stable. On the other hand, very thin films can be grown epitaxially on silicon.
This thesis focuses on testing a novel technique for examining absorption in these thin films. Spectrophotometry was used to measure the reflection and transmission over a spectral range of 0.54 eV to 1.38 eV for various epitaxial thin film Ge on Si samples. The resultant data was then renormalized and used in a custom spline fitting procedure to extract the dielectric/optical constants over the established spectral range.
Analysis of the extracted dielectric function spectra indicates an apparent bias towards thinner films (less than 1000 nm) in producing spectra having good agreement with new theoretical models. Dielectric function spectra from thick samples (over 2000 nm) show well matched general behavior but fail to accurately predict regions of absorption around the band gap.
ContributorsBoone, David (Author) / Menéndez, Jose (Thesis director) / Kouvetakis, John (Committee member) / Barrett, The Honors College (Contributor) / Materials Science and Engineering Program (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Department of Physics (Contributor) / School of Sustainability (Contributor)
Created2025-05
Description
Structural color is the phenomenon where features of the material’s structure interact with light, causing it to interfere with itself, producing color. Examples of structural color are seen everywhere from the rainbow pattern on the back of CDs to the color of a butterfly's wings. Optical thin films that make use of structural color are used in a massive range of industries however, a typical thin film stack is limited to the configuration it is set in upon fabrication, thus tunable devices able to change their configuration would have huge potential for use in multi-functional devices to fill the gap of tunable optical thin film technology. A Floating Solid-State Thin Film (FSTF), where an applied voltage moves a metal film through a dielectric one, producing structure changes which change the device’s color, is one such device and Polymer-assisted Photochemical Deposition is a technique able to 3D print metal thin films of the same element used in prior FSTF research in a desired pattern without vacuum or heating. PPD could greatly improve the efficiency of micro- and opto-electronics manufacturing and the author’s group has previously done work comparing optical thin film structures made with PPD films to those made with conventionally deposited metals and they have shown promising results in this space. The purpose of this project then was to investigate whether a PPD metal film was capable of the migration demonstrated by a conventional film to function in a FSTF device. Devices of several architectures with SiO or PMMA dielectric layers and thermally evaporated or PPD silver metal layers were fabricated using a variety of techniques. The devices were tested by being connected to a 1 V and 4.5 V battery with the voltage applied being measured during testing and the device behaviors were observed. Blindspots and possible points of weakness in the experimental plan were identified post testing in both device testing and device design. These included unaccountability of the testing set-up for voltage drops creating uncertainty in the actual voltage needed and the actual voltage applied to the film as well as metal thin film thickness preventing device function in some cases by reflecting light away from the device cavity. Improvements which address these issues were identified and a new device design as well as improvements to the testing set-up were described which could be used in future work.
ContributorsBorea, Dante (Author) / Wang, Chao (Thesis director) / Yao, Yu (Committee member) / Barrett, The Honors College (Contributor) / Materials Science and Engineering Program (Contributor) / School for Engineering of Matter,Transport & Enrgy (Contributor)
Created2025-05