Graduate Thesis Or Dissertation

 

Studies of Structurally Complex Thin Film Oxides for Electronic Materials Public Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/4m90f209f

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  • In this dissertation, the structure and electronic properties of multiple metal oxide thin films are characterized and presented. Prompt inorganic condensation (PIC) of metal-oxo and –hydroxo clusters was evaluated as a technique for making metal oxide clusters in two separate studies. The first focuses on the synthesis of lithium niobate from simple niobium clusters and the second on mixed gallium oxide and indium oxide thin films from a novel Ga₁₃₋ₓInₓ hydroxo cluster. The reactivity of these clusters was monitored with X-Ray scattering and in-situ and ex-situ variable temperature studies to better understand how these clusters condense to form oxide films. A new synthetic route to K₀.₅Na₀.₅NbO₃ films is explored using sodium and potassium [Nb₆O₁₉]⁸⁻ salts in aqueous solution. This process is advantageous compared to sol-gel processing as it avoids the use of organic ligands or solvents that can cause densification issues during burnout and toxicity concerns during handling. The alkali content is variable based on relative amounts of the Na and K salts used and the pH of the system, which can replace the alkali ions for protons. Polycrystalline films were found to form on sapphire substrates while highly oriented films could be grown on (001) SrTiO₃ substrates. Pristine interfaces are critical for thin film devices so surface quality was evaluated using scanning electron microscopy and atomic force microscopy. Initial electronic and ferroelectric properties were also evaluated for these films. Amorphous InGaZnO₄ thin films were investigated using X-Ray total scattering data and modeled using both computational techniques and Reverse Monte Carlo refinement. The populations of atomic coordination environments present in these models was demonstrated to follow a simple Boltzmann distribution based on attractive and repulsive forces of the nearest neighbor atoms. Sites that are energetically unfavorable can still occur in low populations in amorphous films as these sites are kinetically trapped during deposition. These sites were mapped to simulated density of states from the computational models and found to be responsible for tail and midgap states that occur in the amorphous films. Modeling of the total scattering data also indicated necessary compositional corrections for the final structures that were the root of highly distorted atomic environments.
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  • 2019-01-17 to 2020-02-17

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