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Modification of electrical properties via interfacial manipulation in novel oxide heterostructures
Nikodemski, Stefan
Nikodemski, Stefan
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2016
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2017-02-09
Abstract
Recent advancement in the fabrication of materials with critical dimensions on the nanoscale has resulted in the emergence of new multiphase solid composites (aptly named nanocomposites). Nanocomposites based on oxide, metal, polymer, and hybrid (cermet, organic-inorganic) constituents have been recognized as a potential strategy to join the properties of different materials with the possibility of greatly enhanced properties due in part to the high interfacial area exhibited by nanomaterials. In this thesis, the effects of processing, microstructure, and interfacial design on the electrical properties of novel ionic and electronically conducting nanocomposites is established. Two classes of materials still in their infancy (proton conducting oxides and transparent conducting oxides) served as the composite constituents for the bulk of this work. Physical vapor deposition processes such as sputtering and pulsed laser deposition proved to be instrumental in the ability to fabricate well-defined heterostructures with layers/particles of nanometer thickness. For proton conducting heterostructures (based on the prototypical proton conductor BaCe0.6Zr0.3Y0.1O3-δ - BCZY), order of magnitude enhancement and depletion were observed in BCZY/oxide and BCZY/metal heterostructures, respectively. This abnormal modification in electrical properties was found to coincide with a high spatial density of junctions between the two composite constituents. Multilayer compositing was also used to drastically improve the crystal structure quality and by extension the electrical properties of doped titania thin films on glass. The impact of an ultra-thin interfacial seed layer was clarified, and showed that high oxygen pressure during deposition resulted in the preferential formation of the high electron mobility anatase phase upon annealing. We show that interfaces, when introduced on the nanoscale, have a profound impact on the macroscopic transport characteristics of the composite systems and open the doorway towards new and exciting possibilities.
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