"Nanostructure Designs Derived from Oxide-based Sacrificial Materials" 

Benson Tsai, MSE PhD Candidate 

Advisor: Professor Haiyan Wang

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ABSTRACT

Materials with various nanostructures exhibit distinct electrical, magnetic, and optical properties compared to their bulk counterparts. Despite significant progress in developing diverse nanomaterial synthesize either by solution or vapor-based deposition method. Challenges persist in fabricating nanostructured materials for integration on chips and flexible substrates. The goal of this dissertation is to design and fabricate nanostructured thin films by introducing sacrificial oxide materials to form vertically aligned nanocomposites (VAN) with metal or metal oxides. Two different sacrificial oxide materials are selected here, La₀.₇Sr₀.₃MnO₃ (LSMO) and Sr₃Al₂O₆ (SAO), since they can be etched in water or mild acid solution. Using pulsed laser deposition, both sacrificial oxide materials can self-assemble into a pillar-in-matrix form, where highly textured nanomaterials can remain on the desired substrate and flexible materials.

This dissertation consists of a general review of relevant background and experimental approaches, followed by four research chapters to discuss the details of the experiment. The first chapter involves synthesizing SAO-Au VAN, where metal can be either in nanoparticle form or nanopillar form, depending on the laser frequency for the deposition. In the second chapter, SAO-CeO₂ VAN was synthesized, where the concentration of CeO₂ varies from low to high. Different CeO₂ nanostructures, ranging from rounded nanopillars and faceted nanopillars to nanomaze structures, were synthesized. Next, to investigate the multi-sensing capabilities of the VAN thin film, SAO was deposited as a buffer layer, and BaTiO3(BTO)-Au was placed on top. After integrating BTO-Au VAN into a flexible polymer, the mechanical properties of the VAN thin film and its potential application in multi-functional sensors are demonstrated. Lastly, to expand the possibilities of other sacrificial oxide materials and nanostructures, LSMO-Au was synthesized using oblique angle deposition to obtain zig-zag shape of Au nanostructure. The designs of the nanocomposites using etching or water dissolution have been expanded significantly beyond the typical VAN designs. The derived nanostructures could find various applications in sensor, memristor, and energy harvesting device.