Synthesis of Epitaxially Grown Co3O4 Thin-Films Via Reactive RF Magnetron Sputtering

Co₃O₄ nanorods have been shown through previous work to produce Co metal catalysts that are highly resistant to deactivation via oxidation when reduced, which makes them an effective catalyst for Fischer-Tropsch (F-T) synthesis. This property has been found to be a result of the spontaneous reduction of Co₃O₄ as it forms at high temperatures, such as those used in an F-T reaction environment, as such, it can be considered a “self-healing catalyst”. The temperatures at which these self-healing properties appear have been shown to be highly dependent on the crystal plane exposed on the catalyst surface and occurs at the lowest temperature on the {110} plane. In order to study the specific mechanisms of oxide reduction on each crystal plane and guide future catalyst design, it is necessary to fabricate oxide surfaces that expose only a single crystal plane. In particular, this study is interested in the synthesizing the {110}, {111}, and {001} families of planes. Reactive radio-frequency magnetron sputtering was used to deposit highly textured and epitaxial Co₃O₄ thin of desired planes. This experiment used a cobalt metal target as cobalt source, and oxygen gas was flowed through the chamber as the reactive gas. A factorial design of experiment was devised to systematically vary gun power, oxygen flow rate and substrate material in order to determine the conditions that yielded highly textured and epitaxial thin films. Films grown in this study were characterized using wide-angle x-ray diffraction (XRD) to determine the crystal phase of the sputtered films, and to determine if films were polycrystalline, textured, or epitaxial. Results from XRD indicate that across the parameters tested several conditions yielded highly textured and potentially epitaxial films. In order to fully characterize the exposed plane more advanced surface imaging and XRD techniques such as low-energy electron diffraction and four-circle diffraction will be used in future work.