Metal Oxide Nanoparticles: Examination of Growth Processes to Gain Nanoscale Structural Control

Metal oxide nanoparticles can enable a wide variety of impactful applications due to their structure-dependent properties, tailorable features, and processability. The nanoparticle core is usually the nanoparticle component that lends a functional property to a particular application. Syntheses are required that reliably produce the nanoparticle core with the appropriate structural characteristics (size, shape, crystal phase, crystallinity, etc.) to yield the specific properties demanded by applications. In order to command control over nanoparticle core structure, we must understand the growth processes that lead to the structure. This dissertation examines growth processes by exploiting a unique metal oxide nanoparticle synthesis method. In this method, the synthetic attributes are analogous to living polymerization reactions implying that nanoparticle core structure can be manipulated with the same degree of control that transformed polymer chemistry. Leveraging the merits of the living nanoparticle synthesis, the impact of monomer flux, synthesis temperature, and precursor speciation are investigated. In the indium oxide system, it was found that high flux causes the growth of single-crystal, branched morphologies while low flux results in uniform, faceted morphologies. With increasing synthesis temperature, higher monomer fluxes are required before branched structures are observed. A model is proposed wherein surface diffusion of reactive species plays a key role in dictating nanoparticle morphology. In the iron oxide system, an Fe (III) oleate precursor containing acetylacetonate induces multiple twin defects in magnetite/maghemite nanoparticles. We hypothesize that twinning results from insufficient Fe (II) to grow the magnetite crystal. Synthesis with a mixture of Fe (II) and Fe (III) in the precursor affords well-controlled crystal growth that exhibits living characteristics and results in nanoparticles that are nearly free of defects. Towards building structure-property relationships, the size-dependent magnetic properties of small (< 10 nm) iron oxide nanoparticles were investigated. The nanoparticles exhibited relatively high saturation magnetizations as a result of all but the very surface iron atoms of the nanoparticles contributing to their magnetism. Overall, this research demonstrates the sensitivity of the nanoparticle growth and structure on synthetic variables, and strategies to achieve highly magnetic nanoparticle cores are suggested. This dissertation includes previously published and unpublished co-authored material.2020-08-1