Polyoxometalates and Block Copolymers: Templated Self-Assembly for Nanomaterials Applications
Periodically ordered materials often present unique features. From photonic and phononic crystals to semi-conductors, the periodic structuring of materials has found widespread use in areas such as computing, catalysis, and energy conversion. Magnonic crystals are periodically ordered magnetic materials that are able to propagate spin waves, and are potential candidates for the next generation of computing. The research presented in this thesis explores templated self-assembly to create polyoxometalate (POM) assemblies in the theme of magnonic crystals. Initially, a selection of POMs are synthesized and characterized with various magnetic techniques. Super conducting quantum interference device (SQUID) magnetometry data presents POMs with antiferro- and ferromagnetic exchange interactions, while electron paramagnetic spectroscopy provides information into the electronic structures of POMs. The feasibility of templating POMs with block copolymers is demonstrated in a preliminary ionic exchange reaction. Block copolymers were explored as templates in conjunction with POMs to develop bottomup approaches for magnonic crystal fabrication. A range of block copolymers were investigated for their ability to form sub-100 nm micellar ordering features, in which the POMs would be incorporated into the cores of the micelles. Fourier transformed infrared spectroscopy and thermal gravimetry were used to monitor the success of POMs incorporating into block co polymer networks. Dynamic light scattering and extensive atomic force microscopy were used to evaluate the quality of polymer templated structures. Finally, this thesis presents a block copolymer assisted strategy to fabricate ordered magnetic nanostructures on silicon and permalloy substrates. Block copolymer micelle like structures are used as a template in which POM clusters are able to form in organized arrays. A combination of microscopy, magnetization, and scattering techniques are used to confirm the structural and organizational features of the fabricated materials. The magnetic properties of these materials are investigated with polarized neutron reflectometry, nuclear magnetic resonance, and SQUID magnetization measurements. This work shows that the bottom-up pathway is a viable method for future magnonic crystal design.
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