Designing Multi-scale Nanomaterials with Structural Control over Three Orders of Magnitude

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With support from the Macromolecular, Supramolecular, and Nanochemistry (MSN) program in the Division of Chemistry, Professor Odom will investigate multi-scale nanomaterials that exhibit distinct structural features from one nm to several hundred nm simultaneously. One advantage of artificially structured nanomaterials is direct control over the size and placement of specific features in multi-scale structures without being limited by thermodynamics. Because metals exhibit the most dramatic effects as a result of changes in structure at all three length scales, multi-scale nanomaterials will be designed from noble metal (plasmonic) materials. In particular, (1) small structural changes (tens of nm) can result in drastically different optical properties; (2) surfaces of metals can be functionalized easily with a wide range of thiolated soft materials; and (3) the internal structure can be defined by selective removal of the less noble metal. However, multi-scale structuring of metals cannot easily be achieved by synthetic methods alone, but can be when combined with nanoscale fabrication techniques. A three-dimensional template (fabricated pyramidal shells) will be used to determine how each length scale correlates to new near-field and far-field optical properties. Intrinsic to their multi-scale architecture, pyramids contain specific features spanning three orders of magnitude: the tip is of order 1 nm, the shell thickness is tens of nm, and the overall size is of order 100 nm. This pyramidal particle platform enables a systematic approach to interrogate how individual structural features affect overall optical properties, which are mostly determined by localized surface plasmons. Nature-designed structures with at least two different length scales include wood, seashells, and opals. In all cases, the structural factors play a large role in their physical properties, from mechanical to optical properties. Learning to manipulate a single material over more than two functional length scales is a current grand challenge in nanochemistry, and with support from the Macromolecular, Supramolecular, and Nanochemistry (MSN) program in the Division of Chemistry, this work will uncover the first design rules to create hierarchical structures out of soft and hard materials. These concepts will be integrated with interactive technology tools in freshmen general chemistry, with hands-on, nanoscience labs into college and high school courses, and in public lectures on nanoscience. Locally, freshmen and undergraduate students at Northwestern University, high school and middle school students in the Chicago area, and high school science teachers will be exposed to the science and prospects of multi-scale nanomaterials for improved energy storage, enhanced chemical reactions, and greater bio-inspired properties. Teachers will be able to use multi-scale materials (like photonic crystals, a synthetic opal) as key components of student design projects.