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

在化学系大分子、超分子和纳米化学（MSN）项目的支持下，奥多姆教授将研究同时在1纳米到数百纳米范围内表现出不同结构特征的多尺度纳米材料。人工结构纳米材料的一个优点是可以直接控制多尺度结构中特定特征的大小和位置，而不受热力学的限制。由于金属在所有三个长度尺度上的结构变化都表现出最显著的影响，因此将用贵金属（等离子体）材料设计多尺度纳米材料。特别是，(1)微小的结构变化（几十nm）会导致光学性质的巨大差异；(2)金属表面可以很容易地与广泛的硫化软材料功能化；(3)可通过选择性去除低贵金属来确定内部结构。然而，金属的多尺度结构不能轻易地通过单独的合成方法实现，但可以与纳米尺度制造技术相结合。三维模板（制作金字塔壳）将用于确定每个长度尺度如何与新的近场和远场光学特性相关联。作为多尺度结构的固有特征，金字塔包含了跨越三个数量级的特定特征：尖端为1纳米，外壳厚度为数十纳米，整体尺寸为100纳米。这个金字塔状的粒子平台可以用系统的方法来研究单个结构特征是如何影响整体光学特性的，而这些特性主要是由局部表面等离子体决定的。自然设计的结构至少有两种不同的长度尺度，包括木材、贝壳和蛋白石。在所有情况下，结构因素在它们的物理性能中起着很大的作用，从机械性能到光学性能。学习在两个以上的功能长度尺度上操纵单一材料是当前纳米化学的一个巨大挑战，在化学系大分子、超分子和纳米化学（MSN）项目的支持下，这项工作将揭示第一个设计规则，以创建软硬材料的分层结构。这些概念将与互动技术工具整合到大一新生的普通化学课程中，与动手的纳米科学实验室整合到大学和高中课程中，以及在纳米科学的公开讲座中。在当地，西北大学的新生和本科生、芝加哥地区的高中生和中学生以及高中科学教师将接触到多尺度纳米材料的科学和前景，以改善能量储存、增强化学反应和更大的生物启发特性。教师将能够使用多尺度材料（如光子晶体、合成蛋白石）作为学生设计项目的关键组成部分。

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.