Discovering the Facet-Selective Chemistry that Drives Anisotropic Growth of Metal Nanostructures

纳米结构是在纳米尺度上控制形状的材料，其长度比人类头发直径小1000倍。通过控制纳米结构的形状，科学家可以优化它们的性能，以实现广泛的应用。这可以生产更便宜的太阳能电池、更高容量的电池和更好的催化剂，从而降低生产燃料和化学品所需的能量。许多纳米结构可以从原子中生长出来，从而产生悬浮在液体溶液中的纳米级晶体。然而，纳米结构化学家并不完全了解导致生长具有特定形状的纳米结构的表面化学。在这个项目中，杜克大学的Wiley教授正在开发新的分析工具和方法来测试纳米结构如何以及为什么会形成不同形状的想法。这种理解对于大量生产具有精确控制尺寸和形状的纳米结构是必要的，这种方式可以最大限度地减少纳米结构制造对环境的影响。Wiley教授与国家标准与技术研究所的Moffat博士合作开发这些分析方法。他们还组织专题讨论会，将纳米结构合成和表面化学的研究人员聚集在一起，以新的视角交叉施肥这些学科。威利教授通过在公共场合的实践活动来传播他的工作。他还邀请有前途的高中生到他的实验室进行暑期实习，鼓励他们从事科学研究。纳米结构的生产依赖于某种形式的各向异性生长，但各向异性生长如何以及为什么发生在许多固相金属纳米结构合成中仍然是一个有争议的问题。杜克大学的Wiley教授在化学学部的大分子、超分子和纳米化学（MSN）项目的资助下，通过对单晶表面进行电化学测量，以及将纳米结构本身作为原位电化学石英晶体微平衡、表面增强拉曼光谱、以及表面增强红外吸收光谱测量。这些测量技术被用于验证以下假设：在铜、银和金纳米线的合成过程中，卤化物在（100）面的优先吸附促进了有机封盖剂在（100）面的吸附。这反过来又导致（111）面的优先原子加成。此外，Wiley教授正在通过纳米线生长速率的原位可视化和反应溶液中的单晶电化学测量相结合，确定封盖剂和卤化物在调节纳米线生长速率中的作用。这项工作在金属纳米结构合成和电化学领域之间建立了更强的联系，部分是通过一个新的电化学学会研讨会，将这两个领域的研究人员聚集在一起。在本项目中发展的分析方法和更深入的机理理解可以使基于促进各向异性原子加成条件的快速电化学测量的合成快速发展，具有更高的生产率和更少的浪费。Wiley教授通过杜克大学化学外展项目、达勒姆生命与科学博物馆从事教育外展，并在他的实验室接待高中生暑期实习。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nanostructures are materials whose shape is controlled on the nanoscale, length scales 1000 times smaller than the diameter of a human hair. By controlling the shape of nanostructures, scientists can optimize their properties for a very wide range of applications. This can enable the production of cheaper solar cells, higher capacity batteries, and better catalysts that lower the energy required to produce fuels and chemicals. Many nanostructures can be grown from atoms, resulting in nanoscale crystals suspended in liquid solutions. However, nanostructure chemists do not completely understand the surface chemistry that results in growing nanostructures with a certain shape. In this project, Prof. Wiley of Duke University is developing new analytical tools and methods to test ideas for how and why nanostructures grow to form different shapes. Such understanding is necessary to produce large quantities of nanostructures with precisely controlled sizes and shapes in a way that minimizes the environmental impact of nanostructure manufacturing. Prof. Wiley works with Dr. Moffat at the National Institute of Standards and Technology to develop these analytical methods. They also organize symposia that bring together researchers focused on nanostructure synthesis and surface chemistry to cross-fertilize these disciplines with new perspectives. Prof. Wiley disseminates his work through hands-on activities at public events. He also hosts promising high school students in his lab for summer internships to encourage their pursuit of a career in scientific research. Production of nanostructures relies on some form of anisotropic growth, but how and why anisotropic growth occurs in many solution-phase metal nanostructure syntheses remains a matter of debate. With funding from the Macromolecular, Supramolecular and Nanochemistry (MSN) Program of the Chemistry Division, Professor Wiley at Duke University is providing new insights into the facet-selective surface chemistry that is driving anisotropic atomic addition through the use of electrochemical measurements on single crystal surfaces, as well as by using nanostructures themselves as substrates for in situ electrochemical quartz crystal microbalance, surface-enhanced Raman spectroscopy, and surface-enhanced infrared absorption spectroscopy measurements. These measurement techniques are being used to test the hypothesis that, in syntheses of Cu, Ag, and Au nanowires, preferential adsorption of halides onto (100) facets promotes adsorption of organic capping agents onto (100) facets. This in turn leads to preferential atomic addition to (111) facets. In addition, Prof. Wiley is determining the role of capping agents and halides in modulating the rate of nanowire growth through a combination of in situ visualization of nanowire growth rates, and single-crystal electrochemical measurements in the reaction solution. This work is forging a stronger link between the fields of metal nanostructure synthesis and electrochemistry, in part through a new electrochemical society symposium that brings together researchers from both of these fields. The analytical methods and deeper mechanistic understanding developed during this project could enable the rapid development of syntheses with higher productivities and less waste based on fast electrochemical measurements of the conditions that promote anisotropic atomic addition. Prof. Wiley is engaged in educational outreach through the Duke Chemistry Outreach Program, the Durham Museum of Life and Science, and hosting high school students in his lab for summer internships.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.