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

纳米结构是一种形状在纳米尺度上控制的材料，其长度比人类头发的直径小1000倍。通过控制纳米结构的形状，科学家可以在非常广泛的应用中优化它们的性能。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源。许多纳米结构可以从原子中生长出来，导致纳米晶体悬浮在液体中。然而，纳米结构化学家并不完全了解导致生长出特定形状的纳米结构的表面化学。在这个项目中，杜克大学的威利教授正在开发新的分析工具和方法，以测试纳米结构如何以及为什么会形成不同的形状。这样的了解对于以最大限度地减少纳米结构制造对环境的影响的方式生产具有精确控制尺寸和形状的大量纳米结构是必要的。威利教授与莫法特博士在国家标准与技术研究所合作开发这些分析方法。他们还组织研讨会，将专注于纳米结构合成和表面化学的研究人员聚集在一起，以新的视角交叉培养这些学科。威利教授通过在公共活动中的实践活动来传播他的工作。他还在他的实验室里招待有前途的高中生进行暑期实习，以鼓励他们追求科学研究事业。纳米结构的生产依赖于某种形式的各向异性生长，但在许多溶液相金属纳米结构合成中如何以及为什么会发生各向异性生长仍然是一个争论的问题。在化学系大分子、超分子和纳米化学(MSN)计划的资助下，杜克大学的Wiley教授通过使用单晶表面的电化学测量以及将纳米结构本身用作现场电化学石英晶体微天平、表面增强拉曼光谱和表面增强红外吸收光谱测量的衬底，对推动各向异性原子加成的面选择表面化学提供了新的见解。这些测量技术正被用来检验一种假设，即在合成铜、银和金纳米线时，卤化物在(100)面上的优先吸附促进了有机封顶剂在(100)面上的吸附。这进而导致原子优先加成到(111)面。此外，Wiley教授正在通过结合纳米线生长速度的原位可视化和反应溶液中的单晶电化学测量来确定封顶剂和卤化物在调节纳米线生长速度中的作用。这项工作正在金属纳米结构合成和电化学领域之间建立更紧密的联系，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。在该项目期间开发的分析方法和更深层次的机理理解可以使基于促进各向异性原子加成的条件的快速电化学测量而获得的合成能够快速发展，具有更高的生产率和更少的浪费。威利教授通过杜克化学外展计划、达勒姆生命与科学博物馆从事教育推广活动，并在他的实验室接待高中生进行暑期实习。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.