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

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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.