CAREER: Understanding the Growth Mechanisms and Properties of Metal Nanowires

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TECHNICAL SUMMARYThe objectives of this CAREER proposal, sponsored by the Solid State and Materials Chemistry program, are to clarify the processes by which metal nanowires grow in solution, use this understanding to improve synthetic control over metal nanowire dimensions, and study the structure-property relationship of metal nanowires in the context of practical applications. Nanowire nucleation and growth will be visualized in real-time with dark-field optical microscopy and transition electron microscopy. The kinetic data obtained from visualization will be a powerful tool for addressing several unanswered questions about nanowire growth, including: (1) Does the species adding to the nanowire consist of metal ions, reduced metal atoms, or metal clusters? (2) What is the chemical step that limits the rate of nanowire growth? (3) How does the capping agent alter nanowire growth kinetics and nanowire morphology? A deeper understanding of the role of the capping agent will facilitate the discovery a new capping agents that enable the production of nanowires across a broader range of dimensions. Measurement of the temperature-dependent nucleation rate will facilitate the separation of nanowire nucleation from nanowire growth in time by engineering the temperature profile of the reaction, and thus allow for the production of nanowires with precisely defined lengths and diameters. The well-defined nanowires obtained from synthetic studies will be used as a platform for understanding the structure-property relationships of nanowires in the context of a transparent, conducting film, and an optical polarizer. NON TECHNICAL SUMMARYMetal nanowires, which look similar to pine needles but are 10,000 times smaller, have the potential to reduce the cost and improve the performance of touch screens, solar cells, organic LEDs, flat-panel displays, electrochromic windows, augmented reality displays, lightning strike protection for aircraft, battery electrodes, sensors, catalysts, and wearable electronics. At present, the processes by which nanowires spontaneously grow in liquids are poorly understood, and this is limiting the development of better ways to control the dimensions of nanowires so as to understand and optimize their properties in practical applications. This CAREER proposal, sponsored by the Solid State and Materials Chemistry program, describes an integrated research and educational plan dedicated to discovering why nanowires grow, using this information to grow nanowires with unprecedented precision over a wide range of dimensions, studying the properties of these structures in the context of applications with academic and industrial partners, and disseminating these results to the public though an outreach program that aims to improve participation of underrepresented groups. The research approach will focus on the development of techniques that allow researchers to watch, in real-time, the assembly of atoms into nanowires. Goals of this fundamental study include finding (1) the processes by which nanowires form, (2) the factors that influence the dimensions of a nanowire, and (3) how to control the dimensions of nanowires with greater precision over a greater range of sizes. The structure-dependent properties of nanowires will then be characterized in solar cells, and in contact lenses for augmented reality glasses. The new discoveries generated by this program will be integrated into hands-on activities by African American high-school students working with graduate student mentors, and presented to the broader public through science fairs, classroom demonstrations, museum exhibits and online videos.