Nanofabricated Model Systems for Investigations of Plasmon Enhanced Reactions

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Energy efficiency, sustainability, and climate change are critical issues for our society to ensure prosperity and welfare through economic growth that does not harm the environment. There is growing interest to use solar energy for sustainable chemical manufacturing processes to replace the use of fossil fuels that currently contribute to carbon dioxide emissions and climate change. New catalysts, energy and feedstock sources, and chemical processing engineering strategies are necessary to meet these objectives. For example, fundamental scientific research is required to develop new materials that can capture and convert sunlight into fuels and useful chemical products. This research project addresses this challenge through a systematic study of nanostructured materials that efficiently capture light by a quantum-mechanical phenomenon known as plasmon resonances, wherein the light falling on the nanostructures causes some of the electrons to oscillate in unison. The intense electrical field generated in this manner then can be used to break the strong chemical bonds of carbon dioxide, nitrogen, and water vapor to initiate the chain of chemical reactions required to convert these common atmospheric species into valuable chemical products in a completely decarbonized manner. Little is known, however, about the interplay between these plasmonic resonances and the chemical reactions as well as the roles nanodevice materials and geometry play in maximizing the efficiency of these systems – this is the knowledge gap to be addressed by this research project, one that will train undergraduate and graduate-level engineering students in developing the engineering technology needed to create solar-powered chemical processes.An experimental research program is proposed to investigate plasmon-enhanced photochemistry using a unique surface chemistry approach combined with nanofabrication. Surface plasmon resonances concentrate electromagnetic energy at the nanoscale and have numerous potential applications in solar energy, photocatalysis, and nanoscale sensing. Plasmons are collective charge oscillations of the electron gas that are stimulated by light, and modes can be made resonant at specific frequencies by the choice of materials and nanostructure design. Localized surface plasmon resonances greatly enhance the interaction of light with matter and lead to intense electric fields, generation of hot carriers, and localized heating, all of which can be useful for driving chemical reactions. Non-thermal contributions to reactive processes via hot carriers and enhanced electric fields are especially of interest since they may lead to reactivity at lower temperatures and offer a means of controlling reaction selectivity towards desired chemical product distributions. In this project, model chemical reactions will investigated using nanofabricated structures with tunable resonances and engineered hot spots to learn how to design efficient plasmonic photocatalysts. The intellectual merits of this project are to design experiments that combine features of nanofabrication and surface science to measure reaction rates under well-defined conditions, including integrated optical and temperature measurements. Project goals include measurement of non-thermal contributions to rates of reaction for different nanostructure designs and materials to improve the understanding of hot carrier chemistry. The overall hypothesis to be evaluated by the proposed work is that hot carrier chemistry can be made more efficient by engineering nanostructures with electromagnetic “hot spots” to increase rates of hot carrier generation.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.