Nanofabricated Model Systems for Investigations of Plasmon Enhanced Reactions

能源效率、可持续性和气候变化是我们社会通过不损害环境的经济增长来确保繁荣和福利的关键问题。人们越来越有兴趣将太阳能用于可持续的化学制造过程，以取代目前导致二氧化碳排放和气候变化的化石燃料的使用。为了实现这些目标，需要新的催化剂、能源和原料来源以及化学加工工程战略。例如，需要进行基础科学研究，以开发能够捕捉阳光并将其转化为燃料和有用的化学产品的新材料。这项研究项目通过对纳米结构材料的系统研究来解决这一挑战，这种材料通过一种名为等离子体共振的量子力学现象有效地捕捉光，其中落在纳米结构上的光导致一些电子同步振荡。以这种方式产生的强烈电场可以用来打破二氧化碳、氮气和水蒸气的强烈化学键，启动化学反应链，以完全脱碳的方式将这些常见的大气物种转化为有价值的化学产品。然而，关于这些等离子体共振和化学反应之间的相互作用，以及纳米器件材料和几何结构在最大化这些系统的效率方面所起的作用，人们知之甚少--这是本研究项目要解决的知识缺口，该研究项目将培养本科生和研究生开发创造太阳能化学过程所需的工程技术。本文提出了一个实验研究计划，利用独特的表面化学方法结合纳米制造来研究等离子体增强的光化学。表面等离子体共振在纳米尺度上集中了电磁能量，在太阳能、光催化和纳米传感等领域有着广泛的潜在应用。等离子体是受光刺激的电子气的集体电荷振荡，通过选择材料和纳米结构设计，可以使模式在特定频率下共振。局域表面等离子体共振极大地增强了光与物质的相互作用，导致了强烈的电场、热载流子的产生和局域加热，所有这些都有助于推动化学反应。通过热载流子和增强电场对反应过程的非热贡献尤其令人感兴趣，因为它们可以在较低的温度下导致反应活性，并提供一种方法来控制反应选择性，以获得所需的化学产品分布。在这个项目中，我们将使用具有可调谐共振和工程热点的纳米柔性结构来研究模型化学反应，以学习如何设计高效的等离子体光催化剂。该项目的智能优点是设计了结合纳米制造和表面科学的特征的实验，以在定义明确的条件下测量反应速度，包括集成的光学和温度测量。项目目标包括测量不同纳米结构设计和材料对反应速率的非热贡献，以提高对热载体化学的理解。这项拟议工作要评估的总体假设是，通过设计具有电磁“热点”的纳米结构来提高热载流子产生的速度，可以提高热载流子化学的效率。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。

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.