Radiative and ultrafast non-radiative electronic relaxation in individual and assembled noble metallic nanoparticles of different shapes

技术摘要：这个由固态和材料化学项目支持的更新项目的主要重点是阐明等离子体场对重要光化学和光物理系统（例如聚合物，掺杂和未掺杂的金属氧化物以及蛋白质细菌视紫红质）动力学的影响。由于等离子体银和金纳米粒子的使用大大提高了材料的光催化和光电化学效率，掺杂TiO2近年来引起了科学界的广泛关注。细菌视紫红质是仅有的两种自然发生的光合作用系统之一，除了其重要的化学和生物特性外，还被认为在太阳能转换和电子学中有应用。在所有这些材料中，对强等离子体增强的局部电场对其基本动态光诱导过程的影响知之甚少。动力学可能涉及未知的激发态、中间产物和改变的动力学速率。对光催化和太阳能转换应用最重要的基本过程将被确定，胶体化学将用于合成新的贵金属纳米结构，以选择性地提高光物理事件的概率和/或动力学。该项目将建立在El-Sayed小组在等离子体、金属和半导体纳米结构、光谱学、催化、光化学和光生物学等领域的广泛成就之上。本研究旨在从基本层面确定等离子体纳米粒子与可用于光催化和太阳能转换的材料之间的相互作用，从而阐明等离子体增强性能的机制。成功将为化学家、物理学家、材料科学家和工程师提供如何最好地将贵金属纳米颗粒纳入设备和催化系统的知识。所获得的知识将为胶体化学领域的科学家提供新的合成策略，以及如何优化纳米颗粒的形状、大小、结构、组成和颗粒间排列以用于特定应用。学生、博士后研究员和初级科学家将在化学、光谱学和纳米技术方面获得宝贵的多学科经验，为在学术界或工业界的职业生涯做准备。金和银纳米结构引起的电场增强已经彻底改变了拉曼光谱等整个领域。虽然贵金属的成本非常高，但表面增强拉曼散射的许多数量级增强表明，在优化的系统中只需要极少量的材料。充分利用等离子体效应，同时将成本降至最低，需要详细了解耦合到等离子体场的材料的静态和动态特性，以及可扩展的化学合成，避免昂贵和耗时的技术，如电子束光刻。这一努力的成功将有助于更好地利用阳光作为能源，并减少生产H2等重要工业产品所消耗的能量。由此产生的技术和经济增长，在减缓向环境排放污染物和温室气体的速度的同时，将对全球产生重大影响。

TECHNICAL SUMMARYThe main focus of this renewal project, supported by the Solid State and Materials Chemistry program, is to elucidate the effects of plasmonic fields on the dynamics of important photochemical and photophysical systems (e.g. polymers, doped and undoped metal oxides, and the protein bacteriorhodopsin). Doped TiO2 has attracted much recent attention in the scientific community because the use of plasmonic silver and gold nanoparticles has greatly enhanced the material's photocatalytic and photoelectrochemical efficiency. Bacteriorhodopsin is one of only two naturally-occurring photosynthetic systems and, in addition to its important chemical and biological properties, has been considered for applications in solar-energy conversion and electronics. In all of these materials there is little known about the effects of strong plasmon-enhanced local electric fields on their fundamental dynamical light-induced processes. The dynamics may involve unknown excited states and intermediates and altered kinetic rates. Fundamental processes most important to applications in photocatalysis and solar-energy conversion will be identified and colloidal chemistry will be used to synthesize new noble-metal nanostructures that selectively enhance the probabilities and/or dynamics of photophysical events. This program will build upon the El-Sayed group's extensive accomplishments in the areas of plasmonics, metal and semiconductor nanostructures, spectroscopy, catalysis, photochemistry, and photobiology.NON TECHNICAL SUMMARYThe proposed work seeks to determine at a fundamental level the interactions between plasmonic nanoparticles and materials that can be applied for photocatalysis and solar-energy conversion, so that the mechanisms responsible for plasmon-enhanced performance may be elucidated. Success will provide chemists, physicists, materials scientists, and engineers with knowledge on how best to incorporate noble-metal nanoparticles into devices and catalytic systems. The knowledge obtained will inform scientists in the field of colloidal chemistry on new synthesis strategies and how to optimize nanoparticle shape, size, structure, composition, and interparticle arrangement for particular applications. Students, postdoctoral fellows, and junior scientists will gain valuable multidisciplinary experience in chemistry, spectroscopy, and nanotechnology in preparation for careers in academia or industry.The electric field enhancement caused by gold and silver nanostructures has revolutionized entire fields such as Raman spectroscopy. Although the cost of noble metals is very high, the many orders-of-magnitude enhancement in surface-enhanced Raman scattering suggests that only extremely small amounts of material may be needed in optimized systems. Taking full advantage of plasmonic effects while minimizing cost requires a detailed understanding of the static and dynamical properties of materials coupled to plasmonic fields, as well as scalable chemical syntheses that avoid expensive and time-consuming techniques such as electron beam lithography. Success in this endeavor will help to better utilize sunlight as an energy source and reduce the energy consumed to produce important industrial products such as H2. The resulting technological and economic growth, while slowing the rate of releasing pollutants and greenhouse gases into the environment, will have a significant worldwide impact.