Systematic Study of Plasmon-Induced Charge and Energy Transfer in Metal-Semiconductor Hybrids

光与物质之间的相互作用是自然界、技术和科学中许多过程的基础。通过有针对性地设计材料和器件来控制光/物质相互作用的能力是基础材料科学研究的重要组成部分。金属纳米颗粒具有不同于其本体行为的光学性质，这是由于等离子体激元的形成，等离子体激元是纳米颗粒内部电子云的集体激发。等离子体激元可以是非常强的光吸收体，并且它们的光学性质可以广泛地调节，使它们成为光传感器和太阳能转换等广泛应用的有希望的目标。然而，由于等离子体激元的寿命极短，因此提取等离子体激元中包含的能量具有挑战性。 这项研究是通过结合精心设计的模型系统和超快光谱学来研究物质中等离子体激元和其他激发之间的耦合机制。该项目是强烈的跨学科，结合材料科学，物理学和化学。它为这些学科的本科生和研究生研究提供了许多机会。作为该项目的一部分，正在编制一门新的高等本科课程，内容涉及纳米材料的电子和光学特性。此外，PI正在为特拉华州大学的K-12工程计划开发一个新模块，以支持STEM教育的教师。该模块结合了实践经验和讲座，重点放在纳米材料的光学性质。技术说明该项目的目标是了解在什么条件下可以实现有效的直接等离子体激元诱导电荷和/或能量转移，以及什么参数控制的基本过程。该项目通过超快光谱技术研究具有可调光学特性的贵金属纳米颗粒与具有可调电子特性的半导体之间的等离子体相互作用。该方法结合了模型系统，允许系统地改变参与等离子体激元诱导的能量转移与超快光谱技术，可以识别等离子体激元诱导的激发的形成，动力学和产品的参数。高度有序，均匀，精确可调的二维金属/半导体半球形纳米异质结构阵列作为测试床，以确定电荷转移机制。在可见光和中红外光谱范围内的飞秒瞬态吸收光谱，时域太赫兹发射光谱，和时间分辨太赫兹吸收光谱的模型系统进行了研究。这些超快方法与标准材料表征技术相结合，以测量和识别作为光学和电子材料特性的函数的电荷和能量转移过程的动态。该项目对电荷和能量转移机制进行了详细的预测性理解，这对于合理设计用于太阳能转换和光电子等应用的金属/半导体混合结构是必要的。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical DescriptionThe interaction between light and matter is fundamental to numerous processes in nature, technology, and science. The ability to control light/matter interaction by targeted design of materials and devices is an important part of basic materials science research. Metal nanoparticles possess optical properties that are distinct from their bulk behavior due to the formation of plasmons, the collective excitations of the electron cloud inside a nanoparticle. Plasmons can be very strong light absorbers and their optical properties can be widely tuned, making them promising targets for a broad range of applications such as light sensors and solar energy conversion. However, it is challenging to extract the energy that is contained in plasmons due to their extremely short life time. This research is studying the mechanisms that govern coupling between plasmons and other excitations in matter by combining carefully designed model systems and ultrafast spectroscopies. This project is strongly interdisciplinary, combining Material Science, Physics, and Chemistry. It offers many opportunities for undergraduate and graduate research across these disciplines. A new higher-level undergraduate course, covering the electronic and optical properties of nanomaterials, is being developed as part of the project. In addition, the PI is developing a new module for the University of Delaware’s K-12 Engineering Initiative that supports teachers in STEM education. The module combines hands-on experiences and lectures focusing on the optical properties of nanomaterials.Technical DescriptionThe goal of the project is to understand under what conditions efficient direct plasmon-induced charge and/or energy transfer can be realized and what parameters govern the underlying processes. The project investigates plasmonic interactions between noble metal nanoparticles with tunable optical properties and semiconductors with adjustable electronic properties by ultrafast spectroscopic techniques. The approach combines model systems that allow systematically changing the parameters that are involved in plasmon-induced energy transfer with ultrafast spectroscopic techniques that can identify the formation, dynamics, and the products of plasmon-induced excitations. Highly ordered, homogeneous, and precisely tunable two-dimensional metal/semiconductor hemispherical nano-heterostructure arrays act as test-beds to identify charge transfer mechanisms. The well characterized model systems are investigated by femtosecond transient absorption spectroscopy in the visible and mid-IR spectral range, by time-domain THz emission spectroscopy, and by time-resolved THz absorption spectroscopy. These ultrafast methods are combined with standard materials characterization techniques to measure and identify dynamics of charge and energy transfer processes as a function of optical and electronic material properties. This project develops a detailed predictive understanding of charge and energy transfer mechanisms, that are necessary for rational design of metal/semiconductor hybrid structures for applications such as solar energy conversion and opto-electronics.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.