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

非技术描述光和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。由于等离子体的形成，金属纳米颗粒具有不同于其整体行为的光学性质，等离子体是纳米颗粒内部电子云的集体激发。等离子体可以是非常强的吸光体，其光学性质可以广泛调节，使其成为光传感器和太阳能转换等广泛应用的目标。然而，由于等离子体的寿命极短，提取其所含能量是一项具有挑战性的工作。这项研究通过将精心设计的模型系统和超快光谱相结合，来研究等离子体激子和物质中其他激发之间的耦合机制。这个项目是高度跨学科的，结合了材料科学、物理和化学。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，正在开发一门新的更高级别的本科课程，涵盖纳米材料的电子和光学性质。此外，PI正在为特拉华大学的K-12工程倡议开发一个新的模块，以支持STEM教育中的教师。该单元结合了实践经验和讲座，重点关注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等离子体诱导电荷和/或能量转移，以及什么参数控制潜在的过程。该项目利用超快光谱技术研究具有可调光学性质的贵金属纳米颗粒与具有可调电子性质的半导体之间的等离子体相互作用。该方法将允许系统地改变等离子体诱导能量转移所涉及的参数的模型系统与可以识别等离子体诱导激发的形成、动力学和产物的超快光谱技术相结合。高度有序、均匀、可精确调谐的二维金属/半导体半球形纳米异质结构阵列作为研究电荷转移机制的试验台。用可见和中红外光谱范围内的飞秒暂态吸收光谱、时间域THz发射光谱和时间分辨THz吸收光谱研究了表征良好的模型体系。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属性函数的电荷和能量传递过程的动力学。该项目开发了对电荷和能量转移机制的详细预测性理解，这是合理设计用于太阳能转换和光电子等应用的金属/半导体混合结构所必需的。该奖项反映了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。

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.