Collaborative Research: Probing and Controlling Exciton-Plasmon Interaction for Solar Hydrogen Generation

半导体和金属都可以以纳米粒子的形式生产，其大小比典型的人类头发的厚度小1万倍。某些半导体纳米粒子，被称为半导体量子点，当微小晶体中的电子（也称为激子）在空间上被压缩并暴露在光下时，会表现出新的特性。同样，当一个小金属纳米粒子中的一组电子被限制在空间中并受到光的照射时，这些金属纳米结构中就会产生热电子，即等离子体激元，并表现出新的特性。半导体量子点中的激子与金属纳米结构中的等离子体之间的相互作用有望产生新的基本现象，并在许多新兴技术中发挥重要作用。在这个合作项目中，来自加州大学圣克鲁斯分校的PI Jin Z. Zhang和来自中佛罗里达大学的PI Shengli Zou将研究半导体量子点-等离子体金属纳米结构，这种结构具有受控的电子相互作用，是一种新型的混合纳米材料，称为半导体-金属异质结。与传统的半导体或金属材料不同，这些异质结产生了不同寻常的特性和新的功能。与他们的学生合作，张教授和邹教授将开发创造新的半导体-金属纳米异质结的方法，在这种异质结中，电子通过连接分子以受控的方式进行通信。该项目可以对从纳米光子学到环境和能源的应用产生重大影响，例如推进可再生太阳能燃料发电。该项目还将为培训未来的科学家和工程师提供先进实验和计算技术的机会。每年夏天，他们将通过“开放实验室”，重点研究“海水太阳能氢”，向当地的高中学生和教师介绍这个项目的研究，以提高公众对科学的认识。该合作研究团队将开发新型半导体-金属纳米异质结，利用超快激光光谱从动态角度研究半导体量子点上产生的激子与等离子体金属纳米结构中产生的等离子体激子之间的基本相互作用，这些激子被称为“等离子体激子”。这项研究的动机是需要解决等离子体金属纳米结构中半导体量子点和等离子体激元之间的电子耦合尚未得到很好的理解的挑战，这阻碍了基于半导体-金属异质结的新兴技术中涉及光照明的器件应用。本项目系统研究了等离子体金属纳米结构中半导体量子点和等离子体激元的尺寸、形状和表面等基本因素，这些因素决定了等离子体金属纳米结构中半导体量子点和等离子体激元之间的电子耦合。这将通过开发控制和增强它们之间耦合的设计连接分子来实现。利用时间分辨光致发光、透射电子显微镜、红外光谱、核磁共振、电化学、拉曼光谱和超快泵浦探测激光光谱等方法，对等离子体金属纳米结构中半导体量子点和等离子体激元之间的电子耦合进行表征。独特的导电或芳香配体分子将用于稳定等离子体金属纳米结构中的半导体量子点和等离子体，并改变和增强它们的电子耦合，以便在光子学应用中实现两种纳米结构之间的协同效应，包括光能转化为电能或化学燃料，如氢。计算研究将探索半导体量子点-等离子体激元在等离子体金属纳米结构中的相互作用，并指导和证实实验研究。该项目还将为培训未来的科学家提供先进实验和计算技术的机会。每年夏天，他们将通过“开放实验室”，重点研究“海水太阳能氢”，向当地高中学生和教师介绍该项目的研究成果，以提高公众对科学的认识。该奖项反映了美国国家科学基金会的法定使命，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。

Both semiconductors and metals can be produced in the form of nanoparticles, a size of about 10,000 times smaller than the thickness of a typical human hair. Certain semiconductor nanoparticles, called semiconductor quantum dots, exhibit new properties when the electrons, also called excitons, in the tiny crystals are spatially squeezed and exposed to light. Similarly, when a group of electrons in a small metal nanoparticle are confined in space and subject to light, hot electrons, called plasmons, are generated in these metal nanostructures that exhibit novel characteristics. Interaction between excitons in semiconductor quantum dots and plasmons in metal nanostructures are expected to result in new fundamental phenomenon and to be useful for many emerging technologies. In this collaborative project, PI Jin Z. Zhang from the University of California Santa Cruz and PI Shengli Zou from the University of Central Florida will study semiconductor quantum dots-plasmonic metal nanostructures with controlled electronic interactions as a new class of hybrid nanomaterials called semiconductor-metal heterojunctions. Unlike traditional semiconductor or metal materials, these heterojunctions give rise to unusual properties and novel functionalities. Working with their students, PIs Zhang and Zou will develop ways to create new semiconductor-metal nano-heterojunctions where the electrons communicate in a controlled manner by linking molecules. This project can have significant impacts on applications ranging from nano-photonics to environment and energy, for example advancing renewable solar fuel generation. This project will also provide opportunities for training future scientists and engineers in advanced experimental and computational techniques. Through their “open lab” focusing on “Solar Hydrogen from Seawater” each summer, local high school students and teachers will be introduced to the research of this project to enhance public awareness about science.This collaborative research team will develop novel semiconductor-metal nano heterojunctions to investigate the fundamental interactions between exciton generated on semiconductor quantum dots and plasmon produced in plasmonic metal nanostructures, named “plexciton” from a dynamic perspective using ultrafast laser spectroscopy. This research is motivated by the need to address the challenge that electronic coupling between semiconductor quantum dots and plasmons in plasmonic metal nanostructures is not well understood, hindering device applications in emerging technologies based on semiconductor-metal heterojunctions involving light illumination. The project involves the systematic study of fundamental factors, such as size, shape, and surface of both the semiconductor quantum dots and plasmons in plasmonic metal nanostructures, which determine the electronic coupling between the semiconductor quantum dots and plasmons in plasmonic metal nanostructures. This will be accomplished by developing designer linker molecules that control and enhance the coupling between them. The electronic coupling between semiconductor quantum dots and plasmons in plasmonic metal nanostructures will be characterized using a combination of time-resolved photoluminescence, transmission electron microscopy, infrared spectroscopy, nuclear magnetic resonance, electrochemistry, Raman spectroscopy, and ultrafast pump-probe laser spectroscopy methods. Unique conductive or aromatic ligand molecules will be used to both stabilize the semiconductor quantum dots and plasmons in plasmonic metal nanostructures and alter and enhance their electronic coupling so that synergistic effects are achieved between the two nanostructures for photonics applications including light energy conversion into electricity or chemical fuel such as hydrogen. Computational studies will explore the semiconductor quantum dots-plasmons in plasmonic metal nanostructures interaction and guide and corroborate experimental studies. The project will also provide opportunities for training future scientists in advanced experimental and computational techniques. Through their “open lab” which focuses on “Solar Hydrogen from Seawater” each summer they will introduce the research of this project to local high school students and teachers to enhance public awareness about science.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.