Charge carrier relaxation and energy dissipation in one-dimensional nanostructures

在这个由化学系的大分子、超分子和纳米化学项目资助的奖项中，圣母大学的Gregory V.哈特兰教授、Masaru Kuno教授和Libai Huang博士将与研究生和本科生合作者一起使用超快瞬态吸收显微镜来研究单个纳米结构。 这些实验将在衍射极限空间分辨率下进行。 将被检查的材料包括II-VI纳米线（如CdSe纳米线和CdSe/ZnSe核壳纳米线），金属纳米线（Ag和Au），和碳纳米管（金属和半导体管）。 对于半导体纳米结构，该项目的主要目标是探索电荷载流子捕获的时间尺度如何在不同的纳米结构之间变化，它们如何在给定的纳米结构内空间变化，以及表面化学在这些过程中的作用。 对于金属纳米线，研究人员将探索环境如何控制能量弛豫。 特别是，研究人员感兴趣的是液体性质，如粘度，如何影响这些系统中的振动弛豫。尽管在过去的几十年里进行了广泛的研究，但关于纳米材料光激发后的事件顺序及其时间尺度的许多基本问题仍然存在。 拟议的实验将为这些过程提供新的见解。 例如，研究人员将确定表面特性如何影响半导体纳米结构中电荷载流子的命运，这对于将这些材料集成到太阳能电池等设备中非常重要。 他们还将研究金属纳米线的弹性响应如何受到环境的影响，这与基于这些材料的超灵敏质量传感器的开发有关。 本项目中的能量弛豫过程的测量也与纳米材料的生物成像和光热治疗应用有关。 除了工作的更广泛的技术影响外，该项目还将作为培训材料科学，化学和物理学研究生和本科生的平台。

In this award, funded by the Macromolecular, Supramolecular, and Nanochemistry Program of the Chemistry Division, Prof. Gregory V. Hartland, Prof. Masaru Kuno and Dr. Libai Huang of the University of Notre Dame in conjunction with graduate and undergraduate student co-workers will use ultrafast transient absorption microscopy to study single nanostructures. These experiments will be performed with diffraction limited spatial resolution. The materials that will be examined include II-VI nanowires (such as CdSe nanowires and CdSe/ZnSe core-shell nanowires), metal nanowires (Ag and Au), and carbon nanotubes (both metallic and semiconducting tubes). For the semiconducting nanostructures, the main goals of the project are to explore how the time scales for charge carrier trapping vary between different nanostructures, how they vary spatially within a given nanostructure, and the role of surface chemistry in these processes. For the metal nanowires, the investigators will explore how the environment controls energy relaxation. In particular, the investigators are interested in how liquid properties, such as viscosity, affect vibrational relaxation in these systems. Despite extensive studies over the past few decades, many basic questions remain about the sequence of events that follow optical excitation of nanomaterials, and their timescales. The proposed experiments will provide new insight into these processes. For example, the investigators will determine how surface properties affect the fate of charge carriers in semiconducting nanostructures, which is important for integrating these materials into devices, such as solar cells. They will also examine how the elastic response of metal nanowires is affected by environment, which is relevant to the development of ultra-sensitive mass sensors based on these materials. The measurements of the energy relaxation processes in this project are also relevant to biological imaging and photothermal therapy applications of nanomaterials. In addition to the broader technological impact of the work, the project will serve as a platform for training graduate and undergraduate students in materials science, chemistry and physics.