Visualizing Charge Carrier Dynamics in Semiconductor Nanowires Using Femtosecond Pump-Probe Microscopy

通过这一奖项，化学系化学结构动力学和机制计划资助北卡罗来纳大学教堂山分校的约翰·M·帕帕尼科拉斯教授使用时间分辨显微镜在超快时间尺度上成像一维半导体纳米线中的电荷运动。得出的信息对于理解纳米科学和纳米技术的许多方面是基本重要和关键的。不同结构之间的行为差异(甚至同一结构内不同位置之间的行为)是复杂性的标志，对那些希望在设备应用中使用纳米材料的人构成了重大挑战。除了对复杂纳米结构中的电荷行为提供新的见解外，该项目还将促进未来科学家的发展。研究生、本科生和高中生将参与这项研究。他们将开发技术复杂的仪器，将这些仪器应用于单个纳米结构的研究方法，并参与国家会议上他们的结果交流。帕帕尼科拉斯教授和他的学生将利用一种新的泵浦-探测显微镜技术，在一个空间位置激发纳米线，在另一个空间位置探测它们，时间尺度从飞秒到纳秒不等。他们将使用这种空间分离的泵浦-探测显微镜来可视化具有复杂形状和成分变化的纳米线中电荷(电子和空穴)的运动，包括轴向收缩编码的硅纳米线，以及弯曲和扭结的纳米线。他们还将开发低温能力，使他们能够观察到硅/锗核壳纳米线中的弹道传输。该项目旨在加强对结构特征如何影响通过单个纳米线的电荷流动的基本了解，从而提供可用于未来纳米器件应用的有价值的信息。

With this award, the Chemical Structure Dynamics and Mechanisms Program of the Chemistry Division is funding Professor John M. Papanikolas of the University of North Carolina at Chapel Hill to use time-resolved microscopy to image the motion of charges in one-dimensional semiconductor nanowires on ultrafast time scales. The derived information is fundamentally important and critical to understanding many aspects of nanoscience and nanotechnology. Variation in behavior from structure-to-structure (and even between different locations within the same structure) is a hallmark of complexity and poses a major challenge to those wishing to use nanoscale materials in device applications. In addition to providing new insights into charge behavior in complex nanostructures, the project will promote the development of future scientists. Graduate, undergraduate, and high school students will participate in this research. They will develop the technologically complex instrumentation, apply those instruments to methods for the study of single nanostructures, and take part in the communication of their results at national meetings.Professor Papanikolas and his students will utilize a new pump-probe microscopy technique that excites nanowires in one spatial location and probes them in another, on time scales ranging from femtoseconds to nanoseconds. They will use this spatially-separated pump-probe microscope to visualize the motion of charges (electrons and holes) in nanowires with complex shapes and compositional variations, including Si nanowires encoded with axial constrictions, as well as bent and kinked nanowires. They will also develop low-temperature capabilities that will enable them to observe ballistic transport in Si/Ge core-shell nanowires. This project aims to enhance basic understanding of how structural features influence the flow of charges through individual nanowires, and thereby provide valuable information that could be used in future nano-device applications.