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

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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.