Charge carrier relaxation and energy dissipation in one-dimensional nanostructures

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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.