CAREER: Modifying Electron-Electron Interactions to Control the Optical and Electronic Properties of Carbon Nanotubes

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***TECHNICAL ABSTRACT***Strong Coulomb interactions between charge carriers are a defining feature in low-dimensional electronic systems such as carbon nanotubes (CNTs). Phenomena associated with strong interactions often challenge theoretical descriptions and can lead to new breakthroughs in technology. In this project, electron-electron (e-e) interactions in CNTs will be varied by manipulating the dielectric environment surrounding the CNT. By studying individual CNT devices with e-e interactions "turned on" and then "turned off", the proposed experiments will test theories about bandgap renormalization, photoabsorption cross-section, photocurrent generation efficiency, impact ionization rates, and Luttinger liquid behavior. It is predicted that modifying the e-e interactions will causes dramatic changes in all these properties. Successful completion of the experiments will establish how electron interactions modify the properties of a nanomaterial, thereby generating fundamental knowledge about how to engineer nanomaterials with specific properties. The experiments will also directly contribute to the development of a solar cell design that breaks the conventional limit for solar energy conversion efficiency. The project supports PhD students and undergraduates who will be trained in a powerful combination of nanofabrication and nanometrology techniques. Nanoscience activities developed during the project will reach a broad audience, including rural highschool classrooms and introductory physics classes.***NONTECHNICAL ABSTRACT***Devices such as computer chips and photovoltaic cells are based on our understanding and control of electrons inside of materials. In most materials, electrons move independently of one another, which simplifies theory but limits the possibilities of discovering new phenomena. In materials such as carbon nanotubes, however, the repulsive interactions between electrons are extremely strong due to the nanoscale geometry of the material. If one electron dances about inside a carbon nanotube, the other electrons dance too. New phenomena related to this collective electron dance include faster signal propagation speeds and higher efficiency solar energy conversion. Much work is required to understand and utilize the phenomena related to the strong interactions between electrons in nanomaterials. In this project, measurements of individual carbon nanotubes will be made in a variety of conditions that are designed to promote or suppress the collective electron dance. Successful completion of the experiments will establish how electron interactions modify the properties of a nanomaterial, thereby generating fundamental knowledge about how to engineer nanomaterials with specific properties. The experiments will also directly contribute to the development of a solar cell design that breaks the conventional limit for solar energy conversion efficiency. The project supports PhD students and undergraduates who will be trained in a powerful combination of nanofabrication and nanometrology techniques. Nanoscience activities developed during the project will reach a broad audience, including rural high school classrooms and introductory physics classes.