Fundamental advances of condensed matter physics require a comprehensive understanding of the impact of interactions and disorder on non-interacting electrons in a perfect lattice. One-dimensional (1D) electron systems provide a fertile ground for physicists as interactions and disorder can completely alter their physical behavior. This project will determine the fundamental origin of resistance in single-wall carbon nanotube, an ideal 1D material, and explore the localization phenomena and the consequences of electron-electron interaction in nanotubes of well-defined chiral structure as a function of disorder and interaction strength. The results will have a broad, long-term impact on carbon nanotube technology. Nanotubes are currently being evaluated and developed for a number of transformative applications, including high-speed electronics; transparent, conducting films for solar photovoltaic cells; and conducting supports for battery electrodes. Understanding the impact of phonons and impurities is essential for optimizing carbon nanotube performance in these applications. Beyond training graduate students at UCF and Columbia, this project will support educational outreach activities involving K-12 educators and students, and our respective communities, with emphasis on underrepresented minorities in the New York metropolitan area and the Greater Orlando.
Single-wall carbon nanotubes possess extraordinary electronic properties, which are important for both fundamental and applied nanoscale materials science. In addition to providing a fertile ground for exploring unusual physics in one-dimensional systems, nanotubes are currently being evaluated and developed for a number of transformative applications, including high-speed electronics; transparent, conducting films for solar photovoltaic cells; and conducting supports for battery electrodes. This project will study transport properties of carbon nanotubes of well-defined atomic structure while controlling the experimental environment down to atomic scale, eliminating any unwanted experimental variability. Such unprecedented approach enables this collaborative team to systematically investigate the intrinsic transport properties of carbon nanotubes, which remain poorly understood after years of intensive research. As such, the results will have a broad impact on carbon nanotube science and technology. Finally, this project will support training of graduate students at UCF and Columbia, as well as educational outreach activities involving K-12 educators and students, and our respective communities, with emphasis on underrepresented minorities in the New York metropolitan area and the Greater Orlando.
Carbon nanotubes are cylinders consisting entirely of carbon atoms, in a hexagonal lattice, with diameters in the range of 1 to a few nanometers. Because of their extremely small size, nanotubes are thought of as one-dimensional conductors: electrons in a single nanotube can either move forward or backward. Moreover, depending on their exact crystal structure, nanotubes can either be metallic or semiconducting; the metallic nanotubes are further broken down into highly symmetric ‘armchair’ nanotubes and less symmetric ‘chiral’ metal nanotubes. Beyond their potential use in nanoscale circuitry, nanotubes are an excellent model system in which to study fundamental questions regarding electrical transport in one dimension. One of the most important untested conjectures in nanotube physics is the pseudospin conjecture. ‘Pseudospin’ refers to the symmetry of the forward- and reverse-moving electronic states, which can be summarized in a single index that can be described in the same mathematical way as is used for electron spin. Because reversing the direction of the electron requires changing the pseudospin, nanotubes can be quite insensitive to scattering by external charges, such as those residing in a neighboring dielectric layer. In particular, armchair nanotubes are predicted to be the least sensitive to scattering, semiconductors the most sensitive, and chiral metals in between. However, this conjecture has never been directly proven. Our main objective in this collaborative project was to measure the resistance added by charged adsorbates on nanotubes with different atomic structures. Our approach was to grow and long nanotubes, optically characterize them to identify their crystal structure, pattern a series of electrodes in order to enable measurement of the 1-D resistivity (resistance per unit length), and measure the change in resistivity upon deposition of a known amount of atomic potassium. During the period of this project, we have developed all of the techniques required for these measurements and have directly tested the pseudospin conjecture by measuring the scattering effect of potassium on both metallic and semiconducting nanotubes. The initial data (with more work in progress to confirm the pattern) confirm the pseudospin conjecture, showing larger scattering in semiconducting vs. metallic nanotubes. Intellectual merit: this work has demonstrated an integrated approach to directly test a fundamental conjecture regarding electronic transport in nanotubes. Broader impacts: The technical impact of this work will be to provide a stronger foundation for nanotube (and other nanoscale) electronic devices. The educational impact of this work was chiefly in inter-disciplinary training of graduate students across two groups at Columbia and UCF, and research participation of three undergraduates. The PI gave a lecture on nanotube physics at a high school science teachers’ workshop.
