Browsing by Author "Zhao, Qingzhong"

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    Mechanical and Transport Properties of Carbon Nanotube Systems
    (2004-02-05) Zhao, Qingzhong; Jerry Bernholc, Committee Chair; Frank Mueller, Committee Member; Christopher Roland, Committee Member; Marco Buongiorno Nardelli, Committee Member
    The mechanical and transport properties of carbon nanotube systems are studied by large-scale ab initio, tight-binding and classical molecular dynamics simulations. The ultimate strength of carbon nanotubes is investigated theoretically. While the formation energy of strain-induced topological defects determines the thermodynamic limits of the elastic response and of mechanical resistance to applied tension, it is found that the activation barriers for the formation of such defects are much larger than estimated previously. The theoretical results indicate a substantially greater resilience and strength, and show that the ultimate strength limit of carbon nanotubes has yet to be reached experimentally. Carbon nanotubes are indeed the strongest material known. The electronic transport in a new type of carbon nanotube material: carbon nanotube-metal cluster assembly is investigated for gas absorption. For an Al cluster attached to a metallic nanotube, we have observed that its electrical response dramatically changes upon NH3 adsorption onto the metal cluster. For a semiconducting nanotube-Al cluster assembly, the same gas adsorption enhances the system's conductivity. The results of our ab initio simulations explain the observed behavior in terms of interactions between the molecular species and the nanotube-cluster system, where successive charge transfers between the components tailor the electronic and transport properties. Carbon nanotubemetal cluster assemblies could be a new type of nanotube-based chemical/biological sensors.