The authors demonstrate that ozone exposure of individual multiwalled carbon nanotubes (CNTs) results in up to threefold increase in CNT conductivity and 50% decrease in carrier transport activation energy. Ozone exposure induces bond breaking in the individual shells and promotes cross-shell bridging via sp3 bond formation. Intershell bridging facilitates charge carrier hopping to inner shells, which can serve as additional charge carrier transport pathways, offsetting the effect of defect-scattering-induced conductivity decrease. The CNT etch rate systematically increases with decreasing initial outer diameter and decreases with incremental ozone exposure, which could provide means to controllably tailor the CNT conductance. The results suggest that controlled defect creation could be an attractive strategy to induce electrical conductivity increase in multiwalled CNTs for use in nanodevice wiring and related applications.

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Nanotechnology V 1505Microwave-Assisted Single-Step Functionalization and in situ Derivatization of Carbon Nanotubes with Gold Nanoparticles. -Multiwalled carbon nanotubes are functionalized and derivatized with gold nanoparticles by microwave irradiation of aqueous carbon nanotubes dispersions containing HAuCl4 and ethylene glycol. Additionally, microwave exposure of carbon nanotubes in the presence of boiling water results in the formation of allyl, carbonyl, carboxyl, and hydroxyl groups. The samples are characterized by TEM, Raman, and IR spectroscopy. The simple and convenient approach opens up a new way to synthesize functionalized carbon nanotube heterostructures that could be used in developing device concepts, novel catalysts, and composites. -(RAGHUVEER, M. S.; AGRAWAL*, S.; BISHOP, N.; RAMANATH*, G.; Chem.

We demonstrate that high current densities, combined with air exposure can slice, weld, and chemically functionalize multiwalled carbon nanotubes (CNTs) with carboxyl and allyl moieties, and alter the electrical properties. The conductance of thin film assemblies of CNTs increases by 150%, indicating that the increase in the number of low-resistance pathways caused by CNT junction formation offsets the conductance decrease expected from defect creation, surface functionalization, and fissure. Such welded high-conductance CNT networks of functionalized CNTs could be useful for device and sensor applications, and may serve as high mechanical toughness mat fillers that are amenable to integration with nanocomposite matrices.

Growing aligned carbon nanotubes (CNTs) on electrically conducting and/or optically transparent materials is potentially useful for accessing CNT properties through electrical and optical stimuli. Here, we report a new approach to growing aligned bundles of multiwalled CNTs on a porous back contact of optically transparent and electrically conducting indium tin oxide (ITO) films on silicon and silica substrates without the use of a predeposited catalyst. CNTs grow from a xylene/ferrocene mixture, which traverses through the pores in the thin ITO film, and decomposes on an interfacial silica layer formed via the reaction between ITO and the Si substrate. The CNTs inherit the topography of the silica substrate, enabling back‐contact formation for CNTs grown in any predetermined orientation. These features can be harnessed to form CNT contacts with other substrate materials which, upon reduction by Si, results in a conducting interfacial layer. The ITO‐contacted CNTs exhibit thermally activated ohmic behavior across a 100 ± 10 meV barrier at electric fields below ∼ 100 V cm–1 due to carrier transport through the outermost shells of the CNTs. At higher electric fields, we observe superlinear behavior due to carrier tunneling and transport through the inner graphene shells. Our findings open up new possibilities for integrating CNTs with Si‐based device technologies.