We present a tight-binding theory to analyze the motion of electrons between carbon nanotubes bundled into a carbon nanotube rope. The theory is developed starting from a description of propagating Bloch waves on ideal tubes, and the effects of intertube motion are treated perturbatively on this basis. Expressions for the interwall tunneling amplitudes between states on neighboring tubes are derived which show the dependence on chiral angles and intratube crystal momenta. We find that conservation of crystal momentum along the tube direction suppresses interwall coherence in a carbon nanorope containing tubes with random chiralities. Numerical calculations are presented which indicate that electronic states in a rope are localized in the transverse direction, with a coherence length corresponding to a tube diameter.

Carbon nanotube thin film transistors (CNT-TFTs) are fabricated on flexible substrates using purified, surfactant-based CNT suspensions, with >95% semiconducting CNT fraction. The TFTs are made up of local bottom-gated structures with aluminum oxide as the gate dielectric. The devices exhibit high ON current densities (0.1 μA/μm) and on-off ratios (∼105) with mobility values ranging from 10-35 cm2/Vs. A detailed numerical model is used to understand the TFT performance and its dependence on device parameters such as TFT channel length, CNT density, and purity.

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