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.

MoS₂ is a very attractive material and has been well studied for potential applications in various areas.

The performance of novel graphene-based devices often strongly depends on the electrical quality of the supporting oxide. To elucidate the general governing principles underlying this behavior, we use first-principles simulations to generate representative classes of experimentally known defect centers in passivated silicon dioxide substrates and study their charge transfer with adsorbed graphene. We find that many of the open-shell structural perturbations generated near the interface self-passivate during annealing, leading to occupied-unoccupied pairs of midgap states in the silicon dioxide band structure, but no doping of the graphene occurs. However, dangling bonds or paramagnetic defect centers stable to thermal annealing do lead to partially occupied midgap energy states that are energetically misaligned with the Dirac point of graphene allowing charge to flow to or from the carbon layer. In particular, dangling oxygen bonds in the oxide strongly p dope the graphene. We also study doping from charge donating impurities within the substrate lattice as these also act to limit the performance of graphene-based devices.

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.