Transport in nanotube electronics and organic nanopores

Over the last decade there has been substantial progress in research efforts to build electronic devices with nanometer length-scales. Traditionally, device physics has employed a hierarchical approach, where ab-initio quantum simulations are used to provide bandgap, effective mass and dielectric polarization parameters for use in microscale Poisson-Boltzmann transport models. An ongoing problem for engineers is that the behavior of nanoscale devices cannot easily be related to bulk material properties. In particular, the operation of carbon nanotube based devices is dominated by contact resistance and surface charge density. The challenge at the nanoscale is to predict device operation based on a geometry specific solution to the Schrodinger Equation and an atomically accurate Poisson solution.; We investigate the response of single and multi-wall carbon nanotubes to a uniform electric field, transverse to the tube axis. This situation has applications to carbon nanotube gate capacitors and multiwall nanotube interconnects. A key finding is that a steady-state potential gradient about the nanotube circumference reduces the energy-gap, thereby increasing the room temperature electron-transmission. This offers electronic control of the nanotube energy gap. Density functional theory is used to confirm the observed bandstructure modulation. We show that valence charge redistributes in nanotubes screens the transverse electric field. Outer shells are shown to provide electrical shielding for inner conductors in a double-wall tube configuration. In this way the double wall tube acts as a type of nano-coaxial cable.; In recent experiments, ion transport through organic nanopores has been used to differentiate between DNA bases. A hybrid Molecular Dynamics - Poisson Nernst Planck (MD-PNP) model to predict KCl ion currents in the alpha-hemolysin protein nanopores is presented. The goal of this work is to provide a design tool capable of predicting ion currents for modified pore geometries. The model predicts the experimentally observed rectifying I-V characteristic as a function of the fixed charge potential profile.