We present theoretical study of the atomic, electronic and transport properties of silicon
nanowires and single-walled carbon nanotubes using atomistic simulation. For silicon
nanowires, we present investigation of the atomic structure and electronic properties of
ultrathin nanowires with different surface structures and growth directions and
the trend of such property variations with increasing nanowire diameters using density
functional theory with both local atomic basis and plane waves. For single-walled
carbon nanotubes, we present self-consistent tight-binding study of the electronic
and transport properties of semiconducting carbon nanotubes in contact with metal
electrodes. We discuss insights obtained from such atomistic study on the contact,
and diameter dependence of junction conductance. Finally, we
examine the application of single-walled carbon nanotubes as novel nanofluidic channels by
analyzing the structure and kinetics of water molecules confined and transported through
the nanotube channels using molecular dynamics simulation.
We present theoretical study of carbon nanotubes as novel transport channels for electrons and molecules using atomistic simulation. For electronic transport, we present self-consistent tight-binding study of the electronic and transport properties of semiconducting carbon nanotubes in contact with metal electrodes at different contact geometries. We analyze the Schottky barrier effect at the metal-nanotube interface by examining the electrostatics, the band line up and the conductance of the metal-nanotube wire-metal junction as a function of the nanotube channel length. For molecular transport, we analyze the dynamics of rigid and semi-flexible molecules spontaneously inserted into the nanotubes as engineered flow channels in aqueous environment. We show that in the absence of water solvation, the van der Waals interaction between the molecule and the nanotube wall can induce a rapid spontaneous encapsulation of the molecule inside the nanotube channel. The encapsulation process is strongly impeded for nanotube dissolved in water due to the competition between the van der Waals, hydrophobic and hydrogen bonding interactions in the nanotube/water/molecule complex.
The further miniaturization of integrated optical devices requires investigating optical elements with dimensions on the nano-scale. Methods are therefore needed for detecting and guiding light on a scale much smaller than the wavelength of the light. It is clear that to investigate light-nanostructure interaction in a spatial extension much less than the optical wavelength, one can not in general have confidence in the macroscopic electrodynamics so far popular in near-field optics and photonic band-structures. Instead a microscopic approach treating rigorously the local-field electrodynamics is highly desirable. In this work we present a microscopic theory of near-field optical effect in nanostructured systems. Our theory is based on the rigorous Lagrangian and Hamiltonian formulation of local-field electrodynamics, where the nanostructure optical response is treated quantum mechanically, while the electromagnetic field can be treated either classically or quantum electrodynamically within a unified space-time picture.