Analysis of Carbon Nanotubes under Electrical and Mechanical Stresses: A Study of the Influence of Non-Equilibrium Lattice Vibrations and Strain Deformation

PhD Student: Pierre R. Gautreau

Publication Year: 2014

Advisor: Cemal Basaran

Abstract: Carbon nanotubes (CNTs) have attracted a lot of attention recently due to their impressive thermal, electrical, and mechanical properties. Recent advances in CNT technology have allowed the development of a CNT computer capable of simple calculations. Flexible electronics has become a reality with the use of CNTs and graphene. More reliable and energy efficient carbon based nanoelectronics are being designed to improve the performance of the conventional CMOS structure. Despite all of this attention received in the past twenty years, many of the properties and behavior of CNTs still need to be discovered and understood before further integration of CNTs into nanoelectronics can be made possible.

In this Dissertation, computational models of CNTs are developed for nanoelectronic interconnects applications. The effects of hot phonons on the Joule heating of CNTs under electrical bias are studied via a semi-classical ensemble Monte-Carlo simulation of scattering events between charge carriers and the lattice, taking into account the dynamic evolution of the phonon occupation number and associated electron-phonon scattering rates. The contribution of hot phonons to the Joule heating of CNTs is found to be significant, especially at 300K and below. The results obtained during this Dissertation suggest that the influence of hot phonons on momentum transferred to the lattice of a CNT under electrical loading is negligible.

A model for the calculation of the phonon-phonon scattering rates is developed based on a previous model with improvements made on the computation of the strength of interaction without the need for continuum mechanics approximations. The results of the model are in good agreement with other theoretical models as well as experimental results. The technique presented in this Dissertation has the advantage of calculating phonon mode specific scattering rates.

The influence of uniaxial strain on the phonon dispersion relation is calculated using supercell theory coupled with a molecular mechanics simulation. The results show a clear overall down-shift in phonon energy for CNTs under an applied uniaxial strain.

The effects of uniaxial strain on the phonon-phonon scattering rates are studied using a hybrid model constituted of a molecular mechanics simulation and a molecular dynamics simulation. The results suggest an oscillating behavior with strain for longitudinal acoustic phonon-phonon scattering rates.