Date of Award

Summer 2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Materials Science and Engineering - (Ph.D.)

Department

Committee for the Interdisciplinary Program in Materials Science and Engineering

First Advisor

Trevor Tyson

Second Advisor

Joseph W. Bozzelli

Third Advisor

Ken Keunhyuk Ahn

Fourth Advisor

Reginald Farrow

Fifth Advisor

Huixin He

Abstract

Modeling in the framework of density functional theory has been conducted on carbon nanotubes and graphene nano-structures. The results have been extended to non-carbon systems such as boron nanostructures. Computational studies are complemented by experimental methods to refine the structural models and obtain a better understanding of the electronic structure.

It is observed that the zigzag edged bilayered graphene nanoribbons are highly unstable as compared to their armchair counterparts. A novel approach has been proposed for the patterning of chirality/diameter controlled single walled carbon nanotubes. Nanotube formation is found to be assisted by edge ripples along with the intrinsic edge reactivity of different types of bilayered GNRs.

The effect of bundling on the electronic structure of single walled carbon nanotubes in zigzag single walled carbon nanotubes has been studied. Hydrostatic pressure effects were examined on bundled single walled carbon nanotubes. Nanotubes with chiral indices (3n + 3, 3n + 3) acquire hexagonal cross-sections on application of hydrostatic pressures. The formation of a novel quasi two-dimensional phase of carbon during hydrostatic compression of small and large nanotubes under extreme conditions of pressure is modeled and is understood to be dictated by breaking of symmetry during compression. Nanoscale materials with anisotropic compressibility do not exhibit symmetric compression as in bulk materials.

Structural stability of boron nanoribbons derived from 'α-sheet' and reconstructed {1221} sheets was studied. Antiaromatic instabilities were found to destabilize nanoribbons constructed from reconstructed {1221} sheets when compared to those obtained from the 'α-sheet'. The stability of the nanoribbons was found to increase with increasing width and increase in the hole density (η) of the boron nanoribbons. The study of electronic structure reveals the presence of semiconducting nanostructures.

The presence of nanoscale crystalline domains due to random functionalization has made it difficult to resolve the chemical structure of graphene oxide and it remains a much debated topic to date. A combination of analytical, spectroscopic and density functional techniques have been used to determine the structure and properties of such nano materials. Graphene oxide has unusual exotic properties and belongs to this class of materials. Investigations reveal that the chemical structure of graphene oxide can be visualized as puckered graphene sheets linked by oxygen atoms. Density functional theory has been used to calculate the site projected partial density of states for carbon and oxygen atoms involved in different types of bonding. A comparison of these simulations with carbon and oxygen K-edge absorption spectra has led to an understanding of the basic electronic structure of this material.

Share

COinS