Date of Award

5-1-2014

Degree Type

Dissertation

University or Center

Clark Atlanta University(CAU)

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Ishrat M. Khan, Ph.D.

Abstract

Single-walled carbon nanotubes and graphene are tunable for chemical sensors and field effect transistors (FETs). In order to tune the electronic, structural, and optical properties of these nanomaterials, covalent and noncovalent functionalization has been effective. Covalent functionalization of graphene and carbon nanotubes have many advantages but may greatly compromise the organized rc-electron network within their honey-comb lattice structures. On the other hand, noncovalent functionalization affords the opportunity to maintain the sp2-hybridized planar network of carbons with extended % conjugation, which makes it an ideal material for electronics applications, even though significant impact on the electronics of these systems may not be achieved. This work features theoretical investigations of both covalent and noncovalent interactions between chemicals and the surfaces of carbon nanotubes and graphene.

Both experimental and theoretical investigations have shown that metallic singlewalled carbon nanotubes (SWNTs) have strong interactions with large aromatic molecules, such as pyrene, via tt-ti; stacking. However, pyrene molecules are not effective as dopants of graphene and carbon nanotubes. Polar derivatives of pyrene, however, have been demonstrated to both bind and modulate the properties of graphene. This is a particularly useful tool in biomimetics research. Also, because as-prepared carbon nanotubes are found in 2:1 bundles of metallic to semiconducting tubes, it is crucial that they are separated into tubes of similar type in order to better serve their functions in electronics applications. Experimental studies have shown that pyrene-azo compounds can selectively differentiate between carbon nanotube by (n,m) chirality and type. This project uses first-principles density-functional calculations to investigate mechanisms of interactions between these pyrene compounds and carbon nanomaterials, which will help to further elucidate binding mechanisms.

The binding of radical groups such as hydrogen or fluorine to the surface of graphene, leads to covalent bond formation and the subsequent changing of orbital hybridization from trigonal (sp2) to tetragonal (sp3). Such a transformation drastically modifies graphene's electronic properties, which leads to the opening of a band gap through the removal of the bands near the Fermi level of pristine graphene. A similar phenomenon occurs as a result of covalent functionalization of carbon nanotubes, which has many electronics applications. Using first-principles density-functional calculations, we have investigated the structural and electronic properties of fluorinated graphene as well as carbon nanotubes treated with fluorinated olefins in order to better understand their reaction mechanisms and comparisons to previous experimental work are provided.

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