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Author ORCID Identifier

https://orcid.org/0000-0002-6200-1952

Document Type

Campus-Only Access for Five (5) Years

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Chemical Engineering

Year Degree Awarded

2019

Month Degree Awarded

May

First Advisor

Christos Dimitrakopoulos

Subject Categories

Chemical Engineering

Abstract

Graphene is a promising material for electronic and mechanical applications due to its excellent charge carrier mobility, two-dimensional structure, and tensile strength, which is ten times higher than steel for the same thickness. Chemical Vapor Deposition (CVD) of graphene on metal surfaces is a relatively economical process for producing it. It requires moderate initial capital investment and produces high-quality, large-area, multi-domain graphene on metals that are usually transferred to another appropriate substrate, depending on the application.

We introduce methods of CVD polycrystalline and single crystalline graphene growth and various monolayer graphene transfer techniques from its copper foil growth substrate to a SiO2/Si wafer with nearly 100% graphene coverage and minimal content of defects in the final graphene film. We also stack multiple layers on top of each other to form multilayer graphene.

Theoretical calculations have predicted the opening of an electronic band gap in a graphene bilayer with interlayer covalent bonds, making it a semiconductor, which is vital for electronics applications. Here we investigate the effectiveness of various processing methods in forming such bonds and importantly identify techniques to detect their existence and their distribution in the graphene plane. We have evidence that plasma treatment and annealing in various atmospheres of bilayer or multilayer graphene produce such interlayer covalent bonds. During the process, two-dimensional graphene–diamond nanocomposite superstructures formed through interlayer covalent bonding of twisted bilayer and multilayer graphene. The interlayer bonding is induced by spontaneously patterned hydrogenation that leads to the formation of superlattices of two-dimensional diamond nanodomains embedded between the graphene layers. Raman and FTIR spectroscopy are used for chemical bonding characterization. Transmission Electron Diffraction is used to study the structural change before and after interlayer bond formation. Back-gate graphene field-effect transistors (GFETs) are fabricated for electrical characterization, UV-Vis spectroscopy was conducted to characterize the materials’ optical absorption behavior and the tunable optical bandgap opening after the interlayer bonds formation.

We also demonstrate the importance of controlling the twist angle in bilayer graphene and show how the method of transferring epitaxial single crystalline graphene from SiC wafers enables accurate control of the twist angle.

Available for download on Sunday, May 10, 2020

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