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Engineering Graphene Films from Coal

Vijapur, Santosh H.
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1449157836

Abstract Details

2015, Doctor of Philosophy (PhD), Ohio University, Chemical Engineering (Engineering and Technology).
Graphene is a unique material with remarkable properties suitable for a wide array of applications. Chemical vapor deposition (CVD) is a simple technique for synthesis of large area and high quality graphene films on various metal substrates. Among the metal substrates, copper has been shown to be an excellent support for the growth of graphene films. Traditionally, hydrocarbon gases are used for the graphene synthesis via CVD. Unconventional solid carbon sources such as various polymers and food waste have also shown great potential for synthesis of graphene films. Coal is one such carbon enriched and abundantly available unconventional source. Utilization of coal as a carbon source to synthesize large area, transparent, and high quality few-layer graphene films via CVD has been demonstrated in the present work. Hydrocarbon gases are released as products of coal pyrolysis at temperatures ≥400 °C. This study hypothesized that, these hydrocarbon gases act as precursors for the synthesis of graphene films on the copper substrate. Hence, atmospheric pressure CVD and low temperature of 400 °C were utilized initially for the production of graphene films. These conditions were suitable for the formation of amorphous carbon (a-C) films but not crystalline graphene films that were the objective of this work. The synthesized a-C films on the copper substrate were shown to be uniform and transparent with large surface area. The thickness and surface roughness of the a-C films were determined to have typical values of ~5 nm and 0.55 nm, respectively. The a-C film has >95 % optical transmittance and sheet resistivity of 0.6 MΩ sq-1. These values are comparable to other carbon thin films synthesized at higher temperatures. Further, the a-C films were transferred onto any type of substrate such as silicon wafer and titanium foil, and can be utilized for diverse applications. However, crystalline graphene films were not produced by implementing atmospheric pressure CVD and low temperature operation. Annealing of copper support was required to remove the oxide layer present on its surface and low pressure operation was demonstrated to be suitable for crystalline graphene film formation. The CVD system and the synthesis procedure were modified to address these issues. This was done by increasing the synthesis temperature, incorporating a vacuum pump for low pressure operation, and implementing two step procedure of annealing the copper substrate followed by subsequent coal pyrolysis for the synthesis of crystalline graphene films. The synthesized few layer graphene films were uniform and continuous with thickness in the range of 3-7 nm. The optical transmittance and electrical conductivity measurements demonstrated that the graphene films have >95 % transparency and sheet resistivity of 5.0 kΩ sq-1, respectively. An investigation of growth mechanism of coal derived graphene films synthesized via CVD was conducted utilizing spectroscopy, microscopy, and chromatography techniques. Gas collection was performed at the graphene synthesis conditions utilizing the CVD reactor without vacuum in operation. Various gases released as products of coal pyrolysis in the CVD reactor were collected and analyzed using gas chromatography. The analysis showed the presence of methane, ethane, ethene, propane, propene, carbon monoxide, and carbon dioxide as coal pyrolysis products. The hydrocarbon gases act as precursors for graphene growth. Raman spectroscopy, selected area electron diffraction (SAED), and X-ray photoelectron spectroscopy (XPS) confirmed the formation of crystalline graphene films at 1055 °C and 18-30 min synthesis. The growth mechanism involves copper catalyzed reaction to produce amorphous carbon film within the first few minutes of synthesis. Raman spectroscopy and SAED validated that lower synthesis times (6-12 min) produced hybrid amorphous carbon films. This is followed by hydrogen catalyzed graphitization of the underlying carbon film to form graphene domains. Optical microscopy and Raman spectra demonstrated the formation of these oval shaped graphene domains as synthesis time was increased (18-30 min). The graphene films are formed by growth and merging of these graphene domains on the copper substrate. The growth mechanism of coal derived crystalline graphene films is presented in the current work.
Gerardine Botte (Advisor)
Valerie Young (Committee Member)
Savas Kaya (Committee Member)
David Ingram (Committee Member)
Hugh Richardson (Committee Member)
137 p.
Chemical Engineering; Chemistry; Engineering; Materials Science; Nanoscience; Nanotechnology
Graphene; Amorphous Carbon; Coal; Chemical Vapor Deposition; Graphene Growth Mechanism

Recommended Citations

Citations

  • Vijapur, S. H. (2015). Engineering Graphene Films from Coal [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1449157836

    APA Style (7th edition)

  • Vijapur, Santosh. Engineering Graphene Films from Coal. 2015. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1449157836.

    MLA Style (8th edition)

  • Vijapur, Santosh. "Engineering Graphene Films from Coal." Doctoral dissertation, Ohio University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1449157836

    Chicago Manual of Style (17th edition)

ohiou1449157836
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This open access ETD is published by Ohio University and OhioLINK.