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Control of Size of Graphene Domain Synthesized by Chemical Vapor Deposition

Amini, Negar | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48470 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Ghotbi, Sirus; Karimi Sabet, Javad
  7. Abstract:
  8. The chemical vapor deposition (CVD) of graphene from methane on a copper substrate is the most promising method for production of large-area graphene films. There have been long-standing challenges in this field such as controlling the graphene coverage, film quality, the number of layers, and the nucleation density of graphene domain. These challenges can be overcome by developing a fundamental understanding of the graphene growth process. The main aim of this study is to control nucleation density of graphene domains. Chemical vapor deposition (CVD) graphene is polycrystalline, and grain boundaries in graphene film have been identified to degrade the properties of graphene as a membrane and also decline the electrical and mechanical properties of the film, therefore, the electrical, mechanical and membrane properties of graphene could be improved by increase in the size of single crystal domain. Thus, it is important to control the nucleation and growth of graphene sheet during the chemical vapor deposition method to attain large and high-quality single crystal domains. This study is intended to investigate experimentally and theoretically the effects of main operating parameters of graphene synthesized by chemical vapor deposition on the nucleation density and growth of graphene domains. In the early step of nucleation, the nucleation density was controlled to form a few nucleuses and following that nucleuses was allowed to grow. Firstly, the effect of Synthesis parameters such as annealing time, methane gas flow rate, heating ramp rate, different pretreatment method and copper surface oxidation on nucleation density and nucleus growth was investigated; then the effect of the main parameters including temperature, pressure, and hydrogen flow rate, which are affecting the supersaturation was investigated to control nucleation density and growth of graphene. In this study, Box-Behnken, an optimization method to evaluate the effects and interaction of process parameters on the response, was employed to achieve a graphene film with low nucleation density and large domain size. The response surface model predicted the optimization conditions as follows: the temperature of 1030 c, pressure of 1.02 torr, the hydrogen flow rate of 2 Sccm, methane flow rate of 0.5 Sccm and under this condition nucleation density of graphene could reach to ~ 3132 nuclei/mm2 and the dimension of single crystal grain grow up to ~ 27. Furthermore, a mathematical model based on Classic nucleation theory was proposed to ascertain any correlations between the nucleation density and main Synthesis parameters (temperature, pressure, and methane to hydrogen flow rate). The nucleation density and domain size was measured using both Scanning Electron Microscopy and optical microscope; in addition, Raman Spectroscopy was employed to determine the number of layers, uniformity and quality of the graphene films
  9. Keywords:
  10. Graphene ; Nucleation ; Growth ; Supersaturation ; Chemical Vapor Deposition (CVD)

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