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Carbon Nanotubes and Their Methods of Synthesis


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Carbon Nanotubes and Their Methods of Synthesis

Carbon Nanotubes and Their Methods of Synthesis

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  • 1. Carbon Nanotubes and Their Methods of Synthesis
  • 2. What Are Carbon Nanotubes?
    • CNT can be described as a sheet of graphite rolled into a cylinder
    • 3. Constructed from hexagonal rings of carbon
    • 4. Can have one layer or multiple layers
    • 5. Can have caps at the ends making them look like pills
  • Carbon Nanotubes
    • CNT exhibits extraordinary mechanical properties: Young’s modulus over
    1 Tera Pascal, as stiff as diamond, and tensile strength ~ 200 GPa.
    • CNT can be metallic or semiconducting, depending on (m-n)/3 is an integer (metallic)
    • 6. or not (semiconductor).
  • Nanotube Classification
    • Chirality - twist of the nanotube
    • 7. Described as the vector R (n, m)
    • 8. Armchair vector, R vector, angle Ø
    • 9. Ø= 0º, armchair nanotube
    • 10. 0º < Ø < 30º, chiralnanotube
    • 11. Ø > 30º, zigzag nanotube
  • Multi-walled Nanotubeand Single Walled Nanotube
    • Consist of 2 or more layers of carbon
    • 12. Tend to form unordered clumps
    • Consist of just one layer of carbon
    • 13. Greater tendency to align into ordered bundles
    • 14. Used to test theory of nanotube properties
  • Sources of Carbon
    • Typical Organic/Catalyst Mixtures
    • 15. Xylene/ferrocene (Andrews et al.)
    • 16. Toluene, benzene, xylene, mesitylene, and n-hexane/ferrocene (Vivekchand et al.)
    • 17. Ethylene and ethanol/Fe, Co, and Mo alloys
    • 18. Typical Carrier Gases
    • 19. Argon
    • 20. Hydrogen
  • Chemical Vapor Deposition
    Gas enters chamber at room temperature (cooler than the reaction temperature)
    Gas is heated as it approaches the substrate
    Gases then react with the substrate or undergo chemical reaction in the “Reaction Zone” before reacting with the substrate forming the deposited material
    Gaseous products are then removed from the reaction chamber
  • 21. Nanotube Synthesis By CVD Process
    • Source of carbon atoms usually comes from an organic compound
    • 22. Mixed with a metal catalyst and inert gas
    • 23. Atomized and sprayed into reactor with temperatures ranging from 600ºC to 1200ºC
    • 24. Pyrolysis of organic compound deposits carbon (as soot) and carbon nanotubes on reactor wall (usually a tube constructed from quartz)
  • Nanotube Synthesis By CVD Process
  • 25. Plasma Enhanced CVD Nanotube Synthesis
    • Methane moves toward the catalyst on the substrate
    • 26. Heat of the reactor decomposes methane at the catalyst surface
    • 27. Catalyst is at a slightly cooler temperature so carbon is supersaturated in the catalyst film so carbon precipitates out
    • 28. Carbon forms nanotubes at the surface of the catalyst film
  • Nanotube Synthesis By Arc Discharge in a Magnetic Field
    • Electrodes are composed of high purity graphite (>99.999%)
    • 29. ~70 A at ~18V dc is applied to the electrodes
    • 30. Magnets are placed around electrodes which help align nanotubes during formation
    • 31. Carbon nanotubes are formed at atmospheric pressures from the electrodes
  • Carbon Nanotube Synthesis Using Laser Ablation of Metallic Catalyst
    • A well mixed acetylene-air mixture is burned inside a tube furnace
    • 32. A laser is used to vaporize a metal target (either Fe or Ni)
    • 33. The post-flame exhaust gas is mixed with the metallic vapor and allowed to cool
    • 34. During cooling, carbon nanotubes are formed
  • Medical Applications of CNTs
    • Encase drug into nanotube capsule for more predictable time release
    • 35. DNA sequencing through AFM imaging
    • 36. Nanoelectrodes for implantation
    • 37. Lab on a chip
    • 38. Artificial muscles
    • 39. Vision chip for macular degeneration, retinal cell transplantation