This document discusses carbon nanotubes and their methods of synthesis. It begins by defining carbon nanotubes as sheets of graphite rolled into cylinders that can have single or multiple layers. It then discusses their extraordinary mechanical properties and classification based on chirality. Common synthesis methods are also summarized, including chemical vapor deposition, plasma enhanced CVD, arc discharge in a magnetic field, and laser ablation of metallic catalysts. Medical applications of carbon nanotubes are briefly mentioned at the end.

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 pillsCarbon 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 ClassificationChirality - 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 nanotubeMulti-walled Nanotubeand Single Walled NanotubeMWNTConsist of 2 or more layers of carbon

12. Tend to form unordered clumpsSWNTConsist of just one layer of carbon

13. Greater tendency to align into ordered bundles

14. Used to test theory of nanotube propertiesSources 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. HydrogenChemical Vapor DepositionGas enters chamber at room temperature (cooler than the reaction temperature)Gas is heated as it approaches the substrateGases then react with the substrate or undergo chemical reaction in the “Reaction Zone” before reacting with the substrate forming the deposited materialGaseous 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 filmNanotube Synthesis By Arc Discharge in a Magnetic FieldElectrodes 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 electrodesCarbon Nanotube Synthesis Using Laser Ablation of Metallic CatalystA 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 formedMedical 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