Carbon nano materials

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Carbon nano materials

  1. 1. PRESENTED BY: JUSTIN GEORGE University of Antwerpen 1
  2. 2. Allotropic forms of carbon 2
  3. 3. why carbon naotubes are so special?  Electrical properties depend on geometry of nanotube  Tremendous current carrying capacity 1 billion Amps/cm2  Excellent heat conductor twice as good as diamond  High strength much higher than high-strength steel  Young Modulus ~ 1 TPa (SWNT) and 1.25 TPa (MWNT) (Steel: 230 Gpa)  High Aspect Ratio: 1000 – 10,000  Density: 1.3 – 1.4 g/cm3  Maximum Tensile Strength: 30 GPa  Thermal Conductivity: 2000 W/m.K (Copper has 400 W/m.K) 3
  4. 4. What is carbon nanotubes?  Carbon nanotubes are a hexagonal shaped arrangement of carbon atoms that has been rolled into tubes. Composites Science and Technology 61 (2001) 1899–1912 4
  5. 5. Carbon naotube family 5
  6. 6. Classification of carbon nanotubes  Single walled carbon nanotubes (SWNT) (0.4 -2 nm)  Multiwalled carbon nanotubes (MWNT) (2-100 nm)  Metallic (n =m or n-m =3i, i is an interger)  Semiconductor (all other cases) Depends on the geometry 6
  7. 7. Diameter of the tube and chiral vector.  The diameter d of the carbon nanubes are given by Where is the nearest carbon-carbon bond length and C is the chiral vector or roll-up vector. where the chiral angle 7
  8. 8. Carbon nanotube synthesis  Arc discharge  Laser ablation  CVD (chemical vapour deposition) 8
  9. 9. Arc discharge method  cathode gets consumed, CNTs in cathodic soot  structure of CNTs depends on: current I, voltage V, He gas pressure, anode material, distance between the electrodes 9
  10. 10. Arc discharge method 10
  11. 11. Laser vaporization  Laser vaporizes the graphite target at high temperature in an inert atmosphere  nanotubes formed at the cooler surface of the chamber as the vaporized carbon condenses. 11
  12. 12. Catalytic method  Hydrocarbon in contact with hot metal nano particles and decompose into hydrogen and carbon  If the interaction with catalytic substrate is weak the carbon diffuses down and push the nano particle up “tip-growth model” 12
  13. 13. Characterization of CNT’s  STM (Scanning tunneling microscopy )  AFM (Atomic force microscopy)  TEM (transmission electron microscopy)  SEM (scanning electron microscopy)  Raman spectroscopy 13
  14. 14. Quantum Effect  Conductance appears to be ballistic over micron scales, even at room temperature.  Ballistic = no dissipation in the tube itself = very high current densities are possible.  Conductance increase with more CNTs are in contact with liquid metal.  Frank et al., Science 280, 1744 (1998). 14
  15. 15. Energy Rayleigh Scattering (elastic) The Raman effect comprises a very small fraction, about 1 in 107 of the incident photons. Stokes Scattering Anti-Stokes Scattering h 0 h 0 h 0 h 0 h 0 h m h 0+h m E0 E0+h m Raman (inelastic) Virtual State
  16. 16. Raman scattering of CNT 16
  17. 17. Raman signals in SWNT’s  Radial breathing mode (observed up to 3 nm in SWNTs and MWNTs )  D-band (1350 ) –Resonant nature.  G-band (1530 -1620 )  G’ band (depends on diameter of CNTs)  Other weak features.  Resonance is diameter selective. 17
  18. 18. Significance of Raman signals  RBM is useful to identify the presence of SWNT’s in the carbon material and to determine the diameter of SWNT’s.  G-mode corresponds to planar vibrations of carbon naotubes and is present in graphite like material ( carbon materials )  D-mode generate from the structural defects of graphite like carbon.  G/D ratio is used to find quality of carbon nanotubes (higher ratio, higher quality) 18
  19. 19. Radial-Breathing Mode Diameter of the carbon nanotube Breathing mode : 100 – 350 The growth temperature, Diameter of nanotube increases with increase in growth temperature 19
  20. 20. RBM as a function of diameter  A particular diameter is excited at a given laser frequency (Resonance Raman effect)  In a range of laser frequency the RBM frequency –diameter plot can be made which agree well with the theory. 20
  21. 21. Temperature dependence of G-band  Intensity of G-band decreases exponentially with temperature.  The intensity is independent of surface morphology and preparation method.  This can be used to measure the temperature of the sample.  A shift in the G+ peak can also be observed as the temperature increases. 21
  22. 22. Distinction of SWNTs, DWNTs and MWNTs using Raman spectroscopy  Can distinguish SWNT, DWNT and MWNT from a mixture of sample .  G/D ratio show MWNTs are low quality. 22
  23. 23. Identify metallic and semiconductor SWNT using Raman spectra.  Frequency is independent of diameter but depends on diameter and metallic and semiconductor nature of SWNT .  The frequency downshift of metallic SWNT is more than semiconductor SWNT. 23
  24. 24. Characterization of water filled CNT using Raman spectroscopy  Resonance Raman spectra of SWNT (a) S1 raw sample (c) air oxidized and acid treated sample (used to open the SWNT).  (b) and (d) are S1 and S2 respectively with empty (0) and filled nanotubes.  24
  25. 25. Nanotube elecronics 25
  26. 26. CNT gas sensors  Chemical doping induces a strong change in the conductance.  Detect small concentration gas with high sensitivity at room temperature.  Can detect NO2, NH3 etc. with fast response time. (Shu Peng and Kyeongjae Cho, Department of Mechanical Engineering, Stanford University) 26
  27. 27. AFM (atomic force microscopy )  1. Laser  2. Mirror  3. Photodetector  4. Amplifier  5. Register  6. Sample  7. Probe  8. Cantilever  Uses van der Waals force between the tip and the surface 27
  28. 28. Nanotube as AFM tip  Exceptional mechanical strength and large aspect ratio  Survive tip crash due to accidental contact with observation surface  Slender and well defined tip, so higher resolution. 28
  29. 29. CNT mechanical sensors  Conductance decreases as the AFM tip pushes the nanotube down, but recovers as the tip retracts.  Full reversibility of conductance, so can be used as a mechanical sensor. 29
  30. 30. CNT Nanothermometer •Continuous, uni-dimensional column of Gallium in CNT •Gallium has greatest liquid range (30 – 2,403 °C) and low vapour pressure at high temperature. • Height of liquid gallium varies linearly and reversibly with temperature • Expansion coefficient same as macroscopic gallium. • Gallium meniscus perpendicular to inner surface of CNT • Easy to read and suitable for microenvironment. Gao and Bando, Nature (2002) 30
  31. 31. CNT nanobalance  Nanobalance can measure a mass small as 22 fg (femtogram)  Time dependent voltage applied cause time dependent force and dynamic deflection, by adjusting the frequency resonance excitation can be achieved  E, modulaus , L -length, t - thickness, desnsity , effective mass Most sensitive and smallest balance in the world Poncharal et al., Science (1999) 31
  32. 32. CNT infrared detector  SWNT based IR detectors have excellent sensitivity, response time, dark current characteristics. 32
  33. 33. Applications of carbon nanotubes 33
  34. 34. Blacker than black 34
  35. 35. Electron field emission of CNT  Electric field lines concentrated on sharp regions, since CNT have sharp tip the geometry is favorable for field emission.  Electron emission can be observed with about 100 V on single CNT.  Application in field emission display. 35
  36. 36. Novel hard disk  A novel data storage system capable of 1015 bytes/cm2 is being explored. In this system, H atoms would be designated as 0 and F atoms as 1. A tip that can distinguish between 0 and 1 rapidly and unambiguously is being investigated.  http://www.ipt.arc.nasa.go v/datastorage.html 36
  37. 37. Other applications  Gas storage – as CNT has very large surface area gases like Hydrogen can be absorbed and stored  Super capacitor- can store large amount of energy and can deliver very high peak power (CNT supercapacitor have 7 times more energy density than commercial activated carbon based supercapacitor)  Nanomachines- CNT based nanogear with benzene molecule bonded as teeth. 37
  38. 38. Thank you 38

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