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Carbon nano materials

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  • 1. PRESENTED BY: JUSTIN GEORGE University of Antwerpen 1
  • 2. Allotropic forms of carbon 2
  • 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. 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. Carbon naotube family 5
  • 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. 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. Carbon nanotube synthesis  Arc discharge  Laser ablation  CVD (chemical vapour deposition) 8
  • 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. Arc discharge method 10
  • 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. 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. Characterization of CNT’s  STM (Scanning tunneling microscopy )  AFM (Atomic force microscopy)  TEM (transmission electron microscopy)  SEM (scanning electron microscopy)  Raman spectroscopy 13
  • 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. 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. Raman scattering of CNT 16
  • 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. 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. 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. 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. 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. 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. 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. 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. Nanotube elecronics 25
  • 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. 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. 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. 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. 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. 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. CNT infrared detector  SWNT based IR detectors have excellent sensitivity, response time, dark current characteristics. 32
  • 33. Applications of carbon nanotubes 33
  • 34. Blacker than black 34
  • 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. 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. 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. Thank you 38

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