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SCIENCE August 19, 2005 (Vol. 309)

¹ NanoTech Institute University of Texas, USA & ² CSIRO (textile and fibre technology), Australia. SCIENCE August 19, 2005 (Vol. 309). Why this paper ?. Large, transparent sheets of carbon nanotubes can be produced at a fast rate. Solid state process Simple & Elegant technique

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SCIENCE August 19, 2005 (Vol. 309)

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  1. ¹ NanoTech Institute University of Texas, USA & ² CSIRO (textile and fibre technology), Australia SCIENCE August 19, 2005 (Vol. 309)

  2. Why this paper ? • Large, transparent sheets of carbon nanotubes can be produced at a fast rate. • Solid state process • Simple & Elegant technique • Mass production • Wide application (transparent electrical conductors)

  3. Carbon Nanotubes • Tiny cylinders of carbon atoms • Light • Strong • Good conductivity • Single walled and multi-walled nanotubes

  4. Carbon nanotube sheets- How are they made? • Ancient art of paper making filtration of nanotubes dispersed in water for a week and peeling the dried nanotubes layer (usually isotropic) from the filter • Partial alignment can be achieved by: - application of high magnetic fields during filtration process (OR) - mechanical rubbing of nanotubes that are trapped in the filter pores.

  5. Other methods to make Carbon nanotube sheets • Nanotube aerogel • Langmuir Blodgett deposition • Casting from oleum(Oleum, SO3 dissolved in H2SO4 Chemical formula H2SO4 x SO3 Molecular weights H2SO4:  98.08 g/mol SO3:      80.06 g/mol) • Spin coating

  6. The paper presents.. • A Method to produce carbon nanotube sheets that are: • Highly oriented • Free standing (self support) With high rate of production that appears to be scalable • Method is based on the previous advances in: * Spinning of carbon nanotube yarns from forests & * Introduction of twist to increase by a factor of 1000 Ref: Multifunctional carbon nanotube yarns by down sizing an ancient technology- M. Zhang et. Al. Science Vol. 306 November 19, 2004 page 135

  7. Nanotube forests • Multiwalled nanotube (MWNT) forest is synthesized by catalytic chemical vapor deposition using acetylene gas as the carbon source • Diameter of the MWNT are ~10 nm • Height of the forests range from 70 to 300 µm

  8. Draw-Twist Process for Nanotube yarn

  9. SEM- micrographs

  10. Nanosheet Team From left: Nanotechnologists Mei Zhang, Ray Baughman and ShaoliFang rest while Ali Aliev, Sergey Lee and Anvar Zakhidov remainstanding. The team sees potential commercial uses for their discovery.

  11. Making Carbon nanosheets

  12. Self supporting • sheet • 3.4cm x 1m. • @ 1m/min. • B) SEM Image @ • 35 degrees • 90 degree rotation • to form a sheet • Four sheets with • 45 deg. Rotation • Two sheets that are • @90 degrees • supporting drops of: • water, orange juice and • Grape juice. 50,000 times the mass of the nanotube sheet.

  13. MWNT aerogel sheets • Contacting the forest sidewall with adhesive strip (like 3M Post-it) and drawing it at away at a steady rate. • 1m/min. for hand drawn sheets • 5m/min. with linear translation stage • 10/min. by winding the sheet on a cylinder • The width of the sheet decreased above 7m/min.

  14. MWNT aerogel sheets … • Nanotubes are oriented in the direction in which the sheet is drawn (anisotropy) • Thickness of the MWNT sheets increased with increase in forest height • Typical thickness of ~18m • Weight 2.7µg/cm² (density of 0.0015g/cm³)

  15. Increasing the density • By dipping it in a liquid (like ethanol) • Thickness reduces to 50 nm and density increases to 0.5g/cc ( factor of 360) • Surface tension effects during evaporation of ethanol reduces the aero gel to thin sheet • Sheet resistance of 700   • Decrease in sheet resistance is less than 10% although the anisotropy ratio decreases from the range (50 –70) to about (10-20)

  16. Increasing the density…. • Transmission 85% for  polarization and 65% for ll polarization (400nm to 2µm) • 85% for non-polarized radiation in the range of 2 to 10 µm • Adhesion between substrate and MWNT sheet is better after shrinking because collapse aerogel increases the contact area

  17. 18 sheets of MWNT oriented 465 MPa/(g/cm³) in the same direction Same with neighboring sheets in 175 Mpa/(g/cm³) orthogonal direction (biaxial) Mylar and Kapton films ~ 160 Mpa/(g/cm³) Ultra-high strength steel ~ 125 Mpa/(g/cm³) Aluminum alloy ~ 250 Mpa/(g/cm³) Strength - Comparison

  18. SEM of MWNT sheet after shrinking

  19. Resistance of MWNT sheet

  20. Resistance does not change when the MWNT sheet is flexed * For flexible displays

  21. Sheet resistance of MWNT sheet has a low temperature dependence • Transmission vs. Wavelength • Noise power density lowest for the MWNT sheet (40 ohms)

  22. Applications • Electrodes in flexible display (replacement for Indium Tin Oxide) -- OLEDs • Solar cells • Solid state lighting • Embedded Antenna or heater in the car windows • Polarized light source

  23. MWNT sheet in OLED

  24. Conclusion Amazingly simple process coupled with the high rate of production will lead to the use of MWNT sheets in many applications

  25. Thank you!

  26. Transparent conducting sheet

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