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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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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 • Mass production • Wide application (transparent electrical conductors)
Carbon Nanotubes • Tiny cylinders of carbon atoms • Light • Strong • Good conductivity • Single walled and multi-walled nanotubes
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.
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
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
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
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.
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.
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.
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 ~18m • Weight 2.7µg/cm² (density of 0.0015g/cm³)
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)
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
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
Resistance does not change when the MWNT sheet is flexed * For flexible displays
Sheet resistance of MWNT sheet has a low temperature dependence • Transmission vs. Wavelength • Noise power density lowest for the MWNT sheet (40 ohms)
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
Conclusion Amazingly simple process coupled with the high rate of production will lead to the use of MWNT sheets in many applications