Carbon Nanotubes

1. Carbon Nanotubes Matthew Smith

2. Contents • What they are • Who developed them • How they are synthesised • What their properties are • What they are used for

3. What they are • A graphene sheet rolled into a seamless cylinder • Multi-walled: concentric or spiral • Single-walled: zig-zag, armchair or chiral • Fullerite: polymerised single walled • Torus: nanotube bent into doughnut shape

5. Developers • Sumio Iijima in 1991 • Brought awareness of them to the scientific community • Radushkevich and Lukyanovich in 1952 • Produced the first images by use of the transmission electron microscope http://www.personal.rdg.ac.uk/~scsharip/tubes.htm

6. Synthesis • Carbon Nanotubes can be synthesised in 3 main ways • Arc Discharge: a current passed between 2 graphite electrodes in a helium atmosphere • Laser Ablation: a pulsed laser vaporises graphite, carbon condenses to form CNT’s • CVD: a carbon containing gas is passed over a heated catalyst, the nanotubes grow, with a catalyst at their end.

7. Arc Discharge • First knowingly created by this method in 1991 by Sumio Iijima • A charge of 50-100A is passed between two graphite electrodes in a helium atmosphere • Carbon condenses on the cathode forming multi-walled nanotubes • By adding Cobalt or Nickel to the anode, single walled nanotubes can be produced • A mass yield of 30% is achieved in this way

8. Laser Ablation • Invented by Richard Smalley • An inert gas is bled into the chamber while a graphite target is vaporised by a pulsed laser • The diameter is determined by the temperature • Carbon condenses on cooler parts of the reactor, forming multi-walled nanotubes • By adding a catalyst of Cobalt or Nickel, single-walled nanotubes can be produced • A yield of 70% can be achieved with this method

9. Chemical Vapour Disposition • First achieved in 1993 • A substrate with a layer of Nano sized Ni, Co and/or Fe particles is heated to approximately 700°C • A carbon containing gas is bled into the reactor and broken apart at the catalysts • Nanotubes of both types grow on the catalysts • If a strong electrical field is present, the nanotubes will follow its direction • There is still ongoing research in this field

11. Properties • Carbon nanotubes have a number of types of properties, these include: • Mechanical • Electrical • Kinetic • Thermal

12. Mechanical While a nanotube may buckle under compressive, torsional or bending stress, it only suffers elastic deformation, not plastic, and when pressure is released, it will ‘spring’ back into its original form.

13. Comparative stress • Below, the force needed to be applied to steel and CNT’s, to make them lose their structural integrity is compared. • A wire of diameter 0.02m is considered. Which gives it a cross sectional area of πx0.12 = 3.14 x 10-4 • Force = Area x Stress • Carbon Nanotube • Force = 3.14 x 10-4 x 52 x 109 • Force = 1.63 x 107 = 16.3 M N = 1666 tonnes • Steel • Force = 3.14 x 10-4 x 0.83 x 109 • Force = 2.60 x 105 = 0.260 M N = 26.5 tonnes

14. Electrical • Conductors: Armchair • Semiconductors: Zig-zag, Chiral • Electrons are conducted through ballistic transport. • Therefore resistance independent of length • Current capacity of 1000 MA cm-3 (copper: 1MA cm-3)

15. Kinetic • In a multi-walled nanotube, there is negligible forces between each individual tube. • This effectively allows the tubes to move freely in and out, or spin around • This property has already been exploited in the worlds smallest rotational motor, as the outer tube acts as a bearing, while the inner tube acts as an axle.

16. Current and Past Applications • Nanotubes have been found in Damascus Steel (1100-1700AD) • Scientists create smallest rotational motor (2003) • Scientists demonstrated the use of nanotubes in lightbulbs, replacing a tungsten filamentwith a carbon nanotube one. (2004) • A prototype high-definition 10-centimetre flat screen made using nanotubes was exhibited. (2005) • Applied Nanotech, in conjunction with six Japanese electronics firms, created a prototype of a 25-inch TV using carbon nanotubes. • Nanotubes used as a scaffold for damaged nerve regeneration (2006) • Nanotubes were alloyed into the carbon fibre bike that won the 2006 Tour de France.

17. Future Applications • Combat Jackets: ultrastrong fibres (MIT) • Concrete: stops crack propagation, increase tensile strenght • Space elevator: low density and high tensile strenght • Bridges: replace steel, less cables will be needed • Ultra-highspeed flywheels: good strenght-weight ratio • Computer circuits: high conductivity, ability to make diodes • Buckypaper: 250x stronger than steel, 10x lighter • Magnets: Torus nanotubes, variable magnetic strenghts • Superconductors: at low temperatures due to ballistic transport • Slick surface: slicker than teflon, and waterproof

18. References http://www.npl.co.uk/mass/research.html http://physicsweb.org/articles/world/11/1/9 http://en.wikipedia.org/wiki/Timeline_of_carbon_nanotubes http://www.crhc.uiuc.edu/ece497nc/scribe/nanotube1.pdf http://en.wikipedia.org/wiki/Potential_applications_of_carbon_nanotubes http://news.bbc.co.uk/2/hi/technology/3224329.stm http://www.nec.co.jp/rd/Eng/innovative/E1/myself.html http://www-g.eng.cam.ac.uk/cnt/papers/qi_jmp.pdf http://www.personal.rdg.ac.uk/~scsharip/tubes.htm http://en.wikipedia.org/wiki/Carbon_nanotube