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Nanomaterials - carbon fullerenes and nanotubes

Nanomaterials - carbon fullerenes and nanotubes. Lecture 3 郭修伯. Carbon fullerenes and nanotubes. Carbon graphite form: good metallic conductor diamond form: wide band gap semiconductor Ref:

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Nanomaterials - carbon fullerenes and nanotubes

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  1. Nanomaterials -carbon fullerenes and nanotubes Lecture 3 郭修伯

  2. Carbon fullerenes and nanotubes • Carbon • graphite form: good metallic conductor • diamond form: wide band gap semiconductor • Ref: • “Science of Fullerenes and Carbon nanotubes”, M.S. Dresselhaus, G. Dresselhaus and P.C. Eklund, Academic Press (1996)

  3. Carbon fullerenes • A molecule with 60 carbon atoms C60 • with an icosahedral symmetry • buckyball or buckmister fullerene • C-C distance 1.44 A (~ graphite 1.42 A) • 20 hexagonal faces + 12 pentagonal faces • each carbon atoms: 2 single bonds (1.46 A)+ 1 double bond (1.40 A)

  4. Carbon fullerenes • Initially synthesized by Krätschmer et al. 1990 • C60, C70, C76, C78, C80 Fig 6.1

  5. Carbon fullerenes synthesis • arc discharge between graphite electrodes in 200 torr of He gas • heat at the contact point between the electrodes evaporates carbon • form soot and fullerenes • condense on the water-cooled walls of the reactor • ~15% fullerenes: C60 (13%) + C70(2%) • Separation by mass • liquid (toluene) chromatography

  6. Carbon nanotubes • Ref • M. Terrones, Ann. Rev.Mater. Rev. 33 (2003) 419 • K. Tanaka, T. Yambe and K. Fukui, “The Science and Technology of Carbon Nanotubes” Elsevier, 1999 • R. Saito, G. Dresselhaus and M.S. Dresselhaus, “Physical Properties of Carbon Nanotubes”, Imperial College Press, 1998

  7. Single-wall carbon nanotube (SWCNT) • diameter and chiral angle  • =30° : armchair • = 0° : zigzag • 0° <  < 30° : chiral Fig 6.2 Fig 6.3

  8. Multi-wall carbon nanotube (MWCNT) • Several nested coaxial single-wall tubules (chiral tubes) • typical dimensions: • o.d.: 2-20 nm • i.d.: 1-3 nm • intertubular distance: 0.34 nm • length: 1-100 m

  9. Carbon nanotube synthesis • Initially synthesized by Iijima (1991) by arc discharge • Arc evaporation, laser ablation, pyrolysis, PECVD, eletrochemical • Requires an “open end”: • carbon atoms from the gas phase could land and incorporate into the structure. • Open end maintenance: high electric field, entropy opposing, or metal cluster

  10. Carbon nanotube synthesis • Electric field in the arc-discharge promotes the growth • tubes form only where the current flows on the larger negative electrode • typical rate: 1 mm/min (100A, 20V, 2000-3000°C) • the high temperature may cause the tubes to sinter (defects!!)

  11. Carbon nanotube formation • Single-wall: • add a small amount of transition metal powder (e.g. Co, Ni, or Fe) • Thess et al. (1996) • condensation of laser-vaporized carbon catalyst mixture • low temp: ~1200°C • alloy cluster anneals all unfavorable structure into hexagons -> straight nanotubes

  12. Aligned carbon nanotubes • CVD • on Fe nanoparticles embedded in silica • the catalyst size affects: tube diameter, tube growth rate, vertical aligned tube density • Plasma induced well-aligned tubes • on contoured surfaces • with a growth direction perpendicular to the local substrate surface

  13. Fig 6.5

  14. Fig 6.5 Fig 6.6

  15. Carbon nanotube growth mechanism • Atomic carbon dissolves into the metal droplet • diffuses to and deposits at the growth substrate • mass production • CVD (700~800°C), but poor crystallinity • CVD (2500~3000°C+argon), improved crystallinity • base growth? tip growth?

  16. Tip/base growth • PECVD and pyrolysis: • catalytic particles are found at the tip and explained by the tip growth model • thermal CVD using iron as catalyst: • vertical aligned carbon nanotubes • base growth model • both tip and base growth (depend on catalyst)

  17. Carbon nanotubes purification • Impurities • amorphous carbon and carbon nanoparticles • gas phase method • remove impurities by an oxidation process • burn off many of the nanotubes (especially smaller ones) • liquid phase method • KMnO4 treatment: higher yield than gas phase purification, but shorter length • intercalation methods • reacting with CuCl2-KCl, remove impurities

  18. Carbon nanotube properties • Excellent for stiff and robust structures • carbon-carbon bond in graphite • flexible and do not break upon bending • extremely high thermal conductivity • applications • catalyst, storage of hydrogen and other gases, biological cell electrodes, electron field emission tips, scanning probe tip, flow sensors

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