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Carbon nanotubes

Carbon nanotubes. Stephanie Reich Fachbereich Physik, Freie Universität Berlin. Pure sp 2 & sp 3 carbon. 1991. iron age. 2004. 4 cen BC. 1985. Single-walled carbon nanotubes. Nanotubes are not one, but many materials Nanotubes consist only of surface atoms.

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Carbon nanotubes

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  1. Carbon nanotubes Stephanie Reich Fachbereich Physik, Freie Universität Berlin

  2. Pure sp2 & sp3 carbon 1991 iron age 2004 4 cen BC 1985

  3. Single-walled carbon nanotubes • Nanotubes are not one, but many materials • Nanotubes consist only of surface atoms diameter: 1 – 5 nm, length: up to cm U. Bristol

  4. Single-walled carbon nanotubes • Growth of carbon nanotubes • Zone folding & fundamentals • Electronic properties • Optical properties • Nanotube vibrations • (Functionalization)

  5. Nanotube growth • grow out of a carbon plasma • laser ablation • arc discharge • chemical vapor deposition • metal catalysts • nickel, cobalt, iron … • carbon tubes • diameter ~ 1 nm • length 500 nm – 4 cm • industrial scale production • started 2005 • since 2009 large scale http://home.hanyang.ac.kr/, www.seas.upenn.edu

  6. Chemical vapor deposition • long tubes & high yield • high quality • high degree of control during growth Hata, Science (2004); Zhang, Nat Mat (2004); Milne

  7. Nanotube growth • grow out of a carbon plasma • laser ablation • arc discharge • chemical vapor deposition • metal catalysts • nickel, cobalt, iron … • carbon tubes • diameter ~ 1 nm • length 500 nm – 4 cm • industrial scale production • started 2005 • since 2009 large scale http://home.hanyang.ac.kr/, www.seas.upenn.edu

  8. Nanotube structure • nanotube diameter d & chiral angle Θ determine microscopic structure Carbon nanotubes (Wiley, 2004) , Freitag group

  9. Nanotube structure • nanotube diameter d & chiral angle Θ determine microscopic structure Carbon nanotubes (Wiley, 2004)

  10. Chiral vector - (n,m) nanotube • nanotube diameter d & chiral angle Θ determine microscopic structure • specified by the chiral vector c around the circumference c = na1 + ma2 = 8 a1 + 8 a2 a2 a1 Carbon nanotubes (Wiley, 2004)

  11. Chiral vector - (10,0) nanotube • nanotube diameter d & chiral angle Θ determine microscopic structure • specified by the chiral vector c around the circumference c = na1 + ma2 = 10 a1 a2 a1 Carbon nanotubes (Wiley, 2004)

  12. Nanotube structure • typical samples contain 40 – 100 different chiralities • controlling chirality during growth is impossible (8,8) (6,6) (10,0) (8,3) Carbon nanotubes (Wiley, 2004)

  13. Quantum confinement • circumference – periodic boundary conditions •  = p diameter/p (p integer) Carbon nanotubes (Wiley, 2004)

  14. Confined phase space K  M Carbon nanotubes (Wiley, 2004)

  15. One-dimensional Brillouin zone Carbon nanotubes (Wiley, 2004)

  16. Band structure (10,0) tube Carbon nanotubes (Wiley, 2004)

  17. quantization in (n,0) n+1 allowed lines between G and M G K = 2/3 KM = 1/3 metals(3,0), (6,0), (9,0), (12,0) … semiconductors(2,0), (4,0), (5,0), (7,0) … general conditionmetallic if (n-m)/3 = integer Metal or semiconductor? – (n-m)/3 (10,0) semiconductor (9,0) metal Carbon nanotubes (Wiley, 2004)

  18. Metal & semiconductor in experiment E k

  19. Concept of zone folding • quantization along the circumference • reduced phase space • find nanotube properties by reference to graphene • works for • electrons, phonons, and other quasi-particles • interactions, e.g., electron-phonon coupling • central concept of nanotube research

  20. Graphene – a semimetal • valence and conduction band touch in a single point Reich, Carbon nanotubes (Wiley, 2004)

  21. HOMO & LUMO • HOMO & LUMO are degenerate • Nanotube chiral vector compatible with HOMO/LUMO wave function? Reich, Carbon nanotubes (Wiley, 2004)

  22. Metal or not? • three nanotube families metal semiconductor small gap semiconductor large gap

  23. Electronic properties of nanotubes • quantum confinement • band gap depends on structure • most properties depend on band gap E k metal semiconductors

  24. Optical properties of nanotubes • Every nanotube – colorful • Bulk nanotube samples – black

  25. Transitions between subbands valence conduction

  26. Chirality from luminescence • every (n,m) nanotube has specific pairs of transition energy • use this for assignment Bachilo, Science (2002)

  27. (6,6) (8,4) (10,0) Chirality from luminescence ? • luminescence detects semiconducting tubes, metallic not • some tubes were not observed Bachilo, Science (2002)

  28. Nanotubes, optics & excitons • chirality, electron-electron, and electron-hole interaction • sensitive to environment E. Malic, M. Hirtschulz

  29. Phonons in carbon nanotubes • 100 – 1000 vibrations • strong coupling to electronic system • radial-breathing mode (RBM) • high-energy mode (HEM) • D mode • twiston and low-energy phonons RBM HEM D mode Raman scattering on carbon nanotubes (Springer, 2006)

  30. Phonons in carbon nanotubes • 100 – 1000 vibrations • strong coupling to electronic system • radial-breathing mode (RBM) • high-energy mode (HEM) • D mode • twiston and low-energy phonons • characterizie nanotubes • presence • metallic/semiconductor • chirality RBM RBM HEM HEM D mode D mode

  31. Electron-phonon coupling • doping hardens phonon frequencies • metallic into semiconducting spectrum? • bundling effect? semiconducting metallic H. Farhat

  32. Phonon softening • vibration periodically opens and closes a band gap • softening of the phonon frequencies • phonon dispersion is singular • q = k1 – k2 Kohn (1959)

  33. Phonons limit nanotube transport • ballistic transport • resistance approaches quantum limit 13kΩ/channel • no scattering by defects • ballistic transport breaks down by hot phonons • phonon emission faster than decay Yang PRL (2000); Javey Science (2003)

  34. Functionalization • change nanotube properties • solubility • composite materials • sensitivity & reactivity • tune pristine properties • electron interaction • defects • vibrations

  35. Summary • Nanotube properties depend on their structure;there is no „typical nanotube“ • Growth of carbon nanotubes produces many different tubes = different materials • Nanotube absorb light & show infrared luminescence • Particularly strong electron-phonon coupling • Functionalize nanotubes for further tailoring

  36. Thanks to… • Cinzia Casiraghi (AvH)Antonio Setaro (FUB)Vitalyi Datsyuk (BmBF) • Rohit Narula (FUB)Sebastian Heeg (ERC)Oliver Schimek (DFG)Asaf Avnon (SfB)Thomas Straßburg (BmBF)Stefan Arndt (BmBF) • Ermin Malić (SfB)Megan Brewster (MIT, NSF) • TU BerlinChristian ThomsenJaninaMaultzsch • MITMichael StranoFrancesco StellacchiJing Kong • KITFrank Hennrich • University of CambridgeStefan HofmannJohn Robertson

  37. The end Thank you!

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