Steve Cronin

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Optical and Electronic Measurements of
Individual Carbon Nanotubes

• Steve Cronin
• University of Southern California
• Electrical Engineering - Electrophysics

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What is a Carbon Nanotube?

• Imagine rolling a sheet of graphite into a
  seamless cylindrical tube

Honeycomb Graphite Sheet

• Two integers (n,m) determine all the properties
  of a carbon nanotube.
• Nanotubes can have metallic or semiconducting
  electronic structure, if (n-m)/3.

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AFM of Carbon Nanotube and DNA Molecules
Carbon Nanotube
DNA
Bockrath, et al., Nano Lett., 2, 187 (2002).
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Why Study Carbon Nanotubes?

• 1nm in diameter, up to 1cm in length, aspect
  ratio of 107
• 1 defect in 1012 C atoms gt ballistic conduction
  
• High melting point 3800oC
• High youngs modulus 1TPa (103 times diamond)
• High electronic current carrying capacity
  (109A/cm2) 103 times higher than that of the
  noble metals
• Thermal conductivity 6600W/mK at room temperature
  is twice the maximum known bulk thermal
  conductor, isotropically pure diamond 3320W/mK

Despite 18,000 publications, no large scale
commercial applications of nanotubes
Li , Yu, Rutherglen, Burke, Nano Lett., 4 2003
(2004) Fan, Goldsmith, Collins, Nature Materials,
4, 906 (2005)
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Nanotube Field Effect Transistor (NT-FET)
semiconducting
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Single Nanotube Raman Spectroscopy
Eii
Despite the extremely small geometric
cross-section the Raman signal from a single
isolated nanotube can be observed.

• 105 enhancement in scattering cross-section due
  to singularities in the DOS
• Resonance occurs when ElaserEii
• Only observe nanotubes that are resonant with
  Elaser

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Strain Nanotubes
unstrained length 3.8mm strain 20nm ? 0.53
? 5.3GPa Stress
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Raman Spectra of Strained NT
1mm
AFM tip
unstrained length 3.8mm strain 20nm ? 0.53
? 5.3GPa Stress

• D, G, G bands are downshifted by 16.1, 14.8 and
  27.7cm-1 (5 times bulk)
• Lower phonon frequencies as C-C bond length
  increases

Cronin, et al., PRL, 93, 167401 (2004).
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Raman Spectra of Broken NT

• D, G and G downshift by 27, 14 and 40cm-1
• Broken tube resumes original D, G and G values.
• Strain deformations are elastic

Cronin, et al., PRL, 93, 167401 (2004).
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Thank You!
1mm
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Thank You!
People
Rajay Kumar, Hao Zhou, Adam Bushmaker (USC) A.
Stolyarov, Prof. M. Tinkham (Harvard) R. Barnett,
E. Demler (Harvard) Y. Yin, A. Walsh, Prof. A.K.
Swan, Prof. B.B. Goldberg (BU) Prof. M.S.
Dresselhaus (MIT)