Optical and Electronic Measurements of Individual Carbon Nanotubes

Steve Cronin

University of Southern California Electrical Engineering - Electrophysics

What is a Carbon Nanotube?

• Imagine rolling a sheet of graphite into a seamless cylindrical tube Honeycomb Graphite Sheet Chirality

(n,m)

: C h = 4a 1 + 2a 2 = (4,2) • Two integers

(n,m)

determine all the properties of a carbon nanotube.

• Nanotubes can have metallic or semiconducting electronic structure, if

(n-m)/

3.

AFM of Carbon Nanotube and DNA Molecules

Carbon Nanotube DNA Bockrath, et al., Nano Lett.,

2

, 187 (2002).

Why Study Carbon Nanotubes?

• 1nm in diameter, up to 1cm in length, aspect ratio of 10 7 • 1 defect in 10 12 C atoms => ballistic conduction • High melting point ~3800 o C • High young’s modulus 1TPa (10 3 times diamond) • High electronic current carrying capacity (10 9 A/cm 2 ) ~10 3 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)

Nanotube Field Effect Transistor (NT-FET) on 12 off 1 m m V gate V bias NT Gate SiO 2 doped silicon 10 8 6 4 2 0 -10 semiconducting -5 0

Gate Voltage (V)

5 10 1.2

1 0.8

0.6

0.4

0.2

0 -10 metallic -5 0

Gate Voltage (V)

5 10

Single Nanotube Raman Spectroscopy

Despite the extremely small geometric cross-section the Raman signal from a single isolated nanotube can be observed.

E ii • 10 5 enhancement in scattering cross-section due to singularities in the DOS • Resonance occurs when E laser =E ii • Only observe nanotubes that are resonant with E laser

Metallic Semiconducting RBM

Jorio,

et al

., PRL,

86

, 1118 (2001)

G-band

Strain Nanotubes

1 m m AFM tip unstrained length =3.8

m m strain = 20nm  0.53%  5.3GPa Stress

Raman Spectra of Strained NT

1 m m AFM tip unstrained length =3.8

m m 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).

Raman Spectra of Broken NT

strain=1.65% broken • 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).

1 m m

Thank You!

2 m m 1 m m AFM tip

Thank You!

1 m m

People:

Rajay Kumar, Hao Zhou, Adam Bushmaker (USC) 2 m m 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)

Grants:

1 m m • NSF Grant Nos. DMR-01-16042 and DMR-02-44441 • NSEC Grant No. PHY-01-17795 • Dupont-MIT alliance AFM tip