Steve CroninUniversity of Southern California

Electrical Engineering - Electrophysics

Optical and Electronic Measurements of Individual Carbon Nanotubes

• 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.

What is a Carbon Nanotube?

Chirality (n,m):

Ch = 4a1 + 2a2 = (4,2)

AFM of Carbon Nanotube and DNA Molecules

Bockrath, et al., Nano Lett., 2, 187 (2002).

Carbon Nanotube

DNA

Why Study Carbon Nanotubes?

• 1nm in diameter, up to 1cm in length, aspect ratio of 107

• 1 defect in 1012 C atoms => ballistic conduction • High melting point ~3800oC • High young’s 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)

Vgate

Gate

NT

Vbias

SiO2doped silicon

0

2

4

6

8

10

12

-10 -5 0 5 10

Gate Voltage (V)

AC

Cu

rren

t (n

A)

on off

1m

Nanotube Field Effect Transistor (NT-FET)

0

0.2

0.4

0.6

0.8

1

1.2

-10 -5 0 5 10

Gate Voltage (V)

AC

Cu

rren

t (n

A)

metallic

semiconducting

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

Eii

• 105 enhancement in scattering cross-section due to singularities in the DOS

• Resonance occurs when Elaser=Eii

• Only observe nanotubes that are resonant with Elaser

Semiconducting

Metallic

RBM G-bandJorio, et al., PRL, 86, 1118 (2001)

Strain Nanotubes

AFM tip

1m

unstrained length =3.8mstrain = 20nm 0.53% 5.3GPa Stress

Raman Spectra of Strained NT

unstrained length =3.8m

strain = 20nm 0.53% 5.3GPa Stress

AFM tip

1m

Cronin, et al., PRL, 93, 167401 (2004).

• 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

broken

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).

strain=1.65%

AFM tip

1m

1m

2m

Thank You!

AFM tip

1m

1m

2m

Thank You!

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)

People:

• NIRT ECS-0210752• NSF Grant Nos. DMR-01-16042 and DMR-02-44441• NSEC Grant No. PHY-01-17795• Dupont-MIT alliance

Grants: