Resonance Raman Studies Of Length-Dependent Effects In Carbon Nanotubes

M. S. Dresselhaus, MIT, DMR 04-05538

In 2005, Prof. Dresselhaus worked with graduate students S. G. Chou, H. B. Son, junior faculty J. Kong, and collaborators at Dupont to study length dependent effects on the optical properties of DNA-wrapped single walled carbon nanotubes using Resonance Raman spectroscopy.

The direct correlation observed between nanotube length and relative D-band intensity suggests that the relative D-band intensity can be used as a qualitative gauge to evaluate the length of the nanotubes. Furthermore, the size dependent behavior of the symmetry breaking D-band observed in nanotubes is compared with the size-dependent effects observed in nanographite. The observed spectral differences suggest important differences in optical processes occurring in one and two dimensional carbon materials systems.

Phonon Anomalies in Carbon Nanotubes and Graphite

M. S. Dresselhaus, MIT, DMR 04-05538D-band phonon

Г M K ГElectron Wavevector

15

10

5

0

-5

-10

Ele

ctro

n E

nerg

y (e

V)

M K ГK/2Phonon Wavevector

Pho

non

Fre

quen

cy (

cm-1)

1600

1500

1400

1300

1200

• The D-band phonon opens the dynamical electronic band gap in carbon nanotubes and graphite

• The dynamical electronic band gap lowers the total energy and softens the D-band phonon frequency

• The G'-band (overtone of the D-band) in carbon nanotube bundles shows dispersion with the applied potential when the states near the band gap are emptied

2665

2660

2655

0.0 0.5 1.0Applied Potential (V)

Ram

an

Shi

ft (

cm–

1)

568nm

● ▲

NaClKCl

P. M. Rafailov et al., J. Phys. Chem. B 108, 19241 (2002)

M K ГK/2Phonon Wavevector

Pho

non

Fre

quen

cy (

cm-1)

1600

1500

1400

1300

1200

Phonon Anomalies in Carbon Nanotubes and Graphite

M. S. Dresselhaus, MIT, DMR 04-05538D-band phonon

Г M K ГElectron Wavevector

15

10

5

0

-5

-10

Ele

ctro

n E

nerg

y (e

V)

• The D-band phonon opens the dynamical electronic band gap in carbon nanotubes and graphite

• The dynamical electronic band gap lowers the total energy and softens the D-band phonon frequency

• The G'-band (overtone of the D-band) in carbon nanotube bundles shows dispersion with the applied potential when the states near the band gap are emptied

2665

2660

2655

0.0 0.5 1.0Applied Potential (V)

Ram

an

Shi

ft (

cm–

1)

568nm

● ▲

NaClKCl

P. M. Rafailov et al., J. Phys. Chem. B 108, 19241 (2002)

Education and Outreach

Every year PI, Mildred Dresselhaus meets with a largenumber of students across the United States in a mentoring context. She accepts invitations to deliver colloquia in a wide variety of educational settings and during these visits she tries to include on her agenda achance to hold mentoring sessions with graduate and undergraduate students, as well as postdocs where mentoring and career issues are informally and openly discussed.

Mentoring sessions with women faculty also take place on someof these visits.

Mildred Dresselhaus also regularly accepts invitations to spread public understanding and awareness of science issues and to encourage science literacy to lay audiences. On July 19, 2005 she addressed the Pinhead Town Talk, sponsored by the Pinhead Institute and the Telluride Science Research Center, in Telluride, CO. The day before, she was a guest on the radio show “Rocky Mountain Bedrock”