Length dependence of the Raman spectra of carbon nanotubes

DNA-wrapping technology, combined with size-exclusion chromatography, have made possible the sorting of carbon nanotubes according to length. In particular, length sorted nanotube samples, with finite lengths approaching the exciton size, are now available. Hence, experiments that explore the finite size effects, in addition to length dependence, are now possible. Although there are many experimental and theoretical studies of the diameter dependence of carbon nanotubes, only a few studies of length-dependent effects exist. Raman spectroscopy is a powerful tool for the characterization of carbon nanotubes. Although Raman spectroscopy nominally probes the phonon scattering processes in carbon nanotubes, the technique provides information on a wide variety of phenomena and properties, including diameter and chirality, defects, and electron-phonon coupling. This thesis presents the measurement and analysis of Raman spectra in length sorted, DNA-wrapped carbon nanotubes. Three different samples of short nanotubes having lengths of 100 nm, 70 nm, and 50 nm, where the 100 nm tubes behave quite similarly to long nanotubes, were studied using several different values of laser excitation energy. We study the length and excitation energy dependence of various features, each reflecting different physical processes, in the Raman spectra of the length sorted nanotubes. Specifically, the G-band (which includes the G+ and G- peaks), D-band, G', G*, and RBM Raman features were examined. We have found that the spectra fall into two categories: spectra with a narrow G& peak, and spectra with a broad and asymmetric Gpeak which is commonly observed in metallic nanotubes. Although a mixture of semiconducting and metallic nanotubes are resonant for each laser excitation energy, we tentatively assign the spectra with a narrow G- peak as being from semiconducting tubes, and spectra exhibiting a broad, asymmetric G- peak to metallic tubes.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2009

Author dc:creator

• Zare, Aurea Tucay

Advisor dc:contributor.advisor

• Mildred S. Dresselhaus.

• Electrical Engineering and Computer Science.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/47749

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/47749