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Phys. Rev. Lett. 96, 127403 (2006) [4 pages]

Temperature Dependence of the Optical Transition Energies of Carbon Nanotubes: The Role of Electron-Phonon Coupling and Thermal Expansion

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S. B. Cronin1,2,*, Y. Yin3, A. Walsh3, Rodrigo B. Capaz4,6, A. Stolyarov2, P. Tangney5, Marvin L. Cohen6, Steven G. Louie5,6, A. K. Swan3, M. S. Ünlü3,7, B. B. Goldberg3,7, and M. Tinkham2
1Department of Electrical Engineering, University of Southern California, Los Angeles, California 90098, USA
2Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
3Department of Physics, Boston University, Boston, Massachusetts 02215, USA
4Universidade Federal do Rio de Janeiro, Caixa Postal 68528, Rio de Janeiro, RJ 21941-972, Brazil
5The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
6Department of Physics, University of California at Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
7Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215, USA

Received 2 August 2005; published 30 March 2006

Tunable Raman spectroscopy is used to measure the optical transition energies Eii of individual single wall carbon nanotubes. Eii is observed to shift down in energy by as much as 50 meV, from -160 to 300 °C, in contrast with previous measurements performed on nanotubes in alternate environments, which show upshifts and downshifts in Eii with temperature. We determine that electron-phonon coupling explains our experimental observations of nanotubes suspended in air, neglecting thermal expansion. In contrast, for nanotubes in surfactant or in bundles, thermal expansion of the nanotubes’ environment exerts a nonisotropic pressure on the nanotube that dominates over the effect of electron-phonon coupling.

© 2006 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.96.127403
DOI:
10.1103/PhysRevLett.96.127403
PACS:
78.67.Ch, 73.22.−f, 78.30.Na

*Email address: scronin@usc.edu

Electronic address: http://www-rcf.usc.edu/~scronin/

 
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