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Resonant Raman spectroscopy of armchair carbon nanotubes: Absence of broad G− feature

E. H. Hároz, J. G. Duque, W. D. Rice, C. G. Densmore, J. Kono, and S. K. Doorn
Phys. Rev. B 84, 121403(R) – Published 9 September 2011
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Abstract

The appearance of a broad Raman peak at ∼1550 cm−1 (G− peak) in carbon nanotubes has been conventionally attributed to the presence of metallic nanotubes. Here, we present wavelength-dependent resonant Raman measurements on macroscopic nanotube ensembles enriched in armchair species prepared via density gradient ultracentrifugation. Our data clearly show that the broad G− mode is absent for armchair structures and appears only when the excitation laser is resonant with non-armchair “metals.” Due to the large number (∼1010) of nanotubes across several armchair species probed, our work firmly establishes a general correlation between the G-band line shape and nanotube structure.

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  • Received 22 July 2011

DOI:https://doi.org/10.1103/PhysRevB.84.121403

©2011 American Physical Society

Authors & Affiliations

E. H. Hároz1,2, J. G. Duque3,4, W. D. Rice1,2,5, C. G. Densmore3, J. Kono1,2,5,*, and S. K. Doorn4,†

  • 1Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, USA
  • 2The Richard E. Smalley Institute for Nanoscale Science and Technology, Rice University, Houston, Texas 77005, USA
  • 3Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
  • 4Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
  • 5Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA

  • *kono@rice.edu
  • †skdoorn@lanl.gov

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Vol. 84, Iss. 12 — 15 September 2011

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  • Figure 1
    Figure 1
    Optical absorption of the three nanotube suspensions studied: as-produced (AP-SWNT, blue), “metal”-enriched (ME-SWNT, green), and armchair-enriched (AE-SWNT, red). Note ME-SWNT and AE-SWNT show significant suppression of features due to ν=±1 SWNTs as compared to AP-SWNT, indicating the elimination of ν=±1 species and hence ν=0 enrichment by the DGU process.Reuse & Permissions
  • Figure 2
    Figure 2
    Raman spectra of RBM and G band for AP-SWNT, ME-SWNT, and AE-SWNT samples taken at excitation wavelengths (a) 552 nm and (b) 500 nm where SWNTs from families (2n+m)=24 and 21, respectively, are primarily probed. The appearance of the broad G− feature corresponds to resonance with non-armchair species such as (10,4) in ME-SWNT in (a) and (8,5) in AP-SWNT in (b). In the case of sole resonance with armchair species [(8,8) and (7,7)], a single and narrow G+ peak is observed.Reuse & Permissions
  • Figure 3
    Figure 3
    Raman intensity for AE-SWNT taken as a function of Raman shift and excitation wavelength for family (2n+m)=27. (a) RBM region where two clear RBMs due to the (9,9) and (10,7) are observed. (b) Corresponding G-band region where only the G+ peak is observed when resonating primarily with the (9,9) and the appearance of the broad G− coincides with the maximum of the (10,7) RBM.Reuse & Permissions
  • Figure 4
    Figure 4
    Selected resonant Raman spectra for AE-SWNT taken at excitation wavelengths 655-, 610-, 552-, and 500-nm, where resonance primarily occurs with armchairs (10,10), (9,9), (8,8), and (7,7), respectively. In each case, the G-band reflects contribution mainly from the G+ peak only.Reuse & Permissions
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