ZA-derived phonons in the Raman spectra of single-walled carbon nanotubes

• Verfasst von: Vierck, Asmus [VerfasserIn]
• Verfasst von: Zaumseil, Jana [VerfasserIn]
• Titel: ZA-derived phonons in the Raman spectra of single-walled carbon nanotubes
• Verf.angabe: Asmus Vierck, Florentina Gannott, Manuel Schweiger, Jana Zaumseil, Janina Maultzsch
• Umfang: 7 S.
• Fussnoten: Gesehen am 17.09.2018
• Titel Quelle: Enthalten in: Carbon
• Jahr Quelle: 2017
• Band/Heft Quelle: 117(2017), S. 360-366
• ISSN Quelle: 1873-3891
• DOI: doi:10.1016/j.carbon.2017.02.101
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1581034156

Abstract

We report the observation of four Raman modes in individual, aligned single-walled carbon nanotubes, with frequencies between the RBM and D modes, and above the G± modes. By studying the diameter and excitation-energy dependence, we find that these strongly dispersive and comparatively intense modes share the lowest-frequency helical phonon branch as the origin, which can be derived from the out-of-plane acoustic (ZA) phonon branch of graphene. This ZA phonon is observed due to a defect-assisted, double-resonant process, similar to the D mode; its two-phonon overtones and combinations with transverse optical (TO) phonons do not require defects. Our assignment is supported by a theoretical model based on sixth-nearest neighbour tight-binding and a force-constant approach. We present a complete theoretical evaluation of the diameter and excitation-energy dependence of the ZA, 2ZA, and TO±ZA modes, which fits very well to our experimental results and previous studies of the so-called region of intermediate frequency modes.