G- and G+ in the Raman spectrum of isolated nanotube: a study on resonance conditions and lineshape

• Published in: Physica Status Solidi (b) 2008-10, Vol.245 (10), p.2189-2192
• Main Authors: Telg, H., Fouquet, M., Maultzsch, J., Wu, Y., Chandra, B., Hone, J., Heinz, T. F., Thomsen, C.
• Format: Article
• Language: English
• Subjects: 63.22.+m; 78.30.Na; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Lattice dynamics; Nanotubes; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures; Phonons in low-dimensional structures and small particles; Physics
• ISSN: 0370-1972; 1521-3951
• DOI: 10.1002/pssb.200879658

We analyze the high‐energy Raman modes, G+ and G–, in a pair of one metallic and one semiconducting nanotube grown across a 100 mm wide slit. By combining Raman resonance profiles of the radial breathing mode and the high‐energy modes, we assign the broad G– peak to a metallic and the G+ peak to a semiconducting nanotube. Considering theoretical predictions we show that both peaks, G– and G+, originate from the LO phonon. The G– peak is the longitudinal mode of the metallic tube; it is broadened and downshifted due to strong electron‐phonon coupling in the metallic nanotube. The G+ peak is due to the longitudinal mode in the semiconducting tube. An asymmetric lineshape of the G– peak agrees with observations of the asymmetry to be an intrinsic feature of metallic nanotubes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)