Raman Spectroscopy on Individual Identified Carbon Nanotubes
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Raman Spectroscopy on Individual Identified Carbon Nanotubes
R. Parret1,2, D. Levshov1,2,3, T. X. Than1,2,4, D. Nakabayashi1,2, T. Michel1,2, M. Paillet1,2, R. Arenal5,6, V. N. Popov7, V. Jourdain1,2, Yu. I. Yuzyuk3, A. A. Zahab1,2, and J.-L. Sauvajol1,2 1 Université Montpellier 2, Laboratoire Charles Coulomb, F-34095 Montpellier, France 2 CNRS, Laboratoire Charles Coulomb, F-34095 Montpellier, France 3 Faculty of Physics, Southern Federal University, Rostov-on-Don, Russia 4 Laboratory of Carbon Nanomaterials, Institute of Materials Science, VAST, Hanoi, Vietnam 5 Laboratorio de Microscopias Avanzadas (LMA), Instituto de Nanociencia de Aragon (INA), Universidad de Zaragoza, 50018 Zaragoza, Spain 6 Laboratoire d'Etude des Microstructures, ONERA-CNRS, 92322 Chatillon, France 7 Faculty of Physics, University of Sofia, BG-1164 Sofia, Bulgaria ABSTRACT In this paper, we discuss the low-frequency range of the Raman spectrum of individual suspended index-identified single-walled (SWCNTs) and double-walled carbon nanotubes (DWCNTs). In SWCNTs, the role of environment on the radial breathing mode (RBM) frequency is discussed. We show that the interaction between the surrounding air and the nanotube does not induce a RBM upshift. In several DWCNTs, we evidence that the lowfrequency modes cannot be connected to the RBM of each related layer. We discuss this result in terms of mechanical coupling between the layers which results in collective radial breathing-like modes. The mechanical coupling qualitatively explains the observation of Raman lines of radial breathing-like modes, whenever only one of the layers is in resonance with the incident laser energy. INTRODUCTION Raman measurements on macroscopic ensembles of individualized luminescent semiconducting single-walled carbon nanotubes (SWCNTs), allowed establishing a radial breathing modes (RBM) vs. diameter relationship based on (n,m) assignments from photoluminescence data [1]. In other studies performed on the same kind of samples, the (n,m) indexing of SWNTs was obtained from the best matching between experimental resonance energies and calculated transition energies obtained in the framework of different tight binding approaches. The former was derived from measurements of the RBM excitation profile of a large number of SWCNTs (both semiconducting and metallic) by resonant Raman spectroscopy (RRS). In this way, relationships between RBM frequency and nanotubes’ diameter were derived [2,3,4,5]. More recently, measurements on macroscopic ensembles of SWCNTs, enriched in a specific chirality, permit to discuss the profile of the G-modes of this kind of SWCNTs [6,7]. However, the combination of high resolution transmission microscopy (HRTEM), electron diffraction (ED) and RRS on an individual, spatially isolated, suspended nanotube is the ultimate method to determine unambiguously its structural parameters, optical transitions and Ramanactive phonon modes. We successfully used this combination to determine the RBM and the G bands features, as well as to evaluate the transi
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