Coupled Vibrations in Index-Identified Carbon Nanotubes
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Coupled Vibrations in Index-Identified Carbon Nanotubes Dmitry Levshov1,2, Thierry Michel1, Matthieu Paillet1, Xuan Tinh Than1,3, Huy Nam Tran1, Raul Arenal4, Abdelali Rahmani5, Mourad Boutahir5, Ahmed-Azmi Zahab1, Jean-Louis Sauvajol1 1 University Montpellier 2-CNRS, Laboratoire Charles Coulomb, F-34095 Montpellier, France. 2 Faculty of Physics, Southern Federal University, Rostov-on-Don, Russia. 3 Laboratory of Carbon Nanomaterials, Institute of Materials Science, VAST, Hanoi, Vietnam. 4 Laboratorio de Microscopias Avanzadas (LMA), Instituto de Nanociencia de Aragon (INA), University of Zaragoza, Zaragoza, Spain. 5 Research Team Computational Physics and Nanomaterials, Moulay Ismail University, Meknes, Morocco.
ABSTRACT Combining high resolution transmission electron spectroscopy, electron diffraction, and resonant Raman spectroscopy experiments on the same suspended (free-standing) individual carbon nanotubes is the ultimate approach to relate unambiguously the structure and the intrinsic phonon features of these nano-systems. By using this approach, the effect of coupling between nanotubes on the phonons is investigated in two model nano-systems: (i) a bundle of two non-identical SWNTs (inhomogeneous dimer), (ii) double-walled carbon nanotubes. INTRODUCTION The combination of high resolution transmission microscopy (HRTEM), electron diffraction (ED) and resonant Raman spectroscopy (RRS) on an individual, spatially isolated, and suspended carbon nanostructure is the ultimate method to relate unambiguously its structural parameters, optical transitions and Raman-active phonon modes. From 2005, our group has followed this approach to determine the radial breathing mode (RBM) and the G-modes features, as well as to evaluate the transition energies of individual, achiral and chiral, semiconducting and metallic, index-identified suspended single-walled carbon nanotubes (SWNTs) [1-5]. In this communication, we apply the same approach on two van der Waals-coupled carbon nanostructures, namely: (i) a bundle of two non-identical SWNTs (inhomogeneous dimer) and (ii) double- walled carbon nanotubes (DWNTs). An inhomogeneous dimer of SWNTs is characterized by a weak van der Waals interaction between the neighboring carbons of its two constituting SWNTs. Dimers of SWNTs have three electronic configurations, namely: SC-SC, SC-M and M-M, where SC (resp. M) stands for semiconducting (resp. metallic) SWNT. DWNT is a coaxial structure composed of two layers: an inner and an outer SWNT. DWNTs display four different electronic configurations, namely: SC@SC, SC@M, M@SC and M@M. Properties of DWNTs are related to the individual nature of each layer and to the layer
interactions. It was found that the same inner tube can be contained inside different outer tubes [6] leading to different layer interaction strengths with respect to the interlayer distance. In this paper, vibrations of these two coupled nanostructures are investigated by Raman spectroscopy. We focus here on the low-frequency range of the Raman spectrum where the breath
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