Interactions in Carbon Nanotubes and Polymer/Nanotubes Composites as Evidenced by Raman Spectroscopy (Invited)
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Interactions in Carbon Nanotubes and Polymer/Nanotubes Composites as Evidenced by Raman Spectroscopy (Invited) Serge Lefrant, Jean-Pierre Buisson, Olivier Chauvet, Jean-Michel Benoit Institut des Matériaux*, CNRS/University of Nantes, France M. Baibarac, I. Baltog National Institute of Materials, Bucharest, Romania P. Bernier GDPC, University of Montpellier II, France ABSTRACT Carbon nanotubes systems have revealed large potentialities in terms of applications, especially at a nanometric scale. As a consequence, the different interactions which can take place can be of primary importance. In this paper, we report studies carried out on different carbon systems such as single-walled or multi-walled nanotubes and polymer/nanotubes composites. By using Raman spectroscopy, apart from the expected interactions between tubes in bundles which have initiated experiments on individual entities, we put in evidence strong chemical reactions at the interface metal/nanotubes when Ag or Au surfaces are used to carry out Surface Enhanced Raman Scattering experiments. We show in particular that a different behavior is observed for metallic and semiconducting tubes. Also, a high state of disorder is observed, together with the transformation of nanotubes to other carbon compounds. In the case of multi-walled nanotubes, theoretical calculations allow us to interpret the low frequency Raman modes by introducing interactions in concentric tubes, in rather good agreement with experiments. Finally, in polymer/nanotubes composites, an upshift of the radial breathing mode is observed and we show in this case that it originates from the dynamical stress applied by the polymer on the bundles in response to the breathing vibration. INTRODUCTION Carbon Nanotubes are still extensively studied. The emergence of potential applications, exploiting either mechanical or electrical properties, etc..., has led to enormous research works in different domains using both single-walled or multi-walled carbon nanotubes (referred to as SWNTs or MWNTs respectively) or even carbon nanotubes/polymer composites [1]. SWNTs are produced by several synthesis methods such as laser ablation, electric arc and nowadays, catalytic chemical vapor deposition (CCVD) techniques from which samples with different characteristics are obtained [1]. Nevertheless, all of these synthesis procedures lead to samples with large inhomogeneities in terms of diameter distributions, chiralities, etc. Furthermore, whatever the method used, several parameters are known to influence such characteristics, such as temperature, nature of the gas or gas mixture in the synthesis chamber [2], catalytic mixture in CCVD [3], etc. In addition, thermal annealing treatments have been shown to modify the nature of nanotubes, which can be transformed from SWNTs to larger ones by coalescence, then to MWNTs and graphitic compounds in a further step [4]. So, using carbon nanotubes in devices, especially at a nanometric scale, requires control and reproducibility, which is, at the present time, far from be
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