Hybrid carbon nanotubes: Strategy, progress, and perspectives
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Hybrid carbon nanotubes: Strategy, progress, and perspectives M. Monthiouxa) Centre d’élaboration des Matériaux et d’Etudes Structurales, UPR-8011 CNRS, F-31055 Toulouse cedex 04, France
E. Flahaut Centre Interuniversitaire de Recherche et d’Innovation sur les Matériaux, UMR-5085 CNRS, F-31062 Toulouse, France
J-P. Cleuziou Centre d’élaboration des Matériaux et d’Etudes Structurales, UPR-8011 CNRS, F-31055 Toulouse cedex 04, France (Received 30 June 2006; accepted 7 September 2006)
We introduce the concept of meta-nanotubes, among which are hybrid carbon nanotubes (X@CNTs), which are CNTs whose hollow core is filled—fully or partially—with foreign atoms, molecules, or compounds. The article focuses on the latter, describing their potential interest and the various ways currently available to synthesize them, while providing examples of the resulting materials mainly taken from the author’s works but also from literature, as characterized by means of high-resolution microscopy and related techniques. We discuss advantages and drawbacks of the various synthesis routes to help willing scientists and engineers to define a strategy for X@CNT synthesis with respect to their specific goals and expectations. Some examples of peculiar properties and behaviors of X@CNTs will be provided as well, although such related investigations are still scarcely reported because we are dealing with quite new nanomaterials. I. INTRODUCTION A. Time for a third generation of carbon nanotubes
Although it might not be of common knowledge,1 the evidence for the existence of nanosized, hollow carbon filaments, i.e., carbon nanotubes (CNT), was reported first in 1952,2 as a result of the thermal decomposition of hydrocarbon precursors over transition metal catalysts [a method commonly named catalyst-enhanced chemical vapor deposition (CCVD)]. They were, of course, multi-walled–type CNT (MWNTs), which can be considered the first generation of carbon nanotubes. The second generation of carbon nanotubes was born far later, in 1993, when single-walled CNT (SWNTs) were unexpectedly discovered within the carbon materials produced from electric arc experiments when a graphite anode is loaded with, again, transition metals.3,4 Hence, it has been approximately 13 years for SWNTs, and approximately 50 years for MWNTs (yet definitely boosted by the well-known paper by Iijima5 in Nature in 1991), that CNT have been investigated regarding their possible a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0366 2774
J. Mater. Res., Vol. 21, No. 11, Nov 2006
synthesis routes and properties. Currently, the relevant synthesis processes are defined, and although the electric arc method is still a commercial route, it is clear that CCVD will be the main process for mass production of SWNTs in the near future, as it is for MWNTs already. Likewise, most of CNT properties are now predicted and even demonstrated for many of them. In spite of several aspects that are still worth studying further regarding synthesis
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