Meta- and hybrid-CNTs: A clue for the future development of carbon nanotubes

A new generation of carbon nanotubes (CNTs), which may be named “meta-nanotubes”, is more and more the focus of the research worldwide. They result from the transformation of “regular” CNTs by various ways such as functionalisation, doping, substitution, etc. The new nanomaterials thereby created are likely to exhibit new behaviors, specifically regarding properties that pristine CNTs do not possess (reactivity, solubility, magnetism…). The paper includes the description of the various routes to synthesize hybrid CNTs and their related advantages and limitations, while providing examples of the resulting materials from both literature and author’s team work. Hybrid SWNTs (abbreviated as X@SWNTs) are one example of meta-nanotubes, and consist in SWNTs whose the hollow core is fully or partially filled with foreign atoms, molecules, or compounds. The inserted material may then exhibit a peculiar behavior with respect to the macroscopic state, for several non-exclusive reasons: 1D-dimension preventing electron scattering and enhancing the role of surface atoms, protection from surface adsorption of disturbing molecules by the carbon sheath, anisotropic lattice distortion or creation of new structures due to imposed dimensions, interactions/electron coupling with the surrounding carbon lattice. A wide field is thus open, possibly even wider than for pristine SWNTs

Fluidized bed chemical vapor deposition of copper nanoparticles on multiwalled carbon nanotubes

Multi-walled carbon nanotubes tangled in easy-to-fluidize porous balls have been decorated by pure copper nanoparticles using a pre-industrial fluidized bed chemical vapor deposition process. Copper (II) acetylacetonate Cu(acac)2 was used as precursor. The low precursor volatility led to low deposition rates, responsible for a nonuniformity of the deposit both on the MWCNT balls and from the outer part to the center of the balls. An oxidative pre-treatment of the MWCNTs allowed to increase slightly the deposit weight and uniformity, by creating new nucleation sites on the nanotube surface. It also allowed decreasing the size of Cu nanoparticles by a factor of ten. A decrease of the deposition temperature increased more markedly the deposit weight, by probably favoring the formation of gaseous reactive intermediate species more reactive on the oxidized nanotube surface. A more efficient precursor delivery system would allow reaching higher deposition rates and much more uniform deposits, making possible an industrial production of metallized carbon nanotube

A new insight on the understanding of carbonisation and graphitisation mechanisms

During carbonisation (primary and secondary) and then graphitisation processes, any organic precursor is subjected todeep structural changes which make it evolve from an isotropic to an anisotropic material, with the extent of the anisotropybeing related to the starting elemental composition, and ultimately to the graphitisability. For decades, analysing X-raydiffraction patterns has been used to evidence the related structural evolution of the material, aiming at extracting theaverage crystallite dimension La and Lc as they closely relate to the material physical properties. In particular because of thetwo-dimensional nature of the graphene-based crystallites which develop in the material and, upon heat-treatment, eitherremain so for non-graphitisable carbons or gradually convert partially or fully into three-dimensional crystals forgraphitizable carbons, accurately understanding and analysing XRD patterns has always been an issue. A new approach foranalysing XRD data is described, designated as "bottom-up", meanwhile introducing the concept of Basic StructuralComponent. A better knowledge of the overall thermally-driven structure changes which occur in the material from the cokestage to the ultimate temperature of 2800 °C is achieved, which is expected to apply to any kind of carbons, whatever theirgraphitisability

X-ray diffraction as a tool for the determination of the structure of double-walled carbon nanotube batches

The average structure of double-walled carbon nanotube DWCNT samples can be determined by x-ray diffraction XRD. We present a formalism that allows XRD patterns of DWCNTs to be simulated and we give researchers the tools needed to perform these calculations themselves. Simulations of XRD patterns within this formalism are compared to experimental data obtained on two different DWCNT samples, produced by chemical vapor deposition or by peapod conversion i.e., high-temperature peapod annealing. For each sample, we are able to determine structural aspects such as the number of walls, the diameter distribution of inner and outer tubes, the intertube spacing, and the bundled structure

Ultraviolet photon absorption in single- and double-wall carbon nanotubes and peapods: Heating-induced phonon line broadening, wall coupling, and transformation

Ultraviolet photon absorption has been used to heat single- and double-wall carbon nanotubes and peapods in vacuum. By increasing the laser intensity up to 500 mW, a downshift and a broadening of the optical phonons are observed corresponding to a temperature of 1000°C. The UV Raman measurements are free of blackbody radiation. We find that the linewidth changes for the G+ and G− bands differ considerably in single-wall carbon nanotubes. This gives evidence that the phonon decay process is different in axial and radial tube directions. We observe the same intrinsic linewidths of graphite (highly oriented pyrolytic graphite) for the G band in single- and double-wall carbon nanotubes. With increasing temperature, the interaction between the walls is modified for double-wall carbon nanotubes. Ultraviolet photon induced transformations of peapods are found to be different on silica and diamond substrates

Transport via coupled states in a C60 peapod quantum dot

We have measured systematic repetitions of avoided crossings in low temperature three-terminal transport through a carbon nanotube with encapsulated C60 molecules. We show that this is a general effect of the hybridization of a host quantum dot with an impurity. The well-defined nanotube allows identification of the properties of the impurity, which we suggest to be a chain of C60 molecules inside the nanotube. This electronic coupling between the two subsystems opens the interesting and potentially useful possibility of contacting the encapsulated molecules via the tube.Comment: 6 pages, 3 figure

A new insight on the mechanisms of filling closed carbon nanotubes with molten metal iodides

Filling double-walled carbon nanotubes with iodine and various metal iodides (metals, alkali metals and transition metals) by the molten phase method was performed and the influence of possibly relevant chemical and physical properties of the filling materials on the filling rate was investigated. It was found, within the metal iodides series, that the filling rate can be mainly related to the redox potential (E MIx/M) of the filling material. Other parameters such as the possible formation of dimers, surface tension, or the early release of iodine may also play an additional role in the filling process

Iron deposition on multi-walled carbon nanotubes by fluidized bed MOCVD for aeronautic applications

The fluidized bed MOCVD process has been studied in order to uniformly deposit iron nanoparticles on the outer surface of multi‐walled carbon nanotubes (MWCNTs) tangled in balls of 388 µm in diameter. Using ferrocene as organometallic precursor at atmospheric pressure, various reactive atmospheres of deposition (under N2, air and H2) and an ozone O3 surface pre‐treatment of MWCNTs were tested. Around 10 g Fe/100 g MWNCTs were deposited during each run. Under N2 at 650 °C on the raw MWCNTs, nanoparticles formed of Fe and Fe3C were deposited which have catalyzed the formation of carbon nanofibers (CNFs). 20 h of ozone (O3) pre‐treatment improved the number and distribution of iron nanoparticles but without increasing the surface coverage of nanotubes. A more intense amorphous carbon deposit also appeared. Under H2 at 550 °C, the amorphous carbon was partly eliminated but fewer iron nanoparticles were present. Under air at 450 °C, a part of the MWCNTs was lost and a Fe2O3 shell covered each remaining MWCNTs ball. New works are in progress to increase more markedly the surface reactivity of MWCNTs and to deposit pure iron. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim

The Unexpected Complexity of Filling Double-Wall Carbon Nanotubes With Nickel (and Iodine) 1-D Nanocrystals

A variety of iodine-based one-dimensional (1-D) nanocrystals were introduced into double-wall carbon nanotubes (DWCNTs) using the molten phase method, as an intermediate step for ultimately obtaining encapsulated metal nanowires. Based on high-resolution transmission electron microscopy (HRTEM) observations using different imaging modes (bright field, dark field, and scanningTEM)and associated analytical tools (electron energy loss spectroscopy), it is revealed that the reality of nanotube filling is much more complex than expected. For some iodides (typically NiI2 ), earlier decomposition during the filling step was observed, which could not be anticipated from the known data on the bulk material. Other filling materials (e.g., iodine) show a variety of atomic structuration inside and outside the CNTs, which is driven by the available space being filled. Most of the encapsulated structures were confirmed by modelin