Robert Almairac

ELECTROCHEMICAL INTERCALATION OF LITHIUM INTO MULTIWALL CARBON NANOTUBES

Abstract Electrochemical intercalation of lithium into carbon electrodes containing multiwall nanotubes produced by the arc-electric technique has been carried out in button cells. X-ray diffraction (XRD) and 7 Li NMR spectroscopy coupled with electrochemical characterisation allow us to study the structural modifications induced by the intercalation of the alkali metal between the graphene shells and the nature of interactions between lithium species and the host material. Furthermore, direct observation of individual nanotubes by transmission electron microscopy (TEM) reveals that while the lithiated nanotubes are intercalated very inhomogeneously, the electrochemical intercalation process seems to be reversible and to proceed through the graphene walls via structural defects.

Electrochemical lithium intercalation into multiwall carbon nanotubes : a micro-Raman study

Abstract The electrochemical intercalation of lithium into carbon electrodes containing multiwall carbon nanotubes produced by electric arc technique was carried out in button cells in different electrolytes. An exfoliation of graphene layers was observed with the electrolyte LiPF 6 (1M) dissolved in ethylene carbonate (EC), propylene carbonate (PC) and dimethyl carbonate (DMC) (1:1:3 by volume). Raman spectra were recorded to elucidate the lithium intercalation mechanisms of multiwall nanotubes. The spectral changes of the Raman E 2g band showed that the lithium was intercalated between graphene layers of carbon nanotubes without the formation of n -staged phases with n higher than 2 in contrast to the intercalation into graphite which proceeds via the formation of staged graphite intercalation compounds.

On the diffraction pattern of C

Abstract.We present detailed calculations of the diffraction pattern of a powder of bundles of C60 peapods. The influence of all pertinent structural parameters of the bundles on the diffraction diagram is discussed, which should lead to a better interpretation of X-ray and neutron diffraction diagrams. We illustrate our formalism for X-ray scattering experiments performed on peapod samples synthesized from 2 different technics, which present different structural parameters. We propose and test different criteria to solve the difficult problem of the filling rate determination.

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This article presents a very simple process to align macroscopic quantities of single-wall carbon nanotubes (SWNT), the alignment being controlled by x-ray diffraction. A pellet of SWNT is obtained by pressing a raw nanotube powder up to a pressure of 10 kbars. A detailed study of the most characteristic lines in the diffraction pattern reveals that the tubes have their axis aligned in the plane of the pellet within an out-of-plane spread angle of ∼4°. We also show that the intense small-angle signal—which is observed in all SWNT diffraction diagrams—can be assigned to both the form factor of the isolated nanotubes in the sample and the form factor of the bundles with various size and shape.

peapods

Abstract We perform Raman investigation on two different samples of single-wall carbon nanotube (SWNTs). The first sample (S1) contains a majority of thick bundles, and the second sample (S2) only contains thin bundles and/or isolated SWNT. Our Raman study reports experimental evidences on the vanishing of the Breit–Wigner–Fano (BWF) resonance when the size of the bundle decreases.

Orientation of single-walled carbon nanotubes by uniaxial pressure

The low-frequency excitations of C{sub 60} chains inserted inside single-walled carbon nanotubes (SWNTs) have been studied by inelastic neutron scattering on a high-quality sample of peapods. The comparison of the neutron-derived generalized phonon density of states (GDOS) of the peapods sample with that of raw SWNTs allows the vibrational properties of the C{sub 60} chains encapsulated in the hollow core of the SWNTs to be probed. Lattice dynamical models are used to calculate the GDOS of chains of monomers, dimers, and polymers inserted into SWNTs, which are compared to the experimental data. The presence of strong interactions between C{sub 60} cages inside the nanotube is clearly demonstrated by an excess of mode density in the frequency range around 10 meV. However, the presence of a quasielastic signal indicates that some of the C{sub 60}s undergo rotational motion. This suggests that peapods are made from a mixture of C{sub 60} monomers and C{sub 60} n-mer (dimer, trimer, ..., polymer) structures.

About the profile of the tangential modes in single-wall carbon nanotube bundles

We have investigated the experimental X-ray and far-infrared responses of three polythiophenes synthesized from a thiophene, alpha-bithiophene, and alpha-quaterthiophene monomer. The X-ray data show that the crystallinity of the different polythiophene samples depends on the synthesis conditions. An excellent correlation between the crystallinity of polythiophenes and their far-infrared signatures is demonstrated. In addition, the assignment of the far-infrared phonon modes in polythiophenes is given by using both an experimental filiation procedure and first-principles calculations. In particular, the ring libration inside the polymeric chain, directly involved in the electron-phonon coupling, is assigned.

Low-frequency excitations of C{sub 60} chains inserted inside single-walled carbon nanotubes

Macroscopic fibers of single-wall carbon nanotube bundles were generated in an electric arc experiment in carbon monoxide helium mixtures. The fibers have diameters between 0.1 and 0.5 mm and reached lengths up to 2.5 cm. Scanning and transmission electron microscopy showed that the fibers consist predominantly of bundles of single-wall carbon nanotubes and metal particles but very little contamination of other carbon products. X-ray diffraction measurements suggest a preferable orientation of the nanotubes along the fiber axis.

Correlations between structure and far-infrared active modes in polythiophenes.

Abstract The stability during a long time of a c 70 vapour grown single crystal corresponding to the hexagonal (hcp) phase, has been studied by x-ray diffraction. At room temperature the symmetry of the crystal is orthorhombic. The domain structure of this phase is presented. A strong evolution of the mosaic spread is observed over a period of 4 months. It corresponds to a progressive destruction of the sample.

Macroscopic fibers of carbon nanotubes produced by electric arc discharge

A new synthesis method has been invented for the production of carbon nanotubes. We have called this method the aerosol method since the fundamental synthesis routine is to create aerosols of organic solvent and metal particles by atomising a solution of a metal salt in a solvent using pure hydrogen gas. This method enables us to easily control the size of the catalyst particles. Reactions have been carried out at 700°C and 1000°C and in both cases multi‐walled carbon nanotubes have been produced. The tubes are characterised using scanning and transmission electron microscopy, and X‐ray diffraction.