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We report single-crystal X-ray diffuse scattering measurements on C-60.C8H8 fullerene-cubane showing that the C-60 molecules are orientationally disordered at 300 and 150K and get ordered at low temperatures. Monte Carlo simulations provide further insight in the orientational behavior of both C-60 and C8H8 molecules; low-temperature molecular orientations are predicted.

We present high-resolution electron microscopy and x-ray diffraction studies of the Al63Cu17.5Co17.5Si2 alloy at room temperature. The sample is found periodic in one direction c and presents tenfold symmetry in the l = 0 diffraction plane perpendicular to this direction. The two complementary techniques show that the sample is not in a 2D quasi-crystalline state but in a microcrystalline state, which restores the overall tenfold symmetry in diffraction pattern. On the basis of our present results, we discuss some relationships that could exist between microcrystalline and quasi-crystalline phases.

Direct observations of the soft mode in A-TCNB by inelastic neutron scattering in association with Raman scattering are presented. These measurements indicate a complex dynamic regime which seems to be intermediate between displacive and order-disorder types.

On the basis of HREM and electron diffraction studies and of previous X-ray single crystal diffraction results, we confirm the existence on a non-quasicrystalline microcrystalline state for the decagonal Al63Cu17.5Co17.5Si2 alloy at room temperature. The HREM results are compared to those obtained for the Al65Cu17.5Co17.5 alloy. Moreover for the first time, a high temperature phase transition towards a quasicrystalline state is revealed in the two compounds.

The dynamics of confined systems is of major concern for both fundamental physics and applications. In this Letter, the dynamics of ${\mathrm{C}}_{60}$ fullerene molecules inside single walled carbon nanotubes is studied using inelastic neutron scattering. We identify the ${\mathrm{C}}_{60}$ vibrations and highlight their sensitivity to temperature. Moreover, a clear signature of rotational diffusion of the ${\mathrm{C}}_{60}$ is evidenced, which persists at lower temperature than in 3D bulk ${\mathrm{C}}_{60}$. It is discussed in terms of confinement and of reduced dimensionality of the ${\mathrm{C}}_{60}$ chain.

cited By 15; International audience; We studied structural changes in C60 and C70 peapods - i.e. C60 and C70 chains inserted inside single-walled carbon nanotubes - when submitted to high pressure and temperature conditions. X-ray diffraction experiments showed that while C60 molecules polymerize inside nanotubes at pressures and temperatures consistent with polymerization in bulk C60 phases, no polymerization is observed in C70 peapods, even at pressures and temperatures above the threshold for polymerization in bulk C70. Tubular confinement in the nanotube container prevents the monomers to rearrange in the way needed for polymerization. This result testifies for the strong influence of confinement on the behaviour of C70.

7 pages; International audience; As-produced carbon nanotubes often contain a fraction of impurities such as metal catalysts, inorganic supports, and carbon by-products. These impurities can be partially removed by using acidic dissolution. The resulting nanotube materials have to be dried to form a powder. The processability of nanotubes subjected to regular (thermal vaporisation) drying is particularly difficult because capillary forces pack and stick the nanotubes irreversibly, which limits their dispersability in polymeric matrices or solvents. We show that this dramatic limitation can be circumvented by using freeze-drying instead of regular-drying during nanotube purification process. In this case, the nanotubes are trapped in frozen water which is then sublimated. As a result the final powder is significantly less compact and, more important, the nanotubes can be easily dispersed with no apparent aggregates, thereby greatly enhancing their processability, e.g., they can be used to make homogeneous composites and fibers. Results from coagulation spinning from water-based dispersions of regularly-dried and freeze-dried nanotubes are compared. We also show that freeze-dried materials, in contrast to regularly-dried materials, can be dissolved in organic polar solvents using alkali-doped nanotubes. High resolution TEM and XRD analysis demonstrate that the nanotube structure and quality are not affected at the nanoscale by freeze-drying treatments.

Encapsulated ${\mathrm{C}}_{70}$ molecules packed in single-walled carbon nanotubes display different orientations depending on the nanotube radius. We present x-ray scattering data obtained on a powder of nanotubes filled with ${\mathrm{C}}_{70}$ molecules. Analytical expressions for calculating the diffraction diagram taking into account fullerene orientations are developed. The comparison between calculations and experiments allows us to conclude that the change from the lying to standing orientation---corresponding to the molecule long axis parallel and perpendicular to the tube axis, respectively---takes place when nanotubes reach a diameter of about $1.42\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. Energy calculations are performed using a Lennard-Jones (6-12) potential, leading to a calculated reorientation diameter in good agreement with that determined experimentally.

8 pages; International audience; We report quantitative experimental study correlating the structure and mechanical properties of fibers made from single-walled carbon nanotubes SWNTs and polyvinyl alcohol PVA. A post-synthesis solvent drawing treatment is used to vary nanotube alignment, whose detailed understanding is a prerequisite for fiber development. Quantitative analysis of nanotube alignment within the fibers with different draw ratios is performed using x-ray scattering. The method is described in detail, and we also show that the improvement of nanotube alignment with draw ratio can be understood within a model of induced orientation at constant volume. Young's modulus and tensile strength increase with nanotube alignment. This is modeled using continuum mechanics in qualitative agreement with experiment, however quantitative differences show that nanotube alignment is not the only parameter controlling the fiber mechanical properties. We suggest that interaction between the SWNTs and PVA chains should also play a significant role.

We report low-temperature magnetisation measurements on a large number of purified ropes of single wall carbon nanotubes. In spite of a large superparamagnetic contribution due to the small ferromagnetic catalytical particles still present in the sample, at low temperature ($T < 0.5K$) and low magnetic field ($H < 80 Oe$), a diamagnetic signal is detectable. This low temperature diamagnetism can be interpreted as the Meissner effect in ropes of carbon nanotubes which have previously been shown to exhibit superconductivity from transport measurements., 10 pages 3 figures

In this chapter, our purpose is to introduce carbon materials, situating the nanotubes inside this polymorphic zoo. We aim at giving the reader the basic notions on carbon materials structural and physical properties, necessary for the understanding of the following chapters. The introductory section gives a historical background about the peculiar carbon element and the numerous carbon materials which have been identified up to now. Then in a second part a classical thermodynamic approach is presented to describe the crystalline and non-crystalline forms of carbon, up to fullerenes and nanotubes. It is shown that the choice of the processing ways, including the crucial role played by the temperature, is fundamental to control the final type of material. In particular the different processes to prepare non-crystalline graphitic carbons are described in Sect. 1.3. Based on the texture symmetries different types of classical carbon materials are presented in relation with their numerous industrial applications. Then a general introduction is given concerning mainly the transport properties of the crystalline forms, including the intercalation compounds, but also their 'avatars' as pregraphitic carbons. In a final part, this panorama, which is going from the classical forms to the more molecular ones including nanotubes, is completed by the presentation of similar compounds. Starting from neighboring elements in the periodic classification we show that doped carbons and parent compounds present a similar polymorphism which enlarges this general introduction.

We synthesized aligned multiwalled carbon nanotube multilayers by aerosol-assisted catalytic chemical vapor deposition through sequential injections of aerosols containing both carbon and catalyst precursors. Each sequence was traced by a specific duration or precursor mixture, with the carbon source being possibly enriched in (13)C isotope labels. We discovered that any sequence involved the growth of a new layer on the substrate surface, under any pre-existing one by lifting it up, giving definitive evidence of a base-growth mechanism.

We report a new hot-drawing process for treating wet-spun composite fibers made of single- and multiwall carbon nanotubes and poly(vinyl alcohol). As shown in previous reports, untreated composite nanotube fibers exhibit a very large strain-to-failure, and their toughness, which is the energy needed to break the fibers, exceeds that of any other known materials. However, untreated composite nanotube fibers absorb a very small amount of energy at low strain and become degraded in humid conditions. In this work, we use hot-drawing treatments, a concept inspired from textile technologies, to improve the properties of nanotube/PVA fibers. This treatment yields a crystallinity increase of the PVA and an unprecedented degree of alignment of the nanotubes. These structural modifications lead to a markedly improved energy absorption at low strain and make the fibers resistant to moisture. Hot-drawn nanotube/PVA fibers hold great potential for a number of applications such as bulletproof vests, protective textiles, helmets, and so forth.

We report a study of the initial stages of growth of aligned multiwalled carbon nanotubes (MWNT) synthesised by catalytic chemical vapour deposition (CCVD) of liquid aerosol obtained from toluene/ferrocene solution. A special experimental procedure has been developed to stop the process after short durations (30 s to 2 min). Two different pyrolysis temperatures are considered: 800 and 850 °C. Both scanning and transmission electron microscopy (SEM, TEM) coupled to energy-dispersive X-ray (EDX) analyses are used in order to determine the location of catalyst particles and to examine their chemical nature, morphology and size distribution when nanotubes start to grow. During the early stages (30 s), we observe the formation of a layer of catalyst particles on silicon substrates before the growth of nanotubes. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements indicate the occurrence of iron oxide (γ-Fe2O3 or Fe3O4). In addition, XPS analysis reveals the formation of graphite-like carbon, demonstrating that iron oxide particles catalyse the decomposition of toluene vapour. SEM and TEM observations show that these particles are most often located at the nanotube root, suggesting a base growth mechanism responsible for the formation of aligned nanotube when prolonging growth time (2 min).

International audience; X-ray microdiffraction can be a powerful technique to study nanotube-based materials, as shown here for carpets of aligned multiwall carbon nanotubes synthesized by aerosol-assisted Catalytic Chemical Vapor Deposition. Catalytic particles are found to be iron oxide. Moreover, local analysis of nanotube alignment allows one to understand the effects of the synthesis procedure

Proceedings of Diamond 2004, the 15th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides and Silicon Carbide; The control of the crystallization degree is an important issue for carbon nanotube applications. In this context, we present the evolution of the structure after post-annealing treatment of multiwalled carbon nanotubes (MWNT), obtained by the aerosol pyrolysis process, involving liquid aerosols containing both hydrocarbon source and the metal catalyst precursor. The alignment and the degree of crystallinity of the raw and annealed carbon nanotubes have been quantified by X-ray diffraction measurements also used to analyze the metallic phases inside the nanotubes. The Near-Edge X-ray Absorption Fine Structure (NEXAFS) studies were performed at the C K-edge in order to follow the evolution of the electronic structure with the local structure and the degree of crystallinity of the nanotubes. We confirm that this chemical vapour deposition synthesis method enables to produce well-aligned multiwalled carbon nanotubes. The effect of post-annealing temperature both on local ordering and graphitization degree of nanotube walls are described. The results are compared to the previous observations of individual nanotubes by HRTEM concerning the structural changes occurring during annealing treatments.

The structure of bundles of carbon nanotubes produced by catalytic chemical vapor deposition has been studied by electron diffraction. The experimental results were analyzed with the kinematical theory of diffraction. An interpretation of the diffraction patterns demonstrates unambiguously that some bundles are made of double-walled carbon nanotubes, and not single-walled nanotubes as previously reported in Phys. Rev. B 64, 125425 (2001). In this previous work, we have focused our attention on bundles presenting one or two helicities. The interpretation of our diffraction data based on the assumption of double-walled nanotubes is shown to fit remarkably with experiment. In the present paper, the detailed analysis of an electron diffraction pattern from a small bundle exhibiting two helicities is made and we deduced the most probable wrapping indices of the two tubes constituting the double-walled nanotubes.

Dispersions of single-walled carbon nanotubes in a 4-pentyl-4'-cyano-biphenyl nematic liquid crystal matrix are studied by X-ray scattering. For some mixtures, the addition of nanotubes strongly modifies the properties of the matrix: under a magnetic field, the nematic director is aligned perpendicular to the field, whereas it is parallel to it for pure 4-pentyl-4'-cyano-biphenyl. This original modification of liquid crystal alignment by the addition of nanotubes raises new questions about nanotubes and liquid crystal interactions.

Structural, electrical and thermal methods are applied to characterize single-walled carbon nanotube (SWNT) fibers with post-extrusion stretching as the independent variable. HiPco SWNTs are dispersed in water using sodium dodecyl sulfate (SDS), and then co-extruded with polyvinyl alcohol (PVA)/water through a long syringe into a rotating water/PVA coagulation bath. Partial axial alignment is thereby achieved, and further enhanced by applying tension to the flexible green fibers in the coagulation bath. Our findings include: (1) X-ray diffraction shows that the full width at half maximum (FWHM) of the Bragg peaks decreases from 55 (as-extruded) to less than 30 degrees by 80% elongation. That is, SWNT alignment increases linearly with stretch (up to 80%). (2) In resistivity at room temperature vs. stretch ratio, result shows an initial rapid decrease followed by saturation; essentially all the improvement in electronic transport is obtained once alignment reached 40° FWHM. (3) Annealing in hydrogen at 1000°C is performed to drive out PVA, to improve inter-tube and inter-bundle contacts, and to heal damage on the tube walls. Such annealing is found to increase conductivity by at least 4 orders of magnitude. (4) Below 25 K, resistivity vs. temperature of the annealed fiber is well-represented by Coulomb gap variable range hopping (CG-VRH). It is rationalized that the Coulomb interactions in disordered systems open a gap at the Fermi energy. Above 25 K, the thermal energy is greater than the Coulomb gap, so thermal activation is more probable than correlated electron hops. (5) Finally, a measurable thermal conductivity is observed as stretch alignment increases.

A simple spinning process has been recently developed to assemble carbon nanotubes into long macroscopic fibers. Due to the high aspect ratio of the nanotubes, the fiber’s physical properties are expected to depend significantly on the nanotube orientation. The alignment of the nanotubes is studied by X‐ray scattering. It is characterized by the Full Width at Half Maximum (FWHM) of the azimuthal intensity distribution. Our first studies gave FWHM≈75°. Treatments developed to improve nanotube alignment, such as solvent‐wetting or drawing of the fibers, are reported here. Results obtained from nanotubes synthesized by the arc‐discharge method and by the HiPCO process are discussed. Stretched fibers processed with HiPCO single‐wall nanotubes exhibit FWHMs as low as 32°. Moreover, the above‐mentioned treatments induce a substantial increase (by a factor 4) of their Young’s modulus. An example of electromechanical actuation is reported.

High-pressure polymerization of C60 leads to a variety of new crystalline or amorphous phases which display interesting physical properties. We have prepared one-dimensional (1D, C60 chains) and two-dimensional (2D, C60 layers) polymers from C60 single crystals. The resulting multi-domain crystals have been studied using x-ray diffraction and Raman spectroscopy. The relative orientations of the chains in the “low-pressure” 1D orthorhombic polymer had been characterized previously [1]. We have now determined the specific stacking of the C60 layers in the 2D tetragonal and rhombohedral polymers. Using these results we analyze the relations between the different polymers and the intermolecular environments which may play a role in stabilizing the observed polymer structures.

Following the synthesis of aligned single-wall carbon nanotubes in the channels of AlPO4-5 zeolite single crystals, we present the first X-ray diffraction and diffuse scattering results. They can be analysed in terms of a partial filling of the zeolite channels by nanotubes with diameter around 4A. The possible selection of only one type of nanotube during the synthesis, due to the constraints imposed by the zeolite host, is discussed., Comment: to appear in Solid State Comm

After a general introduction about structural order and disorder in solids and about X-ray scattering, I discuss the two main subjects on which I have worked after my PhD thesis: quasicrystals and fullerenes (pure C60 and polymerized-doped compounds).; Après une introduction générale aux diverses sortes d'ordre et de désordre dans les solides, ainsi qu'à la diffusion des rayons X et à son adéquation pour l'étude de ces phénomènes d'ordre ou de désordre, je présente les deux principaux sujets sur lesquels j'ai travaillé depuis ma thèse : les quasicristaux d'une part, et les fullerènes (C60 pur et composés polymérisés) d'autre part.

Polymerized alkali fullerides KC60 and RbC60 display different electronic properties. Single crystal X-ray diffraction and diffuse scattering studies show that the C60 chains possess different relative orientations about their axes. We will discuss this result in relation with electronic band structure calculations. The influence of pressure will also be discussed.

The KC60 and RbC60 polymer phases exhibit contrasting electronic properties while powder diffraction studies have revealed no definite structural difference. We have performed single crystal X-ray diffraction and diffuse scattering studies of these compounds. It is found that KC60 and RbC60 possess different chain orientations about their axes, which are described by distinct space groups Pmnn and I2/m, respectively. Such a structural difference will be of great importance to a complete understanding of the physical properties., Comment: To be published in Phys. Rev. Lett

First single crystal X-ray diffraction studies of polymerized KC60 and RbC60 are presented. While powder diffraction studies showed no definite structural differences, the single crystal diffraction data analysis reveals different relative chain orientations in the two compounds. They are discussed in relation with semi-empirical energy calculations. The structural difference between KC60 and RbC60 may be a key feature for the understanding of their contrasted conducting and magnetic properties., Comment: Proceedings of the 1998 International Conference on Science and Technology of Synthetic Metals, to appear in Synthetic Metals

International audience

Current microscopic models of the C 60 intermolecular interactions fail to give an accurate description of the ordering phenomena in solid C 60 , where orientational correlations of the fullerene molecules play a leading role. At room temperature these orientational correlations produce x-ray diffuse scattering intensity modulations whose analysis is a good test for the microscopic models. Below the 259K transition, the remaining x-ray diffuse scattering was measured up to large wave vector values. Its analysis confirms that the low-temperature structure is characterised by two nearly degenerate and randomly distributed orientations of the C 60 molecules.

Two-dimensional polymerisation of a C60 single crystal has been obtained under high-pressure high temperature conditions (700 K - 2 GPa). Crystalline order is preserved but the crystal splits into ...

The fulleride salt C60-tetraphenylphosphonium bromide is investigated as a function of temperature by single crystal X-ray diffuse scattering and diffraction. At room temperature, the C60 orientational disorder is found to be more complex than previously expected. Moreover, a structural phase transition, due to the C60 orientational ordering, is evidenced around 120 K. Its relation with the stabilization of a static Jahn-Teller effect is discussed.

We report neutron scattering study of the dispersion of phasons and amplitudons in the n = 4 incommensurate phase II of Biphenyl under hydrostatic pressure. Due to the nature of the molecular instability which is at the origin of the different phase transitions in Biphenyl, pressure lowers transition temperatures. Phase II disappears at a rather low pressure (1.85 kbar) which gives us the opportunity to study its excitations at very low temperature, where their damping constants are small. We measured the frequencies of three well separated modes and their dispersions at different pressure values. In the framework of the Ginzburg-Landau theory, these modes are unambiguously identified as phasons and amplitudons of a four ray star incommensurate structure.

Recent inelastic neutron scattering measurements in pterphenyl under pressure are presented. They reveal a continuous changeover of the high temperature structural instability from an order-disorder regime to a displacive one. Static and dynamic aspect of the phase 111 of p-terphenyl is discused.

We report evidence for the existence of a new incommensurate phase in a crystal of ammonium hydrogen oxalate hemihydrate. This phase is remarkable in two aspects: it exists only above a critical pressure Pc, and the incommensurate wave vector, which is parallel to the vector c* of the reciprocal lattice, has the largest variation ever reported, varying continuously from 0.147c* at 4.3 kbar to ~ 0.25c* at the maximum pressure (8 kbar) used to date.

Dynamics of an n = 4 incommensurate system, the phase II of biphenyl, is investigated by two complementary techniques, neutron and Raman scattering. The experiments are performed under pressure at very low temperature when the damping is considerably reduced.