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Ferromagnetically filled graphitic-carbon foams are a new class of materials characterized by an open-cell structure continuously filled with ferromagnetic crystals. Targeted design for applications requires knowledge of the magnetic ordering and the interaction between magnetic moments in the filling and those due to the spin of the delocalized π-electrons which contribute to thermal and electrical conduction in the graphitic carbon. Magnetometry together with electron spin resonance, thermoelectric, and calorimetric measurements on iron-filled carbon foam reveal ferromagnetic responses at room temperature with a transition to antiferromagnetic behavior in some fraction of the filling at 130 K. This observation is consistent with the α-Fe (bcc) to γ-Fe (fcc) transition at this temperature predicted by others. Seebeck coefficient measurements revealed a behavior typical of unmodified graphitic carbon indicating the absence of any interaction between the magnetic moments of the filling and the conduction electrons in the graphitic carbon.

Boundary layer chemical vapour synthesis is a new technique that exploits random fluctuations in the viscous boundary layer between a laminar flow of pyrolysed metallocene vapour and a rough substrate to yield ferromagnetically filled radial-carbon-nanotube structures departing from a core agglomeration of spherical nanocrystals individually encapsulated by graphitic shells. The fluctuations create the thermodynamic conditions for the formation of the central agglomeration in the vapour which subsequently defines the spherically symmetric diffusion gradient that initiates the radial growth. The radial growth is driven by the supply of vapour feedstock by local diffusion gradients created by endothermic graphitic-carbon formation at the vapour-facing tips of the individual nanotubes and is halted by contact with the isothermal substrate. The radial structures are the dominant product and the reaction conditions are self-sustaining. Ferrocene pyrolysis yields three common components in the nanowire encapsulated by multiwall carbon nanotubes, Fe3C, α-Fe, and γ-Fe. Magnetic tuning in this system can be achieved through the magnetocrystalline and shape anisotropies of the encapsulated nanowire. Here we demonstrate proof that alloying of the encapsulated nanowire is an additional approach to tuning of the magnetic properties of these structures by synthesis of radial-carbon-nanotube structures with γ-FeNi encapsulated nanowires.

Thermoelectric power was used to elucidate the electrical transport properties of aligned and randomly oriented carbon nanotube systems in the temperature range 77--450 K. A weakly negative thermoelectric power, comparable with that of a graphite flake, was observed for a macroscopic bundle of multiwall carbon nanotubes with individual axes aligned parallel to the main axis. However, mats of randomly oriented multiwall carbon nanotubes gave a strongly positive thermoelectric power, as did mats of single-wall nanotubes. This is evidence of the importance of intertube contacts in the interpretation of the thermoelectric power data for carbon nanotube systems. Models for thermoelectric power behavior incorporating contact effects are described.

We propose a model for the low-temperature conductivity of intercalated multiwall carbon nanotube bundles in terms of three-dimensional weak localization, with a weakly temperature-dependent inelastic scattering process, and interaction effect. At a crossover temperature ${T}^{*},$ weak localization conditions collapse and the intrinsic conduction process is observed at $Tg{T}^{*}.$

The electronic and optical properties of nitrogen doped tetrahedral amorphous carbon (ta-C:N) are compared with those of a new form of carbon ta-C film in which nanotube regions are included (ta-C:(NT)). It is found that nanotubes in ta-C inhibit the N doping effect in ta-C and leads to a reduction in conductivity. The results point to the nanotube regions acting as electronically isolated graphitic regions in ta-C. The refractive index in ta-C:(NT) is found to have the opposite dependency on wavelength to that of ta-C. It is proposed that the refractive index can be used as a signature for the presence of nanotubes and other large graphitic regions in ta-C.

We have observed a new angular oscillatory magnetotransport phenomenon in the out-of-plane resistivity of stage 2 SbCl 5 -intercalated graphite. The phenomenon is similar in many respects to the one recently found in organic conductors, which is attributed to a semiclassical geometrical resonance effect inherent in a weakly corrugated cylindrical Fermi surface. Some deviations from the “standard” behavior are found.

The resistivity response upon stretching of a carbon nanotube/thermoplastic elastomer composite fabricated by a solution process with good nanotube dispersion and low percolation threshold $({p}_{c}\ensuremath{\sim}0.35\phantom{\rule{0.3em}{0ex}}\mathrm{wt}\phantom{\rule{0.2em}{0ex}}%)$ is reported. The relationship between resistivity and strain (deformation) shows an exponential relationship with universal, nanotube concentration-independent behavior. The temperature dependence of the resistivity is described by the fluctuation induced tunneling model. The experimental resistivity-strain dependence greater than 5% strain is interpreted in terms of this model by consideration of the gap-width modulation of tunnel junctions. Percolation theory applied to the conductive nanotube network indicates that for less than 5% strain, deformation of the conductive network is the controlling mechanism for changes in resistivity.

Structures of carbon nanotube/ligand complexes were studied by flow linear dichroism (the differential absorption of light polarized parallel and perpendicular to the flow orientation direction) with the aim of establishing linear dichroism as a technique to study such systems. Anthracene, naphthalene, and DNA were chosen as ligands, and the potential for flow linear dichroism to probe ligands noncovalently (as well as covalently) bound to single-walled nanotubes is reported. Linear dichroism enables the determination of approximate orientations of the ligands on the carbon nanotubes.

Field emission properties of B-doped carbon nanotubes are investigated from both theoretical and experimental standpoints. Using tight-binding and ab initio calculations, it is observed that B-saturating tip edges of carbon nanotubes induce the presence of large peaks within the local density of states (LDOS) located in an energy region close to the Fermi level (Ef). These localized states suggest a field emission enhancement for the B-doped tubes. In addition, ab initio theoretical results indicate that the work function for B-doped tubes is 1.7 eV lower when compared to pure carbon-terminated nanotubes. Experimentally, it is found that B-doped tubes, which are produced by arc discharge techniques and contain B mainly at the tips, exhibit stable electron field emission at lower turn-on voltages (1.4 V/mum) when compared to pure single- and multiwalled carbon nanotubes (2.8 and 3.0 V/mum, respectively) measured under the same conditions. We strongly believe our results will bring new insights in the fabrication of stable field emission sources.

DC magnetoresistive effects were observed in above-percolation-threshold loaded Fe-filled carbon nanotube/polyurethane-urea composite samples. A phenomenological model is derived from interpretation of resistance relaxation for a range of axial strains. The large instantaneous magnetoresistance of + 90% observed at low axial strain was a result of conduction pathway breaking caused by preferential orientation of the conducting nanotubes perpendicular to the axial current flow: a result of the magnetic torque experienced by the ferromagnetic nanotube core. At large strain the observed large instantaneous change in resistance of - 90% resulted from voltage-driven relaxation in the conducting nanotube network. At high axial strain the competition between voltage-driven relaxation and a magnetic torque gave rise to an oscillatory component of resistance relaxation.

In this study, thermoplastic polyurethane (TPU) fibres containing multi-walled carbon nanotubes (MWNTs) and fabricated via an extrusion process were demonstrated to possess a tuneable level of electrical conductivity. A simple approach based on the time–temperature superposition applied to the electrical conductivity of carbon nanotube (CNT) percolating in a thermoplastic polyurethane (TPU) melt was also developed to predict the conductivity of the nanocomposite fibres. The observation of Arrhenius dependence of zero-shear viscosity and the assumption of simple inverse proportionality between the variation of conductivity, due to network formation, and viscosity allow a universal plot of time variation of conductivity to be composed, which is able to predict the conductivity of the extruded fibres. The same TPU/CNT fibres were also demonstrated to possess good strain sensing abilities, which makes them good candidates for applications in smart textiles.

We propose a model for the low temperature conductivity of intercalated multiwall carbon nanotube bundles in terms of three-dimensional weak localisation, with a weakly temperature dependent inelastic scattering process, and interaction effect. At a crossover temperature T * weak localisation conditions collapse and the intrinsic conduction process is observed at T>T * .

The electrical conductance of single- and double-wall carbon nanotube systems was measured by a mechanically controllable break-junction technique using freestanding nanotubes not subject to any chemical modification. For metallic single-wall carbon nanotubes, two channels with transmission coefficient of 0.88 contribute to ballistic electronic transport at room temperature. In double-wall carbon nanotubes, one metallic channel contributes to ballistic electronic transport and additional field- and temperature-dependent two-channel contributions were observed.

Low-temperature magnetoresistance measurements on pristine bundles revealed non-oscillatory magnetoresistance behavior comprising positive and negative components. However, upon intercalation of K-atoms, random oscillations about a large negative underlying trend were revealed—features that were also seen for some pristine bundles taken from the same source material. When plotted as magneto-conductance, the amplitude of these oscillations is comparable to that of the ‘universal’ conductance fluctuations recently observed for a single multiwall nanotube [Langer, L. et al, Phys. Rev. Lett. 76 (1996) 479]. This amplitude is temperature-independent below T c ∼3 K. An explanation of these observations is given within the framework of 3D weak localization theory.

Carbon nanotubes are a significant addition to the emerging field of nanotube biotechnology. The biocompatibility, high structural integrity, and unique electronic and mechanical properties of carbon nanotubes complement or surpass those of self-assembled lipid nanotubes, peptide nanotubes, and template-synthesised nanotubes (metals, polymers, semiconductors, and carbons). Carbon nanotubes are candidates for a range of biomolecular applications that is likely to widen considerably in the future.

Composites films of poly (3-octylthiophene)/multi-wall carbon nanotube have been fabricated. Transmission electron microscopy revels multi-wall nanotube structures embedded in an amorphous polymer matrix. After incorporation of the nanotubes an enhancement in the electrical conductivity of up to five orders is observed. Temperature dependent conductivity studies indicate a decrease in the activation energy for the composite films. There is evidence that the composite films are much harder and much more stable than the ‘undoped’ polymer.

A correspondence between Fermi surface parameters determined by semiclassical angular dependent magnetoresistance oscillations (ADMRO) and those by the Shubnikov-de Haas effect in stage-2 SbCl 5 -intercalated graphite is demonstrated. The wavevector underlying most robust ADMRO feature and strongest branch of the Shubnikov-de Haas spectrum is the radius of lower valence band primitive cylinder of the Blinowski-Rigaux model.