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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.

Self-organised ferromagnetic nanowires encapsulated by multiwalled carbon nanotubes produced by CVD methods based on the thermal decomposition of ferrocene commonly contain the elemental phases: α-Fe, γ-Fe, and the carbide Fe 3 C. A continuous α-Fe nanowire and control of nanowire and nanotube length and diameter are desirable. High α-Fe nanowire content has been achieved through synthesis temperature modification, vapour flow-rate, and post-synthesis heat treatment. Length and diameter are intimately related to the self-organisational growth processes; reported approaches include regulation of the vapour supply to minimise dispersion in the nucleation process and introduction of other growth-modifying precursor elements. High vapour flow-rate produces downstream fluctuation resulting in discontinuous nanowires and diameter dispersion, or external decoration with spherical particles, results from rapid evaporation of the ferrocene precursor. We report a low vapour flow-rate and constant evaporation temperature method which achieves continuous α-Fe nanowires on the same scale as the nanotube for lengths >10 μm without the necessity of post-synthesis heat-treatment or introduction of other precursor elements. The low vapour flow-rate regime has the advantage of sustaining the intrinsic temperature gradient at the tip of the forming structure which drives the vapour feedstock to the growth front to guarantee continuous nanowire formation.

Thermoelectric energy conversion within a homogeneous conductor is governed by the charge carrier mobility and the density of electronic states, intrinsic trades-off limit efficiency. Heterogeneous conduction created by the spatial variation of disorder is considered undesirable because it is conceptually difficult and not easily reproduced. However, could it be the basis for unique, exploitable thermoelectric effects? Here we show that the heterogeneous conduction typically found in conducting polymer films can result in thermoelectricity governed by only quantum mechanical tunneling of charge carriers through nanoscale Coulomb barriers at order-disorder boundaries. We conclude this to be the basis of a new category of thermoelectric system centered on heterogeneous conductors or conducting networks. We show that thermoelectricity of this origin can be engineered without doping or intrinsic trades-off. Our findings point to a wide range of alternatives to the doped inorganic semiconductor paradigm.

A simple wet chemical method involving only sonication in aqueous GdCl3 solution was used for surface functionalization of iron-filled multiwalled carbon nanotubes with gadolinium. Functional groups on the sidewalls produced by the sonication provide active nucleation sites for the loading of Gd3+ ions. Characterization by EPR, EELS, and HRTEM confirmed the presence of Gd3+ ions on the sidewall surface. The room temperature ferromagnetic properties of the encapsulated iron nanowire, saturation magnetization of 40 emu/g and coercivity 600 Oe, were maintained after surface functionalization. Heating functionality in an alternating applied magnetic field was quantified through the measurement of specific absorption rate: 50 W/gFe at magnetic field strength 8 kA/m and frequency of 696 kHz. These results point to candidacy for dual-functioning MRI imaging and magnetic hyperthermia structures for cancer therapy.

Carbon nanotubes filled with continuous crystalline nanowires of nanometre-scale diameter and micrometre-scale length of the ferromagnetic phase α-Fe were produced with a new chemical vapour deposition method. We report a new two-stage approach, a perturbed-vapour method of synthesis followed by a post-synthesis heat treatment that produces multiwall carbon nanotubes filled with at least 19 micrometre-length nanowires of α-Fe. Previously reported synthesis routes use steady-state conditions to guarantee nanowire continuity but result only in small (less than one-micrometre length) nanowires comprising isolated or mixed phases of either α-Fe, Fe 3 C, or γ-Fe. Here flower-like clusters of carbon nanotubes continuously filled with α-Fe were produced by perturbation of a laminar ferrocene (Fe(C 5 H 5 ) 2 ) vapour flow in a conventional horizontal chemical vapour deposition reactor. Single-phase filling was achieved by a post-synthesis annealing at 500 °C for 15 h in Ar flow. Electron microscopy studies revealed the high quality of the structural integrity of both nanotubes and encapsulated nanowires. These nanostructures possess a high coercivity of 580 Oe and a very high saturation magnetization of 189.5 emu/g comparable with bulk α-Fe.

We report a new chemical vapor synthesis method that exploits random fluctuations in the viscous boundary layer between a laminar vapor flow and a surface to yield a not previously observed product: radial ferromagnetically filled-carbon-nanotube structures departing from a central particle. The filling of the nanotube capillary is continuous over a scale much greater than that which can be achieved by conventional CVD. This is a simple method which does not require ultra-fine control of process parameters or highly-engineered reactor components in which a single, self-organized, ordered product is formed in randomly fluctuating vapor in the boundary layer by vapor-, liquid-, solid-phase self-organization. These fluctuations create the thermodynamic conditions for formation of the central particle in the vapor which in turn defines the spherically symmetric diffusion gradient that initiates the radial growth. The subsequent radial growth is driven by the supply of vapor feedstock by local diffusion gradients created by endothermic graphitic carbon formation at the vapor-facing tips of the individual nanotubes and is halted by contact with the surface. The radial structures are the dominant product and the reaction conditions are self-sustaining. We argue that the method has potential for scalable production of metal-carbon nanostructures with other unusual morphologies.

Self supporting nickel substrates coated with nickel nanorods having diameters distributed between 110 nm and 170 nm were electrochemically synthesised using a two-step anodisation process, using as freshly anodised nanoporous alumina membrane as template. Field emission from the nanorods was observed at a relatively low bias potential Vbias (Vbias ≤ 1 V) using scanning tunnelling microscopy; the emission current was found to be larger than that from the nickel substrate at least by a factor of 4 at Vbias = 1.0 V. Experimental results were interpreted in the modified Millikan–Lauritsen plot and values of the emission parameters were estimated using the value of the work function measured by the Kelvin probe technique.

Ultra-high molecular weight polyethylene/multi-wall carbon nanotube (UHMW-PE/MWNT) composites have been prepared by a novel approach which involves the use of a mixture of solvents during the gelation process. By combining one of the best known organic solvents for nanotubes, N,N-dimethylformamide (DMF) with xylene and use this mixed-solvent in the gelation/crystallisation process for UHMW-PE/MWNT composite fabrication, an attempt is made to improve the dispersion of carbon nanotubes in UHMW-PE. The obtained films were drawn to obtain highly oriented tapes, which were characterized in terms of electrical and mechanical properties. The conductivity of the drawn tapes is maintained at 10−4 S/m at draw ratio 30, two orders of magnitude higher than the minimum level required to provide electrostatic discharge. Although the mechanical properties are compromised by use of DMF and MWNTs, the Young’s modulus still remains at 25 GPa, in comparison with 35 GPa for pure UHMW-PE tape at draw ratio 30.

We report here the thermally activated growth of carbon composite nanostructures on the faceted TiC(1 1 1) single crystal surface. As a result of a high temperature anneal over 2500 K complex structures are growing from well defined nucleation sites at the cusps of the faceted surface. The growth of the complex shaped nanostructures is initialized by the formation of Ti nanodroplets and is fed by the thermal decomposition of TiC. The shape of the nanostructures is determined by the minimum energy configuration of their encapsulating carbon shell.

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.

Thin film formation of graphite by chemical vapor deposition using 2-methyl-1,2′-naphthyl ketone as a starting material was carried out on Ni film substrates. On Ni films directly deposited on quartz glass, the graphite films were obtained when the Ni film thickness was above 1 000 A and above 5 000 A at 700 °C and 1 000 °C, respectively. Depositions on thinner Ni film substrates comprise amorphous carbon (a-C) or graphite tubes which was owing to the thermal coagulation of the Ni film into droplets. On the other hand, graphite film was obtained on the Ni film with thickness 10 A when a-C was inserted between the Ni film and the quartz glass. The coagulation of the Ni film is considered to be avoided by inserting a-C layer.

The study of potassium-oxygen and cesium-oxygen graphite intercalation compounds (GICs) first synthesized by the authors is presented. It is shown that these GICs are formed in reactions of graphite with alkali metal/alkali Superoxide mixtures or with alkali suboxide (in the case of cesium). Stage 1 and 2 potassium-oxygen GICs Jmterplanar distance 8.44 A), and stages 1, 2 and 5 cesium-oxygen GICs (interplanar distance 9.84 A) were isolated. X-ray diffraction, XPS, TEM electron diffraction and chemical analysis were used to characterize the content and constitution of the GICs synthesized. Metal-like temperature dependence of c -axis resistivity was obtained in the 1.5–300 K range where the resistivity values at room temperature are 0.07, 0.81, 2.6 and 0.089 Ωcm for KO stagel, KO stage 2, CsO stage 1 and CsO stage 2 compounds, respectively. All the GICs exhibit low spin susceptibility (order of 10 −7 emu/g) which suggests the absence of magnetic species O 2 − .

We have observed angular dependent magnetoresistance oscillations (ADMRO) in the out-of-plane resistivity of low-stage SbCl 5 -intercalated graphite. This new phenomenon is a semi-classical geometric resonance effect inherent in quasi two-dimensional systems whose Fermi surface is weakly corrugated in the k z -direction. Typically, ADMRO is characterized by peak positions that are periodic in tan θ. The peaks in ϱ zz occur when the average of the k z -component of electron group velocity around its extended orbit is zero. Significant deviations from ‘standard’ behaviour are found. The implications for electronic structure are discussed.

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 * .

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.

We report the first observation of intercalation into carbon nanotubes without breaking the tubular structure. Both K-intercalated and FeCl 3 -intercalated tubes were produced by a gas-phase reaction of oriented multiwall “buckybundle” material with potassium metal and iron (III) chloride, respectively. The resulting material preserves its oriented structure. It has been studied by X-ray diffraction, SEM, weight uptake and magnetoresistance measurement techniques. Interlayer spacing in the intercalated tubes is very close to that in corresponding graphite intercalation compounds. It has been shown that intercalated buckybundles exhibit some noteworthy galvanomagnetic properties including the random conductance fluctuations. The intercalation process is accompanied by swelling of the tubes. The swollen sections alternate non-intercalated “necks” forming an impressive “bead-line” pattern.

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.