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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.

Hybrid organic–inorganic perovskites have generated considerable research interest in the field of optoelectronic devices. However, there have been significantly fewer reports of their thermoelectric properties despite some promising early results. In this article, we investigate the thermoelectric properties of bismuth-doped CH3NH3PbBr3 (MAPbBr3) single crystals. The high-quality Bi-doped crystals were synthesized by inverse temperature crystallization and it was found that Bi substitutes onto the B-site of the ABX3 perovskite lattice of MAPbBr3 crystals with very little distortion of the crystal structure. Bi doping does not significantly alter the thermal conductivity but dramatically enhances the electrical conductivity of MAPbBr3, increasing the charge carrier density by more than three orders of magnitude. We obtained a negative Seebeck coefficient of −378 μV K−1 for 15% (x = 0.15) Bi-doped MAPb(1−x)BixBr3 confirming n-type doping and also measured the figure of merit, ZT. This work highlights routes towards controlled substitutional doping of halide perovskites to optimise them for thermoelectric applications.

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.

The chapter details the underlying phenomena that underpin electronic applications that have followed from the discoveries of C60 and carbon nanotubes. The reduced dimensionality of these self-organised structures, high electron mobility, weak electromigration, and the plethora of quantum electronic effects exhibited by these structures suggest they are serious candidates for molecular electronics. The detail of the surface chemistry and conditions of synthesis assume greater importance than for conventional electronic materials since all atoms are on the exterior of these structures, as is outlined with references to the wider literature. Essential electronic structure information is given with reference to the transport measurements that have contributed greatly to the evolution of the field with emphasis on the Coulomb blockade and ballistic transport phenomena. The major electronic applications are then outlined, giving the state-of-the-art figures of merit for performance and comments on prospects for realisation.

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.

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.

This research concerns the effect of conductive network formation in a polymer melt on the conductivity of multi-walled carbon nanotube/thermoplastic polyurethane composite systems. An extremely low percolation threshold of 0.13 wt.% was achieved in hot-pressed composite film samples, whereas a much higher CNT concentration (3-4 wt.%) is needed to form a conductive network in extruded composite strands. This is explained in terms of the dynamic percolation behaviour of the CNT network in the polymer melt. The temperature and CNT concentration needed for dynamic percolation to take effect were studied by the conductivity versus temperature behaviour of extruded strands, in an attempt to optimise the processing conditions. © 2008 Elsevier Ltd. All rights reserved.

It is shown that the dominant conduction mechanism in single-wall carbon nanotube networks at room temperature is variable range hopping. Thin networks follow a variable range hopping law throughout the temperature range 4 K < T < 300 K, thick networks display variable range hopping characteristics in the range 50 K < T < 300 K, with deviation to Bloch–Gruneisen behaviour at lower temperatures. The adsorption state of these materials is shown to determine the sign of change in conductance upon subsequent exposure to oxygen. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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 $Tg{T}^{*}.$

Two types of quantum magnetotransport behavior were observed in pristine bundles of helicoidal carbon nanotubes. Universal conductance fluctuations for $Tl10$ K and an underlying positive magnetoconductance to very high magnetic fields for $Tl100$ K are the most notable features of one of these types. Remarkably, this behavior was observed after intercalation of potassium guest atoms into pristine bundles of the other type. This range of phenomena is explained within the theory of weak localization and interaction effect in three dimensions. However, the observed inelastic scattering mechanism for K-intercalated bundles cannot be described by the present theory for a common mechanism of the same dimensionality.

Structures comprising single-crystal, iron-carbon-based nanowires encapsulated by multiwall carbon nanotubes self-organize on inert substrates exposed to the products of ferrocene pyrolysis at high temperature. The most commonly observed encapsulated phases are Fe3C, α-Fe, and γ-Fe. The observation of anomalously long-period lattice spacings in these nanowires has caused confusion since reflections from lattice spacings of ≥0.4 nm are kinematically forbidden for Fe3C, most of the rarely observed, less stable carbides, α-Fe, and γ-Fe. Through high-resolution electron microscopy, selective area electron diffraction, and electron energy loss spectroscopy we demonstrate that the observed long-period lattice spacings of 0.49, 0.66, and 0.44 nm correspond to reflections from the (100), (010), and (001) planes of orthorhombic Fe3C (space group Pnma). Observation of these forbidden reflections results from dynamic scattering of the incident beam as first observed in bulk Fe3C crystals. With small amounts of beam tilt these reflections can have significant intensities for crystals containing glide planes such as Fe3C with space groups Pnma or Pbmn.

The discovery of carbon nanotubes in 1991 spurred an enormous worldwide research effort spanning the physical, chemical, and life sciences. This review will attempt to convey to the reader the unique physical attributes of carbon nanotubes and the range of possible applications.

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.

In this work we have studied the field emission from three different types of carbon films: (i) a-C:H:N deposited using an inductively coupled rf PECVD process, where the N content in the films can be as high as 30 at%. (ii) Cathodic arc deposited tetrahedral amorphous carbon (ta-C) with embedded regions of carbon nanotube and onion structures. (iii) Unoriented carbon nanotube films on a porous substrate. These films were formed by filtering a solution of nanotubes dispersed in alcohol through the pores (0.2 um dia.) and drying.

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.

The growth control of α-Fe inside multiwall carbon nanotubes has challenged researchers for more than a decade owing to the coexistence of this phase with Fe3C and γ-Fe. Previously, long heating treatments of 20 h have been used to decompose the encapsulated Fe-phases in C and Fe; however, these methods were limited by an unusual oxidation process leading to nanotube decomposition. In this letter, we report an alternative chemical vapour deposition approach that through an accurate control of the ferrocene-vapour flow-rate allows to achieve the direct encapsulation of 95% of α-Fe without additional heating treatments.

The importance of the intercalation reaction for the chemistry of carbon cannot be underestimated. More than 200 graphite intercalation compounds (GIC) discovered to date demonstrate how one can alter electronic properties of a host lattice by introducing a certain amount (often a very small amount) of intercalating agent into the spaces between graphene sheets. Intercalation and intercalation-related processes lie at the basis of such recently developed technologies as lithium-ion batteries and expanded graphite materials.

We report high electrical conductance enhancement in sparse single-walled carbon nanotube networks by decoration with Au nanoparticles. The optimized hybrid network exhibited a sheet resistance of 650 Ω sq(-1), 1/1500 of the resistance of the host undecorated network, with a negligible optical transmission penalty (90% transmittance at 550 nm wavelength). The electrical transport at room temperature in the host and decorated networks was dominated by two-dimensional variable range hopping. The high conductance enhancement was due to positive charge transfer from the decorating Au nanoparticles in intimate contact with the host network causing a Fermi energy shift into the high density of states at a van Hove singularity and enhanced electron delocalization relative to the host network which beneficially modifies the hopping parameters in such a way that the network behaves as an integral whole. The effect is most pronounced when the nanoparticle diameter is comparable to the electron mean free path in the bulk material at room temperature and there is minimum nanoparticle agglomeration. For higher than optimal values of nanoparticle coverage or nanoparticle diameter, the conductance enhancement is countered by metallic inclusions in the current pathways that are of higher resistance than the variable range hopping-controlled elements.

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.

Corrected values for the coefficients G0 and T0 in Table 2 as well as the corrected value for the parameter T0 in Eq. (3) are given for the paper by Morgan et al. [Phys. Status Solidi A 205, No. 6, 1394–1398 (2008)]. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

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.

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.

Though the presence of nanotubes in a carbon sample may be clearly detected by electron microscopy, yet it has been difficult to determine if the nanotubes in question belong to a Russian doll or scroll type. This work shows how a chemical reaction with ferric chloride or with potassium metal reveals the differences between the two types of intratube shell arrangement. Scroll nanotubes are intercalated by alien molecules which penetrate from the side of the scroll and fill the intershell spaces. The corresponding intershell spaces expansion was directly observed in this work by TEM. Russian doll nanotubes do not enter the reaction and stay intact. The reaction with scroll nanotubes is accompanied with a remarkable tube swelling which is easily observed by scanning electron microscopy. The presence of intercalated nanotubes may also be detected by X-ray diffraction and Raman spectroscopy.