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The asymmetric functionalization of nanomaterials is desired to develop nanostructures with increasingly exotic properties. Nevertheless, it remains a general challenge and a difficult task. Janus structured multiwalled carbon nanotubes with intratubular junctions between undoped and nitrogen-doped sections have been exclusively considered to date for electronic applications in studies typically requiring only few individual nanotubes. Such structures are here shown to be suitable scaffolds to simply achieve a spontaneous, asymmetric and localized functionalization and patterning at the nanoscale. First, a method to produce large quantities (>100 mg per experiment) and long (>100 μm) vertically aligned multiwalled carbon nanotube forests by a hybrid aerosol assisted and traditional chemical vapor deposition is presented. Scanning and transmission electron microscopy, electron energy loss spectroscopy and Raman spectroscopy characterizations confirm a continuous intratubular transition between nitrogen-doped and undoped sections. Second, and for the first time, the described Janus structures are shown to be suitable scaffolds to achieve an asymmetric, spontaneous and yet spatially controlled reactivity along nanotubes. This is illustrated with the examples of asymmetric oxidation properties and asymmetric immobilization of platinum nanoparticles. Asymmetric functionalization is simply achieved by carefully controlling and exploiting the different surface properties along the Janus structured carbon nanotubes.

Heterostructures of 2D materials are expected to become building blocks of next generation nanoelectronic devices. Therefore, the detailed understanding of their interfaces is of particular importance. In order to gain information on the properties of the graphene - MoS2 system, we have investigated MoS2 sheets grown by chemical vapour deposition (CVD) on highly ordered pyrolytic graphite (HOPG) as a model system with atomically clean interface. The results are compared with results reported recently for MoS2 grown on epitaxial graphene on SiC. Our STM study revealed that the crystallographic orientation of MoS2 sheets is determined by the orientation of the underlying graphite lattice. This epitaxial orientation preference is so strong that the MoS2 flakes could be moved on HOPG with the STM tip over large distances without rotation. The electronic properties of the MoS2 flakes have been investigated using tunneling spectroscopy. A significant modification of the electronic structure has been revealed at flake edges and grain boundaries. These features are expected to have an important influence on the performance of nanoelectronic devices. We have also demonstrated the ability of the STM to define MoS2 nanoribbons down to 12 nm width, which can be used as building blocks for future nanoelectronic devices. © 2016 Elsevier Ltd. All rights reserved.

The addition of multi-wall carbon nanotubes (MWCNTs) to ceramic matrices could provide nanocomposites with enhanced properties. Efforts to produce these materials are normally frustrated by two major issues: firstly, the difficulty of attaining a homogenous distribution of MWCNTs in the matrix and secondly the poor bonding between the MWCNTs and the ceramic matrix. Herein, a processing method that overcomes these problems by using a sol–gel route to produce a low-melting point silica matrix, in combination with a dispersion method for the MWCNTs that is compatible with the sol is reported. This universal method was used to coat mesoporous silica on conventional, nitrogen-doped (CN X ) and boron-doped (CB X ) produced using aerosol assisted chemical vapour deposition (AACVD) as well as commercially available MWCNTs. After hot-pressing the powders, record improvements ( ca. 50%) in hardness for the nanocomposites over the silica were observed and this improvement is enhanced by 50% if spark plasma sintering is used to consolidate the nanocomposites. Nanocomposites containing conventional nanotubes produced from AACVD and commercially available nanotubes have near identical hardness even though the nanotubes have different properties and characteristics.

The butterfly Mimeresia neavei (Joicey & Talbot, 1921) is the only species in the exclusively African subtribal clade Mimacraeina (Lipteninae: Lycaenidae: Lepidoptera) having sexual dimorphism expressed by structurally blue-colored male and pigmentary colored orange–red female phenotypes. We investigated the optical mechanism generating the male blue color by various microscopic and experimental methods. It was found that the blue color is produced by the lower lamina of the scale acting as a thin film. This kind of color production is not rare in day-flying Lepidoptera, or in other insect orders. The biological role of the blue color of M. neavei is not yet well understood, as all the other species in the clade lack structural coloration, and have less pronounced sexual dimorphism, and are involved in mimicry-rings.

Graphene on noble-metal nanostructures constitutes an attractive nanocomposite with possible applications in sensors or energy conversion. In this work we study the properties of hybrid graphene/gold nanoparticle structures by Raman spectroscopy and Scanning Probe Methods. The nanoparticles (NPs) were prepared by local annealing of gold thin films using focused laser beam. The method resulted in a patterned surface, with NPs formed at arbitrarily chosen microscale areas. Graphene grown by chemical vapour deposition was transferred onto the prepared, closely spaced gold NPs. While we found that successive higher intensity (6 mW) laser irradiation increased gradually the doping and the defect concentration in SiO2 supported graphene, the same irradiation procedure did not induce such irreversible effects in the graphene supported by gold NPs. Moreover, the laser irradiation induced dynamic hydrostatic strain in the graphene on Au NPs, which turned out to be completely reversible. These results can have implications in the development of graphene/plasmonic nanoparticle based high temperature sensors operating in dynamic regimes., Comment: 18 pages, 5 figures

Ammonia borane (AB) is among the most promising precursors for the large-scale synthesis of hexagonal boron nitride (h-BN) by chemical vapour deposition (CVD). Its non-toxic and non-flammable properties make AB particularly attractive for industry. AB decomposition under CVD conditions, however, is complex and hence has hindered tailored h-BN production and its exploitation. To overcome this challenge, we report in-depth decomposition studies of AB under industrially safe growth conditions. In situ mass spectrometry revealed a time and temperature-dependent release of a plethora of NxBy-containing species and, as a result, significant changes of the N:B ratio during h-BN synthesis. Such fluctuations strongly influence the formation and morphology of 2D h-BN. By means of in situ gas monitoring and regulating the precursor temperature over time we achieve uniform release of volatile chemical species over many hours for the first time, paving the way towards the controlled, industrially viable production of h-BN.

We report the optimisation of the experimental variables for the synthesis of large-area (90 cm2), mm-thick carpets of vertically aligned multi-wall carbon nanotubes (MWCNTs) using the aerosol-assisted chemical vapour deposition technique. The effect of the reactor size, temperature, time and the flow rate of the carrier gas on the catalytic conversion rate of the precursor, composition of the atmosphere of the reactor and various properties of MWCNTs such as the mass, length, outer diameter, defect density, oxidation resistance and residual catalyst concentration was investigated. By increasing the volume of the reactor from around 0.2 to 8.5 L, the mass of synthesised MWCNTs and the efficiency of the precursor were increased fivefold (up to 14 g/h.) and twice (up to 88%), respectively. Free-standing and on-substrate carpets of MWCNTs could withstand normal handling without falling apart, making them suitable for characterisations and applications from nano to macro scales. The synthesis recipe also improved the production rate of nitrogen-containing MWCNTs by an order of magnitude.

In order to evaluate the applicability of metal-filled carbon nanotubes, it is crucial to understand their behaviour in the presence of electric currents. In this work we exploit the significant advantages of combining in situ experiments with scanning transmission electron microscopy in annular dark-field mode and related analytical techniques to gain further insights into the electrical transport induced transformations in Fe-filled P,N-doped multi-wall carbon nanotubes. With these synergistic analysis techniques, we could monitor in real time the dynamical effects that take place in the carbon nanotubes and their Fe filling as a consequence of the passing of an electric current and subsequent Joule heating. A detailed analysis of the formation, evolution and composition of intermediate phases has been possible employing in situ experiments with transmission electron microscopy, scanning-transmission electron microscopy and analysis techniques. We show that a multistage process occurs in which the Fe filling reacts with nitrogen to form an intermediate alloy phase, which then decomposes. The presence of high concentrations of nitrogen within the inner channel of the tube is found to be crucial to this process.

Commercially available Cu foils are leading candidates as substrates employed for the generation of large-area graphene using chemical vapour deposition (CVD) techniques. However, the growth of high-quality graphene on Cu foils is often hindered by contamination particles, which will also be detrimental for many potential applications of graphene. Here we investigate the influence of typical substrate impurities on the formation of CVD graphene using as-received Cu foils of various purities from different suppliers and the same cleaned by popular methods. Analytical characterisation of the Cu foils revealed that contamination particles consist of calcium, aluminium, and silicon oxides. We show that contamination particles are present on foils with purities ranging between 99.8% and 99.9999% and that these particles influence the nucleation density, growth rate, and growth features of graphene domains. Based on our findings we propose new industrially applicable targeted cleaning procedures of immersion in purposely-selected HCl and KOH solutions to chemically dissolve the aforementioned impurities, bringing about improved growth of graphene.

We report a method for transferring graphene, grown by chemical vapor deposition, which produces ultraflat graphene surfaces (root-mean-square roughness of 0.19 nm) free from polymer residues over macroscopic areas (>1 cm(2)). The critical step in preparing such surfaces involves the use of an intermediate mica template, which itself is atomically smooth. We demonstrate the compatibility of these model surfaces with the surface force balance, opening up the possibility of measuring normal and lateral forces, including friction and adhesion, between two graphene sheets either in contact or across a liquid medium. The conductivity of the graphene surfaces allows forces to be measured while controlling the surface potential. This new apparatus, the graphene surface force balance, is expected to be of importance to the future understanding of graphene in applications from lubrication to electrochemical energy storage systems.

A simple route for the Sn-assisted synthesis of carbon nanocoils (CNCs) by chemical vapor deposition of acetylene on polycrystalline BaSrTiO3 (BST) substrates is reported. In this study, high-quality CNC forests have been synthesized on BST substrates with the presence of Sn. The morphologies and qualities of the CNCs were characterized by scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy, while the structures and compositions of catalysts were investigated by transmission electron microscopy and energy-dispersive X-ray spectroscopy. Structural control over the CNCs was achieved by simply altering the Sn concentration or acetylene flow rates. This study demonstrates that Sn can act as an efficient catalyst for CNC synthesis in conjunction with either perovskite oxides (BST) or transition metals (Fe).

We report a study of aerosol-assisted chemical vapour deposition (ACVD) technique for the large scale production of carbon nanotubes (CNTs) by investigating the reasons behind the variation and inhomogeneity of the morphologies and quality of CNTs alongside the reactor. Our approach in understanding the system is to simplify it by dividing the reactor into sections and then to characterise the CNTs zone by zone using transmission and scanning electron microscopy, Raman spectroscopy and thermogravimetric analysis in order to identify their level of graphitisation, diameter distribution, catalyst content, growth rate and oxidation resistance in relation to their position in the reactor. Moreover, we established a gallery of electron micrographs depicting different morphologies of CNTs and identified the regions where multi-wall, double-wall, and single-wall nanotubes were produced. We conclude that any attempt to scale up the production of uniform CNTs by ACVD should first aim to homogenise the temperature and catalyst concentration throughout the reactor.

We report the study of different aspects of the aerosol-assisted chemical vapour deposition (ACVD) method for the optimised synthesis of multi-wall carbon nanotubes (MWCNTs). Fifteen hydrocarbons (alkanes, benzene derivatives, and cyclohexane derivatives) were used in conjunction with catalyst concentrations of 1–15 wt.% in order to investigate their effect on morphology, residual catalyst content, diameter distribution, defect density and oxidation resistance of MWCNTs. The conversion yield of the precursors was measured and their thermocatalytic cracking behaviour was studied in situ using an integrated mass spectrometer. We believe that each hydrocarbon interacts differently with the catalyst and follows a characteristic cracking route involving the creation of certain intermediate hydrocarbon fragments which are responsible for the formation of MWCNTs with different properties. We show that the properties of MWCNTs can be tuned by altering the composition of the precursor and that the synthesis rate and the precursor conversion yield can be improved by 60% and 80%, respectively, compared to the commonly used carbon sources such as toluene or xylene. Moreover, while maintaining MWCNT sample quality, i.e. MWCNTs have similar or fewer defects densities and higher oxidation resistance, the amount of residual catalyst particles in the MWCNT samples could also be reduced by ca. 50%.

Individual perfect multi-wall carbon nanotubes (MWCNT) can exhibit exceptional properties, such as an elastic modulus of ∼1 TPa. However, integration of carbon nanotubes (CNTs) in bulk ceramic composites has not yet resulted in the significant improvements in mechanical properties that such data suggest to be achievable. Composites with aligned and continuous CNTs and with high CNT volume fractions might be expected to maximise the improvements. We have produced aligned MWCNT preforms by chemical vapour deposition and fabricated dense, aligned and continuous 20% MWCNT/glass composites. This was achieved by infiltration of a ceramic precursor sol into the interstices of a MWCNT preform and consolidation by hot-pressing. The elastic modulus was measured using microcantilever tests and showed a 32% improvement over that of glass. The Young’s modulus inferred for the MWCNTs in the composite was 200 ± 20 GPa. The load–displacement curves showed a non-linear and hysteretic behaviour which was attributed to interwall sliding within the MWCNTs. Apparent bridging of the cracks by the MWCNTs and a load maximum preceding failure were observed in the composite, indicating progressive toughening with crack growth. The results are discussed in terms of the microstructures of the MWCNTs and composites.

We report that the shape, orientation, edge geometry, and thickness of chemical vapor deposition graphene domains can be controlled by the crystallographic orientations of Cu substrates. Under low-pressure conditions, single-layer graphene domains align with zigzag edges parallel to a single 101 direction on Cu(111) and Cu(101), while bilayer domains align to two directions on Cu(001). Under atmospheric pressure conditions, hexagonal domains also preferentially align. This discovery can be exploited to generate high-quality, tailored graphene with controlled domain thickness, orientations, edge geometries, and grain boundaries. ACS Nano

We investigated the effect of the reaction parameters on the structure of multi-walled carbon nanotubes containing different concentrations of nitrogen and boron. The nanotubes were produced using a 'standard' aerosol chemical vapour deposition technique in conjunction with benzylamine, triethylborane, hexane and toluene mixtures. These precursors were thermally decomposed between 800 and 1100 °C under argon at atmospheric pressure. By varying the precursor concentrations, the nitrogen and boron content of the nanotubes could be altered between 0-2.2 and 0-0.5 at.% respectively. Using a typical laboratory-sized 50 cm long tube furnace, yields between 0.3 and 1.5 g of nanotubes/10 min were relatively easily achieved. Moreover, we show that doping carbon nanotubes with heteroatoms, such as B and N, can be used to control nanotube diameters, change their defect density, and manipulate their oxidation resistance within a range of ca. 170 °C. Hence, we show that it is possible to tune nanotube properties within a certain interval and to produce nanotubes with relatively well defined properties in quantities usable for further characterisation and for studying their viability in applications such as composite materials, gas sensors, capacitors, and electronic components. © 2010 Elsevier Ltd. All rights reserved.

We describe a novel sol-gel based approach for producing aluminoborosilicate glass composites containing continuous, aligned carbon nanotubes. The process involves the production of aligned carbon nanotubes (ACNT) via aerosol chemical vapour deposition (CVD), followed by infiltration of the ACNT with aluminoborosilicate sol. The advantages of this process are three fold: (1) aerosol CVD is an efficient method of producing clean, aligned arrays of CNTs, (2) sol-gel chemistry provides a simple route to infiltration of the ACNTs, and (3) carbon nanotube (CNT) agglomeration problems associated with CNT composites are circumvented. ACNTs (carpets) with heights of up to 4.4 mm were grown with areas of 10 mm × 20 mm for composite fabrication. The composite showed extensive pullout of the CNTs on a fracture surface and improved thermal and electrical conductivities of 16 Wm-1 K-1 and 5-8 × 102 S m-1 respectively compared with only 1.2 W m-1 K-1 and 10-13 S m-1 for the monolithic glass. © 2010 Elsevier Ltd. All rights reserved.

Monodisperse, size-controlled Ni-P nanoparticles were synthesised in a single step process using triphenyl-phosphane (TPP), oleylamine (OA), and Ni(ii)acetyl-acetonate. The nanoparticles were amorphous, contained ∼30 at% P and their size was controlled between 7-21 nm simply by varying the amount of TPP. They are catalytically active for tailored carbon nanotube growth. © 2011 The Royal Society of Chemistry.

We tuned the magnetic properties of iron-filled multi-walled carbon nanotubes (Fe@CNTs) by careful manipulation of the synthesis parameters in a two zone furnace. Due to the small dimensions of iron filling in these samples they have some of the highest values of magnetization saturation reported for Fe@CNTs. Magnetic characterization of the Fe@CNTs revealed that their coercivity can be systematically tuned by varying the pyrolysis temperature, whereas the saturation magnetization can be significantly enhanced by optimization of the sublimation temperature. The rate of argon flow is seen to have little influence on either the saturation magnetization or the coercivity. Furthermore, the study of remnant magnetization as a function of time revealed that magnetization decay rates can be considerably varied.

Linearly polarized light microscopy (PM) revealed that graphene grown by chemical vapor deposition (CVD) on stepped Cu substrate may appear colored. The coloration is associated with the coupling of the light of 450-600 nm into propagating mode in the graphene layer when the electric vector (E →) of polarized light is parallel with the step edges and with the scattering when the E → is normal to the step edges. PM is an inexpensive, fast, and contamination free method to efficiently visualize graphene and to map the step structure of Cu substrates used for large area CVD growth of graphene. © 2012 American Institute of Physics.

We describe the systematic study of multi-walled carbon nanotubes with different nitrogen doping produced by aerosol chemical vapor deposition. Benzylamine:toluene mixtures of 0:100, 5:95, 10:90, 25:75, 50:50, 75:25 and 100:0 were thermally decomposed at 800-900 °C under argon at atmospheric pressure, whereby the nitrogen content of the bulk material was varied between 0 and 2.2 at%. We also show how the presence of nitrogen in the precursor changed the nanotube morphology, i.e. nitrogen decreased the number of kinks incorporated into the carbon nanotubes, decreased their length and diameter and increased the proportion of 'bamboo' shaped nanotubes. Furthermore, due to the nitrogen doping, the oxidation resistance of the nanotube material was decreased. With concentrations above 10% benzylamine the increase of the reaction temperature had no significant effect on the quality of the nanotubes, however, at higher temperatures the nitrogen content was decreased. We demonstrate the control over the nanotube geometry, the nitrogen content and oxidation resistance of the nanotubes, and show that these properties are interlinked. © 2008 Elsevier Ltd. All rights reserved.

The evolution of B-doped multiwalled carbon nanotubes in the presence of a passing current has been investigated using the in situ TEM/STM Nanofactory holder. The Joule heating results in the dopant being partially removed as the internal structure of the nanotube is altered, and significant changes in its electrical properties were observed. This is of great importance for electrical applications where doping is used to tune the Fermi level of carbon nanotubes. © 2011 American Chemical Society.

Precise control of graphene properties is an essential step toward the realization of future graphene devices. Defects, such as individual nitrogen atoms, can strongly influence the electronic structure of graphene. Therefore, state-of-the-art characterization techniques, in conjunction with modern modeling tools, are necessary to identify these defects and fully understand the synthesized material. We have directly visualized individual substitutional nitrogen dopant atoms in graphene using scanning transmission electron microscopy and conducted complementary electron energy loss spectroscopy experiments and modeling which demonstrates the influence of the nitrogen atom on the carbon K-edge.

We have correlated the elemental composition with the structure of multi-wall carbon nanotubes synthesised with nitrogen and phosphorus containing precursors and identified two chemically distinct dominant morphologies. The first type are cone-structured tubes and the second are nanotubes with fewer walls which can accommodate N2 gas along their inner channel and contain up to ten times more nitrogen than the cone-structured nanotubes. Phosphorus was present in the catalyst particles but was not detected within the walls of either type of nanotube. Elemental analysis combined with in situ electrical measurements has allowed us to monitor the evolution of the doped nanotubes when current is passed. The N2 gas becomes bonded immediately when current flows and the gas-containing nanotubes restructure more easily than the cone-structured ones. Since the inclusion of heteroatoms in multi-wall carbon nanotubes is generally inhomogeneous, understanding the distribution of elements across the sample is an important step towards the optimization of devices including gas sensors and components in electrical applications.

International audience; The response of pristine, nitrogen and boron doped carbon nanotube (CNT) sensors to NO2, CO, C2H4 and H2O at ppm concentrations was investigated at both room temperature and 150 degrees C. N-doped CNTs show the best sensitivity to nitrogen dioxide and carbon monoxide, while B-doped CNTs show the best sensitivity to ethylene. All tubes (including undoped) show strong humidity response. Sensing mechanisms are determined via comparison with density functional calculations of gas molecule absorption onto representative defect structures in N and B-doped graphene. N-CNTs show decreased sensitivity with temperature, and detection appears to occur via gas physisorption. B-CNTs appear to react chemically with many of the absorbed species as shown by their poor baseline recovery and increasing sensitivity with temperature. This limits their cyclability. Overall gas sensitivity is as good or better than post-growth functionalised nanotubes, and used in combination, CNTs, N-CNTs and B-CNTs appear highly promising candidates for cheap, low power, room temperature gas sensing applications. (C) 2013 Elsevier Ltd. All rights reserved.

All rights reserved.Metal-free growth of carbon nanotubes/fibers (CNT/Fs) using chemical vapor deposition (CVD) on semiconducting and insulating substrates is of interest in the context of the construction of nanoscale electronic devices. However, controllable synthesis of CNT/Fs without the aid of metal catalysts is an ongoing challenge. Here we report the direct CVD synthesis of CNT/Fs on the perovskite oxides SrTiO3 (STO) and Ba0.6Sr0.4TiO3 (BST). A variety of processing steps were used on STO (001) substrates to create a set of six patterns with varying atomic-scale surface roughnesses. These substrates were all subjected to the same CVD growth conditions, and a correlation was found between the surface roughness of the substrates and the density of CNT/Fs. This indicates that nanometer-scale asperities on the substrates act as the catalytically active sites for CNT/F growth. In a separate set of experiments the surfaces of polished polycrystalline BST samples were investigated. The random orientation of the exposed etched facets of the individual grains revealed significantly different catalytic activity for CNT/F growth. Our study demonstrates the great influence of the nature of the crystal surface condition on the catalytic activity of the substrates and is a critical first step towards perovskite oxide catalyst design.

A simple method for the synthesis of multi-walled carbon nanotubes (MWCNTs) containing Si, P-N and N is reported, and their gas sensing properties were investigated. The MWCNTs were synthesised by the thermal decomposition of aerosols containing mixtures of ferrocene/triphenylsilane, ferrocene/ triphenylphosphine/benzylamine, and ferrocene/benzylamine/toluene. Electron microscopy studies revealed that the addition of Si, P, and N alters the structure of CNTs dramatically. Gas sensing experiments were carried out using Si, P-N, N-containing MWCNTs, and were compared with pure MWCNTs synthesised at similar experimental conditions. These experiments showed that the gas sensitivity and selectivity of CNT-based sensors can be indeed tailored without any post-processing of the raw nanotubes. The efficient in situ tailoring of nanotube properties and functionality are important for nanotubes to become viable materials at the industrial scale where low cost processes are required. © 2012 Elsevier Ltd. All rights reserved.

Strain-induced, self-assembled iron silicide nanostructures were grown on Si(001) substrate by reactive deposition epitaxy. The phases and structures were characterized by scanning- and transmission electron microscopy, atomic force microscopy, and by Fourier transform infrared spectroscopy. The electrical characteristics were investigated by I–V and C–V measurements and the point defects were measured by DLTS. The size and shape of the nanoislands depended on the initial Fe thickness and on the annealing. Coexistence of different iron silicide phases was detected. Electrical characteristics show large defect concentration related to Fe.

In this work it has been established that 3D nanoflowers of WS2 synthesised by chemical vapour deposition are composed of few layer WS2 along the edges of the petals. An experimental study in order to understand the evolution of these nanostructures shows the nucleation and growth along with the compositional changes they undergo.

In this work, carbon nanotube samples were produced by aerosol chemical vapour deposition from a solution of ferrocene in benzylamine. The multi-walled nanotubes produced by this method were investigated by TEM, SEM/EDS, scanning tunneling microscopy (STM) and tunneling spectroscopy (STS). The dl/dV curves obtained from the STS measurements showed asymmetric density of states (DOS) in nanotubes, with higher DOS above the Fermi energy. These STS measurements and the EDS analysis indicate successful doping with nitrogen originating from the decomposition of benzylamine.

High performance perfluoro alkoxy (PFA) and chemical vapor deposition-grown multi-walled carbon nanotube (MWCNT) composite films with thicknesses of 30 μm were prepared using a scalable spray deposition technique. A homogeneous distribution of MWCNTs within the PFA matrix was confirmed by electron and optical microscopy. Dielectric and AC conductivity measurements showed a significant enhancement of dielectric permittivity for PFA/MWCNT films at low frequencies, and a very weak dependence of dielectric permittivity on temperature in the range 25-230 °C. Very low percolation threshold volume fractions of ca. 0.0043 and 0.0017 were attained for MWCNTs with two different aspect ratios, which have been explained by an inherent feature of spray route, a microcapacitor model and percolation theory. The combination of PFA/MWCNT composites and the spray deposition route provides a promising approach for the fabrication of industrial scale composite films with well-controlled dielectric properties for micro-electronic and high temperature applications. © 2008 Elsevier Ltd. All rights reserved.

The electrical resistance of 24 different carbon nanotube (CNT) thin film samples in blowing ambient air and 10 different analyte vapor environments was measured. The effects of the CNT growth method, different chemical treatments, ball milling, sample preparation conditions and Ar+-ion irradiation are compared. Significant differences in the response signal curves as a function of time in the case of the studied sensor/vapor combinations show the important role of the defect structure and attached functional groups in the chemical sensing properties of CNTs.

Ge nanocrystals were formed by electron beam evaporation on SiO2 covered Si substrates. The size and distribution of the nanocrystals were studied by atomic force microscopy, scanning electron microscopy and cross-sectional transmission electron microscopy. Dependencies of the nanocrystal size, of the nanocrystal surface coverage, and sheet resistance obtained by van der Pauw method of the Ge layer have been found on the evaporation time. The suggested growth mechanism for the formation of nanocrystals is the Volmer-Weber type. The sheet resistance exhibited a power dependence on the nanocrystal size.

Nitrogen-containing multi-wall carbon nanotubes (N-MWCNTs) were synthesized using aerosol assisted chemical vapor deposition (CVD) techniques in conjunction with benzylamine:ferrocene or acetonitrile:ferrocene mixtures. Different amounts of toluene were added to these mixtures in order to change the N/C ratio of the feedstock. X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy detected pyridinic, pyrrolic, graphitic, and molecular nitrogen forms in the N-MWCNT samples. Analysis of the spectral data indicated that whilst the nature of the nitrogen-containing precursor has little effect on the concentrations of the different forms of nitrogen in N-MWCNTs, the N/C ratio in the feedstock appeared to be the determining factor. When the N/C ratio was lower than ca. 0.01, all four forms existed in equal concentrations, for N/C ratios above 0.01, graphitic and molecular nitrogen were dominant. Furthermore, higher concentrations of pyridinic nitrogen in the outer shells and N2 molecules in the core of the as-produced N-MWCNTs suggest that the precursors were decomposed into individual atoms, which interacted with the catalyst surface to form CN and NH species or in fact diffused through the bulk of the catalyst particles. These findings are important for a better understanding of possible growth mechanisms for heteroatom-containing carbon nanotubes (CNTs) and therefore paving the way for controlling the spatial distribution of foreign elements in the CNTs using CVD processes.

Despite of the very promising foreseen applications, the use of carbon nanotubes in wider range is still limited by the high production costs. In this paper, our latest results concerning two inexpensive methods of carbon nanotube growth with the promise of industrial upscaling are presented. In case of the DC “arc in water” method, the effect of the angle of the two electrodes on the product yield was investigated. The highest nanotube yield and lowest amount of impurities were found at 90° electrode angles. We have studied the applicability of several liquid hydrocarbons and other metallocenes different from the most widely used benzene/ferrocene solution in case of the injection CVD or “spay pyrolysis” method. Toluene, xylene, cyclohexane, cyclohexanone, n-hexane, n-heptane, n-octane and n-pentane were used as carbon source and cobaltocene and nickelocene as catalyst source. All these compounds were found to be suitable for nanotube production. The highest yield and the best quality were obtained when a mixture of ferrocene–nickelocene was used as catalyst and xylene as carbon source.

Large-area synthesis of high-quality graphene by chemical vapour deposition on metallic substrates requires polishing or substrate grain enlargement followed by a lengthy growth period. Here we demonstrate a novel substrate processing method for facile synthesis of mm-sized, single-crystal graphene by coating polycrystalline platinum foils with a silicon-containing film. The film reacts with platinum on heating, resulting in the formation of a liquid platinum silicide layer that screens the platinum lattice and fills topographic defects. This reduces the dependence on the surface properties of the catalytic substrate, improving the crystallinity, uniformity and size of graphene domains. At elevated temperatures growth rates of more than an order of magnitude higher (120 μm min−1) than typically reported are achieved, allowing savings in costs for consumable materials, energy and time. This generic technique paves the way for using a whole new range of eutectic substrates for the large-area synthesis of 2D materials., Innovative substrate engineering is necessary to improve the quality of CVD-synthesized graphene. Here the authors demonstrate in situ fabrication of an eutectic Pt-Si alloy that forms a wetting liquid surface on polycrystalline Pt foils, allowing millimetre-sized graphene crystals to grow in minutes.

Iron–silicides were grown on Si by reactive deposition epitaxy method and by conventional solid phase reaction. The morphology of silicides was investigated by optical microscopy, scanning electron microscopy and by atomic force microscopy. The phases formed were identified by X-ray diffraction. The thickness of the evaporated Fe films ranged from 1.5 to 30 nm and the in situ heat treatments were carried out between 500 and 800 °C. Self-assembled, island like, oriented β-FeSi2 and α-FeSi2 were found to grow on Si(100) substrates under 15 nm initial Fe thickness. The size of the islands was between 20 and 500 nm, and their shape varied from circular to faceted triangular and quadratic depending on the Fe thickness and on the annealing. Above 20 nm evaporated Fe thickness, the samples show islands of β-FeSi2 phase grown into the FeSi matrix indicating a nucleation controlled type transition of the FeSi to β-FeSi2 phase.

An overview of the available data on carbon nanotube Y junctions is given. The structural models and the transport calculations on the Y junctions are reviewed followed by the various methods, which successfully produced these junctions and the available experimental transport and tunneling data of the grown junctions. In the discussion section, the common and different features of the various growth methods are analyzed and some particularities of branched nano-objects are outlined, which have to be taken account in the interpretation of the tunneling data.

A simple mechano-chemical modification of multiwall carbon nanotubes is described. The use of ball-milling in specific atmosphere allows us to introduce functional groups like thiol, amine, amide, carbonyl, chlorine, etc. onto carbon nanotubes. The resulted functional groups are characterized using infrared spectroscopy and X-ray photoelectron spectroscopy.

Straight carbon nanotubes, carbon nanotube ‘knees’, Y-branches of carbon nanotubes, and coiled carbon nanotubes were grown on a graphite substrate by the decomposition of fullerene under moderate heating (450 °C) in the presence of transition metal particles. The grown structures were investigated without any further manipulation by STM. The observed coiled carbon nanotubes are tentatively identified with the theoretically predicted haeckelite.

Multiwall carbon nanotubes grown by the catalytic decomposition of acetylene over supported Co catalyst were subjected to wet and dry oxidation in order to remove the unwanted products and the catalyst traces. The effects of the purification treatment on the Co content Ž. Ž . was monitored by physical methods: Rutherford Backscattering Spectrometry RBS , Particle Induced X-Ray Emission PIXE and Ž. X-Ray Fluorescence XRF . The purified products were investigated by microscopic methods: TEM, Scanning Electron Microscopy Ž. Ž . SEM , Energy Dispersive Spectroscopy EDS and STM. The KMnOrH SO aqueous oxidation procedure was found to be effective in 42 4 reducing the Co content while damaging only moderately the outer wall of the nanotubes. Treatment in HNO rH SO yields a 32 4 bucky-paper like product and produces the increase of the Si and S content of the sample. q 2002 Elsevier Science B.V. All rights reserved.

We doped graphene in situ during synthesis from methane and ammonia on copper in a low-pressure chemical vapour deposition system, and investigated the effect of the synthesis temperature and ammonia concentration on the growth. Raman and X-ray photoelectron spectroscopy was used to investigate the quality and nitrogen content of the graphene and demonstrated that decreasing the synthesis temperature and increasing the ammonia flow rate results in an increase in the concentration of nitrogen dopants up to ca. 2.1% overall. However, concurrent scanning electron microscopy studies demonstrate that decreasing both the growth temperature from 1000 to 900 °C and increasing the N/C precursor ratio from 1/50 to 1/10 significantly decreased the growth rate by a factor of six overall. Using scanning tunnelling microscopy we show that the nitrogen was incorporated mainly in substitutional configuration, while current imaging tunnelling spectroscopy showed that the effect of the nitrogen on the density of states was visible only over a few atom distances.

International audience; Truncated pyramid-shaped Ni nanocrystals were epitaxially grown on SrTiO$_3$(001) surfaces and characterised by scanning tunneling microscopy (STM). These nanocrystals were shown to be catalytically active for the synthesis of carbon nanotubes (CNTs). The narrow size distribution of the Ni nanocrystals results in a similar narrow distribution of CNT diameters.

Herein, we investigate the growth of multi-walled carbon nanotubes (CNT) using three transition metal oxide nanoparticles; namely hematite (Fe 2O3), cobalt oxide (Co3O4) and nickel oxide (NiO). The nanoparticles were synthesised using flame spray pyrolysis (FSP). As the nanoparticle and CNT syntheses are identical for all materials, a direct comparison between the products is possible and a link between catalyst and morphology of the resultant nanostructures can be elucidated. Conventional CNT were grown on Fe2O3 nanoparticles, no discernible nanotubes were observed on the Co 3O4 catalysts whilst a mixture of conventional and coiled CNT (CCNT) were synthesised on the NiO nanoparticles. We investigated the effect of temperature, time and acetylene/hydrogen gas mixtures on the morphology, yield and purity of the CNT produced. By regulating the acetylene pyrolysis temperature for NiO, the CCNT yield can be increased to approximately 70% of the CNT yield. © The Royal Society of Chemistry 2013.

The "doping" of carbon nanotubes with heteroatoms is an established method of controlling their properties. However, variations in heteroatom concentration in multiwalled carbon nanotubes (MWCNTs) tend to produce nanotubes with different morphologies, and hence varying properties, within the same sample. Electron energy loss spectroscopy in conjunction with imaging using a scanning transmission electron microscope (STEM) is a powerful tool to precisely map the spatial variation and bonding state of heteroatoms, e.g., B, N, P, Si, or combinations of these, present in carbon nanotubes exhibiting different structures. TEM analysis revealed that B incorporation during MWCNT growth (B-MWCNTs) results in nanotube morphologies that can be divided into three different types. These include core-shell structures possessing a B-rich core of cones and a C outer layer, B-containing cone structures, and MWCNTs with an irregular inner channel. In situ studies were carried out using Nanofactory() holder experiments in order to investigate the properties of individual B-MWCNTs and to show that the three types of nanotubes undergo different current-induced breakdown. The inhomogeneity in composition, structure, and properties of B-MWCNTs could result from the variation in chemical composition and temperature within the furnace, and this work highlights the importance of developing synthesis techniques that can control the inclusion of heteroatoms into nanotubes.

Multi-walled carbon nanotubes (MWCNTs) have long been anticipated as candidates for electrical components in an increasingly miniaturized electronics industry due to their inherent electrical properties. It is possible to manipulate and control these properties by introducing dopants such as N, B, and P. Although some current-induced structural changes in MWCNTs have been observed, no systematic study has been carried out to explore the correlation of changes in the internal structure with the electronic behavior of doped-MWCNTs in terms of the current densities present. In situ transmission electron microscopy (TEM) investigations are presented here of individual, N-doped MWNCT (N-MWCNTs) using the in situ TEM/scanning tunneling microscopy (TEM/STM) Nanofactory © holder. It is observed for the fi rst time that N-MWCNTs not only undergo current-induced structural transformation; i.e., from the typical bamboo structure of N-MWCNTs to the stacked cones, but also—and most importantly—the complete removal of the dopant causes a signifi cant change in the electronic behavior. This has serious implications for the use of doped CNTs as electronic components, especially since tremendous efforts are being made to synthesize CNTs with controlled dopant concentrations.

A quite wide brunch of the carbon nanotube science, including the utilization of singlewall nanotube for production of nano-electronic devices has being continuously explored even nowadays. Tuning and modifying the synthesis procedures to obtain nanotube junctions of T, Y, H or X shapes lead to inappropriate results concerning the industrial or large scale production. However, the importance and the demand for these junctions are quite large, since these may be the secondary building units of carbon nanotubes based chips or even more complex nanoelectronic devices. Recently, some novel solutions of their preparation have been published. A Taiwanese group described a method to prepare multi-junctioned carbon nanotubes on mechanically pretreated silicon surface applying chemical vapor deposition (CVD) technology using decomposition of methane at 1373 K. The nanotubes were nucleated following the lines prepared by scratching the surface with 600-grit sand paper. Contrary to the physical pretreatment of a substrate surface, chemical reactions can also be used for the preparation of carbon nanotube junctions. P.W. Chu et al. reported interconnecting reactions between functionalized carbon nanotubes . By the described method, the carboxyl groups on the wall of singlewall carbon nanotubes are converted to carbonyl chloride groups by reaction with SOCl2 at room temperature. The formed COCl groups are very reactive on the outer surface and can be reacted easily with various amines, particularly diamines resulting in the formation of amide bonding. When two functionalized carbon nanotubes react with such an amine molecule interconnection of tubes is generated. The resulted carbon nanotube junctions have been investigated by AFM. In this presentation, we report on the results obtained on the preparation of carbon nanotube junctions applying two different procedures. The first method is similar to Chu’s one, which was mentioned above, i.e. we used functionalized multiwall carbon nanotubes and the successful interconnection of them by propylene diamine has been proven by TEM and AFM. The second method demonstrates a novel principle: catalyst material has been deposited on the outer surface of carbon nanotubes and branches of nanotubes were produced at this contact point by catalytic chemical vapor deposition (CCVD) of acetylene. The product has been characterized by TEM.