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Molybdenum disulfide ((MoS2)n) nanotubes are generated when polycrystalline MoS2 powder, covered by Mo foil, is heated to ca. 1300 °C in the presence of H2S. Electron diffraction reveals the presence of zigzag arrangements within the tube walls.

Paramagnetism in boron-containing carbon nanotubes was detected by SQUID measurements, and a g -value of 2.0020, corresponding to the free carrier spin, was observed over a wide temperature range (108–455 K). This value implies intrinsic metallic behaviour and contrasts with thermally activated semiconduction which multi-walled carbon nanotubes usually exhibit.

The morphological and structural features of WS2 nanotubes, generated from WOx (x ≅ 2.7) needles, by an in-situ heating process, have been studied by electron microscopy and X-ray diffraction (XRD), in conjunction with computer simulation. The results show that these inorganic fullerene nanotubes exhibit interesting differences when compared with carbon nanotubes (CNTs). In some cases the tube tips or segments are open. Occasionally the tube walls may be uneven. The sulfur distribution within the tubes is uniform, except for the edge layers which appear to contain less sulfur. Defects are often observed, particularly in the outer shells, which may be due to defective encapsulated WOx phases. Octagonal and square-like defects appear to be associated with the closure of tube caps. Electron diffraction (ED) reveals that nearly half of the non-helical WS2 nanotubes are of the armchair-type. A mechanism has been proposed to account for the extended inorganic nanotube growth.

Nitrogen doped carbon nanotubes have been synthesized using pyrolysis and characterized by Scanning Tunneling Spectroscopy and transmission electron microscopy. The doped nanotubes are all metallic and exhibit strong electron donor states near the Fermi level. Using tight-binding and ab initio calculations, we observe that pyridine-like N structures are responsible for the metallic behavior and the prominent features near the Fermi level. These electron rich structures are the first example of n-type nanotubes, which could pave the way to real molecular hetero-junction devices., Comment: 5 pages, 4 figures, revtex, submitted to PRL

When nanotubes form in a carbon arc, the presence of boron results in long boron-doped carbon nanotubes which are generated as dominant zigzags. Metallic behaviour is observed, in contrast to carbon nanotubes, which are semi-conducting.

Structural and electronic properties as well as the stability of MoS2 nanotubes are studied using the density-functional-based tight-binding method. It is found that MoS2 zigzag ( n,0) nanotubes exhibit a narrow direct band gap and MoS2 armchair ( n,n) possess a nonzero moderate direct gap. Interestingly, the ( n,n) tubes show a small indirect gap similar to the direct gap of ( n,0) nanotubes. Simulated electron diffraction patterns confirm the existence of armchair and zigzag disulphide nanotubes. The structure of the MoS2 nanotube tips is explained by introducing topological defects which produce positive and negative curvature.

Powders of the nanoparticles were obtained from the colloidal solutions by removing the water with a rotary evaporator (bath temperature 50 C). Transmission electron micrographs of the samples were taken using a Philips CM 300 UT electron microscope, working at 300 kV acceleration voltage. A Philips Xpert system was used to measure the X-ray diffraction pattern of powder samples. UV-vis absorption spectra of the colloidal solutions were recorded with a Lambda 40 spectrometer (Perkin‐Elmer). Photoluminescence spectra were recorded with a Spex Fluoromax 2 spectrometer having a spectral resolution of 0.5 nm.

Carbon-encapsulated Sn−Pb nanowires are generated by electrolysis of graphite in molten LiCl containing these metals. SA-EDX analyses indicate a distinctive profile for the metal cores in which Sn predominates at one end and Pb at the other of the individual nanowires; X-ray diffraction measurements reveal that separate crystals of each metal can be distinguished, thus zone refining has occurred. The cores exhibit dynamic behavior under electron irradiation. A growth mechanism is proposed for the nanowires.

We investigate the growth of B-doped carbon nanotubes combining experimental and theoretical techniques. Electron microscopy observations and electron diffraction patterns reveal that B doping considerably increases the length of carbon tubes and leads to a remarkable preferred zigzag chirality. These findings are corroborated by first-principles static add dynamical simulations which indicate that, in the zigzag geometry, B atoms act as a surfactant during growth, preventing tube closure. This mechanism does not extend to armchair tubes, suggesting a helicity selection during growth.

and Ni deposited on a silica plate at 950 °C. High-resolution transmission electron microscopy (HRTEM) studies reveal that these tapered structures are almost completely filled with Ni and are closed at both ends. The diameters of the needles (2–5 μm in length) range between 10–20 nm at one end and 30–200 nm at the other. A surprisingly high degree of graphitization is observed in the walls of the nanotubes. These unique structures may prove useful as electrodes with various applications such as precision probes in biological systems or scanning tunnelling microscope tips.

Novel flower-like nanostructures consisting of silicon oxide nanofibers, radially attached to a single catalytic particle, were generated by solid-solid and gas-solid reactions under a temperature gradient. In this process, a mixture of SiC and Co powders, deposited on silica substrates and heated under an Ar/CO atmosphere at ca. 1500C, produced material with unusual three-dimensional (3D) networks of nanofibers of uniform diameter (ca. 20-120nm) and length (ca. 10-250mu;m). Scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray powder diffraction and energy dispersive X-ray (EDX) analyses reveal that the nanofibres are amorphous and consist only of silicon oxide, generated from the reaction of CO with SiC. Nanostructure formation is catalyzed by Co particles, which act as nucleation sites and templates for 3D growth. Experiments using Si3N4 and Si in conjunction with other catalysts (e.g. Fe, Ni and CoO) yield similar results and confirm that the resulting SiOx fibres display virtually unique and remarkable radial growth starting from single metal particles. These structures exhibit morphologies comparable to radiolarian and diatom skeletons and may provide insight into the formation of microbiological systems.

Pyrolysis of 2-amino-4,6-dichloro-s-triazine over laser-etched thin films of cobalt deposited on an inverted silica substrate generates aligned bundles and films of carbon nanotubes of uniform dimensions. Scanning electron microscopy, high resolution transmission electron microscopy, energy dispersive X-ray analyses, electron energy loss spectroscopy and electron diffraction studies reveal that the aligned tubes, which usually grow perpendicular to the substrate surface, are mainly straight (length ⩽100 μm; 30–50 nm OD), contain traces of nitrogen (

Highly graphitised needle-like elongated carbon nanostructures containing encapsulated Ni, are produced by heating alternating thin films of C60 and Ni on a silica plate at 950 °C. High Resolution Transmission Electron Microscopy (HRTEM) studies reveal that these tapering structures are fully filled with Ni and are closed at both ends. The diameters of the needles (ca. 2–5 μm in length) range between 10–20 nm at one end and 30–200 nm at the other. A surprisingly high degree of graphitisation was observed for the nanostructures. They may prove to be useful as Scanning Tunnelling Microscope (STM) tips due to their shape.

Laser etching of Co, Ni and Fe films, in conjunction with the pyrolysis of solid organic precursors (e.g. aminodichlorotriazine, melamine, etc.) generates aligned carbon nanotube bundles and films of uniform length (< 200 mu m) and diameter (30 Angstrom - 80 Angstrom). However, nanotube alignment strongly depends upon laser etching conditions (e.g. laser power, pulse duration and focus distance). Additionally, condensed-phase techniques, using mixtures of molten LiCl and soft metals (e.g. Bi, Pb, etc.) as electrolytes, generate high yields of metallic nanowires (< 45 % overall material and < 2 mu m in length, < 100 nm OD). Finally, it is shown that novel 3-D flower-like silica nanostructures are produced by a simple and surprising solid-phase approach. It is observed that single catalytic nanoparticles act as nucleation sites, leading to unusual morphologies of silicon oxide nanofibres (20-120 nm OD and < 200 mu m). The latter structures may be useful in the context of catalysis, 3-D composite materials, and optoelectronic devices, thus breaking new ground in nanowire and nanofibre technology.

Since the outstanding transport properties of graphene originate from its specific structure, modification at the atomic level of the graphene lattice is needed in order to change its electronic properties. Thus, topological defects play an important role in graphene and related structures. In this work, one-dimensional (1D) arrangement of topological defects in graphene are investigated within a density functional theory framework. These 1D extended lines of pentagons, heptagons and octagons are found to arise either from the reconstruction of divacancies, or from the epitaxial growth of graphene. The energetic stability and the electronic structure of different ideal extended lines of defects are calculated using a first-principles approach. Ab initio scanning tunneling microscopy (STM) images are predicted and compared to recent experiments on epitaxial graphene. Finally, local density of states and quantum transport calculations reveal that these extended lines of defects behave as quasi-1D metallic wires, suggesting their possible role as reactive tracks to anchor molecules or atoms for chemical or sensing applications.

Surfaces as 2-D manifolds play an important role in the description of structures, from inorganic materials to biological systems. These surfaces which can be planar, spherical or hyperbolic (saddle-shaped), arise as a consequence of interatomic forces. We are concerned with the generation and application of 2-D manifolds, in particular, periodic minimal surfaces. We show that surfaces can be decorated with atoms to obtain structures with different curvatures, related to the mean coordination number CN. When CN = 6 a planar surface or a cylinder can be obtained, if CN 6, an infinite structure, periodic or otherwise, can be generated. Regarding the case CN > 6, we have found that the existence of ordered graphite foams with topologies similar to periodic minimal surfaces is quite possible, various transformations of surfaces, such as the Bonnet transformation, the Goursat transformation and a new combination of both, are analysed, since they might be useful in the description of physical and biological processes.

Invar (Fe65Ni35), a ‘zero’ thermal expansion alloy consisting of Fe and Ni, has been successfully introduced into carbon nanotubes by pyrolysing, at 800 °C, aerosols of NiCp2/FeCp2 mixtures dissolved in C6H6; scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) studies reveal the presence of flake-like structures (ca. 1–2 mm2) consisting of filled/aligned carbon nanotubes (⩽200 μm in length and ⩽80 nm in diameter) in a carpet pile-like configuration; analysis of the filling material (⩽500 nm in length and ⩽40 nm in diameter) by X-ray powder diffraction and high-resolution electron energy loss spectroscopy (HREELS) line scans, confirmed that Invar was formed; this appears, to the best of our knowledge, to be the first report of mixed metal alloy nanowires forming inside carbon nanotubes.

The electronic structure and spin magnetism for few-layer-graphene nanoribbons synthesized by chemical vapor deposition have been investigated using near-edge x-ray absorption fine structure (NEXAFS) and electron-spin resonance (ESR). For the pristine sample, a prepeak was observed below the pi* peak close to the Fermi level in NEXAFS, indicating the presence of additional electronic states close to the Fermi level. The intensity of this prepeak decreased with increasing annealing temperature and disappeared after annealing above 1500 degrees C. The ESR spectra, which proved the presence of localized spins, tracked the annealing-temperature-dependent behavior of the prepeak with fidelity. The NEXAFS and ESR results jointly confirm the existence of a magnetic edge state that originates from open nanographene edges. The disappearance of the edge state after annealing at higher temperatures is explained by the decrease in the population of open edges owing to loop formation of adjacent graphene edges.

Cylindrical ferromagnetic nanowires encapsulated inside multiwalled carbon nanotubes (MWNTs) are synthesized by pyrolyzing either ferrocene powder or ferrocene–toluene mixtures. By changing the way the precursor is thermolyzed, we have been able to control the composition of the ferromagnetic byproducts. In particular, we noted the coexistence of α-Fe and Fe3C phases when only powder ferrocene is theromolyzed in an inert atmosphere. However, when toluene–ferrocene solutions are sprayed and thermolyzed, only Fe3C nanocrystals are produced. Magnetic measurements of the aligned nanotubes containing these cylindrical nanowires revealed large coercive fields as high as 0.22 T at 2 K. Interestingly, these magnetic coercivities strongly depend on the Fe particles’ diameter, and are not affected by the length of the particles, which was also confirmed using micromagnetic simulations. Our experimental and theoretical results indicate that short and well aligned carbon nanotubes containing narrow ferromagnetic nanowires (i.e. 5 nm diameter and 25 nm long) would be suitable for producing prototypes of magnetic recording devices.

We present a simple design of a field effect transistor based on graphene nanoribbons, taking advantage of the metallic and semiconductor nature of nanoribbons with different widths. Such device could be constructed by using lithography techniques. The conductance of the proposed device is obtained by using the Kubo formula, assuming a strong damping due to the substrate and imperfections of the lattice. By removing the control electrodes, the design could also be used as an electrical resistance.

The magnetic and electronic properties of MoS(2) nanoribbons with zigzag and armchair edges are investigated using LSDA-DFT. We found that the properties of the nanoribbons are very different from bulk MoS(2) due to edge states. Armchair nanoribbons could be metallic and exhibit a magnetic moment; however, when passivating with hydrogen, they become semiconducting. Zigzag nanoribbons are metallic and exhibit unusual magnetic properties regardless of passivation. Our results could explain the recent evidence of ferromagnetism in flat MoS(2) clusters, and motivate the synthesis of novel MoS(2) nanosystems.

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A soft method for purifying multi-wall carbon nanotubes (N-doped and undoped) is presented. The technique includes a hydrothermal/ultrasonic treatment of the material in conjunction with other subsequent treatments, including the extraction of polyaromatic compounds, dissolution of metal particles, bundle exfoliation, and uniform dispersion. This method avoids harsh oxidation protocols that burn (via thermal treatments) or functionalize (by introducing chemical groups) the nanotubes. We show a careful analysis of each purification step and demonstrate that the technique is extremely efficient when characterizing the materials using scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDAX), scanning tuneling electron microscopy (STEM), x-ray powder diffraction (XRD), diffuse reflectance Fourier transform infrared (DRFTIR) spectroscopy and thermogravimetric analysis (TGA).

Electronic and magnetic properties of all sp2carbon species with N = 10–14 atoms (non-fullerenes clusters, rings, linear chains, zigzag and armchair ribbons) are investigated using many-body schemes. The correlated π-electrons are treated by means of the single band Hubbard model. The ground-state energy, wave function and the total spin are calculated using the Lanczos numerical diagonalization method. We found that clusters could exhibit spin switching when the electron–electron interaction is increased (a transition from singlet to triplet state) driven by Hund’s rule. Among the magnetic clusters found in this study, we usually observed carbon chain morphologies containing two interconnected clusters joined by one or two bonds. We also investigated the magnetic properties of doped clusters by adding one hole or one electron. In particular, it was found that the addition of one hole in carbon rings with N = 5, 9, 13 (generalized equation is N = 4k + 1 with k ≥ 1) results in a triplet state (S = 1), whereas one-electron doping in carbon rings shows S = 1 for N = 3, 7, 11, 15 (N = 4k − 1 with k ≥ 1). Armchair and zigzag carbon ribbons were also studied, and we found that only the zigzag ribbons exhibit a magnetic moment. In order to understand the magnetic properties and the role of cluster encapsulation in fullerenes, we performed first principles calculations using local spin density approximations. We found that the sandwich 5-membered ring clusters inside fullerenes and carbon nanotubes result in different electronic and magnetic properties.

We investigate the magnetic response and the ring currents induced by the presence of an external magnetic field in different carbon nanostructures using a π-electron tight binding model in conjunction with the London approximation. We consider fullerenes, corrugated and non-corrugated carbon nanotori, and finite graphene sheets. For corrugated carbon nanotori, we have constructed the structures in two different ways: by joining the ends of carbon nanotubes containing pentagonal, hexagonal and heptagonal carbon rings (rectangular and hexagonal Haeckelites); and by coalescing C60 molecules along the three different axes of symmetry (C2, C3 and C5). The non-corrugated carbon nanotori have been constructed by joining the ends of standard carbon nanotubes containing hexagonal rings only. For the graphene ribbons, we considered those exhibiting armchair or zig-zag edges. Our results reveal strong paramagnetic signals in structures containing non-hexagonal carbon rings. For carbon nanotori, the presence of strong paramagnetism causes the electrons to flow around the torus. We also observed that the ring currents of graphene ribbons are small and localised at the edges. Finally, the magnetic moment of nanotori constructed from Haeckelite structures is also described as a function of doping (adding additional electrons or holes).

Graphite is a layered material that is very flexible, in which each layer is able to curve in order to form cages, nanotubes, nanocoils, nanocones, etc. In this paper, we demonstrate that various synthetic routes are capable of producing graphite-like nanomaterials with fascinating electronic and mechanical properties. There are other layered systems, which could curl and bend, thus generating novel nanostructures with positive and negative Gaussian curvature. In this context, we will also demonstrate that hexagonal boron nitride, tungsten disulfide (WS2), molybdenum disulfide (MoS2) and rhenium disulfide (ReS2) are also able to create nanocages, nanotubes and nano-arrangements exhibiting novel physico-chemical properties that could revolutionize materials science in the 21st century.

Elastic, electronic and vibrational properties of seven models of nanoporous carbon are reported. The studied structures are periodic graphitic arrangements with heptagonal and octagonal rings of carbon, known as Schwarzites. The calculations were performed within a non-orthogonal tight binding framework which has been show nt ob er eliable for diamond, graphene layers, fullerenes and carbon nanotubes. In contrast with previous studies, each structure was properly relaxed, so that differences between each model must be assigned to intrinsic properties rather than to differences in their construction. Thermodynamic properties were calculated from the vibrational density of states.

In order to investigate the mechanical properties of carbon nanotubes, dynamic shock wave pressures (⩽50 GPa) were applied on arc-discharge-generated carbon nanotubes containing polyhedral nanoparticles. High-resolution transmission electron microscopy (HRTEM) studies of the shock-recovered samples reveal that: (i) layers of the outer shells of the nanotubes break and transform into curled graphitic structures and (ii) the inner tube walls and bulk material display structural defects. Further X-ray powder diffraction and HRTEM analyses exhibit the presence of diamond nanocrystals which are produced after the shock-wave compression of polyhedral particles (present in the starting material).

Flower-like Si nanostructures are formed in high yield, by heating an SiO 2 plate at ca. 1600 °C (Ta heater) under Ar (100 Torr). The product consists of metal-free cubic phase Si nanowires surmounted by bulbous Si tips. HRTEM observations show that the nanowires contain kink and twinning defects, whereas the tips are generally well-crystallized and covered with a thin layer of amorphous SiO x ( x = 1–2). A growth model is proposed to account for these observations.

Soon after the identification of carbon nanotubes, produced by arc-discharge techniques, the possibility of introducing metals into the inner core of the tubes was considered (Figure 1). This idea followed logically from the successful observation of fullerenes containing endohedral metals. The introduction of metals or metal carbides and oxides into multiwalled nanotubes [usually 2–70 nm outside diameter (OD), x, SiC, MoS2, WS2, etc.) are able to form novel nanowires and fullerene-like morphologies. This review discusses methods for generating these fascinating structures and evaluates their possible applications in materials science and engineering.

We report a high-yield route to two-dimensional arrays (

The extent of nanotube formation arising from the electrolysis of molten LiCl, using graphite electrodes, is reduced by the addition of salts to the electrolyte. In certain cases (99% LiCl+

mixtures. Prolonged electron irradiation of these nanowires leads to axial growth and to dynamic transformations. These observations suggest ways in which materials may be modified by microencapsulation and irradiation.

"La nanociencia y nanotecnología se dedica a la creación de nuevos materiales con propiedades interesantes como dureza, conductividad, propiedades magnéticas. Ahora también, se está estudiando el uso de estos nanomateriales como bloques de construcción para crear nuevos materiales. En este trabajo se estudiaron arreglos ordenados y desordenados: 1) ópalo inverso de carbono y 2) bosques de nanotubos de carbono. Respecto al ópalo inverso de carbono, utilizamos un ópalo con nanopartículas de SiO2 (300 nm) ordenadas de manera FCC como molde para la fabricación de ópalo inverso de carbono. Este ópalo inverso de carbono fue sintetizado mediante la infiltración de una solución conteniendo sacarosa como fuente de carbono; además, en esta misma solución se agrego pirazina como fuente de nitrógeno para así obtener ópalo inverso de carbono dopado con nitrógeno. Por otro lado, utilizamos nanopartículas de SiO2 (10 y 100 nm) desordenadas como molde para sintetizar ópalo inverso de carbono dopado con nitrógeno. Estas muestras se caracterizaron mediante SEM, TEM, espectroscopía Raman, análisis termogravimétrico, adsorción de nitrógeno, difracción de rayos-X y espectroscopía de reflexión óptica. En los resultados obtenidos observamos ligeros cambios en la estructura de las muestras dependiendo de la concentración del dopaje, también observamos el corrimiento del pico de reflexión óptica dependiente a la concentración nitrógeno en la muestra; el corrimiento hacia el azul del pico de reflexión óptica dependiente a la concentración nitrógeno en la muestra. Posteriormente, realizamos el estudio de las propiedades físicas de ópalo inverso dopado con diferente contenido de nitrógeno y tamaño de poro. En general, variando la concentración de nitrógeno y el tamaño de poro se puede variar controladamente sus propiedades físicas como la resistencia, emisión de campo, magnetoresistencia y magnetización. La resistencia se variar desde 0.30 hasta 0.02  cm y dependiendo de su nivel de dopaje el mecanismo de transporte electrónico puede variar. En magnetoresistencia (MR) hay una transición de MR positivo a MR negativo, al variar de bajas hacia altas temperaturas. Así también, la magnetización de las muestras exhiben una transición de paramagnético a diamagnético al incrementar la temperatura; la temperatura de transición es más alta para poros más pequeños." "Nanoscience and nanotechnology are dedicated to the creation of new materials with interesting properties like hardness, conductivity, magnetic properties, among others. Now, there is also interest in the use of these materials as building blocks to create new materials. In this work ordered and disordered arrays were studied: 1) carbon inverse opal and 2) carbon nanotube forests. Regarding the carbon inverse opal, we used an opal with SiO2 nanoparticles (300 nm) ordered in a FCC manner as a template for the fabrication of carbon inverse opal. This carbon inverse opal was synthesized by the infiltration of a solution containing sucrose as a carbon source; also, in this same solution we added pyrazine as a nitrogen source to obtain nitrogen doped carbon inverse opal. On another hand, we used disordered SiO2 nanoparticles as a template to synthesize nitrogen doped carbon inverse opal. These samples were characterized by SEM, TEM, Raman spectroscopy, thermogravimetric analysis, nitrogen adsorption, X-ray diffraction and optical reflection spectroscopy. In the obtained results we observed slight changes in the structure depending on the doping concentration, also we observed the shift of the optical reflection peak depending upon the nitrogen concentration in the sample; observed a blue shift of the optical reflection peak dependent on the nitrogen concentration in the sample. Furthermore, we realized the study of the physical properties of the carbon inverse opal with different contents of nitrogen and pore size. In general, varying the nitrogen concentration and pore size it is possible to vary in a controlled manner the physical properties such as resistance, field emission, magnetoresistance and magnetization. The resistance was varied between 0.30 down to 0.02  cm and depending upon the degree of doping the transport mechanism of electrons may vary. In magnetoresistance (MR) there is a transition from positive MR to negative MR, when varying from low to high temperatures. Also, the magnetization of the samples exhibits a transition from paramagnetic to diamagnetic when increasing the temperature; the transition temperature is higher for smaller pore size. Finally, the carbon inverse opal doped with nitrogen was used as an acetone, ethanol and chloroform sensor, showing that doping with nitrogen effectively increases the sensing response signal."