The double resonance Raman spectra of the disorder-induced D-band and some other non-zone-center phonon modes are discussed for two-dimensional (2D) graphite and to some extent for single wall carbon nanotubes (SWNTs). The phonon dispersion relations of graphite can be determined using Raman spectroscopy b y measuring the non-zone center Raman phonon frequencies in combination with theoretically determined phonon q-vectors. We report a t of the phonon dispersion relations to experimental Raman spectra which were previously observed but have not y et been assigned to speci c phonon branches. We found that the D-band and the G0-band of 2D graphite consist of, respectively, two and one Raman Lorentzian peaks, while 3D graphite shows two G0-band Lorentzian peaks. The appearance of two G0 peaks in the resonance Raman spectra of SWNTs may come from resonances of one laser line with two di erent van Hov e singularities.

Nanowires of magnetic metals (Ho, Gd) have been synthesized inside the hollow interior of single wall carbon nanotubes by the sealed-tube reaction. Amongst the d- and f-series metal chlorides investigated in this study, HoCl3 and GdCl3 fill the SWNTs to a significantly higher extent than FeCl2 and CoCl2. HoCl3 and GdCl3 nanowires have been transformed into the respective metal nanowires via the reduction of the chloride nanowires. The nanowires have been imaged using high-resolution transmission electron microscopy and scanning transmission electron microscopy (STEM). X-ray energy dispersive spectroscopy carried out in conjunction with STEM confirmed the presence of metal chloride and metal nanowires.

In this work, we report the production of MoSe2 (molybdenum diselenide) nanotubes formed by irradiating the samples with high doses of electron irradiation. The irradiation was performed on a 2 MeV Van de Graaff accelerator at the following conditions: voltage 1.3 MeV, current 5μA current, dose rate 25 kGy/min, and total dosage 1 MGy. We observed well-defined nanotubes of several nm long and few nm wide, which suppose to be hollow and capped at one end. As the level of irradiation was increased to 1 MGy, elongated onion-like structures were observed.

To enhance the yield of multi-walled carbon nanotubes (MWNTs), a vortex enhanced CVD reactor (VECVD) design has more advantage over the conventional straight tube CVD. A computational fluid dynamics (CFD) code was applied to analyze heat and mass transfer processes to compare the conventional CVD design performance with a new type. The calculation showed that VECVD has a stronger and more uniform circulation along the reactor than the conventional CVD design.

Using state of the art quantum calculations, we have studied the electronic and transport properties of a variety of nanotube-based structures relevant for the design of nanoscale electronic devices. We have investigated the conductance of carbon nanotubes under mechanica distortions such as bending, defects and tube-tube contacts, and analyzed the behavior of carbon nanotube-metal contacts with the aim of explaining the anomalously large contact resistance observed in nanotube devices. Our results provide a clear interpretation of recent experimenta findings and suggest avenues for the use of carbon nanotubes in electromechanical systems.

A new class of low-angle conical carbon crystals has been described and their characteristics are reported here. These carbon nanocones were found in pores of a glassy carbon (GC) along with cylindrical multiwall nanotubes and graphite polyhedral crystals. The largest cones reach 2 to 3 microns in length, although most are in the submicron range. Scanning Electron Microscopy (SEM) reveals cones protruding from the inner pore surfaces with the tips oriented toward the inside of the pores. Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED) show that cones are made of thick (up to several hundred layers), highly-ordered graphitic walls. Their tips are graphitic as well, and exhibit a dome-like morphology. These cones also differ from any carbon cones observed earlier in that they have a much smaller apex angle, sometimes less than 3°. Small angle carbon nanocones can potentially be used for probes and field emission elements.

Single wall carbon nanotubes (SWNTs) have been processed in different schemes to get clean material for use in various filling experiments. The SWNTs synthesized by different methods require different processing schemes, and this is presumably due to heterogeneous nature of the various contaminants present along with the carbon nanotubes. For the pulsed laser synthesized SWNTs, a combination of nitric acid, hydrogen peroxide and hydrochloric acid treatment gives best results and the purified SWNTs give best ever filling fraction for fullerene, C60 of ~90%. The processing improves the surface cleanliness of SWNTs, in turn giving greater access for the target molecules, and hence the higher filling fraction. For the carbon arc produced SWNTs, air oxidation followed by treatment with nitric acid has been found to work best and the processed SWNTs have been used for filling experiments with metal chlorides. Both these processing schemes still leave a small fraction of catalyst impurities in the final material, thus the material quality of filled material and hence its properties depend on the processed material used for the filling experiments.

Dispersion and alignment of carbon nanotubes in thermoplastic polymers such as polycarbonate have been studied. Dispersion was accomplished by mixing in a conical twin-screw extruder and alignment was carried out using a fiber spinning apparatus. The effects of mixing time and fiber draw ratios on dispersion and alignment were investigated. Uniform dispersions were produced with relatively short residence times in the extruder. Excellent alignment of carbon nanotubes in nanocomposite filaments was obtained when the fiber draw ratio was greater than 7. The ability to closely control the dispersion and alignment of carbon nanotubes in polymers is expected to lead to the development of nanocomposites with desirable electronic and structural properties.

Boron nitride nanotubes, nanocones and nanocables were prepared and their atomic structures were identified by using a 300 kV field emission transmission electron microscope equipped with an electron energy loss spectrometer and energy dispersion X-ray detector. Multiwalled BN nanotubes and nanocones were synthesized by reacting C nanotube templates and boron oxide under nitrogen atmosphere at 1723-2023 K. Additions of metal oxide promoters, e.g. MoO3, CuO, and PbO, significantly improved BN-rich nanotube yield at the expense of B-C-N nanotubes. It was shown that BN nanotubes had preferential “zigzag” chirality and exhibited either hexagonal or rhombohedral stacking between shells. An efficient synthetic route for bulk quantities of BN tube production was also developed, where a B-N-O precursor was used during a CVD process. Nanocones of BN were mostly found to have 240° disclinations which ensure the presence of B-N bonds only. One case was observed of a cone constituted of 300° disclination implying that structures may contain line defects of non B-N bonds. The first synthesis of insulating BN nanocables was carried out, where BN nanotubes were entirely filled with Invar Fe-Ni nanorods. The filled nanotube diameters ranged between 30 to 300 nm, whereas the length of filling reached several microns.

Carbon nanotubes are synthesized using thermal chemical vapor deposition. Various temperature and pressure are used to fabricate carbon nanotubes. It is found that the nanotube-diameter distribution mainly depends on the growth-temperature. With the substrate surface normal either along or against the gravity vector, different growth orientations of multi-walled carbon nanotubes are observed by scanning electron microscopy although the Raman spectra are similar for samples synthesized at different locations. The sizes of these carbon nanotubes in each sample are quite uniform and the length of the tube is up to hundreds of micrometers. These results suggest the gravitation effects in the growth of long and small diameter CNT.

Carbon nanotubes systems have revealed large potentialities in terms of applications, especially at a nanometric scale. As a consequence, the different interactions which can take place can be of primary importance. In this paper, we report studies carried out on different carbon systems such as single-walled or multi-walled nanotubes and polymer/nanotubes composites. By using Raman spectroscopy, apart from the expected interactions between tubes in bundles which have initiated experiments on individual entities, we put in evidence strong chemical reactions at the interface metal/nanotubes when Ag or Au surfaces are used to carry out Surface Enhanced Raman Scattering experiments. We show in particular that a different behavior is observed for metallic and semiconducting tubes. Also, a high state of disorder is observed, together with the transformation of nanotubes to other carbon compounds. In the case of multi-walled nanotubes, theoretical calculations allow us to interpret the low frequency Raman modes by introducing interactions in concentric tubes, in rather good agreement with experiments. Finally, in polymer/nanotubes composites, an upshift of the radial breathing mode is observed and we show in this case that it originates from the dynamical stress applied by the polymer on the bundles in response to the breathing vibration.

We analyze the dependence of the second-order G'-band profile in terms of their (n,m) indices by measuring the resonance Raman spectra of several semiconducting and metalic isolated single wal carbon nanotubes. We show that this profile is very sensitive to the electronic structure, thus making it possible to get structural (n,m) information and to probe the splitting of the van Hove singularities in the electronic density of states due to the trigona warping effect.

Effects of hydrogen sulfide on the structure of carbon nanotubes (CNTs) were studied using high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). The CNTs were synthesized with an iron thin-film catalyst by microwave plasma-assisted CVD on the diamond substrate. The HRTEM images revealed that essentially all of the CNTs obtained in this study were multiwall (MWCNT). The addition of H2S resulted in nanotubes with split skins as cornhusks and/or frills. Electron energy loss spectra of the cornhusks indicated that they consist of sp2, sp3 and amorphous carbon phase. The spectra revealed that the sp3 to sp2 ratio at the points where cornhusks divide from the main stem was more than that at the edge of the cornhusks. No evidence of sulfur incorporation into the MWCNTs grown with the H2S addition was found. We speculate that the chemical nature of sulfur on the CNT growth yields such anomalous structure.

In order to build electrical devices based on carbon nanotubes, it is crucial to understand the effects of the substrate, electrical contacts, defects and junctions on the transport properties of both multi-wall and single-wall carbon nanotubes (MWNT and SWNT). In the present study two different dispositions are analyzed. In one of them, isolated MWNT were deposited onto an insulating oxide layer over a conducting substrate and platinum electrical contacts were prepared via a focused ion beam (FIB) deposition method. An ohmic contact to the substrate allowed us to polarize it at a different potential than the nanotubes themselves. In the second one, a vertical array of MWNT was grown on a template of alumina in which one of the ends was coated with gold, to provide an electric contact. To investigate transport properties, we used an atomic force microscope (AFM) to determine the electric surface potential of MWNT. The technique employed, scanning surface potential microscopy (SSPM), applied a dc-voltage to the tip that equilibrates the local electrostatic potential on the sample so as to eliminate forces on the AFM tip caused by electric repulsion or attraction between tip and sample. There is no alteration of the sample potential caused by the tip. Surface potential measurements on the first system show that the electric transport on the MWNT has a diffusive character. The application of a (4.5V) bias between nanotube and substrate causes the resistance of the nanotube to drop by a factor of four. We can also resolve the voltage drop on the nanotube and at the contacts. The measurements in the second system (vertical arrangement) show that the nanotubes are uncapped and we can observe a contrast that varies with the application of different voltages to the back contact.

Carbon nanotube systems can substantially increase their capacity for Li ion uptake, provided that the nanotube interiors become accessible to the ions. We examine theoretically, with ab initio simulations, the ability of Li ions to enter a nanotube interior. While our calculations show that it is quite unlikely for the ions to pass through pristine nanotubes, they are much more likely to enter via large-sized topological defects consisting of at least 9- or more membered rings. It is unlikely that such defects are formed spontaneously, but it may be possible to induce such topological defects by violent non-equilibrium means such as ball milling, chemical means and/or ion bombardment. Indeed, recent experiments on ball milled nanotube samples do report an important increase in the Li ion uptake.

The growth behaviour of carbon nanotubes on the Fe-deposited Si (001) substrates by thermal chemical vapor deposition (CVD) has been investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The Fe films are deposited for 20 s–20 min by pulse-laser deposition. SEM results show that the growth characteristics of carbon nanotubes strongly depend on the Fe film deposition time. TEM and SEM results show that the pretreatment annealing at 800 °C causes the continuous Fe films to be broken up into nanoparticles 8–50 nm across and discontinuous islands 100 nm– 1.1 μm in size. It is shown that the Fe nanoparticles are essentially required for the formation of aligned carbon nanotubes. SEM results show that the growth behaviors of carbon nanotubes are strongly dependent on the pretreatment atmospheres. In addition, for the Ar gas-pretreated sample, a carbonaceous layer is formed near the surface region. TEM results show direct evidence that a base growth mode is responsible for the growth of carbon nanotubes in the present work. Based on the microscopy results, the pretreatment condition dependence of the growth behaviors of carbon nanotubes is discussed.

We studied the gas adsorption effects on the field emission properties of vertically aligned multiwalled carbon nanotube films by exposing them to polar (H2O) and non-polar (N2O) gas molecules. The charge transfer between adsorbates and carbon nanotubes plays an important role in the field emission properties. With bias voltage ~ 1.2V/μm, the field emission properties of the carbon nanotubes are improved by exposing the nitrous oxide while the bias effect with water exposure is less significant. The improvement of the field emission properties by gas exposure is attributed not only to the change in the work function of the carbon nanotubes caused by a charge transfer, but also to the reactivity of the adsorbate gas with localized-cap states.

Very recently, narrow nanotubes have been observed with a diameter of 5 Å and even with a diameter of 4 Å. It has been supposed that the narrow nanotubes are closed by fragments of C36 and C20 fullerenes. The contribution reports computations on related model nanotubes with stoichiometries like C84, C96 or C80. Computations are carried out at the PM3 (Parametric Method 3), SaM1 (Semi-Ab-Initio Model 1), HF/4-31G (Hartree-Fock SCF approach with the standard 4-31G basis set), and B3LYP/6-31G* (Becke's three parameter functional with the non-local Lee-Yang-Parr correlation functional using the standard 6-31G* basis set) levels, though the geometry optimizations are performed only at the semiempirical levels. Two C36 fullerenes are considered, D6h and D2d, and, for example, at the PM3 level and with the C84 nanotube stoichiometry the D2d cage closure gives a lower energy (by 185 kcal/mol and diameter of 5.42 Å). There is another possible candidate, C32 cage with a D4d symmetry. At the PM3 level and with the C96 nanotube stoichiometry the D4d closure has the nanotube enrgy lower by 210 kca/mol (with the nanotube diameter of 5.43 Å) compared to the D6h nanotube closure. On the other hand, four-membered rings should not play a significant role in the narrow nanotubes with the diameter of 4 Å, where the dodecahedron-related closure should be exclusive as a four-membered ring containing structure is located already much higher in energy.

The use of Raman spectroscopy as a characterization tool for individual single wall carbon nanotubes is briefly reviewed. New physical phenomena occurring at the single nanotube level are discussed, with special emphasis given to the use of resonance Raman scattering for the structural determination of (n, m) for individual nanotubes, based on diameter and chirality dependent phenomena associated with the radial breathing mode, the G-band and the G[prime]-band features. Examples are given to show how single nanotube spectroscopy provides insight into the use of Raman spectroscopy for the characterization of nanotube bundles and for the study of new physical phenomena occurring at the single nanotube level.

Reversible actuation strains in excess of 2% in the sheet direction and over 300% in the thickness direction have been produced by single wall carbon nanotube mats when electrochemically charged to +1.5V (vs. SCE) in aqueous sodium chloride solution. The observed strains represent a ten-fold increase over that previously reported for carbon nanotube actuators, and is considerably larger than that achievable with polymer ferroelectric actuators. The enhanced actuator strains result from a new mechanism of electrochemically induced “pnuematic actuation” where high pressure gas forms within the porous structure of the nanotube mat causing partial delamination and swelling. An erasable “memory” effect was also observed for pneumatic actuation driven by hydrogen gas evolution/storage in the nanotube electrodes.