We develop a new chemical route to prepare carbon nanotubes at room temperature. Graphite powder is immersed in a mixed solution of nitric and sulfuric acid with potassium chlorate. After heating the solution up to 70°C and leaving them in the air for 3 days, we obtained carbon nanotube bundles. This process could provide an easy and inexpensive method for the preparation of carbon nanotubes.
We show that the presence of electrically insulating graphite oxide (GO) within a single wall carbon nanotube network strongly enhances electrical conductivity, whereas reduced graphite oxide, even though electrically conductive, suppresses electrical conductivity within a composite network with single wall carbon nanotubes. Measurements of Young modulus and of Raman spectra strongly support our interpretation of the indirect role of the oxide groups, present in graphite oxide within the single wall carbon nanotubes/graphite oxide composite, through electronic doping of metallic single wall ca…
We report on the temperature dependence of the anharmonic decay rate of zone-center (G mode) optical phonons in both single-walled carbon nanotubes and graphite. The measurements are performed using a pump-probe Raman scattering scheme with femtosecond laser pulses. For nanotubes, measured over a temperature range of 6 K-700 K, we observe little temperature dependence of the decay rate below room temperature. Above 300 K, the decay rate increases from 0.8 to 1.7 ps-1. The decay rates observed for graphite range from 0.5 to 0.8 ps-1 for temperatures from 300 K-700 K. We compare the behavior obs…
We present an analysis of deep-UV Raman measurements of graphite, graphene and carbon nanotubes. For excitation energies above the strong optical absorption peak at the $M$ point in the Brillouin zone ($\approx 4.7\,\text{eV}$), we partially suppress double-resonant scattering processes and observe the two-phonon density of states of carbon nanomaterials. The measured peaks are assigned to contributions from LO, TO, and LA phonon branches, supported by calculations of the phonon dispersion. Moreover, we gain access to the infrared-active $E_{1u}$ mode in graphite. By lowering the excitation en…
We report a general scheme to systematically construct two classes of structural families of superhard sp3 carbon allotropes of cold compressed graphite through the topological analysis of odd 5+7 or even 4+8 membered carbon rings stemmed from the stacking of zigzag and armchair chains. Our results show that the previously proposed M, bct-C4, W and Z allotropes belong to our currently proposed families and that depending on the topological arrangement of the native carbon rings numerous other members are found that can help us understand the structural phase transformation of cold-compressed g…
We present a study on the kinetics of oxygen adsorption and desorption from single-wall carbon nanotube (SWNT) and highly oriented pyrolytic graphite (HOPG) samples. Thermal desorption spectra for SWNT samples show a broad desorption feature peaked at 62 K which is shifted to significantly higher temperature than the low-coverage desorption feature on HOPG. The low-coverage O2 binding energy on SWNT bundles, 18.5 kJ/mol, is 55% higher than that for adsorption on HOPG, 12.0 kJ/mol. In combination with molecular mechanics calculations we show that the observed binding energies for both systems c…
The structure of bundles of single-walled carbon nanotubes (SWNT) has been refined by Rietveld analysis using neutron and X-ray powder diffraction data. Based on previous simulation studies of powder diffraction data of SWNT and standard Rietveld analyses, we have developed a pattern fit technique for SWNT which provides precise structure parameters. We also show that the present technique can be used with the maximum entropy method (MEM), which is complementary to the Rietveld analysis. Using the neutron diffraction data of pristine SWNT, we have successfully reconstructed the density of carb…
Trying to dope graphite flakes we found that the magnetization of pure, several tens of micrometers grain size graphite powder and after a simple treatment with pure water shows clear and reproducible granular superconducting behavior with a critical temperature above 300K. The observed magnetic characteristics as a function of temperature, magnetic field and time, provide evidence for weakly coupled grains through Josephson interaction, revealing the existence of superconducting vortices.
A carbon nanotube (CNT) tip was fabricated at the apex of an etched tungsten wire by chemical vapor deposition and used for scanning tunneling microscopy. The honeycomb lattice of graphite in the STM images was resolved with a CNT tip at T=79 K. The superior spatial resolution originating from the p orbitals of a CNT is responsible for the image of the honeycomb lattice of graphite in the STM images. The CNT tips are useful to image samples whose lattice constants are small and to get orbital information in samples with orbital ordering due to their superior spatial resolution with the sharp p…
Experiments with multiwalled carbon nanotubes and graphite as targets in a source of negative ions with cesium sputtering have shown that nanotubes with nanometer radii and micrometer length can be compared with micrometer size graphite grains to understand the irradiation effects that include the formation, sputtering of carbon clusters and the resulting structural changes. The simultaneous adsorption of cesium on the surface and bombardment by energetic cesium ions is shown to play its role in the cluster formation and sputtering of carbon atoms and clusters and the cesium substituted carbon…
We have studied the changes in the ferromagnetic behavior of graphite powder and graphite flakes after treatment with diluted sulphuric acid. We show that this kind of acid treatment enhances substantially the ferromagnetic magnetization of virgin graphite micrometer size powder as well as in graphite flakes. The anisotropic magnetoresistance (AMR) amplitude at 300 K measured in a micrometer size thin graphite flake after acid treatment reaches values comparable to polycrystalline cobalt.
Fundamentally new families of carbon single walled nanotubes are proposed. These nanotubes, called graphynes, result from the elongation of covalent interconnections of graphite-based nanotubes by the introduction of yne groups. Similarly to ordinary nanotubes, arm-chair, zig-zag, and chiral graphyne nanotubes are possible. Electronic properties, predicted using tight-binding and ab initio density functional methods, show a rich variety of metallic and semiconducting behaviors.
The sheet samples of thermally exfoliated graphite (TEG) carbon nanotubes (CNT) composites (TEG CNT cs) were obtained by persulphate oxidation using chemical (CO) and electrochemical (anode) oxidation (ECAO). Electron microscopy reveals multi layered structures of few layer graphene nanosheets with folded and tubular like fragments.Electron microscopy reveals multilayered structures of few layer graphene nanosheets with folded and tubular like fragments. The effective thermal diffusivity values were estimated by nonstationary photo-pyroelectric thermophysical characterization using the heat pu…
The atomistic simulations of carbon nanotube (CNT) - carbon reinforced composite material are reported. The studied composite samples were obtained by impregnating certain amounts of CNTs (3,3) and (6,6) into pristine graphite matrix. The addition of CNTs is found to be of significant usefulness for nanotube-reinforced carbon composites since it allows to achieve extreme lightness and strength. Being impregnated into graphite matrix, nanotubes are able to increase the critical component of its highly anisotropic Young modulus by 2-8 times. The linear thermal expansion coefficients do not excee…
We show, using ab initio total energy density functional theory, that the so-called Wigner defects, an interstitial carbon atom right besides a vacancy, which are present in irradiated graphite can also exist in bundles of carbon nanotubes. Due to the geometrical structure of a nanotube, however, this defect has a rather low formation energy, lower than the vacancy itself, suggesting that it may be one of the most important defects that are created after electron or ion irradiation. Moreover, they form a strong link between the nanotubes in bundles, increasing their shear modulus by a sizeable…
Energetically the single sheet of graphite (graphene) is more stable than the nanotube. The energy difference between the two systems can be directly related to the strain energy involved in rolling up the graphene sheet to form the nanotube. We have carried out first principle electronic structure calculations and evaluated the strain energy as a function of the nanotube radius. The dependence of the strain energy on the diameter of the nanotube has been found by several groups to be welldescribed by a continuum elasticity model. We attempt to examine why this is the case and show where atomi…
By using a newly fitted multi-parameter potential to describe the van der Waals interaction between carbon and molecular hydrogen, we study the hydrogen storage inside carbon nanotubes (CNT's) under pressure in gigapascal range. Comparing with the results of graphite, we find that the shape change of the nanotubes (the curvature effect) provides a different storage mechanism for hydrogen. The negative free energy change for hydrogen storage inside CNT's makes it possible to use CNT's as the nanocontainer [Carbon 45, 315 (2007)].
Titanic acid nanotubes (with a chemical formula H2Ti2O4(OH)2, abbreviated as TANTs) were synthesized by the hydrothermal method using commercial TiO2 nanoparticle powder (P25, Degussa, Germany) including anatase and rutile phase as a starting material. Conversion from nanoparticles to nanotubes was achieved by treating the nanoparticle powder with 10 M NaOH aqueous solution. Absorption and photoluminescence (PL) data indicate that the nanotubes obtained under slow and suitable drying and heating conditions had very strong and stable visible absorption with three peaks at 515, 575, and 675 nm a…
We studied optical absorption of single-walled carbon nanotubes by varying the dielectric environment. For the two different components of the broad UV absorption feature conventionally referred to as the pi-plasmon, we find that the component at 5.0 - 5.3 eV exhibits remarkable spectral changes, based on which we attribute this to a dipolar radial surface plasmon. However, the component at ~4.5 eV remains unchanged, raising a fundamental question as to its conventional attribution. We discuss its relation with the absorption feature at ~4.5 eV in graphite arising from an interband transition.
The physics of adhesion of one-dimensional nano structures such as nanotubes, nano wires, and biopolymers on different material substrates is of great interest for the study of biological adhesion and the development of nano electronics and nano mechanics. In this paper, we present force spectroscopy experiments of a single wall carbon nanotube loop using our home-made interferometric atomic force microscope. Characteristic force plateaux during the peeling process allows us to access to quantitative values of the adhesion energy per unit length on various substrates: graphite, mica, platinum,…
The Lifshitz theory of the van der Waals force is extended for the case of an atom (molecule) interacting with a plane surface of an uniaxial crystal or with a long solid cylinder or cylindrical shell made of isotropic material or uniaxial crystal. For a microparticle near a semispace or flat plate made of an uniaxial crystal the exact expressions for the free energy of the van der Waals and Casimir-Polder interaction are presented. An approximate expression for the free energy of microparticle- cylinder interaction is obtained which becomes precise for microparticle-cylinder separations much …
We formulate the problem of adsorption onto the surface of a carbon nanotube as a lattice gas on a triangular lattice wrapped around a cylinder. This model is equivalent to an XXZ Heisenberg quantum spin tube. The geometric frustration due to wrapping leads generically to four magnetization plateaus, in contrast to the two on a flat graphite sheet. We obtain analytical and numerical results for the magnetizations and transition fields for armchair, zig-zag and chiral nanotubes. The zig-zags are exceptional in that one of the plateaus has extensive zero temperature entropy in the classical limi…
The double-resonance (DR) Raman process is a signature of all sp2 carbon material and provide fundamental information of the electronic structure and phonon dispersion in graphene, carbon nanotubes and different graphite-type materials. We have performed in this work the study of different DR Raman bands of rhombohedral graphite using five different excitation laser energies and obtained the dispersion of the different DR features by changing the laser energy. Results are compared with those of Bernal graphite and shows that rhombohedral graphite exhibit a richer DR Raman spectrum. For example…
Because of their unique structure, it has been proposed that carbon nanotube ropes may well provide an ideal container for the storage of molecular hydrogen. Indeed, there has been some experimental evidence of enhanced hydrogen uptake in doped Li and other alkali metal systems [Chen et al, Science 285, 91 (1999)]. We have therefore addressed this issue of hydrogen storage in Li-doped graphite and carbon nanotube systems theoretically with ab initio simulations. Our results find no evidence for such enhanced storage, based on the induced structural changes. In addition, we have also investigat…
The present communication highlights that ac conductivity measurement of the multi-walled carbon nanotubes (MWNTs)-polymer composites is a very promising characterizing tool for qualifying any crude MWNT-sample synthesized by electric arc. It distinguishes graphite structures from that of the MWNTs and reflects the relative amount of nearly one-dimensional structures and disorders present within the samples. This new protocol would help in evolving more direct and quantitative criteria for qualification of MWNTs synthesized through diverse techniques and will definitely add up to the conceptua…
The linear coefficient of the radial thermal expansion has been measured on a system of SWNT bundles in an interval of 2.2 - 120K. The measurement was performed using a dilatometer with a sensitivity of 2*10-9 cm. The cylindrical sample 7 mm high and 10 mm in diameter was obtained by compressing powder. The resulting bundles of the nanotubes were oriented perpendicular to the sample axis. The starting powder contained over 90% of SWNTs with the outer diameter 1.1 nm, the length varying within 5-30 um.
Temperature dependent conformations of linear polymer molecules adsorbed at carbon nanotube (CNT) interfaces are investigated through molecule dynamics simulations. Model polyethylene (PE) molecules are shown to have selective conformations on CNT surface, controlled by atomic structures of CNT lattice and geometric coiling energy. PE molecules form entropy driven assembly domains, and their preferred wrapping angles around large radius CNT (40, 40) reflect the molecule configurations with energy minimums on a graphite plane. While PE molecules prefer wrapping on small radius armchair CNT (5, …
We demonstrate that a single zone furnace with a modified synthesis chamber design is sufficient to obtain metal (Fe, Co or Ni) filled carbon nanotubes (CNT) with high filling efficiency and controlled morphology. Samples are formed by pyrolysis of metallocenes, a synthesis technique that otherwise requires a dual zone furnace. Respective metallocene in all three cases are sublimed in powder form, a crucial factor for obtaining high filling efficiency. While Fe@CNT is routinely produced using this technique, well-formed Ni@CNT or Co@CNT samples are reported for the first time. This is achieved…
Optical-absorption cross-sections and energy-loss spectra of aligned multishell carbon nanotubes are investigated, on the basis of photonic band-structure calculations. A local graphite-like dielectric tensor is assigned to every point of the tubules, and the effective transverse dielectric function of the composite is computed by solving Maxwell's equations in media with tensor-like dielectric functions. A Maxwell-Garnett-like approach appropriate to the case of infinitely long anisotropic tubules is also developed. Our full calculations indicate that the experimentally measured macroscopic d…
We report calculations of the effective electronic response of aligned multishell carbon nanotubes. A local graphite-like dielectric tensor is assigned to every point of the multishell tubules, and the effective transverse dielectric function of the composite is computed by solving Maxwell's equations. Calculations of both real and imaginary parts of the effective dielectric function are presented, for various values of the filling fraction and the ratio of the internal and external radii of hollow tubules. Our full calculations indicate that the experimentally measured macroscopic dielectric …
Graphite, with many industrial applications, is one of the widely sought-after allotropes of carbon. The sp2 hybridized and thermodynamically stable form of carbon forms a layered structure with strong in-plane carbon bonds and weak inter-layer van der Waals bonding. Graphite is also a high-temperature ceramic, and shaping them into complex geometries is challenging, given its limited sintering behavior even at high temperatures. Although the geometric design of the graphite structure in many of the applications could dictate its precision performance, conventional synthesis methods for formul…
A study based on ab initio calculations is presented on the estructural, elastic, and vibrational properties of single-wall carbon nanotubes with different radii and chiralities. We use SIESTA, an implementation of pseudopotential-density-functional theory which allows calculations on systems with a large number of atoms per cell. Different quantities like bond distances, Young moduli, Poisson ratio and the frequencies of different phonon branches are monitored versus tube radius. The validity of expectations based on graphite is explored down to small radii, where some deviations appear relat…
A model for the formation of carbon nanotubes (CNTs) and layered graphene in an arc discharge method is developed on the basis of observed erosion of graphite anode under various experimental conditions and analyses of the morphology of the eroded anode-surface, concerned cathode deposits and their constituents. It is predicted that, cold thermal shock, triggered by the rapid movement of the anode-spot, leads to crack microbranching at some selected locations on the anode-surface. These crack-microbranches cleave and fragment the basal planes of pairs of adjacent crystallites into curved graph…
The phase diagrams of $^4$He adsorbed on the external surfaces of single armchair carbon nanotubes with radii in the range 3.42 -- 10.85 Å\ are calculated using the diffusion Monte Carlo method. For nanotubes narrower than a (10,10) one, the ground state is an incommensurate solid similar to the one found for H$_2$ on the same substrates. For wider nanotubes, the phase with the minimum energy per particle is a liquid layer. Curved $\sqrt 3 \times \sqrt 3$ registered solids similar to the ones found on graphene and graphite were unstable for all the tubes considered.
Combining equilibrium and non-equilibrium molecular dynamics simulations with accurate carbon potentials, we determine the thermal conductivity $λ$ of carbon nanotubes and its dependence on temperature. Our results suggest an unusually high value $λ{\approx}6,600$~W/m$\cdot$K for an isolated (10,10) nanotube at room temperature, comparable to the thermal conductivity of a hypothetical isolated graphene monolayer or diamond. Our results suggest that these high values of $λ$ are associated with the large phonon mean free paths in these systems; substantially lower values are predicted and observ…
We have examined the commonly used Tersoff and Brenner empirical interatomic potentials in the context of the phonon dispersions in graphene. We have found a parameter set for each empirical potential that provides improved fits to some structural data and to the in-plane phonon dispersion data for graphite. These optimized parameter sets yield values of the acoustic phonon velocities that are in better agreement with measured data. They also provide lattice thermal conductivity values in single-walled carbon nanotubes that are considerably improved compared to those obtained from the original…
It has been known theoretically that localized states exist around zigzag edges of a graphite ribbon and of a carbon nanotube, whose energy eigenvalues are located between conduction and valence bands. We found that in metallic single-walled zigzag carbon nanotubes two of the localized states become critical, and that their localization length is sensitive to the mean curvature of a tube and can be controlled by the Aharonov-Bohm flux. The curvature induced mini-gap closes by the relatively weak magnetic field. Conductance measurement in the presence of the Aharonov-Bohm flux can give informat…
In the present work, different synthesis procedures have been demonstrated to fill carbon nanotubes (CNTs) with $\mathrm{Fe}_{1-x}\mathrm{Ni}_x$ alloy nanoparticles (x = 0.33, 0.5). CNTs act as templates for the encapsulation of magnetic nanoparticles, and provide a protective shield against oxidation as well as prevent nanoparticles agglomeration. By variation of the reaction parameters, the purity of the samples, degree of filling, the composition and size of filling nanoparticles have been tailored and therefore the magnetic properties. The samples were analyzed by scanning electron microsc…
The Lifshitz-type formulas describing the free energy and the force of the van der Waals interaction between an atom (molecule) and a single-wall carbon nanotube are obtained. The single-wall nanotube is considered as a cylindrical sheet carrying a two-dimensional free electron gas with appropriate boundary conditions on the electromagnetic field. The obtained formulas are used to calculate the van der Waals free energy and force between a hydrogen atom (molecule) and single-wall carbon nanotubes of different radia. Comparison studies of the van der Waals interaction of hydrogen atoms with sin…
We have observed the S- and Q-branch Raman spectra of H2, HD, and D2 adsorbed at 85K and pressures up to 8 atm on single-walled, carbon nanotubes (SWNT). Comparative data for H2 on graphite and C60 were also collected. For each adsorbate, we observed a small shift in the Q-branch frequencies relative to the gas-phase values. To aid in interpreting this result, we constructed an H2-surface potential, including van der Waals and electrostatic terms. Computed shifts based on this potential are in good agreement with our data.
The electronic spectra of carbon nanotubes and other nanoscale systems are quantized because of their small radii. Similar quantization in the phonon spectra has been difficult to observe because of the far smaller energy scale. We probed this regime by measuring the temperature-dependent specific heat of purified single-wall nanotubes. Thee data show direct evidence of one-dimensional quanitized phonon subbands. Above 4 K, they are in excellent agreement with model calculations of individual nanotubes and differ markedly from the specific heat of two-dimensional graphene or three-dimensional …
The radial thermal expansion coefficient (a)r of pure and Xe-saturated bundles of single-walled carbon nanotubes has been measured in the interval 2.2-120 K. The coefficient is positive above T = 5.5 K and negative at lower temperatures. The experiment was made using a low temperature capacitance dilatometer with a sensitivity of 2x10-9 cm and the sample was prepared by compacting a CNT powder such that the pressure applied oriented the nanotube axes perpendicular to the axis of the cylindrical sample. The data show that individual nanotubes have a negative thermal expansion while the solid co…
The effect of oxygen impurities upon the radial thermal expansion (ar) of bundles of closed single-walled carbon nanotubes has been investigated in the temperature interval 2.2-48 K by the dilatometric method. Saturation of bundles of nanotubes with oxygen caused an increase in the positive ar-values in the whole interval of temperatures used. Also, several peaks appeared in the temperature dependence ar(T) above 20 K. The low temperature desorption of oxygen from powders consisting of bundles of single-walled nanotubes with open and closed ends has been investigated
Carbon foams are hypothetical carbon allotropes that contain graphite-like (sp$^2$ carbon) segments, connected by sp$^3$ carbon atoms, resulting in porous structures. In this work the DFTB (Density Functional based Tight-Binding) method with periodic boundary conditions (PBC) was employed to study energetics, the stability and electronic properties of this unusual class of carbon systems. Concerning the most stable phases of carbon (graphite and diamond), foams show high structural stability at very low mass density. The electronic band structure and electronic DOS (density of states) of foams…
Partially Fe filled multi-walled carbon nanotubes (MWCNTs) were grown by chemical vapor deposition with propane at 850 °C using a simple mixture of iron (III) acetylacetonate (Fe(acac)3) powder and conventional photoresist. Scanning electron microscopy revealed that catalytic nanoparticles with an average diameter of 70 nm are formed on the Si substrate which governs the diameter of the MWCNTs. Transmission electron microscopy shows that the nanotubes have a multi-walled structure with partial Fe filling. A site-selective growth of partially Fe filled MWCNTs is achieved by a simple photolithog…
Substantial progress on field effect transistors "FETs" consisting of semiconducting single wall carbon nanotubes "s-SWNTs" without detectable traces of metallic nanotubes and impurities is reported. Nearly perfect removal of metallic nanotubes is confirmed by optical absorption, Raman measurements, and electrical measurements. This outstanding result was made possible in particular by ultracentrifugation (150 000 g) of solutions prepared from SWNT powders using polyfluorene as an extracting agent in toluene. Such s-SWNTs processable solutions were applied to realize FET, embodying randomly or…
This work presents a model that successfully describes the tensile properties of macroscopic fibres of carbon nanotubes (CNTs). The core idea is to treat such a fibre as a network of CNT bundles, similar to the structure of high-performance polymer fibres, with tensile properties defined by the CNT bundle orientation distribution function (ODF), shear modulus and shear strength. Synchrotron small-angle X-ray scattering measurements on individual fibres are used to determine the initial ODF and its evolution during in-situ tensile testing. This enables prediction of tensile modulus, strength an…
The effect of a N2 impurity on the radial thermal expansion coefficient (ar) of single-walled carbon nanotube bundles has been investigated in the temperature interval 2.2 - 43 K by the dilatometric method. Saturation of nanotube bundles with N2 caused a sharp increase in the positive magnitudes of ar in the whole range of temperatures used and a very high and wide maximum in the thermal expansion coefficient (ar)(T) at T about 28 K. The low temperature desorption of the impurity from the N2-saturated powder of bundles of single-walled carbon nanotubes with open and closed ends has been invest…
A continuous model of double-walled carbon nanotube (DWCNT) low-frequency dynamics was constructed. In the frame of the approach proposed formation of a DWCNT low-frequency phonon spectrum from the ones of corresponding single-walled carbon nanotubes (SWCNTs) was considered. Environmental influence on the individual DWCNT phonon spectrum was studied. A combined method of van der Waals interlayer coupling coefficients evaluation was proposed, and it is based on Raman spectroscopy data and known values of graphite elastic moduli. Also DWCNT low-temperature specific heat was calculated. In the mo…
We investigate structural parameters, i.e., bond lengths and bond angles of isolated uncapped zigzag single-wall nanotubes in detail. The bond lengths and bond angles are determined for several radii tubes by using a theoretical procedure based on the helical and rotational symmetry for atom coordinates generation, coupled with Tersoff potential for interaction energy calculations. Results show that the structure of zigzag tubes is governed by two bond lengths. One bond length is found to have a value equal to that of graphite, while the other one is larger. Furthermore, the tube length is fou…
A simple and convenient procedure for single-shot, single-spot ablation threshold measurement has been developed. It is based on the employment of cylindrical lens to obtain elliptical Gaussian laser spot. The ablated spot chords which are parallel to the minor axis were measured across the spot major axis which is proportional to the fluence cross-section thus providing wide range dependence of damaged spot size versus fluence in one spot measurement. For both conventional and new-developed procedures the ablation threshold for typical Nd:YAG laser parameters (1064 nm, 10 ns) has been measure…
Predicting the Realizable Maximum Power Factor using the Jonker and Ioffe formulation: Al-doped ZnO Triangular Microcrystals with Graphite Inclusion Case Study
We present a theoretical model to describe the double-resonant scattering process in arbitrary carbon nanotubes. We use this approach to investigate the defect-induced $D$ mode in CNTs and unravel the dependence of the $D$-mode frequency on the CNT diameter and on the energy of the resonant optical transition. Our approach is based on the symmetry of the hexagonal lattice and geometric considerations, hence the method is independent of the exact model that is chosen to describe the electronic band structure or the phonon dispersion. We finally clarify the diameter dependence of this Raman mode…
The response of fullerenes and carbon nanotubes is investigated by representing each carbon atom by its atomic polarizability. The polarization of each carbon atom produces an induced dipole that is the result of the interaction with a given external field plus the mutual interaction among carbon atoms. The polarizability is obtained from the dielectric function of graphite after invoking the Clausius-Mossotti relation. This formalism is applied to the simulation of electron energy loss spectra both in fullerenes and in carbon nanotubes. The case of broad electron beams is considered and the l…
Brittle fracture is one of the important failure modes of Single-Walled Carbon Nanotube (SWNT) due to mechanical loading. In this paper, the fracture resistance of zigzag SWNTs with preexisting defects is calculated using fracture mechanics concepts based on atomistic simulations. The problem of unstable crack growth at finite temperature, presumably caused by lattice trapping effect, is circumvented by computing the strain energy release rate through a series of displacement-controlled tensile loading of SWNTs (applied through moving the outermost layer of atoms at one end at constant strain …
The electrical resistance of detonation nano-diamond powders was measured from liquid nitrogen temperature to room temperature and in relative humidity environments from around 10% to 100%. After sample exposures of several hours at 100% relative humidity at room temperature (around 295 K), when the temperature was reduced, the resistance increased to the upper measurement limit of our apparatus (120 MΩ) at around 240 K. Upon warming, the resistance dropped back to the room temperature value, with some hysteresis. For sample exposures after several hours at 100% relative humidity at room tempe…
The effect of a normal H2 impurity upon the radial thermal expansion (Ar) of SWNT bundles has been investigated in the interval T = 2.2-27 K using the dilatometric method. It is found that H2 saturation of SWNT bundles causes a shift of the temperature interval of the negative thermal expansion towards lower (as compared to pure CNTs) temperatures and a sharp increase in the magnitude of (Ar) in the whole range of temperatures investigated. The low temperature desorption of H2 from a powder consisting of bundles of SWNTs, open and closed at the ends, has been investigated.
In this paper, we proposed a lattice dynamic treatment for the total potential energy for single-walled carbon nanotubes (SWCNT's) which is, apart from a parameter for the non-linear effects, extracted from the vibrational energy of the planar graphene sheet. Based upon the proposal, we investigated systematically the relaxed lattice configuration for narrow SWCNT's, the strain energy, the Young's modulus and Poisson ratio, and the lattice vibrational properties respected to the relaxed equilibrium tubule structure. Our calculated results for various physical quantities are nicely in consisten…
