Carbon Nanotubes

The laser ablation synthesis of carbon nanotubes is contrasted with the arc discharge method with respect to the synthesis product. A novel combination of two laser systems of different wavelengths for the laser ablation synthesis is presented. The impact of sulfur on the synthesis process is discussed. An excerpt of our quality control protocol is presented.

This paper briefly reviews scanning tunneling microscopy with emphasis on the particularities that have the most significant influence on the STM and STS characterization of both single-wall and multi-wall carbon nanotubes. The experimental results obtained on these carbon nanotubes are surveyed together with computer modeling of the STM images of carbon nanotubes and the role of structural defects is discussed.

The determination of the exact values of (n,m) or equivalently (d, ϑ)for an individual singlewall nanotube (SWNT) is of great importance, in particular for comparison with transport measurements. In this study, the selected area electron diffraction technique is used to investigate the structure of individual carbon nanotubes grown by chemical vapor deposition (CVD) directly on TEM-Si₃N₄ membranes.

Characterization of Vacuum Thermal Annealing of a new variety of Multiwalled Carbon Nanotubes (MWCNT) produced in a Catalytic Chemical Vapor Deposition (CCVD) process by Arkema, France, was preformed by Raman Spectroscopy (RS) and Transmission Electron Microscopy (TEM).

We study by Transmission Electron Microscopy (TEM) in-situ selfassembled carbon nanotubes (CNTs) grown by the Hot Filament Chemical Vapor Deposition (HFCVD) process on silicon substrates used for electronic devices. We present the different methods we have developed for extracting CNTs and studying their interface with the substrate as they are observable by TEM.

Carbon nanotubes (CNTs) can be synthesized from amorphous carbon thin films by electron irradiation in the transmission electron microscope (TEM). We propose that irradiation effects impart a tensile stress and introduce defects to a CNT thus formed and show that the CNTs can be made to fracture by a brittle or ductile mechanism. We also report a healing of the carbon film that is observed after some critical amount of irradiation.

We have studied the scanning tunneling microscopy tip interaction with the naturally formed nanotube-like (NTL) structures on highly oriented pyrolytic graphite (HOPG) surface. Shape variations of the NT-like structures, caused by the modulation of scanning parameters, were observed and analyzed.

The injection chemical vapor deposition (CVD) method allows the semi-continuous production of pure multi-wall carbon nanotubes (MWCNTs). In order to find the most efficient catalyst material and carbon source, we investigated the quality and quantity of carbon nanotubes, when different metallocenes (ferrocene, cobaltocene and nickelocene) and hydrocarbons (benzene, toluene, xylene, cyclohexane, cyclohexanone, n-hexane, n-heptane, n-octane and n-pentane) are injected into the reaction furnace. The obtained samples were analyzed by Transmission Electron Microscopy (TEM). The highest yield and the best quality were obtained when a mixture of ferrocenenickelocene was used as catalyst and xylene as carbon source. The weight of purified carbon nanotubes was higher than 50% of the weight of catalyst material for xylene and reached the 10% for all investigated carbon sources.

We report on the growth of carbon nanotubes by plasma-enhanced chemical vapor deposition (PECVD). We used acetylene and ammonia gas mixtures with a process pressure of 1 Torr for the growth of carbon nanotubes on nickel layers. The metal catalyst, just a few nanometers thick, was patterned on oxidized silicon substrates by electron beam lithography. Our aim was to develop a cheap mass production method to grow high quality, aligned carbon nanotubes. We used different plasma setups and scanned individual growth parameters in order to achieve that goal. In this work, we compare the different results obtained by direct current (DC) plasma deposition.

A novel material made of carbon fabrics with a uniform threedimensional (3D) distribution of carbon nanotubes (CNTs) on the surface was synthesized by an electrochemical deposition (ELD) process.

Carbon nanotubes (CNTs) were grown using three different chemical vapor deposition (CVD) processes. Optimized conditions were studied.

Our investigation aimed at the development of a process capable of producing well ordered, vertically aligned carbon nanotubes (CNTs) arrays, with reproducible properties, for applications such as a position particle detector and a cold cathode emitter for storage devices. The results on catalyst nanoparticles formation from a thin Ni film evaporated on SiO₂ and Si3N₄ substrates are presented. The substrate-catalyst layers have been processed in several gaseous atmospheres and in the temperature range 700-900°C in order to obtain the most appropriate morphology, size and density of the nanoparticles for the subsequent CNTs growth. The smallest nanoparticles have been obtained on the SiO₂ substrate in H₂ atmosphere and at the lowest temperature 700°C. However, the best vertically aligned and well graphitized CNTs resulted from the NH3 annealing process followed by the deposition of CNTs at 900°C in C₂H₂ and NH₃.

Aligned carbon nanotubes (CNTs) were grown in the channels of porous alumina membranes via a non-catalytic chemical vapor deposition (CVD) method. The morphology of the samples was studied.

The purpose of the accomplished work was to use the advantages (ordered porous structure and high surface area) of mesoporous MCM-41 silicas in the pyrolytic synthesis of carbon nanostructures. MCM-41 matrices were used for chemisorption of volatile nickel, cobalt, and iron acetylacetonates with following metal reduction. The synthesis of carbon nanotubes was carried out by two routes: (a)MCM-41 treatment with Ni(acac)₂ or Co(acac)₂ vapor at 150°C, metal reduction with H₂ at 450°C, C₂H₂ pyrolysis over the catalyst at 700°C; (b)MCM-41 modification with Co(acac)₂ or Fe(acac)₂, reduction of supported metal complexes with C₂H₂, and pyrolysis at 700°C (in situ reduction). The TEM data showed that carbon nanotubes were formed with external diameter 10-35 nm for Ni-, 42-84 nm for Co-, and 14-24 nm for Fecontaining matrices. In the absence of metals, low yield of nanotubes (up to 2%) was detected.

We used the Grand-Canonical Monte-Carlo technique (GCMC) to simulate the vapor deposition of carbon in the porosity of various zeolitic nanopores (Silicalite, AlPO4-5, faujasite). The carbon-carbon interactions were described within a Tight-Binding formalism (TB) and the carbon-matrix interactions were assumed to be physisorption. Depending on the pore size and topology, various carbon structures can be obtained.

The symmetry-adapted approach to the study of the vibrational and related properties of carbon nanotubes is presented. The usually very large number of carbon pairs in the unit cell of the nanotubes, that hinders most of the microscopic studies, is conveniently handled in this approach by using the screw symmetry of the nanotubes and a two-atom unit cell. This allows the systematic simulation of various properties (vibrational, mechanical, thermal, electronic, optical, dielectric, etc.) of all nanotubes of practical interest: The application of symmetry-adapted models to the study of some of these properties is illustrated in this review in two cases: a force-constant approach and a tight-binding approach.

The present state of Raman scattering from carbon nanotubes is reviewed. In the first part of the presentation, the basic concepts of Raman scattering are elucidated with particular emphasis on the resonance scattering. The classical and the quantum-mechanical descriptions are presented and the basic experimental instrumentation and procedures are described. Special Raman techniques are discussed. Eventually, a short review on the electronic structure of single-wall carbon nanotubes (SWCNTs) is given. The second part of the presentation deals with Raman scattering from SWCNTs. The group theoretical analysis and the origin of the basic Raman lines are described. For the radial breathing mode, the observed quantum oscillations and the unusual strong Raman cross section are discussed. For the G-line, the resonance behavior and the response to doping are demonstrated and the calculated dependence of the line frequency on the tube diameter is summarized. For the D-line and for the G’-line, the dispersion is demonstrated and its origin from a triple resonance mechanism is described. Finally, the response from pristine and doped peapods is elucidated. In the third part, most recent results are reported from Raman spectroscopy of double-wall carbon nanotubes (DWCNTs). The unusual narrow lines with widths down to 0.4 cm-1 indicate clean room conditions for the growth process of the inner tubes. The (n,m) assignment of these lines and the high curvature effects are discussed. Results for DWCNTs, where the inner tubes are highly 13C-substituted, are reported with respect to Raman and NMR spectroscopy. Eventually, it is demonstrated that the RBM Raman lines of the inner tubes cluster into groups of up to 14 lines where each member of the cluster represents a pair of inner-outer tubes.

Raman spectra of two isolated single-walled carbon nanotubes with close diameters but different chiral angles are presented and discussed.

This chapter briefly reviews the electronic properties of single-wall carbon nanotubes as described by the π-electron tight-binding approximation. The Landauer formalism is introduced next and applied to the study of quantum transport in carbon nanotubes. The electronic properties and electric conductance of intramolecular nanotube junctions are also discussed.

This chapter deals with the electronic transport in carbon nanotubes under the influence of a static disorder. The approach used is the Kubo formalism that is based on fluctuation-dissipation theory developed in real space.

Scanning tunneling microscopy (STM) is capable of providing information on both the geometrical and electronic structure of a carbon nanostructure. Utilizing a pseudopotential model of a nanotube we investigated the three-dimensional wave packet (3D WP) tunneling process through an STM tip – nanotube – support model for different atomic arrangements representing metallic and semiconducting nanotubes.

Ultrathin, transparent, and pure nanotube films have great importance in the optical studies. The samples are free-standing, which eliminates the difficulties caused by the various substrates in wide-range optical measurements. We prepared uniform homogenous thin films from hole-doped and functionalizated single-wall carbon nanotubes (SWNTs) with a simple process. We examined the spectra from the infrared to the ultraviolet range on the same sample. The vibrational transitions of the sidewall groups indicated the chemical composition. The changes in the electronic properties were followed simultaneously by Near-infrared/Visible/Ultraviolet (NIR/VIS/UV) spectroscopies.

We study excited state dynamics of semiconducting single-walled carbon nanotubes (SWNTs) by two-color pump-probe experiments. We find a time constant of 40 fs for the intersubband energy relaxation from EX2 to EX1.

modeling of the linear optical polarizability of singlewalled carbon nanotubes (SWCNTs) of the zigzag type (n,0) with different diameter capped at one end by half of fullerene and tapered at the other end so that it can be connected with different (n,n) armchair nanotubes is carried out. The calculations were carried out within the Su-Schrieffer-Heeger model. It is shown that the localized states demonstrate the nonlinear aspects of excited states in that system. It is found that the molecules with different radius have strong oscillating dependence of the optical polarizability on the incident light energy. The effect of the length, capping of the tube end, and the Coulomb repulsion on the optical polarizability spectrum is studied.

Nonlinear optical properties in single-wall carbon nanotubes (CNTs) illuminated by an external electromagnetic field were investigated using quantum kinetic equations for the density matrix of the π-electrons. In the regime of weak driving field, these equations were solved by the perturbation method and the spectra of the third-order polarizability were calculated. In the case of high-intensive driving field, numerical simulation of the processes in the time-domain was carried out. The π-plasmons excitation was analyzed.

We use the two-fluid, two-dimensional hydrodynamic model, proposed in (Mowbray et al., 2004), to describe the collective response of a carbon nanotube’s σ and π electrons to fast ions moving parallel to the nanotube. In the present contribution, two extensions of this model are being made: (1) to the case of multi-walled carbon nanotubes, where the inter-wall electrostatic interaction gives rise to rich plasma spectra, and (2) generalization to include a dielectric medium surrounding the nanotube.

Single-walled carbon nanotube (SWCNT) resistance arising from point defects can be directly imaged using scanning probe techniques. Here, we combine Scanning Gate Microscopy (SGM) and Kelvin Force Microscopy (KFM) to electronically identify defect sites and study their contributions to SWCNT resistances.

The electronic structure of single-wall carbon nanotubes (SWCNTs) embedded in a crystal matrix is calculated in terms of a linear augmented cylindrical wave method (LACW). In the case of armchair nanotubes, the delocalization of the nanotube electrons into the matrix region is responsible for the high energy shift of the σ-states and growth of the electron density of states at the Fermi level. For the semiconducting nanotubes, it causes a decay of the minimum energy gap and a formation of a metallic state.

Magnetotransport properties of two-dimensional (2D) arrays of single-wall carbon nanotubes (SWCNTs) were investigated. The magnetoresistance (MR) in pulsed magnetic fields and the temperature dependence of the resistance of 2D arrays of SWCNTs were measured in the temperature range 1.8–300 K and in fields up to 9 T. The crossover between metallic and non-metallic temperature dependence of the resistance was observed at T ≈ 125 K. At low temperature, positive MR was observed with decreasing amplitude with the increase of temperature.

Computer modeling of the differential conductance of symmetry connected armchair (n,n) and zigzag (2n,0) nanotubes was carried out in the framework of the surface Green's function matching (SGFM) method. It is shown that the heterojunctions (n,n)/(2n,0) have a band gap in the electron energy spectrum. It is demonstrated that the I-V curve increases with constant values with the increase of the voltage. The height of the I-V curve plateau is bigger for heterojunctions of larger diameter. It is shown that the maximum of the differential conductance of heterojunctions with bigger diameter is at comparatively low voltage.

Physi- and chemisorption are considered within the framework of classical and quantum molecular dynamics and density functional theory. We analyze coating (adsorption of metal monolayer) of carbon nanotubes as the cause of gas adsorption enhancement. Coarse-graining of less relevant degrees of freedom to obtain Hamiltonians spanning large length and time scales is a successful approach. The diffusion of adsorbed substances is modeled as well. Carbon nanotubes are regarded as mass conveyors as an application of diffusion. Charge fluctuations of electron density of the adsorbed molecules and of the carbon tube are the sources of metastability of the physisorption states.

First-principle real-space calculations within a time-dependent local density approximation show fluctuating charge distribution in a methane molecule physisorbed on a finite-size graphene sheet, which in turn bends forming a concave surface under multipole-multipole interaction and the carbon network vibrates in a complex way: a metastable physisorbed state occurs.

Single-wall carbon nanotubes (SWNT) are severely restricted in their applications, as they exist in rope-like bundles. Recently, J. Coleman et al. demonstrated a spectroscopic method to monitor bundle dissociation in low concentration NT-polymer composites. In this work we present the results we obtained with 2,5-dioctyloxy-1,4-distyrylbenzene (pDSB), a short-chain analogues of the well known PPV. We found a strong dependence of the concentration at which individual SWNTs become stable with the nature of the solvent.

Reduction of the gap in a (10,0) carbon nanotube with vacancies is obtained with the CASTEP 4.2 code. Molecular Dynamics simulations show that the vacancy distribution is important for the tube stability under stress.

The mechanical properties of a three-terminal nanotube “bough” junction are described. Interatomic Tersoff-Brenner potential and intermolecular Lennard-Jones potential were used to obtain the strain energy of the “bough” junction upon loading the “branch”. At small strain, the energy increases quadratically with the strain and the “branch” reverts to its initial position without external force. For strains higher than the critical one, the junction falls to a metastable state “branch stuck to stem”.

The oscillation frequency of charged doublewall semiconducting carbon nanotubes (DWCNTs) is found as function of the nanotube mass and geometry. The linear and nonlinear oscillations are analyzed.

We study the equilibrium properties of flexible polymer chains confined in a soft tube by means of extensive Monte Carlo simulations.

Silicon nitride based composites with different amount (1, 3 and 5 wt%) of carbon nanotubes have been prepared. Optimization of the manufacturing processes has been conducted to preserve the carbon nanotubes in composites and to avoid damaging during high temperature processing. The first results show that carbon nanotubes have a good contact to the surface of silicon nitride grains. Moreover, carbon nanotubes may serve as crystallization sites and seeds for silicon nitride grain growth. With increasing the carbon nanotube content a lower densification rate was obtained together with the deterioration of the mechanical characteristics of composites. In the case of 1wt% and 3 wt% carbon nanotube addition, the increase of gas pressure resulted in increase of bending strength.

Carbon Nanotubes were successfully functionalised with different chemical groups, which allowed them to act as an initiator for the polymerisation reaction of a Bisphenol A epoxy resin. Functionalised with traditional amino hardeners they became the “building blocks” for the amino cured epoxy.

We present a study on the composite of 1 wt% single-wall carbon nanotubes (SWNTs) in epoxy resin. Composites were prepared by solution mixing of epoxy resin XY 444 (Vantico), polyamine hardener XV 279 (Vantico) and single-wall carbon nanotubes (SWNTs), as a thin film. We observed that addition of surfactant together with sonification were necessary in order to obtain more uniform composite. We used several techniques to investigate the nanocomposite material, such as scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The observed changes of the glass transition temperature (T _g ) and electron micrographs indicate that the compatibility and interfacial adhesion between the nanotubes and epoxy resin are poor.

The influence of the oxygen chemical plasma treatment parameters on the water contact angle and surface energy of vapor grown carbon nanofibers (VGCFs) was studied. Tensile properties of the composites containing untreated and plasma treated fibers were measured.

The purpose of this investigation is to accentuate the global impact of nanotechnology which encompasses convergence of disciplines, heterogeneity in synthesis routes, metrology, and applications, and pose hierarchical challenges. A global perspective to develop a seamless integration in advancing the field of nanotechnology beyond its fundamental limit is presented.

Our main subject is CNTs and their interaction with DNA biomolecular gel. The electronic properties and vibration modes of CNT and DNA/CNT systems were investigated by TEM and Raman spectroscopy. From the UV-VIS-NIR absorption spectra the principal electronic absorption bands have been estimated. The effect of DNA is revealed by the existence of the 2.5- 3eV and 2 eV bands and shifting of the minima at 2.96 eV, 3.05, 3.34 eV. Using these results, we assert that a system of electronic levels is self-formed at the DNA/CNT interface. The structure of the CNT/DNA blocks is reviewed.

Molecular dynamics simulation of a system consisting of a hydrated lipid bilayer, a nanotube with a cap at one end, and a polypeptide to be pushed through the membrane is reported. This construction is considered to be a delivery vehicle (nanosyringe) which drives the peptide to the membrane surface. Tuning the nanotube (by adding functional groups) one may achieve the selectivity of the nanotube landing area on the cellular membrane. The pressure expulsing the peptide could arise as a result of a chemical reaction that makes the reaction mixture volume increase in the nanotube. As an analogue of the explosive component, blowing Van der Waals spheres are proposed. Different regimes of the penetration are simulated.

It has been recognized that nanofluids, a suspension of nanoparticles or nanotubes with size on the order of nanometers, can exhibit very unusual properties. The thermal conductivity of an individual single wall carbon nanotube is 5-10 times greater than that of very conductive materials such as aluminum or copper. It is not surprising that the thermal conductivity of nanofluids has been reported to be much higher then of their base fluid, even with very low particle concentration. The increase has been reported to have very strong temperature dependence and cannot be explained by existing macroscale theories. We report on initial experiments on the thermal conductivity of nanofluids consisting of different base fluids and a wide range of carbon nanotubes concentrations.

Single wall carbon nanotubes (SWNTs) present interesting tribological properties under boundary lubrication at ambient temperature. Used as additives to polyalphaolefin (PAO) base oil, they lead to a drastic decrease of both friction and wear of antagonist steel surfaces. These results are obtained with only 1 wt% of nanotubes dispersed in oil but with a minimal contact pressure of 0.83 GPa indicating that a structural modification is necessary for such improvements. Characterization of nanotubes by analytical TEM and Raman spectroscopy before and after friction is used to understand how nanotubes behave in the contact area.

A new sorbent with magnetic properties and anion removal ability has been produced by incorporating iron oxide based nanoparticles into the pores of zeolite crystals. The sorbent has been tested for the removal of arsenic (V) species from model aqueous solutions in batch–type equilibrium experiments. Good sorption was observed with maximum capacity of 73.32 mg of As per g of sorbent at pH 3.5.

Carbon deposition from acetylene injection into plasma jet onto sputtered nickel on silicon is investigated. The whole methodology, including the deposition of catalyst, its etching to islands followed by the carbon growth, is implemented in the same reactor. The investigation of structure and morphology shows the formation of nickel particles coated with graphitic layers.

The stability of free standing hexagonal Sc silicide wires is discussed based on ab-initio calculations. It is shown that Sc presence dramatically increases stability.

From the large class of poly-conjugated aromatic polymers which upon doping with electron donors or electron acceptors display metallic conductivities, poly (p-phenylene) is one of the experimentally most investigated systems. This work reports on a combined theoretical investigation of their solid state packing structure of oligomers of poly (p-phenylene). The influence of the torsion angle along the chains has been well documented as having an effect on the electronic and geometric structure of oligomers of poly (p-phenylene). A study of ionization potential, band width and energy gap was performed as a function of the torsion angle along the chains. It demonstrates the evolution of the electronic properties, which are of interest in the conducting polymer area. The coplanar conformation is obviously the ideal for the pioverlap and therefore maximum conductivity.

A compact diode-pumped Q-switched Nd:LSB microchip laser was developed for use in Raman spectrometers. In the paper, the performance of the laser and results of its application for spectrometric analysis of carbon nanotubes are reported.