Concentrated solutions of individualized single walled carbon nanotubes

Solutions of alkali metal salts of single-walled carbon nanotubes (SWNTs) show individualization of the nanotubes without sonication-induced shortening. Bundles are fully exfoliated and length measurements show mean length over one micron, a rare case for liquid formulation of SWNTs. These concentrated solutions of individualized nanotubes in organic solvents can be freeze dried leading to ultralight, highly porous, conducting and mechanically stable carbon nanotube cryogels.     

Environmentally friendly functionalization of single walled carbon nanotubes in molten urea

Using molten urea as the solvent, single walled carbon nanotubes (SWCNTs) are dispersed and functionalized with arenediazonium salts in less than 15 min to afford predominantly unbundled functionalized SWCNTs. This technique provides a rapid and economically viable route to produce covalently functionalized nanotubes in large amounts with an industrially friendly method.     

Selective destruction of individual single walled carbon nanotubes by laser irradiation

We demonstrate selective burnout of individual carbon nanotubes that are electronically resonant with the incident laser energy. Raman spectroscopy and atomic force microscopy are used to quantify the burnout of nanotubes. The threshold laser power for rapid burnout is found to occur between 0.4 and 0.9 W/μm². At lower laser powers of 80 mW/μm², the burnout depends linearly on time, over tens of minutes. Non-resonant nanotubes could not be burned out even with high laser power or long exposure times. This preferential burnout of resonant nanotubes demonstrates the possibility of selective removal of metallic nanotubes from an inhomogeneous sample.     

Anomalous effective hydrodynamic radius of octadecylamine functionalised single walled carbon nanotubes

In a uniform electric field, single walled carbon nanotubes (SWCNTs) in suspension become electrically polarised and are caused to rotate due to the resulting torque acting on the induced dipole moment. This rotation is followed in real time as an induced optical anisotropy, linear dichroism, which is produced as a result. These observations allow the polarisability of the nanotubes and the effective viscosity of the suspending medium to be determined. These techniques are used here to determine the effective radius of an octadecylamine (ODA)-functionalised SWCNT and its polarisability and to compare these values with those found for non-functionalised SWCNTs. The effective radius is found to be a factor 25 times larger than that of a non-functionalised SWCNT and far in excess of the value expected on steric grounds alone. Alternatively the local viscosity seen by the functionalised SWCNTs is 2.2 times greater than the macroscopic viscosity of the dichloroethane in which they are suspended. The polarisability of the metallic SWCNTs is substantially unchanged as a result of the functionalisation.     

Optical anisotropy of single walled carbon nanotubes investigated by spectroscopic ellipsometry

The optical properties of single walled carbon nanotube (SWCNT) films, produced by vacuum filtration, are correlated with their diameter and their in plane preferred orientation by coupling transmission and scanning electron microscopy to conventional ellipsometry. We focused on the optical anisotropy of this material and we demonstrated that it was originated from a breakdown in the selection rules.     

Gas sensors based on thick films of semi-conducting single walled carbon nanotubes

A comparative study was made of sorted semi-conducting single walled carbon nanotube (SWCNT) films and unsorted SWCNT films for gas sensing applications. The transmission line method is used to monitor separately the SWCNTs film resistance and the contact resistance between electrodes and the SWCNTs, thus revealing that the sensing mechanism mainly relies on a modification of the tube conductivity during gas exposure. The fabricated sensors demonstrate a detection limit of 20 ppb NO₂ and 600 ppb NH₃ mainly attributed to experimental setup limitations. Moreover, semi-conducting nanotubes happened to be 2.5 times more sensitive to NH₃ than unsorted ones, thus proving that selectivity can be improved by sorting the SWCNTs. The temperature dependence of the sensor sensitivity was studied, and a good agreement was found between experimental results and the Langmuir adsorption model.     

Controlled attachment of metal nanoparticles to single walled carbon nanotubes as a key step in their seeded growth and lengthening

The present study demonstrates the viability of the reductive attachment step of the single walled carbon nanotube (SWCNT) lengthening process in which long SWCNTs are grown from short nanotube seeds. Aryl sulfonate sidewall-functionalized, carboxylate end-functionalized SWCNTs are attached to an inorganic cluster pro-catalyst (FeMoC) via ligand exchange. The SWCNT-FeMoC complex was electrodeposited onto highly ordered pyrolytic graphite (HOPG), heated and exposed to etching conditions. Pre- and post-treatment AFM imaging shows that controlled reductive etching of the SWCNTs is attainable at a variety of pressures and temperatures in hot surface/cold gas and hot surface/hot gas systems.     

Influence of hot phonons on wind forces in metallic single walled carbon nanotubes

The wind force exerted on the lattice by the flux of electrons under electric loading in single walled carbon nanotubes is studied using an ensemble Monte-Carlo simulation. The momentum transfer between electrons and the lattice is treated using Quantum Mechanics. The phonon distribution and the electron distribution of the carbon nanotubes are allowed to be populated away from thermal equilibrium to study the influence of hot phonons on the wind forces. While the presence of hot phonons creates a net increase in the phonon–electron scattering rates, it appears to have a very small influence on the amount of force exerted on the lattice.     

Diameter dependence of the optoelectronic properties of single walled carbon nanotubes determined by ellipsometry

We report ellipsometric measurement on single walled carbon nanotube (SWCNT) films performed in a large spectral range from 0.07 to 4.97 eV. The complex dielectric functions of SWCNTs are correlated to their diameter distribution extracted from transmission electron microscopy. Here we show that the transition energies between Van Hove singularities are directly related to the strong one dimensional confinement. In the infrared spectral range, the real part of the dielectric function becomes negative. The electronic properties of SWCNTs are extracted from ellipsometry by using a Drude model. The mobility and the mean free path of charge carriers are limited by the high number of SWCNT contacts. In accordance with tight binding simulation, the conductivity and the charge carrier concentration increase with the SWCNT diameter. Finally, we demonstrate that the π-plasmon energy depends on the charge carrier concentration.     

Plasma enhanced growth of single walled carbon nanotubes at low temperature: A reactive molecular dynamics simulation

Low-temperature growth of carbon nanotubes (CNTs) has been claimed to provide a route towards chiral-selective growth, enabling a host of applications. In this contribution, we employ reactive molecular dynamics simulations to demonstrate how plasma-based deposition allows such low-temperature growth. We first show how ion bombardment during the growth affects the carbon dissolution and precipitation process. We then continue to demonstrate how a narrow ion energy window allows CNT growth at 500 K. Finally, we also show how CNTs in contrast cannot be grown in thermal CVD at this low temperature, but only at high temperature, in agreement with experimental data.     

Work function tuning for flexible transparent electrodes based on functionalized metallic single walled carbon nanotubes

We present a method to control the work function of metallic carbon nanotube transparent electrodes by functionalization of the random network with metallic nanoparticles. Flexible functionalized electrodes with high transparency (～90%) can be obtained with work function values ranging from ～4.6 up to ～5.1 eV, depending on the nature of the nanoparticles. The work function values were obtained by comparative in situ Kelvin probe force microscopy under ultra high vacuum and ultraviolet photoelectron spectroscopy measurements. Interestingly, by appropriate choice of the metal source for functionalization, work function engineering can lead to work function values higher or lower than that for pristine metallic nanotubes. This could be of great interest for adjusting the work function of transparent electrodes to active layers in many optoelectronics devices.     

Hierarchical formation of Ni sulfide single walled carbon nanotubes heterostructure on tin-sulfide scaffolds via mediated SILAR process: Application towards long cycle-life solid-state supercapacitors

For the enhancement of cyclic life in supercapacitors (SCs), hierarchically formed metallic single-walled carbon nanotubes (m-SWNTs) mediated nickel sulfides (c–NS–TS) heterostructures are synthesized on tin-sulfides (TS) scaffolds via successive ionic layer adsorption and reaction (SILAR) process. As compared with bare SnS₂, c–NS–TS formation has effects to improve electrical conductivity and to reduce volume expansion in bare SnS₂ scaffolds, leading to better specific capacitance and rate performance in SCs. The film structure, morphology evolution, and capacitive kinetics of c–NS–TS thin films are systematically investigated to understand the behind mechanism on the significantly improved electrochemical performance. Thus, the incorporation of highly conductive, nano-scale m-SWNTs (c–NS–TS) yields high capacitance (1120 Fg^-1) with excellent cyclic stability (95%), possibly due to inter-linkage of pure m-SWNTs in the heterostructure. For the enhanced electro-kinetic activity, this is strongly affected by the preferable formation on 3-dimensional c–NS–TS heterostructures, along with highly conductive m-SWNTs, leading to the initiation of the electroactive sites for enhanced electro-kinetic activity. For practical validation on applicability, LED lighting is successfully demonstrated, anticipating that the synthesis concept and its electrochemical properties will contribute to next-generation high-performance SC devices.     

An easy single step route to synthesize open−ended carbon nanotubes

A simple and easy route is described for the synthesis of multiwalled carbon nanotubes (MWCNTs) by pyrolysis of cetyltrimethyl ammonium decatungstate and cetylpyridinium decatungstate in a specially made LET-LOK union cell. The advantages of using a single component precursor is that the organic moiety present in the precursor acts as the source for carbon and in-situ formed tungsten/tungsten carbide acts as a catalyst for the formation of carbon nanotubes. The method produces large quantities of carbon nanotubes with monodisperse, hollow, open ends. The MWCNTs were characterized systematically using SEM, TEM, HRTEM, Raman and XRD analysis. The MWCNTs have average diameters in the range of 15–35 nm and lengths of several hundreds of nanometers.     

Hydrogen sulfide sensing properties of multi walled carbon nanotubes

This paper investigates the effect of functional groups on the hydrogen sulfide sensing properties of multi-walled carbon nanotubes using carboxyl and amide groups and Mo and Pt nanoparticles as decorated precursors in gaseous state at working temperature. Carbon nanotubes were synthesized by the CVD process and decorated with the nano particles; provide higher sensitivity for H₂S gas detection. The MWCNTs were characterized by scanning electron microscopy combined with energy dispersive X-ray (SEM/EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), ATR-IR absorption and Fourier transforms infrared (FT-IR) analyses. The MWCNTs were deposited as a thin film layer between prefabricated gold electrodes on alumina surfaces. The sensitivity of carbon nanotubes was measured for different H₂S gas concentrations and at working temperature. The results showed that the measured electrical conductance of the modified carbon nanotubes with functional groups is modulated by charge transfer with P-type semiconducting characteristics and metal decorated carbon nanotubes exhibit better performances compared to functional groups of carboxyl and amide for H₂S gas monitoring at room temperature.     

Synthesis of mesoporous molecular sieves as catalytic template for the growth of single walled carbon nanotubes

Mesoporous Mo MCM-41 and Nb MCM-41 molecular sieves were synthesized in various ratios by hydrothermal method and were characterized by XRD, N₂ adsorption isotherm and DRS-UV spectroscopy. The calcined samples were used as catalysts for the growth of carbon nanotubes using acetylene by chemical vapor deposition technique at 700–900 °C. The deposited carbon materials by acetylene decomposition, were found to be more in the case of Nb MCM-41 than in Mo MCM-41, and their catalytic activity was found to be in the order as Si/Nb = 100 > 75 > 50 > 25, and the same trend is followed for Mo MCM-41 molecular sieves. The catalytically synthesised carbon materials were characterized with Raman spectroscopy, SEM and TEM. We have obtained single walled carbon nanotubes in bundles with a tube diameter of 1.06–2.9 nm and 1.08–2.3 nm formed over Mo MCM-41 and Nb MCM-41, respectively, according to Raman spectra. Similarly well graphitised single walled carbon nanotubes formation was observed from TEM. From this observation, it is confirmed that Mo MCM-41 (100) and Nb MCM-41 (100) exist as stable catalysts for the synthesis of single walled nanotube.     

Raman analysis and mapping for the determination of COOH groups on oxidized single walled carbon nanotubes

Raman spectroscopy and mapping, coupled to molecular labelling, is used to analyse and monitor the first stage of carbon nanotube functionalization, i.e. their oxidation, which is usually performed to increase the number of surface carboxylic groups, allowing both a better dispersion in solution and the further attachment of biomolecules. Since the abundance of such surface groups is critical for the final application, it is important to develop a reliable but simple and fast method to investigate their presence on the tube walls. The presented data demonstrate the correlation between the presence and intensity of the Raman peak ascribed to the labelling molecule and the production of COOH groups on the nanotube walls. Between the analysed carbon nanotubes related spectral parameters, the G′ Raman peak position appears to be the most sensitive one to determine the degree of single walled carbon nanotube labelling, which directly depends on the number of COOH groups available for molecular attachment, i.e. on the efficiency of the oxidation treatment.     

Effect of multi‐walled carbon nanotubes dispersity on the light transmittancy of multi‐walled carbon nanotubes/epoxy composites

Two types of multi‐walled carbon nanotubes (MWCNTs), chemically modified and unmodified, were dispersed in epoxy resin with ultrasonication. The light transmittance characteristics of epoxy composites with different ratios of MWCNTs to epoxy resin were measured at wavelengths ranging from 200 to 1100 nm. Results showed that composites with modified MWCNTs had a much higher light transmittance than those with unmodified MWCNTs. This was presumably due to a more uniform dispersion of modified MWCNTs in the epoxy matrix, as indicated by both transmission electron microscopy and optic microscopy. The wavelength dependency of light transmittance of the composites was expressed empirically as a function of weight fraction (f_w) of MWCNTs and the light wavelength (λ). POLYM. ENG. SCI. 46:635–642, 2006. © 2006 Society of Plastics Engineers.     

The influence of doping on the Raman intensity of the D band in single walled carbon nanotubes

The D band in the Raman spectra of single walled carbon nanotubes is considered as an indicator of defects in carbon nanotubes. However, its dependence on charge-transfer doping is generally ignored, despite the studied samples are often naturally doped. We studied the intensity of the D band, the ratio of the intensities of the D band and TG band (I_D/I_TG) and the ratio of the intensities of the D and G′ band (I_D/I_G′) in the Raman spectra of the single walled carbon nanotubes in dependence on a doping level. We tested two laser excitation energies viz 2.41 and 1.92 eV, which are in resonance with semiconducting and metallic tubes, respectively in our sample. It is shown that the D band intensity is significantly attenuated in doped carbon nanotubes sample for both semiconducting and metallic tubes. The I_D/I_TG ratio is weakly dependent on doping for semiconducting tubes but for metallic tubes the I_D/I_TG ratio exhibits strong dependence on doping. The I_D/I_G′ ratio is suggested for evaluation of the defects in carbon nanotubes samples since it is less sensitive to doping both for semiconducting and metallic tubes. Nevertheless, for highly doped samples even the I_D/I_G′ ratio exhibits significant dependence on doping level.     

The alignment of single walled carbon nanotubes in an epoxy resin by applying a DC electric field

The alignment of single walled carbon nanotubes (SWCNTs) in an epoxy monomer liquid medium by the application of a DC electric field has been investigated, taking into account the various transport phenomena involved: the tube rotation in the electric field, the translation of polarized SWCNTs toward each other to form a chain-like structure and the migration of the tubes toward the positive electrode. Moreover, the relaxation mechanism which takes place when the electric field is switched off has also been considered. Experimental tests, performed to verify the effectiveness of the model, are based on the application of an electric field to a liquid epoxy–SWCNT colloid (0.025 wt.%) while measuring the current and observing the system by optical microscopy. As a result of the modeling it is possible to identify the processing conditions that allow the alignment of SWCNTs in an epoxy resin through the short-time application of a DC electric field. Experimental measurements are in agreement with the model’s predictions.