Single-walled Carbon Nanotubes Samples Research Articles

Effects of electron irradiation on single-walled carbon nanotubes

An experimental investigation of the effects of electron irradiation on Single-Walled Carbon Nanotubes (SWNTs) was conducted. The study focused on the modifications induced to the SWNT structure. SWNTs were irradiated at room temperature using a Transmission Electron Microscope (TEM) at 120eV. The effects of irradiation were observed and characterised using electron microscopy and Raman spectroscopy. Samples of SWNTs were observed prior to and following irradiation to discern any changes that in SWNTs occurred as a result of irradiation. Raman spectroscopy was used to characterise the different allotropes of carbon present in irradiated samples of SWNTs. These experiments showed that electron irradiation had a significant and deleterious effect on SWNT structure. The structure was rearranged to form allotropes of carbon which are not carbon nanotube; amorphous carbon and amalgamations of a number of allotropes of carbon were found. The process of amorphisation was observed during the course of electron irradiation and was confirmed using Raman spectroscopy by the gradual weakening of the distinctive SWNT Raman spectral bands as well as the presence of bands characteristic of amorphous carbon.

High performance resonance Raman spectroscopy using volume Bragg gratings as tunable light filters

We designed a near infrared tunable resonance Raman spectroscopy system based on a tandem of thick volume Bragg gratings (VBGs). VBGs are here the constituents of two light filtering units: a tunable laser line filter (LLF) and a tunable notch filter (NF). When adapted in a micro-Raman setup with a single stage monochromator (1800 gr/mm grating), the tandem of LLF and NF allowed measurements of Raman signals down to +/-20 cm(-1). The good performance and fast tunability of the VBG Raman system was demonstrated on a sulfur powder and on a bulk single-walled carbon nanotube sample through a series of 22 Stokes and anti-Stokes spectra recorded at excitation wavelengths between 800 and 990 nm. The main drawbacks of the setup are the limited spectral range to the near infrared and the small angular acceptance of the filters (approximately 1 mrad), which causes mainly attenuation problems with the NF. The impact of the main limitations is discussed and solutions are provided.

Raman intensity measurements of single-walled carbon nanotube suspensions as a quantitative technique to assess purity

A method to assess the purity of single-walled carbon nanotube (SWCNT) bulk samples based on Raman spectroscopy is reported. The new method has higher reproducibility and quantitative precision than those previously used. It consists of measuring the G-band intensity of liquid suspensions of SWCNT samples as a function of solid concentration. A simple equation is proposed in which one of the two adjustable parameters is the SWCNT purity. The method has been applied to a series of samples of similar characteristics, but varying quality. The results are compared to those obtained on the same series of samples using standard analytical techniques, including electron microscopy, thermogravimetric analysis and optical absorption.

GaAs-Carbon Nanotubes Nanocomposite: Synthesis and Field-emission Property

Hybridization of semiconductor materials with carbon nanotubes (CNTs) is a recent field of interest in which new nanodevice fabrication and applications are expected. In this work, nanowire type GaAs structures are synthesized on porous single-wall carbon nanotubes (SWCNTs) as templates using the molecular beam epitaxy (MBE) technique. The field emission properties of the as-synthesized products were investigated to suggest their potential applications as cold electron sources, as well. The SWCNT template was synthesized by the arc-discharge method. SWCNT samples were heat-treated at under an atmosphere to remove amorphous carbon. After heat treatment, GaAs was grown on the SWCNT template. The growth conditions of the GaAs in the MBE system were set by changing the growth temperatures from to . The morphology of the GaAs synthesized on the SWCNTs strongly depends on the substrate temperature. Namely, nano-crystalline beads of GaAs are formed on the CNTs under , while nanowire structures begin to form on the beads above . The crystal qualities of GaAs and SWCNT were examined by X-ray diffraction and Raman spectra. The field emission properties of the synthesized GaAs nanowires were also investigated and a low turn-on field of was achieved. But, the turn-on field was increased in the second and third measurements. It is thought that arsenic atoms were evaporated during the measurement of the field emission.

Aggregation-Dependent Photoluminescence Sidebands in Single-Walled Carbon Nanotube

Aggregation of single-walled carbon nanotubes (SWCNTs) is one of the major obstacles for many nanotube fundamental studies and practical applications, such as nanocomposites, electronic devices, bioimaging, biosensors, and drug-delivery. In this study, two types of SWCNT samples, enriched with (6,5) and (7,5) chiral structures, respectively, were investigated. SWCNT suspensions containing various fractions of bundles were obtained by ultracentrifugation. Dialysis was used to achieve the controlled nanotube rebundling. Results showed that SWCNT photoluminescence (PL) sidebands (the transverse sideband E12,21, the phonon coupled sidebands E22 + G,G′, and the E33 → E11 emission band) are dependent on the nanotube aggregation. We proposed that SWCNT exciton relaxation routes increase upon nanotube aggregation, resulting in the suppression of primary PL peaks and the enhancement of PL sidebands. Furthermore, the correlation between PL sidebands and nanotube aggregation was also demonstrated in diverse dispersi...

Enrichment of Armchair Carbon Nanotubes via Density Gradient Ultracentrifugation: Raman Spectroscopy Evidence

We have used resonant Raman scattering spectroscopy to fully analyze the relative abundances of different (n,m) species in single-walled carbon nanotube samples that are metallically enriched by density gradient ultracentrifugation. Strikingly, the data clearly show that our density gradient ultracentrifugation process enriches the metallic fractions in armchair and near-armchair species. We observe that armchair carbon nanotubes constitute more than 50% of each (2n + m) family.

Analysis of the Size Distribution of Single-Walled Carbon Nanotubes Using Optical Absorption Spectroscopy

The diameter of single-walled carbon nanotubes (SWNTs) is an important characteristic to determine their electronic properties and direct further applications in electronics and photonics. A demand currently exists for an accurate and rapid method of evaluating the mean diameter and diameter distribution of bulk SWNTs. Here, we provide an effective means for quantifying the diameter distribution of SWNTs using optical absorption spectroscopy without a strict prior assumption on the form of the diameter distribution. Verification of this assignment protocol is based upon statistical analysis of hundreds of high-resolution transmission electron microscopy (HRTEM) images as well as comparison with Raman measurements on the same SWNT samples. A good agreement among different techniques indicates that this approach enables accurate and rapid assessment of diameter distribution and can be extended to bulk SWNT samples with various diameter distributions.

Ignition and temperature behavior of a single-wall carbon nanotube sample

The electrical resistance of mats of single-wall carbon nanotubes (SWNTs) is measured as afunction of mat temperature under various helium pressures, in vacuum and in atmosphericair. The objective of this paper is to study the thermal stability of SWNTs produced in ahelium arc discharge in the experimental conditions close to natural conditions of SWNTgrowth in an arc, using a furnace instead of an arc discharge. For each testedcondition, there is a temperature threshold at which the mat’s resistance reachesits minimum. The threshold value depends on the helium pressure. An increaseof the temperature above the temperature threshold leads to the destructionof SWNT bundles at a certain critical temperature. For instance, the criticaltemperature is about 1100 K in the case of helium background at a pressure of about500 Torr. Based on experimental data on critical temperature it is suggested thatSWNTs produced by an anodic arc discharge and collected in the web area outsidethe arc plasma most likely originate from the arc discharge peripheral region.

Calibrating the single-wall carbon nanotube resonance Raman intensity by high resolution transmission electron microscopy for a spectroscopy-based diameter distribution determination

We study a single-wall carbon nanotube (SWNT) sample grown by water-assisted chemical vapor deposition with both resonance Raman scattering (RRS) and high resolution transmission electron microscopy. High resolution transmission electron microscopy measurements of 395 SWNTs determined the diameter distribution of the sample, allowing us to calibrate an RRS radial breathing mode (RBM) map obtained with 51 laser excitation energies from 1.26 to 1.73 eV. Thus, we determined the diameter dependence of the RRS RBM cross-section, which in turn allows the determination of the diameter distribution of any SWNT sample by measuring the RBM Raman signal.

Micro-Raman Study of The Role of Sterilization on Carbon Nanotubes for Biomedical Applications

We investigate the effect of four different types of sterilization procedures on the structural properties and morphological features of single-wall carbon nanotube samples approachable by micro-Raman spectroscopy. Sterilization procedures (treatment in humid heat autoclave or ethylene oxide and irradiation with gamma-rays or UV light) are necessary in view of the use of carbon nanotube sterile samples in in vivo toxicity tests on laboratory rats. Micro-Raman spectroscopy allows us to estimate several details about the morphology of the single-wall carbon nanotube mixture (mainly the presence of disorder and diameter distribution) before and after the sterilization treatment. The best of these treatments, in other words, the one that least affected the morphology and structural properties of carbon nanotubes, was found to be UV irradiation and has thus been selected for future in vivo tests on rats.

Electrochemical hydrogen storage behavior of single-walled carbon nanotubes (SWCNTs) coated with Ni nanoparticles

The electrochemical hydrogen storage properties of Ni nanoparticle coated SWCNT electrodes were investigated. A surface modification technique enabled different amounts of Ni nanoparticles to be deposited on the SWCNT surface, which was first chemically oxidized by 6 N HNO 3. The characteristic properties of the SWCNT samples coated with 4–12 wt.%Ni nanoparticles were examined using a scanning electron microscope with energy dispersive spectroscopy (SEM/EDX); micro-Raman spectroscopy; thermal analysis techniques consisting of both thermogravimetric analysis (TGA) and differential thermal analysis (DTA), and Brunauer–Emmett–Teller (BET) measurements. It was found that all of the SWCNT samples coated with 4–12 wt.%Ni nanoparticles possessed a similar pore-size distribution. According to the electrochemical test results, the highest electrochemical discharge capacity of 1404 mA h g −1 was obtained for the SWCNT electrode coated with 8 wt.%Ni nanoparticles, which corresponded to 5.27 wt.% hydrogen storage. This enhancement of electrochemical hydrogen storage capacity was ascribed to the fact that the Ni nanoparticles act as a redox site, thus leading to an improved electrochemical hydrogen storage capacity. The results indicated that the SWCNT coated with Ni nanoparticles are a potential material for hydrogen storage.

A Raman spectroscopy study of the solubilisation of SWCNTs by polycyclic aromatic hydrocarbons

The effectiveness of polycyclic aromatic hydrocarbons (PAHs) for selective solubilisation of single walled carbon nanotubes (SWCNTs) has been studied by Raman spectroscopy. Polyphenyl and polyacene PAHs of different lengths are used. Selective interaction between the PAHs and SWCNT is investigated by analyzing the Raman radial breathing modes the frequency positioning of which yields information concerning the diameter distribution of the SWCNT sample. Samples were dispersed at concentrations below the debundling limit and deposited on quartz substrates. A combination of four laser excitation energies was utilized to establish the distribution of diameters present. The results show that the PAHs interact with a range of SWCNT diameters. In general a preference for smaller diameter SWCNTs is evident, although the longer PAHs have the capacity to solubilise larger diameter SWCNTs, due to their increased binding energy. Although a small degree of structural specificity is evident, all PAHs solubilise both chiral and nonchiral SWCNTs.

The reaction of lithium metal vapor with single walled carbon nanotubes of large diameters

AbstractRaman spectroscopy was used to evaluate the effect of lithium vapor on single walled carbon nanotubes (SWCNTs) having diameters from 1.2 to 1.6 nm. The Raman spectra were excited by five different laser lines. A strong doping of SWCNTs after the reaction with Li vapor was confirmed by the corresponding attenuation of the Raman signal. The relative intensities and frequencies of the radial breathing mode of the Li vapor treated SWCNT were recovered after subsequent reaction with water. Our data demonstrate that the reaction of Li with large diameter SWCNTs is reversible, which is different from previous results showing irreversible changes for SWCNT samples containing both large diameter and small diameter tubes. The subsequent in situ Raman spectroelectrochemical measurement of our sample confirmed that after water treatment of the Li etched sample there is no significant residual doping of the SWCNT sample.

Spectroscopy of single‐walled carbon nanotubes in aqueous surfactant dispersion

AbstractOptical studies of single‐walled carbon nanotubes (SWNTs) dispersed in aqueous surfactant suspensions have made significant progress since the discovery of their bright band‐gap fluorescence in the near‐infrared region [M. J. O'Connell et al., Science 297, 593–596 (2002)]. In this article we report the systematic investigation of the effect of chemical purification and oxidation on the spectroscopic properties of SWNTs. The SWNTs samples we prepared differ for the percentage of impurities present, the amount of defects introduced in their graphitic structure and/or the functional groups expressed on their surface. The generation of carboxylic groups on the nanotubes surface by oxidative treatment was validated by means of thermal gravimetric analysis and ATR/Fourier transform IR spectroscopies, as well as Raman spectroscopy. We have solubilized pristine, purified SWNTs (p‐SWNTs) and oxidized SWNTs (o‐SWNTS) in Milli‐Q water using sodium dodecylbenzene sulphonate (SDBS). While our Vis‐NIR Absorption spectra of p‐SWNTs and o‐SWNTS dispersions in aqueous SDBS solution show the loss of the resolution of the characteristic van Hove singularities, NIR Photoluminescence spectra are characterized by structured emission peaks.

The effect of length of single‐walled carbon nanotubes (SWNTs) on electrical properties of conducting polymer–SWNT composites

AbstractDC conductivity of conjugated polymer‐single‐walled carbon nanotube (SWNT) composite films has been measured for different SWNT concentrations. The composite was prepared by dispersing SWNTs in the poly (3‐octylthiophene), P3OT matrix already dissolved in xylene. The conductivity of the composite films showed a rapid increase as the SWNT concentration increases beyond a certain value. This behavior is explained in terms of percolating paths provided by the SWNTs in the volume of polymer matrix. To investigate the effect of length of nanotubes on the percolation conductivity, different SWNT samples were employed with similar diameter but varying tube lengths. It was found that the conductivity of the composite films is strongly dominated by the length of the nanotubes. Lower percolation limit and high conductivity value of composite films is observed for longer nanotubes. Furthermore, the conductivity is observed to be dependent on the size of the host polymer molecule also. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 89–95, 2010

Sample preparation protocols for realization of reproducible characterization of single-wall carbon nanotubes

Harmonized sample pre-treatment is an essential first step in ensuring quality of measurements as regards repeatability, interlaboratory reproducibility and commutability. The development of standard preparation methods for single-wall carbon nanotube (SWCNT) samples is therefore essential to progress in their investigation and eventual commercialization. Here, descriptions of sample preparation and pre-treatment for the physicochemical characterization of SWCNTs are provided. Analytical methods of these protocols include scanning electron microscopy (dry, wet), transmission electron microscopy (dry, wet), atomic force microscopy, inductively coupled plasma mass spectrometry, neutron activation analysis, Raman spectroscopy (dry, wet), UV–Vis–NIR absorption and photoluminescence spectroscopy, manometric isothermal gas adsorption and thermogravimetric analysis. Although sample preparation refers to these specific methods, application to other methods for measurement and characterization of SWCNTs can be envisioned.

Sharper and Faster “Nano Darts” Kill More Bacteria: A Study of Antibacterial Activity of Individually Dispersed Pristine Single-Walled Carbon Nanotube

To further our understanding on the antibacterial activity of single-walled carbon nanotubes (SWCNTs), high purity SWCNTs with average diameter of 0.83 nm and (7,5) chirality as dominate (n,m) structure were dispersed in a biocompatible surfactant solution. Ultraviolet-visible-near-infrared radiation absorption spectroscopy was employed to monitor the aggregation of SWCNTs. The results demonstrated that individually dispersed SWCNTs were more toxic than SWCNT aggregates toward bacteria (gram-negative Escherichia coli, Pseudomonas aeruginosa, and gram-positive Staphylococcus aureus, Bacillus subtilis). Individually dispersed SWCNTs can be visualized as numerous moving "nano darts" in the solution, constantly attacking the bacteria; thereby, degrading the bacterial cell integrity and causing the cell death. Controlled experimental results suggested that inhibiting cell growth and oxidative stress were not the major causes responsible for the death of cells. Furthermore, the detrimental effects of Co metal residues (up to 1 mug/mL) on SWCNT samples can be ruled out. Atomic force microscope study conducted in suspension proved that the death rates of bacteria were strongly correlated with their mechanical properties; soft cells were more vulnerable to SWCNT piercing. The antibacterial activity of SWCNTs can be remarkably improved by enhancing the SWCNT physical puncture on bacteria in the following ways: (1) dispersing SWCNTs individually to sharpen the nano darts; (2) increasing SWCNT concentration to raise the population density of nano darts; and (3) elevating the shaking speed of incubation to speed up the nano darts. This study elucidated several factors controlling the antibacterial activity of pristine SWCNTs and it provided an insight in developing strategies that can maximize the SWCNT application potentials while minimizing the health and environment risks.

A comprehensive scenario for commonly used purification procedures of arc-discharge as-produced single-walled carbon nanotubes

The purification of single-walled carbon nanotube (SWCNT) samples was analysed using a multi-technique approach, with structural as well as spectroscopic probes, in order to characterize the samples and to identify important factors for improvement of SWCNT sample quality. The first dry oxidation step (air at 365 °C) is shown to have only a weak selectivity for the removal of the amorphous carbon or weakly organized graphitic species as well as resulting in a partial consumption of the SWCNTs. The functionalization of the SWCNTs is highly specific with formation of carboxyl, hydroxyl and carbonyl groups. On the other hand this oxidation step is highly efficient for the oxidation of the catalytic impurities (Ni, Y) which can be easily removed by subsequent acid treatment. A final high temperature treatment indicates some incomplete restoration of the quality of the SWCNT surface.

Isothermal Microcalorimetry, A Tool for Probing SWNT Bundles

The bundling state of several dry single-walled carbon nanotube (SWNT) samples is compared using isothermal microcalorimetry (IMC). So as to get different dry samples with various bundling states, the pristine SWNTs were pretreated with a solution of an aromatic amphiphile with or without sonication, washed and dried before being studied by IMC. The bundling state of the different SWNT samples, which was first analyzed by TEM, was then correlated to the obtained IMC data thanks to the interpretation of the observed energy transfer phenomena. From our results, IMC appears to be an interesting technique for the surface probing of dry SWNT samples, and herein for the evaluation of the bundling state.

Axially Chiral Facial Amphiphiles with a Dihydronaphthopentaphene Structure as Molecular Tweezers for SWNTs

Syntheses of chiral 6,15-dihydronaphtho[2,3-c]pentaphene derivatives of opposite configurations are reported. Starting from anthracene, the strategy involves two key steps: a Diels-Alder reaction on a prochiral dianthraquinone, and an enantiomeric resolution using (-)-menthol. The final molecules exhibit very strong optical activity, as shown by their circular dichroism spectra, and are examples of chiral facial amphiphiles. Their adsorption at the surface of single-walled carbon nanotubes (SWNTs) has also been studied, and has been found to occur preferentially on 0.8-1.0 nm diameter nanotubes among the population of a high-pressure CO conversion (HiPco) SWNT sample (0.8-1.2 nm). The synthesised facial amphiphiles act as nano-tweezers for the diameter-selective solubilisation of SWNTs in water. The expected optical activities of the SWNT samples solubilised by each of the chiral amphiphiles have been studied by circular dichroism spectroscopy, but the results are not yet conclusive.