Characterization Of Single-walled Carbon Nanotubes Research Articles

Spectroscopic characterization of single-walled carbon nanotubes carrier-doped by encapsulation of TCNQ

Tetracyano-p-quinodimethane (TCNQ) molecules encapsulated single-walled carbon nanotubes (SWNTs) were investigated by using core level and valence band x-ray photoemission spectroscopy as well as near-edge x-ray-absorption fine structure spectroscopy. The $\ensuremath{\pi}$-band and ${\ensuremath{\pi}}^{*}$-band structures in these molecular systems were investigated, and it was clearly confirmed that a charge transfer occurred in TCNQ-doped SWNTs. TCNQ molecules were negatively charged as to be expected. A depletion of the $\ensuremath{\pi}$-band density of states of the SWNTs caused by the charge transfer to the TCNQ molecules was observed.

Structural Characterization of Single-Walled Carbon Nanotube Bundles by Experiment and Molecular Simulation

A procedure, combining molecular simulation, Raman spectroscopy, and standard nitrogen adsorption, is developed for structural characterization of single-walled carbon nanotube (SWNT) samples. Grand canonical Monte Carlo simulations of nitrogen adsorption are performed on the external and internal adsorption sites of homogeneous arrays of SWNTs of diameters previously determined by Raman spectroscopy of the sample. The results show the importance of the peripheral grooves of a nanotube bundle at low relative pressure and the insensitivity of nanotube diameter toward adsorption on the external surface of the bundle at higher pressures. Simulations also reveal that samples containing thin nanotubes have less internal adsorption capacity that saturates at lower pressure than those comprising large diameter nanotubes. The fraction of open-ended nanotubes in a sample can be estimated by scaling the simulated internal adsorption inside nanotubes to obtain a near perfect fit between simulated and experimental isotherms. This procedure allows extrapolation of adsorption properties to conditions in which all nanotubes in the sample are open-ended.

Nanomechanical characterization of single-walled carbon nanotube reinforced epoxycomposites

Nanomechanical properties of single-walled carbon nanotube (SWNT) reinforced epoxycomposites with varying weight percentage (0, 1, 3, and 5 wt%) of nanotubes were measuredby nanoindentation and nanoscratch techniques. Hardness and elastic moduluswere measured using a nanoindenter. Scratch resistance and scratch damage werestudied using the AFM tip sliding against the SWNT reinforced sample surfaces.Nanoindentation/nanoscratch deformation and fracture behaviour was studied by in situimaging of the indentation impressions/scratch tracks. Viscoelastic properties of thenanocomposites were measured using nanoindentation dynamic mechanical analysis tests.The reinforcing mechanisms are discussed with reference to the nanotube dispersion,interfacial bonding, and load transfer in the SWNT reinforced polymer composites.

Spin-On Catalyst: Straightforward and Flexible Route to Substrate-Grown Single Wall Carbon Nanotubes

The synthesis and characterization of single-wall carbon nanotubes (SWNTs) from simple catalytic precursors at 900 °C from methane and hydrogen is demonstrated. The catalyst precursor is comprised of iron nitrate and a commercially available siloxane polymer solution and is applied to various substrates via spin coating or dipping. The siloxane matrix simultaneously provides for the controlled formation of catalytic nanoparticles via phase separation and, upon heating, a smooth, continuous film of SiOx, which prevents catalyst coarsening and agglomeration at growth conditions. Furthermore, the processibility of the polymer enables the formation of complex, 3D structures from which nanotubes can grow. This combination of processing ease, flexibility, and inherent multifunctionality provides facile, controllable growth of single-wall carbon nanotubes on a multitude of substrates and facilitates additional routes toward SWNT-based device fabrication.

Characterization of single-wall carbon nanotubes by N 2 adsorption

N 2 adsorption isotherms at 77 K of single-wall carbon nanotubes (SWNTs), multi-wall carbon nanotubes (MWNTs), and mixtures of these carbon nanotubes (CNTs) were analyzed for differences in their pore size distributions (PSDs). The PSDs, calculated in the microporous region by the Horvath–Kawazoe method and in the mesoporous region by the BJH method, are in agreement with the structures of both types of CNTs deduced from high-resolution transmission electron microscopy. A characteristic peak in the microporous region in the PSD of SWNTs is not present in the PSDs of MWNTs and impurities such as amorphous carbon, metal residues of catalysts, etc. The evaluation of this peak is proposed as a convenient tool for the quantitative characterization of SWNT purity in carbon nanotube-containing samples.

Optical characterization of single-walled carbon nanotubes synthesized by catalyticdecomposition of alcohol

Single-walled carbon nanotubes (SWNTs), synthesized by a catalytic decomposition ofalcohol (alcohol CVD method, ACCVD), are compared with high-pressure CO (HiPco)SWNT samples through optical spectroscopic measurements such as resonant Ramanscattering, optical absorption and near infrared fluorescence. By the ACCVD method,SWNTs were synthesized either on zeolite catalyst-support particles or directly on thesurface of a quartz substrate; in the latter case, a simple dip-coat technique was employedfor mounting the metal catalyst. Specific morphological characteristics of as-grown SWNTsgenerated on zeolite support are presented using SEM and TEM, revealing that theSWNTs produced by the proposed method possess the significant quality of beingalmost free from amorphous carbons or metal particle impurities. The quality anddiameter distribution of SWNTs were investigated and discussed through the resultsof Raman scattering and optical absorption. The average diameter was slightlysmaller for SWNTs grown on zeolite particles than for HiPco SWNTs. Finally,fluorescent emission spectra from isolated SWNTs in an aqueous surfactant suspensionwere measured for various excitation wavelengths to determine the structural(n,m) distribution of the SWNTs. The narrower chirality distribution for ACCVD SWNTs grownon zeolite compared with HiPco SWNTs was demonstrated.

Atomic-scale characterization of single-walled carbon nanotubes on Si(100)-2×1:H with the ultrahigh vacuum scanning tunneling microscope

The atomic-scale topographic and electronic properties of single-walled carbon nanotubes adsorbed onto H-passivated Si(100) surfaces are elucidated by ultrahigh vacuum scanning tunneling microscopy and spectroscopy performed at room temperature. An in situ dry deposition process results in the pristine transfer of predominantly isolated nanotubes to the Si(100)-2×1:H surface and circumvents the need for ambient chemical processing. Electronic features corresponding to a semiconducting nanotube are identified within the band gap of the Si substrate. Nanometer-scale delineation of reactive Si dangling bonds by electron stimulated desorption of hydrogen is observed to result in a local enhancement of the apparent atomic corrugation for a nanotube intercepting the trajectory of the electron current used in the patterning process.

Synthesis and characterization of single-wall carbon nanotubes by hot-filament assisted chemical vapor deposition

We report a simplified production method for single-wall carbon nanotubes (SWNTs) by hot-filament assisted chemical vapor deposition (HFCVD) using pure alcohol vapor (ethanol, methanol and 2-propanol) as a carbon source. Under the optimized conditions, high-purity SWNTs are synthesized for the first time in large quantities. Raman spectra of the synthesized SWNTs show similar G/D ratios and the peak distribution of radial breathing mode to those obtained by the conventional CVD method with an electric furnace. The efficiency of the SWNTs synthesis has been increased by the hot-filament-induced pyrolysis of carbon sources, which promises an easy scale-up of the production of SWNTs at a low cost.

Alignment characterization of single-wall carbon nanotubes by Raman scattering

A novel method for identifying the Raman modes of single-wall carbon nanotubes (SWNT) based on the symmetry of the vibration modes has been studied. The Raman intensity of each vibration mode varies with polarization direction, and the relationship can be expressed as analytical functions. This method avoids troublesome numerical calculation and easily gives clear relations between Raman intensity and polarization direction. In this way, one can distinguish each Raman-active mode of SWNT through the polarized Raman spectrum.

Characterization of single-walled carbon nanotubes catalytically synthesized from alcohol

High purity single-walled carbon nanotubes (SWNTs) were synthesized from ethanol by catalytic CVD method. The yield of SWNTs was determined based on TGA complemented by Raman and TEM analyses. The effects of CVD reaction time and pre-reduction of catalytic metal on the yield and quality of synthesized SWNTs were investigated. The SWNT yield of more than 40% was achieved over the weight of zeolite support powder with Fe/Co catalyst, which corresponded to more than 800% yield over the weight of the catalytic metal, within the CVD reaction time of 120 min assuring as-grown high quality.

Modifications of single-wall carbon nanotubes upon oxidative purificationtreatments

A systematic characterization of single-wall carbon nanotube (SWCNT) materialafter successive purification steps, including reflux treatment with nitric acid, airoxidation, and annealing, has been performed. Inductively coupled plasma–opticalemission spectroscopy shows that a considerable reduction of the metalimpurities by up to 95% can be obtained by the nitric acid reflux treatment.During this process, Raman spectroscopy clearly proves that HNO3molecules are intercalated into the bundles of SWCNTs. At the same time, SWCNTshave suffered a high degree of degradation and defects are being introduced. Thesubsequent thermal processes lead to the removal of further defect carbonmaterials and to the almost complete de-intercalation of the HNO3molecules. Transmission electron microscopy reveals that the remainingSWCNT bundles tend to form thick bundles. Thus the applied purificationprocess results in a high-purity SWCNT material with a drastically reducedcontent of metal nanoparticles and composed of large bundles of SWCNTs.

Purification and Characterization of Single-Walled Carbon Nanotubes Produced by Arc-Discharge

Purification and Characterization of Single-Walled Carbon Nanotubes Produced by Arc-Discharge

Generation and Characterization of Single-Walled Carbon Nanotubes

Generation and Characterization of Single-Walled Carbon Nanotubes

Equivalent-continuum modeling of nano-structured materials

A method has been proposed for developing structure-property relationships of nano-structured materials. This method serves as a link between computational chemistry and solid mechanics by substituting discrete molecular structures with equivalent-continuum models. It has been shown that this substitution may be accomplished by equating the molecular potential energy of a nano-structured material with the strain energy of representative truss and continuum models. As important examples with direct application to the development and characterization of single-walled carbon nanotubes and the design of nanotube-based structural devices, the modeling technique has been applied to two independent examples: the determination of the effective-continuum geometry and bending rigidity of a graphene sheet. A representative volume element of the chemical structure of graphene has been substituted with equivalent-truss and equivalent-continuum models. As a result, an effective thickness of the continuum model has been determined. The determined effective thickness is significantly larger than the inter-planar spacing of graphite. The effective bending rigidity of the equivalent-continuum model of a graphene sheet was determined by equating the molecular potential energy of the molecular model of a graphene sheet subjected to cylindrical bending (to form a nanotube) with the strain energy of an equivalent-continuum plate subjected to cylindrical bending.

Characterization of Single-Walled Carbon Nanotubes (SWNTs) Produced by CO Disproportionation on Co−Mo Catalysts

The disproportionation of CO over Co−Mo/SiO2 catalysts with low Co/Mo ratios results in a high selectivity to single-walled carbon nanotubes (SWNTs) when the reaction is conducted between 700 and 950 °C in a flow of pure CO at a total pressure between 1 and 5 atm. A detailed characterization involving Raman spectroscopy, temperature-programmed oxidation (TPO), and transmission electron microscopy (TEM) shows that the product of this process has a high concentration of SWNTs. Depending on the temperature of operation, the selectivity and nanotube diameter can be varied.

Characterization of single-wall carbon nanotubes produced by CCVD method

Carbon single-wall nanotubes (SWNTs) can be produced by the catalytic chemical vapor deposition (CCVD) method. They are synthesized by catalytic decomposition of methane at 1000 °C on 2.5 wt% Co/MgO catalyst. SWNT samples have been characterized by transmission electron microscopy (TEM) and Raman spectroscopy. Using these two techniques, a comparison between the SWNTs produced by CCVD and synthesized by electric arc discharge has been made. Finally, we give conclusions about the diameter distribution and the electronic structure of SWNTs produced by the CCVD method.

Purification and Characterization of Single-Wall Carbon Nanotubes (SWNTs) Obtained from the Gas-Phase Decomposition of CO (HiPco Process)

A purification method is given for extracting the Fe metal catalyst and non-SWNT carbon from nanotubes produced by the HiPco process.1,2 A multistage purification method has been investigated. Sample purity is documented by ESEM, TEM, TGA, Raman and UV-vis−near-IR spectroscopy. Metal catalyzed oxidation at low temperature has been shown to selectively remove non-SWNT carbon and permit extraction of iron with concentrated HCl. Prolonged catalyzed oxidation has been found to preferentially remove smaller diameter tubes. The onset of oxidation of purified smaller diameter HiPco SWNTs is also found to be approximately 100 °C lower than for purified larger diameter tubes produced in the laser-oven process.

Electrical characterization of single-walled carbon nanotubes with Scanning Force Microscopy

In this work, a study of the possibilities of the Scanning Force Microscope (SFM) for studying transport properties of carbon nanotubes (CNTs) was done. Single-walled carbon nanotubes were deposited on SiO 2. Afterwards, using a mask, the surface was covered with gold, so that some of the carbon nanotubes in the surface stick out underneath the gold. In those areas, topographies and electrical measurements with metallic cantilevers have been carried out. We have developed simultaneous force vs. distance and current vs. distance data along the uncovered length of the nanotubes. In addition, current vs. voltage data was acquired at the maximum loading force during the indentation process. We found that the current rises abruptly when the tip touches the carbon nanotube and it is compared with similar experiments on the gold surface by the carbon nanotube.

Purification and Characterization of Single-Wall Carbon Nanotubes

A purification method has been developed that provides for the removal of metal catalysts and impurity carbon from laser-oven-grown single-wall carbon nanotube (SWNT) material. The oxidation rate of SWNTs in air at elevated temperatures is correlated to the metal content of the sample. Sample purity is documented with SEM, TEM, electron microprobe analysis, Raman, and UV−vis−near-IR. We also note that the relative intensity of the electronic transitions in the near-infrared to the continuum absorption at 400 nm in the UV serves as a useful monitor of the perturbation of the sidewall π-electron density of SWNTs due to sidewall substitution and/or oxidation.

Purification and structural characterization of single-walled carbon nanotubes

The production of single-walled carbon nanotubes (SWNTs) requires the use of catalysts, so the as-obtained compounds can contain traces of iron and nickel. The characterization by XRD and TEM of the nanotubes-based compounds was carried out at different steps of their thermal and chemical purification. Prolongated electron beam exposure results in structural modifications of the nanotubes which were mainly studied by electron energy loss spectroscopy (EELS).