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The influences of synthesis parameters on the mean diameter and diameter distribution of as-grown single-wall carbon nanotubes (SWCNTs) with chemical vapor deposition (CVD) using the mist flow method have been investigated in detail with Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). We found that CVD reaction temperature and flow rate play an essential role in controlling the mean diameter and the quality of as-grown SWCNTs. Furthermore, we found that the carbon supply kinetics can be a dominant factor to determine the diameter of as-grown SWCNTs in the present mist flow method. Under a different combination of various parameters, the mean diameter of SWCNTs can be varied from 0.9 nm to 1.5 nm controllably. A new floating catalyst CVD system for SWCNTs synthesis is reported and characterized by a combined research of Raman spectroscopy, SEM and TEM. Depending on the different combination of various experimental parameters such as ferrocene concentration in ethanol, CVD reaction temperature and total flow rate, the mean diameter of as-grown SWCNTs can be varied from 0.9nm to 1.5 nm. In addition, there is no direct relationship between the diameter of as-grown SWCNTs and catalyst particle size due to the carbon supply kinetics, which can be the dominant factor to determine the diameter of as-grown SWCNTs in the present mist flow method. Control of supply kinetics is significant to achieve structure-selective growth of SWCNTs using the floating catalyst CVD method. [ABSTRACT FROM AUTHOR]

Carbon nanotubes with 1–6 walls have been grown on cobalt-loaded mesoporous silica (i.e., MCM41) by using acetylene catalytic chemical vapor deposition. It is found that titanium grafting on the MCM41 pore walls prior to cobalt loading promotes the growth of nanotubes with 1–6 walls. As-grown nanotube material is found to be a mixture of single-wall carbon nanotubes (SWNTs), double-wall carbon nanotubes (DWNTs) and thin-multiwall carbon nanotubes (t-MWNTs) with 3–6 walls. Annealing of the as-grown nanotubes has reduced the amount of SWNTs in the nanotube mixture. Several structural deformations of the t-MWNTs are observed during transmission electron microscopy (TEM) analysis. Complete or partial collapse of the t-MWNTs is also found due to these structural deformations. Graphite-like domains developed at the collapsed regions stabilize these structural deformations. [ABSTRACT FROM AUTHOR]

Abstract: Single-walled carbon nanotubes (SWCNTs) have been synthesized on zeolite powder with Fe/Co catalysts by a catalytic chemical alcohol-vapor deposition (CCAVD). We have first used a cold wall reactor at the atmospheric pressure, the system having been modified for the zeolite-CCAVD specifications by the use of radio-frequency heating. The G/D ratio (∼25), estimated by analysis of Raman spectroscopy, obtained here is equivalent to that by the conventional CCAVD method under reduced pressure, indicating the high purity of the present specimen. The estimated diameter distributions of the SWCNTs obtained at synthesis temperatures of 900, 1000 °C and constant ethanol temperature of 0 °C are 0.9–1.8 and 1.2–2.2 nm, respectively, whereas that of synthesized at synthesis temperature of 900 °C and ethanol temperatures of 40 °C ranges form 0.8 to 1.4 nm. The diameter distribution shifts towards larger diameters as the synthesis temperature is increased and the carbon supply rate (ethanol temperature) decreases, from which we suggest a selective growth model due to a competition between deposition and etching of carbon atoms. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

We report the synthesis of single-layer graphenes from ethanol using, what we call, “flash cooling” just after chemical vapor deposition. The single-layer graphenes synthesized are high-quality and several micrometers in grain size as revealed by Raman spectroscopy. Detailed comparison of the cooling processes suggests that the single-layer graphene growth does not occur during the carbon precipitation but rather stems from surface diffusions of carbon on a nickel substrate. Because of the present simple and easiness for the large-scale synthesis under an inert gas atmosphere and at atmospheric pressure, the present method can easily be applied for the future large-scale and low-cost graphene production. [ABSTRACT FROM AUTHOR]

We have proposed a possibility of chirality assignment of individual single-walled carbon nanotubes in nanotube field-effect transistors (FETs) by micro-photocurrent spectroscopy. The nanotube FETs were fabricated by utilizing position-controlled nanotube growth technique using alcohol chemical vapor deposition. Photocurrent signal that originated from a single single-walled carbon nanotube was obtained by using microscopic optical measurement system. A peak was observed at 1.73 eV in the photocurrent excitation spectrum. This corresponds to optical absorption by van Hove singularity of the nanotube with a diameter of ∼2 nm. Chirality of the nanotube in the nanotube FET was assigned to be (18, 10) by comparing the experimental results with theoretical calculation. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Single-walled carbon nanotubes (SWNTs) were prepared with ethanol chemical vapor deposition (CVD) on SiO2 flat and pillar-patterned Si substrates. The effect of CVD temperatures from 600 to 800°C on SWNTs yields was investigated. By virtue of its unperturbed environment, an individual suspended SWNT grown between two different SiO2 pillars provides a possibility to study the phonon band structure of SWNT itself at a single-nanotube level. Raman spectra of individual SWNTs grown between pillars were investigated systematically. [Copyright &y& Elsevier]

Abstract: Metal catalyst-free mist flow chemical vapor deposition (CVD) growth of single-walled carbon nanotubes (SWCNTs) with C60 fullerenes has been investigated by using an aqueous colloidal C60 solution. Under the optimum reaction condition, relatively uniform SWCNTs with a mean diameter of 1.28nm can be synthesized without any treatments of C60 prior to CVD. Cap opening, nucleation and the growth of SWCNTs have been occurring almost simultaneously during the present CVD. C60 can be used as the seeds (i.e., end-caps) of SWCNTs, in which oxygen atoms from water molecules provide etching of C60 into caps. Furthermore, the coalescence of C60 caps into a larger one leads to the growth of SWCNTs with larger diameters. [Copyright &y& Elsevier]

Abstract: Single-wall carbon nanotubes (SWCNTs) have been synthesized by supported-catalyst chemical vapor deposition (CCVD) using one-dimensional (1D) channels of mesoporous silica (SBA-15; mean channel diameter, 6.0nm) functionalized with carboxyl groups where Co and Fe complexes are encapsulated. The synthesized SWCNTs have much larger diameters than the SWCNTs synthesized by conventional CCVD. Transmission electron microscope observations reveal that large-diameter SWCNTs (<4.2nm) are grown in 1D channels of SBA-15. Large metal particles formed in the channels should play an important role in the growth of the SWCNTs with larger diameters. [Copyright &y& Elsevier]

Carbon nanotube (CNT) arrays have been synthesized by a repeated growth method using a custom-fabricated plasma-enhanced thermal chemical vapor deposition (PE-thermal CVD) apparatus. The initial catalyst is a layered structure prepared by depositing 10nm of Al followed by 3 nm of Fe on an oxidized silicon substrate. Following CNT growth, the CNT arrays are removed using an ultrasonic cleaner, and another CNT array is grown on the remaining Fe-Al bimetalic nanoparticles without the addition of more catalyst. Annealing the catalytic substrate in air between growth cycles results in the removal of residual amorphous carbon along with the CNTs, and oxidation of the Fe-Al nanoparticles. The diameter of CNTs is reduced with repeated growth-annealing cycles, an effect of which is attributed to the diminishing size of the catalytically active nanoparticles with each cycle. After two growth cycles, SWNTs with the extraordinarily narrow diameter of 0.86 nm are synthesized. The ID/IG ratio derived from the Raman spectrum of these of the SWNT arrays shows the remarkably low value of 0.22. [ABSTRACT FROM AUTHOR]

Abstract: Diameter-controlled single-wall carbon nanotubes (SWCNTs) have been synthesized using Co, Fe/Co and Rh/Pd alloy nanoparticles trapped within the one-dimensional channels of a mesoporous materials (Folded Sheets Mesoporous material: FSM-16) by catalyst-supported chemical vapor deposition (CCVD) using ethanol as carbon source at 973–1173K. The SWCNTs synthesized are characterized by transmission electron microscopy, Raman spectroscopy and photoluminescence spectroscopy. The yield, diameter distribution and quality of the SWCNTs strongly depend on the reaction temperature during CCVD. The product synthesized at 1173K contains only SWCNTs, in marked contrast to those synthesized at lower temperatures. As the reaction temperature decreases, the relative abundance of multi-wall carbon nanotubes against SWCNTs significantly increases, whereas the mean diameter of SWCNTs increases as reaction temperature increases. The results show that a careful control of the reaction temperature is crucial to fabricate diameter-controlled SWCNTs from the channels of FSM-16. [Copyright &y& Elsevier]

Double-wall carbon nanotubes (DWNTs) have been synthesized in high-yield (>80%) by catalytic chemical vapor deposition (CCVD) of acetylene over well- dispersed metal particles (typically Co/Fe binary system) embedded in heat-resistant zeolites at temperatures above 900 °C. The synthetic yield of DWNTs has been sensitively affected by reaction conditions of the CCVD such as zeolite support materials, the sintering of the metal particles, hydrocarbon sources and reaction temperatures. High-resolution transmission electron microscopy together with Raman spectroscopy shows that the outer tube diameter varies from 3 to 6 nm with inner–outer tube separations of 0.36–0.37 nm, which is much larger than the interlayer distance of graphite (0.335 nm). [Copyright &y& Elsevier]