Formation Of Single-walled Carbon Nanotubes Research Articles

Solubilization and debundling of purified single-walled carbon nanotubes using solubilizing agents in an aqueous solution by high-speed vibration milling technique.

Purified single-walled carbon nanotubes (SWNTs) and cyclodextrins (CDs) mixed by a mechanochemical ‘high-speed vibration milling technique’ (HSVM) are soluble in an aqueous solution because of the formation of SWNT·CDs complexes and the debundling of SWNTs.

Ring formation of single-walled carbon nanotubes: Competition between conformation energy and entropy

We investigate ring formation of single-walled carbon nanotubes theoretically in this paper. The conformation energy of the nanotubes is identified as the curvature elastic energy of a curved graphite and the intertube van der Waals interaction. The entropy of ring nanotubes depends on the total number of carbon atoms. Assuming continuity, we find that the ring single-walled carbon nanotube is stable only when the radius of the tube is valued 6.958 \AA{}. The ring diameter ranges from 200 to 700 nm.

The Role of Metal Nanoparticles in the Catalytic Production of Single‐Walled Carbon Nanotubes — A Review

AbstractFor Abstract see ChemInform Abstract in Full Text.

Molecular dynamics in the formation process of single‐walled carbon nanotubes

AbstractThe mechanism of the nucleation and formation of single‐walled carbon nanotubes (SWNTs) was investigated using molecular dynamics simulations. When the initial state was chosen so that carbon and nickel atoms were randomly distributed in a simulation domain, the formation of a random cage structure made up of carbon atoms, which had a few nickel atoms inside it, was observed by 6 ns. The nickel atoms, which move inside or on the surface of the cage, were seen to be preventing the complete closure of the cage and its anneal into the fullerene structure. Further, in order to observe a longer time‐scale growth process, the simulation cell was artificially shrunk by the progress of simulation so that collisions between precursor clusters were promoted to comply with the limitation in the calculation time. Collisions of the imperfect random‐cage clusters led to an elongated tubular cage structure, which could be regarded as an initiation of SWNTs. The simulation results were compared with FT‐ICR mass spectra of the positive clusters generated by a laser‐vaporization supersonic‐expansion cluster beam source. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(8): 690–699, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10123

The role of metal nanoparticles in the catalytic production of single-walled carbonnanotubes—a review

Recent progress in chemical vapour deposition and aerosol synthesis of single-walled carbonnanotubes (SWCNTs) is reviewed with an emphasis on the role of metal nanoparticles inthe processes. The effect of the various parameters on SWCNT formation is reported on thebasis of published experiments. Evolution of the catalyst particle size distribution due tocollision, sintering and evaporation of metal during SWCNT synthesis is discussed.The active catalyst has been demonstrated to be in a reduced metal form bycomparison of the experimental data and calculations regarding the equilibriumconcentration of carbon and oxygen in iron. Also the effect of the catalyst particle size onmelting temperature and carbon solubility in metal is discussed. The stability ofdifferent carbon precursors (hydrocarbons and carbon monoxide) is consideredthermodynamically. Furthermore, estimation of the maximum length of 1 and 2.5 nmdiameter SWCNTs as a function of carbon solubility is conducted to determine whethercarbon dissolution and precipitation are simultaneous or subsequent process steps.

Single-walled carbon nanotube formation with double laser vaporization technique

Single-walled carbon nanotubes (SWNTs) were prepared with double laser vaporization of a graphite target and a metal/alloy target inside an electric furnace at 1200 °C ambient temperature with 500 torr Ar gas atmosphere. Each target was vaporized simultaneously with a different Nd:YAG laser. Several kinds of metal/alloy target (Ni, Co, Fe, and permalloy) were tested in order to see the difference in the resulting SWNT yield and the diameter distribution of them. The Raman spectra of SWNT-containing soot prepared by use of this technique with permalloy/carbon system indicated that permalloy gives almost the same yield as compared with Ni/Co carbon composite rod with single laser vaporization technique, though the diameter distribution of them is slightly different. Also, time-resolved images of the plume by carbon and permalloy nanoparticles after laser vaporization were collected using a high-speed video camera. These images suggest that the hot plumes due to carbon and permalloy nanoparticles do not mix together so extensively, at least in a few hundred microseconds after laser vaporization. The effect of time delay between two laser pulses on the yield and the diameter distribution of SWNTs was also presented and discussed.

Effect of a rotating electrode on the formation of single-walled carbon nanotubes

We investigated the effect of a rotating anode on the formation of single-walled carbon nanotubes (SWNTs) using the plasma rotating electrode process. With rotation of the anode, the diameter distribution of SWNTs was shifted toward smaller diameters, and the yield of SWNTs increased. In addition, optical emission spectroscopy confirmed the increase of plasma temperature by rotating anode. These results indicate that the diameter distribution of SWNTs and the increase of SWNT yield resulted from the change of discharge characteristics by rotation of the anode.

Effects of carbonyl bond, metal cluster dissociation, and evaporation rates on predictions of nanotube production in high-pressure carbon monoxide.

The high-pressure carbon monoxide (HiPco) process for producing single-wall carbon nanotubes (SWNTs) uses iron pentacarbonyl as the source of iron for catalyzing the Boudouard reaction. Attempts using nickel tetracarbonyl led to no production of SWNTs. This paper discusses simulations at a constant condition of 1300 K and 30 atm in which the chemical rate equations are solved for different reaction schemes. A lumped cluster model is developed to limit the number of species in the models, yet it includes fairly large clusters. Reaction rate coefficients in these schemes are based on bond energies of iron and nickel species and on estimates of chemical rates for formation of SWNTs. SWNT growth is measured by the conformation of CO2. It is shown that the production of CO2 is significantly greater for FeCO because of its lower bond energy as compared with that of NiCO. It is also shown that the dissociation and evaporation rates of atoms from small metal clusters have a significant effect on CO2 production. A high rate of evaporation leads to a smaller number of metal clusters available to catalyze the Boudouard reaction. This suggests that if CO reacts with metal clusters and removes atoms from them by forming MeCO, this has the effect of enhancing the evaporation rate and reducing SWNT production. The study also investigates some other reactions in the model that have a less dramatic influence.

The effect of laser power on the formation of carbon nanotubes prepared in CO 2 continuous wave laser ablation at room temperature

Single-walled carbon nanotubes (SWNTs) were prepared by continuous wave CO 2 laser ablation without applying additional heat to the target. Transmission electron microscope and Raman spectrum were used to investigate the effect of laser power on the growth and diameter distribution of the tubes. The average diameter of single wall carbon nanotubes produced by CO 2 laser increases with increasing laser power. We have presented the radial breathing mode of Raman spectrum of SWNTs prepared by using CO 2 continuous laser vaporization in laser power from 500 to 850 W, and the Raman spectrum are also compared with those of single-walled carbon nanotubes produced by pulsed CO 2 laser ablation of previous reports. SWNTs and bamboo-shaped carbon nanotubes were observed from web-like carbon soot in a lower laser power of 500 W. Experiment confirmed that laser power play a crucial role in SWNTs formation and diameter distribution.

Role of the catalyst particle size in the synthesis of single-wall carbon nanotubes

It is argued that the growth mechanism of single-wall carbon nanotubes (SWNTs) is a kind of solid–liquid–solid (SLS) catalytic graphitization of non-graphitic forms of carbon (predominantly amorphous carbon, condensed at early stages of the carbon vapor relaxation) catalyzed by molten supersaturated carbon–metal nanoparticles. The liquefaction of nanoparticles of the catalytic metals in contact with the amorphous carbon below the equilibrium eutectic temperature of the corresponding metal–carbon alloys is considered as a decisive condition for the SWNT formation both at the nucleation and at the growth stages. It leads to a pronounced increment of carbon solubility (up to 50 at.% C), which alters the character of the interaction of the precipitated graphitic form of carbon with the catalyst surface and presumably can result in the SWNT nucleation. Furthermore, it lowers the energy barrier between the initial amorphous and final graphitic carbon phases. The experimental dependencies of the SWNT abundance in the soot on the synthesis temperature, pressure, carrier gas flow velocity, and the initial catalyst content in the target support the idea of the a “catalyst particle size window” in which the supersaturated metal–carbon alloy may remain liquid below the equilibrium eutectic temperature.

Causes of different catalytic activities of metals in formation of single-wall carbon nanotubes

When single-wall carbon nanotubes (SWNTs) were formed by pulsed Nd:YAG laser ablation or arc discharge, the yield depended on the metal catalyst: NiCo> Ni∼NiFe≫Co∼Fe>Pd∼Pt. It appears that an effective catalyst for SWNT growth must satisfy three conditions: it must be a good graphitization catalyst, have low solubility in carbon, and have a stable crystallographic orientation on graphite. NiCo, Ni, and NiFe satisfy these three conditions. The poor catalytic activities of Co, Fe, Pd, and Pt for SWNT formation would be explained by the ineffectiveness of Pt and Pd as graphitization catalysts, crystallographic orientation instability of Co crystals on graphite, and high solubility of Fe in graphite.

Rate-Limiting Processes in the Formation of Single-Wall Carbon Nanotubes: Pointing the Way to the Nanotube Formation Mechanism

Four rate-limiting processes for the formation of single-wall carbon nanotubes (SWCNT) could be identified by varying furnace temperature, gas type, and pressure in a pulsed-laser evaporation setup. One rate-limiting process accounts essentially for all relevant gas-pressure dependencies and can be quantitatively described using a single gas-specific constant. One thermally activated process is related to fullerene formation, whereas another process, following a T2-law, is discussed in terms of the diffusion of carbon through molten catalyst nanoparticles. The data provide strong support for an “undercooled melt” mechanism of nanotube formation.

METAL ATOMS IN CARBON NANOTUBES AND RELATED NANOPARTICLES

The paper reviews the present state of research in the field of metal-carbon nanocomposites and the interaction of metal atoms with graphitic structures. Metal crystals can be encapsulated within graphitic shells of cylindrical, spherical, or other geometry. Various chemical and physical production methods to generate metal containing carbon nanotubes and possible microscopic formation mechanisms are presented. In this context, the role of metals as catalysts in the formation of single-walled carbon nanotubes is discussed. The interaction of metal atoms with the graphitic lattice is of particular interest. In situ electron microscopy is used to study the behaviour of individual metal atoms in a graphitic lattice. Furthermore, novel nanostructures can be generated under electron irradiation. Finally, an overview of theoretical studies using molecular dynamics and tight binding calculations of the carbon-metal interaction is given.

A Study of the Formation of Single- and Double-Walled Carbon Nanotubes by a CVD Method

The reduction in H2/CH4 atmosphere of aluminum−iron oxides produces metal particles small enough to catalyze the formation of single-walled carbon nanotubes. Several experiments have been made using the same temperature profile and changing only the maximum temperature (800−1070 °C). Characterizations of the catalyst materials are performed using notably 57Fe Mössbauer spectroscopy. Electron microscopy and a macroscopical method are used to characterize the nanotubes. The nature of the iron species (Fe3+, α-Fe, γ-Fe−C, Fe3C) is correlated to their location in the material. The nature of the particles responsible for the high-temperature formation of the nanotubes is probably an Fe−C alloy which is, however, found as Fe3C by postreaction analysis. Increasing the reduction temperature increases the reduction yield and thus favors the formation of surface-metal particles, thus producing more nanotubes. The obtained carbon nanotubes are mostly single-walled and double-walled with an average diameter close to 2.5 nm. Several formation mechanisms are thought to be active. In particular, it is shown that the second wall can grow inside the first one but that subsequent ones are formed outside. It is also possible that under given experimental conditions, the smallest (<2 nm) catalyst particles preferentially produce double-walled rather than single-walled carbon nanotubes.

Electron emission from single-walled carbon nanotubes with sharpened bundles

We investigated the influence of grinding as a pretreatment prior to the emitter film formation of single-walled carbon nanotubes (SWNTs) on the field emission and the geometric properties of SWNTs. Field emission from emitter films composed of ground SWNTs was found to be dramatically enhanced as well as to be homogeneous and stable, compared with that from emitter films composed of unground SWNTs. Transmission electron microscopy observations showed that several SWNTs protrude from the ends of ground SWNT bundles. The improved emission current is attributed to the large field enhancement at the sharpened ends of the SWNT bundles.

Study of parameters important for the growth of single wall carbon nanotubes

Abstract We report on the production of single wall carbon nanotubes (SWNTs) using a continuous wave (cw) 10.6 μm CO 2 -laser. A wide range of experimental parameters such as the catalyst composition, the gas-atmosphere, the gas-pressure, the gas-flow, the laser-mode (continuous or pulsed) as well as the temperature environment and their influence on the formation of SWNTs has been investigated. Characterization of the produced SWNT material by various techniques shows the importance of two parameters: the metal in the target rod and the temperature environment for the evaporated carbon and metal species acting as feedstock for the formation of SWNTs. These results will help to develop a controlled and efficient method for the production of SWNTs.

Impact of catalyst coarsening on the formation of single-wall carbon nanotubes

The single-wall carbon nanotube (SWCN) yield as a function of the gas flow velocity for different catalyst contents in a furnace-based pulsed laser evaporation method is shown to depend sensitively on the size distribution and growth conditions of the condensed catalyst nanoparticles in the gas phase. In particular, accelerated particle coarsening should be avoided. Consequently, a high number density of small catalyst nanoparticles leads to a high nanotube yield within the timescale of a few hundred milliseconds. Hence, the attainment of enhanced particle growth control will enable a high yield evaporation-based synthesis of high-quality SWCNT.

Growth mechanisms for single-wall carbon nanotubes in a laser-ablation process

Mechanisms proposed in the literature are compared with a current scenario for the formation of single-wall carbon nanotubes in the laser-ablation process that is based on our spectral emission and laser-induced fluorescence measurements. It is suggested that the carbon which serves as feedstock for nanotube formation not only comes from the direct ablation of the target, but also from carbon particles suspended in the reaction zone. Fullerenes formed in the reaction zone may be photo-dissociated into C2 and other low molecular weight species, and also may serve as feedstock for nanotube growth. Confinement of the nanotubes in the reaction zone within the laser beam allows the nanotubes to be ‘purified’ and annealed during the formation process by laser heating.

Dissolution of Full-Length Single-Walled Carbon Nanotubes

Full-length single-walled carbon nanotubes (SWNTs) were rendered soluble in common organic solvents by noncovalent (ionic) functionalization of the carboxylic acid groups present in the purified SWNTs. Atomic force microscopy (AFM) showed that the majority of the SWNTs ropes were exfoliated into small ropes (2−5 nm in diameter) and individual nanotubes with lengths of several micrometers during the dissolution process. The combination of multiwavelength laser excitation Raman scattering spectroscopy and solution-phase visible and near-infrared spectroscopies was used to characterize the library of SWNTs that is produced in current preparations. The average diameter of metallic nanotubes was found by Raman spectroscopy to be smaller than that of semiconducting nanotubes in the various types of full-length SWNT preparations. This observation sheds new light on the mechanism of SWNT formation.

In Situ Laser-Furnace TOF Mass Spectrometry of C36and the Large-Scale Production by Arc-Discharge

A greatly improved synthesis of C36, obtained as its hydrides C36H4 and C36H6 and oxyhydrides C36H4O and C36H6O, via a high- temperature laser vaporization (laser-furnace) method and the conventional DC arc-discharge method is reported. We have found that doping metal catalysts such as Ni/Co or Ni/Y into the laser target graphite rod or the DC arc-discharge electrode, respectively, significantly enhanced the production of C36 species; the methods have been known for efficient production methods of single-wall carbon nanotubes (SWNTs). The results suggest that the catalytic formation of C36 species and SWNTs is closely related with each other in their early stage of formation. Furthermore, a molecular C36H6 gives C18H3 (m/z = 219) as a magic fragment upon desorption/ionization. By using a high-performance liquid chromatography (HPLC), C36H6 was purified (99%) in milligram quantity for the first time. The purified C36H6 exists as a cluster-assembled material such as oligomers or clusters in the solid state,...