Diameter Distribution Of Single-walled Carbon Nanotubes Research Articles

Towards the preparation of single-walled carbon nanotubes with average diameter of 1.2 nm

Preparation of single-walled carbon nanotubes (SWNTs) with diameters ranging from 1.2 to 1.5 nm has been highly demanded for field-effect transistors with superior properties. In the work, we report the chemical vapor deposition synthesis of SWNTs with an average diameter of 1.2 nm from a rationally designed nickel catalyst supported by magnesia. The high metal dispersion, the suitable reaction temperature, and the use of a methane carbon source co-determine the SWNT diameter distribution. Furthermore, through the synergistic application of poly(9,9-dioctylfluorene-2,7-diylalt-pyridine-2,6-diyl) wrapping and ultracentrifugation, SWNTs with enriched (10,8) species of 1.24 nm are successfully extracted, which is attributed to the selective interaction between the polymer molecules and the targeted SWNTs. This work not only sheds light on the growth of SWNTs with relatively large diameter, but also paves the way towards the preparation of high purity (n,m) species that could meet the requirements of advanced high-tech applications.

Growth modes of single-walled carbon nanotubes on catalysts.

Understanding the growth mechanism of single-walled carbon nanotubes (SWCNTs) and achieving selective growth requires insights into the catalyst structure-function relationship. Using an in situ aberration-corrected environmental transmission electron microscope, we reveal the effects of the state and structure of catalysts on the growth modes of SWCNTs. SWCNTs grown from molten catalysts via a vapor-liquid-solid process generally present similar diameters to those of the catalysts, indicating a size correlation between nanotubes and catalysts. However, SWCNTs grown from solid catalysts via a vapor-solid-solid process always have smaller diameters than the catalysts, namely, an independent relationship between their sizes. The diameter distribution of SWCNTs grown from crystalline Co7W6, which has a unique atomic arrangement, is discrete. In contrast, nanotubes obtained from crystalline Co are randomly dispersed. The different growth modes are linked to the distinct chiral selectivity of SWCNTs grown on intermetallic and monometallic catalysts. These findings will enable rational design of catalysts for chirality-controlled SWCNTs growth.

Side group of poly(3-alkylthiophene)s controlled dispersion of single-walled carbon nanotubes for transparent conducting film.

Controlled dispersion of single-walled carbon nanotubes (SWCNTs) in common solvents is a challenging issue, especially for the rising need of low cost flexible transparent conducting films (TCFs). Utilizing conductive polymer as surfactant to facilitate SWCNTs solubility is the most successful pragmatic approach to such problem. Here, we show that dispersion of SWCNT with polymer significantly relies on the length of polymer side groups, which not only influences the diameter distribution of SWCNTs in solution, also eventually affects their effective TCF performance. Surfactants with longer side groups covering larger nanotube surface area could induce adequate steric effect to stabilize the wrapped SWCNTs against the nonspecific aggregation, as discerned by the optical and microscopic measurements, also evidenced from the resultant higher electrokinetic potential. This approach demonstrates a facile route to fabricate large-area SWCNTs-TCFs exhibiting high transmittance and high conductivity, with considerable uniformity over 10 cm × 10 cm.

Importance of diameter control on selective synthesis of semiconducting single-walled carbon nanotubes.

The coexistence of semiconducting and metallic single-walled carbon nanotubes (SWNTs) during synthesis is one of the major bottlenecks that prevent their broad application for the next-generation nanoelectronics. Herein, we present more understanding and demonstration of the growth of highly enriched semiconducting SWNTs (s-SWNTs) with a narrow diameter distribution. An important fact discovered in our experiments is that the selective elimination of metallic SWNTs (m-SWNTs) from the mixed arrays grown on quartz is diameter-dependent. Our method emphasizes controlling the diameter distribution of SWNTs in a narrow range where m-SWNTs can be effectively and selectively etched during growth. In order to achieve narrow diameter distribution, uniform and stable Fe-W nanoclusters were used as the catalyst precursors. About 90% of as-prepared SWNTs fall into the diameter range 2.0-3.2 nm. Electrical measurement results on individual SWNTs confirm that the selectivity of s-SWNTs is ∼95%. The present study provides an effective strategy for increasing the purity of s-SWNTs via controlling the diameter distribution of SWNTs and adjusting the etchant concentration. Furthermore, by carefully comparing the chirality distributions of Fe-W-catalyzed and Fe-catalyzed SWNTs under different water vapor concentrations, the relationship between the diameter-dependent and electronic-type-dependent etching mechanisms was investigated.

Synthesis of high quality single-walled carbon nanotubes with purity enhancement and diameter control by liquid precursor Ar–H2 plasma spraying

• A new plasma process is proposed for the synthesis of SWCNTs at a large-scale. • High-quality SWCNTs were produced due to the high temperature of the plasma. • Hydrogen plasma contributes to the purity enhancement by selective etching of amorphous carbon. • The in situ diameter control is demonstrated by adjusting the sulfur content in the feedstock. As usage of carbon nanotubes continues to increase in both scientific research and practical applications, there has been a growing interest in the large-scale synthesis of those materials with high quality and high purity. Here we report a new plasma process developed for the large-scale synthesis of high quality single-walled carbon nanotubes (SWCNTs). An induction thermal plasma with a liquid precursor spraying technique was employed for an effective synthesis of SWCNTs from a mixture of toluene and ferrocene. It has been successfully demonstrated in this new process that high quality SWCNTs can be synthesized continuously with a reasonably high-purity, the structural quality of the materials produced being comparable to those of SWCNTs produced from the laser vaporization process. The high temperature of the plasma, over 4000 K, seems to be responsible for the production of high quality SWCNTs and the rapid treatment of a large amount of feedstock, whereas the hydrogen plasma contributes to the purity enhancement by selective etching of amorphous carbon. It is also found that the diameter distribution of SWCNTs can be controlled effectively by varying the sulfur content in the feedstock mixture, which is very promising for many advanced applications of SWCNTs such as SWCNT-based electronics.

Invited Presentation: Charge Generation and Recombination in SWCNT Photovoltaic Active Layers

Single-walled carbon nanotubes (SWCNTs) have many attractive properties for conversion of sunlight into electricity or solar fuels. In solar conversion schemes where SWCNTs are used as absorptive charge donors, it is critical to understand the processes by which initially created excitons are dissociated to produce free charges. In this presentation, I’ll discuss time-resolved spectroscopy studies exploring how photogenerated excitons produce charges in both neat SWCNT films and bilayer heterojunctions designed to dissociate photogenerated SWCNT excitons. In neat SWCNT films, we find charge generation yields of several percent even in the absence of an intentional exciton dissociation interface. We use a thin film of C60 to dissociate SWCNT excitons by interfacial electron transfer from films containing a variety of SWCNT chirality combinations. In these “bilayer” PV active layers, exciton dissociation efficiency varies with the thermodynamic driving force for electron transfer, as well as a number of morphological bilayer properties. Charge mobility and recombination also vary dramatically with bilayer morphology and the diameter distribution of SWCNTs within the film. I will discuss our current understanding of the mechanisms for charge generation and recombination in both neat and bilayer films, and how this understanding helps us envision ways to improve upon SWCNT PV active layers.

Increase in the yield of (and selective synthesis of large-diameter) single-walled carbon nanotubes through water-assisted ethanol pyrolysis

Single-walled carbon nanotubes (SWCNT) were synthesized using Co-MCM-41 catalysts through water-assisted ethanol pyrolysis. The effect of varying the water to ethanol ratio in the reactant mixture was studied. The data from X-ray absorption spectroscopy indicate that with the addition of water, the cobalt metal particles were oxidized. X-ray diffraction analysis of CoCx suggests that the formation of amorphous carbon on the surface of the Co particles was suppressed. Cobalt magnetization measurements were performed to study the size and anisotropy of cobalt particles. Thermogravimetric analysis data demonstrate that with a water concentration of 7%, the yield increases by about 100% relative to pure ethanol synthesis. Raman and photoluminescence excitation spectroscopic data demonstrate that the SWCNT diameter increases (within the diameter range detected) with the water/ethanol ratio. From the statistical SWCNT diameter distribution obtained from transmission electron microscopy, 65% of the SWCNT synthesized with 20% water in ethanol have diameters larger than 1.5nm, but there is a severe decrease in yield and a modest decrease in selectivity of SWCNT. The mechanism of how the water influences the yield and diameter of SWCNT is discussed.

Diameter Tuning of Single-Walled Carbon Nanotubes by Diffusion Plasma CVD

We have realized a diameter tuning of single-walled carbon nanotubes (SWNTs) by adjusting process gas pressures with plasma chemical vapor deposition (CVD). Detailed photoluminescence measurements reveal that the diameter distribution of SWNTs clearly shifts to a large-diameter region with an increase in the pressure during plasma CVD, which is also confirmed by Raman scattering spectroscopy. Based on the systematical investigation, it is found that the main diameter of SWNTs is determined by the pressure during the heating in an atmosphere of hydrogen and the diameter distribution is narrowed by adjusting the pressure during the plasma generation. Our results could contribute to an application of SWNTs to high-performance thin-film transistors, which requires the diameter-controlled semiconductor-rich SWNTs.

Diameter-Dependent Solubility of Single-Walled Carbon Nanotubes

We study the solubility and dispersibility of as-produced and purified HiPco single-walled carbon nanotubes (SWNTs). Variation in specific operating conditions of the HiPco process are found to lead to significant differences in the respective SWNT solubilities in oleum and surfactant suspensions. The diameter distributions of SWNTs dispersed in surfactant solutions are batch-dependent, as evidenced by luminescence and Raman spectroscopies, but are identical for metallic and semiconducting SWNTs within a batch. We thus find that small diameter SWNTs disperse at higher concentration in aqueous surfactants and dissolve at higher concentration in oleum than do large-diameter SWNTs. These results highlight the importance of controlling SWNT synthesis methods in order to optimize processes dependent on solubility, including macroscopic processing such as fiber spinning, material reinforcement, and films production, as well as for fundamental research in type selective chemistry, optoelectronics, and nanophotonics.

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.

Effects of Water Vapor on Diameter Distribution of SWNTs Grown over Fe/MgO-Based Catalysts

With an interest in the H2O-assisted chemical vapor deposition (CVD) process, roles of H2O in tuning the diameter and chirality distributions of single-walled carbon nanotubes (SWNTs) were studied using Fe/MgO-based catalysts. A controlled amount of H2O was found to narrow the diameter distribution of SWNTs by reducing the populations of small- and large-diameter nanotubes. The addition timing of H2O vapor was investigated to understand the interaction between H2O and growing nanotubes or catalyst nanoparticles. Also, the addition of a small amount of Mo in the Fe/MgO catalyst was observed to reduce the diameter distribution of SWNTs, and H2O further promoted the formation of smaller-diameter SWNTs over the Fe−Mo/MgO catalyst. These results elucidate that the surface chemistry of catalyst nanoparticles exerted significant effects on the behaviors of H2O in the CVD process. Consequently, it is proposed that H2O first reacts with the surface of catalyst nanoparticle, and successively plays two aspects of ro...

Dry Contact Transfer Printing of Aligned Carbon Nanotube Patterns and Characterization of Their Optical Properties for Diameter Distribution and Alignment

A scalable and facile approach is demonstrated where as-grown patterns of well-aligned structures composed of single-walled carbon nanotubes (SWNT) synthesized via water-assisted chemical vapor deposition (CVD) can be transferred, or printed, to any host surface in a single dry, room-temperature step using the growth substrate as a stamp. We demonstrate compatibility of this process with multiple transfers for large-scale device and specifically tailored pattern fabrication. Utilizing this transfer approach, anisotropic optical properties of the SWNT films are probed via polarized absorption, Raman, and photoluminescence spectroscopies. Using a simple model to describe optical transitions in the large SWNT species present in the aligned samples, polarized absorption data are demonstrated as an effective tool for accurate assignment of the diameter distribution from broad absorption features located in the infrared. This can be performed on either well-aligned samples or unaligned doped samples, allowing simple and rapid feedback of the SWNT diameter distribution that can be challenging and time-consuming to obtain in other optical methods. Furthermore, we discuss challenges in accurately characterizing alignment in structures of long versus short carbon nanotubes through optical techniques, where SWNT length makes a difference in the information obtained in such measurements. This work provides new insight to the efficient transfer and optical properties of an emerging class of long, large diameter SWNT species typically produced in the CVD process.

Narrowing SWNT diameter distribution using size-separated ferritin-based Fecatalysts

Sensors and devices made from single-walled carbon nanotubes (SWNTs) are most oftenelectrically probed through metal leads contacting the semiconducting SWNTs (s-SWNTs).Contact barriers in general and Schottky barriers (SBs) in particular are usuallyobtained at a metal–semiconductor interface. The unique one-dimensional structure(1D) of SWNTs allows tailoring of the SB heights through the contact metaltype and the size of the s-SWNT bandgap. A large workfunction reduces the SBheight (e.g. using Pd as the metal contact material). The bandgap of an SWNT isinversely proportional to its diameter. Ohmic contacts—the preferable choice—areachieved for s-SWNTs with diameters greater than 2 nm on Pd metal leads. SWNTdevice reproducibility, on the other hand, requires a narrow distribution of theSWNT diameters. Here, we present a method to fabricate SWNTs with a large andadjustable mean diameter (1.9–2.4 nm) and very narrow diameter distribution (± 0.27 nm at mean diameter 1.9 nm). The results are achieved through a size separation of theferritin catalyst particles by sedimentation velocity centrifugation prior to their use in thechemical vapor deposition (CVD) formation of SWNTs.

Selective Diameter Control of Single-Walled Carbon Nanotubes in the Gas-Phase Synthesis

A novel approach for selective diameter control of single-walled carbon nanotubes (SWNTs) is performed in the gas-phase growth using two kinds of carbon sources with different decomposition properties; the one carbon source (1st carbon source) is the organic solvent which is difficult to decompose in the reactor and the another carbon source (2nd carbon source) is facile to decompose. The diameter distributions of SWNTs synthesized with various conditions of the flow rate of the 2nd carbon source were investigated by resonant Raman scattering, optical absorption, and photoluminescence (PL) mapping measurements. It was found that increasing the flow rate of the ethylene tends to decrease the diameter of synthesized SWNTs, probably due to the earlier nucleation of SWNTs induced by the ethylene addition. The controlling the flow rate of the ethylene used as a 2nd carbon source can selectively tune the diameter distribution of SWNTs in our growth system.

Multiple “optimum” conditions for Co–Mo catalyzed growth of vertically aligned single-walled carbon nanotube forests

Carbon nanotubes (CNTs) were grown directly on substrates by alcohol catalytic chemical vapor deposition using a Co–Mo binary catalyst. Optimum catalytic and reaction conditions were investigated using a combinatorial catalyst library. High catalytic activity areas on the substrate were identified by mapping the CNT yield against the orthogonal gradient thickness profiles of Co and Mo. The location of these areas shifted with changes in reaction temperature, ethanol pressure and ethanol flow rate. Vertically aligned single-walled CNT (SWCNT) forests grew in several areas to a maximum height of ca. 30 μm in 10 min. A pure Co catalyst yielded a vertically aligned SWCNT forest with a bimodal diameter distribution. The effects of Mo on the formation of catalyst nanoparticles and on the diameter distribution of SWCNTs are discussed and Mo as thin as a monolayer or thinner was found to suppress the broadening of SWCNT diameter distributions.

Effect of alcohol sources on synthesis of single-walled carbon nanotubes

The effect of oxidant species forming an alcohol molecule for hot-filament chemical vapor deposition (HFCVD) on single-walled carbon nanotubes (SWCNTs) growth has been investigated. To use a graphite rod as a filament for HFCVD to decompose alcohol sources, contamination-free sample surface can be obtained and SWCNTs are successively and densely grown at a lower temperature than those by conventional thermal CVD. It is found that the higher the molecule number of alcohol among CH 3OH, C 2H 5OH, and 2-C 3H 7OH is, the lower the initial growth rate of SWCNTs is. As for CH 3OH, diameter distribution of SWCNTs is dynamically changed with the growth time passed, and a negative growth rate is observed at the later stage of growth. The growth kinetics depending on the alcohol sources is discussed on the basis of a capability of the oxidant species to burn away SWCNTs and deactivation of Co catalysts used for the growth.

CVD catalytic growth of single-walled carbon nanotubes with a selective diameter distribution

Thermal pyrolysis chemical vapor deposition growth of single-walled carbon nanotubes (SWNTs) was demonstrated by using catalytic pads of nickel (3∼4 nm) and SiO 2 (100 nm) deposited by electron-beam evaporation in sequence on the thermal silicon oxide substrate. The diameters of SWNTs on the samples with upper SiO 2 layer of different deposition rates were characterized by atomic force microscopy (AFM) and micro-Raman spectroscopy. It was observed that the average diameter and density of SWNTs increased as the deposition rate of upper SiO 2 layer increased. The differences of the SWNTs diameter distribution were attributed to the differences in the curvature of the SiO 2 porous structure deposited with different deposition rates. The high-resolution transmission electron micrographs and the corresponding diffractogram showed that SWNTs with diameter as low as 0.51 nm could be found and the AFM measurements revealed that a high percentage (∼ 70%) of SWNTs of diameters lower than 1.0 nm was achieved by upper SiO 2 layer deposition rate of 0.5 Å/s, whereas bundles of SWNTs were found with higher SiO 2 deposition rates.

Influence of the substrate loading on the quality and diameter distribution of SWCNT in alcohol‐CVD

AbstractThe optimization of singlewalled carbon nanotubes (SWCNT) synthesis via chemical vapour deposition (CVD) with the use of ethanol vapor as the carbon source is presented. Alcohol CVD process for SWCNT synthesis was performed with regards to the diameter distribution and quality of the sample. In particular the influence of the concentration of the catalyst support (here MgO) was investigated. The manipulation of this process parameter led to the synthesis of bulk quantity and high purity SWCNT. We have found that an increase in the MgO concentration with respect to the catalyst showed limited dependence on the diameter distribution but did show a significant influence on the sample quality for the optimum conditions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Formation of single-wall carbon nanotubes in Ar and nitrogen gas atmosphere by using laser furnace technique

The formation of single-wall carbon nanotubes (SWNTs) by using laser vaporization technique in different ambient gas atmosphere was investigated. SWNTs were prepared with Rh/Pd (1.2/1.2 atom%)-carbon composite rod in Ar and nitrogen gas atmosphere, respectively. Raman spectra of raw carbon materials including SWNTs and photoluminescence mapping of dispersed SWNTs in a surfactant solution demonstrate that the diameter distribution of SWNTs prepared in Ar atmosphere is narrower than those obtained by using CVD technique (e.g. HiPco nanotube), even when the ambient temperature is as high as 1150 ○C. It was also found that nitrogen atmosphere gives wider diameter distribution of SWNTs than that obtained with Ar atmosphere. Furthermore, the relative yield of fullerenes (obtained as byproducts) is investigated by using HPLC (high-performance liquid chromatography) technique. It was found that the relative yield of higher fullerenes becomes lower, when nitrogen is used as an ambient gas atmosphere. Based on these experimental findings, a plausible formation mechanism of SWNTs is discussed.

Effects of composition of catalysts on the preparation of single-walled carbon nanotubes synthesized over W–Co–MgO catalysts

Abstract A series of W–Co–MgO catalysts were prepared for the first time by decomposing a mixture of magnesium nitrate, ammonium paratungstate, citric acid, and cobalt nitrate. Single-walled carbon nanotubes (SWCNTs) were synthesized over these W–Co–MgO catalysts and the effects of the quantity of metal in the catalysts on the synthesis of SWCNTs were investigated by Raman spectroscopy and transmission electron microscopy (TEM). The results show that, among W–Co–MgO catalysts, the W1–Co5 catalyst was found to be most effective for synthesizing SWCNTs. The diameter distribution of as-grown SWCNTs prepared over the W1–Co5 catalyst was estimated to range from 0.72–1.64 nm. When the molar ratios of W:MgO and Co:MgO in the catalysts are more than 2:100 and 5:100, respectively, the amorphous carbon content or defect concentration of SWCNTs may be increased with the increase of the quantity of metal in the catalysts. The dependence of the diameter distribution of SWCNTs on the quantity of W in the catalysts is small. However, the proportion of SWCNTs with larger diameter is increased as the quantity of Co in the catalysts is increased owing to the increase in the number of larger active sites.