Synthesis Of Single-walled Carbon Nanotubes Research Articles

Extended alcohol catalytic chemical vapor deposition for efficient growth of single-walled carbon nanotubes thinner than (6,5)

We performed a comprehensive exploration on alcohol catalytic chemical vapor deposition (ACCVD) synthesis of single-walled carbon nanotubes (SWCNTs), and with more than 70 temperature-pressure sets, we presented an extended ACCVD parametric map that covers a wide range of temperature from 340 to 950 °C and a wide pressure range over 6 orders of magnitude. Efficient synthesis of high quality SWCNTs becomes possible at temperatures down to 400 °C and pressure as low as 10−2 Pa, which benefits from the strong correlation between temperature and pressure newly discovered in this exploration. The underlying mechanism is clarified through a kinetic model, and two growth boundaries on the extended experimental map are explained by a transfer-free transmission electron microscopy (TEM) observation. Most importantly, after extending growth window of ACCVD, successful synthesis at extreme low temperature and pressure gives a significantly enhanced yield for super-small diameter SWCNTs (0.8 nm > dt > 0.62 nm) thinner than (6, 5) that are rarely observed from direct synthesis.

Investigation of growth dynamics of carbon nanotubes.

The synthesis of single-walled carbon nanotubes (SWCNTs) with defined properties is required for both fundamental investigations and practical applications. The revealing and thorough understanding of the growth mechanism of SWCNTs is the key to the synthesis of nanotubes with required properties. This paper reviews the current status of the research on the investigation of growth dynamics of carbon nanotubes. The review starts with the consideration of the peculiarities of the growth mechanism of carbon nanotubes. The physical and chemical states of the catalyst during the nanotube growth are discussed. The chirality selective growth of nanotubes is described. The main part of the review is dedicated to the analysis and systematization of the reported results on the investigation of growth dynamics of nanotubes. The studies on the revealing of the dependence of the growth rate of nanotubes on the synthesis parameters are reviewed. The correlation between the lifetime of catalyst and growth rate of nanotubes is discussed. The reports on the calculation of the activation energy of the nanotube growth are summarized. Finally, the growth properties of inner tubes inside SWCNTs are considered.

Influence of Mo or Cu doping in Fe/MgO catalyst for synthesis of single-walled carbon nanotubes by catalytic chemical vapor deposition of methane

ABSTRACTA series of mono-, bi- or tri-metallic Fe–Mo-Cu/MgO catalysts with the same metal loading of 6 wt% were prepared by impregnation method and used as catalysts for synthesis single-walled carbon nanotubes (SWCNTs) via methane decomposition. XRD, H2-TPR, and nitrogen physisorption techniques were used to characterize the freshly calcined catalysts, while HRTEM, Raman spectroscopy and TGA were employed to investigate the morphology and microstructure of the SWCNTs product. The obtained results indicated that the introduction of Mo or Cu in the Fe/MgO catalyst enhanced the catalytic growth activity. TEM images showed that both bundles and isolated SWCNTs were obtained over Mo containing catalysts, whereas only SWCNTs bundles were grown over the Fe-Cu/MgO catalyst. The obtained SWCNTs having a diameter of around 0.9–2.4 nm. Raman analysis illustrated that all promoted catalysts produced high quality of SWCNTs compared to the unpromoted Fe/MgO catalyst.

Spiral Countercurrent Chromatography Enrichment, Characterization, and Assays of Carbon Nanotube Chiralities for Use in Biosensors.

Single-walled carbon nanotubes (SWCNTs) are synthetic materials that hold great promise for electronics that are smaller and more versatile than the current silica-based technologies. But as-produced SWCNTs are generally a mixture of nanotubes with different structures that have vastly different properties. Separating these SWCNTs from multiwalled and metallic carbon nanotubes is vital to explore their individual properties and commercial utility ranging from optics to semiconductors. Compounding the problem of commercial investigation is that the semiconducting SWCNTs are also a mixture of different diameters and/or chiralities with different properties. Analyzing properties of enriched semiconducting SWCNT chiralities has only recently been possible through separation techniques such as aqueous two-phase solvent systems. Our study illustrates a semipreparative spiral countercurrent chromatography (CCC) separation of a commercial mixture of SWCNTs into distinct enriched fractions. A new mixer–settler spiral disk rotor was applied in this study, in which we compare the enriched SWCNTs for their effectiveness in biosensors with a high-throughput model assay, followed by antibody-mediated detection of Escherichia coli. Our results demonstrate that CCC-enriched responsive SWCNTs for biosensors can be used in our model assay, as well as for the detection of E. coli. To date, we believe that this is the first study along with Liu et al. [Chirality-controlled synthesis of single-wall carbon nanotubes using vapour-phase epitaxy. Nat. Commun.2012, 3, 119923149724] to demonstrate a specific utility of separated SWCNT species.

Characteristics of optical emissions of arc plasma processing for high-rate synthesis of highly crystalline single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) were synthesized with a high growth rate using an arc plasma employing carbon electrodes with a Ni–Y mixture catalyst. However, the mechanism of growth of highly crystalline SWNTs has not been clarified. Reactions between carbon and catalyst are considered to be one of the crucial factors in SWNT growth. Optical emission spectroscopy (OES) provides the information about the species in the plasma. C2, Ni, and Y emissions in the arc plasma at different currents were measured to investigate the relationship between active species in the arc plasma and the SWNT synthesis. On the basis of OES results, it was found that the balance between catalytic metal atoms and C2 radical emissions indicated the crystallinity ratio of SWNTs in thin graphitic or amorphous carbon layers. These results are useful for controlling the growth of SWNTs employing arc plasmas.

Low temperature growth of single-walled carbon nanotubes from Rh catalysts

Here, we carried out synthesis of single-walled carbon nanotubes (SWCNTs) in an ultra-high vacuum chamber by alcohol catalytic chemical vapor deposition (ACCVD) using Rh nanoparticles as catalysts. By optimizing the ethanol pressure precisely, we succeeded in growth of good-quality SWCNTs at 270 °C, which is a record of the lowest temperature for the SWCNT growth. The activation energy for SWCNT growth from Rh catalysts was estimated to be 0.85 eV, which was much smaller than that reported for SWCNT growth by ACCVD using CoMo catalysts. This low activation barrier of Rh catalysts should enable the reduction of growth temperature.

Chirality-Controlled Synthesis and Applications of Single-Wall Carbon Nanotubes

Preparation of chirality-defined single-wall carbon nanotubes (SWCNTs) is the top challenge in the nanotube field. In recent years, great progress has been made toward preparing single-chirality SWCNTs through both direct controlled synthesis and postsynthesis separation approaches. Accordingly, the uses of single-chirality-dominated SWCNTs for various applications have emerged as a new front in nanotube research. In this Review, we review recent progress made in the chirality-controlled synthesis of SWCNTs, including metal-catalyst-free SWCNT cloning by vapor-phase epitaxy elongation of purified single-chirality nanotube seeds, chirality-specific growth of SWCNTs on bimetallic solid alloy catalysts, chirality-controlled synthesis of SWCNTs using bottom-up synthetic strategy from carbonaceous molecular end-cap precursors, etc. Recent major progresses in postsynthesis separation of single-chirality SWCNT species, as well as methods for chirality characterization of SWCNTs, are also highlighted. Moreover, we discuss some examples where single-chirality SWCNTs have shown clear advantages over SWCNTs with broad chirality distributions. We hope this review could inspire more research on the chirality-controlled preparation of SWCNTs and equally important inspire the use of single-chirality SWCNT samples for more fundamental studies and practical applications.

The double-edged effects of annealing MgO underlayers on the efficient synthesis of single-wall carbon nanotube forests.

Recently, the millimetre-scale, highly efficient synthesis of single-wall carbon nanotube (SWCNT) forests from Fe catalysts has been reported through the annealing of the magnesia (MgO) underlayer. Here, we report the double-edged effects of underlayer annealing on the efficiency and structure of the SWCNT forest synthesis through a temperature-dependent examination. Our results showed that the efficiency of the SWCNT forests sharply increased with increased underlayer annealing temperatures from 600 °C up to 900 °C due to a temperature-dependent structural modification, characterized by increased grain size and reduced defects, of the MgO underlayer. Beyond this temperature, the SWCNT fraction also decreased as a result of further structural modification of the MgO underlayer. This exemplifies the double-edged effects of annealing. Specifically, for underlayer annealing below 600 °C, the catalyst subsurface diffusion was found to limit the growth efficiency, and for excessively high underlayer annealing temperatures (>900 °C), catalyst coalescence/ripening led to the formation of double-wall carbon nanotubes. As a result, three distinct regions of synthesis were observed: (i) a "low yield" region below a threshold temperature (∼600 °C); (ii) an "increased yield" region from 600 to 900 °C, and (iii) a "saturation" region above 900 °C. The efficient SWCNT forest synthesis could only occur within a specific annealing temperature window as a result of this double-edged effects of underlayer annealing.

Single-Walled Carbon Nanotubes-Modified Gold Electrode for Dopamine Detection

Modification of gold electrode using single-walled carbon nanotubes (SWCNTs) has been done. The synthesis of SWCNTs on the gold electrode surfaces was carried out using chemical vapor deposition (CVD) method. The performance of the electrodes as a sensor was characterized using dopamine (DA) solution at pH 4 by cyclic voltammetry. A change in electrode capacitance was found before and after DA detection. The detection limit and sensitivity of the electrodes are 0.79 μM and 3.414 μA mm−2 μM−1, respectively. No interference signal was found from ascorbic acid (AA) during DA measurement.

Chirality-dependent growth of single-wall carbon nanotubes as revealed inside nano-test tubes.

Growth dynamics of single-wall carbon nanotubes (SWCNTs) have been studied with nickelocene as a precursor encapsulated in the interior of template SWCNTs. By means of multi-laser Raman spectroscopy, growth curves of nine different SWCNTs, (8,8), (12,3), (13,1), (9,6), (10,4), (11,2), (11,1), (9,3) and (9,2), have been determined upon in situ annealing at various temperatures. The data reveal that the nanotubes grow through fast and slow reaction pathways with high and low activation energies, respectively. While the activation energy of the slow growth is independent of the nanotube's chiral vector, that of the fast growth exhibits a monotonic increase as the tube diameter reduces from ∼1.1 down to 0.8 nm and no dependency on the chiral angle, which can be attributed to the size-dependent properties of catalyst clusters. The chirality dependent catalytic growth properties exploited in this study provide the basis for a large-scale synthesis of single-chiral vector SWCNTs.

Preparation of Horizontal Single-Walled Carbon Nanotubes Arrays.

The synthesis of SWNTs has achieved great success with the development of synthetic methodologies. From the viewpoint of exploiting the exceptional electrical properties of single-walled carbon nanotubes (SWNTs) in advanced applications, one of the most difficult challenges is how to assemble the SWNTs with high degrees of alignment and purity in electronic conducting (mainly semiconducting) behavior into functional nanodevices. Numerous approaches have been developed to reach this goal, which could be divided into two categories. One is direct preparation of SWNT arrays on the substrate, and the other is self-assembly of pre-sorted SWNTs from solution. The former one obtains SWNT arrays via chemical vapor deposition (CVD) growth, with the sorting realized by either selective growth or post-growth treatment; the latter one assembles SWNT into arrays from solution, with the sorting process occurring before the aligning process in most cases. This review will highlight both in situ and post-synthetic approaches for preparing samples of aligned arrays of SWNTs with well-defined electronic properties-including the working mechanism for directional growth of SWNTs, growth/sorting methods like catalyst engineering, cloning/cap engineering, in situ etching, and ex situ selective removal/etching for surface-grown SWNT sample, and assembling technologies from SWNT solution such as dielectrophoresis, adsorption on lithographically patterned and/or chemically functionalized substrates, Langmuir-Blodgett and Langmuir-Schaefer techniques, and evaporation-driven self-assembly-and research efforts towards direct growth of arrays of complex SWNT structures.

Autonomy in materials research: a case study in carbon nanotube growth

AbstractAdvances in materials are an important contributor to our technological progress, and yet the process of materials discovery and development itself is slow. Our current research process is human-centred, where human researchers design, conduct, analyse and interpret experiments, and then decide what to do next. We have built an Autonomous Research System (ARES)—an autonomous research robot capable of first-of-its-kind closed-loop iterative materials experimentation. ARES exploits advances in autonomous robotics, artificial intelligence, data sciences, and high-throughput and in situ techniques, and is able to design, execute and analyse its own experiments orders of magnitude faster than current research methods. We applied ARES to study the synthesis of single-walled carbon nanotubes, and show that it successfully learned to grow them at targeted growth rates. ARES has broad implications for the future roles of humans and autonomous research robots, and for human-machine partnering. We believe autonomous research robots like ARES constitute a disruptive advance in our ability to understand and develop complex materials at an unprecedented rate.

Changing the chirality of single-wall carbon nanotubes during epitaxial growth : A density functional theory study

The energetic of the change in the chirality of single-wall carbon nanotubes (SWCNTs)during epitaxial growth from (n, m) to (n±Δ, mΔ)(Δ=1, 2) was investigated by density functional theory calculations. The calculated energies for changing the chirality of different SWCNTs show a nearly linear decrease with decreasing tube diameter. In the case ofΔ=1, more energy input is needed for near armchair (nAC) SWCNTs to change their chiralities than those for near zigzag (nZZ) SWCNTs with comparable diameters, due to the larger formation energies of pentagon-heptagon defects (5,7-defects) introduced in the nAC-SWCNTs. These larger formation energies for the nAC-SWCNTs come from the larger angles between the orientation of a 5,7-defect and the tube axis than those for nZZ-SWCNTs. The topological connection oftwo adjacent 5,7-defects, which is indispensable for changing the chirality during growth in the case of Δ=2, is found to be energetically most stable. The energies needed to change chirality in the case of Δ=2 are calculated to be less than twice those in the case of Δ=1 for SWCNTs with comparable diameters. These results may help us understand the change in chirality during the epitaxial growth of SWCNTs and guide the future synthesis of SWCNTs with a single-chirality .

Fabrication of 3D carbon nanotube networks

We report on the synthesis and characterization of a hyperbranched polymer englobing single-wall carbon nanotubes (SWCNTs). This new material was obtained by using SWCNTs functionalized with carboxylic groups as starting reagent. The acid groups were firstly converted in acyl chloride moieties and afterwards were bound to hexamethylenediamine (HMDA) via formation of amide functionality. The acquired spectra of attenuated total reflectance and the analysis performed through x-ray photoelectron spectroscopy confirmed the amide bond formation. The hyperbranched polymer characterization was completed by using scanning and transmission electron microscopy, thermo-gravimetric analysis and Raman spectroscopy. The electron microscopy analyses showed the formation of an amorphous polymeric material englobing a dense network of SWCNTs without phase segregation, demonstrating that the reaction with HMDA allows a reorganization of SWCNTs in a complex three-dimensional network.

ChemInform Abstract: Controlled Growth of Semiconducting and Metallic Single‐Wall Carbon Nanotubes

AbstractReview: 69 refs.

Controlled Growth of Semiconducting and Metallic Single-Wall Carbon Nanotubes.

Single-wall carbon nanotubes (SWCNTs) can be either semiconducting or metallic depending on their chiral angles and diameters. The use of SWCNTs in electronics has long been hindered by the fact that the as-prepared SWCNTs are usually a mixture of semiconducting and metallic ones. Therefore, controlled synthesis of SWCNTs with a uniform electrical type or even predefined chirality has been a focus of carbon nanotube research in recent years. In this Perspective, we summarize recent progress on the controlled growth of semiconducting and metallic SWCNTs by in situ selective etching and by novel catalyst design. The advantages and mechanisms of these approaches are analyzed, and the challenges are discussed. Finally, we predict possible breakthroughs and future trends in the controlled synthesis and applications of SWCNTs.

Chemical vapor deposition synthesis of near-zigzag single-walled carbon nanotubes with stable tube-catalyst interface

Chemical vapor deposition (CVD) growth is regarded as the most promising method for realizing structure-specific single-walled carbon nanotube (SWNT) growth. In the past 20 years, many efforts dedicated to chirality-selective SWNT growth using various strategies have been reported. However, normal CVD growth under constant conditions could not fully optimize the chirality because the randomly formed cap structure allows the nucleation of all types of SWNTs and the chirality of an SWNT is unlikely to be changed during the following elongation process. We report a new CVD process that allows temperature to be periodically changed to vary SWNT chirality multiple times during elongation to build up the energetically preferred SWNT-catalyst interface. With this strategy, SWNTs with small helix angles (less than 10°), which are predicted to have lower interfacial formation energy than others, are enriched up to ~72%. Kinetic analysis of the process suggests a multiple redistribution feature whereby a large chiral angle SWNT tends to reach the near-zigzag chirality step by step with a small chiral angle change at each step, and hence, we named this method "tandem plate CVD." This method opens a door to synthesizing chirality-selective SWNTs by rational catalyst design.

Enhanced cold wall CVD reactor growth of horizontally aligned single-walled carbon nanotubes

Synthesis of horizontally-aligned single-walled carbon nanotubes (HA-SWCNTs) by chemical vapor deposition (CVD) directly on quartz seems very promising for the fabrication of future nanoelectronic devices. In comparison to hot-wall CVD, synthesis of HA-SWCNTs in a cold-wall CVD chamber not only means shorter heating, cooling and growth periods, but also prevents contamination of the chamber. However, since most synthesis of HA-SWCNTs is performed in hot-wall reactors, adapting this well-established process to a cold-wall chamber becomes extremely crucial. Here, in order to transfer the CVD growth technology from a hot-wall to a cold-wall chamber, a systematic investigation has been conducted to determine the influence of process parameters on the HA-SWCNT’s growth. For two reasons, the cold-wall CVD chamber was upgraded with a top heater to complement the bottom substrate heater; the first reason to maintain a more uniform temperature profile during HA-SWCNTs growth, and the second reason to preheat the precursor gas flow before projecting it onto the catalyst. Our results show that the addition of a top heater had a significant effect on the synthesis. Characterization of the CNTs shows that the average density of HA-SWCNTs is around 1-2 tubes/μm with high growth quality as shown by Raman analysis.

Synthesis and cryogenic spectroscopy of narrow-diameter single-wall carbon nanotubes

We report chemical vapor deposition and cryogenic photoluminescence studies of narrow-diameter single-wall carbon nanotubes. Our systematic study of synthesis parameters identifies means to control the average length, diameter, and areal density of carbon nanotubes grown on silica substrates. Using synthesis conditions that favor the growth of carbon nanotubes with sub-nanometer diameters, we fabricate samples with spatially isolated suspended nanotubes ideally suited for optical studies. Photoluminescence spectroscopy of individual nanotubes reveals two classes: spectrally broad and narrow single-peak emission at the temperature of liquid helium. The latter class with spectral line widths down to the resolution limit of our spectrometer of 40 μeV indicates that exciton coherence in carbon nanotubes can be substantially improved by controlling the growth conditions and utilized in sources of indistinguishable single photons.

(Invited) Bulk Synthesis of Oxygen-Doped Single-Walled Carbon Nanotubes and Their Application As Fluorescent Probes

It has been found that the photoluminescence (PL) efficiency of single-walled carbon nanotubes (SWCNTs) can be enhanced by substituting oxygen atoms to the carbon network of the tube wall [1]. The oxygen-doped SWCNTs (o-SWCNTs) have been mostly prepared by the exposure of ozone to the SWCNTs solution under the light. This method can provide only a small amount of o-SWCNTs, and the surfactants are normally adsorbed on the surface of the obtained o-SWCNTs, which prevents further applications of the material. Recently, we found a very simple method for obtaining o-SWCNTs in bulk. In this meeting, the synthesis method and the characterization of the o-SWCNTs, and their application as in-vivo and in-vitro near-infrared imaging probes will be reported. 1. S. Ghosh, S. M. Bachilo, R. A. Simonette, K. M. Beckingham, R. B. Weisman, Science, 330, 1656 (2010).