As-grown Single-walled Carbon Nanotubes Research Articles

Controlled growth of single-walled carbon nanotubes with narrow diameter distribution and high areal density on Mn-doped ZrO2-supported Fe catalyst

Single-walled carbon nanotubes (SWCNTs) with a narrow diameter distribution and high areal density hold great promise for a variety of applications, particularly in advanced electronics and biomedical devices. This study utilizes Mn ion doping as a strategic approach both to stabilize the ZrO2-supported Fe catalyst and regulate lattice oxygen release, thereby facilitating the growth of SWCNTs with high areal density and a narrow diameter distribution. The ZrO2-supported Fe catalyst was meticulously dispersed on Si/SiO2 (300 nm) substrates through the optimization of spin-coating speed and solvent viscosity, aiming to enhance the dispersion and uniformity. Investigation into the precise control over the Mn ion content was conducted to regulate the structure and stability of the Mn-doped ZrO2-supported Fe catalyst. Mn ions perform a dual role: they maintain a higher proportion of ZrO2 in the monoclinic phase, which in turn alleviates the monoclinic-tetragonal phase transition during chemical vapor deposition (CVD) growth. Concurrently, the conversion of Mn3+ to Mn4+ ions captures the lattice oxygen released during the formation of zirconium transition oxides. Additionally, first-principles simulations have confirmed the stabilizing impact of Mn ions on the catalyst, which reduces aggregation and maturation, ultimately resulting in a more concentrated diameter distribution of as-grown SWCNTs. This approach has successfully achieved the controlled growth of high areal density SWCNTs with a diameter distribution of 1.73 ± 0.08 nm.

Optoelectronic Characterization and Properties of Single-walled Carbon Nanotubes in a Liquid Dispersion Form

Carbon nanotubes (CNTs) are very promising nanodevices due to their extraordinary electrical, thermal, and optical properties. However, as-grown single-walled CNTs (SWCNTs) contain a mixture of semiconducting and metallic species with great featur

High energy density flexible and ecofriendly lithium-ion smart battery

The rapidly growing battery market demands both high energy density and waste-management solutions for the anticipated global annual battery waste of about two million metric tons. To address the energy-environment dilemma, we developed self-standing composite electrodes for Li-ion batteries without electrochemically inactive metal current collectors, additives, and binders, increasing energy density by up to 40%. The electrodes were prepared via in situ mixing of as-grown single-wall carbon nanotubes (SWNTs) with aerosolized electrode active materials, leading to adequate electrical conductivity and mechanical robustness. The SWNT scaffold exhibits a piezoresistive effect, with resistance depending on the voltage-weighted number of inter-nanotube contacts. We exploit this intrinsic piezoresistance of SWNT network for operando self-monitoring of battery structural health. The proposed solution-free battery fabrication technology and architecture eliminates environmentally harmful components and enables recycling by simple mechanical separation, aiming at safety and circular economy.

(Invited) High Energy Density and Ecofriendly Lithium-Ion Battery with Operando Monitoring

In addition to recent worldwide renewable energy commitments, advances in electrical vehicle technologies, flexible electronics, smart wearable devices, and internet of things, have contributed to the increasing demand for batteries with a wide range of electrochemical and electromechanical properties. In response, the battery industry has launched intensive research and development efforts in search for new materials, technologies, and concepts. However, these rapid developments give rise to a growing concern on the impact of this industry on Nature. Hence, the rapidly growing battery market demands resolutions for both energy and waste-management challenges in anticipation of about two million metric tons of annual battery waste generated globally. One way to resolve this energy and environment dilemma is by revising the conventional battery architecture to assure both high energy density and efficient recyclability aiming at circular economy. Within this strategy we fabricated self-standing composite electrodes that eliminated electrochemically inactive metal current collectors and binders from the Li-ion battery architecture, increasing energy density up to 40%. These electrodes were prepared via in situ mixing of as-grown single-wall carbon nanotubes (SWNTs) with aerosolized electrode active materials in ratios (≥0.25 wt%) that provide adequate electrical conductivity and mechanical robustness under stretching (≤15%), bending (d≥2 mm) and twisting (θ~180o) cycles. Remarkably, the resultant SWNT scaffold in composite electrodes operates as an intrinsic piezoresistive strain sensor (Gauge Factor ~6.2) that for the first time allows in situ/operando self-monitoring of battery structural health without interfering with electrochemical reactions. Moreover, the developed solution-free fabrication method eliminates hazardous, toxic, and environmentally harmful components and procedures from the electrode production line and allows their recycling by simple sonication and recovering of the active materials. In addition, the absence of current collector foils and binder allows for easy recycling and recovery of the constituent materials by using physical separation methods. These new features not only reduce consumption of the natural resources but also promote the eco-friendly circular economy for batteries.

Large thermoelectric power factor in wafer-scale free-standing single-walled carbon nanotube films

Single-walled carbon nanotubes (SWCNTs) have the potential for application in thermoelectric energy generators owing to their advantages, such as good charge-carrier transport properties, mechanical flexibility and robustness, and tunability of polarity. However, the fabrication of SWCNTs still remains a problem due to its complexity and high cost. In this paper, we propose an approach for the direct formation of free-standing SWCNT films from as-grown SWCNT mats without any dispersion or separation processes. We used this approach to develop high-performance SWCNT-based thermoelectric leg materials. The as-grown SWCNT mats were synthesized by an enhanced direct injection pyrolytic synthesis (eDIPS) method. The selectivity of the tube diameter for the eDIPS method clarified the dependence of the thermoelectric performance of the free-standing SWCNT films on the tube diameter. The Seebeck coefficients and thermal conductivities were found to correlate with the tube diameter and agreed with the theoretical predictions. Owing to the dispersion-free film formation, our SWCNT films afforded large thermoelectric power factors. In particular, a power factor of 350 μW/(m K2) was obtained for the mean tube diameter of 1.7 nm without any semiconductor extraction or doping treatments. Our approach allowed the fabrication of thermoelectric legs with an arbitrary size; thus, it offers a useful strategy for the simpler, cheaper, and low-waste manufacturing of high-performance organic thermoelectric devices.

Growth of Homogeneous High-Density Horizontal SWNT Arrays on Sapphire through a Magnesium-Assisted Catalyst Anchoring Strategy.

In-situ growth of high-density single-walled carbon nanotube (SWNT) arrays with homogeneity is highly desirable for integrated circuits. However, disastrous migration and aggregation of catalyst nanoparticles on substrate has greatly limited the area of as-grown SWNT arrays. Herein, we develop a magnesium-assisted catalyst anchoring strategy to restrain catalyst nanoparticles sintering on substrate. Magnesium modification ameliorates sapphire surface by high temperature solid reaction and thus provides a stronger metal-support interaction (SMSI). Hereby, we realize the direct growth of high-density SWNT arrays that fully cover an entire 10×10 mm2 substrate with the local highest density of ≈110 tubes μm-1 using iron as catalyst. This strategy was also proven universal when employing solid carbide catalysts.

Growth of Single-Walled Carbon Nanotubes with Controlled Structure: Floating Carbide Solid Catalysts.

Single-walled carbon nanotube (SWNT) horizontal arrays with specific chirality can be enriched using solid carbide catalysts on substrates. However, scale-up production by continuous loading of the solid catalysts onto the substrates is challenging. Described here is the preparation of a floating carbide solid catalyst (FSC) for the controlled growth of SWNTs. The FSC, titanium carbide (TiC) nanoparticle, was directly obtained in the carrier gas phase by decomposition and carbonization of the titanocene dichloride precursor at high temperature. By using the TiC nanoparticle FSC, both SWNT horizontal arrays and randomly distributed networks can be obtained. The chirality of the as-grown SWNTs were thermodynamically controlled to have fourfold symmetry. Further optimization of growth condition resulted in an abundance of (16,8) tubes with about a 74 % content. This FSC chemical vapor deposition (FSCCVD) method has potential for realizing mass growth of SWNTs with controlled structures.

Synthesis and characterization of SWCNTs/ZnO hybrid nanocomposite for sensor applications

The present work focuses on the synthesis and characterization of single walled carbon nanotubes (SWCNTs)/Zinc oxide (ZnO) hybrid nanocomposite for resistive gas sensors. Both the materials, SWCNTs and ZnO are very well recognized for their individual gas sensing properties but synthesis of ZnO/SWCNT hybrid nanocomposites constitute a low cost solution for gas sensing devices with unique properties. In this research work, SWCNTs have been grown on Iron (Fe) deposited Silicon (Si) substrate and then decorated with ZnO nanoparticles to form hybrid nanocomposites structure. The as-grown SWCNTs and its nanocomposites were analyzed using field emission scanning electron microscope (FESEM), x-ray diffractometer (XRD), high resolution transmission electron microscope (HRTEM) and Raman spectroscopy. As synthesized nanocomposites were exposed with ammonia (NH3) gas so that sensitivity of the gas can be recorded. The sensor response of as-grown SWCNTs and SWCNTs/ZnO sensor was measured to be 80%–100% and 150%–200% respectively, whereas SWCNTs/ZnO sensor response time is 4 − 5 s and recovery time is about 8–10 s, which is higher response time compared to as-grown SWCNT sensor.

Enhanced adsorption and catalytic degradation of organic dyes by nanometer iron oxide anchored to single-wall carbon nanotubes

Abstract Arc discharge method with Fe catalyst was used to prepare single-wall carbon nanotubes (SWCNTs) and there are an amount of iron nanoparticles formed tightly on SWCNTs. Nanometer iron oxide anchored to SWCNT composite (AO-Fe-SWCNTs) was obtained in situ by oxidizing the above as-grown SWCNTs (As-Fe-SWCNTs) in air at 375 °C. AO-Fe-SWCNTs exhibited an excellent performance of adsorption, Fenton and photo-Fenton degradation of methyl blue (MB) and methyl orange (MO) in aqueous solutions. Adsorption of MB and MO by AO-Fe-SWCNTs could reach equilibrium within 10 min and its maximum adsorption capacity for MB and MO was up to 256.69 mg g−1 and 93.58 mg g−1, respectively. MB could almost be decomposed within 10 min depending on their concentration using AO-Fe-SWCNTs as catalyst under the assistance of H2O2. UV–Vis light irradiation further speeded up the above Fenton reaction and the degradation of MB and MO in solutions. It was revealed that the small sizes of iron oxides (several nanometers) and their good dispersion on SWCNTs are the main reason responsible for the good property of AO-Fe-SWCNTs. Furthermore, iron oxides-SWCNTs heterojunctions probably improve electron-hole separation during irradiation and promote the generation of hydroxyl radicals. The present study indicates that AO-Fe-SWCNTs with firm web structure are a promising material for adsorption and degradation of organic dyes.

Arsenic removal from water by nanometer iron oxide coated single-wall carbon nanotubes

Single-wall carbon nanotubes (SWCNTs) were prepared by arc discharge evaporation of a carbon electrode containing Fe catalyst so that there are an amount of iron nanoparticles attached tightly on SWCNTs. The iron oxide nanoparticle coated SWCNT composite was prepared in situ by oxidizing the above as-grown SWCNTs in air at 350°C, which was used as an adsorbent for As5+ removal from water. It was found that the maximum As5+ adsorption capacity of the composite was 42.30mgg−1 at pH8 and 49.65mgg−1 at pH4, respectively. The kinetics data were best fitted with a pseudo-second order, thus suggesting chemical adsorption on the surface and pores of iron oxide nanoparticles. The adsorption isotherm obtained at pH8 was best fitted to the Freundlich model, therefore a non-ideal adsorption on heterogeneous surfaces for As5+ ions on iron oxide nanoparticles was proposed. The firm web structure with high adsorption capacity makes the composite a promising adsorbent for arsenic removal in contaminated water.

Diameter controlled growth of SWCNTs using Ru as catalyst precursors coupled with atomic hydrogen treatment

In this work, we present a practical approach for controlling single walled carbon nanotubes (SWCNTs) diameter distribution through thin film Ru catalyst, coupled with hydrogen pre-treatment. Uniform and stable Ru nanoclusters were obtained after dewetting the Ru thin films under atomic hydrogen pre-treatment. SWCNTs were synthetized by double hot filament chemical vapor deposition (d-HFCVD) on SiO2/Si substrates at different temperatures. We found that the temperature is an important synthesis parameter that influences the diameter distribution of the final SWCNTs. Statistical analysis of the Raman radial breathing modes evidences the growth of highly enriched semi-conducting SWCNTs (about 90%) with narrow diameter distribution that correlates directly with the catalyst particle size distribution. Electrical measurement results on as-grown SWCNTs show good thin-film transistor characteristics.

(Invited) The Evolution of W-Co-C Catalyst during the CVD Growth of Chirality-Selective Growth of Single-Walled Carbon Nanotubes

Bimetallic catalysts such as Fe-Co and Co-Mo have been used for efficient growth of bulk single-walled carbon nanotube (SWNTs) and vertically aligned SWNTs [1]. Recently, bimetallic catalysts such as Co-W [2] or Co-Cu [3] are employed for structure controlled growth of SWNTs. Here, roles of bimetallic catalysts are explored by newly proposed SiO2 grid based in-plane TEM technique, which enables a direct TEM characterization of catalysts on SiO2, CVD growth of SWNTs in normal furnace, and TEM characterization of catalysts and grown nanotubes after CVD. The in-plane TEM results of the traditional Co-Mo bimetallic catalysts were consist with our previous report [1]; metallic Co nanoparticle embedded in Co-Mo oxide is responsible for the nucleation of SWNTs. By using Co-Cu catalysts, we can synthesize vertically aligned SWNTs with subnanometer diameters on quartz (and SiO2/Si) substrates [3]. EDS-STEM and HAADF-STEM imaging of the Co-Cu bimetallic catalyst system showed that small Co catalysts were captured and anchored by adjacent Cu nanoparticles, which grew small diameter of SWNTs. High-melting point W6Co7 alloy produced from metal cluster precursors is reported to grow a single chirality (12,6) with over 90 % abundance [2]. Here, we show that a sputtered Co-W catalyst can selectively grow (12,6) SWNTs by CVD at lower reduction and growth temperatures [4]. Statistical Raman mapping analysis and optical absorption spectrum of the as-grown SWNTs reveal that the abundance of (12,6) is over 60 %. The morphology and structure of catalyst is investigated by the in-plane TEM before and after CVD growth. The catalyst alloy we produced was W6Co6C and the only metallic Co was left after the CVD of 5 min. By comparing the catalyst TEM images with variable CVD period, we can discuss the evolution of the alloy catalysts. The W rich initial catalyst is composed of bcc W bound with W6Co6C. Once ethanol is introduced, additional W will be gradually removed to the gas phase product of WO3 and the ratio of W decreases. It is speculated that after the formation of pure W6Co6C, further loss of W will result the precipitation of Co; nucleation of Co cluster which is primary responsible for growth of an SWNT. This work was supported by JSPS KAKENHI Grant Numbers JP25107002, JP15H05760, and IRENA Project by JST-EC DG RTD, Strategic International Collaborative Research Program, SICORP. Part of this work is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). We also acknowledge supports from Advanced Characterization Nanotechnology Platform of the University of Tokyo, supported by "Nanotechnology Platform" of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

Selective and uniform growth of single-wall carbon nanotubes (SWCNTs) for gas sensing application

In the present work, we have synthesized uniformly distributed single-wall carbon nanotube (SWCNT) networks with a selective diameter suitable for gas sensing device. The SWCNT networks have been synthesized on 2-nm-thick iron (Fe) catalyst-coated silicon (Si) substrates by Plasma-Enhanced Chemical Vapor Deposition (PECVD). The as-grown SWCNTs were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy techniques. Using SWCNT network, the sensitivity of ammonia (NH3) gases/vapors was recognized by their surface adsorption and desorption responses. The response curve was observed from the SWCNT network, which is due to a change in the resistance upon exposure to NH3 gas.

Arrays of horizontal carbon nanotubes of controlled chirality grown using designed catalysts.

The semiconductor industry is increasingly of the view that Moore's law-which predicts the biennial doubling of the number of transistors per microprocessor chip-is nearing its end. Consequently, the pursuit of alternative semiconducting materials for nanoelectronic devices, including single-walled carbon nanotubes (SWNTs), continues. Arrays of horizontal nanotubes are particularly appealing for technological applications because they optimize current output. However, the direct growth of horizontal SWNT arrays with controlled chirality, that would enable the arrays to be adapted for a wider range of applications and ensure the uniformity of the fabricated devices, has not yet been achieved. Here we show that horizontal SWNT arrays with predicted chirality can be grown from the surfaces of solid carbide catalysts by controlling the symmetries of the active catalyst surface. We obtained horizontally aligned metallic SWNT arrays with an average density of more than 20 tubes per micrometre in which 90 per cent of the tubes had chiral indices of (12, 6), and semiconducting SWNT arrays with an average density of more than 10 tubes per micrometre in which 80 per cent of the nanotubes had chiral indices of (8, 4). The nanotubes were grown using uniform size Mo2C and WC solid catalysts. Thermodynamically, the SWNT was selectively nucleated by matching its structural symmetry and diameter with those of the catalyst. We grew nanotubes with chiral indices of (2m, m) (where m is a positive integer), the yield of which could be increased by raising the concentration of carbon to maximize the kinetic growth rate in the chemical vapour deposition process. Compared to previously reported methods, such as cloning, seeding and specific-structure-matching growth, our strategy of controlling the thermodynamics and kinetics offers more degrees of freedom, enabling the chirality of as-grown SWNTs in an array to be tuned, and can also be used to predict the growth conditions required to achieve the desired chiralities.

Linking growth mode to lengths of single-walled carbon nanotubes

Elucidating the key factors that determine the lengths of single-walled carbon nanotubes (SWCNTs) is of great importance for understanding the origin of chiral selectivity. We use transmission electron microscopy to thoroughly investigate as-grown SWCNTs. The lengths and growth modes of SWCNTs were decided by bright-field imaging. Their respective chiral angles were calculated on the basis of nanobeam diffraction patterns. Systematic investigations reveal that there is no correlation between the SWCNT length and its chiral angle. Instead, it shows that SWCNT lengths depend more on their growth mode, i.e. the link between SWCNT and its seeding catalyst particle. Atomistic computer simulations demonstrate that low carbon fractions in the catalyst lead to so-called tangential growth, with a partial wetting of the metal in the tube, where metal catalyst tends to be deactivated by graphite layer encapsulation and results in short SWCNTs. In contrast, a high carbon concentration inside metal particle favors perpendicular growth modes, where only the tube lip is in contact with the catalyst. Catalysts adopting perpendicular mode could have a longer lifetime, thus catalyze the growth of long SWCNTs. Finally, the carbon concentration related growth mode was applied to interpret diverse SWCNT growth results.

Growth of single wall carbon nanotubes using PECVD technique: An efficient chemiresistor gas sensor

In this work, the uniform and vertically aligned single wall carbon nanotubes (SWCNTs) have been grown on Iron (Fe) deposited Silicon (Si) substrate by plasma enhanced chemical vapor deposition (PECVD) technique at very low temperature of 550°C. The as-grown samples of SWCNTS were characterized by field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM) and Raman spectrometer. SWCNT based chemiresistor gas sensing device was fabricated by making the proper gold contacts on the as-grown SWCNTs. The electrical conductance and sensor response of grown SWCNTs have been investigated. The fabricated SWCNT sensor was exposed to ammonia (NH3) gas at 200ppm in a self assembled apparatus. The sensor response was measured at room temperature which was discussed in terms of adsorption of NH3 gas molecules on the surface of SWCNTs. The achieved results are used to develope a miniaturized gas sensor device for monitoring and control of environment pollutants.

Influence of electronic type of SWNTs on the thermoelectric properties of SWNTs/PANI composite films

Single-walled carbon nanotubes (SWNTs) have emerged as one of the leading additives for improving the thermoelectric properties of organic materials due to their unique structure and excellent electronic transport properties. However, since as-grown SWNTs possess different chirality, it is of high interest to determine the influence of electronic type of SWNTs on the thermoelectric properties of SWNTs/PANI composite films. Herein, we utilized metallic SWNTs (SWNT-M) and semiconducting SWNTs (SWNT-S) to prepare SWNTs/PANI composite films and studied their thermoelectric properties, respectively. Experimentally, the maximum thermoelectric power factor reached 51 μW m−1 K−2 for the 19 wt% SWNT-S/PANI composite films, while that value was only 16 μW m−1 K−2 for the 19 wt% SWNT-M/PANI composite films. The better power factor of SWNT-S/PANI composite films may be attributed to the more significantly enhanced Seebeck coefficient resulting from the effective energy filtering effect at the interfaces between SWNT-S and PANI. Our results reveal the influence of electronic type of SWNTs on the thermoelectric properties of composites, which will drive ongoing efforts to utilize SWNTs as fillers in nanocomposites for optimal thermoelectric properties.

Selective Growth of Subnanometer Diameter Single-Walled Carbon Nanotube Arrays in Hydrogen-Free CVD.

Small diameter single-walled carbon nanotube (SWNT) arrays with larger bandgap are more desirable as near-infrared optical absorbers for the fabrication of high performance photovoltaic and photodetector devices. We report herein a rational approach to selective growth of well-aligned subnanometer diameter (∼84% between 0.75 and 0.95 nm) SWNT arrays with a density of 0.3-0.5 tubes/μm on quartz surfaces using solid Mo2C catalysts for short-time growth by low carbon feeding in hydrogen-free CVD. These subnanometer diameter SWNTs have a narrow chirality distribution (the ratio of (8,4), (8,5) and (7,6) is higher than 73%). During nanotube growth, only small size Mo nanoparticles are carbonized into stable Mo2C for catalyzing the growth of SWNTs through low carbon feeding rate over short time in the hydrogen-free environment, whereas larger catalysts are inactive due to underfeeding. Meanwhile, solid Mo2C catalysts are effective in reducing the chirality distributions of the as-grown SWNTs. Additionally, combining an annealing process after loading catalyst on the sapphire substrates, the average density is increased to ∼15 tubes/μm while maintaining small diameter and narrow chirality distribution. Our results offer more choices for structurally controlled growth of aligned-SWNTs, with potential applications in nanoelectronics.

Random networks of carbon nanotubes optimized for transistor mass-production: searching for ultimate performance

Random networks of as-grown single-walled carbon nanotubes (CNTs) contain both metallic (m-CNTs) and semiconducting (s-CNTs) nanotubes in an approximate ratio of 1:2, which leads to a trade-off between on-conductance and the on/off ratio. We demonstrate how this design problem can be solved with a realistic numerical approach. We determine the CNT density, length, and channel dimensions under which CNT thin-film transistors simultaneously attain on-conductance higher than 1 μS and an on/off ratio higher than 104. The fact that asymmetric systems have more pronounced finite-size scaling behavior than symmetric systems allows us additional design freedom. A realization probability of the desired characteristics higher than 99% is obtained for the channels with aspect ratio and normalized size when the CNT length is and the normalized density of CNTs is close to the value where the probability of percolation through only s-CNT pathways reaches its maximum.

(Invited) Revisited Roles of Bimetallic Catalysts for Controlled CVD Growth of Single-Walled Carbon Nanotubes

Bimetallic catalysts such as Co-Mo have been used for efficient growth of vertically aligned single-walled carbon nanotube (SWNTs) for a decade [1]. Recently, different kinds of bimetallic catalyst such as Co-W [2] or Co-Cu [3] are employed for structure controlled growth of SWNTs. Different roles of bimetallic catalysts are revisited by newly proposed in-plane transmission electron microscopy (TEM) technique, which enables a direct TEM characterization of catalysts and CVD grown nanotubes on SiO2 TEM grid. Sputtered and dip-coated cobalt-based catalysts, i.e., Co, Co-Mo, Co-Cu, Co-W are used in alcohol catalytic CVD (ACCVD). We found the Co oxide catalysts can efficiently grow narrower diameter and smaller average diameter SWNTs compared with pre-reduced Co catalysts. The in-plane TEM and X-ray photoelectron spectroscopy (XPS) reveal that Co catalysts are transformed to Co3O4 after reduction-calcination process and then decompose to CoO before growth at a typical growth temperature (800 ºC) in Ar atmosphere. We conclude that an in-situ reduction process occurred on low-mobility CoO after the introduction of ethanol is essential to activate small metallic Co catalysts. The in-plane TEM studies confirmed that Co-Mo bimetallic catalysts have the same mechanism as oxidized Co system, i.e. low mobility oxides and reduced metal, consistent with our previous report [1]. By using Co-Cu catalysts, we can synthesize vertically aligned SWNTs with subnanometer diameters on quartz (and SiO2/Si) substrates [3]. Scanning transmission electron microscopic energy-dispersive X-ray spectroscopy (EDS-STEM) and high angle annular dark field (HAADF-STEM) imaging of the Co/Cu bimetallic catalyst system showed that Co catalysts were captured and anchored by adjacent Cu nanoparticles, and thus were prevented from coalescing into larger size, which contributed to the small diameter of SWNTs. High-melting point W6Co7 alloy is reported to grow a single chirality, (12,6) with over 90 % abundance through high-temperature (1030 ºC) reduction and growth [2]. Here, we show that a sputtered Co-W catalyst can selectively grow (12,6) SWNTs by CVD at lower temperatures. Statistical Raman mapping analysis and optical absorption spectrum of the as-grown SWNTs reveal that the abundance of (12,6) is over 50%. The morphology and structure of catalyst is investigated by the in-plane TEM, which discloses the complicated structure changes before and after growth.