Growth Of Single-walled Carbon Nanotubes Research Articles

Growth of Single-walled Carbon Nanotubes on Substrates Using Carbon Monoxide as Carbon Source

Growth of Single-walled Carbon Nanotubes on Substrates Using Carbon Monoxide as Carbon Source

Growth of Single-walled Carbon Nanotubes at Low-temperatures Using Double-layer Film Consisting of Cobalt and Iron Layers as Catalyst

Growth of Single-walled Carbon Nanotubes at Low-temperatures Using Double-layer Film Consisting of Cobalt and Iron Layers as Catalyst

Understanding Single-Walled Carbon Nanotube Growth for Chirality Controllable Synthesis

ConspectusChirality defines the structural and electronic properties of a single-walled carbon nanotube (SWCNT), and therefore, synthesizing SWCNT samples with single chirality is essential for future high-end applications, such as replacing silicon in next-generation electronics. Since its discovery in 1991, to realize the selective growth of SWCNTs with a unique structure has been a key focus of SWCNT research. Chirality is currently understood to be assigned at birth and might be changed during the growth process. Understanding the mechanism of chirality assignment during nucleation and chirality-dependent growth kinetics is essential for realizing the final goal of SWCNT synthesis, i.e., the large-scale synthesis of SWCNTs with a specific chiral index. From 2003, we have systematically explored chirality assignment during SWCNT nucleation, how the chirality of a SWCNT affects its growth, and how the chirality changes during growth. Together with our experimental collaborators, we have realized the chirality-specific growth of SWCNTs via a few designed experimental routes. In this account, we will review all these studies and present our perspectives on this very important research topic.We will first introduce the screw dislocation theory of SWCNT growth to elucidate how the chirality affects the growth rate of a SWCNT and the abundance of each SWCNT in the final product. Second, a modified screw dislocation theory, which describes the SWCNT’s growth kinetics on a solid catalyst and its impact on chirality control during synthesis is presented. Third, the random chiral angle assignment during SWCNT nucleation on liquid catalysts is discussed as well as why chirality control in SWCNT growth is so challenging. Together with previous experimental reports, we further demonstrate that solid catalysts have a great advantage in realizing chirality-selective SWCNT growth. Based on our current understanding, we propose three strategies to realize chirality-selective SWCNT growth, (i) controlling the symmetry of solid catalyst particles, (ii) varying the growth conditions, and (iii) controlling the feedstock and etching agent during growth. We expect this account will give the reader a comprehensive understanding of the mechanism behind SWCNT growth and motivate further studies on selective growth to achieve the best performance of SWCNT-based devices in the future.

Methods of the Controlled Growth and Post Separation for Chirality-Specific Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) as a promising candidate in a wide range of applications have shown great potentials in optical, electronic, magnetic and mechanical fields. Precisely due to their excellent characteristics and performances, it has attracted widespread attention, and much progress has been made during recent decades. However, due to the huge challenge in controlled synthesis and purification, obtaining SWCNTs with consistent chirality has seriously limited their high-end industrial applications. In this article, we will review the approaches recently developed in chirality-controlled preparation of SWCNTs. Among them, we will introduce the mechanism of templated growth of SWCNTs from chiral affinities, including cloning and seeds designing strategies. The preparation of SWCNTs catalyzed by noble metal and assisted with weak oxidant have been illustrated as well. Meanwhile, we will also discuss some chirality-selective separation approaches, which pay more attention to post-processing strategies by purifying the chiral SWCNTs with functional reagents. We expect that these strategies in controlling the chirality of CNTs will shed more light on the mechanism and process for atomic structural control of CNTs, and may also be applicable in the controlled synthesis of other nanomaterials.

Osmium catalyzed growth of vertically aligned and small-diameter single-walled carbon nanotubes by alcohol catalytic chemical vapor deposition

We showed that single-walled carbon nanotubes (SWCNTs) could be grown on SiO2/Si substrates by alcohol catalytic chemical vapor deposition (CVD) with an Os catalyst in a cold-wall CVD system. At a growth temperature of 700 °C, web-like SWCNTs were grown with diameters distributed below 0.9 nm. At a growth temperature of 800 °C, the SWCNT density increased and vertically aligned SWCNTs (VA-SWCNTs) 70 nm thick were grown on the SiO2/Si substrates after growth for 30 min. Raman and transmission electron microscope results showed that the diameters of the grown SWCNTs were distributed between 0.65 and 1.0 nm, and were much smaller than those of VA-SWCNTs obtained from conventional catalysts such as Fe and Co. Furthermore, compared with Ir, which has been reported to be a suitable catalyst for growth of small-diameter SWCNTs, we showed that Os could grow SWCNTs with even smaller diameters. Additionally, neither an alumina buffer layer nor cocatalyst were necessary to grow VA-SWCNTs with the Os catalyst. We consider that highly efficient suppression of aggregation and the relatively strong carbon-Os bond strength contributed to growth of small-diameter SWCNTs from the Os catalyst. Our studies are the first to report on Os as a catalyst for SWCNT growth, leading to SWCNTs with diameters less than ~1 nm. Hence, period 6 platinum-group metals are likely to be good catalysts for highly efficient growth of small-diameter SWCNTs.

(Invited) In Situ Study on Nucleation and Growth of Single-Walled Carbon Nanotubes on Catalysts

Understanding the growth mechanism is prerequisite to design the methodology for controlled growth of single-walled carbon nanotubes (SWNTs). By using an environmental aberration-corrected transmission electron microscope in combination with in situ synchrotron X-ray absorption spectroscopy, we directly present the structural and composition evolution of cobalt and cobalt-tungsten intermetallic catalysts during the nucleation and growth of SWCNTs under carbon feeding. The co-existence of cobalt and cobalt carbide was generally observed among the pure cobalt catalysts which are active in nucleating tubes. The nucleation and growth behaviors of tubes on solid state cobalt nanoparticles and molten ones have been compared. It was found that the tubes grown from solid state catalysts always present smaller diameter than the catalysts. No structure-correlation between catalyst and nanotube was found. Distinct different from cobalt, no carbides or carbon diffusion induced structural change was observed from the in situ characterization. The atomic structure of Co7W6 was stable when CNTs nucleating. These observations reveal that cobalt-tungsten intermetallic catalysts act as the stable structure template for the chirality controlled growth of SWNTs.

Fluorination-assisted preparation of self-supporting single-atom Fe-N-doped single-wall carbon nanotube film as bifunctional oxygen electrode for rechargeable Zn-Air batteries

Freestanding membrane electrodes with a high electrocatalytic activity and stability are desirable for use in high-performance metal-air batteries. Here, we report a gas-phase fluorination-assisted method to anchor single atom Fe-Nx moieties on a freestanding single-wall carbon nanotube (SWCNT) film that involves fluorination and defluorination/ammoniation processes. It is shown that the fluorination followed by defluorination/ammoniation harvests Fe atoms from the residual Fe nanoparticles used for SWCNT growth to form high density of Fe-Nx active sites, while retaining the flexibility, integrity and high quality of the films so that they can be directly used as a bifunctional oxygen electrode for rechargeable Zn-Air batteries. The single-atom Fe-Nx loaded SWCNT film shows an even better catalytic activity than commercial Pt/C-Ir/C catalysts, and an assembled Zn-Air battery using it exhibits a low charge-discharge voltage gap of 0.84 V under 20 mA/cm2, a high peak power density of 210 mW/cm2, and excellent long-time cycling stability. In addition, a flexible all-solid-state Zn-Air battery was assembled which has a stable open circuit voltage when bent to different angles.

Residence time effect on single-walled carbon nanotube synthesis in an aerosol CVD reactor

• Residence time in aerosol CVD was tuned while nanotube nucleation maintained. • Carbon nanotube length and I G /I D ratio increase with a higher residence time. • The increase in length and defectiveness drops equivalent sheet resistance. • Effect of vortices, diffusion, and thermophoresis on nanotube yield was shown. • SWCNT/HAuCl 4 thin films with equivalent sheet resistance of 51 Ω/□ were obtained. We examine an effect of residence time on the growth of single-walled carbon nanotubes (SWCNTs) in an aerosol (floating catalyst) chemical vapor deposition (CVD) process using CO as a carbon source and ferrocene as a catalyst precursor. The key feature of aerosol CVD reactors, namely stabilization of fine nanoparticles by an extreme dilution, limits the method for catalyst evolution studies. We show an approach to examine the role of the residence time while maintaining all the processes preceding the nanotube growth (catalyst formation, nanotube nucleation). Using the diameter distribution of nanotubes as a fingerprint of the SWCNT nucleation stage, we have proven the latter to be unaffected by changes in the residence time. Using SEM observations, we have revealed a quite intuitive but inspiring correlation between the carbon nanotube length and residence time. We have also found a decrease in the SWCNT yield caused by the drop in the aerosol concentration, which could be attributed to the gas-phase losses as well as the shift in the catalyst activation degree. Nevertheless, the trends observed allowed us to reach a tenfold decrease in an equivalent sheet resistance (sheet resistance of a film with 90% transmittance at 550 nm) by a threefold increase in the residence time at optimal CO 2 concentration. SWCNT films with the equivalent sheet resistance as low as 245 Ω/□ and 51 Ω/□ (for pristine and doped carbon nanotubes, correspondingly) ensure the promising future of the proposed strategy for optimization of both aerosol CVD reactors and SWCNT-based films for optoelectronic applications.

A semi-grand canonical kinetic Monte Carlo study of single-walled carbon nanotube growth

Single-walled carbon nanotubes exist in a variety of different geometries, so-called chiralities, which define their electronic properties. Chiral selectivity has been reported in catalytic chemical vapor deposition synthesis experiments, but the underlying mechanisms remain poorly understood. In this contribution, we establish a simple model for the prediction of the growth rates of carbon nanotubes of different chiralities as a function of energies characterizing the carbon nanotube–catalyst interface and of parameters of the synthesis. The model is sampled efficiently using kinetic Monte Carlo simulations in the semi-grand canonical ensemble, uncovering the interplay of the external experimental conditions and the configuration and energetics of the interface with the catalyst. In particular, the distribution of chiral angle dependent growth rates follows non-monotonic trends as a function of interface energies. We analyze this behavior and use it to identify conditions that lead to high selectivity for a variety of chiral angles.

High-throughput screening and machine learning for the efficient growth of high-quality single-wall carbon nanotubes

It has been a great challenge to optimize the growth conditions toward structure-controlled growth of single-wall carbon nanotubes (SWCNTs). Here, a high-throughput method combined with machine learning is reported that efficiently screens the growth conditions for the synthesis of high-quality SWCNTs. Patterned cobalt (Co) nanoparticles were deposited on a numerically marked silicon wafer as catalysts, and parameters of temperature, reduction time and carbon precursor were optimized. The crystallinity of the SWCNTs was characterized by Raman spectroscopy where the featured G/D peak intensity (IG/ID) was extracted automatically and mapped to the growth parameters to build a database. 1,280 data were collected to train machine learning models. Random forest regression (RFR) showed high precision in predicting the growth conditions for high-quality SWCNTs, as validated by further chemical vapor deposition (CVD) growth. This method shows great potential in structure-controlled growth of SWCNTs.

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.

Selective growths of single‐walled carbon nanotubes from mesoporous supports via CO disproportionation

AbstractMesopore‐confined cobalt catalysts are prepared to control diameters and chirality of single‐walled carbon nanotubes (SWCNTs) via CO disproportionation. Here, we demonstrate four synthetic strategies of growing semiconducting as well as metallic SWCNTs catalyzed by the cobalt nanoparticles with defined locations and sizes. Co‐condensation (catalyst‐1,3) processes provide constrained environment for small catalysts that grow uniform diameters (0.82–0.83 nm) of (7,5) and (8,4) semiconducting SWCNTs. Alternatively, surface‐grafting (catalyst‐2) and ion‐exchange processes (catalyst‐4) provide spacious mesopores toward formation of poly‐dispersed catalysts that grow a mixture of SWCNTs with wide‐range diameter distributions (0.83, 1.2–1.34 nm). Raman and photoluminescence excitation rationally correlate Raman breathing mode vibration to individual chirality and diameters of these SWCNTs. Informative in situ X‐ray absorption experiments reveal H2‐pretreatment (300–700°C) effects toward different oxidation states, bond distances, and coordination numbers of the cobalt catalysts. The CO disproportionation (6 atm, 800°C) reaction provides suitable confined growth of SWCNTs via co‐condensation of cobalt catalysts into mesoporous materials.

SiO2-promoted growth of single-walled carbon nanotubes on an alumina supported catalyst

Developing supported catalyst and elucidating the catalyst activation mechanism are of significant importance for large scale synthesis of single-walled carbon nanotubes (SWNTs). In the work, we designed an alumina-supported iron (Fe–Al2O3) catalyst for catalytic growth of carbon nanotubes by CO chemical vapor deposition (CVD). In the temperature range of 800–1000 °C, the prepared powder catalyst only affords the growth of carbon fibers or multi-walled carbon nanotubes. In contrast, when placing the powder catalyst on flat SiO2 substrates, such as SiO2/Si and quartz, SWNTs were observed to grow at the catalyst-substrate interface, highlighting the contributions of the SiO2 substrate in SWNT synthesis. Systematic characterizations on both the catalysts and carbon nanotubes revealed that the SiO2 substrate promotes the reduction of iron oxide in the adjacent Fe–Al2O3 catalyst, facilitating the generation of small Fe particles at the catalyst-substrate interface, which act as the active phase for the subsequent growth of SWNTs. This work opens a new avenue for growing SWNTs from supported catalyst and sheds light on enhancing SWNT growth efficiency by tuning catalyst reduction behaviors.

Graphene oxide-supported cobalt tungstate as catalyst precursor for selective growth of single-walled carbon nanotubes

Graphene oxide-supported uniform cobalt tungstate nanoparticles (CoWO4/GO) were prepared, which can be used as catalyst precursors for the diameter-controlled growth of single-walled carbon nanotubes (SWCNTs).

Controlling the Tube Diameter of SWCNTs Using High Melting Point Promotors

A particular control of the diameter of Single Walled-Carbon Nanotube (SWCNT) using Chemical vapor Deposition (CVD) system will enable many promising applications in different fields. Here we demonstrate the growth of SWCNT with good control of diameter (1.5 nm ± 0.7) using a high melting temperature metal (Ru) as a catalyst promotor with the main catalyst Co at 850˚C via CVD. We hypothesis that using high melting temperature metal as a promotor, like Ru can limit the mobility/change in the shape of the formed metal nanoparticles and eventually decrease the effects of Ostwald ripening (OR). FTS-GP is used as a carbon precursor. The results have been verified by high-resolution transmission electron microscopy (HR-TEM), atomic force microscopy (AFM) and multi-excitation Raman.

Effect of bimetallic Co:Mo/MgO catalyst on the growth efficiency of single-walled carbon nanotubes

Carbon nanotubes (CNTs) are known for a wide range of applications due to their various properties. Because these unique properties of the carbon nanotubes strongly depend on the structure, the primary aim is high efficiency and controlling the nanotube diameter during the production. In this study, single-walled carbon nanotubes (SWCNTs) were synthesized by chemical vapor deposition of acetylene (C2H2) on the Co–Mo/MgO catalyst. The effects of different catalyst preparation methods, Co/Mo, and support material ratios on the SWCNT growth efficiency were investigated by thermogravimetric analysis. Raman spectroscopy, scanning electron microscopy, and an x-ray diffractometer were also used for the structural and morphological characterization of the SWCNTs. As a result of the experimental studies, the optimum Co:Mo and metal/support ratio was determined as 1:3.5 and 15%, respectively. Considerable CNT growth efficiency (73%) has been achieved with the Co:Mo = 1:3.5/15% MgO catalyst prepared by the solgel method.

Activation of catalyst particles for single-walled carbon nanotube synthesis

In this work, we evaluate the effect of ferrocene delivery in the reactor on the growth of single-walled carbon nanotubes (SWCNTs) in an aerosol CVD utilizing carbon monoxide as a feedstock. For this purpose, we assess the reactor output parameters varying a gas flow rate through a ferrocene vapor injector in the hot zone with other conditions (temperature, total flow rate, and reactant concentration) being fixed. Our experimental results reveal the adjustment of the ferrocene injection strategy (injector flow rate) to cause a 9-fold improvement in the synthesis yield while preserving the SWCNT properties. We show the catalyst injection optimization to enhance catalyst activation degree as a result of a streamline catalyst delivery, preventing particle over-growth; the experimental data are supported by the computational fluid dynamics. We believe our work to highlight the importance of appropriate aerosol CVD reactor engineering and to facilitate the optimization of reactor productivity, which is one of the fundamental milestones towards SWCNT-based technology.

Carbon nanotubes advance next-generation electronics

Abstract Single-walled carbon nanotubes (SWCNTs) are potential candidates for next-generation computing to meet the requirement of device scaling. Here we discuss recent breakthroughs in the CNT-based field-effect transistors (FETs) and highlight key ongoing topics in purification and assembly. A few key challenges that capitalize on the chemical vapor deposition (CVD) of SWCNTs are discussed in which surface science and model systems can enable advances in high-purity synthesis. A full description of the CVD growth and chemical sorting of SWCNTs falls beyond the scope of this opinion, but we focus on the framework of SWCNTs in FETs and draw connections to their requirements for high-quality materials that highlight the underlying mechanisms.

High-precision solid catalysts for investigation of carbon nanotube synthesis and structure.

The direct growth of single-walled carbon nanotubes (SWCNTs) with narrow chiral distribution remains elusive despite substantial benefits in properties and applications. Nanoparticle catalysts are vital for SWCNT and more generally nanomaterial synthesis, but understanding their effect is limited. Solid catalysts show promise in achieving chirality-controlled growth, but poor size control and synthesis efficiency hampers advancement. Here, we demonstrate the first synthesis of refractory metal nanoparticles (W, Mo, and Re) with near-monodisperse sizes. High concentrations (N = 105 to 107 cm-3) of nanoparticles (diameter 1 to 5 nm) are produced and reduced in a single process, enabling SWCNT synthesis with controlled chiral angles of 19° ± 5°, demonstrating abundance >93%. These results confirm the interface thermodynamics and kinetic growth theory mechanism, which has been extended here to include temporal dependence of fast-growing chiralities. The solid catalysts are further shown effective via floating catalyst growth, offering efficient production possibilities.

Precise Catalyst Production for Carbon Nanotube Synthesis with Targeted Structure Enrichment

The direct growth of single-walled carbon nanotubes (SWCNTs) with a narrow distribution of diameter or chirality remains elusive despite significant benefits in properties and applications. Nanoparticle catalysts are vital for SWCNT synthesis, but how to precisely manipulate their chemistry, size, concentration, and deposition remains difficult, especially within a continuous production process from the gas phase. Here, we demonstrate the preparation of W6Co7 alloyed nanoparticle catalysts with precisely tunable stoichiometry using electrospray, which remain solid state during SWCNT growth. We also demonstrate continuous production of liquid iron nanoparticles with in-line size selection. With the precise size manipulation of catalysts in the range of 1–5 nm, and a nearly monodisperse distribution (σg < 1.2), an excellent size selection of SWCNTs can be achieved. All of the presented techniques show great potential to facilitate the realization of single-chirality SWCNTs production.