Support Vector Machine Classification of Single Walled Carbon Nanotube Growth Parameters

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.

The high‐end applications of single‐walled carbon nanotubes (SWCNTs) are hindered by the existence of large amount of impurities, especially the graphene layers encapsulating metal nanoparticles (metal@C NPs). The role of working metal catalysts during chemical vapor deposition (CVD) growth and post purifications by oxidation are not yet fully understood. Herein, the in situ monitoring the role of working metal catalyst NPs for ultrahigh purity SWCNTs by CVD growth and CO2 purifications is carried out in an online thermogravimetric reactor attached with a mass spectrometer. The growth of SWCNTs almost stops after the initial 2 min, then, the mass increase of the samples mainly originates from the metal@CNP formation. Therefore, high‐purity SWCNTs (98.5 wt%) with few metal@CNPs can be available by 2 min CVD growth. Furthermore, CO2 oxidation of the SWCNTs is also investigated in a thermogravimetric reactor. The oxidation of graphene layers surrounding the metal NPs and the SWCNTs occurs during distinct temperature ranges, which is further demonstrated by the significant differences among their oxidation activation energies. Ultrahigh purity of SWNCT with a carbon content of 99.5 wt% can be available by a CO2‐assited purification method. The in situ study of the CVD growth and CO2 oxidation of SWCNTs provides the real time information on the working catalyst during reaction and the reactivity information of metal@CNPs and SWCNTs under an oxidizing atmosphere. The success for the preparation of high‐purity SWCNT lies in the efficient growth of SWCNTs with a low amount of nanocarbon impurities and partial oxidation of metal@CNPs by catalytic CO2 oxidation with proper operation parameters.

Growth of high quality, high density single-walled carbon nanotube forests on copper foils

The physical state of the catalyst and its impact on the growth of single-walled carbon nanotubes (SWNTs) is the subject of a long-standing debate. We addressed it here using in situ Raman spectroscopy to measure Fe and Ni catalyst lifetimes during the growth of individual SWNTs across a wide range of temperatures (500-1400 °C). The temperature dependence of the Fe catalyst lifetimes underwent a sharp increase around 1100 °C due to a solid-to-liquid phase transition. By comparing experimental results with the metal-carbon phase diagrams, we prove that SWNTs can grow from solid and liquid phase-catalysts, depending on the temperature.

Electric-field-directed growth of single-walled carbon nanotubes by chemical-vapor deposition is demonstrated. The field-alignment effect originates from the high polarizability of single-walled nanotubes. Large induced dipole moments lead to large aligning torques and forces on the nanotube, and prevent randomization of nanotube orientation by thermal fluctuations and gas flows. The results shall open up possibilities in directed growth of ordered molecular-wire architectures and networks on surfaces.

The growth of single wall carbon nanotubes (SWNTs) mediated by metal nanoparticles is considered within (i) the surface diffusion growth kinetics model coupled with (ii) a thermal model taking into account heat release of carbon adsorption-desorption on nanotube surface and carbon incorporation into the nanotube wall and (iii) carbon nanotube-inert gas collisional heat exchange. Numerical simulations performed together with analytical estimates reveal various temperature regimes occurring during SWNT growth. During the initial stage, which is characterized by SWNT lengths that are shorter than the surface diffusion length of carbon atoms adsorbed on the SWNT wall, the SWNT temperature remains constant and is significantly higher than that of the ambient gas. After this stage the SWNT temperature decreases towards that of gas and becomes nonuniformly distributed over the length of the SWNT. The rate of SWNT cooling depends on the SWNT-gas collisional energy transfer that, from molecular dynamics simulations, is seen to be efficient only in the SWNT radial direction. The decreasing SWNT temperature may lead to solidification of the catalytic metal nanoparticle terminating SWNT growth or triggering nucleation of a new carbon layer and growth of multiwall carbon nanotubes.

We demonstrate the continued growth of single-walled carbon nanotubes (SWNTs) from ordered arrays of open-ended SWNTs in a way analogous to epitaxy. Nanometer-sized metal catalysts were docked to the SWNT open ends and subsequently activated to restart growth. SWNTs thus grown inherit the diameters and chirality from the seeded SWNTs, as indicated by the closely matched frequencies of Raman radial breathing modes before and after the growth.

Surface growth of single-walled carbon nanotubes from ruthenium nanoparticles

ABSTRACTGrowth of single-walled carbon nanotube (SWCNT) was achieved by an alcohol catalytic chemical vapor deposition (CVD) mechanism that was conducted in a high vacuum using Ru catalysts. By optimizing the ethanol pressure, SWCNTs can grow in a wide range of temperature between 500 °C and 900 °C. Both the yield and crystalline quality of SWCNTs reached their maxima at 700 °C. Significantly, the SWCNT growth was achieved even at 450 °C, which was much lower than the growth temperatures that were required for SWCNT growth using Ru catalysts previously. Raman measurements exhibited that the diameter distribution of the SWCNTs that were grown at 450 °C was quite narrow and (11, 4) nanotubes were dominant. The observations of transmission electron microscope (TEM) suggested that the size of the Ru particles were larger than the diameter of SWCNT. Such a relation was similar to the relation observed in the growth of SWCNTs using Pt catalysts.

ABSTRACTGrowth of single-walled carbon nanotube (SWCNT) was achieved by an alcohol catalytic chemical vapor deposition (CVD) mechanism that was conducted in a high vacuum using Ru catalysts. By optimizing the ethanol pressure, SWCNTs can grow in a wide range of temperature between 500 °C and 900 °C. Both the yield and crystalline quality of SWCNTs reached their maxima at 700 °C. Significantly, the SWCNT growth was achieved even at 450 °C, which was much lower than the growth temperatures that were required for SWCNT growth using Ru catalysts previously. Raman measurements exhibited that the diameter distribution of the SWCNTs that were grown at 450 °C was quite narrow and (11, 4) nanotubes were dominant. The observations of transmission electron microscope (TEM) suggested that the size of the Ru particles were larger than the diameter of SWCNT. Such a relation was similar to the relation observed in the growth of SWCNTs using Pt catalysts.

Due to their excellent properties, single-walled carbon nanotubes (SWNTs) have been regarded as one of the most potential materials for future applications in nanoelectronic devices. However, there is a huge gulf between production and applications. To meet the needs for applications, SWNTs' chirality, metallic/semiconducting property and morphology should be controlled in the growth process. Together with our recent works, we present herein a brief review on the growth of SWNTs on surface with controlled structures, including 1) Cap engineering for SWNTs growth with controlled chirality; 2) Reaction activity diversity induced growth of semiconducting SWNTs; and 3) Combination of two growth modes for fabricating SWNTs on surface with controlled morphology.

High-quality single-walled carbon nanotubes (SWNTs) with narrow diameter distribution can be generated from well-defined Si 8 O 12 nanoclusters structure which form from thermal decomposition of chemically modified polyhedral oligomeric silsesquioxane (POSS). The nanosized Si x O y particles were proved to be responsible for the SWNT growth and believed to be the reason for the narrow diameter distribution of the as-grown SWNTs. This could be extended to other POSS. The SWNTs grown from the nanosized Si x O y particles were found to be semiconducting enriched SWNTs (s-SWNTs). A facile patterning technology, direct photolithography, was developed for generating SWNT pattern, which is compatible to industrial-level fabrication of SWNTs pattern for device applications. The metal-free growth together with preferential growth of s-SWNTs and patterning in large scale from the structure-defined silicon oxide nanoclusters not only represent a big step toward the control growth of SWNTs and fabrication of devices for applications particularly in nanoelectronics and biomedicine but also provide a system for further studying and understanding the growth mechanism of SWNTs from nanosized materials and the relationship between the structure of SWNT and nonmetal catalysts.

The diameter of single-walled carbon nanotubes (SWNTs) has a decisive influence on their electronic structure and optoelectronic properties. This study innovatively explored the mechanism of regulating the diameter of SWNTs by the Mg/Al ratio in magnesium-aluminium layered double oxide (LDOs) catalysts. Fe/Co/Mg/Al-LDOs catalysts with different Mg/Al ratios were synthesized by co-precipitation, and the effect of the Mg/Al ratio on the diameter of SWNTs grown by catalytic growth at 700°C was investigated. The experimental results showed that increasing the Al component is beneficial to selectively growing small- diameter SWNTs, while increasing the Mg component tends to promote the growth of larger-diameter SWNTs. Catalyst characterization indicated that the introduction of Al promoted the migration of Co cations into the support. The unreduced Co2+ could anchor the metal nanoparticles reduced on the support surface, effectively inhibiting the agglomeration of metal nanoparticles, thereby favoring the growth of small-diameter SWNTs. This finding provides a simple and efficient strategy for the controllable synthesis of SWNTs with specific diameters, laying a foundation for the development of high-performance carbon-based nanoelectronic devices.

Carbon:nickel (C:Ni) nanocomposite thin films deposited by ion beam co‐sputtering were used for catalytic chemical vapor deposition (CVD) growth of single‐walled carbon nanotubes (SWCNTs). The SWCNTs were characterized by scanning electron microscopy and Raman spectroscopy. The approach allows a precise and reproducible control of the catalyst diameter, while the embedding carbon matrix prevents the particles from coalescence during catalyst activation and nanotube growth. The SWCNTs obtained from Ni particles with ∼4 nm diameter have a radial breathing mode frequency distribution of 147.5 ± 32 cm−1 and a diameter distribution of 1.6 ± 0.4 nm. Small line widths of the radial breathing mode and ID/IG ratios of 0.05 indicate SWCNTs with a low defect concentration. magnified imageLeft: Scheme of C:Ni nanocomposite based SWCNT synthesis. The dark contrast image regions correspond to the Ni particles. Right: Radial breathing mode Raman spectrum of a structurally highly ordered SWCNT.

In this paper we discuss three optical methods for in situ characterization of single wall carbon nanotube (SWNT) growth by laser vaporization at elevated temperatures: optical absorption spectroscopy, optical incandescence, and light scattering. Optical absorption spectroscopy was successfully used to estimate the size of carbon nanoparticles and to monitor the atomic metal catalyst in the propagating laser ablation plume. These measurements indicate that the aggregation rate of carbon nanoparticles increases rapidly at lower oven processing temperatures. The second method, incandescence, was applied to measure the particle temperature within the propagating plume at different times after ablation. The third approach, imaging of the plume using Rayleigh scattered light, was used to monitor the ejected material inside the hot furnace as well as to observe the plume when it exits the furnace, i.e., in the cold zone of a quartz tube reactor. We demonstrated that Rayleigh scattering imaging combined with TEM analysis of the produced material was very useful for controlling the length of SWNTs and estimation of the growth rates. A general picture of SWNT growth by laser vaporization based on in situ diagnostics of ejected material at different times after ablation is discussed.