Direct Observation of Single-Walled Carbon Nanotube Growth at the Atomistic Scale

Lin, Ming; Tan, Jackson; Boothroyd, Chris; Loh, Kian Ping; Tok, Eng Soon; Foo, Y. L.

doi:10.1021/nl052356k

Cited by 226 publications

(238 citation statements)

References 27 publications

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“…Single SWNT growth rates have also been measured by TEM, and similar initial acceleration, steady growth, and termination phases have all been reported [13]. An initial acceleration phase has also been reported for nanotubes in microbalance experiments which measure the mass of grown material as a function of growth time [14].…”

Section: Resultsmentioning

confidence: 76%

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The dynamics of the nucleation, growth and termination of single-walled carbon nanotubes from in situ Raman spectroscopy during chemical vapor deposition

2009

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The dynamics of the chemical vapor deposition (CVD) of single-walled carbon nanotubes (SWNTs) is extracted experimentally using in situ Raman spectroscopy. Nanotubes are grown using a thin À lm cobalt catalyst and À an ethanol precursor in a miniature hot walled reactor with optical access. Raman spectra at room temperature and at the growth temperature are compared for two growth temperatures. The evolution of the G-band, D-band, and radial breathing mode (RBM) is tracked at the growth temperature with time resolution of a few seconds. There are three identifiable phases in the evolution of the Raman signal intensity: an initial exponential increasing phase, a linear growth phase, and a saturation phase. In situ optical spectroscopy thus enables the study of nucleation, steady growth, and deactivation processes to be investigated separately in real time. The evolution curves for all bands (G, D, and RBM), when scaled, collapse onto the same curve, to within experimental uncertainty.

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Section: Resultsmentioning

confidence: 76%

“…Such forests have been monitored by in situ reÁection Á [5 7], in situ absorption [8], displacement sensing [9], and simple video [10 12]. Also, of interest here are electron beam studies of SWNT growth rates [13] and also microbalance experiments that have been used to track the MWNT carbon yield as a function of time [14].…”

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confidence: 99%

The dynamics of the nucleation, growth and termination of single-walled carbon nanotubes from in situ Raman spectroscopy during chemical vapor deposition

2009

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“…SWNT nucleation requires nanometer-sized catalyst island dimensions [22][23][24] and thus a very thin initial catalyst film. The lowest temperature at which we could detect SWNTs by HRTEM and Raman spectroscopy is 350°C ( Figure 3).…”

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confidence: 99%

Catalytic Chemical Vapor Deposition of Single-Wall Carbon Nanotubes at Low Temperatures

et al. 2006

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We report surface-bound growth of single-wall carbon nanotubes (SWNTs) at temperatures as low as 350°C by catalytic chemical vapor deposition from undiluted C 2 H 2 . NH 3 or H 2 exposure critically facilitates the nanostructuring and activation of sub-nanometer Fe and Al/Fe/Al multilayer catalyst films prior to growth, enabling the SWNT nucleation at lower temperatures. We suggest that carbon nanotube growth is governed by the catalyst surface without the necessity of catalyst liquefaction.Carbon nanotubes (CNTs) have been a driving force for current advances in nanotechnology, both on an applied and on a fundamental level. Single-wall carbon nanotubes have shown the highest Young's modulus and highest axial thermal conductivity of any solid. Moreover, SWNTs have the highest current carrying capacity of any conductor, which makes them an attractive electronic, sensing, or heat sinking material for nano-electromechanical systems (NEMS) and future (hybrid) integrated circuitry. 1,2Defect-free SWNT synthesis is generally thought to require high temperatures (T). 3 This belief arises from the success of high-T deposition processes. Arc-discharge, laser ablation, and high-pressure CO conversion with inherent (local) temperatures in the order of 1000-4000°C have been optimized mainly for bulk CNT production. 3 For device fabrication, these techniques heavily rely on purification from other carbon allotropes and an indirect postgrowth assembly via stable suspensions. In comparison, catalytic chemical vapor deposition (CVD) allows selective, aligned CNT growth directly onto a substrate and thus presently is the only economically viable process for integrating CNTs into a device. 1,[4][5][6] This approach, however, exposes the substrate to the CNT growth temperature and atmosphere, which creates a need for less aggressive, low T processing conditions. Present back-end CMOS technology allows a maximum temperature of 400-450°C, the limit being set by the mechanical integrity of low dielectric constant intermetal dielectrics. 7 Thermal CVD of SWNTs has been reported at 550°C in furnace 8 and cold wall systems. 9 In situ environmental transmission electron microscopy (TEM) experiments show SWNT nucleation at 480°C. 10 Random-network FETs have been fabricated with SWNTs grown at 450°C by remote plasma-enhanced (PE) CVD.11 However, the high temperatures of bulk production techniques still dominate growth model considerations with the assumption that the catalyst cluster has to be liquefied and that the catalyst bulk is ratecontrolling.12,13 These considerations are also transferred to surface-bound CVD. 14 CNT growth below 500°C is not thought to be possible based on calculations of size-corrected melting points 14 and carbon saturation. 15In this Letter, we report SWNT growth at temperatures below 450°C by thermal CVD at cold wall conditions and demonstrate field effects in as-integrated SWNT FETs. We use evaporated thin catalyst films, which allow accurate patterning by standard lithography techniques and thus compa...

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“…Furthermore, the presence of small concentrations of Mo reduce the lower size limit of low-temperature steady-state growth from ∼0.58nmf orpureF eparticlesto ∼ 0.52nm. Our ab initio-thermodynamic modeling explains experimental results and establishes a new direction to search for better catalysts.Critical factors for the efficient growth of single walled carbon nanotubes (SWCNTs) via catalytic chemical vapor deposition (CCVD) 1,2,3 are the compositions of the interacting species (feedstock, catalyst, support 4,5,6,7,8,9,10 ), the preparation of the catalysts, and the synthesis conditions 11,12,13,14,15,16,17,18 . Efficient catalysts must have long active lifetimes (with respect to feedstock dissociation and nanotube growth), high selectivity and be less prone to contamination 19,20,21,22,23 .…”

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Influence of Mo on the Fe:Mo:C nanocatalyst thermodynamics for single-walled carbon nanotube growth

et al. 2008

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We explore the role of Mo in Fe:Mo nanocatalyst thermodynamics for low-temperature chemical vapor deposition growth of single walled carbon nanotubes (SWCNTs). By using the size-pressure approximation and ab initio modeling, we prove that for both Fe-rich (∼ 80% Fe or more) and Mo-rich (∼ 50% Mo or more) Fe:Mo clusters, the presence of carbon in the cluster causes nucleation of Mo2C. This enhances the activity of the particle since it releases Fe, which is initially bound in a stable Fe:Mo phase, so that it can catalyze SWCNT growth. Furthermore, the presence of small concentrations of Mo reduce the lower size limit of low-temperature steady-state growth from ∼0.58nmf orpureF eparticlesto ∼ 0.52nm. Our ab initio-thermodynamic modeling explains experimental results and establishes a new direction to search for better catalysts.Critical factors for the efficient growth of single walled carbon nanotubes (SWCNTs) via catalytic chemical vapor deposition (CCVD) 1,2,3 are the compositions of the interacting species (feedstock, catalyst, support 4,5,6,7,8,9,10 ), the preparation of the catalysts, and the synthesis conditions 11,12,13,14,15,16,17,18 . Efficient catalysts must have long active lifetimes (with respect to feedstock dissociation and nanotube growth), high selectivity and be less prone to contamination 19,20,21,22,23 . Common factors that lead to reduction in catalytic activity are deactivation (i.e. chemical poisoning or coating with carbon), thermal sintering (e.g. caused by highly exothermic reactions on the clusters surface 13,14,24 with insufficient heat transfer 25,26 ) and solid-state reactions (nucleation of inactive phases in the cluster 22,23,25 ).Metal alloy catalysts, such as Fe:Co, Co:Mo and Fe:Mo, improve the growth of CNTs 4,10,20,27,28,29,30,31 , because the presence of more than one metal species can significantly enhance the activity of a catalyst 20,32,33,34 , and can prevent catalyst particle aggregation 20,31,32,33 . In the case of Fe:Mo nanoparticles supported on Al 2 O 3 substrates, the enhanced catalyst activity has been shown to be larger than the linear combination of the individual Fe/Al 2 O 3 and Mo/Al 2 O 3 activities 20,27,28 . This is explained in terms of substantial inter-metallic interaction between Mo, Fe and C 20,35,36 which is congruent with previously observed solid-state reactions between these elements. In fact, the addition of Mo in mechanical alloying of powder Fe and C mixtures 38 promotes solid state reactions even at low Mo concentrations by forming ternary phases, such as the (Fe,Mo) 23 C 6 type carbides 38 .The way in which carbon interacts with transition metals depends on the metal species. Fe and Co belong to the "carbon dissolution-precipitation mechanism" group, where relatively large fractions of carbon dissolve into the cluster before stable carbides are formed, while Mo belongs to the "carbide formation-decomposition" group where carbide formation occurs rapidly at low carbon concentrations 39 . These mechanisms are governed by the interplay between solub...

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Direct Observation of Single-Walled Carbon Nanotube Growth at the Atomistic Scale

Abstract: The growth dynamics of a single-walled carbon nanotube (SWNT) is observed in real-time using an in situ ultrahigh vacuum transmission electron microscope at 650 degrees C. SWNTs preferentially grow on smaller sized catalyst particles (diameter Show more

Cited by 226 publications

References 27 publications

The dynamics of the nucleation, growth and termination of single-walled carbon nanotubes from in situ Raman spectroscopy during chemical vapor deposition

The dynamics of the nucleation, growth and termination of single-walled carbon nanotubes from in situ Raman spectroscopy during chemical vapor deposition

Catalytic Chemical Vapor Deposition of Single-Wall Carbon Nanotubes at Low Temperatures

Influence of Mo on the Fe:Mo:C nanocatalyst thermodynamics for single-walled carbon nanotube growth

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