Moderating carbon supply and suppressing Ostwald ripening of catalyst particles to produce 4.5-mm-tall single-walled carbon nanotube forests

Hasegawa, Kiichi; Noda, Suguru

doi:10.1016/j.carbon.2011.06.061

Cited by 68 publications

(66 citation statements)

References 35 publications

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“…Coarsening of catalyst particles through Ostwald ripening and carbonization of catalyst particles as a result of the excess carbon feed are important deactivation mechanisms. While the former is suppressed at lower temperature, the latter gets more significant at lower temperature and, thus, the C 2 H 2 should be fed at lower partial pressures for lower CVD temperatures [26]. Hence, we fed 0.13-1.3 Pa C 2 H 2 at 400°C, which is two to three orders of magnitude lower than that for the millimeter-tall CNT arrays at 800°C in previous studies [26,28,29].…”

Section: 2mentioning

confidence: 97%

“…The requirement of low CVD temperature is beneficial for preparation of dense catalyst particles on conductive underlayers because both catalyst deactivation as a result of alloying with the underlayer and coarsening through Ostwald ripening [25,26] can be prevented at low temperatures. We selected TiN [18], which is frequently used as a barrier material in LSIs, as the conductive underlayer and deposited Ni onto it.…”

Section: Preparation Of Dense Catalyst Particles On a Conductive Undementioning

confidence: 99%

“…Various carbon containing species, such as C 2 H 2 [26,28,29], C 2 H 4 [2,4], and C 2 H 5 OH [13], can be used as feedstock for millimeter-tall, vertically aligned CNT arrays. However, C 2 H 2 directly fed or forming through the decomposition of hydrocarbon/alcohol has been proven to be an efficient direct precursor for growth of such arrays [30].…”

Section: 2mentioning

confidence: 99%

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Simple and engineered process yielding carbon nanotube arrays with 1.2 × 1013cm−2 wall density on conductive underlayer at 400 °C

Kim

et al. 2015

Carbon

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A B S T R A C TA simple process is presented that realizes carbon nanotube (CNT) arrays that meet the process and structure requirements for use in large-scale integrated circuits. Ni particles are formed densely on a conductive TiN layer on SiO 2 /Si substrates through nucleation and growth by sputtering, which was stopped prior to percolation of the Ni particles. Ni particles as dense as 2.8 · 10 12 cm À2 were formed after annealing at 400°C and chemical vapor deposition (CVD) was carried out at 400°C by feeding C 2 H 2 at partial pressures as low as 0.13-1.3 Pa so as not to kill the catalyst. Scanning electron microscopy with energy dispersive X-ray spectroscopy revealed the mass density of the arrays to be as high as 1.1 g cm À3 . High resolution transmission electron microscopy showed the densely packed CNTs with an average wall number of eight. Atomic force microscopy of the root of the CNT arrays transferred to a SiO 2 /Si substrate enabled direct counting of individual CNTs, revealing areal densities of CNTs and CNT walls as high as 1.5 · 10 12 and 1.2 · 10 13 cm À2 , respectively. The simple process, using conventional sputtering and CVD apparatus, with carefully engineered conditions offers a route for practical application of CNTs.

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Section: 2mentioning

confidence: 97%

Section: Preparation Of Dense Catalyst Particles On a Conductive Undementioning

confidence: 99%

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Simple and engineered process yielding carbon nanotube arrays with 1.2 × 1013cm−2 wall density on conductive underlayer at 400 °C

Kim

et al. 2015

Carbon

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“…There are two ways to employ catalysts, one is by suspending the catalyst in the gas flow [10][11][12][13] and the other is by supporting catalysts on flat substrates [14][15][16][17] or ceramic powders [18][19][20][21]. The former catalyst is used typically for ≤10 s due to the limited residence time of the gas flow whereas the latter catalyst is used typically for 10 min-a few hours until deactivated by carbonization [22,23], oxidation [24], and/or coarsening [22,25]. Catalysts are used for much shorter times in CNT syntheses than in conventional chemical processes such as petrochemistry (typically several months), and therefore it is crucially important to prepare good catalysts quickly via practical processes.…”

Section: Introductionmentioning

confidence: 99%

“…In this work, as the first step, we studied such reactions at ten-second time scale fundamentally by fixing the nanopowders on Si substrates; the nanopowders are exposed to our previously developed electrical current heating method of Si substrates which enables quick heating and cooling in one-second time scale [28,29]. Such short annealing times likely suppresses coarsening of catalyst nanoparticles [22,25], a common problem for CNT production. In addition, the amount of CNTs per catalyst support can be increased because the nanopowders have the high specific surface area of 20−60 m 2 /g [27].…”

Section: Introductionmentioning

confidence: 99%

Catalyst nucleation and carbon nanotube growth from flame-synthesized Co-Al-O nanopowders at ten-second time scale

Shirae

Hasegawa

Sugime

et al. 2017

Carbon

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Flame-synthesized (CoO) x (Al 2 O 3) 1-x spinel nanopowders with primary particles of ~20 nm were used to grow small diameter carbon nanotubes (CNTs). The nanopowder with x ≤ 0.35 grew few CNTs whereas that with x = 0.65 grew CNTs efficiently. Low crystalline and large-diameter multi-wall CNTs grew by annealing and chemical vapor deposition (CVD) at 800 °C for ~10 min, whereas single-wall CNTs with high crystallinity (G-band to D-band intensity ratio of 20−100 by Raman spectroscopy) grew by annealing and CVD at ≥1000 °C for ~10 s. The excess Co in the spinel reduced and segregated to form multiple Co nanoparticles on the surface of the single primary alumina nanoparticles in ~10 s, yielding SWCNTs in ~10 s. Such flame synthesized nanopowders, reduced and activated by H 2 , provide CNTs from C 2 H 2 , all in ten-second time scale, and as such are promising for practical, high-through-put production of small-diameter CNTs.

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Facile Fabrication of Melamine/MXene/FeNi‐PBA Composite Derived Multi‐Interface Magnetic Carbon Foam for High‐Efficiency Microwave Absorption

Yu,

Luo,

et al. 2024

Adv Elect Materials

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The development of novel materials with high‐efficiency microwave absorption is crucial for mitigating the adverse impacts of electromagnetic pollution. In this study, MXene and FeNi Prussian blue analogs (PBA) are assembled onto a melamine foam using self‐assembly and in situ growth technique. Subsequently, magnetic carbon foam, comprising FeNi alloys, TiN and carbon with various morphologies, is synthesized via carbothermal reduction reaction. The surface morphology electromagnetic properties are significantly influenced by the pyrolysis temperature. The results revealed that the magnetic carbon foam composite demonstrated an effective microwave absorption bandwidth of 4.72 GHz at a thickness of only 1.5 mm, with a minimum reflection loss of −24.83 dB at 1.3 mm. The outstanding microwave absorption performance can be attributed to the 3D conductive network formed by N‐doped carbon, as well as the contributions from polarization loss, magnetic loss, and suitable impedance matching. Furthermore, the corresponding absorber coating demonstrated a maximum reduction value of radar cross‐section (RCS) by 13.16 dB m2. This research offers novel insights for the development of lightweight and efficient low‐filled electromagnetic composite for broadband microwave absorption.

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Moderating carbon supply and suppressing Ostwald ripening of catalyst particles to produce 4.5-mm-tall single-walled carbon nanotube forests

Cited by 68 publications

References 35 publications

Simple and engineered process yielding carbon nanotube arrays with 1.2 × 1013cm−2 wall density on conductive underlayer at 400 °C

Simple and engineered process yielding carbon nanotube arrays with 1.2 × 1013cm−2 wall density on conductive underlayer at 400 °C

Catalyst nucleation and carbon nanotube growth from flame-synthesized Co-Al-O nanopowders at ten-second time scale

Facile Fabrication of Melamine/MXene/FeNi‐PBA Composite Derived Multi‐Interface Magnetic Carbon Foam for High‐Efficiency Microwave Absorption

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