Vertically-aligned carbon nanotube at low pressure by cold-wall thermal CVD using a two-phase deposition step

Machado, George; Coelho, Cláudia

doi:10.1016/j.cartre.2021.100087

Cited by 7 publications

(5 citation statements)

References 15 publications

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“…The integration of CNTs in any application requires the control of their synthesis method for yield, alignment, and purity [9]. CNTs can be synthesized using arc discharge, laser ablation, high-pressure carbon monoxide disproportionation (Hipco), and chemical vapor deposition (CVD) [10,11]. In the CVD process, the thermal decomposition of hydrocarbon vapor is achieved in the presence of a metal catalyst [12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Water-Assisted Catalytic VACNT Growth Optimization for Speed and Height

Strobl¹,

Rajab

2023

Processes

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The super-growth approach for carbon nanotubes synthesis is frequently used to boost the growth rate, catalyst lifespan, and height of vertically aligned carbon nanotubes. The elimination of amorphous carbon from catalyst particles, commonly made of iron, by injecting water vapor into a chemical vapor deposition process can enhance the purity, alignment, and height of carbon nanotubes and prevent the partial oxidation of the metallic catalyst. We present the development of a modified growth-optimized water-assisted super-growth vertically aligned carbon nanotube process by optimizing the catalyst layer structure and water vapor concentration for a carbon nanotube growth process for 4” diameter Si wafers. A significant finding is that under optimized water-assisted growth conditions over 4 mm, highly uniform tall, vertically aligned carbon nanotube structures can be grown with a minimum top crust layer of about ~5–10 μm thickness. This was achieved with a catalyst film comprising a >400 mm thermal SiO2 layer on top of a 4” diameter Si wafer that was overcoated with an e-beam batch process run that first deposited a 20 nm SiO2 layer, a 10 nm Al2O3 layer, and a 1.1 nm Fe layer, in a 4-h growth process step.

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Section: Introductionmentioning

confidence: 99%

Water-Assisted Catalytic VACNT Growth Optimization for Speed and Height

Strobl¹,

Rajab

2023

Processes

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“…Recently, Machado Jr. and Coelho (2021) [ 23 ] reported a novel method to obtain 140 µm tall VA‐CNT forests, using a cold‐wall technique based on a two‐phase deposition step. The first phase consists of the flow of NH 3 for a short period of time together with the C 2 H 2 flow to ensure catalyst activation.…”

Section: Introductionmentioning

confidence: 99%

“…The previous studies [ 23 ] demonstrated that, when increasing the time of the deposition step, the expected height increase does not always occur, which is most probably related to the lifetime of the catalyst nanoparticles. The CNT recipe uses carbon precursors which, depending on pressure, temperature, and flow conditions coat the catalyst with amorphous carbon, blocking the nanotube growth.…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, for a recipe with a two‐phase deposition step, increasing the growth time above 30 min results in smaller VA‐CNT forests. [ 23 ] On the other hand, when adding an extra phase of H 2 to the deposition step and purges between the phases, in a total growth time of 33 min, the height increased from 272 to 400 µm. [ 24 ] This suggests that performing multiple purges during the deposition step keeps the catalyst nanoparticles active for a longer time.…”

Section: Introductionmentioning

confidence: 99%

“…[17] The etchant materials generally used are CO 2 , H 2 O, and O 2 , however, excess levels of oxygencontaining compounds can result in etching of the CNTs themselves. [18] Sugime et al ( 2021) [22] using the hot wire filament grew CNT around 14 cm but in this case the industrial growth is far in terms of reproducibility in quantity.Recently, Machado Jr. and Coelho (2021) [23] reported a novel method to obtain 140 µm tall VA-CNT forests, using a coldwall technique based on a two-phase deposition step. The first phase consists of the flow of NH 3 for a short period of time together with the C 2 H 2 flow to ensure catalyst activation.…”

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confidence: 99%

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1.1‐Millimeter Tall Vertically Aligned‐Carbon Nanotubes Grown by Cold Wall CVD Using a Novel Multiple‐Purge Method

Coelho

Machado

2022

Adv Materials Inter

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These processes still have limitation in achieving high yield and quality, and any commercial use of CNTs is limited due to these challenges encountered in large scale synthesis. [17] According to Shi et al. (2017), [18] "The poor reproducibility in CNT synthesis via CVD has been attributed to fluctuations in ambient and reactor-sorbed water vapor, as well as to carbonaceous deposits inside reactors leading to growth hysteresis." The presence of water or oxygen influences the growth gases and contributes to the formation or removal of carbon coated on the catalyst nanoparticles and avoiding this block deposition. The formation of carbon block coated on the catalyst nanoparticles prevents the CNT forests to grow taller, terminating the growth process. Thus, to obtain taller CNT forests, the lifetime of the catalyst should be prolonged. [17] The abrupt saturation point is observed for CNT growth rate controlled by laser with Meshot and Hart ( 2008). [19] The carbon atoms that reach the catalyst nanoparticles contribute to the CNT growth, but they also coat in form of amorphous carbon on the nanoparticle. Xiang et al. ( 2008) [20] refers to the growth limits of CNT carpets, explaining the diffusion mechanism of precursors for several different methods. Xiang et al. ( 2007) [21] refers the catalyst encapsulation occurs and it can be controlled during the growth changing the saturation point, creating a continuous growth mechanism. This deposition can be controlled by continuously supplying an etchant material that etches out the amorphous carbon coated on the catalyst nanoparticles. [17] The etchant materials generally used are CO 2 , H 2 O, and O 2 , however, excess levels of oxygencontaining compounds can result in etching of the CNTs themselves. [18] Sugime et al. ( 2021) [22] using the hot wire filament grew CNT around 14 cm but in this case the industrial growth is far in terms of reproducibility in quantity.Recently, Machado Jr. and Coelho (2021) [23] reported a novel method to obtain 140 µm tall VA-CNT forests, using a coldwall technique based on a two-phase deposition step. The first phase consists of the flow of NH 3 for a short period of time together with the C 2 H 2 flow to ensure catalyst activation. In the second phase, NH 3 flow is replaced by H 2 flow during the remaining growth time, permitting to obtain tall VA-CNT forests. In this work the saturation point was reached before the 40 min on deposition step in order to get 140 µm. Furthermore, the annealing temperature should be lower than the growth temperature to obtain taller forests. [24] Moreover, adding a third phase of H 2 during the deposition step at a temperature 50 °C above the previous phase, including a purge between each phase, allowed to achieve forests as high and uniform as This paper reports a multi-phase deposition for the growth of carbon nanotubes, intercalating phases of effective growth with purges of the reactor, based on the method recently proposed by the author to grow tall vertically aligned carbon nanotubes (VA-CNT) in a c...

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