Effects of ammonia on the alignment of carbon nanotubes in metal-assisted thermal chemical vapor deposition

Choi, Kyuseok; Cho, Y.S; Hong, Sang-Young; Park, J.B; Kim, Dojin

doi:10.1016/s0955-2219(01)00179-0

Cited by 47 publications

(9 citation statements)

References 7 publications

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“…Nitrogen can influence CNT growth in interesting ways. Choi et al observed a marked increase in straight nanotube alignment by co-injecting ammonia and acetylene over a nickel metal catalyst in a CVD reactor heated between 600 and 950 °C. This phenomenon was attributed to the inhibition of amorphous carbon growth .…”

Section: Parameters Influencing Carbon Nanotube Growthmentioning

confidence: 99%

A Review of Carbon Nanotube Synthesis via Fluidized-Bed Chemical Vapor Deposition

and

Harris

2007

Ind. Eng. Chem. Res.

274

152

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Carbon nanotubes (CNTs) are crystalline, tubular, carbon structures with extraordinary mechanical, chemical, optical, and electrical properties. These unique properties make CNTs potentially valuable in a wide range of end-use applications. Currently, research into nanotubes and their applications is hampered by the lack of a suitable technique for manufacturing them in large quantities, which we define here as 10 000 tons per plant per year. Consequently, research into large-scale manufacturing techniques is ongoing. There are three established methods of CNT synthesis: (i) arc discharge, (ii) laser ablation, and (iii) chemical vapor deposition (CVD). Of these, CVD techniques show the greatest promise for economically viable, large-scale synthesis, based upon yields reported in the literature and the inherent scalability of similar technologies, e.g., fluidized catalytic cracking. In particular, the fluidized-bed CVD (FBCVD) technique (where the CVD reaction occurs within a fluidized bed of catalyst particles) has the potential to produce high-quality CNTs, inexpensively in large quantities. In this work, we review the existing literature on CNT synthesis via FBCVD and demonstrate that no systematic study of the key parameters has been undertaken. We demonstrate that there is no clear understanding of the influence of key variables (e.g., temperature, pressure, and carbon source) on CNT properties (e.g., CNT diameter, length, and morphology), which shows that further research is necessary to optimize this process and, ultimately, understand the science behind CNT growth using this technique. We also highlight the assessment of CNT quality as being an issue for further research. CNT quality is usually characterized visually (e.g., from TEM images), and a standard CNT characterization protocol has yet to be elucidated. The successful scale-up of any process requires detailed understanding of key process parameters and their interactions. Hence, further research to optimize the purity, yield, and selectivity of the synthesized CNTs is required before the potential of this technique can be realized.

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Section: Parameters Influencing Carbon Nanotube Growthmentioning

confidence: 99%

A Review of Carbon Nanotube Synthesis via Fluidized-Bed Chemical Vapor Deposition

and

Harris

2007

Ind. Eng. Chem. Res.

274

152

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“…The presence of nitrogen can induce a number of interesting effects on nanotube growth. Choi et al co-injected ammonia with acetylene using a CVD technique with nickel metal catalyst and temperatures between 600 and 950 °C and observed a marked increase in nanotube alignment. Inhibition of amorphous carbon was the suggested mechanism for this effect.…”

Section: Introductionmentioning

confidence: 99%

Carbon Nanotube Formation and Growth via Particle−Particle Interaction

et al. 2005

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Carbon nanotubes are observed to form under a wide range of temperatures, pressures, reactive agents, and catalyst metals. In this paper we attempt to rationalize this body of observations reported in the literature in terms of fundamental processes driving nanotube formation. Many of the observed effects can be attributed to the interaction of three key processes: surface catalysis and deposition of carbon, diffusive transport of carbon, and precipitation effects. A new nanotube formation mechanism is proposed that describes the nanotube structures observed experimentally in a premixed flame and can account for certain shortcomings of the prevailing mechanism that has been repeatedly applied to explain nanotube formation in nonflame environments. The interacting particle model (IPM) attributes the initiation of nanotube growth to the physical interaction between catalyst particles. Coalescence of two (or more) catalyst particles leads to partial blocking of the particle surface, causing a disparity in carbon deposition over the particle surface. The resulting concentration gradient generates a net diffusive flux toward the interparticle contact point. Dimers that separate in this condition can support continuous nanotube growth between the particles. The model can also be extended to multiple particles to account for more complex morphologies. The IPM is consistent with many of the structures observed in the flame-produced material. The validity of the model is evaluated through analysis of diffusion dynamics and a force analysis of particle binding and separation. The IPM is also discussed in relation to identifying the requirements and best conditions to support nanotube growth in the premixed flame. The formation of nanotubes between particles as described by the IPM indicates that a single mechanism cannot completely describe nanotube synthesis; more likely, multiple pathways exist with varying rates that depend on specific process conditions.

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“…gas. Ammonia etching as argued by Choi et al [21] and Teo et al [22] and is crucial in forming nanoislands from continuous film of catalyst to promote aligned array of MWCNT. FESEM image reveals the formation of nanoislands after etching for both samples but with sample deposited by ferrocene vaporization (Figure 2(f)); micrometer size cavities are observed.…”

Section: Resultsmentioning

confidence: 99%

Effect of Different Catalyst Deposition Technique on Aligned Multiwalled Carbon Nanotubes Grown by Thermal Chemical Vapor Deposition

Saheed

Mohamed

Burhanudin

2014

Journal of Nanomaterials

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The paper reported the investigation of the substrate preparation technique involving deposition of iron catalyst by electron beam evaporation and ferrocene vaporization in order to produce vertically aligned multiwalled carbon nanotubes array needed for fabrication of tailored devices. Prior to the growth at 700°C in ethylene, silicon dioxide coated silicon substrate was prepared by depositing alumina followed by iron using two different methods as described earlier. Characterization analysis revealed that aligned multiwalled carbon nanotubes array of 107.9 µm thickness grown by thermal chemical vapor deposition technique can only be achieved for the sample with iron deposited using ferrocene vaporization. The thick layer of partially oxidized iron film can prevent the deactivation of catalyst and thus is able to sustain the growth. It also increases the rate of permeation of the hydrocarbon gas into the catalyst particles and prevents agglomeration at the growth temperature. Combination of alumina-iron layer provides an efficient growth of high density multiwalled carbon nanotubes array with the steady growth rate of 3.6 µm per minute for the first 12 minutes and dropped by half after 40 minutes. Thicker and uniform iron catalyst film obtained from ferrocene vaporization is attributed to the multidirectional deposition of particles in the gaseous form.

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Effects of ammonia on the alignment of carbon nanotubes in metal-assisted thermal chemical vapor deposition

Cited by 47 publications

References 7 publications

A Review of Carbon Nanotube Synthesis via Fluidized-Bed Chemical Vapor Deposition

A Review of Carbon Nanotube Synthesis via Fluidized-Bed Chemical Vapor Deposition

Carbon Nanotube Formation and Growth via Particle−Particle Interaction

Effect of Different Catalyst Deposition Technique on Aligned Multiwalled Carbon Nanotubes Grown by Thermal Chemical Vapor Deposition

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