Molecular Dynamics simulation of Carbon Nanotube Growth

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Molecular Dynamics simulation of Carbon Nanotube
Growth

• Feng Ding, Arne Rosèn, Kim Bolton
• Molecular Physics Group
• Göteborg University, Chalmers University,
• University College of Borås
• Sweden

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VLS model
M. Chhowalla, K. B. K. Teo, C. Ducati, N. L.
Rupesinghe, G. A. J. Amaratunga, A. C. Ferrari,
D. Roy, J. Robertson, and W. I. Milne  JOURNAL OF
APPLIED PHYSICS VOLUME 90, NUMBER 10  
Oleg A. Louchev, Thomas Laude, Yoichiro Sato, and
Hisao Kanda   JOURNAL OF CHEMICAL PHYSICS VOLUME
118, NUMBER 16  
G. Y. Zhang, X. C. Ma, D. Y. Zhong, and E. G.
Wanga)   JOURNAL OF APPLIED PHYSICS VOLUME 91,
NUMBER 11
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The VLS model for CNT growth

• 1. Deposit catalyst particles on a substrate.
• 2. Catalyst dissociates carbon rich gases (CO,
  CH4, C2H2) and produces carbon atoms.
• C atoms dissolve into the catalyst particle.
• Some C atoms precipitate on the surface when
  supersaturated.
• The precipitated C atoms nucleate into carbon
  nanotubes.

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Motivation

• The VLS model is too simple, what are the
  details?
• How does the graphitic island form on the
  catalyst surface?
• How does the island lift off the surface?
• Why does the CNT have the same diameter as the
  catalyst particle?
• What is the driving force for CNT growth
  (temperature or concentration gradient?)
• Does the catalyst particle need to be liquid for
  CNT growth?

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Overview of the potential energy surface for our
MD simulations
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I. Detailed nucleation process
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a. 0 ns
Unsaturated
g. 18 ns
b. 1.5 ns
f. 10 ns
g. 2.8 ns
e. 3 ns
d. 2.5 ns
c. 2.0 ns
Highly Supersaturated
Supersaturated
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A detailed VLS growth model
J. Phys. Chem. B, 108, 17369-17377 (2004)
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II. Is the temperature gradient the essential
driving force for CNT growth?
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Temperature gradient
Concentration gradient
Or
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Is the temperature gradient essential?
Chem. Phys. Lett. 393, 309-313 (2004).
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III. SWNT diameter vs. catalyst particle diameter
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Dependence of Particle Size on Growth
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What determines the diameter of the SWNT
J. Chem. Phys. 121, 2775 (2004).
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IV. Must the catalyst particle be liquid?
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Coalescence of Clusters at below Melting
Temperatures
Phys. Rev. B 70, 075416 (2004).
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Melting Point of Metal Nano-Particles

J. Vac. Sci. Technol. A 22, 1471 (2004).  
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CNT growth from a solid catalyst particle
Carbon, in press
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Conclusion

• MD simulations reveal the details of VLS growth
  of SWNTs.
• The simulated CNTs always have same diameter as
  the catalyst particle
• The temperature gradient is not an essential part
  of the VLS model
• The catalyst particle need not be liquid for CNT
  growth