Carbon%20Nanotube%20Growth%20Enhanced%20by%20Nitrogen%20Incorporation

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Carbon Nanotube Growth Enhanced by Nitrogen
Incorporation

• Tae-Young Kima), Kwang-Ryeol Lee, Kwang Yong Eun
  and Kyu-Hwan Oha)
• Future Technology Research Division, Korea
  Institute of Science and Technology
• a)Department of Materials Engineering, Seoul
  National University

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Carbon Nano-Tubes(CNT)

• Unique Structure and Properties
• Suggested Applications

Strength bending strength Youngs modulus
average 1.8TPa Current Conductivity
resistivitylt10-4 Ohm.cm Thermal Conductivity
nearly that of diamond Capillary effect..
Probe tip
Field emitter
Electrode in batteries
Conducting wire
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Synthesis of CNT

• Arc discharge, Laser ablation, Plasma CVD,
  Thermal CVD
• Thermal CVD

• Reaction hydro-carbon gas with metal catalyst
  particle
• Environment gas affect CNT growth

Most previous results using the CVD process
showed that the vertically aligned CNTs were
obtained in N2 or NH3 gas environments, which
reveals the key role of nitrogen in CNT growth
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Environment gas effect in CNT growth
Synthesis condition Synthesis condition Synthesis condition Synthesis condition CNT Morphology Citation
method Temperatue(oC) Reaction Gas Catalyst CNT Morphology Citation
PE-CVD 666 C2H2NH3 Ni Aligned CNT Science 282, 1105 (1998)
PE-CVD 660 C2H2NH3 Ni Aligned CNT APL 75 1086 (1999)
PE-CVD 825 C2H2NH3 Co Aligned CNT APL 77 830 (2000)
Thermal-CVD 750950 C2H2NH3 Fe Aligned CNT APL 77 3397 (2000)
PE-CVD 825 C2H2NH3 Co Aligned CNT APL 77 2767 (2000)
Thermal-CVD 800 C2H2NH3 Fe Aligned CNT APL 78 901 (2001)
Thermal-CVD 950 C2H2NH3 Ni, Co Aligned CNT TSF 398-399 150 (2001)
Thermal-CVD 850 C2H2H2, C2H2N2 Ni, Co Tangled CNT TSF 398-399 150 (2001)
Thermal-CVD 950 C2H2NH3 Ni Aligned CNT DRM 10 1235 (2001)
Thermal-CVD 950 C2H2H2, C2H2N2 Ni Tangled CNT DRM 10 1235 (2001)
Thermal-CVD 800900 C2H2NH3 Ni Aligned CNT JAP 91 3847 (2002)
Thermal-CVD 600900 C2H2H2 Ni Aligned CNT JAP 91 3847 (2002)
Thermal-CVD 600900 C2H2H2 Ni Tangled CNT JAP 91 3847 (2002)
PE-CVD 660lt C2H2NH3 Ni Aligned CNT APL 80 4018 (2002)
Thermal-CVD 850900 C2H2Ar Ni, Co Tangled CNT APL 75 1721 (1999)
PE-CVD 500 CH4N2 Fe, Ni Aligned CNT APL 75 3105 (1999)
PE-CVD 550 CH4N2 Fe Aligned CNT JAP 89 5939 (2001)
PE-CVD 700 CH4H2 Ni Aligned CNT APL 76 2367 (2000)
Thermal-CVD 800 ferrocenexylene Fe Aligned CNT APL 77 3764 (2000)
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Environment Gas Effect
300nm
3.00?
300nm
N2
H2
H2N2(32)
2.4 vol. C2H2
CNT did not grow in N2, H2 and their mixture gas
environment
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Growth of Vertically Aligned CNTs
Environment gas effect
H2N2 vs. NH3
5.00?
300nm
2.4 vol. C2H2 in H2 N2 (31)
16.7 vol. C2H2 in NH3
But Vertically aligned CNTs grow in an NH3
environment
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Environment Gas Effect on Catalyst
Ni particles after pretreatment for 1h
H2N2 vs. NH3
Reaction(x)
Pretreatment
Add C2H2 to the environmental gas
H 2 , N 2 , H 2 N 2, NH 3
Nitrogen peak was observed only in an NH3
environment
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Activated Nitrogen Effect

• Activated nitrogen in NH3 environment play a
  significant role in the CNT growth kinetics.

• Suggestion
• Activated nitrogen
• Enhance formation of the graphitic layer on the
  catalyst
• Enhance the separation of the graphitic layer
  from the catalyst surface.

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Purpose of Present Work

• Research Reaction Kinetics and Growth Mechanism
  of Vertically Aligned Carbon nano-tube in the
  view point of activated nitrogen.

• When, Where, How does Activated Nitrogen affect
  CNT growth in overall process?.
• Does nitrogen modify the surface of catalyst in
  pretreatment process?
• Does nitrogen affect the CNT growth in reaction
  process?

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Experimental Procedure
Formation of Catalyst Particles
Thermal CVD

• Tube type reactor with quartz tube (50F, 800L)
  at 1 atm.
• Procedure
• à Sample loading after increasing temperature in
  Ar
• Pretreatment for 1hr in H 2 , N 2 ,
• H 2N 2 ,
  NH 3
• à Reaction C2H2 environmental gas
• à Cooling in Ar

300nm
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Purpose of Present Work

• Research Reaction Kinetics and Growth Mechanism
  of Vertically Aligned Carbon nano-tube in the
  view point of activated nitrogen.

• When, Where, How does Activated Nitrogen affect
  CNT growth in overall process?
• Does nitrogen modify the surface of catalyst in
  pretreatment process?
• Does nitrogen affect the CNT growth in reaction
  process?

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Catalyst Pretreatment Effect
Reaction Pretreatment H2C2H2 NH3 C2H2
H2
NH3 H2
NH3
Pretreatment in an NH3 environment is neither a
sufficient nor a necessary condition for the
vertically aligned CNT growth
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Purpose of Present Work

• Research Reaction Kinetics and Growth Mechanism
  of Vertically Aligned Carbon nano-tube in the
  view point of activated nitrogen.

• When, Where, How does Activated Nitrogen affect
  CNT growth in overall process?
• Does nitrogen modify the surface of catalyst in
  pretreatment process?
• Does nitrogen affect the CNT growth in reaction
  process?

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Effect of NH3 Atmosphere in Reaction
0.015
Pretreatment in an NH3 environment is neither a
sufficient nor a necessary condition for the
vertically aligned CNT growth
0.17
0.05
Reaction Various C2H2 ratio ( X
C2H2/C2H2NH3,, fixing NH3 100sccm)
Reaction
Pretreatment
NH3 C2H2
H2
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Activated Nitrogen in CNT
Nitrogen concentration in CNT increased with
increasing CNT growth rate and the degree of
alignment, which exhibits an intimate
relationship between CNT growth and nitrogen
incorporation
Nitrogen in the CNT is chemically bonded with the
carbon atoms of the graphitic basal plane.
Fixing NH3 flux 100sccm
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Role of Nitrogen in CNT
Nitrogen incorporation to the CNT would reduce
the strain energy (Estr) required to form a
tubular graphitic layer. The reduced strain
energy would in turn enhance the nucleation rate
of the graphitic layer on the curved catalyst
surface. Further CNT growth also requires
continuous deposition of the tubular graphitic
layer, where nitrogen incorporation can reduce
the strain energy
PRB, VOLUME 64, 235401

• PRB. VOLUME 59, 5162

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Conclusion

• Surface modification of catalyst by activated
  nitrogen would not affect the vertically aligned
  CNT growth.
• Activated nitrogen in CNT would have relation
  with CNT growth rate.
• --Activated nitrogen incorporated into the CNT
• would decrease the activation energy of
• CNT formation.

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