effect of environmental gas on the growth of cnt in catalystically pyrolyzing c 2 h 2 minjae jung*,...
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Effect of Environmental Gas on the Growth of CNT in Catalystically Py
rolyzing C2H2
Minjae Jung*, Kwang Yong Eun, Y.-J. Baik, K.-R. Lee, J-K. Shin* and S. T. Kim*
Thin Film Technology Research CenterKorea Institute of Science and Technology
* LG Corporation Institute of Technology
Carbon Nano-Tubes (CNT)
• Unique Structure and Properties
• Suggested Potential Applications– Cold Cathode for FED– Hydrogen Storage Materials– Electrode for Fuel Cell– Nanoscale Transistors12.5㎛12.5㎛
Synthesis of CNTs
• Arc Discharge, Plasma CVD, Laser Ablation, Thermal CVD
• Thermal CVD – Decomposition of hydrocarbon gas with Ni, Co, Fe catalyst– Advantages
• Relatively easy to obtain vertically aligned CNTs. • Can be employed for large scale production system.• Easy to understand the reaction behavior (Near Equilibrium).
Reaction kinetics and the growth mechanism Reaction kinetics and the growth mechanism are not fully understood, yet.are not fully understood, yet.
Reaction kinetics and the growth mechanism Reaction kinetics and the growth mechanism are not fully understood, yet.are not fully understood, yet.
• Analogy to carbon filament growth :
The catalyst surface should not be passivated by any reason.
Passivation : Polymeric encapsulation at low temperature Excess decomposition of hydrocarbon at high temperature
• CNT growth behavior in various environmental gases in thermal CVD
We focused on the passivation behavior We focused on the passivation behavior of the metal catalystof the metal catalyst..
We focused on the passivation behavior We focused on the passivation behavior of the metal catalystof the metal catalyst..
The Present Work
Agglomeration of the film
Si(100)
SiO2
Ni, Co film deposition
Heat treatment @ 800oC H2
3.4nm Ni 6.8nm Ni
300nm300nm 300nm300nm
Formation of Catalyst Particles
Loading system
H2O
Hood
Gas inlet
FurnaceSubstrate holder
Tube type reactor with quartz tube (50800L) at 1 atm.
Procedure: Sample loading after increasing temperature in Ar
Pretreatment for 1hr in H2, N2, H2+N2, H2+Ar, NH3
Total gas flow : 200sccm (NH3 : 100sccm)
Add C2H2 to the environmental gas
Cooling in Ar
300nm300nm
300nm300nm
2.4 vol. % C2H2 at 850℃
In N2 Environment
300nm300nm
1.50㎛1.50㎛ 3.00㎛3.00㎛
H2/(H2+N2) = 0.6
(120sccmH2 / 80sccmN2)
H2/(H2+N2) = 0.85
(170sccmH2 / 30sccmN2)
H2/(H2+N2) = 1
(200sccmH2)
The Same Behavior in H2+Ar Environment
In H2+N2 Environment
2.4 vol. % C2H2 at 850℃
Catalyst Surface after Pretreatment in H2+N2 Environment
0 500 1000 1500 2000 2500
Si
O
NiC
After 0.5min sputtering
dY/d
E (
arb.
uni
t)
Kinetic Energy (eV)
As received
NN22 acts like an inert gas. acts like an inert gas.NN22 acts like an inert gas. acts like an inert gas.
C2H2 2C+H2
Lower Decomposition Rate of C2H2Lower Decomposition Rate of C2H2
Prevent the Catalyst PassivationEnhance the CNT Growth
Role of Hydrogen
at 950℃
1.00㎛1.00㎛
300nm300nm
2.4 vol. % C2H2 in H 2/(H2+N2) = 1
3.00㎛3.00㎛
at 850 ℃
2.4 vol. % C2H2 in H 2/(H2+N2) = 0.35
at 750 ℃
40nm40nm
TEM Microstructure of CNT
Bamboo-like GrowthBamboo-like GrowthBamboo-like GrowthBamboo-like Growth
for 7min at 950℃ with 16.7 vol. % C2H2 in pure NH3
6nm
In NH3 Environment
4.8 vol. % C2H2 for 20min 9.1 vol. % C2H2 for 15min
16.7 vol. % C2H2 for 7min 23.1 vol. % C2H2 for 7min
at 950oC in pure NH3 Environment
300nm300nm
at 950 ℃ with 2.4 vol. % C2H2
in N2+H2 : H/(H+N)=0.75at 950℃ with 16.7 vol. % C2H2
in pure NH3
NH3 Environment Effect
300nm300nm
300nm300nm
In H2+N2
In pure NH3
Catalyst Surface after Pretreatment
Ease of Decomposition of NH3
NH3 N + 3/2 H2
• NHNH33 is much easier to be decomposed than N is much easier to be decomposed than N22
• Increase in activated nitrogen.Increase in activated nitrogen.
• NHNH33 is much easier to be decomposed than N is much easier to be decomposed than N22
• Increase in activated nitrogen.Increase in activated nitrogen.
① EEnhance the graphitic layer formation on the catalyst surface nhance the graphitic layer formation on the catalyst surface
② Enhance the separation of the layer from the catalyst surfaceEnhance the separation of the layer from the catalyst surface
① EEnhance the graphitic layer formation on the catalyst surface nhance the graphitic layer formation on the catalyst surface
② Enhance the separation of the layer from the catalyst surfaceEnhance the separation of the layer from the catalyst surface
Role of Activated Nitrogen
at 950℃ with 16.7 vol. % C2H2 in pure NH3 environment
Ni Co
The Catalyst Effect
0 500 1000 1500 2000
C N
O
NiSi
in NH3
in NH3/(H
2+NH
3)=0.33
in NH3/(H
2+NH
3)=0.05
Kinetic Energy (eV)
dN/d
E (a
rb.u
nit)
0 500 1000 1500 2000
C N
O
Co Si
in NH3/(H
2+NH
3)=0.05
in NH3/(H
2+NH
3)=0.33
in NH3
Kinetic Energy(eV)dN
/dE
(arb
.uni
t)
Ni Co
Catalyst Surface after Pretreatment
at 950℃ with 16.7 vol. % C2H2 in pure NH3 Environment
Ni Co
CNT Growth Without Pretreatment
Nitrogen incorporation to the catalyst Nitrogen incorporation to the catalyst is essential in Niis essential in Ni
Nitrogen incorporation to the catalyst Nitrogen incorporation to the catalyst is essential in Niis essential in Ni
Ni
Ni
Co
Co
9.5 vol.% C2H2
In 33 vol.% NH3+H2
9.5 vol.% C2H2
In 5 vol.% NH3+H2
Conclusions
• CNT growth by balancing the carbon supply with the reaction kinetics at the catalyst surface.– Gas concentration in the environment gas and the reaction
temperature
• Activated nitrogen in NH3 environment play a significant role in the CNT growth kinetics.– Enhancing the graphitic layer formation
– Enhancing the separation of the graphitic layer from the catalyst surface
– Depends on the catalyst materials
12.5㎛12.5㎛
Straight form
Tangled form
Growth of Vertically Aligned CNT
70sec (9.8㎛ /min) 4min (1.1㎛ /min) 7min(0.8㎛ /min )
Intimate Relationship Between Intimate Relationship Between the Growth Rate and the Vertically Aligned CNTthe Growth Rate and the Vertically Aligned CNT
Intimate Relationship Between Intimate Relationship Between the Growth Rate and the Vertically Aligned CNTthe Growth Rate and the Vertically Aligned CNT
Evolution of Vertically Aligned CNT
at 950℃ with 16.7 vol. % C2H2 in pure NH3 Environment