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Effect of Environmental Gas on the Growth of CNT in Catalystically Pyrolyzing C 2 H 2

Effect of Environmental Gas on the Growth of CNT in Catalystically Pyrolyzing C 2 H 2. Minjae Jung*, Kwang Yong Eun, Y.-J. Baik, K.-R. Lee , J-K. Shin* and S. T. Kim* Thin Film Technology Research Center Korea Institute of Science and Technology * LG Corporation Institute of Technology.

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Effect of Environmental Gas on the Growth of CNT in Catalystically Pyrolyzing C 2 H 2

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  1. Effect of Environmental Gas on the Growth of CNT in Catalystically Pyrolyzing C2H2 Minjae Jung*, Kwang Yong Eun, Y.-J. Baik, K.-R. Lee, J-K. Shin* and S. T. Kim* Thin Film Technology Research Center Korea Institute of Science and Technology * LG Corporation Institute of Technology

  2. 12.5㎛ Carbon Nano-Tubes (CNT) • Unique Structure and Properties • Suggested Potential Applications • Cold Cathode for FED • Hydrogen Storage Materials • Electrode for Fuel Cell • Nanoscale Transistors

  3. 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 are not fully understood, yet.

  4. The Present Work • 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 of the metal catalyst.

  5. SiO2 Si(100) Formation of Catalyst Particles Ni, Co film deposition Agglomeration of the film Heat treatment @ 800oC H2 300nm 300nm 3.4nm Ni 6.8nm Ni

  6. Furnace Hood Substrate holder Loading system H2O Gas inlet • Tube type reactor with quartz tube (50F, 800L) 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

  7. 300nm 300nm In N2 Environment 2.4 vol. % C2H2 at 850℃

  8. In H2+N2 Environment 300nm 3.00㎛ 1.50㎛ H2/(H2+N2) = 0.6 (120sccmH2 / 80sccmN2) H2/(H2+N2) = 0.85 (170sccmH2 / 30sccmN2) H2/(H2+N2) = 1 (200sccmH2) 2.4 vol. % C2H2 at 850℃ The Same Behavior in H2+Ar Environment

  9. Catalyst Surface after Pretreatment in H2+N2 Environment N2 acts like an inert gas.

  10. Role of Hydrogen 2C+H2 C2H2 Lower Decomposition Rate of C2H2 Prevent the Catalyst Passivation Enhance the CNT Growth

  11. 3.00㎛ 300nm 1.00㎛ at 850 ℃ at 950℃ 2.4 vol. % C2H2 in H 2/(H2+N2) = 1 at 750 ℃ 2.4 vol. % C2H2 in H 2/(H2+N2) = 0.35

  12. 40nm TEM Microstructure of CNT Bamboo-like Growth

  13. 6nm In NH3 Environment for 7min at 950℃ with 16.7 vol. % C2H2 in pure NH3

  14. 9.1 vol. % C2H2for 15min 4.8 vol. % C2H2for 20min 23.1 vol. % C2H2for 7min 16.7 vol. % C2H2for 7min at 950oC in pure NH3 Environment

  15. 300nm NH3 Environment Effect at 950℃ with 16.7 vol. % C2H2 in pure NH3 at 950℃ with 2.4 vol. % C2H2 in N2+H2 : H/(H+N)=0.75

  16. Catalyst Surface after Pretreatment 300nm In pure NH3 300nm In H2+N2

  17. NH3 N + 3/2 H2 Ease of Decomposition of NH3 • NH3 is much easier to be decomposed than N2 • Increase in activated nitrogen.

  18. Role of Activated Nitrogen ①Enhance the graphitic layer formation on the catalyst surface ② Enhance the separation of the layer from the catalyst surface

  19. The Catalyst Effect Ni Co at 950℃ with 16.7 vol. % C2H2 in pure NH3 environment

  20. Co Ni Catalyst Surface after Pretreatment

  21. Co Ni at 950℃ with 16.7 vol. % C2H2 in pure NH3 Environment CNT Growth Without Pretreatment Nitrogen incorporation to the catalyst is essential in Ni

  22. Co Ni Co Ni 9.5 vol.% C2H2 In 33 vol.% NH3+H2 9.5 vol.% C2H2 In 5 vol.% NH3+H2

  23. 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

  24. Growth of Vertically Aligned CNT Straight form Tangled form 12.5㎛

  25. Evolution of Vertically Aligned CNT 70sec (9.8㎛/min) 4min (1.1㎛/min) 7min(0.8㎛/min ) at 950℃ with 16.7 vol. % C2H2 in pure NH3 Environment Intimate Relationship Between the Growth Rate and the Vertically Aligned CNT

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