1. 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

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

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. 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. The Present Work

5. Agglomeration of the film Si(100) SiO 2 Ni, Co film deposition Heat treatment @ 800 o C H 2 3.4nm Ni6.8nm Ni 300nm Formation of Catalyst Particles

6. Loading system H2OH2O Hood Gas inlet Furnace Substrate holder  Tube type reactor with quartz tube (50  800L) at 1 atm.  Procedure:  Sample loading after increasing temperature in Ar  Pretreatment for 1hr in H 2, N 2, H 2 +N 2, H 2 +Ar, NH 3 Total gas flow : 200sccm (NH 3 : 100sccm)  Add C 2 H 2 to the environmental gas  Cooling in Ar

7. 300nm 2.4 vol. % C 2 H 2 at 850 ℃ In N 2 Environment

8. 300nm 1.50 ㎛ 3.00 ㎛ H 2 /(H 2 +N 2 ) = 0.6 (120sccmH 2 / 80sccmN 2 ) H 2 /(H 2 +N 2 ) = 0.85 (170sccmH 2 / 30sccmN 2 ) H 2 /(H 2 +N 2 ) = 1 (200sccmH 2 ) The Same Behavior in H 2 +Ar Environment In H 2 +N 2 Environment 2.4 vol. % C 2 H 2 at 850 ℃

9. Catalyst Surface after Pretreatment in H 2 +N 2 Environment N 2 acts like an inert gas.

10. C2H2C2H2 2C+H 2 Lower Decomposition Rate of C 2 H 2 Prevent the Catalyst Passivation Enhance the CNT Growth Role of Hydrogen

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

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

13. for 7min at 950 ℃ with 16.7 vol. % C 2 H 2 in pure NH 3 6nm In NH 3 Environment

14. 4.8 vol. % C 2 H 2 for 20min 9.1 vol. % C 2 H 2 for 15min 16.7 vol. % C 2 H 2 for 7min 23.1 vol. % C 2 H 2 for 7min at 950 o C in pure NH 3 Environment

15. 300nm at 950 ℃ with 2.4 vol. % C 2 H 2 in N 2 +H 2 : H/(H+N)=0.75 at 950 ℃ with 16.7 vol. % C 2 H 2 in pure NH 3 NH 3 Environment Effect

16. 300nm In H 2 +N 2 In pure NH 3 Catalyst Surface after Pretreatment

17. Ease of Decomposition of NH 3 NH 3 N + 3/2 H 2 NH 3 is much easier to be decomposed than N 2 Increase in activated nitrogen. Increase in activated nitrogen. NH 3 is much easier to be decomposed than N 2 Increase in activated nitrogen. Increase in activated nitrogen.

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

19. at 950 ℃ with 16.7 vol. % C 2 H 2 in pure NH 3 environment NiCo The Catalyst Effect

20. Ni Co Catalyst Surface after Pretreatment

21. at 950 ℃ with 16.7 vol. % C 2 H 2 in pure NH 3 Environment Ni Co CNT Growth Without Pretreatment Nitrogen incorporation to the catalyst is essential in Ni Nitrogen incorporation to the catalyst is essential in Ni

22. Ni Co 9.5 vol.% C 2 H 2 In 33 vol.% NH 3 +H 2 9.5 vol.% C 2 H 2 In 5 vol.% NH 3 +H 2

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 NH 3 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. 12.5 ㎛ Straight form Tangled form Growth of Vertically Aligned CNT

25. 70sec (9.8 ㎛ /min)4min (1.1 ㎛ /min)7min(0.8 ㎛ /min ) Intimate Relationship Between the Growth Rate and the Vertically Aligned CNT Intimate Relationship Between the Growth Rate and the Vertically Aligned CNT Evolution of Vertically Aligned CNT at 950 ℃ with 16.7 vol. % C 2 H 2 in pure NH 3 Environment