The International Conference of Metallurgical Coating and Thin Films ICMCTF 2003 Tae-Young Kim a)b), Kwang-Ryeol Lee a), Seung-Cheol Lee a), Kwang Yong Eun a), and Kyu Hwan Oh b) a) Future Technology Research Division, Korea Institute of Science and Technology b) School of Materials Science and Engineering, Seoul National University Activated Nitrogen Effect on The Growth of Vertically Aligned Carbon Nanotube

Carbon Nano-Tubes(CNT) Unique structure and properties Suggested Application –Probe tips –Cold cathode for FED –Electrode for Fuel cell or secondary battery –Nanoscale transistor

Synthesis of CNT Laser ablation, Arc discharge, Plasma CVD, Thermal CVD Thermal CVD –Thermal 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).

Focus – Previous Results Aligned CNT was obtained in NH3 and N2 environment Synthesis condition CNT Morphology Citation method Temperatue( o C)Reaction GasCatalyst PE-CVD666C 2 H 2 +NH 3 NiAligned CNTScience 282, 1105 (1998) PE-CVD660C 2 H 2 +NH 3 NiAligned CNTAPL (1999) PE-CVD825C 2 H 2 +NH 3 CoAligned CNTAPL (2000) Thermal-CVD750~950C 2 H 2 +NH 3 FeAligned CNTAPL (2000) PE-CVD825C 2 H 2 +NH 3 CoAligned CNTAPL (2000) Thermal-CVD800C 2 H 2 +NH 3 FeAligned CNTAPL (2001) Thermal-CVD 950C 2 H 2 +NH 3 Ni, Co Aligned CNT TSF (2001) 850 C 2 H 2 +H 2, C 2 H 2 +N 2 Tangled CNT Thermal-CVD 950C 2 H 2 +NH 3 Ni Aligned CNT DRM (2001) 950C 2 H 2 +H 2, C 2 H 2 +N 2 Tangled CNT Thermal-CVD 800~900C 2 H 2 +NH 3 Ni Aligned CNT JAP (2002) 600~900C 2 H 2 +H 2 Tangled CNT PE-CVD660<C 2 H 2 +NH 3 NiAligned CNTAPL (2002) Thermal-CVD850~900C 2 H 2 +ArNi, CoTangled CNTAPL (1999) PE-CVD500CH 4 +N 2 Fe, NiAligned CNTAPL (1999) PE-CVD550CH 4 +N 2 FeAligned CNTJAP (2001) PE-CVD700CH 4 +H 2 NiAligned CNTAPL (2000) Thermal-CVD800ferrocene+xylene Fe Aligned CNTAPL (2000) But why?

Previous Result 300nm 2.4 vol. % 2.4 vol. % C 2 H 2 in H 2 + N 2 (3:1) 5.00 ㎛ 16.7 vol. % 16.7 vol. % C 2 H 2 in NH 3 NH 3 vs. H 2 +N 2

Previous Result Ni particles after pretreatment for 1h… Activated Nitrogen 300nm In H 2 +N 2 In pure NH 3 Activated Nitrogen plays a significant role in vertically aligned CNT growth

Motivation How does the activated nitrogen affect the growth of Vertically Aligned CNT ? … But we still don’t know

Role of Nitrogen Possible suggestion : 1.Catalyst surface modification by activated nitrogen  NH3 environment before carbon deposition would be significant. 2.Activated nitrogen may play a significant role during CNT growth.  NH3 environment during CNT growth would be significant.

Experimental Design PretreatmentReaction NH 3 H2H2 H2H2 H2H2 VA-CNT ? ? Role of activated nitrogen during CNT growth? VA-CNT ? ? Catalyst surface modification?

Experimental Procedure I.Formation of Catalyst particle II.Thermal CVD process Tube type reactor with quartz tube at 1atm Processing Condition  Processing Temperature : 950 o C  Pretreatment Time : 1hr Environment : H 2, N 2, H 2 +N 2, NH 3  Reaction : environment gas + C 2 H 2 300nm Furnace Gas In Sample loading system H2OH2O Hood Sample Gas out SiO 2 Si(100) Ni SiO 2 Si(100) Heat o C in H 2

Catalyst Pretreatment Effect NH 3 pretreatment for 4hr No pretreatment Pretreatment(x) Reaction NH 3 + C 2 H 2 Pretreatment Reaction H 2 + C 2 H 2 NH 3

Catalyst Pretreatment Effect NH 3 H2H2 H2H2 H2H2 PretreatmentReaction Catalyst surface modification?

Catalyst Pretreatment Effect NH 3 H2H2 H2H2 H2H2 PretreatmentReaction Role of activated nitrogen during CNT growth?

PretreatmentReaction NH 3 H2H2 H2H2 H2H2

Role of Nitrogen Possible suggestion : 1.Catalyst surface modification by activated nitrogen  NH3 environment before carbon deposition would be significant. 2.Activated nitrogen may play a significant role during CNT growth.  NH3 environment during CNT growth would be significant.

Effect of NH 3 Atmosphere in Reaction 17.1 vol. % 23.1vol. % Pretreatment Reaction H2H2 NH 3 + C 2 H vol % 5.0 vol.% NH 3 C2H2C2H2 Growth rate Degree of alignment

Activated Nitrogen in CNT NH 3 C2H2C2H2 Growth rate Degree of alignment

Activated Nitrogen in CNT

Experimental Observations Pretreatment in NH 3 environment was neither a sufficient nor necessary for vertically aligned CNT growth There are some relationship between nitrogen concentration in CNT and CNT growth rate Nitrogen is chemically bonded with carbon atoms in graphite basal plane Enhanced CNT growth in an NH3 environment is due to nitrogen incorporation into the CNT wall or cap.

Suggestion From Dr. S. Maruyama’s homepage, Mechanical Engineering in the University of Tokyo Strain energy is necessary for formation of tubular or spherical graphite layer Nitrogen incorporation into the CNT would reduces the strain energy

Role of Nitrogen in CNT Growth Y. Miyamoto et al, Solid State Comm. 102, 605 (1997) X. Ma et al, Appl. Phys. Lett. 78, 978 (2001). PECVD

Conclusion Enhanced CNT growth in an N 2 or NH 3 environment is due to nitrogen incorporation into the CNT wall or cap. Nitrogen incorporation can reduce the strain energy required for the formation of tubular or spherical graphitic layer, which would decrease the activation energy for their nucleation on the catalyst surface.