The International Conference of Metallurgical Coating and Thin The International Conference of Metallurgical Coating and Thin Films Films

ICMCTF 2003ICMCTF 2003

Tae-Young Kima)b), Kwang-Ryeol Leea), Seung-Cheol Leea), Kwang Yong Euna), and Kyu Hwan Ohb)

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 Activated Nitrogen Effect on The Growth of Vertically The Growth of Vertically

Aligned Carbon NanotubeAligned Carbon Nanotube

Carbon Nano-Tubes(CNT)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 CNTSynthesis 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 – Focus – Previous ResultsPrevious Results

• Aligned CNT was obtained in NH3 and N2 environment

Synthesis conditionCNT

Morphology

Citationmethod

Temperatue(oC)

Reaction Gas Catalyst

PE-CVD 666 C2H2+NH3 Ni Aligned CNT Science 282, 1105 (1998)

PE-CVD 660 C2H2+NH3 Ni Aligned CNT APL 75 1086 (1999)

PE-CVD 825 C2H2+NH3 Co Aligned CNT APL 77 830 (2000)

Thermal-CVD 750~950 C2H2+NH3 Fe Aligned CNT APL 77 3397 (2000)

PE-CVD 825 C2H2+NH3 Co Aligned CNT APL 77 2767 (2000)

Thermal-CVD 800 C2H2+NH3 Fe Aligned CNT APL 78 901 (2001)

Thermal-CVD950 C2H2+NH3

Ni, CoAligned CNT

TSF 398-399 150 (2001)850 C2H2+H2, C2H2+N2 Tangled CNT

Thermal-CVD950 C2H2+NH3

NiAligned CNT

DRM 10 1235 (2001)950 C2H2+H2, C2H2+N2 Tangled CNT

Thermal-CVD800~900 C2H2+NH3

NiAligned CNT

JAP 91 3847 (2002)600~900 C2H2+H2 Tangled CNT

PE-CVD 660< C2H2+NH3 Ni Aligned CNT APL 80 4018 (2002)

Thermal-CVD 850~900 C2H2+Ar Ni, Co Tangled CNT APL 75 1721 (1999)

PE-CVD 500 CH4+N2 Fe, Ni Aligned CNT APL 75 3105 (1999)

PE-CVD 550 CH4+N2 Fe Aligned CNT JAP 89 5939 (2001)

PE-CVD 700 CH4+H2 Ni Aligned CNT APL 76 2367 (2000)Thermal-CVD 800 ferrocene+xylene Fe Aligned CNT APL 77 3764 (2000)But why?

Previous ResultPrevious Result

300nm

2.4 vol. %2.4 vol. % C2H2 in H2 + N2 (3:1)

5.00㎛

16.7 vol. %16.7 vol. % C2H2 in NH3

NH3 vs. H2+N2

Previous ResultPrevious ResultNi particles after pretreatment for 1h…

Activated NitrogenActivated Nitrogen

300nm

300nm

In H2+N2

In pure NH3

Activated Nitrogen plays a significant role in vertically aligned CNT growth

MotivationMotivation

How does the activated nitrogen affect the growth of Vertically

Aligned CNT ?

… But we still don’t know

Role of NitrogenRole 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 DesignExperimental Design

Pretreatment Reaction

NH3

NH3

H2

H2

NH3

H2

VA-CNT

?

VA-CNT

?

Role of activated nitrogen during CNT growth?

VA-CNT

VA-CNT

?

?

Catalyst surface modification?

Experimental ProcedureExperimental ProcedureI. Formation of Catalyst particle

II. Thermal CVD processTube type reactor with quartz tube at 1atm

Processing ConditionProcessing Temperature : 950oCPretreatment

•Time : 1hr•Environment : H2, N2, H2+N2, NH3

Reaction : environment gas + C2H2

300nm

Furnace

Furnace

Furnace

Furnace

Gas In

Sample loading system

H2O

HoodSample

Gas out

SiO2

Si(100)

Ni SiO2

Si(100)

Heat Treatment@800oC in H2

Catalyst Pretreatment EffectCatalyst Pretreatment Effect

NH3 pretreatment for 4hr

No pretreatment

Pretreatment(x) Reaction

NH3 + C2H2

Pretreatment Reaction

H2 + C2H2NH3

Catalyst Pretreatment EffectCatalyst Pretreatment Effect

NH3

NH3

H2

H2

NH3

H2

Pretreatment Reaction

Catalyst surface modification?

Catalyst Pretreatment EffectCatalyst Pretreatment Effect

NH3

NH3

H2

H2

NH3

H2

Pretreatment Reaction

Role of activated nitrogen during CNT growth?

Pretreatment Reaction

NH3

NH3

H2

H2

NH3

H2

Role of NitrogenRole 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 NHEffect of NH33 Atmosphere Atmosphere in Reaction in Reaction

17.1 vol. %17.1 vol. %

23.1vol. %23.1vol. %Pretreatment Reaction

H2 NH3 + C2H2

1.5 vol %1.5 vol %

5.0 vol.%5.0 vol.%

NH3

C2H2

Growth rateDegree of alignment

Activated Nitrogen in CNTActivated Nitrogen in CNT

NH3

C2H2

Growth rateDegree of alignment

Activated Nitrogen in CNTActivated Nitrogen in CNT

Experimental ObservationsExperimental Observations Pretreatment in NH3 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.

SuggestionSuggestion

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 GrowthRole 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

ConclusionConclusion

• Enhanced CNT growth in an N2 or NH3 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.