Floating Catalyst CVD Methodfor Controllable Synthesis offor Controllable Synthesis of

Single- and Double-walled Carbon Nanotubes

Hui-Ming Cheng

Shenyang National Laboratory for Materials ScienceInstitute of Metal Research, Chinese Academy of Sciences

1

Institute of Metal Research, Chinese Academy of Sciences

Where am I from?Where am I from?

2

Main Directions at my Divisiony

• Synthesis Properties and Applications of Carbon• Synthesis, Properties and Applications of Carbon Nanotubes and Non-Carbon Nanostructures

C b N t b– Carbon Nanotubes– Non-Carbon Nanostructures

• New Materials for Clean Energy Applications– Energy storage materialsgy g– Solar energy materials

• Exploration of Hydrogen Storage Materials• Exploration of Hydrogen Storage Materials• Fabrication and Applications of High-performance

3

Carbon Materials

Main Directions at my Divisiony

• Synthesis Properties and Applications of Carbon• Synthesis, Properties and Applications of Carbon Nanotubes and Non-Carbon Nanostructures

C b N t b– Carbon Nanotubes– Non-Carbon Nanostructures

• New Materials for Clean Energy Applications– Energy storage materialsgy g– Solar energy materials

• Exploration of Hydrogen Storage Materials• Exploration of Hydrogen Storage Materials• Fabrication and Applications of High-performance

4

Carbon Materials

Outline

• Synthesis of CNTs by Floating Catalyst CVD

(SWNT DWNT MWNT )(SWNTs, DWNTs, MWNTs)

• Structural Control of SWNTs and DWNTs

– The effect of sulfur, carrier gas, and carbon feeding rate

S th i f CNT ith di t di t ib ti– Synthesis of CNTs with narrow diameter distribution

• Growth mechanism of SWNTs/DWNTs by FCCVD

• Concluding remarks

5

Potential Applications of CNTs

Large ScaleField emittersField emittersEnergy storageCompositesComposites

IndividualTransistorElectronic devices

STM/AFM tipsSensors

6D Tomànek, NT06 Presentation

Electronic Structure --- Structural Control

torsemiconducmetal

133

⎩⎨⎧

±=−

pp

mn rEgap /1∝

7R Saito et al., Appl. Phys. Lett. 60(1992) 2204 .R Saito et al, Phys. Rev. B 61(2000) 2981.

Challenges for CNT Synthesis

D l t f l t l l f• Development of low-cost, large-scale processes for the synthesis of high-quality CNTs

• Control over the structure and electronic properties of CNTs

• Control over the location and orientation of CNTs on a flat substratea flat substrate

• Development of a thorough understanding of the growth mechanism of CNTs

8J Liu, SS Fan and HJ Dai, MRS Bulletin, 2004.

Pioneered Methods for SWNT Synthesis

Arc Discharge Method Laser Ablation MethodArc Discharge Method Laser Ablation Method

Developed by RE Smalley group(A Thess et al, Science 1996)

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Developed by S Iijima(Nature 1993)

Growth of SWNTs by CVD methody

SWNTsSWNTs

H.J. Dai, et al., Chem. Phys. Lett. 1996

Large scale:• Carbon supply• Catalyst supply• Reaction time

Ferrocene

10

• Reaction time• …

Floating Catalyst CVD Method (FCCVD)

19981998

FerroceneSWNTs

H2 (Ar or their mixture)CH (C H CO C H Alcohol)CH4 (C2H2, CO, C6H6, Alcohol)

Thiophene

Potential for continuous preparation Possibility of structural control

11

HM Cheng et al., Appl. Phys. Lett. 72 (1998) 3282.

HM Cheng et al., Chem. Phys. Lett. 289 (1998) 602.Low cost, high puritySimple post-treatment

SWNTs by FCCVD

12HM Cheng et al., Chem. Phys. Lett.289 (1998) 602.

TEM Images of the SWNTs by FCCVD

13

Synthesis of DWNTs by FCCVD

20Gaussian fit

10

15

Gaussian fit

Mean diameter: 1.52 nm

er o

f DW

NTs

0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.80

5

Num

be

I di t f DWNT ( )Inner diameter of DWNTs (nm)

30

35

15

20

25

30 Gaussian fit

Mean diameter: 2.26 nm

er o

f DW

NTs

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.60

5

10

Num

be

O t di t f DWNT ( )

14> 70%

Outer diameter of DWNTs (nm)

WC Ren, HM Cheng et al., Chem. Phys. Lett. 359 (2002) 196.

CNFs/MWNTs with Different Diameter and Wall Thicknesswith Different Diameter and Wall Thickness

150 nm< 10 nm 50-70nm 70-100 nm20-40 nm

Carbon feeding rate

YY Fan, HM Cheng et al., Carbon 38 (2000)789.

Catalyst particle sizeSulfur concentration

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YY Fan, HM Cheng et al., Carbon 38 (2000) 921.YY Fan, HM Cheng et al., J. Mater. Res. 13 (1998) 2342.

Sulfur concentration

Outline

• Synthesis of CNTs by Floating Catalyst CVD

(SWNT DWNT MWNT )(SWNTs, DWNTs, MWNTs)

• Structural Control of SWNTs and DWNTs

– The effect of sulfur, carrier gas, and carbon feeding rate

S th i f SWNT ith di t di t ib ti– Synthesis of SWNTs with narrow diameter distribution

• Growth mechanism of SWNTs/DWNTs by FCCVD

• Concluding remarks

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The Effect of Sulfur-- Necessary?

F & A

Without the addition of sulfur

Ferrocene & Argon

Without additional carbon

L d ti it17

• Low productivity

The effect of Sulfuron the Purity and Quality of SWNTson the Purity and Quality of SWNTs

with sulfur without sulfur

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• Higher purity• Higher quality and narrower distribution

The Effect of Sulfur on the Diameter Distribution of SWNTson the Diameter Distribution of SWNTs

Without sulfur With sulfur

• Broad diameter distribution!

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The Effect of Sulfur on Diameter and Shell Numberon Diameter and Shell Number

20WC Ren, HM Cheng et al., J. Nanosci. Nanotech. 6 (2006) 1339.

The Effect of Sulfur on the Diameter and Shell NumberSulfur is necessary for the synthesis of SWNTs and DWNTs with a high productivitySulfur plays an important role in the structural control (diameter and shell number ) of CNTson the Diameter and Shell Number

ω = A1/dt+A2

and DWNTs with a high productivitycontrol (diameter and shell number ) of CNTs

1 t 2

21WC Ren, HM Cheng et al., J. Nanosci. Nanotech. 6 (2006) 1339.

The Effect of Carrier GasHydrogen is beneficial to the synthesis of Diameter Narrowly-distributed SWNTs

159170

Diameter Narrowly distributed SWNTs

258220197

1591Ar

40

50

60 Gaussian fit Mean diameter: d= 1.15 nm

of S

WN

Ts

159141284 1554

2613

10

20

30

40

Num

ber o

100 200 300 400 500Raman Shift ( cm-1) 500 1000 1500 2000 2500

1311

Raman Shift ( cm-1)

0.4 0.8 1.2 1.6 2.0 2.4 2.80

10

Diameters of SWNTs (nm)90

139H2

1589

60

70

80

9085% SWNTs with diameters of 1.7±0.2 nm

Gaussian fit Mean diameter: d= 1.72 nmSW

NTs

20

30

40

50N

umbe

r of S

22100 200 300 400 500

Raman shift ( cm-1) 500 1000 1500 2000 2500

2631

Raman shift ( cm-1)

1315

0.4 0.8 1.2 1.6 2.0 2.4 2.80

10

20

Diameters of SWNTs (nm)

The Effect of Carbon Feeding RateLow carbon feeding rate is beneficial to the synthesis of Narrowly-distributed SWNTsthe synthesis of Narrowly distributed SWNTs

Carbon source: Methaney

150 15866ml/min

Inte

nsity

Inte

nsity

145 193

13222634

158910ml/min

nten

sity

168 tens

ity

In Int

1317

2634

23

100 200 300 400 500Raman Shift ( cm-1)

500 1000 1500 2000 2500Raman Shift ( cm-1)

Aligned DWNT ropes by FCCVD

> 10 cm

24WC Ren, HM Cheng et al., J. Phys. Chem. B 109 (2005) 7169.

Typical HRTEM Images of DWNTs

Outer diameter: 1.7-2.0 nm Inner diameter: 1.0-1.3 nm

> 90%

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RBM Mapping of DWNT Ropes

Raman shift cm-1

26Narrow diameter distribution

Outline

• Synthesis of CNTs by Floating Catalyst CVD

(SWNT DWNT MWNT )(SWNTs, DWNTs, MWNTs)

• Structural Control of SWNTs

– The effect of sulfur, carrier gas, and carbon feeding rate

S th i f SWNT ith di t di t ib ti– Synthesis of SWNTs with narrow diameter distribution

• Growth mechanism of SWNTs/DWNTs by FCCVD

• Concluding remarks

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Structural Correlation between SWNTs and the Attached Catalyst Particlesy

200

50

60

70 (a)

SWN

Ts

120

140

160

180 (b)

Fe-N

Ps

20

30

40

Num

ber o

f S

60

80

100

Num

ber o

f F

0.44 nm2 nm

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.00

10

Diameters of SWNTs (nm)2 3 4 5 6 7 8 9 10 11 12 13

0

20

40

Diameter of Fe-NPs (nm)

• The size of catalyst particles : > 5nm

2 nm

• The diameters of SWNTs or DWNTs: < 3 nm (in general)• SWNTs growth on the localized region of the surface of catalyst

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Localized nucleation on big catalyst particlesWC Ren, HM Cheng et al., J. Phys. Chem. B 110 (2006) 16941.

Structural Correlation between SWNTsBundles and the Attached Catalyst ParticlesBundles and the Attached Catalyst Particles

2 nm

Localized nucleation on big catalyst particles

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Tip Structure of SWNTs at the Initial Nucleation Stageat the Initial Nucleation Stage

CapsCaps

F ti f th t tFormation of the cap structure ― Bending of graphite islands on the localized zone

30of the surface of catalyst particles

Role of Sulfur on the Formation of the Small CapsSmall Caps

VLS growth mechanism― Precipitation of carbon from the localized liquid zone

The role of sulfur• Decreasing melting point of localized zone• Decreasing melting point of localized zone

– Key point for the localized nucleation (the diameter of CNTs is closely correlated with the addition amount of sulfur)

• Enhancing the decomposition of carbon sources– Inhibit the continuous extending of graphite– Inhibit the continuous extending of graphite

islands• Introduction of defects in the graphite islands

E h th b di f hit i l d d

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– Enhance the bending of graphite islands and consequently nucleation

Proposed Growth Model

Sulfur-assisted localized nucleation at low temperatureSulfur assisted localized nucleation at low temperature

a

b

c

I II III

c

Fe atoms

Fe-C-S phase

Temperature gradient

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The liquid catalyst

WC Ren, HM Cheng et al., J. Phys. Chem. B 110 (2006) 16941.

Concluding Remarks g

• Developed a floating catalyst CVD method for the synthesis of SWNTs and DWNTsy

• Attempted the diameter and shell number control of CNTCNTs

• Obtained SWNTs and DWNTs with narrow diameter distribution

P d l li d l ti d l f th• Proposed a localized nucleation model for the growth of SWNTs and DWNTs by FCCVD

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Acknowledgment

• Dr. Wencai Ren• Dr. Feng Li• Mr. Qingfeng Liu• Mr. Bilu Liu

• Prof. M Dresselhaus at MIT

• NSFC, MOST, and CAS for financial support

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• JSPS for supporting this visit

Thank you very muchThank you very much for your attention!for your attention!

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