Floating Catalyst CVD Method for Controllable Synthesis of for Controllable Synthesis of
Single- and Double-walled Carbon Nanotubes
Hui-Ming Cheng
Shenyang National Laboratory for Materials Science Institute of Metal Research, Chinese Academy of Sciences Institute of Metal Research, Chinese Academy of Sciences
Where am I from?
Where am I from?
Main Directions at my Division y
• 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
Carbon Materials
Main Directions at my Division y
• 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
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
Potential Applications of CNTs
Large Scale
9 Field emittersField emitters 9 Energy storage 9 Composites
9 Composites
Individual
Transistor
9 Electronic devices 9 STM/AFM tips
9 Sensors
Electronic Structure --- Structural Control
tor semiconduc
metal 1
3 3
⎩⎨
⎧
= ±
− p
m p
n Egap ∝1/ r
R Saito et al., Appl. Phys. Lett. 60(1992) 2204 .
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 substrate
a flat substrate
• Development of a thorough understanding of the growth mechanism of CNTs
J Liu, SS Fan and HJ Dai, MRS Bulletin, 2004.
Pioneered Methods for SWNT Synthesis
Arc Discharge Method Laser Ablation Method Arc Discharge Method Laser Ablation Method
Developed by RE Smalley group
(A Thess et al, Science 1996)
Developed by S Iijima
(Nature 1993)
Growth of SWNTs by CVD method y
SWNTs SWNTs
H.J. Dai, et al., Chem. Phys. Lett. 1996
Large scale:
• Carbon supply
• Catalyst supply
• Reaction time
Ferrocene
• Reaction time
• …
Floating Catalyst CVD Method (FCCVD)
1998 1998
Ferrocene SWNTs
H2 (Ar or their mixture) CH (C H CO C H Alcohol) CH4 (C2H2, CO, C6H6, Alcohol)
Thiophene
9Potential for continuous preparation 9Possibility of structural control
HM Cheng et al., Appl. Phys. Lett. 72 (1998) 3282.
HM Cheng et al., Chem. Phys. Lett. 289 (1998) 602.
9Low cost, high purity 9Simple post-treatment
SWNTs by FCCVD
TEM Images of the SWNTs by FCCVD
Synthesis of DWNTs by FCCVD
20
Gaussian fit
10 15
Gaussian fit
Mean diameter: 1.52 nm
er of DWNTs
0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 0
Numbe 5
I di t f DWNT ( )
Inner diameter of DWNTs (nm)
30 35
15 20 25
30 Gaussian fit
Mean diameter: 2.26 nm
er of DWNTs
1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 0
5 10
Numbe
O t di t f DWNT ( )
> 70%
14Outer diameter of DWNTs (nm)
WC Ren, HM Cheng et al., Chem. Phys. Lett. 359 (2002) 196.
CNFs/MWNTs
with Different Diameter and Wall Thickness with Different Diameter and Wall Thickness
150 nm
< 10 nm 20-40 nm 50-70nm 70-100 nm
# Carbon feeding rate
YY Fan, HM Cheng et al., Carbon 38 (2000)789.
# Catalyst particle size
# Sulfur concentration 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
The Effect of Sulfur-- Necessary?
F & A
Without the addition of sulfur
Ferrocene & Argon
Without additional carbon
L d ti it
• Low productivity
The effect of Sulfur
on the Purity and Quality of SWNTs on the Purity and Quality of SWNTs
with sulfur without sulfur
18
• Higher purity
• Higher quality and narrower distribution
The Effect of Sulfur
on the Diameter Distribution of SWNTs on the Diameter Distribution of SWNTs
Without sulfur With sulfur
• Broad diameter distribution!
The Effect of Sulfur
on Diameter and Shell Number on Diameter and Shell Number
WC Ren, HM Cheng et al., J. Nanosci. Nanotech. 6 (2006) 1339.
The Effect of Sulfur
on the Diameter and Shell Number
Sulfur is necessary for the synthesis of SWNTs and DWNTs with a high productivity
Sulfur plays an important role in the structural control (diameter and shell number ) of CNTs
on the Diameter and Shell Number
ω = A1/dt+A2
and DWNTs with a high productivitycontrol (diameter and shell number ) of CNTs
1 t 2
The Effect of Carrier Gas
Hydrogen is beneficial to the synthesis of Diameter Narrowly-distributed SWNTs
70 1591
Diameter Narrowly distributed SWNTs
258 197220
Ar 1591
40 50
60 Gaussian fit
Mean diameter: d= 1.15 nm
of SWNTs
159
141 284 1554
2613 10
20 30 40
Number o
100 200 300 400 500
Raman 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 2.8 0
10
Diameters of SWNTs (nm) 90
139 H2 1589
60 70 80
90 85% SWNTs with diameters of 1.7±0.2 nm
Gaussian fit
Mean diameter: d= 1.72 nm
SWNTs
20 30 40 50
Number of S
22
100 200 300 400 500
Raman shift (cm-1) 500 1000 1500 2000 2500
2631
( )
1315
0.4 0.8 1.2 1.6 2.0 2.4 2.8 0
10 20
The Effect of Carbon Feeding Rate
Low carbon feeding rate is beneficial to
the synthesis of Narrowly-distributed SWNTs the synthesis of Narrowly distributed SWNTs
Carbon source: Methane
y
150 1586
6ml/min
Intensity Intensity
145 193
1322 2634
10ml/min 1589
ntensity 168
tensity
In Int
1317
2634
100 200 300 400 500
Raman Shift (cm-1) 500 1000 1500 2000 2500
Raman Shift (cm-1)
Aligned DWNT ropes by FCCVD
> 10 cm
24
Typical HRTEM Images of DWNTs
Outer diameter: 1.7-2.0 nm Inner diameter: 1.0-1.3 nm
> 90%
RBM Mapping of DWNT Ropes
Raman shift cm-1
Narrow 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
Structural Correlation between
SWNTs and the Attached Catalyst Particles y
200
50 60
70 (a)
SWNTs 120
140 160
180 (b)
Fe-NPs
20 30 40
Number of S
60 80 100
Number of F
0.44 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 3.0 2 nm
0 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
Localized nucleation on big catalyst particles
Structural Correlation between SWNTs
Bundles and the Attached Catalyst Particles Bundles and the Attached Catalyst Particles
2 nm
Localized nucleation on big catalyst particles
Tip Structure of SWNTs
at the Initial Nucleation Stage at the Initial Nucleation Stage
Caps Caps
F ti f th t t
Formation of the cap structure
― Bending of graphite islands on the localized zone of the surface of catalyst particles
Role of Sulfur on the Formation of the Small Caps
Small 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
– Enhance the bending of graphite islands and consequently nucleation
Proposed Growth Model
Sulfur-assisted localized nucleation at low temperature Sulfur assisted localized nucleation at low temperature
a
b
c
I II III
c
Fe atoms Fe-C-S phase
Temperature gradient
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 CNT
CNTs
• 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
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
• JSPS for supporting this visit
Thank you very much Thank you very much
for your attention!
for your attention!