Carbon nanotubes-based flexible Transparent conducting film
Young Hee Lee
Department of Physics, Department of Nanoscience and Nanotechnology,
Center for Nanotubes and Nanostructured Composites,Sungkyunkwan Advanced Institute of Nanotechnology,
Sungkyunkwan University, Suwon 440-746, [email protected]
http://nanotube.skku.ac.kr/
Outline
1. Introduction2. Material quality 3. Film quality4. Post treatment
- doping effect
Current research topics
- Mass production (t-MWCNTs): Diameter, chirality, length control,aligned nanotubes
- Thermal CVD, microwave PECVD,RF-PECVD, arc discharge
- Catalyst design- Magnetic nanoparticles (Gd, GdFe)
Synthesis- Chirality separation- Doping (Li, K, Na, N, F, Cl)- Purification- Dispersion (macro and nano)- Functionalization
Engineering properties
- Transparent conducting film - All-CNT flexible transparent TFT- Transistor (FET)- Optoelectronic devices- Gas sensor- Field emitter (FED, LCD BLU)
Electronic devices
Applications
- Hydrogen storage- Fuel cell- Hybrid capacitor- Nano refrigerator
(Peltier device)- CDI for water purification
Energy storage- Polymer (PC, PET)/CNT- Metal/CNT- Polymer nanofiber/CNT- LC/CNT
Composites
Group members
Hong Zhang GengKi Kang Kim
Properties of CNTs
- Several tube types- High aspect ratio (1000 - 100000),
diameter (~ nm), length (~ μm)- Hollowness inside , surface area up to 1500 m2/g- Mechanical strength (100 x steel, 10 x kevlar) - Elastic modulus (1-2 TPa),7 times stronger than steel- Thermal conductivity (6000 W/mK),
twice the diamond - Electric conductivity (10,000 S/cm), 1000 times larger than Cu-wire
MWCNT
DWCNT
SWCNT
Single
Mass
Random Aligned
Conducting filmsCompositesGas adsorptionFuel cellsBatteries SupercapacitorsFilters
Mass Mass productionproduction
Chemical Chemical modificationmodification
FED, BLUCathode ray tubesMicrowaveamplifiers
Structure Structure controlcontrol
Bio-technologyDDS
Controlled Controlled growthgrowth
SPMNano-fabrication
Bio-sensorsElectronic devices
LSI memoryLogic
Via-hole wiring
Vast area for CNT applications
Why flexible TCFs?
Future electronic
device
E-paperPCB board
Wearable displays
Flexible displays
Transparency
- Working transistor
- Electrodes
- transparent- conductive
ITO filmExcellent transmittance and conductivity
0 30 60 90 120 150 1800
500
1000
1500
2000
2500
ITO can be cracked easily against bending, yielding poor flexibility
SWCNT film 94% T
SWCNT film 70% T
Sh
eet r
esis
tanc
e (Ω
/sq)
Bending angle (degree)
ITO
CNT film
Flexible TCFs with CNTs
By courtesy of Paul J Glatkowiski, Eikos Inc.
Indium is a limited natural resource!
Blue diamond and gold star: Eikos, Red diamond: PEDOTYellow diamond: ITO, Yellow square: gold or silver metal
Paul J Glatkowiski, Eikos Inc.
Target values
ITO
CNT
Science 305 (2004) 1273
50 nm film was measured to be 30 Ω/sq(resistivity 1.5 X 10-4 Ωᆞcm)
Filtration method
1. The film thickness is readily controlled.2. Homogeneity of the films is guaranteed by
the process itself. 3. They tend to lie straight, gaining maximal
overlap maximal electrical conductivity
J. Am. Chem. Soc. 126, 4462 (2004)
sheet resistance (Rs) of 80 Ω/sq and %T of 80
CNT film by dipping
PEDOT film by ink-jet
Dipping method
Flexible TCFs with CNTs
Diamond and Related Materials 13 (2004) 256
CNT network
CNT-PA CNT-PPy CNT/SOCl2
Transparency (%) 80-90% 62-90% 60-80% 93-99%
resistance, R(Ω) 660 245 400 1.1X103
transparent thin CNT network
network of CNT-PA
sprayed with an air-brush pistolsprayed with
an air-brush pistol
deposit the CP, PA or PPy
on them electrochemically.
deposit the CP, PA or PPy
on them electrochemically.
Flexible TCFs with CNTs
Applied Surface Science 252 (2005) 425
CNT network on PET ITO on PET
Transparency (%) 90 % 78 %
Sheet resistance, Rs(Ω/sq)
1 kΩ/sq 15 Ω/sq
Spray method
Diam. Rel. Mater. 14 (2005) 1882 Nano Letters 6 (2006) 1880
filtration method
Flexible TCFs with CNTsbar coating
Journal Coating method CNTs dispersion polymer substrate Transmitt
ance (%)Sheet
resistance(Ω/sq)
variable
J. Am. Chem. Soc. 126 (2004) 4462 Dipping SWNTs Triton-X 100 X patterned
PET film 80 80
Applied Surface Science 252 (2005) 425 spray SWNTs
MWNTs SDS X PET film 90 1k
Nano Letters6 (2006) 677 Filtration SWNTs SDS X PET 70 1k
Nano Letters6 (2006) 1880 Filtration SWNTs SDS PEDOT PE 87 380
JAP101 (2007) 016102 Filtration SWNTs SDS PET 80 150
APL88 (2006) 123109 Filtration SWNTs SDS PET 80 120
Nano Letters4 (2004) 2513 Filtration SWNTs X X Variable 85 1k
electrode
PET
PET
Science 305 (2004) 1273 filtration SWNTs Triton-X 100 X 70 30
Diamond and Related Materials 13 (2004) 256
Sprayed/electro-chemical
SWNTsMWNTs SDS PA/PPY 70
82
80
245
Diam. Rel. Mater.14(2005) 1882 Bar coating t-MWNTs
SWNTs PEDOT PEDOT 249
APL90 (2007) 121913 Filtration SWNTs SDS 200
More systematic study is required to understand the film performance for materials and the film preparation processes.
Comparison results related to TCFs
What does determine the film performance?
Film performanceSheet resistance, transmittance, hardness (adhesion)
Material parameters
- Types of CNTs- Purity of CNTs- Diameter- Crystallinity of CNT walls
Film parameters
- Dispersion of CNTs in solvent- Film preparation method- Bundle size- Degree of entanglement of CNT network
Film preparation methods
Method Advantage Drawback
Filtration
- Easy process for thin layer (<100 nm)- Easy to remove surfactants- Excellent uniformity
- Limited to filter size- Extra labor to remove filters
Dip coating
- Easy to fabricate and scale up- Cheap cost
- Sensitive to surface functionalization- Take relatively long time - Hard to control uniform coating in large area
spray coating
- Easy to fabricate and scale up- Cheap cost- Excellent uniformity
- Need attention for nozzle blocked
Inkjet printing - Micro-pattern formation - CNT-ink preparation
- Nozzle cloaking
Filtration Dip coating Spray coating
Spray gun
Pump
Filter
Inkjet printing
Solvent
CNT
Process for TCFs
Dispersion Centrifugation
Spray coatingCharacterization
Spray gun
Rs
%T
Characteristics of TCFs using SWCNTs
Arc SWCNTs reveal the best TCF performance! But why?
40 50 60 70 80 90 100101
102
103
104
105
Arc
HiPCO
Laser
Sh
eet r
esis
tanc
e (Ω
/sq)
Transmittance at 550 nm (%)
CVD
Each curve contains several data points from films with different number of sprays by SWCNT solution dispersed in deionized water with SDS
Characteristic of SWCNTs
- Presence of carbonaceous particles- Purity (transition metals)- Crystallinity of CNT walls- Bundle size- Diameter
10 nm
100 nm
Thermogravimmetric analysis (TGA)
• CNTs start burning off in air at high temperature. Transition metals were not burned off at high temperature.
• Burning temperature relies on several parameterscatalyst amounts, bundle diameter, number of walls, crystallinity of CNTs.
0 200 400 600 800
0
20
40
60
80
100
10.02%
425oCTG
(wt%
)(a) CVD
DTG
(w
t%/o C
)
0 200 400 600 800
0
20
40
60
80
100
TG (w
t%)
604oC
4.55%
DTG
(w
t%/o C
)
(b) HiPCO
0 200 400 600 8000
20
40
60
80
100
12.12%
395oC
Temperature (oC)
TG (w
t%)
DTG
(w
t%/o C
)
(c) Laser
0 200 400 600 800
0
20
40
60
80
100
DTG
(w
t%/o C
)
3.54%
503oC
Temperature (oC)
TG (w
t%)
(d) Arc
Resonant Raman spectroscopy
π π∗
2.41 eV ± 0.1
S11
S22
M11
S33
S44
M22
S55
S66
M33
Diameter (nm)
van Hove singularities: diameter & chirality-dependent
Material parameters for SWCNTs: G’-band
• G’-band: double resonance or overtone of D-band.• Metallic tubes reveal larger intensity than semiconducting ones.• Electron-phonon interaction plays a dominant role here.
K. K. Kim et al. submitted
500 1000 1500 2000 2500 3000
26251589
1.52
632.8 nm (1.98 eV)
(b)M
150 180
148
179
164RBM
500 1000 1500 2000 2500 3000
2680
514 nm (2.41 eV)
1.38
1591
150 200
148
172180
RBM
164
(a) S
Inte
nsity
(arb
. uni
ts)
0 500 1000 1500 2000 2500 3000
514 nm (2.41 eV)
1591
1337NHFA-HTT
Pristine
200 250
267260
246204
RBM
183
2400 2600
2670
G'-Band
2659(a) (b) (c)
Inte
nsity
(arb
. uni
ts)
Raman shift (cm-1)
An et al. JACS 127, 5193(05)Seo et al. JACS 127, 15724(05) An et el. JEM 35, 235(06)
SM
(a) (b) (c) (d)
400
450
500
550
600 (b)
Temp. Purity
Bur
ning
tem
pera
tue (o C
)
88
90
92
94
96
CVD
HiPCO
Laser
Arc
Purity (wt%
)
(a) (b) (c) (d)0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4 ArcLaser
HiPCO
CVD
(a)
Dia
met
er (n
m)
Material parameters for SWCNTs
• For semiconductor SWCNTs, the energy gap decreases with increasing diameters.
• Thus larger diameters of SWCNTsshould give higher conductivity in TCFs.
Diameter
The burning temperature is strongly correlated to the metal content.
Burning temperature & purity
Material parameters for SWCNTs: G’-band & D-band
(a) (b) (c) (d) (a) (b (c) (d)0.0
0.2
0.4
0.6
0.8
1.0 633 nm(1.96eV)
514 nm(2.41eV)
Rat
io o
f int
ensi
ty
Types of CNTs
D/G G'/G
The intensity of D-band and G’-band/G-band of four types of SWCNTs
(a) (b) (c) (d)0
10
20
30
40
Inte
nsity
rat
io o
f G'/D
Types of CNTs
514 nm 633 nm
CVD
HiPCO
Laser
Arc
The intensity of G’-band/D-band of four types of SWCNTs at excitation energy of
514 nm and 633 nm.
Material parameters for SWCNTs: G’-band & D-band
• G’-band represents metallic composition in the CNT powder.• The higher the G’-band, the more metallic components.• D-band represents the presence of defects on the tube wall.
(a) (b) (c) (d)0
10
20
Ave
r. in
tens
ity r
atio
of G
'/DTypes of CNTs
Semiconductor Metalic
CVD
HiPCO
Laser
Arc
160 180 200 220 240 260 280 300 320
AM
S-SWCNTs
Inte
nsity
(Arb
. uni
ts)
Raman shift (cm-1)
M-SWCNTsHiPCO SWCNTs
AS
SM
SMDGSM AA
AAIII+
×=)()( /' ),( 633)(514)()( SMSMSM IIAverageI =∑
The sheet conductance of TCFs with different type SWCNT at transmittance of 70 % and 80 %.
Sheet conductivity of TCFs
CVD HiPCO Laser Arc0.000
0.002
0.004
0.006
0.008
0.010
Shee
t con
duct
ance
(S.s
q)Type of SWCNT
70 % T 80 % T
40 50 60 70 80 90 100101
102
103
104
105
Arc
HiPCO
Laser
Sh
eet r
esia
tanc
e (Ω
/sq)
Transmittance at 550 nm (%)
CVD
Can we define any appropriate parameter?
Material quality factorfor film performance
0.8 1.0 1.2 1.40.000
0.002
0.004
0.006
0.008
0.010
80 %T
Shee
t con
duct
ance
(S.s
q)
Diameter (nm)
CVD SWCNT HiPCO SWCNT Laser SWCNT Arc SWCNT
(b)70 %T
80 85 90 95 1000.000
0.002
0.004
0.006
0.008
0.010
80 %T
Purity (wt%)
Shee
t con
duct
ance
(S.s
q)
CVD SWCNT HiPCO SWCNT Laser SWCNT Arc SWCNT
(a) 70 %T
0 5 10 15 200.000
0.002
0.004
0.006
0.008
0.010
Metallic
Aver. intensity ratio of G'/Dfro metallic SWCNT
80 %TSh
eet c
ondu
ctan
ce (S
.sq)
CVD SWCNT HiPCO SWCNT Laser SWCNT Arc SWCNT
(d)70 %T
0 5 10 150.000
0.002
0.004
0.006
0.008
0.010(c)
Aver. intensity ratio of G'/Dfor semiconductor SWCNT
80 %T
Shee
t con
duct
ance
(S.s
q)
CVD SWCNT HiPCO SWCNT Laser SWCNT Arc SWCNT
Semiconductor 70 %T
Conductivity of SWCNTs
)2/exp(0 TkEnn Bgi −=
)exp()2
exp(TkEE
TkE
pB
fi
B
g −−∝
]/)exp[( TkEEnp Bfii −= ]/)exp[( TkEEnn Bifi −=
The intrinsic carrier concentration:
where kB and T are the Boltzmann constant and temperature.
The conductivity can be generally expressed as pn pene μμσ +=
For semiconductor SWCNT For metallic SWCNT
where n and p are n-type (electron) and p-type (holes) carrier concentrations, respectively, and μn and μp are the respective electron and hole mobility. The mobility is dominated by random scattering from collisions with lattice atoms, impurity atoms, other scattering centers.
)exp()2
exp(Tk
EETk
En
B
if
B
pg −−∝
The p-type and n-type carrier concentrations:
Filled DOSat Ef metal
Band gap
Metallic
Semiconducting
Band gap of SWCNTs
Band gap of SWCNTs
)eV( /82.0 DEg =
)eV( /2 0 DaE ccg γ−=
)eV( /105.0 DEpg =
Odom, Teri; et. al. Nature 391 p59 1998
Dresselhaus; et. al. Physics reports 409, 2005, 27
eV 9.2 nm, 142.0 0 ==− γcca
First-principles calculations, pseudogap ~ 0.1 eVP. Delaney, et al, Nature, 39, 1998, 466
M. Ouyang, et al, Science 292, 702 (2001)
Metallic
By fitting experimental data:
(10,10)
(8,8)
STM
Semiconducting
Material quality factor for SWCNTs
Here we define a material quality factor that represents the metallicity of the SWCNTs
D: diameter of SWCNTs; P: purity of SWCNT powder; : average intensity ratio of G’/D-band for semiconductor SWCNTs;: average intensity ratio of G’/D-band for metallic SWCNTs.
One may say that arc SWCNT is the best candidate for TCFs from material point of views
(a) (b) (c) (d)0
2
4
Arc
LaserHiPCO
CVDMat
eria
l qua
lity
fact
or
Types of CNTs
)( 052.0105.0
052.082.0
MD
SD
m IeIePQ ∑×+∑××=−−
)( 22M
TkE
STkEE
TkE
m IeIeePQ B
pg
B
fi
B
g
∑×+∑×××=−−−
MI∑SI∑
)semi( )eV( /82.0 DEg =)metal( )eV( /105.0 DEpg =
fi EE ≈ :SWCNT Intrinsic
nMI μ~∑pSI μ~∑
eV 0.026 :@RT ≈TkB
pn pene μμσ +=
0 1 2 3 4 50.000
0.002
0.004
0.006
0.008
0.010
80 %T
Shee
t con
duct
ance
(S.
sq)
Material quality factor
CVD SWCNT HiPCO SWCNT Laser SWCNT Arc SWCNT
70 %T
The sheet conductance at 70 %T & 80 %T vs material quality factors High material quality factor leads to high conductivity of TCFs.
Arc SWCNTs reveal the best TCF performance in good agreement with the prediction of the material quality factor!
Geng et al. NANO 2, July (07)
Relation of conductance with material quality factor
(a) CVD (b) HiPCO
(c) Laser (d) Arc
Morphology of the SWCNT film
Key parameters for film: Small bundle size, sparseness of CNT network, and entangled random network.
1 μm
50 60 70 80 90 1000
200
400
600
800
1000
1200
FPD
Arc-I
Arc-II
Shee
t res
ista
nce (Ω
/sq)
Transmittance at 550 nm (%)
TS
(b)
200 400 600 800 1000 1200 14000.0
0.5
1.0
1.5
2.0
2.5
Solution-IAbs
orba
nce
(a.u
.)
Wavelength (nm)
Solution-II
(a)
Degree of dispersion of SWCNTs
Key parameters for film: Long, small bundle size or individual SWCNTs give high performance for TCFs.
500 nm500 nm
500 nm500 nm
Illustration of the TCFs
Rs= 100 Ω/sq @ 75 %T
Rs= 250 Ω/sq @ 86 %T
Rs= 400 Ω/sq @ 91 %T
Touch panel
Electrodes
We proposed the material quality factor for CNTs that is directly correlated to the performance of the transparent conducting films.
SummarySummaryTransparent conducting film preparation method
Spray method
SWCNT dispersionDI water dispersion with SDS: sonication and centrifuge
Strong material dependenceArc > Laser > HiPCO > CVD SWCNTs
Film performance* Material quality factor Qm: High purity, large diameter, high IG’/D
* Film preparing condition:Better dispersion, small bundle size, entanglement of CNT networks
Post treatment to improve conductivity
×100,000 ×50,000 ×20,000
×10,000 ×2,000
The properties of TCFs
50 60 70 80 90 1000
200
400
600
800
1000
FPD
Arc SWCNTs
Shee
t res
ista
nce (Ω
/sq)
Transmittance at 550 nm (%)
TS
Sheet resistance vs transmittance curve is obtained by the optimized dispersion condition for arc discharge SWCNTs.
0 20 40 60 80 100 1200
200
400
600
800
1000
1200
1400
Sheet resistance Transmittance
Thickness (nm)
Shee
t res
ista
nce (Ω
/sq)
50
60
70
80
90
100
Transmittance (%
)
Sheet resistance and transmittance as a function of SWCNT film thickness measured by AFM step edges.
(a) Effect of acid treatment for the sheet resistance changed by various acids. Nitric acid shows the best effect to reduce the sheet resistance of TCFs.
HCl HNO3 H2SO4 HClO40.0
0.2
0.4
0.6
0.8
1.0
Rs/R
s0
Acid types
Concentration 6 M 12 M
0.0 0.2 0.4 0.6 0.8 1.0 6 12 18 240.0
0.2
0.4
0.6
0.8
1.0
Rs/R
s0
Nitric acid treatment time (hours)
Pristine
Enhancement conductivity by acid treatment
(b) Sheet resistance change with nitric acid treatment time. Sheet resistance reduced significantly in a short time and fluctuated with long treatment time.
Properties after acid treatment
(a) Transmittance in visible range did not obviously change after nitric acid treatment.
400 500 600 700 8000
20
40
60
80
100
Tran
smitt
ance
(%T)
Wavelength (nm)
Pristine
Acid treated
0 3 6 9 120.0
0.2
0.4
0.6
0.8
1.0
Rs/R
s0
After acid treatment (days)
Rs0=180 Ω/sq Rs0=150 Ω/sq
30 days
(b) Stability of TCFs after nitric acid treatment, sheet resistance did not significantly increased at long time.
286 285 284 2830
5000
10000284.1
C
ount
rate
(arb
. uni
ts)
Binding energy (eV)
Pristine SWCNTHNO3 treatment
30 min 12 hrs
284.5
284.0
C1s
(at%) C1s O1s N1sPristine SWCNTs 96.04 3.96 0.0
HNO3 treatment 30 min 90.13 9.35 0.52HNO3 treatment 12 hours 82.18 15.89 1.94
Table 1 Atomic concentration of the SWCNT samples
XPS of pristine SWCNT powder before and after acid treatment.
Black: pristine SWCNTs, preheat treated at 200 oCfor 20 min to remove humidity;
Red: nitric acid treatment for 30 min;
Blue: nitric acid treatment for 12 hours.
XPS analysis
Sheet resistance as a function of transmittance at 550 nm before and after acid treatment compared with other published results
50 60 70 80 90 1000
200
400
600
800
1000
FPD
Transmittance at 550 nm (%)
Shee
t res
ista
nce (Ω
/sq) As-prepared
Acid treatedRinzlerManoherZhouGrünerYooChhowallaRoth
TS
(d)(c)
Comparison with other’s resultsGeng et al. JACS Comm. 129, 7758 (07)
TCF morphology
taken at 60 degree angle
BeforeSDSor
impuritieson the
surface.
After acid treatment:
Impurities were removed and the protruded
nanotubeswere wet on the surface.
295 290 285 280
C1s (a)
410 405 400 395
iii
ii
SWCNT film HNO3 1 h H2SO4 1 h
N1sNO2
HNO3
-C=N
(c)
i
1080 1075 1070
-SO3Na
iiiii
Na1s (b)
i
175 170 165
-SO3Na
ii
iii
2P 1/2
S2p 2P 3/2
H2SO4
(d)
i
294 292 290 288 286
iiiii
C-O, C=O, -COO...
i
Cou
nt ra
te (a
rb. U
nits
)
Binding energy (eV)
285 284
iiiii
C1s i
540 535 530
Nitrites oxide R-SO3Na
(e)
O1s
Element C1s N1s O1s Na1s S2p
SW film 93.56 0.00 5.69 0.34 0.41
HNO3 88.66 2.22 9.12 0.00 0.00
H2SO4 88.40 0.00 10.44 0.00 1.16
Atomic concentration
XPS analysis
SDS can be efficiently removed by acid treatment and add a little oxide to the surface. The C1s core level was not obviously shifted by both nitric and sulfuric acid.
2600 2700 2800
ii
iii
G'-band
i
1400 1500 1600
iii
ii
i
Treatment time Pristine SWCNT SWCNT film 20 min 40 min 60 min 80 min 100 min
G-band
D
150 200 250
i
ii
iii EM11
633 nm RMB
2600 2700
i
ii
iii
G'-band
Raman shift (cm-1)
150 200
iiiii
ES33
514 nm RBM
i
1400 1500 1600
iiiii
i
Treatment time Pristine SWCNT SWCNT film 20 min 40 min 60 min 80 min 100 min
G-band
D
Raman spectroscopy analysis
After removal of SDS, the metallicity of carbon nanotubes was partially recovered.
Inte
nsity
(arb
. uni
ts)
Dispersion and functionalization of SWCNTs
Sodium Dodecyl Sulfate (SDS)
O’Connell et al. Science 297, 593 (2002)
Diazonium Salts
Modification of Electronic Structure via Functionalization
Chhowalla et al, APL 90, 121913 (2007)
C OOH
HNO3
Strano et al. Science 301, 1519 (2003)
1) Adhesion of SDS in solvent
4a) Physical absorption
2) Wetting of SDS on CNT
3) Removal of SDS from CNT4b) Functionalization
Model for acid treatment process
film
In acidW
ash
and
dr
y
Before acid:
After acid:
Densification of film
Thickness densified ratio = 55 / 74 ≈ 75 %
Pristine SWCNTswith clean edges
and bundles
Dry SWCNT/SDS film without
washing covered by SDS
SWCNT film after rinsing in water
with some residual SDS
Bundles and edges become clean again after acid treatment
SDSSDS
SDSSDS
SDSSDS
SDSSDS
20 nm20 nm
10 nm10 nm
10 nm10 nm 10 nm10 nm5 nm5 nm
10 nm10 nm 10 nm10 nm 10 nm10 nm
TEM images of SWCNT/SDS
Enhancing Conductivity of TCFs
0 30 60 90 1200
1k
2k
3k
4k
5k
6k
Acid treated
Con
duct
ivity
(S/c
m)
Thinckness (nm)
As prepared
(b)
- After acid treatment, the CNTs on PET become densified and the thickness decreased, together with the recovery of metallicity of SWCNTs.- This leads to enhance the conductivity of CNTs by a factor of ~ 4.
SummarySummary
Transparent conducting films were fabricated by a spray method on PET films using SDS-dispersed SWCNT solution.
TCFs were further treated by acid to reduce the sheet resistance without affecting the transmittance and stability for a long time.
XPS analysis indicated that SDS can be efficiently removed by acid treatment, resulting the low contact resistance among CNT networks.
All these effects by acid treatment lead to enhance the conductivity of carbon nanotubes by a factor of ~ 4.
Material quality factor that determines the conductivity of film was determined using diameter, purity, metallicity, and carrier concentration.
Structure of carbon nanotubes
armchair
zigzag
chiral
SWCNT
Classification of carbon nanotubes- Single-wall CNT, double-wall CNT, multi-wall CNTs- Armchair, zigzag, and chiral nanotubes
Carbon nanotubes
SWCNT DWCNT Thin-MWCNT MWCNT
Zigzag
Armchair
Filled circles denote n-m divisible by 3 which give metallicnanotubes.
Electronic structure of SWCNTs
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