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Copyright copy 2009 American Scientific PublishersAll rights reservedPrinted in the United States of America

Journal ofNanoscience and Nanotechnology

Vol 9 7491ndash7495 2009

Fabrication of Flexible Transparent Conductive Film(TCF) Using Single Walled Carbon Nanotubes

Seong-Yong Park13 Pyeong-Gee Kim1 In-Bum Jeong1 Dong-Wook Shin2Ji-Beom Yoo2 and Sang-Hoon Hyun3lowast

1RampD Center Changsung Corporation 11-9 Namdong Industrial Area Namdong-gu Incheon 405-846 Korea2Department Advanced Materials Science and Engineering Center for Nanotubes and Nanostructured Composites

Sungkyunkwan University 300 Chunchun-dong Jangan-gu Suwon 440-746 Korea3Department of Ceramic Engineering Yonsei University 262 Seongsanno Seodaemun-gu Seoul 120-749 Korea

In this work using single walled carbon nanotubes (SWNTs) made by chemical vapor deposition(CVD) process transparent conductive film (TCF) was prepared for mass production The optimumdispersion condition and two step sprays coating of aqueous SWNTs solution and organic polymersolutions have enabled us to achieve the high conductivity excellent flexibility and strong adhe-sion Through the analysis of particle size and zeta potential of dispersed SWNTs in water it wasfound that the particle size and solution stability were reduced as dispersing time increased Acidtreatment of sprayed SWNTs layer removed the surfactant and provided a hole doping effect toSWNTs resulting in significant reduction of the surface resistance of SWNTs film ConsequentlyCVD SWNTs flexible transparent conductive film (surface resistance of 270 ohmsq transmittanceof 823 at 550 nm with substrate effect and of 935 without substrate effect) was developed

Keywords Single Walled Carbon Nanotubes Sonication Dispersion Transparent ConductiveFilm Spray Coating

1 INTRODUCTION

The improvement of conductivity of transparent conduc-tive film (TCF) using conducting filler has received aconsiderable amount of attention in the various fieldssuch as display technologies solar cells flexible electronicdevices and optical devices1ndash7 Development of flexibleTCF is interesting topic for display industry Most mate-rials used for flat panel displays can not be transferredto flexible substrate8 The most popular material used inTCF is Indium Tin Oxide (ITO) But depletion of Indiumand high process cost increased the price of ITO filmIn addition ITO has several limits in various applicationareas such as the flexible display it is brittle and has pooradhesion to plastic substrate large difference in thermalexpansion coefficient with plastic substrateSingle walled carbon nanotubes (SWNTs) is good alter-

native to ITO for the transparent conductive films becauseof its high conductivity high aspect ratio low thermalvariation and excellent flexibility in the form of film9ndash10

In addition SWNTs technology offers a variety of benefi-cial properties including (a) broad range of conductivity

lowastAuthor to whom correspondence should be addressed

(10ndash107 (b) uniform and linear conductance (c) excellenttransparency (d) neutral color tone (e) wet processing(f) good adhesion (g) durability (h) abrasion resistance(i) good chemical resistance (j) flexibility and (k) easeof patterning These properties of SWNTs enable it to beused in conformal or flexible display11 General approachfor fabricating TCF with SWNTs is to disperse the SWNTsin water with sodium dodecyl sulfate (SDS) as dispersantSDS can be removed by acid treatment and then SWNTshave hole doping effects by strong Bronsted acids namelyH2SO4 HNO3 and HCl12

Spray coating which is simple and quick methodfor large scale application was used for deposition ofSWNTs13 The quality of spay coating depends criticallyon the size of droplet usually the smaller droplet thehigher surface quality14

The purpose of this work is to replace ITO with thinfilm based on SWNTs and to develop TCF productionprocess directly applicable to industrial area315 In thiswork SWNTs made by chemical vapor deposition (CVD)process14 were used because of its low price and easy massproduction The oxidation and annealing of CVD SWNTswere included to enhance the conductivity of SWNTsSonication was adapted to disperse CVD SWNTs Well

J Nanosci Nanotechnol 2009 Vol 9 No 12 1533-4880200997491005 doi101166jnn20091781 7491

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes Park et al

dispersed aqueous SWNTs solution was sprayed onto thepolyethylene terephthalate (PET) substrate firstly and sub-sequently organic polymeric solutions were sprayed ontothe SWNTs layer

2 EXPERIMENTAL DETAILS

The CVD SWNTs (Cheap Tube Inc USA) were usedas conductive coating material with average outside diam-eter of 11 nm length of 5sim30 m and purity of 90 wtThe crystallinity and purity were enhanced by anneal-ing at 600 C in nitrogen for 1 hour after oxidation at300 C in air for 1 hour The SWNTs were dispersed in1 wt sodium dodecyl sulfate (SDS Sigma-Aldrich IncUSA) aqueous solution by sonication Various polymersolutions were made by dissolving the thermoplastic poly-mer binders (polyester polyurethane poly vinyl chloride)in methyl ethyl ketone Poly ethylene terephthalate withcorona treated and untreated (PET SK Chemicals Co LtdKorea) were used as flexible substrate with transmittanceof 88 at 550 nm Nitric acid of 60 was used to removethe surfactant and as strong Bronsted acid which gives ahole doping onto the SWNTsOne weight percentage of SDS was dissolved in pure

water and then 01 wt of SWNTs was dispersed in SDSdissolved water using horn type ultrasonic homogenizer(VCX-750 Sonic amp Materials Inc USA) The SWNTsdispersed aqueous solutions were centrifuged by centrifuge(HA-500 Hanil Science Industrial Co Ltd Korea) at6000 rcf for 1 hourParticle size and zeta potential of dispersed SWNTs

in water were measured by zetasizer (Malvern zetasizer3000 HS Malvern instruments Ltd UK) In case of par-ticle size analysis dynamic light scattering (DLS) methodwas used and zeta potential was measured by laser Dopplerelectrophoresis method Zeta potential is a very good indexof the magnitude of the interaction between colloidal par-ticles and zeta potential measurements are generally usedto assess the stability of colloidal systemsThe SWNTs aqueous solution and polymer solutions

were directly sprayed on flexible substrate using spraygun (W-101 ANEST IWATA Co Japan) Firstly welldispersed SWNTs aqueous solution was sprayed ontothe PET substrate To avoid droplet formation the sub-strate was heated to around 100 C during the spray andSWNTsPET film was immersed into 60 nitric acid for30 seconds to remove the surfactant and immersed inpure water immediately to remove nitric acid and then itwas dried completely Secondly organic polymeric solu-tion was sprayed onto the SWNTs layer and then it wasalso dried completely Using this method enhanced con-ductivity increased adhesion and flexibility was achievedCrease test was done by the standard of Chang-

sung Corporation which followed modified ASTMF1683-05e1 The standard is made for the quality

control of conductive paste manufactured by ChangsungCorporation(1) Bend the sample tested line resistance already to theinside thoroughly(2) Put a 20 kg weight on the bended point of sample for1 minute(3) Repeat (1) and (2) procedure to the outside(4) Check the line resistance of creased sample(5) Count this process as 1 time then repeated this pro-cess four times more (total 5 times) and measure the lineresistance

The adhesion strength between the PET substrate andSWNTs conductive layer was determined by peel strengthusing 3M 600 tape which followed ASTM D903-49

0

100

200

300

400

500

600

0 20 40 60 80 100 120 140

Par

ticle

siz

e (n

m)

Sonication time (min)

Amp 30(a)

ndash60

ndash40

ndash20

0

40

60

100

Zet

a po

tent

ial (

mV

)

Sonication time (min)

(b)80

20

ndash80

ndash100

Amp 30

20 40 60 80 100 120 140

Unstable

Stable

Stable

Fig 1 Particle size and zeta potential of dispersed SWNTs in aqueoussolutions (a) particle size with sonication time and (b) zeta potentialwith sonication time

7492 J Nanosci Nanotechnol 9 7491ndash7495 2009

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Park et al Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes

Adhesion strength was measured by the change of surfaceresistance before and after adhesion test

3 RESULTS AND DISCUSSION

Figure 1 shows particle size and zeta potential of dispersedSWNTs in aqueous solutions (a) particle size with son-ication time and (b) Zeta potential with sonication timeFigure 1(a) shows particle size decreased with sonicationtime increasing because SWNTs globules were dissolved

25 ordmC solutionUntreated PET(a)

(b)

(c)

25 ordmC solutionCorona treated PET

60 ordmC solutionCorona treated PET

Fig 2 FE-SEM photographs of SWNTs solutions droplet with sprayconditions (a) 25 C solutionuntreated PET (b) 25 C solutioncoronatreated PET and (c) 60 C solutioncorona treated PET

by sonication In Figure 1(b) a dividing line between sta-ble and unstable dispersions is generally taken at either+30 or minus30 mV particles with zeta potentials more pos-itive than +30 mV and more negative than minus30 mVare normally considered stable As shown in Figure 1the dispersed SWNTs is the most stable when dispersingtime is 5 minutes Especially when the sonication time isover 20 minutes standard deviation (SD) of zeta poten-tial increased greatly It suggests that surface damage andshortening of SWNTs result in very unstable state of dis-persed SWNTs solution when sonication time is increasedFigure 2 shows FE-SEM image of SWNTs solu-

tion droplets with spray conditions Wettability betweenSWNTs solution and PET substrate increased withincrease in the surface energy of PET by corona treat-ment and with decrease in the surface energy of solutiondue to the solution heating In other words the wettabil-ity between SWNTs solution and PET film is much betterwhen the surface energy of them become more similarFigure 3 shows FE-SEM images of SWNTs layers on

PET (a) before and (b) after nitric acid treatment Acidtreatment of SWNTs layers using 60 nitric acid removed

3O s(b)

O s(a)

Fig 3 FE-SEM photographs of SWNTs layers on PET (a) before and(b) after nitric acid treatment

J Nanosci Nanotechnol 9 7491ndash7495 2009 7493

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes Park et al

0

4

75 90

Sur

face

res

ista

nce

(koh

ms

q)

Transmittance ()

1

2

3

80 85

Amplitude 30Sonication time 10 min

SWNTs treated conditions

Oxidation

untreatedAnnealing after oxidation

(a)

0

1

2

3

4

65 70 75 80 85 90

Sur

face

res

ista

nce

(koh

ms

q)

Transmittance ()

Amplitude 30

Sonication time

5 min

10 min20 min60 min120 min

(b)

Fig 4 The change of surface resistance by transmittance ofSWNTsPET films with (a) treated conditions of SWNTs and (b) soni-cation time

the surfactants and gave a hole doping effects on SWNTsby strong Bronsted acids HNO3 As a result the surfaceresistance of SWNTs film was reduced by one order ofmagnitudeFigure 4 shows the change of surface resistance by

transmittance of SWNTsPET films with (a) treated con-ditions of SWNTs and (b) sonication time The annealingof SWNTs made by CVD process enhanced the conduc-tivity The resistivity of SWNTs film was increased whensonication time was too long Surface damage and short-ening of SWNTs with sonication time increasing resultedin higher resistivity of TCF

0

02

04

06

08

10

0 2 4 6 8

PolyurethanePolyvinyl chloride

Polyester

∆ρρ

0∆ρ

ρ0

∆ρρ

0

Content of polymerMEK (ml)

(a)

60

The number of times4321 5

10

ndash05

0

SWNTs film

ITO film

~~ (b)

05

ndash002

ndash001

0

001

002

003

50

The number of times

4321

SWNTs film

ITO film

(c)

Fig 5 The change of surface resistance of polymer binder coatedSWNTsPET films with (a) amount of polymer (b) crease times and(c) times of adhesion test

Figure 5 shows the change of surface resistance of poly-mer binder coated SWNTsPET films with (a) amount ofpolymer (b) creases times and (c) times of adhesion testSurface resistance increased slightly after polymer coating

7494 J Nanosci Nanotechnol 9 7491ndash7495 2009

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Park et al Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes

(a) but flexibility of SWNTs TCF was much better thanITO TCF (b) Adhesion strength is also good enough asshown in TCF (c) Polyester is better than other coatingpolymers

4 CONCLUSIONS

Using Direct Light Scattering (DLS) measurement of par-ticle size and zeta potential measurement we could get theoptimum dispersion condition for SWNTs aqueous solu-tion As sonication time increased the particle size ofSWNTs decreased and the state of SWNTs aqueous solu-tion became more unstable This implies that surface ofSWNTs was damaged and shortening of SWNTs in solu-tion occurred during sonication So the conductivity ofTCF decreased when sonication time became too longTreatment of SWNTs layer using nitric acid removed thesurfactants in SWNTs layer and reduced the surface resis-tance of TCF significantly by hole doping effects Sur-face resistance increased slightly after polyester coatingbut flexibility of SWNTs TCF became much better thanITO film Adhesion strength is also good enough Con-sequently CVD SWNTs flexible transparent conductivefilm (surface resistance of 270 ohmsq transmittance of823 at 550 nm with substrate effect 935 withoutsubstrate effect) was developed Using CVD SWNTs andspray deposition the price of TCFs is inexpensive and

mass production is easy and this process can be directlyapplicable to industrial area

References and Notes

1 J S Moon J H Park T Y Lee Y W Kim J B Yoo C Y ParkJ M Kim and K W Jin Diam Relat Mater 14 1882 (2005)

2 R H Baughman A A Zakhidov and W A de Heer Science 297787 (2002)

3 J Robertson Mater Today 7 46 (2004)4 M Paradise and T Goswami Mater Des 28 1477 (2007)5 K Balasubramanian and M Burghard J Mater Chem 18 3071

(2008)6 R G Gordon MRS Bull 25 52 (2000)7 H Richter M Treska J B Howard J Z Wen S B Thomasson

A A Reading P M Jardim and J B Vander Sande J NanosciNanotechnol 8 6065 (2008)

8 A Schindler J Brill N Fruehauf J P Novak and Z YanivPhysica E 37 119 (2007)

9 S H Jin I H Kang Y S Kim C Y Park and D S LeeJ Nanosci Nanotechnol 8 5076 (2008)

10 E C Venancio P C Wang N C Filho and A G MacDiarmidJ Nanosci Nanotechnol 9 567 (2008)

11 C Weeks Veritas et Visus Touch Panel 1 34 (2006)12 R Graupner J Abraham A Vencelova T Seyller F Hennrich

M Kappes A Hirsch and L Ley Phys Chem Chem Phys 5 5472(2003)

13 M Kaempgen G S Duesberg and S Roth Appl Surf Sci 252425 (2005)

14 Z Li J Zhu and C Zhang Powder Technol 150 155 (2005)15 G Gruner J Mater Chem 16 3533 (2006)

Received 6 January 2008 Accepted 21 February 2009

J Nanosci Nanotechnol 9 7491ndash7495 2009 7495

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes Park et al

dispersed aqueous SWNTs solution was sprayed onto thepolyethylene terephthalate (PET) substrate firstly and sub-sequently organic polymeric solutions were sprayed ontothe SWNTs layer

2 EXPERIMENTAL DETAILS

The CVD SWNTs (Cheap Tube Inc USA) were usedas conductive coating material with average outside diam-eter of 11 nm length of 5sim30 m and purity of 90 wtThe crystallinity and purity were enhanced by anneal-ing at 600 C in nitrogen for 1 hour after oxidation at300 C in air for 1 hour The SWNTs were dispersed in1 wt sodium dodecyl sulfate (SDS Sigma-Aldrich IncUSA) aqueous solution by sonication Various polymersolutions were made by dissolving the thermoplastic poly-mer binders (polyester polyurethane poly vinyl chloride)in methyl ethyl ketone Poly ethylene terephthalate withcorona treated and untreated (PET SK Chemicals Co LtdKorea) were used as flexible substrate with transmittanceof 88 at 550 nm Nitric acid of 60 was used to removethe surfactant and as strong Bronsted acid which gives ahole doping onto the SWNTsOne weight percentage of SDS was dissolved in pure

water and then 01 wt of SWNTs was dispersed in SDSdissolved water using horn type ultrasonic homogenizer(VCX-750 Sonic amp Materials Inc USA) The SWNTsdispersed aqueous solutions were centrifuged by centrifuge(HA-500 Hanil Science Industrial Co Ltd Korea) at6000 rcf for 1 hourParticle size and zeta potential of dispersed SWNTs

in water were measured by zetasizer (Malvern zetasizer3000 HS Malvern instruments Ltd UK) In case of par-ticle size analysis dynamic light scattering (DLS) methodwas used and zeta potential was measured by laser Dopplerelectrophoresis method Zeta potential is a very good indexof the magnitude of the interaction between colloidal par-ticles and zeta potential measurements are generally usedto assess the stability of colloidal systemsThe SWNTs aqueous solution and polymer solutions

were directly sprayed on flexible substrate using spraygun (W-101 ANEST IWATA Co Japan) Firstly welldispersed SWNTs aqueous solution was sprayed ontothe PET substrate To avoid droplet formation the sub-strate was heated to around 100 C during the spray andSWNTsPET film was immersed into 60 nitric acid for30 seconds to remove the surfactant and immersed inpure water immediately to remove nitric acid and then itwas dried completely Secondly organic polymeric solu-tion was sprayed onto the SWNTs layer and then it wasalso dried completely Using this method enhanced con-ductivity increased adhesion and flexibility was achievedCrease test was done by the standard of Chang-

sung Corporation which followed modified ASTMF1683-05e1 The standard is made for the quality

control of conductive paste manufactured by ChangsungCorporation(1) Bend the sample tested line resistance already to theinside thoroughly(2) Put a 20 kg weight on the bended point of sample for1 minute(3) Repeat (1) and (2) procedure to the outside(4) Check the line resistance of creased sample(5) Count this process as 1 time then repeated this pro-cess four times more (total 5 times) and measure the lineresistance

The adhesion strength between the PET substrate andSWNTs conductive layer was determined by peel strengthusing 3M 600 tape which followed ASTM D903-49

0

100

200

300

400

500

600

0 20 40 60 80 100 120 140

Par

ticle

siz

e (n

m)

Sonication time (min)

Amp 30(a)

ndash60

ndash40

ndash20

0

40

60

100

Zet

a po

tent

ial (

mV

)

Sonication time (min)

(b)80

20

ndash80

ndash100

Amp 30

20 40 60 80 100 120 140

Unstable

Stable

Stable

Fig 1 Particle size and zeta potential of dispersed SWNTs in aqueoussolutions (a) particle size with sonication time and (b) zeta potentialwith sonication time

7492 J Nanosci Nanotechnol 9 7491ndash7495 2009

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Park et al Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes

Adhesion strength was measured by the change of surfaceresistance before and after adhesion test

3 RESULTS AND DISCUSSION

Figure 1 shows particle size and zeta potential of dispersedSWNTs in aqueous solutions (a) particle size with son-ication time and (b) Zeta potential with sonication timeFigure 1(a) shows particle size decreased with sonicationtime increasing because SWNTs globules were dissolved

25 ordmC solutionUntreated PET(a)

(b)

(c)

25 ordmC solutionCorona treated PET

60 ordmC solutionCorona treated PET

Fig 2 FE-SEM photographs of SWNTs solutions droplet with sprayconditions (a) 25 C solutionuntreated PET (b) 25 C solutioncoronatreated PET and (c) 60 C solutioncorona treated PET

by sonication In Figure 1(b) a dividing line between sta-ble and unstable dispersions is generally taken at either+30 or minus30 mV particles with zeta potentials more pos-itive than +30 mV and more negative than minus30 mVare normally considered stable As shown in Figure 1the dispersed SWNTs is the most stable when dispersingtime is 5 minutes Especially when the sonication time isover 20 minutes standard deviation (SD) of zeta poten-tial increased greatly It suggests that surface damage andshortening of SWNTs result in very unstable state of dis-persed SWNTs solution when sonication time is increasedFigure 2 shows FE-SEM image of SWNTs solu-

tion droplets with spray conditions Wettability betweenSWNTs solution and PET substrate increased withincrease in the surface energy of PET by corona treat-ment and with decrease in the surface energy of solutiondue to the solution heating In other words the wettabil-ity between SWNTs solution and PET film is much betterwhen the surface energy of them become more similarFigure 3 shows FE-SEM images of SWNTs layers on

PET (a) before and (b) after nitric acid treatment Acidtreatment of SWNTs layers using 60 nitric acid removed

3O s(b)

O s(a)

Fig 3 FE-SEM photographs of SWNTs layers on PET (a) before and(b) after nitric acid treatment

J Nanosci Nanotechnol 9 7491ndash7495 2009 7493

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes Park et al

0

4

75 90

Sur

face

res

ista

nce

(koh

ms

q)

Transmittance ()

1

2

3

80 85

Amplitude 30Sonication time 10 min

SWNTs treated conditions

Oxidation

untreatedAnnealing after oxidation

(a)

0

1

2

3

4

65 70 75 80 85 90

Sur

face

res

ista

nce

(koh

ms

q)

Transmittance ()

Amplitude 30

Sonication time

5 min

10 min20 min60 min120 min

(b)

Fig 4 The change of surface resistance by transmittance ofSWNTsPET films with (a) treated conditions of SWNTs and (b) soni-cation time

the surfactants and gave a hole doping effects on SWNTsby strong Bronsted acids HNO3 As a result the surfaceresistance of SWNTs film was reduced by one order ofmagnitudeFigure 4 shows the change of surface resistance by

transmittance of SWNTsPET films with (a) treated con-ditions of SWNTs and (b) sonication time The annealingof SWNTs made by CVD process enhanced the conduc-tivity The resistivity of SWNTs film was increased whensonication time was too long Surface damage and short-ening of SWNTs with sonication time increasing resultedin higher resistivity of TCF

0

02

04

06

08

10

0 2 4 6 8

PolyurethanePolyvinyl chloride

Polyester

∆ρρ

0∆ρ

ρ0

∆ρρ

0

Content of polymerMEK (ml)

(a)

60

The number of times4321 5

10

ndash05

0

SWNTs film

ITO film

~~ (b)

05

ndash002

ndash001

0

001

002

003

50

The number of times

4321

SWNTs film

ITO film

(c)

Fig 5 The change of surface resistance of polymer binder coatedSWNTsPET films with (a) amount of polymer (b) crease times and(c) times of adhesion test

Figure 5 shows the change of surface resistance of poly-mer binder coated SWNTsPET films with (a) amount ofpolymer (b) creases times and (c) times of adhesion testSurface resistance increased slightly after polymer coating

7494 J Nanosci Nanotechnol 9 7491ndash7495 2009

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Park et al Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes

(a) but flexibility of SWNTs TCF was much better thanITO TCF (b) Adhesion strength is also good enough asshown in TCF (c) Polyester is better than other coatingpolymers

4 CONCLUSIONS

Using Direct Light Scattering (DLS) measurement of par-ticle size and zeta potential measurement we could get theoptimum dispersion condition for SWNTs aqueous solu-tion As sonication time increased the particle size ofSWNTs decreased and the state of SWNTs aqueous solu-tion became more unstable This implies that surface ofSWNTs was damaged and shortening of SWNTs in solu-tion occurred during sonication So the conductivity ofTCF decreased when sonication time became too longTreatment of SWNTs layer using nitric acid removed thesurfactants in SWNTs layer and reduced the surface resis-tance of TCF significantly by hole doping effects Sur-face resistance increased slightly after polyester coatingbut flexibility of SWNTs TCF became much better thanITO film Adhesion strength is also good enough Con-sequently CVD SWNTs flexible transparent conductivefilm (surface resistance of 270 ohmsq transmittance of823 at 550 nm with substrate effect 935 withoutsubstrate effect) was developed Using CVD SWNTs andspray deposition the price of TCFs is inexpensive and

mass production is easy and this process can be directlyapplicable to industrial area

References and Notes

1 J S Moon J H Park T Y Lee Y W Kim J B Yoo C Y ParkJ M Kim and K W Jin Diam Relat Mater 14 1882 (2005)

2 R H Baughman A A Zakhidov and W A de Heer Science 297787 (2002)

3 J Robertson Mater Today 7 46 (2004)4 M Paradise and T Goswami Mater Des 28 1477 (2007)5 K Balasubramanian and M Burghard J Mater Chem 18 3071

(2008)6 R G Gordon MRS Bull 25 52 (2000)7 H Richter M Treska J B Howard J Z Wen S B Thomasson

A A Reading P M Jardim and J B Vander Sande J NanosciNanotechnol 8 6065 (2008)

8 A Schindler J Brill N Fruehauf J P Novak and Z YanivPhysica E 37 119 (2007)

9 S H Jin I H Kang Y S Kim C Y Park and D S LeeJ Nanosci Nanotechnol 8 5076 (2008)

10 E C Venancio P C Wang N C Filho and A G MacDiarmidJ Nanosci Nanotechnol 9 567 (2008)

11 C Weeks Veritas et Visus Touch Panel 1 34 (2006)12 R Graupner J Abraham A Vencelova T Seyller F Hennrich

M Kappes A Hirsch and L Ley Phys Chem Chem Phys 5 5472(2003)

13 M Kaempgen G S Duesberg and S Roth Appl Surf Sci 252425 (2005)

14 Z Li J Zhu and C Zhang Powder Technol 150 155 (2005)15 G Gruner J Mater Chem 16 3533 (2006)

Received 6 January 2008 Accepted 21 February 2009

J Nanosci Nanotechnol 9 7491ndash7495 2009 7495

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Park et al Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes

Adhesion strength was measured by the change of surfaceresistance before and after adhesion test

3 RESULTS AND DISCUSSION

Figure 1 shows particle size and zeta potential of dispersedSWNTs in aqueous solutions (a) particle size with son-ication time and (b) Zeta potential with sonication timeFigure 1(a) shows particle size decreased with sonicationtime increasing because SWNTs globules were dissolved

25 ordmC solutionUntreated PET(a)

(b)

(c)

25 ordmC solutionCorona treated PET

60 ordmC solutionCorona treated PET

Fig 2 FE-SEM photographs of SWNTs solutions droplet with sprayconditions (a) 25 C solutionuntreated PET (b) 25 C solutioncoronatreated PET and (c) 60 C solutioncorona treated PET

by sonication In Figure 1(b) a dividing line between sta-ble and unstable dispersions is generally taken at either+30 or minus30 mV particles with zeta potentials more pos-itive than +30 mV and more negative than minus30 mVare normally considered stable As shown in Figure 1the dispersed SWNTs is the most stable when dispersingtime is 5 minutes Especially when the sonication time isover 20 minutes standard deviation (SD) of zeta poten-tial increased greatly It suggests that surface damage andshortening of SWNTs result in very unstable state of dis-persed SWNTs solution when sonication time is increasedFigure 2 shows FE-SEM image of SWNTs solu-

tion droplets with spray conditions Wettability betweenSWNTs solution and PET substrate increased withincrease in the surface energy of PET by corona treat-ment and with decrease in the surface energy of solutiondue to the solution heating In other words the wettabil-ity between SWNTs solution and PET film is much betterwhen the surface energy of them become more similarFigure 3 shows FE-SEM images of SWNTs layers on

PET (a) before and (b) after nitric acid treatment Acidtreatment of SWNTs layers using 60 nitric acid removed

3O s(b)

O s(a)

Fig 3 FE-SEM photographs of SWNTs layers on PET (a) before and(b) after nitric acid treatment

J Nanosci Nanotechnol 9 7491ndash7495 2009 7493

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes Park et al

0

4

75 90

Sur

face

res

ista

nce

(koh

ms

q)

Transmittance ()

1

2

3

80 85

Amplitude 30Sonication time 10 min

SWNTs treated conditions

Oxidation

untreatedAnnealing after oxidation

(a)

0

1

2

3

4

65 70 75 80 85 90

Sur

face

res

ista

nce

(koh

ms

q)

Transmittance ()

Amplitude 30

Sonication time

5 min

10 min20 min60 min120 min

(b)

Fig 4 The change of surface resistance by transmittance ofSWNTsPET films with (a) treated conditions of SWNTs and (b) soni-cation time

the surfactants and gave a hole doping effects on SWNTsby strong Bronsted acids HNO3 As a result the surfaceresistance of SWNTs film was reduced by one order ofmagnitudeFigure 4 shows the change of surface resistance by

transmittance of SWNTsPET films with (a) treated con-ditions of SWNTs and (b) sonication time The annealingof SWNTs made by CVD process enhanced the conduc-tivity The resistivity of SWNTs film was increased whensonication time was too long Surface damage and short-ening of SWNTs with sonication time increasing resultedin higher resistivity of TCF

0

02

04

06

08

10

0 2 4 6 8

PolyurethanePolyvinyl chloride

Polyester

∆ρρ

0∆ρ

ρ0

∆ρρ

0

Content of polymerMEK (ml)

(a)

60

The number of times4321 5

10

ndash05

0

SWNTs film

ITO film

~~ (b)

05

ndash002

ndash001

0

001

002

003

50

The number of times

4321

SWNTs film

ITO film

(c)

Fig 5 The change of surface resistance of polymer binder coatedSWNTsPET films with (a) amount of polymer (b) crease times and(c) times of adhesion test

Figure 5 shows the change of surface resistance of poly-mer binder coated SWNTsPET films with (a) amount ofpolymer (b) creases times and (c) times of adhesion testSurface resistance increased slightly after polymer coating

7494 J Nanosci Nanotechnol 9 7491ndash7495 2009

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Park et al Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes

(a) but flexibility of SWNTs TCF was much better thanITO TCF (b) Adhesion strength is also good enough asshown in TCF (c) Polyester is better than other coatingpolymers

4 CONCLUSIONS

Using Direct Light Scattering (DLS) measurement of par-ticle size and zeta potential measurement we could get theoptimum dispersion condition for SWNTs aqueous solu-tion As sonication time increased the particle size ofSWNTs decreased and the state of SWNTs aqueous solu-tion became more unstable This implies that surface ofSWNTs was damaged and shortening of SWNTs in solu-tion occurred during sonication So the conductivity ofTCF decreased when sonication time became too longTreatment of SWNTs layer using nitric acid removed thesurfactants in SWNTs layer and reduced the surface resis-tance of TCF significantly by hole doping effects Sur-face resistance increased slightly after polyester coatingbut flexibility of SWNTs TCF became much better thanITO film Adhesion strength is also good enough Con-sequently CVD SWNTs flexible transparent conductivefilm (surface resistance of 270 ohmsq transmittance of823 at 550 nm with substrate effect 935 withoutsubstrate effect) was developed Using CVD SWNTs andspray deposition the price of TCFs is inexpensive and

mass production is easy and this process can be directlyapplicable to industrial area

References and Notes

1 J S Moon J H Park T Y Lee Y W Kim J B Yoo C Y ParkJ M Kim and K W Jin Diam Relat Mater 14 1882 (2005)

2 R H Baughman A A Zakhidov and W A de Heer Science 297787 (2002)

3 J Robertson Mater Today 7 46 (2004)4 M Paradise and T Goswami Mater Des 28 1477 (2007)5 K Balasubramanian and M Burghard J Mater Chem 18 3071

(2008)6 R G Gordon MRS Bull 25 52 (2000)7 H Richter M Treska J B Howard J Z Wen S B Thomasson

A A Reading P M Jardim and J B Vander Sande J NanosciNanotechnol 8 6065 (2008)

8 A Schindler J Brill N Fruehauf J P Novak and Z YanivPhysica E 37 119 (2007)

9 S H Jin I H Kang Y S Kim C Y Park and D S LeeJ Nanosci Nanotechnol 8 5076 (2008)

10 E C Venancio P C Wang N C Filho and A G MacDiarmidJ Nanosci Nanotechnol 9 567 (2008)

11 C Weeks Veritas et Visus Touch Panel 1 34 (2006)12 R Graupner J Abraham A Vencelova T Seyller F Hennrich

M Kappes A Hirsch and L Ley Phys Chem Chem Phys 5 5472(2003)

13 M Kaempgen G S Duesberg and S Roth Appl Surf Sci 252425 (2005)

14 Z Li J Zhu and C Zhang Powder Technol 150 155 (2005)15 G Gruner J Mater Chem 16 3533 (2006)

Received 6 January 2008 Accepted 21 February 2009

J Nanosci Nanotechnol 9 7491ndash7495 2009 7495

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes Park et al

0

4

75 90

Sur

face

res

ista

nce

(koh

ms

q)

Transmittance ()

1

2

3

80 85

Amplitude 30Sonication time 10 min

SWNTs treated conditions

Oxidation

untreatedAnnealing after oxidation

(a)

0

1

2

3

4

65 70 75 80 85 90

Sur

face

res

ista

nce

(koh

ms

q)

Transmittance ()

Amplitude 30

Sonication time

5 min

10 min20 min60 min120 min

(b)

Fig 4 The change of surface resistance by transmittance ofSWNTsPET films with (a) treated conditions of SWNTs and (b) soni-cation time

the surfactants and gave a hole doping effects on SWNTsby strong Bronsted acids HNO3 As a result the surfaceresistance of SWNTs film was reduced by one order ofmagnitudeFigure 4 shows the change of surface resistance by

transmittance of SWNTsPET films with (a) treated con-ditions of SWNTs and (b) sonication time The annealingof SWNTs made by CVD process enhanced the conduc-tivity The resistivity of SWNTs film was increased whensonication time was too long Surface damage and short-ening of SWNTs with sonication time increasing resultedin higher resistivity of TCF

0

02

04

06

08

10

0 2 4 6 8

PolyurethanePolyvinyl chloride

Polyester

∆ρρ

0∆ρ

ρ0

∆ρρ

0

Content of polymerMEK (ml)

(a)

60

The number of times4321 5

10

ndash05

0

SWNTs film

ITO film

~~ (b)

05

ndash002

ndash001

0

001

002

003

50

The number of times

4321

SWNTs film

ITO film

(c)

Fig 5 The change of surface resistance of polymer binder coatedSWNTsPET films with (a) amount of polymer (b) crease times and(c) times of adhesion test

Figure 5 shows the change of surface resistance of poly-mer binder coated SWNTsPET films with (a) amount ofpolymer (b) creases times and (c) times of adhesion testSurface resistance increased slightly after polymer coating

7494 J Nanosci Nanotechnol 9 7491ndash7495 2009

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Park et al Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes

(a) but flexibility of SWNTs TCF was much better thanITO TCF (b) Adhesion strength is also good enough asshown in TCF (c) Polyester is better than other coatingpolymers

4 CONCLUSIONS

Using Direct Light Scattering (DLS) measurement of par-ticle size and zeta potential measurement we could get theoptimum dispersion condition for SWNTs aqueous solu-tion As sonication time increased the particle size ofSWNTs decreased and the state of SWNTs aqueous solu-tion became more unstable This implies that surface ofSWNTs was damaged and shortening of SWNTs in solu-tion occurred during sonication So the conductivity ofTCF decreased when sonication time became too longTreatment of SWNTs layer using nitric acid removed thesurfactants in SWNTs layer and reduced the surface resis-tance of TCF significantly by hole doping effects Sur-face resistance increased slightly after polyester coatingbut flexibility of SWNTs TCF became much better thanITO film Adhesion strength is also good enough Con-sequently CVD SWNTs flexible transparent conductivefilm (surface resistance of 270 ohmsq transmittance of823 at 550 nm with substrate effect 935 withoutsubstrate effect) was developed Using CVD SWNTs andspray deposition the price of TCFs is inexpensive and

mass production is easy and this process can be directlyapplicable to industrial area

References and Notes

1 J S Moon J H Park T Y Lee Y W Kim J B Yoo C Y ParkJ M Kim and K W Jin Diam Relat Mater 14 1882 (2005)

2 R H Baughman A A Zakhidov and W A de Heer Science 297787 (2002)

3 J Robertson Mater Today 7 46 (2004)4 M Paradise and T Goswami Mater Des 28 1477 (2007)5 K Balasubramanian and M Burghard J Mater Chem 18 3071

(2008)6 R G Gordon MRS Bull 25 52 (2000)7 H Richter M Treska J B Howard J Z Wen S B Thomasson

A A Reading P M Jardim and J B Vander Sande J NanosciNanotechnol 8 6065 (2008)

8 A Schindler J Brill N Fruehauf J P Novak and Z YanivPhysica E 37 119 (2007)

9 S H Jin I H Kang Y S Kim C Y Park and D S LeeJ Nanosci Nanotechnol 8 5076 (2008)

10 E C Venancio P C Wang N C Filho and A G MacDiarmidJ Nanosci Nanotechnol 9 567 (2008)

11 C Weeks Veritas et Visus Touch Panel 1 34 (2006)12 R Graupner J Abraham A Vencelova T Seyller F Hennrich

M Kappes A Hirsch and L Ley Phys Chem Chem Phys 5 5472(2003)

13 M Kaempgen G S Duesberg and S Roth Appl Surf Sci 252425 (2005)

14 Z Li J Zhu and C Zhang Powder Technol 150 155 (2005)15 G Gruner J Mater Chem 16 3533 (2006)

Received 6 January 2008 Accepted 21 February 2009

J Nanosci Nanotechnol 9 7491ndash7495 2009 7495

Delivered by Ingenta toYonsei UniversityIP 1651321414

Mon 23 Nov 2009 130502

RESEARCH

ARTIC

LE

Park et al Fabrication of Flexible Transparent Conductive Film (TCF) Using Single Walled Carbon Nanotubes

(a) but flexibility of SWNTs TCF was much better thanITO TCF (b) Adhesion strength is also good enough asshown in TCF (c) Polyester is better than other coatingpolymers

4 CONCLUSIONS

Using Direct Light Scattering (DLS) measurement of par-ticle size and zeta potential measurement we could get theoptimum dispersion condition for SWNTs aqueous solu-tion As sonication time increased the particle size ofSWNTs decreased and the state of SWNTs aqueous solu-tion became more unstable This implies that surface ofSWNTs was damaged and shortening of SWNTs in solu-tion occurred during sonication So the conductivity ofTCF decreased when sonication time became too longTreatment of SWNTs layer using nitric acid removed thesurfactants in SWNTs layer and reduced the surface resis-tance of TCF significantly by hole doping effects Sur-face resistance increased slightly after polyester coatingbut flexibility of SWNTs TCF became much better thanITO film Adhesion strength is also good enough Con-sequently CVD SWNTs flexible transparent conductivefilm (surface resistance of 270 ohmsq transmittance of823 at 550 nm with substrate effect 935 withoutsubstrate effect) was developed Using CVD SWNTs andspray deposition the price of TCFs is inexpensive and

mass production is easy and this process can be directlyapplicable to industrial area

References and Notes

1 J S Moon J H Park T Y Lee Y W Kim J B Yoo C Y ParkJ M Kim and K W Jin Diam Relat Mater 14 1882 (2005)

2 R H Baughman A A Zakhidov and W A de Heer Science 297787 (2002)

3 J Robertson Mater Today 7 46 (2004)4 M Paradise and T Goswami Mater Des 28 1477 (2007)5 K Balasubramanian and M Burghard J Mater Chem 18 3071

(2008)6 R G Gordon MRS Bull 25 52 (2000)7 H Richter M Treska J B Howard J Z Wen S B Thomasson

A A Reading P M Jardim and J B Vander Sande J NanosciNanotechnol 8 6065 (2008)

8 A Schindler J Brill N Fruehauf J P Novak and Z YanivPhysica E 37 119 (2007)

9 S H Jin I H Kang Y S Kim C Y Park and D S LeeJ Nanosci Nanotechnol 8 5076 (2008)

10 E C Venancio P C Wang N C Filho and A G MacDiarmidJ Nanosci Nanotechnol 9 567 (2008)

11 C Weeks Veritas et Visus Touch Panel 1 34 (2006)12 R Graupner J Abraham A Vencelova T Seyller F Hennrich

M Kappes A Hirsch and L Ley Phys Chem Chem Phys 5 5472(2003)

13 M Kaempgen G S Duesberg and S Roth Appl Surf Sci 252425 (2005)

14 Z Li J Zhu and C Zhang Powder Technol 150 155 (2005)15 G Gruner J Mater Chem 16 3533 (2006)

Received 6 January 2008 Accepted 21 February 2009

J Nanosci Nanotechnol 9 7491ndash7495 2009 7495