fabrication of free standing anodic titanium oxide...

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IP 115145200148Thu 06 May 2010 120247

RESEARCH

ARTIC

LE

Copyright copy 2010 American Scientific Publishers

All rights reserved

Printed in the United States of America

Journal ofNanoscience and Nanotechnology

Vol 10 4259ndash4265 2010

Fabrication of Free Standing Anodic Titanium

Oxide Membranes with Clean Surface

Using Recycling Process

Xianhui Meng1 Tae-Young Lee1 Huiyu Chen1 Dong-Wook Shin2 Kee-Won Kwon3Sang Jik Kwon4 and Ji-Beom Yoo12lowast

1School of Advanced Materials Science and Engineering Sungkyunkwan University Suwon 440-476 Korea2SKKU Advanced Institute of Nanotechnology (SAINT) Sungkyunkwan University Suwon 440-476 Korea

3School of Information and Communication Engineering Sungkyunkwan University Suwon 440-476 Korea4Electronics Engineering Kyungwon University Senongnam 461-701 Korea

Large area of self-organized free standing anodic titanium oxide (ATO) nanotube membranes withclean surfaces were facilely prepared to desired lengths via electrochemical anodization of highlypure Ti sheets in an ethylene glycol electrolyte with a small amount of NH4F and H2O at 50 Vfollowed by self-detachment of the ATO membrane from the Ti substrate using recycling processesIn the first anodization step the nanowire oxide layer existed over the well-arranged ATO nanotubeAfter sufficiently rinsing with water the whole ATO layer was removed from the Ti sheet by highpressure N2 gas and a well-patterned dimple layer with a thickness of about 30 nm existed onthe Ti substrate By using these naturally formed nano-scale pits as templates in the second andthird anodization process highly ordered vertically aligned and free standing ATO membranes withthe anodic aluminum oxide (AAO)-like clean surface were obtained The inter-pore distance anddiameter was 154plusmn2 nm and 91plusmn2 nm the tube arrays lengths for 25 and 46 hours were 44 and70 m respectively The present study demonstrates a simple approach to producing high qualitylength controllable large area TiO2 membrane

Keywords Titanium Oxide Nanotube Membrane Recycling Process Dimple Template

1 INTRODUCTION

Nanomaterials have attracted increasing attention over the

past few decades because of their excellent properties

and wide applications as compared to their bulk coun-

terparts One-dimensional nanostructures such as nano-

tubes nanorods nanofibers nanoribbons and nanowires

are expected to play important roles in the fabrication

of functional nanodevices1 Recently special interest has

been focused on TiO2 nanostructures which have many

potential applications in gas sensors2 and biocompatible3

photovoltaic4 and photocatalytic56 materials to name a

few The ability to control the structure and properties of

the nanostructural TiO2 materials will be very useful for

these applications

Generally there are three strategies used in the fabri-

cation of TiO2 nanotubes template synthesis7 hydrother-

mal methods8 and electrochemical synthesis (anodization

lowastAuthor to whom correspondence should be addressed

of a Ti sheet) Typically the template-directed synthesis

method involves the fabrication of a nanoporous template

backfilling with the TiO2 precursors then removing the

template to yield the resulting nanostructures But these

processes are complicated The complete infiltration of the

precursors the uniform formation of the TiO2 nanotube

array and a good transfer of products are always hard

to obtain The hydrothermal method is a simple way to

prepare individual nanotubes but only randomly aligned

tubes can be obtained In addition this approach only pro-

duces protonated titanate nanotubes (H2mTiO2n+m rather

than TiO2 These disadvantages limit the further electrical

applications in nanodevices In 1999 it was reported that

porous TiO2 nanostructures could be fabricated by elec-

trochemically anodizing a Ti sheet in an acid electrolyte

containing a small amount of hydrofluoric acid (HF)9

Since then many research groups have paid considerable

attention to this field because anodization opens up ways

to easily produce closely packed tube arrays with a self-

organized vertical alignment

J Nanosci Nanotechnol 2010 Vol 10 No 7 1533-48802010104259007 doi101166jnn20102209 4259


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Fabrication of Free Standing Anodic Titanium Oxide Membranes with Clean Surface Using Recycling Process Meng et al

So far there have been three generations of anodic tita-

nium oxide (ATO) nanotubes In the first generation TiO2

nanotubes were fabricated in HF-based aqueous solutions

Some other inorganic acids and fluoride compounds such

as H3PO4NaF10 NH4F(NH42SO4

11 and Na2SO4NaF12

were used as a substitute for poisonous HF Due to the

rapid chemical dissolution rate the length of the obtained

nanotube was limited to 500 nm These low-aspect-ratio

tubes could not satisfy the requirements for applications

in dye sensitized solar cells (DSSCs) or filter membranes

Through adjusting the pH of the electrolyte the second

generation of ATO nanotubes was fabricated and tube

length was increased to a few micrometers13 In the third

generation by using an almost water-free polar solution

especially in viscous glycerol14 or ethylene glycol15 elec-

trolytes tens even hundreds of micron-length ATO nano-

tubes were easily prepared

However the above-mentioned TiO2 nanotubes were

attached to the Ti substrate which may limit their wider

application Recently many groups have attempted to

make self-organized free standing TiO2 nanotube arrays

Firstly Jan M Macak and co-workers directly fabricated

a flow-through TiO2 nanotubular membrane by selective

dissolution of Ti substrate and successfully used as a

photocatalytic microreactor16 This method was not only a

laborious process which took more than 10 hours but also

used a toxic bromine-containing methanol solution Then

Wang et al optimized the solution by using pure methanol

evaporation to delaminate the layer between the membrane

and the Ti foil17 Paulose et al described a process includ-

ing a critical point drying method by which nanotube array

films were able to be transformed into free-standing mem-

branes and applied it to control the diffusion of phenol

red18 More recently Park et al reported the preparation of

a membrane by immersing the Ti sheet with ATO in aque-

ous HCl solution for 1 h and made a glass-based DSSC19

However the above membrane surfaces were always cov-

ered by clumps of TiO2 nanotubes or nanowires To use the

free standing TiO2 nanotubes for a variety of applications

eg DSSCs this top layer should be removed to infiltrate

dye molecules and redox electrolytes into nanopores Post

treatments such as sonication or Al2O3 milling sometimes

needed several repetitions to ensure complete removal of

the top layer of nanowires These processes can cause

the membrane to crack So our aim is to end up with

as-received membranes with a clean surface at desired tube

lengths

Herein we report a simple and safe method to achieve

large scale self-organized freestanding and length con-

trollable ATO nanotube membranes by using the dimpled

substrate in the recycling process

2 EXPERIMENTAL DETAILS

Pure titanium foil (250 m in thickness and 997 purity)

was purchased from Sigma Aldrich and cut into the desired

size (40times50 cm) A direct current power supply (Agilent

E3612A) was used as the voltage source for the anodiza-

tion The anodization process was carried out in a two-

electrode configuration with titanium foil as the working

electrode and graphite (50times50 cm) as the counter elec-

trode under constant potential at 20 C The titanium sheets

were ultrasonicated in acetone isopropanol and methanol

each for 5 minutes followed by rinsing with de-ionized

(DI) water and drying in N2 gas The first electrochem-

ical treatment was carried out at 50 V in ethylene gly-

col with 03 wt NH4F and 2 v H2O for 24 hours

The as-prepared sample was rinsed immediately with DI

water for several minutes and dried with high pressure

N2 gas to remove the first ATO nanotube layer Using

the as-prepared patterned substrate without any treatment

the second anodic process was carried out at 50 V for

25 hours Then the sample was rinsed with DI water for

3 minutes and placed on a filter paper to evaporate the

water at room temperature The free standing ATO mem-

brane spontaneously separated from the substrate without

bending Using the same approach we anodized the sub-

strate obtained from the second anodization for 46 hours

in the third process

The morphology of the ATO was examined by JEOL

JSM-7000 field emission scanning electron microscopy

(FESEM) The cross-section photographs were obtained

by observing a mechanically fractured ATO layer trans-

ferred onto an adhesive carbon tape coated with 3 nm

Pt The specimen for transmission electron microscopy

(TEM JEOL-2100F) at 200 kV was prepared by soni-

cating a small part of the ATO membrane in ethanol for

30 minutes and observing on a carbon-coated copper grid

The dimple substrate after first anodization was charac-

terized by Atomic Force Microscopy (AFM) In order to

examine the phase transition the as-prepared sample was

annealed at 450 C in air for 3 hours at a heating rate

of 1 Cmin TEM images were also obtained using the

above-mentioned method X-ray diffraction (XRD) was

performed (Rigaku Rotafles) using CuK (015416 nm)

radiation

3 RESULTS AND DISCUSSION

After anodization for 24 hours the ATO layer with the

Ti substrate was washed with DI water for 3 min A sud-

den color change was observed which indicated that water

had completely penetrated into the pores and reached the

substrate When this happened the ATO layer was eas-

ily removed by subsequent blowing with high pressure N2

gas and broken into several pieces The easy detachment

of the ATO layer discovered here is a notable feature

particularly given that long-time immersion of the ATO

layer in methanol or HCl solution was not required The

ATO membrane and the Ti substrate were characterized as

follows

4260 J Nanosci Nanotechnol 10 4259ndash4265 2010


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Meng et al Fabrication of Free Standing Anodic Titanium Oxide Membranes with Clean Surface Using Recycling Process

(a)

(c) (d)

(b)

Fig 1 FESEM images of the as-prepared sample from (a) top view (b) bottom view (c) and (d) cross-sectional views In Figure 1(c) a TEM image

was inserted to show the tubular structure The sample was anodized for 24 h

Figure 1(a) shows the typical morphology of the top-

surface TiO2 membrane The image clearly reveals that the

entire surface of the ATO layer is covered with a layer

of nanowires which is attributed to the long time split of

the tube induced chemical etching in a ldquobamboo-splittingrdquo

mode2021 The nanowires were randomly arranged and

intersected As shown in Figure 1(b) the bottoms of the

TiO2 nanotubes were closed From the different magnified

cross-section views (Figs 1(c and d)) it can be seen that

the height of the first anodized ATO nanotubes membrane

with the nanowires is about 57 m and there is no tran-

sition area between the wire oxide layer and ordered bulk

ATO nanotubes The TEM image in Figure 1(c) shows the

tubular structure of the titanium oxide nanotubes fabricated

in first process

From the AFM image of the patterned substrate after

removing the first ATO layer in Figure 2 it is evident that

well-patterned dimples existed in the entire Ti sheet The

height of the dimples was approximately 30 nm and the

average inter-distance is approximately 155 nm The dim-

ple size is dependent on the applied potential with bigger

potentials resulting in larger dimples as shown in Figure 3

This corrugated substrate was used as a patterned template

in the second anodization process

After 25 hoursrsquo anodization in the same way as men-

tioned above the as-prepared sample after sufficient wash-

ing with DI water was put on the filter paper for drying at

room temperature without blowing with N2 gas Figure 4

shows a digital image of a brownish free standing TiO2

nanotube membrane obtained directly after self-peeling off

from the substrate Because a large graphite plate electrode

was used instead of the usual Pt wire electrode a more

0

59 nm

4425

295

1475

0191 382 573 764 955 nm

Fig 2 AFM image of the corrugated substrate produced after removing

the TiO2 nanotubes array

J Nanosci Nanotechnol 10 4259ndash4265 2010 4261


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(a) (b)

(d)(c)

Fig 3 FESEM images of the as-prepared sample at different voltages from a bottom view (a) 30 V (b) 40 V (c) 50 V and (d) 60 V The size of

dimple pits increased as the anodization voltage increasing

stable and larger equivalent electrical field was generated

and a large scale free standing sample was obtained The

evaporation of water caused the light brownish membrane

to gradually separate from the Ti substrate as a result of

surface-tension-driven delamination owing to the presence

of water and Fminus ions in the defect areas between the ATO

layer and Ti substrate Also slowly drying instead of fast

drying by heating or N2 gas blowing gave a high area

membrane without cracks

Fig 4 A photograph of a free standing TiO2 nanotube membrane

As shown in Figures 5(a and b) it can be seen that

although the anodizing time was almost the same as the

first step the surface of the second ATO was quite clean

and regular after having used the patterned substrate The

surface looks similar to the anodic aluminum oxide sur-

face in which the tubes are closely packed with each other

and ordered on a large scale instead of yielding indi-

vidual tubes In some places around the cracks of the

AAO-like surface buried TiO2 nanotubes were observed

The morphology of the patterned pits provided preferen-

tial dissolution sites for anodization which worked as pore

nucleation centers for growth of homogeneous pores This

effect can be understood when taking into account the

preexisting balance between the rates of oxide formation

and oxide dissolution As a result when the same voltage

was applied the growth of the nanotube was restricted to

the vertical direction against the substrate and formed an

AAO-like surface The patterned surface oxide layer that

was over the ATO layer protected the outside channel of

the nanotube from the etching fluoride electrolyte so the

tube did not split along the sidewall of the tube There

were no nanowires formed or thinned-out tube walls when

the anodization was carried out for an extended time After

25 hoursrsquo anodization the membrane thickness reached

44 m and there were no clumps of nanotubes from

the side view (Fig 5(c)) The morphology of these open

tube vertical arrays offers an excellent pathway for the



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(a)

(c)

(b)

(d)

Fig 5 FESEM and TEM images of the as-prepared sample from (a) (b) top views (c) cross-sectional view and (d) scale bar= 100 nm The sample

was anodized for 25 hours in the second step

(a)

(c) (d)

(b)

Fig 6 FESEM images of the as-prepared sample from (a) (b) top views and (c d) cross-sectional views The sample was anodized for 46 hours in

the third step



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(a) (b) (c)

Fig 7 Some SEM images of samples with different anodization times (a) 10 min (b) 1 hour and (c) 11 hours The chart shows the correlation

between the thickness of free standing ATO membrane and the anodization time

(a) (b)

(c)

Fig 8 TEM images and related SAED patterns shown in the inset of ATO nanotube membranes (a) before annealing treatment and (b) after annealing

treatment Scale bar is 10 nm (c) XRD patterns of the ATO nanotubes membranes Line ldquoardquo is before annealing treatment and line ldquobrdquo is after

annealing treatment (JCPDS 21-1272)



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percolating and transferring of both electrons and small

molecules (ie dye)

Figure 5(d) shows the transmission electron microscopy

image of nanotubes This TEM image confirms that after

30 minutes of sonication the nanotubes separated from

each other The walls of the nanotubes are very smooth and

straight over their entire length The thickness of the walls

is around 30 nm and the diameter of the walls is about

90 nm

In order to examine whether long durations of anodiza-

tion etched the patterned suface layer or not the third

anodization process was carried out for 46 hours The

results were also shown in Figure 6 The ATO with AAO-

like clean surface (as the same as ATO in the second

step) suggested that chemical dissolution did not etch

the surface regardless of anodized time It was found

that the inter-pore distance diameter and thickness is

154plusmn 2 nm (which agrees well with the AFM data (in

Fig 2)) 91plusmn2 nm and 70 m respectively (Figs 6(a c))

From both bottom and top views comparing to 25 hoursrsquo

sample more and better ordered hexagons were obtained

(Figs 6(b d))

The correlation between the thickness of the free stand-

ing ATO membrane and the anodization time is shown in

Figure 7 One could use this chart to choose the anodiza-

tion time according to the desired tube length which

would be very helpful for further applications

The as-prepared TiO2 nanotube membrane was amor-

phous as revealed by TEM imaging (Fig 8(a)) and the

XRD pattern (Fig 8(c) line a) in which broad spectra

ranging from 20 to 80 degree is clearly evident In order

to use the nanotubular structures of ATO membrane in

DSSCs the initially amorphous phase should be converted

into photoactive anatase or rutile phase Thus the as-

prepared sample was annealed at 450 C in air for 3 h

at a heating rate of 1 Cmin to induce crystallinity In

XRD pattern (Fig 8(c) line b) all the observed peaks

were indexed to anatase (JCPDS 21-1272) No other peaks

related to other phases or impurities were detected From

the TEM image and the SEAD pattern in Figure 8(b) evi-

dence of polycrystalline rings also showed that after the

annealing treatment the amorphous titanium oxide nano-

tubes converted into anatase phase

4 CONCLUSIONS

Several anodization processes were carried out in a

03 wt NH4F2 v H2O C2H6O2 solution at 50 V Large

scale membranes of ATO nanotubes were obtained using

a plate graphite electrode instead of a Pt wire electrode

under a constant voltage Using the 30 nm thickness dim-

ple layer as a patterned titanium substrate obtained after

removing the ATO layer gave the TiO2membranes a clean

surface In this simple recycling method utilizing the

patterned nano-scale pits as templates could get desired

length as a function of the anodization time of titanium

oxide nanotube membranes with clean surfaces

Acknowledgments Financial support from BK21

Project through the School of Advanced Materials Science

and Engineering is gratefully acknowledged

References and Notes

1 S Ju A Facchetti Y Xuan J Liu F Ishikawa P Ye

C Zhou T J Marks and D B Janes Nat Nanotechnol 2 378(2007)

2 S Yoriya H E Prakasam O K Varghese K Shankar M Paulose

G K Mor T A Latempa and C A Grimes Sensor Lett 4 334(2006)

3 J Park S Bauer K V D Mark and P Schmuki Nano Lett 71686 (2007)

4 G K Mor K Shankar M Paulose O K Varghese and C A

Grimes Nano Lett 6 215 (2006)5 G K Mor K Shankar M Paulose O K Varghese and C A

Grimes Nano Lett 5 191 (2005)6 E Balaur J M Macak H Tsuchiya and P Schmuki J Mater

Chem 15 4488 (2005)7 S Chu K Wada S Inoue and S Todoroki Chem Mater 14 266

(2002)8 D V Bavykin V N Parmon A A Lapkina and F C Walsh

J Mater Chem 14 3370 (2004)9 V Zwilling M Aucouturier and E Darque-Ceretti Electrochim

Acta 45 921 (1999)10 K S Raja M Misra and K Paramguru Electrochim Acta 51 154

(2005)11 L V Taveira J M Macak H Tsuchiya L F P Dick and

P Schmuki J Electrochem Soc 152 B405 (2005)12 J M Macak K Sirotna1 and P Schmuki Electrochim Acta 50

3679 (2005)13 J M Macak H Tsuchiya and P Schmuki Angew Chem Int Ed

44 2100 (2005)14 J M Macak H Tsuchiya L Taveira S Aldabergerova and

P Schmuki Angew Chem Int Ed 44 7463 (2005)15 H E Prakasam K Shankar M Paulose O K Varghese and C A

Grimes J Phys Chem C 111 7235 (2007)16 S P Albu A Ghicov J M Macak R Hahn and P Schmuki Nano

Lett 7 1286 (2007)17 J Wang and Z Lin Chem Mater 20 1257 (2008)18 M Paulose H E Prakasam O K Varghese L Peng K C Popat

G K Mor T A Desai and C A Grimes J Phys Chem C 111

14992 (2007)19 J H Park T W Lee and M G Kang Chem Commun 25 2867

(2008)20 J H Lim and J Choi Small 3 1504 (2007)21 A L Friedman E Panaitescu C Richter and L Menon J Nanosci

Nanotechnol 8 5864 (2008)

Received 15 June 2009 Accepted 23 July 2009



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So far there have been three generations of anodic tita-

nium oxide (ATO) nanotubes In the first generation TiO2

nanotubes were fabricated in HF-based aqueous solutions

Some other inorganic acids and fluoride compounds such

as H3PO4NaF10 NH4F(NH42SO4

11 and Na2SO4NaF12

were used as a substitute for poisonous HF Due to the

rapid chemical dissolution rate the length of the obtained

nanotube was limited to 500 nm These low-aspect-ratio

tubes could not satisfy the requirements for applications

in dye sensitized solar cells (DSSCs) or filter membranes

Through adjusting the pH of the electrolyte the second

generation of ATO nanotubes was fabricated and tube

length was increased to a few micrometers13 In the third

generation by using an almost water-free polar solution

especially in viscous glycerol14 or ethylene glycol15 elec-

trolytes tens even hundreds of micron-length ATO nano-

tubes were easily prepared

However the above-mentioned TiO2 nanotubes were

attached to the Ti substrate which may limit their wider

application Recently many groups have attempted to

make self-organized free standing TiO2 nanotube arrays

Firstly Jan M Macak and co-workers directly fabricated

a flow-through TiO2 nanotubular membrane by selective

dissolution of Ti substrate and successfully used as a

photocatalytic microreactor16 This method was not only a

laborious process which took more than 10 hours but also

used a toxic bromine-containing methanol solution Then

Wang et al optimized the solution by using pure methanol

evaporation to delaminate the layer between the membrane

and the Ti foil17 Paulose et al described a process includ-

ing a critical point drying method by which nanotube array

films were able to be transformed into free-standing mem-

branes and applied it to control the diffusion of phenol

red18 More recently Park et al reported the preparation of

a membrane by immersing the Ti sheet with ATO in aque-

ous HCl solution for 1 h and made a glass-based DSSC19

However the above membrane surfaces were always cov-

ered by clumps of TiO2 nanotubes or nanowires To use the

free standing TiO2 nanotubes for a variety of applications

eg DSSCs this top layer should be removed to infiltrate

dye molecules and redox electrolytes into nanopores Post

treatments such as sonication or Al2O3 milling sometimes

needed several repetitions to ensure complete removal of

the top layer of nanowires These processes can cause

the membrane to crack So our aim is to end up with

as-received membranes with a clean surface at desired tube

lengths

Herein we report a simple and safe method to achieve

large scale self-organized freestanding and length con-

trollable ATO nanotube membranes by using the dimpled

substrate in the recycling process

2 EXPERIMENTAL DETAILS

Pure titanium foil (250 m in thickness and 997 purity)

was purchased from Sigma Aldrich and cut into the desired

size (40times50 cm) A direct current power supply (Agilent

E3612A) was used as the voltage source for the anodiza-

tion The anodization process was carried out in a two-

electrode configuration with titanium foil as the working

electrode and graphite (50times50 cm) as the counter elec-

trode under constant potential at 20 C The titanium sheets

were ultrasonicated in acetone isopropanol and methanol

each for 5 minutes followed by rinsing with de-ionized

(DI) water and drying in N2 gas The first electrochem-

ical treatment was carried out at 50 V in ethylene gly-

col with 03 wt NH4F and 2 v H2O for 24 hours

The as-prepared sample was rinsed immediately with DI

water for several minutes and dried with high pressure

N2 gas to remove the first ATO nanotube layer Using

the as-prepared patterned substrate without any treatment

the second anodic process was carried out at 50 V for

25 hours Then the sample was rinsed with DI water for

3 minutes and placed on a filter paper to evaporate the

water at room temperature The free standing ATO mem-

brane spontaneously separated from the substrate without

bending Using the same approach we anodized the sub-

strate obtained from the second anodization for 46 hours

in the third process

The morphology of the ATO was examined by JEOL

JSM-7000 field emission scanning electron microscopy

(FESEM) The cross-section photographs were obtained

by observing a mechanically fractured ATO layer trans-

ferred onto an adhesive carbon tape coated with 3 nm

Pt The specimen for transmission electron microscopy

(TEM JEOL-2100F) at 200 kV was prepared by soni-

cating a small part of the ATO membrane in ethanol for

30 minutes and observing on a carbon-coated copper grid

The dimple substrate after first anodization was charac-

terized by Atomic Force Microscopy (AFM) In order to

examine the phase transition the as-prepared sample was

annealed at 450 C in air for 3 hours at a heating rate

of 1 Cmin TEM images were also obtained using the

above-mentioned method X-ray diffraction (XRD) was

performed (Rigaku Rotafles) using CuK (015416 nm)

radiation

3 RESULTS AND DISCUSSION

After anodization for 24 hours the ATO layer with the

Ti substrate was washed with DI water for 3 min A sud-

den color change was observed which indicated that water

had completely penetrated into the pores and reached the

substrate When this happened the ATO layer was eas-

ily removed by subsequent blowing with high pressure N2

gas and broken into several pieces The easy detachment

of the ATO layer discovered here is a notable feature

particularly given that long-time immersion of the ATO

layer in methanol or HCl solution was not required The

ATO membrane and the Ti substrate were characterized as

follows



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(a)

(c) (d)

(b)

















in first process


















0

59 nm

4425

295

1475

0191 382 573 764 955 nm





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(a) (b)

(d)(c)










































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(a)

(c)

(b)

(d)



(a)

(c) (d)

(b)


the third step



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(a) (b) (c)



(a) (b)

(c)






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molecules (ie dye)







90 nm













(Figs 6(b d))






















4 CONCLUSIONS










































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(a)

(c) (d)

(b)

















in first process


















0

59 nm

4425

295

1475

0191 382 573 764 955 nm





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(a) (b)

(d)(c)










































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(a)

(c)

(b)

(d)



(a)

(c) (d)

(b)


the third step



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(a) (b) (c)



(a) (b)

(c)






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molecules (ie dye)







90 nm













(Figs 6(b d))






















4 CONCLUSIONS










































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(a) (b)

(d)(c)










































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(a)

(c)

(b)

(d)



(a)

(c) (d)

(b)


the third step



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(a) (b) (c)



(a) (b)

(c)






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molecules (ie dye)







90 nm













(Figs 6(b d))






















4 CONCLUSIONS










































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(a)

(c)

(b)

(d)



(a)

(c) (d)

(b)


the third step



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(a) (b) (c)



(a) (b)

(c)






IP 115145200148Thu 06 May 2010 120247

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molecules (ie dye)







90 nm













(Figs 6(b d))






















4 CONCLUSIONS










































IP 115145200148Thu 06 May 2010 120247

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(a) (b) (c)



(a) (b)

(c)






IP 115145200148Thu 06 May 2010 120247

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molecules (ie dye)







90 nm













(Figs 6(b d))






















4 CONCLUSIONS










































IP 115145200148Thu 06 May 2010 120247

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molecules (ie dye)







90 nm













(Figs 6(b d))






















4 CONCLUSIONS









































fabrication of free standing anodic titanium oxide...

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