Electrodeposition from Ionic Liquid of 2D Ordered Ta[sub 2]O[sub 5] on Titanium Substrate Through a Polystyrene Template

Journal of The Electrochemical Society, 156 �11� K186-K190 �2009�K186

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Electrodeposition from Ionic Liquid of 2D Ordered Ta2O5on Titanium Substrate Through a Polystyrene TemplateChristelle Arnould,* Joseph Delhalle, and Zineb Mekhalifz

Laboratory of Chemistry and Electrochemistry of Surfaces, University of Namur, Facultés UniversitairesNotre Dame de la Paix, Namur B-5000, Belgium

Microstructuration of a protective tantalum oxide layer was investigated by the combination of substrate surface patterning withcolloidal particles and electroreduction of TaF5 in ionic liquid. The formation of a two-dimensionally �2D� ordered monolayer ofpolystyrene particles was achieved on a square centimeter area using a facile method, which does not require additives or specificapparatus. Parameters of a previously reported protocol for tantalum electrodeposition on bare titanium were optimized to retainthe integrity of the 2D ordered monolayer of polystyrene particles, and also to lead to the formation of a dense, homogeneous,adherent, and passivating structured layer of Ta2O5.© 2009 The Electrochemical Society. �DOI: 10.1149/1.3206593� All rights reserved.

Manuscript submitted May 26, 2009; revised manuscript received July 22, 2009. Published September 3, 2009. This was Paper 74presented at the San Francisco, California, Meeting of the Society, May 24–29, 2009.

0013-4651/2009/156�11�/K186/5/$25.00 © The Electrochemical Society

The control of surface morphology is important to impart noveland interesting surface properties to materials in basic and appliedsciences. The specific chemical and physical phenomena occurringinside spatially confined micrometer and submicrometer volumesare of particular interest.1,2 For instance, changing the structure froman amorphous to a well-organized state can lead to spectacularmodifications in optical properties. Gemstone opals,1 which arecomposed of spherical particles of amorphous silica, uniform, andpacked regularly in a crystal form, are a well-known natural ex-ample. Usually silica is transparent to visible light, but in this case,it exhibits intense colors due to the change of refractive index at thenumerous interfaces. The critical dependence of the adhesion,spreading, growth, and differentiation of mesenchymal cells on thediameter of vertically aligned anodized TiO2 nanotubes is anotherexample of interest in structured surfaces in the biological field.3

More generally, materials with ordered surface morphology havepotential applications in fields as diverse as catalysis, sensors, pho-tonics, and bioscience.

Structurally organized layers can be obtained in many ways�ablation,4 etching,5 lithography,6 dealloying,7 etc.�, which are usu-ally grouped into two types of approaches: top-down and bottom-up.Electrochemistry plays a significant role in this twofold context. Oneimportant top-down method resorting to electrochemistry consists ofthe anodization of a metallic substrate under specific conditions anda resulting structured material, ranging from porous morphology8 toself-organized and highly ordered nanostructures.9-11 Highly orderednanoporous Ta2O5 layers produced by anodization have been re-ported recently.12 Another direction is to use the template-assistedformation of the inverse porous structure of solid materials.

Tantalum is a metal with attractive chemical and physical prop-erties, high dielectric constant,13,14 biocompatibility,15 radiopacity,16

and high corrosion resistance.17 Due to its cost and density, a greatdeal of attention is focused on the formation of thin layers. Fabrica-tion by electrodeposition of two-dimensionally �2D� and three-dimensionally �3D� ordered ZnO or copper films using polystyrene�PS� templates have been reported from common solvents and fromionic liquid for germanium,18-20 but nothing has been published onthe electrodeposition of Ta through such templates. Among the pos-sible metal deposition techniques,14,21-24 we have chosen elec-trodeposition because of its high level of control. The process ofelectrodeposition of tantalum is usually reported in molten salts,17

which require high temperatures.25 In the present context, room-temperature ionic liquids,26 with their good electrical conductivity,

* Electrochemical Society Student Member.z E-mail: [email protected]

address. Redistribution subject to ECS term128.248.155.225ded on 2014-11-23 to IP

good thermal stability, low vapor pressure, and above all a remark-ably large electrochemical window, are ideal solvents to electroplatemetals such as tantalum.27-29

In this paper, we focused on the study of titanium plate modifi-cations for their use in biomaterials. Titanium and its alloys arewidely used in the orthopedic domain but needs some improvement.The deposition of a thin tantalum oxide layer can bring radiopacity,bioactivity, and increasing corrosion resistance to body fluids. Thecontrol of the surface morphology has been shown to influence thebacterial adherence30 on the implant. We report on the electrochemi-cal deposition of 2D ordered tantalum films through PS templatesformed on a titanium substrate. This layer, upon contact with air,instantaneously forms an oxide layer and leads after post-treatmentto a Ta2O5 composition. The electrodeposition of the tantalum layeron this assembly was performed in an ionic liquid electrolyte in aglove box. The different stages of the sample preparation were in-vestigated by scanning electron microscopy �SEM� and compared toX-ray photoelectron spectroscopy �XPS� data and electrochemicalcharacterizations. The steps of the work are schematically depictedin Fig. 1.

Experimental

Bare titanium pretreatment.— Titanium plates �10 � 15� 1 mm� used as substrates were obtained from Advent �99.98%�.The metal coupons were first mechanically polished by a BuehlerPhoenix 4000 instrument down to 1 �m using silicon carbide gritpapers and diamond pastes. Thereafter, they were rinsed with ultra-pure water and ultrasonically cleaned in ethanol for 15 min. Thecleaning treatment ended with an exposure to UV ozone for 30 min�Jelight 42-220� to remove the physisorbed contaminations beforemodification.

Figure 1. Scheme of the methodology used in this paper.

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K187Journal of The Electrochemical Society, 156 �11� K186-K190 �2009� K187

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PS particles monolayer deposition.— The solution used wascomposed of 10% �w/w� PS particles ��: 1 �m� �Aldrich, 89904�in water.

The optimal deposition was selected out of a series of attemptscarried out with a 0.1% �w/w� PS aqueous solution �Fig. 2�: �a�dip-coating, �b� vertical deposition and evaporation at 60°C, �c�evaporation from a substrate tilted at an angle of 15° �tilted configu-ration�, and �d� evaporation from a substrate lying horizontally�horizontal configuration�.

The effect of the concentration of the PS solution on the templatequality was studied between 0.1 and 5% PS solution by the horizon-tal evaporation method with a 0.1 mL/cm2 of substrate and a0.5 mL/cm2 drop �0.1 mL/cm2 means 0.1 mL per cm2 of the sub-strate�.

Tantalum electrodeposition.— The tantalum electrodeposition ontitanium was performed in an argon-filled glove box �residualamounts of water and oxygen below 30 ppm� usinga Versa-Stat II potentiostat/galvanostat �Princeton AppliedResearch� monitored by a computer and PAR electrochemistrysoftware model 270. The electrolytic solution27,29 containedLiF 0.25 mol L−1, TaF5 0.10 mol. L−1 in the ionic liquid1-butyl-1-methyl bis�trifluoromethylsulfonyl�imide ��BMP�Tf2N��IoLiTec, IL-0035-HP� at room temperature. The salts used were allfrom Aldrich and of purified agent purity. A platinum foil was usedas the reference electrode and a tantalum foil �99.99% purity, Ad-vent� was used as the counter electrode.

After electrodeposition, the samples without PS were immersedin boiling water for 15 min, cleaned ultrasonically in ethanol for 15min, and exposed to UV ozone for 30 min. These three last stepsaimed at removing all electrolytic solution residues and at the rein-forcement of the tantalum oxide layer on the surface.

Film characterization.— XPS was used to assess, qualitativelyand quantitatively, the composition of the bare substrate and thedifferent coatings. The spectra were recorded at a 35° take-off angle�relative to the surface normal� with an SSX-100 spectrometer usingmonochromatized Al K� radiation �1486.6 eV�. The analyzed core-level lines �Ti 2p, C 1s, O 1s, and Ta 4f� were referenced withrespect to the component C 1s of the binding energy set at 285.0 eV,an energy characteristic of alkyl moieties. The signals were analyzedusing mixed Gaussian–Lorentzian curves with a fixed Gaussiancharacter of 80%.

Polarization curves were measured on bare and modified sub-strates in an outgassed �15 min� solution of sodium chloride �0.9%�to assess the corrosion potential, the corrosion current, and the pit-ting potential. The free potential was measured for 30 min. The

1.Dip

2.Withdraw

Evaporating∆ = 60°C



a b c d

Figure 2. Methods for PS deposition: �a� dip-coating, �b� vertical depositionand evaporation at 60°C, �c� evaporation in tilted configuration, and �d�evaporation in horizontal configuration.


working electrode potential was scanned from �1.0 to +1.0V/saturated calomel electrode �SCE� at 1 mV s−1 scan rate. Mea-surements were carried out on an EG&G PAR potentiostat model263A monitored by a computer and a PAR electrochemistry soft-ware model 270. Electrochemical measurements were carried out inan electrolytic spot cell �spot �: 5.2 mm� with an SCE �0.246V/standard hydrogen electrode� as the reference electrode and aplatinum foil as the counter electrode, the substrate playing the roleof the working electrode.

A SEM study was performed using a Philips XL20 and JEOL.

Results and Discussion

The assembly achieved in this paper comprises three steps �Fig.1�. The first step is the formation and optimization of the organizedPS monolayer. The electrodeposition of a tantalum oxide thin layerwas performed on a titanium substrate and characterized with SEM,XPS, and polarization curves. Then, these two steps are combined toform the structured electroplating of tantalum on bare titanium.

Formation of a PS monolayer.— Substrate pretreatment.— Fourmethods were considered to achieve a well-organized monolayer ofPS particles �Fig. 2�. UV ozone pretreatment of the titanium beforedipping was important to create titanium hydroxide on the surfaceand improve good wetting with the aqueous PS solution. Withoutthis step each of the four methods leads to very poor results, i.e.,dispersed particles in dip-coating �Fig. 3� and vertical immersionbecause the solution does not wet the surface properly. Evaporationin tilted and horizontal configurations led to nonhomogeneous PSdeposition, with some uncovered areas and some multilayered parts.Preparation of the PS films.— Figure 4 displays the SEM picturesobtained for each method of deposition on UV ozone treated tita-nium with a concentration of 0.1% �w/w� PS aqueous solution. Thedip-coating is not suitable; the resulting layer is nonhomogeneousand not fully covering. The vertical deposition leaves a visible thickwhite powder covering the sample surface. The SEM pictures revealthe presence of multilayers. This deposition also leads to an insulat-ing substrate, which is detrimental for electrodeposition. The layer

20 µm

Figure 3. SEM picture of PS spheres deposited by dip-coating on nontreatedtitanium.

10 µm10 µm10 µm10 µm

a b c d

Figure 4. SEM pictures of PS particles deposition by �a� dip-coating, �b�vertical deposition, �c� evaporation in tilted configuration, and �d� evapora-tion in horizontal configuration.



K188 Journal of The Electrochemical Society, 156 �11� K186-K190 �2009�K188

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obtained by tilted deposition is also characterized by a wavelikestructure, but multilayers are not observed. The surface is formed ofstrips containing PS particles alternating with empty zones. Thistype of deposition was also observed by Micheletto et al.31 The mosteffective method consists of evaporating the solution on the sub-strate lying in horizontal configuration. A large part of the sample iscovered by an organized monolayer of PS particles. Some holes anddispersed area are still observed for the concentration used, but thissituation can be improved by varying the concentration of the PSsolution.

Concentration effect.— One observation is that 0.5 mL/cm2 is notappropriate; for lower concentrations we have a mix of dispersedand multilayer areas �Fig. 5�. This is because 0.1 mL/cm2 seemedto be just the minimum needed to cover the entire sample with thePS solution. So, 0.5 mL/cm2 led to a multilayering by the thicknessof the drop. For 0.1 mL/cm2, the 0.1 and 0.5% concentrations arenot enough to have a saturated organized monolayer; we still ob-served large dispersed areas on the sample. A concentration of 5%shows an organized and homogeneous deposition, but the major partof the surface is composed of multilayers. The best results are ob-tained by the evaporation of 0.1 mL/cm2 of a 1% PS solution. Theedges pose a problem because multilayers are observed just on the

00

a-1

a-2

b-1

b-2

c-1

c-2

d-1

d-210 µm 10 µm 5 µm 5 µm

10 µm 10 µm 10 µm 5 µm

Figure 5. PS deposition using 0.1 mL in �1� and 0.5 mL in �2�. The concen-trations are �a� 0.1, �b� 0.5, �c� 1.0, and �d� 5.0% w/w PS aqueous solution.

1000 800

35 30 25 20 15

binding energy (eV)

O auger

Bi

10 µm

-1000 -51E-12

1E-11

1E-10

1E-9

1E-8

1E-7

1E-6

1E-5

1E-4

b)

Currentdensity(A/cm2 )

0 200 400 600 800 1000 1200 1400 1600 18000102030405060708090100110120130140150160170180 a)

Bare TiTa/Ti 200°CTa/Ti 25°C

freepotential(mV/SCE)

time (sec)


edges of the substrate. Except for the edges, the monolayer is wellorganized with very few defaults and holes; no multilayers are ob-served on the entire sample surface.

Tantalum electrodeposition.— Optimization on bare titanium.—In a previous work, we optimized the tantalum electrodeposition inthe TaF5 0.25 mol L−1, LiF 0.25 mol L−1 in �BMP�Tf2N at200°C.29 However, aging of the electrolyte was observed with timeand temperature. As the ionic liquid and the lithium fluorine arestable at this temperature and do not degrade easily, it is probablydue to the slow degradation of the tantalum fluoride. A second rea-son for operating at lower temperatures is to avoid destruction of thePS template during the tantalum electrodeposition step.

The best conditions for electrodeposition at room temperature are1 h electrodeposition with a cathodic current of −100 �A/cm2. Fig-ure 6 shows a SEM picture of the resulting tantalum oxide that isvery homogeneous. The XPS spectra reveal tantalum �Ta2O5�, tita-nium, oxygen, and a few carbon contaminations, but no fluorine andelectrolyte residues, thereby validating the cleaning procedure.

The electrochemical characterization of the protection impartedby the tantalum oxide layer is reported in Fig. 7. In both considereddepositions �25 and 200°C�, the free potential observed is higherthan in that of bare titanium due to the very passive properties of thetantalum oxide layer. That observation matches with the polarizationcurves showing a large protection against corrosion. The anodic pro-tection increases with the decrease of the temperature of the electro-plating bath. Two effects may contribute to this result. The first oneis that the titanium substrate is under detrimental conditions duringthe electrodeposition of tantalum in a solution containing fluorideions at 200°C; high temperatures could increase the corrosion rateof the substrate. The second one is the kinetics of the electrodepo-sition. We showed previously that increasing the growth rate of thetantalum layer led to a poorer deposition, crackling, andadherence.29 As temperature decreases the kinetics of electrodeposi-tion slows down. It is thus likely that smaller nucleation �Fig. 8�,compact covering, and better corrosion resistance are achieved at alower temperature �room temperature in our case�.

400 200 0

O1s

Ti2p+Ta4p1/2

Ta4p3/2

C1sTa4d

Ta4f

nergy (eV)

Figure 6. SEM picture and XPS spectraof a tantalum oxide layer on bare titaniumobtained by electrodeposition at roomtemperature, 1 h at −100 �A/cm2.

0 500 1000

Bare TiTa/Ti 200°CTa/Ti 25°C

tial (mV/SCE)

Figure 7. �a� Free potential and �b� polar-ization curves of bare titanium and tanta-lum oxide layers electrodeposited at 25and 200°C.

600

nding e

00

Poten



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Electrodeposition of tantalum on PS template.— Electrodepositionof tantalum at room temperature through the PS template assembledon titanium �100 �A/cm2 for 1 h at 25°C� was carried out. Theremaining difficulty was the cleaning procedure to remove the PSparticles. Figure 9 shows the SEM picture and XPS spectra obtainedafter three different cleaning procedures. The choice of procedure isbased on a combination of the efficient cleaning of the tantalumlayer and the methods reported to remove the PS spheres. The firstmethod �Fig. 9a�, using temperature for the PS calcination,32 leadsto a poor cleaning; the fluorine ratio of 27% and carbon ratio of 42%reveal that the electrolyte solution is entrapped in the assembly,showing that the layer is not completely freed from PS. The SEMpicture shows another disadvantage of this type of cleaning. Tanta-lum seems to have reorganized, and the holes have shrunk. The useof toluene18 to dissolve PS was attempted under abundant rinsingconditions �Fig. 9b�. The XPS ratios of carbon and fluorine, 48 and

5 µm 5 µµm

Figure 8. SEM pictures of tantalum layers electrodeposited at �a� 200 and b�25°C.

1100 1000 900 800 700 600 500 400 300 200 100 0

Ta

C - 48 %O - 25 %F - 15 %S - 3 %Ti - 1 %Ta - 8 %

Ta

FTi

C

Ta

O

F

STi

Intensity(Arb.units)

Binding energy (eV)1100 1000 900 800 700 600 500 400 300 200 100 0

Intensity(Arb.Units)

F

O

C

STa TaTa

C - 42 %O - 18 %F - 27 %S - 9 %Ti - 3 %Ta - 1 %

Binding energy (eV)1100 10

Intensity(Arb.units)

680

a) b) c)

10 μm 10 μm

470 468 466 464 462 460 458 456 454 452 450

Ti2pTa 4p

1/2


binding energy (eV)470 465 460 455 450

Ti 2pTa 4p1/2


binding energy (eV)


a) b)

10 µm 10 µm


15%, respectively, are again not satisfactory. The last method com-bines the use of toluene with an ultrasonic bath.33 The results arenow satisfactory: no fluorine is detected and the level of carbon iscomparable to that resulting from atmospheric contamination.

Using the above optimized conditions, the effect of electrodepo-sition time on the tantalum oxide layer quality was studied by XPSand SEM �Fig. 10�. For 2 and 4 h of tantalum electrodeposition, theSEM pictures show that no tantalum grew at the contact pointsbetween the sphere and the titanium substrate. The XPS results con-firm this observation. As the electrodeposition time increases, theTa/Ti ratio increases: from 1.3 to 3.0 after 2 and 4 h, respectively. Itrequires 6 h of tantalum electrodeposition before the Ti signal is notdetected by XPS, which corresponds to a full coverage by Ta. Weassume that the growth of the tantalum layer pushes up the PSspheres.

Conclusion

In this paper, the formation of a 2D ordered layer of PS wasoptimized and achieved on titanium over square centimeter areas.Surface pretreatment of Ti was important to achieve good quality PStemplates. The method reported here was very simple and requiredno use of additives, surfactants, PS pretreatments, or specific equip-ments like surface pressure control.

We also showed that it was possible to achieve the electrodepo-sition of a thin tantalum layer on titanium at room temperature inionic liquid. The oxide layer was passivating and its protection wasfound to be better than that of the tantalum layers obtained at highertemperatures �200°C�.

00 700 600 500 400 300 200 100

695 700

)

Ti

TaC

TiTa

F

C - 24 %O - 50 %F - 0 %S-- 0 %Ti - 24 %Ta - 2%

O

Binding energy (eV)

10 μm

Figure 9. SEM pictures and XPS surveyspectra of the microstructured tantalumwith cleaning treatment: �a� 15 min boil-ing water, 3 h at 500°C in oven, and 15min UV ozone; �b� 15 min boiling water,rinsing with toluene, and 15 min UVozone; and �c� 15 min boiling water, 2� 15 min ultrasonic bath in toluene, and15 min UV ozone.

465 460 455 450

binding energy (eV)

0 µm Figure 10. SEM pictures and Ti 2p XPSspectra of structured tantalum oxide layerafter electroplating times of �a� 2, �b� 4,and �c� 6 h.

00 900 8

685 690

Binding energy (eV

F1s

470

c)

1



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The combination of these two steps and the search for an effi-cient cleaning procedure led to a covering tantalum oxide layer pat-terned with sub-micrometric cavities. A complete covering of thetitanium with tantalum oxide was obtained after 6 h of electrodepo-sition.

References1. J. V. Sanders, Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystal-

logr., 24, 427 �1968�.2. P. H. Mayrhofer, C. Mitterer, L. Hultman, and H. Clemens, Prog. Mater. Sci., 51,

1032 �2006�.3. J. Park, S. Bauer, K. Von Mark, and P. Schmuki, Nano Lett., 7, 1686 �2007�.4. L. De Stefano, I. Rea, M. A. Nigro, F. G. Della Corte, and I. Rendina, J. Phys.:

Condens. Matter, 20, 265009 �2008�.5. M. Gowtham, L. Eude, C. S. Cojocaru, B. Marquardt, H. J. Jeong, P. Legagneux,

K. K. Song, and D. Pribat, Nanotechnology, 19, 035303 �2008�.6. Y. Masuda, S. Wakamatsu, and K. Koumoto, J. Eur. Ceram. Soc., 24, 301 �2004�.7. J. Zhu, E. Seker, H. Bart-Smith, M. R. Begley, R. G. Kelly, G. Zangari, W.-K. Lye,

and M. L. Reed, Appl. Phys. Lett., 89, 133104 �2006�.8. N. K. Kuromoto, R. A. Simao, and G. A. Soares, Mater. Charact., 58, 114 �2007�.9. D. Kim, J. M. Macak, F. Schimidt-Stein, and P. Schmuki, Nanotechnology, 19,

305710 �2008�.10. J. M. Macak, H. Hildebrand, U. Marten-Jahns, and P. Schmuki, J. Electroanal.

Chem., 621, 254 �2008�.11. A. Mozalev, G. Gorokh, M. Sakairi, and H. Takahashi, J. Mater. Sci., 40, 6399

�2005�.12. W. Wei, J. M. Macak, N. K. Shrestha, and P. Schmuki, J. Electrochem. Soc., 156,

K104 �2009�.13. A. Cappellani, J. L. Keddie, N. P. Barradas, and S. M. Jackson, Solid-State Elec-

tron., 43, 1095 �1999�.


14. S. Yildirim, K. Ulutas, D. Deger, E. O. Zayim, and I. Turhan, Vacuum, 77, 329�2005�.

15. T. Miyazaki, H.-M. Kim, T. Kokubo, C. Ohtsuki, H. Kato, and T. Nakamura,Biomaterials, 23, 827 �2002�.

16. M. Li, G. Xiong, Z. Wang, S. Fan, Q. Zhao, and K. Lin, Sci. China, Ser. A: Math.,Phys., Astron., 42, 865 �1999�.

17. P. Chamelot, P. Palau, L. Massot, A. Savall, and P. Taxil, Electrochim. Acta, 47,3423 �2002�.

18. Q. Zhou, J. Zhao, W. Xu, H. Zhao, Y. Wu, and J. Zheng, J. Phys. Chem. C, 112,2378 �2008�.

19. D. Lan, Y. Wang, W. Ma, H. Cao, T. Xie, and C. Yao, Appl. Surf. Sci., 254, 6775�2008�.

20. X. Meng, R. Al-Salman, J. Zhao, N. Borissenko, Y. Li, and F. Endres, Angew.Chem., Int. Ed., 48, 2703 �2009�.

21. F. Z. Tepehan, F. E. Ghodsi, N. Ozer, and G. G. Tepehan, Sol. Energy Mater. Sol.Cells, 59, 265 �1999�.

22. N. Ozer and C. M. Lampert, J. Sol-Gel Sci. Technol., 8, 703 �1997�.23. C. Corbella, M. Vives, A. Pinyol, I. Porqueras, C. Person, and E. Bertran, Solid

State Ionics, 165, 15 �2003�.24. Y.-C. Nah, K.-S. Ahn, and Y.-E. Sung, Solid State Ionics, 165, 229 �2003�.25. G. M. Haarberg and J. Thonstad, J. Appl. Electrochem., 19, 789 �1989�.26. S. Pandey, Anal. Chim. Acta, 556, 38 �2006�.27. S. Zein El Abedin, H. K. Farag, E. M. Moustafa, U. Welz-Biermann, and F. Endres,

Phys. Chem. Chem. Phys., 7, 2333 �2005�.28. S. Zein El Abedin, U. Welz-Biermann, and F. Endres, Electrochem. Commun., 7,

941 �2005�.29. C. Arnould, J. Delhalle, and Z. Mekhalif, Electrochim. Acta, 53, 5632 �2008�.30. A. Schildhauer Thomas, B. Robie, G. Muhr, and M. Koller, J. Orthop. Trauma, 20,

476 �2006�.31. R. Micheletto, H. Fukuda, and M. Ohtsu, Langmuir, 11, 3333 �1995�.32. J. P. Zhao, Y. Li, W. H. Xin, and X. Li, J. Solid State Chem., 181, 239 �2008�.33. Y. Yasukawa, H. Asoh, and S. Ono, Electrochem. Commun., 10, 757 �2008�.



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Electrodeposition from Ionic Liquid of 2D Ordered Ta[sub 2]O[sub 5] on Titanium Substrate Through a Polystyrene Template