ezAFM2

Please citsubstrates

ARTICLE IN PRESSG ModelAPSUSC-28056; No. of Pages 7Applied Surface Science xxx (2014) xxxxxx

Contents lists available at ScienceDirect

Applied Surface Science

jou rn al h om ep age: www.elsev ier .com/ locate /apsusc

Fabrica anoxide s

Sevde Ala Micro and Na ra 065b Department o 0, Turk

a r t i c l

Article history:Received 31 OReceived in reAccepted 3 JunAvailable onlin

Keywords:BiomaterialsNeural tissue engineeringCuesAnodized aluminum oxideConductive surfacePVD

ion oral reluminal cu

regeneration is still very limited. Herein, we report the fabrication and characterization of conductiveAAO (CAAO) surfaces for the ultimate goal of integrating electrical cues for improved nerve tissue behav-ior on the nanoporous substrate material. Paralm was used as a protecting polymer lm, for the rsttime, in order to obtain large area (50 cm2) free-standing AAO membranes. Carbon (C) was then depositedon the AAO surface via sputtering. Morphological characterization of the CAAO surfaces revealed that thepores remain open after the deposition process. The presence of C on the material surface and insidethe nanopores was conrmed by XPS and EDX studies. Furthermore, IV curves of the surface were usedto extract surface resistance values and conductive AFM demonstrated that current signals can only beachieved where conductive C layer is present. Finally, novel nanoporous C lms with controllable pore

1. Introdu

Developneering reqelectrical cuSignicant combinatiofor increaseas enhanceals with nastructure oadsorption/faces with twhich havesuccessful n

CorresponE-mail add

http://dx.doi.o0169-4332/ e this article in press as: S. Altuntas, F. Buyukserin, Fabrication and characterization of conductive anodic aluminum oxide, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.06.007

diameters and one dimensional (1-D) C nanostructures were obtained by the dissolution of the templateAAO substrate.

2014 Elsevier B.V. All rights reserved.

ction

ment of effective biomaterials for neural tissue engi-uires the optimization of topographic, chemical andes that inuence the cellmaterial interactions [14].amount of research has been conducted to utilizens of these cues on a rainbow of different substratesd cell adhesion, proliferation and alignment as welld neurite outgrowth. For instance, using biomateri-noscale topography that resembles the hierarchicalf the extracellular matrix promotes select proteinbioactivity and cell interaction [36]. Patterned sur-hese features create opportunities to align the neurons

potential to be used as neuron guidance conduits foreuroregeneration. Regarding chemical cues, a variety of

ding author. Tel.: +90 3122924513.ress: [email protected] (F. Buyukserin).

different strategies were employed for promoting nerve regenera-tion. These involve the modication of substrate surface with ECMproteins or neuroactive peptides as well as doping the substratewith biochemicals such as drugs and growth factors [6,7]. Finally,studies over the past few decays have demonstrated that electricalstimulation can accelerate neural tissue regeneration. Here, bulk ornanober-based conducting polymeric scaffolds [5,7,8] and carbonnanotubes [9,10] are emerging as novel conductive platforms thatcan improve the modulation of neuronal responses.

Nanoporous anodic aluminum oxide (AAO) membranes are aunique class of biomaterials that can be synthesized by anodiza-tion of high purity aluminum [11,12]. Their intrinsic propertiesallow one to tune several parameters for obtaining improved tissueregeneration, and hence these biomaterials are widely used espe-cially for bone tissue engineering applications [13,14]. For instance,the native porous structure provides a nanoscale topography uponwhich improved osteoblast adhesion and matrix formation wasattained when compared with non-porous counterpart that doesnot promote osseointegration [15]. Furthermore, the pores of this

rg/10.1016/j.apsusc.2014.06.0072014 Elsevier B.V. All rights reserved.tion and characterization of conductiveubstrates

tuntasa, Fatih Buyukserinb,

notechnology Graduate Program, TOBB University of Economics and Technology, Ankaf Biomedical Engineering, TOBB University of Economics and Technology, Ankara 0656

e i n f o

ctober 2013vised form 2 June 2014e 2014e xxx

a b s t r a c t

Biomaterials that allow the utilizatneuronmaterial interaction and neuapplications. The nature of anodic acontrol over topographic and chemicodic aluminum

60, Turkeyey

f electrical, chemical and topographic cues for improvedgeneration hold great promise for nerve tissue engineeringum oxide (AAO) membranes intrinsically provides delicatees for enhanced cell interaction; however their use in nerve

Please cit d characterization of conductive anodic aluminum oxidesubstrate .007

ARTICLE IN PRESSG ModelAPSUSC-28056; No. of Pages 72 S. Altuntas, F. Buyukserin / Applied Surface Science xxx (2014) xxxxxx

biocompatible material can be lled with chemicals or bioactivematerials to promote osseointegration [11,15]. Despite the abilityto manipulate such topographic and chemical cues, the research forutilizing AAO membranes for neural tissue engineering is still verylimited andraphy in cefull potentition by utiligreat potenit currently

In this stconductive sue behavioapproach foby the use oCAAO surfasputtering tterization onanoporousafter the re

2. Experim

2.1. Prepara

High puAesar) werewater (18 Ming to roomwas appliedelectropolis5 wt% H2SOsubjected ton the desireter were oanodizationelectrolyte were then temperatur

In orderdiameter, twas follow50 V in a 5at 5 C. A thboth sides composed oond anodizthe rst one5 vol% H3POwith 100 nmthrough thibound to thated.

AAO lmfree-standinthat is sandachieved bof one of tfoil were thAAO membwas dissolv(Bemis) waunprotectedto expose tCuCl22H2O

chematic representation of free-standing AAO membrane production viaication of protecting polymer layer.

ranes were obtained by dissolving the paralm in n-hexaneAldrich). Nail polish (Plomar), Poly (methyl methacry-PMMA, Aldrich, 350,000 MW) and lacquer (Polisan) wereed as alternative protecting layers; however, best resultsbtained with paralm as discussed in the following sec-

eparation and characterization of CAAO surfaces

released AAO membranes have two distinct surfaces, the side and the solution side [21]. Nanopores with 100 or

pore diameters are located on the solution side of theranes. In order to create CAAO surfaces, the solution sides

membranes were coated with 20-nm-thick C layer viaring (GATAN Presicion Etching & Coating System) unlessnedepenadin

ion (terizrgy tomver, -AlpAO sstrucurce

ross-sectional drawing of the masked C or Au sputtered AAO surface used inesistance calculation (a), and top view optical image of the masked structure

the 100 m-gap created by the mask.e this article in press as: S. Altuntas, F. Buyukserin, Fabrication ans, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.06

the related studies mainly focus on the role of topog-llmaterial interaction [1618]. Hence, exploiting theal of AAO as a promising substrate for neuroregenera-zing the topographic, chemical and electrical cues has atial for neural tissue engineering applications, however,

still remains to be a challenge.udy, we focus on the fabrication and characterization ofAAO (CAAO) substrates to eventually control nerve tis-r via utilizing electrical cues. We rst introduce a newr producing large area free-standing AAO membranesf paralm as an AAO protecting layer. We then show thatces with open nanopores can be prepared by carbon (C)hrough morphological, chemical and electrical charac-f the material. Finally, we report the formation of novel

C lms and one dimensional (1-D) C nanostructuresmoval of the AAO templates.

ental details

tion of the free-standing AAO membranes

rity Al foils (99.999%, Puratronic, 1 mm thickness, Alfa sanded with 600 grit sand paper, rinsed with deionized, Sartorius) and annealed at 450 C for 4 h. After cool-

temperature, an electrochemical polishing step at 15 V to the foils using a Pb cathode for 90 min at 75 C. Thehing solution consisted of 95 wt% H3PO4 (BDH Prolabo),4 (Fluka) and 20 g/ml CrO3 (Fluka). These foils were theno single or two-step anodization processes dependinged nal nanopore size. Nanopores with 250 nm diam-btained using a single step anodization where 160 V

potential was applied to the Al foils in a 0.4 M H3PO4at 0 C against a stainless steel cathode. The nanoporeswidened in an aqueous chromic acid solution at roome for 22 min.

to obtain monodisperse nanopores with 100 nm porehe well-known two-step anodization method [19,20]ed. Here, the rst anodization step was carried out at

wt% aqueous oxalic acid electrolyte solution for 18 hick non-uniform alumina (Al2O3) lm that forms on

of the Al foil was removed using an aqueous solutionf 0.4 M H3PO4 and 0.2 M CrO3 (Fluka) at 75 C. A sec-

ation step was then applied at the same conditions of for 5 min and the substrate was then immersed into a4 solution to widen the nanopores to yield AAO lms

ordered uniform nanopores were attained. Note thats report, AAO structures are named as lms if they aree underlying Al, and membranes when they are liber-

s form on both sides of the Al foil and obtainingg AAO membranes requires the removal of the Al foilwiched between these lms (Fig. 1). This is typically

y applying a protecting polymer layer on the surfacehe AAO lms. The unprotected AAO lm and the Alen removed in appropriate solutions and free-standingranes were achieved after the protecting polymer layered in an organic solvent (Fig. 1). In our case, paralms used, for the rst time, as the protecting layer and the

AAO lm was dissolved in 1 M NaOH (BDH Prolabo)he metalic Al surface. Al was then oxidized in 0.1 M

(Alfa Aesar) + 6.1 M HCl (Merck) solution, and AAO

Fig. 1. Sthe appl

memb(Sigmalate) (also uswere otions.

2.2. Pr

Thebarrier250 nmmembof thesputtementioby indness redeviatcharacan EneFEG), Acantile(XPS, Kthe CAof the 210 so

Fig. 2. Csurface rshowing otherwise. The C thickness value was also verieddent ellipsometer studies which conrmed the thick-g from the sputtering instrument with less than 10%data not shown). These CAAO surfaces were thened by using Scanning Electron Microscope (SEM) withDispersive X-ray (EDX) detector (ESEM, Quanta 200ic Force Microscope (AFM, EZ-AFM, tapping mode, PPPNanomagnetics), X-Ray photoelectron spectroscopyha, Thermo Scientic). The electrical characterization ofurfaces was made by measuring the surface resistancetures via a DC Voltage/Current Source (Yokogawa GSmeter). Here, CAAO surfaces were rst fabricated by


ARTICLE IN PRESSG ModelAPSUSC-28056; No. of Pages 7S. Altuntas, F. Buyukserin / Applied Surface Science xxx (2014) xxxxxx 3

Fig. 3. Photogby using paraCAAO. SEM iman AAO memb

sputtering mask with and a secon

The maapplied acroues were reused to obtcoating conwas characIn this setuthe whole mask was a conductivcurrent betsubstrate suareas.

2.3. Liberat1-D C nanos

C coatedsolution foe this article in press as: S. Altuntas, F. Buyukserin, Fabrication and ch, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.06.007

raphs showing (a) large area free-standing AAO membrane obtainedlm as a protecting layer, (b) the color difference of naked AAO andage (c) of CAAO surface that was formed by coating 20-nm-thick C onrane grown in H3PO4 electrolyte.

AAO membranes with C or Au (as a control) layers. A100 m width was then placed on the CAAO surfaced 50-nm-thick Au layer was sputtered (Fig. 2).sk was removed and ve different potentials weress the top Au pads and the corresponding current val-corded. The slope of the resultant IV curve was thenain the surface resistance value corresponding to eachdition. Further conrmation of surface conductivityterized by conductive AFM (hp-AFM, Nanomagnetics).p, part of an AAO substrate was masked and thenAAO surface was exposed to C sputtering. After theremoved a voltage bias (3.5 V) was applied betweene AFM tip (Pt/Ir cantilever) and the substrate. Theween the conductive tip and the partially C coatedrface was then monitored to distinguish the C coated

ion and characterization of nanoporous C lms andtructures

AAO membranes were dissolved in 1 M aqueous NaOHr 4 h. Template synthesized nanoporous C lms and

Fig. 4. (a) AFMin the AFM miences to colorarticle.)

1-D C nanwas lterealcohol. Heto imagingof nanoporried out byBiotwin). Tstructures this concengrid.

3. Results

The genbrane is tosides of thebased mate[24]. Prior these threeto a certainor the nalbe noted thpH CuCl2 svated temparacterization of conductive anodic aluminum oxide

image of CAAO surface, and (b) depth prole across a line (red linecrograph) that depicts the open pores.(For interpretation of the refer-

in this gure legend, the reader is referred to the web version of the

ostructures were imaged by SEM after this solutiond and extensively washed with water and isopropylre, a 5-nm-thick AuPd layer was sputtered prior

for improved image quality. Further conrmationous C lms and 1-D C nanostructures were car-

Transmission Electron Microscopy (TEM, FEI TechnaiEM images were obtained after the ltered nano-were transferred to a minute volume of ethanol andtrated dispersion was dropped on a 300-mesh TEM

and discussion

eral rationale for obtaining free-standing AAO mem- protect one of the two AAO faces that form on both

Al foil (Fig. 1). Popular protecting layers are polymer-rials including lacquer [22], nail polish [23] or PMMAto developing our own methodology, we have tried

agents as protecting layers. Despite being successful extent, several problems involving surface adherence

removal of the protecting layer were faced. It shouldat the oxide or metal removal steps, occurring in lowolutions, are extremely vigorous and proceed at ele-eratures. These conditions result in surface adherence

Please citsubstrate


Fig. 5. XPS dat(b) and from t

problems foAAO membobserved insive crosslinthe solutionas protectinbased unprAl dissolutiAAO-parain hexane tmembranes

The conical vapor d[27,28] or Cvated temp(PVD)-basetool to creafrom the AArial turns inThe electroFig. 3c whi(235.28 1in H3PO4 el

AFM wasurface, ande this article in press as: S. Altuntas, F. Buyukserin, Fabrication and chs, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.06.007

a from the surface of a CAAO substrate (a), and EDX and SEM results of a conductive AAO mhe proximity of the surface (c).

r the protecting layer in addition to the breaking of therane to small pieces. On the other hand, the difculty

the nal polymer removal step should be due to exten-king of the polymer layers [25] as the temperature ofs can rise well above 110 C. The application of paralmg layer proved to be useful during the rst NaOH-

otected AAO lm removal as well as the second acidicon step. After the observation of the metal removal, thelm assembly was washed and paralm was dissolvedo reproducibly yield 50 cm2-area free-standing AAO

(Fig. 3a).ventional approach for coating C on AAO is via chem-eposition (CVD) [26] where carbon nano tubes (CNTs)NT membranes [29] can be successfully produced at ele-eratures. Here, we have used physical vapor depositiond sputtering as an alternative, practical and versatilete CAAO surfaces. They can be visually distinguishedO membranes after 20 nm C coating and as the mate-to a gray color compared to the white AAO (Fig. 3b).n micrograph of a CAAO substrate is illustrated inch reveals that the pore diameters are relatively large4.72 nm) as expected from an AAO membrane preparedectrolyte.s also used to demonstrate the topography of the CAAO

in particular, the state of the pores (Fig. 4). The dark

circular areimage was300 nm wdepth proand pore dreal pore dAFM tips inent from Fideposition.

The chenanopores of the CAApeak whereenergy of 2phous C onof C insideken into haSEM and Esurface, andtigated.

The EDXof C near tent on arein additionwas expecaracterization of conductive anodic aluminum oxide

embrane cross-section obtained further from the conductive surface

as indicate the positions of the pores. A line across this chosen to demonstrate the pore to pore distance ofhich is parallel to the SEM data. More importantly, thele across this line illustrates that the pores are openepth is 90 nm. This value is much smaller than theepth (20 m) and stems from the limited ability of theside the nanochannels, but nevertheless, it is appar-g. 4b that the periodic pores are not blocked due to C

mical characterizations of CAAO surface as well as theare shown in Fig. 5. High resolution C 1s XPS spectrumO surface (Fig. 5a) illustrates the presence of a broad

the maximum intensity corresponds to the binding85 eV, and dictates the dominant presence of amor-

the CAAO surface [29]. In order to conrm the presence the nanopores, a C coated AAO membrane was bro-lf and the membrane cross-section was analyzed byDX. Two different areas, one, close to the conductive

the other, further down from this surface were inves-

data (Fig. 5b and c) displays the abundant presencethe conductive surface and comparably low C con-as that are placed further deep into the membrane

to the components of the Al2O3-based material. Thisted from a C deposition by a regular sputterer for



Table 1The surface resistance values of C or Au coated AAO substrates.

AAO coating material Thickness (nm) Resistance (M)

Carbon (C)

Gold (Au)

electron minor substramal coatingimproved csuffer from[30,31].

The elecby calculatitially C coaobtain surfaon masked were used tand Au coaAs expectedcoated AAOC coated onthe coatingresearcherstional use ofailed in oubrane.

In ordersurface, parsputtering a voltage b(Pt/Ir cantilthis selectivis shown inspond to thand they doever, whendistinction apparent (Fthe maskedues up to 0.0C-sputteredresponsibleAAO area.

Completgroup of strstructures ain the nanoD structurewhich reeH3PO4 electhesis [33], uniform anwith monowere rst soxalic acid template, n(50 nm dialter mater

FM micrographs showing the topographic view (a) and current prole (b)ctively C coated AAO surface.

ions of such structures are reported for the rst time in there and potential applications involving ltration [34] and

g [35] can be foreseen by the control over initial templateze.eful investigation of the 1D nanostructures and comparisonn the previously published electron micrographs of tem-

ynthesized CNTs [2729] dictates that these particles are notr. Note that, after C coating, the pores of the CAAO mate-re open. One reason behind this observation can be thee of the C-coating inside the nanopores during the tem-issolution process. It is also suspected that the non-uniform0 15 195.24 2.9725 624.54 10.130

15 22.77 1.1025 28.65 2.05

croscopy use as there is no control of working pressurete temperature that are essential in obtaining confor-

[30]. It is also worth mentioning that, despite theharacteristics for sputtering, PVD methods generally

conformal coating of substrates with deep features

trical properties of the CAAO surfaces were investigatedng their surface resistance values and by imaging a par-ted AAO substrate with a conductive AFM. In order toce resistance values, different DC voltages were appliedsubstrates (see Section 2) and the resultant IV curveso extract the resistance data. As a comparison, uncoatedted AAO substrates were also investigated (Table 1)., the naked AAO substrates were insulators, and Au

surfaces had lower resistivity values compared withes. In both cases, surface resistance value increased as

got thicker, and similar trend was reported by other in the literature [32]. It should be noted that, the tradi-f four-point probes for surface resistance calculationr study due to the fragile nature of the AAO mem-

to conrm the conductive characteristic of the CAAOt of an AAO substrate was selectively blocked from Cvia the use of a mask. After the mask was removed,ias (3.5 V) was applied between a conductive AFM tipever) and the substrate. A large area topographic view ofely blocked CAAO surface as well as its current prole

Fig. 6. The tiny darker-colored dots in Fig. 6a corre-e locations of nanopores that are 250 nm in diameter,

not appear clearly in this large area AFM scan. How- the AFM is switched to the conductive mode, a sharpbetween the C coated vs. non-coated area becomesig. 6b). There is no current ow between the tip and, non-conductive AAO substrate where as current val-5 nA can be obtained while the tip scans the conductive

region. The imperfections in the masking should be for the local current signals observed in the masked

e dissolution of a CAAO substrate yields two distinctuctures, namely, nanoporous C lms and 1-D C nano-s demonstrated in Fig. 7. The diameters of the poresporous C lm (Fig. 7b) as well as the diameter of 1-s (Fig. 7b and c) are on the order of 240270 nm,cts the starting template pore size attained by using

Fig. 6. Aof a sele

formatliteratusensinpore si

Carbetweeplate stubularial wecollapsplate de this article in press as: S. Altuntas, F. Buyukserin, Fabrication and ch, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.06.007

trolyte. Utilizing the versatile nature of template syn-it is also possible to fabricate porous C lms with mored smaller diameter nanopores. Here, AAO templatesdisperse nanopores having 100 nm pore diametersynthesized via the use of two-step anodization [19] inelectrolyte (Fig. 7d). After C coating and dissolution ofanoporous C lms with ordered and smaller nanoporesmeter) were attained (Fig. 7e, curled lm resting on theial). To the best of our knowledge, the template-based

conformal tion of sucof CNTs upsition condCNT fabricasuch condicharacterizof this worreport.aracterization of conductive anodic aluminum oxide

C coating by sputtering has a role in the observa-h structures as opposed to the theoretical formationon dissolution. Note that, by ne tunning the depo-itions involving substrate temperature and pressure,tion by sputtering is plausible. Systematic control overtions for CNT production via sputtering and detailedation of the 1-D C nanostructures is beyond the scopek, and is currently under investigation for a separate

Please citsubstrate


Fig. 7. Low (atemplate witha C deposited structures.

4. Conclus

We havematerial in membranesparalm aswith C via after C coatence of C e this article in press as: S. Altuntas, F. Buyukserin, Fabrication and chs, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.06.007

) and high (b) magnication TEM images of nanoporous C lms and 1-D C nanostructu large pores (d = 250 nm), (d) AAO template with 100 nm uniform nanopores prior to C dAAO template with 100 nm nanopores. Note that, the porous underlying substrate in (c) a

ion

fabricated conductive AAO surfaces to be used as a bio-nerve tissue engineering. Large area free-standing AAO

were rst fabricated by a novel procedure that utilizes a protecting lm. These substrates were then coatedsputtering. The morphology of the open nanoporesing was characterized by SEM and AFM studies. Pres-on the CAAO surface and within the pores that are

close to thanalysis. Thby DC voltaby using mwith controobtained bdissolutionCAAO substbeing invesaracterization of conductive anodic aluminum oxide

res. SEM images of (c) 1-D C nanostructures after dissolving a AAOeposition, and (e) a curled nanoporous C lm obtained by dissolvingnd (e) is lter membrane and it is not related with the nanoporous C

e sputtered face was characterized by XPS and EDXe conductivity of the CAAO surfaces was conrmedgecurrent reading as well as conductive AFM setupsasked CAAO substrates. Unique nanoporous C lmsllable pore dimensions and 1-D C nanostructures werey the virtue of template synthesis upon the complete

of sputtered AAO templates. The potential of AAO andrates for neural adherence and regeneration is currentlytigated and promising results including cell growth

Please cit d chsubstrates .007


stimulation was observed, and these will be the topic of an upcom-ing report.

Acknowledgment

This research was supported by The Scientic and Technologi-cal Research Council of Turkey (Tubitak), grant no: 111M686. Wewould like to thank Ms. Hilal Gzler from Nanomagnetics Instru-ments for her assistance with AFM images.

References

[1] C.E. Schmidt, J.B. Leach, Neural tissue engineering: strategies for repair andregeneration, Annu. Rev. Biomed. Eng. 5 (2003) 293347.

[2] J.W. Xie, M.R. MacEwan, S.M. Willerth, X.R. Li, D.W. Moran, S.E. Sakiyama-Elbert,Y.N. Xia, Conductive core-sheath nanobers and their potential application inneural tissue engineering, Adv. Funct. Mater. 19 (2009) 23122318.

[3] J.T. Seil, T.J. Webster, Electrically active nanomaterials as improved neural tis-sue regeneration scaffolds, Wiley Interdiscip. Rev. Nanomed. Nanobiotechnol.2 (2010) 635647.

[4] E.C. Spivey, Z.Z. Khaing, J.B. Shear, C.E. Schmidt, The fundamental role of subcell-ular topography in peripheral nerve repair therapies, Biomaterials 33 (2012)42644276.

[5] S.K. Seidlits, J.Y. Lee, C.E. Schmidt, Nanostructured scaffolds for neural applica-tions, Nanomedicine 3 (2008) 183199.

[6] G. Kang, R. Ben Borgens, Y.N. Cho, Well-ordered porous conductive polypyrroleas a new platform for neural interfaces, Langmuir 27 (2011) 61796184.

[7] J.W. Xie, M.R. MacEwan, A.G. Schwartz, Y.N. Xia, Electrospun nanobers forneural tissue engineering, Nanoscale 2 (2010) 3544.

[8] C.E. Schmidt, V.R. Shastri, J.P. Vacanti, R. Langer, Stimulation of neurite out-growth using an electrically conducting polymer, Proc. Natl. Acad. Sci. U.S.A. 94(1997) 89488953.

[9] C.A.C. Abdullah, P. Asanithi, E.W. Brunner, I. Jurewicz, C. Bo, C.L. Azad, R. Ovalle-Robles, S.L. Fang, M.D. Lima, X. Lepro, S. Collins, R.H. Baughman, R.P. Sear, A.B.Dalton, Atrol the gr22 (2009)

[10] J.Y. Hwancarbon na487497.

[11] K.C. PopaGrimes, Tosteoblas

[12] H. Hillebrnanotube

[13] D. BruggeNanomat

[14] A.M.M. Jaadvances58 (2013)

[15] A.R. Walpole, Z.D. Xia, C.W. Wilson, J.T. Triftt, P.R. Wilshaw, A novel nano-porous alumina biomaterial with potential for loading with bioactive materials,J. Biomed. Mater. Res. A 90A (2009) 4654.

[16] B. Wolfrum, Y. Mourzina, F. Sommerhage, A. Offenhausser, Suspendednanoporous membranes as interfaces for neuronal biohybrid systems, NanoLett. 6 (2006) 453457.

[17] F. Haq, V. Anandan, C. Keith, G. Zhang, Neurite development in PC12 cells cul-tured on nanopillars and nanopores with sizes comparable with lopodia, Int.J. Nanomed. 2 (2007) 107115.

[18] W.K. Cho, K. Kang, G. Kang, M.J. Jang, Y. Nam, I.S. Choi, Pitch-dependent accel-eration of neurite outgrowth on nanostructured anodized aluminum oxidesubstrates, Angew. Chem. -Int. Ed. 49 (2010) 1011410118.

[19] H. Masuda, K. Fukuda, Ordered metal nanohole arrays made by a 2-stepreplication of honeycomb structures of anodic alumina, Science 268 (1995)14661468.

[20] F. Buyukserin, C.R. Martin, The use of reactive ion etching for obtaining freesilica nano test tubes, Appl. Surf. Sci. 256 (2010) 77007705.

[21] F. Buyukserin, M. Aryal, J.M. Gao, W.C. Hu, Fabrication of polymeric nanorodsusing bilayer nanoimprint lithography, Small 5 (2009) 16321636.

[22] J.M. Montero-Moreno, M. Sarret, C. Muller, Inuence of the aluminum surfaceon the nal results of a two-step anodizing, Surf. Coat. Technol. 201 (2007)63526357.

[23] T.T. Xu, R.D. Piner, R.S. Ruoff, An improved method to strip aluminum fromporous anodic alumina lms, Langmuir 19 (2003) 14431445.

[24] L.K. Tan, H. Gao, Y. Zong, W. Knoll, Atomic layer deposition of TiO2 to bond free-standing nanoporous alumina templates to gold-coated substrates as planaroptical waveguide sensors, J. Phys. Chem. C 112 (2008) 1757617580.

[25] B.A. Miller-Chou, J.L. Koenig, A review of polymer dissolution, Prog. Polym. Sci.28 (2003) 12231270.

[26] M. Kumar, Y. Ando, Chemical vapor deposition of carbon nanotubes: a reviewon growth mechanism and mass production, J. Nanosci. Nanotechnol. 10 (2010)37393758.

[27] S.H. Jeong, H.Y. Hwang, S.K. Hwang, K.H. Lee, Carbon nanotubes based on anodicaluminum oxide nano-template, Carbon 42 (2004) 20732080.

[28] J.T. Chen, K. Shin, J.M. Leiston-Belanger, M.F. Zhang, T.P. Russell, Amorphouscarbon nanotubes with tunable properties via template wetting, Adv. Funct.Mater. 16 (2006) 14761480.

[29] S.A. Miller, V.Y. Young, C.R. Martin, Electroosmotic ow in template-preparedbon na. Mado

ed., C. Kongondurorodtchelimagn

ls, Rev. Mart

(199Cohenphene. Siwychnol.e this article in press as: S. Altuntas, F. Buyukserin, Fabrication an, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.06

ligned, isotropic and patterned carbon nanotube substrates that con-owth and alignment of Chinese hamster ovary cells, Nanotechnology

205102.g, U.S. Shin, W.C. Jang, J.K. Hyun, I.B. Wall, H.W. Kim, Biofunctionalizednotubes in neural regeneration: a mini-review, Nanoscale 5 (2013)

t, E.E.L. Swan, V. Mukhatyar, K.I. Chatvanichkul, G.K. Mor, C.A..A. Desai, Inuence of nanoporous alumina membranes on long-termt response, Biomaterials 26 (2005) 45164522.enner, F. Buyukserin, J.D. Stewart, C.R. Martin, Template synthesizeds for biomedical delivery applications, Nanomedicine 1 (2006) 3950.mann, Nanoporous aluminium oxide membranes as cell interfaces, J.er. 2013 (2013) 460870.ni, D. Losic, N.H. Voelcker, Nanoporous anodic aluminium oxide:

in surface engineering and emerging applications, Prog. Mater. Sci. 636704.

car[30] M.J

2nd[31] B.H

of cmic

[32] A. Pnoncoi

[33] C.R266

[34] D. gra

[35] Z.Sotearacterization of conductive anodic aluminum oxide

notube membranes, J. Am. Chem. Soc. 123 (2001) 1233512342.u, Fundamentals of Microfabrication: the Science of Miniaturization,RC press, Boca Raton, FL, 2002., M.K. Choi, H.K. Cho, J.H. Kim, S. Baek, J.H. Lee, Conformal coating

ctive ZnO:Al lms as transparent electrodes on high aspect ratio Sis, Electrochem. Solid State Lett. 13 (2010) K12K14.ntsev, B. de Halleux, Thickness and conductivity determination of thinetic coatings on ferromagnetic conductive substrates using surface. Sci. Instrum. 69 (1998) 14881494.in, Nanomaterials: a membrane-based synthetic approach, Science4) 19611966.-Tanugi, J.C. Grossman, Water desalination across nanoporous, Nano Lett. 12 (2014) 36023608., M. Davenport, NANOPORES: graphene opens up to DNA, Nat. Nan-

5 (2010) 697698.

Fabrication and characterization of conductive anodic aluminum oxide substrates1 Introduction2 Experimental details2.1 Preparation of the free-standing AAO membranes2.2 Preparation and characterization of CAAO surfaces2.3 Liberation and characterization of nanoporous C films and 1-D C nanostructures

3 Results and discussion4 ConclusionAcknowledgmentReferences

Documents

ezAFM2