ContentslistsavailableatSciVerseScienceDirect
Applied
Surface
Science
j o ur na l ho me p age :w w w . e l s e v i e r . c o m / l o c a t e / a p s u s c
Growth
of
vertically
aligned
carbon
nanotubes
over
self-ordered
nano-porous
alumina
films
and
their
surface
properties
Kuldeep
Rana
a,
Gokce
Kucukayan-Dogu
b,
Erman
Bengu
a,∗aDepartmentofChemistry,BilkentUniversity,06800Ankara,Turkey
bInstituteofEngineeringandScience,MaterialsScienceandNanotechnologyGraduateProgram,BilkentUniversity,06800Ankara,Turkey
a
r
t
i
c
l
e
i
n
f
o
Articlehistory:Received27January2012
Receivedinrevisedform31March2012 Accepted2April2012
Available online 6 April 2012
Keywords: Anodization Porousaluminafilm Chemicalvapordeposition Carbonnanotube Contactangle
a
b
s
t
r
a
c
t
Nanoporousanodicaluminumoxide(AAO)withself-organizedarraysofuniformnanoporeshavebeen usedforvariousapplicationsinthefieldsofsensing,storage,separationandtemplate-basedfabricationof metalnanowires,carbonnanotubes,oxidesandpolymers.Theworkpresentedhereinvolvesthe produc-tionanduseofAAOtemplatesforgrowthofalignedmultiwalledcarbonnanotubearrays.AAOtemplates wereformedbyelectrochemicaloxidationofaluminumindifferentelectrolytesolutionscontaining sul-furic,oxalicandphosphoricacid.SEMwasusedfortheanalysisofthesurfacemorphologyoftheAAO films.Theporousstructureswithporesizeintherangeof25–120nmwereobserved.Poresizeswere correlatedwiththetypeofacidicsolutionsusedastheelectrolyte.Finally,AAOsurfaceshavebeenused assubstratesforthegrowthofverticallyalignedcarbonnanotubesthroughchemicalvapordeposition technique,whichshowedsuper-hydrophobicbehaviorasconfirmedbycontactanglemeasurements.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Variousnanostructurebasedmaterialsarealreadyfinding appli-cationsintheindustry,suchaselectronicdevices[1],biosensors [2],photonics[3],materialsforenergystorage[4]andas separa-tionmembranesforbio-materials[5].Anodizedaluminumoxide (AAO)templatebasedsynthesishasbeenemployed[6]asoneofthe well-knownproductiontechniquesenablingcontrolof morphol-ogy,patterningandsizeofnanomaterials.Throughitsporesize, densityanddistribution,AAOtemplateshavesignificantinfluence onthefinalpropertiesofthenanostructuredmaterialsandthusthe variousstructuralpropertiesofnanomaterialscanbeengineeredby these“knobs”[4].
Discoveryofself-orderedAAOmembraneswasfirstreported byMasudaandFukuda[7–9],which,havegrownby electrochemi-caloxidationofaluminum(Al)andusedinnumerousapplications in thefollowingyears [8].Thestructure ofporousaluminacan bedescribedasaclose-packedarrayofcolumnarcells,each con-taining a central pore of which the size and interval can be controlledbychangingthesynthesisconditions[10].AAOwitha hexagonalarrangementstableathightemperaturehasbecomea populartemplatesystemforthesynthesis ofvariousfunctional nanostructures[5,11,12].Furthermore, AAOfilmsfind potential applicationsindiversefieldsashighdensitymagneticstorage[13],
∗ Correspondingauthor.Tel.:+903122902153;fax:+903122664068. E-mailaddress:bengu@fen.bilkent.edu.tr(E.Bengu).
DNAtranslocation[14]andintribologyascoatingswithcontrolled lubricantreleasereservoirs[15].Recently,anodizationofAlfilms depositedonmetalorsemiconductorsubstratesarealsostudiedto fabricatenanostructuresonsubstratesusingtheporousAAOfilm asamask[16].
Thesynthesisofself-organizedorderedstructuresbyanodizing ofAlhasbeenwidelyreportedfromoxalic[7,10,17],phosphoric [5,18]andsulfuricacidsolutions[19,20].Athickandporouslayer ofaluminumoxide(upto200m)canbeformedbyanodization inadiluteacidicsolution.Bytheapplicationofapotential differ-encebetweentheelectrodes,hydrogenionsarereducedtoproduce hydrogengasatcathodesurfaceandAlisoxidizedintoAl3+.A
por-tionofthecationsisdissolvedintheelectrolyteandtherestforms anoxidelayeronthemetalsurface.TheporestructureofAAO(size, densityanddistribution)canbecontrolledbychangingthevoltage, currentdensityandacidconcentrationinthebathduringprocess [21].
Some ofthe studieson AAO filmsproduced by themethod outlinedabovearetargetingapplicationsrelatedtotheusageof AAO ordering as template for the growth of carbon nanotube (CNT)arrays[22],nanowiresandpatternedstructures[23].Besides, inducingapattern,AAOtemplateswithCNTsmightbeusedalsoas hybridstructures.SimilarAAO/CNThybridstructureshavebeen showed tohavepotential inthe following applicationssuchas membrane[24],catalystsupport[25],drugdelivery[26–28]and fieldemitters[29].
The mainaimofthepresent workis tocontrol ofpore size anddistributionoverAAOlayersbychangingtheelectrolytebath 0169-4332/$–seefrontmatter © 2012 Elsevier B.V. All rights reserved.
poresize controlof AAOfilmswhich couldenabletheiruseas suitabletemplatesforcompositeAAO/CNTstructures.
2. Experimentalprocedure
Alfoilsof300mthicknesses(99.9%,Merck)werecutin rectan-gles(70mm×15mm)andthenannealedunderinertatmosphere at 450◦C for 5h. The annealed Alfoils werewashed with ace-toneanddoubledistilledwaterinordertoremovedirtandthen driedusingdryairblower.Thebacksurfaceandtheedgesofthe sampleswerecoveredbytheinsulatingtape.Theanodizationof thesesampleswerecarriedoutbyatwo-stepanodization proce-dureunderconstantcellvoltagesof25V,40Vand100Vforthree differentelectrolytesolutionbaths(sulfuric,oxalicand phospho-ricacid,respectively)atthetemperatureof10◦C.Theelectrolyte bathswerekeptovermagneticstirrerforcontinuousstirringof solutiontomaintaintheuniformconcentrationinthebathduring theanodizationstep.After60minoffirstanodization,initial alu-minumoxideformedonAlfilmwasremovedbychemicaletching inamixtureofphosphoric(6wt%)andchromicacid(1.8wt%)at 70◦C.Immediatelyfollowingtheoxideremovalstep,Alfoilwas re-anodizedfor 2hunder identicalconditions usedforthefirst anodizationstep.AnodizationofAldepositedovertheSi(100) sub-stratewasalsocarriedoutinanidenticalmannerasusedforpure Alfoils.
Co–Alcatalystsolution(5mmol/L)waspreparedbydissolving Al(NO3)3·9H2OandCo(NO3)2·6H2Opowdersinethanol(Co–Alat
1:1)forCNTgrowth.ThecatalystlayerwasappliedonAAO sur-faceseitherviadrop-wisemethodorviadippingmethodusingthe preparedcatalystsolution.Inthedrop-wisemethod,20L/cm2
ofCo–AlbasedcatalystsolutionhasbeendroppedovertheAAO surfacesandthesurfacesleftforairdrying.Inothercatalyst applica-tionmethod,AAOsurfacesweredippedintothecatalystsolutionat 50◦Cfor15minandleftforairdrying.TheAAOsurfaceswithCo–Al catalystloadedtotheCVDchamberforCNTgrowthprocess.The reductionstepproceededunderH2andAratmospheres(flowrates
20sccmand150sccm,respectively)at600◦Cfor15min.Following thisstep,theCNTgrowthwasperformedatthesametemperature andgasmixtureswithpureethanolasacarbonsourcefor30min. ThealignedCNTshavebeengrownovertheAAOsurfacesbyCVD at600◦Csimilartoourprevioustechnique[32].
ThestructuralcharacterizationofAAOnanostructureswas per-formedbyusingaCarl-ZeissEVO40scanningelectronmicroscope (SEM).Thecontactanglemeasurementshavebeencarriedouton thesesurfaces(DataphysicsOCA 15plus). Thesynthesized car-bonaceousmaterialoverAAOsubstratewascharacterizedbyusing differentcharacterizationtechniquessuchasSEM,contactangle measurementandRamanspectroscopy(HoribaJobin-Jvon-532nm wavelength).
3. Resultsanddiscussion
TheoxidationofAlduringanodizationprocesshasbeen mon-itoredbythemeasuredoxidationcurrentversustimeasshown inFig.1.Themeasuredcurrentbetweenelectrodesishigherat
ofpureAlmetal.ThiscurrentdecreasessharplyfrompointAto
pointB,whichisattributedtotheformationofaluminumoxide
barrier layeronthesurface which alsoindicatestheformation
ofnanopores.Thereisaslightincreaseinthecurrentfrompoint
BtopointCduetothedecreasingthicknessofthebarrierlayer
whichiscausedbytheincreaseinporedepthasshowninFig.1.
BeyondpointC,equilibriumisestablishedbetweenthecompeting processesofoxideformationanddissolution(poregrowth). Real-timeoxidationcurrentvs.timedatacanbeusedtocontrol/tunethe oxidationperiodandconsequentlytoengineerporegeometry,e.g. poredepth.Maincharacteristicsofthisbehaviordonotvarywith thetypeofelectrolytebathused.
Fig.2 shows the SEMimage of top portionof theanodized Alstripspreparedwiththreedifferentelectrolytesused(sulfuric, oxalicandphosphoricacid).Fig.2ashowsSEMimageofAAO syn-thesizedusingphosphoricacidastheelectrolytewhichshowsa uniformporedistributionalloverthesurface.TheimagesfromSEM showtheporedistributionandtheirFastFourierTransforms(FFT) astheinsetsareshown.Theaverageporesizemeasurementshave beencarriedoutonmultipleSEMimagesfromtheAAOsurfacesby employingthe“particle-sizeanalysis”optionontheImageJ soft-ware[31].ForFig.2a,theaverageporediameterisfoundtobe around100±25nm(mean±standarddeviation)seeTable1.The largevariationforporediameterscanbeattributedtothe pres-enceofhighsurfaceenergyregions,suchasmicro-scratcheson thesurfaceofasreceivedsamples,whereanodizationprocessis acceleratedresultinginlargerporediameters.Fig.2bshowsthe SEMmicrographofthetopsurfaceofAAOtemplatepreparedin oxalicacidelectrolytebath.Thetopviewofporestructureafter anodizationshowswell-orderedporestructure andtheaverage porediameterisfoundtobearound40±10nm.Theaveragepore diameterobtainedduetoanodizationinoxalicacidelectrolytebath
Fig.1. Typicalcurrentdensity–timecurveforanodizationprocessunder constant-voltagemodeatavoltageof40Vandina3wt%oxalicacidbath,maintainedat 15◦C.
Fig.2.SEMmicrographofAAOimageobtainedafteranodizationwithdifferentelectrolytesused:(a)phosphoricacid,(b)oxalicacid,and(c)sulfuricacid.(d)SEMmicrograph ofAAOoverSianodizedinphosphoricacidsolution.
issmallercomparedtothatobtainedusingphosphoricacidbath requiringahighervoltageforporeformation.Fig.2cshowsthe SEMmicrographofthesurfaceafteranodizationusingsulfuric elec-trolyte;anodizationhasbeencarriedoutat20Vforthissample. Theporesaredistributedinaregularhexagonalmannerwithan averageporediameter20±9nmascalculated.Theaveragepore diameterobtainedwithsulfuricacidissmallestamongallthree acidsusedfortheelectrolytebathinthisstudy.
Furthertoensureaconstantporedepthacrossoursample,a 400nmthickAlfilmhasbeendepositedoverSisubstratevia ther-maldepositionmethod.Thisfilmwasthenanodizedinphosphoric electrolytebath.Fig.2dshowstheSEMimageofAAOstructureover Sisubstrate,whichshowsthatAAOfilmwasdeveloped success-fullyandmaximumporedepthcanbecontrolledbycontrollingthe thicknessofdepositedAllayer.Suchfilmswithtunedporedepths canbeusedforelectronicapplication.
Theporeformationoccursduetoelectric-fieldassistedoxide dissolution. Atthis stagethecurrent beginstoincrease, due to decreasein resistanceasoxidelayerthicknessreducesin front oftheinitiatingpores.Thecurrentstableswhenadynamic equi-librium is established between the competing mechanisms of aluminum oxide growth and its partial dissolution leading to pore formation at the surface [33]. Initially an irregular array ofpore structuresformonthesurface astheporesarecreated randomlyonthe sample. However,due tothe repulsiveforces betweenneighboring poresa self-organizedpore array eventu-allyforms.Themechanicalstressassociatedwiththeexpansion oftheAlduringoxideformationiscitedasthecauseofrepulsive forcesbetweenneighboringporeswhichleadstoself-organization [10].
We investigated theself-organization behavior of the pores usingtheFFTimagesprovidedastheinsetsofFig.2.TheFFTimages werecalculatedfromtherespectiveSEMimagesusingImageJ soft-ware[31].Threedifferentpatternsforporesareobservedthrough theexaminationoftheFFTimages.TheFFTimagesofanodized samplesin phosphoric and oxalic acidsshow sixdistinct spots formingahexagon(Fig.2aandb).Thisobservationindicatesa sin-gledomainofwell-ordered,long-rangeperiodic2-Dlatticeformed
bythepores[34].TheFFTimageofanodizedsurfaceinsulfuric acidshows a ring shape form(Fig.2c). Thissuggests the pres-enceofimperfectionsintheperiodicityofthesurfaceandmultiple domainsofordered2-Dlatticeofpores.AsshowninFig.2d,theFFT imageindicatesadiffuseringforthecaseofAAOoverSisample preparedwithphosphoricacidwhichrevealsthepresenceof dis-ordereddomainsonthesurface.Intheliterature,Sulkaetal.[34] concludedthathighstressesonthesurfaceofAlcandestroythe long-rangearrangementofporesandhence,theexactmechanism ofporeorderingisstillopenfordebate.Accordingtothis,multiple domainformationontheanodizedsurfaceusingphosphoricacid mightbeduetothepresenceofnon-homogenousdistributionof stressesintheAlfilmdepositedoverSisubstrate.
Asmentionedearlier,insomecasespreparationof nanostruc-turesusingporousAAOastemplatesinvolvestheintroductionof dissolvedmaterialsintotheporesofthemembranes.Onewayto determinewhetherthedissolvedsolventsaregoingtofillinthe poresistoinvestigatethewettingbehaviorofcommonsolvents on theAAO surfaces.Hence, we investigatedthe contact angle ofwaterontheseAAOsurfaces.Thecontactanglemeasurement showsthatallthreesurfacesarehydrophilicinnaturewith ini-tialcontactanglesare59◦,44◦and57◦respectivelyforAAOsheets anodizedinsulfuric,oxalicandphosphoricacidasshowninFig.3a. Twodifferentvalueofcontactangleshavebeenobservedattwo endsofdroplet,whichshowsthatsurfaceenergyisvaryingregion toregionofAAOsurface.Contactanglevaluedecreaseswithtime andafter5minwemeasured22◦,22.7◦and40◦respectivelyfor sul-furic,oxalicandphosphoricacidsasshowninFig.3b.Thedecrease incontactanglesinallthreecasesafterafewminutesisduetothe seepingofthewaterdropintoporesofAAO.WettingofAAOshas beenexplainedasfollow;ifaliquidisallowedtospreadonthepore wallsofAAOs,firsttheliquidisbroughtintocontactwiththeAAO surfaceslow-energyliquidsspreadrapidlyonhigh-energysurfaces andthedrivingforcesinvolvedinthisprocessaredueto short-rangeaswellaslong-rangepolarinteractionsbetweenthewetting liquidandtheporewalls[35].Afterwettingthewallsofnanoholes, thewaterdispersedrapidlyintotheholeascontactangledecreases veryfastasshowninFig.3b.
Fig.3.(a)DemonstrationofsurfacewettingabilitybycontactangleofAAOinsulfuric,oxalicandphosphoricacidand(b)thegraphforcontactangleswithtimeontheAAO surfacesareshown.
ThefinalsectionofthestudyinvolvestheapplicationofAAOs asatemplatefortheverticallyalignedCNTgrowth.Thevertically alignedCNTshavebeengrownovertwodifferenttemplates:AAO andAAO/Sisubstratesanodizedinphosphoricacid.Fig.4shows theSEMimagesofCNTsgrownoverAAOsubstrate,inonecasethe catalystlayerwasappliedviadrop-wiseapplicationovertheAAO surface(Fig.4a)whileinothercasetheAAOsubstratedippedinto thecatalystsolutionfor15min.(Fig.4b).SEMimageofCNTsin Fig.4ashowsthatCNTsarenotaligned;insteadtheyaretangled witheachotherasshowninFig.4b.MostoftheCNTsareappeared onthesurfaceandveryfewarecomingfromtheporesofAAOin thedrop-wisecase.Thisshowsthatmostofthecatalysts parti-clesstayedonthetopsurfaceoftheAAOandveryfewpenetrated throughthepores.Fig.4bshowsthealignmentofCNTsgrownon AAOsubstrate inwhich catalysthasbeendepositedbydipping substrateintothevialcontainingthecatalystsolutionat50◦Cfor 15min.Theas-grownCNTsareapparentlystraightandparallelto eachotherformingadensesurfacewithtubeheightabout3m measuredfromFig.4b.ThegrowthofdenseCNTs(Fig.4b)indicates thatthecatalyststaysonthesurfaceaswellasitpenetratesinto theporechannelsforthiscase,whichmakesitclearthatthefinal CNTalignmentisaffectedbythemethodofcatalystdeposition.
CNTs were also grown on the well-ordered AAO template formedonSisubstrateandSEMimagesareshowninFig.5attwo differentmagnifications.CNTs areverydense, verticallyaligned
and distributeduniformlyallover theAAOsurface (Fig.5a).To demonstrateabetterviewforthealignmentofCNTsinside the template,across-sectionalSEMimageisshowninFig.5b.CNTsare indeedwellalignedandlengthsareveryclosetoeachotherabout 3mlong.TherootsoftheCNTsarelocatedatthebottomofthe poresasshowninFig.5b.Theseresultsconfirmthatbychanging theporedepth(throughcontrollingthethicknessofAllayerover Si),thecatalystsolutioncanpenetrateeasilyinsidetheporeand hencethegrowthofalignedanddenseCNTscanbeachieved.
FirstandsecondorderRamanspectraofCNTsgrownoverAAO andAAO/SisubstrateareshowninFig.6.ThefirstorderRaman spectrashowstwointensepeakswhicharewellknownasGand Dpeak(Fig.6a).TheGmode(TM–tangentialmode)corresponds tothein-planevibrationoftwoatomsinahexagonallattice.In ourstudy,thismodeislocatedaround1578cm−1and1584cm−1 respectivelyforCNTsgrownoverAAO/SiandAAOsubstrate.The D-band(disorderbandislocatedbetween1330and1360cm−1)is expectedtobeobservedinmultiwalledcarbonnanotubes (MWC-NTs), which is 1338cm−1 and 1348cm−1 respectivelyfor CNTs grownoverAAO/SiandAAOsubstrates.FirstorderRamanspectra ofCNTsaresimilarforbothsurfaces.
RamanfeaturesareanalyzedbyusingaLorentzianfittothe DandGpeaks.Theratioof integratedintensityof GtoD-band (IG/ID)givesthedegreeoforderinthecarbonaceousmaterial.IG/ID
ratiofortheCNTsgrownoverAAO/SiandAAOsubstratesare0.85
Fig.4. SEMimagesofCNTsgrownoverAAOsubstratesanodizedinphosphoricacidwherethecatalystlayerwasappliedvia(a)drop-wisetechniqueand(b)dipping technique.
Fig.5.(a)Topand(b)crosssectionalSEMimagesofCNTsgrownoverAAO/Sisubstratesanodizedinphosphoricacid.Insetof(b)showstheTEMimageofCNTs.
Fig.6.(a)Firstorderand(b)secondorderRamanspectraofCNTsgrownovertwodifferentsubstrates:AAOandAAO/Si.
and0.60,respectively.ThisshowsthatCNTsgrownoverAAO/Si substratearemoreorderedandlessdefectiveascomparedtothe CNTsoverAAOsubstrates.TheCNTsgrownoverAAOsubstratesare entangledtoeachotherandtwistedwhichcreatesmoredefectson CNTsurface,howeverinothercase;CNTsarestraightandparallelto eachotherandhavehigherIG/IDvaluewhichmeansfewerdefects.
SecondorderRamanspectraintheregionbetween2400cm−1and 3400cm−1 areshown inFig.6b,whichshowssharpand strong peakcenteredat2679cm−1and2689cm−1respectivelyforCNTs grownoverAAO/SiandAAOsubstrates.Thesepeakareassigned as2DorG-band(2700cm−1).Thisbandisanintrinsicproperty ofwell-orderedsp2carbons[36]andcloselyrelatedtotheband
structureofgraphenelayersincarbon.Ithasbeenreportedthat 2D-bandfurtherdownshiftsduetodisorderordefectspresencein carbonlattice[36].Theotherbandalmostatsimilarpositionaround
2922cm−1isrelatedtothecombinationofGandD-band(G+D)in carbonaceousmaterials[37].
ThewettingabilityoftheCNTsurfacesisanimportant prop-erty which is governedboth by the surface chemistry and the microstructureofthesurfaceincontactwiththesolvent[38,39]. ThecontactanglewasmeasuredforthetwodifferenttypesofCNTs; alignedforestlikeandentangledCNTsgrownoverAAO/SiandAAO substrates,respectively(Fig.7).TheverticallyalignedCNTsover AAO/Sisubstrateclearlydisplayasuperhydrophobicbehaviorwith acontactangleof180◦(Fig.7aandseeSupplementaryVideo)while theentangledCNTsgrownoverAAOsubstratehavecontactangle around163◦(Fig.7b).SimilarbehaviorwasalsoreportedbyWang etal.[40,41]inwhichthecontactanglevaluesmeasuredagainst waterforalignedCNTsoffewmicrometerslongandentangledCNTs were174◦ and144◦,respectively[42].Thecontactanglevalues
anassumptionmadebyPaveseetal.[42]whichstatesthat super-hydrophobicbehaviordependsontheactualcontactsurfacearea betweenthewaterdropandCNTs.Thus,inthecaseofvertically alignedCNTs,theactualcontactsurfaceareaisverysmalllimited tothetipsofCNTs.InthecaseoftheentangledCNTs,themeasured valueofcontactangleislower(163◦)becauseofthedisorderinthe alignmentoftheCNTswithrespecttothesubstratesurfaceandthe side-wallsofthemisalignedCNTsincreasingthetotalcontactarea.
4. Conclusions
Inthisstudy,wehavesynthesizedAAOtemplateswith differ-entporesizesusingvariouselectrolytebaths.Tounderstandthe wettability/porefillingbehavior,contactanglemeasurementshave beencarriedoutwhichshowhydrophilicnaturesofthesesurfaces. Thisresulthasa practicalimportanceshowingthatwater solu-blematerialscouldbeeasilyutilizedforfillingtheporousalumina templates. For instance, using ethanol based catalyst precursor solutions wewereable tosuccessfullygrowaligned and dense CNTforestsover both AAO and AAO/Sisubstrates.Such hybrid structurescombiningpatternedconductorandinsulatorarrayscan bepotentiallyappliedintheelectronicsindustryasstructuresfor buildinglightemittingdiodes,solarcellsandsupercapacitors.
Acknowledgements
G. Kucukayan-Dogu thank the Scientific and Technological Research CouncilofTurkey (Tubitak)for financial support.This workwaspartially supportedbyTubitak Projects109T026 and 107T892.
AppendixA. Supplementarydata
Supplementary data associated with this
arti-cle can be found, in the online version, at
http://dx.doi.org/10.1016/j.apsusc.2012.04.008.
References
[1] J.Goldberger,R.He,Y.Zhang,S.Lee,H.Yan,H.-J.Choi,P.Yang,Single-crystal galliumnitridenanotubes,Nature422(2003)599–602.
[2]P.Kohli,M.Wirtz,C.R.Martin,Nanotubemembranebasedbiosensors, Electro-analysis16(2004)9–18.
[3]J.S.King,D.Heineman,E.Graugnard,C.J.Summers,Atomiclayerdepositionin porousstructures:3Dphotoniccrystals,Appl.Surf.Sci.244(2005)511–516. [4]P.Banerjee,I.Perez,L.Henn-Lecordier,S.B.Lee,G.W.Rubloff,Nanotubular
metal–insulator–metalcapacitorarraysforenergystorage,Nat.Nanotechnol. 4(2009)292–296.
[5]S.B. Lee,D.T.Mitchell, L.Trofin,T.K.Nevanen,H.Söderlund, C.R.Martin, Antibody-basedbio-nanotubemembranesforenantiomericdrugseparations, Science296(2002)2198–2200.
[6]B.Nandan,B.K.Kuila,M.Stamm,Supramolecularassembliesofblock copoly-mersastemplatesforfabricationofnanomaterials,Eur.Polym.J.47(2011) 584–599.
[7]H.Masuda,K.Fukuda,Orderedmetalnanoholearraysmadebyatwo-step replicationofhoneycombstructuresofanodicalumina,Science268(1995) 1466–1468.
[8]G.E.Thompson,G.C.Wood,Porousanodicfilmformationonaluminium,Nature 290(1981)230–232.
[9] R.C.Furneaux,W.R.Rigby,A.P.Davidson,Theformationofcontrolled-porosity membranesfromanodicallyoxidizedaluminium,Nature337(1989)147–149.
ananodizedAlalloysurfaceaslubricantreservoir,Curr.Appl.Phys.11(2011) S182–S186.
[16] Y.Kanamori,K.Hane,H.Sai,H.Yugami,100nmperiodsiliconantireflection structuresfabricatedusingaporousaluminamembranemask,Appl.Phys.Lett. 78(2001)142–143.
[17]L.Ba,W.S.Li,Influenceofanodizingconditionsontheorderedporeformation inanodicalumina,J.Phys.D33(2000)2527–2531.
[18]H.Masuda,M.Ohya,K.Nishio,H.Asoh,M.Nakao,M.Nohtomi,A.Yakoo,T. Tamamura,Photonicbandgapinanodicporousaluminawithextremelyhigh aspectratioformedinphosphoricacidsolution,Jpn.J.Phys.Part239(2000) 1039–1041.
[19]W.Y.Zhou,Y.B.Li,Z.Q.Liu,D.S.Tang,X.P.Zou,G.Wang,Self-organized forma-tionofhexagonalnanoporearraysinanodicalumina,Chin.Phys.10(2001) 218–222.
[20] G.C.Wood,J.P.O’Sullivan,Theanodizingofaluminiuminsulphatesolutions, Electrochim.Acta15(1970)1865–1876.
[21]G.D.Sulka,K.G.Parkoa,Anodisingpotentialinfluenceonwell-ordered nanos-tructuresformedbyanodisationofaluminiuminsulphuricacid,ThinSolid Films515(2006)338–345.
[22]J.Li,C.Papadopoulos,J.M.Xu,M.Moskovits, Highly-orderedcarbon nan-otube arrays for electronics applications, Appl. Phys. Lett. 75 (1999) 367–369.
[23] L.Piraux,A.Encinas,L.Vila,S.Matefi-Tempfli,M.Matefi-Tempfli,M.Darques,F. Elhoussine,S.Michotte,Magneticandsuperconductingnanowires,J.Nanosci. Nanotechnol.5(2005)372–389.
[24]Z.Wang,F.Hu,P.K.Shen,Carbonizedporousanodicaluminaaselectrocatalyst supportforalcoholoxidation,Electrochem.Commun.8(2006)1764–1768. [25] S.Sigurdson,V.Sundaramurthy,A.K.Dalai,J.Adjaye,Effectofanodicalumina
porediametervariationontemplate-initiatedsynthesisofcarbonnanotube catalystsupports,J.Mol.Catal.A:Chem.306(2009)23–32.
[26] H.Hillebrenner,F.Buyukserin,J.D.Stewart,C.R.Martin,Templatesynthesized nanotubesforbiomedicaldeliveryapplications,Nanomedicine(Lond.)1(2006) 39–50.
[27]J.L.Perry,R.Martin,J.D.Stewart,Drug-deliverystrategiesbyusing template-synthesizednanotubes,Chem.-Eur.J.17(2011)6296–6302.
[28] S.Kataoka,T.Yamamoto,Y.Inagi,A.Endo,M.Nakaiwa,T.Ohmori, Synthe-sisoforderedmesoporouscarbonthinfilmsatvarioustemperaturesinvapor infiltrationmethod,Carbon46(2008)1358–1360.
[29] G. Che, B.B. Lakshmi, E.R. Fisher, C.R. Martin, Carbon nanotube mem-branesforelectrochemicalenergystorageandproduction,Nature393(1998) 346–349.
[30]C.-S.Li,S.-H.Su,H.-Y.Chi,M.Yokoyama,Applicationofhighlyorderedcarbon nanotubestemplatestofield-emissionorganiclight-emittingdiodes,J.Cryst. Growth311(2009)615–618.
[31]M.D.Abramoff,P.J.Magalhaes,S.J.Ram,ImageprocessingwithImageJ, Biopho-ton.Int.11(2004)36–42.
[32]B.Baykal,V.Ibrahimova,G.Er,E.Bengü,D.Tuncel,Dispersionofmulti-walled carbonnanotubesinanaqueousmediumbywater-dispersibleconjugated polymernanoparticles,Chem.Commun.46(2010)6762–6764.
[33]G.E.Thompson,Porousanodicalumina:fabrication,characterizationand appli-cations,ThinSolidFilms297(1997)192–201.
[34]G.D.Sulka,S.Stroobants,V.V.Moshchalkov,G.Borghs,J.-P.Celis,Effectoftensile stressongrowthofself-organizednanostructuresonanodizedaluminum,J. Electrochem.Soc.151(2004)B260–B264.
[35]R. Redon, A.Vazquez-Olmos,M.E.Mata-Zamora,A. Ordonez-Medrano,F. Rivera-Torres,J.M.Saniger,Contactanglestudiesonanodicporousalumina, J.Colloid.InterfaceSci.287(2005)664–670.
[36]P.C.Eklund,J.M.Holden,R.A.Jishi,Vibrationalmodesofcarbonnanotubes: spectroscopyandtheory,Carbon33(1995)959–972.
[37]H.Maeta,Y.Sato,Ramanspectraofneutron-irradiatedpyrolyticgraphite,Solid StateCommun.23(1997)23–25.
[38]P.Kim,C.M.Lieber,Nanotubenanotweezers,Science286(1999)2148–2150. [39]B.J.Hinds,N.Chopra,T.Rantell,R.Andrews,V.Gavalas,L.G.Bachas,Aligned
multiwalledcarbonnanotubemembranes,Science303(2004)62–65. [40]Z.Wang,L.Ci,L.Chen,S.Nayak,P.M.Ajayan,N.Koratkar,Polarity-dependent
electrochemicallycontrolledtransportofwaterthroughcarbon nanotube membranes,NanoLett.7(2007)697–702.
[41]K.K.S.Lau,J.Bico,K.B.K.Teo,M.Chhowalla,G.A.J.Amaratunga,W.I.Milne,G.H. McKinley,K.K.Gleason,Superhydrophobiccarbonnanotubeforests,NanoLett. 3(2003)1701–1705.
[42] M.Pavese,S.Musso,S.Bianco,M.Giorcelli,N.Pugno,Ananalysisofcarbon nanotubestructurewettabilitybeforeandafteroxidationtreatment,J.Phys. Condens.Matter20(2008)1–7.
