The role of viscous flow of oxide in the growth of self ordered.pdf

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1、ARTICLESPUBLISHEDONLINE:12APRIL2009

2、DOI:10.1038/NMAT2423Theroleofviscousflowofoxideinthegrowthofself-orderedporousanodicaluminafilmsJerrodE.HouserandKurtR.Hebert*Porousanodicalumina(PAA)filmsarewidelyusedastemplatesforfunctionalnanostructures,becauseofthehighregularityandcontrollabilityofthepore

3、morphology.However,growthmechanismshavenotyetbeendevelopedthatcanexplainquantitativerelationshipsbetweenprocessingconditionsandoxidelayergeometry.Here,wepresentamodelforsteady-stategrowthoftheseamorphousfilms,incorporatingthenovelfeaturethatmetalandoxygenionsaretransportedbycoupledelectricalmi

4、grationandviscousflow.Theoxideflowinthemodelarisesnearthefilm–solutioninterfaceattheporebottoms,inresponsetotheconstraintofvolumeconservation.Thehypothesisofviscousflowwassuccessfullyvalidatedthroughdetailedcomparisonstoobservationsofthemotionoftungstentracersinthefilm.Predictionsoflocalizedtensil

5、estressnearnanoscaleridgesatthemetal–filminterfaceweresupportedbyobservationsofvoidsatthesesites.WesuggestthattheorderingofPAAmaybeexplainedbyamechanisminwhichmetal–filminterfacemotionisregulatedbythecombinationofionicmigrationintheoxideandstress-driveninterfacediffusionofmetalatoms.orousanodic

6、alumina(PAA)filmsareformedbyabrPelectrochemicaloxidationofaluminiuminacidicsolutions1.zSince1995,whenMasudaandFukudademonstratedfor-mationoffilmswithself-organizedhexagonalporearrays2,PAAhasbeenintensivelyexploredasatemplatefornanostructuredfunctionaldevices.However,manyaspectsofthefilmformat

7、ionmechanismremainunexplained.Forexample,porediameterandspacingdependlinearlyonappliedvoltage3,buthighlyorderedR1θofilmscanbeformedonlyatspecificvoltagesdeterminedbythetypeR4,52ofacidused.Aquantitativeunderstandingofporousfilmforma-tionwouldstreamlineandacceleratefilmformationprocedures,0.2μm

8、andhelpdevelopnewmethodstoproduceporousfilmscomposedoffunctionalmaterialssuchasoxidesemiconductors6.Sofar,Figure1jReactionandtransportprocessduringfilmgrowth.a,TEMmathematicalmodelsofPAAformationhavebeendevisedonthecross-sectionoftheporebasere