The mechanism of protrusion formation on PTFE surface by ion-beam irradiation

Surface&CoatingsTechnology203(2009)2406–2409

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Surface&CoatingsTechnology

journalhomepage:http://www.mianfeiwendang.com/locate/surfcoat

ThemechanismofprotrusionformationonPTFEsurfacebyion-beamirradiation

AkaneKitamuraa, ,TomohiroKobayashib,TakashiMegurob,AkihiroSuzukia,TakayukiTeraia

ab

DepartmentofNuclearEngineeringandManagement,SchoolofEngineering,TheUniversityofTokyo,7-3-1Hongo,Bunkyo-ku,Tokyo113-8656,JapanRIKEN(TheInstituteofPhysicalandChemicalResearch),2-1Hirosawa,Wako-shi,Saitama350-0198,Japan

articleinfoabstract

Ion-beamirradiationcausesapolytetra uoroethylene(PTFE)surfacetobecoveredwithalargenumberofsmallprotrusionsperpendiculartothesurface.Theprotrusionshaveaverylargeaspectratio(theaveragediameterofthetopis100nmandtheheightis70μm),andtheshapeswereproducedonlybyirradiation.Inthisstudy,weinvestigatedanunknownmechanismthatproducesPTFEsurfacechanges,inducedbyN+ion-beamirradiation.ThePTFEsurfaceswereirradiatedwithN+ion uencesandwereobservedbyscanningelectronmicroscopy(SEM).In-situobservationswerealsoperformedusingafocusedionbeam,equippedwithascanningionmicroscope(FIB/SIM),toinvestigatethemechanismofmorphologicalchanges.Theirradiatedsurfaceswereanalyzedbyattenuatedtotalre ectance/Fouriertransforminfrared(ATR/FT-IR)spectroscopyandX-rayphotoelectronspectroscopy(XPS).Atthe uenceof1×1015ions/cm2,microporesandameltedlayer,withCfOandOHbonds,wereformedonthesurface.Themeltedlayeractedasamaskagainstirradiation.Increasingthe uence,themeltedlayergraduallydiminishedandthemicroporesenlarged.Whenthemeltedlayervanished,manyprotrusionswereproducedonthesurfaceandthefunctionalgroupscouldbeobservedatlower uences.In-situobservationsshowedstretchingandevaporationatthetopoftheprotrusions.Itwasclari edthattheprotrusionswerenotformedbydepositionofsputteredmonomersfromthesubstrate,butbystretchingofthePTFEitself.

©2009ElsevierB.V.Allrightsreserved.

Availableonline1March2009Keywords:PTFE

Ionirradiation

1.Introduction

Polytetra uoroethylene(PTFE)hasasimplelinearchainmolecularstructure.Itisknownforitsexcellentchemicalinertness,highthermalstability,lowsurfaceenergyandbiocompatibility.Itcanbestretchedrapidlytocreateastrongmicroporousmaterialknownasexpandedpolytetra uoroethylene(ePTFE).Thismaterialisalsonontoxic,leavesnoresidue,anddoesnotdegradeinvivo,becauseofitshighchemicalstability.Recently,ePTFEhasbeenwidelyusedforarti cialreplace-mentofvarioussofttissues,includingbloodvessels.Ithasbeenreportedthatwhenitssurfaceisirradiatedwithanionbeamthebiocompatibilityisenhanced[1].ThedifferencebetweenePTFEandPTFEisthesurfacemorphologyafterirradiation.TheirradiatedePTFEsurfaceismicroporous[1];ontheotherhand,themorphologyofthePTFEsurfacechangeswithincreasing uences[2–6].WhileculturingcellsontheirradiatedPTFEsurfaces,weobservedthattheproliferatedcellsspreadonthesurfaces.Thecell-adhesivestrengthcanbechangedbytreatingtheinterfacebetweenthecellsandthesubstrate.Bymodifyingthesurfacemorphology,theirradiatedPTFEcanbeused

asanewbiomaterialwithcontrolledcell-adhesionstrength.TheaimofthisworkistoinvestigatethemechanismofthechangesinthePTFEsurfaceinducedbyirradiation,throughsurfaceobservationandanalysis.ThePTFEsheetswereirradiatedwithN+withvarying uencesusingaconventionalionaccelerator.Afterirradiation,thesurfacepropertieswereanalyzedbyscanningelectronmicroscopy(SEM),attenuatedtotalre ectance/Fouriertransforminfrared(ATR/FT-IR)spectroscopyandX-rayphotoelectronspectroscopy(XPS).Thein-situobservationwasperformedusingafocusedionbeam(FIB)equippedwithascanningionmicroscope(SIM).2.Experimental

ThePTFEsheets(thickness0.5mm,Nichias)werecutinto40×40mm2squares.Theywerecleanedwithethanolanddriedatroomtemperaturebeforeirradiation.ThePTFEsampleswereirradiatedinavacuumchamberwith40keVN+ionsusinganionaccelerator(TK-100ionimplanter,RIKEN)from1×1015to1×1017ions/cm2.Thebeamcurrentdensitywasapproximately2μA/cm2.Afterionirradiations,thesurfacemorphologyofthesampleswasobservedusingSEM(JSM-6330F,JEOL).Thein-situobservationsofthesurfacemorphologyduringirradiationwereperformedbyFIB/SIM(FB2100,HITACHI)using40keVGa+ions.Abeamcurrentdensityof20μA/cm2wasselected.The

Correspondingauthor.Tel.:+81358416961;fax:+81338183455.E-mailaddress:kitamura@nuclear.jp(A.

The mechanism of protrusion formation on PTFE surface by ion-beam irradiation

Kitamura).0257-8972/$–seefrontmatter©2009ElsevierB.V.Allrightsreserved.doi:

The mechanism of protrusion formation on PTFE surface by ion-beam irradiation

10.1016/j.surfcoat.2009.02.038

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