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Analysis

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Analysis

    Analysis

    Science

    Press

    Availableonlineat,^,,vw.sciencedirect.corn

    ccE

    @.

    Trans.NonferrousMet.Soc.China16(2006)s753s758

    Transactionsof

    NonferrousMetals

    SocietyofChina

    wwv~.CSU.edu.cn/ysxb/

    AnalysisofairadsorptiveonsolidsurfacesbyAFMandXPS WANGRong-guang,MitsuoKIDO

    FacultyofEngineering,HiroshimaInstituteofTechnology,1-2-1Miyake,Saeki

    Ku,Hiroshima731-5193,Japan

    Received10April2006;accepted25April2006 Abstract:SolidsurfacesofHOPGpurecopper,chromium,zinc,copperandSUS304steelwer

    eobservedinambientairwithana.c.

    non-contactmodeofatomicforcemicroscope(AFM).Atypeoffilmlike

    domains(adsorptive)wasdetectedontheabovesurfaces. Thethicknessoftheadsorptivewasabout1.22.4nlTIinthiscase.Thefilmlike

    adsorptivewasconfirmedtobealiquidlayerbythe staticcontact

    modescanning,themeasurementoftheelasticityandviscosityimages,andthedetectionofth

    econdensation/

    evaporationphenomenawhentherelativehumiditychanged.Theliquidlayerisconsideredto

    becondensedwatercoveredwith

organiccontaminant.

    Keywords:atomicforcemicroscope;a.c.non

    contactmode;surface;water;organiccontaminants;filmlikeadsorptive

    1Introduction

    Manyevents,suchascorrosion,photocatalytic reaction,frictionandtribology,onsolidsurfacesare largelyinfluencedbytheadsorptionofwaterandorganic contaminantsinambientairn41.Manyresearcheshave

    beencarriedouttoinvestigatetheinfluenceofair adsorptiveontheaboveevents[2——51;however,the

    morphologyoftheairadsorptivehasbeenpoorly understoodduetothelimitsofcurrentobservation techniques[6,71.Ontheotherhand,thankstotherecent applicationofana.c.non.contactmode(alsocalledas tappingmodeordynamicmode)ofanatomicforce microscope(AFM)technique,theauthorshave successfullyimagednanometer-scalemicro.water dropletsandevaluatedtheirwettabilityonvarious surfaces[8l11.Inthisobservation,difierentfromRef.[6, 7,biasvoltagewasnotappliedonthecantileverduring observation.Asatentativeresult,nanometer.scale (micro.)waterdropletsaremorestableandwettablethan millimeter-scale(macro.,waterdropletsinambientair. Thisobservationmodeisalsoexpectedtobeusefulto imagetheadsorptiveshapesonsolidsurfaces. Hereinthiswork.severalsolidsurfaceswere observedafterexposureinambientairforacertain periodbythea.c.non.contactmodeofAFMandthe surfacecompositionwasanalyzedbytheX.ray photoelectronspectroscopy(XPS).Thecharacteristic,

    compositionandstructureoftheairadsorptivestructure areaccordinglydiscussed.

    2Experimental

    Highlyorientedpyrolyticgraphite(HOPG),pure copper(purity:99.9%,massfraction),chromium (99.9%),zinc(99.7%),copper(99.7%)andSUS304 stainlesssteel(0.08%C1.0%Si,2.0%Mn,0.045%P. 0.030%S.18.0%Cr.8.0%Ni;solutiontreated)sheets wereusedasspecimens.TheHOPGwasfreshlycleaved iustbeforeobservation.Metalsurfaceswerefinelywet polishedwith150nmalumnapowder,ultrasonically cleanedinacetoneanddriedbywarmairblastbeforeuse. Thewetpolishedpurechromiumspecimenswerefurther oxidizedat523Kfor3.6ksinairwithanotherultrasonic cleaninginacetone.Allthemetalsurfaceschemistrywas analyzedwiththeX-rayphotoelectronspectroscopy (XPS,ShimadzuCo,AXISUL]rRA).

    Inadvanceofobservations.metalspecimenswere heldindesiccatorswitharelativehumidityfh.1of 25%-30%or50%-60%at(298~3)Kaftertheyare

    ultrasonicallycleanedinacetone.Afteracertainperiod, specimensweretakenoutofthedesiccatorsandtheir surfacemorphologies(topview)wereobservedin 50%-60%r.h.airat(298~3)Kusingthea.c.non.contact modeofatomicforcemicroscope(AFM,ShimadzuCo: Fonndationitem:PartofthisworkwassupportedbyMEXT.HAITEKU,2004

    ;andJSPSGrantinAidforscientificresearch(18560093) Correspondingauthor:WANGRongguang;Tel:+81829214462;Fax:+8182

    9218973;E-mail:wangrg@cc.ithiroshima.ac.jp

    s754WANGRongguang,etal/Trans.NonferrousMet.Soc.China16(2006) SFT-9800).IntheAFMapparatus,asiliconcantilever (NANOSENSORCo,NCHRW;typicalsize:T=4pm,

    C=42N/m,typicalresonancefrequency330kHz,

    radiusoftiDcurvature<10nm)wasused.The scanning/imagingratewasabout3.9nm/sinthevertical directionand2000nmfsinthelateraldirection.Inall theobservation.asshowninFig.1,theoscillation amplitudeduringthescanningwiththeinteractiveforce betweenthecantilevertipandthespecimensurface,was settobeabout2/3Ofthatbeforetheapproachofthe cantilevertiptothespecimensurface.Intheprevious report[12l,anattractiveforcebetweenthecantilevertip andmicrodropletswascalculated.Inthiswork,the interactiveforcebetweenthecantilevertipandthe specimensurfacewasabout0.13nN.Furthermore.the phaseimage,elasticityimageandviscosityimageonthe coppersurfacewererecordedbyanotheratomicforce microscope(ShimadzuCo:SPM9500J3)equippedwith

    aphaseanalysissystem.Inthissystem,therelative elasticityandviscosityvalueswereobtainedbythe phasechangeofthevibrationofthecantilever. j

    B

    j

    0

    /l

    A0

    .

    {'.

Ar

    w

    -^^,,,.,..

    295-30300-30

    Frequency,flHz

    A0

    

    n'

    scanning

    Fig.1Frequenc~outputofoscillationamplitudeonphoto detector,andoperationpomtfOP)settingsofcantileverfora.c. noncontactmodeofAFM

    3Resultsanddiscussion

    3.1Film.ilke.domainsonsolidsurface

    ThefreshlycleavedHOPGsurfacemorphologies beforeandafter1.9×10ksexposurein50%60%r.h.air

    areshowninFigs.2(a)and(b),respectively.Thesurface afterthefleshcleavage(Fig.2(a))wasflatattheatomic level[13].InallAFMtopviewimages,thehigl1 brightnessshowslargerheightvaluethere.Although almostnochangewasobservedonthesurfaceafter3.6 ksexposureintheobservationenvironmentOf 50%-60%r.h.air,manyfilmlikedomainspresentedon

    thesurfaceafter1.9×10ksexposureinthisenvironment. Thesemicrodomainscombinedwithothersbutwerenot unifornlenoughtocovertheentiresurface.Theexposed lowerareawastheHOPGsubstrate.These

    film..1ike..domainsoughttobetheadsorptiveadhered fromairduringtheexposure.Accordingtotheprofile measurement(Fig.2(d)),itisknownthatthethickness

oftheabovedomainlikelayerswasabout1.9nn1.

    Theaboveobservationonthefreshlycleaved HOPGsurfaceaimsataneasyiudgmentofwhetherwhat appearedonthesurfaceisairadsorptiveornot,because thereisnothingexceptcarbon(graphite)atomsonthe fleshandflatsurface.Suchmorphologyofairadsorptive canbeusedtocomparewithwhataDpearsonmetal surfaceinthefollowingobservation.

    Fig.3showssurfacemorphologiesofpurecopper, chromium.zincandSU$304steelafterexposurein 25%-30%r.h.airfor64.8-86ksafterthespecimens weretakenoutofacetone.Filmlikedomains,which

    werealmostsimilartothosepresentedinFig.1(b),also presentedoneachsurface.Thethicknesswasmeasured fromprofilesasabout2.2nmforpurecopper,2.4mnfor purechromium.1.9nmforpurezincand1.2nmfor SU$304stee1.Incomparisonwiththemorphologyofair adsorptiveobservedontheHOPGsurface.allthe filmlikedomainsontheabovemetalsurfacesoughtto bealsoairadsorptive,whichadheredonthesurfaceafter thespecimensweretakenoutofacetoneandexposedin ambientair

    3.2Confirmationandpropertiesoffilm.1ike. adsorptive

    Firstly,thefilm..1ike..domainspresentedonthe HOPGsurfacein50%-60%r.h.airhadalmost

    disappearedafter65ksexposurein25%-30%r.h.air,

    likeparticles(Fig.2(c)) andonlyremainedasseveraldot

    Theaverageheightandradiusofthereparticleswere about2.3nmand31.4nmrespectivelyaccordingtothe

    profilemeasurement(Fig.2(e)).Thisleadstoa conclusionthattheadsorptivecanevaDoratetoairwhen therelativehumidityoftheambientairdecreases.Itis alsoknownthattheamountofthefilm..1ike..adsorptive wouldnotchangemuchwithinshortobservationperiod (hereisabout5.4ks)in50%-60%r.h.airbyother observations.

    Thechromiumsurfaceafterexposurein50%-60% r.h.airwasscannedwiththestaticcontactmodeofthe AFM(repulsiveforce?50nN)andthenobservedwith

    

    WANGRong-guangelal:q-ransNont~zrrousMetSoc.CllinaI6(2006 24

    

    

    "r-

    3676,R

    s755

    Fig.2SurfacemorphologiesofHOPGafterlieshlycleavageimmediate1)~a),exposurein50'

    l60%JhairRlrl9x10ks(b)then

    be{"gfunherheldin25%

    30%air65ks(profileofline,il]FLgs.2(b,[d]andprofileoflineinFigs2(c),c)

    mmorphologies.fpurcc.ppePu?hromium(b)purezinc(ca1dSUS31Ms

    eelId)snsdn

    ern

    50%60%.

    airror648-86ks

    0

    _I.....r====r????—_____I?丁??____-_-_ii

    s756\~ANORonggaang,eal,~Trans.Nonferrousk,letSocChina16~2006) thcacn.n_contactm.de.Thcsurr

    cesbeforeandafterscanningWithcontinualobservation,theiramotlutkept

    thcc0ntactmodescanningareshowninFigs.4a)andchanging(Fig.4(c1).Accordingly,theadsorptieis b)movablewiththescanningofthecantilevertipandca" condenseandevaporatedynamically.

    (Fig4(a)}.Theiralnonntgraduallyincreasedwith 1158surl~eechemistry'wasagainanalyzedbyXPSafterthe nobservationThereveasa[nlostl10"1rcecomposition indicatingthatdlegradually

    :uincreaseddonlainsreally

    IJadsorptivewasfurtherconfirmedaccordingtoFig5and 817

    Fig.4Surthcemorphologiesofparechromiumafterexposure in25%30%r.h.for648ks(a).thencontactmodescanning(h1

    andthenbeingheldin50%~50%r.hforI2ksfc)

    TheIocationsofthesefilm?1ikeadsorptivechanged

    andtheiramountdecreasedafterthecontactmode

    tileXPSanalysis

    Thetopviewimage,phaseimage,elasticityimage andviscosjty1magethaiweresiIIIIlancouslvteenrded onthesameposition0tapurecopperspeclnlenafter bein1leldin50%-60%I1-airfor86ksareshown11

    Fig.6.Thehighbrightnesslnelasticityandviscosity imagesshows1jgherellstictvand1owervIseositv

    valuesAccordingtothisresaIt.weknowthatthe

c1asticityoftheadsorptivewasowerandtheirviscosity

    wasl1iuherthanthesubstrate

    ACOOrdin2to:1)thesefilm.1kc4tomains

    cadsorptive)caneasilybemovedbvthecantiIcvcroF AFMtFig.4).2,theycanbecondensedorevaporated Figs.2.4and5),3)theirelasticitywaslowerandtheir viscositywashigherthanthesubstrate(Fig.61andthe ln1.1ikeadsorptiveoneachsurceshouldbea1iquid lavercondensedioambientair.

    3.3SurfaeeAnalvsis

    AccordjngtotileXPSarialvsjs.CIs,0IsandM2p (MwasCuCr.Z11_NlorFe)electronphotopeaksae

    detectedoneachmetasurrecAsanetanip.the

    specErdorClsandOsderjvedffonlthechromium

    speclmenarcshownIFig7Bothofoxlde,,'hydroxIdeof metals.organiccarbonelenlentsanda1ittleanlountof waterWCYCdetectedoneachsurfaeeThepresence()fC Is[35%5O%l1indicatesthaiaotol'organle

    contaminantsexjstoneachsurface『】41.

    Asit1sklro~~q1.injerowalelandorganic

    contamlnantscompetitivevadsorbOilmaterialsurfaCCS namblentair.Ontheotherhand.postwetted

    microwaterdropletsOiltileabovesureewereexcluded fromthefilmlike-domains.byreferringtheprevious report[I5]Accordingly.tilehydropbobicorganicspecies 14shouldbepositionedontheadsorbedwatcrsurface Theaehematiestructureoftheapecimensurfaeeis ..

    WANGRongguangetal'TransNonferrousMetSocChinaI6(2006 Scatmingdirection

    s757

    s758WANGRongguang,etal/Trans.NonferrousMet.Soc.China16(2006) Bindingenergy,Eb/eV

    Fig.7TypicalcurveresolutionofClsandO1sphotopeakson purechromiumafterexposurein50%60%r.h.airfor64.8ks

    OrganicAbsorbed

    ;/////;jf;+;,4/.,;1d-',;;;二乏;;j

    .

    /,,,l,

    ,

    t

    /,2/,i2iti/,-i,e/t,,,,:,,

    ?j0Xide/hydr0xide

    :f'l,,c''';'-..

    ;;,,j;

    Metal

    Fig.8Schematicsurfacestructureofmetalinambientair showninFig.8,i.e.,theinterioroftheliquidlayershould beadsorbedwaterlayer,andtheouterpartofthelayer shouldbetheorganiccontaminants.

    4Conclusions

    Atypeoffilm??like??domains(adsorptive)onthe HOPG,purecopper,chromium,zinc,copperand SUS304steelsurfacesafterexposureinambientairwas observedwithana.c.non-contactmodeofAFM.The thicknessoftheadsorptivewasabout1.2-2.4aminthis

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