石墨烯分散液光限幅特性的温度调控.pdf 6页

'中国科技论文在线http://www.paper.edu.cnControlofOpticalLimitingPropertyofGraphene#DispersionsbyTuningSolventTemperature*5LiheYan,HuanhuanXu(ShaanxiKeyLabofInformationPhotonicTechnique,SchooloftheElectronicandInformationEngineering,Xi’anJiaotongUniversity,Xi"an710049)Abstract:Theopticallimiting(OL)propertiesofgraphenedispersionsinchlorobenzene(CB)andN-methy1-2-pyrrolidinone(NMP)werestudiedusingananosecondlaser.Bymeasuringthenonlinear10scattering(NLS)light,wedemonstratedthatNLSeffectoriginatingfromlaserinducedsolventmicro-bubblesand/ormicro-plasmasplayedanimportantroleinOLprocessofgraphenedispersions.Bychangingthesolventtemperature,theOLabilityofgraphenedispersionwasabletobecontrolled.TheinfluenceoftemperatureontheOLpropertyofthematerialswasattributedtothesurfacetensionchangeofsolvents,whichwasresponsibletotheNLSintheOLprocessofthedispersions.15Keywords:opticallimiting,graphene,nonlinearoptics0IntroductionAsarepresentativecarbonnanomaterial,graphenehasattractedsignificantresearchinterest[1-2]owingtoitsremarkablemechanical,thermal,electricalandopticalproperties,thatis,high20thermalconductivity,carriermobility,andthird-ordernonlinearpolarizability.Theemergenceof[3]graphenemotivatesthedesignandfabricationofnanoscaleoptoelectronicandphotonicdevices.Opticallimiterisaneffectiveprotectiondeviceforopticalsensorsandhumaneyesfromintenselaserbeams,whichhashugeapplicationpotentialformilitary.Anidealopticallimitershouldstronglyattenuateintense,potentiallydangerouslaserbeams,whileexhibitinghightransmittance[4-5]25forlowintensityambientlight.Alongwithopticallimiting(OL)studiesonfullerenesand[6-7]carbonnanotubes,theOLpropertiesofgraphenehavemadegreatprogressesoveradecade.TheexperimentalresultsindicatethatthegraphenedispersionsdisplayexcellentOLbehavioroverabroadwavelengthrangefromthevisibletothenear-infrared,resultingfromnonlinearscattering[8-9](NLS)bylaser-inducedmicrobubblesandmicroplamases.30ThethermallyinducedNLSisconsideredastheprinciplemechanismforOL.AccordingtotheMiescatteringtheory,theincidentbeamcannotbescatteredeffectivelybynanoparticlesalone.Theeffectivescatteringarisesfromtheformationofscatteringcentreswithsizeoftheorderofthewavelengthoftheincidentlaserbeam.Thelaser-inducedscatteringcentersarecomposedofsolventmicro-bubblesandcarbonmicro-plasmas.Theformeroriginatesfromthethermalenergy35transferfromthegraphenetothesolventandthelatterisinducedbytheionizationofgraphenebyintenselaserpulses.Becausethescatteringefficiencyislargelydependentontheformationdynamicsofthescatteringcenters,theopticallimitingperformancecanbeinfluencedbythethermodynamicpropertiesofthesolventusedtodispersethegraphene.Theheat-inducedmicrobubblesorplasmasgrowfasterinasolventwithlowersurfacetensionandboilingpoint,so40theycanreachthecriticalsizeforscatteringinashortertime;consequently,amoreeffectivelimitingcanbeachieved.Inthiswork,weinvestigatedtheOLbehaviorofsingle-layergraphenedispersionsindifferenttemperature.TheOLperformanceofthedispersionscanbeenhancedorsuppressedfreelybyadjustingthetemperature.ThedispersionsinCBhaveabetterOLperformancebecause45oflowersurfacetensionandboilingpointwhichcanaffecteffectivelythesizeofthescatteringFoundations:Ph.D.ProgramsFoundationofMinistryofEducationofChina(No.20130201120025)Briefauthorintroduction:LiheYan(1986-),Male,Doctor,associateprofessor,Femtosecondlaserandultrafastspectroscopy.E-mail:liheyan@mail.xjtu.edu.cn-1- 中国科技论文在线http://www.paper.edu.cncenters.1ExperimentaldetailsThesingle-layergraphene(thickness:~0.8nm,diameter:0.5-2μm,purity:~99%,singlelayerratio:>80%)wasobtainedfromNanjingXFNanoMaterialsTechCo.,Ltd.,(Nanjing,China).In50thiswork,highqualitygraphenedispersionsinCBandNMPwereemployedforOLstudy.The[10]preparationprocedureissimilartoourpreviouswork.Theinitialconcentrationoftwodispersionswere0.15mg/ml.Ingeneral,initialdispersionswereproducedbysonicatingfor2hinanicebath,followedbycentrifugedat5000rpmfor30mintoremoveanylargeaggregates.Thesampleswerestableagainstsedimentationandwithlitteraggregationoccurringinafewdays.The55finaldispersionswerethenconsecutivelydilutedtoproducedispersionswithalineartransmittanceabout60%.Themicrostructureofthedispersedgraphenewasobservedusingtransmissionelectronmicroscopy(TEM,JEOLJEM-2100).Figures1(a)and1(b)showthetypicalTEMimageofgraphenedispersedinCBandNMP,respectively.Ahighpercentageofthesamplesinsolventswassingle-layergrapheneonaccountoflargeflakeswithmultilayerwere60seldomobservedinourdispersions.Fig.1TEMimageofsingle-layergraphenedispersedin(a)CBand(b)NMP.Amodifiedopen-apertureZ-scanapparatus,asillustratedinFig.2,wasusedtoinvestigatetheOLpropertyofthegraphenedispersionsunderdifferenttemperature.Atemperaturecontrol65systemwasintroducedintotheZ-scansetuptotunethetemperatureinthespecialcuvettewherethedispersionsampleswereplaced.Thetotaltransmittancesthroughthesamplesasafunctionofincidentpowerdensityweremeasuredatafixedpositionandwhilethesamplesweregraduallymovedthroughthefocusofalens(alongthez-axis)atdifferenttemperature.Allexperimentswereperformedusing10nspulsesfromaQ-switchedNd:YAGlaser.Thelaserwasoperatedat70thesecondharmonicof532nm,withapulserepetitionrateof10Hz.Thebeamwasspatiallyfilteredtoremovehigher-ordermodesandtightlyfocusedusinga20cmfocallengthlens.-2- 中国科技论文在线http://www.paper.edu.cnFig.2.Schematicofthemodifiedopen-apertureZ-scan.752ResultsanddiscussionItiswellknownthatOLbehaviorofgraphenearisesmainlyfromnonlinearabsorptionand/ornonlinearscattering.Inourpreviouswork,wehaveconfirmedthedifferentmechanismsofgrapheneinvarioussurroundingenvironments.Forexample,bycollectingthescatteringlightusingaphotodiode,wedrawaconclusionthatnonlinearscatteringwasthemainmechanism80responsiblefortheobservedOLpropertiesinCBandNMP.Thermallyinducednonlinearscattering(NLS)isoriginatedfromthegenerationofsolventbubblesand/ortheionizationofnanoparticles.IntheNLSprocess,grapheneindispersionswereheatedbytheintenselightandtransferredthethermalenergytothesurroundingsolvents.Whenthetemperaturewashighenough,thesurroundingsolventswouldbeevaporated,resultingintheformationofgasbubbles,85alongwithsomegraphenenanoparticalswereionizated,whichformedthescatteringcenter.BasedontheMiescatteringtheory,theeffectivescatteringoccurswhenthescatteringcentersreachcomparablesizetothewavelengthoftheincidentlaserbeam.Inotherwords,thescatteringefficiencyislargelydependentonthescatteringcrosssection,hencethesizeofscatteringcenters.Therefore,thethermodynamicpropertiesofthesolventusedtodispersethegraphenecan90influencetheopticallimitingperformancethroughimpactontheformationdynamicsofthescatteringcenters.Intheassumptionofequilibriumcondition,therelationshipbetweenthebubblesizerandB[8-9]thetemperatureTcanbeestimatedthroughtheequation3nRT2Pr(1)2B4rB95whereisthesurfacetension,nisthenumberofmolesofgas,RistheuniversalgasconstantandPisthepressurefarfromthebubble.BysubstitutingrealisticvaluesofnandTforthebubblesingraphenedispersionsintoEq.1.,wefoundthatalowersurfacetensionresultsinalargerbubblesize,hence,producingmoreeffectivescatteringandopticallimiting.Therefore,thebetterlimitingbehavioratthesame100temperatureoftheG-CBdispersionsinourexperimentcouldbemainlyattributedtothelowersurfacetensionoftheCB(33dyn/cmsurfacetensionat25℃)solventthanthatofNMP(41dyn/cmsurfacetensionat25℃).Ontheotherhand,thesurfacetensionwillalsochangewiththeincreasingordecreasingoftemperature.Therelationshipcouldbedefinedbythefollowingequations-3- 中国科技论文在线http://www.paper.edu.cn105()TabT(2)Whereaandbisconstantforanyliquid.FromEq.2.,thesurfacetensionwouldreducegraduallywiththeincreasingoftemperature.Therefore,ahighertemperaturewillleadtoalargersizeofbubblesandscatteringcrosssection.Inaddition,thehigherfundamentaltemperaturewas,thelessertheincidentenergyneededtoinitiateabubbleandtheshortertimeneededtoestablisha110scatteringprocess,henceamoreeffectivescattering.Itisreasonablethatthenonlinearresponseofthegraphenedispersionscanbeadjustedbytuningthetemperature.Fig.3depictstheOLpropertyofCBandNMPdispersionsatdifferenttemperatures,respectively.Thelineartransmittanceissetat~75%tounity.Incomparisonwiththatatroomtemperature,theopticallimitingperformanceswereimproveddramaticallyatthehighertemperatureinbothCBandNMPdispersions.The115temperaturehaveagreaterinfluenceinlimitingbehaviorforCBdispersions.Fig.3.OLresultsfortheCBandNMPdispersionsatdifferenttemperaturesFigure4showsthevariationofthenonlineartransmittanceforgraphenedispersionsinCBandNMPatdifferenttemperature.Thedispersionswereheatedbyincreasingthetemperature120fromRT(~20°C)tohigherconstantvalues,suchas,30,40,50,or70°C.Itwasobservedthatthetransmittancereducedsignificantlywiththeincreaseoftemperatureinbothdispersions.Thehigherthetemperaturewas,thelowerthetransmittancewas.ThetransmittanceofthedispersionpreparedinCBwaslowerthanthatinNMPatthesametemperature,indicatingabetteropticallimitingbehavior.Thegraphenedispersionswerequitestableforafewhourswhenthe125temperaturewasraisedupto70°C,whichwouldbemeaningfulwhenitcomestoreal-lifeapplicationsastheperformanceofacapableopticallimiterisexpectedtoremainstablewithchangingenvironmentaltemperature.-4- 中国科技论文在线http://www.paper.edu.cn130Fig.4thenonlineartransmittanceforgraphenedispersionsinCBandNMPwithincreasingoftemperatureInordertoeliminatetheinfluenceoftemperaturechangeondispersibilityofmaterials,wemeasuredthetransmittancewiththedecreasingoftemperature.TheresultsareshowninFig.5.Itisclearlyseenthatthetransmittancetrendwerevariedreversibly.Therangeofvariationwasalmostsame.Theresultsprovedthatthetemperaturewouldnotchangethedispersibilityof135graphenedispersions.Fig.5.thenonlineartransmittanceforgraphenedispersionsinCBandNMPwithdecreasingoftemperature3ConclusionInthispaper,wehavestudiedtheOLpropertiesofgraphenedispersionsinCBandNMP140werestudiedusingananosecondlaser.BymeasuringtheNLSlight,wedemonstratedthatNLSeffectplayedanimportantroleinOLprocessofgraphenedispersions.Bychangingthesolventtemperature,theOLpropertiesofgraphenedispersionswereabletobecontrolled.TheinfluenceoftemperatureontheOLpropertyofthematerialswasattributedtothesurfacetensionchangeofsolvents,whichwasresponsibletotheNLSintheOLprocessofthedispersions.145References[1]BonaccorsoF,SunZ,HasanT,etal.Graphenephotonicsandoptoelectronics[J].NaturePhotonics,2010,4(9):611-622.[2]FrankIW,TanenbaumDM,VandZAM,etal.Mechanicalpropertiesofsuspendedgraphenesheets[J].150JournalofVacuumScience&TechnologyBMicroelectronics&NanometerStructures,2007,25(6):2558-2561.[3]BalandinAA,GhoshS,BaoW,etal.Superiorthermalconductivityofsingle-layergraphene.[J].NanoLetters,2008,8(3):902-907.[4]SmilowitzL,WangH,WudlF,etal.Enhancedopticallimitinginderivatizedfullerenes[J].Opticsletters,1996,21(13):922-924.155[5]SunYP,RiggsJE,LiuB.Opticallimitingpropertiesof60fullerenederivatives[J].Chemistryofmaterials,-5- 中国科技论文在线http://www.paper.edu.cn1997,9(5):1268-1272.[6]VivienL,LanconP,RiehlD,etal.Carbonnanotubesforopticallimiting[J].Carbon,2002,40(10):1789-1797.[7]MishraSR,RawatHS,MehendaleSC,etal.Opticallimitinginsingle-walledcarbonnanotubesuspensions[J].ChemicalPhysicsLetters,2000,317(3):510-514.160[8]WangJ,BlauWJ.Solventeffectonopticallimitingpropertiesofsingle-walledcarbonnanotubedispersions[J].TheJournalofPhysicalChemistryC,2008,112(7):2298-2303.[9]WangJ,HernandezY,LotyaM,etal.Broadbandnonlinearopticalresponseofgraphenedispersions[J].AdvancedMaterials,2009,21(23):2430-2435.[10]XiongY,YanL,SiJ,etal.Cascadedopticallimiterwithlowactivatingandhighdamagethresholdsusing165single-layergrapheneandsingle-walledcarbonnanotubes[J].JournalofAppliedPhysics,2014,115(8):083111.石墨烯分散液光限幅特性的温度调控闫理贺，许欢欢170（西安交通大学，电子与信息工程学院，陕西省信息光子技术重点实验室，西安，710049）摘要：利用纳秒激光研究了石墨烯分别在氯苯和N-甲基吡咯烷酮中分散液的光限幅性能。通过测量材料非线性透过率和非线性散射光随随入射光的变化规律，验证了非线性散射效应效应在石墨烯分散液光限幅过程中起着重要的作用。通过改变溶剂的温度控制溶剂的表面张力，可以影响分散液中的光诱导非线性散射的强度，进而控制分散液的光限幅性能。175关键词：光限幅效应；石墨烯；非线性光学中图分类号：O437-6-'