纳米材料学Introduction to the Nanoworld英文课件

IntroductiontotheNanoworld,ColloidScienceHavingfunwithOpticalTweezersandDigitalVideoMicroscopy,LectureOutline,IntroductionWhatarecolloids?ColloidalMicrospheresDigitalVideoMicroscopyOpticalTweezers,Measuringtinyinteraction3-dimensionalTrackingBuildingstructureswithopticaltweezers,Whatarecolloids?,WhatisaColloid?,Acolloidisaparticleatleastonenanometerindiameterandsmallerthanonemicrometer.Thepropertiesofcolloidsdependontheirpositioninbetweenlargemoleculesandsmallsolids.Itischaracterizedbyhavingalargesurfaceareatovolumeratio.Colloidsarecomposedofsubstancessuspendedinsideofothersubstances.Examples:solid-liquid:muddywater,solid-gas:smoke.liquid-solid:creams,liquid-gas:aerosol,gas-solid:marshmallow,orgas-liquid:foams.,Examplesofastableandofanunstablecolloidaldispersion,ColloidalSystems,HumanBlood,ColloidalSystems,Milk,Otherexamplesincludecoffee,cosmetic,etc.,PS,PMMA,SiO2,Au,ShapeSpherical(silica,PMMA)Colloidalmolecules(dumbbells,beadchains)Rodlikeandflexible(TMVandfdvirus,silicarods)Platelike(clays),Colloids,Acc.Chem.Res.,35(10),847-855,2002,干酪素又称：酪蛋白,Alternative:Cryo-EM,toavoidharshstainingwhichmaychangethestructureofyoursamplestabilizationofsamplebyrapidfreezingofsampleinliquidethanetoformvitreousiceintoelectronmicroscopeatlowtemperaturestokeepsamplestableinhydratedstateinvacuumthicknessoficelayerassmallaspossible!,Advantage:samplestructureunchangedinnerstructureofmoleculeisaccessible,Sodiumdodecylsulfate(SDS),AOT(2-乙基己基)琥珀酸酯磺酸钠,Single-BandUpconversionEmissioninLanthanide-DopedKMnF3NanocrystalsAngewandteChemie123(2011)10553,980nmEX,680nmEM,ColloidalCrystals,Whatisacolloidcrystal?Acolloidisasystemofparticles1to1,000nanometersindiameterdispersedinanotherphase.Acolloidalcrystalisaperiodicarrayofcolloidalparticles.Acrystallinestructurecanbeachievedbyself-assemblyofthesphericalsolidparticlesinaliquidundercertainconditions.,Inthesamewaythatatomicormolecularcrystalscausex-raydiffraction,asyntheticcolloidalcrystaldiffractsradiationwithwavelengthcomparablewiththespheresspacing.,Forasuitablechoiceofcolloidsize,diffractionofvisiblelightoccursandthecrystalexhibitsbrightcolors.,NaturalOpals,ColloidalCrystals(NaturalOpal),NaturalOpalsconsistofsmalltiny(micron-size)silicaspherearrangedinregulararray,givingrisetotheircolorfulnature.Silicaisthesamematerialformakingglass.,ColloidalCrystals(SyntheticOpal),SyntheticOpalsaremadebypackingofmicrospheresinregulararray.Theytooareverycolorful.ThemicrospherescanbemadeofSilicaorpolystyrene.,Highlyuniformpolymericmicrospheres,DiffractionpatternfromacolloidalcrystalmadefromPMMAspheresthathavebeenindexedmatchedtothesolvent.Thisisabinarycolloidalalloycrystal,formedfromamixtureoftwodifferentsizesofparticles.Theonlyinterparticleinteractionisvolumeexclusion,andthecrystallizationispurelyentropicinorigin.ThecrystalstructureisAB13.HarvardUniversity,Prof.D.A.Weitz,PolystyreneColloid,TechnologiesforAll-OpticalNetworks,Currentdevelopmentsinopticsandphotonics:Thenumberofbitsperseconddoubleseveryninemonth.Opticsandphotonicsareatthestagethatelectronicsexpierenced30yearsagowiththedevelopmentsandintegrationofcomponentpartsintolargersystems,PhotonicCrystals,PhotonicCrystals,WavePropagationatfrequenciesbelowthebandgap,Wavepropagationatfrequenciesinthebandgap,WavePropagationatfrequenciesabovethebandgap,singlecolumnofthearray,PhotonicCrystalSimulation,ApplicationsofColloidalPhotonicCrystals,Photoniccrystalsmaywellbethecoreofanewparadigmforphotonicintegration,adisruptivetechnologythatwillactasakey-enablerfornext-gene-rationopticalnetworks.Aphotoniccrystalisastructurewheretheindexofrefractionisperiodicallymodulatedonthescaleofthewave-lengthoflight.Thismodulationcanbeattractivelyimplementedincolloidalcrystals,whichareformedwhenidenticalpolymerspheres(d1001000nm)sedimentfromasolutiontoaclose-packed,orderedarray.,Topromoteanearflawlessgrowthofthecrystal,wepatternthesubstratewiththinfilmsactingastemplates,directingthegrowthprocess.Weinvestigatethefabricationofwaveguidesincolloidalphotoniccrystals.Thesewaveguidesdonotsufferlossesattightbends,aphenomenonthatplaguesdielectricwaveguides.Weshownumericalmethodsthatprovidedetailedinsightintothepropertiesofthewaveguidesandprescriptionsformaterialproperties.,PhotonicCrystals,Aphotoniccrystalhasattractiveproperties:Photonicbandgaps:frequencybandsforwhichpropagationofEMwavesisstrictlyprohibited,Opticalfeedback,duetoreducedgroupvelocityd/dt.Capabilityofmoldingtheflowoflight.Wonderfulapplicationsforphotonicnetworks:Tunablefilters,Low-losswaveguideswithsharpbends,Integratedcompactdevices.Muchresearchefforthasbeeninvestedintotheoryandfabricationof“raw”photoniccrystals.Wearenowcontemplatingthefabricationoffunctionaldevices!,Photoniccrystalsareartificialstructuresexhibitingaperiodicmodulationoftherefractiveindexonthescaleofthewavelengthoflight.,GAP,Formedwhenmicrospheres(d1001000nm)sedimenttoformaself-assembledorderedarray.,Advantagesofcolloidalphotoniccrystals:SimplicityVersatilityDecouplingofmaterialandstructuralproperties,Filter,Dispersionofmicrospheres,Colloidalcrystal,ColloidalCrystals,Mesoscaleepitaxy!,Colloidalcrystalsareasimpleandelegantroutetohigh-qualityphotoniccrystals.,UsingPatternedSubstrates,Optimizegrowthprocess:Usepatternedsubstrate“Seed”forcolloidalgrowthPhotonicepitaxy,ElectrophoresisofspheresBettercontrolofdepositionprocessFormshigh-qualityprimarylayerForcesmonocrystallinity,Patternedsubstrate:AzobenzeneinPMMAonITO,ColloidonITOandongrating,toMakeWaveguides!,Advantages:NolossatbendsCompactphotoniccomponentsPlatformforphotonicintegration,BuriedDielectricWaveguide,Low-lossphotoniccrystalwaveguide,Alineardefect(e.g.arowofmissingspheres)willguidelightatwavelengthsinsidethegap,Guidedmodes,GAP,Colloiddepositiononsubstratewithridge,Magnetic-field-inducedFormationofPhotonicCrystalsFrommagnetitecolloidalnanoparticles,磁控制光波导？,(a):3DrepresentationofatransmissivePCwaveguidecavity.(b):Correspondingtransmissionspectrum.(c):Fielddistributionforpeaktransmission.,ApplicationsofColloidalPhotonicCrystals,低损耗、无信号延迟可传输高功率激光大角度传输流失率低光线传输,高性能反射镜光子晶体波导光子晶体微腔光子晶体光纤光子晶体超棱镜光子晶体偏振器,ColloidalSystems,ColloidalMicrospheres,Veryinterestingandusefulmodelsystemforstudyingphysicalproblems.,ColloidalMicrospheres&OpticalTweezers,Microsphere,Madeofpolystyrene(materialformakingplastic)Hasnegativechargesonitssurface(duetonegativeionsSO3-onthesurface)Diametercanbe100nmto20mmHerewetalkaboutsizerange0.3mmto2.0mm.,ColloidalSystems,TwoMicrospheresinWater,Waterconsistsofmanydifferentkindofionsthatcarrypositiveornegativecharges.Ifthemicrospheresarenegativelycharged,thennearthespheres,onewouldfindahigherconcentrationofpositivecharges.Thesepositivechargesattempttosticktothespherebuttheyarecompetingwiththethermalfluctuationenergythatwillkeepthemawayfromthespheres.Thenetresultisequilibriumdistributionofchargessurroundingthespheres.,Howdothemicrospheresinteractwitheachother?,Likechargesrepel:microspheresrepeleachother.Therepulsiveforcestrengthisreducedduetoacloudofoppositelychargedionssurroundingeachsphere.WecallthisScreenedCoulombInteraction.,InWater,MicrospheresInteraction,InWater,Hereristhecenter-to-centerseparationbetweenspheresofradiusa,-1istheDebye-Hckelscreeninglengthwhichmeasurestherangeofelectrostaticinteractionsinanelectrolyteofz-valentcounterionsatconcentrationn,andisthedielectricconstantofthewater.Eqn.(1)resemblesaYukawarepulsion,withtheterminbracketsaccountingforexclusionofcounterionsfromthespheresinteriors.,ClassicalDerjaguin-Landau-Verwey-Overbeek(DLVO)theory,德亚盖因,RandomWalk,Inwater,microsphereisinconstantlycollisionwithagitatedwatermolecule.ResultinErraticMotionAlldirectionsequallyprobableSuchmotioniscalledBrownianmotionorRandomWalk.,DigitalVideoMicroscopy,SampleCell,SampleCells,DigitalVideoMicroscopyTakelotsofvideoofthebehaviorofthecolloidalsystemandanalyzethevideoimagestolearnaboutscience.,O.Z.Lab,3-dimensionalTracking,Challenge:liketohave3Dinformation,Canwetrackthethree-dimensionalmotionofthemicrospheres?,ObjectiveLensofmicroscope,MirrorReflectionGivesHeightInformation,MirrorReflectionGivesHeightInformation,Mirror-ImageTechnique,Itisreallyamirrorreflection!,Lookingatthingsfromadifferentangle,ExperimentalData,Scalebar=5microns,3DimensionalTracking,Videoclip,SphereHeightCalibration,Calibration,3DTrack,OpticalTweezers,OpticalTweezers,Tweezers:toolforgrabbingthings.OpticalTweezers:Herewegrabthesphereusingfocusedlaserbeam(s).Allowsustomanipulatethemicrospheres,OpticalTweezers,Forcefromtheopticaltweezersdependsonafewfactors.Inparticular,themicrospheresmusthavearefractiveindexnhigherthanthatofthemedium(water).,Forceduetoopticaltweezers,Radiusofmicrospheres,Refractiveindexofmicrospheres,Refractiveindexofmedium(water),nnw.:合力总是指向焦点。,合力指向焦点:捕获,Measuringtinyinteraction,Interactionbetweentwomicrospheres,Howdowemeasurethereallytinyinteractionbetweentwomicrospheres?UseopticaltweezerstograbtwomicrospheresLetgoandfollowtheirmotion,r(t+Dt)=Separationofthespheresaftersometime(Dt),Sphere-sphereInteraction,Sphere-sphereInteraction,Snapshotsofconsecutivevideoimages:(a)Twomicrospherestrappedbyanopticaltweezers(b,c)Thespheresmoveawayfromeachotherduetotheirrepulsiveinteraction.,Sphere-sphereInteraction,Videoclip,Sphere-sphereInteraction,R(now),R(now),R(now),R(later),R(later),R(later),NoInteractionRepulsionAttraction,R(now)=R(later)line,Sphere-sphereInteraction,Everysingledotshererepresenttheresultofanalysisof1imageframe.Herewehaveabout60,000frames.,Separationofsphere“now”,Separationofsphere“later”,Sphere-sphereInteraction,Deviationfromthehorizontallineindicatearepulsiveforcebetweenthemicrospheres,Sphere-sphereInteraction,MoreSphere-sphereInteraction,Videoclip,Buildingstructureswithopticaltweezers,MultipleSpotsOpticalTweezers,UseDiffractiveOpticalElements(DOE)togeneratemultiplespots.,DOEsplitstheincidentlaserbeamintomanysmallerbeams.Wehavemultipletweezersspots.Eachspotcantrapasphere,Thesurfacestructuresareeitheretchedinfusedsilicaorotherglasstypes,orembossedinvariouspolymermaterials.,Trappinganarrayofspheres,Usingthemultiplespotsopticaltweezers,wecantrapanarrayofsphereandinvestigatethepropertiesofspheresinthiscase.,Trappinganarrayofspheres,Notethatatsomelocation(markedbycircle),eventhoughalaserspotispresent,buttherearenospheresaroundtobetrapped.,TrappingManySpheresataTime,Videoclip,Trappingandcagingmicrospheres,Herewehaveonly64laserspotsbutweareactuallytrappingmorethan64microspheresbecausesomespheresaretrappedbytheirneighborsduetotheirrepulsiveinteraction.,Trappingandcagingmicrospheres,TrappedSpheresandCagedSpheres,Videoclip,TrappedSpheresvsCagedSpheres,Trappedspheres:microspherestrappedbylaserspot.Theyareverystronglyheldandhenceshowverylittlemovement.Cagedspheres:microspheresboxed-inbyrepulsiveforcefromitsneighbor.Theyarenotasstronglyconfinedandhencetheyexplorearoundtheirarea,butdonothaveenoughenergytoescapethecageformedbythefourneighbors.,Tweezers-AssistedAssembly,MicrostructuresmadewiththehelpofOpticaltweezersasour“hands”inthesmalltinyworld.,TweezersAssistedSpheresAssembly,Videoclip,TweezersAssistedSpheresAssembly,Videoclip,MakingTemplate,Wecanusethistechniquetoengineerarrayofspheresastemplateforgrowingdifferenttypeofcrystalstructure.Wecanalsousethistechniquetoengineerstructureswithinterestingopticalproperties.,Spotweldingusinglasers,Onelaser(redone)wasusedtoholdontoamicrosphe