纳米材料和纳米结构第七讲.ppt

纳米材料和纳米结构第七讲.ppt

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第七讲,PhysicalVaporDeposition物理气相沉积,纳米材料和纳米结构,PhysicalVaporDeposition（PVD）,DefinitionFilmdepositionbycondensationfromvaporphaseThreeStepsofPVDGeneratingavaporphasebyevaporationorsublimationElectron-beamevaporationMolecular-beamepitaxyThermalevaporationSputteringCathodicarcplasmadepositionPulsedlaserdepositionTransportingthematerialfromthesourcetothesubstrateFormationoffilmbynucleationanddiffusion,ApplicationCoatingsofelectronicmaterialsInsulatorSemiconductorConductorSuperconductorNanometerscalemultilayerstructuresAdvancedelectronicdevicesAbrasionresistantcoatings,ConcernedProblemsandChallengesContaminationattheinterfacesorintermixingMulti-materialsystemsinvolvedCostofequipmentandmaintenanceComplexionofoperationSystemsDescribedinThisSectionSputteringPulsedlaserdeposition,1Sputtering（溅射）,1-1PrincipleofSputtering1-2SputteringSystem1-3PreparingMultilayerStructuresbySputtering1-4CurrentStatusofSputtering,1-1PrincipleofSputtering,EjectionofAtomsfromtheTargetEnergeticparticlesbombardingatargetsurfacewithsufficientenergy（50eV1000eV）TargetCathode,connectedtoanegativevoltagesupplyComposedofthematerialstobedepositedSubstrateAnodeMaybegrounded,floated,orbiased,GlowDischargeMediuminSputteringChamberAgasoramixtureofdifferentgases,mostcommonlyArorHeInreactivesputtering:

introducereactivegasessuchasO2orN2Pressure:

afewmTorrtoseveralhundredsmTorrProcedureGenerationofpositiveions:

ionizingthesputteringgasbyglowdischargeBombarding:

acceleratedpositiveionstostrikethetargetsurfaceandremovemainlyneutralatomsCondensation:

neutralatomsleavethetargetandcondenseonthesubstratesurface,andformintothinfilms,AnImportantConcept:

SputteringYieldAmeasurementoftheefficiencyofsputteringRatioofthenumberofemittedparticlestothenumberofbombardingones,1-2SputteringSystem,TypicalTypesofSputteringSystemsDirectcurrent（dc）diodesputteringUsedforsputteringconductingmaterialsRadiofrequency（rf）diodesputteringUsedforsputteringinsulatingmaterialsMagnetrondiodesputteringMostcommonlyusedtodayPlasmabeconfinedaroundthetargetsurfacebyamagnetfieldAdvantagesofusingmagnetronsputteringFeasibilityoflargecathodesizeHighsputteringyieldLessbombardmenttothesubstrate,用于制备TiN/VN多层膜的磁控溅射系统,氩气,流量表,流量控制阀,压力传感器,低温泵,低温泵,靶1,靶2,旋转衬底支架,衬底,流量表,阀门,流量表,流量控制阀1,流量控制阀2,主流量控制阀,质谱仪,阀门,锁定装置,Waystoreducethedamageandre-sputteringofgrowingfilmDamagecausedbynegativeioneffectandradiationenhanceddiffusionImprovementmethodUsehighgaspressure:

toreducetheenergyofthenegativeionsUseoff-axissputtering:

toavoidthesubstratedirectlyfacingthecathodeDisadvantageofoff-axissputtering:

lowdepositionratesmalldepositionareaDepositionofmagneticmaterials:

facingtargetsputteringsystems,偏轴溅射系统示意图Schematicofoff-axissputteringsystem,可360度旋转的衬底支架,陶瓷加热器,负离子撞击区,衬底,靶,溅射枪溅射源,屏蔽闸,空间屏蔽区,正面溅射系统示意图Schematicofthefacingtargetsputteringsystem,衬底,靶,磁体,冷却水,氩气,1-3PreparingMultilayerStructuresbySputtering,TypesandPropertiesofMultilayerStructuresTypesofarchitecturesMetal/metalCeramic/ceramicMetal/ceramicSemiconductor/semiconductorStructuralandphysicalpropertiesWithstructurallymodulatedarchitecturesWithcompositionallymodulatedarchitecturesHighinterfacevolumefractionLargeintrinsicstressWithstructuraland/orcompositionalgradientExhibitinguniqueandenhancedelectric,dielectric,magnetic,andmechanicproperties,BaTiO3NanolayerFerroelectricThinFilmCapacitorsAdvantage:

higherrelativedielectricconstantDisadvantage:

highleakagecurrentElectricalpropertiesstronglydependingupontheprocessingcondition,microcrystalstructure,andchoiceofbottomelectrodeAmorphous:

lowdielectricconstant（16at105V/cm）,lowleakagecurrentPolycrystalline:

highdielectricconstant（400at105V/cm）,highleakagecurrentAimofnanolayerstructureBaTiO3filmcapacitor:

highdielectricconstantandlowleakagecurrent,RealizationandeffectsSubstrate:

Ru/SiO2/SiTechnique:

rfmagnetronsputtering,sputteringinterruptionbetweenlayerstochangethesubstratetemperatures（680C,60C）Layerstructure:

n-cyclealternatelayersofamorphousandpolycrystallineBaTiO3（microcrystallinebeobtainedbyannealingamorphouslayer）ResultsobtainedLeakagecurrentdensitybeconsiderablyreduced,andtheeffectbecomingbetterwithincreasingcyclenumberDielectricconstantbetwoorthreetimeshigherthansingleamorphouslayerbutlowerthanasinglepolycrystallinelayer,具有纳米多层结构的BaTiO3薄膜电容器横截面示意图,NanolayerMoSi2/SiCSubstrate:

singlecrystalsilicon（sc-Si）Techniques:

MagnetronsputteringfordepositionofMoSi2rfsputteringfordepositionofSiCMoSi2/SiClayeredcompositesbepreparedbycyclicallypassingthesamplesbeneaththetwotargetswithaspeed（thicknessof10nm/3nm）Heattreatmentorannealing:

inducingrecrystallizationintheMoSi2/SiCmultilayeredfilmPropertiesafterannealing:

SuperioroxidationresistanceSignificanthardness,MoSi2/SiC多层膜的剖面透射电镜图片Cross-sectionalTEMimageofMoSi2/SiCmultilayeredfilm,MoSi2/SiC多层膜退火前的电子衍射花样ElectronDiffractionPatternofMoSi2/SiCmultilayeredfilmbeforeannealing,经过800C，1h退火处理的MoSi2/SiC多层膜的低放大倍数亮场电镜照片,NanolayerCu/NbSubstrate:

（100）sc-SiTechniques:

dcmagnetronsputteringLayerthickness:

（100nm/100nm）Properties:

HighstrengthSuperiorthermalconductivitySuperiorelectricalconductivity,通过磁控溅射技术沉积的Cu/Nb多层膜的剖面透射电镜图像,Cu/Nb多层膜的电子衍射花样ElectrondiffractionpatternofCu/Nbmultilayer,1-4CurrentStatusofSputtering,AdvantagesMostwidelyusedsputteringmethodWell-establishedcoatingtechniquesformicroelectronicapplicationsManynanometermultilayerstructuresbepreparedbysputteringShortcomingsMaterialssystemlimitation:

mainlyconductorsornitridesDifficultyincontrolstoichiometry,lowdepositionrateetc.Bequestionabletobeusedasthemaincoatingtoolinmicroelectronicsindustry（althoughsuccessfulforSrTiO3,BaTiO3,andBa1-xSrxO3）,2-1PrinciplesofPLD2-2DepositionofNano-ScaleMetalOxideThinFilms2-3MultilayerStructuresPreparedbyPLD2-4CurrentStatusofPLD,PulsedLaserDeposition（PLD，脉冲激光沉积）,2-1PrinciplesofPLD,AdvantagesandPropertiesofPLDSimplestdepositiontechniqueamongallthinfilmgrowthtechniquesStoichiometricremovalofconstituentspeciesfromtargetVersatiledepositionofawidevarietyofmaterialsMetalsSemiconductorsNitridesDielectricmaterialsOxidesOrganiccompounds/ploymersTernarycompounds,TechnicalDescriptionofPLDBasedonphysicalvapordepositionImpactofhigh-powershortpulsedlaserradiationonsolidtargetsRemovalofmaterialsfromimpactzoneEquipmentconstituentHighpowerlaser:

externalenergysourcetovaporizetargetmaterialsVacuumchamberwithaquartzwindowTargetholderormultipletargetholderSubstrateholder（withaheater）Integrationwithothertypeofevaporationsources,脉冲激光沉积系统（示意图）SchematicdiagramofaPLDsystem,激光束,加热器,衬底,喷流,靶,2-2DepositionofNanoscaleMetalOxideThinFilms,ImportanceMetaloxidescouldexhibitversatilepropertiesHightemperaturesuperconductivityFerroelectricityColossalmagnetoresistivityNon-linearopticalpropertiesMetaloxidesberecognizedaspossiblecandidatesfornextgenerationelectronicmaterialsduetotheirdiverseproperties,SubstratesforMetalOxideFilmsImportance:

properchoiceofsubstratebeessentialforaccomplishingperfect2-dimensionalepitaxyofmetaloxideheterostructuresRequirementsforagoodsubstrateGoodinplanelatticematchThermalexpansioncoefficientclosetothatoffilmAtomicallysmoothsurfaceGoodchemicalcompatibilitywiththefilm,CommonlyusedsinglecrystalsubstratesYttria-stabilizedzirconia（YSZ）MgOLaAlO3SrTiO3NdGaO3（LaAlO3）0.3（Sr2AlTaO6）0.7SapphireSurfacetreatmentofsubstratesIonmilling+insituannealingIonmilling+pre-depositionChemicaletching+annealingSurfaceterminating,InitialGrowthofMetalOxideFilmsObservationandmonitortechniquesInsitu:

reflectedhighenergyelectrondiffraction（RHEED）,laserlightscattering,real-timeopticaldiagnosisExsitu:

scanningtunnelingmicroscope（STM）,atomicforcemicroscopy（AFM）,cross-sectionaltransmissionelectronmicroscopy（TEM）,X-raydiffractionGrowthModeHighlydependinguponthequalityofsubstrateStranski-Krastanovmode（layerplusislandgrowth）toVolmer-Webermode（islandgrowth）atacriticalthicknessScrew-growthinthickerfilms,Layerplusislandgrowth（ThicknessCriticalThickness）,Islandgrowth（ThicknessCriticalThickness）,YBCO薄膜的早期生长模式及其转变,D.-W.Kimetal.,PhysicaC313（1999）246,CharacterizingmultilayerthicknessbyX-raydiffractionYBCO/PrBCOsuperlattice:

anewman-madeperiodicityThemodulationthicknessinsuperlatticesismeasuredbythepositionofsatellitespeaks,givenbyD=（/2）/（sinn+1-sinn）DisthemodulationthicknesswithD=dYBCO+dPrBCO;isthewavelengthofX-raysource;n+1andnarepositionsofthenthandthe（n+1）thsatellitepeaksThesatellitepeaksuptothefourthorderindicateatomicallysharpandflatinterfaces,NominalThickness2.4nm/12nm,CalculatedThickness14.6nm,C.Kwonetal.,Appl.Phys.Lett.62（2004）1289,X-ray-2scanaround（001）and（002）peaksofaYBCO/PrBCOsuperlattice,CharacteringfilmthicknessbylowangleX-raydiffractionCharacteringfilmthicknessbySTM,AFM,SEM,andTEM,C.Kwonetal.,Appl.Phys.Lett.62（2004）1289,AlowangleX-rayreflectionofanominally27.6nmthickYBCOonNdGaO3,SuperconductivityinaUnit-cellThickYBCOAimedQuestions:

Whatistheminimumunitneededfortheoccurrenceofsuperconductivity?

HowessentialistheinterlayercouplingbetweenCu-Oplanesindeterminingthetransitiontemperature?

Waytothequestion:

usingsuperlatticestructuresasmodelsystem（possiblecouplingorotherparameterscanbechangedartificiallybyinterposingothermaterialsinbetweentheCu-Oplanesorunit-cells）SystemComposing:

UltrathinYBCOlayers+nonsuperco