纳米材料和纳米结构第六讲.ppt

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1、ChemicalVaporDeposition化学气相沉积纳米材料和纳米结构第六讲1IntroductionInchemicalvapordeposition(CVD),thevaporizedprecursorsareintroducedintoaCVDreactor,wheretheprecursormoleculesadsorbontoasubstrateheldatanelevatedtemperature.Theseadsorbedmoleculeswillbeeitherthermallydecomposedorreactedwithothergas

2、es/vaporstoformasolidfilmonthesubstrate.Suchagas-solidchemicalreactionatthesurfaceofasubstrateiscalledtheheterogeneousreaction（多相反应）.ABriefDescriptionAprocesswithpotentiallygreatcomplexityAprocessofgreatversatilityandflexibilityMetals,semiconductorsandceramicsAmorphous,polycrystallin

3、eorsinglecrystallinePhysicalproperties,dependingupongrowthconditionsTechniqueFeaturesContentsinTheChapterPrinciplesofCVDmasstransportationreactionkineticsnucleationandgrowthCVDandmodifiedCVDsystemsExamplesinsynthesizingnanostructuredmaterials2PrinciplesofChemicalVaporDepositionTherm

4、odynamicsisessentialtounderstandtheCVDprocessandtheunderlyingscienceforthekeyfactorsincludingvaportransport,reactionkinetics,nucleationandgrowthofdepositedmaterials.Formostofthesystems,CVDrequireshightemperatureandlowpressure.Undertheseconditions,achemicalsystemwillrapidlyfalltothemi

5、nimumGibbsfreeenergyandleadtotheformationofsolidreactionproducts.ThermodynamicsinCVDProcessMasstransportofreactantstothegrowthsurfacethroughaboundarylayerbydiffusion;Chemicalreactionsonthegrowthsurface,incorporatingthenewmaterialintothegrowthfront;Removalofthegas-phasereactionby-prod

6、uctsfromthegrowthsurface.ThreeStepsConsistingtheCVDProcess反应物化学反应气态副产物边界层化学气相沉积过程的扩散模型（1）反应物输运通过边界层；（2）表面反应形成固态沉积物；（3）去处气相反应副产物.衬底Step1andStep3aredependent,bothofthemaffectthechemicalreactionrateandarecoupledbythestoichiometryofthereactionStep2isexceedinglycomplex,involvingsurfaceand

7、/orgaseousreaction,simultaneouschemical/physicaladsorption-desorption,andnucleationprocessBoundarylayer:aspaceabovethesubstrateresistingdiffusion,varyingwithtime,thedistanceinthehorizontalreactoretc.KeyPointsDescriptiononCVDProcessThegrowthrateisdeterminedbythesloweststepKineticcontr

8、olofCVDproce