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1、ChemicalVaporDeposition化學(xué)氣相沉積納米材料和納米結(jié)構(gòu)第六講1IntroductionInchemicalvapordeposition(CVD),thevaporizedprecursorsareintroducedintoaCVDreactor,wheretheprecursormoleculesadsorbontoasubstrateheldatanelevatedtemperature.Theseadsorbedmoleculeswillbeeitherthermallydecomposedorreactedwithothergas
2、es/vaporstoformasolidfilmonthesubstrate.Suchagas-solidchemicalreactionatthesurfaceofasubstrateiscalledtheheterogeneousreaction（多相反應(yīng)）.ABriefDescriptionAprocesswithpotentiallygreatcomplexityAprocessofgreatversatilityandflexibilityMetals,semiconductorsandceramicsAmorphous,polycrystallin
3、eorsinglecrystallinePhysicalproperties,dependingupongrowthconditionsTechniqueFeaturesContentsinTheChapterPrinciplesofCVDmasstransportationreactionkineticsnucleationandgrowthCVDandmodifiedCVDsystemsExamplesinsynthesizingnanostructuredmaterials2 PrinciplesofChemicalVaporDepositionTherm
4、odynamicsisessentialtounderstandtheCVDprocessandtheunderlyingscienceforthekeyfactorsincludingvaportransport,reactionkinetics,nucleationandgrowthofdepositedmaterials.Formostofthesystems,CVDrequireshightemperatureandlowpressure.Undertheseconditions,achemicalsystemwillrapidlyfalltothemi
5、nimumGibbsfreeenergyandleadtotheformationofsolidreactionproducts.ThermodynamicsinCVDProcessMasstransportofreactantstothegrowthsurfacethroughaboundarylayerbydiffusion;Chemicalreactionsonthegrowthsurface,incorporatingthenewmaterialintothegrowthfront;Removalofthegas-phasereactionby-prod
6、uctsfromthegrowthsurface.ThreeStepsConsistingtheCVDProcess反應(yīng)物化學(xué)反應(yīng)氣態(tài)副產(chǎn)物邊界層化學(xué)氣相沉積過程的擴(kuò)散模型（1）反應(yīng)物輸運(yùn)通過邊界層；（2）表面反應(yīng)形成固態(tài)沉積物；（3）去處氣相反應(yīng)副產(chǎn)物.襯底Step1andStep3aredependent,bothofthemaffectthechemicalreactionrateandarecoupledbythestoichiometryofthereactionStep2isexceedinglycomplex,involvingsurfaceand
7、/orgaseousreaction,simultaneouschemical/physicaladsorption-desorption,andnucleationprocessBoundarylayer:aspaceabovethesubstrateresistingdiffusion,varyingwithtime,thedistanceinthehorizontalreactoretc.KeyPointsDescriptiononCVDProcessThegrowthrateisdeterminedbythesloweststepKineticcontr
8、olofCVDproce
