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1、SynthesisofNanoparticlesNucleationandGrowthA.IntroductionTechniquesforthesynthesisofnanoparticles:top-downbottom-up.A-1.Top-downapproaches:millingorattrition,repeatedquenching,andlithography.Attrition:arelativelybroadsizedistribution,variedparticleshape,containasignigicantamountof
2、impuritiesanddefects#6#7#8Twocategories:thermodynamicequilibriumapproachandkineticapproach.Repeatedthermalcycling(material:verysmallthermalconductivitybutalargevolumechangeasafunctionoftemperature):veryfineparticlescanbeproduced,difficulttodesignandveryfinecontrolA-2.Bottom-upappr
3、oachesbyhomogeneousnucleationfromliquidorvapor,orbyheterogeneousnucleationonsubstrates.#9Thermodynamicapproach:(i)generationofsupersaturation,(ii)nucleation,and(iii)subsequentgrowth.kineticapproachlimitingtheamountofprecursorsavailableforthegrowth(e.g.,molecularbeamepitaxy,)orconf
4、iningtheprocessinalimitedspace(micellesynthesis.)#19#20Thischapterwilltakethesolutionsynthesisofnanoparticlesasanexample.Forthefabricationofnanoparticles,asmallsizeisnottheonlyrequirement.Otherimportantcharacteristics:(i)identicalsizeofallparticles,i.e.,monosizedorwithuniformsized
5、istribution;(ii)identalshapeormorphology;(iii)identicalchemicalcompositionandcrystalstructure;(iv)individuallydispersedormonodispersed,i.e.,noagglomeration(orreadilyredispersible.)Crystallinestructure:singlecrystal,polycrystallineandamorphousparticlesMorphologies:spheres,cubesandp
6、latelets.Nanoparticlesofsinglecrystalline:nanocrystalsNanoparticleswithquantumeffects:quantumdotsB.NanoparticlesthroughHomogeneousNucleationasupersaturationofgrowthspeciesmustbecreated,bye.g.,areductionintemperatureorinsituchemicalreactions.Threemediums:liquid,gasandsolidB-1.Fumda
7、mentalsofhomogeneousnucleationAsolutionwithsoluteexceedingthesolubilityorsupersaturationpossessesahighGibbsfreeenergy;theoverallenergyofthesystemwouldbereducedbysegregationsolutefromthesolutioni.e.,byformingasolidphaseandmaintaininganequilibriumconcentrationinthesolution.#2#3#10#1
8、1ThisreductionofGibbsfreeenergyis
