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1、核壳结构纳米材料入门 1Nano-Chemistry,LZU,xxLecture9:g Semiconductingnanoparticles (3)core-shell nanostructuresNano-Chemistry,LZU,xxTodaySemiconductor-SemiconductorSemiconductor-MetalMetal-Polymer Metal-MetalMetal-SemiconductorNano-Chemistry,LZU,xx1.21Energy Banddiagram ofdifferent materialsFreeelectronsE FE0V
2、acuum levelFermilevel(Valence band)(conduction band)(band gap)E0E FMetalSemiconductorNano-Chemistry,LZU,xxSemiconductor Quantum WellNano-Chemistry,LZU,xxWhat are2D,1D,0D nanosturectures?Nano-crystallite ofsemiconductor materialthat confinescarriers(electrons andholes)in all three dimensionsQuantumWe
3、ll2DQuantum Wire1DQuantum Dot0DBohr nexciton radiusis thecriticaldimensionDensity ofstates(DOS)Nano-Chemistry,LZU,xxMolecule,e Nanoparticleand aBulk SemiconductorMOLECULELUMOHOMOCBVBEgBULK SOLID?E?EEnergyNANOPARTICLE2Nano-Chemistry,LZU,xxInorganic SemiconductorsTrapstates arecaused bydefects,such as
4、vacancies,local latticemismatches,dangling bonds,or adsorbatesat thesurfaceNano-Chemistry,LZU,xx2.2Semiconductor NanoparticlesQuantumdots aresemiconductors particlesthat hasallthreedimensions confinedto the1-100nm lengthscaleGroup14(old groupIV)Si,GeIII-V Materials:GaN,GaP,GaAs,InP,InAsII-VI Materia
5、ls:ZnO,ZnS,ZnSe,CdS,CdSe,CdTeColloidal CdSequantum dotsdispersed inhexaneNano-Chemistry,LZU,xx3.Core-shell nanoparticlesNanoparticle Engineeringand SurfaceModification coreshellNano-Chemistry,LZU,xxWhy Core-Shell?Tuning ofPhysical PropertiesChemicaland ColloidalStability?Nanoparticle degradationthro
6、ugh chemicaletching?Agglomeration causedby strongvan derWaals attractiveforces?Collective properties of nanoparticleassemblies are influenced to a largeextent bythe separationbetween theparticles.?Coating theparticles witha uniformshell ofinert materialcould controlthe distancebetween theparticlesCo
7、ntrol ofe InterparticleInteractions WithinAssembliesFor example,the opticalpropertiesofmetal nanoparticlesareinfluencedby theirenvironments.Controlled surfacemodification canalter thesepropertiesNano-Chemistry,LZU,xxTypes of Core-Shell Nanoparticles?Semiconductor-Semiconductor?Semiconductor-Metal?Me
8、tal-Polymer?Metal-Metal?Metal-SemiconductorNano-Chemistry,LZU,xx3.1Semiconductor-Semiconductor core-shell structures3Nano-Chemistry,LZU,xxEnergies ofVarious Semiconductors1.4GaAs2.25GaP1.7CdSe2.5CdS3.2ZnO3.2WO33.2TiO23.0TiO2Energy(eV)Values atpH=1Nano-Chemistry,LZU,xxSemiconductor onSemiconductorTai
9、loring opticalpropertiesEnhancing theluminescence of the coreCoreShellcoreshell coreshellEnergyNano-Chemistry,LZU,xxExamples forSemiconductor-Semiconductor Core-Shell NanoparticlesJ.Phys.Chem.B.1997,101,9463J.Phys.Chem.B.1998,102,1884J.Phys.Chem.1993,97,5333J.Phys.Chem.1996,100,6381J.Phys.Chem.1996,
10、100,8927J.Phys.Chem.1996,100,13226J.Phys.Chem.1996,100,xx1Examples include:ZnS onCdSeCdS onCdSeCdSe onCdS,etcNano-Chemistry,LZU,xx3.1.1CdSe Coatedwith ZnSNanoparticlesMe2Cd+TOPSe CdSe?T300o C(TMS)2/Me2Zn/TOPCdSeZnSTEM pictureof(CdSe)ZnS nanocrystalsJ.Phys.Chem.1996,100,468Nano-Chemistry,LZU,xxCdSe C
11、oatedwith ZnSNanoparticlesJ.Phys.Chem.1996,100,468Absorption spectrumof the(CdSe)TOPO(dotted line)and the(CdSe)ZnSnanocrystals(solid line).The fluorescenceof the(CdSe)ZnS isalso shown(solid line)Normalized fluorescencespectra of CdSe-TOPO(dotted line)and CdSeZnS(solid line)with470nm excitationNano-C
12、hemistry,LZU,xxObservations onthe OpticalCharacteristics of CdSe/ZnS NanoparticlesFluorescenceof CdSe-TOPO showsthe broadtail,due tosurface traps.CdSe/ZnS fluorescencespectrum hasa flatbaseline;this indicatesthat theZnS reducesthe trapspresent onthe CdSe(TOPO)surfaceFluorescence ofCdSe(CdSe/ZnS)was
13、stablefor monthspared touncapped CdSeNoreduction in the CdSequantum yieldwas observedfor monthswith theCdSe/ZnS nanoparticlesJ.Phys.Chem.1996,100,4684Nano-Chemistry,LZU,xx(Top)Emission spectra of severalsizes ofCdSe-ZnS quantumdots,with excitationat350nm inall cases.(Bottom)Idealized mixed-surface Q
14、D-protein conjugate.Antibodies labeledwith biotin(生物素)bind efficientlyto QDsurfaces dueto thegreat strengthof theirinteraction withbridging avidin(抗生物素蛋白抗生物素蛋白)molecules Nano-Chemistry,LZU,xx3.1.2Synthesis of HgS/CdS Core-Shell NanostructuresHgS core CdSshellHgCl2+H2S+sodium polyphosphateHgSHgS+Cd(C
15、lO4)2+H2SHgS/CdSCdS coreHgS shellCd(ClO4)2+H2S+sodium polyphosphateCdSCdS+HgCl2+H2SCdS/HgSJ.Phys.Chem.1993,97,5333Note:Due tothe muchlower solubilityofHgSpared withCdSparticles resultin anexchange ofCd2+by Hg2+(CdS)n+mHgCl2(CdS)n-m(HgS)m+mCdCl2Nano-Chemistry,LZU,xxCdS/HgS MixedColloidsHgS nanopartic
16、lesHgScoated withCdSJ.Phys.Chem.1993,97,5333Nano-Chemistry,LZU,xxAbsorption Spectraof Core-Shell CdSonHgS NanoparticlesA=HgSJ.Phys.Chem.1993,97,5333More CdSNano-Chemistry,LZU,xxFluorescence SpectraofCore-Shell CdSonHgS NanoparticlesHgSnanoparticles donot fluoresceCdScoated HgSnanoparticles fluoresce:Possibly dueto removalof trapsfor nonradiativerebinationsorFluorescencecould arisefrom bandto bandrebination inHgScoreJ.Phys.Chem.1993,97,5333More CdSNano-Chemi
