Nanomaterials-and-nanotechnology(6)-1

6.Nanomaterialsandnanotechnology材料学院张英强NanoscienceandnanotechnologyprimarilydealwithNanoscienceandnanotechnologycharacterizationsynthesisExplorationofnanostructuredmaterialsexploitationSizecomparisonsofnanocrystalswithbacteria,viruses,andmolecules6.1Welcometothemicroworldandnanoworld6.2What’sSoSpecialAboutNano?Usingnewscientifictools,wehavefoundthatnanosizedparticlesofagivensubstanceexhibitdifferentpropertiesthanlargerparticlesofthesamesubstanceAswestudythesematerialsatthenanoscale,weareLearningmoreaboutthenatureofmatterDevelopingnewtheoriesLearninghowtomanipulatetheirpropertiestodevelopnewproductsandtechnologiesSize-DependentPropertiesPropertiesofamaterialDescribehowthematerialactsundercertainconditionsAreoftenmeasuredbylookingatlarge(~1023)aggregationofatomsormoleculesTypesofpropertiesthatoftenchangeOptical(e.g.color,transparency)Electrical(e.g.conductivity)Physical(e.g.hardness,boilingpoint)Chemical(e.g.reactivity,reactionrates)OpticalPropertiesExample–GoldBulkgoldappearsyellowincolorNanosizedgoldappearsredincolorTheparticlesaresosmallthatelectronsarenotfreetomoveaboutasinbulkgoldBecausethismovementisrestricted,theparticlesreactdifferentlywithlight12nanometergoldparticleslookred“Bulk”goldlooksyellow“Traditional”ZnOsunscreeniswhiteZincoxidenanoparticlesNanoscaleZnOsunscreenisclearOpticalPropertiesExample–ZincOxide(ZnO)LargeZnOparticlesBlockUVlightScattervisiblelightAppearwhiteNanosizedZnOparticlesBlockUVlightSosmallcomparedtothewavelengthofvisiblelightthattheydon’tscatteritAppearclearMeaninglessPropertiesAtthenanoscale,somepropertiesdon’tmakesenseOneexampleisboilingtemperatureVaporpressurebecomeslessandlessmeaningfulwhenyouhavesmallerandsmallernumbersofparticlesWhenyouhave50moleculestherearenobubbles!WhyDoPropertiesChange?FourimportantwaysinwhichnanoscalematerialsmaydifferfrommacroscalematerialsGravitationalforcesbecomenegligibleandelectromagneticforcesbegintodominateQuantummechanicsisusedtodescribemotionandenergyinsteadofclassicalmechanicsGreatersurfacetovolumeratiosRandommolecularmotionbecomesmoreimportantDominanceofElectromagneticForcesBecausethemassofnanoscaleobjectsissosmall,gravitationalforcebecomesnegligibleGravitationalforceisafunctionofmassandisweakbetweennanosizedparticlesElectromagneticforcesarenotaffectedbymass,sotheycanbeverystrongevenwhenwehavenanosizedparticlesElectromagneticforcesbetweentwoprotonsare1036timesstrongerthangravitationalforcesQuantumMechanicalModelNeededClassicalmechanicalmodelsexplainphenomenawellatthemacroscalelevel,butoftenbreakdownatthenanoscalelevelFourphenomenathatquantummechanicalmodelscanexplain(butclassicalmechanicalmodelscannot)DiscretenessofenergyThewave-particledualityoflightandmatterQuantumtunnelingUncertaintyofmeasurementSurfacetoVolumeRatioIncreasesAssurfacetovolumeratioincreasesAgreateramountofasubstancecomesincontactwithsurroundingmaterialThisresultsinbettercatalysts,sinceagreaterproportionofthematerialisexposedforpotentialreactionRandomMolecularMotionisSignificantRandommotionatthemacroscaleSmallcomparedthesizeoftheobjectWecanbarelydetectmotionofdustparticlesonthesurfaceofwaterRandommotionatthethenanoscaleLargewhencomparedtothesizeoftheobjectThemoleculesthatmakeupthedustparticlearemovingwildlycomparedwiththesizeoftheparticleWhatDoesThisAllMean?Thefollowingfactorsarekeyforunderstandingnanoscale-relatedpropertiesDominanceofelectromagneticforcesImportanceofquantummechanicalmodelsHighersurfacetovolumeratioRandom(Brownian)motionItisimportanttounderstandthesefourfactorswhenresearchingnewmaterialsandpropertiesExamplesofnanomaterialsSize(approx.)MaterialsNanocrystalsandclusters(quantumdots)Diam.1-10nmMetals,semiconductors,magneticmaterialsOthernanoparticlesDiam.1-100nmCeramicoxidesNanowiresDiam.1-100nmMetals,semiconductors,oxides,sulfides,nitridesNanotubesDiam.1-100nmCarbon,layeredmetalchalcogenidesNanoporoussolidsPorediam.0.5-10nmZeolites,phosphatesetc.2-dimensionalarrays(ofnanoparticles)Severalnm2~μm2Metal,semiconductors,magneticmaterialsSurfacesandthinfilmsThickness1-1000nmAvarietyofmaterials3-dimensionalstructures(superlattices)SeveralnminthethreedimensionsMetal,semiconductors,magneticmaterialsSomenanomaterialsSingleWallednanotubesMulti-WallednanotubesFullereneC60QuantumdotsClassificationofNanostructuresbyDimensionalityFig.6.3.Typesofnanostructures.ExamplesofSomeNanostructuresMethodsofsynthesisandinvestigationofnanomaterialsScale(approx.)SyntheticmethodStructuraltoolTheoryandsimulation0.1～10nmCovalentsynthesisVibrationalspectroscopyNMRDiffractionmethodsElectronicstructure＜1nm～100nmTechniquesofself-assemblyScanningprobemicroscopiesMoleculardynamicsandmechanics100nm～1μmProcessing,modificationSEM,TEMCoarse-grainedmodelsetc.Thematerialsarecharacterizedbyatleastonedimensioninthenanometer(1nm10−9m)range.Nano-Materialscanbedefinedasfollows:Fromtheexamples,woknowthat:（一）Nanotechnology“Nano”–FromtheGreekwordfor“dwarf”andmeansfor10-9,oronebillionth.Inthiscaseitrefersto10-9meters,or1nanometer(nm).1nmisabout3atomslon