Fundamentals+of+Nanomaterials(纳米材料基础)

FundamentalsofNanomaterials1.Introductiontonanoscalematerials•Fourkeywords:–Macroscopic,mesoscopic,microscopic,nanoMacroscopic:hasminimumlimit(threshold),notoplimit,suchasthenormalvisiblematter.Mesoscopic:aintermediatelengthscaleMicroscopic:hasupperlimit,nominimumlimit,suchasatom,molecule,nucleusNano:anewmetrology,1n=10-9.NanoasnextsemanticrevolutionwaveNano:servingsocietyneedsNanoscienceandnanotechnologyXeatomsonNisurfaceFeatomsonCusurface•Nanotechnology(sometimesshortenedtonanotech)isthestudyofmanipulatingmatteronanatomicandmolecularscale.Generally,nanotechnologydealswithdevelopingmaterials,devices,orotherstructurespossessingatleastonedimensionsizedfrom1to100nanometres.Quantummechanicaleffectsareimportantatthisquantum-realmscale.•Hasthebuildingblockswhichhasatleastonedimensioninthenanometerscale(1-100nm);•HasthedifferentcharacteristiccomparingwiththebulkmaterialsNanomaterialsClassificationofnanoscalematerials•AccordingtothespatialdimensionZerodimension:threedimensionsareallinnanometerscaleOnedimension:twodimensionsareinnanometerscaleTwodimension:onlyonedimensionisinnanometerscale•Accordingtoquantumproperties(P3-5)–Bulkmaterial–Quantumwells–Quantumwires–Quantumdots•Accordingtotheshapeandchemicalcomposition(P3-8)–Nanostructuredmaterials–Nanostructures–NanocompositesMoore’sLaw•Moore'slawdescribesalong-termtrendinthehistoryofcomputinghardwarewherebythenumberoftransistorsthatcanbeplacedinexpensivelyonanintegratedcircuitdoublesapproximatelyeverytwoyears.Theperiodoftenquotedas18monthsisduetoDavidHouse,anIntelexecutive,whopredictedthatperiodforadoublinginchipperformance(beingacombinationoftheeffectofmoretransistorsandthembeingfaster).Atomisticsimulationresultforformationofinversionchannel(electrondensity)andattainmentofthresholdvoltage(IV)inananowireMOSFET.Notethatthethresholdvoltageforthisdeviceliesaround0.45V.NanowireMOSFETslietowardstheendoftheITRSroadmapforscalingdevicesbelow10nmgatelengths.2.Nanometereffectsofnanoscalematerials•2.1SmallsizeeffectThesizeofthesuperfineparticlesisclosetosomecharacteristiclength,thepropertieswillbechangedsignificantly.•Opticalproperties:allthesuperfinemetalparticlesshowBLACK.•Thermodynamicproperties:themeltingpointofthesuperfineparticlesdecreases.••Magneticproperties:superparamagnetism•Mechanicalproperties:Ceramiccanshowgoodtenacity.•2.2QuantumsizeeffectAsthematerialisminiaturizedinnano-scale,theenergyspectrumbecomesdiscrete.Asaresult,thebandgapbecomessizedependent.Thereisasmallandfiniteseparationbetweenenergylevels.ConductorSemiconductorInsulator•2.3SurfaceeffectLargespecificsurfacearealeadtothehighsurfaceenergy.(P30.Fig.2.4)•2.4Macroscopicquantumtunneleffect–2.4.1BallistictransportBallistictransportisthetransportofelectronsinamediumwithnegligibleelectricalresistivityduetoscattering.(P31Fig.2.5)–2.4.2TunnelingTunnelingreferstophenomenaofaparticle'sabilitytopenetrateenergybarrierswithinelectronicstructures.•Anelectronwavepacketdirectedatapotentialbarrier.NotethedimspotontherightthatrepresentstunnellingelectronsQuantumtunnellingthroughabarrier.Theenergyofthetunnelledparticleisthesamebuttheamplitudeisdecreased.–2.4.3Resonancetunneling3.Propertiesofnanoscalematerials•3.1MechanicalpropertiesInallcasetheHall-Petcheffectisrelatedtothephenomenaofdislocationgenerationanddislocationmotioninmaterials.Hardnesstypicallyincreaseswithdecreasinggrainsizeasthegrainsizeisreduceddowntothenanoscaleregion.•PositiveHall-Petchslopes(K0)•NegativeHall-Petchslopes(K0)•PositiveandnegativeHall-Petchslopes–ddcK0–ddcK0•Kchangeswithddecreasing–K0,Kdecreases–K0,Kincreases•DeviationofHall-Petch(Nonlinear)dcdc•3.2ThermalpropertiesNanoparticlesexhibitenhancedspecificheatascomparedtothebulkmaterial.Nanoparticleshavehighercoefficientofthermalexpansioncomparingwithbulkmaterial.NanoparticlesofAl2O380nm105nm5um•3.3MagneticpropertiesFerromagnetismParamagnetismDiamagnetismSuperparamagnetismHysteresisloopofferromagneticmaterialM:magnetization(intensity)H:magneticfieldintensityB:magneticinduction(intensity)Mr:RemanenceHCM:CoerciveforceHystersisloopofthemagnetitenanoparticleswithsuperparamagnetismMagneticdomaindecribesaregionwithinamagneticmaterialwhichhasuniformmagnetization.Thismeansthattheindividualmagneticmomentsoftheatomsarealignedwithoneanotherandtheypointinthesamedirection.Theregionsseparatingmagneticdomainsarecalleddomainwalls,wherethemagnetisationrotatescoherentlyfromthedirectioninonedomaintothatinthenextdomain.RotationoforientationandincreaseinsizeofmagneticdomainsduetoanexternallyappliedfieldDomainstructureofashape-memoryalloyDomainstructureofaexamplarymagneticbubbledomainDomainstructureofaexamplarymeanderdomainMagnetoopticalimagesofdomainstructuresWhenheatedaboveacertaintemperature,apieceofferromagneticmaterialundergoesaphasetransition,andtheuniformmagnetizationwithinadomainspontaneouslydisappears:eachatomhasitsowndirectionofmagneticmoment,independentfromitsneighbouringatoms(typicaloftheparamagneticstate).Curietemperature:thetransformationtemperature(criticaltemperature)offerromagnetandparamagneticsubs