材料結(jié)構(gòu)及其性能

One-DimensionalNanomaterials

——CarbonNanotubesReporter:Teammates:Wan

jun

WuYuanhe

WangBinbin

YangYongzhu11423OutlineIntroductionStructureandPropertiesPreparationApplicationsIntroductionSumioIijimaCarbonnanotubes(CNTs)wasfirstdiscoveredbyIijimain1991CNTs:rollingupathingraphenesheet.CNTsSWCNTs

MWCNTsProductionMethods1.Arc-dischargemethod2.LaserVaporization

method3.ChemicalVaporDeposition(CVD)PreparationCVDmethodshavebeensuccessfullyappliedinmakingcarbonnanotubes.Thegrowthprocesswiththismethodinvolvesheatingacatalystmaterialtohightemperaturesinatubefurnaceandflowingahydrocarbongasthroughthetubereactorforaperiodoftime.Materialsgrownoverthecatalystarecollecteduponcoolingthesystemtoroomtemperature.parameters:

hydrocarbons,

catalysts:

suchas

transition-metalnanoparticles

growthtemperature.Leftdiagram:

basegrowthmode.

Rightdiagram:tipgrowth

modeCVDgrowthmechanismProcess

:

Dissociationofhydrocarbonmoleculescatalyzedbythetransitionmetal.Dissolutionandsaturationofcarbon

atomsinthemetalnanoparticle.

Precipitationofcarbonfromthesaturatedmetalparticleleadstotheformationoftubularcarbonsolidsinsp2structure.GrowthmechanismofacarbonnanotubeatanopenendbytheabsorptionofC2dimersandC3trimers(inblack),

respectivelyTheadsorptionofaC2dimeroraC3trimer

attheactivedanglingbondedgesitewilladdonehexagontotheopenend.

Tubuleformationisfavoredoverotherformsofcarbon,becauseatube

containsnodangling

bondsandthereforeisinalowenergy

form.Schematicexperimental

setupsforothertwonanotube

growthmethodsSingle-walled

nanotubesgrownbylaser

ablationStructureandProperties

Theuniquenessofthenanotubearisesfromitsstructureandtheinherentsubtletyinthestructure,whichisthehelicityinthearrangementofthecarbonatomsinhexagonalarraysontheirsurfacehoneycomblattices.

Thehelicity(localsymmetry),alongwiththediameter(whichdeterminesthesizeoftherepeatingstructuralunit)introducessignificantchangesintheelectronicdensityofstates,andhenceprovidesauniqueelectroniccharacterforthenanotubes.CNTssuperiormechanicalpropertieslowmassdensityhighelectronmobilitylargecurrent-carryingcapabilityhighthermalconductivitylargeaspectratioWetSpinningAn

aqueoussuspensionofcarbonnanotubes,

stabilizedbyasurfactant,isinjectedintoa

flowingsolutionofpolyvinylalcoholwhich

causesthefibertocoagulate.Itisthenremoved

fromthebathandwashedtoremove

excesspolymer.OrganizationintoFibersDrySpinningDryspinningfromcarbonnanotubeforests.(a)Atypical“forest”ofmultiwall

carbonnanotubesgrownfromasubstrate.(b)Photograph

ofthespinningofacarbonnanotubefiberfromaforestofmultiwallnanotubes.(a)PictureofaSWNTsforest.(b)SEMimageoftheSWNTsforestledge.(c)HRTEMimageofSWNTs.(d)Alarge

area

TEMimage.(e)SEMimageofSWNTcylindricalpillars.OrganizationonSurfacesVacuumMicroelectronics:

Electronfieldemissionmaterialshavebeeninvestigatedextensivelyfortechnologicalapplications,suchasflatpaneldisplays,electrongunsinelectronmicroscopes,microwaveamplifiers.EnergyStorage:rechargeablelithiumbatteries,HydrogenStorage.FilledComposites:reinforcementsinhighstrength,lightweight,highperformancecomposites,suchasspacecraftandaircraftbody.NanoprobesandSensors:suchashighresolutionimaging,nano-lithography,nanoelectrodes,drugdelivery,sensorsandfieldemitters.Templates:fabricateone-dimensionalnanowires.ApplicationsCathode-RayLightingElementsDemonstrationfieldemissionlightsourceusingcarbonnanotubesasthe

cathodesLeft:Schematicofaprototypefieldemissiondisplayusingcarbonnanotubes.Right:Aprototype4.5''fieldemissiondisplayfabricatedby

SamsungusingcarbonnanotubesFlatPanelDisplay(c)Stress-strainrelationship

observedduringthetension/compressiontestingofthenanotube-epoxy

composite(thecurvethatshowslargerslope,bothonthetension

andcompressionsidesofthestress-straincurve,belongstothenanotubeepoxy

composite).Itcanbeseenthattheloadtransfertothenanotubeishigherduring

thecompressioncycle(seenfromthedeviationofthecompositecurvefromthat

ofthepureepoxy),becauseintensiontheindividuallayersofthenanotubesslide

withrespecttoeachother.Resultsfromtheopticalresponseofnanotube-dopedpolymersandtheiruseinOrganicLightEmittingDiodes(OLED).TheconstructionoftheOLEDisshownintheschematicof(top).ThebottomfigureshowsemissionfromOLEDstructures.Nanotubedopingtunestheemissioncolor.WithSWNTsinthebufferlayer,holesareblockedandrecombinationtakesplaceinthetransportlayerandtheemissioncolorisred.Withoutnanotubespresentinthebufferlayer,theemissioncolorisgreen.UseofaMWNTasanAFMtip.Atthecenterofthe

VaporGrownCarbonFiber(VGCF)isaMWNTwhichformsthetip.The

VGCFprovidesaconvenientandrobusttechniqueformountingtheMWNTprobe

foruseinasca