材料结构及其性能英文版).ppt

《材料结构及其性能英文版).ppt》由会员上传分享，免费在线阅读，更多相关内容在PPT专区-天天文库。

1、One-DimensionalNanomaterials——CarbonNanotubesReporter:Teammates:WanjunWuYuanheWangBinbinYangYongzhu11423OutlineIntroductionStructureandPropertiesPreparationApplicationsIntroductionSumioIijimaCarbonnanotubes(CNTs)wasfirstdiscoveredbyIijimain1991CNTs:rollingupathingraph

2、enesheet.CNTsSWCNTsMWCNTsProductionMethods1.Arc-dischargemethod2.LaserVaporizationmethod3.ChemicalVaporDeposition(CVD)PreparationCVDmethodshavebeensuccessfullyappliedinmakingcarbonnanotubes.Thegrowthprocesswiththismethodinvolvesheatingacatalystmaterialtohightemperature

3、sinatubefurnaceandflowingahydrocarbongasthroughthetubereactorforaperiodoftime.Materialsgrownoverthecatalystarecollecteduponcoolingthesystemtoroomtemperature.parameters:hydrocarbons,catalysts:suchastransition-metalnanoparticlesgrowthtemperature.Leftdiagram:basegrowthmod

4、e.Rightdiagram:tipgrowthmodeCVDgrowthmechanismProcess:Dissociationofhydrocarbonmoleculescatalyzedbythetransitionmetal.Dissolutionandsaturationofcarbonatomsinthemetalnanoparticle.Precipitationofcarbonfromthesaturatedmetalparticleleadstotheformationoftubularcarbonsolidsi

5、nsp2structure.GrowthmechanismofacarbonnanotubeatanopenendbytheabsorptionofC2dimersandC3trimers(inblack),respectivelyTheadsorptionofaC2dimeroraC3trimerattheactivedanglingbondedgesitewilladdonehexagontotheopenend.Tubuleformationisfavoredoverotherformsofcarbon,becauseatub

6、econtainsnodanglingbondsandthereforeisinalowenergyform.SchematicexperimentalsetupsforothertwonanotubegrowthmethodsSingle-wallednanotubesgrownbylaserablationStructureandPropertiesTheuniquenessofthenanotubearisesfromitsstructureandtheinherentsubtletyinthestructure,whichi

7、sthehelicityinthearrangementofthecarbonatomsinhexagonalarraysontheirsurfacehoneycomblattices.Thehelicity(localsymmetry),alongwiththediameter(whichdeterminesthesizeoftherepeatingstructuralunit)introducessignificantchangesintheelectronicdensityofstates,andhenceprovidesau

8、niqueelectroniccharacterforthenanotubes.CNTssuperiormechanicalpropertieslowmassdensityhighelectronmobilitylargecurren