国家发展改革委办公厅关于组织实施生物医药高技术产业化专项的通

Enhancedfieldemissionpropertiesofthin-multiwalledcarbonnanotubes:RoleofSiOxcoatingJ.S.Moon,P.S.Alegaonkar,J.H.Han,T.Y.Lee,andJ.B.Yooa
SchoolofAdvancedMaterialsScienceandEngineering,SungKyunKwanUniversity,440-746Suwon,KoreaJ.M.KimSamsungSDICo.Ltd.,CorporateR&DCenter,449-577Yongin,Korea
Received31May2006;accepted30August2006;publishedonline16November2006Wereportthefabrication,characterization,andfieldemissionpropertiesof
siliconoxideSiOxcoatedthin-multiwalledcarbonnanotubes
t-MWNTs.Thecoatedt-MWNTsshowimprovedfieldemissionbehavior.Initially,rawt-MWNTs
diameter5–8nmwerefunctionalizedbyacidtreatment.UsingspinonglassasaSiprecursor,SiOxwascoatedonthenanotubesbyroutinechemicalmethods.Thecoatedsampleswerecharacterizedbyhighresolutiontransmissionelectronmicroscopy
HRTEM,Fouriertransforminfrared
FTIRspectroscopy,andthermogravimetricanalysis
TGAtechniques.TheHRTEMresultsshowthatthelocalthicknessofthecoatingvariesfrom1to2nm.TheFTIRinvestigationsshowtheformationofnanophases,suchasSi–C,Si–O–C,andintercalatedSi–O,atthecoating/nanotubeinterface.TheTGArevealsthatthecoatingpreventsthehigh-temperatureoxidationanddegradationofthenanotubes.Thefieldemissioncharacteristicsofthecoated,functionalized,andrawnanotubesshowthattheturn-onfieldsandcurrentdensityareimprovedforthecoatednanotubes.ThisimprovementwasattributedtotheloweringoftheworkfunctionanddielectricconstantoftheC/SiOxinterfacelayerandthelocalizationofthedensityofstatesclosetotheFermienergyforthecoatednanotubes.Theanalysisoftheemissionstabilityspectrashowsthatthecoatednanotubeshaveamorefavorablelifetime.Theobservedenhancementwasattributedtotheprotectionofthenanotubesfromthereactivesputteretchingduringthefieldemissionprocess.Thedetailsoftheanalysisarepresented.©2006AmericanInstituteofPhysics.DOI:10.1063/1.2384795I.INTRODUCTIONThehighaspectratio,low-thresholdfieldforemissionandhighemissioncurrentdensity1–6ofcarbonnanotubes
CNTsmakethemusefulforseveraltypesofdeviceappli-cations,suchasfieldemissiondisplays
FEDs,microwavepoweramplifiertubes,andcompactx-raysources.InspiteoftheconsiderableeffortthathassofarbeenmadetouseCNTsasfieldemitters,thepracticalapplicationofthesedevicesremainslimitedduetoissuessuchastheiremissionstabilityandcharacteristics,aswellasalackofeasymethodsofpreparingthefieldemittersamples.Itisobservedthat,dur-ingthefieldemissionprocess,theemittedelectronsionizetheresidualgasspeciestoformmetastableionsinthevacuumchamber.TheseionsinteractwiththeCNTsthroughcollisionsandbombardments,whichleadtoseveraleffects,suchastheheightdegradationoftheCNTsandthepeelingoffoftheCNTsfromthesubstrate.Asaresult,thefieldemissioncharacteristicsandemissionstabilityofthesamplescouldbeaffected.7,8IthasbeensuggestedthatoxidecoatingssuchasSiO2orMgOontheCNTscouldovercomethisproblem.9Suchcoatingssignificantlyreducetheemissioninstabilitiesbyprotectingthecarbonnanotubesfromthere-activesputteretchingduringthefieldemissionprocess.Inaddition,SiO2andMgOarewidebandgapoxidematerials.Consequently,theircoatingonthenanotubescoulddecreasetheeffectiveworkfunction,
o,oftheCNTemittersandsubstantiallyenhancetheiremissionproperties.10Ingeneral,twoapproachescanbeadoptedtocoatoxidemateriallayersonCNTs;vaporphasedepositiontechniques10androutinechemicalsynthesis.11,12Althoughthesetechniquesbothhavetheirownmeritsanddemerits,ithasbeendemonstratedthat13,14thechemicalsynthesisrouteisasimple,convenient,andwellsuitedtechniqueforthefabricationofrobustCNT-reinforcedcompositeswiththinlayercoatings.However,thedetailedcharacterizationandfieldemissionanalysisofthinSiOxcoatedthin-multiwalledcarbonnanotubes
t-MWNTspreparedbythechemicalsynthetismethodhavenotyetbeenreportedintheliterature,andthisprovidesthemotivationforthisstudy.Thepresentworkdescribesthesynthesis,characteriza-tion,andfieldemissionpropertiesofSiOxcoatedt-MWNTs.AroutinechemicalmethodisadoptedforcoatingSiOxontothet-MWNTs,andthesamplesarecharacterizedusingthehighresolutiontransmissionelectronmicroscopy
HRTEM,Fouriertransforminfrared
FTIR,andthermogravimetricanalysis
TGAtechniques.ThefieldemissionpropertiesofthethinSiOxcoatedt-MWNTsarecomparedwiththoseoftherawandfunctionalizedt-MWNTs.Theanalysisrevealsthattheturn-onfields,currentdensities,andcurrentstabili-tiesareimprovedforthecoatednanotubes.aElectronicmails:[e-mail]@yurim.skku.ac.krJOURNALOFAPPLIEDPHYSICS100,104303
20060021-8979/2006/10010
/104303/7/$23.00©2006AmericanInstituteofPhysics100,104303-1Downloaded29Jun2010to221.224.90.35.RedistributionsubjecttoAIPlicenseorcopyright;see5to8nmandtheirlengthwas75–80m.Thet-MWNTs/SiOxcom-positewasfabricatedasfollows:initially,acidtreatmentofthet-MWNTswascarriedoutinamixtureofconcentratedsulfuricandnitricacids
95%H2SO4:65%HNO3=3:1vol-umeratiotoinducetheformationofvariousfunctionalgroupssuchas–COOH,–OH,vCO,andC–Oonthesidewalls15ofthenanotubes.Theacidtreatmentwascarriedoutundermildultrason