场发射平板显示器

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