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1、PHYSICALREVIEWB,VOLUME64,195419StructuralandelectronicpropertiesofcarbonnanotubetapersV.Meunier,*M.BuongiornoNardelli,C.Roland,andJ.BernholcDepartmentofPhysics,NorthCarolinaStateUniversity,Raleigh,NorthCarolina27615-8202~Received11May2001;published29Oc
2、tober2001!Carbonnanotubetapersareasetofnanostructurescomprisedofstraighttubularsectionswithdecreasingdiameters,joinedtoeachotherviaconicalfunnelsandterminatedwithahemisphericalcap.Thefunnelsareformedwiththehelpoftopologicaldefects,whichminimallyinclude
3、atleastonepentagon-heptagonpair.Thestructural,electronic,andtransportpropertiesoftapersareanalyzedusingrealistictight-bindingmodels.Speci®cally,itisshownthatstraightnanotubetapersaremonochiralobjects.Amongavarietyofpossibletaperstructures,kineticsofthe
4、growthprocesssuggeststhatthemostprevalenttaperswillhaveeitherzigzagorarmchairstructures.Theirscanningtunnelingmicroscopy~STM!imageshavebeensimulatedforidenti®cationpurposes.TheSTMimagesoftapersaredominatedbyaprotrudingpentagoninherentinthetaperstructur
5、e,whichunfortunatelydoesnotallowforaneasyidenti®cationofthechiralityoftheunderlyingnanotubes.Turningtotransportproperties,itisshownthatzigzag-basedtaperswilllikelybepoorconductors,becauseofgapsinducedbythesemiconductingsegments.Armchair-basedtapers,ont
6、heotherhand,arecharacterizedbya®niteconductanceatlowbiasvoltagesandmakeattractiveprototypesfornanoscaleprobesanddevices.DOI:10.1103/PhysRevB.64.195419PACSnumber~s!:73.63.FgI.INTRODUCTIONnanotubejunctions,14,15andofcoursenanotubecapswith16differenttypes
7、ofsymmetries.Inthispaper,weexamine1Sincetheirinitialdiscoveryin1990byIijima,carbontheoreticallythestructural,electronic,andtransportproper-nanotubeshavecomeundereverincreasingscienti®cscru-tiesofananotubetaper.Ananotubetaperismadeupoftiny.Theynotonlyha
8、veoutstandingmechanicalandelectri-seriesofstraightnanotubesectionswithdecreasingdiameter,calproperties,butalsoshowconsiderabletechnologicalpo-joinedtogetherviatopologicaldefects,andeventuallytermi-2tentialas®eldemittersandelectrochemica
