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1、APPLIEDPHYSICSLETTERSVOLUME83,NUMBER54AUGUST2003Directobservationofconfinedstatesinmetallicsingle-walledcarbonnanotubesa)TheophilosMaltezopoulos,Andre´Kubetzka,MarkusMorgenstern,andRolandWiesendangerInstituteofAppliedPhysics,UniversityofHamburg,Jungiusstr.11,D-20355Hamburg,GermanySergeG.LemayandCeesD
2、ekkerDepartmentofNanoscienceandDIMES,DelftUniversityofTechnology,Lorentzweg1,2628CJDelft,TheNetherlands~Received3April2003;accepted4June2003!Weinvestigatedthelocaldensityofstates~LDOS!ofextendedindividualmetallicsingle-walledcarbonnanotubesusinglow-temperaturescanningtunnelingspectroscopy.Weobserved
3、thattheLDOSoscillateswithenergyclosetotheFermilevel.Theoscillationperiodofabout50meVvarieswithpositiononthenanotube.MapsoftheLDOSrevealthatthepeaksintheoscillationarerelatedtocon®nedstates.ThewidthsofthepeaksincreasewithincreasingdistancefromtheFermilevel.©2003AmericanInstituteofPhysics.@DOI:10.1063
4、/1.1598282#Single-walledcarbonnanotubes~SWCNTs!areconsid-InordertopermitSTMandSTSonSWCNTs,wesoni-1catetherawSWCNTmaterialindichloroethaneanddepositeredpromisingcandidatesformolecularelectronics.ItisthereforehighlydesirabletounderstandtheirelectronicadropletofthesolutiononafreshlyevaporatedAu/micapro
5、pertiesindetail.Inparticular,theeffectofdefectsonsurface.ThisisacommontechniqueforpreparingSWCNTs13transportpropertiesmustbeunderstoodandiscurrentlyun-onAu.Aftercheckingthesurfacecontaminationwithderdebate.EarlyexperimentsgenerallyassumedballisticAFM,thesamplewastransferredintotheSTM.transportinSWCN
6、Ts.Indeed,themeanfreepathinindi-Althoughthesamplepreparationisdoneinair,veryre-vidualaswellasinropesofmetallicSWCNTsappearedtoproducibleSTMimagesrevealingatomicresolutionareob-berestrictedbythecontacts.2±4Laterexperiments,however,tained.TheinsetofFig.1showsanexample.Usingatech-foundevidencefordefect
7、sinsemiconductingSWCNTsbyniquedescribedinRef.14,werelatethisSWCNTtoausinganatomicforcemicroscope~AFM!tiptolocally~15,6!-typewithachiralangleof13.9°.Accordingto(nchangethetransportpropertiesofthetube.5
