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Near-fieldOpticalImagingof

CarbonNanotubes

AchimHartschuh,HuihongQianTobiasGokus,DepartmentChemieundBiochemieandCeNS,UniversitätMünchenNeilAnderson,LukasNovotnyTheInstituteofOptics,UniversityofRochester,Rochester,NYNice1WhyHighSpatialResolutionNear-fieldOptics?WhyOptics?

electronicandvibronic

energiesDOS

excited

state

dynamics....Nice2WhyNear-fieldOptics?Nice3WhyNear-fieldOptics?Nice4WhyNear-fieldOptics?spatialresolutionislimitedbydiffractionl/2Nice5

DiffractionLimitAbbé,Arch.Mikrosk.Anat.9,413(1873)Uncertaintyrelation:Nice6Tip-EnhancedSpectroscopyWessel,JOSAB2,1538(1985)Nice7Tip-EnhancedSpectroscopyTheory:EnhancedelectricfieldconfinedtotipapexMechanism:Lightningrodandantennaeffect,plasmonresonanceslaserilluminatedmetaltipNovotnyetal.PRL79,645(1997)Nice8Tip-EnhancedSpectroscopySEMmicrographdiameter=22nmenhancedelectricfieldconfinedwithin20nm?……………….Opticalimagingwith20nmresolution?!……………….Signalenhancement!?Nice9ExperimentalSetupConfocalmicroscopeOpticalImagesandSpectraasharpmetaltipisheldatconstantheight(~2nm)abovethesampleusingatuning-forkfeedbackmechanismTopographyofthesample2nmK.Karraietal.,APL66,1842(1995)Tip-sampledistancecontrol+Nice10Tip-enhancedSpectroscopyS.M.Stoeckleetal.,Chem.Phys.Lett.318,131(2000)N.Hayazawaetal.,Chem.Phys.Lett.335,369(2001)A.Hartschuhetal.Phys.Rev.Lett.90,95503(2003)B.Pettingeretal.,Phys.Rev.Lett.92,96101(2004)N.Andersonetal.,J.Am.Chem.Soc.127,2533(2005)C.C.Neacsuetal.,Phys.Rev.B73,193406(2006)D.Methani,N.Lee,R.D.Hartschuhetal.J.RamanSpectrosc.36,1068(2005).................................Ramanscattering

Two-photonexcitedfluorescenceE.J.Sánchezetal.,Phys.Rev.Lett.82,4014(1999)H.G.Freyetal.,Phys.Rev.Lett.81,5030(2004)J.Farahanietal.Phys.Rev.Lett.95,017402(2005)A.Hartschuhetal.NanoLett.5,2310(2005)(Examples…………)FluorescenceNice11Single-WalledCarbonNanotubes(SWCNT)Graphenesheet+rollup

single-walledcarbonnanotubefromShigeoMaruyamalengthuptommdiameter~1-2nmmodelstructure(n,m)determinesproperties:(n-m)mod3=0metallicelsesemiconductingNice12Near-fieldRamanImagingofSWCNTsonlySWCNTdetectedinopticalimage chemicallyspecificopticalcontrastwith25nmresolutionenhancedfieldconfinedtotipHartschuhetal.PRL90,95503(2003)500nm500nmRamanimage(G’band)TopographyNice13Near-fieldRamanSpectroscopyheight:0-1.9nmRamanimage(Gband)TopographyimageRBMat199cm-1diam=1.2nmstructure(n,m)

(14,2)

metallicSWCNTGRBMNice14ResolutionenhancementFarfieldNear-fieldnotip samearea withtipNice15SignalEnhancementNice16SignalEnhancementtip-enhancedsignal>signal*2500Hartschuhetal.Phil.Trans.R.Soc.LondA,362(2004)Nice17DistanceDependencetip-enhancementisnear-fieldeffect=>tiphastobeclosetosample~d-12dEnhancedRamanscatteringsignalNice18Near-fieldRamanSpectroscopywRBM=251cm-1

(10,3)wRBM=191cm-1

(12,6)(semiconducting)(metallic)N.Anderson,unpub.RBMG30nmsteps

intramolecularjunction(IMJ)pn-junctionNice19SimultaneousRamanandPLSpectroscopyPhotoluminescenceRaman(7,5)(8,3)(9,1)RamanEmissionExcitationat633nm

EmissionandRamansignalsarespectrallyisolated(6,4)A.Hartschuhetal.Science301,1394(2003)Nice20Near-fieldopticalimagingofSWCNTsFarfieldRamanimageDNA-wrappedSWCNTsonmicaTopographyRaman(G-band)Photoluminescence

correlateRamanandphotoluminescenceproperties

lengthofemissivesegment~70nm

changesinchirality(n,m)?

couplingtosubstrate?Nice21LocalizedPL-EmisssiononGlassEmissionspatiallyconfinedtowithin10–20nm

LocalizedexcitedstatesBoundexcitons?roleofdefects?substrate?PhotoluminescenceRamanscatteringPhotoluminescenceSWCNTsonglassNice22Near-fieldPL-SpectroscopyTopographyPhotoluminescencePLspectra:30nmstepsbetweenspectra123456A.Hartschuhetal.NanoLett.5,2310(2005)

Emissionenergycanvaryonthenanoscale(causedbychangesinlocaldielectricenvironmente)Nice23

Spatial

resolution<15nm

Signalamplification

Tipasnanoscale„lightsource“

Tip-enhancedMicroscopy

Nice24SignalEnhancementEnhancementofincidentfieldandscatteredfieldSRaman~(Elocal/E0)2(Elocal/E0)2=f4RamanscatteringPhotoluminescenedissipativeenergytransfertometalquenchingofPL

knonrad:

kex:enhancedexcitationfield SPL~(Elocal/E0)2=f2Qisincreased(Q0~10-4)cyclingrateisincreased

krad:Purcell-effectkrad+knonradkradQ=kexkradknonradlocalfieldattipfieldwithouttipPLEnhancementdependsonQ0!

SPL~f2Q/Q0EinEoutNice25SignalEnhancement SPL~f2Q/Q0Ramanenhancement500nmFar-fieldRaman~2000counts/sNear-fieldRaman~4000counts/sRaman-enhancement~6000/2000

~

3SRaman~f4PLenhancement500nmNofar-fieldPL<200counts/sNear-fieldPL~17000counts/sPL-enhancement>17000/200

~85

PLquantumyieldisincreasedbytip(SEF)Nice26SignalEnhancement(Firstdata)

PLquenchingforverysmalldistances

optimumdistanceforPLenhancementdkexkradknon-radNice27SignalEnhancement(Firstdata)dkexkradknon-radP.Angeretal.Nice28SignalEnhancementTopographyRamanscatteringPhotoluminescence290nm290nm290nmtip-nanotube-distanceRamanscatteringPhotoluminescenceDNA-wrappedSWCNTs(schematic)Nice29Near-fieldInteractionsUncertaintyrelation:Diffractionlimitforpropagatingwaves:

k-vectorsoftipenhancedfieldsextend throughBZ!

selectionrulesforopticaltransitions?Highresolutionprovidedbyevanescentfieldsthathavehigherk-vectors:Nanotubes:Nice30SummaryHigh-resolutionopticalmicroscopyofcarbonnanotubesusin