石墨烯光學(xué)介紹課件

OpticsonGrapheneGate-VariableOpticalTransitionsinGrapheneFengWang,YuanboZhang,ChuanshanTian,CaglarGirit,AlexZettl,MichaelCrommie,andY.RonShen,

Science320,206(2008).DirectObservationofaWidelyTunableBandgapinBilayerGrapheneYuanboZhang,Tsung-TaTang,CaglarGirit1,ZhaoHao,MichaelC.Martin,AlexZettl1,MichaelF.Crommie,Y.RonShenandFengWang

(2009)Graphene

(AMonolayerofGraphite)2DHexagonallatticeElectrically:

Highmobilityatroomtemperature, Largecurrentcarryingcapability

Mechanically:

LargeYoung’smodulus.

Thermally:

Highthermalconductance.PropertiesofGrapheneQuantumHalleffect,BarryPhaseBallistictransport,KleinparadoxOthersExoticBehaviorsQuantumHallEffectY.Zhangetal,Nature

438,201(2005)OpticalStudiesofGrapheneOpticalmicroscopycontrast;Ramanspectroscopy;Landaulevelspectroscopy.OtherPossibilitesSpectroscopicprobeofelectronicstructure.Interlayercouplingeffect.Electricalgatingeffectonopticaltransitions.

OthersCrystallineStructureofGraphiteGraphene2DHexagonallatticeBandStructureofGrapheneMonolayerP.R.Wallace,Phys.Rev.71,622-634(1947)BandStructureofMonolayerGrapherep-ElectronBandsofGrapheneMonolayerBandStructureinExtendedBZRelativisticDiracfermion.BandStructurenearKPoints~10eVVerticalopticaltransitionVanHoveSingularityKKMonolayerBilayerBandStructuresofGrapheneMonolayerandBilayernearKEFisadjustablexxExfoliatedGraphene

MonolayersandBilayersMonolayerBilayerReflectingmicroscopeimages.K.S.Novoselovetal.,Science

306,666(2004).

20mRamanSpectroscopyofGrapheneA.S.Ferrari,etal,PRL97,187401(2006)(AllowingIDofmonolayerandbilayer)ReflectionSpectroscopy

onGrapheneExperimentalArrangementDopedSiGrapheneGold290-nmSilicaOPADetInfraredReflectionSpectroscopy

toDeduceAbsorptionSpectrumDifferentialreflectionspectroscopy:DifferencebetweenbaresubstrateandgrapheneonsubstrateAB-dR/R

(RA-RB)/RAversuswRA:baresubstratereflectivityRB:substrate+graphenereflectivity20mdR/R=-Re[h(w)s(w)]h(w)fromsubstrates(w)fromgraphene:interbandtransitons freecarrierabsorptionRes(w)/w:AbsorptionspectrumSpectroscopy

onMonolayerGrapheneMonolayerSpectrumxdR/R2EFC:capacitanceExperimentalArrangementDopedSiGrapheneGold290-nmSilicaOPADetVgGateEffectonMonolayerGraphene

XXXSmalldensityofstatesclosetoDiracpointE=0CarrierinjectionbyapplyinggatevoltagecanleadtolargeFermienergyshift.EFcanbeshiftedby~0.5eVwithVg~50v;

Shiftingthresholdoftransitionsby~1eVdR/R2EFIfVg=Vg0+Vmod,thenshouldbeamaximumatVaryOpticalTransitionsbyGatingLaserbeamVarygatevoltageVg.MeasuremodulatedreflectivityduetoVmodatV(AnalogoustodI/dVmeasurementintransport)ResultsinGrapheneMonolayer=350meVThemaximumdeterminesVgforthegivenEF.MappingBandStructurenearKFordifferentw,thegatevoltageVg

determinedfrommaximum isdifferent,followingtherelation,dR/R2EFSlopeofthelineallowsdeductionofslopeofthebandstructure(Diraccone)2DPlotofMonolayerSpectrumExperimentTheoryD(dR/R)(dR/R)

60V

-(dR/R)-50VVg=0StrengthofGateModulationBilayerGraphene

(Gate-TunableBandgap)BandStructureofGrapheneBilayerForsymmetriclayers,D=0Forasymmetriclayer,D0E.McCann,V.I.Fal’ko,PRL96,086805(2006);DoublyGatedBilayerAsymmetry: DD(Db+Dt)/2

0CarrierinjectiontoshiftEF:FdD=(Db-Dt)SamplePreparationEffectiveinitialbiasduetoimpuritydopingTransportMeasurementMaximumresistanceappearsatEF=0LowestpeakresistancecorrespondstoDb=Dt=0.OpticalTransitionsinBilayerI:Directgaptransition (tunable,<250meV)II,IV:Transitionbetween conduction/valencebands (~400meV,dominatedby vanHovesingularity)III,V:Transitionbetween conductionandvalence bands(~400meV, relativelyweak)IfdEF=0,thenIIandIVdonot contributeBandstructureChangeInducedbyTransitionsII&IVinactiveTransitionIactivexxIVIIDifferentialBilayerSpectra(dD=0)

(DifferencebetweenspectraofD0andD=0)IILargerbandgapstrongertransitionI becauseothigherdensityofstatesIVChargeInjectionwithoutChangeofBandstructure(Dfixed)xdD=0dD0TransitionIVbecomesactive PeakshiftstolowerenergyasDincreases..TransitionIIIbecomesweakerand shiftstohigher energyasDincreases.IVIIIDifferenceSpectraforDifferentD

between

dD=0.15v/nmanddD=0LargerDBandgapversusDD(dR/R)(dR/R)

60V

-(dR/R)-50ViscomparabletodR/RinvalueStrengthofGateModulationSummaryGrahpeneexhibitsinterestingopticalbehaviors:.Gatebiascansignificantlymodifyopticaltransitionsoverabroad spectralrange.SinglegatebiasshiftstheFermilevelofmonolayergraphene. Spectraprovidesinformationonbandstructure,allowing deductionofVF

(slopeoftheDiracconeinthebandstructure).Double