纳米材料在生物医学中的应用

HoneycombCarbon:AReviewofGrapheneChemicalReviews,2010,Vol.110,No.1

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Figure7.(a)STMimageofgraphiteshowingonlythethreecarbonsthateclipseaneighborinthesheetdirectlybelow.(b)Incontrast,allsixcarbonsareequivalentandthusvisibleinmechanicallyexfoliatedsingle-layergraphene.(Reprintedwithpermissionfromref79.Copyright2007PNAS.)

Figure8.Ramanspectroscopyisapowerfuldiagnostictoolforthestudyofgraphene.BoththeG(near1584cm-1)andG′(near2700cm-1)bandsundergosigni cantchangesduetothethicknessofABstacked akes,asproducedbymechanicalexfoliation.(Reprintedwithpermissionfromref80.Copyright2006AmericanPhysicalSociety.)

ofexperimentsonsingle-layergraphene.Theseledtoanumberofextraordinaryproof-of-conceptdevices.

4.1.High-SpeedElectronics

Theoreticalpredictionslongsuggestedextremelyhighcarriermobilityandanambipolar eld-effectingraphene.87,88Thismotivatedthevery rstexperimentsthatwired-upmechanicallyexfoliated akesbye-beamlithography.2,18Beyondcon rminganumberofpredictions,thosemeasure-mentsgeneratedsigni cantinterestingrapheneasapossiblematerialforthenextgenerationofsemiconductordevices.Thatattentionmayormaynotbewarranted,butmanyagreethatourabilitytosustainMoore’slawwillultimatelybecomeaquestionofcarriermobility.

Extraordinaryelectronicpropertiesingraphenearereallyduetothehighqualityofits2Dcrystallattice.9,19,89-91Thathighqualityimpliesanunusuallylowdensityofdefects,whichtypicallyserveasthescatteringcentersthatinhibitchargetransport.In2008,Kim’sgroupatColumbiamea-suredacarriermobilityinexcessof200,000cm2/(Vs)forasinglelayerofmechanicallyexfoliatedgraphene(seeFigure9).7Intheirexperiments,substrate-inducedscatteringwasminimizedbycleverlyetchingunderthechanneltoproducegraphenecompletelysuspendedbetweengoldcontacts.Atsuchhighcarriermobility,chargetransportisessentiallyballisticonthemicrometer-scaleatroomtemperature.This

Figure9.Suspendedgrapheneshowsextremelyhighmobilityduetotheminimizationofsubstrate-inducedscattering.(a)SEMimageofasuspendedsheetafteretching.(b)Field-effectmeasurementsindicatemobilitygreaterthan200,000cm2/(Vs).(Reprintedwithpermissionfromref7.Copyright2008Elsevier.)