纳米材料在生物医学中的应用

132Chem.Rev.2010,110,132–145

HoneycombCarbon:AReviewofGraphene

MatthewJ.Allen, VincentC.Tung, andRichardB.Kaner*, ,

DepartmentofChemistryandBiochemistryandCaliforniaNanoSystemsInstitute,andDepartmentofMaterialsScienceandEngineering,University

ofCalifornia,LosAngeles,LosAngeles,California90095

ReceivedFebruary20,2009

Contents

1.Introduction

2.BriefHistoryofGraphene2.1.ChemistryofGraphite3.DowntoSingleLayers

3.1.CharacterizingGrapheneFlakes3.1.1.ScanningProbeMicroscopy3.1.2.RamanSpectroscopy

4.ExtraordinaryDeviceswithPeeledGraphene4.1.High-SpeedElectronics4.2.SingleMoleculeDetection

5.AlternativestoMechanicalExfoliation

5.1.ChemicallyDerivedGraphenefromGraphite

Oxide

5.1.1.Depositions

5.1.2.DefectDensityinChemicallyDerived

Graphene

5.1.3.Field-EffectDevices5.1.4.PracticalSensors

5.1.5.TransparentElectrodes5.2.TotalOrganicSynthesis

5.3.EpitaxialGrapheneandChemicalVapor

Deposition

6.GrapheneNanoribbons7.FutureWork8.Conclusions

9.Acknowledgments10.References

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1.Introduction

Grapheneisthenamegiventoatwo-dimensionalsheetofsp2-hybridizedcarbon.Itsextendedhoneycombnetworkisthebasicbuildingblockofotherimportantallotropes;itcanbestackedtoform3Dgraphite,rolledtoform1Dnanotubes,andwrappedtoform0Dfullerenes.Long-rangeπ-conjugationingrapheneyieldsextraordinarythermal,mechanical,andelectricalproperties,whichhavelongbeentheinterestofmanytheoreticalstudiesandmorerecentlybecameanexcitingareaforexperimentalists.

Whilestudiesofgraphitehaveincludedthoseutilizingfewerandfewerlayersforsometime,1the eldwasdeliveredajoltin2004,whenGeimandco-workersatManchesterUniversity rstisolatedsingle-layersamplesfromgraphite(seeFigure1).2Thisledtoanexplosionofinterest,inpart

DepartmentofChemistryandBiochemistryandCaliforniaNanoSystemsInstitute.

DepartmentofMaterialsScienceandEngineeringandCaliforniaNano-SystemsInstitute.

becausetwo-dimensionalcrystalswerethoughttobether-modynamicallyunstableat nitetemperatures.3,4Quasi-two-dimensional lmsgrownbymolecularbeamepitaxy(MBE)arestabilizedbyasupportingsubstrate,whichoftenplaysasigni cantroleingrowthandhasanappreciablein uenceonelectricalproperties.5Incontrast,themechanicalexfo-liationtechniqueusedbytheManchestergroupisolatedthetwo-dimensionalcrystalsfromthree-dimensionalgraphite.Resultingsingle-andfew-layer akeswerepinnedtothesubstratebyonlyvanderWaalsforcesandcouldbemadefree-standingbyetchingawaythesubstrate.6-9Thismini-mizedanyinducedeffectsandallowedscientiststoprobegraphene’sintrinsicproperties.

Theexperimentalisolationofsingle-layergraphene rstandforemostyieldedaccesstoalargeamountofinterestingphysics.10,11Initialstudiesincludedobservationsofgraphene’sambipolar eldeffect,2thequantumHalleffectatroomtemperature,12-17measurementsofextremelyhighcarriermobility,7,18-20andeventhe rsteverdetectionofsinglemoleculeadsorptionevents.21,22Thesepropertiesgeneratedhugeinterestinthepossibleimplementationofgrapheneinamyriadofdevices.Theseincludefuturegenerationsofhigh-speedandradiofrequencylogicdevices,thermallyandelectricallyconductivereinforcedcomposites,sensors,andtransparentelectrodesfordisplaysandsolarcells.

Despiteintenseinterestandcontinuingexperimentalsuccessbydevicephysicists,widespreadimplementationofgraphenehasyettooccur.Thisisprimarilyduetothedif cultyofreliablyproducinghighqualitysamples,espe-ciallyinanyscalablefashion.23Thechallengeisreally2-foldbecauseperformancedependsonboththenumberoflayerspresentandtheoverallqualityofthecrystallattice.19,24-26Sofar,theoriginaltop-downapproachofmechanicalexfoliationhasproducedthehighestqualitysamples,butthemethodisneitherhighthroughputnorhigh-yield.Inordertoexfoliateasinglesheet,vanderWaalsattractionbetweenexactlythe rstandsecondlayersmustbeovercomewithoutdisturbinganysubsequentsheets.Therefore,anumberofalternativeapproachestoobtainingsinglelayershavebeenexplored,afewofwhichhaveledtopromisingproof-of-conceptdevices.

Alternativestomechanicalexfoliationincludeprimarilythreegeneralapproaches:chemicaleffortstoexfoliateandstabilizeindividualsheetsinsolution,27-32bottom-upmeth-odstogrowgraphenedirectlyfromorganicprecursors,33-36andattemptstocatalyzegrowthinsituonasubstrate.37-43Eachoftheseapproacheshasitsdrawbacks.Forchemicallyderivedgraphene,completeexfoliationinsolutionsofarrequiresextensivemodi cationofthe2Dcrystallattice,whichdegradesdeviceperformance.31,44Alternatively,bot-tom-uptechniqueshaveyettoproducelargeanduniform

10.1021/cr900070d 2010AmericanChemicalSociety

PublishedonWeb07/17/2009