Honeycomb Carbon A Review of Graphene 石墨烯综述(12)

adsorptionofeitherelectronwithdrawingordonatinggroupscanleadto“chemicalgating”ofthematerial,whichcanbeeasilymonitoredinaresistive-typesensorsetup.

In2007,singlemoleculesensitivitytoNObytheManchester21,22groupforthe2andNH rstgraphene-3wasdemonstratedbasedsensor(seeFigure11).Inthecaseofeitheranalyte,adsorptioneventsinducedsomepopulationoffreecarriersandtheresistivityofasinglelayer akedecreaseduponexposure.AHall-typecon gurationcon rmedtheoppositesignofcarriersgeneratedbythetwogases,withanelectron-withdrawingspecies(e.g.,NO2)inducingconductionbyholes(p-type)andanelectron-donor(e.g.,NH3)inducingconduc-tionbyelectrons(n-type).

Withsuchexcitingearlyresults,experimentswithgraphene-basedsensorshavecertainlyjustbegun.Whiletherearefewquestionsaboutthelimitsofsensitivityforthesedevices,therealdrawbackthusfarisalackofselectivity.Asensorisratherimpracticalifitrespondsinasimilarwayuponexposuretoanyanalyte.Thisisanexcellentareaofopportunityforchemists.Modi cationofthebasalplaneoritsedgescouldcertainlyincorporateanalyte-speci clock-and-keytypebindingsites.Suchanapproachwouldnotonlyprovideselectivesensitivitytoalargevarietyofchemicalspeciesbutperhapsalsoenabledetectionofbiologicalagentsaswell.Similarschemeshavebeensuccessfullydemon-stratedwithcarbonnanotubesandquantumwires.92-95

5.AlternativestoMechanicalExfoliation

Excitingprogressinthe eldofgraphene,andespeciallysosoonafteritsinitialdiscovery,begantosuggestabrightfuture.Thelimitingstepformostexperimentswassimplyobtaininggoodsinglelayersbymechanicalexfoliation.Thiswouldhavegreaterimplicationsforreal-worlddevicesbecausetheprocessislowthroughputandunlikelytobeindustriallyscalable.Withthisinmind,thechallengeof ndinganalternateroutetosingle-layergraphenebecamethefocusofagreatdealofresearch.

Oneshouldkeepinmindthreeimportantfactorsbeyondscalabilitywhenconsideringthepro ciencyofanysyntheticroutetographene.Firstandforemost,aprocessmustproducehighqualityinthe2Dcrystallatticetoensurehighmobility.Second,themethodmustprovide necontrolovercrystallite

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