纳米材料在生物医学中的应用

140ChemicalReviews,2010,Vol.110,No.1Allenet

al.

Figure13.Free-standinggraphene lmsshowextremelyhightensilestrength.(a)Cross-sectionalSEMimageofgraphiteoxidestackingina lmproducedby ltration.[ReprintedwithpermissionfromNature(),ref105.Copyright2007NaturePublishingGroup.](b)Chemicalreductionproducesa lmwithshinyluster[ReprintedwithpermissionfromScience(),ref125.Copyright2008AmericanAssociationfortheAdvancementofScience.]

Figure14.Solutionprocessingallowsdepositionofsynthesized/modi edgrapheneinavarietyofdensities.(a)SEMimagesofdifferent lmsspin-coatedfromhydrazine.(b)SEMandatomicforcemicroscopyimagesofagraphiteoxide lmdepositedbyLangmuir-Blodgettassembly.(Reprintedwithpermissionfromref107.Copyright2009AmericanChemicalSociety.)(c)Multilayercoatingsarestillquitetransparent.[ReprintedwithpermissionfromNature(),ref109.Copyright2008NaturePublishingGroup.]

deviceswerefabricatedbye-beamlithographyon akesaround1µm2insize.31Morerecently,Ruoff’sgroupandourownhaveproducedmuchlarger akes,whichenabledustodemonstratescalablearraysof eld-effectdevicesusingconventionalphotolithography(seeFigure15).96,101

Thequalityofthe2Dlatticeinchemicallyderivedgrapheneissacri cedduringoxidationasthehybridizationofmanycarbonschangesfromplanarsp2totetrahedralsp3andthesheetpuckers.Thishasseveralconsequencesindeviceperformance.Unlikethosemadefrommechanicallyderivedgraphene,weobservedp-typecurrentmodulationfortop-contactandback-gated eld-effectdevices.Weattributethistoresidualoxidation,whichprovidesdeeptrapstatesforelectronsandlimitsanygatemodulationtothatofholes.Anotherconsequenceisinhibitedmobility,whichweestimateatlessthan1000cm2/(Vs).

Whilethesepropertieshaveledsometoquestiontheappropriatenessofchemicallyderivedgraphene-basedde-

vices,thematerialhasprovidedanexcellentplatformfortestingnoveldevicestructures.Furthermore,researchershavegainedvaluableexperienceintegratingasolution-basedtechniqueintodevicefabrication.Thosemethodswillcarryovershouldaless-severeroutetocompleteexfoliationbedeveloped.

5.1.4.PracticalSensors

Whilesingle-moleculedetectionfrommechanicallyex-foliatedgraphenewasanexcitingproof-of-principle,thedif cultyofproducingthinspecimensandtherequirementofultrahighvacuumlimitsthepracticalityofthesedevices.Recently,anumberofgroups,includingRobinson’sattheNavalResearchLaboratoryandourown,havedemonstratedgoodsensitivityforNO2,NH3,anddinitrotolueneunderambientconditionsusingchemicallyderivedgraphene(seeFigure16).103,110