Honeycomb Carbon A Review of Graphene 石墨烯综述(17)

141

Figure15.(a)SEMimageofalargesinglesheetdepositedonSiO2.(b)Schematicviewofatop-contact,back-gateddevice.(c)Photograph(left),opticalimage(middle),andSEMimage(right)ofaworkingdevicewithachannellengthof7µm.(Reprintedwithpermissionfromref101.Copyright2009NaturePublishingGroup.)

Figure16.Chemicallyderivedgrapheneprovidesapracticalroutetographene-basedresistivesensors.Theresistanceofthep-typematerialdecreasesuponexposuretoelectronwithdrawers(e.g.,NO2)andincreasesuponexposuretoelectrondonors(e.g.,NH3).(Reprintedwithpermissionfromref103.Copyright2009AmericanChemicalSociety.)

Itisinterestingtonotethedifferencesinresponseofchemicallyderivedgraphenesensorsandmechanicallyexfoliatedones.Asdiscussedearlier,electrondonatingorwithdrawinggroupsincreaseelectronorholepopulationsinpristinegrapheneandthusbothleadtoincreasedconductiv-ity.Chemicallyderivedgrapheneisnominallyp-type.Therefore,electronwithdrawinggroupscontributeadditionalcarriers,butelectrondonatorsactuallyservetodepleteholesfromthevalenceband.Hence,NO2andNH3ledtooppositedirectionsofresponseinoursensors.

solarcell,whichhadapowerconversionef ciency(PCE)of0.26%.Chhowalla’sgrouplaterfabricatedapolymersolarcellwithaPCEof0.1%usingasimilar lm.112,113TheperformanceofthesecellswaslessthanthatofthecorrespondingcontroldevicesonITO,buttheyprovideaproof-of-conceptforlow-costtransparentcoatingsbasedongraphene.

5.2.TotalOrganicSynthesis

Althoughgraphiteoxidehasproducedthe rstchemicallyderivedmicrometer-scalegraphene,synthetictechniquesforsmallerplanar,benzene-basedmacromoleculeshavebeenknownforsometime.33,34,114-117Thesegraphene-likepolya-cyclichydrocarbons(PAHs)occupyaninterestingplaceinbetween“molecular”and“macromolecular”structuresandarenowattractingnewinterestasapossiblealternativeroutetographene.

PAHsareattractivebecausetheyarehighlyversatileandcanbesubstitutedwitharangeofaliphaticchainstomodifysolubility.36Thusfar,themajordrawbackofPAHshasbeentheirlimitedsizerange.Thisisduetothefactthatincreasingmolecularweightgenerallydecreasessolubilityandincreasestheoccurrenceofsidereactions.Undertheseconditions,preservationofdispersibilityandaplanarmorphologyforlargePAHshasbeenverychallenging.

Amajoradvancecamein2008,whenMullenandco-workersreportedthesynthesisofnanoribbon-likePAHsupto12nminlength(seeFigure17).35Althoughtheelectronicpropertiesofthesenanoribbonshaveyettobecharacterized,

5.1.5.TransparentElectrodes

Solutionprocessingofchemicallyderivedgrapheneandthedepositionsachievedsoonledresearcherstoconsiderusingthematerialintransparentconductors.Thedemandforsuchcoatingshasgrownrapidlyduetooptoelectronicdevicesincludingdisplays,LEDs,andsolarcells.Whilethecurrentindustrystandardisindiumtinoxide(ITO),carbonnanotubeshavelongbeentoutedasapossiblealternativeduetotheirlowdimensionalityandabilitytoformapercolatingconductivenetworkatextremelylowdensities.Thesamemeritsmakegrapheneanobviouschoice.

Mullenandco-workersdemonstratedthe rstgraphene-basedtransparentconductor.111Filmsweredepositedbydip-coatingwithGOandreducingbythermalannealing.Sheetresistancesaslowas0.9k /)wereobtainedat70%transmittance.WhiletheperformancewasconsiderablylessthanthatofITO(70 /)at90%transmittance),the lmswerelow-costanddidnotrequirevacuumsputtering.Thegroupalsousedthe lmastheanodeinadye-sensitized

搜索“diyifanwen.net”或“第一范文网”即可找到本站免费阅读全部范文。收藏本站方便下次阅读，第一范文网，提供最新教学研究Honeycomb Carbon A Review of Graphene 石墨烯综述(17)全文阅读和word下载服务。