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NANOEXPRESSOpenAccessPolycationstabilizationofgraphenesuspensionsKamranulHasan1*,MatsOSandberg2,OmerNur1andMagnusWillander1AbstractGrapheneisaleadingcontenderforthenext-generationelectronicdevices.
Wereportamethodtoproducegraphenemembranesinthesolutionphaseusingpolymericimidazoliumsaltsasatransferringmedium.
Graphenemembraneswerereducedfromgrapheneoxidesbyhydrazineinthepresenceofthepolyelectrolytewhichisfoundtobeastableandhomogeneousdispersionfortheresultinggrapheneintheaqueoussolution.
Asimpledevicewithgoldcontactsonbothsideswasfabricatedinordertoobservetheelectronicproperties.
IntroductionTheuniquephysical,electronic,andopticalpropertiesofgraphenehavebeenreportedmanytimes[1-4]andpromiseawidevarietyofapplications.
Differentmeth-odshavebeenadoptedforobtaininggraphene,e.
g.
,mechanicalexfoliationofgraphite[5],epitaxialgrowth[6],andchemicalexfoliationindifferentsolutions[3,7-9].
Averypromisingrouteforthebulkproductionofthegraphenesheetscanbechemicalreductionanddispersionofgrapheneinaqueoussolutions.
Twostepsareinvolvedinmakingwaterdispersiblegra-phene:(1)firstchemicaloxidationofgraphitetohydrophi-licgraphiteoxideand(2)exfoliatingitintographeneoxide(GO)sheetsinaqueoussolution.
GOsheetsaregraphenesheetshavingoxygenfunctionalgroups.
TheseGOsheetsarepreventedfromagglomerationbyelectrostaticrepul-sionalone[10].
TheinsulatingGOcaneasilybereducedtohighlyconductinggraphenebyhydrazinereduction.
However,thereductionofGOsoonleadstoagglomera-tion,whileastabledispersioniskeytothepossibilityoflarge-scaleprocessing.
Polymericimidazoliumsaltscanbeagoodwaytoformastabledispersionofgraphene.
Organicsaltsbasedontheimidazoliummoietyareaninterestingclassofions.
Lowmolecularweightimidazo-liumsaltscanhavealowmeltingpointandarethentermedionicliquids(ILs).
Thus,ILsaremoltensaltsattheroomtemperatureandconsistofbulkyorganiccationspairedwithorganicorinorganicanions.
Imidazoliumionicliquidshavemanyadvantageousproperties,suchasnoflammability,awideelectrochemicalwindow,highthermalstability,wideliquidrange,andverysmallvaporpressure[11].
Theyarealsoknowntointeractstronglywiththebasalplaneofgraphiteandgraphene.
Polymericimidazoliumsaltswouldthereforebeinterestingtoexploreasdispersingagentsforgraphene.
ExperimentalGrapheneoxidewaspreparedbythemodifiedHummer'smethod[12,13].
Thegraphiteflakes(PN332461,4g;SigmaAldrich,Sigma-AldrichSwedenAB,)werefirstputinH2SO4(98%,12mL)andkeptat80°Cfor5h.
Theresultingsolutionwascooleddowntoroomtemperature.
Mildsonicationwasperformedinawaterbathfor2htofurtherdelaminategraphiteintoafewmicronflakes.
Soni-cationtimeandpowerareverycriticalastheydefinethesizeoftheresultinggrapheneoxidesheets.
Excessivesoni-cationleadstoextremelysmallflakes.
Then,thesolutionwasdilutedwith0.
5Ldeionized(DI)waterandleftover-night.
ThesolutionwasfilteredbyNylonMilliporefilters(Billerica,MA01821).
TheresultingpowderwasmixedwithKMnO4andH2SO4andputinacoolingbathunderconstantstirringfor1.
5h.
ThesolutionwasdilutedwithDIwater,and20mLH2O2(30%)wasaddedtoit.
Thesupernatantwascollectedafter12handdispersedindiluteHClinordertoremovethemetalionresidueandthenrecoveredbycentrifugation[12,13].
CleanGOwasagaindispersedinwatertomakeahomogeneousdispersionandwascentrifugedat8,000rpmfor40mininordertoremovethemultilayerfragments.
Weaddedapolymericimidazoliummoltensaltintotheaqueousdis-persionofGOataconcentrationof1mgmL-1andstronglyshookthesolutionforafewminutes.
Theimida-zoliumsaltusedbyuswaspolyquaternium16(PQ-16)soldunderthetradenameLuviquatExcellencebyBASF*Correspondence:kamran.
ul.
hasan@liu.
se1DepartmentofScienceandTechnology(ITN),LinkpingUniversity,CampusNorrkping,SE-60174Norrkping,SwedenFulllistofauthorinformationisavailableattheendofthearticleulHasanetal.
NanoscaleResearchLetters2011,6:493http://www.
nanoscalereslett.
com/content/6/1/4932011Hasanetal;licenseeSpringer.
ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommonsAttributionLicense(http://creativecommons.
org/licenses/by/2.
0),whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited.
(Ludwigshafen,Germany),acopolymerwith95%molarofimidazoliumchlorideand5%molarofvinylimidazole.
Useofthispolymericsaltforgraphenedispersionisnotfoundinliterature.
Then,thesolutionwasreducedbyhydrazinemonohydrateat90°Cfor1htoobtainastabledispersionofgrapheneinaqueoussolution.
ResultsanddiscussionThisaqueousPQ-graphenedispersionwasfoundtobestableevenafter2months,whereasthereducedGOwithouttheadditionofPQ-16formedagglomer-atessoonafterreductionwithhydrazine.
Thus,PQ-16isthemaincauseofastabledispersionofgra-phenemembranesinaqueoussolution.
Theunderly-ingmechanismhasbeenaffiliatedwithadsorptionofsomeofthepolycationsonthesurfaceofthegra-phenemembranesbynon-covalentπ-πinteractionsbetweentheimidazoliumringsofthesaltandgra-phene,soonafterreductionwithhydrazinemonohy-drate[14].
ThegraphenewasdepositedontoSi/SiO2(SiO2thicknessapproximately300nm)substratesbydip-coating.
SchematicofthewholeprocessisshowninFigure1.
ThesamplewasrinsedwithDIwateranddriedwithnitrogen.
Thedriedsampleswerefurthertreatedat400°Cfor2hinAr/H2tofurtherreducethegrapheneoxideandalsotosublimatethesolutionresidue.
Theopticalmicroscopeimagesweretakeninordertoidentifygra-phene[15].
Atomicforcemicroscopemeasurementswerecarriedouttoconfirmthepresenceofsingle-andfew-layergraphenebymeasuringstepheight[7].
Gra-pheneshowstypicalwrinkledstructurewhichisintrinsictographene[16]overrelativelylargesheetsizes.
Verylargegraphenemembraneswithsizesaround10*10μmwereidentified.
Thesizewasfoundtobedirectlyrelatedwithsonicationpowerandtime.
Exces-sivesonicationresultsinverysmallgraphenesheets,whereasinsufficientsonicationresultsinincompleteexfoliationofgraphiteoxide.
Wemeasuredtheheightprofilesofthegraphenemem-branesbyatomicforcemicroscopy(AFM)afterdropcastingthemonarelativelyflatSiO2/Sisubstrate.
TheaveragethicknessofaGOsheetwasapproximately1nm(Figure2),whichwasinagreementwiththeprecedingresearch,confirmingthatthegraphiteoxidewascomple-telyexfoliated.
Weobservedheightsfromslightlylessthan1nmtoafewnanometersthick.
Weassignedthesheetswithheightapproximately1nm,approximately1.
5nm,approximately2nm,andupto5nmtobeone-,two-,three-,andfew-layeredGOsheets,respectively.
ThiswasinagreementwiththereportedAFMresultsonfew-layergraphenesheets[5,8,17],wherethesingle-layergrapheneisalwaysapproximately1nm,probablyduetodifferentattractionforcebetweenAFMtipsandgra-pheneascomparedtoSiO2andimperfectinterfacebetweengrapheneandSiO2.
AFMimageofourchemicallyreducedGOsheetafteradditionofPQ-16,depositedonSiO2/Sisubstratebydropcasting,isshowninFigure3.
Thegraphiteinterlayerspa-cingisabout0.
34nmwhichshouldideallycorrespondtothethicknessofamonolayergraphene.
Conversely,thethicknessofsinglePQ-Gwasdeterminedtobeapproxi-mately1.
9nm.
IfweassumethatmonolayeredPQ-16cov-eredbothsidesofgraphenesheetwithoffsetface-to-faceFigure1Aqueoussolutionsofgrapheneoxideandgrapheneafterhydrazinereduction.
Inthepresenceofpolyelectrolyte,schematicofthetransfermechanism.
ulHasanetal.
NanoscaleResearchLetters2011,6:493http://www.
nanoscalereslett.
com/content/6/1/493Page2of6orientationviaπ-πinteractions(mechanismofstabiliza-tion),theestimateddistancebetweenPQandthegra-phenesheetisapproximately0.
35nm[18].
Accordingly,theaveragethicknessofthegraphenesheetinthePQ-Glayercanbederivedtobearound1.
9nm.
ThisassumptionisfurthersupportedbyFigure3b,whichshowsthestepheightfortheregionwithbilayergraphene.
Thestepheightofthegraphene-grapheneinterfacewasalsoobservedtobeapproximately1.
9nminvariousmeasurements.
Transmissionelectronmicroscopy(TEM)isalsoaveryimportanttoolforinvestigatingthequalityofexfo-liatedgraphene.
Wedroppedasmallquantityofthedis-persionontheholeycarbongridbypipetteanddriedthesamples.
Figure4ashowsbright-fieldTEMimage,Figure4bshowsthehigh-resolutiontransmissionelec-tronmicroscope(HRTEM)imageofthegraphenesur-face,andFigure4cdepictstheelectrondiffractionpatternobservedfromthesamearea.
Theanalysisofthediffractionintensityratiowasusedtoconfirmthepresenceofmonolayergraphene[19].
WeusetheBravais-Miller(hkil)indicestolabelthepeakscorre-spondingtothegraphitereflectionstakenatnormalincidence[19].
AfteranalyzingalargenumberofTEMimages,wewereabletoconcludethatourdispersioncontainsaverygoodfractionofmonolayergraphene.
Wefabricatedabottom-gatedgraphenefield-effecttran-sistor(FET)byputtingamonolayerofreducedGOFigure2TappingmodeAFMimageofGOonSiO2/Siwithstepheightprofile.
Figure3AFMimageofpolyquaternium-stabilizedgraphenemembranewithheightprofiles.
ulHasanetal.
NanoscaleResearchLetters2011,6:493http://www.
nanoscalereslett.
com/content/6/1/493Page3of6membraneinbetweenthermallyevaporatedgoldelectro-des.
Thechannellengthbetweensourceanddrainelectro-deswas5μm.
Theschematicandthescanningelectronmicroscope(SEM)imageofthedeviceareshowninFigure5.
Figure5cshowsthedraincurrent(Id)vs.
gatevoltage(Vg)curveofFETpreparedwiththisreducedmonolayergraphenemembrane.
TheFETgateoperationexhibitsholeconductionbehavior.
Puretwo-dimensionalgraphenehasazerobandgapthatlimitsitseffectiveappli-cationinelectronicdevices.
WebelievethatthisreducedGOfromPQdispersionhasakindofdopingeffectthatmakesitmorefavorableforapplicationsduetoitsimprovedelectronicproperties.
Thereweretheoreticalsimulations[20,21],whichwerelaterconfirmedexperi-mentally[22]thatthe100%hydrogenationoffreestandinggrapheneresultsinametaltoinsulatortransition.
Hydro-genationofgrapheneonasilicondioxide(SiO2)substratehasalsoledtotheenergygapopening[23].
Here,wecanattributethedeficiencyofambipolarbehaviortoholedop-ingcausedbyresidualoxygenfunctionalitiesresultinginap-typebehaviorandafield-effectresponse[2,24].
Thus,chemicalfunctionalizationisapossibleroutetomodifytheelectronicpropertiesofgraphene,whichcanbeimpor-tantforgraphene-basednanoelectronics[25],althoughthereisroomforfurtheroptimizationoftheprocessforimprovingtheproperties,inordertomakeitidealforindustriallevelapplications.
ConclusionsInsummary,wereportamethodtoproduceandfunc-tionalizegraphenemembranesinthesolutionphaseusingpolymericimidazoliummoltensaltsasatransfer-ringmedium.
Graphenemembraneswerereducedfromgrapheneoxidebyhydrazineinthepresenceofapoly-electrolytewhichwasfoundtobeaverystabledisper-sionforthegraphenemembranesintheaqueoussolution.
ThereducedGOmembranesweretransferredtoaSiO2/SisubstratebysimpledropcastingandwerefurtherreducedbyannealinginH2/Ar.
Asimpledevicewithgoldcontactsonboththesideswasfabricatedinordertoobservetheelectronicproperties.
Weconcludethatchemicalfunctionalizationisapossibleroutetomodifyandimprovetheelectronicpropertiesofgraphene.
Figure4Electronmicroscopyofgraphene.
(a)Bright-fieldTEMimagesofmonolayergraphene,(b)HRTEMimagefromthesamelocation,and(c)electrondiffractionpatternofthegraphenesheetin(a)withdiffractionspotslabeledbyMiller-Bravaisindices.
ulHasanetal.
NanoscaleResearchLetters2011,6:493http://www.
nanoscalereslett.
com/content/6/1/493Page4of6AcknowledgementsWeacknowledgethehelpofAmirKarim(AcreoKista)forhistechnicalsupportinTEMimaging.
Authordetails1DepartmentofScienceandTechnology(ITN),LinkpingUniversity,CampusNorrkping,SE-60174Norrkping,Sweden2AcreoABBredgatan34,SE-60221Norrkping,SwedenAuthors'contributionsAllauthorscontributedequally,readandapprovedthefinalmanuscript.
CompetinginterestsTheauthorsdeclarethattheyhavenocompetinginterests.
Received:14May2011Accepted:16August2011Published:16August2011References1.
GeimAK,NovoselovKS:Theriseofgraphene.
NatMater2007,6:183-191.
2.
GiljeS,HanS,WangM,WangKL,KanerRB:Achemicalroutetographenefordeviceapplications.
NanoLetters2007,7:3394-3398.
3.
KimT,LeeH,KimJ,SuhKS:Synthesisofphasetransferablegraphenesheetsusingionicliquidpolymers.
ACSNano4:1612-1618.
4.
StollerMD,ParkS,ZhuY,AnJ,RuoffRS:Graphene-basedultracapacitors.
NanoLetters2008,8:3498-3502.
5.
NovoselovKS,GeimAK,MorozovSV,JiangD,ZhangY,DubonosSV,GrigorievaIV,FirsovAA:Electricfieldeffectinatomicallythincarbonfilms.
Science2004,306:666-669.
6.
HassJ,deHeerWA,ConradEH:Thegrowthandmorphologyofepitaxialmultilayergraphene.
JournalofPhysics:CondensedMatter2008,20:323202.
7.
HernandezY,NicolosiV,LotyaM,BligheFM,SunZ,DeS,McGovernIT,HollandB,ByrneM,Gun'KoYK,BolandJJ,NirajP,DuesbergG,KrishnamurthyS,GoodhueR,HutchisonJ,ScardaciV,FerrariAC,ColemanJN:High-yieldproductionofgraphenebyliquid-phaseexfoliationofgraphite.
NatNano2008,3:563-568.
8.
LiX,WangX,ZhangL,LeeS,DaiH:Chemicallyderived,ultrasmoothgraphenenanoribbonsemiconductors.
Science2008,319:1229-1232.
9.
PichonA:Graphenesynthesis:chemicalpeel.
NatChem2008.
10.
CoteLJ,KimF,HuangJ:Langmuir-Blodgettassemblyofgraphiteoxidesinglelayers.
JournaloftheAmericanChemicalSociety2008,131:1043-1049.
11.
CarriónF,SanesJ,BermúdezM-D,ArribasA:Newsingle-walledcarbonnanotubes-ionicliquidlubricant.
Applicationtopolycarbonate-stainlesssteelslidingcontact.
TribologyLetters41:199-207.
12.
DongX,SuC-Y,ZhangW,ZhaoJ,LingQ,HuangW,ChenP,LiL-J:Ultra-largesingle-layergrapheneobtainedfromsolutionchemicalreductionanditselectricalproperties.
PhysicalChemistryChemicalPhysics12:2164-2169.
13.
HummersWS,OffemanRE:Preparationofgraphiticoxide.
JournaloftheAmericanChemicalSociety1958,80:1339-1339.
14.
ZhouX,WuT,DingK,HuB,HouM,HanB:Dispersionofgraphenesheetsinionicliquid[bmim][PF6]stabilizedbyanionicliquidpolymer.
ChemicalCommunications46:386-388.
15.
BlakeP,HillEW,NetoAHC,NovoselovKS,JiangD,YangR,BoothTJ,GeimAK:Makinggraphenevisible.
AppliedPhysicsLetters2007,91:063124-063123.
16.
StankovichS,DikinDA,DommettGHB,KohlhaasKM,ZimneyEJ,StachEA,PinerRD,NguyenST,RuoffRS:Graphene-basedcompositematerials.
Nature2006,442:282-286.
17.
GuptaA,ChenG,JoshiP,TadigadapaS,Eklund:Ramanscatteringfromhigh-frequencyphononsinsupportedn-graphenelayerfilms.
NanoLetters2006,6:2667-2673.
Figure5ElectronicdevicesbasedonreducedGOmembrane.
(a)Schematicofadevicewith30-nm-thickthermallyevaporatedAucontactsasthesource(S)anddrain(D)electrodes,(b)SEMimageofthedevice,and(c)source-draincurrent(Isd)vs.
source-drainvoltage(Vsd)asafunctionofgatevoltage(Vg)withp++siliconservingasabackgate.
ulHasanetal.
NanoscaleResearchLetters2011,6:493http://www.
nanoscalereslett.
com/content/6/1/493Page5of618.
XuY,BaiH,LuG,LiC,ShiG:Flexiblegraphenefilmsviathefiltrationofwater-solublenoncovalentfunctionalizedgraphenesheets.
JournaloftheAmericanChemicalSociety2008,130:5856-5857.
19.
MeyerJC,GeimAK,KatsnelsonMI,NovoselovKS,ObergfellD,RothS,GiritC,ZettlA:Ontheroughnessofsingle-andbi-layergraphenemembranes.
SolidStateCommunications2007,143:101-109.
20.
SofoJO,ChaudhariAS,BarberGD:Graphane:atwo-dimensionalhydrocarbon.
PhysicalReviewB2007,75:153401.
21.
BoukhvalovDW,KatsnelsonMI,LichtensteinAI:Hydrogenongraphene:Electronicstructure,totalenergy,structuraldistortionsandmagnetismfromfirst-principlescalculations.
PhysicalReviewB2008,77:035427.
22.
EliasDC,NairRR,MohiuddinTMG,MorozovSV,BlakeP,HalsallMP,FerrariAC,BoukhvalovDW,KatsnelsonMI,GeimAK,NovoselovKS:Controlofgraphene'spropertiesbyreversiblehydrogenation:evidenceforgraphane.
Science2009,323:610-613.
23.
BoukhvalovDW,KatsnelsonMI:Modelingofepitaxialgraphenefunctionalization.
Nanotechnology2011,22:055708.
24.
AllenMJ,TungVC,GomezL,XuZ,ChenL-M,NelsonKS,ZhouC,KanerRB,YangY:Softtransferprintingofchemicallyconvertedgraphene.
AdvancedMaterials2009,21:2098-102.
25.
BoukhvalovDW,KatsnelsonMI:Chemicalfunctionalizationofgraphenewithdefects.
NanoLetters2008,8:4373-4379.
doi:10.
1186/1556-276X-6-493Citethisarticleas:ulHasanetal.
:Polycationstabilizationofgraphenesuspensions.
NanoscaleResearchLetters20116:493.
Submityourmanuscripttoajournalandbenetfrom:7Convenientonlinesubmission7Rigorouspeerreview7Immediatepublicationonacceptance7Openaccess:articlesfreelyavailableonline7Highvisibilitywithintheeld7RetainingthecopyrighttoyourarticleSubmityournextmanuscriptat7springeropen.
comulHasanetal.
NanoscaleResearchLetters2011,6:493http://www.
nanoscalereslett.
com/content/6/1/493Page6of6
Wereportamethodtoproducegraphenemembranesinthesolutionphaseusingpolymericimidazoliumsaltsasatransferringmedium.
Graphenemembraneswerereducedfromgrapheneoxidesbyhydrazineinthepresenceofthepolyelectrolytewhichisfoundtobeastableandhomogeneousdispersionfortheresultinggrapheneintheaqueoussolution.
Asimpledevicewithgoldcontactsonbothsideswasfabricatedinordertoobservetheelectronicproperties.
IntroductionTheuniquephysical,electronic,andopticalpropertiesofgraphenehavebeenreportedmanytimes[1-4]andpromiseawidevarietyofapplications.
Differentmeth-odshavebeenadoptedforobtaininggraphene,e.
g.
,mechanicalexfoliationofgraphite[5],epitaxialgrowth[6],andchemicalexfoliationindifferentsolutions[3,7-9].
Averypromisingrouteforthebulkproductionofthegraphenesheetscanbechemicalreductionanddispersionofgrapheneinaqueoussolutions.
Twostepsareinvolvedinmakingwaterdispersiblegra-phene:(1)firstchemicaloxidationofgraphitetohydrophi-licgraphiteoxideand(2)exfoliatingitintographeneoxide(GO)sheetsinaqueoussolution.
GOsheetsaregraphenesheetshavingoxygenfunctionalgroups.
TheseGOsheetsarepreventedfromagglomerationbyelectrostaticrepul-sionalone[10].
TheinsulatingGOcaneasilybereducedtohighlyconductinggraphenebyhydrazinereduction.
However,thereductionofGOsoonleadstoagglomera-tion,whileastabledispersioniskeytothepossibilityoflarge-scaleprocessing.
Polymericimidazoliumsaltscanbeagoodwaytoformastabledispersionofgraphene.
Organicsaltsbasedontheimidazoliummoietyareaninterestingclassofions.
Lowmolecularweightimidazo-liumsaltscanhavealowmeltingpointandarethentermedionicliquids(ILs).
Thus,ILsaremoltensaltsattheroomtemperatureandconsistofbulkyorganiccationspairedwithorganicorinorganicanions.
Imidazoliumionicliquidshavemanyadvantageousproperties,suchasnoflammability,awideelectrochemicalwindow,highthermalstability,wideliquidrange,andverysmallvaporpressure[11].
Theyarealsoknowntointeractstronglywiththebasalplaneofgraphiteandgraphene.
Polymericimidazoliumsaltswouldthereforebeinterestingtoexploreasdispersingagentsforgraphene.
ExperimentalGrapheneoxidewaspreparedbythemodifiedHummer'smethod[12,13].
Thegraphiteflakes(PN332461,4g;SigmaAldrich,Sigma-AldrichSwedenAB,)werefirstputinH2SO4(98%,12mL)andkeptat80°Cfor5h.
Theresultingsolutionwascooleddowntoroomtemperature.
Mildsonicationwasperformedinawaterbathfor2htofurtherdelaminategraphiteintoafewmicronflakes.
Soni-cationtimeandpowerareverycriticalastheydefinethesizeoftheresultinggrapheneoxidesheets.
Excessivesoni-cationleadstoextremelysmallflakes.
Then,thesolutionwasdilutedwith0.
5Ldeionized(DI)waterandleftover-night.
ThesolutionwasfilteredbyNylonMilliporefilters(Billerica,MA01821).
TheresultingpowderwasmixedwithKMnO4andH2SO4andputinacoolingbathunderconstantstirringfor1.
5h.
ThesolutionwasdilutedwithDIwater,and20mLH2O2(30%)wasaddedtoit.
Thesupernatantwascollectedafter12handdispersedindiluteHClinordertoremovethemetalionresidueandthenrecoveredbycentrifugation[12,13].
CleanGOwasagaindispersedinwatertomakeahomogeneousdispersionandwascentrifugedat8,000rpmfor40mininordertoremovethemultilayerfragments.
Weaddedapolymericimidazoliummoltensaltintotheaqueousdis-persionofGOataconcentrationof1mgmL-1andstronglyshookthesolutionforafewminutes.
Theimida-zoliumsaltusedbyuswaspolyquaternium16(PQ-16)soldunderthetradenameLuviquatExcellencebyBASF*Correspondence:kamran.
ul.
hasan@liu.
se1DepartmentofScienceandTechnology(ITN),LinkpingUniversity,CampusNorrkping,SE-60174Norrkping,SwedenFulllistofauthorinformationisavailableattheendofthearticleulHasanetal.
NanoscaleResearchLetters2011,6:493http://www.
nanoscalereslett.
com/content/6/1/4932011Hasanetal;licenseeSpringer.
ThisisanOpenAccessarticledistributedunderthetermsoftheCreativeCommonsAttributionLicense(http://creativecommons.
org/licenses/by/2.
0),whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited.
(Ludwigshafen,Germany),acopolymerwith95%molarofimidazoliumchlorideand5%molarofvinylimidazole.
Useofthispolymericsaltforgraphenedispersionisnotfoundinliterature.
Then,thesolutionwasreducedbyhydrazinemonohydrateat90°Cfor1htoobtainastabledispersionofgrapheneinaqueoussolution.
ResultsanddiscussionThisaqueousPQ-graphenedispersionwasfoundtobestableevenafter2months,whereasthereducedGOwithouttheadditionofPQ-16formedagglomer-atessoonafterreductionwithhydrazine.
Thus,PQ-16isthemaincauseofastabledispersionofgra-phenemembranesinaqueoussolution.
Theunderly-ingmechanismhasbeenaffiliatedwithadsorptionofsomeofthepolycationsonthesurfaceofthegra-phenemembranesbynon-covalentπ-πinteractionsbetweentheimidazoliumringsofthesaltandgra-phene,soonafterreductionwithhydrazinemonohy-drate[14].
ThegraphenewasdepositedontoSi/SiO2(SiO2thicknessapproximately300nm)substratesbydip-coating.
SchematicofthewholeprocessisshowninFigure1.
ThesamplewasrinsedwithDIwateranddriedwithnitrogen.
Thedriedsampleswerefurthertreatedat400°Cfor2hinAr/H2tofurtherreducethegrapheneoxideandalsotosublimatethesolutionresidue.
Theopticalmicroscopeimagesweretakeninordertoidentifygra-phene[15].
Atomicforcemicroscopemeasurementswerecarriedouttoconfirmthepresenceofsingle-andfew-layergraphenebymeasuringstepheight[7].
Gra-pheneshowstypicalwrinkledstructurewhichisintrinsictographene[16]overrelativelylargesheetsizes.
Verylargegraphenemembraneswithsizesaround10*10μmwereidentified.
Thesizewasfoundtobedirectlyrelatedwithsonicationpowerandtime.
Exces-sivesonicationresultsinverysmallgraphenesheets,whereasinsufficientsonicationresultsinincompleteexfoliationofgraphiteoxide.
Wemeasuredtheheightprofilesofthegraphenemem-branesbyatomicforcemicroscopy(AFM)afterdropcastingthemonarelativelyflatSiO2/Sisubstrate.
TheaveragethicknessofaGOsheetwasapproximately1nm(Figure2),whichwasinagreementwiththeprecedingresearch,confirmingthatthegraphiteoxidewascomple-telyexfoliated.
Weobservedheightsfromslightlylessthan1nmtoafewnanometersthick.
Weassignedthesheetswithheightapproximately1nm,approximately1.
5nm,approximately2nm,andupto5nmtobeone-,two-,three-,andfew-layeredGOsheets,respectively.
ThiswasinagreementwiththereportedAFMresultsonfew-layergraphenesheets[5,8,17],wherethesingle-layergrapheneisalwaysapproximately1nm,probablyduetodifferentattractionforcebetweenAFMtipsandgra-pheneascomparedtoSiO2andimperfectinterfacebetweengrapheneandSiO2.
AFMimageofourchemicallyreducedGOsheetafteradditionofPQ-16,depositedonSiO2/Sisubstratebydropcasting,isshowninFigure3.
Thegraphiteinterlayerspa-cingisabout0.
34nmwhichshouldideallycorrespondtothethicknessofamonolayergraphene.
Conversely,thethicknessofsinglePQ-Gwasdeterminedtobeapproxi-mately1.
9nm.
IfweassumethatmonolayeredPQ-16cov-eredbothsidesofgraphenesheetwithoffsetface-to-faceFigure1Aqueoussolutionsofgrapheneoxideandgrapheneafterhydrazinereduction.
Inthepresenceofpolyelectrolyte,schematicofthetransfermechanism.
ulHasanetal.
NanoscaleResearchLetters2011,6:493http://www.
nanoscalereslett.
com/content/6/1/493Page2of6orientationviaπ-πinteractions(mechanismofstabiliza-tion),theestimateddistancebetweenPQandthegra-phenesheetisapproximately0.
35nm[18].
Accordingly,theaveragethicknessofthegraphenesheetinthePQ-Glayercanbederivedtobearound1.
9nm.
ThisassumptionisfurthersupportedbyFigure3b,whichshowsthestepheightfortheregionwithbilayergraphene.
Thestepheightofthegraphene-grapheneinterfacewasalsoobservedtobeapproximately1.
9nminvariousmeasurements.
Transmissionelectronmicroscopy(TEM)isalsoaveryimportanttoolforinvestigatingthequalityofexfo-liatedgraphene.
Wedroppedasmallquantityofthedis-persionontheholeycarbongridbypipetteanddriedthesamples.
Figure4ashowsbright-fieldTEMimage,Figure4bshowsthehigh-resolutiontransmissionelec-tronmicroscope(HRTEM)imageofthegraphenesur-face,andFigure4cdepictstheelectrondiffractionpatternobservedfromthesamearea.
Theanalysisofthediffractionintensityratiowasusedtoconfirmthepresenceofmonolayergraphene[19].
WeusetheBravais-Miller(hkil)indicestolabelthepeakscorre-spondingtothegraphitereflectionstakenatnormalincidence[19].
AfteranalyzingalargenumberofTEMimages,wewereabletoconcludethatourdispersioncontainsaverygoodfractionofmonolayergraphene.
Wefabricatedabottom-gatedgraphenefield-effecttran-sistor(FET)byputtingamonolayerofreducedGOFigure2TappingmodeAFMimageofGOonSiO2/Siwithstepheightprofile.
Figure3AFMimageofpolyquaternium-stabilizedgraphenemembranewithheightprofiles.
ulHasanetal.
NanoscaleResearchLetters2011,6:493http://www.
nanoscalereslett.
com/content/6/1/493Page3of6membraneinbetweenthermallyevaporatedgoldelectro-des.
Thechannellengthbetweensourceanddrainelectro-deswas5μm.
Theschematicandthescanningelectronmicroscope(SEM)imageofthedeviceareshowninFigure5.
Figure5cshowsthedraincurrent(Id)vs.
gatevoltage(Vg)curveofFETpreparedwiththisreducedmonolayergraphenemembrane.
TheFETgateoperationexhibitsholeconductionbehavior.
Puretwo-dimensionalgraphenehasazerobandgapthatlimitsitseffectiveappli-cationinelectronicdevices.
WebelievethatthisreducedGOfromPQdispersionhasakindofdopingeffectthatmakesitmorefavorableforapplicationsduetoitsimprovedelectronicproperties.
Thereweretheoreticalsimulations[20,21],whichwerelaterconfirmedexperi-mentally[22]thatthe100%hydrogenationoffreestandinggrapheneresultsinametaltoinsulatortransition.
Hydro-genationofgrapheneonasilicondioxide(SiO2)substratehasalsoledtotheenergygapopening[23].
Here,wecanattributethedeficiencyofambipolarbehaviortoholedop-ingcausedbyresidualoxygenfunctionalitiesresultinginap-typebehaviorandafield-effectresponse[2,24].
Thus,chemicalfunctionalizationisapossibleroutetomodifytheelectronicpropertiesofgraphene,whichcanbeimpor-tantforgraphene-basednanoelectronics[25],althoughthereisroomforfurtheroptimizationoftheprocessforimprovingtheproperties,inordertomakeitidealforindustriallevelapplications.
ConclusionsInsummary,wereportamethodtoproduceandfunc-tionalizegraphenemembranesinthesolutionphaseusingpolymericimidazoliummoltensaltsasatransfer-ringmedium.
Graphenemembraneswerereducedfromgrapheneoxidebyhydrazineinthepresenceofapoly-electrolytewhichwasfoundtobeaverystabledisper-sionforthegraphenemembranesintheaqueoussolution.
ThereducedGOmembranesweretransferredtoaSiO2/SisubstratebysimpledropcastingandwerefurtherreducedbyannealinginH2/Ar.
Asimpledevicewithgoldcontactsonboththesideswasfabricatedinordertoobservetheelectronicproperties.
Weconcludethatchemicalfunctionalizationisapossibleroutetomodifyandimprovetheelectronicpropertiesofgraphene.
Figure4Electronmicroscopyofgraphene.
(a)Bright-fieldTEMimagesofmonolayergraphene,(b)HRTEMimagefromthesamelocation,and(c)electrondiffractionpatternofthegraphenesheetin(a)withdiffractionspotslabeledbyMiller-Bravaisindices.
ulHasanetal.
NanoscaleResearchLetters2011,6:493http://www.
nanoscalereslett.
com/content/6/1/493Page4of6AcknowledgementsWeacknowledgethehelpofAmirKarim(AcreoKista)forhistechnicalsupportinTEMimaging.
Authordetails1DepartmentofScienceandTechnology(ITN),LinkpingUniversity,CampusNorrkping,SE-60174Norrkping,Sweden2AcreoABBredgatan34,SE-60221Norrkping,SwedenAuthors'contributionsAllauthorscontributedequally,readandapprovedthefinalmanuscript.
CompetinginterestsTheauthorsdeclarethattheyhavenocompetinginterests.
Received:14May2011Accepted:16August2011Published:16August2011References1.
GeimAK,NovoselovKS:Theriseofgraphene.
NatMater2007,6:183-191.
2.
GiljeS,HanS,WangM,WangKL,KanerRB:Achemicalroutetographenefordeviceapplications.
NanoLetters2007,7:3394-3398.
3.
KimT,LeeH,KimJ,SuhKS:Synthesisofphasetransferablegraphenesheetsusingionicliquidpolymers.
ACSNano4:1612-1618.
4.
StollerMD,ParkS,ZhuY,AnJ,RuoffRS:Graphene-basedultracapacitors.
NanoLetters2008,8:3498-3502.
5.
NovoselovKS,GeimAK,MorozovSV,JiangD,ZhangY,DubonosSV,GrigorievaIV,FirsovAA:Electricfieldeffectinatomicallythincarbonfilms.
Science2004,306:666-669.
6.
HassJ,deHeerWA,ConradEH:Thegrowthandmorphologyofepitaxialmultilayergraphene.
JournalofPhysics:CondensedMatter2008,20:323202.
7.
HernandezY,NicolosiV,LotyaM,BligheFM,SunZ,DeS,McGovernIT,HollandB,ByrneM,Gun'KoYK,BolandJJ,NirajP,DuesbergG,KrishnamurthyS,GoodhueR,HutchisonJ,ScardaciV,FerrariAC,ColemanJN:High-yieldproductionofgraphenebyliquid-phaseexfoliationofgraphite.
NatNano2008,3:563-568.
8.
LiX,WangX,ZhangL,LeeS,DaiH:Chemicallyderived,ultrasmoothgraphenenanoribbonsemiconductors.
Science2008,319:1229-1232.
9.
PichonA:Graphenesynthesis:chemicalpeel.
NatChem2008.
10.
CoteLJ,KimF,HuangJ:Langmuir-Blodgettassemblyofgraphiteoxidesinglelayers.
JournaloftheAmericanChemicalSociety2008,131:1043-1049.
11.
CarriónF,SanesJ,BermúdezM-D,ArribasA:Newsingle-walledcarbonnanotubes-ionicliquidlubricant.
Applicationtopolycarbonate-stainlesssteelslidingcontact.
TribologyLetters41:199-207.
12.
DongX,SuC-Y,ZhangW,ZhaoJ,LingQ,HuangW,ChenP,LiL-J:Ultra-largesingle-layergrapheneobtainedfromsolutionchemicalreductionanditselectricalproperties.
PhysicalChemistryChemicalPhysics12:2164-2169.
13.
HummersWS,OffemanRE:Preparationofgraphiticoxide.
JournaloftheAmericanChemicalSociety1958,80:1339-1339.
14.
ZhouX,WuT,DingK,HuB,HouM,HanB:Dispersionofgraphenesheetsinionicliquid[bmim][PF6]stabilizedbyanionicliquidpolymer.
ChemicalCommunications46:386-388.
15.
BlakeP,HillEW,NetoAHC,NovoselovKS,JiangD,YangR,BoothTJ,GeimAK:Makinggraphenevisible.
AppliedPhysicsLetters2007,91:063124-063123.
16.
StankovichS,DikinDA,DommettGHB,KohlhaasKM,ZimneyEJ,StachEA,PinerRD,NguyenST,RuoffRS:Graphene-basedcompositematerials.
Nature2006,442:282-286.
17.
GuptaA,ChenG,JoshiP,TadigadapaS,Eklund:Ramanscatteringfromhigh-frequencyphononsinsupportedn-graphenelayerfilms.
NanoLetters2006,6:2667-2673.
Figure5ElectronicdevicesbasedonreducedGOmembrane.
(a)Schematicofadevicewith30-nm-thickthermallyevaporatedAucontactsasthesource(S)anddrain(D)electrodes,(b)SEMimageofthedevice,and(c)source-draincurrent(Isd)vs.
source-drainvoltage(Vsd)asafunctionofgatevoltage(Vg)withp++siliconservingasabackgate.
ulHasanetal.
NanoscaleResearchLetters2011,6:493http://www.
nanoscalereslett.
com/content/6/1/493Page5of618.
XuY,BaiH,LuG,LiC,ShiG:Flexiblegraphenefilmsviathefiltrationofwater-solublenoncovalentfunctionalizedgraphenesheets.
JournaloftheAmericanChemicalSociety2008,130:5856-5857.
19.
MeyerJC,GeimAK,KatsnelsonMI,NovoselovKS,ObergfellD,RothS,GiritC,ZettlA:Ontheroughnessofsingle-andbi-layergraphenemembranes.
SolidStateCommunications2007,143:101-109.
20.
SofoJO,ChaudhariAS,BarberGD:Graphane:atwo-dimensionalhydrocarbon.
PhysicalReviewB2007,75:153401.
21.
BoukhvalovDW,KatsnelsonMI,LichtensteinAI:Hydrogenongraphene:Electronicstructure,totalenergy,structuraldistortionsandmagnetismfromfirst-principlescalculations.
PhysicalReviewB2008,77:035427.
22.
EliasDC,NairRR,MohiuddinTMG,MorozovSV,BlakeP,HalsallMP,FerrariAC,BoukhvalovDW,KatsnelsonMI,GeimAK,NovoselovKS:Controlofgraphene'spropertiesbyreversiblehydrogenation:evidenceforgraphane.
Science2009,323:610-613.
23.
BoukhvalovDW,KatsnelsonMI:Modelingofepitaxialgraphenefunctionalization.
Nanotechnology2011,22:055708.
24.
AllenMJ,TungVC,GomezL,XuZ,ChenL-M,NelsonKS,ZhouC,KanerRB,YangY:Softtransferprintingofchemicallyconvertedgraphene.
AdvancedMaterials2009,21:2098-102.
25.
BoukhvalovDW,KatsnelsonMI:Chemicalfunctionalizationofgraphenewithdefects.
NanoLetters2008,8:4373-4379.
doi:10.
1186/1556-276X-6-493Citethisarticleas:ulHasanetal.
:Polycationstabilizationofgraphenesuspensions.
NanoscaleResearchLetters20116:493.
Submityourmanuscripttoajournalandbenetfrom:7Convenientonlinesubmission7Rigorouspeerreview7Immediatepublicationonacceptance7Openaccess:articlesfreelyavailableonline7Highvisibilitywithintheeld7RetainingthecopyrighttoyourarticleSubmityournextmanuscriptat7springeropen.
comulHasanetal.
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nanoscalereslett.
com/content/6/1/493Page6of6
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