photoelectronwww.20ren.com

2015WILEY-VCHVerlagGmbH&Co.
KGaA,Weinheim2148wileyonlinelibrary.
comCOMMUNICATIONSubstrate-InducedGrapheneChemistryfor2DSuperlatticeswithTunablePeriodicitiesLinZhou,LeiLiao,JinyingWang,JingwenYu,DenghuaLi,QinXie,ZhirongLiu,YanlianYang,XuefengGuo,andZhongfanLiu*Dr.
L.
Zhou,Dr.
L.
Liao,Dr.
J.
Wang,J.
Yu,Dr.
Q.
Xie,Prof.
Z.
Liu,Prof.
X.
Guo,Prof.
Z.
LiuCenterforNanochemistryBeijingScienceandEngineeringCentreforNanocarbonsBeijingNationalLaboratoryforMolecularSciencesCollegeofChemistryandMolecularEngineeringPekingUniversityBeijing100871,P.
R.
ChinaE-mail:ziu@pku.
edu.
cnDr.
D.
Li,Prof.
Y.
YangNationalCenterforNanoscienceandTechnologyBeijing100190,P.
R.
ChinaDOI:10.
1002/adma.
201505360pseudo-magneticeldsingrapheneandengineeritselectronicstructure.
Strain-inducedsuperlatticescanproducesignicantenergygapsingrapheneandshowapseudo-magneticquantumhalleffect.
[21]Recently,itwasalsoshownthatstraininggra-pheneleadstoasubstantialincreaseofitsreactionratewithdiazoniumsaltsandthenalmodicationdegree.
[22,23]Sub-strate-inducedcharge(holeorelectron)puddlesarefoundtoincreasethechemicalreactivityofgraphenetowarddiazoniumfunctionalization.
[18]Thesephenomenastronglysuggestthepossibilityofsubstrateengineeringforcontrollinggraphene'schemicalreactivityonitsbasalplaneforthepurposeoffabri-cating2Dsuperlattices.
Inthispaper,wereportasubstrateengineeringapproachtoperiodicallypatternthegraphenebasalplaneforthepur-poseoffabricating2Dgraphenesuperlattices(Figure1a).
Thismask-freepatterningtechniqueisinspiredbytheoldChineserubbingprinting,inwhichthepigmentisdepositedoverpro-trusionsbyrubbinghardrenderingmaterialsoverpaperwhilethedepressionsremainunpigmented.
Inourapproach,thereactivespeciesactasthepigmentandthechemicalreactionofgrapheneisguidedbytheunderlyingsubstratewithperi-odicprotrusions.
Thesepredesignedprotrusionsintroduceperiodiccompressivestrainintothegraphenebasalplanebythermalannealingtreatmentbecauseofgraphene'snegativethermalexpansioncoefcient.
[24,25]Moreover,theSiO2protru-sionscouldinducechargepuddlesingraphene,whichfurtherincreasethechemicalreactivityofattachedgraphene.
[18]Theexistenceoflocalstrainandchargepuddlescouldenhancethechemicalreactivityofgraphene,leadingtoalocalizedperiodicfunctionalizationonthegraphenesheet.
Asaresult,graphenesuperlatticecanbeachievedwiththepredesignedsubstrate.
Wehavesuccessfullyfabricatedvariousgraphenesuperlatticeswithdifferentperiodicitiesinsuchaway.
Thissubstrateengineeringtechniqueallowsforawell-controlledperiodicmodicationofgraphene,enablingtheconstructionofvariousgraphene-basedelectronicandoptoelectronicdevices,chemo/biosensorsandthestudiesofrichphysicsof2Dsuperlattices.
Aschematicofthefabricationprocessof2Dgraphenesuper-latticebasedonthelocalsubstrateengineeringofgraphenechemistryisillustratedinFigure1b.
First,theperiodicallypat-ternedsubstrate(PPS)wasfabricatedbyself-assemblingmono-dispersedcolloidalSiO2nanospheresmonolayerontoSiO2/Sisubstrate.
Second,chemicalvapordeposition(CVD)-growngraphenewastransferredontosuchpatternedsubstrates.
Poly(methylmethacrylate)(PMMA)thinlmwasusedasthetransfermedium,andthenremovedbyhotacetone.
Tointroduceperiodiccompressivestrainintothegraphenelm,Theadventofgraphene,a2Dcrystallinemonolayermadeofsp2-bondedcarbonatomsarrangedinahoneycomblattice,hasledtoanexplosionofinterestinscienticandindustrialcommunitiesbecauseofitsfascinatingelectrical,thermal,andmechanicalproperties.
[1,2]Auniquefeatureofgrapheneisthatallthecarbonatomsinitsbasalplanearechemicallyacces-sible,providingapowerfulpathwaytotailorthephysicalandchemicalpropertiesofpristinegraphenebyusingchemicalapproaches.
Althoughgrapheneisgenerallychemicallyinertbecauseofitsgiantdelocalizedπsystem,covalentfunctionali-zationhasbeendemonstratedtobepossibleforthepurposesofachievingbandgapengineering,doping-levelmodulation,chemo-andbiosensing,newcompositesynthesisandlarge-scalesolution-processedproduction.
[3–10]Thecovalentchem-istryofgraphenealsoprovidesafreedomtocreatenew2Dmaterialsand/or2Dgraphenesuperlatticesbeyondgraphene,creatingaroutetostudytherichphysicsexpectedinattrac-tivequantumsystems.
[10–12]Todate,severalapproacheshavebeenreportedforfabricating2Dgraphenesuperlattices.
[13,14]However,mostoftheseexamplesarebasedonthemasktech-nique,whichlimitsthestructuralresolutiontoonlymicro-meterscales.
Aneffectivechemicalapproachtothenanometerscalegraphenesuperlatticeswithtunableperiodicitiesishighlydesirable,whichiscrucialforgeneratingabandgapinthezero-gappristinegrapheneforelectronicsandoptoelectronicsapplications.
[14]Becauseofitsatomicallythinfeature,grapheneisstronglyinuencedbysubstratewhichcaninduceexternalinuences,e.
g.
,strain[15,16]andchargepuddles.
[17,18]Straindistortsthegra-phene'slatticeandhencestronglyinuencesitsphysicalandchemicalproperties.
Bothexperimental[19,20]andtheoretical[21]studieshavedemonstratedthatstraincanbuildenormousAdv.
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KGaA,WeinheimCOMMUNICATIONthus-obtainedsampleswereannealedat350°Cfor2hinforminggas(30sccmH2/100sccmAr)underatmosphericpressure.
Then,thegraphenesamplewasimmersedintoa4-nitrobenzenediazoniumtetrauoroboratesolutionat40°Cforcovalentmodication.
Thefollowingchemicalreactionisexpectedtotakeplace.
[26]Thediazoniumsaltreceiveselec-tronsfromgraphene,generatingactivenitrobenzenefreeradi-cals,whichattachtothegrapheneskeletonviacovalentbonds(Figure1c).
Finally,thenitrobenzene-terminatedgraphenesuperlatticewasdelaminatedfromthePPSsurfaceandtrans-ferredontoaattargetsubstrate.
Figure1dshowsthetypicalRamanspectraofgrapheneonthePPSbeforeandafterchemicalmodication,revealingtheformationofsp3defects.
Forpristinegraphene,noRamanDpeakisobserved,indicativeofitshighquality.
Afterthereac-tionwithdiazoniumsalt,aprominentdisorder-inducedDpeakappearsat1350cm1togetherwithadefect-inducedD′peakat1620cm1.
Inaddition,thedouble-resonance2Dpeakisstronglyweakened.
Theseobservationssuggestthepresenceofalargenumberofsp3defects,[27]whichoriginatefromcova-lentgraftingofnitrobenzenegroupsontothegrapheneplane.
FurtherX-rayphotoelectronspectroscopy(XPS)studyalsocon-rmsthereactionbetweengrapheneanddiazoniumsaltbyrevealinganN1speakonthemodiedgraphene.
Asseenfromthehigh-resolutionN1sspectrainFigure1e,twoprominentpeaksemergeat405.
8and399.
7eVafterreaction.
ThepeakatAdv.
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2016,28,2148–2154www.
advmat.
dewww.
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comFigure1.
Graphenesuperlatticefromsite-selectivechemicalreaction.
a)Schematicofperiodicchemicalfunctionalizationofgrapheneviasubstrateengineering.
b)Experimentalprocedureforfabricatinggraphenesuperlattices.
c)Covalentattachmentofnitrobenzenegroupsongraphenebasalplanebyreactionwithdiazoniumsalt.
d)Ramanspectraofgraphenebefore(blue)andafter(red)chemicalmodication.
e)High-resolutionXPSN1sspectraofgraphenebefore(black)andafter(red)diazoniumreaction,inwhichthegraphenesamplewastransferredontoaat300nmSiO2/Sisubstrate.
2150wileyonlinelibrary.
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KGaA,WeinheimCOMMUNICATION405.
8eVisattributedtothenitrogroups,conrmingthepres-enceofnitrophenylgroupsonthefunctionalizedgraphene.
ThelowerbindingenergyN1speakat399.
7eVisassociatedwithareducednitrogenspecies,possiblygeneratedbytransfor-mationsfromnitrotoaminegroupscausedbyelectronsusedforneutralizationintheXPSchamber.
[26]TheseRamanandXPSresultsstronglysuggestthatnitrobenzenegroupshavebeensuccessfullygraftedontothegraphenelattice.
Figure2ashowsthescanningelectronmicroscopy(SEM)imageofpristinegrapheneonthecloselypackedmonolayerof150nmSiO2spheresafterthermalannealing.
CompressivestrainandchargepuddlesareexpectedtobeintroducedintotheregionsofgrapheneinclosecontactwithSiO2spheres.
Figure2bexhibitsthetypicalopticalmicroscopeimageofchemicallyfunctionalizedgrapheneafterdelaminationfromthePPSsurfaceandtransferringontoaatSiO2/Sisubstrate.
Asisclearlyseen,thegra-phenelmkeepsitsintegrityanddoesnotexhibitobviousopticalcontrastbetweendif-ferentareas.
However,theSEMimageofthesamegraphenelmdisplayedinFigure2ciscompletelydifferent,whichischaracter-isticofaperiodicblackdiskstructurewithaperiodicitymatchingwiththeoriginalclose-packingnanospheresmonolayer.
Asacon-trolexperiment,thesamethermalannealingtreatmentofgraphenewasdoneonthenano-spheresassemblywithoutchemicalreaction.
Nodiscerniblepatternsareobservedongra-phenesheetinthiscase(Figure2c,topinset),whichexcludedthepossiblecontributionofPPS-inducedphysicaleffectafterthermalannealingonthepatternformation.
Inaddi-tion,whenthesamechemicalreactionofgraphenewasdoneonaatSiO2/Sisub-strate,onlyuniformmodicationoccurredonthewholegraphenesurface(Figure2c,bottominset).
Theabovephenomenasuggestthatthenanosphere-contactedareashaveenhancedthechemicalreactivityofgraphenewithdiazoniumsalt,leadingtothesite-selec-tivereactionofgraphenesheet.
Furtheratomicforcemicroscopy(AFM)studiesconrmedtheperiodicpatternstruc-tureongraphenesheet(Figure2d).
TheAFMtopographicimageexhibitstwodistinctareaswithdifferentheightsarrangedinaclose-packingstructuresimilartotheoriginalPPSpattern.
Figure2e,fgivesthestatisticaldistributionsofbrightdiskheightsandtheirperiodicitiesintheAFMimage,respectively.
Theheightsdifferencesbetweentwodis-tinctareasfallintoarangeof1.
6–2.
6nmwithameanvalueof2.
1nm.
Thisvalueislargerthanthatestimatedfromonesinglenitrobenzenegroup,whichisattributedtotheformationofnitrobenzeneoligomerandthelatticedistortionofgraphenefromsp2tosp3hybridization.
[28]Ontheotherhand,theperiodicityofthenearestneighbordisksfallsintoarangeof145–170nmwithameanvalueof155nm.
ThisdistanceiswellconsistentwiththediameterofSiO2spheres(≈150nm)inthecloselypackedmonolayer.
Electrostaticforcemicroscopy(EFM)isadirectmeasurementofthelocalrelativeworkfunctionwithananometerscalespatialresolution.
EFMwasalsoutilizedtocharacterizethepatternedstructureongrapheneafterchemicalmodication.
Figure3a,bpresentstheAFMandcorrespondingEFMimagesofchemicallypatternedgraphene.
Obviously,thebrightareasintheAFMimagehavesignicantlydifferentworkfunctionswiththesurroundings.
Thelocalelectrostaticpoten-tialsareestimatedtobe0.
143and0.
128Vforthebrightareasandthesurroundings,respectively.
Thisdifferenceinworkfunctionsofthetwokindsofregionsclearlyindicatesthedifferenceoftheirchemicalnatures.
Adv.
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comFigure2.
GraphenesuperlatticeformationonSiO2nanospheresassembly.
a)SEMimageofagraphenesheetontheclose-packingmonolayerof150nm-SiO2spheresafterthermalannealing.
Scalebar:1m.
b)Opticalmicroscopeimageofgraphenesheetafterchemicalreac-tiononnanospheresassembly,whichwastakenaftertransferredontoaatSiO2/Sisubstrate.
Scalebar:50m.
c)SEMimageofgraphenesheetin(b).
Thetopandbottominsetspresented,respectively,theSEMimagesofgraphenesheetannealedonnanospheresassemblywithoutchemicalreactionandofthatreactedonaatSiO2/Sisubstrate.
AlltheimagesweretakenaftertransferredontoaatSiO2/Sisubstrate.
Scalebar:1m.
d)AFMimageofthefunctionalizedgraphenesheetshownin(c).
Scalebar:1m.
e,f)Histogramsofdiskheightandperiodicitydistributionsofgrapheneafterchemicalreaction.
2151wileyonlinelibrary.
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KGaA,WeinheimCOMMUNICATIONFromtheaboveexperimentalobservations,weconcludethatasite-selectivechemicalreactionhastakenplaceongraphenesheet,originatingfromthesubstrate-inducedenhancementofchemicalreactivity.
Inotherwords,thechemicalreactivityofgraphenecanbelocallymodulatedbythestructuraldesignofunderlyingsubstrate.
Thisoffersastraightforwardwaytofabricategraphenesuperlatticesbyusingclose-packingnano-spheresassembly.
WecansimplychangethediametersofSiO2nanospheresintheassemblytomodulatetheperiodicityofgra-phenesuperlattice.
Adv.
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comFigure3.
Originofgraphenesuperlattices.
a,b)AFMandcorrespondingEFMimagesofgrapheneon150nmSiO2nanospheresassemblyafterthermalannealingandchemicalmodication,respectively.
ThedatawereobtainedaftertransferredontoatSiO2/Sisubstrates.
Scalebar:500nm.
c)Ramanspectraofgrapheneonnanospheresassemblybefore(top)andafter(bottom)thermalannealingtreatment,normalizedtothe2Dpeakheightd)ScatterplotsofFWHMvaluesofRaman2Dbandversus2Dpeakpositionbeforeandafterannealing(121spectra).
e)Calculatedenergy(Esc)andbondingdistance(RCC)changesasafunctionofstrainingraphene.
2152wileyonlinelibrary.
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KGaA,WeinheimCOMMUNICATIONThermalannealingtreatmentwasfoundtobecriticalfornetuningchemicalreactivityofgraphenebasalplaneontheclose-packingSiO2nanospheresassembly.
Toinvesti-gatetheeffectofthermalannealingprocess,Ramanspec-troscopywasperformedtotracktheannealingprocess.
AsshowninRamanspectraofgrapheneonPPSbeforeandafterannealing,theDpeaknear1300–1350cm1isverysmallanddoesnotshowanyobviouschangeafterannealing(FigureS1,SupportingInformation).
Thisobservationindi-catesthatnoremarkabledefectsareinducedduringthisannealingprocess.
TheGbandsplitsintotwopeaks:oneissimilartotheGpeakbeforeannealingandtheothershowsalargeupshiftalongwithabroadening(FigureS2,SupportingInformation).
Figure3cpresentsrepresentativeRaman2Dbandchangesofgrapheneonnanospheresassemblybeforeandafterthermalannealing.
Beforeannealing,the2Dpeakiscenteredat≈2689cm1,indicatingthatthepristinegrapheneisnearlyintrinsicgraphene.
[29]Afterannealingandcoolingtoroomtemperature,the2Dbandsplitsintotwopeaks:oneissimilartothe2DpeakbeforeannealingandtheothershowsalargeupshiftofΔw2D=26cm1alongwithabroadening.
Figure3dexhibitsthestatisticsresultsoffullwidthathalfmaximum(FWHM)ofthe2Dpeakofgraphenebeforeandafterannealingagainstitsspectralposition.
TheremarkablechangesofGand2Dbandsarestrongevidenceoftheexist-enceofcompressivestrainonthegrapheneplaneinducedbythermalannealing.
[25,30]Twosplitting2Dpeaksarecorre-spondingtothesuspendingareaswithoutmechanicalstrainandtheSiO2-contactedareaswithcompressivestrain,respec-tively.
ThecompressivestrainarisesfromthedifferenceinthermalexpansioncoefcientsbetweengrapheneandtheunderlyingSiO2spheres.
[25]Asthetemperatureincreases,graphenecontractswhiletheunderlyingSiO2spheresexpand.
Ontheotherhand,grapheneexpandswhiletheunderlyingsubstrateshrinksinthecoolingprocess.
Relativeslippingoccursbetweenthegraphenesheetandthesubstrateoveracriticaltemperature,determinedbyvanderWaalsforcesbetweenthem.
LocalcompressivestrainremainsinthegrapheneplaneattheSiO2nanosphere-contactingareas,asevidencedbytheaboveRaman2Dbandchanges.
[30]Inaddi-tion,theSiO2-contactedgraphenehasmuchlargerFWHMof2Dbandthansuspendedone.
ThelargerFWHMof2Dbandmightbecontributedtothepresenceofelectron-holepuddlesonSiO2-contactedgraphenebecauseelectron-holepuddlesongraphenewhosesizeissmallerthanRamanlaserspotsizewouldleadtoabroader2Dband.
[18]WetheoreticallycalculatedthestraineffectonthechemicalreactivityofgraphenebasedonthefollowingformulasEEEEEEEEEEE()()=+σσσ()bCMGGCFscbb0CMGCMG0GG0whereEbisthebindingenergy,EGistheenergyofgraphene,ECMGistheenergyofchemicallymodiedgraphene,ECFistheenergyofthefunctionalgroup,andEscisthedifferenceofthereactionenergybetweengraphenewithandwithoutstrain.
Thesuperscriptsσand0denotethevaluewithandwithoutisotropicstrainongraphene,respectively.
Figure3eshowsthechangeofEscvalueasafunctionofstrainongraphene.
Apparently,Escdecreasesforbothtensileandcompressivestrains,indicatingthatgrapheneunderstrainismoreener-geticallyfavorableforchemicalreactionsasexpected.
Atastrainlessthan0.
02,thereisnodistinctdifferencebetweentensileandcompressivestrainsongraphene'sreactivity.
Atalargerstrain,however,thecompressivestrainismoreeffec-tiveforenhancingthereactivity(Esc=1.
65eVforσ=0.
05;Esc=0.
21eVforσ=0.
05).
Inaddition,asthecompressivestrainincreases,thedistancebetweengrapheneandfunc-tionalgroupgraduallydecreases.
Thistheoreticalresultwellsupportsourexperimentalobservation,i.
e.
,thelocalcom-pressivestraininducedbySiO2nanospherescanenhancethechemicalreactivityofgraphenewithdiazoniumsalt.
Thus,thecompressivestraincombinedwithchargepuddlesenhancedanddifferentiatedSiO2-contactedgraphene'sreactivityfromthesurroundings,enablingthemask-freechemicalpatterningofgraphene.
Variousgraphenesuperlatticescanbefabricatedbydesigningthesupportingsubstratesofgraphenesheetbasedonthislocalsubstrate-inducedchemicalreactionapproach.
TheperiodicityofgraphenesuperlatticecanbesimplymodulatedbyvaryingthediametersofSiO2nanospheres.
Graphenesuperlatticeswithaperiodicityof400(Figure4e),150(Figure4f),and114nm(Figure4g)havebeenfabricatedinsuchaway.
ByusingaSiO2nanoholearraysubstrateshowninFigure4d,agraphenesuperlatticewithreversedpatternstructurehasbeensuccess-fullyfabricated(Figure4h).
Itshouldbeemphasizedthatthecontrolofreactiontimeiscriticaltotheformationofsuperlat-tice.
Takinga150nmSiO2nanospheresassemblyasthesup-portingsubstrate,wegraduallyincreasedthereactiontimeofgraphenewithdiazoniumsaltfrom0.
5to4h.
Atthebeginning,nodiscerniblepatternstructurewasobserved(Figure4i).
Thegraphenesuperlatticeappearedafter1hreaction(Figure4j).
However,anover-reactionalsodestroyedthesuperlatticestruc-tureasseeninFigure4k.
Thereasonisthatthereactionhasoccurredonthewholegraphenesurfaceinanelongatedreac-tiontime.
Moreover,thereisalsoabigfreedomforgraftingdifferentfunctionalgroupsontographenesheetusingthepre-sentedapproach.
GiveninFigure4lisanexampleofgraphenesuperlatticemadebyphotomethylationreaction,inwhichgra-phenewasperiodicallymodiedbymethylgroupsinsteadofnitrobenzene.
Insummary,wepresentauniversalsubstrateengi-neeringapproachtofabricategraphenesuperlatticesbasedonthesubstrate-enhancedchemicalreactivityofgraphene.
Variousgraphenesuperlatticesdowntonanometerscalehavebeenmadebyusingtheclose-packingmonolayerofSiO2nanosphereswithdifferentperiodicities.
Ithasbeenprovedthatsuchastrategycanbeappliedtofabricatearbi-trarygraphenesuperlatticessimplybynanostructuringthesupportingsubstratesofgraphenesheets.
Thereisalsoafreedomforthechoiceofchemicalreactions,asdemon-stratedbydiazoniumsaltreactionandphotomethylationreactioninthiswork.
Thisallowsustomakeaperiodicmodificationofgraphenesheetwithdesiredfunctionalities.
Thismask-freetechniqueprovidesaneffectiveandversa-tilerouteforfabricatinggraphenesuperlatticewhichcanbeutilizedingraphene-basedelectronicandoptoelectronicdevices,chemo/biosensorsandforstudyingtherichphysicsof2Dsuperlattices.
Adv.
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2016,28,2148–2154www.
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com2153wileyonlinelibrary.
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KGaA,WeinheimCOMMUNICATIONAdv.
Mater.
2016,28,2148–2154www.
advmat.
dewww.
MaterialsViews.
comExperimentalSectionPreparationofPPS:Aminopropylmethyl-diethoxysilanewasaddedtoastocksolutioncontaining1wt%monodispersecolloidalSiO2nanospheres(UnisizeTechnology,China).
Afterheatingthesolutionto100°Cfor8–12h,theresultingsolutionwaswashedthreetimeswithethanolandthenultrasonicatedinmethanol.
Then,thechemicallymodiedSiO2sphereswereself-assembledontoSiO2/SisubstratesbyusingLangmuir–Blodgetttechnique.
TheSiO2nanoholearraysubstratewasfabricatedthroughthefollowingprocedures:commercialpolyethylenespheresweredepositedontoSiO2/Sisubstratetoformaclose-packingmonolayer;thenthesphereswereshrunkdownbyplasmaetchingtreatment;a10nmSiO2layerwasthermallydepositedontothesubstrateandthesphereswereremovedafterultrasonictreatmentintoluene.
BeforetransferringgrapheneontoPPS,theas-preparedPPSwastreatedwithoxygenplasmafor30min(15W)toremoveorganiccomponentsonthespheresurface.
Site-SelectiveModicationofGraphene:TheCVDgrowngrapheneonCufoilswastransferredontoPPSbyusinga"drytransfer"method[31]toavoidwatertrappingbetweengrapheneandsubstrate.
AftertransferringthegraphenelmontoPPS,thesamplewasannealedat350°Cfor2hinforminggas(30sccmH2/100sccmAr)underambientpressure.
Then,thegraphenesampleswereimmersedintoamixedaqueoussolutionof20mM4-nitrobenzenediazoniumtetrauoroborate(≈10mL)and1wt%sodiumdodecylsulfateaqueoussolution(2mL),wheretheywerereactedfor1.
5hat40°C.
Forthephotomethylationprocess,thegraphenesampleswereimmersedindi-tert-butylperoxide(99%)andirradiatedunderUVlightwiththewavelengthrangefrom320to500nm.
Aftersite-selectivechemicalmodication,thesampleswererinsedwithdeionizedwater,immersedindeionizedwaterfor2h,anddriedwithnitrogengas.
TonondestructivelydelaminatethefunctionalizedgraphenelmfromPPS,thesampleswereimmersedina10%HFaqueoussolutionatroomtemperatureusingPMMAlmasthetransfermedium.
AfterdetachingthegraphenefromPPS,weleftthePMMA-supportedgrapheneoatinginHFsolutionfor20minbeforetransferringittoatSiO2/SisubstratesforcompletelyremovingtheresidualSiO2.
ThePMMAlmwasnallyremovedbyhotacetone.
Characterizations:RamanspectrawerecollectedwithaHoribaJobinYvonLabRAMHR800systemwitha514.
5nmexcitationlaser.
Thelaserspotsizewas≈1m.
XPSmeasurementswereperformedonaKratosAxisUltraspectrometerwithAlKαmonochromatedradiationatlowpressuresof5*109–1*108Torr.
TheXPScollectionareawas≈300*700m2.
Tocorrectforcharging,thehighestpeakinC1sspectrumwasshiftedto284.
5eV.
AFMandEFMwereconductedonaBrukerDimensionIconatomicforcemicroscopeintappingmode.
ForEFMmeasurements,thetopographicinformationwasobtainedintherstpass,andthenthetipwasliftedbyagivenconstantheightof20nmabovethesamplesurfaceandbiasedaDCvoltageVtipinthesecondpass.
Conductingtips(SCM-PIT,Bruker)witharesonancefrequencyofca.
70kHzandspringconstantofca.
2.
8Nm1wereused.
TheoreticalCalculations:Toperformgeometryoptimizationandenergycalculationsforgrapheneandchemicallymodiedgrapheneunderdifferentstrains,densityfunctionaltheoryimplementedintheViennaabinitiosimulationpackage[32]wasused.
Consideringspinpolarization,weadoptedthegeneralgradientapproximationwiththePerdew–Burke–Ernzerhofexchangecorrelationfunctional[33]andacut-offenergyof520eV.
Geometryoptimizationcontinueduntilalltheatomicforceswerelessthan0.
01eV/.
TheMonkhorst–Packgridmeshwas7*7*1forallsystemsintheself-consistentelditeration.
Adjacentsheetswereseparatedbyatleast20toavoidinteractionsbetweenthem.
SupportingInformationSupportingInformationisavailablefromtheWileyOnlineLibraryorfromtheauthor.
Figure4.
Versatilegraphenesuperlattices.
a–c)SEMimagesof400,150,and114nmSiO2nanospheresassemblyusedforsuperlatticeformation,respectively.
d)SiO2nanoholearraywithaperiodicityof200nmusedforsuperlatticeformation.
eh)Graphenesuperlatticesmadefrom(a–d)afterreactingwithdiazoniumsaltandtransferredontoatSiO2/Sisubstrates.
i–k)SEMimagesofgraphenesheeton150nmSiO2nanospheresassemblywithareactiontimeof0.
5,1,and4h,respectively.
l)SEMimageofgraphenesuperlatticeobtainedfrom150nmSiO2nanospheresassemblybyphotomethylationreaction.
Thescalebarsin(ac)and(eg)are500nm,andin(d),(h–l)are200nm,respectively.
2154wileyonlinelibrary.
com2015WILEY-VCHVerlagGmbH&Co.
KGaA,WeinheimCOMMUNICATIONAdv.
Mater.
2016,28,2148–2154www.
advmat.
dewww.
MaterialsViews.
comAcknowledgementsL.
Z.
andL.
L.
contributedequallytothiswork.
ThisstudywasfundedbytheMinistryofScienceandTechnologyofChina(GrantNos.
2013CB932603,2012CB933404,and2011CB933003),theNationalNaturalScienceFoundationofChina(GrantNos.
51432002and51121091),theMinistryofEducation(20120001130010),andtheInternationalPostdoctoralExchangeFellowshipProgram(GrantNo.
20130002).
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