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US 2020/0051709A1 Feb.13,2020 7 alyadedorbondedoxygenorhydrogen.Thisisapowerful electricalandthermalconductivityascomparedtopolycrys aproachtolarge-scalepreparationofpristineNGPs. talinegraphite.Asanexample,RGOthinfilmsofaproxi [07]Afteraditionalresearchanddevelopmentwork, mate10-30nmthicknesexhibit typicalelectricalcon wefurtherdiscoveredthatasurfactantisnotneededifthe graphiteparticlesaremixedwithacertainliquidorsolvent thatmetsaspecificsurfaceenergyrequirement[A.Zhamu andBorZ.Jang,U.S.Pat.No.8,26,801,Jul.24,2012].The resultingsurfactant-fremixtureofpristinegraphiticpar ticles(non-preintercalated,un-oxidized,un-fluorinated,etc.) andsolventisthensubjectedtodirectultrasonication.This improvementissignificantsinceiteliminatesthenedto removeasurfactantfromthisliquidorsolvent.Theproces isfastandenvironmentalybenign.Itcanbeeasilyscaled-up electronicandopticalbehaviorifsodesired. formasproductionofhighlyconductinggraphene.Again, [081]Therearemanyproceses,withorwithoutatem itisimportanttoemphasizethat,inalpriorartproceses, plate,thatcanbeusedtoproducemetalnanowires,andthese arewelknownintheart.Awidelyused aproach to ofgraphite(i.e.,afterfirstexpansion)and,inmostcases, fabricatemetalnanowiresisbasedontheuseofvarious ultrasonificationwasusedafterintercalationandoxidation afterthermalshockexposureoftheresultingGICorGO templates,whichincludenegative,positive,andsurfacestep templates.Negativetemplatemethodsuseprefabricated tionprocesdoesnotinvolvepre-oxidizingorpre-interca cylindricalnano-poresinasolidmaterialastemplates.By latingthestartinggraphiteparticles. depositingmetalsintothenano-pores,nanowireswitha (aftersecondexpansion).Incontrast,thedirectultrasonica [0078] Inaditiontotheaforementioneddirectultrasoni cation,alsoreferedtoasliquidphaseproduction,other procesescanbeusedtoproducepristinegraphene. [082]Thepositivetemplatemethoduseswire-likenano Examplesaresupercriticalfluidexfoliation,graphitediso structures,suchasDNAandcarbonnanotubesastemplates, lutioninselectsolvent(e.g.NMP),alkalimetalintercalation andwater-inducedexplosion,andmoreexpensiveepitaxial growth.Thealkalimetalintercalationrouteinvolvesexpos inggraphitetoanalkalimetalmeltoramoltenmixtureof twoalkalimetals(e.g.eutectic).Thiscanbeconductedata temperaturetypicalylowerthan30°C.,butinahighly controledenvironment(e.g.insideaglovebox). [079]Normaly,apristinegrapheneisasingle-grainor single-crystaline structureofhexagonal carbon atoms whereinthegrapheneplaneisesentialydefect-freexcept atthegrapheneplaneedges.Further,thepristinegraphene and nanowires are formed on the outer surface of the templates.Unlikenegativetemplates,thediametersofthe nanowiresarenotrestrictedbythetemplatesizesandcanbe controledbyadjustingtheamountofmaterialsdepositedon thetemplates.Byremovingthetemplatesafterdeposition, wire-likeandtube-likestructurescanbeformed. [0083] Atomic-scalestepedgesonacrystalsurfacecanbe usedastemplatestogrownanowires.Themethodtakes advantageofthefactthatdepositionofmanymaterialsona surfaceoftenstartspreferentialyatdefectsites,suchas surfacestep-edges.Forthisreason,themethodissometimes caled“stepedgedecoration.”Asexamples,severalresearch normaly does not contain any non-carbon atoms (e.g. oxygenandhydrogen).Thepristinegrapheneisfundamen groupspreparedmetalnanowiresonvicinalsinglecrystal surfacesusingthephysicalvapordeposition(PVD)method. lineandinherentlyhasasignificantamountofnon-carbon Othersfabricatedmetalnanowiresof1-2atomiclayerthick talydistinctfromtheCVD graphene,whichispolycrystal withacontroled“width”andwirespacing. phenecontainsmanydefects,e.g.,grainboundaries,line [0084]Metalnanowires,CNTs,and/orpristinegraphene defects,vacancies,andotherlaticeimperfections,suchas maybedispersedinaliquidmediumwithorwithouta atomschemicalybondedthereto.Moreover,theCVD gra thosemanycarbonatomsthatarearangedinpentagons, heptagons,oroctagons,asoposedtothenormalhexagonin pristinegraphene.Theterm“pristinegraphene”asclaimed intheinstantaplicationinherentlydoesnotincludethe CVD graphene. surfactanttoformasolution,suspension,orink.Thegra phene-,metalnanowire-,CNT-,orhybrid-basedfilmsmay bedepositedfromsolution,suspension,orinkusinga varietyofmethods,includingspraypainting,dropcasting, spincoating,vacum-asistedfiltration,electrostaticdepo sition,anddipcoating. [0085]Inaspraypaintingproces,thesolution/suspen sion/inkcanbespraypaintedontoaheatedornon-heated substrate.Thesubstratemayberinsedduringthespraying [0080] Asindicatedearlier,diferenttypesofNGPshave diferentoxygencontents.Pristinegraphenehasesentialy 0%oxygen.Grapheneoxide(GO)has0.01%-46%by weightofoxygenandreducedgrapheneoxide(RGO)has 0.01%-2.0%byweightofoxygen.BothGOandRGO procestoremovethesolubilizationagent,orsurfactant. containsahighpopulationofedge-andsurface-borne chemicalgroups,vacancies,oxidativetraps,andothertypes ofdefects,andbothGOandRGOcontainoxygenandother elements,e.g.hydrogen.Hence,GOandRGOarecom monlyconsideredinthescientificcommunityasaclasof 2-Dnanomaterialthatisfundamentalydiferentanddis tinctfrompristinegraphene.Thisdistinctionanddiference incompositionandstructureisalsoreflectedinmanyof theirproperties.Forinstance,GOisesentialyanelectri calyinsulatingmaterial.Evenafterheavyoxidationtreat ment,theresultingRGOstilexhibitsarelativelylow Thesprayingsolution/suspension/inkmaybeofanycon centration.Thesubstratesurfacemaybefunctionalizedto aid in adhesion of the deposited species (i.e., metal nanowires,CNTs,and/orgraphene).Thesprayingrateand thenumberofsprayingpasesmay bevaried toobtain diferentamountsofdepositedspecies. [086] Inadropcastingproces,adropofthesolution/ suspension/inkcanbeplacedontoasubstrateforaperiodof time.Thesubstratemaybefunctionalizedtoenhanceadhe sionofdepositedspecies.Thesubstratewithgraphenemay berinsedbyapropriatesolvents.Alternatively,thesolution ductivityof50-720S/cm,evensignificantlylowerthanthe 1,250S/cmofpolycrystalinegraphite[Ref.13;X.Wang,et al].Incontrast,thepresentstudydemonstratesthatpristine graphene-basedthin film shetsofcomparablethicknes exhibitanelectricalconductivityoftypicaly5,0-15,0 S/cm.Thesepristinegrapheneshetsarepracticalydefect fre,aresingle-crystaline,andcontainnooxygenorhydro gen.Thepristinegraphenecanbeoptionalydopedwitha chemicalspecies,suchasboronornitrogen,tomodifyits diameterpredeterminedbythediameterofthenano-pores arefabricated.PDF Image | HIGHLY CONDUCTING AND TRANSPARENT FILM AND PROCESS
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