OptimizingFree-FloatingGrapheneontheSurfaceofWater
SeanHackett1,2,RafaelFerreira2,3,PabloFerreira2,DavidLloyd2,Anubhav Wadehra4,Dr.ScottBunch2
HolyInnocents’EpiscopalSchool,805MountVernonHwy,Atlanta,GA1;BostonUniversity,Boston,MA0221522;Av.dosEstados,5001- Bangú,SantoAndré- SP,
09210-580,Brazil3;PECUniversityofTechnology,Chandigarh,India4
Abstract
Contaminationduringgrowthandtransferphasesprovesto
beamajorobstacleininvestigatingpropertiesandusesfor
monolayergraphenegrownwithCVD[1].Transferof
graphenewithasupportivefilmofpolymerfromCufoilsuch
aspolymethyl methacrylate(PMMA),oneofthemost
popularandreliablepolymersusedinwettransfers,will
leaveresiduewhenremovedandpreventmanyexperiments
frombeingtestedwiththegraphenecreated[2][3].We
investigatepossiblemethodsofwettransferwithouttheuse
ofpolymerbyfree-floatinggrapheneonthesurfaceofCu
etchantandwater.Inthispaper,theprimarysuccessof
monolayergraphenefree-floatingisdiscussed,aswellasthe
resultsoftreatmentsonthegraphenesuchasanAr plasma
treatmentandatransfermethodinvolvingacohesivelayer
ofhexaneaboveCuetchantandadistillationprocess,
showinginitialsuccess.
Methods
VariationintheGrowth
Inordertochangetheinitialqualityofthemonolayergraphene,theflowratesofhydrogen
andmethanegaswerealteredduringthegrowthstageoftheCVDprocess.Weusethe
differentgraphenesamplesinthesamewet-transferprocesstodeterminethequalityofthe
graphenegrown.
VariationinDirectGrapheneTreatment
EvidencesuggeststhatanAr plasmatreatmentdirectlyongraphenemaystrengthenthe
sample.TheAr plasmatreatmentistestedindifferentflowrates,powers,andtimesagainst
sampleswithnoAr plasmatreatmentwiththesamegrowthspecsandthesamewettransfer
process,andtheresultsarecheckedwithanopticalmicroscope.ARamanspectroscopy
microscopeisalsousedifthegraphenecanbeanalyzedinaspotwithmonolayergraphene.
VariationinWet-TransferProcess
Wetestahexanelayeronthesurfaceofthetransfersolutiontocreateafullyremovable
cohesivelayerthatlimitsgraphenefrombreaking,andadistillationprocessthatlimitsthe
amountofmovesfromonedishtoanothertolimitsurfaceenergyofthetransfersolution.A
metalcanisterandplasticsheetingisusedtopreventhexaneevaporation.
Introduction
GrapheneBasics
Grapheneisa1-atomthickmaterialconsistingofcarbon
atomsbondedinahexagonformation.Becauseofitsunique
bondingproperties,grapheneisoneofthestrongestand
mostconductivematerialseverdiscovered[1].Inaddition,
graphenecanbemadeatalowcost,makingitofextreme
interestforstudy.
Fig.1a)TEMscanofgraphene[5]
Fig.1b)3Dmodelofgraphenestructure
(AlexanderAlUS viaWikimediaCommons)
StandardProcedure
First,wecuttheCufoil,rinsewithacetone,isopropylalcohol,
andDIwater,andplaceitintotheCVDfurnace,withapeak
temperatureof1000˚CtodepositgrapheneontheCufoil.
Afterthegrowth,wetaketheCufoilwithgraphenecoatedon
bothsides,sealoffonesidewithplasticandtape,andexpose
theothertoanO2plasmatreatmenttoremovetheexcess
grapheneonasingleside.
H2
CH4
Time(min)
Heating
10
0
25
Annealing
10
0
40
Growth
5
15
10
Cooling
10
0
Cool
Wehavesuccessfullyfree-floatedgraphenewithsparsepatchesofmonolayergraphenewith
notreatmentorstructuralaidwithPMMA,butmuchofitwascrumpled.TreatmentswithAr
plasmahavebeenshowntoimprovethestrengthofgrapheneinwater,yieldinglarger
grains,butwithlarged-peaks(Fig.1).ThebestAr plasmarecipewasa100flowrate,a100W
power,anda30secondexposuretime.
WithoutAr plasma,thehexane-distillmethodoutlinedaboveprovidedpositiveresults.The
grapheneobtainedproducedlarge,high-qualitygrainsofmonolayergrapheneandalow
d-peak.
8000
Furthermore,thehexane-distillmethodforafree-floating
graphenewet-transferprovedtobemoresuccessfulthan
previousmethodswithoutPMMA.Thehexane-distill
methodalsoshowspromiseforbeingaviablepolymer-free
wet-transfertechniqueandallowlaboratoriestoperform
experimentsonresidue-freemonolayergrapheneinthe
future.
References
Counts
Counts
Fig.4b)HexaneDistillMethod
(LowD-Peak)
[3]Bhaviripudi, S.;Jia,X.;Dresselhaus, M.S.;Kong,J.NanoLettersNanoLett.2010,10(10),4128–4133.
[5]Suh, Y.;Park,S.;Kim, M.Microscopy andMicroanalysisMicrosc Microanal 2009,15(S2), 1168–1169.
[6]Zheng YanAndrew R.Barron,CharacterizationofGraphenebyRamanSpectroscopy. OpenStax CNX.
[7]Zhang,G.;Güell, A.G.;Kirkman,P.M.;Lazenby,R.A.;Miller,T.S.;Unwin, P.R.ACSAppl.Mater.Interfaces
ACSApplied Materials&Interfaces2016,8(12), 8008–8016.
1500
2000
RamanShift(cm-1)
2500
3000
Acknowledgements
3000
2000
4000
Fig.4c)Ideal
monolayer
graphene[6]
[2]Deokar,G.;Avila,J.;Razado-Colambo, I.;Codron, J.-L.;Boyaval,C.;Galopin, E.;Asensio, M.-C.;Vignaud, D.
Carbon2015, 89,82–92.
4000
1000
Fig.2e)PMMAisreducedwith
UVradiation, butnotfully
removed
Conclusions
6000
4000
Counts
ToreducetheamountofPMMA,we
thenplacethesampleindirect
exposuretoUVrays.However,the
PMMAwillnotbefullyremoved,
whichlowerstheconductivityofthe
graphene.Ourmethodwill
drasticallyreducetheresidueon
graphenethroughamethodthat
doesnotusePMMA[2].
Thehexane-distillmethod(Fig.3a-3c)ismoresuccessfulin
producingmonolayergraphenewithalowd-peakmethod
overothermethodsthatdonotusePMMAbecauseofits
abilitytolimitthesurfaceenergyandminimizegraphene
contactwiththeCuetchantandairthatcanripapart
grapheneinanormalsystem.
Becausehexaneismucheasier
toremovefromgraphenethan
PMMA,thereissignificantly
lessresidue,ifany,onthe
graphene[7].Theabilityto
transfergraphenetoaSiwafer
orothersubstratewithout
Fig.6)Graphenefilmproduced
residueallowsexperiments
byhexane-distillmethod(Fig.
involvingconductivityand
4),approximately4mmacross
wrappingwiththegraphene.
[4]López-Polín, G.;Gómez-Navarro,C.;Parente,V.;Guinea,F.;Katsnelson, M.I.;Pérez-Murano,F.;
Gómez-Herrero,J.NaturePhysics 2014,11(1),26–31.
D-Peak
2000
Fig.2d)Graphenetransferredto
waterwithspoon, scoopedoffwith
Siwafer
Theresultsofthehexanedistillmethod(Fig.3a-3c)
areverysimilartothe
Ramanspectrumas
pristinemonolayer
graphene(inblue)
(Fig.4c)
[1]Her,M.;Beams,R.;Novotny, L.Physics LettersA2013,377(21-22), 1455–1458.
Fig.4a)
Argontreated
graphene
(HighD-Peak)
Fig.2c) PMMAisspunon
graphene,windowiscreated,
placedonCuetchant
Fig.5)TheresultsofAr
plasmatreatedgraphene
(inred)[4]matchour
results(Fig.4a)
AlthoughAr plasmatreatedgraphenebecomesmorerigid
andcohesivewhenfree-floatinginCuetchantandwater,it
hasahighd-peakwhenthetransferiscompleted.
Results
Underthegrowth:
Fig.2b)O2plasma removesexcess
graphene
Next,weremovethetapeandplastic,andweuseaspinnerto
coattheremainingsurface(withgraphene)witha200nm
layerofPMMA.Next,wecutoutawindowmadeoutofa
plasticadhesiveintheshapeofthesubstrate,andstickit
directlyonthesurfaceofthePMMA-coatedsideoftheCu
foil.Wethenplacethefoilina20mLCuetchantand40mL
waterbathtoetchawaytheCufoilfor5hours.Next,we
transfertheplasticwindowwiththePMMAandgrapheneto
aDIwaterbathandletitsoakfor2hours.Lastly,wetakea
cleanSiwafer(cleansedwithacetone,isopropylalcohol,and
DIwater)toextractthePMMAandgraphene.
MeasuringtheResults
Weremovethesamplesfromthe
wet-transferprocessbyscooping
themoutwithacleanSiwaferand
analyzingthesamplequalitatively
underanopticalmicroscope.Ifthe
samplehaspatchesofmonolayer
graphenethatcanbefurther
analyzed,theyareputundera
Ramanspectroscopymicroscopeto
quantitativelycheckthequalityof
thegraphenethroughad-peak
measurement.
Fig.3d)Pictureofthe
canisterusedtoblock
lightandair
Fig.3c)Cuetchantisdilutedwith
watertolimitsurfaceenergyand
cleansegraphene
Phases
Fig.2a)CVDcarbon depositsonCu
foiltoformgraphene
Fig.3b)Cuetchantisdrainedthrough
syringe
Fig.3a)Metalandplasticsheetingseal
offlightandair,Cuunderhexane
Discussion
Ar plasmatreatedsamplesaremuchstronger,moredurable,
andmorestableinthewettransferthansampleswithoutan
Ar plasmatreatment.Therecipe100/100/30isthemost
superiorrecipefortheCuetchantandwatersolution.The
reasonforthismaybethattheAr plasmatreatmentpokes
sparseenoughholesinthegraphene,tolimittheenergyin
whichcarbonatomscantradeenergymakingitmorerigid,
butnotenoughtoeradicatethegraphene[4].Thistheory
explainstheincreasedperformanceinliquid,butalsothe
highd-peak.
1500
2000
RamanShift(cm-1)
3000
2000
2500
3000
2D-Peak
G-Peak
1000
1500
2000
RamanShift(cm-1)
2500
3000
IwouldliketothankDr.ScottBunchforallowingmeandotherRISEinterns
toparticipateinhislab.IwouldalsoliketothankDavidLloyd,Lauren
Cantley,andKailu Songforbeinginvaluablereferencesduringtheprocessof
learningtheinsandoutsofthelaboratorysettingandtheBunchlabin
particular.ImustgiveaspecialthankstoRafaelFerreirawhoguidedme
throughtheprocessoflearninghowallthemachineryandscientificprocess
worksinthelab.AverybigthanksgoesouttoDr.AnnaGreenswag ofthe
RISEprogramforallowingmetospendmysummerhereandlearnallabout
thelifeofascientistandtherealitiesofresearch.Lastly,Imustthankmy
parentsforlettingspendanamazingsixweekshereatBostonUniversity
awayfromhometoexploreapossiblescientificcareer.
Optimizing Free-Floating Graphene on the Surface of Water
Sean Hackett1,2, Rafael Ferreira2,3, Pablo Ferreira2, David Lloyd2, Anubhav Wadehra4,
Scott Bunch2
Holy Innocents’ Episcopal School, 805 Mount Vernon Hwy, Atlanta, GA1; Boston
University, Boston, MA 022152; Av. dos Estados, 5001 - Bangú, Santo André - SP,
09210-580, Brazil3; PEC University of Technology, Chandigarh, India4
Abstract:
Contamination during growth and transfer phases proves to be a major obstacle in
investigating properties and uses for monolayer graphene grown with CVD [1]. Transfer
of graphene with a supportive film of polymer from Cu foil such as polymethyl
methacrylate (PMMA), one of the most popular and reliable polymers used in wet
transfers, will leave residue when removed and prevent many experiments from being
tested with the graphene created [2][3]. We investigate possible methods of wet transfer
without the use of polymer by free-floating graphene on the surface of Cu etchant and
water. In this paper, the primary success of monolayer graphene free-floating is
discussed, as well as the results of treatments on the graphene such as an Ar plasma
treatment and a transfer method involving a cohesive layer of hexane above Cu etchant,
showing initial success.
References:
[1] Her, M.; Beams, R.; Novotny, L. Physics Letters A 2013, 377 (21-22), 1455–1458.
[2] Deokar, G.; Avila, J.; Razado-Colambo, I.; Codron, J.-L.; Boyaval, C.; Galopin, E.;
Asensio, M.-C.; Vignaud, D. Carbon 2015, 89, 82–92.
[3] Bhaviripudi, S.; Jia, X.; Dresselhaus, M. S.; Kong, J. Nano Letters Nano Lett. 2010,
10 (10), 4128–4133.