DTIC ADA573720: A Direct Transfer of Layer-Area Graphene

0.32 MB·English

by  Defense Technical Information Center

APPLIEDPHYSICSLETTERS96,113102(cid:1)2010(cid:2)
A direct transfer of layer-area graphene
William Regan,1,2 Nasim Alem,1,2,3 Benjamín Alemán,1,2,3 Baisong Geng,1,4 Çağlar Girit,1,2
Lorenzo Maserati,1,5 Feng Wang,1,2,3 Michael Crommie,1,2,3 and A. Zettl1,2,3,a(cid:1)
1DepartmentofPhysics,UniversityofCaliforniaatBerkeley,Berkeley,California94720,USA
2MaterialsSciencesDivision,LawrenceBerkeleyNationalLaboratory,Berkeley,California94720,USA
3CenterofIntegratedNanomechanicalSystems(COINS),Berkeley,California94720,USA
4SchoolofPhysicalScienceandTechnology,LanzhouUniversity,Lanzhou730000,
People’sRepublicofChina
5PolitecnicodiMilano,20133Milano,Italy
(cid:1)Received 10 December 2009; accepted 6 February 2010; published online 15 March 2010(cid:2)
Afacilemethodisreportedforthedirect(cid:1)polymer-free(cid:2)transferoflayer-areagraphenefrommetal
growth substrates to selected target substrates. The direct route, by avoiding several wet chemical
steps and accompanying mechanical stresses and contamination common to all presently reported
layer-area graphene transfer methods, enables fabrication of layer-area graphene devices with
unprecedented quality. To demonstrate, we directly transfer layer-area graphene from Cu growth
substrates to holey amorphous carbon transmission electron microscopy (cid:1)TEM(cid:2) grids, resulting in
robust, clean, full-coverage graphene grids ideal for high resolution TEM. © 2010 American
Institute of Physics. (cid:3)doi:10.1063/1.3337091(cid:4)
Graphene, a single atomic monolayer of sp2-bonded Asademonstrationofprinciple,wechoseanamorphous
hexagonal carbon with extraordinary mechanical, electronic, carbon (cid:1)a-C(cid:2) transmission electron microscopy (cid:1)TEM(cid:2)
andopticalproperties,hasbecomeasubjectofgreatinterest grid—SPIAuQuantifoilwith1.2micronholeya-Cfilm—as
in materials science following its experimental isolation by the target substrate. However, as discussed below, other tar-
themechanicalcleavageofgraphite.1,2Intheyearssincethis get substrates are possible. The structure of graphene makes
development, more synthesis methods have emerged to iso- it ideally suited for use as a TEM support.9–13 Graphene is
latesingletofewlayergraphene,suchasepitaxialgrowthon only a single carbon atom thick, an order of magnitude thin-
SiC,3,4 oxidative/thermal intercalation and ultrasonication of ner than the best currently available amorphous TEM sup-
graphite,5andmostrecentlybychemicalvapordepositionon ports. This thinness and the low atomic number of carbon
metal substrates such as Ni6 and Cu.7 In particular, Cu makegraphenealmostcompletelytransparenttotheelectron
growthhasgarneredconsiderableinterestduetoitsabilityto beam.Theslightbeaminteractionwiththehexagonalcarbon
produce macroscopic areas of mostly monolayer graphene, monolayer generates a well-defined signal that can be easily
with domain sizes comparable to the size of the largest subtracted from resulting images and diffraction patterns.
flakes that can be produced by mechanical exfoliation. In Somewhat counterintuitively, one can often achieve higher
order for growth on Cu to be a viable route to large-scale resolution images of a graphene-supported object than of a
graphene applications,8 there must be a reliable method for similarsuspendedobjectbecause,despitenotbeingperfectly
transparent to the electron beam, the graphene support helps
transferring the graphene from metallic Cu substrates to
more useful (cid:1)e.g., insulating(cid:2) substrates. To date, transfer of dampen vibrations that would blur the suspended object.
Graphene may therefore be the best possible TEM support
layer-area graphene has been achieved using a polymer
coating—typically polymethyl methacrylate (cid:1)PMMA(cid:2) or for studying a variety of materials, namely, nanostructures
polydimethylsiloxane(cid:1)PDMS(cid:2)—asatemporaryrigidsupport and biological molecules that could otherwise not be re-
solved with conventional TEM supports.10,11 While exfoli-
during etching of the metal to prevent folding or tearing of
thegraphene.6,7Unfortunately,theuseofthesepolymersne- ated graphene has been previously isolated on TEM
grids,9,10,12,13 these methods require delicate or cumbersome
cessitates several wet chemical steps that can contaminate
processing and limit the suspended graphene area to exfoli-
and mechanically damage the graphene.
ated flake sizes, 100 microns in diameter at most. Such a
In this letter, a simple method is described for the direct
small target makes sample preparation difficult and unreli-
transfer of layer-area graphene from Cu growth substrates to
able.Thus,areliable,cleantransferoflayer-areagrapheneto
varioustargetsubstrates.Surfacetensionandevaporationare
TEM grids would be a significant advance for high reso-
used to pull Cu-supported graphene into intimate contact
lution microscopy.
with the targets, simultaneously achieving the desired
Figure1illustratestworoutes,astandardpolymer-based
graphene/targetbondandprovidingarigidgraphenesupport method (cid:1)left(cid:2) and our direct method (cid:1)right(cid:2), to transfer
(cid:1)the target substrate(cid:2) during subsequent Cu etching.9 This
graphene from Cu growth substrates to TEM grids. Both
direct transfer is cleaner and gentler than polymer-based
transfers begin with layer-area graphene growth on a Cu
methods, making it ideal for the fabrication of a variety of
foil—Alfa Aesar No. 13382, 25 microns thick—via low-
optical, chemical, and electronic devices that utilize large, pressure chemical vapor deposition.7 A rigid support is
uniform graphene sheets.
neededtopreventdestructionoftheatomicallythingraphene
film during Cu etching. In the standard transfer, this support
a(cid:2)Electronicmail:[email protected]. isapolymer,suchasPMMAappliedviaspin-coating.Inthe
0003-6951/2010/96(cid:2)11(cid:1)/113102/3/$30.00 96,113102-1 ©2010AmericanInstituteofPhysics
Author complimentary copy. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp
Report Documentation Page Form Approved
OMB No. 0704-0188
Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and
maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information,
including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington
VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it

does not display a currently valid OMB control number.
1. REPORT DATE 3. DATES COVERED
15 MAR 2010 2. REPORT TYPE 00-00-2010 to 00-00-2010
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
A direct transfer of layer-area graphene
5b. GRANT NUMBER
5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
5e. TASK NUMBER
5f. WORK UNIT NUMBER
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
University of California at Berkeley,Department of REPORT NUMBER
Physics,Berkeley,CA,94720
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S)
11. SPONSOR/MONITOR’S REPORT
NUMBER(S)
12. DISTRIBUTION/AVAILABILITY STATEMENT
Approved for public release; distribution unlimited
13. SUPPLEMENTARY NOTES
14. ABSTRACT

15. SUBJECT TERMS
16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF
ABSTRACT OF PAGES RESPONSIBLE PERSON
a. REPORT b. ABSTRACT c. THIS PAGE Same as 3
unclassified unclassified unclassified Report (SAR)
Standard Form 298 (Rev. 8-98)
Prescribed by ANSI Std Z39-18
113102-2 Reganetal. Appl.Phys.Lett.96,113102(cid:2)2010(cid:1)
FIG. 3. (cid:1)a(cid:2)Atypical image of a low-defect region with large atomically
cleanareas.Scale=25 nm.(cid:1)b(cid:2)SADofthisregionshowingthehexagonal
structure of the (cid:1)0001(cid:2) basal plane. Tilt measurements performed in this
regionyieldedinvariantdiffractionintensities,astrongindicatorofmono-
layergraphene.
floating the sample on a solution of aqueous FeCl (cid:1)0.1
3
g/mL(cid:2) for approximately 2 h. After Cu etching, the direct
transfer process is complete.The sample, now referred to as
agrapheneTEMgrid,isfloatedonde-ionized(cid:1)DI(cid:2)waterand
rinsed in IPAto wash off remaining Cu etchant, remove or-
ganics, and encourage effective drying. The standard trans-
fer,however,requiresseveraladditionalstepswhichdamage
and contaminate the graphene.After removal of the Cu, the
FIG. 1. (cid:1)Color online(cid:2) A comparison of the standard (cid:1)e.g., PMMA(cid:2) and delicate PMMA/graphene film is transferred to a DI bath to
directtransferoflayer-areagraphenetoholeya-CTEMgrids. wash off remaining etchant and then extracted from the DI
bath by pulling it out onto the target TEM grid. Finally, the
PMMAis removed with acetone and the sample is rinsed in
direct transfer, this support is provided by the target sub-
IPA.Inshort,thedirecttransferprocessismuchcleanerthan
strate, specifically the TEM grid’s a-C film. To bond the
the standard polymer transfer as it involves fewer potential
grapheneanda-C,theTEMgridisplacedontopofgraphene
on Cu and a drop of isopropanol (cid:1)IPA(cid:2) is gently placed on contaminants (cid:1)PMMA, acetone(cid:2). Additionally, by anchoring
thegrid’sa-Cfilmtothegrapheneintheinitialwetstep,the
topofthegridtowetboththegrid’sa-Cfilmandtheunder-
direct transfer process avoids mechanical damage suffered
lying graphene film. As the IPA evaporates, surface tension
draws the graphene and a-C together into intimate contact.9 during wet transfers of the graphene/PMMAfilm, producing
(cid:1)To achieve strong adhesion, the evaporative surface tension a much more robust graphene TEM grid than the standard
polymer transfer.
must be strong enough to slightly warp either the Cu foil or
Characterization of direct transfer graphene TEM grids
thetargetsubstrate,socaremustbetakenwhenchoosingCu
foil and target thickness.(cid:2) The completeness of the adhesion is performed on a JEOL 2010 TEM operated at 100 kV.
Figure2showsthegraphenegridatdifferentmagnifications.
between the graphene and a-C can be confirmed by optical
Macroscopicgrid-widegraphenecoverageisapparentinFig.
microscopy, as optical interference effects give a noticeable
2(cid:1)a(cid:2), an optical micrograph captured near the end of the
contrastdifferencebetweenadheredandnonadheredregions.
Figure 2(cid:1)a(cid:2) shows a grid near the end of this evaporative evaporativeadhesionstep.Darkerregionsinthisimageshow
where graphene has bonded to the a-C support. Figure 2(cid:1)b(cid:2),
process, when all but the top portion of the grid has been
a subset of a grid frame captured by TEM, reveals large
adhered onto the graphene on Cu.A10 to 20 min bake on a
unperturbed graphene sheets with occasional folds and
hot plate at 120 °C helps to evaporate any remaining IPA
cracks. Figure 2(cid:1)c(cid:2) shows a higher magnification image of a
andstrengthenthegraphene/a-Cbond.Thenextstepinboth
single graphene domain covering an a-C hole. Figure 3(cid:1)a(cid:2)
transfer processes is to etch away the Cu foil, achieved by
shows a typical view of the suspended graphene, with large
(cid:1)tens of nanometers(cid:2) atomically clean regions separated by
scattered amorphous and/or organic materials covering the
highly reactive graphene surface, rivaling the cleanliness
seen earlier with exfoliated graphene flakes transferred to
TEM grids.10 We detect no evidence of polycrystalline Cu
residueonthesurface,suggestingacompleteandcleanetch.
Selected area diffraction (cid:1)SAD(cid:2) of the region in Fig. 3(cid:1)a(cid:2) is
showninFig.3(cid:1)b(cid:2),revealingthedistinctivehexagonalstruc-
ture of graphene. The invariant intensity of the diffraction
FIG. 2. (cid:1)Color online(cid:2) (cid:1)a(cid:2) Optical microscopy showing nearly complete pattern during tilting gives unambiguous evidence that the
adhesion(cid:1)topedgenotyetadhered(cid:2)betweentheTEMgrid’sa-Cfilmand membrane is indeed a single layer.12,14
thegrapheneonCu,shownduringtheevaporativestickingprocess.Scale Figure 4(cid:1)a(cid:2) reveals a fold or grain boundary. Folds are
=0.5 mm. (cid:1)b(cid:2) Portion of a grid frame showing large-domain, clean
graphene sheets with some cracks and folds. Scale=10 (cid:1)m. (cid:1)c(cid:2) Clean, commonly seen in metal-based layer-area graphene growth,
singlegraingraphenecoveringa-Chole.Scale=0.5 (cid:1)m. possibly forming to relieve stress during the cooling of the
Author complimentary copy. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp
113102-3 Reganetal. Appl.Phys.Lett.96,113102(cid:2)2010(cid:1)
We thank W. Gannett for assistance with experiments
andB.KesslerandM.Rousseasforhelpfuldiscussions.This
work was supported in part by the Office of Naval Research
MURI program under Grant no. N00014–09–1–1066 which
provided for development of the fabrication method, by the
Director, Office of Energy Research, Materials Sciences and
Engineering Division, of the U. S. Department of Energy
under Contract No. DE-AC02–05CH11231 through the
sp2-bonded Materials Program which provided for growth
facilities, and by the National Science Foundation through
the Center of Integrated Nanomechanical Systems under
FIG.4. (cid:1)a(cid:2)Aregionwithafoldorgrainboundaryinthegraphene.Scale Grant No. EEC-0832819, and through Grant No. DMR
=50 nm.(cid:1)b(cid:2)SADofthisregionshowingthehexagonalgraphenestructure, 0906539, which provided for microscopy and diffraction
withsmallandlargeangleseparationofdiffractionspotsduetosheetmis-
characterization. W.R. acknowledges support through a Na-
alignmentsresultingfromthefoldorgrainboundary.
tional Science Foundation Graduate Research Fellowship,
B.A. acknowledges support from the UC Berkeley A. J.
graphene and metal from the high synthesis temperature
Macchi Fellowship Fund in the Physical Sciences, and B.G.
down to room temperature. The corresponding SAD in Fig.
acknowledges support from the China Scholarship Council.
4(cid:1)b(cid:2) again shows the characteristic hexagonal structure of
this region. The large and small angle separation of the dif-
1K.S.Novoselov,A.K.Geim,S.V.Morozov,D.Jiang,Y.Zhang,S.V.
fraction spots results from the sheet misalignment caused by
Dubonos,I.V.Grigorieva,andA.A.Firsov,Science 306,666(cid:1)2004(cid:2).
the fold or grain boundary. 2Y. Zhang, J. P. Small, W. V. Pontius, and P. Kim, Appl. Phys. Lett. 86,
Asshown,opticalmicroscopyandTEMconfirmthatour 073104(cid:1)2005(cid:2).
direct transfer results in complete grid coverage, a strong 3C.Berger,Z.Song,T.Li,X.Li,A.Y.Ogbazghi,R.Feng,Z.Dai,A.N.
bond between the grid support film and the graphene, and a Marchenkov,E.H.Conrad,P.N.First,andW.A.deHeer,J.Phys.Chem.
B 108,19912(cid:1)2004(cid:2).
highly uncontaminated graphene surface, making the
4E.Rollings,G.-H.Gweon,S.Zhou,B.Mun,J.McChesney,B.Hussain,
grapheneTEMgridwellsuitedforhighresolutionTEM.The
A.Fedorov,P.First,W.deHeer,andA.Lanzara,J.Phys.Chem.Solids
resulting grid is substantially easier to work with than previ- 67,2172(cid:1)2006(cid:2).
ous grids made with exfoliated flakes.9,10,12,13 Millimeter- 5M.J.McAllister,J.-L.Li,D.H.Adamson,H.C.Schniepp,A.A.Abdala,
scale graphene coverage avoids the need for precise aiming J.Liu,M.Herrera-Alonso,D.L.Milius,R.Car,R.K.Prud’homme,and
whenpreparinggraphene-supportedsamples,andgridprepa- I.A.Aksay,Chem.Mater. 19,4396(cid:1)2007(cid:2).
6A.Reina,X.Jia,J.Ho,D.Nezich,H.Son,V.Bulovic,M.S.Dresselhaus,
ration is fast and reliable. Additionally, target materials be-
andJ.Kong,NanoLett. 9,30(cid:1)2009(cid:2).
sides holey a-C are compatible with this technique.We have 7X.Li,W.Cai,J.An,S.Kim,J.Nah,D.Yang,R.Piner,A.Velamakanni,
achievedgraphenetransferstodifferentmaterialswithvaried I.Jung,E.Tutuc,S.K.Banerjee,L.Colombo,andR.S.Ruoff,Science
geometries,includingAugilderfinebarTEMgrids,AuTEM 324,1312(cid:1)2009(cid:2).
gridswithlaceycarbon,formvar-coatedQuantifoilgrids,and 8A.K.Geim,Science 324,1530(cid:1)2009(cid:2).
plastic transparency film. Although not a necessary condi- 9J.C.Meyer,Ç.Ö.Girit,M.F.Crommie,andA.Zettl,Appl.Phys.Lett.
92,123110(cid:1)2008(cid:2).
tion,itappearsthatperforatedtargetgeometriesimprovethe
10J.C.Meyer,Ç.Ö.Girit,M.F.Crommie,andA.Zettl,Nature(cid:1)London(cid:2)
efficacy of the transfer process, perhaps as a result of varia- 454,319(cid:1)2008(cid:2).
tions in surface tension forces near perforations and/or sol- 11M.D.FischbeinandM.Drndić,Appl.Phys.Lett. 93,113107(cid:1)2008(cid:2).
vent evaporation pathways through the target. Beyond pro- 12J.C.Meyer,A.K.Geim,M.I.Katsnelson,K.S.Novoselov,D.Obergfell,
ducing excellent graphene TEM grids, our clean, gentle S.Roth,Ç.Girit,andA.Zettl,SolidStateCommun. 143,101(cid:1)2007(cid:2).
13T. J. Booth, P. Blake, R. R. Nair, D. Jiang, E. W. Hill, U. Bangert, A.
graphene transfer technique may facilitate a multitude of
Bleloch, M. Gass, K. S. Novoselov, M. I. Katsnelson, and A. K. Geim,
graphene studies and applications in such areas as hydrogen
NanoLett. 8,2442(cid:1)2008(cid:2).
storage, gas sensing, electrochemistry, catalysis, and other 14J.C.Meyer,A.K.Geim,M.I.Katsnelson,K.S.Novoselov,T.J.Booth,
advanced electrical/optical fields. andS.Roth,Nature(cid:1)London(cid:2) 446,60(cid:1)2007(cid:2).
Author complimentary copy. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp