This document describes a new method for transferring chemical vapor deposition (CVD) graphene to polymeric substrates called direct dry transfer assisted by a spin coater (DDT-SC). The key innovation is depositing a thin polymer film on the graphene using a spin coater before the transfer process. This improves contact between the polymer and graphene by preventing air bubbles or moisture at the interface. The document compares transfers of graphene to five different polymers using DDT-SC versus the standard DDT method. DDT-SC resulted in substantially more graphene being transferred and higher quality transfers for all polymers tested.

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Chemical vapor deposition graphene transfer process to a polymeric substrate assisted by a
spin coater
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2016 Mater. Res. Express 3 035601
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2. Mater. Res. Express 3 (2016) 035601 doi:10.1088/2053-1591/3/3/035601
PAPER
Chemical vapor deposition graphene transfer process to a polymeric
substrate assisted by a spin coater
Felipe Kessler1,2
, Caique O C da Rocha1
, Gabriela S Medeiros1
and Guilhermino J M Fechine1
1
Graphene and Nanomaterials Research Center—MackGraphe, Mackenzie Presbyterian University, São Paulo, Brazil
2
Present address: School of Chemistry and Food, Federal University of Rio Grande, Rio Grande, Brazil
E-mail: guilherminojmf@mackenzie.br
Keywords: CVD graphene, transfer process, polymer
Supplementary material for this article is available online
Abstract
A new method to transfer chemical vapor deposition graphene to polymeric substrates is
demonstrated here, it is called direct dry transfer assisted by a spin coater (DDT-SC). Compared to the
conventional method DDT, the improvement of the contact between graphene-polymer due to a very
thin polymeric film deposited by spin coater before the transfer process prevented air bubbles and/or
moisture and avoided molecular expansion on the graphene-polymer interface. An acrylonitrile-
butadiene-styrene copolymer, a high impact polystyrene, polybutadiene adipate-co-terephthalate,
polylactide acid, and a styrene-butadiene-styrene copolymer are the polymers used for the transfers
since they did not work very well by using the DDT process. Raman spectroscopy and optical
microscopy were used to identify, to quantify, and to qualify graphene transferred to the polymer
substrates. The quantity of graphene transferred was substantially increased for all polymers by using
the DDT-SC method when compared with the DDT standard method. After the transfer, the intensity
of the D band remained low, indicating low defect density and good quality of the transfer. The DDT-
SC transfer process expands the number of graphene applications since the polymer substrate
candidates are increased.
1. Introduction
A major breakthrough in large-scale production of graphene (G) films was due to the chemical vapor deposition
(CVD) technique, which initially used metal foil as the starting substrate, and from the G–metal compound,
several products can be obtained [1]. However, most of the final applications of G need a process to transfer G to
a target substrate. Transparent conductive films are an example when a polymer (P) is used as a substrate. The
method most widely used to transfer large areas of G (G, which is obtained by the CVD technique) for different
types of substrates, such as Si wafer and P films, has several steps (including etching) and a long total process time
—‘wet transfer’ [2]. The final product may have some problems, such as cracks, wrinkles, and residues of metal
or P. Many other G transfer methods have been developed, examples of these are as follows: roll to roll [3], layer
by layer [4], clean lift [5], fractal surface evolution [6], nanoimprinter [7], and metal-etching-free direct
delamination [8]. Some advancements have been recently developed to minimize some problems cited
previously [9]. However, these G transfer methods also have some limitations due to the presence of a chemical-
etching step and/or only apply to relatively low areas of transferred G. Recently, a new method to transfer CVD
G to a P substrate was developed. This new method transfers G directly onto the P substrate without a chemical
process; it is called ‘direct dry transfer’ (DDT) [10]. The process is based on the fact that the binding energy
between the molten P and the G (Bpol-g) has to be higher than the binding energy between the G and the metal
(Bg-metal). According to the chemical structure of the P, some parameters (temperature and pressure) have to be
changed to increase Bpol-g and to obtain an efficient transfer. Beyond that, independent of the chemical structure
and the optimization of the experimental parameters involved in the DDT process, the contact between the P in
RECEIVED
4 January 2016
REVISED
24 February 2016
ACCEPTED FOR PUBLICATION
29 February 2016
PUBLISHED
24 March 2016
© 2016 IOP Publishing Ltd

3. the molten state and the G is extremely important. The results already presented using the DDT process showed
that some Ps with low adhesion to the G are more dependent on contact with the G to obtain a good result, rather
than with the optimization of the parameters. Metal foils used to grow G by CVD usually show degrees of
roughness, which may reduce the contact with the P during the DDT transfer process. Here, we experimentally
study a new approach to improve the DDT process by increasing the contact between the G and the P during the
transfer process. The new process is called DDT assisted by a spin coater (DDT-SC). A precoating of G with a
very thin P film before the DDT process using the spin coater was used as a way to overcome the roughness of the
metal substrate. The evaluation of the improvement in the DDT transfer process was done via optical
microscopy and Raman spectroscopy (spectra and mappings) and by comparing the DDT standard method and
the DDT-SC using five different Ps: acrylonitrile-butadiene-styrene co-P (ABS), high impact polystyrene
(HIPS), poly(butadiene adipate-co-terephthalate) (PBAT), poly(lactide acid) (PLA), and a styrene-butadiene-
styrene co-P (SBS). This set of Ps was chosen because the transfer results using the DDT standard process for
these Ps resulted in either no transfer or only a small and heterogeneous area of G being transferred. X-ray
diffraction (XRD) and surface analysis by interferometry were used to analyze the P film morphology in contact
with G before and after transfer, respectively.
2. Experimental
2.1. Transfer of G
Figure1describestheDDT-SCprocess.TheDDTstandardprocesscorrespondedtosteps‘c’–‘e’[10].The
innovationofthisworkistheimplementationofsteps‘a’and‘b’thatimprovethecontactbetweenthePandtheG
and,therefore,abettertransferisreached.InthecaseofthenewapproachfortheDDTprocess,averythinfilmof
thesamePusedforDDTwasfirstdepositedontoaG–copper(C)foilusingaspincoater.Thesolventusedtoprepare
thePsolutionsforspincoatingwaschloroform.TheCpeelingillustratedinstepewasdistinctforeachPusedhere.
Theway(speedandforce)theCfoilwasdetachedmanuallyfromtheGPfilmhadtobeadjustedaccordingtothe
stiffnessofthePinordertokeeptheintegrityoftheGstructureandPsubstrate.Avideowithademonstrationofthe
DDT-SCmethodcanbeseeninthesupplementarymaterial.Amoderatepressurewasusedforalltransfers.
2.2. Materials
ABS, HIPS, PBAT, PLA, and SBS were used for the transfers. PLA and PBAT are semicrystalline Ps, and ABS,
HIPS, and SBS are amorphous Ps. G grown by CVD on the C foil was always used as the G/metal source. The
CVD G used in this work was also transferred to a microscope slice by the wet transfer method [2] to have a
spectrum of the neat G since glass does not influence the position of the G bands on Raman spectroscopy
analyses [11]. Figure 2 presents the Raman spectrum of CVD G. As can be seen on this spectrum, D, G, and 2D
bands are located at 1347.5, 1592.5, and 2692.8 cm−1
, respectively. Full width at half maximum (FWHM) of the
2D band is 26 cm−1
. The values of the band positions, intensity ratio between the 2D and the G bands, and
FWHM of the 2D band are in agreement with those reported in literature for monolayer G [12]. However, there
are few regions where bilayers of G can also be found.
Table 1 presents the temperatures used for each P in the transfer process for both methods, DDT and DDT-
SC. The temperatures were chosen according to the first point on the heating that the Ps start to flow.
2.3. Characterization
A 100× objective lens with a numerical aperture of 0.95 was used for the optical images. The Raman spectra and
mapping were measured with a WITec Alpha 300R Raman system. The excitation source was a 532 nm laser
with a laser power below 5 mW on the sample to avoid laser induced local heating. The Raman mapping area size
was limited by the roughness of the GP films since the focus was lost easily at long distances. The temperature
sweep oscillatory rheological tests were performed within the linear viscoelastic regime under oscillatory shear at
Figure 1. DDT-SC. Deposition of a P film under CVD G by spin coating (a); a GP thin film on C (GPC) (b); positioning of GPC onto a
P thick film (c); application of pressure and temperature (d); C peeling and final GP film (e).
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Mater. Res. Express 3 (2016) 035601 F Kessler et al

4. a frequency of 1 Hz and strain of 0.5% using a MCR 302- Anton Paar rheometer (plate–plate, diameter of
25 mm, gap of 950 μm). XRD measurements of P films were carried out using a Rigaku MiniFlex II
diffractometer with Cu Kα radiation. Surface analyses of GP films were made with a Bruker Contour GT-K
vertical scanning interferometer (vertical resolution of ∼1 nm).
3. Results and discussion
As reported before, the chemical structure (data from simulations) and rheological properties of the Ps have a
strong influence on the G transfer process by the DDT method [10]. The complex viscosity (η*
) of the P showed
to be the most important property beyond the chemical structure to enable a good contact between the G and the
P during the transfer process. To demonstrate the improvement of the method by the inclusion of the spin-
coater step, the experiments performed here did not use the temperature that allows the best value of η*
for the
Ps (8000 Pa s) nor the P chemical structure for which simulations indicate good adhesion with G as reported
before [10]. The values of η*
for HIPS, PLA, ABS, SBS, and PBAT used for the transfers were 7300, 11 000,
13 800, 73 000, and 2900, respectively, according to the temperatures expressed in table 1 and complex viscosity
curves of the Ps presented in figure 3. The value of η*
for HIPS is very close to 8000, therefore, polystyrene did not
show simulation results with respect to good adhesion with G [10].
Figure 4 compares the optical images and compiles the Raman mapping of the FWHM of a 2D band of G
from the GP substrates after the transfers using the DDT and the DDT-SC methods. Figures 4(a)–(d), (e)–(h),
(i)–(m), (n)–(q), (r)–(u) are representative with HIPS, PLA, ABS, SBS, and PBAT, respectively. Figures 4(a), (b),
(e), (f) show optical images and Raman mapping with no signal of G. It means that the DDT parameters (P and T)
used for HIPS and PLA were not enough to promote a good adhesion between P and G. These results were
expected once the HIPS and PLA were very stiff Ps, comparing with ABS, SBS, and PBAT. During the
solidification of these stiff Ps, the debonding energy overcame the adhesion force [13], and even if the G had been
transferred at the end of the process, it was detached from the P surface. For the Ps ABS (figure 4(i)) and SBS
(figure 4(n)), small quantities of G were transferred by DDT. PBAT shows the best results by using the DDT
Figure 2. Raman spectrum of CVD G transferred to a glass substrate.
Table 1. P and temperatures
used for the transfer process
of G.
P Temperature (°C)
ABS 180
HIPS 200
PBAT 125
PLA 155
SBS 120
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Mater. Res. Express 3 (2016) 035601 F Kessler et al

5. Figure 3. Complex viscosity of the Ps as a function of temperature.
Figure 4. Optical images of G transferred to HIPS (a), PLA (e), ABS (i), SBS (n), PBAT (r) by the DDT method. Raman mapping of the
FWHM of the 2D band obtained from the G transferred to HIPS (b) and PLA (f), ABS (j), SBS (o), PBAT (s) by the DDT method.
Optical images of G transferred to HIPS (c), PLA (g), ABS (l), SBS (p), PBAT (t) by the DDT-SC method. Raman mapping of the
FWHM of the 2D band obtained from the G transferred to HIPS (d), PLA (h), ABS (m), SBS (q), PBAT (u) by the DDT-SC method.
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Mater. Res. Express 3 (2016) 035601 F Kessler et al

6. method (figure 4(r)); however, small areas of G are still not transferred to the P. In the case of the PBAT, it is clear
that the area without G was due to an irregularity of the P film. Probably, bubbles of air or the presence of
humidity are the cause of the irregularities, which led to poor contact between the G and the P during the
transfer. The problem with the moisture is more pronounced for the PBAT because it is a very hygroscopic P due
to ester linkage in its main chain.
For all polymers, the DDT-SC method resulted in a large increase in G transferred. Even using HIPS, small
flakes of G were transferred. The most impressive result can be observed in figures 4(g), (h) where the PLA has
shown the largest increase in the transferred areas of G. It also reached the extreme case of total transfer of G
when SBS (figures 4(p), (q)) and PBAT (figures 4(u), (t)) were used.
Figure 5 presents the spectra of all Ps without G on the surface and with G transferred to the surface by the
DDT and DDT-SC methods. The representative spectra of the Raman mapping areas without and with G are
shown in figure 4. All results from figure 5 are compiled in table 2. The positions of the G and 2D bands of G
transferred to all Ps can be seen shifted on the Raman spectra when compared with CVD G. The shift
phenomena of the G band could represent two possible aspects, deformation of the structure of G [14] or doping
of G [15]. The doping aspect sometimes could be observed due to interaction of G with the substrate as described
by Tsukamoto et al [16] or by the presence of interfacial water layers [17]. The G of G transferred to all the Ps
showed a redshift indicating a possible deformation of the G structure. This deformation could have occurred
because of the pressure used in the DDT and DDT-SC methods. The P is melted, and a force is applied on the
direction of G deposited on the C foil that is not completely flat. Shear forces are generating on the interface of
PG and, because of this, G undergoes localized deformations (see the illustrations in figure 6). The shift of the 2D
band could be related to strain similar to the shift of the G band, however, the presence of multilayer regions also
generates a shift phenomenon of the 2D band. As can be seen in figure 4, there are some areas with values of
FWHM around 50 cm−1
, indicating bilayers or more layers of G. Consequently, the 2D band could not be used
to obtain conclusions about doping or strain in samples with heterogeneous numbers of G layers.
Beyond the quantity of G transferred, the quality of G is also very important. The ratio between the
intensities of the D and G bands is used to evaluate the G, and low ratios (D/G) are indicative of good quality
[18]. The D and G bands of G were positioned around 1350 and 1585 cm−1
[19], respectively, and it was
observed for the CVD G used here. However, some Ps have their own Raman bands around the position of the D
band of G (HIPS, PLA, ABD, and SBS), and the calculation of the D/G ratio has to be done by deconvolution of P
and G bands, and its intensities and positions were obtained. It was done to eliminate the influence of the P
bands on the intensity of the D band of G. The D/G ratio values calculated are the average values extracted from
the Raman mapping shown in figure 4 for areas covered by G. The all D/G ratio values are, at most, equal to 0.2
indicating a good quality of G transferred. It is also very interesting that the D/G ratio values did not change
significantly for G transferred by the DDT and DDT-SC methods.
The opticalimagesand Ramanmapping resultsindicatethat,inadditiontothechemical affinitybetweenP
melted andG, theincreaseinthecontact areaalso has astrong influenceonthetransferprocess. Theinitialstep
madebythe spin coater led toareductioninthepossiblepresence ofairbubbles and/ormoisture betweenP and G.
Another fact isthat thisstepallowedtheP to reachdeeper regionsofG that previouslycould notbereachedsince
theC substrateisnotcompletelyflat and the melted Pcouldnotcomeinto directcontact with deeperregions.
The idea is that spin coating promotes better contact between GP; therefore, significant changes in the
morphology of the P film in direct contact with G also were observed when semicrystalline Ps were used as PLA
and PBAT. Semicrystalline Ps present larger expansion and contraction during the heating and cooling,
respectively. The destruction (melting) and formation of the spherulites (solidification) present in
semicrystalline Ps is the cause of this phenomena [20]. As an example, figure 7 shows the XRD of PBAT films
obtained by spin coating and compression molding. The diffractogram shown in figure 7(a) presents some
crystalline peaks under an amorphous halo, meanwhile, only an amorphous halo can be seen in figure 7(b). This
result indicates that P molecules in contact with G are in the amorphous state when the spin coater is used (DDT-
SC) and semicrystalline when the P film produced by compression machine is used directly for the transfer
process (DDT). When the temperature rose during the DDT-SC G transfer method, no P expansion occurred at
the interface GP since the molecules were already in the amorphous state and only a contraction during the
solidification occurred. There are other techniques for the formation of thin P films as well as the generation of
amorphous P material; however, the technique spin coater enables these two things simply.
A reflection of the difference in molecular expansion in the GP interface can be observed by the roughness
presented by the films (GP) obtained by the DDT and DDT-SC methods. Figure 8 presents the surface image of
the G-PBAT film obtained by the DDT and DDT-SC methods. The roughnesses calculated from the image are
7.43 and 4.72 μm for samples obtained by using the DDT and DDT-SC methods, respectively. These results
confirm that the P molecular expansion step is suppressed when an amorphous film is in contact with G during
the transfer, leading to a less rough surface.
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Mater. Res. Express 3 (2016) 035601 F Kessler et al

7. Based on the observed results, it is possible to note that the strong influence of P complex viscosity can be
decreased by an additional step in the DDT technique. This step allows the P to reach all defects and morphology
of G, reflecting on the quality and quantity of the transferred areas. Further studies will be developed with special
attention for interface interactions, such as the wettability of the P in the molten state and its correlation with the
G wettability where the surface tension of G remains under discussion and the subject of great debate [21–24].
4. Conclusions
AsetofunusualPsubstratecandidateswasusedtoevaluateanewroutetotransferCVDG.DDT-SCisbasedon
promotingbettercontactbetweentheGandthePduringthetransferprocess.ThethinPfilmdepositedonGbefore
Figure 5. Single Raman spectra of HIPS (a), PLA (c), ABS (e), SBS (h), PBAT (l). Single Raman spectra of G transferred to ABS (f), SBS
(i), PBAT (m) by the DDT method. Single Raman spectra of G transferred to HIPS (b), PLA (d), ABS (g), SBS (j), PBAT (n) by the DDT-
SC method. The D (D band), G (G band), and 2D (2D band) of G.
6
Mater. Res. Express 3 (2016) 035601 F Kessler et al

8. thetransferimprovedtheinterface,preventedairbubblesand/ormoisture,andavoidedPmolecularexpansiononthe
GPinterfaceduringthetransfer.TheDDT-SCmethodprovedtobeabreakthroughintheDDTmethodsincethe
resultsshowasubstantialincreaseinthequantityofGtransferredtotheP.TheuseofalargewiderangeofPsas
substratesforGisthegreatcontributionoftheDDT-SCprocesssinceanexpansionoftheapplicationsforGcouldbe
envisionedwhenthenumberofpossibilitiesofPsubstratesareincreased.MostoftheGtransfermethodsareonly
concernedwiththetotalcoverageofGanddonotcareaboutthetypeofsubstrateanditspropertiesinwhichGis
Table 2. Raman characteristics of G after transfer to the different Ps by the DDT and DDT-SC methods. Positions of the D, G, and 2D bands,
FWHM of the 2D band, and the ratio between intensity of D and G (D/G) are presented.
Polymer/method D band (cm−1
) G band (cm−1
) 2D band (cm−1
) FWHM of the 2D band (cm−1
) D/G
HIPS/DDT-SC 1345.2 1589.0 2688.1 26.0 0.2
PLA/DDT-SC 1339.5 1590.1 2683.8 25.6 0.1
ABS/DDT 1342.0 1590.7 2685.6 26.2 0.2
ABS/DDT-SC 1344.6 1590.9 2681.6 25.3 0.2
SBS/DDT 1339.5 1588.5 2679.5 26.5 0.2
SBS/DDT-SC 1344.6 1588.5 2681.6 25.4 0.2
PBAT/DDT 1342.4 1591.2 2686.4 28.3 0.1
PBAT/DDT-SC 1339.1 1590.7 2683.3 27.9 0.1
Figure 6. Illustration of the DDT transfer method. Positioning of the P film and CVD G before the pressure application (a). P chains
promoting shear stress (white arrows) on G grown under C when pressure and temperature are applied (b).
Figure 7. XRD of a PBAT film prepared by compression molding (a) and the spin-coater technique (b).
7
Mater. Res. Express 3 (2016) 035601 F Kessler et al

9. transferred.TheexpansionofGapplicationsdemonstratedwiththeDDT-SCmethodincludenotonlyimprovement
onGcoverages,butalsothemeansthatdistinctpropertiesofthesubstrates,suchasflexibility(ABSandSBS),stiffness
(HIPS),biocompatibility(PLA),andbiodegradability(PBAT),canbeexploited.
Acknowledgments
G J M F acknowledges the financial support from Brazilian Funding Agencies (FAPESP Grants No. 2012/50259-
8 and No. 2014/22840-3 and Mackpesquisa Grant No. 170/2013). F K acknowledges a postdoctoral scholarship
from Brazilian Funding Agency (FAPESP Grant No. 2014/08448-3). G S M acknowledges an undergraduate
scholarship from Mackpesquisa. All authors are grateful to Professor D E Weibel for the profilometer tests and to
A Paar do Brazil for the rheological measurements.
Contributions
G J M F and F K coordinated the study; F K, C O C R, and G S M conducted the data analyses; all authors
reviewed, revised, commented on, and approved the final version of the article.
Competing interests
The authors declare no competing financial interests.
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Figure 8. Images of the contour GT-K profilometer data from G-PBAT obtained by DDT (a) and DDT-SC (b).
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