In our paper we provided an experimental evidence that the single-layer graphene (SLG) deposited on SiO 2 grating substrate exhibits very strong out-of-plane piezoelectric effect, several times greater than that of the best piezoceramics such as lead-zirconate titanate

C Stampfer

G da Cunha Rodrigues

MA Bissett

P Shemella

TC Nguyen

Y Shi

Y-J Kang

Nature Communications

PubMed

Rodrigues, Goncalo da Cunha

Zelenovskiy, Pavel

Romanyuk, Konstantin

Luchkin, Sergey

Kopelevich, Yakov

Kholkin, Andrei

Repositório Institucional da Universidade de Aveiro

Correspondence: Reply to ‘On the nature of strongpiezoelectricity in graphene on SiO2’Gonc¸alo da Cunha Rodrigues1, Pavel Zelenovskiy2, Konstantin Romanyuk1,2, Sergey Luchkin1, Yakov Kopelevich3& Andrei Kholkin1,2Nature Communications 7:11571 doi: 10.1038/ncomms11571 (2016); Published 17 May 2016In our paper1 we provided an experimental evidence that thesingle layer graphene (SLG) deposited on SiO2 grating substrateexhibits very strong out of plane piezoelectric effect, severaltimes greater than that of the best piezoceramics such aslead zirconate titanate. Simultaneously, the in plane straindistribution was measured by micro Raman scattering in anattempt to relate such unusual activity to the strain gradientexpected in suspended graphene near the ridges. We appreciatethe comment by Stampfer and Reichardt2 who noticed that ourcalculations of the in plane strain based on ref. 3 were incorrect.The overestimation of the strain values, however, does not changethe main conclusion of our paper, since the piezoresponseforce microscopy measurements give the value of out of planea.c. deformation, fully decoupled from the d.c. in planestrain measured by micro Raman. We recalculated the strainmap and corrected the strain values that vary now in therange from  0.078 to þ 0.078%. Nevertheless, the strain ratiobetween supported and suspended graphene is still 2.5 (strain forsuspended graphene is about þ 0.02%). Figure 1a,b displays boththe corrected strain map and cross section of the position ofRaman line and recalculated strain. Below we reply in detail toother issues raised by Stampfer and Reichardt in theircommunication2.Gruneisen parameter suggested by Stampfer and Reichardt2 isrelated to graphene produced by mechanical exfoliation, whereasin our work1 we used graphene sheets prepared by CVD. Thesetwo materials differ by the number of intrinsic defects and,therefore, their behaviour under uniaxial or biaxial strain isdifferent. This was exactly demonstrated in ref. 3, where theopposite sign of Gruneisen parameter for G band was revealedfor CVD graphene with respect to the exfoliated one. Therefore,we used the value reported in ref. 3 for our calculations whichgave us a maximum strain of 0.078%.Stampfer and Reichardt2 questioned why we used theGruneisen parameter for uniaxial strain. We believe that usingthe value for uniaxial strain is dictated by the nature of thesubstrate. Being periodical in one direction only, this featurenaturally deﬁnes the symmetry of the graphene deformations aswell. Therefore, we considered uniaxial strain in our work.Stampfer and Reichardt2 claim that our paper ‘ydirectlylinked the observed piezoelectricity in graphene to thesupposed high in plane strain induced by the substratey’.1,588.01,587.51,587.01,586.51,586.01,585.50 1 2 3 4 5 6 7 8 90.060.050.040.030.020.010.00Strain, %Strain, %Position, cm–1+0.078%–0.078%4 µmX, µma bFigure 1 | Strains in the single-layer graphene on the silicon grating. (a) Strain map. (b) Variation of G-band position and strain across the grating (blueline in a); shaded rectangles correspond to supported graphene, dashed line denotes the initial (unstressed) value of G-band position.DOI: 10.1038/ncomms11571 OPEN1 Department of Physics & CICECO Aveiro Institute of Materials, University of Aveiro, 3810 193 Aveiro, Portugal. 2 Institute of Natural Sciences, Ural FederalUniversity, Ekaterinburg 620000, Russia. 3 Instituto de Fı´sica, UNICAMP, Campinas, Sa˜o Paulo 13083 859, Brasil. Correspondence and requests for materialsshould be addressed to A.K. (email: kholkin@ua.pt).NATURE COMMUNICATIONS | 7:11571 | DOI: 10.1038/ncomms11571 | www.nature.com/naturecommunications 1Indeed, the observed piezoresponse distribution (Fig. 3(b)of ref. 1) apparently correlates with the mechanical straindistribution in graphene. However, it does not mean that theobserved piezoelectricity is associated with this strain (and itsvalue!). Since no ampliﬁcation of the piezoresponse is observednear the grating edges where the maximum strain gradient isexpected, we only ruled out the in plane symmetry breakinginduced by discussed in plane strain. Therefore, the conclusion ofthe paper remains the same, that is, chemical bonds generatedbetween O and C atoms can indeed induce piezoelectric effectand, at the same time, affect the G band position.Stampfer and Reichardt2 cast some doubt that the C O bondscan form at the interface with graphene based on some data oncarrier mobility. The formation of strong C O bonds betweengraphene and SiO2 has been already proven both experimentallyand theoretically (see, for example, refs 3 6). This fact is stronglysupported by the observed p type conductivity in graphene via acharge transfer from the carbon in graphene layer to theoxygen terminated surface of SiO2 (ref. 4). As such, theobservation of a strong piezoelectricity due to formation ofpolar C O bonds is not a surprise. Though some authors7 claimthat only weak bonds are formed for the most stable geometry ofC atoms, the very existence of the strong polarity of thegraphene SiO2 interface proves that it is not the case.All in all, we highly appreciate the comment by Stampfer andReichard1 concerning the overestimation of the in plane strain,however, it does not change the main conclusion of the paper,that is, the experimental observation of strong piezoelectricity ingraphene/SiO2. We emphasize that, while an inhomogeneousinteraction between graphene and underlying SiO2 substrate(caused for example, by the substrate morphology) can beresponsible for the in plane strain seen in Raman measurements,the observed piezoresponse is attributed to the formation ofout of plane polar C O bonds that may not be directly related tothe in plane deformation.References1. da Cunha Rodrigues, G. et al. Strong piezoelectricity in single-layer graphenedeposited on SiO2 grating substrates. Nat. Commun. 6, 7572 (2015).2. Stampfer, C. & Reichardt, S. Correspondence: On the nature of strongpiezoelectricity in graphene on SiO2. Nat. Commun. 7, 11570 (2016).3. Bissett, M. A., Izumida, W., Saito, R. & Ago, H. Effect of domain boundaries onthe Raman spectra of mechanically strained graphene. ACS Nano 6, 10229(2012).4. Shi, Y., Dong, X., Chen, P., Wang, J. & Li, L.-J. Effective doping of single-layer graphene from underlying SiO2 substrates. Phys. Rev. B 79, 115402(2009).5. Kang, Y.-J., Kang, J. & Chang, K. J. Electronic structure of graphene and dopingeffect on SiO2. Phys. Rev. B 78, 115404 (2008).6. Shemella, P. & Nayak, S. K. Electronic structure and band-gap modulationof graphene via substrate surface chemistry. Appl. Phys. Lett. 94, 032101 (2009).7. Nguyen, T. C., Otani, M. & Okada, T. Semiconducting electronic property ofgraphene adsorbed on (0001) Surfaces of SiO2. Phys. Rev. Lett. 106, 106801(2011).Additional informationCompeting ﬁnancial interests: The authors declare no competing ﬁnancial interests.Reprints and permission information is available online at http://npg.nature.com/reprintsandpermissions/How to cite this article: da Cunha Rodrigues, G. et al. Correspondence: Reply to‘On the nature of strong piezoelectricity in graphene on SiO2’. Nat. Commun. 7:11571doi: 10.1038/ncomms11571 (2016).This work is licensed under a Creative Commons Attribution 4.0International License. The images or other third party material in thisarticle are included in the article’s Creative Commons license, unless indicated otherwisein the credit line; if the material is not included under the Creative Commons license,users will need to obtain permission from the license holder to reproduce the material.To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/CORRESPONDENCE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms115712 NATURE COMMUNICATIONS | 7:11571 | DOI: 10.1038/ncomms11571 | www.nature.com/naturecommunications

Correspondence: Reply to 'On the nature of strong piezoelectricity in graphene on SiO2'

Rodrigues

Goncalo da Cunha

Pavel

Konstantin

Sergey

Yakov

Andrei

Repositorio da Producao Cientifica e Intelectual da Unicamp

Correspondence: Reply to ‘On the nature of strong
piezoelectricity in graphene on SiO2’
Gonc¸alo da Cunha Rodrigues1, Pavel Zelenovskiy2, Konstantin Romanyuk1,2, Sergey Luchkin1, Yakov Kopelevich3
& Andrei Kholkin1,2
Nature Communications 7:11571 doi: 10.1038/ncomms11571 (2016); Published 17 May 2016
In our paper1 we provided an experimental evidence that the
single-layer graphene (SLG) deposited on SiO2 grating substrate
exhibits very strong out-of-plane piezoelectric effect, several
times greater than that of the best piezoceramics such as
lead-zirconate titanate. Simultaneously, the in-plane strain
distribution was measured by micro-Raman scattering in an
attempt to relate such unusual activity to the strain gradient
expected in suspended graphene near the ridges. We appreciate
the comment by Stampfer and Reichardt2 who noticed that our
calculations of the in-plane strain based on ref. 3 were incorrect.
The overestimation of the strain values, however, does not change
the main conclusion of our paper, since the piezoresponse
force microscopy measurements give the value of out-of-plane
a.c. deformation, fully decoupled from the d.c. in-plane
strain measured by micro-Raman. We recalculated the strain
map and corrected the strain values that vary now in the
range from  0.078 to þ 0.078%. Nevertheless, the strain ratio
between supported and suspended graphene is still 2.5 (strain for
suspended graphene is about þ 0.02%). Figure 1a,b displays both
the corrected strain map and cross-section of the position of
Raman line and recalculated strain. Below we reply in detail to
other issues raised by Stampfer and Reichardt in their
communication2.
Gruneisen parameter suggested by Stampfer and Reichardt2 is
related to graphene produced by mechanical exfoliation, whereas
in our work1 we used graphene sheets prepared by CVD. These
two materials differ by the number of intrinsic defects and,
therefore, their behaviour under uniaxial or biaxial strain is
different. This was exactly demonstrated in ref. 3, where the
opposite sign of Gruneisen parameter for G-band was revealed
for CVD graphene with respect to the exfoliated one. Therefore,
we used the value reported in ref. 3 for our calculations which
gave us a maximum strain of 0.078%.
Stampfer and Reichardt2 questioned why we used the
Gruneisen parameter for uniaxial strain. We believe that using
the value for uniaxial strain is dictated by the nature of the
substrate. Being periodical in one direction only, this feature
naturally defines the symmetry of the graphene deformations as
well. Therefore, we considered uniaxial strain in our work.
Stampfer and Reichardt2 claim that our paper ‘ydirectly
linked the observed piezoelectricity in graphene to the
supposed high in-plane strain induced by the substratey’.
1,588.0
1,587.5
1,587.0
1,586.5
1,586.0
1,585.5
0 1 2 3 4 5 6 7 8 9
0.06
0.05
0.04
0.03
0.02
0.01
0.00
Strain, %
Strain, %
Po
si
tio
n,
 c
m
–
1
+0.078%
–0.078%
4 µm
X, µm
a b
Figure 1 | Strains in the single-layer graphene on the silicon grating. (a) Strain map. (b) Variation of G-band position and strain across the grating (blue
line in a); shaded rectangles correspond to supported graphene, dashed line denotes the initial (unstressed) value of G-band position.
DOI: 10.1038/ncomms11571 OPEN
1 Department of Physics & CICECO—Aveiro Institute of Materials, University of Aveiro, 3810-193 Aveiro, Portugal. 2 Institute of Natural Sciences, Ural Federal
University, Ekaterinburg 620000, Russia. 3 Instituto de Fı´sica, UNICAMP, Campinas, Sa˜o Paulo 13083-859, Brasil. Correspondence and requests for materials
should be addressed to A.K. (email: kholkin@ua.pt).
NATURE COMMUNICATIONS | 7:11571 | DOI: 10.1038/ncomms11571 | www.nature.com/naturecommunications 1
Indeed, the observed piezoresponse distribution (Fig. 3(b)
of ref. 1) apparently correlates with the mechanical strain
distribution in graphene. However, it does not mean that the
observed piezoelectricity is associated with this strain (and its
value!). Since no amplification of the piezoresponse is observed
near the grating edges where the maximum strain gradient is
expected, we only ruled out the in-plane symmetry breaking
induced by discussed in-plane strain. Therefore, the conclusion of
the paper remains the same, that is, chemical bonds generated
between O and C atoms can indeed induce piezoelectric effect
and, at the same time, affect the G-band position.
Stampfer and Reichardt2 cast some doubt that the C–O bonds
can form at the interface with graphene based on some data on
carrier mobility. The formation of strong C–O bonds between
graphene and SiO2 has been already proven both experimentally
and theoretically (see, for example, refs 3–6). This fact is strongly
supported by the observed p-type conductivity in graphene via a
charge transfer from the carbon in graphene layer to the
oxygen-terminated surface of SiO2 (ref. 4). As such, the
observation of a strong piezoelectricity due to formation of
polar C–O bonds is not a surprise. Though some authors7 claim
that only weak bonds are formed for the most stable geometry of
C atoms, the very existence of the strong polarity of the
graphene–SiO2 interface proves that it is not the case.
All in all, we highly appreciate the comment by Stampfer and
Reichard1 concerning the overestimation of the in-plane strain,
however, it does not change the main conclusion of the paper,
that is, the experimental observation of strong piezoelectricity in
graphene/SiO2. We emphasize that, while an inhomogeneous
interaction between graphene and underlying SiO2 substrate
(caused for example, by the substrate morphology) can be
responsible for the in-plane strain seen in Raman measurements,
the observed piezoresponse is attributed to the formation of
out-of-plane polar C–O bonds that may not be directly related to
the in-plane deformation.
References
1. da Cunha Rodrigues, G. et al. Strong piezoelectricity in single-layer graphene
deposited on SiO2 grating substrates. Nat. Commun. 6, 7572 (2015).
2. Stampfer, C. & Reichardt, S. Correspondence: On the nature of strong
piezoelectricity in graphene on SiO2. Nat. Commun. 7, 11570 (2016).
3. Bissett, M. A., Izumida, W., Saito, R. & Ago, H. Effect of domain boundaries on
the Raman spectra of mechanically strained graphene. ACS Nano 6, 10229
(2012).
4. Shi, Y., Dong, X., Chen, P., Wang, J. & Li, L.-J. Effective doping of single-
layer graphene from underlying SiO2 substrates. Phys. Rev. B 79, 115402
(2009).
5. Kang, Y.-J., Kang, J. & Chang, K. J. Electronic structure of graphene and doping
effect on SiO2. Phys. Rev. B 78, 115404 (2008).
6. Shemella, P. & Nayak, S. K. Electronic structure and band-gap modulation
of graphene via substrate surface chemistry. Appl. Phys. Lett. 94, 032101 (2009).
7. Nguyen, T. C., Otani, M. & Okada, T. Semiconducting electronic property of
graphene adsorbed on (0001) Surfaces of SiO2. Phys. Rev. Lett. 106, 106801
(2011).
Additional information
Competing financial interests: The authors declare no competing financial interests.
Reprints and permission information is available online at http://npg.nature.com/
reprintsandpermissions/
How to cite this article: da Cunha Rodrigues, G. et al. Correspondence: Reply to
‘On the nature of strong piezoelectricity in graphene on SiO2’. Nat. Commun. 7:11571
doi: 10.1038/ncomms11571 (2016).
This work is licensed under a Creative Commons Attribution 4.0
International License. The images or other third party material in this
article are included in the article’s Creative Commons license, unless indicated otherwise
in the credit line; if the material is not included under the Creative Commons license,
users will need to obtain permission from the license holder to reproduce the material.
To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/
CORRESPONDENCE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms11571
2 NATURE COMMUNICATIONS | 7:11571 | DOI: 10.1038/ncomms11571 | www.nature.com/naturecommunications


English

Correspondence: Reply To 'on The Nature Of Strong Piezoelectricity In Graphene On Sio2'

Institutional repository of Ural Federal University named after the first President of Russia B.N.Yeltsin

Rodrigues, Gonçalo da Cunha

Correspondence: reply to 'On the nature of strong piezoelectricity in graphene on SiO2'

Gonçalo da Cunha Rodrigues

Pavel Zelenovskiy

Konstantin Romanyuk

Sergey Luchkin

Yakov Kopelevich

Andrei Kholkin

Crossref

Correspondence: Reply to ‘On the nature of strong piezoelectricity in graphene on SiO2’

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Correspondence: Reply to 'On the nature of strong piezoelectricity in graphene on SiO2'

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Repositório Institucional da Universidade de Aveiro

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