This is a pre-print of an article published in
Journal of Materials Science: Materials in Electronics.
The final authenticated version is available online at:
Defect Formation in Supported Graphene Irradiated by Accelerated Xenon
Egor A. Kolesov1, Mikhail S. Tivanov1,*, Olga V. Korolik1, Pavel Yu. Apel2, 3, Vladimir A.
Skuratov2, 3, 4, Anis Saad5, Ivan V. Komissarov6
1 Belarusian State University, 4 Nezavisimosti Av., 220030 Minsk, Belarus
2 Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna, Russia
3 Dubna State University, Dubna, Russia
4 National Research Nuclear University MEPhI, Moscow, Russia
5 Al-Balqa Applied University, PO Box 4545, Amman 11953, Jordan
6 Belarusian State University of Informatics and Radioelectronics, 6 P. Brovka, 220013 Minsk,
* Corresponding author: E-mail firstname.lastname@example.org; Phone +375172095451; Fax +375172095445;
Address: 4 Nezavisimosti Av., 220030 Minsk, Belarus.
Raman spectroscopy and Monte-Carlo simulation studies for supported graphene irradiated
by 160 MeV Xe ions are presented. Changes in the density and dominating types of defects with
increasing fluence were observed. In order to analyze contribution of defect formation
mechanisms, in which the substrate is involved, a comparative study was performed for graphene
on SiO2/Si, copper and glass substrates. The major defining mechanisms were found to be
atomic recoils and formation of defects induced by hot electrons. For graphene on copper, the
impact of substrate recoil atoms was found to be greater comparing to graphene on silicon oxide
and glass, where the recoils participated approximately equally. Moreover, a possibility of defect
formation in graphene due to hot electrons generated in the substrate near the interface was
noted. Finally, a linear dependence of air-induced doping on D and G peak intensity ratio that
represents defect density in graphene was found. The study is useful for solving the long-
standing controversy on major mechanisms of defect formation in irradiated graphene, as well as
for graphene-based nanoelectronic device engineering.
Keywords: graphene; irradiation; swift heavy ions; interface; TRIM; adsorption.
Graphene is a promising material for a variety of applications due to its unique physical
properties . At present, graphene is used in transparent electrodes, field effect transistors,
sensors and other applications. Engineering of several graphene-based nanoelectronic devices
such as biosensors, as well as graphene functionalization techniques, requires structural
modification of the material through a controlled defect introduction [2-4]. Swift heavy ions
(SHI) irradiation method is a versatile and convenient tool for this purpose . It allows one to
control defect densities varying type, energy and fluence of ions. However, the mechanism of
defect formation in SHI-irradiated graphene still requires additional clarification.
It is known that the events of energy transfer to both target lattice nuclei (producing
recoils) and electron sub-system (producing hot electrons) participate in the ion-matter
interaction process, the latter giving non-negligible contribution to the defect formation in
graphene . Moreover, the substrate was ambiguously reported to affect graphene stability
under the irradiation, leading either to creation of additional defects [7, 8] or to reduction of the
resultant defect yield .
Raman spectroscopy is a versatile tool for obtaining information on the structural
properties of various materials. This method is particularly useful for graphene studies due to
monoatomic thickness of the material . Purpose of the present work is to study defect
formation processes in SHI-irradiated supported graphene using Raman spectroscopy and
Monte-Carlo TRIM simulations in order to understand the contributions of different defect
Graphene was obtained using an atmospheric-pressure chemical vapor deposition (CVD).
Prior to the synthesis, copper substrate was electrochemically polished in 1 M phosphoric acid
solution for 5 min with an operating voltage of 2.3 V. The CVD process was performed in a
tubular quartz reactor with a diameter of 14 mm using reagent grade chemicals. Copper foil was
pre-annealed at 1050 °C for 60 min under the following gas flow rates: H2 – 150 cc/min, N2 –
100 cc/min. The synthesis was performed under the following conditions: reactor temperature of
1050 °C, C10H22 (decane) flow rate of 4 μl/min, H2 flow rate of 60 cc/min, N2 carrier flow rate of
100 cc/min, and synthesis time of 30 min. After the hydrocarbon flow had been terminated, the
sample was cooled down to room temperature at a rate of ~ 50 °C/min.
Graphene was transferred to SiO2/Si (oxide thickness of 600 nm) and glass substrates by a
wet-chemical room-temperature etching without polymer support in two steps. First, one side of
copper foil was treated for 3 min in a solution of H2NO3 and H2O mixed in a volume ratio of 1:3.
Then, the copper foil was totally dissolved in a water solution of FeCl3. Graphene film was
washed several times in a distilled water bath prior to being placed onto the substrate.
Graphene was irradiated by 160 MeV xenon ions with fluences of 108, 109 and 1011 cm-2 at
the IC100 cyclotron at the FLNR JINR in Dubna . Ion beam homogeneity over the irradiated
sample surface was controlled using beam scanning in the horizontal and vertical directions and
was better than 5%.
Raman spectra were obtained with a spectral resolution better than 3 cm-1 using a
Nanofinder HE (LOTIS TII) confocal Raman spectrometer. For excitation of Raman radiation, a
continuous solid-state laser with a wavelength of 473 nm was used. Room-temperature Raman
measurements were carried out using laser power of 800 µW, the diameter of laser spot on the
sample surface being of about 0.6 µm.
The simulations were performed using binary collision Monte-Carlo approach
implemented in TRIM (the Transport of Ions in Matter) code . TRIM group of programs
uses quantum-mechanical collision treatment considering screened Coulomb interaction between
an ion with effective charge and an atom, including exchange and correlation interactions for the
overlapping electron shells and creation of electron excitations and plasmons inside the target
. In order to estimate the role of various defect formation mechanisms in the evolution of
graphene-substrate system under ion irradiation, the Monolayer Collision mode (for every
collision to be calculated without any approximations) with 100,000 incident 160 MeV xenon
ions was utilized for graphene monolayer simulated located on a substrate layer with the
thickness of 300 Å.
It is important to note that TRIM code treats target as an amorphous matrix with a
homogenous mass distribution (which is not generally applicable for nanostructures) and
calculates each collision impact regardless of collision density. Thus, TRIM simulation of
graphene irradiation cannot be used in order to obtain specific quantitative results. However,
TRIM code can still be used for statistical qualitative estimations [12-14]. Besides, supported
graphene can be considered a bulk system within the scale of several effects such as substrate
sputtering. Thus, we preferred TRIM code for the simulation since we were interested in a
statistical description of various defect formation mechanisms attributed to the substrate as a
bulk system participating in the process.
Results and discussion
Typical Raman spectra of pristine and SHI-irradiated graphene on SiO2/Si substrate are
presented in Fig. 1. As seen, D peak in pristine graphene spectrum has relatively low intensity
(ID/IG ~ 0.18), which corresponds to a small disorder of the sample structure [1, 15]. At the same
time, Raman spectra of irradiated graphene demonstrate increase in ID/IG intensity ratio of up to
0.5 (in several points – up to 1.0) as the irradiation fluence changes from 108 to 1011 cm-2,
indicating an increase of defect concentration. Moreover, position shift of the second-order 2D
peak from 2687 to 2691 cm-1, the decrease of I2D/IG intensity ratio from 1.7 to 1.0, and the
increase of 2D peak width from 33 to 43 cm-1 are observed. These changes together with the
shift of G peak position from 1587 to 1595 cm-1 can be attributed to adsorption doping of air-
exposed defected graphene and are discussed later.
1200 1500 1800 2100 2400 2700
FWHM = 38 cm-1
FWHM = 35 cm-1
Intensity, arb. un.
Raman Shift, cm-1
FWHM = 33 cm-1
FWHM = 43 cm-1
Figure 1. Typical Raman spectra of pristine and SHI-irradiated graphene on SiO2/Si substrate.
Irradiation fluence is given to the right of the plots.
In order to obtain information on defect distribution over the sample surfaces, Raman
mappings of 20×20 µm2 areas were obtained (Fig. 2). A uniform increase of ID/IG intensity ratios
(and therefore, the defect densities) is observed with increasing fluence. Raman map of graphene
irradiated with the fluence of 1011 cm-2 also demonstrates presence of high defect density
regions, possibly corresponding to a partial destruction of graphene lattice.
Figure 2. Raman maps (20×20 µm2) of ID/IG intensity ratio representing defect density distribution over
the sample surface for pristine and irradiated graphene on SiO2/Si substrate; scanning step of 1 µm.
Raman process leading to D peak arising in the spectrum implies relaxation of zero-
wavevector selection rule and includes events of elastic scattering on a defect and inelastic
scattering on A1g phonon at the Brillouin zone edge ; therefore, ID/IG ratio is directly related
to the defect density. This dependence includes regions of inverse proportionality (high density
of defects) and direct proportionality (low-density region) . However, the former means the
disorder is large enough to affect G and 2D peak profiles , and that was not observed in the
experimental spectra. Thus, we assume that the performed irradiation introduced degree of
disorder specific for a low-density region, and therefore ID/IG is directly proportional to the
defect density, which is confirmed by the relationship between the experimental fluence and
ID/IG values. It is also important to note that since the ID/IG ratio does not depend on a defect
geometry , its values represent the average interdefect distance as well as corresponding
density for all Raman active defect sites that are involved in elastic scattering events.
As it was shown in , information on dominating defect type can be provided by ID/ID’
intensity ratio in Raman spectra of graphene. The average ID/ID’ values obtained from the maps
are presented in Table 1. Raman spectra of pristine graphene demonstrate <ID/ID’> values of
about 1.5, corresponding to grain boundaries as dominating defects . At the same time,
Raman spectroscopy data for the irradiated graphene shows <ID/ID’> ~ 4.1 – 7.5. According
to dependencies presented in , these values indicate presence of both grain boundaries and
vacancies, with the role of vacancies increasing for greater fluences (Table 1).
Table 1. Peak intensity ratios calculated from the Raman spectra of pristine and irradiated graphene on
Irradiation fluence, cm-2
Fig. 3 demonstrates Raman maps of ID/ID’ intensity ratio representing the distribution of
different types of defects over the sample surface for pristine and irradiated graphene. As seen,
grain boundaries are mostly typical for pristine graphene, with several regions demonstrating
ID/ID’ values corresponding to sp3-bonding complexes. The map for graphene irradiated with 108
cm-2 fluence clearly shows the uniform increase of ID/ID’ ratio, indicating the formation of
irradiation-induced vacancies. As the fluence increases, further growth of vacancy density, as
well as formation of more sp3-bonding complexes are observed.
Figure 3. Raman maps (20×20 µm2) of ID/ID’ intensity ratio representing defect type distribution over the
sample surface for pristine and irradiated graphene on SiO2/Si substrate; scanning step of 1 µm. The types
of dominating defects corresponding to specific ID/ID’ values are indicated to the left of the color scale.
The observed ID/IG increase is stronger than expected considering literature data for various
ion types and energies, including data for suspended graphene [7, 17-19]. At the same time, it
was reported that defect yields for suspended and supported graphene can differ significantly
since the substrate can play an important role in defect formation process [7, 8, 17, 18, 20].
Particularly, the substrate might be involved through various different events such as energy
transfer from a recoiled substrate atom to graphene lattice. Moreover, one cannot exclude the
possibility of defect formation mechanism dependence on the crystallinity of the substrate
material. Thus, a correct analysis of the obtained results requires paying a close attention to
irradiation-induced substrate effects.
According to , the defect formation process in SHI-irradiated graphene includes
defects generated through an indirect process of substrate sputtering. In order to determine the
role of sputtered substrate atoms in graphene irradiation effects, comparison was carried out for
graphene irradiated with a fixed fluence of 108 cm-2 on copper (as-synthesized), SiO2/Si and
glass substrates. We performed TRIM simulations for graphene on each substrate in order to
obtain specific values of substrate sputtering yields, sputtered atom energy distributions, nuclear
and electronic stopping power (it should be noted that TRIM code is quantitatively applicable for
this case, since it is a bulk target being sputtered). Based on these values as well as defect yield /
nuclear stopping power dependencies from , we estimated approximate defect yields for
sputtered atoms. As an additional verification of structural modification trends obtained during
the simulation, Raman maps of pristine and irradiated graphene were scanned on each substrate,
whereupon average <ID/IG> and <ID/ID’> parameters were determined. The comparison of the
obtained values for graphene on various substrates is given in Table 2. Naturally, the number of
backscattered ions was negligibly small for all cases.
Table 2. Values calculated from Raman spectra of pristine and irradiated (fluence of 108 cm-2) graphene
on various substrates, as well as parameters obtained using TRIM simulations.
Nuclear stopping power Sn, keV/nm
Electronic stopping power Se, keV/nm
Sputtering yield Ys
Sputtered atom energies, keV
Estimated defect yields for sputtered atoms
Due to the fact that <ID/IG> value of 0.15 for pristine as-grown graphene is quite close to
those of 0.16 and 0.18 for graphene transferred to SiO2/Si and glass, we can confirm that the
transfer process introduced only a minor amount of defects into graphene lattice. It is seen that
<ID/IG> increase after graphene irradiation on SiO2/Si and glass has close values, while one for
copper is slightly greater. At the same time, the evolution of the defect system in graphene with
the irradiation has similar direction for all three substrates: from grain boundaries domination in
pristine graphene to both grain boundaries and vacancies in the irradiated material. However,
vacancy formation turned out to be the most discernible effect for graphene on silicon oxide,
according to utilized Raman dependencies from .
Due to a high energy of the incident ions, the energy transferred to the substrate nuclei for
all three materials is much smaller than that transferred to the electron sub-system, all the
sputtering yields being less than one (for copper, however, the sputtering yield is almost two
orders of magnitude greater). Performing simple estimations considering presented in Table 2
defect yields for sputtered atoms, sputtering yields and fluence, one can obtain the following
approximate total maximum defect concentrations created by sputtered substrate atoms during
the irradiation: 2.4·107 cm-2 for copper, 9.6·105 cm-2 for SiO2/Si and 9.0·105 cm-2 for glass. These
values are by several orders of magnitude smaller than the typical intrinsic defect density for a
pristine material; thus, greater obtained Ys value for copper still implies a weak participation in
the defect generation process. Thus, we do not consider substrate sputtering to play a major role
in the defect formation in graphene irradiated with 160 MeV xenon ions: substrate sputtering
yields have maxima at smaller incident ion energies (less than 1 MeV). Besides, other works
demonstrate that the sputtering damage of graphene itself effectively takes place for incident ion
energies as small as 20 eV , while still occurring most actively for irradiation by heavy ions
[18, 22]. Thus, using high-energy ions (more than ~ 30 MeV, according to our TRIM
simulations) for controlled defect induction in supported graphene can minimize the amount of
defects induced by substrate sputtering.
However, according to our simulation results, there is a non-negligible role of substrate
recoil atoms that do not leave the sample but become moved away from their positions at this
irradiation energy. Due to the energy transferred from the incident ions, such recoils can reach
graphene-substrate interface and participate in the defect formation. Fig. 4 demonstrates spatial
recoil distributions statistically obtained for graphene on copper, SiO2/Si and glass substrates as
another important output of TRIM simulation procedures. The greatest amount of recoils
reaching graphene-substrate interface region is observed for graphene on copper. For graphene
supported by SiO2/Si and glass, almost similar situation is observed, with the amount of oxygen
atoms reaching the interface being slightly greater; however, Na atoms also participate in the
Figure 4. Statistical depth recoil distributions for graphene irradiated by xenon ions on (a) copper, (b)
SiO2/Si and (c) glass substrates. For glass substrate, the distribution of other element atoms present in
glass (Ca, Mg, Al) is not shown due to its negligibly small rate.
According to our estimations, the approximate amount of displacements which can be
created by recoil atoms in graphene layer was 6·109 cm-2 for copper, 4·109 cm-2 for SiO2/Si and
5·109 cm-2 for glass substrate, these values being more realistic than those estimated for substrate
sputtering damage. Thus, we can consider recoil-dominated damage to be more intensive
mechanism of defect formation in SHI-irradiated supported graphene than the substrate
sputtering in our case.
Another reported mechanism to contribute to the defect formation in graphene irradiated
by swift heavy ions is an electronically-stimulated surface desorption . Due to a high energy
of Xe ions used in our experiment, it can dissipate through an electronic excitation event, and
thus the incident ions (or recoil atoms) can be considered as the hot electron source (that mostly
relates to collisions with reduced direct kinetic energy transfer, i.e. non-central collisions with an
impact outside the target atom cross section) . In turn, the hot electrons disrupt graphene
lattice, leading to the in-plane carbon bonds breakage . According to our calculations, the
electronic stopping energy loss in graphene for the case of 160 MeV xenon ions is 17.2 keV/nm,
with this value being quite enough for the surface atoms to desorb. It should be noted that the
keV/nm units are used here for a comparative purpose only, as in ; the physical meaning of
nanometers in the denominator is not defined for graphene and requires adaptation to be
correctly used both for three- and two-dimensional targets.
Naturally, the substrate does not affect the amount of energy lost for ionization in graphene
within the utilized approach; however, according to our calculations, electronic stopping energy
loss for 160 MeV xenon ions in copper is 36.3 keV/nm (it can be considered quantitative since
the substrate is a bulk target). A large value of this parameter suggests an idea that the
contribution to the defect formation in graphene is possible from substrate hot electrons
produced near the interface. Due to silicon oxide giving the greatest contribution to electronic
stopping in glass, the ionization energy loss for SiO2/Si and glass has almost similar values: 14.5
and 14.6 keV/nm, respectively. Energy lost for ionization by recoil atoms turned out to be small
(less than 2 eV), as well as the amount of recoil-induced ionization events for all three cases.
It should be noted that the simulation performed did not take into account the fact that
graphene on copper is as-grown, but it nevertheless agreed with the supporting Raman
experiments qualitatively well for both pristine and irradiated graphene, leading to a conclusion
that substrate-induced irradiation effects in case of a relatively strong graphene-metal interaction
manifest themselves much stronger than the residual synthesis effects such as chemical bonds at
Finally, considering the possibility of doping for air-exposed graphene, we analyzed
indicative in this case Raman spectra parameters (G and 2D peak positions, I(2D)/I(G) ratio )
for graphene on SiO2/Si substrate. As it was seen in Fig. 1, the evolution of these parameters is
observed as the fluence increases, suggesting the increasing hole doping for greater defect
density values . Summarizing corresponding obtained values for each spectrum in a batch
processing sequence, we obtained fluence-dependent average values of hole concentration
presented in Fig. 5. A near-linear dependence on <ID/IG> is observed in this case, demonstrating
that ‘SHI irradiation + functionalization’ sequence can be considered a comparable alternative to
the low-energy ion beam implantation  for graphene doping. Peak ratio value corresponding
to the initial defect density of pristine graphene which is not determined by the irradiation effects
still fits into the obtained line well. This fact suggests that for graphene functionalization
methods based on a defect induction through SHI irradiation, a small but present initial amount
of defects represented by grain boundaries or vacancies does not strongly affect dependencies
needed for controllability of the process. Presented observation can be taken into account in
order to simplify graphene-based nanoelectronic device engineering process.
0.1 0.2 0.3 0.4 0.5 0.6 0.7
Hole concentration ( 1013 cm-2)
0 108 109 1011
Figure 5. Hole concentration dependence on <ID/IG> ratio representing the average sample defect density
(fluence also indicated) for graphene on SiO2/Si irradiated with 160 MeV Xe ions. Squares represent
experimental data obtained from Raman spectra and solid line shows a linear fit.
A systematic Raman study, as well as corresponding Monte-Carlo simulations for
supported graphene irradiated by swift xenon ions (energy of 160 MeV) were performed. As the
fluence increased, changes in the defect density and dominating defect types were observed. In
order to analyze the contributions of defect formation mechanisms in which the substrate is
involved, a comparative study was performed for graphene on SiO2/Si, copper and glass
substrates. The contribution of sputtered substrate atoms was small for all cases, while the major
defining mechanisms were atomic recoils reaching graphene-substrate interface and
electronically-stimulated surface desorption. A role of substrate recoils reaching the interface
was found to be greater for graphene on copper, while for SiO2/Si and glass substrates atom
recoils participated approximately equally. Moreover, a possibility of defect formation in
graphene due to substrate hot electrons, generated near the interface, was noted. Considering the
possibility of doping for the air-exposed graphene, a linear hole concentration dependence on the
<ID/IG> was found, with the initial defectiveness point (not defined by the irradiation effects) still
fitting into the obtained dependence well. The present study provides further insight into the
contributions of different defect formation mechanisms in irradiated graphene. The obtained
results are useful for graphene-based nanoelectronic device engineering, including devices that
require controlled graphene functionalization as well as controlled introduction of a known
amount of disorder into graphene structure.
 A.C. Ferrari, D.M. Basko, Nature Nanotech. 8, 235-246 (2013). DOI: 10.1038/nnano.2013.46
 A.K. Geim, Science 324, 1530-1534 (2009). DOI: 10.1126/science.1158877.
 B. Guo, Q. Liu, E. Chen, H. Zhu, L. Fang, J.R. Gong, Nano Lett. 10, 4975–4980 (2010).
 D.W. Boukhvalov and M.I. Katsnelson. Nano Lett. 8, 4373–4379 (2008). DOI:
 J. Zeng, H.J. Yao, S.X. Zhang, P.F. Zhai, J.L. Duan, Y.M. Sun, G.P. Li, J. Liu, Nucl. Instr.
Meth. Phys. Res. B 330, 18-23 (2014). DOI: 10.1016/j.nimb.2014.03.019.
 S. Akcöltekin, H. Bukowska, T. Peters, O. Osmani, I. Monnet, I. Alzaher, B. Ban d’Etat, H.
Lebius, M. Schleberger, Appl. Phys. Lett. 98, 103103 (2011). DOI: 10.1063/1.3559619.
 G. Compagnini, F. Giannazzo, S. Sonde, V. Raineri, E. Rimini, Carbon 47, 3201–3207
(2009). DOI: 10.1016/j.carbon.2009.07.033.
 S. Zhao, J. Xue, Y. Wang, S. Yan, Nanotechnology 23, 285703 (2012). DOI: 10.1088/0957-
 S. Mathew, T.K. Chan, D. Zhan, K. Gopinadhan, A.-R. Barman, M.B.H. Breese, S. Dhar,
Z.X. Shen, T. Venkatesan, J.T.L. Thong, Carbon 49, 1720–1726 (2011). DOI:
 B.N. Gikal, S.N. Dmitriev, G.G. Gul’bekyan, P.Yu. Apel’, V.V. Bashevoi, S.L. Bogomolov,
O.N. Borisov, V.A. Buzmakov, I.A. Ivanenko, O.M. Ivanov, N.Yu. Kazarinov, I.V. Kolesov,
V.I. Mironov, A.I. Papash, S.V. Pashchenko, V.A. Skuratov, A.V. Tikhomirov, M.V. Khabarov,
A.P. Cherevatenko, N.Yu. Yazvitskii, Phys. Part. Nucl. Lett. 5, 33-48 (2008). DOI:
 J.F. Ziegler, M.D. Ziegler, J.P. Biersack, Nucl. Instr. Meth. Phys. Res. B 268, 1818-1823
(2010). DOI: 10.1016/j.nimb.2010.02.091.
 R. Giro, B. S. Archanjo, E. H. Martins Ferreira, R. B. Capaz, A. Jorio, C. A. Achete, Nucl.
Instr. Meth. Phys. Res. B: Beam Interact. Mater. At. 319 (2014), 71–74. DOI:
 A.V. Krasheninnikov and K. Nordlund. J. Appl. Phys. 107 (2010), 071301. DOI:
 D.C. Bell, M.C. Lemme, L.A. Stern, J.R. Williams and C.M. Marcus. Nanotechnology 20
(2009), 455301. DOI: 10.1088/0957-4484/20/45/455301.
 L.G. Cançado, A. Jorio, E.H. Martins Ferreira, F. Stavale, C.A. Achete, R.B. Capaz, M.V.O.
Moutinho, A. Lombardo, T.S. Kulmala, A.C. Ferrari, Nano Lett. 11, 3190-3196 (2011). DOI:
 A. Eckmann, A. Felten, A. Mishchenko, L. Britnell, R. Krupke, K.S. Novoselov, C.
Casiraghi, Nano Lett. 12, 3925-3930 (2012). DOI: 10.1021/nl300901a.
 W. Li, X. Wang, X. Zhang, S. Zhao, H. Duan & J. Xue. Sci. Rep. 5 (2015), 9935. DOI:
 O. Lehtinen, J. Kotakoski, A. V. Krasheninnikov, A. Tolvanen, K. Nordlund, and J.
Keinonen. Phys. Rev. B 81 (2010), 153401. DOI: 10.1103/PhysRevB.81.153401.
 J. Zeng, J. Liu, H.J. Yao, P.F. Zhai, S.X. Zhang, H. Guo, P.P. Hu, J.L. Duan, D. Mo, M.D.
Hou, Y.M. Sun. Carbon 100 (2016), 16. DOI: 10.1016/j.carbon.2015.12.101.
 S. Mathew, T.K. Chan, D. Zhan, K. Gopinadhan, A.R. Barman, M.B.H. Breese, S. Dhar,
Z.X. Shen, T. Venkatesan, John TL Thong. Carbon 49 (2011), 1720–1726. DOI:
 P. Ahlberg, F.O.L. Johansson, Z.-B. Zhang, U. Jansson, S.-L. Zhang, A. Lindblad, and T.
Nyberg. APL Materials 4 (2016), 046104. DOI: 10.1063/1.4945587.
 K. Yoon, A. Rahnamoun, J.L. Swett, V. Iberi, D.A. Cullen, I.V. Vlassiouk, A. Belianinov,
S. Jesse, X. Sang, O.S. Ovchinnikova, A.J. Rondinone, R.R. Unocic, and A.C.T. van Duin. ACS
Nano 10 (2016), 8376–8384. DOI: 10.1021/acsnano.6b03036.
 A.V. Krasheninnikov, Y. Miyamoto, D. Tománek. Phys. Rev. Lett. 99 (2007), 016104.
 M. Lenner, A. Kaplan, Ch. Huchon, and R. E. Palmer. Phys. Rev. B 79 (2009), 184105.
 R. Beams, L. Gustavo Cançado, L. Novotny. J. Phys. Condens. Matter 27 (2015), 083002.
 P. Willke, J.A. Amani, A. Sinterhauf, S. Thakur, T. Kotzott, T. Druga, S. Weikert, K. Maiti,
H. Hofsäss, and M. Wenderoth. Nano Lett. 15 (2015), 5110–5115. DOI: