Supplementary Information
Tuning the Properties of Graphene by a Reversible
Gas-Phase Reaction
Lin Gan1, Jian Zhou2, Fen Ke3, Hang Gu1, Danna Li1, Zonghai Hu3, Qiang Sun2,
Xuefeng Guo*1,2
1
Center for NanoChemistry, Beijing National Laboratory for Molecular Sciences
(BNLMS), State Key Laboratory for Structural Chemistry of Unstable and Stable
Species, College of Chemistry and Molecular Engineering, Peking University, Beijing
100871, P. R. China.
2
Department of Materials Science and Engineering, Peking University, Beijing
100871, P. R. China.
3
College of Physics, Peking University, Beijing 100871, P. R. China.
*To whom correspondence should be addressed. Email: guoxf@pku.edu.cn
Fig. S1: Schematic representation of the fabrication procedure to form graphenebased transistor arrays.
b
a
c
SLG
250 mm
d
70 mm
e
Intensity (a.u.)
2D
G
SLG
1200
1600
2000 2400 2800
Raman Shift (cm-1)
3200
4 nm
Fig. S2: a, An optical image of large-area graphenes after PMMA-mediated
nanotransfer process on a silicon wafer. b, Schematic representation of the SLG
device array. c, The enlarged optical image of a representative device. The average
width of graphene sheets is  70 mm. d, A representative Raman spectrum of the
grown graphene. e, A representative high-resolution TEM image of SLG.
Intensity (a.u.)
Fig. S3. Intensity profile plot along the line indicated by the arrows in Fig. 3e. The
intensities of the diffraction spots from outer hexagon is equivalent to that from inner
hexagon, confirms that our graphene samples are single-layer1.
Intensity (a.u.)
Before plasma methylation
After plasma methylation
O 1s
C 1s
N 1s
350
400
450
N 1s
O 2s
0 10 20 30 40 50 200 300 400
Binding Energy (eV)
500
600
Fig. S4. XPS spectra of a SLG sample before and after plasma methylation. Inset
shows the enlarged N 1s XPS spectra. We find that the amount of O and N atoms were
strongly suppressed after plasma treatment.
a
1.2
8 nm
Height =  0.49 nm
Height (nm)
0.8
0.4
0.0
-0.4
-0.8
0 nm
-1.2
0.0
1 mm
b
0.5
1.0
1.5
2.0
1.5
2.0
Distance (mm)
1.2
8 nm
Height =  0.70 nm
0.8
Height (nm)
0.4
0.0
-0.4
-0.8
-1.2
-1.6
0 nm
1 mm
-2.0
0.0
0.5
1.0
Distance (mm)
Fig. S5. AFM images of the same SLG sample before (a) and after plasma
methylation (b). The average changes in graphene thickness after plasma methylation
is  0.21nm.
Theoretical computations. Our calculations were based on density functional theory
(DFT) with generalized gradient approximation (GGA) for the exchange-correlation
energy. We have used the Perdew-Burke-Ernzerhof (PBE)2 for the GGA and a
plane-wave basis set with the projector-augmented-wave (PAW) method originally
developed by Blochl3 and adapted by Kresse and Joubert in the Vienna ab initio
simulation package (VASP)4. We used periodic boundary condition to simulate the
two-dimensional methylated SLG along x and y direction, and along z direction we
set vacuum space of 15 Å to avoid the interactions between two neighboring images.
We also applied Monkhorst-Pack meshes5 of (7  7  1) to represent the reciprocal
spaces. All the structures were relaxed through conjugated gradient method without
any symmetric constraints. The energy cutoff and convergence criteria for energy and
force were set to be 400 eV, 1  10-4 eV, and 0.01 eV/Å, respectively. The accuracy of
the above procedure has been well tested in our previous work6.
Band structures of graphene after plasma treatment. In order to better understand
the methylated SLG sheets, we performed first-principles density-functional
calculations to investigate their band structure, orbital distribution, and elastic
modulus using Vienna Ab initio Simulation package (VASP)3. Based on the
experimental finding, the geometry of methylated SLG sheets is shown in Fig. S6(a).
After geometric relaxation, the unit cell lattice constant is found to be 4.98 Å and the
C-C bond lengths with sp3 and sp2 hybridizations in the graphene are 1.51 and 1.53 Å,
respectively. Such a configuration is found to be energetically most stable with at least
0.913 eV lower in energy than other configurations (Supplementary Fig. S7). Due to
the surface absorption, graphene could not retain its planar structure and the sp3 C
atoms move outward. The formation energy, defined as Ef (=Emethylated SLG – ESLG –
ECH4), is found to be 1.97 eV/unit cell. The positive value indicates that the reaction of
surface decoration is endothermic, and thus the demethylation and dehydrogenation
process can be achieved easily. It should be noted that the reaction of full
hydrogenation on SLG (forming graphane) is exothermic, suggesting that it is more
difficult to remove its surface hydrogen atoms. To gain some details of bonding
features, let’s check the electron redistribution upon the surface decoration, as shown
in Fig. S6(b) for the charge difference density △ρ (=ρmethylated SLG – ρCH3 – ρH – ρSLG).
We can see that electrons are slightly accumulated around the functional groups
(methyl and hydrogen).
a
y
x
b
Fig. S6. a, Geometric model of the methylated SLG and its corresponding bond
lengths. The dashed rhombus is the unit cell. b, Isosurface of charge difference density
of the methylated SLG, green for positive and blue for negative values.
Fig. S7. Relative energies and magnetic moments per unit cell of different
configurations of the methylated and hydrogenated SLG. As shown in this figure, we
examine the relative energies and magnetic moments per unit cell of the three
configurations with fixed methyl and hydrogen concentration. It shows that the most
energetically favorable conformer is that hydrogen absorbs at the para-position of the
methyl, while the conformer of hydrogen at meta-position of the methyl has the
highest energy. This is because the ortho-position absorption will induce larger
distortion and the meta-position absorbed conformer is magnetic7.
We then examined the electronic properties of this methylated SLG. The
calculated band structure and partial density of states (PDOS) are shown in Fig. S8.
The system is found to be nonmagnetic with an indirect band gap of 3.63 eV around
the Fermi level, which is comparable with that of graphane (3.50 eV with a direct
band gap)8. The PDOS shows that the gap is mainly dominated by the 2p orbitals of
the C atoms. In order to examine it in detail, we plotted wave functions of the highest
valence band (HVB) and the lowest conductance band (LCB). We can see that both of
them are contributed by the C atoms of SLG; the HVB has delocalized π character
while the LCB has localized π* character. We then anticipate that the band gap of
SLG can be modulated in a large range under different coverages.
5
0
0
-5

K
M
Energy (eV)
EF
5
p
s
-5
-10 -10
0

5
10
15
PDOS (e/eV)
Fig. S8. Band structure (right), PDOS (middle) and wave functions of frontier bands
(left) for the methylated SLG.
Finally, we considered the mechanical property of the methylated SLG. A
rectangle unit cell is used to calculate the elastic constant C along x and y directions.
The elastic constant can be written as C  2E /  S0 l2 / l2  where E and l
are deformation energy and lattice constant along α (= x and y) directions,
respectively. The total energy variation with respect to unit cell deformation is plotted
in Fig. S9, where we can deduce the values of Cx (326.6 N/m) and Cy (419.9 N/m),
respectively. These values are comparable to the average experimental elastic
modulus of 342 N/m in pristine graphene sheet9 but they are larger than those of
graphdiyne (158.57 and 144.90 N/m)10.
10
along x
8
E (meV)
along y
6
4
2
0
-0.004
-0.002
0.000
l /l0
0.002
0.004
Fig. S9. Total energy variation per unit cell with respect lattice deformation along x
and y directions. The curves are the parabola fitting.
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