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Synthesis of 2D Heterostructures: MOS2/GO and
MOS2/Graphene via Microdrop and CVD Deposition
Diogo Jos!e Horst*, Charles Adriano Duvoisin and Rog!erio De Almeida Vieira
Laboratory of Materials and Mechanical
Manufacturing — LMMM
Department of Chemistry
Federal University of S~ao Paulo
Rua S~ao Nicolau 210, 5th Floor
ZIP 09913-030, Diadema, S~ao Paulo, Brazil
*diogohorst@gmail.com
Jesús Alejandro Arizpe, Esther Alejandra Huitrón Segovia
and Alejandra García-García†
Laboratory of Synthesis and Modi¯cation of Nanostructures and M2D
Center for Investigation of Advanced Materials — CIMAV, S.C
Area of Polymeric Nanostructures and Nanocomputes
PIIT Park, ZIP 66628, Apodaca, Nuevo Le!on, Mexico
†alejandra.garcia@cimav.edu.mx
Received 9 August 2021
Accepted 12 November 2021
Published
The main objective of this work was to study the synthesis and characteristics of two-
dimensional heterostructures (2D/2D) using pure molybdenum disul¯de (MoS2Þ and doped with
phosphorus at 5% and 15% combined with graphene oxide (GO) and graphene monolayer. These
were deposited on silicon and copper substrates using two di®erent deposition methods: Micro-
drop casting and chemical vapor deposition. Chemical and structural information of the samples
were characterized by Raman spectroscopy, Energy Dispersion X-ray Spectroscopy (EDS),
Scanning Electron Microscopy (SEM) and Kelvin Probe Force Microscopy (KPFM). The results
prove the synergy between the materials resulting in electronic coupling, making this system
potential for applications in electronic devices such as sensors, resistors and capacitors.
Keywords: Van der Waals heterostructures; bidimensional materials; graphene; graphene oxide;
phosphorus doping.
1. Introduction
Molybdenum disul¯de (MoS2Þ is a favorable candi-
date to be combined with several carbon-derived
nanomaterials in order to obtain new hybrid
nanostructures with excellent physicochemical
and electronic properties; the design and production
of new two-dimensional heterostructures using
modern techniques presents a promising perspective
for current nanotechnology.1 Signi¯cant e®orts
in the catalytic applications of transition metal
International Journal of Nanoscience
Vol. 20, No. 6 (2021) 2150050 (8 pages)
#.c World Scienti¯c Publishing Company
DOI: 10.1142/S0219581X21500502
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https://dx.doi.org/10.1142/S0219581X21500502
dichalcogenides (TMDs) have been made, mainly
focusing on the design and synthesis of vertically
aligned structures, including expanded layer spac-
ing, seeking maximized exposure of active edge
sites. However, vertically aligned TMD hetero-
structures are rare.2 The combination of two highly
versatile materials such as graphene oxide (GO) and
molybdenum disul¯de forms layered GO-MoS2
hybrids presenting great potential for detection
applications such as eletro-chemical sensors.3
While graphene is chemically inert as a gapless
semimetal, its isostructural analogue, MOS2, is
chemically versatile with band gaps, thus ¯nding
signi¯cant use in a myriad of applications.4 De-
signing the structure and/or boundary density and
grain boundary in 2D materials is a promising way
to customize their performance.5
Grain boundaries in layers of two-dimensional
materials have an impact on their electrical, op-
toelectronic and mechanical properties. Therefore,
it is worth investigating the availability of simple
approaches to synthesis and characterization of
these 2D heterostructures.6
In this study, we demonstrate two di®erent
ways the microdrop casting and chemical vapor
deposition methodologies to create 2D hetero-
structures using molybdenum disul¯de, monolayer
graphene and graphene oxide. The chemical and
structural information of the samples was evaluated
by Raman spectroscopy, Energy Dispersion X-ray
Spectroscopy (EDS), Scanning Electron Microscopy
(SEM) and Kelvin Probe Force Microscopy
(KPFM).
2. Materials and Methods
This section presents the materials and methods
used in this work to meet the main objective.
2.1. Graphene Oxide (GO) reduction and
MoS2 synthesis
The GO used in this study was prepared under the
synthesis protocol developed at the CIMAV Labo-
ratory for synthesis and modi¯cation of nanos-
tructures and M2D.7 Reduction of a colloidal
suspension of exfoliated GO sheets in water with
hydrazine hydrate results in their aggregation and
subsequent formation of a high surface area carbon
material consisting of thin graphene-based sheets.
Before growth, a drop of GO-hydrazine solution was
centrifuged on the substrate. Before depositing the
microdroplet, the substrate was washed in iso-
propane, sonicated and then allowed to dry. Then, a
solution of PTAS (50!M) or PTCDA (26mg in
5mL of deionized water) was used to treat the
substrate, being heated at 90"C for 1 h. MoS2 syn-
thesis was performed following the protocols used in
the laboratory according to Rubio-Govea.8 First,
MoO3 and Sulfur (S) powder were placed in a tube
furnace at 600"C under N2 °ow. Afterward, a post-
treatment via recrystallization was carried out at
800"C for 1 h. After the heating process, the oven
was allowed to cool to room temperature under N2
°ow. The synthesis of MoS2-F was done via hy-
drothermal synthesis. First, an amount of AHMo
was dissolved in deionized water and left under
magnetic stirring for 10min. Then, thiourea and
citric acid were added to the reaction mixture until
complete dissolution and the resulting solution was
transferred to a Te°on coated autoclave. The au-
toclave was transferred to an oven and kept at
180"C for 24 h. After natural cooling of the auto-
clave to room temperature, the precipitate was
washed several times with deionized water and
ethanol and dried at 90"C. A post-heat treatment
at 180"C for 30min was applied to eliminate pos-
sible organic remnants without a®ecting the °oral
morphology obtained.
2.2. Microdrop casting
In this assay, 1 microdrop (2!L) containing colloi-
dal suspensions of pure MoS2 and with phosphorus
doping at 5 and 15% and GO (liquid–liquid phase)
was dripped on plates of polished crystalline silicon
and also copper measuring approximately 1 # 1 cm.
Previously MoS2 and GO nanoparticles were added
in 5ml of deionized H2O 200!L of ethanol for di-
lution, the aqueous suspension was sonicated for
20min to homogenize the mixture. The microdrop
was deposited using a micropipette and for evapo-
ration of the colloidal suspension, the Si and Cu
plates were subjected to heating using 100–120"C
put for 1–3min.9
After evaporating the solvent, the sediments
were deposited on the plate, obtaining depositions
of superimposed monolayer ¯lms of Si+MoS2+GO
and Si+MoS2+monolayer graphene, and Cu+MoS2
+GO and Cu+MoS2+monolayer graphene.
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2.3. Chemical vapor deposition — CVD
MoS2 ¯lms were synthesized on SiO2/Si and Cu
substrates in a blast furnace; some samples were
doped with 5% and 15% phosphorus in order to
verify their energy potential. The MoS2 depositions
were performed on silicon plates (1 # 1 cm) using a
quartz tube oven (Lindberg/Blue M — Thermo
Scienti¯c). Subsequently, graphene layers were de-
posited on the Si+Mos2 and Cu+MoS2 plates using
a fast thermal processor (RTP-system, AS-Micro
Annealsys) with preheating at 750"C and reaching
950"C in a quartz tube using several gases with the
following control parameters: N2 (1000 ccm), H2
(10 ccm) and CH4 (5 ccm).
2.4. Characterization
The chemical and structural characterization of
GO/MoS2 hybrids were evaluated by Raman and
X-ray Energy Dispersion Spectroscopy (EDS),
scanning electron microscopy (Jeol EDS-System)
using an analytical equipment (LabRAM HR Evo-
lution Horiba) coupled to a microscope (AIST-NT
Horiba) and KPFM using AC240 TMR3 (Asylum)
cantilever with k ¼ 2N/m and F ¼ 0:70 kHz using
a Transmission Electron Microscope (TEM) equip-
ment (Bruker).
3. Results and Discussion
This section presents a discussion of themain
results achieved in this study.
3.1. Raman spectroscopy
Chemical and structural information of the studied
materials are shown in Fig. 1 showing the light
scattering in the Raman spectrum:
By direct analysis, which consists of individual
mapping of the corresponding peaks, it indicates
di®erent numbers of layers. Thus, the layers can be
found by determining the distance between two
¯ngerprint peaks (observed at % 383 and
% 406 cm& 1Þ, thus indicating the deposition of 1–3
layers of MoS2. Regarding graphene, its main
spectral characteristic is derived from the move-
ment in the plane of the carbon atoms and appears
close to 1580 cm& 1 referring to the G-band, being
extremely sensitive to stress e®ects and also a good
indicator of the number of graphene layers. As the
number of layers increases, the position of the
G-band shifts to lower frequencies, following a 1/n
dependence on the number of layers. B and D is
known as the band for crystals in disarray. This
peak is due to the movement of the lattice away
from the center of the Brillouin zone and its pres-
ence between 1270 and 1450 cm& 1 (which depends
on the excitation wavelength) indicates defects or
edges in the graphene sample.
A de¯nitive explanation of its origin and depen-
dence on the excitation wavelength is derived from
the double resonance theory originally proposed by
Thomsen and Reich.10 In this theory, the intraband
phonon scattering of the electron requires momen-
tum that is easily absorbed by defects, which is why
this band was ¯rst observed in defective crystals. In
this work an intense band is observed at 1340 cm& 1
corresponding to the D band together with the G
band at 1597 cm & 1 which corroborates the research
by Singh et al.11
In this work, the Raman analysis revealed peaks
at 1350 and 1588 cm& 1 for the D and G bands due
to the doping of Mos2/GO with phosphorus. The D
band corresponds to the scattering of defects or
local disturbances present in the carbon, and the G
bands originate from the tangential elongation in
the plane of the C& C bonds in the graphite struc-
ture. MoS2 exhibited characteristic bands at 379
and 406 cm& 1, corresponding to the E12g and A1g
¯rst-order mode of the 2H.22a phase.
The E12g mode can be associated with the op-
posite in-plane vibration of two S atoms with re-
spect to the Mo atom, while the A1g mode
originates from the out-of-plane vibration of only
S atoms in the opposite directions. 22b, 23
These results can con¯rm the formation of the
2D–2D architecture of the MoS2/GO compound.
Fig. 1. Raman spectrum of samples.
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The ampli¯ed band for the A1g mode with the total
width greater at half the maximum (FWHM) than
the MoS2 by mass indicated that the MoS2 has a few
layer structure in the composite. 22a (These crystals
have two types of viewing locations: terrace and
edge.) Furthermore, in the MoS2/GO compound,
the intensity of the A1g mode was much higher than
the E12g mode, indicating that the MoS2 leaves
were terminated at the edges, 11 h, 24, otherwise the
E12g mode would be preferentially excited to ter-
minate on the terrace in nano¯lm due to polariza-
tion dependence. The edge termination structure
can enrich the exposed edge sites and, therefore,
increase the catalytic activity, which corroborates
the research by Wang et al.12
3.2. X-ray energy dispersive
spectroscopy — EDS
Figure 2 presents information on the elemental
analysis of the studied samples using the two dif-
ferent deposition methodologies, CVD and micro-
drop casting.
The image and quantitative mapping obtained
through EDS analysis reveal the distributions of
C, O, S, Mo and Si, thereby con¯rming the presence
Fig. 2. X-ray energy dispersive spectroscopy.
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of MoS2 °akes con¯rming the stable deposition of
MoS2/GO heterostructures and MoS2/monolayer
graphene. Samples 1 and 2 were prepared via CVD
(solid–liquid) while samples 3 and 4 were prepared
by microdrop (liquid–liquid phase). Only sample 4
lacked Mo content, indicating that the deposition
was ine±cient in this case mainly due to rapid sol-
vent evaporation, thereby not adhering to the Si
and Cu substrates.
Table 1 presents the mass composition of
samples taking into account the two di®erent
methodologies.
Table 2 shows the atomic composition of the
samples.
3.3. Scanning electron microscopy —
SEM
Figure 3 shows the growth morphology demon-
strating the grain boundary of graphene/MoS2 and
MoS2/GO deposited on copper and silicon sub-
strates via both methods.
As can be seen in Figs. 3(a) and 3(b), grain
boundary and grain boundary of graphene/MoS2
deposited via CVD on a copper plate; ((c), (d), (e),
(f), (g)) growing MoS2/GO grains on silicon sub-
strate) and in the form of ribbons and nano°owers;
(h) reduced GO covering Si substrate; ((i), (j), (k),
(l)) ribbons growth and later forming of MoS2
nano°owers growth over graphene oxide.
According to Sitek et al.,13 the ability of the
substrate to create bonds signi¯cantly in°uences the
dynamics of adsorbates at the substrate surface,
especially the surface di®usion mechanism. In typi-
cal three-dimensional (3D) materials, that is, with
unsaturated bonds on the surface, including Si, SiO2
or sapphire, the mechanism of surface di®usion is
described by a hopping model in which adsorbed
species are localized at high-energy-binding sites on
the surface, for example, active hydroxyl groups on
SiO2. The movement of the species is allowed only
between these binding sites. These hydroxyl groups
can also become nucleation sites for MoS2 growth as
the predicted activation energies of R3–Si–O–MoS2
from R3–Si–OH are similar to the thermal energy of
gas molecules at the growth temperature, that is,
156meV and 135meV, respectively.
3.4. Kelvin probe ¯eld microscopy —
KPFM
Figure 4 shows the imaging results of the KPFM
analysis.
The analysis reveals that the MoS2/GO and
MoS2/graphene heterostructures present electronic
synergy in regions of layers with dimensions corre-
sponding to 400 nm which reach from & 20meV to
0.4V. Other regions of vertical layers with a diam-
eter of 60 nm have properties electronics in the
range of & 20 to 315mV, which corroborates the
Table 1. Mass composition of samples — EDS analysis.
Mass (%) Sample 1 CVD Sample 2 CVD Sample 3 Microdrop Sample 4 Microdrop
C 46.00 54.53 50.65 14.67
O 10.09 18.72 4.60 1.04
Si 16.86 10.39 30.61 75.39
S 12.83 7.69 5.70 8.90
Mo 14.22 8.67 8.44 —
Total 100.00 100.00 100.00 100.00
Table 2. Atom composition of samples — EDS analysis.
Atom (%) Sample 1 CVD Sample 2 CVD Sample 3 Microdrop Sample 4 Microdrop
C 68.28 70.82 71.96 28.76
O 10.24 18.25 4.91 1.53
Si 10.71 5.77 18.60 63.18
S 7.13 3.74 3.03 6.53
Mo 2.64 1.41 1.50 —
Total 100.00 100.00 100.00 100.00
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Fig. 4. Surface potential microscopy image.
Fig. 3. Surface morphology and grain growth.
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research by Ma et al.14 and Miha and Scopel15 by
presenting binding energy values for the MoS2/
graphene heterostructure of 21.0meV and 3.66V. It
is worth noting that lower mobilities in ¯eld e®ect
transistors based on GO/MoS2 can originate from
the defect limits and displacements in MoS2 ¯lms, as
mentioned by Barua et al.16
4. Conclusion
The two methodologies studied proved to be viable,
in the liquid–liquid phase, the microdrop deposition
proved to be simple and practical to achieve stable
MoS2/GO heterostructures. The CVD deposition,
in the solid–liquid phase, was possible to obtain
graphene/MoS2 heterostructures, both indicating
being favorable for industrial-scale growth of these
materials. Raman analysis revealed peaks at 1350
and 1588 cm& 1 indicating the D and G bands of
monolayer graphene. MoS2 was identi¯ed at 379
and 406 cm& 1, corresponding to the E12g and A1g
¯rst-order mode of the 2H.22a phase.EDS analysis
reveals the mass and atomic elemental distributions
of C, O, S, Mo and the image analysis con¯rmed the
growth of MoS2 °akes with stable deposition of
MoS2/GO and MoS2/monolayer graphene hetero-
structures. SEM analysis showed the growth of
MoS2 crystals in the form of ribbons, nano°owers
and pyramidal shapes and stable formation of gra-
phene evidenced by its grains boundary. KPFM
analysis revealed that the number of graphene/
MoS2 layers was from 1 to 10. The surface potential
of samples ranged from & 21.0meV to 3.66V, and
the images obtained revealed some surface defects.
We are currently investigating the e®ect of phos-
phorus doping on the surface potential of these
heterostructures, as well as changes in the deposi-
tion parameters that a®ect the super¯cial potential
response.
Acknowledgments
The authors would like to thank the National
Council for Scienti¯c and Technological Develop-
ment (CNPq, Brazil) for the DTI level scholarship,
the Ministry of Science and Technology for their
support in the Public Call CNPq/ MCTIC/
SEMPI No. 01/2020, \Developments and Tech-
nological Solutions in the Area of Graphene",
and also thank the Brazilian Institute of Sciences
and Innovations — IBCI — and the National
Council of Science and Technology of Mexico —
CONACYT — for the support of laboratory
facilities.
ORCID
Diogo Jos!e Horst https://orcid.org/0000-0003-
4971-4912
Rog!erio de Almeida
Vieira
https://orcid.org/0000-0002-
4950-6198
Charles Adriano https://orcid.org/0000-0002-
8598-2597
Jesús Alejandro
Arizpe Duvoisin
https://orcid.org/0000-0002-
3959-4876
Esther Alejandra
Huitrón Segovia
https://orcid.org/0000-0003-
2830-0462
Alejandra García-
García
https://orcid.org/0000-0001-
7794-135X
References
1. Z. Bojarska, M. Mazurkiewicz-Pawlicka, S. Gier-
lotka and L. Makowski, Nanomaterials 10, 1865
(2020), doi: 10.3390/nano10091865.
2. H. J. Lee et al.,Mater. Chem. Front. 5, 3396 (2021),
doi.org/10.1039/D1QM00051A.
3. R. Kumar et al., IEEE Trans. Electron Dev. 65,
3943 (2018), doi: 10.1109/TED.2018.2851955.
4. N. A. Kumar et al., Mater. Today 18, 286 (2015),
doi: 10.1016/j.mattod.2015.01.016.
5. Y. He et al., Nat. Commun. 11, 57 (2020), doi:
10.1038/s41467-019-13631-.
6. X. Fan et al., ACS Appl. Mater. Interfaces 12,
34049 (2020), doi: 10.1021/acsami.0c06910.
7. B. E. Rodríguez, M. Armendariz-Ontíveros, R.
Quezada, E. A. Huitrón-Segovia, H. Estay and A.
García-García, Polymers 12, 2860 (2020), doi:
10.3390/polym12122860.
8. R. Rubio-Govea, D. P. Hickey, R. García-Morales,
M. Rodriguez-Delgado, M. A. Domínguez-Rovira,
S. D. Minteer, N. Ornelas-Soto and A. García-
García, Microchem. J. 155, 104792 (2020), doi:
10.1016/j.microc.2020.104792.
9. Y. Shi, M. Osada, Y. Ebina and T. Sasaki, ACS
Nano 14, 15216 (2020), doi: 10.1021/acsna-
no.0c05434.
10. C. Thomsen and S. Reich, Phys. Rev. Lett. 85, 5214
(2000), doi: 10.1103/PhysRevLett.85.5214.
Synthesis of 2D Heterostructures
2150050-7
January 3, 2022 5:40:58pm WSPC/175-IJN 2150050
2nd Reading
11. K. K. Singh et al., ACS Omega 4, 14569 (2019), doi:
10.1021/acsomega.9b01799.
12. M. Wang et al., Chem. Cat. Chem., 11, 1789
(2019), doi: 10.1002/cctc.201900156.
13. J. Sitek et al., ACS Appl. Mater. Interfaces 12,
45101 (2020).
14. Y. Ma et al., Nanoscale 3, 3883 (2011), doi:
10.1039/C1NR10577A.
15. R. H. Miwa and W. L. Scopel, J. Phys. Condens.
Matter 25, 445301 (2013).
16. S. Barua, H. S. Dutta, S. Gogoi, R. Devi and R.
Khan, ACS Appl. Nano Mater. 1, 2 (2018), doi:
10.1021/acsanm.7b00157.
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	Bookmarks
	Synthesis of 2D Heterostructures: MOS2/GO and MOS2/Graphene via Microdrop and CVD Deposition
	1. Introduction
	2. Materials and Methods
	2.1. Graphene Oxide (GO) reduction and MoS2 synthesis
	2.2. Microdrop casting
	2.3. Chemical vapor deposition — CVD
	2.4. Characterization
	3. Results and Discussion
	3.1. Raman spectroscopy
	3.2. X-ray energy dispersive spectroscopy — EDS
	3.3. Scanning electron microscopy — SEM
	3.4. Kelvin probe field microscopy — KPFM
	4. Conclusion
	Acknowledgments
	ORCID
	References