Direct synthesized graphene-like film on SiO₂: Mechanical and optical properties
Exploiting CVD technique for carbon deposition from C₂H₂+H₂+N₂ mixture, a graphene-like film synthesized directly on SiO₂ surface of SiO₂-Si structure was obtained. The graphene-like film was grown under thin Ni layer that is easy exfoliated from graphene-SiO₂-Si structure. Surface of the film was s...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2016
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| Cite this: | Direct synthesized graphene-like film on SiO₂: Mechanical and optical properties / E.G. Bortchagovsky, A.V. Vasin, P.M. Lytvyn, S.I. Tiagulskyi, A.M. Slobodian, I.N. Verovsky, V.V. Strelchuk, Yu. Stubrov, A.N. Nazarov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2016. — Т. 19, № 4. — С. 328-333. — Бібліогр.: 19 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-1216522025-02-23T17:28:35Z Direct synthesized graphene-like film on SiO₂: Mechanical and optical properties Bortchagovsky, E.G. Vasin, A.V. Lytvyn, P.M. Tiagulskyi, S.I. Slobodian, A.M. Verovsky, I.N. Strelchuk, V.V. Stubrov, Yu. Nazarov, A.N. Exploiting CVD technique for carbon deposition from C₂H₂+H₂+N₂ mixture, a graphene-like film synthesized directly on SiO₂ surface of SiO₂-Si structure was obtained. The graphene-like film was grown under thin Ni layer that is easy exfoliated from graphene-SiO₂-Si structure. Surface of the film was sufficiently smooth and reveals no winkles and holes; it has a good homogeneity and perfect adhesion to SiO₂ layer. Studying the micro-Raman spectra showed a graphene-like structure of the film; using atomic force microscopic technique, the thickness of film was determined (0.6 nm). Using spectroscopic ellipsometry and simple Cauchy model enabled us to estimate optical parameters of this graphene-like film. This work has been partially supported by Ministry of Education and Science of Ukraine (Project F2904). 2016 Article Direct synthesized graphene-like film on SiO₂: Mechanical and optical properties / E.G. Bortchagovsky, A.V. Vasin, P.M. Lytvyn, S.I. Tiagulskyi, A.M. Slobodian, I.N. Verovsky, V.V. Strelchuk, Yu. Stubrov, A.N. Nazarov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2016. — Т. 19, № 4. — С. 328-333. — Бібліогр.: 19 назв. — англ. 1560-8034 DOI: 10.15407/spqeo19.04.328 PACS 68.65.Pq, 78.67.Wj https://nasplib.isofts.kiev.ua/handle/123456789/121652 en Semiconductor Physics Quantum Electronics & Optoelectronics application/pdf Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Exploiting CVD technique for carbon deposition from C₂H₂+H₂+N₂ mixture, a graphene-like film synthesized directly on SiO₂ surface of SiO₂-Si structure was obtained. The graphene-like film was grown under thin Ni layer that is easy exfoliated from graphene-SiO₂-Si structure. Surface of the film was sufficiently smooth and reveals no winkles and holes; it has a good homogeneity and perfect adhesion to SiO₂ layer. Studying the micro-Raman spectra showed a graphene-like structure of the film; using atomic force microscopic technique, the thickness of film was determined (0.6 nm). Using spectroscopic ellipsometry and simple Cauchy model enabled us to estimate optical parameters of this graphene-like film. |
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| author |
Bortchagovsky, E.G. Vasin, A.V. Lytvyn, P.M. Tiagulskyi, S.I. Slobodian, A.M. Verovsky, I.N. Strelchuk, V.V. Stubrov, Yu. Nazarov, A.N. |
| spellingShingle |
Bortchagovsky, E.G. Vasin, A.V. Lytvyn, P.M. Tiagulskyi, S.I. Slobodian, A.M. Verovsky, I.N. Strelchuk, V.V. Stubrov, Yu. Nazarov, A.N. Direct synthesized graphene-like film on SiO₂: Mechanical and optical properties Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Bortchagovsky, E.G. Vasin, A.V. Lytvyn, P.M. Tiagulskyi, S.I. Slobodian, A.M. Verovsky, I.N. Strelchuk, V.V. Stubrov, Yu. Nazarov, A.N. |
| author_sort |
Bortchagovsky, E.G. |
| title |
Direct synthesized graphene-like film on SiO₂: Mechanical and optical properties |
| title_short |
Direct synthesized graphene-like film on SiO₂: Mechanical and optical properties |
| title_full |
Direct synthesized graphene-like film on SiO₂: Mechanical and optical properties |
| title_fullStr |
Direct synthesized graphene-like film on SiO₂: Mechanical and optical properties |
| title_full_unstemmed |
Direct synthesized graphene-like film on SiO₂: Mechanical and optical properties |
| title_sort |
direct synthesized graphene-like film on sio₂: mechanical and optical properties |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2016 |
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https://nasplib.isofts.kiev.ua/handle/123456789/121652 |
| citation_txt |
Direct synthesized graphene-like film on SiO₂: Mechanical and optical properties / E.G. Bortchagovsky, A.V. Vasin, P.M. Lytvyn, S.I. Tiagulskyi, A.M. Slobodian, I.N. Verovsky, V.V. Strelchuk, Yu. Stubrov, A.N. Nazarov // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2016. — Т. 19, № 4. — С. 328-333. — Бібліогр.: 19 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
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2025-11-24T02:25:30Z |
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| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 328-333.
doi: https://doi.org/10.15407/spqeo19.04.328
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
328
PACS 68.65.Pq, 78.67.Wj
Direct synthesized graphene-like film on SiO2:
Mechanical and optical properties
E.G. Bortchagovsky1, A.V. Vasin1,2, P.M. Lytvyn1, S.I. Tiagulskyi1, A.M. Slobodian2,
I.N. Verovsky1, V.V. Strelchuk1, Yu. Stubrov1 and A.N. Nazarov*,1,2
1V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kyiv, Ukraine
2National Technical University of Ukraine “KPI”,
Department of General Physics and Solid State Physics, Kyiv, Ukraine
*Corresponding author: phone/fax :+38 (044) 525 61 77; e-mail: nazarov@lab15.kiev.ua
Abstract. Exploiting CVD technique for carbon deposition from C2H2+H2+N2 mixture, a
graphene-like film synthesized directly on SiO2 surface of SiO2-Si structure was
obtained. The graphene-like film was grown under thin Ni layer that is easy exfoliated
from graphene-SiO2-Si structure. Surface of the film was sufficiently smooth and reveals
no winkles and holes; it has a good homogeneity and perfect adhesion to SiO2 layer.
Studying the micro-Raman spectra showed a graphene-like structure of the film; using
atomic force microscopic technique, the thickness of film was determined (0.6 nm).
Using spectroscopic ellipsometry and simple Cauchy model enabled us to estimate
optical parameters of this graphene-like film.
Keywords: directly grown graphene on SiO2, chemical vapor deposition, micro-Raman,
AFM, spectroscopic ellipsometry.
Manuscript received 26.05.16; revised version received 30.08.16; accepted for
publication 16.11.16; published online 05.12.16.
1. Introduction
Graphene film on dielectric structure is a basis to form Si
compatible nanoelectronic devices. Nowadays, the main
method to create a qualitative graphene film on a
dielectric substrate is low-pressure CVD on Cu foil with
following transferring the graphene film onto the
dielectric substrate [1]. However, this method has several
steps, which leads to pollution of the film by organic
inclusions. The synthesis of graphene film directly on
different dielectric layers opens wide possibilities for
employment of this very promising material in silicon
nano- and optoelectronics. In recent years, several
methods for graphene synthesis directly on dielectric
substrates were proposed: high-temperature CVD
synthesis of graphene on dielectric surface via the
sacrificial copper film [2]; high-temperature CVD
synthesis on dielectric surface under the Ni film which
was preliminary high-temperature annealed in He ambient
[3]; direct CVD synthesis of nanocrystalline graphene
flakes on dielectric [4]; CVD graphene film growth on
dielectric surface using remote catalyzation, which
includes employing floating Cu and H atoms for
decomposition of the hydrocarbons [5]. The very
attractive approach is direct synthesis of graphene film on
dielectric under the Ni layer, since this method allows us
to avoid the lithographic process on graphene film and
replace them by a simple lithographic process on nickel.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 328-333.
doi: https://doi.org/10.15407/spqeo19.04.328
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
329
In this paper, we have presented the results on
synthesis of uniform graphene film under the Ni layer on
SiO2/Si structure, without special additional annealing,
which has morphological, electrical and optical properties
suitable for fabrication of photoelectrical devices.
2. Experimental samples
and measurement techniques
The structure of Ni-SiO2-Si with the Ni thickness close
to 110 nm and the SiO2 thickness 420 nm was located in
CVD reactor with hot walls. Heating the structure in
flow of H2(57%) + N2(43%) gas was performed at
760 °C, and maintaining the temperature for 10 min
C2H2 was introduced into the reactor. After that, the
structure was cooled in nitrogen atmosphere during
5 min to 550 °C. The Ni films was covered by “moss”
from carbon whiskers, and the Ni film with carbon
whiskers was easily laminated from SiO2-Si structure
exposing the surface with dense carbon film (Fig. 1).
The surface morphology of the synthesized films
was studied using optical microscopy (Axioscop 2 MAT,
Carl Zeiss); surface topography and viscoelastic
homogeneity of the films were investigated by
Dimension 3000 NanoScope IIIa scanning probe
microscope operating in the AFM tapping mode [6]. The
tapping mode provides substantial reduction of contact
force, improves resolution and could be used for
estimation of surface homogeneity by simultaneous
mapping of height and phase images (difference between
phase angle of tip oscillation excitation signal and AFM
tip response [7]). Chemical composition and local
structure of the films were analyzed using micro-Raman
spectroscopy (mRS, triple Raman spectrometer T-64000
Horiba Jobin-Yvon, equipped with electrically cooled
CCD detector and excitation by the 514-nm line of an
Ar-Kr ion laser). The resistivity of the films was
measured using the four-probes methods with Agilent
4156C Semiconductor Analyzer. Optical constants of the
deposited films were determined by spectroscopic
ellipsometer M-2000 with rotating compensator from
J.A. Woollam Co., Inc. in the wavelength range from
200 up to 1600 nm.
3. Results and discussion
3.1. Raman spectroscopy measurements
Raman spectra in the range of Raman shifts from 1250
to 2800 cm–1 measured for the studied samples are
presented in Fig. 2. The clearly pronounced G band
(~1600 cm–1) that indicates hexagonal graphene lattice
formation [8] and appearance of 2D band (~2700 cm–1)
that originates from the two-phonon double resonance
Raman process [9], are Raman signatures of sp2
graphitic materials [8]. The large D band (~1335 cm–1)
indicates the high defect densities within the as-
synthesized thin films. So, we can name this film as
graphene-like (GrL) material.
Fig. 1. Schematic description of the process, indicating the
graphene-like film growth below Ni film under CVD
conditions, and then removal of Ni by using the adhesive tape.
Fig. 2. Raman spectra measured in different points of the
carbon film. Inset: light microscopy micrograph of the
graphene-like film.
3.2. Atomic force microscopy
Surface of the film was sufficiently smooth, and optical
microscopy reveals no winkles and holes (inset in Fig. 2)
with the value of root mean square (RMS) surface
roughness close to 0.3 nm, which was obtained from
AFM measurements (Fig. 3). AFM reveals a nano-
granular fine structure of film. The mean value of grain
diameter equals 10 nm with the standard deviation 2 nm
(note, this value over estimated due to the tip effect and
could be smaller). The sharp and clear edge of film
makes it possible to measure film thickness and estimate
elasticity relatively to the underneath SiO2 layer (lower-
right corner of AFM image). Two maxima in the height
map histogram (Fig. 3c) indicate the averaged film
thickness value about 0.6 nm and phase shift histogram
(Fig. 3d) maxima from softer film and stiffer substrate
indicate difference 1.5°. This phase shift is constant over
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 328-333.
doi: https://doi.org/10.15407/spqeo19.04.328
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
330
Fig. 3. Topography (a) and phase contrast (b) AFM images of the graphene-like film edge on SiO2. Corresponding histograms of
height and phase shift shown in (c) and (d).
a large area of AFM scans (not shown here), which
testifies good homogeneity of film. AFM scratch test of
film confirms perfect adhesion and plastic nature of film
deformation under AFM tip.
Resistivity of the graphene-like film determined
using the four-probes method [10] was in the range from
200 to 350 kOhm/sq. For control measurements, we used
single layer CVD graphene on SiO2 layer (385 nm
thickness) fabricated by Graphene Supermarket Co [11]
that showed the value of resistivity about 470 Ohm/sq.,
which was comparable with that of our measurements
obtained on these films by using the transmission line
technique [12].
3.3. Spectroscopic ellipsometry
Optical constants of the deposited film were determined
using reduction of ellipsometric data to the model of a
silicon substrate covered with the silicon oxide film and
the deposited film with the thickness of 0.6 nm
determined from AFM measurements. The bare part of
the substrate was measured separately, and the thickness
of silicon oxide was determined from these
measurements equaled to 415.7 nm. The results of
spectroscopic measuring the ellipsometric parameters for
SiO2-Si and GrL-SiO2-Si structures are presented in
Fig. 4. The presence of graphene-like film on the surface
of SiO2 layer noticeably changes the ellipsometric
spectra of the structure shifting and changing the
contrast of the interference structure created by silicon
oxide (Fig. 4c, d).
Fixing the thickness of the GrL film to the result of
AFM (0.6 nm) allows to determine optical constants of
the film independently for each spectral point.
Unfortunately, such a direct determination of optical
constants independently for each spectral point gave no
appropriate results and could not be interpreted as any
regular dependence for solid material. It may be
explained by strong nonlinear dependence of
ellipsometric data on optical parameters of the system,
so the reverse problem has multiple solutions. Also, it is
produced by the standard problem of the optics of thin
films, namely: measurements of only the so-called
“phase” thickness instead of separate thickness and
optical constants as well as strong correlation of
ellipsometric data for these films [13]. So, only smooth
dispersion models were applied for the data reduction.
Detailed analysis and comparison of different models
will be given in the forthcoming article. Here, we
restricted our discussion only by general results.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 328-333.
doi: https://doi.org/10.15407/spqeo19.04.328
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
331
Fig. 4. Variable angle spectroscopic ellipsometry of graphene-like film on SiO2-Si substrate: (a) Ψ and (b) Δ spectra for
different angles of incidence θ measured on a graphene-like film; (c) Ψ and (d) Δ spectra measured at θ = 45°, 50° and 55° for
the bare substrate and the substrate with a graphene-like layer.
The best fitting was obtained using the simple
Cauchy model describing the behavior of the refractive
index. The standardly used in WVASE software Cauchy
model also includes Urbach absorption, which in its
definition describes exponential tail of the absorption at
energies lower than the bandgap. Literal Urbach tail of
the absorption index exponentially decays with
wavelength, so the model has the constant β > 0, where β
is the fitted coefficient in the exponent describing the
dispersion. It is interesting to note that application of the
standard model gave dispersionless absorption of the
film. It can be understood if to remember that the
absorption of graphene monolayer approaches the value
πα for long wavelengths according to the model [14],
where α is the fine structure constant 1/137. It requires
increasing the absorption index in proportion to the
wavelength k ~ λ. This behavior contradicts with the
Urbach tail dependence and explains the dispersionless
behavior of fitted absorption obtained with this model.
However, if to lift the restriction β ≥ 0 allowing β to be
negative, it improves fitting. Optical constants obtained
with this simplest model for the isotropic layer are
shown in Fig. 5a.
In spite of weak sensitivity of ellipsometry to the
transverse anisotropy [15], introduction of such an
anisotropy into the model improved fitting. Results of
this fitting are practically insensitive to allowing the
existence of extraordinary absorption, which is rather
low. Existence of the transverse absorption may be
explained by ripples of graphene layers.
Approaching the constant limit in the absorption is
native behavior of the Drude model, where the
absorption index linearly rises with the wavelength.
Combination of the Drude model with the Lorentz line
was proposed for description of the optical parameters of
graphene [16]. The pure Drude model gave not so
satisfactory results in our case, but its accomplishing by
one Lorentz line remarkably improved the situation.
Again, introduction of transverse anisotropy improves
fitting, however, only if the Cauchy model is used for
the dispersion of the transverse optical constant. Like to
the previous case, the obtained transverse absorption is
rather negligible and practically does not affect the
quality of fitting. It explains why the use of similar
combination Drude+Lorentz for transverse constants
was not successful, because this combination has
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 328-333.
doi: https://doi.org/10.15407/spqeo19.04.328
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
332
intrinsic noticeable absorption. It is worth to note that
the obtained spectral position of the Lorentz line is about
4 eV, which is close to the value reported in [14].
However, in spite of more physical achievement of
approaching the constant value for absorption and
position of the Lorentz oscillator in this model,
discrepancy of the fitting and experimental data is a bit
larger in these cases than for the analogous Cauchy
models.
Fig. 5a presents the results of modeling the optical
constants k and n for our graphene-like film. The
obtained results show that n changes from 2.1 to 2.6, and
k is about 2.25 in the wavelength range from 400 up to
1000 nm. If to compare these values with those for
graphene, which lie usually within the regions from 2.5
to 2.8 for n and from 1.2 to 1.8 for k [14, 17], we can see
that in our case k is a bit higher than that of graphene
layer. Unfortunately, preparation of the GrL layer on
silicon substrate makes it impossible to directly measure
the transmission for confirming it, so only modeling the
absorption of our layer on the base of obtained
parameters is possible. It is necessary to note that the
result of measuring the phase thickness for thin films,
fixing the thickness at some reasonable value
(0.3…1 nm) gives corresponding scaling for obtained
optical constants. However, it does not practically
change calculated from these data transmission of this
free standing film with fixed thickness. For the case of
the Drude+Lorentz model, the transmission approaches
the value 0.97, what is a bit lower that πα ≈ 0.977 [14,
17]. The calculated spectra reproduce minimum in the
transmission in the region 4…4.5 eV reported earlier
[14, 17]. It is not surprising for the Drude+Lorentz
model, where additional Lorentz resonance is situated in
that spectral range, but this minimum is reproduced by
even Cauchy model with parameters shown in Fig. 5a. It
is explained by the fact that due to film boundaries
transmission of thin films is defined not by the
absorption index but the imaginary part of the dielectric
function divided by the wavelength [18, 19], which in
our case demonstrates necessary minimum. It is easy to
show that after account of the interference in the layer
with boundaries the transmittance of a thin freely
suspended film is described by the expression
λ
π−≈
dknT 412 , where n is the refraction index of the
material (real), i.e., is described by the imaginary part of
the dielectric function ε″ = 2nk [18, 19]. It is this
dependence that creates the minimum in transmittance
for smooth behavior of both refraction and absorption
indices shown in Fig. 5b. Modeled for absorption of a
slab with the thickness 0.335 nm of a continuous
material and ( 21 T− ) for free standing layer with
calculated optical constants is shown in Fig. 5b.
Reflectivity of such a film may be omitted as it is the
value of the second order of magnitude according of the
small parameter d/λ. Together with those curves, the
dependences k/λ and ε″/λ are shown by dash lines, too.
The discrepancy is explained by the use of exact
expressions for the absorption and transmission.
Thus, we can conclude that absorbance in our GrL
film is lower than in graphene in deep IR part.
4. Conclusions
Using a simple CVD technique and Ni-SiO2-Si structure,
the graphene-like film with thickness about 0.6 nm was
directly synthesized on SiO2 surface. The synthesized
film has a good surface morphology and homogeneity
but reinforced defectiveness, which results in increased
resistance, but light absorption is a bit lower than that in
the graphene single layer film. However, the films
fabricated using this simple technique can be useful for
photosensors operating in a wide range of wavelengths.
Acknowledgments
This work has been partially supported by Ministry of
Education and Science of Ukraine (Project F2904).
Fig. 5. Reconstructed optical constants (a) and absorption
(b) of the graphene-like film.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 328-333.
doi: https://doi.org/10.15407/spqeo19.04.328
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
333
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