Morphology and optical constants of nanographite films created by thermal vacuum deposition
The method for nanographite films preparation using thermal sublimation in vacuum of graphite nanoparticles under ultrasound treatment was proposed. Studied in the system nanographite film – substrate were composition and morphology of a multilayer interface system by using ellipsometry and Raman sc...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2015
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| Zitieren: | Morphology and optical constants of nanographite films created by thermal vacuum deposition / V.V. Kozachenko, O.S. Kondratenko, F.Le Normand // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2015. — Т. 18, № 1. — С. 106-109. — Бібліогр.: 12 назв. — англ. |
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irk-123456789-1207372017-06-13T03:03:04Z Morphology and optical constants of nanographite films created by thermal vacuum deposition Kozachenko, V.V. Kondratenko, O.S. Normand, F.Le The method for nanographite films preparation using thermal sublimation in vacuum of graphite nanoparticles under ultrasound treatment was proposed. Studied in the system nanographite film – substrate were composition and morphology of a multilayer interface system by using ellipsometry and Raman scattering. It has been ascertained that the optical parameters of discontinuous nanographite films strongly depend on morphology of the surface layer. Using the results of ellipsometric measurements, we determined the effective optical onstants, thickness of the films and calculated the volume composition of the solid phase in the film within the framework of the model of effective environment by Bruggeman 2015 Article Morphology and optical constants of nanographite films created by thermal vacuum deposition / V.V. Kozachenko, O.S. Kondratenko, F.Le Normand // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2015. — Т. 18, № 1. — С. 106-109. — Бібліогр.: 12 назв. — англ. 1560-8034 DOI: 10.15407/spqeo18.01.106 PACS 78.30.Ly, 78.67.Rb, 78.67.Wj http://dspace.nbuv.gov.ua/handle/123456789/120737 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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The method for nanographite films preparation using thermal sublimation in vacuum of graphite nanoparticles under ultrasound treatment was proposed. Studied in the system nanographite film – substrate were composition and morphology of a multilayer interface system by using ellipsometry and Raman scattering. It has been ascertained that the optical parameters of discontinuous nanographite films strongly depend on morphology of the surface layer. Using the results of ellipsometric measurements, we determined the effective optical onstants, thickness of the films and calculated the volume composition of the solid phase in the film within the framework of the model of effective environment by Bruggeman |
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Kozachenko, V.V. Kondratenko, O.S. Normand, F.Le |
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Kozachenko, V.V. Kondratenko, O.S. Normand, F.Le Morphology and optical constants of nanographite films created by thermal vacuum deposition Semiconductor Physics Quantum Electronics & Optoelectronics |
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Kozachenko, V.V. Kondratenko, O.S. Normand, F.Le |
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Kozachenko, V.V. |
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Morphology and optical constants of nanographite films created by thermal vacuum deposition |
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Morphology and optical constants of nanographite films created by thermal vacuum deposition |
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Morphology and optical constants of nanographite films created by thermal vacuum deposition |
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Morphology and optical constants of nanographite films created by thermal vacuum deposition |
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Morphology and optical constants of nanographite films created by thermal vacuum deposition |
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morphology and optical constants of nanographite films created by thermal vacuum deposition |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2015 |
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Morphology and optical constants of nanographite films created by thermal vacuum deposition / V.V. Kozachenko, O.S. Kondratenko, F.Le Normand // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2015. — Т. 18, № 1. — С. 106-109. — Бібліогр.: 12 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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AT kozachenkovv morphologyandopticalconstantsofnanographitefilmscreatedbythermalvacuumdeposition AT kondratenkoos morphologyandopticalconstantsofnanographitefilmscreatedbythermalvacuumdeposition AT normandfle morphologyandopticalconstantsofnanographitefilmscreatedbythermalvacuumdeposition |
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2025-07-08T18:29:36Z |
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 1. P. 106-109.
doi: 10.15407/ spqeo18.01.106
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
106
PACS 78.30.Ly, 78.67.Rb, 78.67.Wj
Morphology and optical constants of nanographite films
created by thermal vacuum deposition
V.V. Kozachenko
1
, O.S. Kondratenko
2
, F.Le Normand
3
1
Taras Shevchenko Kyiv National University, Department of Physics
64, Volodymyrska str., 01601 Kyiv, Ukraine
2
V. Lashkaryov Institute of Semiconductors Physics, NAS of Ukraine,
45, prospect Nauky, 03028 Kyiv, Ukraine
3
Institut d’Electronique du Solide et des Systèmes (InESS),
23 rue du Loess, 67037 Strasbourg Cedex 2, France
Abstract. The method for nanographite films preparation using thermal sublimation in
vacuum of graphite nanoparticles under ultrasound treatment was proposed. Studied in
the system nanographite film – substrate were composition and morphology of a multi-
layer interface system by using ellipsometry and Raman scattering. It has been
ascertained that the optical parameters of discontinuous nanographite films strongly
depend on morphology of the surface layer. Using the results of ellipsometric
measurements, we determined the effective optical constants, thickness of the films and
calculated the volume composition of the solid phase in the film within the framework of
the model of effective environment by Bruggeman.
Keywords: nanographite films, ultrasound, optical constants, ellipsometry, Raman.
Manuscript received 15.10.14; revised version received 22.12.14; accepted for
publication 19.02.15; published online 26.02.15.
1. Introduction
Recently, attention of scientists was attracted by the
graphene – graphite monoatomic layer due to its
properties, namely: high transparency in a wide spectral
range, electric conductivity and durability
characteristics, which makes it a promising element in
electronics [1]. However, the lack of graphene band gap
leads to difficulties in creation of the field-effect
transistor. One solution of this problem is to create
graphene nanotape, where quantum size effects allow
getting the band gap of the required width [2]. Some
interest is also caused by another form of carbon –
graphite nanocrystals composed of a few to several tens
of parallel flat graphene layers [3]. Unlike other carbon
nanomaterials, nanographite can be prepared much
easier. Particularity of nanoscale materials is that their
properties are very dependent on their shape and size,
which creates a wide field for researches.
In this study, the new method for preparation of
nanographite films by using the thermal vacuum
deposition process was proposed. As demonstrated
experimentally [4], it is possible to realize nanographite
powder synthesis in various solvents under powerful
ultrasound (US) treatment. Researches of this
nanographite showed that the action of ultrasound
(frequency of 20.4 kHz, power density of 0.1…1 W/cm
3
)
for 5…10 min forces the graphite to transform to
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 1. P. 106-109.
doi: 10.15407/ spqeo18.01.106
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
107
nanographite particles with the lateral sizes
300…500 nm and thickness of 30 up to 50 graphene
layers. Optical methods are used to determine the
geometrical parameters of heterosystem and optical
constants of their components. Since the optical
parameters determine efficiency (sensitivity) of certain
devices, determination of these parameters and ways of
their modification is a problem that needs to be solved.
2. Experimental techniques
In our work, we prepared nanographite by dispersing
graphite powder (average particle size of 75 μm) in
acetone by entering ultrasound with the specific power
close to 2 W/cm
2
at the frequency 40 kHz. Graphite was
crushed in the ultrasonic bath for 10 hours. We used a
much longer time for exposing the graphite to US,
higher frequency and higher specific power of US. After
treatment and evaporation of the solvent, we obtained
superdispersed nanographite, powder substance was dark
grey. The size of graphite nanoparticles was tens of
nanometers.
Based on the presence of nanosized particles in
graphite powder obtained, it was suggested that they can
sublimate when heated. For sublimation of atoms and
whole clusters of matter, the method of thermal
deposition in vacuum was used. The temperature of
evaporator with nanographite powder was 1000 °C. It
was determined by the pyrometric temperature
measurement method for luminance of evaporator and
strength of the current passing through it. The pressure
in the vacuum chamber was about 10
–5
Torr, substrate
temperature during deposition remained equal to 20 °C.
As substrates, glass plates with the thickness of 500 μm
were used.
Optical properties of the samples were studied
using the ellipsometry methods and Raman scattering.
Ellipsometric measurements were carried out on a
monochromatic ellipsometer LEF-3M with working
wavelength λ = 632.8 nm and within the working range
of light incidence angles from 45 to 90 degrees.
Surface morphology of nanographite film was
studied using atomic force microscopy (AFM). In this
paper, for studying the surface of nanographite film, the
AFM of type NT-MDT NTEGRA Prima Scanning Probe
Microscope was used. Measurements were carried out in
air at room temperature using the silicon nitride tip on
the elastic console element with the stiffness ratio
0.01…0.6 N/m in the semi-contact mode.
3. Results and discussion
Thermogravimetric (TG) study of nanographite powder
shows high temperature stability of nanographite particles
in air up to the temperature 600 °C, above which active
carbon oxidation takes place. The minimum derivative of
the weight loss (the most intense carbon oxidation) is
observed at the temperature 750 °C (Fig. 1). For
temperatures higher than 850 °C, the residual weight was
smaller and limited to the error in weight not exceeding
0.25%, which indicates absence of impurities. Besides, in
the 200 °C temperature region, the derivative of the
weight loss reaches its peak, which is associated with
active evaporation of moisture, carbon monoxide and
carbon dioxide adsorbed onto the powder surface
developed. Their total concentration was about 5% (wt.).
To obtain nanographite film by thermal evaporation
of material in vacuum, we precipitated graphite
nanoparticles on glass substrates. Our assumption was
based on the fact that the temperature of the evaporator
is not enough [5] for sublimation of graphite single
atoms and, therefore, only integer quantity of
nanographite particles can be settled on a substrate. It is
obvious that, in nanographite powder obtained, there
were significantly large variations in particle size, and in
the process of thermal deposition onto a substrate, the
probability for the smallest particles to get on a substrate
was the highest one.
The resulting film was semitransparent, of
yellowish color. It may indicate to a change of optical
properties of nanocrystalline graphite as compared to the
bulk material.
One of the most effective optical methods of
researching the properties of the interface of two media
and thin-film heterostructures is ellipsometry, when two
quantitative characteristics (amplitude ratio Ψ and phase
difference Δ) of polarized light reflected from the
surface are examined simultaneously, which allows to
determine both the thickness and optical constants of
layers. This change in optical constants of layers serves
as the characteristic that contains information about
microstructure, composition of multicomponent layers
and porosity.
According to the ellipsometric measurements of the
polarization angles Ψ(φ) and Δ(φ), the optical constants
are determined: refraction index n, absorption coefficient
k and thickness d of nanographite film by solving the
inverse ellipsometric task using the method of
minimizing the quadratic objective function [6]. The
one-layer model was used to calculate the optical
0 200 400 600 800 1000
-100
-50
0
M
as
s
lo
st
(
%
)
T (
o
C)
5 %
-6
-4
-2
0
2
d
T
G (%
, m
in
)
0 200 400 600 800 1000
Fig. 1. TG results for nanographite powder.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 1. P. 106-109.
doi: 10.15407/ spqeo18.01.106
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
108
Fig. 2. AFM image of nanographite film.
parameters of the structure: effective composite layer of
nanographite film consisting of nanoparticles of graphite
and air on the semi-infinite substrate (glass). The
obtained optical constants of the effective nanographite
film are N = 1.69 – i0.69. Because of the different
structure and other defects, optical constants of
semitransparent films are different from those for bulk
materials. It turned out that the complex refractive index
of nanographite layer at the optical wavelength λ =
632.8 nm was less than the corresponding bulk material
parameter (for example, [7, 8]) due to porosity of the
composite layer of material.
Using optical parameters of the structure,
determined by the multi-angle ellipsometry method, the
fraction of solid phase f of nanographite layer was
determined. To reach it, the model of effective
(statistical) composite medium by Bruggeman was
applied [9]. Modeling the system within a two-
component model for effective film “nanoparticles of
graphite and air (cavity)” on the substrate surface
allowed us to define the parameters of the system. The
parameters obtained for graphite: dopt = 30.00 nm, fgraph=
46.2%, fair= 53.8%.
These optical studies are in good correlation with the
studies of surface morphology of nanographite film
through the atomic force microscope investigation
(AFM). The picture of the nanographite film surface
obtained from the AFM measurements is shown in Fig. 2.
Analysis of the results of these studies shows that
the graphite film in its structure is not solid but has an
island nature. Using this method for obtaining
nanographite film, grains of different sizes in height and
diameter are formed on the substrate. So, we can see
some large grains with the average height 80…100 nm,
but their concentration is lower as compared to the main
area of the sample. Basically, the film consists of grains,
the average diameter of which is within the range 80 nm;
the average height of individual nanoparticles reaches
approximately 25…30 nm.
1000 1200 1400 1600 1800
0
500
1000
1500
2000
2500
3000 G-line
In
te
n
si
ty
(
re
l.
u
n
.)
Raman shift (cm
-1
)
1
3
4
7
1
5
9
8
1
5
3
3
1
6
1
2
1
1
6
7
1
0
7
3
D-line
Fig. 3. Raman spectrum of nanographite film.
To ensure that our film is actually composed of
nanographite particles, the Raman scattering spectrum
was measured (Fig. 3). In the high-frequency region of
the spectrum, two typical bands of the Raman spectrum
of the first order, the so-called D- and G-bands (~1350
and ~1590 cm
–1
, respectively) are observed.
Decomposition of the Raman spectra of the first order
gave 6 peaks located at 1073, 1168, 1347 (D-line), 1533,
1598 (G-line) and 1612 cm
–1
(D'-line). From [10], we
know what can be responsible for these D-, G- and D'-
lines. G-band corresponds to
22gE vibration that is a
sign of ordered graphite. D- and D'-lines describe the
double resonance. Their appearance is related with the
presence of defects at the edges and inside the graphene
planes. The presence of this band indicates the
availability of particles in the nanographite film under
study [11]. The peak at 1168 cm
–1
can be attributed to
the local vibration mode at the boundary [12]. The peak
at 1530 cm
–1
reflects the presence of disorder in the
structure in the form of amorphous carbon, which exists
in the form of both intermediate defects outside the
plane of the aromatic rings of sp
3
bonds [11] and rings
with an odd number of carbon atoms.
Using the Raman spectrum, the average lateral size
of the nanocrystals contributing to the D-line can be
calculated. The average lateral size La is inversely
proportional to the relative intensities of the D-line to G-
line. The proportionality coefficient is an empirical value
[12], and for La the formula can be written as follows:
D
G
l
a
I
I
E
L
4
560
nm , (1)
where El is the laser energy used to excite transitions in
the Raman spectrum. If, instead of the energy, one uses
the respective laser wavelength, the formula (1) can be
written as
D
G
la
I
I
L 410104.2nm . (2)
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2015. V. 18, N 1. P. 106-109.
doi: 10.15407/ spqeo18.01.106
© 2015, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
109
In this case, the ratio of the intensities of the G- and
D-lines was IG /
ID = 1.13. Having substituted the laser
wavelength λl = 532 nm, we can estimate the average
lateral size of nanographite crystallites. It was equal
approximately to 40 nm, which correlates with the
results of atomic force microscopy.
4. Conclusions
Thus, we have proposed the method for creating films
with 2-D array graphite nanoparticles by thermal
sublimation of graphite particles with average lateral
size of 40 nm in vacuum 10
–5
Torr on the surface of
glass substrates, the graphite particles being preliminary
dispersed using ultrasound treatment. The Raman
scattering and AFM technique were used to show
morphology of films with graphite nanoparticles.
The ellipsometric measurements have proved that
optical parameters of discontinuous nanographite films
strongly depend on morphology of the surface layer.
Effective optical constants of the film change depending
on the modification type of surface. It has been shown
that using the results of ellipsometric measurements
makes it possible to calculate not only the optical
constants and thickness of the film but also to determine
the volume composition f of the solid phase in the film
within the framework of the model of effective medium
by Bruggeman.
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