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Corona discharge plasma application for the deposition of nanocomposite coatings
Materials Today: Proceedings xxx (xxxx) xxx
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Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Corona discharge plasma application for the deposition of nanocomposite coatings Kirill Tyurikov a,⇑, Sergey Alexandrov a, Gleb Iankevich b a b
Peter the Great St. Petersburg Polytechnic University, Polytechnicheskaya, 29, St., Petersburg 195251, Russia Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, Eggenstein-Leopoldshafen, 76344, Germany
a r t i c l e
i n f o
Article history: Received 18 December 2019 Accepted 30 December 2019 Available online xxxx Keywords: Corona discharge Nanocomposite coatings Silicon dioxide Molybdenum disulfide Chemical vapor deposition
a b s t r a c t Corona discharge in helium plasma was used to perform deposition process of nanocomposite coating in ‘‘molybdenum disulfide – silicon dioxide” system. 2 kV amplitude and 28 kHz frequency discharge was applied to tetraethoxysilane vapors for them to decompose and form silicon dioxide layers. Negative 2 kV bias was used to route negatively charged in plasma nanoparticles to the deposition region. Plasma absorbed power effect in the range of 50–90 W was studied. Ó 2020 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the Materials Science: Composites, Alloys and Materials Chemistry.
1. Introduction Nanocomposite materials are multiphase solid materials in which one of the phases is nanosized, i.e., has size less than 100 nm, at least in one dimension. Nanocomposites exhibit unique properties due to the nanoscale effects compared to conventional composite materials even with a low filler content and therefore development of their technologies has been an important direction of research in materials science for the last two decades [1–5]. Methods of the formation of nanocomposite coatings are of particular interest, since in many practically important cases it is necessary to ensure only special properties of the surface of the products, which itself can be made of cheaper material [6]. Obviously, the processes of deposition, carried out at atmospheric pressure and allowing to apply the coating at relatively low temperatures, are the most attractive both because there is no need to use an expensive vacuum equipment and it is possible to generate layers on thermally unstable materials. Among the various methods of applying nanocomposite coatings at atmospheric pressure, chemical vapor deposition (CVD) with various activation methods is one of the technologies that allows to form not only high-quality layers, but also to synthesize various types of nanomaterials such as nanopowders [7], nanotubes [8], nanofibers [9], nanorods [10], capable of acting as fillers ⇑ Corresponding author. E-mail address: [email protected] (K. Tyurikov).
for nanocomposite materials [11], and even directly nanocomposites. The undoubted advantage of the CVD method is its universal nature. First, it allows to obtain a wide variety of nanocomposite materials in which the composition of the nanosized fillers and matrix material are determined only by the choice of required reagents. This makes it possible to obtain new nanocomposite materials with a unique set of properties that cannot be synthesized by other known methods. Secondly, the potentially widespread use of this method in various fields of technology is associated with the possibility of forming coatings of nanocomposite materials on objects of complex shape. However, the chemical deposition of nanocomposite materials from the gas phase is characterized by a complex multistage mechanism, including the processes of homogeneous synthesis of nanoparticles, transport of nanoparticles by a gas stream, their incorporation into the deposited matrix, and heterogeneous formation of the composite matrix. These processes are insufficiently studied, and therefore the identification of their physicochemical laws is an urgent problem in the fields of chemical technology and materials science [12–15]. To date, various methods have been developed for the formation of nanocomposite materials by chemical vapor deposition, including various methods for initiating a chemical reaction — thermal, plasma, photoactivation [16–18]. Typical temperatures for the implementation of thermally activated processes range from 500 °C and above [19], plasma activation of the reagents allows to lower the deposition temperature to 200–500 °C [20].
https://doi.org/10.1016/j.matpr.2019.12.385 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the Materials Science: Composites, Alloys and Materials Chemistry.
Please cite this article as: K. Tyurikov, S. Alexandrov and G. Iankevich, Corona discharge plasma application for the deposition of nanocomposite coatings, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.385
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K. Tyurikov et al. / Materials Today: Proceedings xxx (xxxx) xxx
In addition to the traditional methods of supplying the reagent in the form of vapors, there are also known methods of forming nanocomposites using, for example, aerosols, which has both its drawbacks and advantages. This paper describes some features of the use of corona discharge plasma for the formation of wear-resistant nanocomposite coatings at atmospheric pressure. The composites were prepared based on silicon dioxide used as the material of the nanocomposite matrix and molybdenum disulfide, which acts as a filler of the composite material. 2. Methods The nanocomposite material was formed in a vertical quartz reactor, which provides of a two-stage CVD process for the deposition of nanocomposite coatings in the MoS2 (filler) - SiO2 (matrix) system. The schematics of the reactor is shown on Fig. 1. The reactor consisted of two main parts: the upper zone, intended for the synthesis of molybdenum disulfide nanoparticles, and the lower zone, used for plasma-chemical deposition of nanocomposite coatings at atmospheric pressure by maintaining a low-frequency corona discharge (27 kHz). MoS2 nanoparticles were synthesized in a gas stream by pyrolysis of aerosol particles of a solution of (NH4)2MoS4 in dimethylformamide, and then transported by a gas stream to the deposition zone, where the substrates were placed on a grounded steel substrate holder, and into which vapors of tetraethoxysilane (TEOS) reagent were introduced for the deposition of silicon dioxide. The upper zone of the reactor was a quartz tube equipped with two resistive heaters arranged in series. The first heater, designed to evaporate the solvent from aerosol particles, was heated to temperatures of 150– 750 ± 10 °C. A second heater used for heating ammonium thiomolybdate pyrolysis zone to 800 ± 10 °C. An aerosol of a solution of ammonium thiomolybdate in dimethylformamide, created by a piezoelectric atomizer operating at a frequency of 2.4 MHz,
Fig. 1. Schematic diagram of the reaction chamber used for atmospheric pressure PECVD on nanocomposite coatings. 1 – piezoelectric nebulizer, 2 – quartz reactor, 3 – heaters, 4 – high voltage electrode, 5 – substrate plate.
was transported to the reactor using a carrier gas (high-purity helium) with a flow rate of about 0.3 l*min 1. The concentration of the ammonium thiomolybdate solution was in the range of 0.0025–0.01 mol*l 1. The lower part of the reactor was used for plasma-chemical deposition of nanocomposite coatings by codeposition of MoS2 particles coming from the upper part of the reactor and a layer of silicon dioxide formed from tetraethoxysilane vapor on the substrate surface. Tungsten high-voltage electrode was placed at a distance of 25–30 mm above the grounded substrate holder, heated to 300 °C. A corona discharge at atmospheric pressure was created in this zone using an AC (27 kHz) voltage source with an amplitude of about 1.8–2.2 kV. Typical discharge power values were 40–90 W. Tetraethoxysilane vapors were fed into the reactor from a thermostabilized (70 °C) quartz evaporator, the design of which provided a constant level of evaporated liquid. A helium carrier gas saturated with TEOS vapor was introduced into the upper part of the deposition zone approximately 30 mm downstream of the first zone through an injection nozzle. The total helium flow rate through the evaporator was varied within the range of 0–1 l*min 1. In the same range, the flow rate of helium-diluent was varied so that the total flow rate was 1 l*min 1. 3. Results and discussion The use of plasma chemical technologies allows chemical deposition processes to be carried out at lower temperatures in comparison with more traditional thermal deposition processes, however, it has some characteristic features, which are described below. Because the distance to the electrode increases radially from the center of the substrate to its edges, the films deposited in the experiments were inhomogeneous in thickness. The maximum film thickness in all experiments was observed in the center of the substrate, at the point where the tip of the electrode was located closest to the substrate, and decreased to the edges of the substrate with increasing distance to the electrode. Fig. 2 shows an example of the dependence of the film thickness on the distance to the center of the substrate. The film was obtained at room temperature, the power absorbed by the discharge, 90 W and the flow rates of the carrier gas of TEOS and diluent gas of 0.3 and 0.3 l*min 1. It was found that the film thickness is inversely proportional to the distance to the electrode and decreases from the center of the substrate to its edges.
Fig. 2. Dependence of the film thickness on the distance to the center of the substrate.
Please cite this article as: K. Tyurikov, S. Alexandrov and G. Iankevich, Corona discharge plasma application for the deposition of nanocomposite coatings, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.385
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The dimensions of the area with maximum thickness were about 2.5 to 3 mm in diameter. The film thickness in all experiments was measured in the center of the substrate by the ellipsometric method. The quality of the films and their deposition rate should be significantly affected by the electric power absorbed by the discharge. For precipitation at atmospheric pressure, transporting active particles from the region of discharge formation to the deposition zone will be more difficult than for traditional processes of plasma chemical deposition in a remote low-pressure plasma, due to the short mean free path and, as a consequence, the short life time of active particles. Therefore, it can be expected that the electric power absorbed in the discharge will strongly affect the growth rate and properties of the film due to the influence of this power on the concentration and energy of excited particles. To verify this, a series of experiments was carried out to study the effect of power in the range of 50–90 W on the growth rate of the deposited films, the results of which are visible in Fig. 3. With increase in power increases the concentration of active particles in the plasma, therefore, increasing the speed of dissociation of the molecules of TEOS, and, hence, and the speed of growth of the film dioxide silicon. The increase in power led to an almost linear increase in the growth rate, which reflects a corresponding increase in the number of collisions of particles in a corona discharge plasma, such as electrons, radicals, excited helium atoms, and, consequently, an increase in the concentration of reactive particles, such as excited silicon-containing radicals, oxygen atoms in the region above the substrate. As can be seen from Fig. 4, an increase in the power absorbed by the discharge leads to a steady decrease in the normalized peak intensity, which reflects the content of CH3 groups included in the growing films due to incomplete rearrangement of chemical bonds in TEOS during surface chemical reactions. The increase in power also leads to an increase in the energy density and concentration of excited particles on the surface of the substrate and, therefore, provides more favorable conditions for the complete occurrence of chemical reactions of the formation of silicon oxide films. An increase in power leads to the formation of a larger number of excited oxygen-containing particles, and this can also affect the properties of the deposited films, including the refractive index. The refractive index of amorphous stoichiometric silicon oxide films is about 1.46. In Fig. 6, lower values of the refractive index
Fig. 3. Dependence of the film growth rate on the power absorbed by the discharge.
Fig. 4. The dependence of the normalized peak intensity of 970 cm electrical power absorbed by the discharge.
1
on the
Fig. 5. Dependence of pore density and normalized absorption band intensity in the IR transmission spectra of SiO2 films with a maximum at 970 cm 1 on the absorbed power.
for films obtained at a power of less than 80–90 W indicate a low density of the deposited films, due to the lack of active particles and energy delivered from the region of discharge generation to the reagent particles in the gas phase and to the substrate surface. An increase in the electric power of the discharge leads to an increase in the energy density and fluxes of excited particles directed to the surface, thereby providing more favorable conditions for the complete course of chemical reactions involved in the formation of the film. This, in turn, allows one to obtain denser and closer to stoichiometric silicon oxide films Fig. 5 and Fig. 6. At higher discharge powers, the refractive index is close to that of amorphous stoichiometric SiO2. The results of preliminary experiments on the formation of composite coatings showed that MoS2 nanoparticles did not deposit on substrates located in the heated deposition zone, but deposited on the inner walls of the reactor despite the fact that the wall temperature was higher because an external substrate heater was used. Most likely, thermophoresis in the conditions under study did not play a significant role, and the particles, acquiring a predominantly negative charge in the corona discharge
Please cite this article as: K. Tyurikov, S. Alexandrov and G. Iankevich, Corona discharge plasma application for the deposition of nanocomposite coatings, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.385
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K. Tyurikov et al. / Materials Today: Proceedings xxx (xxxx) xxx
References
Fig. 6. Dependence of pore density and refractive index on the power absorbed by the discharge.
field (a characteristic phenomenon for low-temperature nonequilibrium plasma), moved along the electric field in the direction of the nearest grounded electrode, which was the spiral of the heater surrounding the region the reactor in which the substrate holder was placed. To prevent this effect during further work, the substrate heater was mounted directly in the substrate holder, which made it possible to collect the deposited particles on the substrate with a constant temperature. In addition, a negative high DC voltage (up to 6 kV) was applied to the high voltage electrode through an LC filter to use it as an electrostatic filter. Using a filter allowed the collection of particles on the surface of silicon substrates. 4. Conclusions Thus, the use of corona discharge plasma for the formation of composite composite coatings was successfully demonstrated. An AC corona discharge is used to initiate the decomposition of tetraethoxysilane and the production of silicon dioxide. The application of a constant voltage to the electrode generating the discharge makes it possible to change the potential and use electric field of the discharge as an electrostatic filter for trapping particles and direct them onto the substrate together with the vapors of silicon dioxide, which leads to the formation of a dense, nonporous layer of the nanocomposite coating. Declaration of Competing Interest
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The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Please cite this article as: K. Tyurikov, S. Alexandrov and G. Iankevich, Corona discharge plasma application for the deposition of nanocomposite coatings, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.385
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Corona discharge plasma application for the deposition of nanocomposite coatings Kirill Tyurikov a,⇑, Sergey Alexandrov a, Gleb Iankevich b a b
Peter the Great St. Petersburg Polytechnic University, Polytechnicheskaya, 29, St., Petersburg 195251, Russia Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, Eggenstein-Leopoldshafen, 76344, Germany
a r t i c l e
i n f o
Article history: Received 18 December 2019 Accepted 30 December 2019 Available online xxxx Keywords: Corona discharge Nanocomposite coatings Silicon dioxide Molybdenum disulfide Chemical vapor deposition
a b s t r a c t Corona discharge in helium plasma was used to perform deposition process of nanocomposite coating in ‘‘molybdenum disulfide – silicon dioxide” system. 2 kV amplitude and 28 kHz frequency discharge was applied to tetraethoxysilane vapors for them to decompose and form silicon dioxide layers. Negative 2 kV bias was used to route negatively charged in plasma nanoparticles to the deposition region. Plasma absorbed power effect in the range of 50–90 W was studied. Ó 2020 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the Materials Science: Composites, Alloys and Materials Chemistry.
1. Introduction Nanocomposite materials are multiphase solid materials in which one of the phases is nanosized, i.e., has size less than 100 nm, at least in one dimension. Nanocomposites exhibit unique properties due to the nanoscale effects compared to conventional composite materials even with a low filler content and therefore development of their technologies has been an important direction of research in materials science for the last two decades [1–5]. Methods of the formation of nanocomposite coatings are of particular interest, since in many practically important cases it is necessary to ensure only special properties of the surface of the products, which itself can be made of cheaper material [6]. Obviously, the processes of deposition, carried out at atmospheric pressure and allowing to apply the coating at relatively low temperatures, are the most attractive both because there is no need to use an expensive vacuum equipment and it is possible to generate layers on thermally unstable materials. Among the various methods of applying nanocomposite coatings at atmospheric pressure, chemical vapor deposition (CVD) with various activation methods is one of the technologies that allows to form not only high-quality layers, but also to synthesize various types of nanomaterials such as nanopowders [7], nanotubes [8], nanofibers [9], nanorods [10], capable of acting as fillers ⇑ Corresponding author. E-mail address: [email protected] (K. Tyurikov).
for nanocomposite materials [11], and even directly nanocomposites. The undoubted advantage of the CVD method is its universal nature. First, it allows to obtain a wide variety of nanocomposite materials in which the composition of the nanosized fillers and matrix material are determined only by the choice of required reagents. This makes it possible to obtain new nanocomposite materials with a unique set of properties that cannot be synthesized by other known methods. Secondly, the potentially widespread use of this method in various fields of technology is associated with the possibility of forming coatings of nanocomposite materials on objects of complex shape. However, the chemical deposition of nanocomposite materials from the gas phase is characterized by a complex multistage mechanism, including the processes of homogeneous synthesis of nanoparticles, transport of nanoparticles by a gas stream, their incorporation into the deposited matrix, and heterogeneous formation of the composite matrix. These processes are insufficiently studied, and therefore the identification of their physicochemical laws is an urgent problem in the fields of chemical technology and materials science [12–15]. To date, various methods have been developed for the formation of nanocomposite materials by chemical vapor deposition, including various methods for initiating a chemical reaction — thermal, plasma, photoactivation [16–18]. Typical temperatures for the implementation of thermally activated processes range from 500 °C and above [19], plasma activation of the reagents allows to lower the deposition temperature to 200–500 °C [20].
https://doi.org/10.1016/j.matpr.2019.12.385 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the Materials Science: Composites, Alloys and Materials Chemistry.
Please cite this article as: K. Tyurikov, S. Alexandrov and G. Iankevich, Corona discharge plasma application for the deposition of nanocomposite coatings, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.385
2
K. Tyurikov et al. / Materials Today: Proceedings xxx (xxxx) xxx
In addition to the traditional methods of supplying the reagent in the form of vapors, there are also known methods of forming nanocomposites using, for example, aerosols, which has both its drawbacks and advantages. This paper describes some features of the use of corona discharge plasma for the formation of wear-resistant nanocomposite coatings at atmospheric pressure. The composites were prepared based on silicon dioxide used as the material of the nanocomposite matrix and molybdenum disulfide, which acts as a filler of the composite material. 2. Methods The nanocomposite material was formed in a vertical quartz reactor, which provides of a two-stage CVD process for the deposition of nanocomposite coatings in the MoS2 (filler) - SiO2 (matrix) system. The schematics of the reactor is shown on Fig. 1. The reactor consisted of two main parts: the upper zone, intended for the synthesis of molybdenum disulfide nanoparticles, and the lower zone, used for plasma-chemical deposition of nanocomposite coatings at atmospheric pressure by maintaining a low-frequency corona discharge (27 kHz). MoS2 nanoparticles were synthesized in a gas stream by pyrolysis of aerosol particles of a solution of (NH4)2MoS4 in dimethylformamide, and then transported by a gas stream to the deposition zone, where the substrates were placed on a grounded steel substrate holder, and into which vapors of tetraethoxysilane (TEOS) reagent were introduced for the deposition of silicon dioxide. The upper zone of the reactor was a quartz tube equipped with two resistive heaters arranged in series. The first heater, designed to evaporate the solvent from aerosol particles, was heated to temperatures of 150– 750 ± 10 °C. A second heater used for heating ammonium thiomolybdate pyrolysis zone to 800 ± 10 °C. An aerosol of a solution of ammonium thiomolybdate in dimethylformamide, created by a piezoelectric atomizer operating at a frequency of 2.4 MHz,
Fig. 1. Schematic diagram of the reaction chamber used for atmospheric pressure PECVD on nanocomposite coatings. 1 – piezoelectric nebulizer, 2 – quartz reactor, 3 – heaters, 4 – high voltage electrode, 5 – substrate plate.
was transported to the reactor using a carrier gas (high-purity helium) with a flow rate of about 0.3 l*min 1. The concentration of the ammonium thiomolybdate solution was in the range of 0.0025–0.01 mol*l 1. The lower part of the reactor was used for plasma-chemical deposition of nanocomposite coatings by codeposition of MoS2 particles coming from the upper part of the reactor and a layer of silicon dioxide formed from tetraethoxysilane vapor on the substrate surface. Tungsten high-voltage electrode was placed at a distance of 25–30 mm above the grounded substrate holder, heated to 300 °C. A corona discharge at atmospheric pressure was created in this zone using an AC (27 kHz) voltage source with an amplitude of about 1.8–2.2 kV. Typical discharge power values were 40–90 W. Tetraethoxysilane vapors were fed into the reactor from a thermostabilized (70 °C) quartz evaporator, the design of which provided a constant level of evaporated liquid. A helium carrier gas saturated with TEOS vapor was introduced into the upper part of the deposition zone approximately 30 mm downstream of the first zone through an injection nozzle. The total helium flow rate through the evaporator was varied within the range of 0–1 l*min 1. In the same range, the flow rate of helium-diluent was varied so that the total flow rate was 1 l*min 1. 3. Results and discussion The use of plasma chemical technologies allows chemical deposition processes to be carried out at lower temperatures in comparison with more traditional thermal deposition processes, however, it has some characteristic features, which are described below. Because the distance to the electrode increases radially from the center of the substrate to its edges, the films deposited in the experiments were inhomogeneous in thickness. The maximum film thickness in all experiments was observed in the center of the substrate, at the point where the tip of the electrode was located closest to the substrate, and decreased to the edges of the substrate with increasing distance to the electrode. Fig. 2 shows an example of the dependence of the film thickness on the distance to the center of the substrate. The film was obtained at room temperature, the power absorbed by the discharge, 90 W and the flow rates of the carrier gas of TEOS and diluent gas of 0.3 and 0.3 l*min 1. It was found that the film thickness is inversely proportional to the distance to the electrode and decreases from the center of the substrate to its edges.
Fig. 2. Dependence of the film thickness on the distance to the center of the substrate.
Please cite this article as: K. Tyurikov, S. Alexandrov and G. Iankevich, Corona discharge plasma application for the deposition of nanocomposite coatings, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.385
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K. Tyurikov et al. / Materials Today: Proceedings xxx (xxxx) xxx
The dimensions of the area with maximum thickness were about 2.5 to 3 mm in diameter. The film thickness in all experiments was measured in the center of the substrate by the ellipsometric method. The quality of the films and their deposition rate should be significantly affected by the electric power absorbed by the discharge. For precipitation at atmospheric pressure, transporting active particles from the region of discharge formation to the deposition zone will be more difficult than for traditional processes of plasma chemical deposition in a remote low-pressure plasma, due to the short mean free path and, as a consequence, the short life time of active particles. Therefore, it can be expected that the electric power absorbed in the discharge will strongly affect the growth rate and properties of the film due to the influence of this power on the concentration and energy of excited particles. To verify this, a series of experiments was carried out to study the effect of power in the range of 50–90 W on the growth rate of the deposited films, the results of which are visible in Fig. 3. With increase in power increases the concentration of active particles in the plasma, therefore, increasing the speed of dissociation of the molecules of TEOS, and, hence, and the speed of growth of the film dioxide silicon. The increase in power led to an almost linear increase in the growth rate, which reflects a corresponding increase in the number of collisions of particles in a corona discharge plasma, such as electrons, radicals, excited helium atoms, and, consequently, an increase in the concentration of reactive particles, such as excited silicon-containing radicals, oxygen atoms in the region above the substrate. As can be seen from Fig. 4, an increase in the power absorbed by the discharge leads to a steady decrease in the normalized peak intensity, which reflects the content of CH3 groups included in the growing films due to incomplete rearrangement of chemical bonds in TEOS during surface chemical reactions. The increase in power also leads to an increase in the energy density and concentration of excited particles on the surface of the substrate and, therefore, provides more favorable conditions for the complete occurrence of chemical reactions of the formation of silicon oxide films. An increase in power leads to the formation of a larger number of excited oxygen-containing particles, and this can also affect the properties of the deposited films, including the refractive index. The refractive index of amorphous stoichiometric silicon oxide films is about 1.46. In Fig. 6, lower values of the refractive index
Fig. 3. Dependence of the film growth rate on the power absorbed by the discharge.
Fig. 4. The dependence of the normalized peak intensity of 970 cm electrical power absorbed by the discharge.
1
on the
Fig. 5. Dependence of pore density and normalized absorption band intensity in the IR transmission spectra of SiO2 films with a maximum at 970 cm 1 on the absorbed power.
for films obtained at a power of less than 80–90 W indicate a low density of the deposited films, due to the lack of active particles and energy delivered from the region of discharge generation to the reagent particles in the gas phase and to the substrate surface. An increase in the electric power of the discharge leads to an increase in the energy density and fluxes of excited particles directed to the surface, thereby providing more favorable conditions for the complete course of chemical reactions involved in the formation of the film. This, in turn, allows one to obtain denser and closer to stoichiometric silicon oxide films Fig. 5 and Fig. 6. At higher discharge powers, the refractive index is close to that of amorphous stoichiometric SiO2. The results of preliminary experiments on the formation of composite coatings showed that MoS2 nanoparticles did not deposit on substrates located in the heated deposition zone, but deposited on the inner walls of the reactor despite the fact that the wall temperature was higher because an external substrate heater was used. Most likely, thermophoresis in the conditions under study did not play a significant role, and the particles, acquiring a predominantly negative charge in the corona discharge
Please cite this article as: K. Tyurikov, S. Alexandrov and G. Iankevich, Corona discharge plasma application for the deposition of nanocomposite coatings, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.385
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References
Fig. 6. Dependence of pore density and refractive index on the power absorbed by the discharge.
field (a characteristic phenomenon for low-temperature nonequilibrium plasma), moved along the electric field in the direction of the nearest grounded electrode, which was the spiral of the heater surrounding the region the reactor in which the substrate holder was placed. To prevent this effect during further work, the substrate heater was mounted directly in the substrate holder, which made it possible to collect the deposited particles on the substrate with a constant temperature. In addition, a negative high DC voltage (up to 6 kV) was applied to the high voltage electrode through an LC filter to use it as an electrostatic filter. Using a filter allowed the collection of particles on the surface of silicon substrates. 4. Conclusions Thus, the use of corona discharge plasma for the formation of composite composite coatings was successfully demonstrated. An AC corona discharge is used to initiate the decomposition of tetraethoxysilane and the production of silicon dioxide. The application of a constant voltage to the electrode generating the discharge makes it possible to change the potential and use electric field of the discharge as an electrostatic filter for trapping particles and direct them onto the substrate together with the vapors of silicon dioxide, which leads to the formation of a dense, nonporous layer of the nanocomposite coating. Declaration of Competing Interest
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The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Please cite this article as: K. Tyurikov, S. Alexandrov and G. Iankevich, Corona discharge plasma application for the deposition of nanocomposite coatings, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.12.385