I. Denysenko - Academia.edu (original) (raw)
Papers by I. Denysenko
Physical Review E, 2011
Transparency of a two-layer plasma structure in an external steady-state magnetic field, perpendi... more Transparency of a two-layer plasma structure in an external steady-state magnetic field, perpendicular to the wave incidence plane, is studied. The case of the p-polarized electromagnetic wave is considered. The electromagnetic wave is obliquely incident on the two-layer structure and is evanescent in both layers. The conditions for total transparency of the two-layer structure are found. The parametric dependencies of the transparency coefficient on the plasma slab widths, the magnitude of the wave number component, as well on the magnetic field magnitude are obtained.
Physical Review E, 2006
The response of complex ionized gas systems to the presence of nonuniform distribution of charged... more The response of complex ionized gas systems to the presence of nonuniform distribution of charged grains is investigated using a kinetic model. Contrary to an existing view that the electron temperature inevitably increases in the grain-occupied region because of enhanced ionization to compensate for the electrons lost to the grains, it is shown that this happens only when the ionizing electric field increases in the electron depleted region. The results for two typical plasma systems suggest that when the ionizing electric field depends on the spatially averaged electron density, the electron temperature in the grain containing region can actually decrease.
Physical Review E, 2005
The electric as well as the positive-and negative-ion drag forces on an isolated dust grain in an... more The electric as well as the positive-and negative-ion drag forces on an isolated dust grain in an electronegative plasma are studied for large negative-ion densities, when the negative ions are not Boltzmann distributed. The investigation is carried out for submicrometer dust particles, so that the theory of Coulomb scattering is applicable for describing ion-dust interaction. Among the forces acting on the dust grain, the negative-ion drag force is found to be important. The effects of the negative-ion density, neutral-gas pressure, and dust-grain size on the forces are also considered. It is shown that by increasing the density of the negative ions one can effectively manipulate the dust grains. Our results imply that both dust voids and balls can be formed.
A surface diffusion model for multi-wall carbon nanotube (MWCNT) growth in plasma-enhanced chemic... more A surface diffusion model for multi-wall carbon nanotube (MWCNT) growth in plasma-enhanced chemical vapor deposition (PECVD) is developed. It is assumed that growth is due to deposition of hydrocarbon (HC) molecules, ions and an etching gas (atomic hydrogen) from plasma. The model accounts for reactions of HC neutrals and carbon atoms with an etching gas, decomposition of absorbed particles due to ion bombardment, decomposition of HC ions on MWCNT surface, thermal decomposition of HC neutrals on MWCNT surface, in addition to the film growth between MWCNTs, etching of the film and carbon sputtering. Using the model, MWCNT growth rates are calculated for different substrate temperatures and HC, hydrogen and ion fluxes on the substrate. It is shown that at low substrate temperature the MWCNT growth is mainly due to reactions of ions with HC neutrals and the decomposition of HC ions on the MWCNT surface. Meanwhile, at large ion and low hydrogen fluxes on the substrate the film growth be...
Journal of Plasma Physics, 2005
The effect of density and size of dust grains on the electron energy distribution function (EEDF)... more The effect of density and size of dust grains on the electron energy distribution function (EEDF) in low-temperature complex plasmas is studied. It is found that the EEDF depends strongly on the dust density and size. The behavior of the electron temperature can differ significantly from that of a pristine plasma. For low-pressure argon glow discharge, the Druyvesteyn-like EEDF often found in pristine plasmas can become nearly Maxwellian if the dust density and/or sizes are large. One can thus control the plasma parameters by the dust grains.
Journal of Applied Physics, 2002
This article presents the results on the diagnostics and numerical modeling of low-frequency ͑ϳ46... more This article presents the results on the diagnostics and numerical modeling of low-frequency ͑ϳ460 KHz͒ inductively coupled plasmas generated in a cylindrical metal chamber by an external flat spiral coil. Experimental data on the electron number densities and temperatures, electron energy distribution functions, and optical emission intensities of the abundant plasma species in low/ intermediate pressure argon discharges are included. The spatial profiles of the plasma density, electron temperature, and excited argon species are computed, for different rf powers and working gas pressures, using the two-dimensional fluid approach. The model allows one to achieve a reasonable agreement between the computed and experimental data. The effect of the neutral gas temperature on the plasma parameters is also investigated. It is shown that neutral gas heating ͑at rf powersу0.55 kW) is one of the key factors that control the electron number density and temperature. The dependence of the average rf power loss, per electron-ion pair created, on the working gas pressure shows that the electron heat flux to the walls appears to be a critical factor in the total power loss in the discharge.
Journal of Applied Physics, 2008
A theoretical model to describe the plasma-assisted growth of carbon nanofibers ͑CNFs͒ is propose... more A theoretical model to describe the plasma-assisted growth of carbon nanofibers ͑CNFs͒ is proposed. Using the model, the plasma-related effects on the nanofiber growth parameters, such as the growth rate due to surface and bulk diffusion, the effective carbon flux to the catalyst surface, the characteristic residence time and diffusion length of carbon atoms on the catalyst surface, and the surface coverages, have been studied. The dependence of these parameters on the catalyst surface temperature and ion and etching gas fluxes to the catalyst surface is quantified. The optimum conditions under which a low-temperature plasma environment can benefit the CNF growth are formulated. These results are in good agreement with the available experimental data on CNF growth and can be used for optimizing synthesis of related nanoassemblies in low-temperature plasma-assisted nanofabrication.
Contributions to Plasma Physics, 2005
Different aspects of the plasma-enhanced chemical vapor deposition of various carbon nanostructur... more Different aspects of the plasma-enhanced chemical vapor deposition of various carbon nanostructures in the ionized gas phase of high-density, low-temperature reactive plasmas of Ar+H2+CH4 gas mixtures are studied. The growth techniques, surface morphologies, densities and fluxes of major reactive species in the discharge, and effects of the transport of the plasma-grown nanoparticles through the near-substrate plasma sheath are examined. Possible growth precursors of the carbon nanostructures are also discussed. In particular, the experimental and numerical results indicate that it is likely that the aligned carbon nanotip structures are predominantly grown by the molecular and radical units, whereas the plasma-grown nanoparticles are crucial components of polymorphous carbon films.
Computational Materials Science, 2004
ABSTRACT
Physics of Plasmas, 2004
A complex low-pressure argon discharge plasma containing dust grains is studied using a Boltzmann... more A complex low-pressure argon discharge plasma containing dust grains is studied using a Boltzmann equation for the electrons and fluid equations for the ions. Local effects, such as the spatial distribution of the dust density and external electric field, are included, and their effect on the electron energy distribution, the electron and ion number densities, the electron temperature, and the dust charge are investigated. It is found that dust particles can strongly affect the plasma parameters by modifying the electron energy distribution, the electron temperature, the creation and loss of plasma particles, as well as the spatial distributions of the electrons and ions. In particular, for sufficiently high grain density and/or size, in a low-pressure argon glow discharge, the Druyvesteyn-like electron distribution in pristine plasmas can become nearly Maxwellian. Electron collection by the dust grains is the main cause for the change in the electron distribution function.
AIP Conference Proceedings, 2003
The results on the diagnostics and numerical modeling of low-frequency (∼460 KHz) inductively cou... more The results on the diagnostics and numerical modeling of low-frequency (∼460 KHz) inductively coupled plasmas generated in a cylindrical metal chamber by an external flat spiral coil are presented. Experimental data on the electron number densities and temperatures, and optical emission intensities of the abundant plasma species in low/intermediate pressure argon discharges are included. The spatial profiles of the plasma density, electron temperature, and excited argon species are computed, for different RF powers and working gas pressures, using the 2D fluid approach. The model allows one to achieve a reasonable agreement between the computed and experimental data. The effect of the neutral gas temperature on the plasma parameters is also investigated. It is shown that neutral gas heating at higher (> 1 kW ) RF powers is among the key factors that control the electron number density and temperature. The dependence of the average RF power loss, per electron-ion pair created, on the working gas pressure shows that the electron heat flux to the walls appears to be a critical factor in the total power loss in the discharge.
2008 IEEE 35th International Conference on Plasma Science, 2008
Summary form only given. We present a theoretical model describing a plasma-assisted growth of ca... more Summary form only given. We present a theoretical model describing a plasma-assisted growth of carbon nanofibers (CNFs), which involves two competing channels of carbon incorporation into stacked graphene sheets: via the surface diffusion and through the bulk of the catalyst particle (on top of a nanofiber) and accounts for a range of ion- and radical-assisted processes on the catalyst surface. Using this model, it is found that at low surface temperatures Ts, the CNF growth is indeed controlled by the surface diffusion. On the other hand, both the surface and bulk diffusion channels provide a comparable supply of carbon atoms to the stacked graphene sheets at elevated synthesis temperatures. It is also shown that at low Ts, insufficient for effective catalytic precursor decomposition, the plasma ions play a key role in production of carbon atoms on the catalyst surface. More importantly, these results quantify and explain a number of observations and semi- empirical conclusions of earlier experiments.
Journal of Physics D: Applied Physics, 2008
ABSTRACT A theoretical model describing the plasma-assisted growth of carbon nanofibres (CNFs) th... more ABSTRACT A theoretical model describing the plasma-assisted growth of carbon nanofibres (CNFs) that accounts for the nanostructure heating by ion and etching gas fluxes from the plasma is developed. Using the model, it is shown that fluxes from the plasma environment can substantially increase the temperature of the catalyst nanoparticle located on the top of the CNF with respect to the substrate temperature. The difference between the catalyst and the substrate temperatures depends on the substrate width, the length of the CNF, the neutral gas density and temperature as well as the densities of the ions and atoms of the etching gas. In addition to the heating of the nanostructure, the ions and etching gas atoms from the ionized gas environment also strongly affect the CNF growth rates. Due to ion bombardment, the CNF growth rates in plasma enhanced chemical vapour deposition may be much higher than the rates in similar neutral gas-based thermal processes. The CNF growth model, which accounts for the nanostructure heating by the plasma-generated species, provides the growth rates that are in better agreement with the available experimental data on CNF growth than the models in which the heating effects are ignored.
Applied Physics Letters, 2007
... of the CNF growth rate due to surface diffusion appears to be the same as that of the constan... more ... of the CNF growth rate due to surface diffusion appears to be the same as that of the constant of carbon incorporation into graphene sheets. ... At low , the loss of C on the catalyst surface in aplasma-based process is mainly due to etching gas deposition on the catalyst. ...
We study propagation of a p-polarized electromagnetic wave through a two-layer plasma structure i... more We study propagation of a p-polarized electromagnetic wave through a two-layer plasma structure in an external magnetic field perpendicular to the incidence plane. It is shown that normally opaque plasma layer can be made absolutely transparent. The conditions for resonant transmission are obtained and analyzed. The influence of the external magnetic field on resonant transmission is studied. We show that one can control electromagnetic radiation transmitted through the plasma structure by altering the magnetic field.
Physical Review E, 2004
A global, or averaged, model for complex low-pressure argon discharge plasmas containing dust gra... more A global, or averaged, model for complex low-pressure argon discharge plasmas containing dust grains is presented. The model consists of particle and power balance equations taking into account power loss on the dust grains and the discharge wall. The electron energy distribution is determined by a Boltzmann equation. The effects of the dust and the external conditions, such as the input power and neutral gas pressure, on the electron energy distribution, the electron temperature, the electron and ion number densities, and the dust charge are investigated. It is found that the dust subsystem can strongly affect the stationary state of the discharge by dynamically modifying the electron energy distribution, the electron temperature, the creation and loss of the plasma particles, as well as the power deposition. In particular, the power loss to the dust grains can take up a significant portion of the input power, often even exceeding the loss to the wall.
Physics of Plasmas, 2009
The charge of an isolated dust grain and ion drag forces on the grain in a collisionless, high-vo... more The charge of an isolated dust grain and ion drag forces on the grain in a collisionless, high-voltage, capacitive rf sheath are studied theoretically. The studies are carried out assuming that the positive ions are monoenergetic, as well as in more realistic approximation, assuming that the time-averaged energy distribution of ions impinging on the dust grain has a double-peaked hollow profile. For the nonmonoenergetic case, an analytical expression for the ion flux to the dust grain is obtained. It is studied how the dust charge and ion drag forces depend on the rf frequency, electron density at plasma-sheath boundary, electron temperature and ratio of the effective oscillation amplitude of rf current to the electron Debye length. It is shown that the dust charge and ion drag forces obtained in the monoenergetic ion approximation may differ from those calculated assuming that the ions are nonmonoenergetic. The difference increases with increasing the width of the ion energy spread in the ion distribution.
Applied Physics Letters, 2007
Growth kinetics of carbon nanofibers in a hydrocarbon plasma is studied. In addition to gas-phase... more Growth kinetics of carbon nanofibers in a hydrocarbon plasma is studied. In addition to gas-phase and surface processes common to chemical vapor deposition, the model includes ͑unique to plasma-exposed catalyst surfaces͒ ion-induced dissociation of hydrocarbons, interaction of adsorbed species with incoming hydrogen atoms, and dissociation of hydrocarbon ions. It is shown that at low, nanodevice-friendly process temperatures the nanofibers grow via surface diffusion of carbon adatoms produced on the catalyst particle via ion-induced dissociation of a hydrocarbon precursor. These results explain a lower activation energy of nanofiber growth in a plasma and can be used for the synthesis of other nanoassemblies.
Physical Review E, 2011
Transparency of a two-layer plasma structure in an external steady-state magnetic field, perpendi... more Transparency of a two-layer plasma structure in an external steady-state magnetic field, perpendicular to the wave incidence plane, is studied. The case of the p-polarized electromagnetic wave is considered. The electromagnetic wave is obliquely incident on the two-layer structure and is evanescent in both layers. The conditions for total transparency of the two-layer structure are found. The parametric dependencies of the transparency coefficient on the plasma slab widths, the magnitude of the wave number component, as well on the magnetic field magnitude are obtained.
Physical Review E, 2006
The response of complex ionized gas systems to the presence of nonuniform distribution of charged... more The response of complex ionized gas systems to the presence of nonuniform distribution of charged grains is investigated using a kinetic model. Contrary to an existing view that the electron temperature inevitably increases in the grain-occupied region because of enhanced ionization to compensate for the electrons lost to the grains, it is shown that this happens only when the ionizing electric field increases in the electron depleted region. The results for two typical plasma systems suggest that when the ionizing electric field depends on the spatially averaged electron density, the electron temperature in the grain containing region can actually decrease.
Physical Review E, 2005
The electric as well as the positive-and negative-ion drag forces on an isolated dust grain in an... more The electric as well as the positive-and negative-ion drag forces on an isolated dust grain in an electronegative plasma are studied for large negative-ion densities, when the negative ions are not Boltzmann distributed. The investigation is carried out for submicrometer dust particles, so that the theory of Coulomb scattering is applicable for describing ion-dust interaction. Among the forces acting on the dust grain, the negative-ion drag force is found to be important. The effects of the negative-ion density, neutral-gas pressure, and dust-grain size on the forces are also considered. It is shown that by increasing the density of the negative ions one can effectively manipulate the dust grains. Our results imply that both dust voids and balls can be formed.
A surface diffusion model for multi-wall carbon nanotube (MWCNT) growth in plasma-enhanced chemic... more A surface diffusion model for multi-wall carbon nanotube (MWCNT) growth in plasma-enhanced chemical vapor deposition (PECVD) is developed. It is assumed that growth is due to deposition of hydrocarbon (HC) molecules, ions and an etching gas (atomic hydrogen) from plasma. The model accounts for reactions of HC neutrals and carbon atoms with an etching gas, decomposition of absorbed particles due to ion bombardment, decomposition of HC ions on MWCNT surface, thermal decomposition of HC neutrals on MWCNT surface, in addition to the film growth between MWCNTs, etching of the film and carbon sputtering. Using the model, MWCNT growth rates are calculated for different substrate temperatures and HC, hydrogen and ion fluxes on the substrate. It is shown that at low substrate temperature the MWCNT growth is mainly due to reactions of ions with HC neutrals and the decomposition of HC ions on the MWCNT surface. Meanwhile, at large ion and low hydrogen fluxes on the substrate the film growth be...
Journal of Plasma Physics, 2005
The effect of density and size of dust grains on the electron energy distribution function (EEDF)... more The effect of density and size of dust grains on the electron energy distribution function (EEDF) in low-temperature complex plasmas is studied. It is found that the EEDF depends strongly on the dust density and size. The behavior of the electron temperature can differ significantly from that of a pristine plasma. For low-pressure argon glow discharge, the Druyvesteyn-like EEDF often found in pristine plasmas can become nearly Maxwellian if the dust density and/or sizes are large. One can thus control the plasma parameters by the dust grains.
Journal of Applied Physics, 2002
This article presents the results on the diagnostics and numerical modeling of low-frequency ͑ϳ46... more This article presents the results on the diagnostics and numerical modeling of low-frequency ͑ϳ460 KHz͒ inductively coupled plasmas generated in a cylindrical metal chamber by an external flat spiral coil. Experimental data on the electron number densities and temperatures, electron energy distribution functions, and optical emission intensities of the abundant plasma species in low/ intermediate pressure argon discharges are included. The spatial profiles of the plasma density, electron temperature, and excited argon species are computed, for different rf powers and working gas pressures, using the two-dimensional fluid approach. The model allows one to achieve a reasonable agreement between the computed and experimental data. The effect of the neutral gas temperature on the plasma parameters is also investigated. It is shown that neutral gas heating ͑at rf powersу0.55 kW) is one of the key factors that control the electron number density and temperature. The dependence of the average rf power loss, per electron-ion pair created, on the working gas pressure shows that the electron heat flux to the walls appears to be a critical factor in the total power loss in the discharge.
Journal of Applied Physics, 2008
A theoretical model to describe the plasma-assisted growth of carbon nanofibers ͑CNFs͒ is propose... more A theoretical model to describe the plasma-assisted growth of carbon nanofibers ͑CNFs͒ is proposed. Using the model, the plasma-related effects on the nanofiber growth parameters, such as the growth rate due to surface and bulk diffusion, the effective carbon flux to the catalyst surface, the characteristic residence time and diffusion length of carbon atoms on the catalyst surface, and the surface coverages, have been studied. The dependence of these parameters on the catalyst surface temperature and ion and etching gas fluxes to the catalyst surface is quantified. The optimum conditions under which a low-temperature plasma environment can benefit the CNF growth are formulated. These results are in good agreement with the available experimental data on CNF growth and can be used for optimizing synthesis of related nanoassemblies in low-temperature plasma-assisted nanofabrication.
Contributions to Plasma Physics, 2005
Different aspects of the plasma-enhanced chemical vapor deposition of various carbon nanostructur... more Different aspects of the plasma-enhanced chemical vapor deposition of various carbon nanostructures in the ionized gas phase of high-density, low-temperature reactive plasmas of Ar+H2+CH4 gas mixtures are studied. The growth techniques, surface morphologies, densities and fluxes of major reactive species in the discharge, and effects of the transport of the plasma-grown nanoparticles through the near-substrate plasma sheath are examined. Possible growth precursors of the carbon nanostructures are also discussed. In particular, the experimental and numerical results indicate that it is likely that the aligned carbon nanotip structures are predominantly grown by the molecular and radical units, whereas the plasma-grown nanoparticles are crucial components of polymorphous carbon films.
Computational Materials Science, 2004
ABSTRACT
Physics of Plasmas, 2004
A complex low-pressure argon discharge plasma containing dust grains is studied using a Boltzmann... more A complex low-pressure argon discharge plasma containing dust grains is studied using a Boltzmann equation for the electrons and fluid equations for the ions. Local effects, such as the spatial distribution of the dust density and external electric field, are included, and their effect on the electron energy distribution, the electron and ion number densities, the electron temperature, and the dust charge are investigated. It is found that dust particles can strongly affect the plasma parameters by modifying the electron energy distribution, the electron temperature, the creation and loss of plasma particles, as well as the spatial distributions of the electrons and ions. In particular, for sufficiently high grain density and/or size, in a low-pressure argon glow discharge, the Druyvesteyn-like electron distribution in pristine plasmas can become nearly Maxwellian. Electron collection by the dust grains is the main cause for the change in the electron distribution function.
AIP Conference Proceedings, 2003
The results on the diagnostics and numerical modeling of low-frequency (∼460 KHz) inductively cou... more The results on the diagnostics and numerical modeling of low-frequency (∼460 KHz) inductively coupled plasmas generated in a cylindrical metal chamber by an external flat spiral coil are presented. Experimental data on the electron number densities and temperatures, and optical emission intensities of the abundant plasma species in low/intermediate pressure argon discharges are included. The spatial profiles of the plasma density, electron temperature, and excited argon species are computed, for different RF powers and working gas pressures, using the 2D fluid approach. The model allows one to achieve a reasonable agreement between the computed and experimental data. The effect of the neutral gas temperature on the plasma parameters is also investigated. It is shown that neutral gas heating at higher (> 1 kW ) RF powers is among the key factors that control the electron number density and temperature. The dependence of the average RF power loss, per electron-ion pair created, on the working gas pressure shows that the electron heat flux to the walls appears to be a critical factor in the total power loss in the discharge.
2008 IEEE 35th International Conference on Plasma Science, 2008
Summary form only given. We present a theoretical model describing a plasma-assisted growth of ca... more Summary form only given. We present a theoretical model describing a plasma-assisted growth of carbon nanofibers (CNFs), which involves two competing channels of carbon incorporation into stacked graphene sheets: via the surface diffusion and through the bulk of the catalyst particle (on top of a nanofiber) and accounts for a range of ion- and radical-assisted processes on the catalyst surface. Using this model, it is found that at low surface temperatures Ts, the CNF growth is indeed controlled by the surface diffusion. On the other hand, both the surface and bulk diffusion channels provide a comparable supply of carbon atoms to the stacked graphene sheets at elevated synthesis temperatures. It is also shown that at low Ts, insufficient for effective catalytic precursor decomposition, the plasma ions play a key role in production of carbon atoms on the catalyst surface. More importantly, these results quantify and explain a number of observations and semi- empirical conclusions of earlier experiments.
Journal of Physics D: Applied Physics, 2008
ABSTRACT A theoretical model describing the plasma-assisted growth of carbon nanofibres (CNFs) th... more ABSTRACT A theoretical model describing the plasma-assisted growth of carbon nanofibres (CNFs) that accounts for the nanostructure heating by ion and etching gas fluxes from the plasma is developed. Using the model, it is shown that fluxes from the plasma environment can substantially increase the temperature of the catalyst nanoparticle located on the top of the CNF with respect to the substrate temperature. The difference between the catalyst and the substrate temperatures depends on the substrate width, the length of the CNF, the neutral gas density and temperature as well as the densities of the ions and atoms of the etching gas. In addition to the heating of the nanostructure, the ions and etching gas atoms from the ionized gas environment also strongly affect the CNF growth rates. Due to ion bombardment, the CNF growth rates in plasma enhanced chemical vapour deposition may be much higher than the rates in similar neutral gas-based thermal processes. The CNF growth model, which accounts for the nanostructure heating by the plasma-generated species, provides the growth rates that are in better agreement with the available experimental data on CNF growth than the models in which the heating effects are ignored.
Applied Physics Letters, 2007
... of the CNF growth rate due to surface diffusion appears to be the same as that of the constan... more ... of the CNF growth rate due to surface diffusion appears to be the same as that of the constant of carbon incorporation into graphene sheets. ... At low , the loss of C on the catalyst surface in aplasma-based process is mainly due to etching gas deposition on the catalyst. ...
We study propagation of a p-polarized electromagnetic wave through a two-layer plasma structure i... more We study propagation of a p-polarized electromagnetic wave through a two-layer plasma structure in an external magnetic field perpendicular to the incidence plane. It is shown that normally opaque plasma layer can be made absolutely transparent. The conditions for resonant transmission are obtained and analyzed. The influence of the external magnetic field on resonant transmission is studied. We show that one can control electromagnetic radiation transmitted through the plasma structure by altering the magnetic field.
Physical Review E, 2004
A global, or averaged, model for complex low-pressure argon discharge plasmas containing dust gra... more A global, or averaged, model for complex low-pressure argon discharge plasmas containing dust grains is presented. The model consists of particle and power balance equations taking into account power loss on the dust grains and the discharge wall. The electron energy distribution is determined by a Boltzmann equation. The effects of the dust and the external conditions, such as the input power and neutral gas pressure, on the electron energy distribution, the electron temperature, the electron and ion number densities, and the dust charge are investigated. It is found that the dust subsystem can strongly affect the stationary state of the discharge by dynamically modifying the electron energy distribution, the electron temperature, the creation and loss of the plasma particles, as well as the power deposition. In particular, the power loss to the dust grains can take up a significant portion of the input power, often even exceeding the loss to the wall.
Physics of Plasmas, 2009
The charge of an isolated dust grain and ion drag forces on the grain in a collisionless, high-vo... more The charge of an isolated dust grain and ion drag forces on the grain in a collisionless, high-voltage, capacitive rf sheath are studied theoretically. The studies are carried out assuming that the positive ions are monoenergetic, as well as in more realistic approximation, assuming that the time-averaged energy distribution of ions impinging on the dust grain has a double-peaked hollow profile. For the nonmonoenergetic case, an analytical expression for the ion flux to the dust grain is obtained. It is studied how the dust charge and ion drag forces depend on the rf frequency, electron density at plasma-sheath boundary, electron temperature and ratio of the effective oscillation amplitude of rf current to the electron Debye length. It is shown that the dust charge and ion drag forces obtained in the monoenergetic ion approximation may differ from those calculated assuming that the ions are nonmonoenergetic. The difference increases with increasing the width of the ion energy spread in the ion distribution.
Applied Physics Letters, 2007
Growth kinetics of carbon nanofibers in a hydrocarbon plasma is studied. In addition to gas-phase... more Growth kinetics of carbon nanofibers in a hydrocarbon plasma is studied. In addition to gas-phase and surface processes common to chemical vapor deposition, the model includes ͑unique to plasma-exposed catalyst surfaces͒ ion-induced dissociation of hydrocarbons, interaction of adsorbed species with incoming hydrogen atoms, and dissociation of hydrocarbon ions. It is shown that at low, nanodevice-friendly process temperatures the nanofibers grow via surface diffusion of carbon adatoms produced on the catalyst particle via ion-induced dissociation of a hydrocarbon precursor. These results explain a lower activation energy of nanofiber growth in a plasma and can be used for the synthesis of other nanoassemblies.