Effect Of Plasma Parameters Research Articles

Characteristic of ion acoustic shock waves in a dissipative quantum pair plasma with dust particulates

The behavior of quantum dust ion-acoustic (QDIA) shocks in a plasma including inertialess quantum electrons and positrons, classical cold ions and stationary negative dust grains are studied, using a quantum hydrodynamic model (QHD). The effect of dissipation due to the viscosity of ions is taken into account. The propagation of small but finite amplitude QDIA shocks is governed by the Kortoweg-de Vries-Burgers (KdVB) equation. The existence regions of oscillatory and monotonic shocks will depend on the quantum diffraction parameter (H) and dust density (d) as well as dissipation parameter (η0). The effect of plasma parameters (d,H,η0), on these structures is investigated. Results indicate that the thickness and height of monotonic shocks; oscillation amplitude of the oscillatory shock wave and it’s wavelength effectively are affected by these parameters. Additionally, the possibility of propagation of both compressive and rarefactive shocks is investigated. It is found that depending on some critical value of dust density (dc), which is a function of H, compressive and rarefactive shock waves can’t propagate in model plasma. The present theory is applicable to analyze the formation of nonlinear structures at quantum scales in dense astrophysical objects.

Arbitrary amplitude solitary and shock waves in an unmagnetized quantum dusty electron-positron-ion plasma

The behavior of quantum dust ion acoustic soliton and shocks in a plasma including inertialess quantum electrons and positrons, classical cold ions, and stationary negative dust grains are studied, using arbitrary amplitude approach. The effect of dissipation due to viscosity of ions is taken into account. The numerical analysis of Sagdeev potential for small value of quantum diffraction parameter (H) shows that for chosen plasma, only compressive solitons can exist and the existence domain of this type of solitons is decreased by increasing dust density (d). Additionally, the possibility of propagation of both subsonic and supersonic compressive solitons is investigated. It is shown that there is a critical dust density above which only supersonic solitons are observed. Moreover, increasing d leads to a reduction in the existence domain of compressive solitons and the possibility of propagation of rarefactive soliton is provided. So, rarefactive solitons are observed only due to the presence of dust particles in this model quantum plasma. Furthermore, numerical solution of governed equations for arbitrary amplitude shock waves has been investigated. It is shown that only compressive large amplitude shocks can propagate. Finally, the effects of plasma parameters on these structures are investigated. This research will be helpful in understanding the properties of dense astrophysical (i.e., white dwarfs and neutron stars) and laboratory dusty plasmas.

Effects of plasma parameters on increasing the purity of nitrogen atom encapsulated fullerene in an RF plasma

Abstract Relatively high purity of nitrogen atom encapsulated fullerene (N@C 60 ) has been synthesized by an electron beam superimposed radio frequency (RF) discharge plasma method. Nitrogen species are characterized by an optical emission spectroscopy (OES); and a relationship between optical emission spectra and the purity of N@C 60 has been examined. It is observed that the increased amount of nitrogen molecule ions impinging on the sublimated fullerenes enhance the synthesis of N@C 60 . Here, it is cleared that the efficient synthesis of N@C 60 is possible by controlling the parameters of electron beam superimposed RF plasma. As a consequence, comparatively high purity of about 0.08% of N@C 60 has been obtained.

Nonlinear ion-acoustic structures in a nonextensive electron–positron–ion–dust plasma: Modulational instability and rogue waves

The nonlinear propagation of planar and nonplanar (cylindrical and spherical) ion-acoustic waves in an unmagnetized electron–positron–ion–dust plasma with two-electron temperature distributions is investigated in the context of the nonextensive statistics. Using the reductive perturbation method, a modified nonlinear Schrödinger equation is derived for the potential wave amplitude. The effects of plasma parameters on the modulational instability of ion-acoustic waves are discussed in detail for planar as well as for cylindrical and spherical geometries. In addition, for the planar case, we analyze how the plasma parameters influence the nonlinear structures of the first- and second-order ion-acoustic rogue waves within the modulational instability region. The present results may be helpful in providing a good fit between the theoretical analysis and real applications in future spatial observations and laboratory plasma experiments.

Surface functionalization of vertically-aligned carbon nanotube forests by radio-frequency Ar/O2 plasma

Vertically-aligned carbon nanotube (CNT) forests were modified using radio-frequency Ar/O2 plasma. The effect of plasma parameters on surface morphology, atomic composition and structure of CNT forests were studied. Functionalized CNT forests preserved vertical alignment and showed dramatic change in surface morphology, and bundle-like patterns were observed from scanning electron microscopy examination. X-ray photoelectron spectroscopy and Raman analyses reveal that the amount of sp2-hybridized graphite-like carbon bond in CNTs decreased significantly and oxygen-containing functionalities like C–O and O–CO groups were introduced after treatment. And the functionalization occurred exclusively on outer surface of CNT forests. Ar/O2 plasma was found to be more efficient than pure Ar plasma for oxygen functionalization.

Electrical Equivalent Circuit for Microstrip Micro-Plasma: Control of EM Propagation and Numerical Simulations

An approach to determine an equivalent electrical circuit of a micro planar discharge on a microstrip printed circuit is reported. The micro discharge is used to realize a dynamic microwave switching circuit. This approach is based on the measurement of the discharge current and the transmission coefficient for a given frequency 2.45 GHz. Numerical methods like FEM can be used to study the effect of plasma parameters on the propagation of electromagnetic waves through a microstrip printed circuit. Plasma behaves as flexible elements that can change its electrical proprieties such as conductivity.

Effect of plasma parameters on growth and field emission of electrons from cylindrical metallic carbon nanotube surfaces

The effect of plasma parameters (e.g., electron density and temperature, ion density and temperature, neutral atom density, and temperature) on the growth (without a catalyst), structure, and field emission of electrons from a cylindrical metallic carbon nanotube (CNT) surfaces has been theoretically investigated. A theoretical model of charge neutrality, including the kinetics of electrons, positively charged ions, and neutral atoms, and the energy balance of the various species in plasma, has been developed. Numerical calculations of the radius of the cylindrical CNT for different CNT number densities and plasma parameters have been carried out for the typical glow discharge plasma parameters. It is found that, on increasing the CNT number density and plasma parameters, the radius of cylindrical CNT decreases and consequently, the field emission factor for the metallic cylindrical CNT surfaces increase.

Nonlinear Korteweg–de Vries–Burger equation for ion-acoustic shock waves in the presence of kappa distributed electrons and positrons

The ion-acoustic shock waves are studied in electron–positron–ion plasma. The plasma system is composed of three components, specifically relativistic adiabatic ions, kappa distributed electrons and positrons. The Korteweg–de Vries–Burger equation is derived, solved analytically. The effects of plasma parameters on the shock strength and steepness are investigated. The numerical results are presented graphically for illustration. The results may have importance in non-thermal and relativistic plasmas of pulsar magnetosphere (Arons 2009 Astrophys. Space Sci. Library 357 373; Blasi and Amato arXiv:1007.4745V1 [astro-Ph.HE]).

Electrostatic compressive and rarefactive shocks and solitons in relativistic plasmas occurring in polar regions of pulsar

The electrostatic shocks and solitons are studied in weakly relativistic and collisional electron-positron-ion plasmas occurring in polar regions of pulsar. The plasma system is composed of relativistically streaming electrons, positrons while ions are taken to be stationary. Dissipative effects in the system are due to collision phenomena among the constituents of relativistic plasma. Nonlinear dynamics of the dissipation and dispersion dominated relativistic plasma systems are governed by Korteweg-de Vries Burger (KdVB) and Korteweg-de Vries (KdV) equations respectively. Numerical results, exploring the effects of plasma parameters on the profile of nonlinear waves are expedited graphically for illustration. Positron to electron temperature ratio plays the role of a decisive parameter. It is noticed that compressive shocks and solitons evolve in the system if the positron to electron temperature ratio is less than a critical value. However, there exists a threshold value of positron to electron temperature ratio beyond which the system supports the rarefactive shocks and solitons. The results may have importance in the relativistic plasmas of pulsar magnetosphere.

Effect of plasma parameters on growth and field emission properties of spherical carbon nanotube tip

The effect of plasma parameters (e.g., electron density and temperature, ion density and temperature, neutral atom density and temperature) on the growth (without a catalyst), structure, and field emission properties of a spherical carbon nanotube (CNT) tip has been theoretically investigated. A theoretical model of charge neutrality, including the kinetics of electrons, positively charged ions, and neutral atoms and the energy balance of the various species in plasma, has been developed. Numerical calculations of the radius of the spherical CNT tip for different CNT number densities and plasma parameters have been carried out for the typical glow discharge plasma parameters. It is found that upon an increase in the CNT number density and plasma parameters, the radius of the spherical CNT tip decreases, and consequently the field emission factor for the spherical CNT tip increases.

Relating plasma processing, surface morphology, and electronic properties of nanomaterials

Current approaches for analysis of the interrelations among plasma processing, morphological characteristics, electronic and optical properties of nano-structured materials are reviewed briefly. Practical implementation of these approaches is demonstrated for the cases of the plasma-assisted formation of silicon–germanium (Si1−xGex, 0 ⩽ x ⩽ 1.0) nano-structures on Si substrates with different crystalline orientations. Both numerical simulations and experimental studies on the effects of plasma parameters, germanium concentration, boron doping, crystalline orientations of the substrate on low-temperature photoluminescence (PL) of the Si1−xGex structures are considered. Different mechanisms of Si1−xGex morphology formation (e.g. traditional Stranski–Krastanov route as well as new approaches like cluster fluxes created in the plasmas) are compared; the latter ones are more flexible and exhibit wider range of the potential applications. Furthermore, effects of morphological characteristics and phonon confinement as well as energetic characteristics of the optic and acoustic phonons on the PL and electronic parameters of the experimentally studied nano-structures are analysed within the generalized Skettrup model and ‘displaced oscillator’ approximation.

Analysis of scattering by conducting objects covered with arbitrarily magnetised plasma using finite element-boundary integral-fast multipole algorithm

The electromagnetic (EM) scattering by conducting objects covered with arbitrarily magnetised plasma is computed using the hybrid vector finite element-boundary integral-fast multipole method (FE-BI-FMM). The relative permittivity tensor of arbitrarily magnetised plasma is described. The FE-BI-FMM formulation for scattering by three-dimensional (3D) conducting objects covered with arbitrarily magnetised plasma is derived in detail. The validity of FE-BI-FMM is verified by comparing numerical results with analytical values. The radar cross-sections (RCS) of conducting objects covered with magnetised plasmas are simulated and the effects of plasma parameters on RCS are analysed. Numerical results indicate that magnetised plasma cover layer is effective on reducing the back scattering if appropriate parameters of plasma are chosen.

Spectroscopic plasma diagnostics on a low-temperature plasma probe for ambient mass spectrometry

Since the inception of ambient desorption/ionization mass spectrometry, plasma ionization sources have played an increasing role in molecular mass spectrometry. Although a variety of discharge designs and geometries, along with a range of applications, have been introduced, very little published work has focused on the characterization and fundamental examination of these discharges, especially on the desorption/ionization processes they employ. In the present work, a simple yet effective ambient desorption/ionization source based on a dielectric-barrier discharge, the low-temperature plasma (LTP) probe, was optically characterized. By means of a spatially selective detection system, maps of reactive species created in both the plasma and the afterglow regions were recorded. From these maps, the origin of impurities important in mass spectrometric analyses, such as H2O, N2, and O2, was deduced. Electron number densities and rotational temperatures for the LTP were found to be similar to those reported for other dielectric-barrier discharges. Lastly, the effect of plasma parameters on emission spectra was correlated with mass spectral results previously reported for the same ionization source.

Surface Texturing of n- and p-Doped c-Si Using a Novel Plasma Chemical Texturing Process

Abstract n- and p-doped c-Si (100) are textured by a SF 6 /O 2 plasma chemical etching, under conditions avoiding ion bombardment. The study of the effects of plasma parameters on morphology and on surface reflectance of textured c-Si reveals a strong impact of silicon doping on texturing characteristics. SF 6 /O 2 plasma etches anisotropically n-type c-Si creating a square-based hillock-like morphology with a surface reflectivity of 6%. Conversely, for p-type Si, a H 2 plasma pretreatment is necessary to activate silicon etching and obtain a nano-textured surface with a reflectivity of 16%.

Plasma density induced formation of nanocrystals in physical vapor deposited carbon films

The effect of plasma parameters on the nanostructures formed during physical vapor deposition growth of carbon films has been studied. It was shown that the formation and nature of nanostructures strongly depend on plasma density and ion energy during the deposition. High plasma density results in formation of nanocrystals with preferred orientation even at low negative substrate bias (300 V) while at low plasma density higher substrate bias (500 V) is required for the nanocrystals. Moreover, at the same plasma density the nature of the nanostructures strongly depends on the ion energy. At higher ion energies, carbon nanotubes are formed in the microstructure while at lower ion energies, graphitic nanostructures are more stable. It was also found that prior to the formation of preferred orientation, an amorphous layer is formed at the silicon/carbon interface. Through electron energy loss spectroscopy, it is shown that the structure of this layer strongly depends on ion energy during the deposition.

Adherence in vitro of Candida albicans to plasma treated acrylic resin. Effect of plasma parameters, surface roughness and salivary pellicle

The adhesion of Candida albicans to surfaces is the prerequisite for occurrence of denture stomatitis. Objective Hence, this study investigated if surface modifications with plasma treatments could reduce the adherence of C. albicans to a denture base resin. Methods Specimens ( n = 180) with roughened and smooth surfaces were made and divided into five groups: control—specimens were left untreated; experimental groups—specimens were submitted to plasma treatments to obtain surfaces with different hydrophobicity (Ar/50 W; ArO 2/70 W; AAt/130 W) or incorporation of fluorine (Ar/SF 670 W). Contact angle measurements were performed immediately after the treatments and after immersion in water for 48 h. For each group, half of the specimens were incubated with saliva prior to the adhesion assay. The number of adherent yeasts was evaluated by XTT reduction method. Results For the experimental groups, there was significant change in the mean contact angle after 48 h of immersion in water. Groups ArO 2/70 W and ArSF 6/70 W showed significantly lower absorbance readings than the other groups, regardless the presence or absence of saliva and surface roughness. Conclusions Results demonstrated that ArO 2/70 W and ArSF 6/70 W plasma treatments showed promising potential for reducing the adherence of C. albicans to denture base resins.

Charging, Coagulation, and Heating Model of Nanoparticles in a Low-Pressure Plasma Accounting for Ion–Neutral Collisions

Low-pressure silane-argon plasmas allow the production of silicon particles of different sizes and morphologies. A better understanding of the correlations between dusty-plasma properties and particle morphology is very important for understanding and optimizing the particle synthesis. An analytical model predicting the nanoparticle charging, coagulation, and heating in a low-pressure plasma is here presented. The model includes the effect of collisions between ions and neutrals in proximity of the particles. In agreement with experimental evidence for pressures of a few torr, a charge distribution that is less negative than the prediction from the collisionless orbital-motion limited theory is obtained. The reduced charging causes an enhanced ion current to the particle while still preventing coagulation and conserving a monodisperse particle size distribution. Ion-electron recombination at the particle surface, together with other particle heating and cooling mechanisms typical of silane-argon plasmas, are studied in a particle-heating model which predicts the nanoparticle temperature. The effect of plasma parameters on the nanoparticle temperature is discussed, and the predictive power of the model is demonstrated from the appearance of photoluminescent properties in silicon nanoparticles, a property present only in crystalline particles. A correlation between plasma power, ion density, particle temperature, and particle crystallinity is finally developed.

Effects of plasma parameters and collection region on synthesis of iron and nickel aluminide composite particles during thermal plasma processing

Iron and Nickel aluminide composite particles were synthesized by non-transferred DC plasma spray torch at atmospheric pressure. Irregular shaped ball milled, micron sized powders were fed in to the plasma flame using argon as carrier gas. The particles got molten and vaporized. The vapour condensed on the walls of the reaction chamber and nanoparticles were formed. The molten particles got spheroidized due to surface tension forces. Powders as formed were collected in the plasma reactor at three different sections (Section A, B and C). These powder particles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The particle size and morphology of the composite particles strongly varied depending on the processing parameters and collection region. The results were discussed.

Comparison of CH, C3, CHF, and CF2 Surface Reactivities during Plasma-Enhanced Chemical Vapor Deposition of Fluorocarbon Films

The overall character of films deposited using plasma-enhanced chemical vapor deposition relies on the interactions of gas-phase molecules with the depositing film surface. The steady-state surface interactions of CH, C3, CHF, and CF2 have been characterized at the interface of depositing fluorocarbon (FC) films using the imaging of radicals interacting with surfaces (IRIS) technique. IRIS measurements show that the relative gas-phase densities of CH, C3, CHF, and CF2 in mixed FC plasmas depend on the CH2F2/C3F8 ratio. Similar results are found using optical emission spectroscopy to monitor the production of excited-state plasma species. The effects of plasma parameters, such as the feed gas composition and substrate bias on the radical surface, were measured. Under all conditions, the surface reactivity for CH radicals is near unity, whereas those for C3, CHF, and CF2 exhibit very low surface reactivity but also show some dependence on experimental parameters. Under some conditions, CF2 and CHF are generated at the surface of the depositing film. Surface reactivity measurements indicate that CF2, CHF, and C3 may contribute to FC growth only when adsorbing at reactive sites at the film surface. Moreover, the low surface reactivities of singlet species such as C3, CF2, and CHF may be related to the electronic configuration of the molecules.

Measurement and analysis of plasma antenna input impedance

The frequency dependence of plasma-column antenna input impedance has been measured by a vector network analyzer with different applied exciting power. The experimental results show obvious resonance behavior of the impedance. The effect of plasma parameters on the input impedance was established by means of an equivalent circuit model and the characteristics of input current. This method is useful for the research of plasma antenna dynamic reconfiguration and the realization of fast impedance matching.