Capacitive RF Discharge Research Articles

Determination of the excited argon states densities in high-frequency capacitive discharge

An experimental measurement of the density of excited argon states 1s5, 1s4, 1s3, and 1s2 was carried out for an rf capacitive discharge in argon at a frequency of 13.56 MHz and 81 MHz for two pressures of 50 and 100 mTorr in a wide range of discharge applied power. A collision-radiative model was developed to calculate the densities of 1s states from the known electron density and the electron energy distribution function. The electron energy distribution function is obtained from a self-consistent discharge simulation based on the Particle in cell with Monte Carlo collisions model. It is shown that the calculated densities of the metastable states of argon are in good agreement with the experimentally measured ones. The calculated resonance state densities are underestimated.

Obtaining of composite material based on carbon nanowalls and micro- and nanoparticles

This article is dedicated to the production of composite materials based on carbon nanowalls (CNWs) and micro- and nanoparticles of metal oxides, which today can be used as materials for supercapacitor electrodes due to their high specific surface, mechanical and electrochemical wear resistance. Synthesis of CNWs on the surface of alumina and titanium oxide particles was carried out by chemical vapor deposition in the plasma of a radio-frequency (RF) capacitive discharge of a mixture of argon and methane gases. The obtained samples were examined by using a Quanta 3D (SEM, FEI, USA) scanning electron microscope and NThegra Spectra Raman spectroscope. After PECVD synthesis on aluminum and titanium oxides, the microscopic and spectroscopic analysis of the samples showed different results.

Influence of external magnetic field on dust acoustic waves in a capacitive RF discharge

AbstractThis paper reports experiments on self‐excited dust acoustic waves (DAWs) and its propagation characteristics in a magnetized rf discharge plasma. The DAWs are spontaneously excited in dusty plasma after adding more particles in the confining potential well and found to propagate in the direction of streaming ions. The spontaneous excitation of such low‐frequency modes is possible due to the instabilities associated with streaming ions through the dust grain medium. The background E‐field and neutral pressure determine the stability of excited DAWs. The characteristics of DAWs strongly depend on the strength of external magnetic field. The magnetic field of strength B < 0.05 T only modifies the characteristics of propagating waves in dusty plasma at moderate power and pressure, P = 3.5 W and p = 27 Pa, respectively. It is found that DAWs start to be damped with increasing the magnetic field beyond B > 0.05 T and get completely damped at higher magnetic field B ∼ 0.13 T. After lowering the power and pressure to 3 W and 23 Pa respectively, the excited DAWs in the absence of B are slightly unstable. In this case, the magnetic field only stabilizes and modifies the propagation characteristics of DAWs while the strength of B is increased up to 0.1 T or even higher. The modification of the sheath electric field where particles are confined in the presence of the external magnetic field is the main cause of the modification and damping of the DAWs in a magnetized rf discharge plasma.

Research of the effect of radio-frequency capacitive plasma treatment in the medium of hydrocarbon gas on properties of the surface of glass fibers

The paper presents the results of a study of the effect of radio-frequency (RF) capacitive low-pressure discharge on the properties of glass fibers. It is shown that RF capacitive plasma modification in the medium of hydrocarbon gas imparts hydrophobic properties of the material surface.

Surface activation of polyamide fibers by radio-frequency capacitive plasma for application of functional coatings

The results of experimental researches on the modification of polyamide fibrous materials for technical purposes by low-pressure radio-frequency capacitive discharge plasma are presented. The effect of plasma modification on the wettability of polyamide fibers and their adhesive properties was studied.

BASIC PLASMA FEATURES OF PLANAR JET FORMED BY CAPACITIVE RF DISCHARGE IN ATMOSPHERE PRESSURE ARGON

Upgraded method of determining basic parameters of weakly ionized plasma by means of photometric study of bremsstrahlung emission continuum in visible spectrum range is described. Time-averaged spatial distributions of electron temperature and density in planar plasma jet formed by capacitive RF discharge in atmosphere pressure argon at the discharge glow in a low-current α-mode are experimentally obtained.

Heavy-particle induced secondary electrons in capacitive radio frequency discharges driven by tailored voltage waveforms

Particle-in-Cell/Monte Carlo Collision simulations are performed to investigate the effects of heavy-particle induced secondary electrons (SEs) on the ionization dynamics and on the control of ion properties at the electrodes in geometrically symmetric capacitively coupled argon discharges driven by tailored voltage waveforms. The driving voltage waveform is composed of a maximum of four (1≤N≤4) consecutive harmonics of the fundamental frequency of 13.56 MHz and is tailored by adjusting the identical phases of the even harmonics, θ. The simulations are carried out at neutral gas pressures of 3 Pa (nearly collisionless low-pressure regime) and 100 Pa (collisional high-pressure regime). Different approaches are used in the simulations to describe the secondary electron emission (SEE) at the electrodes: we adopt (i) constant ion-induced secondary electron emission coefficients (SEECs), γ, and (ii) realistic, energy-dependent SE yields for ions and fast neutrals. The mean ion energy at the electrodes, ⟨Ei⟩, can be controlled by θ at both pressures, for both approaches adopted to describe the SEE in the simulations. At a low pressure of 3 Pa, we obtain largely different dependencies of the ion flux at the electrodes, Γi, on θ, depending on the value of the γ-coefficient. For γ=0.2, Γi remains nearly constant as a function of θ, independently of the choice of N, i.e., the mean ion energy can be controlled separately from the ion flux by adjusting θ. However, for values of γ different from 0.2, the quality of the separate control of the ion properties changes significantly. At a high pressure of 100 Pa, independently of the choice of γ, for a given N≥2, the ion flux varies as a function of θ. At both pressures, the surface conditions affect the plasma parameters and the quality of the separate control of ion properties at the electrodes. Adopting realistic, energy-dependent SE yields for heavy particles in the simulations can lead to significantly different results compared to those obtained by assuming constant SEECs.

Spatial structure of radio-frequency capacitive discharge plasma with ring-shaped hollow electrode using Ar and O2 mixture gases

The spatial structures of plasma parameters in a radio-frequency capacitive discharge plasma with a ring-shaped hollow electrode operated in argon were measured at various oxygen gas concentrations for plasma processing by moving a cylindrical Langmuir probe. Their distinctive profiles are obtained around the ring-shaped hollow trench. The electron temperature Te at the hollow trench of radial position r = 37.5 mm has a peak value at an O2 gas concentration of 0%, whereas at O2 gas concentrations of 5 and 10% Te decreases everywhere except for positions close to the hollow trench. The plasma potential Vs at an O2 gas concentration of 0% is higher than that at O2 gas concentrations of 5% and 10%. The electron density ne has a peak value at the hollow trench at all O2 gas concentrations and decreases with increasing O2 gas concentration. Their axial profiles indicate unique distributions around the hollow inlet at a radial position of r = 37.5 mm, while at a radial position of r = 0 the profiles are almost uniform. It is found that a double layer is formed from the axial profiles of the plasma potential at r = 37.5 mm for all oxygen gas concentrations.

Investigation of Synthesis of Carbon Nanowalls by the Chemical Vapor Deposition Method in the Plasma of a Radio Frequency Capacitive Discharge

In this paper, the synthesis of carbon nanowalls (CNWs) by the chemical vapor deposition method in the plasma of a radio frequency (RF) capacitive discharge is considered. The so-called “CNWs” are one of the allotropes of carbon, which are interesting from both the practical and theoretical points of view. Because of their large surface, CNWs are a perfect electrode material for electronic devices. CNWs were synthesized at relatively low values of RF power, and it was found that an increase in the discharge power caused a decrease in the height of CNWs and an increase in their thickness. The study of graphitization of the CNW structure showed that synthesized CNWs had a low number of defects in the structure. The obtained results could be useful for the low-cost production of CNWs by the plasma-enhanced chemical vapor deposition (PECVD) method.

The Radio-Frequency Capacitive Normal Glow Discharge in Transverse Magnetic Field

The problems of computer simulation of the two-dimensional structure of a radio-frequency capacitive (RFC) glow discharge are discussed. The diffusion-drift computational model of the discharge, burning in a quasi-stationary mode, was used to analyze the behavior of the RFC-discharge in a transverse magnetic field. The calculations were performed for a two-dimensional RFC-glow discharge at a pressure of 5-10 Torr and an emf of 520-1000 V power source with a frequency of 13.59 MHz. The magnetic field vector with induction B = 0.2 T is directed across the current column of the RFC-discharge.

Electrical Characteristics of Capacitive Coupled Radio Frequency Discharges in Argon and Hydrogen

A symmetric radio frequency (RF) (13.56 MHz) electrode discharge system with different geometry has been investigated at low pressure. All electrical properties of symmetric capacitive RF discharge in pure argon (Ar) and pure hydrogen (H2) have been obtained from the current and voltage waveforms. Here, the changes of voltage and current were investigated according to external electrical discharge parameters. The electron densities of these discharges were measured with a single Langmuir probe. A homogeneous model of capacitive coupled RF (CCRF) discharge was used to determine the electrical properties of a parallel-plate RF discharge system and their dependences on the input RF power and gas pressure .

Measurement of the electron energy distribution in moving striations at low gas pressures

The time-resolved Electron Energy Distribution Functions (EEDFs) have been measured at different phases of moving striations in a positive column of DC discharge in argon gas. A very low gas pressure of 10 mTorr, a high energy resolution (to resolve the low energy part of the EEDF), and the dynamic range up to 3–4 orders of magnitude (to resolve the EEDF tail) with a temporal resolution of 2.5 μs distinguish our work from previous publications. The measured EEDFs reveal drastic changes in time of their low energy parts with the formation of a low energy peak. The observed EEDF dynamics is explained in the framework of nonlocal electron kinetics as electric field reversals and the trapping of low-energy electrons in potential wells propagating with striation along the discharge tube. The formation of the low energy peak in the EEDF is similar to that in rf capacitive and inductive discharges at low gas pressures where the low-energy electrons are trapped in the potential well created by the ambipolar electric field and cannot penetrate into the areas of electron heating by strong rf electric fields.

Role of sheath dynamics in multiple double layer formations in expanding RF plasma

Potential double layers are observed to form as nested cylindrical sheaths that energize charge particles in the absence of any externally applied magnetic field. These visibly glowing nested cylindrical sheaths are named as “Fire Tube” in the present work. Sheaths, in unmagnetized collisionless plasmas, have been observed to be functional in generating energetic charge particles. Two characteristically different plasma sources are compared in terms of the dependence of potential and density profiles on the plasma sheath formations near the source boundary. The sheath structures, complex fire tube formation, and space charge formations demarcate the two sources in terms of complex structure formations and motion of the charge particles. We present here the characteristic study of high pressure collisional boundary sheath formations through systematic experiments carried out during the transition from unmagnetized to magnetized charge particles, in the case of two different plasma sources designed. The cylindrical ambient plasma sheaths are observed to energize the charge particles, in the absence of any external magnetic field. The fire tube formations essentially represent a non-neutral region located radially away from the plasma source boundary, connecting the ion sheath with the electron sheath. The probe diagnostic results suggest a significant role of energetic electrons in the formation of multiple double layer structures in the present operational regime. Generation of nonthermal electrons during the formation of MDL in radio frequency capacitive discharges is subjected to interactions of the plasma with the electrodes as well as the confining wall material.

Ion energy and angular distributions in low-pressure capacitive oxygen RF discharges driven by tailored voltage waveforms

We investigate the energy and angular distributions of ions reaching the electrodes in low-pressure, capacitively coupled oxygen radio-frequency discharges. These distributions, as well as the possibility of the independent control of the ion flux and the ion energy are analysed for different types of excitation: single- and classical dual-frequency, as well as valley- and sawtooth-type waveforms. The studies are based on kinetic, particle-based simulations that reveal the physics of these discharges in great detail. The conditions cover weakly collisional to highly collisional domains of ion transport via the electrode sheaths. Analytical models are also applied to understand the features of the energy and angular distribution functions.

Experimental investigations of the magnetic asymmetry effect in capacitively coupled radio frequency plasmas

The electrical asymmetry effect allows control of the discharge symmetry, the DC self-bias, and charged particle energy distribution functions electrically by driving a capacitive radio frequency discharge with multiple consecutive harmonics with fixed, but adjustable relative phases. Recently, Trieschmann et al (2013 J. Phys. D: Appl. Phys. 46 084016) and Yang et al (2017 Plasma Process. Polym. 14 1700087; 2018 Plasma Sources Sci. Technol. 27 035008) computationally predicted that the discharge symmetry can also be controlled magnetically via the magnetic asymmetry effect (MAE). By particle-in-cell simulations they demonstrated that a magnetic field, that is parallel to the electrodes and inhomogeneous in the direction perpendicular to the electrodes, induces a discharge asymmetry due to different ion densities adjacent to both electrodes. This, in turn, is predicted to lead to the generation of a DC self-bias as a function of the difference of the magnetic field at both electrodes. In this way the MAE should allow control of the mean ion energy at both electrodes as a function of the magnetic field configuration. Here, we present the first experimental investigation of the MAE. In a low pressure discharge operated in argon at 13.56 MHz, we use a magnetron-like magnetic field configuration at the powered electrode, which leads to an inhomogeneous profile of the magnetic field perpendicular to the electrodes. By measuring the DC self-bias and the ion flux-energy distribution function at the grounded electrode as a function of the magnetic field strength at the powered electrode, the driving voltage amplitude and the neutral gas pressure we experimentally verify the concept of the MAE and demonstrate this technology to be a powerful method to control the discharge symmetry and process relevant energy distribution functions.

Multi frequency matching for voltage waveform tailoring

Customized voltage waveforms composed of a number of frequencies and used as the excitation of radio-frequency plasmas can control various plasma parameters such as energy distribution functions, homogeneity of the ion flux, or ionization dynamics. So far this technology, while being extensively studied in academia, has yet to be established in applications. One reason for this is the lack of a suitable multi frequency matching network that allows for maximum power absorption for each excitation frequency that is generated and transmitted via a single broadband amplifier. In this work, a method is introduced for designing such a network based on network theory and synthesis. Using this method, a circuit simulation is established that connects an exemplary matching network to an equivalent circuit plasma model of a capacitive radio-frequency discharge. It is found that for a range of gas pressures and number of excitation frequencies the matching conditions can be satisfied, which proves the functionality and feasibility of the proposed concept. Based on the proposed multi frequency impedance matching, tailored voltage waveforms can be used at an industrial level.

Emission spectral diagnosis of argon-helium plasma produced by radio frequency capacitive discharge

Optically pumped metastable rare-gas laser (OPRGL) have been proposed to overcome the shortcomings of diode-pumped alkali-vapor laser in the recent years. The OPRGL promises to realize high-scale output. But how to achieve enough particle density of metastable atoms is still an open problem. Usually, plasma produced by discharge serves as a gain medium of the OPRGL. Here in this paper, we are to reveal the effects of different discharge parameters on the plasma properties, such as particle density of metastable argon atoms. Gas discharge at a radio frequency of 13.56 MHz is adopted to excite argon atoms. Emission spectrum is employed to study argon and helium radio frequency discharge of optically pumped argon laser at high pressure, different powers of discharge and various content of argon. Gas temperature is obtained by analyzing rotational spectrum (A2∑+ → X2Π) of OH radical generated by residual water vapor and comparing simulated spectrum with the measured spectrum. The electronic excitation temperature relating to electron temperature is obtained by the method of Boltzmann's plot. Stark broadening of the spectrum is used to determine the electron density. The results show that gas temperature rises slightly with the increase of pressure and varies little with content and discharge power changing. The electronic excitation temperature increases with the decrease of pressure evidently and decreases slightly with the increase of content. The electron density is on the order of 1015 cm-3 under various conditions controlled by us. Long time discharge test reveals that residual water vapor can lead to the decrease of electron temperature, and thus reducing the yield of argon metastable state. In conclusion, considering that the higher gas temperature can improve the collision relaxation rate of helium and argon, and the higher electron temperature can improve the rate of production of argon metastable state. Thus a proposal is put forward that appropriately heating gas and reducing gas pressure can obtain higher particle density of metastable argon. Furthermore, It can be found from these results that heating and cleaning the gas during discharge may be candidate methods to obtain and sustain the higher particle density in the plasma.

Mathematical simulation of the low-temperature plazma at the interaction with oil products

Self-consistent mathematical models of a non-equilibrium low-temperature plasma of a radio frequency capacitive discharge in argon in different pressure ranges have been created. These mathematical models allow us to calculate the internal structure and discharge parameters for controlling parameters of the plasma torches at solving the target problems in order to optimize their functioning. The methods for numerical realization of the proposed models are developed. The results of numerical calculations for test problems are analyzed.

Electron energy probability function modulation with external electron beam in capacitive coupled radio frequency discharges

We investigate the effect of external electron beam injection on plasma kinetics of a radio‐frequency (rf) capacitive argon discharge at a pressure of 100 mTorr. The rf voltage is applied to the one electrode. Monoenergetic electron beam is injected from the other electrode, with a laboratory accessible injection current and energy. The electron beam injected electrode is grounded. A direct‐implicit particle‐in‐cell/Monte‐Carlo method is used to self‐consistently simulate the plasma density, electron temperature, plasma potential, electron energy probability function (EEPF), and the electron and ion fluxes. The presence of the electron beam increases the plasma density, while decreases the electron temperature and the plasma potential. The plasma density can increase by a factor of 5, at the same time the electron temperature can decrease from 3 to 0.5 eV. The reason is that, with the electron injection, there are more low‐energy electrons occupation in the EEPF. The EEPF is sensitive to the beam modulation: even a small beam current of 0.01A can modify the EEPF significantly. This may have crucial importance for plasma processing of polymers and graphene, where low energy treatment is desired. In addition, electron and ion fluxes to the ground electrode, are also significantly modified with increasing flux and decreasing bombardment energy.

Modeling of radio-frequency capacitive discharge under atmospheric pressure in Argon

We consider a one-dimensional self-consistentmathematical model of capacitive radiofrequency discharge in Argon between symmetrical electrodes at atmospheric pressure in the local approximation. The model incorporates electrons, atomic and molecular ions, metastable atoms, Argon dimers, and ground-state atoms. The numerical algorithm for the model is based on a finitedimensional approximation of the problem using difference schemes with subsequent iterations. A software package in the MatLab environment has been developed to implement the numerical algorithm. Using this software for a model problem, we have obtained the characteristics of a radiofrequency discharge in a plasmatron with interelectrode distances of 0.2 and 2 cm at atmospheric pressure. The results of numerical calculations are in good agreement with data known from literature of field experiments and calculations.