RF Plasma Discharge Research Articles

Characterization of RF Discharge in Liquid n-Hexane and its Application to Synthesize Carbon Nano-Particles

The RF plasma discharge in liquid n-hexane is used to synthesize carbon nanoparticles. The results show that amorphous carbon nanoparticles with size of 5–25 nm are the main product in the plasma in liquid n-hexane. Carbon nano-tubes of average diameter of 19 nm and length of 500 nm are also observed. The energy efficiency for carbon nanoparticles production is 2.9 mg/kJ which is more than 10 times larger than that of typical arc discharge synthesis method. The high speed observation indicates that the RF plasma in liquid has an alternating behaviour and it does not continuously emit light. The OES results show that H and C2 are the main observed species in the plasma. Based on the OES data, it is shown that plasma temperature is 4,030 K and the electron density is 2.54 × 1022 m−3. Our results suggest that this method can be considered as a new route for carbon nanostructures production.

Dust charge measurement in a strongly coupled dusty plasma produced by an rf discharge

The electric charge on silica microparticles (5 µm in diameter) levitating in the sheath of an rf discharge plasma is determined in a newly installed device for dusty plasma experiments at the IASST. The sheath potential profile is measured using an emissive probe and the electric field is obtained in order to determine the dust charge. The measured dust charge in the pressure range 0.50–5.0 Pa using the electric field value at the levitation height is found to be of the order of 104 elementary charges. Dust charge is also examined using the vertical resonance method which gives a similar order of charges. The experimentally measured charge is compared with the estimated values based on the orbital motion limited charging model. The coupling strength between the particles forming a 2D plasma crystal lattice is estimated using the measured dust charge.

Frequency stabilization of an external-cavity diode laser to metastable argon atoms in a discharge

A laser stabilization scheme using magnetic dichroism in a RF plasma discharge is presented. This method has been used to provide a frequency stable external-cavity diode laser that is locked to the 4s[3/2](2) → 4p[5/2](3) argon laser cooling transition at 811.53 nm. Using saturated absorption spectroscopy, we lock the laser to a Doppler free peak which gave a locking range of 20 MHz when the slope of the error signal was maximized. The stability of the laser was characterized by determining the square root Allan variance of laser frequency fluctuations when the laser was locked. A stability of 129 kHz was measured at 1 s averaging time for data acquired over 6000 s.

Ion energy distribution measurements in rf and pulsed dc plasma discharges

A commercial retarding field analyzer is used to measure the time-averaged ion energy distributions of impacting ions at the powered electrode in a 13.56 MHz driven, capacitively coupled, parallel plate discharge operated at low pressure. The study is carried out in argon discharges at 10 mTorr where the sheaths are assumed to be collisionless. The analyzer is mounted flush with the powered electrode surface where the impacting ion and electron energy distributions are measured for a range of discharge powers. A circuit model of the discharge, in combination with analytical solutions for the ion energy distribution in radio-frequency sheaths, is used to calculate other important plasma parameters from the measured energy distributions. Radio-frequency compensated Langmuir probe measurements provide a comparison with the retarding field analyzer data. The time-resolved capability of the retarding field analyzer is also demonstrated in a separate pulsed dc magnetron reactor. The analyzer is mounted on the floating substrate holder and ion energy distributions of the impinging ions on a growing film, with 100 ns time resolution, are measured through a pulse period of applied magnetron power, which are crucial for the control of the microstructure and properties of the deposited films.

Microstructure of a Liquid Two-Dimensional Dusty Plasma under Shear

The microstructure of a strongly coupled liquid undergoing a shear flow was studied experimentally. The liquid was a shear melted two-dimensional plasma crystal, i.e., a single-layer suspension of micrometer-size particles in a rf discharge plasma. Trajectories of particles were measured using video microscopy. The resulting microstructure was anisotropic, with compressional and extensional axes at around ±45° to the flow direction. Corresponding ellipticity of the pair correlation function g(r) or static structure factor S(k) gives the (normalized) shear rate of the flow.

The influence of external parameters on the peculiarities of a hybrid low-pressure radio-frequency discharge

This paper deals with the experimental study of the patterns of the RF power input into the plasma of a hybrid RF discharge that was sustained by an RF power unit, which consisted of a spiral antenna connected in parallel with capacitor electrodes. At low values of RF generator power, RF power has been shown to be derived in the hybrid discharge through the capacitive channel; the role of the inductive channel becomes more significant at higher RF generator power as the power of the RF generator increases. It was demonstrated that at a low power of the RF generator the RF power occurs in the hybrid discharge essentially through the capacitive channel and then increases as the power of the RF generator increases. The larger the contribution of the inductive channel is, the smaller the value of the dividing capacity included in the capacitive discharge chain is.

Radio frequency discharge with control of plasma potential distribution

A RF discharge plasma generator with additional electrodes for independent control of plasma potential distribution is proposed. With positive biasing of this ring electrode relative end flanges and longitudinal magnetic field a confinement of fast electrons in the discharge will be improved for reliable triggering of pulsed RF discharge at low gas density and rate of ion generation will be enhanced. In the proposed discharge combination, the electron energy is enhanced by RF field and the fast electron confinement is improved by enhanced positive plasma potential which improves the efficiency of plasma generation significantly. This combination creates a synergetic effect with a significantly improving the plasma generation performance at low gas density. The discharge parameters can be optimized for enhance plasma generation with acceptable electrode sputtering.

Optical constants from 370 nm to 900 nm of Titan tholins produced in a low pressure RF plasma discharge

Determining the optical constants of Titan aerosol analogues, or tholins, has been a major concern for the last three decades because they are essential to constrain the numerical models used to analyze Titan’s observational data (albedo, radiative transfer, haze vertical profile, surface contribution, etc.). Here we present the optical constant characterization of tholins produced with an RF plasma discharge in a (95%N2–5%CH4) gas mixture simulating Titan’s main atmospheric composition, and deposited as a thin film on an Al–SiO2 substrate. The real and imaginary parts, n and k, of the tholin complex refractive index have been determined from 370nm to 900nm wavelength using spectroscopic ellipsometry. The values of n decrease from n=1.64 (at 370nm) to n=1.57 (at 900nm) as well as the values of k which feature two behaviors: an exponential decay from 370nm to 500nm, with k=12.4×e−0.018λ (where λ is expressed in nm), followed by a plateau, with k=(1.8±0.2)×10−3. The trends observed for the PAMPRE tholins optical constants are compared to those determined for other Titan tholins, as well as to the optical constants of Titan’s aerosols retrieved from observational data.

Loss of hydrogen atoms in H2 plasma on the surfaces of materials used in EUV lithography

Lowpressure hydrogen is an important component of the working medium in extreme ultraviolet (EUV) projection lithography. Under the action of EUV photons and fast secondary electrons on the gas medium, plasma and atomic hydrogen, actively interacting with the surface, are produced. This interaction is very important, because it largely determines the lifetime of the multilayered EUV optics. In this study, the loss of atomic hydrogen under the conditions of a low pressure (<10 Torr) RF plasma discharge on the sur� faces of materials used in EUV lithography is investigated. The surface loss probabilities of H atoms on these materials are measured. It is shown that surface recombination of atomic hydrogen goes according to the Eley-Rideal mechanism via direct recombination of H atoms from the gas phase with chemically and phys� ically adsorbed atoms. In this case, the surface recombination probability is mainly determined by the density of chemical adsorption sites. The density of adsorption sites and the desorption energy of H atoms are esti� mated. The desorption energy of physically adsorbed H atoms on pure metal surfaces (or surfaces exposed to plasma) is about 0.5 eV, and the density of sorption sites is close to the surface density of atoms. This results in a high loss probability of H atoms on metals (~0.1). Therefore, to provide efficient transportation of hydro� gen atoms, it is necessary to use materials with the lowest loss probability of H atoms, i.e., dielectrics.

Measurement of the sheath capacitance of a planar probe

The sheath capacitance was measured on a planar probe dc-biased with respect to the plasma potential using the phase sensitive detection method in the region separated from the rf discharge plasmas by an immersed grid. It was observed that the sheath capacitance was negative when the collecting electrode of the probe was positioned downward toward the grid and biased near the plasma potential. This indicates that a double sheath had built up near the probe electrode. This tendency can be explained by the sheath capacitance, which is calculated using Poisson’s equation with a non-zero electrical field and an ion velocity condition at the sheath edge.

Lead selenide nanowire growth by vapor-liquid-solid mechanism under mask during plasma processing

Data on the formation of lead selenide (PbSe) nanowires under a stencil mask during the processing of epitaxial PbSe films in high-density inductively coupled plasma (ICP) of low-pressure argon RF discharge are presented. The nanowires were studied by high-resolution scanning electron microscopy and energy-dispersive X-ray spectroscopy. A physical model is proposed that explains the local formation of PbSe nanowires in terms of their catalytic growth according to the vapor-liquid-solid mechanism.

Phase-resolved optical emission of dusty rf discharges: Experiment and simulation

The spectral emission of atoms in a dusty radio frequence (rf) discharge plasma in argon and helium has been measured with a gated ICCD camera. The spatially and temporally resolved emission/excitation of the argon and helium atoms during the rf cycle in the dusty discharge was compared to the dust-free case. In the bulk plasma above the dust cloud, the emission is clearly enhanced in the dusty discharge with respect to the pure discharge, whereas in the sheath the emission is reduced. In addition, the emission of a dusty argon plasma is studied via particle-particle particle-mesh (P³M) simulations. The rf dynamics with a single dust particle trapped in the sheath was calculated. Like in the experiment the dust modifies the atomic emission. The spatiotemporal excitation pattern of the experiment is reproduced and a detailed understanding of the difference in excitation of the discharge with and without dust is presented.

Experimental study of the synthesis of supramolecular complexes in hybrid dusty plasma

The processes that form the reaction volume as plasma-dust entities during the injection of protein drug powders into RF-discharge plasma (plasma trap) have been investigated. Using albumin and acetylsalicylic acid as an example, plasma-assisted vapor deposition of sublimable organic compounds onto the surface of particles levitating in the plasma trap was studied. The geometry of the reaction volume, the dynamics of the dust particles, and the intensity of the vapor fllux can be effectively controlled using a continuous or pulse-periodic electron beam. The thickness and degree of adhesion of the deposited layer are determined by the electron beam parameters, whereas the characteristics of RF discharge have an effect only on the initial geometry and stability of the reaction volume.

Crystal and liquid structures in strongly nonideal dusty plasmas under laboratory and microgravity conditions

This review presents the results obtained in a cycle of interrelated experimental works that have a priority character in the study of dusty plasma crystals and liquids under laboratory and microgravity conditions (on board the Mir Orbital Complex and the International Space Station) over wide ranges of temperatures and pressures: in a DC glow-discharge plasma and a low-pressure RF discharge plasma at room and cryogenic temperatures, in a nuclear-excited plasma and an UV-induced plasma, and in a thermal plasma at atmospheric pressure.

Enhanced Bone Cells Growth and Proliferation on TiO2 Nanotubular Substrates Treated by RF Plasma Discharge

AbstractTitanium implants are well known for their biocompatibility, especially if bioinertness is desired, due to the TiO2 native oxide which is thermodynamically and chemically very stable. One of the major problems with this material involve its inability to induce enhanced cellular adhesion and proliferation on its surface without complicated structural approaches, leading to the possible lack of bone‐implant interfacial interaction and rejection. In order to potentially improve osseointegration of such implants self‐assembled vertical and ordered nanotubular TiO2 arrays were fabricated by electrochemical anodization and were plasma treated under O2, N2, O2 + N2, and He gaseous environments and their properties analyzed by various analytical procedures. Osteoblast bone cells (MC3T3‐E1) were grown on TiO2 nanotube‐arrayed substrates and their proliferation was analyzed and quantified. Oxygen and nitrogen plasma treatments were found to significantly improve the proliferation of the bone cells over the TiO2 nanoarray substrates, with the O2 + N2 combination yielding the most significant improvements. These findings may be explained by the interactions between the cells and the changes in the surface chemistry induced by the O2 and N2 groups introduced by the plasma discharge treatment onto the TiO2 surfaces

Charging of submicron structures during silicon dioxide etching in one- and two-frequency gas discharges

A model that combines the Monte Carlo method for calculating electron and ion trajectories in three-dimensional geometry and an analytic approach developed for calculating an electric field in two-dimensional geometry is used to simulate the charging of the surface of periodic submicron SiO2 structures by electron and ion fluxes in the plasma of a one- and a two-frequency capacitive RF discharge. The energy distribution function of the electrons and ions that come to the bottom of a submicron structure in an argon and an argon-containing plasma is calculated for structures with a width of 11–45 nm and an aspect ratio of d/w = 1–10 (where d and w are the depth and width of the structure). It is shown that secondary electronelectron emission plays an important role in the redistribution of the electric charge and, accordingly, of the electric potential in a submicron structure. It is demonstrated that, when the secondary electron-electron emission mechanism is taken into account, the ion energy spectrum at the bottom of a submicron structure is shifted toward lower energies and becomes broader in comparison with the spectrum of an ion flux from an RF discharge plasma. Moreover, the shift and broadening depend only on the secondary electron-electron emission coefficient, the energy of the charged particles, and the aspect ratio.

Self-consistent electrodynamics of large-area high-frequency capacitive plasma discharge

Capacitively coupled plasmas (CCPs) generated using high frequency (3–30 MHz) and very high frequency (30–300 MHz) radio-frequency (rf) sources are used for many plasma processing applications including thin film etching and deposition. When chamber dimensions become commensurate with the effective rf wavelength in the plasma, electromagnetic wave effects impose a significant influence on plasma behavior. Because the effective rf wavelength in plasma depends upon both rf and plasma process conditions (e.g., rf power and gas pressure), a self-consistent model including both the rf power delivery system and the plasma discharge is highly desirable to capture a more complete physical picture of the plasma behavior. A three-dimensional model for self-consistently studying both electrodynamic and plasma dynamic behavior of large-area (Gen 10, &amp;gt;8 m2) CCP is described in this paper. This model includes Maxwell’s equations and transport equations for charged and neutral species, which are coupled and solved in the time domain. The complete rf plasma discharge chamber including the rf power delivery subsystem, rf feed, electrodes, and the plasma domain is modeled as an integrated system. Based on this full-wave solution model, important limitations for processing uniformity imposed by electromagnetic wave propagation effects in a large-area CCP (3.05×2.85 m2 electrode size) are studied. The behavior of H2 plasmas in such a reactor is examined from 13.56 to 200 MHz. It is shown that various rectangular harmonics of electromagnetic fields can be excited in a large-area rectangular reactor as the rf or power is increased. The rectangular harmonics can create not only center-high plasma distribution but also high plasma density at the corners and along the edges of the reactor.

Synthesis of biocompatible surfaces by nanotechnology methods

The modification of the surface of low-density polyethylene (LDPE) and polyurethane (PU) by means of the pulsed ion-plasma deposition of nanostructural carbon coatings at 20–60°C has been studied. The effect of this low-temperature treatment on the biocompatibility of the LDPE and PU has been assessed. Optimum technological parameters for the formation of mosaic carbon nanostructures with a thickness of 0.3–15 nm and a cluster lateral size of 10–500 nm are determined. These structures give the polymer surface increased hemocompatible properties. The surface of samples was studied by methods of scanning electron microscopy, scanning probe microscopy, and Raman spectroscopy. The effect of the UV light of a krypton lamp (λ = 123.6 nm) and white synchrotron radiation on the surface of poly(methyl methacrylate) (PMMA) preliminarily treated in an oxygen-containing RF discharge plasma has been investigated by varying the duration of exposure (from several minutes to several dozen minutes) and the residual gas pressure (2 and 100 Pa). This processing ensures the smoothing of the surface relief on micro- and nanoscale levels, which can improve the biocompatibility of the modified PMMA film surface. The principles of a two-stage technology for rendering the titanium (implant) surface biocompatible are developed. This technology consists of the chemical pretreatment of the surface for creating a microrelief (2–3 μm roughness), followed by the deposition of a titanium oxide film with controlled composition (TiO2) and thickness (10–60 nm). The influence of the mechanisms and technological parameters of the oxide film deposition on its composition, structure, uniformity (conformal coating of involved shapes), and biocompatibility of the modified surface have been studied.

Behavior of RF Discharge Plasmas in the Uragan‐3M and Uragan‐2M Torsatrons

AbstractIn the Uragan‐3M (U‐3M) and Uragan‐2M (U‐2M) torsatrons possibilities and prospects of Alfvén method utilization for wall conditioning, plasma production and heating are studied. In U‐3M the effect of fast ion loss on H‐like mode formation is investigated. In U‐2M the wall conditioning associated with the chemical reactivity of the atomic hydrogen to create volatile substances is used. A compact four‐strap antenna is proposed for Alfvén resonance heating in U‐2M (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Evaluation of the scavenging effect by low temperature laboratory plasmas driven with radiofrequency

Proposed materials for ITER are beryllium for first wall and tungsten tiles (plus carbon fibre composites) for the divertor. The use of carbon materials at the divertor plates of ITER can be problematic due to the formation of tritium-containing co-deposits coming from the products of chemical erosion and physical sputtering. Scavenging effect in the hidden regions of the divertor has been proposed as a possible technique to eliminate the formation of amorphous carbon films. Nitrogen gas has been proposed as a good scavenger. Although a complete suppression of the formation of amorphous carbon films by nitrogen was achieved in laboratory experiments (in a low temperature plasma), only a moderate reduction (<30–40%) was seen at JET in type-III ELM discharges (Tabares et al 2005 J. Nucl. Mater. 337–339 867–71). This justifies further analyses for an understanding of physicochemical processes for the deposition/inhibition of carbon films. In this work, experiments in RF plasma discharges at low pressures of CH4/N2 admixtures were carried out. The formation of amorphous carbon films was investigated under different physical conditions, with high and low energetic ions on powered and floating electrodes, respectively. Optical emission spectroscopy of ion and neutral species was employed as the main diagnostic.