Radio Frequency Plasma System Research Articles

Effects of powder particle charging during RF plasma spheroidisation process

Plasma spheroidisation converts irregular shaped particles to spherical morphology. The transformation occurs rapidly due to the high temperature of the plasma. This study highlights the effects of particle charging during spheroidisation of Ti6Al4V utilising a 15 kW radio frequency (RF) inductively coupled Tekna plasma system. Particles introduced into the RF plasma system acquire an equilibrium charge below 10-9 seconds. The determined Coulomb coupling parameters of the particle in the RF plasma indicates that the particle will form a Coulomb crystal when flowing through the plasma section.

Effect of Plasma Treatment on the Impact Behavior of Epoxy/Basalt Fiber-Reinforced Composites: A Preliminary Study

Hydrophobic surfaces are highly desired for several applications due to their exceptional properties such as self-cleaning, anti-icing, anti-friction and others. Such surfaces can be prepared via numerous methods including plasma technology, a dry technique with low environmental impact. In this paper, the effect of a one-step sulfur hexafluoride (SF6) plasma treatment upon the low velocity impact behavior of basalt/epoxy composites has been investigated by using several characterization techniques. A capacitive coupled radiofrequency plasma system was used for the plasma surface treatment of basalt/epoxy composites, and suitable surface treatment conditions were experimentally investigated with respect to gas flow rate, chamber pressure, power intensity, and surface treatment time by measuring the water droplet contact angle of treated specimens. The contact angle measurements showed that treating with SF6 plasma would increase the hydrophobicity of basalt/epoxy composites; moreover, the impact results obtained on reinforced epoxy basalt fiber showed damage in a confined area and higher impact resistance for plasma-treated basalt systems.

An Inductively-Coupled Plasma Electrothermal Radiofrequency Thruster

The “cubesat” form factor has been adopted as the defacto standard for a cost effective and modular, nano-satellite platform. Many commercial options exist for nearly all components re- quired to build such satellite; however, there is a limited range of thruster options that suit the power and size restrictions of a cubesat. Based on the prior work on the “Pocket Rocket” electro- thermal capacitively-coupled radiofrequency (RF) plasma thruster operating at 13.56 MHz, a new design is proposed which is based on an inductively-coupled radiofrequency plasma system operat- ing at 40.68 MHz. The new thruster design, which includes a compact and efficient radiofrequency matching network adjacent to the plasma cavity is presented, together with the first direct thrust measurements using argon as the propellant with the thruster immersed in vacuum and attached to a calibrated thrust balance. These initial results of the unoptimised first prototype indicate an up to 40% instantaneous thrust gain from the plasma compared to the cold gas thrust: typical total thrust at 100 SCCM of argon and 50 W RF power is ∼ 1.1 mN.

A Multitorch RF Plasma System as a Way to Improve Temperature Uniformity for High-Power Applications

This article presents a new approach and preliminary modeling results of the temperature field nonuniformity reduction by using a multitorch radio frequency (RF) plasma system. This is also a way to achieve technical and economic feasibility for plasma systems with plume power over 200 kW, significantly reducing the development and production cycle. The mixing of plasma jets was numerically simulated by solving a system of equations, describing high-temperature turbulent plasma flows. The data obtained could be used for engineering of high-power plasma systems, including the ones for testing high-temperature thermal protection materials, waste to power, syntheses of new materials, and so on.

Effect of the low- and radio-frequency oxygen plasma treatment of wood fiber on mechanical properties of wood fiber/HDPE composite

Wood fibers were treated in different plasma frequencies (radio frequency (RF) and low frequency (LF)) using oxygen (O2) for different plasma powers to increase the interface adhesion between wood fiber and high-density polyethylene (HDPE) matrix. The influence of various plasma frequencies on mechanical properties of wood fiber-reinforced HDPE composites was reported. Tensile, flexure, short beam shear tests were used to determine the mechanical properties of the composites. The interlaminar shear strength (ILSS) increased from 11.5 MPa for the untreated wood fiber/HDPE composite to 19.8 and 26.3 MPa for LF and RF O2-plasma-treated wood fiber/HDPE composites, respectively. O2 plasma treatment also improved the tensile and flexural strengths of wood fiber/HDPE composites for both plasma systems. It is clear that O2 plasma treatment of wood fibers by RF plasma system instead of using LF plasma system brings about greater improvement on the ILSS of wood/HDPE composites. Improved fiber/matrix adhesion is able to be seen in scanning electron microscopy micrographs of fracture surfaces of the wood fiber/HDPE composite.

Enhancement of electrical conductivity of plasma polymerized fluorene-type thin film under iodine and chlorine dopants

Electrical and optical properties of plasma-polymerized fluorene-type (C13H10) iodine-and chlorine-doped thin films are investigated. Fluorene-type thin films are produced using a mixture of biphenyl (C12H10) and methane (CH4) inside a single capacitively coupled radio frequency plasma system. The dopants are mixed with the plasma directly as vapor during the deposition. The chemical structures of the generated functional compounds, evaluated by a Fourier transform infrared spectroscopy, exhibit a changeable extension conjugation providing high crosslinking and branching. The structural orders of the doped films are analyzed using X-ray diffraction measurements. The film thickness is measured by ellipsometry. Measured difference in thickness due to doping varies from 16nm to 50nm. The structural characterization shows that the doped films are stable and of high quality. The current–voltage characteristics of devices are obtained using two-point probe measurements. As a result of doping, electrical conductivity as high as two orders of magnitude compared to that of the undoped films is measured. In addition, ultraviolet-visible spectroscopy is used to characterize the optical properties. Optical energy band gaps of the doped films as low as 2.4eV are obtained. In conclusion, plasma processing is proven to improve the optical and electrical properties of the doped films.

Effect of Main Operating Parameters on Al 2 O 3 Spheroidization by Radio Frequency Plasma System

Micro-fine spherical alumina (Al2O3) powders with mean diameters of 7, 30 and 75 μm have been synthesized by the SY119-30kW radio frequency induction plasma spheroidization system. The effect of main operating parameters on spheroidization process was investigated. The results show that different axial positions of the injection probe strongly influence the effectiveness of the spheroidization treatment and Z=12.9 cm is the best position for Al2O3 spheroidization process as it is the middle of coil center for this spheroidization system. The obtained powders with smooth surface exhibit fantastic sphericity and preferable density. The spheroidization efficiency of synthesized powders is almost 100% at feeding rate of 65 g/min with the chamber pressure of 0.079 MPa. In addition, the chamber pressure is also the vital factor that influences the fabrication process and it should be coordinated with the carrier gas flow rate. The phase compositions characterized by X-ray diffraction (XRD) shows the same results under different sheath gas (Ar or N2) conditions. Furthermore, the purity of the fabricated powders is improved after high temperature spheroidization treatment.

Fecal Coliforms and Total Coliforms Removal in Water Using Radio-Frequency (RF) Plasma System

A radio-frequency plasma system (RF) was used to investigate the removal of microorganisms from water.Plasma generated by RF radiation can produce active compounds (H•, •OH, H2O2, O3, etc.) that have a highoxidation potential and can kill microorganisms present in water (fecal coliforms and total coliforms). Thefrequency of the plasma system was set to 3.0, 3.3 and 3.7 MHz and applied to river water for 60 minutes. Theresults show that in all runs, the pH of the water produced was in the range from 7.4 to 7.9. The removalefficiencies of fecal coliforms achieved were between 83.75 and 95% and were higher than the removalefficiencies of total coliforms, which were between 82.61 and 93.48%. Meanwhile, the death rate (kD) of fecalcoliforms wasfaster than that of total coliforms. Therefore, the removal of total coliforms is the key to removingmicroorganisms fromwater. RF plasma treatment can be used for treatment of drinking water to decreasemicroorganisms.

Radio Frequency Titanium Plasma Modified Vanadium Oxide for Electrochromic Applications

Titanium tetrachloride plasma were used to enhance the electrochromic properties of vanadium oxide (V2O5) powder. The plasma treatments were performed in a rotating 13.56 MHz radio frequency plasma system with optimized parameters. Titanium tetrachloride plasma treated and untreated V2O5 powders were deposited by pyrolysis spraying methods on to indium tin oxide conductive electrodes and the electrochromic properties were investigated. The film characterizations were carried out by using cyclic voltammetry, optic spectroscopy, scanning electron microscope and energy dispersive X-ray spectrometer. The properties of electrochromic devices were investigated with optic transmission changes in visible spectral range.

An Experimental and Analytical Study of an Asymmetric Capacitively Coupled Plasma Used for Plasma Polymerization

Plasma processing is widely used to provide novel surface modifications to materials for a variety of applications. Typically, the systems used to carry out these modifications are poorly characterised. Here we describe the basics of a global model for a capacitively coupled asymmetric parallel plate radiofrequency plasma system routinely used to produce plasma polymers. An analytical global model was developed for argon, for which cross‐sections are known, at a constant pressure of 1 Pa, and includes an electrical model and a power balance. The main parameters of interest were ion flux and self‐bias voltages. The argon modelling results were then compared to experimental results for a range of operating gases (argon, oxygen, amines, acids, alcohols, ethers, siloxanes) including both saturated and unsaturated compounds with molecular weights ranging from 40 to 162 g · mol−1, for different inter‐electrode separations and from 2 to 50 W using an Impedans OctIV probe. Importantly, it is shown that the RF power transfer efficiency is dependent on the gas. The results show that the argon model results can be used to predict the plasma parameters for other gases when the RF power transfer efficiency is taken into account.

Zinc oxide (ZnO) grown on sapphire substrate using dual-plasma-enhanced metal organic vapor deposition (DPEMOCVD) and its application

This study reports the use of dual-plasma-enhanced metal organic chemical vapor deposition (DPEMOCVD) in forming low-temperature-grown zinc oxide (ZnO). The proposed method uses a direct voltage (DC)-driven capacitor-coupled electrodes and a radio-frequency (RF) plasma system. The DC plasma system enhances the dissociation of oxygen gas (O2), while the RF plasma system helps maintain the dissociated free radicals in the chamber. The optimum substrate temperature for undoped ZnO grown by DPEMOCVD system is 185°C, which yields the highest transmittance of 85%, and the lowest resistivity of 6.5×10−3Ωcm. The DPEMOCVD-deposited ZnO was used to the transparent conductive layer (TCL) of InGaN/GaN LED. As compared to the conventional InGaN/GaN light-emitting diode (LED), InGaN/GaN LED with DPEMOCVD-deposited ZnO TCL shows a lower turn-on voltage and higher light output intensity. This indicates that the DPEMOCVD-deposited ZnO can be the TCL for InGaN/GaN LEDs.

Oxygen plasma treatments of jute fibers in improving the mechanical properties of jute/HDPE composites

The surfaces of jute fabrics have been oxygen plasma treated using low frequency (LF) and radio frequency (RF) plasma systems at different plasma powers (30, 60, and 90 W) for 15 min to improve the mechanical properties of jute fiber/HDPE (high density polyethylene) composites. The effect of oxygen plasma treatment on the functional groups of jute fibers was examined by X-ray photoelectron spectroscopy (XPS) analysis. Effects of oxygen plasma treatments on the mechanical properties of jute fiber/HDPE composites were investigated by means of tensile, flexure, and short-beam shear tests. Surface morphology of the fractured surfaces of composites was observed by using scanning electron microscopy (SEM). When RF plasma system was used, the interlaminar shear strength (ILSS) values of the composites increased with increasing plasma power. Similarly, in LF plasma system, ILSS values showed a tendency to increase at plasma powers of 30 and 60 W. However, increasing of plasma power to 90 W decreased the ILSS value of jute/HDPE composite. Also, tensile and flexure strengths of the composites showed similar trends.

Study on the electrical and surface properties of polyester, polypropylene, and polyamide 6 using pen-type RF plasma treatment

The plasma treating process used to adjust the functional groups and modifying surface properties and mechanical behavior is a very important treatment method. Many researches have shown the results, especially in the versatility of polymer material fields. In this study, a pen-type radio frequency plasma system was used to modify the surface of various organic materials, such as polyester, polypropylene, and polyamide 6. Because of the short distance between two stainless steel electrodes, argon has been selected to trigger the plasma. The Taguchi method was used to decide the optimal combinations of the experimental parameters such as argon gas flow amount, plasma irradiation power and time, and the distance between the plasma torch and the organic fabric samples. The L9 orthogonal arrays were also used to analyze the nine combinations of samples and achieve the optimal results for improving the hydrophilic ability of polyester, polypropylene, and polyamide 6. Then, the analysis of three different types of conductive resin coating on the matrix and surface resistance of the polyester, the 50d fabric type, exhibited much higher conductive ability. After washing, the fabric treated with poly-3,4-ethylenedioxythiophene showed higher decent resistance. The experimental results found that the surface resistivity of the polyester fabric would improve by three orders and the contact angle, until reaching 180°.

Direct Synthesis of Yttrium Aluminum Garnet Particles in an Inductively Coupled Radio-Frequency Plasma System

Advanced phosphor materials such as cerium-doped yttrium aluminum garnet (YAG) are of interest for a variety of applications, including light-emitting diodes. Previous studies have shown that it is difficult to produce the desired YAG phase without ex-situ annealing irrespective of the synthesis technique used. This study focuses on direct synthesis of YAG phosphor particles using an inductively coupled thermal plasma system with a ceramic tube inserted coaxially into the chamber. Numerical modeling indicates that the tube provides a more uniform high-temperature region, without flow recirculation. This is hypothesized to aid in size and phase control through selective particle collection and in-flight annealing. Experiments conducted with the tube-insertion setup indicate that phase and size control of the particles is possible to a certain extent, depending on the size of the tube. Characterization results of the synthesized particles showed that submicron-sized YAG particles are synthesized as the majority phase through the tube-insertion setup.

Adhesion of functional layer on polymeric substrates for optoelectronic applications

The use of plastic film substrates for organic electronic devices promises to enable new applications, such as flexible displays. Plastic substrates have several distinct advantages, such as ruggedness, robustness, ultra lightness, conformability and impact resistance over glass substrates, which are primarily used in flat panel displays (FPDs) today. However, high transparency, proper surface roughness, low gas permeability and high transparent electrode conductivity of the plastic substrate are required for commercial applications. Polyesters, both amorphous and semicrystalline, are a promising class of commercial polymer for optoelectronic applications. Surface modification of polyester films was performed via chemical solution determining hydrolysis or oxidation. Hydrolysis was carried out by means of sodium hydroxide solution and oxidation by using standard clean 1 (SC-1) of RCA procedure [1]. For this work we have used commercial polymer films of 100µm in thickness: AryLite™ [2], supplied by Ferrania Imaging Technologies S.p.A. and characterised by very high glass transition temperature, Mylar™ (Polyethylene Terephthalate PET) and Teonex™ (Polyethylene Naphthalate PEN) both supplied by Dupont. More over, a bioriented and semicrystalline PET have been used. The aim of this study is modifying the polymer surface to improve the adhesion between organic-inorganic layer. It was found that the NaOH and SC-1 treatment cause a decrease of contact angles. In the present study we have deposited a thin films of amorphous hydrogenated silicon (a-Si:H) and its oxide (SiO2) on a new high temperature polymer substrate, AryLite™, by plasma enhanced chemical vapour deposition (PECVD) [3], with a radio frequency plasma system.

Electrical properties measurements on individual carbon nanofibers by scanning spreading resistance microscopy

Vertically aligned 850-nm-long carbon nanofibers (CNFs) are grown on a titanium nitride (TiN) layer by a radio-frequency plasma system at 560 °C. Electrical properties of individual CNFs are statistically determined by a current sensing atomic force microscopy mode. An interpretation based on electrical contact resistance model classically used to describe macroscopic observations, combined with a semiclassical approach commonly used for such nano-objects, is proposed here to explain dispersion in obtained values. Roughness of the TiN layer is responsible for this dispersion by varying contact surface between CNF and the TiN layer, while interface oxidation equally affects the transport by adding a barrier at the interface. Some CNFs exhibit very low resistances (few kilohms), implying that good contact is obtained between the nanofiber and the substrate, while others CNFs exhibit high resistance, attributed to local poor electrical contacts between CNFs and TiN layer.

Radio-frequency plasma system to selectively grow vertical field-aligned carbon nanofibers from a solid carbon source

Vertical field-aligned carbon nanofibers (CNFs), exhibiting a “herring-bone” and a “bamboo-like” structure, were grown at 560 °C using nickel (Ni) as a catalyst and an innovative radio-frequency (RF) plasma-enhanced chemical vapor deposition system. To limit the carbon supply, thereby providing a highly selective growth process with no detrimental parasitic carbon layer formation, a solid graphite sample-holder, RF-polarized, was used as a single carbon source in combination with a pure H 2 feed gas. The morphology and the dimensions of the obtained CNFs are investigated with respect to the growth duration. High-resolution transmission electron microscopy analyses typically display a Ni particle at the fiber tip, but this particle is not encapsulated by graphene layers, allowing its easy removal with a chemical acid treatment. Moreover, the particle’s upper surface consists of a peculiar polycrystalline area, assumed to be essential for the growth mechanisms and possibly made of nickel carbide. The crucial role played by the average vertical electric field, naturally created in the plasma sheath and responsible for sample-holder and substrate bombardment by cationic species, is highlighted to understand the growth mechanisms of these as-grown oriented CNFs and their progressive base destruction by etching phenomena.

Direct Conversion of Methane into Methanol and Formaldehyde in an RF Plasma Environment II: Effects of Experimental Parameters

ABSTRACTTo provide information on the conversion of methane in a non-catalyzed radio-frequency (RF) plasma system into valuable chemicals, such as HCHO, CH3OH, C2H6, C2H4 and C2H2, an experiment was conducted to convert methane directly into methanol and formaldehyde. The effects of experimental parameters—specific energy (power or flow variation) and CH4 and O2 feeding concentrations—were examined. Carbon-based by-products generated in a CH4/O2/Ar RF plasma system included CO, CO2, HCHO, CH3OH, C2H6, C2H4 and C2H2. The methane conversion ratio increased as the feeding concentration of O2 and the specific energy was increased, but decreased with feeding of CH4. Increasing power in the RF plasma system did not favor the partial oxidation of CH4 toward CH3OH and HCHO, but did favor the production of C2-hydrocarbons (C2H6, C2H4 and C2H2), CO, and CO2. The CH4 feeding concentration of under 15% or an O2 content of under 10% favored the formation of CH3OH and HCHO. CO concentration decreased as the feeding concentration of CH4 increased, and increased as the feeding concentration of O2 increased. The yield of CH3OH was less than 1%. No carbon black or deposition was observed. Further research will seek to increase the yield of CH3OH and HCHO by adding catalysts to the system.

Direct Conversion of Methane into Methanol and Formaldehyde in an RF Plasma Environment I: A Preliminary Study

The direct conversion of methane (CH4) into methanol (CH3OH) and HCHO in an Argon (Ar) 50W radio-frequency plasma system was applied and the effects of various feed compositions, CH4/O2 ratio, and plasma discharge areas were compared. Additionally, the effects of various methane to oxygen ratios and plasma discharge areas were studied. It was found that in an Ar stream, the CH3OH conversion ratio in the CH4/O2 plasma system was higher than that in CH4/CO, CO/H2 and CH4/H2/O2 plasma systems. The conversion of CH4 reached 19.1% at CH4/O2 = 40/60; the yield of CH3OH was 1.12% and 16.0% CO, the major product, was produced. A larger plasma discharge area, resulting in a longer residence time, corresponded to higher CH4 conversion, but a lower CH3OH conversion ratio, because of further decomposition into CO and CO2. Interestingly, no carbon deposition was observed in the RF plasma system, and the carbon balance was between 0.94 and 1.19.

Effects of experimental parameters on NF 3 decomposition fraction in an oxygen-based RF plasma environment

Clean procedure is one of the major emitters of perfluorinated compounds (PFCs) in semiconductor manufacturing. Nitrogen trifluoride (NF 3) is increasingly the process gas of choice for eliminating PFC emissions. However, its toxic to human and similar global warming potential compared to most other PFCs made NF 3 warranted much more investigation. This study demonstrated a radio-frequency plasma system for decomposing NF 3. The effects of experimental parameters: input power, O 2/NF 3 ratio, operational pressure and NF 3 feeding concentration on NF 3 decomposition fraction ( η NF 3 ) and energy efficiency ( E NF 3 ) were examined in detail. The analytical results demonstrated that the NF 3 was almost completely decomposed (>99%) at input power = 30 W, [NF 3] in = 1.0% and η NF 3 increased with input power. However, adding O 2 to the system inhibited NF 3 decomposition and decreased E NF 3 . Moreover, η NF 3 and E NF 3 decreased with gradually increasing operational pressure. Notably, increasing the NF 3 feeding concentration increased molecule density, reducing η NF 3 , but increasing E NF 3 . Furthermore, the products detected in the NF 3/O 2/Ar plasma system were NO 2, NO, N 2O, SiF 4, N 2 and F 2. Potential reaction pathways in the oxygen-based NF 3 plasma environment were built-up and elucidated.