Plasma Gas Species Research Articles

Influence of Controlling Plasma Gas Species and Temperature on Reactive Species and Bactericidal Effect of the Plasma

In this study, plasma gas species and temperature were varied to evaluate the reactive species produced and the bactericidal effect of plasma. Nitrogen, carbon dioxide, oxygen, and argon were used as the gas species, and the gas temperature of each plasma was varied from 30 to 90 °C. Singlet oxygen, OH radicals, hydrogen peroxide, and ozone generated by the plasma were trapped in a liquid, and then measured. Nitrogen plasma produced up to 172 µM of the OH radical, which was higher than that of the other plasmas. In carbon dioxide plasma, the concentration of singlet oxygen increased from 77 to 812 µM, as the plasma gas temperature increased from 30 to 90 °C. The bactericidal effect of carbon dioxide and nitrogen plasma was evaluated using bactericidal ability, which indicated the log reduction per minute. In carbon dioxide plasma, the bactericidal ability increased from 5.6 to 38.8, as the temperature of the plasma gas increased from 30 to 90 °C. Conversely, nitrogen plasma did not exhibit a high bactericidal effect. These results demonstrate that the plasma gas type and temperature have a significant influence on the reactive species produced and the bactericidal effect of plasma.

Plasma Gas Temperature Control Performance of Metal 3D-Printed Multi-Gas Temperature-Controllable Plasma Jet

The aim of the study was to design and build a multi-gas temperature-controllable plasma jet that can control the gas temperature of plasmas with various gas species, and evaluated its temperature control performance. In this device, a fluid at an arbitrary controlled temperature is circulated through the plasma jet body. The gas exchanges heat with the plasma jet body to control the plasma temperature. Based on this concept, a complex-shaped plasma jet with two channels in the plasma jet body, a temperature control fluid (TCF) channel, and a gas channel was designed. The temperature control performance of nitrogen gas was evaluated using computational fluid dynamics analysis, which found that the gas temperature changed proportionally to the TCF temperature. The designed plasma jet body was fabricated using metal 3D-printer technology. Using the fabricated plasma jet body, stable plasmas of argon, oxygen, carbon dioxide, and nitrogen were generated. By varying the plasma jet body temperature from −30 °C to 90 °C, the gas temperature was successfully controlled linearly in the range of 29–85 °C for all plasma gas species. This is expected to further expand the range of applications of atmospheric low temperature plasma and to improve the plasma treatment effect.

Effect of the chamber wall on fluorocarbon-assisted atomic layer etching of SiO2 using cyclic Ar/C4F8 plasma

The authors studied the effect of the temperature and chemical state of the chamber wall on process performance for atomic layer etching of SiO2 using a steady-state Ar plasma, periodic injection of a defined number of C4F8 molecules, and synchronized plasma-based Ar+ ion bombardment. To evaluate these effects, the authors measured the quartz coupling window temperature. The plasma gas phase chemistry was characterized using optical emission spectroscopy. It was found that although the thickness of the polymer film deposited in each cycle is constant, the etching behavior changed, which is likely related to a change in the plasma gas phase chemistry. The authors found that the main gas phase changes occur after C4F8 injection. The C4F8 and the quartz window react and generate SiF and CO. The emission intensity changes with wall surface state and temperature. Therefore, changes in the plasma gas species generation can lead to a shift in etching performance during processing. During initial cycles, minimal etching is observed, while etching gradually increases with cycle number.

A compact lithium pellet injector for tokamak pedestal studies in ASDEX Upgrade

Experiments have been performed at ASDEX Upgrade, aiming to investigate the impact of lithium in an all-metal-wall tokamak and attempting to enhance the pedestal operational space. For this purpose, a lithium pellet injector has been developed, capable of injecting pellets carrying a particle content ranging from 1.82 × 10(19) atoms (0.21 mg) to 1.64 × 10(20) atoms (1.89 mg). The maximum repetition rate is about 2 Hz. Free flight launch from the torus outboard side without a guiding tube was realized. In such a configuration, angular dispersion and speed scatter are low, and a transfer efficiency exceeding 90% was achieved in the test bed. Pellets are accelerated in a gas gun; hence special care was taken to avoid deleterious effects by the propellant gas pulse. Therefore, the main plasma gas species was applied as propellant gas, leading to speeds ranging from 420 m/s to 700 m/s. In order to minimize the residual amount of gas to be introduced into the plasma vessel, a large expansion volume equipped with a cryopump was added into the flight path. In view of the experiments, an optimal propellant gas pressure of 50 bars was chosen for operation, since at this pressure maximum efficiency and low propellant gas flux coincide. This led to pellet speeds of 585 m/s ± 32 m/s. Lithium injection has been achieved at ASDEX Upgrade, showing deep pellet penetration into the plasma, though pedestal broadening has not been observed yet.

Surface Hydrophilization of Polyimide Films Using Atmospheric Damage-Free Multigas Plasma Jet Source

Atmospheric-pressure plasma jet sources have proven useful for surface treatments; however, conventional plasma and near-plasma sources have limitations in the number of different plasma gas species that they can handle. We previously developed a damage-free multigas plasma jet source that can generate stable atmospheric-pressure plasma using various gas species without thermal/electrical discharge damage. Herein, we investigate the fundamental characteristics of the generated plasma such as gas temperature (<;57°C) and emission properties. In addition, we evaluate the industrial potential of the jet source by using it with various gas species to induce surface hydrophilization in a polyimide film. The jet source proved useful, and carbon dioxide proved the most effective of the studied gas species for the purpose with the hydrophilized surface maintaining a contact angle of about 30° for over 32 days after plasma irradiation.

Crystallization of ITO and TiO2 by RF plasma treatment

The crystallization of amorphous thin films was achieved with using a novel technology in which 13.56 MHz RF (radio frequency) plasma is applied to the film samples for few minutes without heating. The key parameter of this plasma crystallization process is the plasma gas pressure. The best plasma gas pressure depends on the plasma gas species and applied RF power and is independent to film materials and substrate materials. Easiness of plasma crystallization of ITO (Indium Tin Oxide) and TiO2 films was found to depend on the film preparation conditions and to correlate with Hall mobility. The experimental results suggest that the excitation process in crystallization on plasma treatment should be different from that on heat treatment.

Anatase TiO2 Films Crystallized by RF Plasma Treatment

Anatase-phase TiO2 films were prepared from amorphous TiO2 films with using a novel crystallization technology in which 13.56 MHz rf (radio frequency) plasma is applied to the film samples for few minutes without heating. The obtained anatase TiO2 films have almost the same photocatalytic degradation activity as that of the thermally-crystallized anatase TiO2 films. Although the key parameter of this plasma crystallization process is the plasma gas pressure, the best plasma gas pressure depends on the plasma gas species and applied rf power and is independent to film materials nor substrate materials. Experimental results strongly suggest that the plasma crystallization is realized by the application of alternating rf electric field into the film materials. Easiness of plasma crystallization of TiO2 films is found to depend on the film preparation conditions and this relation between crystallization easiness and preparation condition is different from the relation in the heat crystallization.

Surface characterization of hydrophilic coating obtained by low‐pressure CH4O2 plasma treatment on a polypropylene film

AbstractThe use of surface treatments at industrial level is generalized as they allow obtaining a wide variety of properties such as soft in the touch, hydrophilic behavior, and biocompatibility. The use of low‐pressure plasma techniques with organic gases or organic mixtures is an easy way to obtain surface coatings very small in depth through plasma‐polymerization processes that can be assimilated to a plasma‐enhanced chemical vapor deposition (PECVD) process. In this work, we have carried out a plasma‐polymerization process on a polypropylene (PP) film to obtain a hydrophilic coating. To obtain this, the film surface has been treated on a low‐pressure plasma reactor with a methane–oxygen mixture gas with a volume ratio of 80 : 20, respectively. The chemistry changes in the outermost layers of the deposited coating have been investigated with X‐ray photoelectron spectroscopy (XPS). The different processes that take part as a consequence of the interaction between the plasma gas species and the PP film surface mainly drive to the deposition of an organic layer, which is functionalized with oxygen‐based species as XPS study reveals. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Room-temperature crystallization of amorphous films by RF plasma treatment

The crystallization of amorphous thin films was achieved by 13.56 MHz RF (radio frequency) plasma treatment. This crystallization process has a strong advantage that the sample temperature is lower than 120 °C during the plasma treatment even without compulsory cooling and various amorphous films are crystallized after 2 min or so. This treatment works on amorphous films of various materials, independently of the film preparation method and substrate materials. Crystallization has been confirmed on amorphous thin films of sputtered ITO (tin doped indium oxide) deposited on soda-lime glass and PET (polyethylene terephthalate), of sputtered TiO 2 on soda-lime glass, of sol–gel derived TiO 2 on silicon wafer and of sputtered hydrogen-doped silicon on soda-lime glass. The plasma gas pressure was found to be the key parameter in the plasma crystallization process. The appropriate gas pressure depends on the plasma gas species and not on film or substrate materials. A Cu electrode, attached to the backside of the substrate and is electrically floated from the electric ground, was found to enhance the plasma crystallization performance.

Studies on x-ray and UV emissions in electron cyclotron resonance x-ray source

A novel electron cyclotron resonance x-ray source is constructed based on the ECR technique. In this paper, the possibility of using the ECR x-ray source for producing UV rays by optimizing the plasma parameters is explored. X-ray and UV emissions from the ECR x-ray source are carried out for argon, nitrogen, and CO(2) plasma. The x-ray spectral and dose measurements are carried with NaI(Tl) based spectrometer and dosimeter, respectively. For UV measurement, a quartz window arrangement is made at the exit port and the UV intensity is measured at 5 cm from the quartz plate using UV meter. The x-ray and UV emissions are carried out for different microwave power levels and gas pressures. The x-ray emission is observed in the pressure range < or =10(-5) Torr, whereas the UV emission is found to be negligible for the gas pressures <10(-5) Torr and it starts increasing in the pressure range between 10(-5) and 10(-3) Torr. At high-pressure range, collision frequency of electron-atom is large which leads to the higher UV flux. At low pressure, the electron-atom collision frequency is low and hence the electrons reach high energy and by hitting the cavity wall produces higher x-ray flux. By choosing proper experimental conditions and plasma gas species, the same source can be used as either an x-ray source or an UV source.

Room temperature crystallization of indium tin oxide films on glass and polyethylene terephthalate substrates using rf plasma

The crystallization of amorphous indium tin oxide (ITO) films was achieved by rf (13.56MHz) plasma treatment. Although the films were crystallized after 2min, the sample temperature was lower than 90°C without compulsory cooling even after 10min of treatment and polyethylene terephthalate (PET) substrates had no damage. Plasma-crystallized sputtered ITO films have a bixbite structure and the resistivity reached to 1.6×10−4Ω∙cm. ITO thin films have almost the same resistivity in both cases of PET and glass substrates used and plasma-treated PET ITO films have a bit higher resistivity than that of glass ITO films, while mass spectroscopy measurements indicated that ITO films deposited on PET substrates are expected to include no apparent gas species ejected from PET substrate. It was found that the plasma gas pressure is the key parameter for the effective crystallization and the appropriate gas pressure depends on the plasma gas species.

Sampling modulation technique in radio-frequency helium glow discharge emission source by use of pulsed laser ablation.

An emission excitation source comprising a high-frequency diode-pumped Q-switched Nd:YAG laser and a radio-frequency powered glow discharge lamp is proposed. In this system sample atoms ablated by the laser irradiation are introduced into the lamp chamber and subsequently excited by the helium glow discharge plasma. The pulsed operation of the laser can produce a cyclic variation in the emission intensities of the sample atoms whereas the plasma gas species emit the radiation continuously. The salient feature of the proposed technique is the selective detection of the laser modulation signal from the rest of the continuous background emissions, which can be achieved with the phase sensitive detection of the lock-in amplifier. The arrangement may be used to estimate the emission intensity of the laser ablated atom, free from the interference of other species present in the plasma. The experiments were conducted with a 13.56 MHz radio-frequency (rf) generator operated at 80 W power to produce plasma and the laser at a wavelength of 1064 nm (pulse duration:34 ns, repetition rate:7 kHz and average pulse energy of about 0.36 mJ) was employed for sample ablation. The measurements resulted in almost complete removal of nitrogen molecular bands (N(2)(+) 391.44 nm). Considerable reduction (about 75%) in the emission intensity of a carbon atomic line (C I 193.03 nm) was also observed.

The influence of plasma gas species on the adhesion of thermoplastic to organic fibers

AbstractAdhesion between organic fibers and thermoplastics in a composite material is usually weak because of the lack of chemical and mechanical bonding. This study investigated the influence of plasma gas species in a novel technique to improve interfacial adhesion of Kevlar 49 fibers to polycarbonate. Single Kevlar fibers were exposed to radio‐frequency plasma discharge in atmospheres of argon, oxygen, and ammonia. Plasma treatment has been shown to generate reactive free radicals on polymer surfaces. The fibers that were coated immediately with a polycarbonate melt while still in the vacuum environment of a plasma reactor showed an increase in interfacial shear strength that was maximum at 4.1 s exposure and decreased at longer exposure times. At 4.1 s exposure, Ar and O2 plasma treatment increased shear strength by 20 and 18%, respectively. NH3 plasma treatment produced only a statistically insignificant increase at 4.1 s of exposure and a significant decrease in adhesion at 8.3 s of exposure. Fibers that were exposed to air for 1 h before coating showed no statistically significant increase or decrease in adhesion. The increase in adhesion of the directly coated fibers was attributed to free radical‐initiated formation of covalent bonds between the Kevlar and the polycarbonate. © 1993 John Wiley &amp; Sons, Inc.

Physical properties of a planar magnetron glow discharge

Continued work with a planar magnetron glow discharge plasma device which uses permanent magnets located behind a planar cathode to trap plasma electrons in circular orbits parallel to the cathode surface is described. This results in a significant reduction in plasma voltage, and stable operation is achieved over an extended range of pressures and cathode current densities. The plasma has the form of a ring extending from the cathode surface to several millimeters from the surface. The plasma geometry is determined by the locus of greatest magnetic field strength. Cathode current density values greater than 100 mA cm 2 are easily achieved for pressures in the range 0.0007 Torr (0.093 Pa) to over 2.5 Torr (330 Pa). Over this range, the plasma voltage is under 500 V. Spatially-resolved emission spectral data are presented showing the effects of plasma current and pressure on line intensities from plasma gas species as well as from cathodically-sputtered species. Data are presented for a pure Cu cathode and for a Zn-based alloy used as a standard reference material.

Spectrometric studies of excitation mechanisms on singly-ionized copperemission lines in Grimm-type glow discharge plasmas with helium mixture technique

Excitation mechanisms of copper ionic emission lines were investigated in Grimm-type discharge plasmas. Addition of He to the Ar or Ne plasma gas was used to study the plasma characteristics. It was concluded that the excitations can be principally attributed to (resonance) charge transfer reactions between Cu atoms and plasma gas species.