Generation Of Atmospheric Pressure Plasma Research Articles

Antibacterial Evaluation of Zirconia Coated with Plasma-Based Graphene Oxide with Photothermal Properties.

The alternative antibacterial treatment photothermal therapy (PTT) significantly affects oral microbiota inactivation. In this work, graphene with photothermal properties was coated on a zirconia surface using atmospheric pressure plasma, and then the antibacterial properties against oral bacteria were evaluated. For the graphene oxide coating on the zirconia specimens, an atmospheric pressure plasma generator (PGS-300, Expantech, Suwon, Republic of Korea) was used, and an Ar/CH4 gas mixture was coated on a zirconia specimen at a power of 240 W and a rate of 10 L/min. In the physiological property test, the surface properties were evaluated by measuring the surface shape of the zirconia specimen coated with graphene oxide, as well as the chemical composition and contact angle of the surface. In the biological experiment, the degree of adhesion of Streptococcus mutans (S. mutans) and Porphyromonas gingivalis (P. gingivalis) was determined by crystal violet assay and live/dead staining. All statistical analyzes were performed using SPSS 21.0 (SPSS Inc., Chicago, IL, USA). The group in which the zirconia specimen coated with graphene oxide was irradiated with near-infrared rays demonstrated a significant reduction in the adhesion of S. mutans and P. gingivalis compared with the group not irradiated. The oral microbiota inactivation was reduced by the photothermal effect on the zirconia coated with graphene oxide, exhibiting photothermal properties.

Electron dynamics and metastable species generation in atmospheric pressure non-equilibrium plasmas controlled by dual LF–RF frequency discharges

In this work, we report an approach to control electron dynamics and metastable species generation and enhance the density of atmospheric pressure non-equilibrium plasmas by using dual-frequency excitation sources. The atmospheric dielectric barrier discharge (DBD) of an α-mode radio frequency (RF = 5 MHz) discharge controlled by a low-frequency (LF = 50 kHz) bias is studied based on a one-dimensional (1D) fluid model. Results show that the variation in amplitude ratio of RF and LF modulates the electron dynamic process, resulting in different spatial distributions of electron and metastable particle densities. Moreover, it is further shown that the electron density is substantially increased when the LF component voltage amplitude is larger than 300 V for the initial setting. The discharge process is characterized by fast Fourier transform of the spatio-temporal evolution of the electron power absorption and discharge current. As the LF is applied, three-wave interactions induced by LF and RF coupling are clearly observed, where the sum and beat frequencies between LF and RF are increased, which results in a substantial increase in the electron density. On the other hand, the high RF harmonics, especially for the fundamental and the third harmonic components, are suppressed when increasing the LF component. This work demonstrates that dual-frequency excitation is efficacious to modulate the electron dynamic behaviors and metastable species generation of atmospheric pressure plasma, which can provide a possible approach of optimizing plasma parameters.

Hybrid atmospheric pressure plasma generation and DC electrospray aerosolization of plasma‐activated water for surface pathogen disinfection

AbstractWe demonstrate the synergistic effects of combining atmospheric pressure plasma generation together with aerosolization of the resultant plasma‐activated water using direct current electrospraying for effective chemical‐free spray‐based surface disinfection. Besides facilitating the efficient aerosol generation of the atmospheric pressure plasma pretreated water, the DC electrospray itself also constitutes a secondary plasma generation source that can further enhance the plasma‐activation of water to result in a further increase in the concentration of reactive species in the aerosols. This, in turn, can be seen to translate into an enhancement in bacteria inactivation efficacy. Additionally, we show that pretreating stainless steel surfaces using this hybrid spray‐deposition technique before pathogen exposure leads to almost complete inactivation of the bacteria colonies.

Plasma and Superconductivity for the Sustainable Development of Energy and the Environment

The main aim of this review is to present the current state of the research and applications of superconductivity and plasma technologies in the field of energy and environmental protection. An additional goal is to attract the attention of specialists, university students and readers interested in the state of energy and the natural environment and in how to protect them and ensure their sustainable development. Modern energy systems and the natural environment do not develop in a sustainable manner, thus providing future generations with access to energy that is generated from renewable sources and that does not degrade the natural environment. Most of the energy technologies used today are based on non-renewable sources. Power contained in fuel is irretrievably lost, and the quality of the energy is lowered. It is accompanied by the emissions of fossil fuel combustion products into the atmosphere, which pollutes the natural environment. Environmental problems, such as the production of gaseous and solid pollutants and their emission into the atmosphere, climate change, ozone depletion and acid rains, are discussed. For the problem of air pollution, the effects of combustion products in the form of carbon oxides, sulfur and nitrogen compounds are analyzed. The plasma and superconductivity phenomena, as well as their most important parameters, properties and classifications, are reviewed. In the case of atmospheric pressure plasma generation, basic information about technological gas composition, pressure, discharge type, electromagnetic field specification, electrode geometry, voltage supply systems, etc., are presented. For the phenomenon of superconductivity, attention is mainly paid to the interdependencies between Tc, magnetic flux density Bc and current density Jc parameters. Plasma technologies and superconductivity can offer innovative and energy-saving solutions for power engineering and environmental problems through decreasing the effects of energy production, conversion and distribution for the environment and by reductions in power losses and counteracting energy quality degradation. This paper presents an overview of the application of technologies using plasma and superconductivity phenomena in power engineering and in environmental protection processes. This review of plasma technologies, related to reductions in greenhouse gas emissions and the transformation and valorization of industrial waste for applications in energy and environmental engineering, is carried out. In particular, the most plasma-based approaches for carbon oxides, sulfur and nitrogen compounds removal are discussed. The most common plasma reactors used in fuel reforming technologies, such as dielectric barrier discharge, microwave discharge and gliding-arc discharge, are described. The advantages of solid waste treatment using plasma arc techniques are introduced. Applications of superconductors for energy generation, conversion and transmission can be divided into two main groups with respect to the conducted current (DC and AC) and into three groups with respect to the employed property (zero resistivity, ideal magnetism/flux trapping and quench transition). Among the superconductivity applications of electrical machines, devices for improving energy quality and storage and high field generation are described. An example that combines the phenomena of hot plasma and superconductivity is thermonuclear fusion. It is a hope for solving the world’s energy problems and for creating a virtually inexhaustible, sustainable and waste-free source of energy for many future generations.

Direct-Deposited Graphene Oxide on Dental Implants for Antimicrobial Activities and Osteogenesis

ObjectiveTo determine the effects of graphene oxide (GO) deposition (on a zirconia surface) on bacterial adhesion and osteoblast activation.MethodsAn atmospheric pressure plasma generator (PGS-300) was used to coat Ar/CH4 mixed gas onto zirconia specimens (15-mm diameter × 2.5-mm thick disks) at a rate of 10 L/min and 240 V. Zirconia specimens were divided into two groups: uncoated (control; Zr) group and GO-coated (Zr-GO) group. Surface characteristics and element structures of each specimen were evaluated by field emission scanning electron microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and contact angle. Additionally, crystal violet staining was performed to assess the adhesion of Streptococcus mutans. WST-8 and ALP (Alkaline phosphatase) assays were conducted to evaluate MC3T3-E1 osteoblast adhesion, proliferation, and differentiation. Statistical analysis was calculated by the Mann–Whitney U-test.ResultsFE–SEM and Raman spectroscopy demonstrated effective GO deposition on the zirconia surface in Zr-GO. The attachment and biofilm formation of S. mutans was significantly reduced in Zr-GO compared with that of Zr (P < 0.05). While no significant differences in cell attachment of MC3T3-1 were observed, both proliferation and differentiation were increased in Zr-GO as compared with that of Zr (P < 0.05).SignificanceGO-coated zirconia inhibited the attachment of S. mutans and stimulated proliferation and differentiation of osteoblasts. Therefore, GO-coated zirconia can prevent peri-implantitis by inhibiting bacterial adhesion. Moreover, its osteogenic ability can increase bone adhesion and success rate of implants.

Steering of surface discharges on through-glass-vias combined with high-density nonequilibrium atmospheric pressure plasma generation

The concept of using a glass substrate with fine through-holes filled with metal, called through-glass-vias (TGVs), for an inner wall of an enclosure of a nonequilibrium atmospheric pressure plasma source was validated to extend its processing area with high plasma densities maintained. When applying the TGV substrate into an inner wall of the plasma source, the generated discharge was less likely to drift along with the gas flow, which resembled the behavior of locally high electric fields of the plasma source, called the creeping mode. The decrease in breakdown voltage was also observed. These phenomena are caused by the TGV areas acting as a steering control material in the enclosure of the plasma source. The location of the TGV areas affected the behavior of the generated plasma. The shape of the plasma was accomplished to arbitrarily and locally control by the placement of TGVs.

Effective generation of atmospheric pressure plasma in a sandwich-type honeycomb monolith reactor by humidity control

Large-volume atmospheric-pressure plasma based on corona discharge was successfully generated in a sandwich-type plasma reactor by controlling the humidity of the feed gas. The reactor comprised a 5-cm-high and 9-cm-wide commercial honeycomb monolith and two perforated stainless-steel disk electrodes with 3-mm holes, which covered up both sides of the monolith. The high-voltage applied disk electrode was placed 2 ~ 6 mm away from the monolith, whereas the counter ground electrode typically touched it. The characteristics of air plasma such as power delivery, breakdown voltage, current, and impedance were found to strongly depend on the water vapor content in the feed gas as well as in the monolith, exhibiting an exponential increase of discharge power with increasing the humidity. The discharge characteristics also depended on the gas flow rate and the electrode-monolith distance. Better discharge performance was observed as the electrode was closer to the monolith, and as the air flow rate was higher. Discharge power above 30 W was achieved under the condition of gas flow rate 75 L/min, applied voltage 25 kV, and humidity 2.1%(v/v) when the high-voltage electrode was 2 mm away from the monolith, and the ground electrode kept up against it. The air plasma produced reactive species, being demonstrated by the formation of ozone at several tens of ppm, depending on specific energy input. The plasma source has potential applications in the abatements of odor, organic compounds, and NOx with high throughputs.

Hydrophilicity Improvement of Quartz Glass Surface by a Large-Area Atmospheric Pressure Plasma Generator

In this article, experimental study of a device combining the advantages of dielectric barrier discharge (DBD) and atmospheric pressure plasma jet (APPJ) has been presented. This device with a total length of 500 mm was capable of generating stable uniform atmospheric pressure plasma (APP) with a length of 400 mm, which was operated using a 12-kV HV supply and the air flow rate of 20–30 L/min. The plasma spectra were obtained by optical emission spectroscopy (OES), in which N2(C-B) and N2+ can be observed, and the rotational temperature was calculated to be 360 K. The macroscopic temperature was measured by an infrared camera. The result showed that the central temperature was room temperature. In addition, quartz glass substrates were treated by this device. The surface properties of quartz glass were investigated by water contact angle (WCA), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The results revealed that hydrophilicity and surface roughness of the quartz substrates were gradually increased with increasing treatment time. However, the results of XPS indicated that the content of hydrophilic groups at the surface had a slight change. Therefore, hydrophilicity of quartz glass improved effectively after APP treatment, which was due to the change in surface morphology and the increase in roughness.

Weibull analysis of atmospheric pressure plasma generation and evidence for field emission in microwave split-ring resonators

The generation of atmospheric pressure microplasmas using microwave resonators is promising for many applications due to the possibility of high electron densities and low electrode degradation. In particular, such plasmas may help enable reconfigurable metamaterials operating from GHz to THz. Since plasma metamaterials may require the generation of tens to hundreds of plasmas, it is important to find ways to reduce the power required for plasma breakdown. Here, we study gold and silver microwave split-ring resonators (SRRs) with a variety of materials near the interelectrode gap (Cu, CuO nanowires, aluminum oxide). We focus on those fabricated using a traditional thick film technique, screen-printing, and using fs- and ns-laser ablation. The use of laser ablation allows us to explore small interelectrode gap sizes (7–100 μm) and the use of different lasers and laser parameters enables us to produce a variety of microstructures. We utilize Weibull statistics to examine breakdown in atmospheric pressure Ar with and without deep ultraviolet illumination of SRRs. Fabrication methods and materials are shown to influence both Q-factor of the SRRs and breakdown voltage independently. It is found that superior performance in terms of breakdown voltage and consistency in breakdown is related to Weibull modulus. The power requirement for breakdown varied as widely as an order of magnitude depending on fabrication method and material used for the SRRs. Furthermore, we consider the performance differences seen between various resonators and relate this to microstructure/material which suggests that field-emission may play a role in providing the seed electrons required for breakdown. This need for seed electrons appears to be especially important for gap sizes of 40 μm and smaller.

Generation of atmospheric pressure plasma in molecular gas flows

We have investigated an atmospheric pressure discharge, similar to a plasma jet, in the N2 and CO2 gas flows. We have also carried out an experimental modeling with the argon Ar flow. It has been shown that the use of a tantalum cathode and a copper anode provides a stable discharge in the nitrogen and carbon dioxide flows. We have studied the dependence of the discharge voltage on the discharge current (VAC). Optical emission spectra of discharge glow was investigated also. Using a single probe and a thermocouple, we have studied the axial distribution of the floating potential in the plasma jet and the gas temperature at the anode nozzle exit of the plasma generator. In applying to polymer surface modification, we have determined the optimal operation conditions: gas flow rate up to 5 l·min−1; continuous or pulsed working regime; discharge current about 80 mA; pulse duration up to 10 µs; pulse repetition rate 50 kHz.

Development and characterization of an atmospheric pressure plasma reactor compatible with spatial ALD

Dielectric Barrier Discharges (DBD) are widely used for atmospheric pressure plasma generation. The possibility of their adaptation in custom-made configurations makes them potential candidate to assist deposition processes. In fact, the increased need of high-quality thin films forces to improve the deposition techniques. New processes should be able to work in less constrained conditions such as atmospheric pressure rather than vacuum and to have faster deposition rates while respecting the same high quality of the deposited films. In this paper we present the development of a surface dielectric barrier discharge plasma reactor to assist an atmospheric spatial atomic layer deposition process. The reactor was fabricated with 3D printing and the plasma was generated by a surface dielectric barrier discharge powered by a microsecond pulsed high voltage power supply. The dissipated power was measured for different configurations, and thanks to the micro discharges imaging, it was observed that the thickness and the shape of the dielectric barrier influenced the micro discharges distribution on the dielectric surface. The plasma reactor exhaust gas was chemically analyzed by FTIR spectroscopy and micro gas chromatography. The ozone concentration was determined as function of frequency of the power supply.

Inactivation Efficacy of a Non-thermal Atmospheric Pressure Plasma Generator against Mycobacterium tuberculosis

Inactivation Efficacy of a Non-thermal Atmospheric Pressure Plasma Generator against <i>Mycobacterium tuberculosis</i>

High-voltage electrode optimization towards uniform surface treatment by a pulsed volume discharge

In this study, the shape and material of the high-voltage electrode of an atmospheric pressure plasma generation system were optimised. The research was performed with the goal of achieving maximum uniformity of plasma treatment of the surface of the low-voltage electrode with a diameter of 100 mm. In order to generate low-temperature plasma with the volume of roughly 1 cubic decimetre, a pulsed volume discharge was used initiated with a corona discharge. The uniformity of the plasma in the region of the low-voltage electrode was assessed using a system for measuring the distribution of discharge current density. The system's low-voltage electrode - collector - was a disc of 100 mm in diameter, the conducting surface of which was divided into 64 radially located segments of equal surface area. The current at each segment was registered by a high-speed measuring system controlled by an ARM™-based 32-bit microcontroller. To facilitate the interpretation of results obtained, a computer program was developed to visualise the results. The program provides a 3D image of the current density distribution on the surface of the low-voltage electrode. Based on the results obtained an optimum shape for a high-voltage electrode was determined. Uniformity of the distribution of discharge current density in relation to distance between electrodes was studied. It was proven that the level of non-uniformity of current density distribution depends on the size of the gap between electrodes. Experiments indicated that it is advantageous to use graphite felt VGN-6 (Russian abbreviation) as the material of the high-voltage electrode's emitting surface.

Optimization Design of Atmospheric Pressure Plasma Generator for Sterilization of Endoscope

Endoscopy is an important tool that can be used to identify and treat diseases and is essential to avoid cross infection when used on different people. Cold atmospheric-pressure plasmas (CAPs) offer the prospect of a future basic technology for decontaminating and sterilizing of endoscope. In this paper, we intend to design an endoscope sterilization device based on CAPs. The various lengths of gap between electrodes and electrodes themselves are considered, and the plasma distribution and its evolution are investigated.

Optimizing the electrical excitation of an atmospheric pressure plasma advanced oxidation process

The impact of pulse-modulated generation of atmospheric pressure plasma on the efficiency of organic dye degradation has been investigated. Aqueous samples of methyl orange were exposed to low temperature air plasma and the degradation efficiency was determined by absorbance spectroscopy. The plasma was driven at a constant frequency of 35kHz with a duty cycle of 25%, 50%, 75% and 100%. Relative concentrations of dissolved nitrogen oxides, pH, conductivity and the time evolution of gas phase ozone were measured to identify key parameters responsible for the changes observed in degradation efficiency. The results indicate that pulse modulation significantly improved dye degradation efficiency, with a plasma pulsed at 25% duty showing a two-fold enhancement. Additionally, pulse modulation led to a reduction in the amount of nitrate contamination added to the solution by the plasma. The results clearly demonstrate that optimization of the electrical excitation of the plasma can enhance both degradation efficiency and the final water quality.

Observations of ionic species produced in an atmospheric pressure pulse-modulated RF plasma needle

Pulse-modulated generation of atmospheric pressure plasma promises lower operating temperatures and enhanced energy efficiencies compared with those generated using continuous excitation. In this study, the effect of pulse modulation on the ionic content of a radio-frequency helium plasma needle was explored using molecular beam mass spectrometry (MBMS). In all cases reported the pulse repetition frequency was held constant at 6 kHz while the duty cycle and distance between the plasma needle and MBMS were varied from 30% to 90% and 4 mm to 10 mm, respectively. Decreasing the duty cycle was seen to enhance the negative ion flux to the MBMS and yields a clear shift to higher masses for positive ion species. Time-resolved ion intensity measurements (5 µs resolution) demonstrated that negative ions were created almost exclusively in the pulse off-time while positive ions were generated mainly in the on-time. The ions detected were also seen to change as the distance between the sampling orifice and tip of the plasma needle increased, highlighting the effect of different ion mobilities in the flowing gas stream and the presence of an extended cooler afterglow region. The results suggest that there is a possibility of tailoring the ionic plasma chemistry through pulsed modulation, increasing the versatility of the already widely studied plasma needle device.

Stripping Photo-Resist with RF Dielectric Barrier Atmospheric Pressure Plasma

A novel radio frequency single-dielectric-barrier-discharge atmospheric pressure plasma generator was designed and utilized to strip AZ9912 photo-resist (PR). Argon (Ar) and oxygen (O2) were employed as the working gases under atmospheric pressure in ambient air. The PR stripping rate was measured as functions of time, input power, and the flow rates of the oxygen/argon. Optical Emission Spectroscopy (OES) was used to measure the optical emission spectra of the plasma to study the mechanism of PR stripping process. It is presumable that C-H bands were broken by high energy electron in the plasma and OH was generated in the process with the participation of O atom. Optical Microscope, Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM) were used to measure the surface of the silicon substrate after the stripping. It is proved that this kind of novel device could strip the AZ9912 PR effectively as high as 850nm/min, without residues and ion bombardment damage on the wafer substrate.

Generation of Atmospheric Pressure Plasma by Repetitive Nanosecond Pulses in Air Using Water Electrodes

Dielectric barrier discharge (DBD) excitated by pulsed power is a promising method for producing nonthermal plasma at atmospheric pressure. Discharge characteristic in a DBD with salt water as electrodes by a home-made unipolar nanosecond-pulse power source is presented in this paper. The generator is capable of providing repetitive pulses with the voltage up to 30 kV and duration of 70 ns at a 300 Ω resistive load. Applied voltage and discharge current are measured under various experimental conditions. The DBD created between two liquid electrodes shows that the discharge is homogeneous and diffuse in the whole discharge regime. Spectra diagnosis is conducted by an optical emission spectroscopy. The air plasma has strong emission from nitrogen species below 400 nm, notably the nitrogen second positive system.

Atmospheric plasma treatment to improve durability of a water and oil repellent finishing for acrylic fabrics

In this study, the influence of an atmospheric plasma treatment on the durability of a commercial water and oil repellent finish was tested. Acrylic fabrics were processed with a RF atmospheric pressure plasma generator and afterwards a fluorocarbon finish was applied through a traditional pad-dry-cure method. Two gas mixtures were tested (helium and helium/oxygen) with different plasma treatment times. The ageing of the finishing was simulated through repeated accelerated laundry cycles. The water and oil repellencies were measured through standard test methods. While the initial water and oil repellency did not change, the plasma treatment improved the durability of the finish after artificial ageing. Scanning electron microscopy analyses were carried out to highlight morphological changes.

Application of Atmospheric Pressure Plasma in the Ultrasmooth Polishing of SiC Optics

This paper presents a novel, rapid and damage-free method to polish the ultra-smooth surface of the SiC optics. First, the basic philosophy of this method is introduced, which uses the active radicals got from CF4 in the atmospheric pressure plasma zone to react with the SiC material at the optics surface to generate the vaporization of SiF4. Then, the design of the atmospheric pressure plasma jet and the corresponding prototyping polishing facility are introduced. The theoretical analysis on the necessary conditions to generate the excited radicals is also presented in this part. To verify the effectiveness of this novel polishing method, experiments on the generation of atmospheric pressure plasma and the SiC optics polishing are carried out with our prototyping facility. The experiment results show that plasma discharge is stable at the atmospheric pressure and sub-nanometer roughness of the polished SiC surface can be obtained.