Pressure Plasma Jet Research Articles

Nitrogen fixation and H2O2 production by an atmospheric pressure plasma jet operated in He–H20–N2–O2 gas mixtures

AbstractAtmospheric pressure plasmas are widely used for nitrogen fixation processes to produce ammonia NH3 or nitrogen oxides NOx, including, for example, nitrite NO2− or nitrate NO3−. Small‐scale atmospheric pressure plasma jets (APPJs) can provide the production of these species on demand at the site of consumption. The species of interest are generated by the plasma and can be dissolved in liquids, for example, to use them. In this work, liquid treatments were performed by an APPJ operated in a He––– gas composition to investigate the influence of the gas composition on the production of hydrogen peroxide , and . A validation of two diagnostics showed that the spectrophotometric approach using ammonium metavanadate was interfered by other species when was added to the system. Thus, electrochemical sensing of was performed. The concentrations of and were measured by commercially available test kits based on the o‐phythalaldehyde method and the Griess reagent, respectively. At low admixtures, the dominant species was with a maximum concentration of 0.9 mM, while became dominant at admixtures of 0.5% and higher with concentrations of up to 1.5 mM. was also present in the system and could be measured at low concentrations of less than 0.2 mM in the liquid. By varying the treatment distance and the gas flow rate, insights into the transport phenomena of the species and their dissolution into the liquid could be gained. Low‐frequency pulsing of the radio frequency (RF) jet led to an accumulating effect on , a reduced production of and a switch from ‐dominated production to ‐dominated production.

Visualization of electrical interaction among close-packed atmospheric pressure plasma jets

Plasma jet arrays can flexibly generate large-scale plasma in ambient air for surface treatment. Close arrangement of plasma jets inevitably induces a complex electrical interaction, which reshapes plasma plumes and destabilizes the treatment process. Understanding electrical interaction is a prerequisite for optimizing parameters in surface treatment. In this study, we employ a linear electro-optic technique to visualize the electrical interaction on the cross section perpendicular to plume trajectories. The strength of the interaction is featured by the density of the deposited surface charge. Results show that plasma jet arrays can simultaneously deposit like-charged groups onto the substrate. However, the electrical interaction is proven to behave with a tendency toward convergence rather than the repulsion caused by electrostatic interaction. It is inferred that electrons at the head of ionization waves (IWs) shield electrostatic repellence between positive charge groups. The collision ionization by electrons in the interval guides the coalescence of adjacent IWs. This study clarifies the electrical interaction between multiple jets, which is instructive for stable control of large-scale non-thermal plasmas for surface treatment.

Phase-shifted counterpropagating atmospheric pressure plasma jets: Characterization and interaction with materials

This study investigates the interaction between two counterpropagating atmospheric pressure plasma jets when their respective streamer ignition times are varied by introducing a phase difference between the AC waveforms used to generate them. When the plasma jets are driven in phase, the streamers form at approximately the same time, resulting in a dark region between the two jets. As the phase difference increases, this dark region shifts toward one of the electrodes. With a sufficiently large phase difference, this region vanishes, giving rise to a uniform plasma channel spanning the distance between the electrodes. High-speed imaging reveals that the interaction between the streamers within the channel reduces the streamer propagation length at intermediate phase differences. At large phase differences, the propagation distance of each streamer is enhanced due to the absence of the opposing streamer. Increasing the phase from 0° to 160° reduced the power consumption of the two jets by about 10%, while there was no significant change in the electron density or the N2 vibrational/rotational temperature. Finally, we show how phase-shifting enhances the interaction with three-dimensional objects located between the opposing jets, enabling the treatment of 3D substrates.

Employing Atmospheric Pressure Plasma Jet Technology in Surface Treatment Iron Oxide Films for Industrial Applications

In this study, pure iron oxide nanostructures were prepared by a physical method (laser-induced plasma) inside a vacuum using a second harmonic laser Nd: YAG with a wavelength of 532 nm, a laser energy of 500 mJ and a number of pulses of 300 pulses per second. The effect of the plasma generated from argon gas under normal atmospheric pressure was studied using a "cold plasma jet" system with an output voltage of 13 kV and a frequency of 50 Hz. Iron oxide nanostructures were exposed to cold plasma for different periods. The optical and structural properties of the nanostructures were measured before and after exposure, and there was a clear change in them, thus improving the properties of the nanostructures for use in industrial applications such as gas sensors, photovoltaic cells, diodes, detectors, and solar cells.

Enhancing mechanical properties of surface hardness and abrasion resistance of Fe-Mn-Al alloy by using atmospheric pressure plasma jet nitriding

This study investigates the use of a N2/H2 mixture gas and an atmospheric pressure plasma jet (APPJ) for nitriding Fe-Mn-Al alloy. Pure metals, iron, manganese, and aluminum, were used as the reference metallic substrates. Various characterization techniques, including X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Vickers hardness test, and optical emission spectroscopy (OES), were employed to analyze the material properties and plasma species. XRD analysis revealed the formation of nitride compounds on metals after the nitriding process. The plasma-nitrided Fe-Mn-Al alloy showed the mixture phases of Fe4N and Al, while plasma-nitrided pure metals possessed their specific metal nitrides. After nitriding process, the surface hardness increased to approximately 596 ± 6 HV0.025 for the Fe-Mn-Al alloy, 1307 ± 9 HV0.025 for manganese, 467 ± 4 HV0.025 for aluminum, 646 ± 5 HV0.025 for iron, and, compared to the pristine values of around 346 ± 4 HV0.025, 972 ± 6 HV0.025, 145 ± 3 HV0.025, and 125 ± 3 HV0.025, respectively. After the nitriding process, the Fe-Mn-Al alloy exhibited notable enhancements in both its resistance to abrasion and its capacity to endure impact loads, as indicated by the conducted tests. The OES test results identified NH radicals generated by the atmospheric pressure plasma jet beam as the active chemicals responsible for the success of the nitriding process. Overall, this study provides valuable insights into the strengthening of metal surfaces through nitriding using an N2/H2 mixture gas and APPJ. The results demonstrate significant improvements in surface hardness and surface free energy for iron, manganese, aluminum, and Fe-Mn-Al alloy, highlighting the effectiveness of NH radicals in the nitriding process.

Optimization and test of a ring-ring typed atmospheric pressure plasma jet for optical fabrication

In recent years, the atmospheric pressure plasma jet (APPJ) has gained considerable attention in the field of optical fabrication because the chemical etching approach offers the advantage of avoiding mechanical damage to workpieces. This paper presents the development of an atmospheric pressure plasma machining system with a ring-ring typed APPJ, which exhibits several favorable characteristics. It has a relatively low processing temperature, no electrode corrosion, no plasma contamination, and a long discharge plume, etc. Optimization of the dimensional parameters and analysis of reactive gas flow rate are conducted through experimental investigations. Comparative experiments are carried out with the commonly used needle-ring typed APPJ, revealing significant improvements of the ring-ring typed APPJ, i.e., a fourfold increase in machining distance, a tenfold increase in machining efficiency, and a 58% enhancement in the stability of the material volumetric removal rate. Furthermore, on-line temperature monitoring of the footprint has been achieved due to the specific traits of the extended discharge plume. Fabrication experiments are conducted to demonstrate the significant correlation between the temperature and material removal rate, which shows the possibility of improving the accuracy of optical fabrication based on the ring-ring typed APPJ.

Reagent‐Free Covalent Immobilization of Biomolecules in a Microfluidic Organ‐On‐A‐Chip

AbstractMicrofluidic systems have become integral for lab‐on‐a‐chip and organ‐on‐a‐chip applications across numerous disciplines. These systems, typically fabricated using polydimethylsiloxane (PDMS) chips on glass substrates, lack the bioactivity required for such applications. To overcome this, biomolecules are immobilized using either oxygen (O2) plasma treatment or chemical reagents like amino silanes. However, O2 plasma treatments are unstable and cannot covalently immobilize biomolecules, while wet‐chemistry approaches are toxic, time‐consuming, and expensive. A novel microfluidic platform that combines two plasma surface treatments: Plasma‐activated coating (PAC) and atmospheric pressure plasma jet (APPJ), to enable reagent‐free covalent immobilization of biomolecules is described here. These surface treatments, unlike O2 plasma, covalently immobilized fibronectin on PDMS and glass, and significantly improved endothelial cell attachment and proliferation. By combining PAC and APPJ, a hybrid microfluidic platform with equivalent bond strength to standard O2 plasma devices, but with significantly enhanced endothelial cell growth in and artery‐on‐a‐chip model, is developed. This platform is also amenable to high‐shear applications such as coronary shear, with endothelial cells aligning with flow, as seen in human arteries. By providing reagent‐free covalent immobilization of biomolecules within a microfluidic system, this technology has the potential to radically improve organ‐on‐a‐chip development as well as lab‐on‐a‐chip systems, point‐of‐care diagnostics, and sensors.

Interaction of atmospheric pressure helium plasma jet with non-planar substrates: path selectivity of surface ionization wave

Most surfaces treated by atmospheric pressure plasma jets (APPJs) in practical applications are notably three-dimensional. However, non-planar surfaces exhibit a diverse array of geometries, such as variations in curvature, roughness, and texture, complicating the prediction of surface ionization waves (SIWs) propagation behavior across varied surface shapes, in the absence of sufficient experimental data. In this study, we made measurements of APPJ interactions with the non-planar substrates using the spatio-temporal resolved image method. Non-planar substrates encompassed wavy surfaces, arrayed hemispheres, and randomly textured raised surfaces. We tracked the morphology and velocity of SIW propagation over these surfaces. The results indicate that the SIW propagation on non-planar surfaces is significantly influenced by surface geometry and displays path selectivity, i.e. the SIW tends to propagate along valleys. The average propagation velocity of the SIW increases with the increasing radius of the wavy surface, as well as with the increased height of the arrayed hemispheres. This is attributable to the surface geometry constraining the dispersion of the SIW, causing it to concentrate and propagate in a singular direction. Moreover, the surface geometry markedly affects the distribution of the plasma treatment area, with the plasma inclined to enter valleys (where the light emission is significantly stronger than that of peaks) and to closely adhere to hemispherical surfaces. These patterns suggest a potential positive impact on treating skin surfaces such as pores, reducing bacteria in wrinkles, and addressing pimples.

Impact of open‐air processing on atmospheric pressure plasma deposition of poly(ethylene oxide) coatings for antifouling applications

AbstractAtmospheric pressure plasma deposition (APPD) of poly(ethylene oxide) (PEO)‐like antifouling coatings provides an attractive way to reduce biofouling for reliable biosensor operation. Cold atmospheric pressure plasma jets are designed to operate in open air. This paper demonstrates the impact of open‐air processing on the composition and properties of PEO‐like coatings by APPD with vinyl ether precursors. The open‐air environment inhibits polymerization as indicated by low deposition rates, oxygen incorporation in the coatings, and instability of the coatings in water. The composition and stability of the coatings improve by appropriate nozzle design and by deposition in an environment with lower air content. The resulting PEO‐like coatings are stable and antifouling for an antibody solution and inhibit adhesion of human fibroblast cells.

Evolution of solid-in-hollow structured plasma bullet: Modulated by pulse repetition frequency and rising time

Plasma bullets in atmospheric pressure plasma jets have drawn much scholarly attention in the past decade, especially its shape. This Letter reports the formation and evolution mechanism of a solid-in-hollow structured bullet. At high pulse repetition frequency (≥20 kHz) and long rising time (≥200 ns), the traditional hollow ring bullet turns into the solid-in-hollow structure, and the plasma plume correspondingly appears as a purple external plume with an extra internal filamentary red core under bare eyes. An image process method based on color recognition and decoupling is designed to separate the images of the external plume and the internal filamentary core and is then used to analyze the discharge mechanism together with the intensified charge-coupled device imaging and spectrum measurement. Analyses reveal that the dominant ionization sources for external ring and internal core are N2 and He, respectively, and the internal discharge can be enhanced by increasing the pulse repetition frequency, which might be explained by the electron oscillating heating in high frequency. Finally, the evolution mechanism of the internal filamentary core is studied, and the internal discharge is initially a hollow ring as well when it just exits the tube end, making the bullet a hollow-in-hollow structure, but quickly contracts into a solid core due to the Coulomb repulsion between the two plasma rings.

Dielectric barrier discharge plasma pretreatment: A cleaner new way to improve energy efficiency and quality of wolfberry drying

Pulsed electric fields (PEF) and cold plasma (CP) show the potential to improve drying efficiency, but the understanding of their comparison and combined effects in PEF-driven dielectric barrier discharge (DBD) is lacking. This study aims to develop a non-chemical pre-treatment to improve drying efficiency and quality by exploring the effects of using PEF, atmospheric pressure plasma jet, and PEF-driven DBD for pre-treating wolfberry. Exploring the synergistic effects and mechanisms of PEF and CP in pre-treatment innovatively provided a new dimension for efficient drying. Results showed that DBD pre-treatment reduced the drying time by 50.6% and energy consumption by 46.0% compared to untreated wolfberry. DBD-pre-treated wolfberries showed better sensory quality and retained critical nutrients by reducing enzyme activities and drying time. DBD combined cold plasma etching and PEF cell disintegration to increase the surface area and pore volume of wolfberry. Furthermore, DBD affected the molecular and tissue structure, altering the binding state of water molecules.

Unwinding the correlation between atmospheric pressure plasma jet operating parameters and variation in antibiotic wastewater characteristics

The influence of plasma operating parameters such as gas medium, electrode distance, applied voltage, gas flow rate, and their interdependency on reactive species generation was investigated. Full factorial design-based response surface methodology (RSM) was used to establish the correlation between the operating parameters. The optimization studies were carried out by taking energy yield and degradation efficiency as response parameters. The operating voltage of 9 kV, the airflow rate of 2 LPM, and the electrode distance of 5 mm are optimum for the system studied. The higher voltage of 9 kV and a flow rate of 2 LPM give maximum yield due to the increased rate of gas atoms undergoing ionization. However, at the low voltage (5 kV), the increase in air flow rate from 0.5 to 2 LPM, the energy yield decreases from 67.5 to 54.2 mg/kWh. These observations are further supported by measuring OH (A-X) intensity in an air medium using optical emission spectroscopy. The studies also reveal that the degradation efficiency is adversely affected by scavenges, with a maximum from isopropyl alcohol, followed by tert-butyl alcohol and methanol. TOC and LC-MS analyses established complete mineralization and its degradation pathway. Phytotoxicity studies suggest that treated effluent, rich in nitrates, is suitable for irrigation, promoting seed germination. In short, the studies provide a strategy to optimize the generation of reactive chemical species in a reactor and how such optimization would help attain optimum energy yield, especially when there is a fluctuation in target pollutant concentration.

Effect of atmospheric pressure plasma jet treatment on the performance of needleless electrostatic spinning with low concentration of PCL solution

PCL nanofibers were prepared by needle-free electrostatic spinning using atmospheric atmospheric pressure plasma to pretreat Polycaprolactone (PCL) electrostatic spinning solution. The results show that the conductivity and acidity of the plasma-treated polymer solution increase significantly, and the viscosity increases and then decreases. The untreated and treated solutions were then subjected to electrostatic spinning, and it was found by scanning electron microscopy that the solutions obtained after plasma treatment had fewer beads on the surface of the fibers, and the nanofibers were more uniformly distributed in diameter and finer. It was also found that the plasma treatment affected the size of the molecular chain segments of the PCL, and the crystal structure of the fibers was altered.The XPS results showed that the surface elements of the nanofibers do not change before and after the plasma treatment, and the chemical bonding between the carbon and oxygen elements is consistent.

Atmospheric pressure plasma jet: Green technology advancements for metals deposition potential

This study explored the utilization of an atmospheric pressure plasma jet (APPJ) for the deposition of metal layers, employing Ar + 2 % H2 as the working gas. The research focuses on three distinct metals - silver (Ag), copper (Cu), and nickel (Ni). Through the application of optical emission spectroscopy, significant peaks of Ar-related and hydrogen-alpha (Hα) species are observed, accompanied by atomic characteristic emission lines specific to Ag, Cu, and Ni, respectively. The XRD examination indicates the successful deposition of metal layers onto the substrates, a confirmation supported by the EDS line scan. Examination of the surface morphology reveals that the metal particles have clustered together, creating a porous structure. The resistivity measurement obtains the values of 5.18, 3.81, and 9.21 μΩ-cm for Ag, Cu, and Ni layers, respectively. Moreover, the paper presents a proposed mechanism for depositing metallic conductive layers using an atmospheric pressure plasma jet (APPJ), elucidating the complex processes inherent in this novel technique.

Spatially- and time-resolved measurements of HO2 radicals in a ns pulse atmospheric pressure plasma jet

The absolute, spatially-resolved, and time-resolved number density of the hydroperoxyl radical is measured in a quasi-two-dimensional, atmospheric pressure ‘curtain’ plasma jet powered by a train of ns discharge pulses. The spatial distribution of HO2 is measured across the shorter dimension of the jet. The measurements are made in two different configurations, (a) H2O–O2–He jet impinging on a copper foil target, and (b) O2–He jet incident on the liquid water surface. In the first configuration, the water vapor is added to the O2–He flow in a bubbler filled with distilled, deionized water. The measurements are made using the previously developed pulsed cavity ring down spectroscopy diagnostic near 1.5 μm. The ring-down cavity is formed between two high-reflectivity mirrors placed at the ends of the stainless steel ‘arms’ purged with dry air, with the plasma jet placed in the gap between the arms. The objectives of this work are to use the HO2 number density to assess the accuracy of the modeling predictions using a previously developed ‘global’ reaction mechanism, and to estimate the efficiency of hydrogen peroxide generation in the ns pulse discharge plasma. HO2 was detected only in the first configuration, most likely due to the rapid decay of the metastable He atoms and O atoms generated in the plasma, which prevents the generation of H atoms (dominant HO2 precursors) in the evaporation/mixing layer. Both the water vapor in the jet and HO2 generated in the plasma have been measured. The results exhibit a rapid accumulation of HO2 during the ns pulse discharge burst, followed by the decay in the afterglow on a ms time scale. The kinetic model overpredicts the quasi-steady-state HO2 number density, as well as the HO2 decay rate after the discharge is turned off. The relatively slow HO2 decay in the afterglow suggests that it may be affected by diffusion, along with the surface adsorption and desorption of radicals. The present approach demonstrates the utility of a 2D curtain plasma jet for the line-of-sight absorption spectroscopy measurements of radicals and excited species present in small concentrations in ambient plasma environments.

Atmospheric pressure argon plasma jets I – Measurements of spatial distribution for visible emission spectrum and vacuum ultraviolet

AbstractThis paper describes the observed position dependent emission spectrum and vacuum ultraviolet (VUV) to clarify the optical structure of argon atmospheric pressure plasma jets (APJs). Visible emission spectra of argon, nitrogen, and OH molecules were measured as a function of position from the nozzle of plasma jet generator to gas flow direction. From the results, we realized that a certain electric field is required for producing high energy excited atoms of argon in the jet from the high voltage electrode in the device to the ground positioned at downstream side. Moreover, VUV was detected along the plasma jet through the downstream direction. Thus, we could picture that the light pattern of plasma jet of which intensity weaken depend to the distance from the nozzle is sustained by the above two factors with the present steady state experiments.

Low-Temperature Atmospheric Pressure Plasma Jets and their Applications in the Surface Activation of some Polymeric Substrates for Advanced Electronic Packaging

The present study applied low-temperature atmospheric plasma (LTAPP) jets to modify polymer substrates used in chip packaging. These substrates include bismaleimide triazine (BT), polyimide (PI) and PTFE materials. All these materials play important roles in modern semiconductor packaging. During the study, focuses were aimed the effects of reactive species (mainly OH and atomic oxygen) generated by atmospheric plasma jets on surface energy, water contact angle (WCA) and surface composition of these three substrates. In order to better understand and apply LTAPP jets, another focus will be on the understanding of the relationship among (1) the generation and distribution of various reactive species, (2) parameters for generating LTAPP jet, and (3) plasma characteristics. The plasma activation mechanism of these substrates was also discussed. In addition to plasma generation using AC high-voltage supplies, plasma characterization using optical emission spectroscopy (i.e., analysis of electron density, electron temperature, plasma temperature, and reactive species), XPS and water WCA analysis were used to understand surface activation mechanisms. In sum, Ar and Ar-O2 plasma jets can be used to modify the surfaces of these three substrates, although the latter relies on the generation of O radicals, while the former relies on OH radicals more. According to the results obtained by XPS analysis, the formation of C-O and C=O bond after plasma treatment is the main reason for surface activation in this study.

Surface surgery on TiNb2O7 electrode via N2/Air atmospheric pressure plasma jet for high-rate lithium-ion battery anode

TiNb2O7 (TNO) is regarded as a potential anode material for its high capacity compared to Li4Ti5O12 and high safety due to its adequate Fermi level in lithium-ion batteries. This work represents a promising method of modifying the electrode, which includes polyvinylidene fluoride (PVDF), conductive carbon, and TiNb2O7, using an atmospheric pressure plasma jet (APPj) treatment. Our results reveal that atmospheric pressure plasma jet improves the electrochemical performance by N-doped decoration on conductive carbon, electrolyte wettability enhancement on polyvinylidene fluoride binder, and defects manufacturing in TiNb2O7 anode materials. Good wettability of surface free energy to 44.6 mJ/m2 in the APPj-treated (APP-10) sample contributes to improved cycling performance. Both N-doped carbon and modified TiNb2O7 promote the high-rate capability. The C-rate performance of APP-10 improves by over 200 % at 10C compared to the non-treated sample (APP-0). APP-10 sample also shows 81.9 % retention after 300 cycles at 1C. The formation of Li3N or LiNxOy after cycling due to the nitro-group in the electrode with atmospheric pressure plasma jet offers good protection and high ionic-conductivity interface. This work demonstrates a potential solution to achieve a roll-to-roll modification without any complex synthesis processes, which is a promising technology for the affordable manufacturing of lithium-ion battery.

Concentration measurements of atomic nitrogen in an atmospheric-pressure RF plasma jet using a picosecond TALIF

The absolute concentration and spatial distribution of ground-state atomic nitrogen (N) in an atmospheric pressure plasma jet were measured using the two-photon absorption laser-induced fluorescence. The jet was ignited by radio frequency voltage in argon (or argon with nitrogen admixture) flowing through a silica tube. The spatially resolved measurements of atomic nitrogen concentration were realized in the effluent of the jet. In a pure argon plasma, the N concentration was increased with the distance from the silica tube and reached the maximum value ( 3.5⋅1014 cm−3) at the distance of 15 mm, and then sharply decreased at the end of the plume. On the contrary, plasma ignited in Ar with nitrogen admixture, the maximum N concentration was located directly at the end of the silica tube, where plasma starts to blow out into the ambient air. The highest N concentrations for 0.5% and 2% of N2 in the feed gas were 1.3⋅1015 cm−3 and 4⋅1015 cm−3, respectively.

Numerical investigation on the discharge formation in micrometer pores in structured catalyst irradiated by a helium atmospheric pressure plasma jet

Abstract Non-thermal plasma catalysis is a promising way to achieve high efficiency in applications such as energy conversion and chemical engineering. Although synergistic effects between plasmas and catalysts have been preliminarily considered as an underlying mechanism of this type of catalysis, the formation of discharges in small-size catalyst pores, which is possibly a crucial factor in plasma-activated catalysis, is still not well understood. In this paper, investigations on the interactions between a helium atmospheric pressure plasma jet (APPJ) and catalysts with micrometer-sized pores of different shapes and sizes are conducted with a 2D fluid model. Simulation results show that the existence of pores makes a subtle difference to the APPJ by changing the equivalent capacitance, indicating the potential to achieve moderate and stable APPJ-catalyst interactions. Traces of air impurities in helium can promote discharges in catalyst pores, and thus allow discharges to form in smaller pores. In the case when the catalyst channel is too small for direct APPJ penetration, we propose a method by producing a prior discharge in a relatively large cavity to supply seed electrons to ignite discharges inside the channel. The effects of channel and cavity sizes are discussed from the perspectives of discharge behavior and plasma-surface interactions. This work will contribute to the preparation of structured catalysts to potentially achieve higher efficient plasma catalysis, and better understanding of the physical processes in plasma-surface interactions inside micrometer pores.