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In this letter, a dipole sheet method is proposed to theoretically study the adsorption and decomposition of C5F10O over-discharged Cu (111) and Al (111) surfaces. A synergistic effect of external electric fields and surface excess charges shows up for jointly promoting the adsorption of C5F10O, accompanied by the enhancement of C-F bond elongation and charge transfer process. The decomposition of C5F10O is facilitated in the discharged region and the initial decomposition is found most likely to occur via the cleavage of the C-F single bond. The results indicate that the decomposition of C5F10O over the metal electrode surfaces is much accelerated when discharge faults occur and free F atoms could be generated from C5F10O before its carbon chain breakage. These findings help to elucidate the underlying decomposition tendency of C5F10O in discharged systems and provide a practical method for evaluating and designing new insulation gases.

Solvated electrons (eaq−) generated by atmospheric pressure plasmas in contact with liquids are a key source of plasma-induced liquid chemistry that enable applications in biotechnology and nanoparticle synthesis. In this paper, we report liquid phase reactive species concentrations near an anodic plasma-liquid interface as described by a fluid model. In particular, the interfacial structures and plasma-induced reactive species in NaCl and AgNO3 solutions as generated by a pulsed plasma are highlighted. The results show that the magnitude and the penetration depth of the eaq− concentration in AgNO3 solution are smaller than that in the NaCl solution due to the scavenger reactions of eaq− by Ag+ and NO3−. The early products of the plasma-induced Ag+ reduction are also presented, and the impact of the current density, the pulse width, and the AgNO3 concentration on the silver reduction is analyzed. It is further shown that a typical OH radical flux present in such plasmas can highly impact the eaq− concentration and the Ag+ reduction while the impact of vacuum ultraviolet radiation, H, and H2O2 is less pronounced.

In this study, the mechanism of the photoresist (PR) etching by means of a kHz AC atmospheric pressure plasma jet (APPJ) is investigated. The scanning electron (SEM) and the polarizing microscope are used to perform the surface analysis, and the mechanical profilometry is applied to diagnose the etch rate. The results show that granulated structure with numerous microparticles appears at the substrate surface after APPJ treatment, and the etch rate in the etch center is the fastest and gradually slows down to the edge of etch region. In addition, the pin-ring electrode APPJ has the highest etch rate at but easy to damage the Si wafer, the double-ring APPJ is the most stable but requires long time to achieve the ideal etch result, and the etch rate and the etch result of the multi-electrode APPJ fall in between. Ar APPJ had much higher PR etch rate and more irregular etch trace than He APPJ. It is speculated that Ar APPJ is more energetic and effective in transferring reactive species to the PR surface. It is also observed that the effective etch area initially increases and then decreases as plasma jet outlet to the PR surface distance increases.

Atmospheric pressure plasma jets have great potential for the surface modification of polymers. In this work, the authors report on polystyrene etching by a radio frequency driven atmospheric pressure plasma jet with a focus on the role of H ⋅, O ⋅, and ⋅ OH radicals in this process. The absolute flux of H ⋅, O ⋅, and ⋅ OH radicals reaching the surface of the polymer was determined by a comsol multiphysics reacting fluid dynamics model incorporating detailed transport phenomena in the boundary layer near the substrate. The simulated results of H ⋅ and ⋅ OH densities in the jet effluent were experimentally verified by two-photon absorption laser induced fluorescence and laser induced fluorescence, respectively. The carbon atom removal flux from the polystyrene surface was taken from previously reported measurements using the same plasma source. The authors show that the boundary layer effects in the interfacial region above the substrate can have a significant impact on the calculated etching probabilities. The reaction probability ( β) has a significant uncertainty although a variation of 2 orders of magnitude in β leads to uncertainties of approximately 1 order of magnitude variation in the determined etching probability. The etching probability of polystyrene by ⋅ OH radicals was confirmed to be at least an order of magnitude larger than the polystyrene etching probability by O ⋅ radicals. The authors also confirmed the weak polystyrene etching probability by H ⋅ radicals. The model suggests that the presence of a 30 ppm O 2 impurity can lead to the production of ⋅ OH radicals in the far effluent of the Ar + 1 % H 2 plasma jet close to the substrate at sufficient densities to enable effective etching.

The in teraction of an atmospheric pressure plasma jet (APPJ) ignited in helium with a small admixture of molecular oxygen ( 2 additive. The plasma-surface contact area reduces by increasing O 2 concentration. The optical emissions of reactive oxygen nitrogen species (RONS) are enhanced significantly at the plasma/surface interfacial regions as compared with those of free jet region. The emission spectra indicates that there is a relative optimum fraction of O 2 in the He/02 gas mixture from 0 to 1.5% for the relative larger intensity of the characteristic atomic oxygen line at 777 nm. The fluid model is used to provide insight into the effect of O 2 admixture on the discharge dynamics and the reaction pathways that lead to the production and destruction of the dominant reactive oxygen species. The simulation results show that the Penning ionization at low oxygen concentration, and the increasingly important role of electron attachment as the oxygen concentration increases play significant role at the plasma-surface interfacial region.

A numerical study of the influence of the N 2 admixture contents on the discharge structures and the ionic compositions outside the dielectric tube of a He atmospheric pressure plasma jet is presented. The working gas is He, He$/ \mathrm {N}_{2}=99.85 /0.15$, He$/ \mathrm {N}_{2}=99.7 /0.3$, and He$/ \mathrm {N}_{2}=99 /1$mixtures. The N 2 admixture in the working gas enhances the discharge of plasma jets, and the discharge for the plasma jet in He with 0.3% N 2 admixture is the strongest. The role of the Penning ionization reactions is considered to be prior to the electron excitation reactions of N 2 molecules when the N 2 admixture is within 1%. However, the energy consumed by the vibration and excitation reactions of N 2 molecules is also important for the plasma jet in He with 1% N 2 admixture. The N 2 admixture accelerates the transition from the annular structure to the solid shape of the plasma bullet outside the dielectric tube. The ionic compositions of plasma jets outside the dielectric tube are strongly dependent on the N 2 concentrations in the working gas. He $_{2}^{+}$determines the positive charge for the plasma jet in He, $\mathrm {N}_{2}^{+}$and $\mathrm {N}_{4}^{+}$both play an important role for the plasma jet in He$/ \mathrm {N}_{2}=99.85 /0.15$and in He$/ \mathrm {N}_{2}=99.7 /0.3$mixtures, and $\mathrm {N}_{4}^{+}$is completely dominating the positive charge for the plasma jet in He$/ \mathrm {N}_{2}=99 /1$mixtures.

A 2D axisymmetric model of the problem considering three charged species is used to study the impact of the needle tip radius, the needle to plane spacing, and the photoionization on the negative corona discharge in atmospheric air. The commercial software COMSOL is used to simultaneously solving three convection-diffusion equations, Poisson’s equations and the three-exponential Helmholtz equations. The Trichel pulse frequency, corona current, electron density and the distribution of electric field will be discussed. The simulation results suggest that the peak electric field is closely related to the needle tip radius, thus the characteristics of the corona pulse are significantly affected by the needle tip radius. The Trichel pulse frequency and the time averaged corona current are both inversely proportional to the needle tip radius. However, the Trichel pulse can not be realized with needle tip radius equal to or larger than 0.1 mm. The electric field is weakened by the increase of the needle to plane spacing, resulting in a decrease of the Trichel pulse frequency and the corona current. The numerical results are in acceptable agreement with the experimental values. The effect of photoionization is fairly small in negative corona discharge. The peak of the first pulse current could be slightly weakened by photoionization, but the peak and the start time of current pulses are unaffected by photoionization.

In recent years, as environmental protection requirements have expanded, SF6/N2 mixed gases have been selected as an insulating medium for high-voltage equipment such as GIL (gas insulated transmission line) without undertaking breaking tasks, which is superior in terms of insulation, economy and environmental protection. The development of streamers and the two-dimensional distribution of positive and negative ions over time in an SF6/N2 mixed gas system are shown in this research. The SF6/N2 mixed gas is adopted as the research object, and the discharge model for a needle-plate electrode under mixed gas conditions is built. COMSOL Multiphysics is used to develop a fluid dynamics model for the SF6/N2 mixed gas discharge in a non-uniform field. The spatio-temporal evolution processes for the electron, positive ion and negative ion densities and the electric field strength during discharge are obtained through numerical simulations. At the same time, the influence of the voltage amplitude and mixed gas ratio on the development process of streamers is studied. The presented simulation results can provide a certain microscopic interpretation for the needle-plate discharge defects that appear in power equipment using SF6/N2 mixed gas.

The numerical study of a cold atmospheric pressure helium plasma jet in a free flow region and when the jet is impinging on substrates of different dielectric constant is presented. A single nanosecond pulse voltage is applied to the dielectric tube through which the helium diffuses into the ambient air. The helium and air mole fraction is first solved by the Navier-Stokes and the species mass conservation equations. A self-consistent, multi-species, two-dimensional axially symmetric plasma model is used to describe the propagation of the plasma jet. The simulation results suggest that the electron impact ionization of He and He∗ concentrated in the streamer head while Penning ionization dominates the ionization reactions in plasma channel. When the plasma jet impinges on substrates, the simulation results provide that the plasma discharge event consists of three parts: a surface discharge propagating along the dielectric tube, a constricted fast ionization wave propagating along the helium-air interface and a surface ionization wave propagating along the dielectric substrate. The surface ionization wave ceases to propagate when helium mole fraction under a critical value for further propagation. The electrical properties and surface charge distribution on the treated material are discussed. High relative permittivity promotes more charging at the substrate surface which leads to a higher electric field at the substrate surface. The lower permittivity promotes the surface ionization wave propagation. The surface charge on substrate surface has a maximum on the jets axis and decreases along the radial direction.

In this paper, the mechanism of negative streamer formation and branching between planar electrodes is studied using a two dimensional particle-in-cell/Monte Carlo collisional model. Super-particles, each one of which represents many physical particles, are used in our model to reduce the calculation and memory usage. The electric field applied to the gap between electrodes is constant and is above the breakdown value already before the streamer formation. For nitrogen at standard temperature and pressure, the simulation is first performed in the background field of 10 MV/m. The results show that prior to branching, the streamer head is flattened, and the non-uniform distribution of electrons accelerated to energies above 50 eV is obtained at the flat streamer head, which then leads to streamer branching. Then, additional simulations in the background fields of 9 MV/m, 11 MV/m, and 12 MV/m are performed to investigate the effects of background field. The results show that the streamer propagates faster, has larger plasma density, and branches more rapidly in a stronger field. The simulation results of argon are also given at a standard temperature and pressure in the background field of 10 MV/m. The results show that more branches can be obtained in argon compared with nitrogen, which agrees well with the experimental results.

Based on a 2D axisymmetric plasma fluid model, the effect of the levels of O2 admixtures on the plasma dynamics of an atmospheric pressure He plasma jet incident on a dielectric surface situated normal to the jet axis has been studied. The introduction of O2 admixture in the feedstock gas changes the shape of the discharge ionization rate that approaches the target surface from a ring to a solid disk. As the streamer extinguishes radial propagation along the dielectric surface, comparatively larger plasma-surface contact areas were obtained for O2 additions to the He plasma of less than 0.5% relative to that for the discharge in pure He, while in the case of 2% O2, the radial propagation distance dropped off significantly. The propagation of an ionization wave peaked in the range 0.2%–1% for the O2 admixture. The enhanced ionization reactions are considered to predominate for small concentrations of O2 as additive, and the negative role played by the excitation energy loss and the attachment of electrons to O2 is more important with the addition of 2% O2. There was a remarkable incremental gain in the flux intensity of O on the surface center, while the flux of N was mainly concentrated on the streamer head. The magnitude of the O flux on the surface showed a peak at the 0.5% O2 admixture level, and the flux of O3 on the surface was directly proportional to the O2 concentration.

This is a computational modeling study of a cold atmospheric pressure helium plasma jet impinging on a dielectric surface placed normal to the jet axis. This study provides insights into the propagation mechanism of the plasma jet, the electrical properties, and the total accumulated charge density at the dielectric surface. For the radial streamer propagation along the dielectric surface, Penning ionization and the electron impact ionization of helium atoms are the major ionization reactions in the streamer head, while Penning ionization is the only dominant contributor along the streamer body. In addition, the plasma bullet velocity along the dielectric surface is 10–100 times lower than that in the plasma column. Increasing tube radius or helium flow rate lowers air entrainment in the plasma jet, leading to a decrease of the radial electric field and the accumulated charge density at the dielectric surface. Furthermore, the tube radius has weaker influence on the plasma properties as tube radius increases. For a target dielectric with lower relative permittivity, a higher radial electric field penetrates into the material, and the surface ionization wave along the dielectric surface extends farther. Higher relative permittivity of the treated dielectric results in more charging at the dielectric surface and more electron density in the plasma column.

This work investigates the hydrodynamic characteristics of a coaxial double-ring electrode helium plasma jet by means of a “Z-type” Schlieren imaging system. The Schlieren images and visual optical photographs made show that a transition point from a laminar region to a turbulent region exists for gas flow without plasma when the helium flow rate exceeds a certain value. After plasma ignition, the laminar region shrinks with voltage increases, and the maximum length of the plasma plume is confined to the laminar region. The heat transfer equation and the spectral broadening of the He I 667.8 nm were used to estimate the increased gas temperature in the plasma jet, and the change in gas velocity by ionic momentum transfer was found by application of a double sphere collision model. As a result, gas heating is considered to be the dominant factor for the earlier onset of turbulence after plasma ignition, whereas the role of ion momentum transfer to neutral gas molecules is comparatively weak. The hydrodynam...