Plasma Chemistry and Plasma Processing最新文献

The jet stability of a DC plasma torch affects not only the service life of the torch but also processing consistency in industrial applications. To evaluate both instantaneous and longstanding jet stabilities of a plasma torch, a novel jet stability evaluation method has been developed in this study. The collected raw signals were first analyzed using the fast Fourier transform and filtered with identified characteristic frequencies. Based on the filtered signals, a 200 ms sliding window method was employed to evaluate the relative fluctuation of arc voltage in terms of both longstanding and instantaneous jet stabilities of the plasma torch. The results show that: (1) the proposed method can effectively evaluate both instantaneous and longstanding jet stability of a DC plasma torch; (2) the arc voltage and arc current signals contain a characteristic frequency, which is strongly influenced by the gas flow rate; (3) the laminar plasma torch operates stably at an arc current of 90 A, and its longstanding jet stability improves with increasing gas flow rate. The findings and proposed method provide informative guidance to those interested in the improvement of plasma jet stability and processing consistency.

The paper reports and discusses the results of a detailed investigation of transient products and mineralization extent achieved in treatments of perfluorooctanoic acid (PFOA) in a radial plasma discharge reactor. The efforts were warranted by the excellent performance of this reactor in terms of process efficiency and by the need to verify that the quality of the treated water was of matching value. Minor amounts of transient products were detected and quantified, as a function of plasma treatment time, by means of LC/MS and LC/MS/MS analyses. These products arise from sequential chain-shortening, an established route for plasma induced PFOA degradation, and defluorination via fluorine substitution by -H and -OH groups. We focussed on the latter less known type of products (“substitution products”), which are formed in small amounts, cumulatively accounting, at any treatment time, for less than 2% of the total carbon content initially present as PFOA. In our system, hydroxy-containing substitution products with 8–6 carbon atoms are remarkably less reactive than their perfluoro- and hydro-substituted homologues, an effect attributed to improved solubility into the aqueous phase and removal from the plasma/liquid reactive interface. Mineralization extent and carbon mass balance were also determined by performing experiments with PFOA at high initial concentration (1∙10^− 4 M) to afford quantification of the CO₂ released into the gas phase by means of GC-TCD analysis. Despite the low rate of PFOA decomposition entailed by these abnormally high concentrations, remarkable carbon mass balance of 75% and mineralization extent of 67% were achieved in 90 min.

Continued advances in semiconductor manufacturing depend on the 3D integration of complex materials, with nano-scaling precision patterning being a key limiting factor. This article discusses several important aspects of plasma-surface interactions to support atomic scale precision in patterning novel materials. This includes the effect of ions that control the etch anisotropy, the role of surface chemistry that dictates reaction specificity and etch selectivity, and the broader impact of the plasma applications on chemical processing sustainability. A systematic approach is discussed for developing an atomic layer etch process, which allows for independent control of surface modification and product volatilization at low temperatures. This approach starts with predicting a plausible etch product and thermodynamic screening of possible reaction mechanisms, choosing the appropriate half-cycle reactants, leveraging chemical reactivity, and counterbalancing etch and deposition as possible pathways of achieving greater selectivity. This can be followed by experimental verification of the etch rates, product formation, and etch selectivity. Finally, it discusses how these ALE processes can be leveraged to enhance the overall chemical processing sustainability.

In this study, the effect of Mg addition on the composition and aging of water samples treated with nitrogen plasma was analyzed. The study focused on the measurements of the pH of the samples and the comparison of chosen oxygen and nitrogen reactive species (RONS) concentrations formed as a result of the plasma reaction and their changes over time. The results showed that the addition of Mg increased the concentration of RONS compared to the control samples. The pH changes resulting from the reaction of magnesium with water were also observed. Stability studies of the resulting composition also showed that the addition of Mg improved the stability of H₂O₂, NO₃⁻, and NO₂⁻ ions in water samples. The results suggest that it may be useful in water purification processes, environmental decontamination, and in analytical techniques requiring accurate control of chemical components in solutions. Additionally, it can be used in medicine and agriculture, where accurate analysis and stabilization of the composition of solutions are crucial.

Graphical Abstract

Driven by the “dual-carbon” policy, arc steam plasmas provide high-temperature, low-cost, and environmentally friendly heat sources for a variety of applications. However, severe anode erosion caused by steam condensation has limited the large-scale application of arc steam plasma torches. Suppressing condensation depends on reducing heat loss from steam in the anode cold boundary layer, a process that is influenced by plasma flow field characteristics, yet the effects of these characteristics have not been systematically reported. This study investigates two representative flow fields: one generated by a trumpet-shaped anode, which forms stratified flow between the cold boundary layer and the plasma, and the other produced by a stepped anode, which enhances boundary layer turbulence. Through systematic experiments and numerical simulations, the study comparatively analyzes their electro-thermal characteristics, anode exit temperatures, anode erosion behavior, and physical properties inside the torch. The results show that plasma flow field characteristics have a significant impact on anode erosion: stratified flow fields lead to severe erosion, while turbulence-enhanced flow fields can significantly suppress it. Moreover, only under turbulence-enhanced flow fields is the electron temperature at the torch exit higher and sensitive to changes in current. These findings highlight the importance of turbulence-enhanced flow fields for extending the operational lifetime of steam plasma torches.

In this study, a dielectric barrier discharge (DBD) reactor operating in open air was used to activate water with two gas mixtures, argon–nitrogen (Ar + N₂) and argon–oxygen (Ar + O₂), under identical operating conditions. Optical emission spectroscopy (OES) revealed distinct excitation dynamics: Ar + N₂ exhibited strong N₂ second positive system (SPS) bands (337.1 and 357.7 nm), whereas Ar + O₂ featured dominant atomic oxygen lines (777.4 and 844.6 nm). The electron densities were on the order of 10¹⁵ cm⁻³ (Ar + N₂ ≈ 3.3 × 10¹⁵ cm⁻³; Ar + O₂ ≈ 2.9 × 10¹⁵ cm⁻³). After 20 min of treatment, PAW from Ar + N₂ contained 98.7 ppm NO₃⁻, 14.8 ppm NO₂⁻, and 9.9 ppm H₂O₂, whereas Ar + O₂ produced 64.2 ppm H₂O₂, 4.1 ppm NO₂⁻, and 12.2 ppm NO₃⁻. During generation (0–20 min), Ar + O₂ consistently yielded a higher oxidation–reduction potential (ORP) and electrical conductivity than Ar + N₂, indicating a more oxidative and ionically enriched environment. During storage (up to 4 weeks in the dark), Ar + N₂ samples retained higher residual reactive nitrogen species (RNS) levels and sustained ORP despite their lower initial oxidative strength, whereas H₂O₂ in Ar + O₂ PAW decayed more rapidly despite its higher initial concentration. These gas-dependent differences demonstrate the potential tunability of PAW chemistry, which could be exploited for targeted biomedical, agricultural, or catalytic applications.

Plasma technology has emerged as a promising nonthermal approach to improve seed germination and crop development through plasma–biomaterial interactions and surface activation. In this study, a helium atmospheric-pressure plasma jet (APPJ) was applied to H-392 hybrid maize (Zea mays) seeds under four voltage conditions (3810, 4080, 4619, and 4888 V), with a control group receiving no treatment. Morphological analysis was performed by evaluating germination rate, root length, and shoot height over a 13-day period. The 3810 V treatment produced the most significant enhancement, increasing germination by 17% and promoting substantial improvements in root (57.85 mm) and shoot (20.26 mm) growth compared to the control. Plasma diagnostics included optical emission spectroscopy (OES) and electrical analysis using Lissajous figures (charge–voltage plots), which confirmed the generation of reactive nitrogen and oxygen species (RONS) as well as a progressive increase in dissipated power with higher voltage levels. These results demonstrate a stable capacitive discharge regime and energy-efficient plasma–seed coupling. Overall, these findings support the use of non-thermal plasma jets as an efficient and controllable tool for tailoring plasma–biomaterial interactions in seed treatment applications.

Cold atmospheric plasmas (CAP) are a versatile tool in medical applications like wound healing. Its therapeutic benefits are partially attributed to the generation of biologically active reactive oxygen and nitrogen species (RONS). Characterization of RONS, however, typically only occurs after treatment. Here we report the first real-time in situ detection of CAP-generated nitric oxide (NO), and the simultaneous detection of cellular calcium ions (Ca²⁺) release using electrochemical sensors during CAP treatment of murine wounds. In vivo, NO rose rapidly within the first minute of CAP treatment but accumulated less overall than in PBS, reflecting reactions with wound-bed targets. In situ measurements revealed nearly double the concentrations of static endpoint assays, underscoring the importance of real-time detection. Ca²⁺ signals displayed transient, burst-like increases, likely due to CAP-induced membrane permeability and as response to oxidative stress. We also investigated the sensitivity, selectivity, and stability of the graphene oxide coated NO sensors and ion-selective Ca²⁺ sensors. Interference studies showed that the NO sensor also responds to H₂O₂ and NO₂⁻ yet remains most sensitive to NO. Raman microscopy revealed progressive degradation of the graphene oxide layer after only one hour of CAP exposure, drastically reducing sensor currents. Improvements in NO sensor design will enable more accurate measurements for feedback control for plasma-based wound therapies. Ca²⁺ sensors are more robust and retained full functionality after three hours and repeated use providing a reliable diagnostic for immediate biological response. The results establish real-time electrochemical sensing as a powerful approach to monitor CAP-tissue interactions.

Cooling the substrate to stimulate chemical reactions can seem rather counterintuitive. However, this is one of the advantages often observed in plasma cryogenic etching. This article discusses the interactions between plasma and the surface at low temperature. It begins by reviewing the fundamental theories of adsorption as applied to etching. The theoretical concepts are then illustrated in the second part of the article by two different cryogenic processes developed and studied as part of research programs: the reinforcement of the SiO_xF_y passivation layer in the STiGer cryogenic deep silicon etching process and cryogenic Atomic Layer Etching (cryo-ALE) of SiO₂ from physisorbed C₄F₈ molecules.

C₄F₇N and C₅F₁₀O have been identified as promising eco-friendly alternatives to SF₆. Unlike previous studies that assumed local thermodynamic equilibrium (LTE), switching arcs often exhibit pronounced non-equilibrium (NLTE) behavior, especially in the presence of strong temperature gradients or insufficient electron concentration. This paper investigates the thermodynamic properties (mass density, specific enthalpy, and specific heat), transport coefficients (electrical conductivity, viscosity, and thermal conductivity), and radiation coefficients of two-temperature (2T) plasmas of C₄F₇N and C₅F₁₀O mixed with CO₂, N₂ and O₂ under NLTE conditions. We also propose, for the first time, the method for determining the radiation coefficients of 2T plasmas. Results show that the product of mass density and specific heat in C₄F₇N and C₅F₁₀O plasma mixtures is primarily governed by molecular dissociation, with multiple peaks appearing below 5000 K and around 8000 K under LTE, while these peaks shift to higher temperatures under NLTE due to delayed dissociation. For transport coefficients, electrical conductivity decreases with increasing non-equilibrium degree below 15,000 K, with the peak shifting towards higher temperatures, whereas viscosity is mainly determined by collision integrals and is largely insensitive to composition at extreme temperatures. Thermal conductivity is successively dominated by heavy particle translational, reaction, and electron translational contributions, and its peaks shift to higher temperatures with stronger non-equilibrium, indicating delayed energy transfer. Radiation coefficients depend on accurate monochromatic absorption, with continuum absorption linked to electron temperature and line absorption to heavy-particle temperature. At low temperatures, higher CO₂ or N₂ concentrations reduce radiation coefficients, whereas at high temperatures their influence becomes negligible. These findings provide comprehensive 2T plasma property datasets essential for magnetohydrodynamic modeling of C₄F₇N- and C₅F₁₀O-based plasma mixtures, thereby facilitating the evaluation of their arc-quenching capability and advancing their application as eco-friendly SF₆ replacements.