In-liquid plasma electrolysis refers to the ignition of a plasma in a thin vapor layer surrounding a solid electrode immersed in a liquid electrolyte and its associated processes. Over the last century, this phenomenon has been described under various names and is frequently denoted as Contact Glow Discharge Electrolysis. Previous works could show that the plasma might not solely consist of a glow that extends through the entire vapor layer, as the name implies, but consists of multiple filamentary discharges. Building on our previous work on the statistical evaluation of such discharges (J. Phys. D: Appl. Phys. 58 (2025) 215204), here we study the discharge properties, such as their general appearance, gas temperature, electron density, current density, electron production mechanism, and the discharge voltage, using optical emission spectroscopy, scanning electron microscopy imaging, and electrolyte potential measurements. Our results indicate that the discharges do not solely consist of glow discharges. Instead, the possible co-existence of other discharges, such as arcs and sparks, is discussed.

Microdischarges formed in bubbles immersed in liquids are of interest for materials synthesis and chemical conversion applications in the frame of plasma-driven electrochemistry. A key challenge associated with controlling such processes is the limited understanding of the gas-phase chemical kinetics in these microdischarges. Due to their large electron densities, and high gas temperatures, both electron and gas temperature-driven chemistry are likely to be important. Here, a 0-D modeling approach, informed by experimental measurements, is used to study the chemical kinetics in these systems. A new reaction scheme is developed for microdischarges in water vapor, including reactions for both high electron density, and high gas temperature regimes. Microdischarges formed during plasma electrolytic oxidation are used as a test case, however, the key results are expected to be transferable to other plasma electrolysis systems with similar properties. Experimentally measured power densities are used as input to the 0-D model, together with estimates of temperatures and gas pressures within the gas bubble. Comparison of measured and simulated electron densities shows good agreement, given the limitations of both model and experiment. In the base case microdischarge, H 2 O is found to be highly dissociated during the period of peak power density, with H and O making up the majority of the neutral gas in the bubble. The maximum ionization degree is around 0.31%, and the electronegativity during the period of peak electron density is found to be low. Species formation and reaction pathways are analyzed under variation of the neutral gas temperature from 2000 K to 6000 K. At all temperatures, electron, ion, and neutral reactions with high threshold energies are found to be important for the overall chemical kinetics.

Excitation of a plasma with microwaves has the advantage that the lifetime of ions and electrons is much longer than the oscillation period. At a frequency of 2.45 GHz, the electron density is constant in time; therefore, one expects a constant conductivity. In spite of this, harmonics, i.e., nonlinear transport, can be detected at pressures < 50 Pa. We identified two possible mechanisms for this nonlinear behavior, depending on the type of excitation: ICP or capacitively coupled plasma (CCP).

Cold atmospheric plasma (CAP) has emerged as a promising tool in biomedical applications, including the treatment of precancerous neoplasias. The clinical application of low-thermal argon plasma devitalization (ltAPD) using electrosurgical argon plasma coagulation (APC) probes demonstrated significant clinical efficacy in the treatment of cervical intraepithelial neoplasia (CIN) across several prospective clinical trials. Building on the previously demonstrated antineoplastic efficacy of ltAPD treatment, we investigated a prototype dielectric barrier discharge (DBD) plasma source as an alternative plasma generation principle for the treatment of larger areas under preclinical conditions. Both devices were characterized regarding their electrical properties, reactive oxygen and nitrogen species (RONS) generation, biological efficacy, and penetration depth. Electrical measurements revealed a significantly lower current and reduced energy output for the DBD compared to the clinically approved APC probe. Reactive species analysis demonstrated comparable hydrogen peroxide generation between both devices in argon atmospheres, while the APC probe generated higher levels of ·OH and NO2- in argon atmosphere. As the gas composition is defined entirely by the externally supplied mixture, the DBD allowed the working gas to be tuned systematically by adding small fractions of air (87.5% argon/12.5% air) which strongly enhanced nitrogen-species formation and biological efficacy. Implementation of nitrogen or air to the APC could likewise lead to an increase in nitrogen species. Ex vivo treatment of human cervical tissue displayed staining for the DNA damage marker γ-H2AX throughout the epithelial layer for both devices, without detectable structural tissue damage. Agarose gel experiments under controlled laboratory atmospheres revealed greater reactive species penetration depth for the APC probe, whereas the DBD prototype provided a larger treatment area. While DBD efficacy was demonstrated under defined laboratory gas conditions in a controlled chamber setup, these findings establish a first preclinical rationale for DBD as a complementary plasma geometry.

Plasma electrolytic oxidation (PEO) is a technique used to create oxide-ceramic coatings on lightweight metals, such as aluminium, magnesium, and titanium. PEO is known for producing coatings with high corrosion resistance and strong adhesion to the substrate. The process involves generating short-lived microdischarges on the material surface through anodic dielectric breakdown in a conductive aqueous solution. To investigate single microdischarges during PEO, a single microdischarge setup was developed, where the active anode surface is reduced to the tip of a wire with a diameter of 1 mm. In this work the focus is on the effect of electrolyte concentration, anode material, and electrical parameters on the microdischarges. The electrolyte is composed of distilled water with varying concentrations of potassium hydroxide (0.5 - 4 g/l). High-speed optical measurements are conducted to gain insights into the formation and temporal evolution of individual microdischarges and the induced gas bubble formation. Optical emission spectroscopy is used to estimate surface and electron temperatures by fitting Bremsstrahlung and Planck's law to the continuum spectrum of the microdischarges. To evaluate the impact of the microdischarges on coating morphology, the resulting oxide layers on the metal tips are analysed using scanning electron microscopy. The study demonstrates that microdischarge behaviour is significantly influenced by the substrate material, treatment time, and electrolyte concentration, all of which impact the coating morphology. Under the conditions studied in this work, aluminium exhibits longer microdischarge and bubble lifetimes, with fewer cracks on the top layer of the coating, whereas titanium showed faster, shorter-lived bubbles due to more rapid microdischarge events.

Non-thermal plasma-based technologies have emerged as versatile tools for various industrial processes due to their ability to induce chemical reactions efficiently under ambient conditions. In particular, dielectric barrier discharges (DBDs) are of interest because of their robust and reliable design and scalability. This study investigates the role of pressure in tuning conversion, plasma parameters, and flow patterns in a plasma-assisted chemical reaction using a surface DBD (SDBD) reactor. The removal of O2 traces in H2 was used as a model reaction, where an unexpected increased conversion at elevated pressure was observed at high powers. This effect was studied using high-speed photography to analyze streamer dynamics and optical emission spectroscopy to determine plasma parameters. With increasing pressure, both the plasma area and the number of individual streamers decreased, and the electron density decreased as well. Fluid simulations were conducted to examine the impact of increased pressure on mass transport pointing to an enhanced contact time as the origin of the increased conversion at high dissipated powers. The findings highlight the importance of optimizing pressure and power conditions to maximize the efficiency of plasma-based chemical processes.

This study investigates the correlation between flow fields induced by a surface dielectric barrierdischarge (SDBD) system and its application for the volatile organic compound gas conversionprocess. As a benchmark molecule, the conversion ofn-butane is monitored using flameionization detectors, while the flow field is analyzed using planar particle image velocimetry.Two individual setups are developed to facilitate both conversion measurement andinvestigation of induced fluid dynamics. Varying the gap distance between two SDBD electrodeplates for three differentn-butane mole fractions reveals local peaks in relative conversionaround gap distances of 16-22 mm, indicating additional spatially dependent effects. The lowestn-butane mole fractions exhibit the highest relative conversion, while the highestn-butane molefraction conversion yields the greatest number of converted molecules per unit time. Despitemaintaining constant energy density, the relative conversion exhibits a gradual decrease withincreasing distances. The results of the induced flow fields reveal distinct vortex structures at thetop and bottom electrodes, which evolve in size and shape as the gap distances increase. Thesevortices exhibit gas velocity magnitudes approximately seven times higher than the appliedexternal gas flow velocity. Vorticity and turbulent kinetic energy analyses provide insights into these structures' characteristics and their impact on gas mixing. A comparison of line profilesthrough the center of the vortices shows peaks in the middle gap region for the same gapdistances, correlating with the observed peaks in conversion. These findings demonstrate acorrelation between induced flow dynamics and the gas conversion process, bridging plasmaactuator studies with the domain of chemical plasma gas conversion.

Non-thermal plasma conversion of carbon dioxide (CO 2 ) has attracted much interest in recent years because it can be operated at low temperatures and under atmospheric pressure. The development of new conversion technologies, comparison with other applied methods, and understanding of complex processes require numerical modeling. A crucial part of modeling is the calculation of the electron impact dissociation. Due to the linear configuration of CO 2 in the ground state and the different multiplicity of products, the dissociation is a complicated process with several sequential stages. Very different electron impact dissociation cross sections can be found in the literature. Using optical emission spectroscopy and mass spectrometry, a radio frequency plasma jet (COST-jet) operated with a He/CO 2 /N 2 gas mixture is characterized and CO 2 conversion along the discharge is simulated. The applied method can help to select a reliable cross section of electron impact dissociation of CO 2 and to determine the probability of heterogeneous recombination.

A gliding arc plasmatron (GAP) is used for the production of hydrogen and acetylene via plasma-assisted methane pyrolysis. The working gas consists of argon with variable admixtures of methane. By applying camera measurements and optical emission spectroscopy the temperatures and electron density inside the GAP are measured. Two temperature regions are determined: the filamentary plasma, with 3470-5960 K, and a diffuse region characterized by black body emission of hot carbon containing dust at a temperature of 2230-2770 K. An analysis of the product gas stream shows a maximum methane conversion of 44% at a specific energy input of 301 kJ/mol CH 4 and selectivities towards hydrogen and acetylene between 25%-81% and 75%-89%, respectively.

The transition dynamics from the electrostatic to electromagnetic (E-H) coupling in a 2.45 GHz excited inductively coupled plasma (ICP) source is investigated using a set of microwave time-resolved records at different frequencies. This method, coming from semiconductor physics, has been newly adapted for plasma investigations. Nitrogen and oxygen plasmas have been analyzed in the range 20 - 1000 Pa with a constant excitation power of 40 W. With a resolution better than 100 ns, one can identify, depending on pressure, the coexistence of the E and H modes, a hybrid EH mode, and, in the case of oxygen plasma, the transition from negative to positive ions. The E-H transition time increases with pressure.

Simulation and characterization of plasma-chemical kinetics for laser-induced filamentation experiments become increasingly critical as novel laser systems give access to increasing repetition rates, where accumulation effects cannot be ruled out due to the short time between pulses [1]. Previous studies of filament plasmas have focused mainly on retrieving the electron density, neglecting the plasma's molecular composition and its effect on its optical properties. Therefore, we focused on investigating how accumulation effects affect the photochemical reactions at higher laser repetition rates and their influence on the molecular composition of the resultant plasma by measuring the time-dependent plasma dynamics and parameters (gas temperature, electron temperature, electron density, and species-specific decay times) of laser-induced filaments at a repetition rate of 10 kHz.

A twin surface dielectric barrier discharge was used with a two-component coating to oxidize 300 ppm n-butane to CO2 and H2O in synthetic air at room temperature and at 160 degrees C. The integration of BaTiO3 as a base material allowed the successful use of otherwise discharge ignition-inhibiting materials such as MnO2-CuO applied as a full coating. Pure BaTiO3 led to highly porous coatings that do not hinder the discharge ignition and show a negligible influence on n-butane conversion while reducing byproduct formation. The two-component coatings strongly increased the CO2 selectivity, reaching a maximum of 91.6% at an energy density of 450 J L-1 and 160 degrees C for the 1:2 ratio of BaTiO3:catalyst.

Introduction:High-grade squamous intraepithelial lesions (HSIL), such as cervical intraepithelial neoplasia grade 3 (CIN3), are precursors to invasive cancer. Although cancer develops in only 1-2 out of 10 patients with CIN3, all patients typically undergo invasive procedures. This overtreatment affects approximately 90% of CIN3 patients, especially young women, posing risks to fertility and pregnancy outcomes. Non-invasive physical plasma (NIPP) treatment via low thermal argon plasma devitalization (APD) technology offers a novel, outpatient alternative with potential tissue-preserving and antineoplastic properties. Methods:This prospective, monocentric, randomized, controlled phase IIb trial (NCT04753073) evaluated the efficacy of APD in achieving histological remission of CIN3, compared to the natural course in an untreated control group. Forty premenopausal women aged 18 years or older with confirmed CIN3 were enrolled and randomized into two groups: 20 underwent a single APD treatment session followed by large loop excision of the transformation zone (LLETZ) 6-8 weeks later, and 20 served as untreated controls undergoing LLETZ only. Pain perception and patient satisfaction were assessed via visual analog scale and the Freiburg Index of Patient Satisfaction (FIPS), respectively. Statistical analyses included Fisher's exact tests and odds ratio (OR) calculations and were conducted using SPSS. Results:Complete histological remission of CIN3 was observed in 33.3% of APD-treated patients compared to 5.0% in the control group (p = 0.025, OR = 9.43). Partial remission occurred in 27.8% of APD patients and 15.0% of controls, while persistent CIN3 was more common in controls (80.0% vs. 38.9% in APD-treated patients). APD treatment also facilitated R0 resection during consecutive LLETZ in 94.4% of cases versus 65.0% in the control group (p = 0.082). No severe adverse events were reported, and patient satisfaction was comparable between groups. Conclusion:APD treatment demonstrates significant efficacy in inducing histological remission of CIN3, reducing lesion severity, and preserving tissue. This innovative approach offers a promising, minimally invasive alternative to conventional surgical methods, particularly for women of childbearing age. Given the current issue of overtreatment with invasive procedures, APD could significantly reduce unnecessary interventions. Larger, multicenter trials are warranted to confirm these findings and establish APD as a standard treatment for HSIL. Clinical trial registration:https://www.clinicaltrials.gov/study/NCT04753073, identifier NCT04753073.

Measurement of resonances requires data acquisition at different frequencies. Tracing the evolution of a resonance, therefore, requires a long time for each step. Reproducible events allow us to record data in the time domain at different fixed frequencies and then to rebuild the resonance shapes at different times. Using this method, the ignition process and the transition from electrostatic to electromagnetic coupling (E-H) have been investigated for plasma formation in different gases (He, Ar, N-2, and O-2) and pressures (20-2000 Pa). The microwave source used offers a miniature model of an inductively coupled plasma (ICP) inside a quartz tube and has a relatively narrow resonance in the range of 2.4-2.5 GHz with or without plasma. After a short time with only capacitive coupling, at low pressures, there is a coexistence of two resonances, indicating that capacitive and inductive coupling exist. At high pressures, the ignition time is much longer, and a common hybrid resonance appears. Helium and argon show an increase in time over tens of microseconds of the resonance frequency corresponding to inductive coupling, which means, in our global model, a very slow increase of the electron density. Nitrogen and oxygen show, on the contrary, a relatively long initial phase of capacitive coupling and then a stable electron density with inductive coupling. Moreover, oxygen at high pressures shows a plateau, initially indicating an attachment of electrons to oxygen atoms (O $<^>{-}$ ) and after hundreds of microseconds followed by the formation of positive oxygen ions.

A low-pressure double-inductively coupled plasma device is used to study the fundamental plasma parameters, plasma chemistry, and UV photon emission from the first excited state of nitric oxide, NO(A), in gas mixtures of nitrogen and oxygen. In addition to the gas mixture, rf power and gas pressure are varied, and the E-H mode transition of the inductively coupled plasma is studied specifically. The gas temperature and UV photon emission are measured by optical emission spectroscopy, the absolute density of the nitric oxide electronic ground state by laser-induced fluorescence, as well as electron density and electron temperature by a multipole resonance probe. A simple collisional-radiative model for UV emission from NO(A) is developed, which takes the measured densities of ground state nitric oxide and electrons, as well as the electron temperature and neutral gas temperature, as input parameters. The results reveal the links between the absolute densities of ground state nitric oxide, the excitation of this species driven by electron impact and collisions with nitrogen metastables, quenching of the nitrogen metastables, and the resulting UV photon emission rate. The density of ground state nitric oxide is shown to increase with power, while the discharge remains in E-mode, and to decrease significantly with the transition into H-mode, when sufficient rf power is deposited in the discharge. Despite the lower densities of ground state nitric oxide in H-mode, the UV photon emission intensity increases continuously with higher rf powers and over the E-H transition. This effect is shown to be caused by increased excitation of NO(A) by nitrogen metastables in H-mode, which is sufficient to overcompensate the decrease in ground state nitric oxide density.

A twin surface dielectric barrier discharge on the microsecond scale was used in combination with a two-component coating to oxidize 300 ppm n-butane as a model volatile organic compound to CO2 and H2O in synthetic air at room temperature and at 160 C. The integration of BaTiO3 as a base material for the coating allowed the successful use of otherwise discharge-ignition-inhibiting materials such as MnO2-CuO applied as a full coating. Application of pure BaTiO3 led to highly porous coatings that do not hinder the discharge ignition and show a negligible influence on n-butane conversion while reducing byproduct formation. Thus, BaTiO3 was identified as a suitable structure-directing agent in two-component coatings, using 1:1 and 1:2 ratios of BaTiO3:catalyst coatings. Coated electrode configurations were compared to their respective uncoated state to highlight the coating-induced changes. The two-component coatings strongly increased the CO2 selectivity, reaching a maximum of 91.6 for the 1:2 ratio, corresponding to an increase of 51.0 uncoated electrode.

Contact Glow Discharge Electrolysis (CGDE) denotes a plasma inside a vapor layer surrounding a gas-evolving electrode immersed in an aqueous electrolyte and operated at high voltages. We used a high-speed camera to image the formation of the vapor layer as well as its dynamic behavior during continuous CGDE on a Au wire cathode. The plasma ignites with a spark within a large bubble at the tip, which expands along the wire to the top, leaving a stable glow within the vapor layer behind. Using an in-house developed open-source Python-based software we deduced, from a thorough statistical analysis of images taken during continuous CGDE, a vapor layer thickness between 0.1 and 0.4 mm. Furthermore, we provide information on the dynamic behavior of individual discharges through the vapor layer from a series of images. The discharges are confined within the vapor layer and, thus, the extent of the discharges is similar to the vapor layer thickness. We find that the discharges have approximately the shape of oblate spheroids, which appear either as circles or ellipses in the camera images, depending on the orientation of the discharge with respect to the camera. We discuss the relevance of our results for the fundamental understanding of atomic scale surface structural changes and products formed in the solution in the presence of the plasma.

The increasing availability of high-power Yb-based ultrafast laser-amplifier systems has opened the possibility of air filamentation at high repetition rates >1 kHz. In this new regime, accumulation effects cannot be ruled out; therefore, characterizing the plasma parameters and afterglow plasma-chemical kinetics becomes increasingly relevant. In this work, we use optical emission spectroscopy to measure nanosecond dynamics of gas temperature and electron temperature, species-specific decay times, and electron density of an atmospheric air laser filament produced by a high-average power femtosecond laser at a high repetition rate of 10 kHz. The molecular excitation mechanisms behind the nitrogen photoemissions are derived from vibrational distributions and temporal behavior of the studied emission bands. The presented diagnostic technique offers a complementary but more holistic measurement approach to optical probe schemes to characterize the laser-filament-induced plasma wake for high repetition rate filaments.

Dielectric barrier discharges (DBDs) are frequently utilized in various gas conversion processes. For industrial applications a low flow resistance and scalability are crucial. In this study a tenfold scaled-up reactor based on a surface dielectric barrier discharge (SDBD) was employed for the removal of oxygen traces from H2/N2/O2 gas mixtures. The conversion efficiency of the reactor with ten electrode configurations was investigated for different admixtures of O2, and high degrees of conversion were observed that decreased with increasing flow rate, but remained constant when raising the pressure to 2 bar(g). A new generator based on silicon carbide field-effect transistors (SiC-FETs) was used and compared to a generator based on classical metal oxide semiconductor field-effect transistors (MOS-FETs). A surface dielectric barrier discharge is utilized for the removal of oxygen traces in hydrogen-rich gases. The scaled-up reactor aims for industrial application and is operated at increasing flow rates and pressures. Two different generator designs are investigated regarding their electrical efficiency. image

AbstractVapor phase infiltration (VPI) has emerged as a promising tool for fabrication of novel hybrid materials. In the field of polymeric gas separation membranes, a beneficial impact on stability and membrane performance is known for several polymers with differing functional groups. This study for the first time investigates VPI of trimethylaluminum (TMA) into poly(1‐trimethylsilyl‐1‐propyne) (PTMSP), featuring a carbon–carbon double bond as functional group. Saturation of the precursor inside the polymer is already attained after 60 s infiltration time leading to significant densification of the material. Depth profiling proves accumulation of aluminum in the polymer itself, but a significantly increased accumulation is visible in the gradient layer between polymer and SiO2 substrate. A reaction pathway is proposed and supplemented by density‐functional theory (DFT) calculations. Infrared spectra derived from both experiments and simulation support the presented reaction pathway. In terms of permeance, a favorable impact on selectivity is observed for infiltration times up to 1 s. Longer infiltration times yield greatly reduced permeance values close or even below the detection limit of the measurement device. The present results of this study set a strong basis for the application of VPI on polymers for gas‐barrier and membrane applications in the future.