Purpose: Direct application of atmospheric-pressure plasma jets (APPJs) has been established as an effective method of microbial decontamination. This study aimed to investigate the bactericidal effect of direct application of an APPJ using helium gas (He-APPJ) on Porphyromonas gingivalis biofilms on sandblasted and acid-etched (SLA) titanium discs. Methods: On the SLA discs covered by P. gingivalis biofilms, an APO with helium (He) as a discharge gas was applied at 3 different time intervals (0, 3, and 5 minutes). To evaluate the effect of the plasma itself, the He gas-only group was used as the control group. The bactericidal effect of the He-APPJ was determined by the number of colony-forming units. Bacterial viability was observed by confocal laser scanning microscopy (CLSM), and bacterial morphology was examined by scanning electron microscopy (SEM). Results: As the plasma treatment time increased, the amount of P. gingivalis decreased, and the difference was statistically significant. In the SEM images, compared to the control group, the bacterial biofilm structure on SLA discs treated by the He-APPJ for more than 3 minutes was destroyed. In addition, the CLSM images showed consistent results. Even in sites distant from the area of direct He-APPJ exposure, decontamination effects were observed in both SEM and CLSM images. Conclusions: He-APPJ application was effective in removing P. gingivalis biofilm on SLA titanium discs in an in vitro experiment.

In this study, we investigated the antimicrobial effects of plasma activated fine droplet (PAD) produced from arc discharge plasma on planktonic Listeria monocytogenes and Escherichia coli O157:H7. NaCl (0.9%, w/v) was used as the feeding solution for the plasma discharge. The inactivation mechanism of the PAD treatment was also investigated. PAD mainly contains H ₂ O ₂ and OCl ⁻ , which play a significant role in the inactivation process against L. monocytogenes and E. coli O157:H7. The population of L. monocytogenes and E. coli O157:H7 was significantly reduced by approximately 3 and 4 log units, respectively, within 5 min of exposure to PAD. However, the bactericidal effects of PAD against L. monocytogenes and E. coli O157:H7 showed different trends by showing 0.58 and 4.13 log reductions, respectively, after 1 min of PAD exposure time. The change of membrane integrity was evaluated using two DNA-binding fluorescence dyes, SYTO 9 and propidium iodide (PI). The breakage of the cell wall and membrane of both microorganisms was evidenced by the uptake of PI by cells after 5 min of exposure to PAD, but the effect was less in L. monocytogenes compared to E. coli O157:H7 after 1 min of PAD exposure time. The transmission electron microscopy results clearly showed morphological changes in both microorganisms, including denaturation or leakage of intracellular materials as a consequence of PAD treatment. These findings suggest that PAD-induced chemical species can eventually affect the intracellular materials of bacterial cells by passing through or attacking the cell envelope. In addition, L. monocytogenes are less susceptible to PAD compared with E. coli O157:H7.

Lee JY, et al. J Periodontal Implant Sci. 2021 Jun;51(3):213-223. https://doi.org/10.5051/jpis.2007300365

We present an experimentally validated, engineering-oriented framework for the design and operation of pin-to-water (PTW) atmospheric discharges to produce hydrogen peroxide (H₂O₂) on demand. Motivated by industrial needs for safe, point-of-use oxidant supply, we combine time-resolved diagnostics (FTIR, OES), liquid-phase analysis (ion chromatography, pH, conductivity), and coupled plasma-chemistry/fluid simulations to link plasma state to aqueous H₂O₂ yield. Under the tested conditions (14.3 kHz, 0.2 kW; electrode to quartz wall distance 12–14 mm; coolant setpoints 0–40 °C), H₂O₂ concentration follows a reproducible non-monotonic trajectory: rapid accumulation during the early treatment (typical peak at ~15–25 min), followed by decline with continued operation. The decline coincides with a robust vibrational-temperature (T_vib) threshold near ~4900 K measured from N₂ emission, and with concurrent NO_X accumulation and bulk acidification. Global chemistry modeling and Fluent flow fields reproduce the observed trend and show that both vibrational excitation (kinetics) and convective transport (mass/heat transfer) determine the productive time window. Based on these results, we formulate practical design rules—electrode gap (power density), discharge current control, thermal/flow management, water quality, and OES-based T_vib monitoring with an automated stop rule—that maximize H₂O₂ yield while avoiding NO_X-dominated suppression. The study provides a clear path for transforming mechanistic plasma insights into deployable, industrial H₂O₂ generator designs.

Cold plasma jets represent one of the most attractive and versatile plasmas, and active studies on plasma properties such as electron density ( n _e ) and temperature ( T _e ) have facilitated the development and implementation of plasma jets. Here we demonstrate the temporal evolution of n _e and T _e in a radio-frequency (rf)-driven argon plasma jet operating at atmospheric pressure. The plasma jet is driven by 5 MHz sinusoidal rf power modulated by a 50 kHz square pulse with a 75% duty ratio. A 532 nm Nd:YAG laser is applied to the plasma, and laser Thomson scattering measurements are performed using a triple-grating spectrometer coupled to an intensified CCD camera. From this investigation, we find that n _e and T _e vary during the pulse repetition period of 20 μ s in the ranges of (2–12) × 10 ¹⁸ m ⁻³ and 0.3–6.0 eV, respectively. With respect to the 5 MHz period (200 ns), T _e varies with the rf oscillating field while n _e remains constant. Special attention is given to three distinct electron characteristics depending on the pulse phase in the plasma jet—ionizing (on-pulse), stationary and recombining (off-pulse) states. Our measurements will be valuable for related experimental and numerical plasma research and provide further insights into the effect of rf pulsing on the electron kinetics in atmospheric-pressure plasmas.

Conventional capacitively coupled plasma (CCP) discharges face the inherent challenge of low etch uniformity due to their planar structure and relatively poor etch selectivity compared to inductively coupled plasma (ICP) discharges. Accordingly, it makes it difficult to etch silicon structures with a high aspect ratio (HAR). Previous studies have shown that phase-controlled etching can effectively control the etching performance using a triode-type CCP chamber. However, no academic evidence has yet been found on whether this technique is practical for HAR applications. Therefore, in this study, we conducted an in-depth investigation of phase-controlled etching through cross-validation with simulations and real wafer studies; and most importantly, we provided the first experimental results of phase-controlled etching using a SiO₂/Si₃N₄ pair-layered pattern wafer with HAR structures. The experimental results were in good agreement with simulation results based on a hybrid plasma equipment model. We also demonstrated that optimal control of the phase difference between the two opposite electrodes in the triode-type CCP chamber could effectively control the plasma density and sheath thickness and significantly improve the etching performance, resulting in a 14% improvement in the neck critical dimension (CD) of the mask layer and a 32% improvement in the bottom CD of the HAR pattern. Based on the results, we conclude that phase-controlled etching can be a useful solution in semiconductor manufacturing for a wide range of HAR applications.