Low-temperature Plasma Research Articles

Polycaprolactone scaffold surface modification with soft X-ray/extreme ultraviolet (SXR/EUV) radiation and low-temperature oxygen and nitrogen plasma for biomedical applications

Modification of the surfaces of polymeric scaffolds is often required to make the material suitable for specific tissue engineering applications. Physico-chemical properties of scaffolds can be altered using various methods, such as plasma treatment, laser processing, chemical modifications, grafting with nanoparticles, or surface coating. In this paper physico-chemical modification of polycaprolactone (PCL) surface fibers was performed by exposing PCL samples to simultaneous soft X-ray/extreme ultraviolet (SXR/EUV) radiation and low-temperature, SXR/EUV-induced, nitrogen, and oxygen plasmas. The physical and chemical changes on modified PCL surfaces were examined using a scanning electron microscope and X-ray photoelectron spectroscopy, respectively. The effects of physico-chemical scaffold surface changes were verified with biological tests, i.e., MTT assay and immunofluorescence on murine osteoblast cell line (7F2). It was found that exposure of scaffolds to ionizing radiation and low-temperature plasmas induced strong chemical changes on their surface, i.e., appearance of various new chemical groups. Also, smoothing of the surface of PCL fibers, i.e., disappearance or significant reduction of the size of micropores on their fibers was also observed. Increased viability and adhesion of 7F2 osteoblasts on modified PCL samples after 24 h cell culture compared to non-treated PCL was also confirmed.Graphical abstract

An experimental study on low-temperature plasma tissue ablation and its thermal effect

Low-temperature plasma ablation has been recently used for minimally invasive surgeries. However, more research is still needed on its generation process during tissue ablation and the underlying mechanism of tissue thermal damage. In this paper, high-speed camera footage, voltage–current signal collection, temperature analysis, and histological analysis were used to investigate the dynamic process of plasma tissue ablation and its thermal effect of dual-needle electrodes immersed in normal saline, which were driven by a high-frequency DC power supply with an output voltage ranging from 220 V to 320 V and a squire wave of 100 kHz. Microbubbles occurred around the ground electrode and merged to form a vapor layer that could completely cover the ground electrode. Plasma capable of ablating tissue would occur in the vapor layer between the ground electrode and tissue. The effect of electrical parameters on plasma generation and its thermal effect are analyzed by statistical results. The experimental results indicated that the voltage applied to the electrodes significantly influenced both the generation and stability of plasma, as well as the heat generation and tissue damage around the electrodes. Furthermore, under the same voltage, the existence of biological tissue promotes the formation of a vapor layer around the electrode, thereby facilitating the generation and stability of plasma. Notably, the temperature rise around the ground electrode is much higher than that around the powered electrode. These results have direct application to the design of plasma tissue ablation systems, which could achieve tissue ablation effects with minimal thermal damage.

Comprehensive analysis and treatment of intraoral thyroglossal duct cysts with intraoperative techniques: a 7-case series review in a tertiary care center

ObjectiveIntraoral thyroglossal duct cyst is a relatively rare clinical disease. This article reviews the diagnosis and treatment process of 7 patients and explores the clinical characteristics of diagnosis and treatment of intraoral thyroglossal duct cyst in combination with past literature reports. MethodA retrospective analysis was conducted on 7 cases of intraoral thyroglossal duct cyst admitted to the Otolaryngology ward of Dalian Municipal Central Hospital from January 2017 to January 2024. The cases were recorded in terms of gender, age, symptoms, physical signs, radiological examinations, surgical methods, and postoperative complications. All cases were followed up, and the latest follow-up results were recorded. ResultsAmong the 7 cases, 6 patients underwent laryngoscopic and radiological examinations before surgery, and 1 child was found to have a cyst during surgery. All cases were diagnosed with intraoral thyroglossal duct cyst and treated with plasma radiofrequency surgery. None of the patients had postoperative complications, and no recurrence was found in the six-month follow-up after discharge. ConclusionIntraoral thyroglossal duct cyst is rare in clinical practice. It is important to pay attention to its differential diagnosis clinically, and careful review of images is required before surgery. Cryoablation with low-temperature plasma radiofrequency is not only minimally invasive and has a quick recovery but also has few complications and a low recurrence rate. It is a safe and effective treatment method that is worthy of clinical promotion. Level of EvidenceLevel 3.

Surface Modification of Zr48Cu36Al8Ag8 Bulk Metallic Glass through Glow Discharge Plasma Nitriding

Bulk metallic glasses are modern engineering materials with unique functional properties. Zr-based alloys are particularly attractive as they exhibit high glass forming ability as well as good mechanical properties. Due to their relatively high thermal stability, reaching as much as 400 °C, they can be surface-treated in low-temperature plasma to further improve their mechanical properties. The subject of this study was to determine the influence of the technological parameters of nitriding in low-temperature plasma on the structure and mechanical properties of Zr48Cu36Al8Ag8 bulk metallic glass. In the course of this study, the influence of the ion accelerating voltage on the structure and micromechanical properties of the bulk metallic glass was analyzed. The produced samples were characterized in terms of nanohardness, layer adhesion by using the scratch test, and wear resistance by using the ball-on-disc method. As a result of low-temperature plasma nitriding, a significant increase in the surface nanohardness of the Zr48Cu36Al8Ag8 bulk metallic glass was obtained. The produced layers exhibited high adhesion to the substrate and they improved the wear resistance of the glass. The present study indicates the possibility of modifying the surface properties of bulk metallic glasses by using diffusion processes in low-temperature plasma without substrate crystallization.

Energy levels and characteristic features in photoionization of Cl III using the R-matrix method

We report study of Cl III for its large number of fine structure bound levels, 890, with n ≤ 10 and l ≤ 9, and 1/2 ≤ j ≤ 19/2 of even and odd parities with spectroscopic designation and photoionization cross sections (σPI) of the levels revealing various characteristic features. Various resonant structures and the shapes of the background, and their interference in σPI are illustrated for the ground, excited equivalent electron, low and high lying excited levels with single valence electron, and effects of fine structure couplings. σPI of the ground level shows Rydberg series of resonances on smooth background, and of equivalent electron levels producing strong closely spaced Rydberg series of resonances belonging to the low lying core ion excitation thresholds. They will impact applications in low temperature plasma. For the single valence electron excited levels, we find that σPI of low lying excited states are dominated by Rydberg series of resonances and of high lying excited states exhibit prominent broad feature of Seaton resonances. Partial photoionization cross sections of the ground level for leaving the core ion in the ground and various excited levels are also presented for applications in plasma modeling. The study was carried out in relativistic Breit–Pauli R-matrix method using a large close coupling wave function expansion of 45 levels of the core ion configurations 3 s23 p2, 3 s3 p3, 3 s23 p3 d, 3 s23 p4 s, 3 s3 p23 d, and 3 p4 with closed 1s, 2s, 2p orbitals. They belong to the optimized set of 13 configurations of Cl IV, 3 s23 p2, 3 s3 p3, 3 s23 p3 d, 3 s23 p4 s, 3 s23 p4 p, 3 s23 p4 d, 3 s3 p23 d, 3 s3 p24 s, 3 s3 p24 p, 3 p4, 3 p33 d, 3 p34 s, and 3 p34 p. Cl III energies are in good agreement with measured values. σPI features of low lying levels were benchmark with observation carried out at Advanced Light Source at LBNL with very good agreement. The present set of high accuracy data should complete for any practical applications.

Science challenges and research opportunities for plasma applications in microelectronics

Low-temperature plasmas (LTPs) are essential to manufacturing devices in the semiconductor industry, from creating extreme ultraviolet photons used in the most advanced lithography to thin film etching, deposition, and surface modifications. It is estimated that 40%–45% of all process steps needed to manufacture semiconductor devices use LTPs in one form or another. LTPs have been an enabling technology in the multidecade progression of the shrinking of device dimensions, often referred to as Moore’s law. New challenges in circuit and device design, novel materials, and increasing demands to achieve environmentally benign processing technologies require advances in plasma technology beyond the current state-of-the-art. The Department of Energy Office of Science Fusion Energy Sciences held a workshop titled Plasma Science for Microelectronics Nanofabrication in August 2022 to discuss the plasma science challenges and technical barriers that need to be overcome to continue to develop the innovative plasma technologies required to support and advance the semiconductor industry. One of the key outcomes of the workshop was identifying a set of priority research opportunities (PROs) to focus attention on the most strategic plasma science challenges to address to benefit the semiconductor industry. For each PRO, scientific challenges and recommended strategies to address those challenges were identified. This article summarizes the PROs identified by the workshop participants.

Deposition of a polymer thin film on a silver surface for surface plasmon sensing

We report a deposition method of a polymer thin film on the silver surface of a surface plasmon sensor for preventing sensitivity degradation in refractive index measurements due to the poor chemical stability of the silver. The deposition of a poly(methyl methacrylate) thin film with a ∼15 nm thickness was conducted by employing a spin coating technique along with a hydrophilicity enhancement of the silver surface using an atmospheric low-temperature plasma treatment. We experimentally verified the thickness by measuring the propagation constant of the surface plasmon. The measured propagation constants that showed the standard deviation at the order of 10−4 indicated microscopical uniformity. Furthermore, the reproducibility of thickness was experimentally verified.

Low-Temperature Plasma Radiofrequency Ablation for Congenital Epiglottic Cysts.

Objectives: Congenital epiglottic cysts are rare disorders of the larynx with symptoms such as laryngeal stridor and inspiratory dyspnea and are life-threatening in severe cases. This study aimed to investigate the usefulness of low-temperature plasma radiofrequency ablation for congenital epiglottic cysts and provide a reference for clinicians to develop treatment options. Methods: The clinical data of children (n = 7, 4 males and 3 females) with congenital epiglottic cysts, who were admitted to the Second Affiliated Hospital of Wenzhou Medical University and Yuying Children's Hospital from March 2018 to March 2023, were analyzed retrospectively. Following preoperative examinations, all patients underwent low-temperature plasma radiofrequency ablation under general anesthesia, and the curative effect was evaluated. Following surgery, regular patient follow-up examinations were conducted to monitor recurrence. Results: The age at the time of operation ranged from 1 day to 99 days, with an average of 37.57 ± 35.01 days. The surgical procedure was successfully completed in all the children; dyspnea disappeared and no surgical complications were observed. In addition, during the postoperative follow-up period of 6 months to 5 years, recurrence was not observed. Conclusions: Low-temperature plasma radiofrequency ablation is a safe and effective procedure for treating congenital epiglottic cysts and deserves clinical application and promotion.

Properties of Cast Tungsten Carbide and Peculiarities of Its Preparation in a Low-Temperature Plasma under Gas Pressure

Properties of Cast Tungsten Carbide and Peculiarities of Its Preparation in a Low-Temperature Plasma under Gas Pressure

The capability of a deep learning based ODE solution for low temperature plasma chemistry

The capability of a deep learning based ODE solution for low temperature plasma chemistry

Void closure in a pulsed complex plasma in microgravity

A new experimental method for creating void-free complex (dusty) plasmas under microgravity conditions is presented. The method is based on a pulsed operation mode of a four-channel radio frequency generator for plasma sustainment. A dust cloud of micrometer-sized particles can be immersed in the bulk of a low temperature plasma under microgravity conditions. It typically contains a central volume depleted of particles—the void—that prevents the generation of large, continuous clouds. Experiments performed at different neutral gas pressures and discharge volumes during the microgravity phase of a parabolic flight show that the central void is closed completely once the pulsed operation mode is applied. The particle cloud shape and the density distribution within the cloud are practically independent of the pulse period within the investigated parameter range and mainly depend on the overall discharge parameters neutral gas pressure and discharge volume. This indicates that the pulsed operation of the plasma source does not introduce new physical effects on the particles aside from the void closure. The proposed method has great potential for future application in experimental facilities dedicated to fundamental studies of large three-dimensional, homogeneous complex plasma systems in microgravity.

CFIRM: An Integrated Code Package for the Low-Temperature Plasma Simulation on Structured Grids

CFIRM: An Integrated Code Package for the Low-Temperature Plasma Simulation on Structured Grids

Effect of plasma treatment of Ag/ZnO hybrid photocatalysts on the optical properties and morphology of Ag nanoparticles

Subject of study. This study investigates Ag/ZnO hybrid photocatalysts and the role of silver nanoparticles as the active phase of these hybrid photocatalysts after treatment with low-temperature plasma generated from a dielectric barrier discharge. Aim of study. The aim is to determine how plasma treatment affects the optical properties and morphology of silver nanoparticles in Ag/ZnO hybrid photocatalysts as well as to explore the relationship between plasma-induced morphological changes and the photocatalytic activity of Ag/ZnO in the photodegradation of methyl orange and caffeine. Method. Ag/ZnO hybrid photocatalysts and silver nanoparticle ensembles were treated with dielectric barrier discharge plasma in air at normal pressure. The photocatalytic performances of the original and plasma-treated materials were evaluated through the degradation of methyl orange and caffeine in aqueous solutions under ultraviolet light, and the concentrations of methyl orange and caffeine were measured by spectrophotometry. The effects of plasma modification were analyzed using photoluminescence spectroscopy, spectrophotometry, and atomic force microscopy. Main results. A plasma-induced reduction in the size of silver nanoparticle agglomerates was observed, accompanied by an increase in the number of individual nanoparticles. The nanoparticle size changes were dependent on the energy and duration of plasma treatment. Additionally, the plasma treatment of ZnO-based hybrid photocatalysts led to a marked increase in the fluorescence lifetime of ZnO, contributing to enhanced photocatalytic activity in the degradation of organic pollutants in aqueous media. Practical significance. Improving the efficiency of Ag/ZnO photocatalysts for the removal of organic impurities from aqueous media through photodegradation represents a significant advancement in environmental management.

Experimental and numerical study of stabilized flame in inverse coflow turbulent jet using nanosecond repetitively pulsed discharges

Methane has become increasingly popular in rocket propulsion, but low stability and limited flammability range have always been a concern about methane-powered systems. Many stabilization methods have been developed to change the geometrical or flow characteristics of the burner. However, most of these efforts have yet to be practically successful due to cost and compatibility issues. Alternatively, other methods such as microwave, dielectric barrier, and nanosecond repetitive pulse (NRP) discharges have been proven to be efficient by modifying the kinetic and transport pathways. NRP discharges have shown promising results as one of the most effective low-temperature plasma (LTP) methods. In this paper, chemiluminescence imaging is used to study the effect of NRP discharge on liftoff and blowout, as the important stabilization parameters, by recording the liftoff height and liftoff/blowout velocities under a wide range of discharge (f=0–10 kHz and V=11–19 kV) and jet velocity (ν=2–60 m/s). Depending on these parameters, four different discharge regimes of corona, diffuse, filamentary, and arc were observed. The results have shown that high-intensity plasma in a filamentary discharge regime can provide a significant advantage in delaying the liftoff conditions, but no improvements in the blowout were observed. It was also found that NRP discharge can reduce the liftoff height. To explore the cause of the increased stability, a parametric numerical study is conducted using detailed plasma-assisted methane kinetic modeling coupled to a 1D opposed diffusion flame simulation. Results show that the extinction limits of diffusion flames can be dramatically enhanced by LTP due to the local formation of high radical and excited species concentrations, with subsequent recombination leading to increased temperature and higher reactivity in the flame zone. In addition, a 1D laminar flame speed evaluation shows that the plasma-generated active species can dramatically increase the flame speed, which, in turn, reduces the lifted flame height above the burner surface.

Enhanced Hydrogen Generation through Low-Temperature Plasma Treatment of Waste Aluminum for Hydrolysis Reaction.

This study investigates the low-temperature hydrogen plasma treatment approach for the improvement of hydrogen generation through waste aluminum (Al) reactions with water and electricity generation via proton-exchange membrane fuel cell (PEM FC). Waste Al scraps were subjected to ball milling and treated using two different low-temperature plasma regimes: Diode and magnetron-initiated plasma treatment. Hydrolysis experiments were conducted using powders with different treatments, varying molarities, and reaction temperatures to assess hydrogen generation, reaction kinetics, and activation energy. The results indicate that magnetron-initiated plasma treatment significantly enhances the hydrolysis reaction kinetics compared to untreated powders or those treated with diode-generated plasma. Analysis of chemical bonds revealed that magnetron-initiated hydrogen plasma treatment takes advantage by promoting a dual procedure: Surface cleaning and Al nanocluster deposition on top of Al powders. Moreover, it was modeled that such H2 plasma could penetrate up to 150 Å depth. Meanwhile, electricity generation tests demonstrate that only 0.2 g of treated Al powder can generate approximately 1 V for over 300 s under a constant 2.5 Ω load and 1.5 V for 2700 s with a spinning fan.

A comparative study on the spectral characteristics of nanosecond pulsed discharges in atmospheric He and a He+2.3%H2O mixture

Nanosecond pulsed discharges at atmospheric pressure in a pin-to-pin electrode configuration are well reproducible in time and space, which is beneficial to the fundamentals and applications of low-temperature plasmas. In this experiment, the discharges in helium (He) and He with 2.3% water vapor (H2O) are driven by a series of 10 ns overvoltage pulses (~13 kV). Special attention is paid to the spectral characteristics obtained in the center of discharges by time-resolved optical emission spectroscopy. It is found that in helium, the emission of atomic and molecular helium during the afterglow is more intense than that in the active discharge, while in the He+2.3%H2O mixture, helium emission is only observed during the discharge pulse and the molecular helium emission disappears. In addition, the emissions of OH(A-X) and Hα present similar behavior that increases sharply during the falling edge of the voltage pulse as the electrons cool down rapidly. The gas temperature is set to remain low at 540 K by fitting the OH(A-X) band. A comparative study on the emission of radiative species (He, He2, OH and H) is performed between these two discharge cases to derive their main production mechanisms. In both cases, the dominant primary ion is He+ at the onset of discharges, but their He+ charge transfer processes are quite different. Based on these experimental data and a qualitative discussion on the discharge kinetics, with regard to the present discharge conditions, it is shown that the electron-assisted three-body recombination processes appear to be the significant sources of radiative OH and H species in high-density plasmas.

Optimization of pellet design parameters to achieve deep fueling depth in EAST plasma with PAM code

Deep pellet fueling depth is necessary to achieve a high-density high confinement operation and to conduct some pellet-related researches in current devices, such as trigger of internal transport barrier, and to achieve high fusion power and tritium burn-up fraction in future fusion devices. The newly developed PAM code which can make a fast evaluation on pellet ablation and deposition is applied to optimize injection parameters to achieve deep pellet fueling. Systematic scans on pellet injection parameters including pellet injection positions, injection angles, sizes and speeds are performed for optimization purpose, while at the same time demonstrating flexibility and time efficiency of the PAM code. Dependences of the pellet fueling depth on these injection parameters are revealed by simulation results and analyzed. Simulation results indicate that pellet penetration contributes more to the deep pellet deposition than the ∇B -induced plasmoid drifts in low temperature plasmas, while deep pellet fueling in reactor relevant high temperature plasmas has to rely on plasmoid drifts. Though a shallow penetration is expected in high temperature plasmas, the ∇B -induced plasmoid drift is expected to be larger than that in relatively low temperature plasmas.

Low-Temperature Plasma Pretreatment Enhanced Cholesterol Detection in Brain by Desorption Electrospray Ionization-Mass Spectrometry Imaging.

Cholesterol is a primary lipid molecule in the brain that contains one-fourth of the total body cholesterol. Abnormal cholesterol homeostasis is associated with neurodegenerative disorders. Mass spectrometry imaging (MSI) technique is a powerful tool for studying lipidomics and metabolomics. Among the MSI techniques, desorption electrospray ionization-MSI (DESI-MSI) has been used advantageously to study brain lipidomics due to its soft and ambient ionization nature. However, brain cholesterol is poorly ionized. To this end, we have developed a new method for detecting brain cholesterol by DESI-MSI using low-temperature plasma (LTP) pretreatment as an ionization enhancement. In this method, the brain sections were treated with LTP for 1 and 2 min prior to DESI-MSI analyses. Interestingly, the MS signal intensity of cholesterol (at m/z 369.35 [M + H - H2O]+) was more than 2-fold higher in the 1 min LTP-treated brain section compared to the untreated section. In addition, we detected cholesterol, more specifically excluding isomers by targeted-DESI-MSI in multiple reaction monitoring (MRM) mode and similar results were observed: the signal intensity of each cholesterol transition (m/z 369.4 → 95.1, 109.1, 135.1, 147.1, and 161.1) was increased by more than 2-fold due to 1 min LTP treatment. Cholesterol showed characteristic distributions in the fiber tract region, including the corpus callosum and anterior commissure, anterior part of the brain where LTP markedly (p < 0.001) enhanced the cholesterol intensity. In addition, the distributions of some unknown analytes were exclusively detected in the LTP-treated section. Our study revealed LTP pretreatment as a potential strategy to ionize molecules that show poor ionization efficiency in the MSI technique.

Performance enhancement of Ge/Si avalanche photodetector by specific sidewall passivation using remote oxygen plasma treatment

We report an obvious improvement in the performance of a separated absorption charger-layer multiplication Ge/Si avalanche photodetector, achieved by passivating the sidewalls with a low-temperature remote oxygen plasma (ROP) treatment. The dangling bonds on the Ge surface can be efficiently passivated by the formation of an ideal Ge/GeO2 interface. With ROP passivation, the leakage current of the device shows a three- to fourfold decrease at 300 K, resulting in a dark current (I dark) of 3.5 × 10−6 A at 90% avalanche voltage (V br) and 3.4 × 10−7 A at punch-through voltage (V puhch-through) for the 26 μm-diameter device. A reduction of over tenfold is demonstrated at 200 K and the passivation mechanism is revealed. In addition, a multiplication gain of 94 is obtained under 1550 nm illumination. The device with ROP passivation shows an improved gain bandwidth product of 190 GHz. The enhanced high-frequency response of the device with ROP passivation can be attributed to the alleviation of the retarding effect caused by the interface state on the sidewalls. Without using a trans-impedance amplifier, an opening eye diagram at 28 Gbps is demonstrated, indicating reliable device transmission performance.

Coordinated d-p hybridized hcp@fcc NiRu alloy doped by interstitial atoms for boosting urea-assisted simulated seawater electrolysis at industrial current densities

The production of hydrogen through seawater electrolysis has recently garnered increasing concern. However, hydrogen evolution reaction (HER) by alkaline seawater electrocatalysis is severely impeded by the slow H2O adsorption and H* binding kinetics at industrial current densities. Herein, a face-centered cubic/hexagonal close packed (fcc/hcp) NiRu alloy heterojunction was fabricated on Ni foam (N doped NiRu-inf/NF) by a low-temperature nitrogen plasma activation. Simultaneously, nitrogen atoms are introduced into the alloy to facilitate d-p hybridization. When N doped NiRu-inf/NF is integrated into a dual-electrode cell for urea-assisted seawater electrolysis, it achieves 100 mA cm−2 with an ultra-low voltage of 1.36 V and excellent stability. Density functional theory (DFT) verifies that the robust d-p hybridization among Ni, Ru and N exhibits more energy level matching for H2O molecule adsorption at the Ru sites, while simultaneously reducing the interaction between H* and Ni sites in N-doped NiRu-inf.