Reliable determination of electron temperature (Te) in cold atmospheric pressure plasma (CAPP) remains challenging because the commonly used Boltzmann plot method is distorted by non-equilibrium effects such as stepwise excitation from metastable levels, radiative cascades, and self-absorption. We present a semi-empirical approach that enhances the robustness of Boltzmann plot analysis by introducing dual selection criteria for spectral lines. First, a deviation factor (Delta(ij)) to filter transitions dominated by spontaneous decay. Second, a branching-ratio test compares measured intensity ratios of transitions from the same upper level with the corresponding Einstein coefficient value ratios, allowing detection and exclusion of self-absorbed lines. The method is applied to optical emission spectra (OES) of argon plasmas generated in three distinct sources (10 MHz Teslacoil APPJ, 2.45 GHz microwave APPJ, and 13.56 MHz RF hollow cathode). In all cases, the refined Boltzmann plot yields linear fits (Pearso's r > 0.9) with markedly improved consistency and the extracted T-e values agree with the results from a collisional-radiative model (CRM). These findings demonstrate that the proposed semiempirical filtering significantly improves the reliability of Boltzmann plot based temperature diagnostics under atmospheric pressure, non-LTE conditions, providing a practical alternative when full CRM is not feasible.

This study reports the development and application of a large-area (50 cm2) radio frequency (RF) hollow cathode (HC) cold plasma device operating at 13.56 MHz for the decontamination of radioactive waste. Parametric optimization experiments identified a gas mixture of 6 LPM He, 2 LPM Ar, 20 SCCM CF4, and 10 SCCM O2 as optimal for achieving the highest etching rate with stable plasma formation suitable for long-duration operation. Material characterization of the etched tantalum (Ta) substrate using weight-loss measurement, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) confirmed the conversion of Ta to volatile TaF3, leading to the observed weight loss. Notably, the presence of O2 in the plasma resulted in a thin surface oxide layer on the Ta, but this layer did not hinder the etching process. Furthermore, chemical etching studies employing the optimized plasma composition were conducted on synthetic radioactive samples. These experiments demonstrated the effectiveness of the composition in etching uranium (U) samples, as evidenced by a reduction in their alpha radioactivity counts. Decontamination of U surrogates in controlled experiments highlights the potential of this cold plasma approach as a foundation for future development of solid radioactive waste treatment technologies.

This study investigates reactive species dynamics in cold atmospheric pressure plasma (CAPP) and bacterial inactivation pathways in Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus) using a Tesla coil-based radiofrequency (10 MHz) plasma jet with four gas compositions: Ar, Ar-O2, Ar-N2, and Ar-dry air (3:1) at a 10 mm treatment distance. Optical emission spectroscopy identified center dot OH and OI, while absorption and fluorescence spectroscopy quantified H2O2 and center dot OH. UV radiation and O3 were also measured. Electron temperature (Te) and density (ne) were determined via collisional-radiative modeling and Stark broadening analysis. Pure Ar plasma achieved complete inactivation, whereas gas admixtures, with lower Te and ne, reduced reactive species production. Despite its thicker peptidoglycan layer, S.aureus was more susceptible than E.coli, likely due to E. coli's outer membrane limiting radical penetration. Ar-N2 caused a 3-log reduction in S.aureus but only 2-log in E. coli, while Ar-O2 and Ar-dry air had minimal effects on E.coli but reduced S.aureus by 1-log and 2-log, respectively. H2O2 and UV played key roles in oxidative stress and DNA damage, with H2O2 facilitating intracellular center dot OH generation via Fenton reactions. Pure Ar plasma demonstrated strong bactericidal efficiency at 10 mm, driven by long-lived species (H2O2, UV) essential for contactless treatment.

Fluorine gas (F2) is indispensable in industries ranging from fluoropolymer synthesis to semiconductor fabrication, but its high toxicity, extreme reactivity, and storage hazards limit its applicability. On-demand in situ production could eliminate the need for bulk storage and transport. Here, we demonstrate fluorine generation from CF4 using a Tesla coil-based 2 MHz cold atmospheric plasma (CAP) device. Plasma was generated with Ar (Case I), Ar + CF4 (Case II), and Ar + CF4 + O2 (Case III). Optical emission spectroscopy (OES) and direct gas sensing used to detect species. Adding O2increased F2emission while reducing CF, CF2, and C2bands, and simultaneously decreased stainless steel electrode erosion. The oxygen effect is attributed to carbon scavenging and oxide film formation, enhancing F2yield while protecting electrodes. These findings establish the feasibility of plasma-based, switch-on/switch-off fluorine production.

This study investigates the influence of shape of Inconel 600 substrate on the deposition process using Microwave Plasma Chemical Vapor Deposition (MPECVD) for carbon nanofibers (CNFs) and graphene nanowalls (GNWs) on Inconel 600 substrates. The unique shape of the substrate significantly directs the deposition, revealing a noteworthy shape influenced transition. Notably, a novel pathway emerges for the electric field-driven transformation of Carbon Nanofibers (CNFs) into GNWs—an observation unprecedented in MPECVD processes. Comprehensive characterization, incorporating FESEM, Raman spectroscopy, and fully electromagnetic 3D frequency domain simulations, illuminates the subtle yet impactful interplay between substrate morphology and nanomaterial formation, providing valuable scientific insights.

A novel Tesla coil-based cold atmospheric pressure plasma (CAPP) device has been developed from the first principle for biomedical applications. This device has been characterized by electrical and optical diagnostics to determine its efficacy for biological applications. These characterization results showed that eight-LPM Ar plasma at 16.5-W operating power produces stable plasma with low discharge current. The device was then tested as bactericide on Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli . While E. coli could be completely annihilated after 120 s of plasma treatment at a 2-mm distance from plasma tip; inactivation of S. aureus starts after 60 s due to its thicker cell wall and complete annihilation requires 240 s of plasma exposure. Potent bactericidal plasma emission bands, such as OH (similar to 309 nm), N (SPS) (similar to 337 nm), and OI (similar to 777.4 nm), have been observed and electron microscopy analysis of bacteria supports cell damage post-plasma treatment. The study indicates that similar to 4-6 mm away from the plasma tip, the effect of charged particles vanishes but emitted UV and reactive oxygen species (ROS) from CAPP still eradicates bacteria in short exposure time (< 8 min). Demonstrating microbial inactivation at a distance underscores the potential for noncontact, remote sterilization applications. This innovative capability opens doors to industries where the maintenance of pristine, germ-free environments is of paramount importance.

Background: This in vitro study investigated the time-dependent bactericidal effects of cold atmospheric argon plasma treatment of periodontal hand scalers as well as the scanning electron microscopic view of the scaler tip surfaces before and after plasma treatment. Materials and Methods: The study used 34 periodontal hand scalers which were divided into test and control groups. The scaler tips were inoculated with Escherichia coli and Staphylococcus aureus bacteria, following which the scalers in the control and test groups were subjected to conventional sterilization and argon plasma sterilization, respectively. Varying exposure times of plasma treatment were done on the test group samples to evaluate the minimum time required for complete sterilization. Subsequently, streaks were made on plate count agar using each of these instruments. The agar plates were then kept in an incubator for 24 h, following which bacterial colony count was assessed (colony-forming units/mL). Furthermore, the scanning electron microscopic (SEM) view of the scaler tip was studied before and after plasma treatment. Results: A complete elimination of bacterial load (Gram-positive as well as Gram-negative) from the instrument surface was achieved by the plasma exposure time of 15–20 s. SEM analysis did not show a significant difference before and after plasma treatment as not many organic residues were present on the scaler tip. Conclusion: Cold atmospheric pressure plasma is an efficient and time-saving method of sterilization, capable of destroying both Gram-positive and Gram-negative bacteria.

Diagnostics of the inductively coupled plasma (ICP) generated using a flat spiral antenna are performed using radio frequency (RF) compensated Langmuir probe (CLP). The measurements on the generated plasma are made under the varying influence of the RF self-biased substrate electrode immersed in the plasma. From the $V$ – $I$ characteristics of the Langmuir probe taken at different radial locations in the plasma volume at a fixed axial distance of 5 cm from the quartz isolation window, electron energy probability functions (EEPFs) at various locations are obtained. It is observed that there is a strong correlation between the plasma parameters and EEPF with the bias on the substrate electrode. At a constant RF power in antenna coils, the EEPF evolved from bi-Maxwellian to Maxwellian with an increase in the bias level on the substrate electrode. The evolution of the EEPF with a variation of operating pressure is explained in terms of different heating mechanisms in plasma. Furthermore, EEPF evolution in the plasma from Maxwellian to bi-Maxwellian under the varying influence of RF power fed to the antenna coils keeping RF self-bias level on the substrate electrode constant is also explained.

Graphene nanowalls (GNWs) also known as carbon nanowalls (CNWs) and GNWs-carbon nanofibers (CNFs) hybrid nanostrucrures are grown on metallic wires using a two-step microwave plasma enhanced chemical vapour deposition (MW-PECVD) process. Here, plasma is generated in two steps (first at lower pressure and then at higher operating pressure) to avoid arcing on the metallic wire during the growth. Combination of Raman and transmission electron microscopy studies revealed presence of herringbone CNFs in the hybrid nanostructures that are grown with -100 V bias compared to pristine GNWs that are grown without any bias. A new approach for field emission (FE) analysis is created by combining FN equation with 'orthodoxy test' in a modified approach to avoid spurious results. Here, hybrid nanostructures exhibited higher current and more repeatable field emission characteristics over 4 cycles of operation. Post FE investigations indicate that while pristine GNWs underwent many deformities and structural changes, hybrid structures remain almost unscathed. These investigations point out that a novel synthesis mechanism can be used to grow GNW based hybrid nanostructures for different applications like X-ray sources which involves FE at the core.

This article studies the influence of in-situ temperatures (30 degrees C, 60 degrees C, 90 degrees C, and 120 degrees C) and loading rates (1 mm/min and 100 mm/min) on the out-of-plane flexural performance of Glass fiber reinforced epoxy composite with and without carbon nanofiber (CNF) (GE and CNF-GE). Improved stress transfer in CNF-GE composites than GE composite resulted in enhanced flexural properties at 30 degrees C. The crack propagation time is reduced as the loading rate increases. Due to the substantial obstruction of CNF against crack propagation, CNF-GE composites displayed higher flexural properties than GE composites. However, with the rise in temperature over 60 degrees C, CNF-GE composites showed a severe decrement in flexural properties than GE composites due to the generation of thermal stresses at the CNF/epoxy interface. The evidence of interfacial debonding at the fiber/epoxy and CNF/epoxy was obtained through fractography, satisfying the explanation provided during flexural analysis.Copyright (C) 2022 Elsevier Ltd. All rights reserved.Selection and peer-review under responsibility of the scientific committee of the 3rd International Conference on Processing and Characterization of Materials 2021 (ICPCM 2021).

Traditional disinfection methods against pathogens have numerous shortcomings, and inventive methods like cold plasma are required for virus inactivation. Here, an atmospheric pressure 13.56 MHz radio-frequency hollow cathode (RF–HC) cold plasma device has been used to build a cold plasma sterilization device, and its virucidal activity is assessed against P2 bacteriophage, a model surrogate for pathogenic viruses. The heart of this device contains a three-layered sterilization chamber which is a rectangular parallelopiped of 42 × 32 × 30 cm 3 . Optimization experiments were performed to make each corner of this chamber completely virus free after cold plasma treatment. This two-pronged study was conducted to establish the requirement of minimum vol. % H 2 O 2 in minimum time for the complete elimination of phages inside this sterilization chamber even when plasma is not in the direct line of sight. In initial experiments, the effect of the direct plasma line of sight was seen as the top and bottom layers showing less phage killing as compared to the middle of the sterilization chamber. Complete sterilization of bacteriophage, in all the three layers inside the sterilization chamber, was achieved by plasma treatment with 6% H 2 O 2 for 10 min in 80 watts of plasma operating power. It was also seen that 6% H 2 O 2 mist alone is not sufficient to provide a high degree of sterilization, and normal water mist combined with cold plasma can provide a higher level of sterilization at each corner of the chamber.

In this article, the optimization of spatial parameters of a 2.45-GHz atmospheric pressure plasma jet (APPJ) at different operational parameters has been done. For this purpose, simulations and experiments have been carried out to investigate the spatial dimensions of the microwave cold plasma jet generated from the device. To achieve this, the plasma discharge behavior and jet formation have been studied at different working gas flow rates and input microwave power. The 3-D simulations have been carried out by using the plasma module and electromagnetic wave module of COMSOL Multiphysics v. 5.5. Experimental validation was achieved and simulated spatial dimensions of plasma jet showed good correspondence with the experimental results. Simulated variations of jet length and diameter with gas flow rate and applied power matched closely with experimental results. Intrinsic plasma parameters, such as electron temperature ( $T_{e}$ ) and number density ( $n_{e}$ ), were also obtained with the simulation model and compared with experimental findings based on optical emission spectroscopy (OES) results and $T_{e}$ values matched well in both cases.

Atmospheric pressure cold plasma generated using a radio frequency hollow cathode (RFHC) device recently showed its potent virucidal characteristics. For this purpose, the atmospheric pressure cold plasma of Ar was generated with a specially designed electrode using RF (13.56 MHz) power. In order to establish a correlation between the generated plasma species and its virucidal activity, systematic optical emission spectroscopy (OES) investigations were conducted on the plasma. OES studies revealed that the generated plasma using this device shows the emission of important species in the ultraviolet (UV) region and reactive oxygen species (ROS) in the optimized operation condition, required for virucidal action. Furthermore, investigations revealed that similar active species can be generated by placing a commercial nebulizer in front of plasma. Investigations conducted on the aerosol capturing efficiency of N-95 mask revealed that cold plasma treatment leaves functional aspects of this medical personal protection equipment (PPE) unchanged. The results indicate that such an RF-HC device in combination with a nebulizer for introducing water mist in plasma can effectively destroy bacteriophage of Aeromonas bacteria at low operating power (70–90 W).

Splitting of D band is observed in vertically aligned graphene nanowalls (VAGNWs) during analysis of Raman spectroscopy for the first time and two distinct peaks were observed, designated as D-1 and D-2. Evolution of D band with increasing laser power is studied and it is seen that intensity and full width at half maxima (FWHM) of D-2 get reduced with increasing laser power. I-D/I-G values of deposited VAGNWs showed a decreasing trend with increasing laser power indicating that defects have slightly reduced with increasing laser power. It is also observed that D-/ peak at high laser power almost merged with G peak like highly defective graphene sheets. Defect analysis showed that all the samples have high degree of stage 2 defect. Interestingly, no splitting was observed in G(/) band by increasing laser power and VAGNWs kept their turbostratic nature intact through this peak.

Langmuir probe (LP) diagnostics is performed on an inductively coupled plasma (ICP) generated using a flat spiral antenna. The current-voltage (I-V) characteristics are measured using a radio frequency (RF) compensated LP to mitigate the effect of RF distortion in I-V measurements. All-important plasma parameters such as electron density (ne), electron temperature (T e ), plasma potential (V p ), and electron energy distribution function (EEDF) are measured in a cylindrical-shaped ICP. The plasma is generated by feeding RF (13.56 MHz) current in the planer multiple spiral antennas. It is seen that the plasma is uniform over an area with 200 mm diameter, with an electron number density in the range from~10 11 to 10 12 cm -3 . Typically for plasma processing of materials, the required density fall in that region. Variation of plasma parameters is investigated as a function of applied RF power and operating pressure and the observed results are discussed.

The Schottky Conjecture (SC) suggests the use of a multiscale cathode to increase the local electric field at a field-emitting tip. A similar increase in local field also occurs when the anode is in close proximity to the cathode. The authors take advantage of these twin effects to design a compound cathode consisting of a macroscopic base with a much smaller wire-protrusion having an end-cap. Field emission experiments were performed using two different compound-cathode setups, each consisting of an adjustable-height Kovar wire with graphene nanowalls deposition as the end-cap, and a macroscopic base on which the Kovar wire is mounted. The field emission data was recorded for both compound-cathodes at different anode positions. Experimental results indicate remarkable improvement in field emission current density while adopting an optimized diode architecture. Stable emission was observed and a maximum current density of 46 mA/cm2 was extracted from the sample. An analysis of the experimental data, aided by additional numerical simulations, clearly shows the combined effect of the recently proposed Corrected Schottky Conjecture and the anode proximity effect. It is thus possible to realize an efficient field emitter device by tweaking the geometry of the diode structure.

Atmospheric pressure cold plasma is a promising technology in fighting pathogenic micro-organisms. In times of Covid-19 pandemic, it was decided to modify two types of cold plasma devices to study their effectiveness in the killing of pathogenic micro-organisms. These studies have shown that both the devices are efficient in this purpose. While pencil like microwave based device can destroy Aeromonas bacteria and its bacteriophage from 6 cm distance in 2 min, the larger (~ 40 cm2) RF plasma based device could do the similar killing ability for the larger possible area in 4 min. Optical Emission Spectroscopy (OES) studies revealed that both these devices produce OH radicals which helped in the destruction of both bacteria and its bacteriophage. With suitable modifications, these devices, especially the larger area device may even be implemented for the elimination of Covid-19 affected wards of hospital without using any sensitive chemical process.

Carbon nanowalls (CNWs) have been synthesized by electron-cyclotron resonance chemical vapour deposition (ECR-CVD) method on Si substrates. During deposition, processing gas compositions were varied to improve growth rate and it was found that replacing inflammable H-2 by safer and cheaper N-2 improves growth rate of CNWs. Energy dispersive x-ray spectroscopy and Fourier transform Infra-red spectroscopy results showed that N-2 did not take part in bond formation. Emissive probe diagnostics showed that increasing precursor gas to 90% of total gas mixture increases impinging ions' energy by 3.5 times leading to deposition of vertically oriented CNWs on Si substrate.

Plasma is probably the most underused tool applied for nuclear waste management. To study the feasibility of putting this technology in practice, a non-thermal microwave based atmospheric pressure plasma jet (APPJ) had been developed. The device was characterized by spectroscopic technique prior to its actual deployment inside glove box to narrow down its operational regime and also tested on Ta, a known surrogate of Pu which showed its efficacy in etching. The device was then used for removal of Pu based synthetic radioactive wastes inside radioactive glove box. Thereafter, optimization studies were conducted to maximize decontamination efficiency and it was seen that oxygen in plasma plays a significant role. The same device was later scaled up to a multi-electrode model and used for similar radioactive waste removal. Both these devices under optimized condition could remove ∼92% radioactive wastes and the scaled up model reduced duration by 50%.