Accurate plasma-chemical modeling of methane conversion requires reliable ionization data in relevant gas mixtures such as Ar:CH4. In this study, the apparent reduced effective ionization coefficient, αea/N, which includes contributions from mixture-specific ionization processes was determined experimentally using a steady-state Townsend discharge in Ar:CH4 mixtures (e.g., 99%Ar:1%CH4, 97%Ar:3%CH4, 95%Ar:5%CH4, 90%Ar:10%CH4, 75%Ar:25%CH4, 50%Ar:50%CH4, and 25% Ar:75%CH4) over a broad pressure range of 10–800 Torr and reduced electric field strengths E/N ranging from 40 to 1200 Td. The measured αea/N values were compared with theoretical αe/N values calculated using the Boltzmann equation solver BOLSIG+. Deviations between experimental αea/N and calculated αe/N exceeded 20% at low E/N. Improved agreement was achieved by including Penning ionization from Ar excited states, specifically Ar (3p53d, 13.84 eV) and Ar (3p54p, 12.91–13.48 eV). These results demonstrate that Penning ionization induced by Ar excited states (3p54p, 12.91 eV and upwards) must be considered for accurate modeling of Ar:CH4 plasmas, particularly at moderate to atmospheric pressures and low E/N.

Methane (CH4) has a high heating value, is relatively inexpensive, and is a widely available gas. For the conversion of methane into liquid products, a novel approach proposes to use non-thermal plasma processes. Efficient utilization of plasma requires precise plasma chemical models that rely on accurate input data such as the reduced effective ionization coefficient alpha(ea)/N. Such data are available for pure CH4, but N-2 or O-2 are typically also present in plasma reforming of CH4, and no experimental data about reduced effective ionization coefficient exist for these mixtures. The present study determined the alpha(ea)/N in CH4:N-2 and CH4:O-2 gas mixtures in the pressure range of 10-800 Torr and reduced electric field strength E/N range of 40-1200 Td utilizing a steady-state non-self-sustaining Townsend discharge. Experimental results were compared with calculations of the Boltzmann equation solver BOLSIG+ and a more accurate model that accounted for detachment from O-2, as well as O-3(-) formation and charge transfer reactions. In CH4:N-2 mixtures, alpha(ea)/N decreased with N-2 content, and BOLSIG+ calculations agreed reasonably well with measurements. In CH4:O-2 mixtures, alpha(ea)/N did not change with the mixture composition, and at low E/N values, the data calculated by the refined model fitted the experimental data markedly better compared to fitting with BOLSIG+ calculations. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International (CC BY-NC-ND) license (https://creativecommons.org/licenses/by-nc-nd/4.0/).

N-2:O-2 gas mixtures are important for applications of atmospheric pressure plasmas such as ozone production, air purification from VOCs and NOx and surface treatments. Fundamental parameters such as the effective ionization coefficient are inputs for theoretical plasma models for applications and must thus be accurately known. This work determined the apparent effective ionization coefficient in N2:O2 mixtures in a broad reduced electric field strength E/N range of 150-1200 Td with two separate methods and compared with BOLSIG+ calculations of reduced effective ionization coefficient. Additionally, the equilibrium distance required to establish a steady-state electron energy distribution was estimated from spatial profiles of optical emission.

Ar:CO2 gas mixtures have recently received research interest due to the possibly beneficial effects of Ar addition to CO2 for CO2 conversion using electrical discharges. For any gas discharge, knowledge of fundamental parameters, such as the effective ionization coefficient, is necessary to optimize the efficiency of the discharge for a particular application. The reduced apparent effective ionization coefficient αea/N is a measure of total ionization. αea/N is influenced by electron impact ionization, electron attachment and also by charge transfer reaction, Penning ionization, and photoionization. This study determined the αea/N of Ar:CO2 gas mixtures in the pressure range of 10–800 Torr and reduced electric field strength E/N range of 40–1200 Td utilizing a steady-state non-self-sustaining Townsend discharge. Experimental results were compared with calculations of Boltzmann equation solver BOLSIG+. Differences between measurements and calculations increased with decreasing CO2 content in the mixture down to 20%, and the differences were highest at low E/N values (below 150 Td). As the simple modification of the model, contribution of ionization of CO2 by Penning transfer from Ar* 3p53d excited states (13.86 eV) was added to the BOLSIG+ calculations, which resulted in good fit of the experimental measurements. Comparison of CO2 addition to Ar with the addition of O2 or N2 revealed that ionization of CO2 or O2 from Ar* 3p53d excited states influences ionization in Ar:CO2 and Ar:O2 mixtures but not in Ar:N2 mixtures, due to the different ionization energies of CO2, O2, and N2.

The present study investigated the production of reactive chlorine species (RCS) by Ar/O-2 and He/O-2 radiofrequency plasma jets in saline solution, and the sensitivity of the liver cancer cell line HepG2 to RCS and H2O2. Both plasma jets were able to produce RCS; however, at similar plasma powers, pressures, and feed gas flow rates, the He/O-2 jet was more efficient for RCS production. The lower RCS yield in the case of the Ar/O-2 plasma jet was mainly due to the higher RCS quenching. At a low production rate, RCS can be produced in the open air. Viability tests showed that HepG2 cells were more sensitive to H2O2 than RCS.

He:O 2 gas mixtures are popular in many non-thermal plasma applications because of the good thermal conductivity of He and high production of reactive oxygen species. The applications utilizing reactive oxygen species, in particular, applications in biomedicine require accurate knowledge of the fundamental ionization parameters of gases such as the ionization coefficient. This study was focused on experimental determination of the reduced apparent effective ionization coefficient α ea /N in He:O 2 mixtures. Experiments were conducted in the absolute pressure range of 10–800 Torr and reduced electric field E/N range of 40–1000 Td utilizing a steady-state non-self-sustaining Townsend discharge. Experimental results were compared with a theoretical model which was based on BOLSIG + calculation of ionization and attachment coefficients and additionally considered the ion conversion of O − to O 2 − , detachment from O 2 − and formation of O 3 − and Penning ionization by He metastable species. The measurements agreed reasonably well with model calculations. Comparison with model suggest that He metastable species affect net ionization in He:O 2 mixtures with O 2 concentrations up to 10% often encountered in the applications and thus should be included in models of atmospheric pressure plasmas. The attachment of electrons became important at O 2 concentrations above 10% and is therefore less important in most applications.

Precise knowledge of the fundamental ionization properties of gases, such as the effective ionization coefficient, is crucial for discharges in mixtures of Ar:O2, which are significant for a wide range of plasma applications. This study determined the effective ionization coefficient in electronegative gas mixtures of Ar:O2 in the pressure range of 10–800 Torr and reduced electric field strength E/N range of 40–1200 Td utilizing a steady-state non-self-sustaining Townsend discharge. The reduced effective ionization coefficient αe/N increased with E/N and decreased with increasing O2 content in the gas mixture. The experimental results were compared with a model which was based on calculating the ionization and attachment coefficients with BOLSIG+. The ion conversion of O− to O2−, detachment from O2−, and formation of O3 were accounted for similarly as has been done with N2:O2 mixtures. Reasonably good agreement between the measurements and the model calculations was achieved for Ar:O2 mixtures with the O2 content between 20% and 70%. A discrepancy of more than 20% between measurement and calculations was observed at low E/N values when the O2 content was below 20% and at high E/N values when the O2 content was above 70%. Several possible explanations were proposed for the observed discrepancy; however, more elaborate models are required. The reduced critical electric field E/Ncrit, where the apparent effective ionization coefficient is zero, was determined as a function of the O2 content in the Ar:O2 mixtures. E/Ncrit increased with increasing O2 content in the mixture.

First Townsend ionization coefficient α in gas mixture of He with N2 is relevant for modeling of the development and chemical activity of atmospheric pressure plasma jets. This study determined α from measurements of current versus electrode separation in a steady-state non-self-sustaining Townsend discharge set-up. The measurements were carried out in absolute pressure range of 10–800 Torr and reduced electric field E/N range of 20–1000 Td. The effect of the N2 concentration in the gas mixture on the density normalized ionization coefficient α/N depended on the reduced electric field strength E/N. At E/N values below 200 Td, increased N2 content reduced the α/N while at E/N values above 200 Td, increased N2 content increased the plateau value of α/N. Reasonably good coincidence was observed between calculation performed with Bolsig+ and measured α/N. The discrepancy between experimental results and calculations at N2 percentage in the mixture below 5% and E/N values below 200 Td can be attributed to the Penning effect.

The present study investigated the effect of plasma-produced reactive oxygen (ROS) and nitrogen (RNS) species on cancer cell viability. Reactive species were generated in deionized water by using an atmospheric pressure Ar plasma jet within the controlled ambient gases (air, O2 or N2), which allowed the production of plasma-activated water containing only ROS (e.g. O3, H2O2) or both ROS and RNS (e.g. H2O2, NO2–, NO3–). A considerable amount of H2O2 was produced in all ambient gases, and its generation rate was highest in N2 and lowest in O2. The latter was connected with a H2O2 precursor, OH, efficient quenching in O2 ambient gas. Small quantities of NO2– were generated during short (< 5 min) plasma treatments in ambient air and N2. The highest amount of NO3– was produced in N2 ambient gas. Ozone was detected only in the case of O2 environment. Cell viability studies were carried out by utilizing two cancer cell lines: 4T1 (breast cancer) and PPC-1 (prostate cancer). The results of the colorimetric succinate dehydrogenase activity assay showed that the studied cell lines had a similar sensitivity to the plasma activated medium. The impact of medium produced in the O2 ambient environment was determined by H2O2 content. The equivalent amount of H2O2 in the plasma activated medium produced in the N2 ambient environment caused an almost two-fold higher viability than in the case of the O2 ambient gas. It is proposed that this was due to the cellular proliferation enhancing effect of NH3.

The present study compares the operation of two cold atmospheric plasma jet (CAPJ) configurations: needle-to-cylinder electrode configuration (CAPJ I) and single high-voltage cylinder electrode around the quartz tube (CAPJ II). The CAPJs were operated in argon flowing through a quartz capillary with 0.5-mm inner diameter into the ambient air, and the plasma was generated by sinusoidal kHz frequency AC power supplies. The main emphasis of the study was on the mechanism of the initiation of ionization waves for these two configurations. For both CAPJs, there appeared several ionization waves during one half-period of the applied voltage waveform, and the number of ionization waves increased at higher voltage amplitudes. However, we discovered marked differences in the initiation of the ionization waves for two different CAPJ configuration. The applied voltage controlled the initiation of consecutive ionization waves, which propagated from the grounded electrode towards the tube orifice in CAPJ I. In the case of CAPJ II, certain time had to pass for the initiation of a new ionization wave, and subsequent ionization waves within the same half-period started at the tube orifice. In addition to the differences in the initiation of the ionization waves, we observed that the CAPJ I was ignited and sustained at lower voltages, while CAPJ II produced a longer plasma jet. The observed advantages and deficiencies of investigated CAPJ configurations point out their potential in different applications.

Present study investigates the effect of gas environment on the chemical composition of plasma activated media (PAM). PAM was produced by argon RF plasma jet (13.56 MHz) at constant plasma power (10 W) in contact mode and in controlled atmosphere of air, O 2 or N2. The long-lifetime chemical species (H 2 O 2 , O 3 , $\text{NO}_{2^{-}}$ and $\text{NO}_{3^{-}}$ ) monitored in the PAM by using UV absorption spectroscopy method [1] after plasma treatment. The duration of treatment was varied (0–30 min).

Reactive oxygen and nitrogen species (RONS) are known to have several biological activities, with multiple potential applications, including cancer therapy. Present study investigated the differential effect of plasma-produced reactive oxygen (ROS) and nitrogen (RNS) species on cancer cell viability. ROS and RNS were generated in deionized water using atmospheric pressure Ar plasma jet operating in the controlled ambient gases (air, O 2 or N2) which allowed to generate plasma-activated medium (PAM) containing only ROS (O 3 , H 2 O 2 ) or both ROS and RNS $(\mathrm{H}_{2}\mathrm{O}_{2},\ \mathrm{N}\mathrm{O}_{2}^{-},\ \mathrm{N}\mathrm{O}_{3}^{-})$ . The concentrations of O 2 , O 3 , H 2 O 2 , $\mathrm{N}\mathrm{O}_{2}^{-}$ and $\mathrm{N}\mathrm{O}_3^{-}$ were determined using UV absorption spectroscopy. H 2 O 2 was produced in all ambient gases, its generation rate was higher in air or N2 and lowest in O 2 . Small quantities of $\mathrm{N}\mathrm{O}_{2}^{-}$ were generated during short (<5 min) plasma treatment in air and N2. The highest amount of $\mathrm{N}\mathrm{O}_3^{-}$ was generated in ambient N2 gas, with its production rate nearly proportional to the treatment time. Finally, ozone was generated only in the case of ambient O 2 .

Present study investigated the applicability of the macro-kinetic description for RONS production by an atmospheric pressure micro-plasma jet operated in He gas flow. The concentrations of H2O2, NO2− and NO3− in the deionized water were measured using UV absorption spectroscopy. The contact and non-contact modes were identified and the concentrations of H2O2, NO2− and NO3− were higher in the contact mode. In the contact mode the concentrations of H2O2 and NO3− increased with the applied voltage and treatment duration while He flow rate also influenced the concentrations. The production rates of H2O2 and NO3− correlated with the amount of transferred charge of ionization waves during positive half period. The dependence of the production rates of RONS on the He flow rate suggests that the gas flow influences the gas composition in active discharge zone and limits the applicability of macro-kinetic model with the used plasma jet setup. As a potential application the plasma treated water was applied to prostate cancer cells. The viability of prostate cancer cell decreased linearly with the increase of H2O2 and NO3− concentrations while the NO2− concentration had no clear correlation with cell viability. The H2O2 was found to be the main agent responsible for the decreased cell viability. The amount of dissolved NO3− on the other hand determined the pH of the plasma treated water.

From the year 2008, the Innovation Centre of the Information Technology Foundation for Education in Estonia runs the process of awarding "Estonian e-Course Quality Label" to applicants from different national vocational and higher education institutions. The process of awarding quality labels is structured on three tiers: self-assessment, organizational and expert level. The process which is described in our previous article (Villems, 2013), needs well defined criteria as considerable bases for evaluation. For self-assessment and expert level evaluations, the quality criteria are prepared in the form of two rubrics, both with more than 20 quality criteria. Both rubrics coincide in majority of questions, but the self-evaluation rubric has additional criteria, which only authors of the course are able to evaluate. To make the process of evaluation smoother and easier to manage, interactive web-based software was developed. As the real responsibility for the content of the course is in the hands of particular educational organization, we did not prepare e-learning course evaluation criteria for them. Their evaluation has to reflect students' feedback and agreement with the quality of the content. In this paper we will discuss the choice of criteria used in the above-mentioned rubrics, and how we explain their four levels, from poor to excellent. We also describe the process of choosing and further development of these criteria and explain how these are connected with our "Quality Manual for e-Courses (Pilt, 2010). Feedback on the described quality process is gathered during quality assessment evaluation process from different parties each year (applicants i.e. authors of the e-courses, expert evaluators and quality team members). Based on this feedback continuous further development of quality criteria and rubrics is taking place. We enhance the list of criteria in rubrics, criteria explanations, interactive web tool and all other aspects of this e-learning quality process.

The annual international conference Functional Materials and Nanotechnologies (FM&NT) was started in 2006 by scientists from the Institute of Solid State Physics, University of Latvia. The warm welcome and open atmosphere of this scientific conference has turned it into an event where people from different countries and different fields come and meet under the shared umbrella of functional materials and nanotechnology. It is particularly important for early stage scientists who are looking for new knowledge and contacts with people from various fields to build their own network. Our Latvian colleagues, with their success in internationalization, made us neighbouring Estonians so jealous that we could not help but propose organising the conference every second year in Estonia. In a way, this conference is a continuation of the idea of the famous Baltic seminars which took place over several decades in the last century. Due to political constraints, these seminars were only open to scientists of former Eastern Europe countries, but had a great popularity and attendance from over the whole Soviet Union. Many collaborations started from the initial personal contact between scientists at these twice yearly seminars, held alternately in Latvia and Estonia. At the FM&NT 2012 conference, the decision was made that Institute of Physics, University of Tartu would organise the next event in Tartu in 2013. FM&NT-2013 was hence held in Tartu (Estonia) from 21–24 April 2013 at the Dorpat Conference Centre. The main selected topics of the conference were: (i) multifunctional materials, (ii) nanomaterials, (iii) materials for sustainable energy applications and (vi) theory. Additionally, the focus in this conference was on studies with the help of synchrotron radiation and other novel light sources such as free electron lasers. The conference provided an opportunity for 300 scientists from 21 countries to meet, establish contacts, exchange knowledge and discuss their research. During the three days of the conference, 14 invited talks were given, 45 oral and five commercial talks by companies were delivered and more than 200 posters were presented and discussed. As an outcome of the conference, 14 contributions were selected as regular papers to be submitted as a special section in Physica Scripta , and they are published in this issue. Additionally, 62 papers submitted based on the conference contributions, were included in IOP Conference Series : Materials Science and Engineering and are available at http://iopscience.iop.org/1757-899X/49/1. Additional information about FM&NT-2013 is available at its homepage http://fmnt.ut.ee/. Future information regarding the conference will be published on the website. Photograph. Participants of FM&NT-2013, the photo was taken in front of the Science Centre AHHAA on 23 April 2013.Acknowledgement The Organizing Committee would like to thank all the speakers, contributors, session chairs and other staff involved for their personal efforts in making FM&NT-2013 successful and memorable. We express our thanks to all the authors for their research contribution presented in this issue. We express our gratitude to all of the reviewers and editors with special thanks to the Editor-in-Chief of Physica Scripta Dr Suzy Lidstrom, who took part of the conference with an invited talk. The efforts of members of the IOP Publishing team, especially the publisher Yasmin McGlashan, and the guest editor from the local organizing committee Dr Rainer Parna, are also gratefully acknowledged. We would like to acknowledge financial support by Tartu University Development Fund, Estonian national projects supporting Materials Science, Science Internationalisation and Centre of Excellence programs based on the contribution of the European Structural Funds and Estonian national funding. Also, the graduate school on 'Functional Materials and Technologies' supported by the European Social Fund has given a generous contribution to assist in the participation of our early stage researchers. This support is gratefully acknowledged. We also would like to acknowledge and thank all the sponsors, companies (Raith, Bruker, Vistec Lithography, Saint-Tech, The Doma Group, Armgate and American Elements) who create conditions for our everyday research in the Baltics. We hope that the continuation of the tradition introduced with this conference will strengthen the international cooperation of scientists from Baltic states with researchers from other countries. In particular, we very much value the communication between new generations of researches which takes place, ensuring the fruitful development of science in our countries. The Organizing Committee hopes that the conference FM&NT-2013 gave the participants good insight into recent progress in nanotechnology, sustainable energetics, the processing and modelling of multifunctional materials and research enabled by the use of synchrotron radiation or other novel light sources such as free electron lasers. We sincerely hope that the conference has provided support for the circulation of information and brought together many young and experienced scientists from different fields, leading to fruitful discussions. We hope that all of the participants had an ejoyable and memorable time in Tartu. We welcome you back in the future.

The ozone production rate as a function of gas pressure and electric field strength is measured in a synthetic air dc low-current non-self-sustained discharge. The reduced field strength, E/N, is varied in the range 160?520?Td and the pressure, p, in the range 6.5?162?kPa. The ozone generation efficiency, i.e. the amount of ozone produced per energy unit absorbed by electrons in the discharge in air, is measured for the first time. The results obtained are compared with theoretical calculations of other authors.

The International Conference Functional Materials and Nanotechnologies (FM&NT – 2013) was held in Tartu, 21–24 April 2013 at the Dorpat Conference Centre. The conference was organised by Institute of Physics, University of Tartu.

The ozone production rate in a dc low-current non-self-sustained discharge (dark discharge) in oxygen is measured systematically as a function of gas pressure and electric field strength in the range of reduced field strengths E/N = 120-800 Td and pressures p = 7-160 kPa. The fraction of energy consumed by electrons in the dark discharge is calculated and the ozone generation efficiency (the maximal energetic yield of ozone in an idealized discharge with negligible ion losses) is estimated. The reaction rate coefficient for oxygen dissociation by electron impact, deduced from the efficiency curve, is proposed.