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The present review is devoted to the electron cyclotron resonance (ECR) plasmas. Considering that the electromagnetic wave absorption using the ECR concept has been employed since the 1960s, it becomes obvious that the coverage of the field of the ECR plasma physics, engineering, applications, and prospectives in its entirety would be a utopia in the context of a single report. Thus, the backbone of this work is a meaningful categorization of the wide applications of the ECR plasmas (Secs. III, V, and VI), by citing representative publications. The applications mainly refer to surface processes (etching, deposition, nano-construction, functionalization, cleaning, etc.), biotechnology, thrusters, and ion sources. The text also focuses on the details of different ECR setup designs, as they are tailored for specific projects. At the same time, physical parameters and the pros and cons of the ECR discharges are evaluated. This approach leads to a brief but telling compilation of the state of the art of the ECR-driven plasmas over the last 60 years (mainly 1960–2023) as well as of their prospective aspects. An introductory discussion on the ECR plasma history (Sec. I) and on the fundamental principles of the ECR heating, multipolar confinement, technical aspects, practical setups, and features of ECR plasmas (Sec. II) is given at the early beginning of this work, facilitating, thus, the consideration of the topics that follow. Special attention is paid to the distributed or modular ECR plasmas (Sec. IV) since they may mirror the road map for engineering the future ECR plasma systems. The review is throughout supported by future-proof classic and up-to-date bibliographies to encourage further reading and to fill any information gap that inevitably appears in the present work. It is underlined that the main claims or conclusions of most of the cited works are here reproduced intentionally. In other words, it is the pretension of the present article to become a quick, but pithy, guide on the ECR plasmas and on the results achieved over the last 60 years, for potential readers of different disciplines and various backgrounds. Finally, Sec. VII recaps the present perspective on the ECR plasmas, and it points to the ECR plasma prospectives. [ABSTRACT FROM AUTHOR]

The scope of this paper is to present a comprehensive approach for simulating low-temperature atmospheric dielectric barrier discharge plasmas. The proposed methodology categorizes the primary physical phenomena: (i) discharge dynamics, (ii) ionic motion, and (iii) fluid flow, according to their respective time scales and simulates each independently. This allows for the use of distinct solution procedures tailored to each of the three stages of the problem. Such separation offers significant flexibility in choosing appropriate models and numerical schemes for each stage, enabling the simulation of complex geometries and large-scale applications without the excessive computational costs associated with a monolithic approach. As a case study, we apply the proposed algorithm to the surface dielectric barrier discharge plasma actuator for flow control, which is powered by alternating high voltages. The algorithm successfully described the actuator's behavior while maintaining low computational cost. Additionally, a parametric study is conducted to examine the effect of key input parameters on the generated electrohydrodynamic force and the resulting velocity. Finally, an overall assessment of the three-stage model is provided, highlighting its efficiency and accuracy. [ABSTRACT FROM AUTHOR]

In the present work, a capillary dielectric-barrier discharge of the coaxial electrode configuration, commonly employed to atmospheric-pressure cold plasma jet production, is studied in terms of thermal effects. The discharge is driven by sinusoidal high voltage in the kHz range and operates with helium gas channeled into a capillary dielectric tube having one end opened to the atmospheric air. The voltage amplitude and frequency, gas flow rate, and discharge volume are varied independently, and thermal effects are investigated by experimentally acquired results coupled with numerically determined data. The experiments refer to electrical power measurements, time-resolved temperature measurements, infrared imaging, and high resolution optical emission spectroscopy. The numerical modelling incorporates an electro-hydrodynamic force in the governing equations to take into account the helium-air interplay and uses conjugate heat transfer analysis. The comparison between experimental and numerical data shows that power is principally consumed in the dielectric barrier-helium interface resulting in the dielectric heating. A linear relation between steady state temperatures and supplied power, independent of the designing and operating conditions, is experimentally established. However, the gas flow rate affects the thermal effects differently compared to the other parameters, supporting the idea of a twofold nature of these systems, i.e., electrical and hydrodynamic. The main claim states the possibility of correlating (both experimentally and numerically) designing and operating parameters for evaluating heat distribution and gas temperature in capillary dielectric-barrier discharges used for plasma jet production. This is of high importance for processing temperature-sensitive materials, including bio-specimens. [ABSTRACT FROM AUTHOR]

Plasma chemistry at atmospheric pressure and low temperature has met an increased interest due to the effective production of reactive species (mainly reactive nitrogen species and reactive oxygen species) which are demanded in many applications like in biomedicine. The generation of such emissive reactive species is herein studied. A single parameter, i.e., the gas composition, is tuned and abundant chemical species are obtained in a quite controllable manner. The system refers to a small dielectric barrier discharge based reactor fed with He-N2/O2 or Ar-N2/O2 gases, which provides plasma in the form of "guided streamers." The plasma is sustained by positive high voltage pulses, and the emissive transitions versus the gas composition is determined by UV-VIS optical emission spectroscopy. The relative intensities of emissive species are recorded in the ambient air where the streamers propagate. The evolution of dominant species as a function of the gas composition is mapped, and optimal conditions in terms of species production are clearly revealed. The results show that additives do not necessarily enhance the density of all species, implying the need for plasma chemistry optimization in respect to every application. The study is extended inside the reactor, supporting the above statements. Finally, the rotational and vibrational distributions of critical probe molecules are recorded, testing the dependence of the gas temperature and energy transfer, respectively, on the gas composition. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) and contact angle measurements have been made to characterize patterned organic light-emitting-diode (OLED) substrates comprising indium-tin-oxide and a photoresist, both of which are modified by treatment with oxygen and tetrafluoromethane in a radiofrequency (13.56 MHz) low-power (∼1 W) capacitively coupled plasma as a function of time. Correlations between the surface chemical compositions from XPS and the contact angle, θ, are evaluated in order that the wettability of very small areas may be predicted. Very clear correlations for both the indium-tin-oxide and the photoresist surfaces are obtained enabling the prediction of the contact angles for these plasma-treated OLED materials from XPS data to a standard uncertainty of 9% in cos θ. These correlations need to be extended to a wider range of compositions in order to establish the physicochemical properties of particular surface functional groups that control water contact angles by this method. [ABSTRACT FROM AUTHOR]

Patterned organic light-emitting-diode substrates were treated by oxygen (O2) and tetrafluoromethane (CF4) radio-frequency (rf, 13.56 MHz) plasmas of low-power (close to 1 W) that were capacitively-coupled. An unexpected wettability contrast (water contact angle difference up to 90°) between the indium-tin-oxide anode and the bank resist regions was achieved, providing excellent conditioning prior to the ink-jet printing. This selectivity was found to be adjustable by varying the relative exposure time to the O2 and CF4 sequential plasmas. Static contact angle measurements and extensive x-ray photoelectron spectroscopy analyses showed that the wetting properties depend on the carbon and fluorine chemical functional groups formed at the outermost surface layers, whereas atomic force microscopy images did not show a morphological change. Plasma optical emission spectroscopy and ion mass spectroscopy suggested that surface functionalization was initiated by energy transfer from ionic species (O+, O2+, CF+, CF2+, and CF3+) and excited neutrals (O* and F*). The absolute ion fluxes measured on the substrates were up to 1014 cm-2 s-1 and the ion energies up to 20 eV, despite the low powers applied during the process. [ABSTRACT FROM AUTHOR]