Nikolay Britun

Optical characterization of a microwave pulsed discharge used for dissociation of CO2

Conversion of CO2 into CO and O is studied in a flowing gas surfaguide pulsed microwave discharge operating with CO2 and CO2 + N2 gas mixtures under different conditions. Optical emission spectroscopy, including actinometry (using N2), vibrational (N2 molecule) and rotational (CO and N2 molecules) analysis are utilized. Both time- and space-resolved measurements are performed. The results show the essential changes of the CO2 conversion rate, its energetic efficiency, and the gas and vibrational temperatures along the gas flow direction in the discharge. The spatial distribution of the power absorbed in the plasma is analyzed. It is also confirmed that the vibrational excitation is a key factor in the CO2 dissociation process in this type of plasma. It is suggested that the obtained dissociation rates can be further optimized by varying the gas composition, as well as the power applied to the discharge.

Plasma diagnostics for understanding the plasma–surface interaction in HiPIMS discharges: a review

The physical and chemical aspects of plasma–surface interaction in high-power impulse magnetron sputtering (HiPIMS) discharges are overviewed. The data obtained by various plasma diagnostic methods representing the important sputtering discharge regions, namely the cathode vicinity, plasma bulk, and substrate vicinity, are reported. After a detailed introduction to the problem and description of the plasma characterization methods suitable for pulsed magnetron discharge analysis, an overview of the recent plasma diagnostics achievements in both non-reactive and reactive HiPIMS discharges is presented. Finally, the conclusions and perspectives suggesting possible directions and research strategies for increasing our knowledge in this domain are given.

The influence of power and frequency on the filamentary behavior of a flowing DBD-application to the splitting of CO2

In this experimental study, a flowing dielectric barrier discharge operating at atmospheric pressure is used for the splitting of CO2 into O2 and CO. The influence of the applied frequency and plasma power on the microdischarge properties is investigated to understand their role on the CO2 conversion. Electrical measurements are carried out to explain the conversion trends and to characterize the microdischarges through their number, their lifetime, their intensity and the induced electrical charge. Their influence on the gas and electrode temperatures is also evidenced through optical emission spectroscopy and infrared imaging. It is shown that, in our configuration, the conversion depends mostly on the charge delivered in the plasma and not on the effective plasma voltage when the applied power is modified. Similarly, at constant total current, a better conversion is observed at low frequencies, where a less filamentary discharge regime with a higher effective plasma voltage than that at a higher frequency is obtained.

OH radicals distribution in an Ar-H2O atmospheric plasma jet

Recently, plasma jet systems found numerous applications in the field of biomedicine and treatment of temperature-sensitive materials. OH radicals are one of the main active species produced by these plasmas. Present study deals with the investigation of RF atmospheric pressure plasma jet in terms of OH radicals production by admixture of H2O into argon used as a feed gas. Generation of OH radicals is studied by laser-induced fluorescence spectroscopy. The excitation dynamics of OH radicals induced by the laser photons is studied by time-resolved spectroscopy. It is shown that vibrational and rotational energy transfer processes, which are sensitive to the surrounding species, can lead to the complication in the OH radicals diagnostics at high pressure and have to be considered during experiments. The axial and radial 2D maps of absolute densities of hydroxyl radicals at different water contents are obtained. The highest density of 1.15 × 1020 m−3 is measured in the plasma core for the case of 0.3% H2O. I...

Rarefaction windows in a high-power impulse magnetron sputtering plasma

The velocity distribution function of the sputtered particles in the direction parallel to the planar magnetron cathode is studied by spatially- and time-resolved laser-induced fluorescence spectroscopy in a short-duration (20 μs) high-power impulse magnetron sputtering discharge. The experimental evidence for the neutral and ionized sputtered particles to have a constant (saturated) velocity at the end of the plasma on-time is demonstrated. The velocity component parallel to the target surface reaches the values of about 5 km/s for Ti atoms and ions, which is higher that the values typically measured in the direct current sputtering discharges before. The results point out on the presence of a strong gas rarefaction significantly reducing the sputtered particles energy dissipation during a certain time interval at the end of the plasma pulse, referred to as “rarefaction window” in this work. The obtained results agree with and essentially clarify the dynamics of HiPIMS discharge studied during the plasma...

Altering the sulfur content in the propanethiol plasma polymers using the capacitive-to-inductive mode transition in inductively coupled plasma discharge

The effect of the transition from capacitive (E) to inductive (H) mode on propanethiol plasma polymer films properties was investigated by optical emission as well as by x-ray photoelectron spectroscopy. The E mode is characterized by low deposition rate and by high sulfur content in the films (∼40% vs ∼20% in H mode). After aging, a strong decrease of sulfur to carbon content (from ∼0.75 to 0.13), attributed to desorption of unbounded sulfur-based molecules (e.g., H2S), is detected at low power in E mode. The importance of the E-H transition for altering the film properties is highlighted.

Particle visualization in high-power impulse magnetron sputtering. II. Absolute density dynamics

Time-resolved characterization of an Ar-Ti high-power impulse magnetron sputtering discharge has been performed. The present, second, paper of the study is related to the discharge characterization in terms of the absolute density of species using resonant absorption spectroscopy. The results on the time-resolved density evolution of the neutral and singly-ionized Ti ground state atoms as well as the metastable Ti and Ar atoms during the discharge on- and off-time are presented. Among the others, the questions related to the inversion of population of the Ti energy sublevels, as well as to re-normalization of the two-dimensional density maps in terms of the absolute density of species, are stressed.

Influence of air diffusion on the OH radicals and atomic O distribution in an atmospheric Ar (bio)plasma jet

Treatment of samples with plasmas in biomedical applications often occurs in ambient air. Admixing air into the discharge region may severely affect the formation and destruction of the generated oxidative species. Little is known about the effects of air diffusion on the spatial distribution of OH radicals and O atoms in the afterglow of atmospheric-pressure plasma jets. In our work, these effects are investigated by performing and comparing measurements in ambient air with measurements in a controlled argon atmosphere without the admixture of air, for an argon plasma jet. The spatial distribution of OH is detected by means of laser-induced fluorescence diagnostics (LIF), whereas two-photon laser-induced fluorescence (TALIF) is used for the detection of atomic O. The spatially resolved OH LIF and O TALIF show that, due to the air admixture effects, the reactive species are only concentrated in the vicinity of the central streamline of the afterglow of the jet, with a characteristic discharge diameter of ~1.5 mm. It is shown that air diffusion has a key role in the recombination loss mechanisms of OH radicals and atomic O especially in the far afterglow region, starting up to ~4 mm from the nozzle outlet at a low water/oxygen concentration. Furthermore, air diffusion enhances OH and O production in the core of the plasma. The higher density of active species in the discharge in ambient air is likely due to a higher electron density and a more effective electron impact dissociation of H2O and O2 caused by the increasing electrical field, when the discharge is operated in ambient air.

Resonant optical absorption spectroscopy of Ce

Resonant optical absorption of ground state Ce atoms is demonstrated. Ce I resonant emission line at 461.05 nm (Aij = 28 × 108 s−1) corresponding to the transition 4f5d6s2–4f2(1G)5d (2I)6s is utilized. In a magnetron sputtering discharge used as an atomic source, the absolute densities of atomic ground state Ce sputtered in pure Ar and in Ar–O2 (oxidized magnetron cathode) gas mixtures are found to be nearly 2 × 108 cm−3 (pure Ar) and 1 × 107 cm−3 (Ar + O2). The phenomena inherent in reactive sputtering, such as the non-oxidized–oxidized regime transition and the hysteresis of the transition point, are detected. The obtained data are compared with the existing results of a similar absorption analysis performed in the Ti dc magnetron discharges. The discrepancies in the obtained Ce and Ti absolute ground state densities are analysed.

DBD in burst mode: solution for more efficient CO2 conversion?

CO2 conversion into value-added products has gained significant interest over the few last years, as the greenhouse gas concentrations constantly increase due to anthropogenic activities. Here we report on experiments for CO2 conversion by means of a cold atmospheric plasma using a cylindrical flowing dielectric barrier discharge (DBD) reactor. A detailed comparison of this DBD ignited in a so-called burst mode (i.e. where an AC voltage is applied during a limited amount of time) and pure AC mode is carried out to evaluate their effect on the conversion of CO2 as well as on the energy efficiency. Decreasing the duty cycle in the burst mode from 100% (i.e. corresponding to pure AC mode) to 40% leads to a rise in the conversion from 16--26% and to a rise in the energy efficiency from 15 to 23%. Based on a detailed electrical analysis, we show that the conversion correlates with the features of the microfilaments. Moreover, the root-mean-square voltage in the burst mode remains constant as a function of the process time for the duty cycles \textless{}70%, while a higher duty cycle or the usual pure AC mode leads to a clear voltage decay by more than 500 V, over approximately 90 s, before reaching a steady state regime. The higher plasma voltage in the burst mode yields a higher electric field. This causes the increasing the electron energy, and therefore their involvement in the CO2 dissociation process, which is an additional explanation for the higher CO2 conversion and energy efficiency in the burst mode.