Conversion of CO 2 into CO and O is studied in a flowing gas surfaguide pulsed microwave discharge operating with CO 2 and CO 2 + N 2 gas mixtures under different conditions. Optical emission spectroscopy, including actinometry (using N 2 ), vibrational (N 2 molecule) and rotational (CO and N 2 molecules) analysis are utilized. Both time-and space-resolved measurements are performed. The results show the essential changes of the CO 2 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 CO 2 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.

A chemical kinetics model is developed for a CO 2 /N 2 microwave plasma, focusing especially on the vibrational levels of both CO 2 and N 2 . The model is used to calculate the CO 2 and N 2 conversion, as well as the energy efficiency of CO 2 conversion, for different power densities and for N 2 fractions in the CO 2 /N 2 gas mixture ranging from 0 till 90%. The calculation results are compared with measurements, and agreements within 23% and 33% are generally found for the CO 2 conversion and N 2 conversion, respectively. To explain the observed trends, the destruction and formation processes of both CO 2 and N 2 are analyzed, as well as the vibrational distribution functions of both CO 2 and N 2 . The results indicate that N 2 contributes in populating the lower asymmetric levels of CO 2 , leading to a higher absolute CO 2 conversion upon increasing N 2 fraction. However, the effective CO 2 conversion drops, because there is less CO 2 initially present in the gas mixture, and thus also the energy efficiency drops with rising N 2 fraction.

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.

In order to characterize a nonequilibrium molecular plasma from the point of view of translational, vibrational and rotational degrees of freedom and their interaction, the characteristic temperatures of such a plasma were measured in an ICP rf reactor. Both pure nitrogen and argon–nitrogen mixture plasmas were examined for this purpose.The experimental results of rotational (Tr), vibrational (Tv) and electron (Te) temperatures are presented. Vibrational and rotational temperatures were measured as a function of nitrogen content for both E and H modes of ICP discharge using a power range of 45–200 W and pressure range of 2.6–13.3 Pa. Additionally, the pressure dependence of electron temperature in a pure nitrogen discharge was studied. Results show that rotational temperature is ≈370 K for E mode and ≈470 K for H mode and almost does not depend on either the applied rf power or the nitrogen content in the discharge. Vibrational temperature groups in the range 5000–12 000 K increase with applied rf power and constantly decay with an increase of nitrogen content. The measured values and behaviour of electron temperature are comparable with those for the positive column of the dc glow discharge. The results also prove that these three temperatures obey the classical inequality Te > Tv > Tr, as well as clarifying the differences in both vibrational and rotational temperature for different modes of the ICP discharge.

Mass spectrometry of atmospheric pressure plasmas S Große-Kreul, S Hübner, S. Schneider et al. Clusters in intense FLASH pulses C Bostedt, M Adolph, E Eremina et al. Dissociative attachment and vibrational excitation in electron collisions withCl2 M-W Ruf, S Barsotti, M Braun et al. Ionization dynamics of XUV excited clusters: the role of inelastic electron collisions M Müller, L Schroedter, T Oelze et al. Plasma diagnostics for understanding the plasma-surface interaction in HiPIMS discharges: a review Nikolay Britun, Tiberiu Minea, Stephanos Konstantinidis et al.Abstract. Intense laser fields are known to induce strong ionization in atoms. In nanoclusters, ionization is only stronger, resulting in very high charge densities that lead to Coulomb explosion and emission of accelerated highly charged ions. In such a strongly ionized system, it is neither conceivable nor intuitive that energetic negative ions can originate. Here we demonstrate that in a dense cluster ensemble, where atomic species of positive electron affinity are used, it is indeed possible to generate negative ions with energy and ion yield approaching that of positive ions. It is shown that the process behind such a strong charge reduction is extraneous to the ionization dynamics of single clusters within the focal volume. Normal and well-known charge transfer reactions are insufficient to explain the observations. Our analysis reveals the formation of a manifold of Rydberg excited clusters around the focal volume that facilitate orders of magnitudes more efficient electron transfer. This phenomenon, which involves an active role of laser-heated electrons, comprehensively explains the formation of copious accelerated negative ions from the nano-cluster plasma.

The influence of the capacitive (E)-to-inductive transition (H) in inductively coupled plasma discharges is investigated for propanethiol plasma polymerization. In the E mode, at low plasma density, the sulfur content in the layers, measured by XPS, is quite high and strongly decreases after aging in the air. This phenomenon is attributed to the desorption of trapped sulfur-based molecules (e.g., H 2 S). In the H mode, presumably higher surface temperature prevents the trapping scenario during the layer growth and, as a consequence, yields a lower sulfur content which is stable after aging. Mass spectrometry measurements reveal important variations of the plasma chemistry depending on the discharge mode. The major change concerns the complete disappearance of the precursor in the H mode accompanied by the large production of CS 2 molecules. Furthermore, a linear correlation is found between the concentration of the CS 2 species and the atomic sulfur content in the Hmode synthesized layers. In addition, based on DFT calculations, different pathways of fragmentation are proposed as a function of the plasma parameters. The whole set of results highlight the importance of the E−H transition for the growth of thiol-based plasma polymers.

Time-resolved characterization of an Ar-Ti high-power impulse magnetron sputtering discharge has been performed. This paper deals with two-dimensional density mapping in the discharge volume obtained by laser-induced fluorescence imaging. The time-resolved density evolution of Ti neutrals, singly ionized Ti atoms (Ti þ ), and Ar metastable atoms (Ar met ) in the area above the sputtered cathode is mapped for the first time in this type of discharges. The energetic characteristics of the discharge species are additionally studied by Doppler-shift laser-induced fluorescence imaging. The questions related to the propagation of both the neutral and ionized discharge particles, as well as to their spatial density distributions, are discussed. V C 2015 AIP Publishing LLC.

Time evolution of sputtered metal ions in high power impulse magnetron sputtering (HiPIMS) discharge with a positive voltage pulse applied after a negative one (regime called “bipolar pulse HiPIMS”—BPH) is studied using 2-D density mapping. It is demonstrated that the ion propagation dynamics is mainly affected by the amplitude and duration of the positive pulse. Such effects as ion repulsion from the cathode and the ionization zone shrinkage due to electron drift towards the cathode are clearly observed during the positive pulse. The BPH mode also alters the film crystallographic structure, as observed from X-ray diffraction analysis.