A needle-water DC microplasma system working at atmospheric pressure in N₂/O₂ gas mixtures is used to study the fundamental mechanisms of nitrate/nitrite synthesis in highly complex and yet little-known plasma–water systems. Plasma properties are investigated by means of optical emission spectroscopy while the activated water is analyzed following the treatment using ionic chromatography and UV-Vis absorbance spectroscopy. Experiments highlight that the energy efficiency and selectivity of the process are influenced by the oxygen content and the plasma-induced water heating, with strong differences when the water surface is the anode or the cathode electrode. Nitrates are successfully synthesized without residual nitrites in the solution with a comparatively higher energy efficiency when the water is the cathode. The possible reactions involved in the gas phase and aqueous phase chemistry are presented and future scope for the optimization of the system is discussed.

The formation of nanoparticles in low temperature plasmas is of high importance for different fields: from astrophysics to microelectronics. The plasma based synthesis of nanoparticles is a complex multi-scale process that involves a great variety of different species and comprises timescales ranging from milliseconds to several minutes. This contribution focuses on the synthesis of nanoparticles in a low temperature, low pressure capacitively coupled plasma containing mixtures of argon and aniline. Aniline is commonly used for the production of polyaniline, a material that belongs to the family of conductive polymers, which has attracted increasing interest in the last few years due to the large number of potential applications. The nanoparticles which are formed in the plasma volume and levitate there due to the collection of negative charges are investigated in this contribution by means of in-situ FTIR spectroscopy. In addition, the plasma is analyzed by means of plasma (ion) mass spectroscopy. The experiments reveal the possibility to synthesize nanoparticles both in continuous wave and in pulsed discharges. The formation of particles in the plasma volume can be suppressed by pulsing the plasma in a specific frequency range. The in-situ FTIR analysis also reveals the influence of the argon plasma on the characteristics of the nanoparticles.

A simultaneous oxidation and reduction of nitrogen is performed for nitrogen fixation with a DC plasma-electrolysis operated in N ₂ .

Aging (or “hydrophobic recovery”) of plasma‐modified polymer surfaces has been known and documented in the literature over several decades; to the best of our knowledge, the present study appears to be the first in which this is done for two vastly different rough surface structures: (i) electrospun nanofibrous (NF) mats, and (ii) flat films (FF), for three polymers of well‐documented interest in biotechnological applications: poly(lactic acid); poly(urethane); and poly(caprolactone). Two different plasma treatments are applied: low‐pressure (LP) radio‐frequency (rf) glow discharges in flows of O₂ and NH₃ under mild power conditions. Measured time‐dependent surface compositions (from X‐ray photoelectron spectroscopy survey spectra) and water contact angles (WCA) were found to tend toward asymptotic limiting values after ca. 30 days of storage in clean air, as previously reported by these and other authors. An entirely novel aspect of this work is to examine and compare time‐dependent WCA behaviors of NF and FF samples in terms of Wenzel (W) and Cassie‐Baxter (C‐B) model behaviors, including possible transitions from C‐B to W and their interpretation.

Low pressure capacitively coupled radiofrequency plasmas operated in a mixture of aniline vapor and argon are used for the deposition of thin films on silicon substrates. The influence of the aniline vapor fraction in the gas mixture upon the plasma properties and the characteristics of the deposited thin film is analyzed. Plasmas diagnostics are carried out using mass spectrometry and optical emission spectroscopy and the thin films are characterized by means of Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and near‐edge X‐ray absorption fine‐structure spectroscopy. Experiments highlight that the use of a low aniline/argon ratio leads to the deposition of an amorphous film whereas high‐aniline/argon ratios allow the synthesis of a plasma polymer similar to polyaniline. The properties of such plasmas and the mechanisms involved in the deposition process are discussed in detail.

Low temperature plasmas, in particular when they are operated in molecular (organic) gases, are rather complex systems. Their distinct non equilibrium nature, characterized by low neutral gas temperatures (close to room temperature) and relatively high electron temperatures (easily reaching values up to several eV) make them a breeding place for a great variety of different species and depending on the precursor gas and the process conditions even a source for nanoparticles. The formation of nanoparticles has been observed in various discharge types operated in different kinds of gases or gas mixture as e.g.in silane, in fluorocarbons such as CF4 or C2F6 or in hydrocarbons as e.g. acetylene. The formation of nanoparticles in a plasma is either an unwanted side effect, occurring for example during the plasma based deposition of thin films (or the etching of microstructures) or it is the deliberate result of a process used e.g. for the production of nanoparticle deposits. In either way the understanding of the underlying mechanisms which are eventually responsible for the nanoparticle formation in low temperature plasmas is indispensable for the control of the whole process. However, the plasma based formation of nanoparticles is a rather complex procedure, which involves different plasma species, various timescales and several physical and chemical processes. The process starts with the dissociation of the original parent molecule due to electron impact reactions. These reactions are responsible for the initial formation of molecular fragments which can induce subsequent polymerization reactions leading by and by to the formation of larger and larger molecules and eventually to the formation of nanometer sized clusters. These initial protoparticles can further grow due to coagulation and/or accretion processes till they reach a size of some 10 nanometer. Once the particles have reached this size they become rapidly negatively charged and their further growth is mainly governed by the collection of positive ions and neutral radicals. In contrast to CVD processes which are mainly driven by neutral molecules and radicals plasma based processes involve also charged species, namely electrons and different kinds of ions. Depending on the precursor gas used for the given process this ionic component can include positive as well as negative ions. This contribution will focus on the nanoparticle formation in two exemplary systems: discharges operated in argon/acetylene and argon/aniline mixtures. While acetylene plasma are frequently used for the production of DLC films, the use of aniline discharges has been intensively studied for the (conformal) deposition of (ultra) thin polyaniline films or the production of polyaniline nanoparticle deposits. In particular the latter material class possess interesting potential applications in the field of biosensors and for the production of supercapacitors. Based on various in-situ plasma diagnostics (plasma ion mass spectroscopy, in-situ multi-pass FTIR spectroscopy, microvawe interferometry, laser light scattering and optical emission spectroscopy) and different discharge designs the particle formation in both systems is studied aiming to understand the underlying formation mechanisms in order to either promote or prevent the generation of nanoparticles. Special emphasis is paid to the role of the negative ion component. In non-pulsed discharges (low energy) negative ions are trapped in the positive plasma potential inside the plasma bulk and while not contributing to the flux of species reaching the wall of the plasma chamber they can be a dominant species inside the plasma volume. They may play therefore an important role in the initial formation of protoparticles i.e. in the early nucleation phase. Acknowledgments The authors would like to acknowledge the support obtained by the French National Research Agency via the project PlasmaBond. This work has received also funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 730872 (CALYPSO plus for the work at the HZB BESSY II synchrotron, Berlin) and under grant agreement No766894 FETOPEN project PEGASUS.