In this study, we examine the statistical properties of asymmetric surface dielectric barrier discharges (SDBD) produced by applying a periodic high voltage between two conducting displaced electrodes, located at the opposite sides of a flat dielectric panel. Here, the asymmetry refers to the fact that the lower electrode is fully covered with an insulating material, while the upper one, glued onto the dielectric surface, is otherwise left exposed to the air. Such a configuration allows the formation of a thin layer of plasma above the insulating surface. A single cycle signal consists of two well-separated half-cycle patterns, denoted as forward and backward strokes, corresponding to positive and negative voltages, respectively. They display a quite complex discharge pattern constituted by a sequence of individual peaks (bursts) of varying current and time duration. Specifically, we find that backward stroke bursts carry a positive mean charge $⟨Q⟩\simeq 0.3$ nC and mean current $⟨I⟩\simeq 35$ mA, with a mean duration $⟨\tau ⟩\simeq 15$ ns, while forward stroke bursts have a negative mean charge $⟨Q⟩\simeq -0.1$ nC, a mean current $⟨I⟩\simeq -20$ mA, and a mean duration $⟨\tau ⟩\simeq 11$ ns. The statistical analysis suggests that power injection can be tailored to produce the active agents in the plasma needed for a particular application. We also determined discharge spatial correlation patterns from measurements of the associated stimulated optical emission. The optical excitations occur as a result of the ionizing effect of the electromagnetic waves which ignite the discharge, followed by the electric current flow. In particular, we point out that one of the phases of the discharge is compatible with a cathode directed streamer phenomenon (backward stroke), while the mechanism acting for a forward stroke has a different structure.

In this work, a novel 0D model for the evaluation of O₃ and NO₂ produced by a surface dielectric barrier discharge (SDBD) in a closed environment is presented. The model is composed by two coupled sub-models, a discharge sub-model and an afterglow one. The first one, simulating the discharge regime and consequently including electron impact reactions, aims to calculate the production rates of a set of key species (atomic oxygen, excited states of molecular oxygen and molecular nitrogen). These latter are the input of the afterglow sub-model, that simulates the afterglow regime. We introduce a methodology to relate the production rates of the above mentioned species to the input power of the SDBD reactor. The simulation results are validated by a comparison with experimental data from absorption spectroscopy. The experimental measurements are carried out as follows. First, the discharge is turned on until the NO₂ number density reaches steady state. Then, the discharge is turned off for several minutes. Finally, the discharge is turned on again to observe the effects of the NO₂ concentration on ozone dynamics. The entire process is done without opening the box. The system operating in all the above-listed conditions is simulated for three different levels of input power.

Plasma-assisted supersonic jet deposition (PA-SJD) is a precise technique for the fabrication of thin films with a desired nanostructured morphology. In this work, we used quadrupole mass spectrometry of the neutral species in the jet and the extensive characterization of TiO₂ films to improve our understanding of the relationship between jet chemistry and film properties. To do this, an organo–metallic precursor (titanium tetra–isopropoxide or TTIP) was first dissociated using a reactive argon–oxygen plasma in a vacuum chamber and then delivered into a second, lower pressure chamber through a nozzle. The pressure difference between the two chambers generated a supersonic jet carrying nanoparticles of TiO₂ in the second chamber, and these were deposited onto the surface of a substrate located few centimeters away from the nozzle. The nucleation/aggregation of the jet nanoparticles could be accurately tuned by a suitable choice of control parameters in order to produce the required structures. We demonstrate that high-quality films of up to several µm in thickness and covering a surface area of few cm² can be effectively produced using this PA-SJD technique.

We compared spectra and intensity light of different sources, such as a UV-A lamp, a UV-C lamp, and a visible bulb, and atmospheric nonthermal plasma emission. Spectroscopic measurements were performed with an optical emission spectrometer and radiometric measurements with a radiometer to which UV-A, UV-C, and visible probes were coupled to measure the light intensity per unit surface. For each light source, we measured the emission spectrum and light intensity using different probes and also varying the relative distance. The nonthermal atmospheric plasma was generated by means of a surface barrier dielectric discharge varying the relevant parameters. This work allowed us to create the experimental setup suitable for further studies on volatile organic compound abatement by plasma-catalysis processing and compared it to the photocatalysis techniques based on UV and visible lamps.

An experimental study of the plasma gas phase in low pressure radiofrequency discharges of oxygen is presented. The plasma phase has been studied by means of mass spectroscopy of the neutral and of the charged species, directly sampling the plasma gas phase. We also measured the ion energy distributions. We have studied the influence of the operating conditions on the plasma gas-phase composition. Ion density and energy have been measured as a function of discharge parameters. In particular, we have identified operating conditions in low pressure discharges allowing the extraction of ions from the plasma state with energies exceeding 50 eV. This makes plasma processing with energetic oxygen ions feasible in our device.