Abstract High-power impulse magnetron sputtering (HiPIMS) delivers higher ionisation of the target material at the expense of lower deposition rates than conventional magnetron sputtering. A fine optimisation of the deposition conditions is crucial for specific applications. Chopped or multi-pulse HiPIMS (segmenting pulses into shorter micropulses) has been proposed to enhance the degree of ionisation of the film-forming flux fraction while maintaining the deposition rate. This study investigates how micropulse length and the delay time between segments influence energy flux, deposition rate, and the ionised flux fraction (IFF) in both chopped and standard HiPIMS (s-HiPIMS). These quantities are evaluated by passive thermal probe, biasable QCM and mass spectrometer measurements at the substrate position. Deposition-averaged and pulse-averaged power is kept constant for all conditions to facilitate meaningful comparison. Results indicate that chopping the HiPIMS pulse consistently leads to higher energy flux and total deposition rate compared to s-HiPIMS at the same total pulse length, primarily due to increased ion flux. In chopped HiPIMS, increasing the delay time between micropulses beyond 30 μ s simultaneously improved the deposition rate and the IFF. In comparison, s-HiPIMS, operated at higher frequencies and shorter pulse lengths, demonstrated similar performance with even higher total energy fluxes, but this can be attributed to a higher fraction of process-gas ions in the flux to the substrate, rather than to an increased IFF of the film-forming species.
The intensity ratio of the N2+ first negative system to the N2 second positive system is widely used for non-invasive diagnostics of the reduced electric field ( E/N) in low-temperature plasmas. However, the reliability of this method depends on fulfilling specific validation criteria, whose verification remains challenging because severe spectral overlap obscures the vibrational distribution functions of the N2+(B2 Sigma u+) state. In this work, we investigate the vibrational distributions of the N2+(B2 Sigma u+) electronic state arising under streamer discharge conditions. Time-resolved emission spectra between 200-500 nm were obtained and analyzed in a point-plane DBD geometry during the streamer formation phase in pure nitrogen and synthetic air at various pressures below 300 Torr. Advanced analysis of the emission spectra based on simultaneous fitting of the SPS and the FNS allowed for the complete decoupling of the overlapping molecular bands and the accurate determination of vibrational distributions and rotational temperatures of the N2+(B2 Sigma u+) and N 2(C 3 Pi u) electronic states. The results reveal that at early times, the VDFs in both cases adhere closely to a Franck-Condon-like distribution, dictated by dominant direct electron-impact excitation. Furthermore, we demonstrate that the enhanced population of the N2+(B2 Sigma u+,v=2) level could serve as a diagnostic marker for estimating the vibrational temperature of the N2(X1 Sigma g+). At higher pressures ( >= 25 Torr), rapid vibrational relaxation and strong collisional quenching cause a prominent decay of higher vibrational populations over nanosecond timescales. We also reveal for the first time the diagnostic potential of the fourth positive system of N 2 under high E/N conditions.
Abstract Surface microstructure is an effective approach for modulating dielectric barrier discharges (DBDs). In this study, a two-dimensional (2D) plasma fluid model is employed to investigate the influence of micron-scale surface structures (0–50 μ m) on a single-filament atmospheric-pressure air DBD driven by a sinusoidal voltage, with a focus on volume and surface streamer dynamics. The results show that larger microstructures can lead to discharge timing delay or advancement, current waveform distortion, and streamer morphology modification. For the studied sinusoidal profiles, surface streamer splitting can be induced by a microstructure size (peak-to-peak amplitude) as small as 25 μ m, whereas noticeable changes in volume streamer parameters require a larger size (e.g. 50 μ m). Furthermore, the discharge exhibits asymmetry between consecutive positive and negative half-cycles due to the memory effect, and the influence of microstructure differs distinctly with voltage polarity. The local electric field distortion, the residual ion density and seed electron level, and the distribution of surface charges are identified as key factors through which microstructures govern the discharge behaviors. This work provides new insights into the active control of DBDs via surface microstructures.
Abstract An analysis of an E × B Hall-type discharge is performed by the use of a radial-axial particle-in-cell simulation in cylindrical coordinates. Five test cases with different curvatures are analyzed. The results show that the average axial current density does not depend on the curvature of the device, while internal electron temperature and density do. When the radius of curvature is low, the density peak is larger and the temperature peak smaller. The results also show that the curvature has an impact on the electron temperature radial profile: the electrons are not isothermal in the radial direction. The analysis of the edge-to-center density ratio, i.e. the h- factor, shows that the Tonks–Langmuir model, adjusted to cylindrical coordinates, is not adapted in this case. The strong axial acceleration of the ions reduces the wall losses, i.e. the value of the h- factor, with respect to the usual values for collisionless plasmas.
