In this work, the kinetics of nitrogen fixation via plasma-induced N 2 oxidation in a 10 ns pulsed atmospheric pressure water-contacting discharge sustained in air is investigated. Two pulse regimes, a single pulse and a three-pulse burst of 100 kHz, are considered. The densities of relevant radicals (NO, O) are studied by time-and space-resolved laser-induced fluorescence spectroscopy. It is concluded that in a single pulse mode, O atoms are mainly generated by O 2 reacting with electronically excited states of N 2 (A 3 Σ + u , B 3 Π g , C 3 Π u ) and are primarily reduced as a result of O 3 formation. The O density shows a maximum at ∼100 ns after the plasma pulse with number density of ∼10 23 m −3 . NO radicals, on the other hand, are primarily formed by reacting with the N 2 A 3 Σ + u state (up to ∼1 μs after the pulse) and with OH radicals (up to ∼10's of μs), peaking at approximately 60 μs with a peak density of ∼10 21 m −3 . The NO loss pathway is represented by the reversed Zeldovich mechanism at short time delays (∼10's μs), whereas at longer delays (>100's of μs) HNO 2 and NO 2 formation causing NO loss start to be dominant. In the burst mode, the energy efficiency of NO formation decreases despite higher N 2 conversion, for which three reasons are suggested:(1) NO removal by the generated O( 1 D) after the discharge pulse through the reverse Zeldovich mechanism, (2) NO oxidation via the accumulated O 3 , (3) pre-ionization induced by high pulse repetition rate (100 kHz) leading to shrinkage of the plasma bulk.
Physical backgrounds of nitrogen fixation process in a nanosecond pulsed discharge in the presence of a plasma/liquid interface are reported. The role of OH radicals and O atoms in NO...
In this work, the direct current (DC) hot magnetron sputtering (HMS) of Nb has been studied and compared with the conventional cold magnetron sputtering (CMS) discharge. Particularly, these two magnetron systems were investigated in terms of current-voltage trends, behaviour of spectral lines, target temperature, and deposition rate. The current-voltage evolution showing strong variations over time in the HMS system was used to monitor the moment when a thermionic emission becomes considerable. Meanwhile, thanks to the time-resolved optical emission spectroscopy (OES), the dynamics of plasma particles and the population of their electronic levels were analysed as a function of the target temperature. The target temperature was measured owing to both pyrometry and OES-based approach, i.e., by fitting an emission spectrum baseline. Finally, in the configuration used in this work, the deposition rate up to 100 nm/min was obtained at the applied power density of 30 W/cm2, which is 3 times higher than the maximum power density applicable to the classical CMS system. However, with further increase in the power density, the deposition rate values were found to be saturated, which is likely caused by a significant increment in a number of thermal electrons in the discharge area.
Impulse magnetron discharge (pulse duration 20 ms) with uncooled Cr target has been investigated with a specially designed Langmuir probe setup in a wide range of parameters (magnetic field and discharge power). The spatial distributions of electron temperature and plasma density have been measured in the gasless self-sputtering mode. It has been shown that in the gasless high-power pulsed discharge with hot Cr target, plasma density is as high as 5 × 10 18 m −3 at a pulsed power density of 1430 W/cm 2 , while the electron temperature drops to values below 1 eV.
A drastic change in the spatial ion distribution in bipolar magnetron sputtering discharge is reported upon changing the magnetic field topology. In our case, a significant increase in ion number density at certain time delays is registered when topology is changed toward the unbalanced type. A transitory torch-shaped ionization zone consequently disappears, along with the low-energy part of the ion energy distribution, due to no additional ionization in this case.
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