“…On the other hand, two models were suggested to explain spark discharging. According to the first model [21,22], the appearance of spark discharging comes as a consequence of dielectric breakdown of the oxide layer in a strong electric field (∼10 7 V/cm), while the second model [23,24] considers spark discharging as gas discharging occurring in micropores of the oxide films. Atomic and ionic lines in luminescence spectrum during spark discharging generally originate from the species present in the substrate and in the electrolyte.…”