Emission spectroscopy detection of N2 active species in plasma nitriding process

The present paper is a review of recent works related to the optical emission spectroscopy applied to the determination of ground state densities of N atoms in Ar-N₂ flowing post-discharges. The effect of small quantities of H₂ in the Ar-N₂ discharge on N atom densities within the post-discharge has been analysed. The authors demonstrate that optical emission of Na impurity may be applied to the determination of the vibrational temperature of N₂(X,v) states at the temperatures usual for nitriding of metals in Ar-N₂ post-discharge. From the diagnostic of Ar-N₂ post-discharges, it is clearly specified that nitriding of iron base alloys in a flowing post-discharge reactor is originating in N atoms, especially when a few H₂ molecules are admixed into the Ar-N₂ discharge. Finally, correlation between the N-atom density and the thickness of the iron nitrided layers when H₂ is introduced into the Ar-N₂ discharge are given. Dedicated to Prof. Jan Janča on the occasion of his 60^th birthday.