The optical diagnostics of a DC pulsed plasma used for iron nitriding is carried out for various plasma conditions. The fluorescence of the first negative and the second positive systems of is observed in the time afterglow, in order to obtain some insights into the creation and the loss processes of and states. An iron emission line is also observed which is indicative of the sample sputtering. Particular attention is paid to the influence of the gas pressure on the respective durations of the discharge and the afterglow. Analysis of the plasma both during the discharge and during the post-discharge leads to the determination of favourable conditions for the surface treatment. It is also shown that the electron density in the discharge can be deduced from the line intensity decay in the afterglow.

A theoretical determination of oscillator strengths for the cesium atom is proposed. The values obtained are compared with experimental results deduced from the emission spectra of a slightly ionized quiescent cesium plasma discharge.

No abstract

A pure nitrogen plasma operating in a low-frequency ( < 1 kHz) OC pulsed mode is used for iron nitriding and is characterized by means of Optical emission spectroscopy. Line intensities related to N, or N: states involved in the surface treatment, as well a s an iron line linked to the cathode sputtering. are maintained during the discharge and the temporal post-discharge, and are compared with the electron density evolution. The processes governing the population of excited states are quite different when the discharge is on (electron collisions) and when the discharge voltage is cut off (importance of long lifetime metastable N, states)-justifying the interest of the post-discharge phase during which active species are created in a surface treatment process.