Optical emission spectroscopy is used to characterize the production of
active species as a function of hydrogen concentration in the mixture under
different operating conditions. A major concern is to enhance the
concentration of the active species by hydrogen addition that carry several
electron volts energy above their ground states, and thus affect the surface
chemistry. The emission intensity of the selected optical transitions of
molecular and atomic species is measured to determine the functional
dependence of their radiative states. The relative ground state molecular
ion density [N2+] is measured from the emission intensity of the
first negative band head (λ = 391.4 nm, 0–0) by considering the
fact that in low temperature plasma, ion with single charge is produced by
the electron impact, and the ion density is proportional to the electron
density. It is found that the concentration of the active species may be
enhanced significantly by selecting an appropriate gas composition and
operating parameters. The SS-304 samples are nitrided under the optimum
conditions for 4, 8, 12 and 16 hours and hardness values are found to
increase five times for 16 hours treatment time. The optimized discharge
conditions are found favorable for plasma ion nitriding.