Optical emission spectroscopy of abnormal glow region in nitrogen plasma

Optical emission spectroscopy of the active species in N-2 plasma is carried out to investigate their concentration as a function of discharge parameters such as filling pressure (2.0 - 7.0 mbar), source power (100 - 200W) and gas flow rate (50 - 300 mg/min). The primary motivation of this work is to obtain reliable information about the concentration of the active species of N-2 plasma, which play an important role in plasma surface nitriding processes. Emission intensity from the selected electronic excited states of molecular and atomic species is evaluated as a function of discharge parameters to investigate their concentration. The emission intensity ratio I(N-2(+))/I(N-2) and I(N+)/I(N) of the electronic transitions is also evaluated as a function of discharge parameters to investigate the relative dependence of their concentrations. It is observed that the concentration of the active species of N-2 plasma is strongly affected by the filling pressure and source power whereas flow rate has no signicant effect. An increased occurrence of N-2(+) molecular ions in comparison with N-2 molecules, and N+ ions in comparison with N atoms is observed with source power whereas decreased occurrence of N-2(+) molecular ions in comparison with N-2 molecules, and N+ ions in comparison with N atoms is observed with the rise in filling pressure.