Optical Emission Spectroscopy of Abnormal Glow Region in Nitrogen Plasma

Abstract

Optical emission spectroscopy of the active species in N2 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 (100–200 W) 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 N2 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(N2) 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 N2 plasma is strongly affected by the filling pressure and source power whereas flow rate has no significant effect. An increased occurrence of N 2 + molecular ions in comparison with N2 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 N2 molecules, and N+ ions in comparison with N atoms is observed with the rise in filling pressure.