Emission spectroscopy of the plasma in the cathode region of N₂-H₂abnormal glow discharges for steel surface nitriding

Plasma analysis using emission spectroscopy has been carried out in the cathode fall and the negative glow of N 2 -H 2 abnormal glow discharges for steel surface nitriding. The spatial distributions of the selected excited states of N 2 , N, N 2 + , N + , NH, H 2 , H and Fe have been measured in terms of their dependence on the main process parameters, such as the cathode temperature (400-550 degrees C), H 2 percentage in the gas mixture (10-70%) and total pressure in the nitriding reactor (400 and 800 Pa), corresponding to the given values of the discharge current (115-260 mA) and applied voltage (465-635 V). The experimental data presented yield reliable information on the occurrence of excited states in the cathode region and on the effect of the process parameters on the cathode fall thickness, which determines the energy distributions of ions bombarding the cathode and is an important input parameter in plasma process modelling.