Near cathode optical emission spectroscopy in N2–H2 glow discharge plasma

Optical emission spectroscopy (OES) is a non-intrusive diagnostic technique, widely used to study different kinds of plasmas. In the present work, a locally resolved OES technique was used to obtain near cathode (substrate) emission spectra for N2–H2 glow discharges. It was observed that, along with N2+ and N2 lines, the characteristic atomic nitrogen lines at 742.3 nm (3p 4S03/2 → 3s 4P1/2), 744.2 nm (3p 4S03/2 → 3s 4P3/2), 746.8 nm (3p 4S03/2 → 3s 4P5/2) and Hα (656.3 nm) were the main emissions coming from the sheath region that shrouded the cathode. A qualitative analysis of the spectral lines near the cathode has been done in order to understand the mechanism of plasma nitriding and the role played by the hydrogen in the nitriding process. The decrease in local intensity of these atomic lines with hydrogen composition suggests that the effect of hydrogen is to enhance the sticking/adsorption of N on the cathode surface.