Emission spectroscopy is used to investigate the effect of inert gas mixing in nitrogen plasmas generated in inductively coupled plasma (ICP) and electron cyclotron resonance (ECR) plasma sources. Vacuum ultraviolet (VUV) emission of resonance lines is used to determine concentration of atomic nitrogen while electron temperature is obtained from optical emission spectra. It is found that electron temperature can be either raised or reduced effectively by mixing helium or argon in a nitrogen discharge. Electron-electron collisions and superelastic collisions involving metastable species are key factors in electron temperature tuning.

In-situ optical emission spectroscopy was used to systematically study the influence of nitrogen on the growth of carbon nanotubes (CNTs) by microwave-plasma enhanced chemical vapor deposition at different CH concentrations in a CH4/N2 gas mixture. The results show that CN and C2 co-exist in the plasma and emission intensities of the two species are correlated. The morphology and microstructure of the samples vary with the CH4 concentration. Well aligned nanotubes are obtained at 20% CH4- With the participation of N2-, the CNTs present a polymerized nanobell structure. More importantly, the length and thickness of each nanobell can be modulated by varying the CH4 concentration. Without N2-, conventional cylindrical CNTs are obtained.

A new technique, adding argon or helium into nitrogen plasma, has been used to regulate the electron temperature in an inductively coupled plasma. The electron temperature is determined by analysing the intensity ratio of two nitrogen spectrum lines. The results show that, when the total pressure is 0.7Pa, the electron temperature increases with the increase of the He partial pressure in He/N2 plasma, but the electron temperature decreases with the increase of the Ar partial pressure in Ar/N2 plasma. The regulation e ect of electron temperature is weaker in higher pressure N2/He plasma of 2.6Pa.