M. A. Naveed

Diagnostics of nitrogen plasma by trace rare-gas-optical emission spectroscopy

Trace rare-gas–optical emission spectroscopy is carried out to characterize the nitrogen plasma as a function of discharge parameters. The functional dependence of N2(CΠu3) and N2+(BΣu+2) excited states is monitored by measuring the emission intensities of the bandheads of second positive and first negative systems. The excited-state population density of N atoms and N2 molecules, extracted from their optical emission, is related to the ground-state population density after normalizing the changes for excitation cross section and electron energy distribution function by optical actinometry. The electron temperature is determined from the plasma-induced optical emission of trace rare gas by the line-to-line method. The obtained data may help us to adjust the optimum discharge conditions for the production of active species, which are considered to be important for the desired treatment of the samples.

Determination of excitation temperature and vibrational temperature of the N2(C 3Πu, ν′) state in Ne–N2 RF discharges

Optical emission spectroscopy is used to investigate the effect of neon mixing on the excitation and vibrational temperatures of the second positive system in nitrogen plasma generated by a 13.56?MHz RF generator. The excitation temperature is determined from Ne I line intensities, using Boltzmanns plot. The overpopulation of the levels of the N2 (C?3?u, ?) states with neon mixing are monitored by measuring the emission intensities of the second positive system of nitrogen molecules. The vibrational temperature is calculated for the sequence ?? = ?2, with the assumption that it follows Boltzmanns distribution. But due to overpopulation of levels, e.g. 1, 4, a linearization process was employed for such distributions allowing us to calculate the vibrational temperature of the N2 (C?3?u, ?) state. It is found that the excitation temperature as well as the vibrational temperature of the second positive system can be raised significantly by mixing neon with nitrogen plasma. It is also found that the vibrational temperature increases with power and pressure up to 0.5?mbar.

Optical emission spectroscopy of the active species in nitrogen plasma

Optical emission spectroscopy is used to study the production of active species in nitrogen plasma excited by a 50 Hz pulsed-dc power source. The emission intensities of the band heads of the second positive (λ=337.1 nm; 0–0) and first negative (λ=391.4 nm; 0–0) systems are used to investigate the dependence of their radiative states N2(C 3Π u ) and population density on operating parameters. The emission intensity of the radiative state is used to determine the relative dependence of ion density on operating conditions by considering the fact that, in low-temperature plasmas, the dominant mechanism of the population of ) state starts from the ground state mainly by electron collisions. It is found that the production of these active species has a significant dependence on the discharge parameters and may be optimized under typical operating conditions.

Glow Discharge Plasma Nitriding of AISI 304 Stainless Steel

Glow discharge plasma nitriding of AISI 304 austenitic stainless steel has been car- ried out for different processing time under optimum discharge conditions established by spectro- scopic analysis. The treated samples were analysed by X-ray diffraction (XRD) to explore the changes induced in the crystallographic structure. The XRD pattern confirmed the formation of an expanded austenite phase (γN) owing to incorporation of nitrogen as an interstitial solid solu- tion in the iron lattice. A Vickers microhardness tester was used to evaluate the surface hardness as a function of indentation depth (μm). The results showed clear evidence of surface changes with substantial increase in surface hardness.

Optical actinometry of the N-atom density in nitrogen plasma

Trace-rare-gas optical actinometry is used to measure the N-atom density in 50 Hz pulsed dc nitrogen plasma as functions of the discharge parameters. The excited-state population density of N atoms is extracted from their respective optical transitions and is related to the ground-state population density by considering the changes in the electron energy distribution function. This technique provides reliable information on the atomic N concentration in the gas discharge, which is vital in the synthesis of nitrides owing to its high chemical reactivity.