The optical emission spectroscopy technique is used to determine the vibrational temperature of the second positive band system,$$ N_{2} (C,\upsilon^{^{\prime}} - B,\upsilon^{^{\prime\prime}}$$ N 2 ( C , υ ′ - B , υ ″ ) in the wavelength range 367.1–380.5 nm by using the line-ratio and Boltzmann plot methods. The electron temperature is evaluated from the intensity ratio of the selected molecular bands corresponding to $$N_{2}^{ + } (B,\upsilon - X, \upsilon^{^{\prime}} , $$ N 2 + ( B , υ - X , υ ′ , 391.44 nm), and, $$N_{2} (C,\upsilon^{^{\prime}} - B,\upsilon^{^{\prime\prime}}$$ N 2 ( C , υ ′ - B , υ ″ , 375.4 nm) transitions, respectively. The selected bands have a different threshold of excitation energies and thus serve as a sensitive indicator of the electron energy distribution function (EEDF). The electron density has been determined from the intensity ratio of the molecular transitions corresponding to $$N_{2}^{ + } (B,\upsilon - X, \upsilon^{^{\prime}} , $$ N 2 + ( B , υ - X , υ ′ , 391.44 nm), and, $$ N_{2} (C,\upsilon^{^{\prime}} - B,\upsilon^{^{\prime\prime}}$$ N 2 ( C , υ ′ - B , υ ″ , 380.5 nm) for different levels of pressure and radio frequency power. The results show that the vibrational temperature decreases with increasing nitrogen fill pressure and radio frequency power. However, the electron temperature increases with radio frequency power and reduces with fill pressure. The electron density increases both with nitrogen fill pressure and radio frequency power that attributes to the effective collisional transfer of energy producing electron impact ionization. Plasma parameters show a significant dependence on discharge conditions and can be fine-tuned for specific surface treatments. Article Highlights Spectrum analysis of RF-driven nitrogen plasma for varying discharge conditions Evaluation of vibrational temperature using line-ratio and Boltzmann plot methods Comparison of vibrational temperatures for line-ratio and Boltzmann plot methods Evaluation of electron temperature and density using the intensity-ratio of bands Correlation of temperature and density with varying fill pressure and RF power

The paper reports on the development and application of a swept Langmuir probe to characterize plasma between two disc-like electrodes. A battery was added to a probe circuit to offset against the cathode fall voltage, and to make the sweep voltage effective at the probe tip. This arrangement allowed the collection of the electron and ion parts of the probe current and the subsequent construction of time-resolved current–voltage IP(V) characteristics with a time resolution of about one millisecond. The probe collected electron current in the lower voltage region of the discharge waveform where it surmounted the cathode fall voltage, whereas the ion current was collected continuously due to an accelerating field for the ions. The results highlighted how the cathode fall voltage limits the collection of the electron and ion parts of the probe current and how to handle the problem with a series battery in the probe circuit. In addition to the swept single-probe, a triple-probe was used simultaneously to compare and validate the results.

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