Vibrational Temperature Estimation of Nitrogen Molecules in Radio-Frequency (RF) Produced Plasma

Abstract

A capacitive coupled radio frequency (RF) plasma system has been developed for producing tungsten coated graphite tiles using plasma assisted chemical vapor deposition (PACVD) technique. To characterize the deposition chamber for optimal plasma parameters, small amount of air is released into the hydrogen plasma purposefully to measure its gas temperature using spectral bands of nitrogen molecule. Optical emission spectra in the wavelength range 350 to 900 nm have been recorded with a miniature spectrometer. Molecular spectral bands of N 2 (B 3 g -A 3 + u ) have been observed and identified as three bands from the nitrogen 1PS (Δν = 2, 3 & 4). These bands are simulated using MATLAB code developed in-house by considering Boltzmann distribution of particles in the vibrational states. The experimental spectra have been modelled with the simulated spectrum through the best-fit technique by iterating the latter one with different temperature values. Boltzmann plot method is also utilized to evaluate plasma gas temperature using identified vibrational bands. The estimated temperature using spectral modelling method matches fairly well with Boltzmann plot method. The estimated vibrational temperatures are in the range of ∼7000 -8000 K, an order higher than the room temperature ∼300 K.

Optical emission spectroscopy study in CO2 methanation with plasma

“…OES was performed to estimate the excited species generated by electron impact. [22][23][24][25][26][27][28][29][30][31][32] The light from the whole plasma area is focused using a lens. The lens is placed on the upper side of the reactor, and the focused light was guided to the spectrometer with an optical fiber.…”

“…Then, CO(B) is de-excited to the lower level species CO(A) emission. In addition, in the spectrum, the peaks between 600 and 640 nm are called the Fulcher band, and are produced by the emission species arising from H 2 as represented by the following equation; [30][31][32] H d H x h . 6…”

“…In addition, OES is a useful method for estimating the vibrational temperature. 25,[30][31][32] The vibrational excitation state is often represented by a parameter referred to as the vibrational temperature, which is calculated based on the assumption that the distribution of the vibration excitation state follows the Boltzmann distribution. Plasma-based CO 2 recycling and decomposition technologies are attracting more attention, and more studies aim to elucidate the behavior of vibrationally excited species by OES.…”

Changing pattern of N2 dissociation in N2–Ar RF plasma during E–H mode transition

“…The emission peaks that are used in the Boltzmann plot (figure 7(b)) to calculate T vib are highlighted in blue in figure 7(a). The details of the Boltzmann plot method are given elsewhere [15,52,55]. The parameters involved in this Boltzmann plot are listed in table 1 along with their respective values.…”