On the validity of neutral gas temperature by emission spectroscopy in micro-discharges close to atmospheric pressure

Abstract

The neutral gas temperature (Tg) of a single micro-hollow cathode discharge (MHCD) elaborated on silicon wafer is investigated. The MHCD is continuously powered in DC yielding a plasma in He, Ar and N 2 gases close to atmospheric pressure. Values of Tg determined by means of optical emission spectroscopy inside and in the vicinity of a single cavity of 100 µm diameter. In this work, the use of the resonant broadening to infer Tg is thoroughly reconsidered taking into account the reevaluation of an empirical coefficient as well as including the weaker contribution of the Van der Waals interaction in the line profile analysis. Tg is found to be around 360 K in He while in Ar it ranges from 460 K to 860 K depending on the current. A temperature gradient is observed between the cavity and the surrounding gas, which is correlated with the design of the MHCD reactor.A second approach involves the study of the relative rotational population distributions of several N 2 (C-B) vibrational bands to infer the rotational temperature (Trot). While the latter is commonly assumed to approximated Tg, its validity will be discussed based on experimental results. Discrepancies between Trot from different vibrational bands as well as with values found with the resonant broadening are investigated using different operating regimes of the MHCD. The validity of both approaches will be discussed supported by a comprehensive evaluation of the Tg and Trot uncertainty estimations. The analysis of resonant atomic line profile appears to be a reliable and accurate method to measure Tg in absolute room temperature atmospheric pressure plasma sources used in industrial processes as well as in environmental and biomedical applications.

Disproportionation of nitrogen induced by DC plasma-driven electrolysis in a nitrogen atmosphere

“…2). 54 The relative intensity of each ro-vibrational transition is calculated according to,with v ′, J ′ and v ′′, J ′′ the upper and lower vibrational, rotational excited states respectively. N n ′ is the number density of N 2 (C 3 Π u → B 3 Π g ) in the excited state n ′, q v ′, v ′′ is the so-called Franck–Condon factor and S J ′, J ′′ the Hönl–London factor – or line strength of the rotational state–.…”

Electric field strengths within a micro cavity plasma array measured by Stark shift and splitting of a helium line pair

“…In this study, the plasma source is operated at atmospheric pressure. The gas temperature is estimated to be 360 K obtained in a similar device by analysing the line width of a resonance broadened helium transition including a Van der Waals contribution [31]. This yields to a FWHM of f L ≈ 0.10 nm being a factor of about 100 larger than the negligible Doppler broadening.…”

Electrodeless atmospheric secondary induced ionization jet (EASII-jet): Dynamics and properties of a transferred helium plasma source

“…The spectral resolution of the system is (25 ± 1) pm at the band head (380.5 nm) of the N 2 (C-B)(0-2) vibrational band. The analysis of the rotational spectra is performed with a numerical tool developed in a previous study 28 . The parameters of the simulated spectrum are optimized with a non-linear leastsquare minimization algorithm to fit the experimental data.…”