What is it about?
Broadened hydrogen Balmer lines are observed in a DC glow discharge sustained in Ar-SiH4- N2 gas mixture. This broadening is due to the Doppler frequency shift. H atoms translational energy distribution is calculated in different positions between the two electrodes of the discharge along the inter electrode axis and in different gas mixtures. Three main components are observed at 0.6 (+/-0.5)eV, 12(+/-3)eV, 62(+/-6)eV and 1(+/-1)eV, 28(+/-6)eV and 105(+/-12)eV for Hα and Hβ, respectively. They correspond to hydrogen dissociation by electron impact producing H(n=3, 4) atoms and to dissociative recombination of ion in the cathode fall or to back-scattered fast H atoms on the cathode surface. The density ratio nH2/nAr ranges from 44% to 13% or from 10% to 3% when a=nH/nH2=0.01 and 0.1, respectively, in function of the gas mixture. So large hydrogen density could be due to hydrogen desorption from the wall and cathodes and/or to the gas recirculation within the reactor. A new low energy component is observed in Hα line profile, when silane and nitrogen concentration decreases and increases, respectively. It could also be due to H atom desorbing from the reactor wall or to NHx species dissociated by electron impact within the reactor.
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Why is it important?
The study of the Doppler broadening of Hydrogen Balmer lines can be efficient to investigate elementary reactive processes produced in plasma reactor.
Perspectives
This work performed in hydrogen gas mixtures on broadened hydrogen Balmer line, confirms the interest of the Balmer line shapes to study the translational energy distribution of H atoms for investigations on reactive processes and on the dynamic of the plasma. It points out the role of the gas recirculation and of the reactor wall or the one of electrode surfaces in the plasma chemistry.
jean-louis jauberteau
University of Limoges UMR 7315 CNRS IRCER
Read the Original
This page is a summary of: Hydrogen Balmer line broadening in Ar-N2-SiH4 DC glow discharge, Journal of Applied Physics, October 2022, American Institute of Physics,
DOI: 10.1063/5.0105384.
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