Surface Loss Probability of Nitrogen Atom on Stainless-Steel in N₂Plasma Afterglow

Abstract

We investigated the loss kinetics of nitrogen (N) atoms in a N 2 plasma afterglow using a vacuum ultraviolet absorption spectroscopy technique with an atmospheric-pressure microdischarge hollow cathode lamp. The decay curves of N atom density were fitted with single exponential functions at pressures from 1.33 to 13.3 Pa. The dependence of the decay time constant on the pressure showed that the N atoms were predominantly lost through diffusion to the wall surface. The surface loss probability of N atoms on stainless-steel based on the decay time constant as a function of pressure was estimated to be 0.03. #

Wall loss of atomic nitrogen determined by ionization threshold mass spectrometry

“…In spite of similarities in discharge geometries, discharge volumes, pressure range, and similar power densities, the measured wall loss times of Refs. 5,6 are at least one order of magnitude higher than the values of the present work. Because both Refs.…”

“…Because both Refs. 5,6 apply the same model as in the present work this difference in t wN leads also to more than one order of magnitude difference in β N . We can only speculate about the reason for this.…”

“…Takashima et al 5 determined t wN in the afterglow of a pulsed capacitively-coupled N 2 plasma with vacuum ultraviolet absorption spectroscopy (VUVAS) in the pressure range from 1.3 to 27 Pa. The measured t wN corresponds to the wall loss time.…”

“…For low-pressure plasmas atomic nitrogen is mainly produced by electron-induced dissociation of N 2 which is predominantly affected by the electron density and electron temperature of the respective plasma. The loss of atomic nitrogen in such plasmas is determined by the flux to the wall [3][4][5][6][7][8] . In our case, as in most other cases, the wall loss is determined by recombination of atomic nitrogen to form molecular nitrogen which desorbs from the surface.…”

“…To our knowledge, measurements of the wall loss time at two different positions in the same plasma chamber were not yet published neither for nitrogen nor for other wall loss times of radical species such as hydrogen or oxygen. In addition, contrary to most spectroscopic determination [5][6][7] of the nitrogen radical density where the density is averaged over the line of sight this work measures the local radical density at two very different positions.…”