The effect of nitrogen on analytical glow discharges studied by high resolution Fourier transform spectroscopy

Abstract

The conditions in an analytical glow discharge may be considerably affected by a small amount of a foreign gas in the working gas (usually argon). Intensities of emission lines can change drastically, significantly influencing quantitative analysis by glow discharge optical emission spectrometry (GD-OES). However, gaseous elements are present as compounds or occluded gas in many samples; for example, nitrogen is a very important element in depth profiling nitrided steels or in the analysis of coatings containing nitrides. Analytically important nitrogen emission lines are in the vacuum ultraviolet (VUV) region, and the VUV Fourier transform (FT) spectrometer at Imperial College, London, was used to record the spectra emitted by Grimm-type sources using argon with various cathode materials, representing matrices of different reactivity with nitrogen. Controlled amounts of nitrogen were added to the working gas. Intensities and line profiles of emission lines—sample, argon (both atomic and ionic) and nitrogen (atomic and molecular band)—were recorded over wide spectral regions and the observed trends are presented. The self-reversal observed for the Ar I 811.5 nm and Ar I 763.5 nm resonance lines was reduced by the addition of nitrogen, implying a reduction in the population of argon metastable atoms.