Impact of Pulsing a Radio Frequency Glow Discharge Lamp on Emission Yields and Analytical Figures of Merit in Glow Discharge Optical Emission Spectroscopy

Abstract

The impact of pulsing a radio frequency (RF) glow discharge lamp on analytical aspects in glow discharge optical emission spectrometry (GD-OES) was investigated. The experiments were done with a LECO GDS950 spectrometer. This instrument has a fixed pulse frequency of 320  Hz and adjustable pulse duty cycles (PDC) 100%–6.4%. In the first part, emission yields (EY) were studied by measuring coated steel samples in compositional depth profiling (CDP) mode. Variations in EY were measured by integrating the intensity of emission lines from several elements through the entire coatings at several PDC settings. The results show generally small EY variations. For improved accuracy, a set of correction constants is suggested. In the second part, the impact on signal-to-background (S/B), signal-to-noise-noise (S/N), and precision was investigated using “high current” pulsing. This means increased pulse power leaving the average power constant at the different PDC settings. The samples were a low alloy steel and a high purity iron blank (background) sample. The results showed significant increase of the S/B and S/N for four out of six spectral lines investigated at increasing pulse power, showing potential for improved detection limits (DL). Furthermore, there was a tendency towards improved precision with higher pulse power. Finally, the effect on depth resolution in CDP was investigated by running a ZnNi coated steel using “high current” pulsing. It was found that the depth resolution was unaffected up to 30% PDC.

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