Optical emission spectroscopy (OES) reveals cathode sheath parameters using Stark polarization spectroscopy of neon lines in Grimm-type glow discharge sources (GDSs).
A recent study in the journal Spectrochimica Acta Part B: Atomic Spectroscopy, authored by Nikola V. Ivanović, Nikodin V. Nedić, Ivan R. Videnović, Dj. Spasojević, and Nikola Konjević of the University of Belgrade, Serbia, explores optical emission spectroscopy (OES) applied to neon spectral lines in direct current (DC) glow discharge sources (GDSs), specifically the standard Grimm analytical source, and a modified plane cathode Grimm design (1).
The Grimm glow discharge source (GDS) is designed for elemental analysis of solid samples. It utilizes glow discharge spectroscopy, generating a plasma discharge on a sample surface to excite and subsequently analyze the emitted light, allowing for elemental analysis.
In the pursuit of a more comprehensive understanding, the researchers employed a modification to the Grimm GDS that enables both end-on and side-on spectra recordings. The traditional Grimm GDS only permits end-on observations, where radiation is collected perpendicular to the cathode surface. However, the modification allows for side-on observations, capturing radiation from a narrow slice parallel to the cathode surface. This innovation facilitates spatially resolved Stark polarization spectroscopy within the cathode sheath (CS) region.
In the context of OES, Stark polarization spectroscopy involves the application of an external electric field to a sample, causing shifts in the emission lines of the observed sample spectrum. This analytical technique yields information on the electronic structure and energy levels of the atoms or ions in the sample, providing detailed elemental composition characterization.
The neon spectral lines, Ne I 503.775 nm and Ne I 508.038 nm, were the focal points of the study. The side-on observations provided unique insights into the Stark shifts of differently polarized line components (σ, π, or unpolarized) within the CS region, demonstrating their dependence on the macroscopic CS electric field strength. These Stark components, observed in the CS, manifested as characteristic features in the end-on recordings, presenting as wavy wings with intensity maxima corresponding to distinctly resolved Stark components in the CS.
The researchers conducted a series of OES measurements under varying discharge conditions, including pressure, voltage, and current. Notably, they observed a sustained correlation between the maximum electric field strength (Emax) within the CS and the shifts (Δλe) in the end-on recorded wing features. This correlation, established through extensive measurements, allows for the extrapolation of cathode sheath parameters such as Emax and CS thickness (dc) in the standard Grimm-type GDS, which has only end-on optical access.
The implications of this research extend to improved understanding of glow discharge sources and the critical role played by cathode sheath parameters. By leveraging polarization spectroscopy of neon spectral lines, the study provides a nuanced perspective on the interplay between electric field strength and spectral features. This approach not only enhances our comprehension of the physics within glow discharge sources but also offers a practical methodology for estimating cathode sheath parameters in analytical setups.
In conclusion, the research presented here may help to unravel the intricacies of cathode sheath parameters through innovative optical techniques. The incorporation of side-on observations and Stark polarization spectroscopy opens avenues for more nuanced investigations into glow discharge sources.
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(1) Ivanović, N. V.; Nedić, N. V.; Videnović, I. R.; Spasojević, D.; Konjević, N. Stark Polarization Spectroscopy of Neon Spectral Lines for Estimating Cathode Sheath Parameters in Grimm-Type Glow Discharge Sources. Spectrochim. Acta, Part B 2023, 208, 106775. DOI: 10.1016/j.sab.2023.106775