Glow discharge optical emission spectroscopy elemental mapping: elucidation of the underlying mechanisms and development toward nanoparticle characterization

Date

2022-08

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Abstract

Glow discharge optical emission spectroscopy (GDOES) is a powerful tool for the direct analysis of solid samples, with little-to-no sample preparation in very rapid timeframes due to the inherently fast sputtering rates. Other advantages include high sensitivity, simultaneous multi-elemental capabilities, multi-matrix calibration schemes, depth profiling with resolution at the nanometer scale, and low operating costs. Elemental mapping (EM) has been made possibly through the use of pulsed-power schemes and higher than typical operating pressures. Nevertheless, the fundamental mechanisms that are occurring under these conditions are not well understood, therefore leaving an area of interest to elucidate using plasma diagnostic techniques. The method of choice when available is laser scattering techniques due to the inherent advantages over OES, Langmuir probes, etc., including no prior assumption of local thermodynamic equilibrium conditions, minimal to no plasma perturbation, and direct probing of species without error propagation between calculations for fundamental parameters. However, low-density plasmas are inherently difficult to measure using laser scattering approaches due to the low scattered intensities and spectral information being found very close to the probe laser wavelength. Furthermore, there are relatively few applications that have been developed for GDOES EM, even though there are clear advantages over other approaches. One such area of interest is nanoparticle characterization due to the wide variety of applications and prevalence of them eventually found in environmental systems with relatively unknown toxicity. Herein, a transmission-type triple grating spectrograph was developed, characterized, and implemented for the fundamental elucidation of a GD plasma operated under OES EM conditions. The information obtained was spatiotemporally resolved for insights into the mechanisms governing the discharge as a function of time along the plasma pulse train. Furthermore, the development of GDOES EM for the successful characterization of nanoparticles (both pure elements and complex core-shell structures) based on composition and structural dimensions is presented. This is the first time GDOES in any form has been applied for nanoparticle characterization and GDOES EM provides many advantages over current techniques, with the most notable being the extremely rapid analysis times (high sample throughput).

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Keywords

Glow Discharge Optical Emission Spectroscopy, Elemental Mapping, Fundamental Studies, Laser Scattering, Nanoparticle Characterization, Instrumentation Development

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