Investigating recent developments and applications of optical plasma spectroscopy: A review

Abstract

Optical spectroscopy is a powerful, nonintrusive diagnostic tool that can provide unparalleled insight into fundamental plasma properties. Specifically, these techniques are widely employed to qualitatively and quantitatively characterize interactions of species within a discharge. This work is comprised of two parts: (1) a brief review of recent literature on the application of optical emission spectroscopy from the past decade, ranging from the study of atomic rare gas to more complex environmentally and technologically relevant plasma systems and (2) the presentation of new data that illustrate the power of optical spectroscopy techniques beyond simple species identification. Specifically, time-resolved optical emission spectroscopy was utilized to provide kinetic information about excited state species formation, ultimately lending mechanistic insights into a range of plasma processes. In addition, by combining optical emission and broadband absorption spectroscopies, rotational and vibrational temperatures for both excited and ground state species were determined. These data provide a thermodynamic base for enhanced understanding of the fundamental chemistry in plasma systems. The two platforms explored here were plasma-assisted catalysis systems containing NxOy species and fluorocarbon plasmas utilizing a range of precursors to evoke either etching or deposition, depending on the plasma conditions.

Spectroscopic Characterization of an Atmospheric Pressure Plasma Jet Used for Cold Plasma Spraying

“…Former measurements on APPJs for cold plasma spray using thermocouples showed low gas temperatures of ≤400 K at a working distance of 20 mm from the nozzle exit [5,7]. While differences between gas and rotational temperatures were one explanation, it should be noted that in our experiment no particles for deposition were added to the jet, and studies showed a great influence of substrates on gas-phase chemistry [13]. As the validity range for electron-density determination was exceeded, it can only be stated that the electron density was lower than the limit of 5 × 10 15 cm −1 although this is in agreement with the literature for atmospheric-pressure non-thermal nitrogen jets [31].…”

“…Changes in gas composition, well studied for the influence of water, lead to a change in kinetics and therefore a strong variation in plasma temperatures, electron densities, and excited species densities can be observed [9][10][11][12]. The presence of substrates can have similar effects, but many jets are monitored under laboratory conditions, and not many studies focus on substrate interactions [13]. Recent developments have focused on the application of OES for the monitoring and controlling of plasma.…”

Efforts Toward Unraveling Plasma-Assisted Catalysis: Determination of Kinetics and Molecular Temperatures within N2O Discharges

“…Larsson described a selective energy transfer (SET) model to explain catalyst–reactant interactions, − where the catalyst provides the energy required to populate higher vibrational levels within a molecule. This model suggests that vibrationally excited N 2 molecules can interact with a material and scatter with some energy loss, potentially through an energy transfer mechanism . Larsson investigated numerous catalytic systems [e.g., hydrocarbon cracking over zeolites and ethane hydrogenolysis over Pt, Ni, Fe, and Co catalysts], applying the SET model to probe vibrational resonance processes.…”

“…This model suggests that vibrationally excited N 2 molecules can interact with a material and scatter with some energy loss, potentially through an energy transfer mechanism. 49 Larsson investigated numerous catalytic systems [e.g., hydrocarbon cracking over zeolites 50 and ethane hydrogenolysis over Pt, Ni, Fe, and Co catalysts 51 ], applying the SET model to probe vibrational resonance processes. In many of the SET systems reported in the literature, little chemisorption of the intact molecule onto the catalyst surface is observed, depending on the catalyst.…”

Nanoparticles in analytical laser and plasma spectroscopy – a review of recent developments in methodology and applications

“…[58][59][60] Apart from the identication of species present in a plasma, the two main parameters that are predominantly determined by OES are the number concentration of electrons (electron density, n e ) and the electron temperature (T e ). 61 In order to support the following sub-chapter, we will briey mention some widely used methods for calculating n e and T e , usually employed during the monitoring of plasma-based NP synthesis.…”