Fundamental Plasma Processes

Fang, Duencheng; Marcus, R. Kenneth

doi:10.1007/978-1-4899-2394-3_2

Cited by 18 publications

(20 citation statements)

References 72 publications

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“…Possible small changes in the EEDF, as the cathode material is changed, do not influence the emission yield significantly, when effects of discharge voltage and cathode surface area are taken into account. 32 This confirms the experience of relatively low matrix effects and linear calibration behaviour observed in GD-OES. The samples used for this experiment are mixture of Fe, Ni, and Cr.…”

Section: Dependence On Concentrationsupporting

confidence: 78%

Characterisation of a pulsed rf-glow discharge in view of its use in OES

Nelis

Aeberhard

Hohl

et al. 2006

J. Anal. At. Spectrom.

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Section: Dependence On Concentrationsupporting

confidence: 78%

Characterisation of a pulsed rf-glow discharge in view of its use in OES

Nelis

Aeberhard

Hohl

et al. 2006

J. Anal. At. Spectrom.

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“…LA particles must be subjected to sufficient heat to completely vaporize them, after which collisions with plasma electrons or He metastable atoms (i.e., Penning collisions) affect the excited state populations of the atomic vapor. 26 Discharge current would be expected to play a role in the gas kinetic temperature of the plasma as well as in the rate of excited state-populating collisions. To a first approximation, higher discharge currents, and correspondingly higher power densities, would be expected to yield higher plasma temperatures (e.g., better vaporization), while also providing higher electron–atom collision rates.…”

Section: Resultsmentioning

confidence: 99%

“…The plasma characteristics (i.e., plasma temperatures, electron number density, and robustness) have been investigated recently in hopes of a better understanding of the LS-APGD's potential as an excitation–ionization source for liquid samples. 23,26 While the plasma excitation temperature (*2600 K) may not be as high as that of a typical ICP (typically 7000–10 000 K), the electron number density (3 × 10 15 cm –3 ) is on the same order of magnitude. Rotational temperatures determined through OH and N 2 band emission are *1000 K. 23 While such values seem to be low in terms of vaporization capacity, the device has been shown to be effective as a secondary excitation–ionization source for particles generated by both nanosecond and femtosecond laser ablation.…”

Section: Introductionmentioning

confidence: 99%

Liquid Sampling–Atmospheric Pressure Glow Discharge as a Secondary Excitation Source for Laser Ablation-Generated Aerosols: Parametric Dependence and Robustness to Particle Loading

et al. 2015

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Liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma is being developed as a secondary vaporization-excitation source for the optical emission analysis of laser ablation (LA)-generated particle populations. The practicalities of this coupling are evaluated by determining the influence of source parameters on the emission response and the plasma's robustness upon LA introduction of easily ionized elements (EIEs). The influence of discharge current (45-70 mA), LA carrier gas flow rate (0.1-0.8 L min(-1)), and electrode separation distance (0.5-3.5 mm) was studied by measuring Cu emission lines after ablation of a brass sample. Best emission responses were observed for high-discharge currents, low He carrier gas flow rates, and relatively small (<1.5 mm) electrode gaps. Plasma robustness and spectroscopic matrix effects were studied by monitoring Mg(II) : Mg(I) intensity ratios and N2-derived plasma rotational temperatures after the ablation of Sr- and Ca-containing pellets. Plasma robustness investigations showed that the plasma is not appreciably affected by the particle loadings, with the microplasma being slightly more ionizing in the case of Ca introduction. In neither case did the concentration of the concomitant element change the robustness values, implying a high level of robustness. Introduction of the LA particles results in slight increases in the rotational temperatures (∼10% relative), with Ca-containing particles having a greater effect than Sr-containing particles. The observed variation of 9% in the plasma rotational temperature is in the same order of magnitude as the short-term reproducibility determined by the proposed LA-LS-APGD system. The determined rotational temperatures ranged from 1047 to 1212 K upon introducing various amounts of Ca and Sr. The relative immunity to LA particle-induced matrix effects is attributed to the relatively long residence times and high power densities (>10 W mm(-3)) of the LS-APGD microplasma.

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“…Discharge current and pressure are two of the three primary controlling parameters in the performance of any GD source, the third of which is the applied potential . In practice, the three parameters are interdependent.…”

Section: Resultsmentioning

confidence: 99%

“…In the experiments performed here, the voltage was left as the dependent variable, with the pressure and current operated at fixed values during a given analysis. The interdependence of the discharge conditions results in differences in the atomization/excitation characteristics in all GD sources, particularly hollow cathodes . To a first approximation, discharge current affects the particle flux to the surface (i.e., sputtering events) and the density of the electrons in the gas phase (i.e., excitation events).…”

Section: Resultsmentioning

confidence: 99%

Sampling and Analysis of Particulate Matter by Glow Discharge Atomic Emission and Mass Spectrometries

et al. 1999

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The direct introduction of particulate matter into glow discharge atomic emission and mass spectrometry sources through a particle beam/momentum separator apparatus is described. Vacuum action through a narrow (0.0625 in. i.d.) stainless steel tube allows the introduction of discrete samples of NIST SRM 1648 urban particulate matter (UPM) and caffeine in powder form. Introduction of "ambient" airborne particulate matter is also possible. Particles passing through the aerodynamic momentum separator impinge on the heated (∼200-250 °C) inner surface of the glow discharge plasma volume and are flash-vaporized. The resultant atoms/molecules are subjected to excitation/ionization collisions within the low-pressure (0.5-5 Torr of He or Ar) plasma, producing characteristic photon emission and/or signature ionic species. In this way, atomic emission and mass spectrometry identification of particle constituents is possible. Basic design aspects of the apparatus are presented, and demonstrations of atomic emission detection of the constituents in the NIST SRM illustrate the general characteristics of the approach. Transient atomic emission signals are captured for the introduction of preweighed, discrete samples, with the integrated areas used to construct analytical response curves. Limits of detection using this relatively simple atomic emission system are on the order of tens of nanograms for sample masses of ∼50 μg. Mass spectrometric monitoring of introduced caffeine particles and a mixture of polycyclic aromatic hydrocarbons (PAHs) illustrates the ability of the glow discharge plasma to produce high-quality, library (electron impact) searchable mass spectra of molecular species while also yielding isotopic identification of elemental components of the UPM. Limits of detection for Fe in the NIST SRM are on the order of 175 ng of material, equivalent to ∼7 ng of analyte Fe. It is believed that the small size, low power consumption, ease of operation, and multimode sampling capabilities (AES/MS) of the particle beam-glow discharge (PB-GD) apparatus hold promise for applications in continuous monitoring and discrete particle sampling.

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Fundamental Plasma Processes

Cited by 18 publications

References 72 publications

Characterisation of a pulsed rf-glow discharge in view of its use in OES

Characterisation of a pulsed rf-glow discharge in view of its use in OES

Liquid Sampling–Atmospheric Pressure Glow Discharge as a Secondary Excitation Source for Laser Ablation-Generated Aerosols: Parametric Dependence and Robustness to Particle Loading

Sampling and Analysis of Particulate Matter by Glow Discharge Atomic Emission and Mass Spectrometries

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