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Microsecond Pulsed Glow Discharge (μs-PGD) was applied to commercially available spectrometers specified for OES elemental analysis with Grimm type sources, in order to have a look at the benefits which PGD can bring for practical bulk analysis. Intensities of more than 70 spectral lines of different elements together with background and noises were compared between μs-PGD and continuous Glow Discharge (GD) using CCD and PMT detectors. In comparison to continuous GD, the detection limits with PGD were 1.5–14 times lower for different spectral lines. The reasons for such a moderate improvement are discussed. [ABSTRACT FROM AUTHOR]

Two commonly used discharge cells (Grimm type and hollow cathode) were studied and compared in respect of their analytical capabilities. Semiconductive (silicon, silicon carbide, gallium nitride) and nonconductive (quartz and alumina) samples were considered. In this connection a combined hollow cathode was used, which consists of a cylindrical cathode and a flat sample in the bottom of the cylinder. Aluminum, copper, and tantalum cylindrical cathodes were applied. The comparison of the discharge cells was made by the OES signal intensities of sample components at equal power and similar pressure conditions, either at continuous RF or pulsed DC power supply modes. Operating in continuous RF mode, the combined hollow cathode source was shown to give almost the same or higher intensities compared with the Grimm cell. The application of the hollow cathode with continuous RF mode has an appreciable advantage only for thick dielectric samples, because in contrast to the Grimm cell, for the hollow cathode the analytical signal was found to be independent on sample thickness. Operating in pulsed DC mode, the combined hollow cathode system produces up to several orders of magnitude higher intensities than the Grimm cell, especially for dielectric samples. The pulsed mode has also shown good ratios of sample to cathode intensities compared with the continuous one. The sputtering mechanism in the combined hollow cathode cell was investigated and found to be connected with the formation of a thin conductive layer on the sample surface. The composition and thickness of the latter, depending on operating parameters and sputtering time were studied. It was shown that the surface layer is generated as a result of hollow cathode disc material deposition, sample material redeposition and enrichment of the less sputtered sample component. [ABSTRACT FROM AUTHOR]

This computational study present a LTE-based model (LTE: local thermodynamic equilibrium) and a two-temperature model of an inductively coupled plasma (ICP) operated in a standard Fassel-type torch. In addition, a computational model for a low-argon-flow torch, which consumes only 0.6 L min−1 of Ar, is presented for the first time. The latter is a special modification of the ICP torch, where the Ar cooling gas stream is replaced by an outer stream of compressed air. The two models include a comprehensive simulation of torch wall temperature as well as tangential Ar flow inside the torches. It can also be applied to other new geometries of ICP torches. Plasma properties in both torches are simulated over a wide range of operational parameters. The models are validated by comparing the simulated electrical and internal ICP properties to experimental data. [ABSTRACT FROM AUTHOR]

Emission of argon, analyte atoms and ions, and OH lines in standard and low-argon-flow inductively coupled plasmas (ICPs) was studied spatially using a novel imaging acousto-optical spectrometer (AOS). Unique characteristics of the AOS (wavelength range: 250–800 nm, spectral resolution: 0.05–0.5 nm, time resolution: 5 ns, change of wavelength: 0.2 ms, spatial resolution: ＞125 μm) allowed the measurement of high quality images at 21 different wavelengths for each set of plasma conditions within approximately 20 min. Fundamental plasma properties were determined over a wide range of operational parameters. Rotational, excitation, and electron temperatures were ranging from 4580–5120 K, 4360–5000 K, and 8770–10 840 K in the analytical zone of the low-argon-flow ICP, and 3230–4250 K, 3000–5560 K, and 6130–10 200 K in the analytical zone of the standard ICP, respectively. The emission investigations were complemented by IR-measurements of the torch wall temperature and measurements of electrical properties of the ICP. RF voltages and RF currents were measured directly in the load coil and were used to calculate the plasma power. Depending on plasma conditions, the measured power differs from the indicated one (vendor software) by up to a factor of two. [ABSTRACT FROM AUTHOR]

This article describes the compositional depth profiling (CDP) of diamond-like carbon (DLC) layers by Glow Discharge-Optical Emission Spectrometry (GD-OES). The DLC layers were deposited on flat steel samples. Analysis by using a Charge Coupled Device (CCD) GD-OES instrument revealed saturation effects of the carbon lines at 156 nm and 165 nm. Therefore, the application of these lines for CDP of DLC layers is not possible. A third line at 193 nm was not affected by this saturation effect and is therefore a good choice for calibration. A second effect was observed as a non-flat crater in combination with large differences of the sputtering rate factor of the substrate (1.1) and the DLC (0.032) led to an unusual behaviour at the interface between the DLC layer and substrate. Both measurements of the crater shape and of the sputtered coating weight up to the interface and just behind it showed clearly that about 30% of the DLC layer remains at the crater edge, once the crater centre reaches the interface. This was found to be the main reason for the incorrect DLC-layer thickness, if the intersection between the carbon and iron concentration was used as a measure for the end of the DLC layer. [ABSTRACT FROM AUTHOR]

New probes for the direct measurement of high radio-frequency (RF) voltage and current in the load coil of an inductively coupled plasma (ICP) are presented. Based on these measurements, a method for the calculation of power in the ICP is developed. Electrical parameters of the ICP are measured for a wide range of operational conditions in a standard ICP torch with wet aerosol introduction. Further, changes of the electrical parameters are monitored when operating the ICP with a very low argon flow rate of only 0.6 L min−1 using a so-called “Static High-Sensitivity ICP” (SHIP) torch. Direct measurements with the new RF probes allow following the evolution of plasma properties as a function of time. Noteworthy, it is found that there is a strong correlation between the plasma power and temperature changes in the RF generator itself. Depending on the plasma parameters, the measured plasma power was shown to differ significantly from the applied power (in the vendor software settings). [ABSTRACT FROM AUTHOR]

A Monte-Carlo based model is developed for simulating the evolution of Ar concentration, temperature and flow in time and space. Potentially, the model could be used for gas simulations in a wide range of different applications. Here, the model is incorporated into an existing but modified model of a microsecond pulsed glow discharge (μs PGD) in a Grimm-type plasma excitation source. Results of the simulations reveal that a thermal mechanism is responsible for the formation of the electrical prepeak and pressure waves, two phenomena that take place at the leading edge of the μs pulse in this source. [ABSTRACT FROM AUTHOR]

A novel Acousto-Optical imaging Spectrometer (AOS) was developed with unique features that make it attractive for different applications and fundamental investigations in atomic spectroscopy. Spatial resolution of the AOS is approximately 125 μm. Spectral resolution varies from 0.05 nm to 0.3 nm (full width at half maximum, FWHM) between 250 nm and 800 nm, respectively. Time resolution is 5 ns. Thus, the constructed AOS provides enough spatial, spectral and time resolution for applications in glow discharge imaging spectroscopy. Fast switching between different spectral lines within 200 μs can be used e.g. to investigate the evolution of different spectral lines quasi-simultaneously. [ABSTRACT FROM AUTHOR]