Fundamental studies on a planar-cathode direct current glow discharge. Part I: characterization via laser scattering techniques

A laser-scattering-based instrument was used to study an argon d.c. planar-diode glow discharge. The gas-kinetic temperature (T_g) was determined via Rayleigh scattering and the electron number density (n_e), electron temperature (T_e), and shape of the electron energy-distribution function were determined by Thomson scattering. Axial profiles of these parameters were obtained as the discharge current, voltage, and pressure were varied. Trends in the profiles of T_g and in the other parameters show the interdependence of these plasma species and properties. The results will be compared with current theoretical computer models in order to improve our understanding of the fundamental processes in glow discharges sustained under conditions appropriate for spectrochemical analysis.     

Fundamental aspects and applications of fourier-transform ion-cyclotron resonance spectrometry

The operating principles, features, advantages, applications and potential of Foourier-transform ion-cyclotron resonance (F.t./i.c.r. or F.t.m.s.) mass spectrometry are discussed. It is shown that F.t./i.c.r. technology creates a high-performance mass spectrometer with high speed, high sensitivity, ultrahigh mass resolution, very wide mass range and unparalleled versatility.     

Modeling of glow discharge sources with flat and pin cathodes and implications for mass spectrometric analysis

A set of three-dimensional models for a direct current glow discharge in argon, developed previously in our group, is applied to analytical glow discharge cells with either flat or pin-type cathodes. Among other quantities, the densities of the plasma species are calculated and compared for these two cathode shapes. A comparison is also made for the computed argon and sputtered cathode (copper) ion currents leaving the glow discharge cell and entering the mass spectrometer, because this is of major interest from the analytical point of view. Finally, for the pin cell, the influence of sampling distance (i.e., distance between cathode pin and exit slit to the mass spectrometer) on the calculated plasma quantities is investigated.     

A glow discharge ion source with fourier transform ion cyclotron resonance mass spectrometric detection

A glow discharge (CD) ion source has been coupled to a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer using a four-element electrostatic lens to accelerate and focus ions generated external to the instrument’s high magnetic field into its analyzer cell. Like other CD mass spectrometers, GD-FT-ICR can provide a quantitative measure of bulk analyte concentration with good precision and accuracy. Although detection limits currently attainable are several orders of magnitude higher than the commercially available magnetic sector-based instrument, CD-FT-ICR holds promise for ultrahigh resolving power elemental mass analysis. Several schemes are proposed to lower the detection limits of the technique while still providing high enough resolution to resolve isobaric interferences.     

Design and characterization of a direct current glow discharge lamp for analytical applications

This paper describes a compact, small volume direct current glow discharge lamp operating at low wattage for atomic emission spectrometric analysis and its process optimization for copper and brass solid samples. The design aspects, fundamental characteristics and analytical performance are described in detail. The discharge is observed end-on, with water-cooled cathode surface parallel to the spectroscopic entrance slit. The anode diameter is 7 mm and the minimum sample diameter required is 20 mm. The sample is located outside the lamp for easy access and interchangeability. The lamp is powered by a dc power supply capable of delivering 300 mA (max.) and 1500 V. The studies of fundamental characteristics include the current-voltage relationship and their dependence on pressure and the emission intensity of copper spectral line (324.7 nm). The studies were made in the pressure range of 2-7 mbar. Long-term stability of optical emission spectra was also recorded to be within ±0.75%. The performance of the lamp is quite linear in the pressure range 3.5-7 mbar at an applied voltage of about 450 V.     

Characterization of a glow discharge ion source for the mass spectrometric analysis of organic compounds

A glow discharge ion source has been constructed for the mass spectrometric analysis of organic compounds. Characterization of the source has been made by studying the effect of pressure and discharge current on ionic distributions by anodic ion sampling along the discharge axis. Ion and electron densities and electronic temperatures have been calculated by using the single Langmuir probe technique to correlate the extraction efficiency with measured ion distributions and gain some insight into the ionization of organic molecules. The spectra obtained for several classes of organic compounds show that formation of parent-molecular ions by proton transfer, resulting partly from the background water molecules, is a major low energy process while charge transfer, Penning ionization, and electron ionization ace probably responsible for the fragmentation observed. The spectra result from the simultaneous occurrence of high and low energy reactions, and their structural information content is very high, yielding both molecular and extensive fragment ion information. The glow discharge ion source has proved to be essentially maintenance-free, easy to operate, stable, and can be used at reasonable mass resolution (up to 70001. The source also provides picogram range detection limits and has a linear response range of about six orders of magnitude, which makes it an interesting ion source for routine analysis. Preliminary work conducted with chromatographic interfaces indicates that its use can be easily extended to both gas and liquid chromatography.     

Mass spectrometric diagnosis of the surface nitriding mechanism in a d.c. glow discharge

Reactive constituents have been investigated in a molecular beam generated in the cathode surface glow area and surface boundary layer. Mixtures of nitrogen and hydrogen form NH_x(x=0–4) compounds, which are of relevance in heterogeneous, plasma vs. metal nitriding reactions. Ammonia decomposition leads to NH_x(x=2–4). Strong cataphoretic enrichment of hydrogen has been observed in the cathode glow area. Heterogeneous reactions of NH_x with iron lead to the formation of iron nitrides via intermediates such as FeNH_2–3. In a pulsed d.c. glow discharge, increased sputtering and decreased hydrogen enrichment have been observed.     

Fundamental aspect and behavior of saturated fluorocarbons in glow discharge in absence of potential source of hydrogen

The glow discharge of a series of saturated fluorocarbons, C_nF_2n+2 (n = 1, 2, 4, 6, and 8), was studied with glass substrates which do not contain any hydrogen. It was found that the deposition rate was a function of the F/C ratio of the starting fluorocarbons. That is, fluorocarbons with higher F/C ratio, such as CF₄ and C₂F₆, hardly polymerized, while fluorocarbons with lower F/C ratio, such as C₈F₁₈, polymerized as well as C₂F₄. After plasma exposure, the surface of glass substrate was characterized by measurements of water contact angle, water droplet rolling-off angle, and ESCA. Although all saturated fluorocarbon plasmas could alter the surface more hydrophobic than before, the deposited materials from fluorocarbons with higher F/C were not stable. Also, in plasmas with high F/C fluorocarbons, i.e., CF₄ and C₂F₆, sputtering of the electrode material was observed. © 1992 John Wiley & Sons, Inc.     

Powering the analytical glow discharge

The glow discharge may be powered by direct current (dc), radio frequency (rf) and pulsed discharge sources. Each has specific advantages and special features that should be considered by analysts using the various forms of glow discharge spectroscopy. This paper reviews some of the factors that contribute to the selection of a power source for the glow discharge.     

Microsecond-pulse glow discharge atomic emission

A microsecond pulsed glow discharge was produced with high pulse magnitude and small duty cycle. Time resolved emission and absorption spectroscopy was applied to study the processes of atomization, excitation and ionization in the glow discharge. Experimental results show that, without overheating the sample, the emission peak intensity is several orders greater than that obtained in the conventional dc mode. This implies that a much more intense plasma is generated during pulsed "on" region.     

Microsecond-pulse glow discharge atomic emission

A microsecond pulsed glow discharge was produced with high pulse magnitude and small duty cycle. Time resolved emission and absorption spectroscopy was applied to study the processes of atomization, excitation and ionization in the glow discharge. Experimental results show that, without overheating the sample, the emission peak intensity is several orders greater than that obtained in the conventional dc mode. This implies that a much more intense plasma is generated during pulsed on region.     

Powering the analytical glow discharge

The glow discharge may be powered by direct current (dc), radio frequency (rf) and pulsed discharge sources. Each has specific advantages and special features that should be considered by analysts using the various forms of glow discharge spectroscopy. This paper reviews some of the factors that contribute to the selection of a power source for the glow discharge.     

Analytical glow discharge mass spectrometry

Various types of glow discharge mass spectrometric systems as well as their applications are considered. Special attention is paid to radiofrequency and pulsed glow discharges combined with time-of-flight mass spectrometers. Along with typical application fields of glow discharge mass spectrometry, analysis of semiconductors, polymers, and dielectrics, as well as isotope analysis and depth profiling are also reviewed. Some methods of standard-free mass spectrometric analysis of solids are considered. Prospects for combining glow discharge mass spectrometry with preliminary chromatographic separation are discussed.     

New hardware for radio frequency powered glow discharge spectroscopies and its capabilities for analytical applications

A new radio frequency (rf) hardware is developed for glow discharge spectroscopic methods. The resulting features and its capabilities for analytical applications are discussed. The electrical equipment developed allows to work as quickly, stably, reliably and easily as known from the direct current (dc) mode. Moreover, the rf power measurement has been improved. The hardware has been developed, optimised and tested for glow discharge optical emission spectroscopy (GDOES), but nevertheless it is possible to use it for all procedures applying glow discharge sources.     

New hardware for radio frequency powered glow discharge spectroscopies and its capabilities for analytical applications

A new radio frequency (rf) hardware is developed for glow discharge spectroscopic methods. The resulting features and its capabilities for analytical applications are discussed. The electrical equipment developed allows to work as quickly, stably, reliably and easily as known from the direct current (dc) mode. Moreover, the rf power measurement has been improved. The hardware has been developed, optimised and tested for glow discharge optical emission spectroscopy (GDOES), but nevertheless it is possible to use it for all procedures applying glow discharge sources.     

辉光放电质谱技术应用进展

对辉光放电质谱(GDMS)在金属与半导体、非导体、薄层与深度分析、分子信息分析方面的应用和一些新装置、新方法进行了综述.着重介绍了近20年来我国学者在辉光放电质谱方面的成就,并结合国际上的报道对该领域的发展现状进行了总结.     

Spatial and temporal studies of a glow discharge

A demountable glow discharge tube was constructed with the objective of studying the various processes taking place in the discharge and resolving these both spatially and temporally. Argon and neon were used as fill gases. Continuous wave laser excited fluorescence was used to study the spatial distribution of sodium atoms which were sputtered off the cathode; a value for the diffusion coefficient of sodium in argon was obtained from time-resolving these experiments. From the population ratios of the various excited levels which we observed, we conclude that no single excitation temperature predominates anywhere between the electrodes under our conditions; instead, several population inversions were observed. Emission intensities of lines from atoms and ions were resolved as a function of the axial position between the electrodes. A temporal region was found where the signal-to-noise ratio for the detection of small quantities of analytes may be optimized. In addition to numerous atomic lines from the fill gas, we also detected fill gas ions as well as Fe, Fe⁺ and Cr when using stainless steel as a sample.     

Guiding DC glow discharge in microchannels

This work describes the conditions, in terms of dimensions and geometry, to guide a dc glow discharge preferentially through a microchannel in simple networks. Two- and three-channel microfluidic structures were studied. A preference towards a wider channel, in a two-channel network, was observed when the difference in width was at least 18% and the length was at least 10 mm. In a three-channel structure, a change in glow discharge intensity was observed when the network was downscaled from a pathlength of 2 to 0.5 cm. While the intensity within the path with fewer turns decreased with a reduction in size, the intensity of the path with greater number of turns increased.