The concept of constant emission yield in GDOES

This review paper describes the evolution of the quantification procedure for compositional depth profiling (CDP) in glow discharge optical emission spectrometry (GD-OES), based on the constant emission yield concept. The concept of emission yield (EY) is defined and ways of measuring it experimentally are discussed. The history of the development of quantitative CDP is reviewed, which shows that all of the different approaches depend on the assumption that the EY is essentially a matrix-independent quantity. Particular emphasis is placed on the dependence of the EY on the plasma parameters of current, voltage, power and pressure. In short, impedance changes (current voltage) can significantly affect the emission yield and should either be corrected mathematically or the impedance should be kept constant by pressure regulation in order to obtain reliable results from GDOES CDP. On the other hand, the effect of varying the pressure on the emission yield can be considered to be minor within the limits of practical operating conditions for most CDP applications. It is worth, however, bearing in mind that varying the discharge pressure has a significant effect on the plasma processes, and does affect the emission yield when these variations are large. The experimental results obtained for the emission yield are related to the results from theoretical model calculations published on the subject.     

Comparative study on emission characteristics of d.c.- and r.f.-powered Grimm glow discharge plasmas. Use of argon spectral lines

Equivalent discharge conditions, where the intensities of the analyte are almost the same between the d.c. and the r.f. power modes, have been investigated in Grimm glow discharge emission spectrometry. The two plasmas have similar emission and sputtering characteristics, enabling the conditions to be found easily. Various emission lines of argon ion are commonly observed from the argon discharges regardless of the power modes. A method to determine the equivalent discharge conditions is suggested, based on intensity analysis of the argon ionic lines.     

Wavelength table of chromium emission lines in argon glow discharge optical emission spectrometry

A wavelength table of chromium lines emitted from an argon glow discharge plasma, which comprises 2049 atomic and ionic emission lines in the wavelength range of 200–440 nm, is presented. The relative intensities are rather different from the data of published wavelength tables based on arc-excited and spark-excited spectra. Emission lines of Ar, Ti, V, Fe, Ni, and Cu in the neighborhood of the prominent Cr emission lines are also compiled as a table. These tables could be employed for the analytical applications in glow discharge optical emission spectrometry. All of the data are presented as Supplementary Electronic Material.     

Selective excitation of singly-ionized silver emission lines by Grimm glow discharge plasmas using several different plasma gases

The relative intensities of silver emission lines from Grimm glow discharge plasmas were investigated in the wavelength range from 160 to 600 nm when using different plasma gases. It was characteristic of the plasma excitation that the spectral patterns were strongly dependent on the nature of the plasma gas employed. Intense emission lines of silver ion were observed when argonhelium mixed gases were employed as the plasma gas. Selective excitation of the ionic lines could be principally attributed to the charge transfer collisions between silver atoms and helium ions.     

Radio frequency glow discharge optical emission spectroscopy: a new weapon in the depth profiling arsenal

While the array of analytical methods routinely applied for depth profile analysis was fairly static over the decades of the 1980s and 1990s, there appears to be an emerging technique that has a number of very positive and complementary attributes, and warrants serious consideration by the thin film community. Radio frequency glow discharge optical emission spectroscopy (rf-GD-OES) is a technique that provides depth-resolved elemental composition information on a wide variety of sample types. In a manner very much like most depth profiling methods, the rf-GD plasma utilizes an ion sputtering step to ablate sample material in a layer-by-layer fashion. Different from the more commonly applied methods, the device operates at elevated pressures [2-10 Torr Ar (266-1,330 Pa)] and has the inherent capability of sputtering electrically insulating materials directly, without any auxiliary means of charge compensation. In addition, sputtering rates on the order of 1 micro m/min provide rapid analysis, with depth resolving powers that are comparable to high-vacuum sputtering methods. Three examples of the use of the rf-GD-OES method are presented as examples of its analytical potential: (1) boron-implanted silicon wafer, (2) a barrier-type alumina film, and (3) a porous-type alumina film. It is believed that the method holds a great deal of promise as part of the arsenal of weapons in the thin films laboratory.     

Design and properties of a microwave boosted glow discharge lamp

The operation of a glow discharge lamp with integrated microwave resonator for the analysis of electrically conducting solid samples by atomic emission spectrometry is described. While the glow discharge in argon at a pressure of 300 Pa mainly serves for the production of free sample atoms by cathodic sputtering, a 40 W microwave discharge is applied for additional excitation of the ablated material. The construction of the lamp and the optimization of the working conditions are described. The intensities as well as the signal-to-background ratios of many analytical lines were found to be improved as compared to a conventional glow discharge lamp. The analytical performance is demonstrated by analysis results for steel samples. Detection limits for 13 elements in steel are between 0.05 and 1 μg/g. Because of the optically thin plasma the new lamp shows a large linear dynamic range.     

Layer model approach to background correction in r.f.‐GDOES

Two methods are presented for dealing with variable background signals in radiofrequency glow discharge optical emission spectroscopy (r.f.‐GDOES). Their aim is to improve elemental analysis at trace levels, in bulk analysis or in compositional depth profiling, without having to measure background signals during the analysis. Each method uses background signals measured away from the analytical emission lines of interest during calibration only. The background signal is first determined during calibration for each material type of interest. During analysis in the first method the estimated background signal is varied according to the material type being analysed. In depth profiles this means identifying the various layers present as different material types, hence the name ‘layer model’. The second method is a more conventional approach, where part of the background signal is estimated as a spectral interference. Results are presented for the bulk analysis of a tool steel and for two depth profiles: TiO₂ coating on silicon and TiN‐coated tool steel. The two methods give similar results in the depth profiles, both significantly better than with a constant background. Copyright © 2004 John Wiley & Sons, Ltd.     

The design and characteristics of direct current glow discharge atomic emission source operated with plain and hollow cathodes

A compact direct current glow discharge atomic emission source has been designed and constructed for analytical applications. This atomic emission source works very efficiently at a low-input electrical power. The design has some features that make it distinct from that of the conventional Grimm glow discharge source. The peculiar cathode design offered greater flexibility on size and shape of the sample. As a result the source can be easily adopted to operate in Plain or Hollow Cathode configuration. I-V and spectroscopic characteristics of the source were compared while operating it with plain and hollow copper cathodes. It was observed that with hollow cathode, the source can be operated at a less input power and generates greater Cu I and Cu II line intensities. Also, the intensity of Cu II line rise faster than Cu I line with argon pressure for both cathodes. But the influence of pressure on Cu II lines was more significant when the source is operated with hollow cathode.     

Quantitative depth profile analysis of metallic coatings by pulsed radiofrequency glow discharge optical emission spectrometry

In recent years particular effort is being devoted towards the development of pulsed GDs because this powering operation mode could offer important analytical advantages. However, the capabilities of radiofrequency (rf) powered glow discharge (GD) in pulsed mode coupled to optical emission spectrometry (OES) for real depth profile quantification has not been demonstrated yet. Therefore, the first part of this work is focussed on assessing the expected advantages of the pulsed GD mode, in comparison with its continuous mode counterpart, in terms of analytical emission intensities and emission yield parameters. Then, the capability of pulsed rf-GD-OES for determination of thickness and compositional depth profiles is demonstrated by resorting to a simple multi-matrix calibration procedure. A rf forward power of 50 W, a pressure of 600 Pa, 1000 Hz pulse frequency and 50% duty cycle were selected. The quantification procedure used was validated by analysing conductive layers of thicknesses ranging from a few tens of nanometer up to about 20 μm and varied compositions (hot-dipped zinc, galvanneal, back contact of thin film photovoltaic solar cells and tinplates).     

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.     

Novel use of glow discharge optical emission spectroscopy (GDOES) to study corrosion of AA2024‐T3 in the presence and absence of inhibitors – part 3: investigating the effects of various proportions of inhibitor in the coating matrix or in nanocontainers

Elemental depth profiling by glow discharge optical emission spectroscopy has been used to characterize the corrosion products on AA2024‐T3. In previous work, the aluminium, oxygen and copper depth profiles were shown to provide information regarding surface roughening, the thickness of corroded layers and extent of copper de‐alloying/relocation. Nitrogen, sulfur, phosphorus and chromium depth profiles were examined in the hope of detecting inhibitor species within the corroded/altered layers after 5 h of exposure to a corrosive solution. In the present work, the study is extended to longer exposure time. The work presents a further study of the leaching of benzotriazole from the coating matrix or from nanocontainers during various times of exposure to a corrosive environment. Copyright © 2016 John Wiley & Sons, Ltd.     

Excitation of singly-ionized argon species in helium-matrix Grimm glow discharge plasmas II – Comparison between argon and neon

A considerable intensity enhancement of several Ar II lines assigned to the 3p(4)4p-3p(4)4s transition in a helium-argon Grimm glow discharge plasma has been previously reported and attributed to argon ions excited by metastable helium atoms. In this paper the behavior of Ne II lines assigned to the 2p(4)3p-2p(4)3s transition in a helium-neon plasma was investigated to obtain detailed information on the excitation of plasma gases in the helium-matrix plasmas. No Ne II lines with enhanced emission intensities have been found; on the contrary, the intensities of the doublet Ne II lines decreased in the helium-matrix plasma.     

Some basic characteristics of the Grimm magnetic field glow-discharge source with reference to steel analysis

The fundamental characteristics of a new type of glow discharge source as designed by Grimm are described. The source incorporates a permanent magnet which causes the electrons in the plasma to execute a spiral motion about the lines of force of the electric field leading to enhanced collisional excitation, sputtering and light output as compared to the conventional source. The performance of the magnetic field glow discharge source in the analysis of mild and stainless steels is evaluated.     

Modeling of glow discharge optical emission spectrometry: Calculation of the argon atomic optical emission spectrum

The optical emission spectrum of the argon atomic lines in a glow discharge is calculated, using a collisional–radiative model for argon, which was recently developed (A. Bogaerts et al., Collisional–radiative model for an argon glow discharge, J. Appl. Phys., vol. 84, No 1, 1998). It is shown that the lines corresponding to 4p→4s transitions clearly dominate the spectrum. They are, however, not responsible for the characteristic visible light in the glow discharge, because they are lying between 700 and 1000 nm, which is mainly in the near infrared. The characteristic blue light of the glow discharge is caused by the lines corresponding to 5p→4s transitions (lying in the blue–violet part of the spectrum). Beside these two most important line groups (the so-called `red' and `blue' lines) a large number of other lines are present, making the entire argon spectrum quite complex. The calculated spectrum is compared with experimental spectra from the literature, and excellent qualitative agreement is obtained.The calculated spatial distributions of optical emission lines originating from low excited levels (i.e., 4p, 3d, 5s, 5p, 4d, 6s) show a maximum in the cathode glow, caused by fast argon ion and atom impact excitation, to these levels, and a second maximum in the beginning of the negative glow, due to electron impact excitation. The maximum in the cathode glow is very pronounced for lines originating from the 4p levels, which is in agreement with experimental observations. The higher excited levels are not populated by fast argon ion and atom impact excitation but only by electron impact excitation; hence, lines originating from these levels exhibit only a maximum in the beginning of the negative glow.     

Polymer screening by radiofrequency glow discharge time-of-flight mass spectrometry

The aim of this work is to optimise and evaluate radiofrequency glow discharge (RF GD) time-of-flight mass spectrometry (TOFMS) for identification of organic polymers. For this purpose, different polymers including poly[methylmethacrylate], poly[styrene], polyethylene terephthalate-co-isophthalate and poly[alpha-methylstyrene] have been deposited on silicon wafers and the RF GD-TOFMS capabilities for qualitative identification of these polymeric layers by molecular depth profiling have been investigated. Although some molecular information using the RF continuous mode is available, the pulsed mode offers a greater analytical potential to characterise such organic coatings. Some formed polyatomic ions have proved to be useful to identify the different polymer layers, confirming that layers having similar elemental composition but different polymer structure could be also differentiated and identified.     

Self-absorption and Doppler temperatures of emission lines excited in a glow discharge lamp

The shapes of the emission lines of calcium and chromium emanating from a Grimm type glow discharge lamp have been determined by use of a pressure-scanning Fabry—Perot interferometer using various excitation conditions for different concentrations of these metals in standard matrices. Assuming a certain model for the light source, theoretical line profiles were calculated.The Doppler temperature as a function of current at constant voltage was determined from a comparison of the experimental and theoretical profiles. Also determined was the degree of absorption in emitting and non-emitting layers of the model.It was found that considerable self-absorption and reversal occur in the lamp at higher currents and concentrations.     

Wavelength table of chromium emission lines in argon glow discharge optical emission spectrometry

A wavelength table of chromium lines emitted from an argon glow discharge plasma, which comprises 2049 atomic and ionic emission lines in the wavelength range of 200–440 nm, is presented. The relative intensities are rather different from the data of published wavelength tables based on arc-excited and spark-excited spectra. Emission lines of Ar, Ti, V, Fe, Ni, and Cu in the neighborhood of the prominent Cr emission lines are also compiled as a table. These tables could be employed for the analytical applications in glow discharge optical emission spectrometry. All of the data are presented as Supplementary Electronic Material. Recieved: 22 December 1999 / Revised: 25 February 2000 / Accepted: 25 February 2000