Grimm-type Glow Discharge Lamp Research Articles

Multielement capability of a non-dispersive coherent forward scattering resonance monochromator

A two-element coherent forward scattering resonance monochromator (CFSRM) was developed. It worked without any additional monochromator. In this report, a Cu-Fe CFSRM was investigated. Transmission signals for each element were recorded with one photomultiplier via time-sharing by a gated pulse-counting technique. Background from stray and leakage light through the crossed polarizers was corrected. The transmission efficiency of the CFSRM could be varied separately for each element. Radiation from a Grimm-type glow discharge lamp with an Fe-Cu alloy cathode (0, 2, 5 and 10 mg g Cu) was filtered through a Cu-Fe CFSRM and a linear analytical curve could be obtained for Cu. The investigated two-element CFSRM can be easily extended to a multielement CFSRM system that also works without any additional dispersive instrumentation.

Background suppression of Ar lines in glow discharge atomic emission spectrometry by a lock-in amplifier and Kalman filter deconvolution

The Ar spectral lines are suppressed in Grimm-type glow discharge lamp atomic emission spectrometry (GDL-AES) by a double voltage modulation technique. The GDL is modulated between two voltage levels, typically 400 and 700 V. At the lower voltage level mainly Ar emission contributes whereas at the higher voltage level both Ar and atoms sputtered from the cathode contribute to the emission. The Ar emission spectrum at the lower voltage level is multiplied by a constant factor to scale it up to the same level of Ar emission found at the higher voltage level. This signal is then subtracted from the signal obtained at the higher voltage level by a lock-in amplifier to obtain the net analyte signal. The digital Kalman filter technique is also applied to background suppression; it is known to be the optimum filter for deconvolution of mixtures in noisy environments. The detection limits are found to be improved by nearly a factor of 10 with both double voltage modulation and Kalman filter techniques.

Excitation of the spectra of neutral and singly ionized atoms in the Grimm-type discharge lamp, with and without supplementary microwave excitation

Selected parts of the spectra of copper, aluminium and iron excited in a Grimm-type glow discharge lamp with and without supplementary microwave excitation have been measured for a wide range of experimental conditions, using argon or neon as the carrier gas. The changes produced by the supplementary discharge on different classes of spectral lines have been identified and shown to follow a consistent pattern in all the cases studied. Atomic lines of the carrier gas become more intense, with weaker ionic lines. Many atomic lines of the sputtered material are greatly enhanced; those ionic lines which are likely to be excited by charge exchange with carrier gas ions become much weaker whilst other ionic lines become somewhat more intense. The results clearly emphasize the role of the charge exchange mechanism in the excitation of ionic spectra.

Application of a modulated Grimm-type glow discharge plasma as primary light source for simultaneous reading atomic absorption spectrometry

The Grimm-type glow discharge lamp (GDL) working in a modulated way can be used as primary light source for atomic absorption measurements. The number of element radiations is given by the composition of the target (sample on GDL) which becomes sputtered. Its composition can be adopted to the analytical problem to be solved. It is easy to change the target.

State of the art of glow discharge lamp spectrometry. Plenary lecture

The development of glow discharge sources for atomic spectroscopy is traced. The electrical characteristics of the analytically relevant sources, sample volatilisation and the predominant excitation and ionisation processes are discussed. The possibilities of using the Grimm-type glow discharge lamp with a flat cathode for the spectral emission analysis of compact metallic samples, for non-conducting powders, after mixing with metal powder and making into pellets and for in-depth profiling are described. New types of lamps and the features of glow discharges with hollow cathodes are evaluated. The use of glow discharges as atom reservoirs for atomic absorption and fluorescence spectrometry and recent advances in glow discharge mass spectrometry are also covered.

Depth profiling of thin films using a Grimm-type glow discharge lamp

A Grimm-type glow discharge lamp was used for depth profiling of thin films. The sample surface was etched by cathodic sputtering at a rate of 1–100 nm s −1. Optical emission signals from the discharge were monitored with an optical spectrometer which yielded a depth profile of the chemical composition. The detectability is typically around 0.01 wt.%. For depth calibration purposes, the sputtering rate as a function of the discharge parameters was determined in a number of pure metals, alloys and copper oxide. The possibility of quantitative determinations is discussed. It is suggested that the relative intensities of the emission lines can be empirically described as functions of the discharge parameters and the sputtering rate. This makes it possible to use existing spectroscopic standards and a matrix correction procedure for quantitative analysis.

A contribution to the solution of the problem of quantification in surface analysis work using glow discharge atomic emission spectroscopy

The emission intensity from spectral lines has been studied in a Grimm-type glow discharge lamp (GDL). The variation in intensity of Ar I lines was investigated in order to exclude the influence of the sample sputtering rate. The variations in intensity of several analytical lines were then studied and compared with the sample sputtering rate. It was concluded that the sample atom number density in the plasma saturates with increasing voltage. An empirical intensity expression, taking into account the current, voltage and sample composition is presented. This expression was used for the determination of elemental concentrations in Cu based alloys, using a single steel reference sample as standard. An application of this procedure to a surface analysis problem is presented, and the results are compared with atomic absorption measurements. Good agreement was obtained, indicating that surface analysis data can be quantified in a simple and straightforward manner.

Use of a boosted-output lamp for analysis of powdered rocks and metals

Precise and accurate determinations of metals in powdered samples may be made by emission spectroscopy using a boosted-output lamp as the source. The non-conducting rock material is mixed with a conducting powder, e.g. copper, and pressed to form the cathode of the glow discharge. The cathode requires no preparation other than de-gassing in the lamp by use of a high sputtering current. The intensity of an analytical line reaches equilibrium in 3–4 min. Linear calibration curves were obtained in the analysis of cathodes pressed from mixtures of silver, copper and gold powders and this result shows that factors such as spectral interference and changing conductivity of the discharge plasma as metal atoms are introduced are not responsible for the non-linearity and change of slope of calibration curves reported in the literature for determinations made on silver-copper-eold alloys usine a Grimm-type glow-discharge lamp.

Redeposition of Sputtered Material in a Glow-Discharge Lamp Measured by Means of an Ion Microprobe Mass Analyser

The redeposition of sputtered material on the target in a Grimm-type glow-discharge lamp was studied by means of an ion microprobe mass analyser (IMMA) using 16O2+ ions as bombarding species. The target was an aluminium disc with a cylindrical copper insertion, one mm in diameter. The lamp was operated at currents of 50 mA and 100 mA and a voltage of 1200 V. It is estimated that 17% of the copper atoms sputtered are redeposited and may be resputtered.

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.

Emission spectral analysis with the glow discharge source and a resonance detector

A Grimm-type glow discharge lamp was found to have emission lines which are narrow enough to allow the advantageous use of resonance detection. Design of a cathodic sputtering cell which has an exchangeable cathode is described. The fluorescence signal from this lamp was detected electronically by either a synchronous (lock-in) detection system or a dual-gated integration (boxcar) system. It was found that the dual-gated system improved detection limits by a factor of 50 over the synchronous detection system. Calibration curves for copper in aluminium and silver in gold were found to be linear from the detection limit (about 1 ppm for both elements) up to approximately 20% in the case of copper in aluminium, and 5% silver in gold. Reproducibility of signal measurements was 1%.