Time- and wavelength-resolved emission line profiles for pulsed Cu and Ag hollow cathode lamps

Time-resolved, line emission wavelength profiles were obtained for a copper and a silver pulsed hollow cathode lamp with the use of a piezoelectrically driven interferometer. A computer was used to control the timing of the sweep of the interferometer, the pulsing of the source, and the acquisition, averaging, sorting and display of data. Minor manipulation of the data stored in core facilitated the presentation of intensity vs wavelength emission profiles in a time-resolved form. Ten sequential line profiles spaced at 21 μsec time intervals were obtained.The copper hollow cathode lamp was driven at 100 Hz with pulse currents of up to 400 mA. Pulses lasted for up to 300 μsec. Line profiles changed dramatically during a pulse and showed extreme self-reversal of the resonance emission lines after 100 μsec. Variations of line profile with dc background current level and spatial position within the discharge were also investigated. Uncorrected line widths of each of the doublets of the Cu(I) 324.7 nm resonance line measured during the first 21 μsec of the discharge, where they were narrowest, ranged from 0.0012 to 0.0022 nm, including an instrumental broadening contribution estimated to be less than 0.0004 nm. The silver lamp showed extreme self-reversal even during the first 21 μsec.     

Characterization of a circular thin film plasma source for atomic emission spectroscopy

A plasma source for analytical atomic emission spectroscopy is described based on the electrical vaporization by capacitive discharge of a thin Ag film deposited on a polycarbonate membrane filter. The source is designed for the rapid, direct analysis of solid powder samples collected by filtration from fluid media. A concentric electrode system consisting of a ring-shaped graphite electrode placed on the thin film surface and a pointed graphite rod located under the membrane substrate results in a plasma with cylindrical symmetry and a radial current path. Discharge current vs time and intensity vs time profiles are compared for the concentric electrode geometry and the linear geometry used in previous studies. Two values of tank circuit inductance also are compared. Both neutral-atom and ion line radiation from an Mn sample are more intense when the center electrode is initially cathodic. The inside diameter of the ring-shaped electrode and thus the surface area of the Ag film exposed to the plasma have relatively little effect on the intensity of continuum background and line radiation from a sample deposited near the center of the film. Particle size effects, while significant, are smaller than with the linear electrode geometry. Analytical curves are presented for several lines using both a low-inductance and a high-inductance discharge. Log-log slopes range from about 0.85 to 1.05 for ion lines. Detection limits are somewhat poorer than with the linear geometry.     

Use of radiofrequency power to enable glow discharge optical emission spectroscopy ultrafast elemental mapping of combinatorial libraries with nonconductive components: nitrogen-based materials

Combinatorial chemistry and high-throughput techniques are an efficient way of exploring optimal values of elemental composition. Optimal composition can result in high performance in a sequence of material synthesis and characterization. Materials combinatorial libraries are typically encountered in the form of a thin film composition gradient which is produced by simultaneous material deposition on a substrate from two or more sources that are spatially separated and chemically different. Fast spatially resolved techniques are needed to characterize structure, composition, and relevant properties of these combinatorial screening samples. In this work, the capability of a glow discharge optical emission spectroscopy (GD-OES) elemental mapping system is extended to nitrogen-based combinatorial libraries with nonconductive components through the use of pulsed radiofrequency power. The effects of operating parameters of the glow discharge and detection system on the achievable spatial resolution were investigated as it is the first time that an rf source is coupled to a setup featuring a push-broom hyperspectral imaging system and a restrictive anode tube GD source. Spatial-resolution optimized conditions were then used to characterize an aluminum nitride/chromium nitride thin-film composition spread. Qualitative elemental maps could be obtained within 16.8 s, orders of magnitude faster than typical techniques. The use of certified reference materials allowed quantitative elemental analysis maps to be extracted from the emission intensity images. Moreover, the quantitative procedure allowed correcting for the inherent emission intensity inhomogeneity in GD-OES. The results are compared to quantitative depth profiles obtained with a commercial GD-OES instrument.     

Some spatial effects observed in the axially viewed filament argon microwave induced plasma with solution nebulization

Spatial profiles of analyte emission in an axially viewed argon filament microwave induced plasma sustained in the TE₁₀₁ rectangular cavity have been measured along a discharge tube cross-section for neutral atoms as well as ion lines of several elements. The filament diameter was approximately 1 mm. The analyte solution was introduced by means of an ultrasonic nebulizer without desolvation. The radial emission distribution depends on the operating parameters and is different for each of the analytes examined. Spatial distributions of excitation temperature (4000–6000 K) measured with Ar I lines by the Boltzmann plot method as well as electron temperature (6000–8000 K) by line to continuum emission ratio measurements at Ar I 430 nm and electron number density (1–1.5×10¹⁵ cm⁻³) by the Stark broadening method of the H_β line were determined to support the evidence of plasma processes. In the presence of excess sodium the enhancement of emission intensity and its shift to the plasma center appears to be the result of increased analyte penetration to the plasma. Changes in spatial emission profiles for Ca atoms and ions suggest that for this element ambipolar diffusion may be important as an additional interference mechanism. A possibility of minimizing spectral interferences from argon emission lines by choosing an off-axis plasma region for emission intensity measurements is indicated.     

Time-resolved measurement of emission profiles in pulsed radiofrequency glow discharge optical emission spectroscopy: Investigation of the pre-peak

Radiofrequency glow discharge coupled to optical emission spectroscopy has been used in pulsed mode in order to perform a detailed study of the measured temporal emission profiles for a wide range of copper transitions. Special attention has been paid to the early emission peak (or so-called pre-peak), observed at the beginning of the emission pulse profile. The effects of the important pulse parameters such as frequency, duty cycle, pulse width and power-off time, have been studied upon the Cu pulse emission profiles. The influence of discharge parameters, such as pressure and power, was studied as well.     

Density distribution of high energy electrons in pulsed corona discharge of NO+N2 mixture

Emission spectroscopy of the high-voltage pulsed positive corona discharge in a line-cylinder reactor is used to investigate the high-energy electron density distribution in the discharge gap. The relative overall emission intensity spatial distribution profile of the A2Sigma+ --> X2Pi transition of NO is successfully recorded against a severe electromagnetic pulse interference coming from the corona discharge at one atmosphere. The spectroscopic investigation shows that the high-energy electron density in the discharge has a nonlinearly decline in the radial distribution. When varying the discharge voltage, the absolute emission intensity of NO is different but the radial distribution profile is similar. If an oxygen flow was introduced into the discharge reactor, the emission intensity of NO decreases tremendously and, therefore, the high-energy electron density decreases reasonably.     

Diagnosis of OH Radical by Optical Emission Spectroscopy in Atmospheric Pressure Unsaturated Humid Air Corona Discharge and its Implication to Desulphurization of Flue Gas

OH radical in the corona discharge with pipe–nozzle–plate electrode has been diagnosed by optical emission spectroscopy. Spatial variations of OH radical emission in discharge gap have been measured. Relative intensity of OH radical emission spectroscopy increases with increasing water vapor flux injected into the reactor or intensity of electric field supported. In positive pulsed corona discharge, relative intensity is higher than that in positive DC corona discharge and lower than that in negative DC corona discharge. Strongest intensity of OH radical spectrum appears within the range of 5 mm near the discharge nozzle- electrode. In addition, it is proved that the efficiency of desulphurization from flue gas by pulsed corona discharge plasma processes can be improved when OH radical is produced in the reactor.     

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).     

Study of Spark Discharge Assisted to Enhancement of Laser-Induced Breakdown Spectroscopic Detection for Metal Materials

In this work, laser triggered spark discharge was combined with laser-ablation under Air and Ar gases to investigate the characteristics of laser-ablated plasma emission. The experimental results show that the optical emission intensity is significantly enhanced by electric discharge compared to without discharge and the spectral emission time of plasma is much longer than that without discharge. The enhancement effect is more apparent in the presence of Ar ambient. In addition, the plasma temperature and electron density as well as limits of detections (LOD) have been determined. The better LOD can be attributed to the improvement of plasma. The higher plasma temperature and electron density indicate that the enhanced mechanism in emission intensity is predominated by the further excitation/ionization of the laser-ablated material by the spark discharge due to the energy deposition in the plasma.     

Novel use of glow discharge optical emission spectroscopy (GDOES) to study corrosion of AA2024‐T3 in the presence and absence of inhibitors

Recent interest in environmentally friendly alternatives to chromate‐based corrosion inhibitors has led to the development of a range of novel coating formulations. The work described herein is aimed at developing a novel methodology to contribute to investigation of the self‐healing and active corrosion protection of the new coatings. An experimental procedure has been developed to model a defect in the coating by fixing coated specimens in close proximity to the uncoated AA2024‐T3, each separated by a narrow gap containing sodium chloride solution. After exposure to the corrosive environment, elemental depth profiles of the uncoated specimens were acquired by glow discharge optical emission spectroscopy (GDOES). The depth profiles of selected elements (notably aluminium, oxygen and copper) were shown to have characteristics which can be correlated with bulk surface roughening/intensity of corrosion, the thickness of the corroded layer and de‐alloying/re‐distribution of copper. An unanticipated inhibitory effect was noted in the case of a coating doped with γ‐Al₂O₃ (γ‐alumina or AluOx). Copyright © 2015 John Wiley & Sons, Ltd.